Alternate Carbon Sources for Sintering of Iron Ore (Acasos)

Alternate carbon sources for sintering of iron ore (Acasos)

Research and Innovation EUR 25151 EN EUROPEAN COMMISSION Directorate-General for Research and Innovation Directorate G — Industrial Technologies Unit G.5 — Research Fund for Coal and Steel

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Contact: RFCS Publications

European Commission B-1049 Brussels European Commission Research Fund for Coal and Steel

Alternate carbon sources for sintering of iron ore (Acasos)

Roland Pietruck VDEh-Betriebsforschungsinstitut (BFI) Sohnstraße 65, 40237 Düsseldorf, GERMANY Joachim Janz, Elke Unland ArcelorMittal Bremen GmbH Carl-Benz-Straße 30, 28237Bremen, GERMANY Giuseppe Ventrella ILVA S.p.A. Via Appia km 648, 74100 Taranto TA, ITALY Trevor A.T. Fray, Maria Martinez.Pacebo, Mohammad Zandi Tata Steel UK Ltd 30 Millbank, London, SW1P 4WY,UNITED KINGDOM Herbert Schmid voestalpine Stahl GmbH voestalpine-Straße3, 4020 Linz, AUSTRIA

Grant Agreement RFSR-CT-2007-00003 1 July 2007 to 31 December 2010

Final report

Directorate-General for Research and Innovation

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Luxembourg: Publications Office of the European Union, 2013

ISBN 978-92-79-22676-2 doi:10.2777/58105

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Table of contents Page

1. Final Summary 5

1.1 Identification and characterization of ACASOS 5

1.2 Pre-processing of ACASOS 5

1.3 Briquetting/Pelletizing of ACASOS 6

1.4 Thermal evaluation of ACASOS at sinter pot 7

1.5 Field test & best practice 8

1.6 Conclusion and comparative evaluation of ACASOS 8

2. Scientific and technical description of results 9

2.1 Objectives of the project 9

2.2 Description of activities and discussion 9 2.2.1 Identification and Characterization of ACASOS 9 2.2.1.1 Alternative Carbon Materials 9 2.2.1.2 Alternate carbon rich in-house dust and sludge 10 2.2.1.3 Alternate biological carbon sources 11 2.2.2 Pre-Processing of ACASOS 13 2.2.2.1 Material composition and features for pre-processing 13 2.2.2.2 Evaluation of different pre-treatment processes 13 2.2.2.3 BF Sludge pre-processing: Hydro cyclone – filter press – blade crusher 17 2.2.2.4 BF sludge pre-processing: magnetic separator 20 2.2.2.5 Determination of process parameter - Discussion 22 2.2.3 Briquetting/Pelletizing of ACASOS 22 2.2.3.1 Development of mixture composition and briquette features 22 2.2.3.2 Investigation of parameter for pelletizing and briquetting at pilot scale (Task 3.2) 25 2.2.3.3 Discussion of results and transfer 28 2.2.4 Thermal Evaluation of Pre-Treated ACASOS 30 2.2.4.1 Thermal lab scale tests 30 2.2.4.2 Technical scale tests using ACASOS for evaluating sinter parameter and quality 33 2.2.4.3 Comparison of environmental aspects 40 2.2.5 Field Tests and Best Practice 41 2.2.5.1 Pre-treatment for field tests 41 2.2.5.2 Use of ACASOS at the sinter plant and influence on emission 42

2.3 Conclusion and Comparative Evaluation 46 2.3.1.1 Technical influence 46 2.3.1.2 Economical aspects 48 2.3.1.3 Influence on emission 49 2.3.1.4 Adherence to LCA principles 49

2.4 Exploitation and impact of the research results 51 Application of anthracite for sintering 51 Application: Pre-processing of BF sludge for sintering 51 Publication 54

List of Figures 55

List of Tables 56

List of References 57

Summary of main results 68

Appendices

1. Final Summary

1.1 Identification and characterization of ACASOS

In the work package the alternate carbon sources were physically and chemically analyzed. The properties are summarized in the data base (appendix). As alternate carbon sources BF dust and sludge, pet coke, anthracite and different kind of biomasses were evaluated.

The chemical analysis show that the alternative carbon sources vary in a wide range of carbon content in between 19 and 95 %. Also the volatile content and the calorific values vary in the range of 2 – 83 % and 13 - 36 MJ/kg.

Biomass is characterized by a high volatile content and in comparison to coke breeze by a low fixed carbon content. Nevertheless biomass is already used as combustion fuel for heating where as much as 70 % of the heat generated can be derived from the volatile matter. Thereby the volatile carbon content is devolatilized gaseous and combusted with oxygen. This process is influenced by the speed of devo- latilisation, i.e. by the particle size, as well as from the oxygen content and the temperature In comparison with the coke breeze it can be observed from the chemical analyses that the biomass materials have lower sulphur level and a much lower ash content,

BF dust and sludge are characterized in comparison to the coke breeze by a low carbon content and a small particle size but also a low volatile content. Due to the small particle size the utilization is not optimised although it is already agglomerated in sinter mixture. The BF dust and sludge can have a higher sulphur/carbon ratio than coke breeze, even if the absolute sulphur content sometimes is lower. This aspect could probably become a limiting factor for the substitution of coke breeze by pre- processed in-house BF dust and sludge. The availability is determined by the dust emission of the blast furnace and is in the range of 10 – 20kg/tpig iron beside the amount of deposited BF dust.

Pet coke and anthracite are characterized by a high fixed carbon content. The volatile content is slightly higher than carbon breeze and also the combustion reactivity is higher than carbon breeze. Most pet coke and some anthracite brands have significant higher sulphur content than coke breeze. Also for the price of fuel-grade petroleum coke the sulphur content is a main determining parameter. The quantities of pet coke imported in Western Europe were in the range between 2 and 4 million tons a year.

1.2 Pre-processing of ACASOS

The requirements to the pre-processing techniques are given by the sintering process. Generally coke is blended with the other sinter mix components before granulation. Several studies have shown that the size distribution of the coke in the sinter mix has to be in a range of 1 – 3 mm to obtain high performance and good sinter quality parameters.

For biomass a cutting mill was applied as a consequence of the soft, fibrous nature of the alternate carbon source. To evaluate the particle size laboratory sinter pot tests were carried out to compare flame front speed in the sinter bed with that for the coke breeze. So it was found that the peek temperature for the biomass reaches a maximum for the material in the size range which is lower than the optimal carbon breeze size. Also the time to peek temperature and the width of the thermal profile at 1000 °C are also most closely aligned to the coke figure for the biomass. These data indicate that the biomass needs to be finer than the coke breeze that it replaced.

In case of blast furnace sludge a pre-processing was investigated to separate the content of heavy metals as lead and zinc and gain the carbon rich sludge as alternative carbon source. Limits of harmful components for the recycling of the BF sludge are a lead content of 0.5% and a zinc content of 1%. The investigation were based on the knowledge that a separation can be achieved by classifying the BF sludge at between 8 - 15 µm due to the fact that the heavy metals are accumulated in the very fine BF sludge fraction. To separate the heavy metals as lead, zinc, cadmium and mercury from the sludge a hydro-cyclone pilot device has been installed and utilized successfully. Additional a filter press has

5 been applied to agglomerate the separated carbon rich BF sludge and reduce the moisture content. Due to the separation a carbon rich mass fraction of about 70% of the BF sludge input can be obtained in hydro-cyclone underflow and about 73% of the total C of the BF sludge can be utilized as ACASOS at the sinter plant via the underflow. More than 73% of lead, zinc and cadmium were enriched in the overflow which has to be land filled.

Dewatering of hydro-cyclone underflow (ACASOS fraction to be utilized in sinter mix) and overflow (fraction to be land filled) was tested first at lab-scale, then with a pilot filter press similar to the existing industrial filter press. Results showed that the underflow fraction exhibits an excellent dewatering behavior, while the fine sized overflow fraction is very difficult to be pressed into a strong filter cake with low moisture. To get a grain size distribution fitting well into the sinter mix blade crusher was applied successfully.

The heavy metal rich fraction of the BF sludge was also processed with a wet operated high intensity magnetic separator with the aim to separate and concentrate the heavy metal fraction. But a further separation of hydro cyclone overflow fraction from heavy metals was not achieved which was traced back on small differences of magnetic properties between heavy metals and carbon.

1.3 Briquetting/Pelletizing of ACASOS

In advance of the technical briquetting and pelletizing trials the influence of mixture composition, type of binder and the influence of the moisture content on the pellet cold strength have been evaluated in Laboratory scale. A binder content of 10 % Calcium hydrate, a 10 % moisture content and a curing time of about 3 days seem to be appropriate to reach a sufficient cold strength for the pellets.

In laboratory and semi technical scale die press and a continuous roller press as well as built up agglomeration processes, a disc pelletizer, produced stable pellets which satisfy the mechanical demands of the sinter raw material preparation. This was tested by an abrasion tests in comparison to coke breeze. In combustion tests it was shown that the combustion reactivity of the BF dust pellets produced with die press was in between the reactivity of the sinter fuel and the anthracite. Additional the thermal tests have shown that the addition of coke breeze does not seem to increase the reactivity of the pellets. The transfer to industrial scale indicated that for a stable production a tight range of material properties as moisture content and particle size have to be realized when using a die press. Fluc- tuation of material properties and composition lead to plugging of the die and to long non-operating periods. Due to the fluctuating material properties the utilisation of a die press for pelletizing BF dust and sludge was not feasible. Tests using the continuous roller press to agglomerate BF dust and BF sludge have shown that the required small particle volume of the pellets leads to a decrease of the productivity and also to a reduction of the economic feasibility, which was the reason to skip the industrial pelletizing with a continuous roller press.

Alternatively the pellet production using a disc pelletizer has been tested. The pelletizing process has also a high demand on the material properties, particle size and moisture content. Nevertheless deviations caused by fluctuation of the input materials could be adjusted more easily. As known from the drum granulation a fine material has due be added to gain a stable pellet. So additional to the BF dust cast house dust was added as fine fraction.

The knowledge was transferred to an intensive Eirich mixer which combines the mixing properties and the disc pelletizing due to the skewness of the mixing drum. In industrial scale also the content of calcium hydrate, as binder, in the mixture as well as the moisture content was increased in comparison to the basic receipt which was derived for the press agglomeration. Abrasion tests after a curing time of at least 3 days showed sufficient pellet strength in comparison to the carbon breeze as well as to the

6 pellets from die press. About 180 t of BF dust pellets were produced for the industrial scale tests at a sinter plant.

1.4 Thermal evaluation of ACASOS at sinter pot

Sinter pot tests were carried out from ILVA, Tata steel and VASL using sample of the pre-treated and alternate carbon sources to substitute carbon breeze and evaluate the carbon replacement factor, i.e. the ratio of the carbon content of coke breeze to the carbon content of the ACASOS. As ACASOS pet coke, anthracite, anode coke, BF dust, BF sludge and mixtures of BFdust+sludge containing also cast house dust and binder as well as biomass as olive pits and wood pellets were evaluated. Within the sinter pot tests it was in general assumed that the carbon replacement factor is 1 when the carbon breeze was substituted by the alternate carbon sources. Additional voestalpine has carried out a number of pot tests twice with a presumed carbon replacement factor of 0.5 and of 1.

The carbon replacement factor of ACASOS when replacing coke breeze at the sinter pot trials was evaluated mainly on the basis of the return of fine balance of the sinter pot tests when using ACASOS and in comparison to a standard sinter pot test at a balanced return fine ratio carried out with coke breeze only. Beside this quality and performance date were also discussed and compared to the standard test. Deviations of the return of fines balance when replacing coke breeze by ACASOS from the standard sinter pot test mean also that the replacement factor deviate from the assumed replacement factor. Although it was not possible to give exact figure for carbon replacement factor, it can be stated that

• When substituting 10% of the carbon breeze by pet coke, anthracite , anode coke, pelletized BF dust , granulated BF sludge or pellets from mixtures the return fine balance as well as the quality and performance data of the sinter pot trials vary only slightly so that the a carbon replacement factors were estimated in the range up to almost 1.

• When substituting 20% of the carbon breeze by BF dust+ sludge pellets/briquettes at ILVA the quality and performance data deviate from the standard test and the return fines balance of decrease which indicate lower replacement factor. The carbon replacement factor of pet coke and anthracite were still in range of 1 which was deduced from the balanced return of fine ratio and the performance and quality data in comparison to the standard trial.

• The substitution of 30% up to 50% of coke breeze trials was only carried out for pet coke and anthracite. The substitution causes an increased deviation on the return fine balance as well as on the quality and performance data of the sinter pot trials so that the a carbon replacement factors were estimated in the range up to almost 1

• Biomass products, i.e. olive pits and wood pellets, were substitutes in the range of 5 – 15% at the sinter pot tests. The sinter performance and quality figures of return fines balance deviate considerable from standard tests, according to their consistence, so replacement of 1 cannot be reached. Limiting factor was also the VOC emission. A specification less than 1 mm is recommended when applying ACASOS with high volatile content in sintering.

The sinter pot tests delivered the basis for the industrial tests. These results indicate that the agglomeration of fine dust and sludge fractions with high content of fixed carbon is increasing the carbon replacement factor. Materials with high volatile carbon content do not reach the replacement factors according to their calorific value.

Environmental aspects concern emissions of SO2 and volatile organic carbon (VOC). SO2 can be a limitation criterion especially for pet coke but also for BF dust and sludge, if sulphur/carbon ratio is significantly higher than that of coke breeze.

VOC emissions are also a strong limiting criterion for utilization of all kinds of sinter fuel. The results from Tata indicate that biomass fuels can potentially increase VOC emissions in the sintering process. Also pet coke causes VOC emissions in dependence of the type and brand of pet coke. On the other

7 hand, if the application is limited to rather small portions of coke substitution and therefore VOC emissions are kept low, utilization of biomass ACASOS has advantages on SO2 emissions and CO2 balance due to regenerative resources.

1.5 Field test & best practice

In industrial scale coke breeze was substituted by over 60 % of low sulphur anthracite. This led to a slight reduction of sinter productivity of about 2 %. The replacement factor is more or less 1. Because of the low sulphur and volatile content in the anthracite and very slight reduction of the sintering performance, it seems possible to substitute the carbon breeze by anthracite.

The results of industrial application of the granulated BF sludge indicate that the carbon replacement factor is about 1. The CO-content of the waste gas did not increase, this also indicates that carbon is combusted as complete as coke breeze. Also lead and zinc content of sinter stayed in the same range as before, this indicates that heavy metal separation works properly. Regarding influences on sinter productivity and quality figures, changes caused by ACASOS are could not be detected, since changes of general mix composition and especially sinter basicity has much higher influence.

The utilization of the BF dust pellets at the sinter plant shows a positive effect on the utilization of the carbon content. Due to the pelletizing the carbon replacement factor was increased from 0.6 to 1. The increase of the sinter plant productivity, when adding the BF dust pellets, was assumed to be linked to the increased amount of calcium hydrate used as binder in the BF dust agglomerate. The green strength was adequate for the handling of the pellets.

1.6 Conclusion and comparative evaluation of ACASOS The investigation indicate that the grain size distribution of sinter fuel for alternative carbon sources with high content of fixed carbon content has a high influence on the carbon utilisation. The agglomeration of fine dust and sludge fractions with high content of fixed carbon seems to increase the replacement factor. In contrast replacement factor of alternative carbon sources with high volatile content is considerable below 1, although improved by fine grinding. The substitution is also limited by the emission of volatile organic components. The investigation have also shown that the anthracite as alternate carbon source can substitute carbon breeze to a large extent with a high replacement factor.

For calculating effects of replacing coke breeze by biomass on CO2 emissions models predicted that replacing 15% of coke breeze by olive pits will lead into 10% reduction of CO2 emissions at the sinter plant. A comparison of two sinter plants one using coke breeze and the one benefiting from CO2- sustainable ACASOS material showed that the utilization of biomass is economical feasible, although it depends on CO2 and biomass prices in the future.

2. Scientific and technical description of results

2.1 Objectives of the project This proposal addresses the Steel RTD programme. The proposed research is in complete accordance with the priority “Rational use of energy resources and residues management” of the Strategic Re- search Agenda of ESTEP with high relevance for the RFCS programme. Its technical objective is to find ways to substitute coke breeze by applying alternate carbon sources for sintering of iron ore. Alternate carbon sources (ACASOS) that will be investigated in this project are: - biological renewable carbon sources (TATA), - carbon rich deposited dusts and wastes, (BFI, AMB) - alternate carbon sources (anthracite, petroleum coke, coke dust etc.) (Ilva) - carbon rich in house sludge of BF (voestalpine) The objectives that are aimed in the project are: - the identification of biological carbon sources , chemical and physical characterization of all alternate carbon sources as a basis for pre-processing and comparison. Checking of availability and costs. - the improved pre-processing to approach ACASOS to the demand of sintering, to increase the amount of ACASOS at high productivity and sinter quality, to support the pelletizing into the sinter raw mixture and to improve the replacement factor for coke breeze - the transfer of knowledge evaluated in lab and pilot scale to industrial scale. This implies the production of ACASOS and the carrying out of sinter plant trials to evaluate the influence of ACASOS on performance, quality and emission. - to set up a database which delivers information about the properties of the ACASOS - evaluation of the availability and cost of ACASOS.

