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that in practice the waste remaining after A modern flue- sorting has to be disposed of by inciner- ation. The shortage of suitable makes cleaning system for incineration – within the framework of total waste management – the only practicable solution. Nevertheless, a common criticism waste incineration of this solution is that a third of the waste still remains afterwards, mainly in the form of plants slag. This is only half the truth. While it is true that incineration reduces the waste to just a third of its mass, it reduces it at the same time to one tenth of its volume, and Since 1990, waste incineration plants in Germany have had to comply with this is what matters most in the context of Europe’s strictest emissions legislation – a clean-air decree known as landfilling. the ‘17th BImSchV’. Building on the clean-air limits contained in the 1986 German decree ‘TA-Luft’, it also forms the core of the European Union’s New legislation is more rigorous guideline for the thermal treatment of hazardous waste that took effect Legislation and regulations applying to in 1993. Total Cleaning and Recycling (TCR) is a process, developed by waste incineration plants have become far ABB, which ensures compliance with the ‘17th BImSchV’, in some cases more stringent in recent years. The German guaranteeing results well below the limits given in it. Because TCR clean-air decree ‘TA-Luft’ was passed in systems are of modular design, they can be easily retrofitted to older 1986, and in 1990 the emission limits were incineration plants. Results from a full-scale demonstration system in reduced once more through a further operation in Hobro, Denmark, confirm the good performance of the new decree known as the ‘17th BImSchV’. The ABB technology. European Union guideline for the thermal treatment of hazardous waste that has existed since 1993 is also largely based on Public approval of municipal waste inciner- the impact this has on the environ- the stipulations contained in the ‘17th ation plants is low mainly as a result of the ment. BImSchV’. Table 1 shows how the limits for emitted by facilities that were built More recently, a general rethinking of the emissions and pollutants have been back in the 1970s and early 1980s. This has situation has become apparent. The con- reduced since the 1986 decree. led, understandably, to criticism of thermal sensus is that the thermal treatment of the Besides fulfilling these requirements, disposal as such and fuelled an ongoing waste after sorting – and its avoidance, plant operators are also making a strong debate about the best way to change the where possible, in the first place – should be effort to utilize the energy produced by the public’s ‘use and throw-away’ mentality. For tied into a total waste management pro- thermal process and to recover and recycle some time now, society has perceived gramme. A new German decree regulating the residual materials. The extremely low waste incineration as a mainstay of this atti- the disposal of domestic waste (‘TA Sied- emission levels have a political goal, namely tude. lungsabfall’) points the way. This makes it to gain public acceptance of thermal waste In Germany even new, stricter legislation, unlawful to dump materials with an organic disposal. Although they should not be seen calling for a drastic two-stage reduction in content of more than 5 percent, meaning as a solution to the overall emissions situ- flue-gas emissions from waste incineration ation as it applies in Germany, they are plants and upgrading of older plants in the inevitably providing new benchmarks for short term has not been able to change this industry as a whole. perception. Dr. Jürgen Gottschalk Waste incineration plants equipped with Dr. Peter Buttmann Modern flue-gas cleaning with TCR modern flue-gas cleaning technology emit ABB Umwelttechnik GmbH The more stringent regulations have led the practically no dioxins into the atmosphere. environmental control industry to step up its On the contrary, they act as dioxin sinks, Torgny Johansson development programmes in a dramatic destroying the dioxins which are naturally ABB Fläkt Industri AB way. present in the waste and actually lessening ABB has developed its own advanced

ABB Review 1/1996 29 WASTE INCINERATION

Incineration Bag filter Scrubber Filsorption SCR denox

Ammonia Natural gas H2O

Activated coke

Milk of lime Mixture of activated coke and lime 2

To incinerator

Hg-bearing activated carbon Heavy-metal condensate 3 Gypsum 6 Glass granules 30 Quantity in kg per tonne of waste 15 Lime sludge

Vitrification HCl production Gypsum production

TCR process, with resource recovery, for flue-gas cleaning in waste incineration plants 1

process, which it calls Total Cleaning and bag filter, where the is removed. The containing heavy metals is also removed Recycling, or TCR. high efficiency of the bag filter has a very with the dust. As the process schematic 1 of the positive effect on the performance of the In the first scrubber, quenching is fol- modular TCR facility shows, the scrubbing stages, and especially on the lowed by wash-out of the hydrochloric acid first passes from the incineration grate recovery of resources from the scrubbing (HCl) under acidic conditions. The second to the heat-recovery and then to a liquids. The majority of the particulate scrubber absorbs the sulfur dioxide. This solves the initial problem of removing the principal acidic constituents of the flue

Table 1: gas. In addition, the first scrubber dissolves Allowed pollutant emissions for waste incineration plants and separates the gaseous heavy metals 3 (in mg/Nm , dry, 11 % O2) – average daily values and mean value (eg, ) and the residual heavy metal during sampling particles.