2.2 Description of activities and discussion

2.2.1 Identification and Characterization of ACASOS The objective of the work package is to identify and characterize the alternate carbon sources physically and chemically and also to evaluate the economical feasibility. A data base was set up by the partner and is added in the appendix. The alternate carbon sources can be compared among each other and with coke breeze . 2.2.1.1 Alternative Carbon Materials

The saleable world anthracite production in 2009 was estimated to 161 Mio.t/a [3]. Main producer was China which was estimated to produce about 53% of the world production. The main producer in east- ern Europe are Ukraine and Russia producing with about 4% and 6% of the world production. In trad- ing classification anthracite is the highest rank of coal, with low volatile matter, typically less than 10% (dry basis); fixed carbon is normally >80%; and high hardness, i.e. good “grindability” (HGI <40) [3]. However, there is some variation in the definition with some countries seemingly also report- ing so-called “semi-anthracite” - having volatiles 10-12% (or even up to 15%) and fixed carbon <80% - as “full anthracite”. These grades are typically sold into low volatile PCI and power-generation mar- kets. The anthracite which was used for pelletizing trials had a fixed carbon content of about 95%, a volatile matter of 1.9%, and an ash content of 3.3%. The sulphur content was very low with about 0.9%. ILVA has measured the gravity weight of anthracite by a “pycnometer” procedure of 1,65 t/m3, using a sam-

9 ple size smaller than 0.075 mm with the aim to erase a larger quantity of bubbles, besides it has veri- fied the bulk density of 0.7 t/m3. The mean size of the anthracite was 1,02 mm and the calorific value 33.7 MJ/kg.

Global production of petroleum coke in the year 2008 was estimated to approx. 90 Mil. t/a [4], with increasing tendency, mostly in the USA and South America, with most of the yield being consumed directly in the USA. The quantities imported in Western Europe were range between 2 and 4 million tons a year [4]. In Germany, petroleum coke production is concentrated at two locations, each of which has a capacity of roughly 200 000 to 300 000 t/a. In 2008 the price of the latter was in the range of 130-140 US $/t (West European ). The present cost of petroleum coke with sulphur contents of <3% is also at about that same level.[4]. One parameter for the price of fuel-grade petroleum coke is its sulphur content, because, unlike hard coal for example, the other parameters of globally traded petroleum coke (ash, volatile constituents, calorific value) differ only in a small range. The properties of the petroleum coke alternate carbon fuels are summarized in the data base in the appendix. The median diameter of the evaluate Pet coke was 1.8 mm. Pet coke is similar to anthracite characterized by a high content of fixed carbon of 87% and a volatile matter (V.M.) of about 11% and sulphur content of 1.9 %. The ash composition of pet coke was not analyzed because of the small quantity of ash. The calorific value is in the range of 32 MJ/kg and the bulk density is about 0.7 kg/m3.

2.2.1.2 Alternate carbon rich in-house dust and sludge

An alternate carbon inhouse source is the carbon rich BF dust. The BF dust is already used as supplemental fuel at sinter plants saving coke breeze consumption but with a low replacement factor, i.e the true utilization of the carbon content of the alternate carbon source in stead of the carbon from carbon breeze, which is estimated to be 0.5. The low replacement factor is traced back by the addition via the blending beds and on the granulation the sinter raw mixture. Due to the small particle size it can be assumed that the carbon content of the dust is embedded into the quasi-particle during sinter mix preparation which decreases the utilisation. The investigation are focused on the pelletizing of the BF dust to improve the utilisation of the carbon content in the BF dust at the sintering process.

As inhouse dust deposited BF dust and “fresh” BF dust have been sampled and analysed at AMB during the first half year of the project. Within the sampling periode the carbon content of the BF dust varied in the range of 20% to 56%. The average carbon content was about 41.2%. The average ash content was about 55% and the average volatile content was about 2.3 %. The average calorific value was 11.3 MJ/kg. Also mechanical properties as particle size distribution and void fraction or compressibility were analysed due to there influence on the pelletizing process and therefore on the utilisation of the carbon content. The “ash content” of the BF dust is in comparison to the coke breeze very high and contains mainly iron oxides. Minor components of the BF dust are SiO2 and CaO. The median diameter D50 diameter is about 0.2 mm for BF dust. In comparison the median diameter of the sinter fuel is 1.2 mm. The bulk density of the BF dust and the deposited BF dust is very similar in the range of 0.8-0.9 t/m3. The availabilty is determined by the dust emission of the blast furnace and is in the range of 10 – 20 kg/tpig iron beside the amount of deposited BF dust which was estimated about 60 000t. The investigations on the sludge at VASL concentrate on BF sludge from two different types of blast furnace, i.e. with and without top pressure (BF A and old BF). It was estimated that the amount of sludge from BF A with top pressure yield about 10 000 t/year. Average chemical composition of the sludge types show only slight differences regarding carbon content (old BF: 34%; BF A: 30%) as well as iron (Fe2O3 old BF: 48%; BF A: 55%) and slag components (see Data Base). Deviations are in a normal range of one type of BF sludge. The main difference of the slag from two different types of blast furnace, i.e. with and without top pressure, is the contents of lead and especially zinc. Sludge from old BF’s (without top pressure) has a zinc concentration 10-15 times higher than from BF A (with top pressure). Therefore this type of sludge is more difficult to process in order to extract a mass fraction utilisable as an alternate carbon source for sintering. Referring to mechanical and thermal properties, especially in terms of its utilisa-

10 tion in the sinter mix, grain size distribution is of high importance. Although both sludge have rather the same maximum size of about 400 µm, sludge from BF with top pressure is much coarser regarding mean diameter. Bulk density is about 2000 kg/m³. Regarding to thermal properties, the calorific value is in the range of 11 to 13 MJ/kg. 2.2.1.3 Alternate biological carbon sources

The main aim of Tata Steel within this project was to consider the partial replacement of coke breeze in the sintering operation by a biomass material. Common biomass substances, such as wheat straw and wood pellets have calorific values ranging from about 14.5 MJ/kg to a maximum value of about 18 MJ/kg respectively. This compares with coke breeze that normally has a calorific value between 28 to 30 MJ/kg, about double that of the common biomass materials. These figures indicate that based on calorific values, approximately double the tonnage of biomass. If wheat were to be considered as the biomass material with a yield about 8 tonnes per hectare in the UK, then 13,000 hectares would be required to provide the estimated amount of wheat. In 2002 there were about 644,000 hectares of farmland in the Government set aside scheme, almost 50 times the area required to grow the estimated amount of biomass fuel.

It is evident that enough farmland resources could be made available for the amount of biomass fuel considered without upsetting the balance of land for food sources and providing the farming industry with another customer for its products. However, conditions can change rapidly so that in 2009 all set aside has been withdrawn in order that more wheat can be grown to meet the demands arising from poor harvests worldwide in 2007 and to a lesser extent in 2008.

In common with most consumer goods in a free market agricultural crops or a fuel derived from re- cently living organisms are price dependent upon the demand / availability relationship. Unlike many manufactured goods, agriculturally derived goods are highly dependent upon the weather conditions prevailing at various times through the farming year, i.e. in the sowing, growing, nurturing, harvesting and post harvesting periods.

The price variation between 2001 and 2007 for rape seed is shown in Figure 1. It is evident that the price was relatively low from the beginning of 2001 up to September 2002 when there was a considerable rise in price that held until about May 2004. From this moment there was a significant decrease in the price through to the low point situated in about July 2004. This low price was held from July 2004 through to the end of 2005. It is thought that at about this time there was increased interest in biodiesel from both the producers and the UK Government and a steady increasing price trend can be seen across 2006. The adverse weather conditions experienced in the UK in June 2007 undoubtedly led to a reduction or potential short-fall in the availability of rape seed at a time of high demand from the biodiesel producers. As a consequence the price of rape seed reflected high demand and reduced availability in a massive rise.

300

250

200 2001 2002 2003 150 2004 2005 2006 £/tonne ex. farm 2007 100

0 013263952 Week No.

Figure 1 Annual trends in UK rape seed prices, £/tonne ex. farm

There is also a concern that a resource for which no current demand exists will increase in price if a useful application such as a fuel in an industrial process is found. If this occurs, the resource would no longer represent a financial proposition. An example of this may be the case for olive pits, where a use close to the source would prove an environmentally sound option.

Analysis indicated that the biomass appearing to be the most suited as partial replacements for coke breeze in sinter making could be drawn from the following types [7]: • Agricultural crops – Seeds e.g. wheat, rape seed – Plants e.g. short rotation coppice (src) willow, Miscanthus grass • Residues from biofuel manufacture – Possibly pressings from oil extraction – Residues from ethanol production • Agricultural residues – Straw – Shredded rape seed plants from combine. • Residues from food processing (non-animal) – Shells from nuts e.g. hazel nuts, walnuts, almonds – Husks from sun flower oil production – Pits from olives Of the two types of agricultural crops that could be used as biofuels those that are normally used for foods for both humans and animals, e.g. wheat, were (spring 2008) commanding high prices of about 440$/t due to the poor harvests throughout the world in 2007. These prices were falling in 2009 to 220$/t again after the 2008 harvest . This may make this a more financially attractive crop again but politically the use of a food crop specifically as a fuel would be considered inappropriate. Under these circumstances wheat cannot be considered as a commercial biofuel for partial replacement of coke breeze in sintering.

From the chemical analyses the residues from biofuel manufacture have been rejected because the amount of volatile matter appeared excessive (83.2%, with a H2 content of > 8%) and the material easily degrades into fine, oily particles that do not appear suitable for pelletizing into micro pellets ahead of the sintering operation. In addition these oils might cause problems in a sinter plant ESP (glow fires).

Of the agricultural residues shredded rape seed plants from the combine (rape straw) has a low energy density and would require considerable further treatment to improve the energy density. In the current situation this material is best either used on the farm as a supplement to cattle feed or returned to the soil. Commercially available straw pellets were considered in a previous scoping study. Again the energy density is relatively low (7950 MJ/m³) compared with coke breeze (24640 MJ/m³) and of- ten additives (molasses) are made to render the pellets more palatable to livestock which causes them to burn in the sinter process with the evolution of copious quantities of smoke. For these reasons these residues was not considered.

From the foregoing discussion it is apparent that only one type of biomass material has been identified that could satisfactorily be used in sinter making, i.e. the residues from food processing, as olive residues, sunflower pellets and “Bagasse” pellets [6].

In comparison with the coke breeze it can be observed from the chemical analyses that the biomass materials have (see data base in appendix): 1. a lower sulphur level 2. much lower ash content 3. higher phosphorus levels 4. higher CaO and MgO levels (making the ash basic rather than acid in respect of their slag formation, but with the significant exception of the bagasse pellets)

Olive pits [1] which was used at the thermal trials are characterized bys a carbon content of 52% and a high oxygen content of 40%. The volatile matter is about 81% and the fixed carbon content about 18,5%. The calorific value on dry basis is about 19 MJ/kg.

2.2.2 Pre-Processing of ACASOS

2.2.2.1 Material composition and features for pre-processing

The requirements to the pre-processing techniques are given by the sintering process. Generally coke is blended with the other sinter mix components before granulation. Several studies in the literature have shown that the size distribution of the coke in the sinter mix has to be in a range of 1 –3 mm to obtain high performance and good sinter quality parameters.

Due to different characteristics concerning chemical composition, thermal behavior and granulometric properties, a wide range of these in house sludge cannot be recycled without appropriate techniques of pre-processing. The pre-processing was carried out especially to obtain a minimum content of harmful components and optimized grain size distribution for maximum utilization of the carbon content. Lim- its of harmful components for the recycling of the BF sludge are a lead content of 0.5% and a zinc content of 1%.

Also the very fine size distributions of the BF sludge was processed to fit into a normal sinter mixture. Therefore compacting methods, e.g. a filter press, has been applied to agglomerate the fine sludge and reduce the moisture content.

When using entirely new materials such as biomass in the sintering process the familiar criteria for pre-processing of materials will not necessarily apply. Under these circumstances it becomes necessary to use an iterative process – set a condition, test in the sintering operation, analyze the results and adjust the condition accordingly.

2.2.2.2 Evaluation of different pre-treatment processes

There is little scope for extensive pre-processing of biomass where a straight substitution for coke breeze in sintering is intended. There is at least, however, a requirement to ensure that the biomass is sized correctly for the sintering operation. It is not possible to effect a size reduction of biomass in

13 the same way as for coke breeze, as a consequence of the soft, fibrous nature of the biomass. Through researching the problem it was discovered that one way to achieve size reduction of biomass starting with the biomass in the “as received” condition is to use a cutter mill as shown in Figure 3. It may be possible to use more conventional systems if drying or further processing of the biomass were under- taken but this would add costs. Figure 2 shows estimated costs for pre-processing biomass material. Process Costs (€/t) Energy consumption/t input

Breaking chipping, shredding 6.00 15 kWh Grinding 12.50 25 kWh Pulverisation 31.0 40 kWh Mechanical separation 9.50 10 kWh Pelletizing 7.50 to 25.00 15 to 80 kWh Mechanical dewatering (75%) 3.00 1.4 kWh Drying (50%) 7.00 Thermal drying (15%) 31.0 3 GJ

Figure 2 Costs of pre-processing ACASOS material.

Size reduction in a cutting mill takes place through cutting and shearing forces. The sample passes through the hopper and into the centre of the mill grinding chamber where it comes into contact with a rotor equipped with 3 cutting blades (see Figure 3). These blades are rotated at high speeds (in excess of 1200 revs per minute) and comminuting occurs between these rotating blades and the stationary ledges set around 80% of the chamber circumference. The dwell time in the chamber is relatively short; as soon as the material can pass through the mesh openings at the bottom of the chamber it dis- charges into the collection chamber below. Nevertheless the dwell time increases with decreasing mesh size.

Figure 3 Cutter mill used in this work for pre-processing ACASOS material.

For initial tests in a small laboratory sinter pot the biomass was reduced to less that 2 mm (as per the discharge mesh in the cutter mill, Figure 3) and then screened to - 2 mm, + 0.85 mm. The aim was the try to ensure that the particles were mostly in the 1 to 2 mm range; the coke breeze was also screened to this size range for the comparative experiments. The sintering pot is shown in Figure 4 and Figure 5. It has a raw sinter mix capacity of 1.0 kg, a bed diameter of 100 mm and a height of 150 mm.

150 mm

Figure 4 Schematic diagram of the sinter- Figure 5 Photograph of the sinterpot pot

In the first sets of experiments with the small sinter pot, crushed refractory material (alumina chips) was used to form an inert sinter bed instead of a standard type sinter mix. This facilitates comparison between the results for normal coke breeze and the biomass materials. The refractory material was sized < 3.15 mm, >2.8 mm and the biomass were in the size range < 2 mm, + 0.85 mm.

The thermal profiles of the laboratory sinter pot tests in Figure 6 indicate that for the biomass materials there seem to be a miss-match between the flame front speed and the heat front speed through the bed, i.e. the time temperature profiles for the biomass are relatively broad compared with that for the coke breeze. This is probably a consequence of a difference in reactivity between the coke breeze and the biomass.

1400

1200

1000

800 Coke Sunflower Alm ond 600 Hazel Temperature, °C Temperature,

400

200

0 180 200 220 240 260 280 300 time,s

Figure 6 Comparison of thermal profiles at TC/4 position

To investigate the influence the difference the sunflower husk pellets were milled and screened into 4 size ranges: -4 +2 mm, -2 +0.85 mm (size as used in the previous tests), -0.85 +0.6 mm and -0.6 +0.2 mm.

Figure 7 illustrates 3 characteristics of thermal profile, peek temperature, time to peek temperature and curve width at 100°C, of the laboratory sinter pot tests at the T/C 4 position for the variously sized crushed sunflower husk pellets.

Comparison of thermal profile measurements of coke breeze and variously sized crushed sunflower husk pellets

1400 250

200

1300 150

100 s Time, 1200 Temprature, deg. C 50

1100 0 reference 2 - 4 mm 0.85 - 2 mm 0.6 - 0.85 0.2 - 0.6 mm coke 2 - 4 mm mm size ranges

Peek temperature, deg. C time to peek temperature, s Curve width at 1000 deg.C, s

Figure 7 Comparison of thermal profile characteristics at T/C 4 position for the reference coke and differently sized, crushed sunflower husk pellets.

The peek temperature for the biomass reaches a maximum for the material in the size range 0.6 to 0.85 mm of 1313 °C compared with 1370 °C for the coke breeze. The time to peek temperature and the width of the thermal profile at 1000 °C are also most closely aligned to the coke figure for the biomass in the size range 0.6 to 0.85 mm. These data indicate that the biomass needs to be finer than the coke breeze that it replaced.

2.2.2.3 BF Sludge pre-processing: Hydro cyclone – filter press – blade crusher

Based on the results of the characterization lab-scale tests at Leoben Montan-university with two different types of hydro cyclone (Dorr-Oliver Ceramic cyclone 1 and 2 inch), were carried out. Test results were evaluated by grain size distributions of over- and underflow, and separation efficiency was described by the partition number as a function of particle size for each cyclone type. ( Figure 8 and Figure 9)

100

80 3,6 Vol.% 5,9 Vol.% 70 9,8 Vol.%

20 Partition for underflow, number % 10

0 1 10 100 1000 Particle size, µm

Figure 8 Partition number and separation particle size for 1 inch lab-cyclone for different solids content (labscale)

100

90 9,5 Vol.% 80 13,5 Vol.%

20 Partition number for underflow, % underflow, for number Partition 10

0 1 10 100 1000 Particle size, µm

Figure 9 Partition number and separation particle size for 2inch lab-cyclone for different solids content (labscale)

A pilot device was built in the BF sludge dewatering station with one full-scale hydro cyclone, (Figure 10). Separation tests under varying conditions were carried out, followed by extensive analysis work and evaluations.

Figure 10 Pilot hydro cyclone station in the dewatering plant at voestalpine Linz

100

90 Overflow BF old Underflow BF old 80 Overflow all BF's 70 Underflow all BF's Overflow BF A 60 Underflow BF A 50

30 Cumulative passing, % passing, Cumulative 20

0 0,1 1 10 100 1000 Grain size according to CILAS-Analysis, µm

Figure 11 Grain size distribution of overflow and underflow fraction for different BF sludge types (pilot scale)

100

90 Underflow BF old 80 Underflow all BF's 70 Underflow BF A 60

10 Distribution figure for underflow, % underflow, for figure Distribution 0 110100 Grain size acc. To CILAS Analysis, µm

Figure 12 Partition numbers calculated from grain size distributions, for different BF sludge types (pilot scale)

The characteristic separation size of the pilot cyclone is also in the range of 10 – 20 µm similar to results in lab scale. Mass balances and analysis of solids in under- and overflow were carried out to evaluate the distribution of the solids and the components. Details of mass distribution between hydro cyclone overflow and underflow are shown in Table 1 and chemical analysis of over- and underflow for different test conditions are shown in (types of BF sludge) Table 2 and Table 3.

Table 1 Mass distribution of solids and water (pilot scale)

Table 2 Chemical analysis of over- and underflow. only BF old (without top pressure) (pilot scale)

Table 3 Chemical Analysis of over- and underflow. only BF with top pressure (pilot scale)

Due to its finer grain size distribution sludge from old BF has a smaller yield in hydro cyclone underflow, which is expected to have only small content of heavy metals, especially lead and zinc.

The main results of the lab tests could be approved in pilot scale, showing that a mass fraction of about 70% of BF sludge can be obtained in hydro cyclone underflow and about 73% of the total C of the BF sludge can be utilized as ACASOS at the sinter plant via the underflow. Heavy metals such as lead, zinc, cadmium and mercury are accumulated in the overflow fraction which has to be land filled.

For evaluating a concept to use an existing chamber filter press for dewatering the hydro cyclone underflow fraction, lab scale pressure filtration tests were carried out. Results showed that the filter cake is rather easy to dewater and a moisture content of 18% was reached, but to obtain a grain size of about minus 10mm which is suitable for sintering, the filter cake has to be crushed.

Field tests have been carried out by a specially adapted so-called blade-crusher. The results of the field tests were successful and lead to the development of a prototype blade-crusher which would be able for in-situ crushing of the filter cake of the industrial chamber filter press. The crushed ACASOS material has a grain size distribution which is ready to use in the sinter mixture having chemical and thermal properties similar to BF dust, which is commonly utilized in sinter plants.

2.2.2.4 BF sludge pre-processing: magnetic separator

Additional to investigations on separation techniques via centrifugal forces (hydro cyclone), separation with a magnetic method was investigated (Figure 13). For this purpose, an existing lab scale high intensity magnetic separator was adapted to act as a wet-operated separator for treating slurry feed, i.e. a glass tube was filled with a matrix of steel wool and inserted into the gap of the magnetic flux system to enhance flux density gradient and thus magnetic forces. Slurry was fed into the tube, nonmagnetic fraction dropped down while magnetic particles were captured by the steel wool matrix and washed out after removing the tube from the magnetic field.

Figure 13 Dry high intensity magnetic separator, adapted to wet operation mode to treat slurries

Product Magnet.Prod.Nonmag.Prod. Mass-% 27,8 72,2 Carbon 26,6 40,5 Iron 35,7 24,2 Content % Lead 0,3 0,3 Zink 2,3 3,2 Carbon 20,2 79,8 Iron 36,3 63,7 Distribution % Lead 22,7 77,3 Zink 21,8 78,2 Table 4 Magnetic separation of BF sludge (mixture of sludge from all BF’s).

From the test results in Table 4 it can be seen, that distribution numbers of carbon and heavy metals (lead and zinc) are almost the same, this means that although iron was concentrated in the magnetic fraction, no separation between carbon and the heavy metals lead and zinc could be obtained.

To find out if limitations of the rather poor separation result was due to locked particles, i.e. heavy metals adsorbed in the pores of the carbon particles, electron-microscope and microprobe investigations were carried out. Results shown in Figure 14 and Figure 15 did not indicate that a strong intergrowth between heavy metals and carbon was the limiting parameter for a further separation but rather low differences in magnetic properties. High concentrations of lead and zinc do not correspond with high concentrations of carbon. This means that further separation of heavy metals from carbon-bearing BF-sludge is not impossible in principal, but magnetic separation is not an appropriate method.

Figure 14 Back scattered electron (BSE) microscopy of hydro cyclone overflow of BF sludge. Black: carbon particles. Grey: iron ore particles. White: lead and zinc concentrated particles

Figure 15 Concentration maps of PbO from microprobe analysis.

2.2.2.5 Determination of process parameter - Discussion

It has been recognized in the UK power industry that biomass materials are difficult to mill, especially down to the sizes required. A cutter type mill has been found that is capable of reducing the selected biomass materials to sizes suitable for the sintering process.

For the BF sludge separation tests, first in lab scale and then in a pilot-scale hydro cyclone station were carried out. Investigations concerning separation efficiency and its dependence on grain size distribution lead to the conclusion that up to 70% of the sludge from the furnace with top pressure (which is by far more mass than sludge from the old BF’s without top pressure) can be utilized in the sinter plant, having chemical and thermal properties similar to BF dust, which is commonly utilized in sinter plants. Heavy metals such as lead, zinc, cadmium and mercury are accumulated in the overflow fraction which has to be land filled.

Based on lab tests, dewatering field tests with an existing chamber filter press were carried out, followed by lab and field crushing tests with a so-called pilot blade-crusher, to obtain a grain size distribution < 10 mm of the ACASOS fraction to fit into sinter mix.

In order to minimize the fraction to be land filled, the BF sludge was also processed with a wet operated high intensity magnetic separator. As the results showed, that further separation of carbon-bearing hydro cyclone overflow fraction from heavy metals was not achieved sufficiently, electron microscope and microprobe analysis were carried out. Results showed that main reason for poor separation results is not (as presumed before) due to intergrowth between carbon and heavy metals within the grains, but rather too less difference of magnetic properties between heavy metals and carbon. Nevertheless, further iron and heavy metal separation would be possible by magnetic separation.

An amount of pre-treated ACASOS for sinter port tests was produced on the basis of optimized mixture composition and parameter adjustment for thermal evaluation.

2.2.3 Briquetting/Pelletizing of ACASOS

Carbon rich BF-dust and sludge was pre-treated to substitute coke breeze and recycle the very fine dust. Therefore different briquetting and pelletizing processes, i.e. die pressing, continuous roller pressing and a pelletizing dish were evaluated.

The aim of the pelletizing is also to produce optimised carbon rich agglomerates in the size range of coke breeze consisting of mixtures from BF dust and to influence the replacement factor. Also additives and binder were evaluated at the different briquetting and pelletizing processes as well as their parameter for the pre-treatment at different kind of presses. The evaluated briquetting/pelletizing processes were compared and parameters were transferred to technical scale.

2.2.3.1 Development of mixture composition and briquette features

The influence of the pellet mixture, content and type of binder and moisture content on the pellet strength was evaluated. The pellet strength must be high enough to withstand the mechanical stress due to conveying, feeding, mixing and pelletizing processes.

Therefore pressure strength tests were carried out using a pelletizing press and a compression test device. Within the tests the composition of the mixtures were varied using BF-dust. Different binders as Aluminate cement (AC). Portland cement (PC), Calcium hydrate (CH) and Water glass (WG) were varied. Furthermore the influences of the sinter coke content (C) and of the moisture content on the pressure strength were determined. The range of composition of the pellets is shown in Table 5.

BF-dust Sinter coke Filter Portland Aluminat Calcium Water Water (BF) (C) Dust cement cement hydrate glass (PC) (AC) (CH) % % % % % % % % 54-90 0-27 0-10 0-10 0-10 0-10 0-10 0-15

Table 5 Composition of BF-pellets

For the evaluation of the pellet strength in laboratory scale cylindrical tablets with a diameter of 3 cm and height of 2 cm were pressed with a tablet press applying a pressure of 5 MPa and a pressure hold- up time of 30 seconds. Afterwards the pressure strength of the tablets was measured by a laboratory pressure test device at the BFI. To evaluate the curing time the pressure tests were carried within 3 weeks after the pelletizing.

In Figure 16 the influence of the moisture content of the mixture on the pressure strength of the tablet is shown. The moisture content was increased by water addition in the range of 0-15%. The pelletizing of BF-dust without water was not successful. The addition of 10% water lead to an increase in pressure strength. The addition of 15% water didn’t increase of pellet strength (Figure 16)

1000 900 800 700 600 0.0% 10.0% 500 15.0% 400 15.0% (rep.) 300 pressure strength [N] 200 100 0 0 1 7 14 21 Ageing [Day]

Figure 16 Influence of moisture content on pellet strength

Also the influence of the different binders on the pellet strength was investigated. During the tests 10 weight-% of binder was added to the BF-dust. As binder Aluminate cement (AC). Portland cement (PC), Calcium hydrate (CH) were applied. The pressure strength in dependence of the ageing time is shown in Figure 17. The use of water glas and Portland cement show the lowest strength. Calcium hydrate lead to remarkable increase in pellet strength after one day and the addition of Aluminate cement lead to the highest pressure strength.

1000 900 800 700 AC 600 CH 500 PC PC2 400 without 300 pressure strength [N] 200 100 0 0171421 Ageing [Day]

Figure 17 Influence of binder on pellet strength

For the evaluation of the influence of the carbon content on the pellet strength and later on the combustion rate of the pellets sinter coke was added additionally to the binder Aluminate cement (AC), Portland cement (PC), Calcium hydrate (CH) and Water glass (WG) to the pellet raw mixture. The pressure strength in dependence of the ageing time is shown in Figure 18. The trend of the pellet strength with sinter fuel is comparable to the trend without sinter fuel. Nevertheless the pellet strength increase slightly with addition of the sinter fuel. The green pellet strength seems to be independent of the kind of binder.

Figure 18 Influence of carbon content on pellet strength

On the basis of the laboratory tests a mixture containing 60% BF dust, 30 % sinter coke and 10% binder having a moisture content of about 10% was defined as basic mixture for the semi-technical pelletizing tests. Calcium hydrate was chosen as binder. Also a curing time of 3 days seem to appropriate to reach a sufficient cold strength.

2.2.3.2 Investigation of parameter for pelletizing and briquetting at pilot scale (Task 3.2)

2.2.3.2.1 Die Press

On the basis of the laboratory investigation pelletizing tests were carried out with a semi-technical ring die press. The aim was to determine technical parameter of the die for the production of stable pellets with a diameter of 3 mm. Furthermore the mixture composition and binder content was varied • to optimise the strength of the pellets with respect on the conveying and mixing before feeding of the sinter mixture on the strand • to produce a sample of pellets for a thermal evaluation at the sinter pot. The press consists of a ring die and pressing rollers shown in the following figure. In operation, the ring die rotates, making the rollers turn and press the material through the cylindrical holes of the ring die. The cylindrical pellets rotate with the ring die and are cut by a blade.

Figure 19 Die press

The diameter of the applied semi-technical ring die was 300 mm and the width 60 mm. The die contains 1880 borehole. The throughput of the die press is in the range of 400 – 500 kg/h . The main mechanical parameter of a die press are the diameter of the borehole, varied between 3 and 4.5 mm, and the borehole length, varied in the range of 10 – 15 mm.

The parameter of the mixture are shown in Table 6

BF dust Sinter coke AMB Binder (Calcium hydrate) Moisture content % % % % 50- 100 0-50 0-20 17-23 Table 6 Parameter of the pellet mixture

In the Figure 20 produced BF dust-pellets with a diameter of 3 mm and a BF-dust content of 60%, a binder content of 10% and a sinter coke content of 30% are shown. This is the basic receipt was transferred to the thermal evaluation.

Figure 20 Pellets (3 mm diameter) from die press (BF dust 60%, sinter coke 30%, binder 10%)

2.2.3.2.2 Roller Press

At ILVA laboratory a “Hutt” roller press with a productivity of about 250kg/d for briquetting tests is available. It can be used with various types of compacting rolls to ensure the best briquetting performance, at desired size and hardness.

Figure 21 “Hutt roller press at Ilva and briquettes from best practice tests

Tests were carried out in order to obtain a stable brick with a similar size and volume of the coke breeze particle (Figure 22). The tests have shown that the brick yield decreases with the reduction of the volume of the briquettes and mainly when the volume was less than 9 cm3.

To reduce the volume below 9 cm3, tests were carried out with an extrusion method by a hydraulic piston. So briquettes with a volume of 0.1 cm3 could be produced

0.1 cm3

Figure 22 Briquette shape and volume of continuous roller press

The brick mixture was made of BF dust (20%), sludge (40%), lame scales (40%) and as binder bentonite (5%), with a moisture content of about 5 %. These parameters give a average briquette hardness in a range of 5 - 9 kg/briq. with a bulk density of 2 g/cm3. The drying time of the briquette is of about 48 h. before their use in the sintering tests. Also sinter pot tests with the produced briquettes were carried out (Chapter 2.3.4.2.2)

The laboratory trials have shown that production of bricks/pellets from a raw mixture of dust and sludge is limited due to the low production rate. On the basis of this experience a feasibility study was carried out to evaluate the transfer of the briquetting to a continuous roller press in industrial scale.

2.2.3.2.3 Disc pelletizer

In laboratory scale at AMB and ILVA tests with a disc pelletizer were carried out to evaluate the granulation of different mixtures from BF-dust, BF sludge, lame scale and cast house dust. The mixtures were mixed with Eirich mixer. The compositions of the raw mixture are given in Table 7. Content [%] Mixture AMB Mixture Ilva BF dust 71 36-54 BF sludge / 9 Cast house dust 17 / Lame scale / 36-54 Cement 8 / Lime 4 1

Table 7 Raw mixture composition for disc pelletizing

At Ilva moisture content of 12 % was adjusted. For the sinter pot tests Ilva used the pellets in-between 3 – 8mm after a curing time of 48 h and with a carbon content of 23-32%. A sample of the pellets of mixture AMB produced with disc pelletizer is shown in Figure 23.

Figure 23 Pellets from a disc pelletizer

2.2.3.2.4 Abrasion tests with pellets

The strength of the dry pellets was evaluated by determining the content of the fraction smaller than 1 mm in dependence of the stress during screening. The aim was to estimate the whether the pellets could withstand the stress during the sinter mix preparation before they get charged on the strand. For

27 comparison the test was also carried out with sinter fuel from AMB, because sinter fuel is not getting crushed remarkable during the sinter mix preparation. A similar strength means that the pellets could withstand the stress during the pre-treatment.

For determining the abrasion strength screening tests were carried out and the contents of the fraction smaller than 1 mm for the different materials in dependence of the stress were measured. The stress at the screening test was varied by changing the amplitude and the screening time. The Figure 24 shows the content of the pellets smaller than 1 mm in dependence of the stress for sinter fuel, pellets from the die press and the disc pelletizer.

Figure 24 Abrasion Strength - content < 1mm after screening

The contents < 1 mm of the pellets from the die press as well as the pellets from the disc pelletizer are smaller than that of the sinter fuel, so the abrasion strength is higher. Furthermore the content < 1 mm of pellets from the disc pelletizer at high stress is lower than that from the die press.

On basis of the results it can be assumed that the pellets from the disc pelletizer, which were stored and dried, will withstand the stress during the transportation process during the sinter raw material preparation.

2.2.3.3 Discussion of results and transfer

Extensive trials have been carried out using a die press, a continuous roller press and a disc pelletizer in laboratory scale for the pelletizing of the in house dusts. Also various binder as Portland and aluminat cement, Calcium hydrate and water glass have been applied in combination with different raw material mixtures.

On the basis of the laboratory tests a mixture containing 60% BF dust, 30 % sinter fuel and 10% binder having a moisture content of about 10% was defined as basic mixture for the semi-technical pelletizing tests at a die press. Calcium hydrate was chosen as binder for cost reasons. At the die press it was found that the strength of pellets with 10% binder is clearly higher than sinter fuel which means also that the content of binder can be reduced to save binder and costs.