Pollutants TA Luft ’86 17th BlmSchV EU Guideline The scrubbing stages are followed by a second bag filter in which a process Dust 30 10 10 known as filsorption – a name taken from Carbon monoxide 100 50 50 and adsorption – takes place. The Organic materials (C tot) 20 10 10 filsorption filter uses a mixture of activated Sulfur oxides as SO2 100 50 50 Gaseous anorg. comp. of chloride as HCl 50 10 10 coke and lime hydrate, and is largely Gaseous anorg. comp. of fluorine as HF < 5 1 1 responsible for the exceptionally good Nitrogen oxides as NO 500 200 – 2 clean-gas data. It is especially good at

Cd, Tl v 0.2 0.05 0.05 adsorbing dioxins and furans as well as any Hg 0.05 0.05 residual mercury left after scrubbing, while it Sb, As, Pb, Cr, Co, Cu, Mn, Ni, V, Sn – 0.5 0.5 also removes any harmful acids, dust and Dibenzodioxins/-furans 3 heavy metals still present. As a result, clean- in ng/Nm , dry, 11% O2 –0.10.1 (Toxic equivalent (TE) in accordance with NATO-CCMS gas values even lower than the detection limits are achieved.

30 ABB Review 1/1996 WASTE INCINERATION

Filsorption is offered by ABB as its pre- • The sorbent material used in the filsorp- Further development ferred alternative to coke bed filters. With tion process is led directly back to the of the dual- process reactors containing several hundred cubic furnace in order to destroy the dioxins ABB has developed a particularly interesting meters of activated coke, the latter repre- and furans contained in it. Alternatively, variation of the TCR process for washing sent a genuine fire hazard. Both processes the material can be vitrified together with out the harmful acidic . It combines employ the highly efficient technology the dust collected in the first filter. the ABB spray scrubber 2 with the dual- known generically as adsorption. The TCR concept is so new that all the alkali process developed by ABB especially A direct comparison shows the filsorp- modules making up the facility could not yet for waste incineration plants. tion process to be better not only in terms of be installed and used together in the same The state of the art is to separate the safety but also with regard to dust, heavy incineration plant. However, each individual acidic gases (HCl) and metal and carbon monoxide emissions. module has been tested in the field on a sulfur dioxide (SO2) in consecutive scrub- With regard to all the other components, the large scale. The flue-gas cleaning system, bing stages. Prior to the absorption (ie, dur- two processes perform at similar levels. for example, is operating in several plants, ing quenching) the flue gas is cooled to its The denox stage, which employs selec- and reliable emission data with this system wet-bulb temperature by co-current spray- tive catalytic reduction (SCR), is usually is now readily available. ing of a liquid into the flue-gas flow. In the positioned by ABB at the end of the flue- gas cleaning process. The filsorption filter upstream provides optimum protection for ABB spray scrubber used in combination with the dual-alkali process 2 for washing out harmful acidic gases the catalyst. Since the denox process can take place at a temperature of 200 ˚C or 1 Quenching stage 2 HCl stage 3 SO2 stage lower, long residence times are possible. Reasons can also be given, however, for installing the catalyst immediately after the scrubbers. In this case, a combined catalyst is used. It first reduces the nitrogen oxides

(NOx) and then oxidizes the organic sub- stances, in particular the dioxins and furans. 3 The operating temperature with this con- figuration is about 300 ˚C. Its advantage is that the dust collected in the filter is prac- tically free of dioxins. The residues produced by flue-gas clean- ing are treated in different process stages: • The fly ash from the incinerator and the dust collected in the first bag filter are 2 passed through the DEGLOR process [1], in which an electrically heated fur- 1 nace melts them into a harmless glassy slag suitable for use in, eg, sand-blasting or road construction, plus a ‘heavy metal concentrate’ which can be processed in specialized metallurgical plants. • The draw-off from the scrubbing process can be treated in different stages (distil- lation, evaporation, crystallization, filtra- tion, etc) to recover valuable resources. Some possible products are hydrochloric acid, sodium chloride for chlorine- alkali electrolysis, and gypsum (eg, for use in manufacturing wall-board).