The laboratory trials applying a continuous roller press have shown that production of briquettes from a raw mixture of dust and sludge is limited due to the low production rate. On the basis of this ILVA has carried out a feasibility study to produce ACASOS (briquettes) at industrial pressing Koppern machine. This study is carried out in teamwork with ILVA engineers of Koppern machine. The conditions were:

• The bricc. mixture size distribution < 3mm • Bricc. size and shape are about 2 cm length and 0.5 cm thickness • Bricc max use in the sinter plant ≤ 1,52% (coke reduction of 0,4%) • Mix moisture > 5% • Bricc. annual production ≈ 100 Kt (for a sinter production of 10 Mt) In the graph below there is the scheme of the briquetting plant, the data are reported below: • Silos binder: 50 t • Silos BF dust: 100 t • Silos mill scales: 100 t • Screening 1: 40 t/h • Conveyor belt: 40 t/h • Dryer : 20 t/h • Screening 2: 30 t/h • Silos mix dust: 25 t • Screening 3: 40 t/h • Mixer: 40t/h • 4 workers per shift

Figure 25 Briquetting plant

The total cost of the plant is of about 20 M€. Actually ILVA is not planning to realize the plant for the production of ACASOS briquettes because of the high zinc content. In laboratory it was found that the briquette yield is too low when the briquette volume is less than 9 cm3. Due to this a technical trial using the continuous roller press and industrial realisation was skipped. At the labor disc pelletizer a mixture of 71% BF dust, 17% cast house dust and 12% binder was applied to produce stable pellets. As binder a mixture of cement and Calcium hydrate was used to reach a sufficient strength.

An amount of pellets for sinter pot tests was produced and was send to voestalpine for the comparative sinter pot tests. The composition is given in the Data base in the appendix.

2.2.4 Thermal Evaluation of Pre-Treated ACASOS

In the next step reactivity tests and sinter pot tests were carried out from by the partner using sample of the pre-treated and alternate carbon sources to substitute carbon breeze and evaluate the carbon replacement factor, i.e. the ratio of the carbon content of coke breeze to the carbon content of the ACASOS. As ACASOS pet coke, anthracite, anode coke, BF dust, BF sludge and mixtures of BF dust+sludge containing also cast house dust and binder as well as biomass as olive pits and wood pellets were evaluated. Within the sinter pot tests it was in general assumed that the carbon replacement factor is 1 when the carbon breeze was substituted by the alternate carbon sources. Additional voestalpine has carried out a number of pot tests twice with a presumed carbon replacement factor of 0.5 and of 1.

The evaluation of carbon replacement factor of ACASOS when replacing coke breeze at the sinter pot trials was based mainly on the return of fine balance of the sinter pot and in comparison to a standard sinter pot test at a balanced return fine ratio carried out with coke breeze only. Beside quality and performance date were also taken into account and compared to the standard test. A high replacement factor at the substation is reached at a slightly deviation of the performance and quality data in comparison to the standard test at a balanced return fines ratio.

Characteristic parameters which have been evaluated are:

• Flame front, sintering temperature, sintering speed and time,

• Efficiency and sinter quality parameter according to ISO standard tests (Tumbler, Shatter, RDI, grain size distribution analysis, etc.)

Also their environmental impact (mainly VOC and SO2) was determined.

2.2.4.1 Thermal lab scale tests

2.2.4.1.1 Thermal lab scale tests: Determination of reactivity pellets

In order to evaluate and to compare the reactivity and determine the influence of the pelletizing on the combustion rate pellets produced with the semi technical die press and the disc pelletizer as well as different kind of alternate fuel were burned in air in a laboratory tube furnace at 1200°C.

The furnace was heated under a nitrogen stream until 1200°C, than the sample of about 0.5 g was inserted into the furnace and the atmosphere was switched to air. The off gas components CO2, CO and O2 the volume flow and the furnace temperature were measured continuously.

On the basis of the CO2 and CO content in the off gas, the volume flow and temperature the combustion reactivity was calculated based on the mass balance and a reaction model.

The Figure 26 shows the combustion reactivity k of the BF dust pellets with and without coke breeze addition in the raw mixture, untreated sinter coke, untreated pet coke and anthracite in dependence of the carbon content.

0.0020 pellets untreated fuel 0.0016

0.0012

0.0008 Pellets

reactivity k [g^0.5/s] k reactivity Sinter coke AMB 0.0004 Pet-coke Ilva Anthracite Ilva

0.0000 0 20406080100

Carbon Content [%]

Figure 26 Reactivity of the pellets, sinter mixture sinter coke, pet coke and anthracite in dependence of the carbon content

The reactivity of the BF dust pellets varies in between the reactivity of the sinter coke of AMB and the pet coke and the anthracite of Ilva. A clear influence of the sinter coke content within the BF dust pellets on the reactivity can not be determined which lead to the conclusion not to add of sinter coke in the pellet raw mixture. An additional advantage is that the volume which has to be mixed and pelletized was reduced

2.2.4.1.2 Thermal lab scale sinter pot tests with pretreated biomass

To evaluate the replacement factor of biomass further sinter pot tests were carried out with the small laboratory sinter pot with a diameter of 10 cm (Figure 4 and 5) at Tata steel. The base tests contained coke breeze at a level of 4 % of the mix on a wet basis and the moisture content was also 4 %. A quar- ter of this coke breeze was removed from the base mix and substituted for the biomass on a carbon replacement basis. In these tests the biomass materials investigated were hazel nut shells (haz), almond shells (alm) and crushed sunflower husk (sun) briquettes. The mix components were mixed dry in a rotating drum for 10 minutes, the moisture was added and the wet mixture was subjected to a further 10 minutes in the rotating drum.

Two base comparator tests were done with just coke breeze, 3 tests each with hazelnut (haz) shells and the sunflower husk (sun) material and 4 tests with the almond shells. In each test the temperature thermal profile was recorded and the waste gas was analyzed for CO, CO2, O2 and SO2. In the last of tests for each trial the NOx was also measured in the waste gas. The time temperature profile of the laboratory sinter pot tests is illustrated in Figure 27.

T/C 4 curves

1400

1200

1000

800

600

400 Temperature, °C

200

0 0 100 200 300 400 500 time, s

Coke 2 Sun 1 Haz 3 Alm 3

Figure 27 Typical thermal profile down the bed

The thermal profile for coke breeze is the same shape as those generated using a sinter mix in a larger sized sinter box. In comparison the highest temperature is achieved with the coke breeze base test. The sunflower husk material has the next highest peak temperature but about 150 °C lower than the coke breeze achieved and occurring marginally earlier than the coke breeze peak. The tests with almond and hazelnut shells have much lower peak temperatures. The curves post the peak temperatures have quite different shapes compared with the coke breeze test reminiscent of miss-matched profiles reported in the 1950’s by Wild and others. On the heating side the biomass materials tend to run slightly ahead of the coke breeze curve possibly a reflection of the structural composition of the biomass materials. The lower peak temperatures achieved with the biomass materials could be a reflection of this loss of heating potential. There could be a case to look for hydrogen in the off gas to determine if volatilization and loss of the volatile matter is occurring and to quantify the effect. Beside it shows that the replacement factor must be considerable lower than 1.

The average combustion efficiencies, calculated from CO2/[CO2+CO], are shown in Figure 28, for each material. If the efficiency was 100% there would be only CO2 in the waste gas and no CO. It is a characteristic of sintering that there is always some CO in the off gas as it is swept away from the hot zone before it can be oxidised. In these tests with the inert beds there is no calcination occurring so the combustion efficiency calculated from this formula should relate directly to the fuel. From Figure 28 it is evident that the average efficiencies differ little but is marginally lower for the sunflower husk material than for the other fuels. The peak occurring near the end of the test cannot currently be ex- plained but it is noted that it appears earlier for the biomass materials than the coke breeze.

1.000

0.800

0.600 Coke ave Sun ave Haz ave 0.400 Alm ave CO2/CO+CO2

0.200

0.000 0 100 200 300 400 500 time, s

Figure 28 Average combustion efficiencies in an inert bed

The SO2 results are shown in Figure 29. The lower SO2 emissions for the biomass materials compared with the coke breeze are significant and reflect the lower S loads carried in the biomass materials i.e. coke breeze has a S content of about 0.6 % compared with the biomass materials that are less than 0.14% S. No significant differences in the NOx emissions were observed but these data are base on only one test per fuel.

160

140

120

100 Ave coke Ave Sun 80 Ave Haz

SOx, ppm v ppm SOx, 60 Ave Alm

0 0 100 200 300 400 500 time, s

Figure 29 Average SOx analysis, combustion in inert beds

2.2.4.2 Technical scale tests using ACASOS for evaluating sinter parameter and quality

2.2.4.2.1 Sinter pot tests with Biomass at Tata steel

Sinter pot tests were conducted by reducing the amount of coke breeze in the base case and replacing it with a weight of olive pits containing the equivalent total carbon removed in the coke breeze. (Table 8)

No. Trial number Carbon replacement, (%) Coke breeze, (kg) Olive pits,(kg) 1 Base case 0 11.20 0.00 2 2460 5 10.15 0.98 3 2462 15 9.09 2.93 4 2464 15 + 0.1% coke breeze 9.43 2.93 5 2466 5 10.15 0.98 6 2468 10 + 0.1% coke breeze 9.96 1.96 7 2470 10 + 0.1% coke breeze 9.96 1.96 Table 8 Designed experiments and biomass/coke breeze content.

The ore blend used for this work was based upon the standard blend for Tata Steel Scunthorpe sinter plant for 2008/09. The iron ore blend was composed of 100% South America ores. The aim was for a sinter with a CaO/SiO2 of 1.52 and a MgO level of 1.42 (using olivine to provide the MgO). The return fines level was set at 30 % .

The raw mix was blended in a cement mixer to ensure complete mixing. Sufficient mix was prepared for three replicate sinter tests to be conducted in one day. The sinter boxes were 375 mm square with a 300 mm diameter core of sinter mix and a bed height of 500 mm. The space between the inner cylin- der and the sinter box was filled with iron ore concentrates to prevent air leakage and the grate bars covered with a hearth layer of the -16+10mm fraction. The aim for the base case mixture was 7.5 % moisture and 2.4 % coke breeze. Sintering was carried out under a suction pressure of 58 mbar.

The hearth layer and return fines were made on the previous days with the fan run on full to give weak sinter that can be easily broken up. To reproduce on-strand conditions the sintered ore was dropped 5 metres from a shatter tower and stabilised in an ISO drum for 80 revs (2.5 minutes). It was then screened over Triton screens into +25, +16, +10 and +6.3mm fractions. The material < 6.3 mm was screened again at 5 mm to provide the return fines fraction.

Tests were conducted by reducing the amount of coke breeze in the base case and replacing it with a weight of olive pits containing the equivalent total carbon removed in the coke breeze. Base 2460 2466 2468 2470 2462 2464 Coke breeze % 100 95 95 90 90 85 85 Olive pit % 0 5 5 10 10 15 15 Mix moisture % 6.3 7.6 6.7 7.15 7.15 7.49 7.48 Permeability BPU 89 90.5 91.67 81.5 73.5 77.5 86.5 T/C 3 peek °C 1324.5 1336.85 1268.9 1238.5 1331.5 1262.1 1276.1 Yield % 69.7 66.49 66.23 - 60.56 60.03 63.07 Returns balance in/out % 105.4 115.91 94.37 - 110.2 80.74 104.76 Sinter mean size mm 18.5 16.35 15.21 - 16.36 13.47 14.88 Relative production rate t/m²/24h 23.9 22.45 19.83 - 16.87 13.43 20.11 % + ISO Tumble Test 6.3mm 73.4 73.33 71.13 - 73.27 69.87 73.2 FeO % 3.87 4.25 2.79 2.28 3.84 2.33 3.21 Table 9 Sinter characteristics for the trials.

In terms of sinter process trials 2460 and 2464 gave the best results. Both runs showed good production rates, cold strength values as well as coke consumption. The fines balance is slightly higher in 2460 but, coke breeze reduction by 0.1% would bring it back to 100%. By adding only 0.1% extra coke breeze to 2460, sinter process improved significantly (Trial 2464) which indicates that sinter box is very sensitive to small changes in the blend and responds to the smallest changes in recipe or procedure. Although trials 2460 and 2466 were similar in terms of the raw material and biomass/coke breeze content, run 2466 had much lower moisture i.e. 6.7% and the decrease in sinter quality was a consequence

34 of lower bed temperatures. Run 2470 also showed good cold strength values but coke consumption was quite high and productivity was low, mainly due to long sintering time. Hence, permeability is very low which can be due to high bulk density and moisture content of the blend compared to 2466. By comparing production rates it can be seen that runs 2460 and 2464 had the highest production rates among the runs.

In summary, 15% carbon replacement by olive pits plus 0.1% extra coke breeze (run 2464), looks very promising. In this run, right ignition, moisture content, granulation and bed permeability resulted in the best results compared to other tests. Although in comparison the performance and quality data were below the base test data which indicate a carbon replacement factor below 1.

2.2.4.2.2 Sinter pot tests at ILVA

Ilva has also carried out sinter pot tests to investigate the influence of non-briquetted and briquetted dust and sludge mixes as well as non-briquetted alternate carbon sources as anthracite and pet coke on the sintering process.

At first a standard sinter pot trials has been carried out to compare influences of the alternate carbon sources in the sinter mixture. For the standard sinter pot tests a standard mix has been prepared containing a simple mix of five iron ores mixture, fluxes (as olivine, limestone and lime) and circulating materials (such as scales). The simplified ore blend was used during the whole project period So the granulometric distribution and its chemical and technological properties could be better control. The target was • a self-fluxing sinter the aimed IB2 index was between 1,80 and 2. • the FeO target in the standard sinter is 4%. Concerning mechanical properties the aimed was to adjust that return fines ratio(< 5 mm) within the range of 0.95÷1.05. Also other mechanical properties were investigated as shatter index (JIS M 8711) and ASTM tumble index. Furthermore Rid (reducibility index) and RdI (reduction degradation index) were evaluated.

At the sinter pot tests 10 – 50% of the coke breeze was substituted with non-briquetted alternate carbon sources as well as briquetted and pelletized BF dust and sludge mixtures. For the evaluation of the results and the replacement factor performance and quality data were compared to the standard sinter mix (see Appendix, Table 18).

The substitution of carbon breeze by Pet–coke up to 50% has caused an increase of the sinter productivity. It was assumed that this was caused by the higher volatile matter content that supports combustion ignition and by the increased permeability that allows a faster cooling. The chemical composition and mechanical properties were not greatly influenced by the addition of pet-coke. As a consequence of a higher final permeability the reducibility increased. Also RDI increased except for the sinter with a 50% of pet – coke content.

When coke breeze was replaced by anthracite up to 30% the sinter yield decreased slightly. Especial- ly for a high anthracite content the balance index increased. The sintering time decreased for the mixtures with increasing anthracite content due to the better ignition characteristics in comparison to coke breeze; because of the higher volatile content that supports the combustion. The sinter productivity increased only for low anthracite content because an increasing of the return fines. The size distribution is not really influenced by anthracite addition, only the mix with 30% of anthracite shows an increase of fine size fraction. Instead the Shatter Index decreased for anthracite addition. As a consequence of a higher final permeability the reducibility and the RDI increased. Chemical composition wasn’t greatly influenced by anthracite addition, only the sulphur content slightly increased with increasing anthracite. The wustite content is greater than standard sinter mix but is quite stable in the anthracite sinter tests.

When coke breeze was substituted by the untreated sludge mix (47% BOF sludge, 32% BF dust, 16% BF sludge, 5% Dredging sludge) and a mix of BF dust and sludge in the range of 10 -20 % the sinter yield decreased when 10% was substituted. Instead the yield increased when 20% was substituted. The sintering time increases for the mixtures with the sludge and dust content. Also the size distribution is influenced by sludge and dust addition. There is an increase of fine size fraction mainly for the mixture with the sludge mix (Mix 156 – Mix 157). The Shatter Index decreased for all the tests. There is an in-crease of the RDI and an increase of reducibility only for the tests with the sludge mix content, instead the reducibility decreases for the mix with the BF sludge and dust. The sinter is greatly influenced by sludge mix addiction than BF sludge + BF dust. Chemical composition is influenced and mainly for the wustite, alkali and zinc. Also the fines balance indicated that the carbon replacement factor is far below 1.

At the sinter pot tests ILVA has also analyzed the relationships between waste gas/sinter temperatures of the ACASOS materials (Appendix, Table 19). Temperatures in the sinter feed were monitored by 3 Pt/Pt(Rh) thermocouples. The cooling rate has been calculated on “high thermocouple”, between its maximum temperature and the one it has when the adjacent thermocouples shows its max temperature value. Flame front speed is calculated by the maximum thermocouples temperature, knowing distance between two adjacent thermocouples (15 cm).

When coke breeze was replaced by Pet – coke, the flame front temperature ranges from ~ 1250 °C to ~ 1350 °C in the middle of the cake. Modifications in flame front temperature are probably due to pet- coke high content in volatile matters. Flame front speed was not influenced by pet-coke addition, but sinter productivity raise because of the higher volatile matter content that supports combustion ignition and because of the increased permeability that allows a faster cooling.

About the anthracite, the thermal sinter behavior shows a slightly increase of max gas temperature and an increase of the flame front average speed. The cooling speed is higher for the sinter with anthracite addition and may be related to the higher sinter permeability.

About the sludge mix and BF sludge + BF dust additions, there is an increase of max gas temperature and an increase of the flame front average speed only for the low ACASOS materials content (10%). The cooling speed decreases except for the mix 158 (Appendix, Table 19).

Also sinter pot tests with pelletized/briquetted ACASOS material were carried out.

Briquetts were produced with a laboratory continuous roller press. The brick mixture is made of BF dust (20%) and sludge (40%), lame scales (40%) and as binder bentonite (5%), with a moisture content of about 5 %. These parameters give an average briquette hardness in a range of 5 - 9 kg/briq. with a bulk density of 2 gr/cm3. (Appendix, Table 20) the coke breeze was substituted by 10-20% of BF dust and sludge pellets.

A pelletized ACASOS mix was produced in an Eirich device and in a tilted dish. Two pellet mixtures were used: • 54% lame scales, 36% BF dust, 9% BF sludge, 1% lime • 36% lame scales, 54% BF dust, 9% BF sludge, 1% lime with a moisture content of 12%. The size distribution utilized in the sinter mix range was between 3 – 8 mm. The drying time of the pellet is of about 48 h and the carbon content is of about 23 – 32%.

For the sinter pot tests 10% and 20% of coke breeze was substituted by the pelletized and briquetted ACASOS.

When 10% of coke breeze was substituted the sintering data related to these tests show a decrease of shatter Index, and an increase of RdI and reducibility, but the deviation are limited for low briquetting content. The sintering time and the sinter yield are approximately the same, instead there is an increase of the start permeability.

Great differences there are about sinter chemical composition; it is mainly influenced in relation to the briquette content and mainly for the wustite that decrease in relation to ACASOS increasing and for zinc that increase in relation to ACASOS increasing. For Taranto steel plant the actual limit for the zinc into the sinter is less than 0.01%, this is the main impediment for an industrial use of this kind of briquettes at industrial scale.

Beside the tests with “briquettes” ACASOS material the Lab has carried out some tests, with the aim to study the waste gases composition (NOx, SO2, O2, CO, CO2) and its behaviour in relation to sintering process. The behavior of SO2 shows the presence of two peaks related both to the ignition start and to the end of the test process. The NOx is related with the sintering time. The O2, CO, CO2 show a typical behaviours of a sintering process in which the consumption of oxygen (due to coke combustion) is related to the production in the waste gas of CO and CO2 . Only for the “pellet” test there is a faster decrease of O2, related to the start of the sintering process. The addition of briquettes into the sinter mixture doesn’t worsen the waste gases quality.

2.2.4.2.3 Comparative sinter pot tests at voestalpine

Comparative sinter pot tests using the prepretaed ACASOS from the partner were carried out at voestalpine. To compare different ACASOS materials from the project partners, an internationally common, averaged sinter mix composition without low grade ore was defined and a new, almost cylindrical sinter pot was built with a decline angle of only 0.5 degrees. The composition of the sinter mixture, regarding ores and recycling materials as well as bacisity, coke breeze and return fines was taken from average values over all EBFC sinter plant data. On the basis of a few tests with this mixture, a reduction of return fines input from 360 kg to 300 kg per ton of sinter turned out to make sense. The ACASOS tests were carried with a bed height of 600 mm, which is close to EBFC average.

Pressure drop was 110 mbar which is significantly lower than EBFC average. Direct comparison of productivity between pot tests and sinter strands under the same conditions generally exhibits higher values for pot tests, which normally cannot be reached at the plant. One main reason is false air at sinter strands, which is very low in sinter pot equipment, so it seems more appropriate to represent flame front propagation rather than pressure drop.

For the evaluated ACASOS the carbon replacement factor which yield a sufficient performance and quality figures is unknown at the stage of sinter mix preparation. Therefore, the process of calculating an adequate carbon replacement factor can only be done by iteration, comparing the results of tests with different carbon replacement factor assumed before.

So at first the sinter pot tests a carbon replacement factor of 1 was assumed, i.e. at the sinter pot tests 10 % of the carbon from coke breeze was replaced by 10% of the carbon from the ACASOS. At a second sinter pot trial the carbon replacement factor was assumed to be 0.5. It means 10 % of the carbon from coke breeze was replaced by 20% of the carbon from the ACASOS material. On the basis of results of the sinter pot tests with different a carbon replacement factor was evaluated. The tests were at first carried out with pre-processed BF sludge (Figure 43), briquetted in-house dust mixes (Figure 20) and raw pet coke.

With a return fines input of 300 kg/tsinter and slight adaption of the return fines output coefficients, after a few pre-tests finally in the two reference tests (without alternate carbon sources in the mix) an exact- ly balanced input/output ratio of return fines (i.e. 1:1) could be obtained.

Test No SV30/09 SV31/09 SV33/09 SV34/09 SV35/09 SV36/09 SV37/09 SV38/09 Test descrip- BF dust BF dust Basis Basis BFsludge BFsludge Pet coke Pet coke tion pellets pellets Assumed Re- placement fac- 1 0.5 1 0.5 1 0.5 tor Burn through 25.2 25.7 27.3 25.2 25.4 24.4 26.1 23.9 time, min Burn through 389 403 402 406 381 381 381 381 temp., °C Productivity, 37.1 35.3 34.0 36.7 36.2 38.2 35.5 39.0 t/24h/m² Return fines / 304.2 304.8 296.2 274.2 303.1 285.1 299.1 285.0 sinter, kg/t Return fines 1.01 1.02 0.99 0.91 1.01 0.95 1.00 0.95 balance out/in RDI-Test frac- 32.3 38.95 41.05 37.1 39.4 38.6 40.9 36.1 tion - 3,15 mm [%] Table 10 Test conditions, performance and quality results.

The most important test conditions and the main results for sintering time, sinter productivity, calculated as yielded mass of sinter divided by pot cross section area, and return fines figures, can be seen in Table 10. From the return fines balance in the last row it can be seen that for all three tested ACASOS materials, when the carbon replacement factor was assumed to 1, return fines output / input balance is very close to 1, but with a mixture with assumed replacement factor of 0.5 (i.e. 20% of coke breeze carbon of basis mix is supplied by ACASOS material, and additionally 90% of the coke breeze of basis mix) the mass of output return fines is significantly lower than 1. This leads to the conclusion that there was more effective fuel in the mixture than in the basis mix, and therefore the carbon replacement factor for all three tested materials is closer to 1 than to 0.5.

Additional sinter pot tests with Olive pits, Wood pellets, Anode coke and Pet coke were carried out at voestalpine. (Figure 30)

Figure 30 Olive pits: crushed to < 2mm (left); anode graphite coke: < 8mm (middle); wood pellets: Ø 8mm, length up to 25mm (right).

The tests with olive pits, wood pellets and anode coke were based upon equal conditions as with the basis tests and with the pre-processed inhouse dusts & sludges and pet coke. Calculation of sinter yield, return fines ratio and specific sinter productivity was carried out in the same way as described.

Test No SV39/09 SV40/09 SV44/09 SV45/09 SV46/09 SV47/09 Test description Olive Olive Anode Anode Wood Wood pits pits coke coke pell. pell.

Assumed Replacement factor 1 0.5 1 0.5 1 0.5 Burn through time 32.2 30.3 27.7 26.1 34.4 31.9 T=200 °C+ 6 min Burn through temperature, °C 409 392 445 442 431 426 Sinter productivity, t/24h/m² 28.1 30.5 33.6 36.0 23.6 27.2 Return fines / sinter, kg/t 357 323 303 282 471 364 Return fines balance out / in 1.09 1.04 0.99 0.91 1.36 1.13 RDI-Test ISO4696-2 38.3 35.6 30.1 31.5 39.8 38.4 fraction – 3.15 mm [%] Table 11 Test conditions and performance and quality results.

From the return fines it can be seen that for both biomass products, i.e. olive pits and especially wood pellets, production of return fines is higher than input. For olive pits, the difference is rather small, this indicates that there is a noticeable contribution of the olive pits to fuel effect. With wood pellets, especially for a presumed replacement factor of 1 on carbon basis, the high value of generated return fines indicate that the carbon replacement factor by wood pellets does by far not reach values near 1.

On the other hand, using crushed coke from used graphite anodes a replacement factor of 1 on carbon basis exhibits a return fines balance very close to 1. Presuming a carbon replacement factor of only 0.5 (i.e. 20% carbon as anode coke plus 90% of coke breeze input of the reference test, expecting that 20% carbon from ACASOS material coke counts for only 10% of carbon from coke breeze) generates less return fines than the reference tests, so this is an indication for higher fuel input, therefore replacement factor must be significantly higher than 0.5.

Reduction Disintegration Index according to ISO4696-2 tests show that for anode coke the values for the fraction < 3.15mm are in the same range as standard reference sinter pot tests as well as pre-treated ACASOS materials from BF sludge and dust with values in the range of 23-33% < 3.15mm, where differences within this range are caused by the type of ACASOS material and the presumed replacement factor. Compared to the results of standard mix and the pre-processed ACASOS from in house dust and sludge, the tests with both biomass samples exhibit a significantly higher low-temperature breakdown, expressed by RDI-fractions < 3.15mm between 36 and 40%. This is a further indication for lower carbon replacement factor than for pre-processed ACASOS or alternate carbon sources such as pet coke or coke from recycled graphite anodes.

2.2.4.2.4 Comparison of flame front propagation

Thermocouple measurements were carried out for the sinter pot tests of VASL to evaluate the flame front. In Figure 31 the flame front at the height of 38 cm of the sinter pot for a basic mixture and also when 10% coke breeze was substituted by BF dust pellets from AMB/BFI, Pet coke, olive pits and wood pellets are shown.

From these results it can be seen that biomass products, especially with high volatile content, tend to lower maximum temperature and a wider flame front in comparison to the basic mixture. The flame front curve in the sinter mixture when 10% carbon breeze was substituted of the Bf dust pellets and the

Pet coke were similar to the basic mixture

1400

Basis -38cm 1200 AMB-BFI-38cm Pet coke -38cm

1000 Olive pits -38cm Wood pellets -38cm

800

600

400 Temperature from TC NiCr-Ni, °C 200

0 0 5 10 15 20 25 30 Sintering time, min

Figure 31 Temperature measurement in height position -38 cm from top

2.2.4.3 Comparison of environmental aspects

At sinter pot tests also the emission as CO-, CO2-, SOx- and volatile organic carbon content in the off gas were measured at voestalpine while the coke breeze was substituted with the different alternate carbon sources. In Table 12 emission of the sinter pot trials with pre treated BF sludge, BF dust pellets and Pet coke are shown. Test No SV30/09 SV31/09 SV33/09 SV34/09 SV35/09 SV36/09 SV37/09 SV38/09 Test descrip- BF BF BF dust BF dust tion Basis Basis sludge sludge pellets pellets Pet coke Pet coke Assumed Re- placement factor 1 0.5 1 0.5 1 0.5

O2 [%] 13.0 13.6 11.9 12.2 12.3 12.9 11.8 11.7 CO [%] 1.33 1.22 1.55 1.66 1.78 1.82 1.62 1.7

CO2 [%] 8.5 7.7 9.3 9.0 8.9 8.1 9.5 9.6

SO2 [ppm] 287 283 380 395 236 268 394 422 VOC [ppm] 25 22 27 28 21 29 130 129 Table 12 Gas analysis of sinter pot tests

Significant differences to the basis tests are obvious for the averaged SO2-concentration of the tests with pet coke and pre-processed BF sludge. Both input materials have considerably higher sulphur content relative to their carbon content than coke breeze. For all materials, the test with assumed carbon replacement factor of 0.5 lead to higher SO2 concentrations in off-gas due to higher fuel input. Volatile organic carbon concentration, measured via Flame Ionization Detection (FID), is in the range of basis mixture for pre-processed BF sludge (voestalpine) and BF dust pellets of AMB/BFI, but is 5 times higher for pet coke.

Dust emission measurements during the substitution of carbon breeze were carried out at the trials in industrial scale. Negative effects which could be traced back on the substitution of coke breeze by alternate carbon sources could not be detected.

Also at the sinter pot trials with pre treated olive pits, anode coke and wood pellets the emission as CO-, CO2-, SOx- and volatile organic carbon were measured. As can be seen from Table 13, significant differences to the basis tests are obvious for the averaged SO2-concentration of anode coke and olive pits. Anode coke with a sulphur content of about 1.5%, which is in the same range as pet coke, generates more SO2, whereas biomass products generally, in special the olive pits investigated in this project, lowers SO2-concentration significantly. Besides the CO2-sustainability of biomass fuels, lower SO2-emissions are a main advantage of all biomass fuels. Test No SV39/09 SV40/09 SV44/09 SV45/09 SV46/09 SV47/09 Test description Anode Anode Wood Olive pits Olive pits coke coke pellets Wood pell. Assumed Replacement factor 1 0.5 1 0.5 1 0.5

O2 [%] 12.46 13.13 12.62 12.8 11.78 11.24 CO [%] 1.77 1.62 1.6 1.73 1.84 2.08

CO2 [%] 8.98 7.98 8.13 8.22 9.26 9.6

SO2 [ppm] 187 166 284 315 n.d. n.d. VOC [ppm] 148 136 22 31 276 280 Table 13 Average gas analysis of sinter pot tests

On the other hand, according to a higher content of hydrogenated organic carbon, all tests with biomass generated higher emissions of volatile organic carbon (VOC). It is noticeable that with addition of pellets mainly from spruce wood, VOC-emissions are by far higher than with olive pits. This may be a result of different fixed carbon content, i.e. olive pits consist of very hard wood with lower volatile matter than soft spruce wood. Nevertheless, smoke generation and VOC-emissions can limit the utilization of biomass fuels in sintering. But a comparison of VOC- and the CO emission from when Pet coke and olive pits show that they were in the same range although the volatile content of the olive pits is 6 to 8 times higher than pet coke. This indicates that a part of the volatile content has also be utilized at the sintering.

2.2.5 Field Tests and Best Practice

The objectives are to transfer and apply the knowledge in industrial scale. Field tests were carried out at the sinter plants of AMB, ILVA and VASL. In Table the basic data of the sinter plants are shown AMB ILVA VASL Suction area m2 150 472 252 Strand length m 50 74 Strand width m 3 3.5 Power of suction MW 7.5 Capacity Mt/a 2.8 6.5 3.3 Productivity t/m2/24h 53 37.5 41 Table 14 Sinter plants for industrial tests

At AMB pelletized BF-dust was used as ACASOS. Voestalpine utilized the pre processed BF sludge and at ILAV coke breeze was replaced by anthracite.

2.2.5.1 Pre-treatment for field tests BF sludge was treated with a hydro cyclone station and a blade crusher to grind the ACASOS fraction dewatered by an existing filter press. The results were: • about 65-70% of the treated BF sludge can be recycled. • separation efficiency , concerning grain size distribution and heavy metals separation is sufficient with a single-stage hydro cyclone-device

• dewatering with a chamber-filter-press down to a moisture content of about 20% is sufficient so that no negative effects on materials handling which can be causes by frozen material in winter was observed • no up-concentration of heavy metals such as lead and zinc in sinter was observed In Table 15 the results of hydro cyclone treatment of the BF sludge are shown. Underflow = ACASOS to Material / product recycling via sinter plant Overflow = landfill Feed: sludge BF A Mass sludge total, t/a 15000 30000 45000 Solids content, % 66.7 13.3 31 Yield Mass total, % 71.4 28.6 100 Yield C in underflow, % 68.4 31.6 100 Yield Fe in underflow, % 72.3 27.7 100 Yield Pb in underflow, % 25.0 75.0 100 Yield Zn in underflow, % 24.3 75.7 100 Table 15 Results of hydro cyclone treatment of the BF sludge

For the production of BF dust agglomerates in industrial scale AMB has rented a mixing unit consisting of a hopper, conveyer and dosing system to adjust the mixture composition and an intensive mixer RV 24 from Eirich to mix and agglomerate the raw mixture. The intensive mixer was charged batch- wise with about 2000kg/charge. The raw mixture consisting of 70% BF dust, 10% cast house dust, 20% of calcium hydrate and about 9% of water. The composition of the agglomerate is given in (see Data Base AMB appendix).

Figure 32 BF-dust agglomerates from intensive mixer

In comparison to the semi-technical trials the binder was increased to guarantee the strength of the pellets. The optimal total moisture content, the sum of added moisture and moisture of the mixture, of the agglomerates was found to be around 16%. About three charges per hour were mixed and agglomerated. About 180 t of BF-dust agglomerates were produced. In Figure 32 BF-dust agglomerates from the Eirich mixer are shown.

2.2.5.2 Use of ACASOS at the sinter plant and influence on emission

2.2.5.2.1 Application of pre-treated BF sludge in industrial scale

Based on the results of lab and pilot scale tests, a three-stage industrial process was implemented, comprising heavy metal separation, dewatering and compacting in a filter press and crushing to a sinter-mix-compatible grain size distribution in a blade-crusher.

In Figure 33 the coke consumption of the VASL sinter plant and the input of BF dust and pre- processed BF sludge is shown over a range of 3 month. About 10 – 20% of the carbon breeze was replaced by the carbon of the BF sludge.

40 udge

30 BF dust and pre-processed BF sludge, kg /t sinter Coke consumption dry, kg/t sinter 25

10 Coke and dustCoke BF + pre-processed sl 5

0 Jul-09 Aug-09 Okt-09 Nov-09 Jan-10 Mrz-10 Apr-10 Jun-10 Aug-10 Sep-10

Figure 33 Coke consumption and input of BF dust and ACASOS = pre-processed BF sludge.

From operational data in Figure 33 it can be seen that with increasing input of ACASOS (mix of BF dust and pre-processed BF sludge – for logistic reasons merged to one product identification number) coke breeze consumption is lowered in February 2010. This indicates total carbon utilization and a carbon replacement factor of 1. Since implementation of the process, CO-content of the waste gas did not increase, this also indicates that carbon is combusted as complete as coke breeze. Also lead and zinc content of sinter stayed in the same range as before, this indicates that heavy metal separation works properly. Regarding influences on sinter productivity and quality figures, changes caused by ACASOS introduction are could not be detected, since changes of general mix composition and especially sinter basicity has much higher influence.

2.2.5.2.2 Application of high Anthracite content in industrial scale

ILVA has carried out industrial tests and has substituted 30 and 62% of coke breeze by anthracite. It was found that the sinter yield and the sinter productivity was decreased up to 2% when the anthracite content was increased which correspond with experimental results at the sinter pot trials.

At industrial scale the quality properties (Rid, RDI and Shatter Index) were stable when coke breeze was replaced by anthracite. The results differ from the lab scale. In lab the reducibility and of RDI increased and the Shatter Index decreased with increasing anthracite content. This was traced back on the unlike sintering procedure in lab scale (homogenizing, temperature, etc.). Sinter productivity and quality as well as emission data of the tests are shown in Figure 34.

39.0 60.0 48.0 43.8 46.2 38.0 50.0 36.9 Y 37.0 36.5 40.0 36.0 36.0 30.0 mg/Nm3 35.0 20.0 PRODUCTIVIT

34.0 10.0 DUST-GAS CONCENTRATION 33.0 0.0 0.0 30.1 62.2 0.0 30.1 62.2 % ANTRACITE % ANTRACITE

350.0 240.0 208.9 271.1 220.0 300.0 197.2 234.1 235.1 200.0 173.7 250.0 180.0

200.0 160.0 SOx mg/Nm3 SOx NOx mg/Nm3NOx 140.0 150.0 120.0

100.0 100.0 0.0 30.1 62.2 0.0 30.1 62.2 % ANTRACITE % ANTRACITE

90.0 80.5 85.0 78.4 74.0 75.9 80.0 72.0 D 75.0 70.0 67.9 68.7 68.4 70.0 )

(%) 68.0 65.0 66.0 RID (% RID SINTER YIEL SINTER 60.0 64.0 55.0 62.0 50.0 60.0 0.0 30.1 62.2 0.0 30.1 62.2 % ANTRACITE % ANTRACITE

30.0 26.2 25.1 94.0 28.0 25.2 92.0 90.1 90.6 26.0 90.0 ) 24.0 90.0 22.0 88.0 20.0

RDI (%) 18.0 86.0

16.0 84.0 14.0 SHATTER INDEX (% 82.0 12.0 10.0 80.0 0.0 30.1 62.2 0.0 30.1 62.2 % ANTRACITE % ANTRACITE

Figure 34 Results of Sinter plant trial with anthracite replacement

The replacement of coke breeze by anthracite led also to a slightly increasing SOx emission whereas the NOx emission was decreasing with increasing anthracite content. The dust concentration in the off gas was not influenced remarkable.

Because of the decreasing sinter productivity and the sinter yield with increasing anthracite content the carbon replacement factor of the anthracite is slightly below 1 although the return of fines ratio is not kown. The SOx emission are increasing with increasing anthracite content in the raw mixture but still the sulphur content of the utilised anthracite was not an limiting factor for the substition.

2.2.5.2.3 BF dust pellets in industrial application – AMB

At the sinter plant trials at AMB 180 t of BF dust pellets were added to the sinter plant within two campaigns. In a third campaign untreated BF dust was added in order to compare both, sintering with pellets and the dust.

At the trials the carbon content of the coke breeze was replaced with the carbon content of the BF dust. The replacement was adjusted via the sinter fuel adjustment system of AMB to obtain the setpoint data. As replacement factor the amount of reduced carbon content of coke breeze when adjusted to the

44 feed carbon content by the Acasos was calculated. To avoid an overshoot when adding BF dust, the carbon content of the ore mixture was reduced about 1 % by reducing coke breeze about 1.5%, referring to the ore mixture.

In Figure 34 the carbon content in the ore introduced by coke breeze and BF dust pellets as well as the total carbon content during the first two campaigns are shown. Furthermore the speed of the sinter strand is shown, to indicate the deviation caused by the addition of BF dust pellets.

In the first campaign a carbon replacement factor of about 0.45 was set. As result of the replacement the sinter strand speed increased in total about 1.2 m/min when adding BF pellets and the sinter fuel adjustment system started to reduce the total carbon content. Due to the shortness of the campaign the adjustment process couldn’t be finished. But the deviation of the strand speed showed that the replacement factor must be higher than 0.45. For the first campaign an increase of the sinter productivity of 3 % was measured while the content of return fines was constant.

In the second campaign the carbon replacement factor was set to 0.6 by adding BF dust pellets and reducing coke breeze content. Again the strand speed increased and the sinter fuel adjustment system reduced the total carbon input (see arrow in Figure 34 ) by reducing the coke breeze while the carbon addition via the BF dust pellets was kept constant. At 16:20 a replacement factor of about 1 (black line in Figure 35) was reached, i.e. 1.5% of the carbon in the ore of the coke breeze was replaced by 1.5% carbon content feed by the BF pellets until the carbon content was increased which lead again to increase of the sinter strand speed. For the second campaign an increase of sinter productivity of 1 % was measured. An influence of BF dust pellets on the sinter quality was not found.

Figure 35 Carbon content in the ore introduced by coke breeze and BF dust agglomerate; Total carbon content and sinter strand velocity at 1. and 2. campaign

A third campaign (Figure 36) was carried out to evaluate the influence of non agglomerated BF dust on the sinter process. At the trial the carbon replacement factor was set to 0.6 by adding untreated BF dust and reducing coke breeze content. Due to the unsteady sinter plant operation a clear influence on the sinter strand speed could not be determined. But the carbon adjustment system did not reduce the total carbon content by reducing the coke breeze. So it can be assumed, that the increased carbon content due to the addition of the non agglomerated BF dust is necessary for the sinter process. An increase of the sinter productivity was not found.

Figure 36 Carbon content in the ore introduced by coke breeze and untreated BF dust; Total carbon content and sinter strand velocity at 3 campaign

The pelletizing of the BF dust shows a positive effect on the utilisation of the carbon content within. Due to the pelletizing the replacement factor was increased from 0.6 to 1. The increase of the sinter plant productivity, when adding the BF dust agglomerate, was assumed to be linked to the increased amount of calcium hydrate used as binder in the BF dust agglomerate. The green strength was adequate for the handling of the agglomerates. Influences on the sinter chemistry (Table 21, Table 22, see appendix) as well as on the emission could not be detected. For the application in industrial scale the content of the binder has to be optimised and the influence on the sinter process has to be evaluated. The trials have also shown that the adjustment of the moisture content is very important for the pelletizing process.

2.3 Conclusion and Comparative Evaluation

2.3.1.1 Technical influence

Different kind of alternative carbon sources as biomass, low volatile coal, pet coke and carbon containing dust and sludge have been evaluated for the replacement of coke breeze on carbon basis. The differences can be seen at the volatile content (2- 83 %), carbon content (19 – 95 %) content but also at the particle size distribution and the bulk density. Due to the diversity in properties also different pre-processing and pretreatment processes were applied to prepare the alternate carbon sources as sinter fuel. Thereby the pre-treatment of the carbon sources was mainly driven by the idea to reach the desired particle range of the coke breeze which is between 1 and 3 mm. Therefore different kind of cutting and crushing techniques as well as pelletizing processes had been investigated.

For biomass cutting mill were applied as a consequence of the soft, fibrous nature of the alternate carbon source. In an iterative process between cutting and thermal evaluation of milled biomass at a laboratory sinter pot it has been found that the best particle size for the thermal utilization of the biomass seem to be beneath the particle size of the optimal coke breeze. This was traced back on the reactivity of the biomass. Nevertheless due to the fine particle size the dwelling time at the mill increased and the through put decreased so as the economical feasibility. But the transfer to an industrial is hindered by the high effort of cutting the biomass to such a small size.

For the very fine BF sludge also separation processes have been investigated to separate heavy metal fractions from the carbon material. The separation of heavy metal fraction in BF sludge was successfully realized using a hydro cyclone having a separation size in the range of 6 – 15µm. The main part of the fraction could be applied as alternative carbon sources at sintering. In a chamber filter press the fine carbon rich sludge was dewatered and agglomerated to filter cake which has to crushed to obtain a suitable particle size of 1 – 3 mm for the sintering process The magnetically separation of the heavy metal fraction could not be realized

The aim of the pre-treatment of the fine, carbon rich BF dust with an average diameter of 0.2 mm was also to enlarge the particle size and to improve the low replacement factor. Therefore press agglomeration processes as die press and continuous roller press as well as built up agglomeration processes have been investigated. Although at die press stable pellets have been produced in laboratory and semi technical scale on a basis of a developed mixture receipt which satisfy the operational demands of the sinter raw material preprocessing, the transfer to industrial scale was not realized. An intensive raw material conditioning and adjustment would be necessary to realize a continuous pellet production without long non operating periods due to plugging caused by fluctuating of the raw material properties. The agglomeration trials of BF dust and sludge using the laboratory continuous roller press have shown that the production of pellets in the size range of the optimal coke breeze is limited due to the low production rate. Therefore the industrial application of a continuous roller press is economical not feasible. A transfer from laboratory scale to industrial scale was not carried out. Instead a built up agglomeration has been applied and stable pellets in the size range of the optimal sinter fuel have been produced in laboratory scale. The pelletizing process has also a tight demand on the material properties especially regarding the particle size distribution as well as a higher demand of binder moisture content. Nevertheless a transfer from laboratory to industrial scale was carried out and 180t of BF dust pellets were produced.

Sinter pot tests have been carried out from ILVA, Tata steel and VASL using sample of the pre treated alternate carbon sources to substitute carbon breeze. For the tests it was mostly assumed that the carbon replacement factor is 1 when the carbon breeze was substituted by the alternate carbon sources. For comparison voestalpine has carried out some pot tests with a presumed carbon replacement factor of 0.5. The evaluation of carbon replacement factor was mainly based on the return of fine balance. Deviations from the return of fines balance at the sinter pot test mean also the replacement factor deviate from the assumed replacement factor of 1. Although it was not possible to give exact figure for carbon replacement factor, on the basis of the sinter pot tests it can be stated that:

• ACASOS with high fixed carbon content can substitute carbon breeze with a increased replacement factor when agglomerated.

• When substituting 10% of the carbon breeze by pre-processed BF dust (ABM & BFI), sludge (voestalpine) or mixed pellets (ILVA) a carbon replacement factors in the area of 0.8 up to almost 1 can be reached at sinter pot of ILVA as well as VASL, although the carbon content of the pellets varied 19% and 50 %. Only slight effects on sinter quality were detected at the ILVA sinter pot tests. When 20% of the carbon breeze was substituted by BF dust and sludge pellets at ILVA the return fines balance decreased. Although the productivity was still high the quality parameter as RDI and Shatter Index also dropped down. This can traced back on the low carbon content of the pellets and the low energy density.

• Also the carbon replacement factor of pet coke seem to be about 1 up to coke breeze substitution of 30% based on the return fines balance at the ILVA sinter pot. The limiting factor for the utilization of pet coke at the sinter pot test were SOx emission, although a pet coke with low sulphur content was applied.

• When coke breeze was substituted by anthracite at the sinter pot up to 30 % the sinter yield decreased slightly with increasing substation rate of the carbon breeze . Also the quality and

chemical composition of the sinter were influenced only slightly, only the sulphur content increased with increasing anthracite.

• Biomass products have different influences on sinter performance and quality figures, according to their consistence. The results show that only biomass products with a rather hard struc- ture and low volatile content are suitable to substitute coke breeze although a carbon replacement factor of 1 can not be reached. Limiting factor is also the VOC emission. A specification less than 1 mm is recommended when applying ACASOS with high volatile content in sintering

The sinter pot tests delivered the basis for the industrial tests. These results correspond with statements in literature for carbon sources with high content of fixed carbon that grain size distribution of sinter fuel has a high influence on the carbon utilisation. In order to obtain a high carbon replacement factor, the agglomeration of fine dust and sludge fractions with high content of fixed carbon seen to increase the replacement factor.

In industrial scale coke breeze was substituted by over 60 % of low sulphur anthracite. This led to a slight reduction of sinter productivity of about 2 %. The replacement factor is approx.. 1. Because of the low sulphur content in the anthracite and very slight reduction of the sintering performance, ILVA has meanwhile fully substitute the carbon breeze by anthracite.

The results of industrial application of the pre-processed BF sludge indicate that the carbon replacement factor is about 1. The CO-content of the waste gas did not increase; this also indicates that carbon is combusted as complete as coke breeze. Also lead and zinc content of sinter stayed in the same range as before, this indicates that heavy metal separation works properly. Regarding influences on sinter productivity and quality figures, changes caused by ACASOS introduction are could not be detected, since changes of general mix composition and especially sinter basicity has much higher influence. The industrial application of the BF dust pellets up to 25% of carbon content of carbon breeze was substituted by the carbon of BF dust pellets. The tests showed a positive effect on the utilisation of the carbon content, i.e. the replacement factor was increased from 0.6 to 1. The increase of the sinter plant productivity, when adding the BF dust agglomerate, was assumed to be caused by the amount of calcium hydrate used as binder in the BF dust agglomerate. The green strength was adequate for the handling of the agglomerates. 2.3.1.2 Economical aspects

Based on a sinter plant production of 5,473,241 tonne sinter per year and a coke breeze rate of 48.2 kg per tonne with a carbon content of 86%, a biomass substitution of 15% with a carbon replacement factor of 1 and a CO2 price of 15 £ per tonne Tata has carried out a simple comparison of carbon costs of two sinter plants: one using conventional coke breeze (15 £ per tonne) and the other one using 15% biomass material (80 £ per tonne) (Table 16).

Table 16 A simple comparison of costs of two sinter plants: one using conventional coke breeze and the other one using ACASOS material.

It shows that the utilisation of biomass can be profitable, however that depends on CO2 prices, the prices for biomass in the future and also on the carbon replacement factor of biomass. On the basis of the assumed CO2 saving and prices 1 % of biomass input means about 0.5 % saving of total annual fuel costs.

2.3.1.3 Influence on emission

Most pet coke and some anthracite brands have significant higher sulphur content than coke breeze. But also BF dust and sludges can have a higher sulphur / carbon ratio than coke breeze, even if the absolute sulphur content sometimes is lower. This aspect could probably become a limiting factor for the substitution of coke breeze by pre-processed in house BF dust and sludge, especially in sinter plants where the gas cleaning system only consists of ESP, which has poor desulphurization capabil- ity, compared to gas cleaning systems with fabric filter.

VOC emissions are also a strong limiting criterion for utilization of all kinds of biomass. The results from Tata Steel indicate that biomass fuels can potentially increase VOC emissions in the sintering process. However, this conclusion was expected as two thirds of biomass material is volatile matter released from biomass in early stages of sintering..

2.3.1.4 Adherence to LCA principles

Of all materials, steel can be considered to be one of the most comprehensively studied and character- ised in terms of Life Cycle Assessment (LCA). Tata Steel RD&T has developed two models for benchmarking a typical integrated steelworks. Each model is based on different assumptions. For this work, both models have been employed for calculating effects of replacing coke breeze by olive pits on CO2 emissions from a typical integrated steelworks.

Real data were used in the development of the models. Annual data were collected using a spreadsheet adapted from an industry standard, for the steel products from a typical integrated steelworks. The data were collected according to product and process and were derived from a variety of sources, including direct measurement, financial records, calculations and estimates. Allocation by mass of product was generally employed where data could not otherwise be broken down into further detail. Checks and verification of the data were performed both by the data collectors and by the LCA practitioners. Table 17 shows a typical CO2 balance for a typical integrated steelworks calculated by CO2 benchmark model.

CO2 Balance CO2 Generation

CO2 equivalent %

Coke plant 1,141,008 t 15.7% Sinter plant 920,811 t 12.7% Pellet plant 231,156 t 3.2% Lime kiln 226,383 t 3.1%

Blast furnace 1,314,711 t 18.1% BOF shop 194,894 t 2.7%

Secondary metallurgy 3,556 t 0.0% Continuous casting 5,578 t 0.1% Hot strip mill 337,922 t 4.7% Power plant 2,837,123 t 39.1% Flares 45,803 t 0.6% Total 7,258,945 t 100.0% 1,815 kg/t HRC

Table 17 CO2 balance for a typical integrated steelworks using CO2 Tool Benchmark, (HRC is Hot Rolled Coil).

In this work, CO2 emissions from a typical integrated steelworks was calculated for the whole process (Total), only the site (Steelworks) and a typical sinter plant (Sinter). Figure 37 shows the final results using both models. Two scenarios have been studied:

1) An integrated steelworks having one sinter plant consuming typical coke breeze, and

2) An integrated steelworks having one sinter plant consuming typical coke breeze with 15% olive pits used in ACASOS.

CO2 Tool predicted slightly higher levels of CO2 compared to LCA model as these two models use different assumptions. However, both models predicted that replacing 15% of coke breeze by olive pits will lead into 1% reduction of CO2 emissions from a typical integrated steelworks (Figure 37). Therefore 10% reduction in CO2 emissions can be achieved at the sinter plant by replacing coke breeze by biomass material.

CO2 Balance

2000

1800

1600

1400

1200

1000

800 CO2 kg/t HRC

600

400

200

0 CO2 Total CO2 Steelworks CO2 Sinter plant

LCA Benchmark LCA with 15% Olive pits CO2 Tool Benchmark CO2 Tool 15% Olive pits

Figure 37 Carbon Dioxide Emissions Comparison.

2.4 Exploitation and impact of the research results On the basis of the investigation a pre-processing device for BF sludge for the separation of heavy metal and agglomeration of treated sludge were set up and put into operation. Also carbon breeze were substituted to large extent by the anthracite

Application of anthracite for sintering

Due to the results of ACASOS trials, ILVA is now using anthracite at 100% on one sinter line. During the ACASOS tests lowest anthracite content was dictated by availability. ILVA sees no technical limit for the application of anthracite because the anthracite sulphur is very low ( 0.9 % ; see Appendix, Data base, Ilva) and because it doesn't reduce drastically the performance of sintering production.

The price of anthracite is in the range of 60-70% of coke breeze price, so the substitution is economical feasible.

Application: Pre-processing of BF sludge for sintering Based on the promising results of lab and field tests, a full-scale pre-processing device for BF sludge consisting of a hydro cyclone station (Figure 38, Figure 39) and a blade crusher (Figure 42) to grind the ACASOS fraction dewatered by an existing filter press (Figure 40, Figure 41), was installed at voestalpine. Up to now, approx. 10000 t of pre-processed BF sludge (Figure 43) have been utilized in the sinter plant. It means 70% of the sludge from BF A can be recycled as pre-processed ACASOS material containing 3350 tons of carbon and 4050 tons iron. The material is stored and then transported to the blending yards together with BF dust..

Figure 38 Hydro cyclone station with pump, valves and inductive mass flow measurement

Figure 39 Hydro cyclones in operation

Figure 40 Dewatering of hydro cyclone underflow with an existing filter press

Figure 41 Discharging unit of filter press. Filter cake falls down to blade crushers

Figure 42 The blade crusher consists of a 4-blade-unit and a 2-blade unit. Here shown: 4-blade- unit

Figure 43 Final product ready to be transported to the blending yard: Pre-processed BF sludge fraction with low content of heavy metals, low moisture and a grain size distribution fitting well into a sinter mix. 10000 t have been utilized so far. Publication Zandi,M.; Martinez-Pacheco,M.; Fray,T.; Biomass for iron ore sintering, Minerals Engineering Volume 23, Issue 14, November 2010, Pages 1139-1145 The publication was admitted by the project partner and the EU-commission.

List of Figures Figure 1 Annual trends in UK rape seed prices, £/tonne ex. farm ...... 12 Figure 2 Costs of pre-processing ACASOS material...... 14 Figure 3 Cutter mill used in this work for pre-processing ACASOS material...... 14 Figure 4 Schematic diagram of the sinter-pot ...... 15 Figure 5 Photograph of the sinter-pot ...... 15 Figure 6 Comparison of thermal profiles at TC/4 position ...... 16 Figure 7 Comparison of thermal profile characteristics at T/C 4 position for the reference coke and differently sized, crushed sunflower husk pellets...... 16 Figure 8 Partition number and separation particle size for 1 inch lab-cyclone for different solids content (labscale) ...... 17 Figure 9 Partition number and separation particle size for 2inch lab-cyclone for different solids content (labscale) ...... 17 Figure 10 Pilot hydro cyclone station in the dewatering plant at voestalpine Linz...... 18 Figure 11 Grain size distribution of overflow and underflow fraction for different BF sludge types (pilot scale) ...... 18 Figure 12 Partition numbers calculated from grain size distributions, for different BF sludge types (pilot scale) ...... 18 Figure 13 Dry high intensity magnetic separator, adapted to wet operation mode to treat slurries ...... 20 Figure 14 Back scattered electron (BSE) microscopy of hydro cyclone overflow of BF sludge...... 21 Figure 15 Concentration maps of PbO from microprobe analysis...... 21 Figure 16 Influence of moisture content on pellet strength ...... 23 Figure 17 Influence of binder on pellet strength ...... 24 Figure 18 Influence of carbon content on pellet strength ...... 24 Figure 19 Die press ...... 25 Figure 20 Pellets (3 mm diameter) from die press (BF dust 60%, sinter coke 30%, binder 10%) ...... 26 Figure 21 “Hutt roller press at Ilva and briquettes from best practice tests ...... 26 Figure 22 Briquette shape and volume of continuous roller press ...... 26 Figure 23 Pellets from a disc pelletizer ...... 27 Figure 24 Abrosion Strength - content < 1mm after screening ...... 28 Figure 25 Briquetting plant ...... 29 Figure 26 Reactivity of the pellets, sinter mixture sinter coke, pet coke and anthracite in dependence of the carbon content ...... 31 Figure 27 Typical thermal profile down the bed ...... 32 Figure 28 Average combustion efficiencies in an inert bed ...... 33 Figure 29 Average SOx analysis, combustion in inert beds ...... 33 Figure 30 Olive pits: crushed to < 2mm (left); anode graphite coke: < 8mm (middle); wood pellets: Ø 8mm, length up to 25mm (right)...... 38 Figure 31 Temperature measurement in height position -38 cm from top ...... 40 Figure 32 BF-dust agglomerates from intensive mixer ...... 42 Figure 33 Coke consumption and input of BF dust and ACASOS = pre-processed BF sludge...... 43 Figure 34 Results of Sinter plant trial with anthracite replacement ...... 44 Figure 35 Carbon content in the ore introduced by coke breeze and BF dust agglomerate; Total carbon content and sinter strand velocity at 1. and 2. campaign ...... 45 Figure 36 Carbon content in the ore introduced by coke breeze and untreated BF dust; Total carbon content and sinter strand velocity at 3 campaign ...... 46 Figure 37 Carbon Dioxide Emissions Comparison...... 51 Figure 38 Hydro cyclone station with pump, valves and inductive mass flow measurement ...... 52 Figure 39 Hydro cyclones in operation ...... 52 Figure 40 Dewatering of hydro cyclone underflow with an existing filter press ...... 53 Figure 41 Discharging unit of filter press. Filter cake falls down to blade crushers ...... 53 Figure 42 The blade crusher consists of a 4-blade-unit and a 2-blade unit. Here shown: 4-blade-unit ...... 54 Figure 43 Final product ready to be transported to the blending yard: ...... 54

List of Tables Table 1 Mass distribution of solids and water (pilot scale) ...... 19 Table 2 Chemical analysis of over- and underflow. only BF old (without top pressure) (pilot scale) ...... 19 Table 3 Chemical Analysis of over- and underflow. only BF with top pressure (pilot scale) ...... 19 Table 4 Magnetic separation of BF sludge (mixture of sludge from all BF’s)...... 20 Table 5 Composition of BF-pellets ...... 23 Table 6 Parameter of the pellet mixture ...... 25 Table 7 Raw mixture composition for disc pelletizing ...... 27 Table 8 Designed experiments and biomass/coke breeze content...... 34 Table 9 Sinter characteristics for the trials...... 34 Table 10 Test conditions, performance and quality results...... 38 Table 11 Test conditions and performance and quality results...... 39 Table 12 Gas analysis of sinter pot tests ...... 40 Table 13 Average gas analysis of sinter pot tests ...... 41 Table 14 Sinter plants for industrial tests ...... 41 Table 15 Results of hydro cyclone treatment of the BF sludge ...... 42 Table 16 A simple comparison of costs of two sinter plants: one using conventional coke breeze and the other one using ACASOS material...... 49 Table 17 CO2 balance for a typical integrated steelworks using CO2 Tool Benchmark, (HRC is Hot Rolled Coil)...... 50 Table 18 Sinterpot tests with BF-dust and BF-sludge mixtures, Pet coke and Anthracite ...... 64 Table 19 Temperature and flamefront measurements at sinter pot tests with with BF-dust and BF-sludge mixtures, Pet coke and Anthracite ...... 65 Table 20 Sinter pot tests wit BF dust and sludge pellets ...... 66 Table 21 Industrial tests AMB, Analysis of Sinter at 1. and 2. campaign ...... 66 Table 22 Industrial tests AMB, Analysis of Sinter 3. campaign...... 67

56 - 57 -

List of References

[1] Miranda.T.; Esteban, A.; Rojas, S.; Montero, I.; Ruiz, A.; Combustion Analysis of Different Olive Residues, Int. J. Mol. Sci. 2008, 9, 512-52

[2] Pietsch, W.: Pelletizing Processes. Wiley-VCH Verlag GmbH: Weinheim 2002

[3] Resource net, Brussel, Belgium, 2010; www.resource-net.com

[4] Matschekwitz, U.; Pulverized petroleum coke as an economical fuel for the brick and tile industry, Brick and Tile Industriy International, 10, 2008

[5] Statistik der Kohlenwirtschaft e.V.; www.kohlenstatistik.de

[6] Ooi, T C, The study of sunflower biomaterial as a substitute in the iron ore sintering process: Pyrometallurgy 2007, Mineral Engineering Journal

[7] Biomass Energy Centre at http://www.biomassenergycentre.org.uk/

Appendices ,

Data base

Data Base ACASOS AMB Pellets Lab scale Pellets Ind.scale 60%BF dust 70%BF dust BF Deposited Sinter 30% S.coke 10% Casthouse d. Chem. Composition dust BF dust coke 10% CaOH 20% CaOH C % 41.2 25.3 85.1 52.8 29.9 H % 0.3 0.5 0.3 0.3 0.5 O % - - N % 0.6 0.5 0.6 0.6 0.2 S % 0.3 0.3 0.4 0.3 0.34 Cl % 0.4 <0.05 0.0 0.2 0.12 Ash content % 55.0 70.0 9.4 36.1 Volatile content % 2.3 4.4 4.6 2.9 10.6 Moisture 13.0 13.6 11.5 11.6 16.6 Fe (met.) % 0.2 0.7 0.5 0.3 0.43

Fe2O3 % 38.7 43.3 - FeO % 3.8 9.9 - Fe ges % 23.8

SiO2 % 8.7 5.9 5.4 7.0 4.3

Al2O3 % 2.2 1.8 3.6 2.5 CaO % 3.0 5.1 0.6 12.0 19 MnO % 0.08 1.47 0.11 0.08 MgO % 0.49 0.23 0.29 0.3

Na2O % 0.09 0.31 0.03 0.06 0.09

K2O % 0.28 0.28 0.05 0.18 0.3

TiO2 % 0.17 0.20 - 0.31 Zn % 0.31 0.11 - (ZnO) 0.241 Pb % (PbO) 0.06 P % 0.04 0.05 0.01 0.03 (P2O5)0.05

SO3 % 0.8 0.8 - Particle size distribution (D50) mm 0.2 0.2 1.2 Ø 3 Bulk density kg/m3 780 880 822 739 Void fraction % Calorific value MJ/kg 11.3 7.1 29.6 16.5 6.6

Data Base ACASOS voestalpine Sludge old Sludge BF BF's A (no top pres- (top pres- Wood Anode Pet Chem. Composition sure) sure) Olive pits pellets coke coke C % 34 30 49 49.6 96 96 H % 0.2 0.2 5.6 6.1 0.02 O % 0.5 0.5 34.5 0.9 N % 0.5 0.5 1.9 0.1 0.7 S % 1.8 0.3 0.2 0.1 1.5 1.5 Cl % 0.5 0.6 0.04 Ash content % 8.8 0.3 1.2 1.5 Volatile content % 69.3 0.3 Fixed carbon % 21.9 Moisture

Ash composition Fe (met.) %

Fe2O3 % 48 55 FeO %

SiO2 % 6 5 0.1

Al2O3 % 2.5 1.9 CaO % 2.7 2.1 MnO % 0.52 0.54 MgO % 0.7 0.5

Na2O % 0.38 0.15

K2O % 0.36 0.25

TiO2 % 0.1 0.11 Zn % 2.9 0.2 Pb % 0.5 0.2 P %

SO3 % Mechanical Properties Particle size distribution mm < 0.4 < 0.4 < 2 Ø 8 < 8 Bulk density kg/m3 2000 2000 1560 Void fraction % 24.3 Thermal properties Calorific value MJ/kg 11 - 13 11 - 13 19.9 18.6 32.6 32.5

Data Base ACASOS Tata Steel Hazel Almond Rape Coke Sunflower nut shells Rape seed Chem. Composition breeze husks shells (BD straw pressings Ctotal % 85.4 50.0 55.1 48.8 54.1 H % 0.3 6.2 6.1 6.4 8.6 O N % 1.3 0.7 0.4 0.2 4.1 S % 0.60 0.14 0.04 0.03 0.11 0.60 Fixed C % 84.4 12.3 20.0 8.8 6.0 3.6 Ash content % 12.1 3.2 1.1 0.5 2.8 4.5 Volatile content % 1.5 76.4 67.9 81.4 81.3 83.2 Moisture % 5.5 9.3 11.0 9.3 9.8 8.1

Ash analyses Fe (met.)

Fe2O3 % 10.4 4.7 6.4 FeO

SiO2 % 46.6 4.4 20.0

Al2O3 % 26.2 0.7 1.2 CaO % 3.0 19.0 27.7 MnO MgO % 0.9 12.0 6.8

Na2O

K2O % 01.0 30.9 15.9

TiO2 Zn Pb

P2O5 % 0.6 8.9 9.7

SO3 % 10.6

Mechanical Properties Particle size distribution Bulk density kg/m³ 880 544 565 286 126 Void fraction Thermal properties Calorific value MJ/kg 28 16 18.2 16.7 17.4 Energy density MJ/m3 24.6 8.7 10.3 4.8

Data Base ACASOS Tata Steel Bagasse Sun husk Commercial Olive pit Chem. Composition Olive cake Pellets pellets char coal [1] C % 42.5 43.9 44.2 82.2 52.3 H % 5.01 5.41 5.17 4.51 7.5 O % - 40.1 N % 1.33 0.20 0.66 0.58 0.1 S % 0.12 0.04 0.11 0.02 <0.1 Cl % 0.22 0.01 0.03 0.09 Ash content % 7.9 5.8 2.7 4.5 0.6 Volatile content % 60.2 73.1 66.5 32.7 81.0 Cfix 18.5 Total Moisture 14.5 8.9 13.0 4.6 9-10

Ash composition Fe (met.) %

Fe2O3 % 2.86 4.81 1.98 1.1 0.9 FeO %

SiO2 % 17.07 63.11 2.78 3.2 13.0

Al2O3 % 3.74 9.62 0.66 0.98 0.9 CaO % 14.05 6.17 22.6 61.7 8.4 MnO % 0.08 0.27 0.07 0.05 MgO % 7.63 4.06 14.03 4.8 1.5

Na2O % 1.39 0.40 0.23 0.95

K2O % 43.3 6.7 46.9 2.2 42.9

TiO2 % 0.95 0.05 0.07 Zn % Pb %

P2O5 % 8.3 2.8 6.9 3.4 3.4

SO3 % 1.49 1.17 3.82

Mechanical Properties Particle size distribution mm Bulk density kg/m3 286.0 Void fraction %

Thermal properties Calorific value (dry) MJ/kg 20.21 18.30 20.37 33.1 19.0

Data Base ACASOS ILVA Pellets 20%BFdust Sludge BF Coke Pet 40%BFsludge Chem. Composition BF Dust mix Sludge Anthracite breeze Coke 40%millscale C % 26.8 19.4 27.1 94.8 81.3 88.6 18.9 H % O % N % S % 0.24 0.20 0.40 0.88 0.79 1.94 0.23 Cl % 0.26 0.17 0.05 Ash content % 3.3 14.2 0.6 Volatile content % 1.9 4.4 10.8 Moisture Ash composition Fe (total) % 39.5 45.2 36.7 0.9 1.1 48

Fe2O3 % FeO % 17.6 27.5 6.5

SiO2 % 5.9 3.3 5.7 0.8 5.2 6.9

Al2O3 % 1.63 1.30 1.91 0.40 2.51 2.4 CaO % 5.34 6.69 5.61 0.19 2.30 3.1 MnO % 0.25 0.36 0.23 0.01 0.01 0.3 MgO % 1.33 0.90 0.84 0.07 0.29 0.7

Na2O % 0.39 0.26 0.81 0.02 0.25

K2O % 0.04

TiO2 % 0.23 0.22 0.21 0.02 0.14 0.13 Zn % 0.01 0.20 0.98 0.2 Pb % 0.18 0.03 0.18 P % 0.03 0.04 0.04 0.00 0.03

SO3 % Mech.Properties Median diameter mm 0.14 1.09 1.09 1.02 1.14 1.82 Bulk density kg/m3 830 1177 1047 734 529 734 Void fraction % 71.3 55.7 71.9 40.1 Gravity density kg/m3 830 1655 1225 Thermal properties Calorific value MJ/kg 5.9 33.7 30.5

6 5.08 1.09 2.91 6.63 0.62 1.72 9.29 0.85 1.83 1.78 53.85 27.66 55.05 71.35 36.10 85.00 77.90 19.27 35.18 14.71 76.20 0.0063 0.0052 0.0580 0.0540 0.1100 0.0100 0.0460 439.14 974.02 ###### ###### -2.8300 Mix (20%) 159 6 6.1 4.99 1.02 3.28 0.43 75.9 1.50 9.38 1.07 1.88 1.81 42.79 26.30 57.79 31.85 81.00 77.70 35.45 22.56 18.88 83.70 0.0064 0.0051 0.0490 0.0130 0.1000 0.0100 0.0470 412.77 894.08 ###### ###### -0.5300 Mix (10%) 158 6 5.1 ) 4.96 1.16 2.91 3.04 1.36 (0.46 + 0.90) 2.71 (0.92 + 1.79) 0.42 77.1 1.42 9.17 0.89 1.85 1.73 41.75 27.97 57.86 39.53 85.86 83.70 42.54 24.40 17.95 80.20 0.0060 0.0051 0.0500 0.0180 0.1100 0.0460 0.0110 345.46 767.23 ###### ###### -0.4300 6 1.52 4.94 1.11 3.28 5.82 0.47 1.54 9.46 1.08 1.91 1.82 46.88 26.80 57.60 75.89 38.93 81.00 82.80 36.41 21.34 18.79 80.20 0.0052 0.0037 0.0620 0.0160 0.1000 0.0460 0.0140 419.00 746.95 ###### ###### -0.4900 6 5.28 1.09 5.33 2.55 0.35 0.94 1.54 1.37 1.90 1.82 46.94 24.76 57.09 75.71 30.78 76.00 81.40 29.39 19.26 23.82 80.70 10.04 6 4.77 1.12 5.11 0.33 2.91 0.63 1.40 1.05 9.53 2.00 1.86 48.72 25.46 57.93 77.16 34.94 82.00 81.30 19.58 18.30 30.28 80.20 6 4.78 1.08 5.32 0.43 0.31 3.28 1.59 1.06 9.78 2.05 1.94 56.99 23.88 57.50 76.31 30.26 80.00 79.90 18.60 16.59 29.15 81.20 Sinterparameters and properties 6 6.06 4.91 1.05 0.33 1.82 1.49 1.21 9.85 2.01 1.90 1.67 ###### ##### ###### 6 5.29 5.11 1.18 0.42 1.48 2.55 1.00 9.82 1.92 1.80 1.04 6 5.30 5.21 1.15 0.42 1.55 2.91 3.36 0.99 9.92 1.90 1.80 0.70 0.0047 0.0042 0.0048 0.0040 0.0050 0.0045 0.0042 0.0045 0.0042 0.0041 0.0044 0.0038 0.0530 0.0550 0.3090 0.0600 0.0550 0.0710 6 6.62 5.37 1.10 1.02 1.63 3.28 4.78 1.01 9.92 1.85 1.79 0.35 6 4.10 5.00 1.17 1.46 0.34 3.64 0.98 5.31 1.92 1.79 9.60 415.0791.3 499.89 950.52 475.28 1037.00 469.70 988.73 571.65 936.76 529.07 923.71 473.87 916.37 530.62 837.39 48.12 51.02 50.70 53.61 48.94 Mix 144 Mix 145 (10%) Mix 146 (20%) Mix 147 (30%) Mix (50%)154 Mix 149/152 (10%) Mix 151 (20%) Mix 153 (30%) Mix 156 (10%) Mix (20% 157 standard pet-coke 10% pet-coke 20% pet-coke 30% pet-coke 50% anthracite 10% anthracite 20% anthracite 30% Sludge mix 10% Sludge mix 20% 10% dust) + sludge ( BF 20% dust) + sludge (BF /h /h *day 3 3 # # # % % 23.89% % 28.46 26.29%% 27.18 57.53% 77.72 22.00 56.55 0.1200 73.53 57.16 0.0900 75.75 57.33 0.0700 76.11 0.0700 57.60 75.63 0.1200 0.1100 0.0700 0.1100 % % % % 17.00 17.83 17.71 17.53 20.48 %% 0.0390 0.0047 0.0400 0.0400 0.0390 0.0460 0.0470 0.0390 0.0500 % % 83.00 82.00 82.00 82.00 80.00 % % 0.0450 % ##### ##### ##### ##### ##### % 79.70 79.00 80.70 83.10 79.70 % % 0.0160 0.0130 0.0150 0.0130 0.0120 0.0140 0.0150 0.0110 % -0.2900 -0.7500 -0.4700 -0.4800 -0.5000 -0.4300 -0.4200 -0.4300 % ##### 2 min 21.43 19.53 17.52 18.42 19.18 min 39.55 36.38 32.37 31.03 32.21 mm 32.82 31.50 28.64 30.77 32.91 m m t/m 3 2.8 3 2 2 O O tot 2 2 S %S 0.0150 0.0180 0.0180 0.0170 0.0200 0.0180 0.0190 0.0200 Moisture Moisture Sinter parameters Coke % Anthracite Max Permeability Sinter Yield Testing Time Reducibility - R Reducibility FeO Fe TiO P Al CaO Waste Material Sinter Productivity Chemical composition SiO Cl Zn Pb MgO Mn Start Permeability Pet - Coke Shatter Index (JIS M 8711) % 83.81 82.70 83.70 81.70 85.70 Alkali Fe Sintering Time Balance Sinter Quality Mean S. < 5 mm L.O.I. (1000°C) Ib2 Ib4 Tumbler Test ASTM >6.3mmTumbler Test ASTM <0.595mm % % 77.35 76.46 77.70 RDI-

Table 18 Sinterpot tests with BF-dust and BF-sludge mixtures, Pet coke and Anthracite

) 3 7 2 1190. 4 0 ) Mix 159 (20% 894.08 974. 0 ix(10% 158 )M 3 767.2 5 Sludge mix sludge BF dust and )(10%) Mix 156 (20% Mix 157 1264.861 1363.29 1236.64 1354.24 1359. 0 )(30% 153 Mix 5 Anthraci te ) Mix 151 (20% 1180.209 1190.67 1165.714 1289.90 1266.81 1268.6 ix 149 (10% )M 7 ix(50% 154 )M 988.73 936.76 923.71 916.37 837.3901 746.9 Si nter Thermal behavi our 1212.46 1132.7 )(30% 147 Mix 9 3 Pet coke 1037.2 2 ) Mix 146 (20% 950.5 1233.36 1164.4 1347.29 1328.21 1300.63 1343.11 1143.076 1231.2 ix 145 (10% 3 8 3 791.3 1233. 1287. Mix 144 M Standard i n 1.81 1.83 1.65 1.79 2.19 3.055 2.55 2.865 1.83 1.40 2.16 1. 77 i ni n 2.39 1.45 2.11 1.62 2.46 1.24 1.91 1.68 2.84 1.79 2.924 3.205 2.59 2.25 4.054 2.216 1.75 1.92 1.39 1.41 2.42 1.91 1. 97 1. 61 /h/h 415.00 499.89 475.28 469.70 571.65 529.33 473.87 530.6221 419.00 345.46 412.77 439. 14 C C 3 3 °C 1193.7 1349. 1 1258.29 1358.48 1273.35 1222.362 1232.69 1146.439 1319.29 1346.92 1236.27 1369. 61 m cm/m e m .° .° p p le Te le p le Tem le le Tem le p p ocou perature °C 412.0 428. 6 400.48 458.05 435.81 437.69 548.29 477.62 431.26 409.43 458.33 438 ocou eabi lit y Therm as Tem as h Therm g ax perm ax G ax edium M Start cold permeabi li ty m Low Thermocou "Sinter" temperatures M Hi gh TC Cool ing Speed(1 - 2) Fl Front ame Speed °C/min(2 - 3) cm/m Fl Front ame Speed (1 - 3) Fl cm/m Front ame Averag 142.13 144.08 144.19 125.83 164.7 176.28 162.96 160.90 127.59 99.73 151.41 109. 11 Hi M 3 1 2 Table 19 Temperature and flamefront measurements at sinter pot tests with BF-dust and BF-sludge mixtures, Pet coke and Anthracite

Sinter parameters and properties

Moisture % 5,9 6,01 Sinter parameters pellet A 10% pellet B10% pellet A 20% pellet B 20% Mix 0809 Mix 1509 Mix 3809 Mix 4009 Coke % 3,283,282,902,90 Pet - Coke % Anthracite % Waste Material % 1,521,523,053,05 Start Permeability m3/h 334,00 349,00 375,00 361,00 Max Permeability m3/h 680,00 704,00 752,00 671,00 Sinter Yield % 86,00 86,00 87,00 86,00 Sinter Productivity t/m2*day 47,83 49,58 52,47 42,80 Testing Time min 44 38 34,00 44,00 Sintering Time min 23,42 20,28 20,11 25,40 Balance # 1,01 1,01 0,80 0,84 Sinter Quality

Mean S. mm 29,83 29,63 24,86 24,60 < 5 mm % 14,19 14,00 13,41 12,80 Shatter Index (JIS M 8711) % 84,02 83,77 81,23 85,65 Tumbler Test ASTM >6.3mm % Tumbler Test ASTM <0.595mm % RDI-2.8 % 35,92 33.74 40,99 40,89 Reducibility - R % 72,55 73.83 77,96 77,60

Chemical composition

SiO2 % 5,325,235,565,37

Al2O3 % 1,361,401,451,45 CaO % 9,91 9,93 9,68 9,46 MgO % 1,56 1,63 1,61 1,57 Mn % 0,310,300,310,26

Fetot % 56,79 56,33 56,98 57,40 FeO % 5,916,496,487,34

Fe2O3 % S %

TiO2 % 0,0780 0,0780 0,1020 0,0780 P % 0,0340 0,0370 0,0400 0,0350 Cl % Zn % 0,0083 0,0167 0,0118 0,0133 Pb % 0,0038 Alkali % 0,0640 L.O.I. (1000°C) % Ib2 # 1,86 1,90 1,74 1,76 Ib4 # 1,72 1,74 1,61 1,62

Table 20 Sinter pot tests wit BF dust and sludge pellets

Reference 1.campaign Reference 2.camgaign Reference 10:45 12:00 15:30 17:50 20:00 Fe total % 58,03 57,87 57,77 57,14 57,57 CaO % 10,00 10,19 10,17 10,38 9,57 MgO % 0,89 0,97 1,00 1,05 0,88

SiO2 % 5,35 5,75 5,93 6,11 6,15 MnO % 0,56 0,61 0,61 0,60 0,58

Al2O3 % 1,17 1,30 1,21 1,22 1,19 P2O5 % 0,09 0,09 0,09 0,09 0,09 TiO2 % 0,13 0,14 0,13 0,13 0,12 PbO % 0,005 0,005 0,005 0,005 0,004 ZnO % 0,025 0,029 0,028 0,032 0,020 S % 0,009 0,021 0,014 0,019 0,012 Table 21 Industrial tests AMB, Analysis of Sinter at 1. and 2. campaign

2.camgaign Reference 11:00 13:45 Fe total % 59,51 58,57 CaO % 8,99 9,14 MgO % 0,84 0,99

SiO2 % 4,43 5,25 MnO % 0,55 0,61

Al2O3 % 1,11 1,23

P2O5 % 0,10 0,11

TiO2 % 0,12 0,12 PbO % 0,004 0,005 ZnO % 0,012 0,013 S % 0,01 0,012 Table 22 Industrial tests AMB, Analysis of Sinter 3. Campaign

Summary of main results

Short characterisation of ACASOS

Chem. Compo- Coke Biological Anode BF dust BF sludge Pet coke Anthracite sition breeze Acasos coke Total C % 85 42 - 55 25 - 41 27 – 34 95 89 96 S % 0.6 0.04 – 0.6 0.3 0.2 – 1.8 0.9 1.9 1.5 Volatile con- % 1.5 60 – 83 1.4 / 1.9 10.8 0.3 tent Particle size mm 1 - 3 / 0.15 0.05 1.0 1.8 < 8 Bulk density kg/m³ 880 350 830 / 730 740 Calorific value MJ/kg 28 16 – 20 6 – 9 11 - 13 36 34 32.6

Applied pre-treatment processes

Lab trials Die press Continuous Disc pelletizer Crusher Chamber filter roller press press Materials BFdust BF dust BF dust Olive pit BF sludge Coke breeze BF sludge Cast house dust BF dust Lame scale BF sludge Lame scale Moisture > 17% >5% > 17% / ~18% content Curing time 72 h 48 h 72 h / / Binder CaOH Bentonite CaOH / / Binder 10% 5% 1-12% / / content Pellet size 3 mm 3-8mm < 1 mm <10 mm Limits - Material prop- - Size of pellets Material proper- erties - Abrasion ties particle size, Moisture content moisture - Abrasion

Sinter pot tests with coke breeze substituted by Acasos

Acasos Components Pre-treatment Substituted coke Assumed breeze on C-basis Replacement factor Pet coke 100% Pet coke Non 10 – 50 % 1:1

Anthracite 100% Anthracite Non 10 – 30% 1:1

Anode coke 100% Anode coke Non 10% 1:1; 1:2

Sludge+Dust 47%BOF sludge, Non 10-20% 1:1 mix 32 % BF dust, untreated 16%BF sludge, 5% Dredging sludge BF dust + BF dust, BF sludge None 10 - 20% 1:1 sludge untreated BF dust BF dust Pellets 10% 1:1; 1:2 pellet (Die press) BF sludge BF sludge Granules 10 - 20% 1:1; 1:2 granules (Chamber filter press) Olive pits 100% Olive pits Crusher 5-15% 1:1; 1:2 chrushed BF dust + 36-54% lame scale Pellets 10-20% 1:1 sludge 36-54%BF-dust (Disc Pelletizer) pellet A/B 9% BF sludge Wood pellets 100% Wood Pellets 10% 1:1; 1:2 (Die press)

Results from sinter pot tests

Acasos Substitu- Return fine Result tion ratio Pet coke Up to 30% 0.98-1.01 Increasing productivity, low influence on quality indices Up to 50% 1,21 Decreased productivity, small influence on quality Substitution limited by S content of Pet coke (SO2 emission) Anthracite Up to 20% 1.05-1.06 Low influence on productivity and quality indices

Up to 30% 1.37 Slightly decreased productivity and quality Anode coke 10% 0.99 Low influences on productivity and on quality

Sludge+Dust Up to 20% 0.89-1.08 Decreasing productivity and quality indices mix untreated BF dust + Up to 20% 0.85-1.07 Decreasing productivity and quality indices sludge untreated BF dust 10% 0.99 Low influences on productivity and on quality indices Pellets BF sludge 10% 1.01 Low influences on productivity and on quality indices Granules Olive pits, 5-15% 0.81-1.15 Decreasing productivity and quality indices, crushed Replacement limited by VOC emission BF dust + 10% 1.01 Low influences on productivity and on quality sludge 20% 0.8 Decrease of productivity and quality indices pellet A/B Wood pellets 10% 1.36 Lead to decreased productivity and quality indices Substitution limited by VOC emission

Emission at sinter pot tests when substituting 10% coke breeze by ACASOS

Acasos O2 [%] CO [%] CO2 [%] SO2 [ppm] VOC [ppm] Results Standard 13.0 1.33 8.5 287 25 Pet coke 11.8 1.62 9.5 394 130 high SO2 and VOC Anode coke 12.6 1.6 8.13 284 22 BF dust 12.3 1.78 8.9 236 21 Pellets BF sludge 11.9 high SO2 1.55 9.3 380 27 Granules Olive pits 12.5 high VOC 1.77 8.98 187 148 crushed Wood pellets 11.8 1.84 9.26 n.d. 276 high VOC

Field tests and best practice

Acasos Components Pre-treatment Substituted Coke Assumed Estimated breeze on C-Basis Replacement Replacement factor factor BF + Cast 70% BF-dust Pellets ca, 25% 0.6 ≈1 house dust 10% Cast house dust (Intensive mixer) 20% CaOH BF dust 100% BF dust non ca.25 0.6 ≈0.6

BF BF-dust Granules 10-20% 1:1 ≈1 sludge+BF BF sludge (Chamber filter dust press)

Anthracite 100% Non Up to 60% 1:1 ≈1

European Commission

EUR 25151 — Alternate carbon sources for sintering of iron ore (Acasos)

Luxembourg: Publications Office of the European Union

2013 — 71 pp. — 21 × 29.7 cm

ISBN 978-92-79-22676-2 doi:10.2777/58105 HOW TO OBTAIN EU PUBLICATIONS Free publications: • via EU Bookshop (http://bookshop.europa.eu); • at the European Union’s representations or delegations. You can obtain their contact details on the Internet (http://ec.europa.eu) or by sending a fax to +352 2929-42758.

Priced publications: • via EU Bookshop (http://bookshop.europa.eu).

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KI-NA-25151-EN-N

In the RFCS project ‘Acasos’, alternative carbon sources, for example olive pits, sunflower husks, blast furnace (BF) dust and sludge, anthracite and pet coke, were analysed, pre-treated and evaluated by sinter pot tests and industrial sinter plant trials. It was found that pre-treatment is essential for the utilisation of alternate carbon sources. The crushing of the evaluated biomass to a particle size smaller than the optimal coke breeze size improved thermal utilisation at sintering, although productivity and quality could not reach the level of carbon breeze. At the industrial scale it was shown that the pelletising of carbon-rich BF dust and sludge led to the increased utilisation of their carbon content without negative effects on productivity. The substitution of coke breeze with 60 % anthracite at the industrial scale led to a slight reduction in sinter productivity.

Environmental aspects were considered, especially concerning emissions of

SO2 and volatile organic carbon (VOC). SO 2 can be a limitation criterion for pet coke, anthracite, and BF dust and sludge if the sulphur/carbon ratio is significantly higher than that of coke breeze. On the other hand, VOC emission is a strong limiting criterion for the utilisation of all kinds of biomass, although biomass Acasos has advantages over SO2 emissions and CO2 balance due to regenerative resources.

Studies and reports

doi:10.2777/58105