ABB Review 1/1996 31 WASTE INCINERATION

Flue-gas Limestone Soda outlet

Flue-gas inlet

Lime Gypsum Soda Limestone Spray scrubber mixing sedimen- mixing sedimen- SO2 stage tank tation tank tank tation tank

Gypsum dewatering stage Gypsum

Flow chart of the dual-alkali system developed by ABB. Gypsum is precipitated by this patented process. 3

first scrubber the HCl in the flue gas is uses limestone rather than a caustic soda Important benefits in respect of the SO2 absorbed by an acidic solution comprising solution. Another reason for this preference separation are: HCl and . At the top of the HCl stage is that many operators prefer gypsum • Since a clear solution is used, the resis- very fine droplets of the scrubbing agent are (CaSO4 • 2 H2O) to sodium sulfate as an tance to mass transfer during the ab- sprayed into the gas flow in the counter-cur- end-product, since the former has more sorption process and oxidation to sulfate rent direction. The diluted hydrochloric acid commercial uses. is very low. that is produced collects at the bottom of Although the above considerations • The ratio of the liquid to flue gas in the the tank and is pumped back to the nozzle weigh heavily, scrubbers using a caustic scrubber is small. level in the circuit. The scrubbing liquid is soda solution have several clear technologi- • There is only a small pressure drop; the drawn off and replaced by fresh water cal advantages over those which use lime- residence time is short. according to the acid concentration. The stone, particularly in the areas of operation To be able to take advantage of the bene- drawn-off liquid can be processed to obtain and reliability. These benefits can be sum- fits of a scrubber that uses a caustic concentrated hydrochloric acid, etc. marized as follows: soda solution and produce gypsum at In the second scrubbing stage the sulfur • All feed material and reaction products the same time, ABB has further develo- dioxide is absorbed by mixing caustic soda are in the form of aqueous solutions; no ped the so-called dilute mode dual- or lime hydrate () with the solids are involved. alkali process, modifying it for flue-gas scrubbing agent to keep it neutral. Use • No protection against erosion has to be cleaning in waste incineration plants. In of crushed limestone (CaCO3) as a neutral- provided. this process 3 , which has been pat- izing agent is also possible. Continuous • Since there are no sediments, the liquid ented, the solution drawn off from the measurement of the pH value is necessary does not have to be circulated to prevent neutral SO2 stage of the scrubber has in this stage. sedimentation. lime hydrate (Ca(OH)2) added to it. The type of neutralizing agent chosen will • Only minimal maintenance of the Through this simple ion interchange, generally depend on the overall costs. Cal- demister is required. gypsum is precipitated and the caustic cium hydroxide and limestone being much • The alkaline stage can be installed simply soda solution is regenerated: cheaper than caustic soda, incineration on top of the acid stage, saving floor plant operators often prefer a scrubber that space as well as costs. Na2SO4 + Ca(OH)2 ––> CaSO4 + 2NaOH

32 ABB Review 1/1996 WASTE INCINERATION

Although it is usual for the lime hydrate to tation of the sulfate). One of the main goals plant. In addition, the theoretical risk of the be added in the dry state, lime milk or even of the development work was to ensure that gypsum quality varying was far greater, due slaked quicklime can also be used. the process has only a minimal effect on the mainly to the operating conditions in a In a second stage, a very small quantity availability and operation of the scrubber. waste incineration plant fluctuating more of soda (Na2CO3) is added to the solution This is often the key to reliable operation of strongly than in a , where the regenerated with lime hydrate in order to the incineration plant. The separate process quality of the remains relatively con- replace the Na+ ions lost during the pro- stages also provide numerous possibilities stant. The recovery of products from waste cess. The use of soda, which is relatively for optimizing plant operation, for example incineration is also a political issue, since cheap, also has the effect of softening the through the installation of intermediate stor- they are automatically considered to be regenerated solution according to age tanks or the use of parallel or common ‘dirtier’ than the same material originating systems for more than one incineration line. from other sources. The goal was to 2+ + Na2CO3 + Ca ––> CaCO3 + 2Na The scrubber may also be operated with achieve a gypsum quality that would allow just fresh caustic soda solution if required. disposal in Class I landfills as per the before it passes back to the scrubber, thus An installation of the type described has German ‘TA Siedlungsabfall’ decree. This reducing the risk of sedimentation in the been built in the Hobro waste incineration reduces the cost of landfilling substantially, scrubber cycle. plant in Denmark, allowing full-scale field compared with the alternative of gypsum The calcium carbonate which is pro- experience to be gained for the first time disposal in Class II landfills, as is usually duced is precipitated, separated from the with this technology. necessary when the calcium salts come clear regenerated solution and re-used in Initially, the quality of the gypsum pro- from a treatment plant in which the waste- the effluent treatment plant. duced in the Hobro plant was evaluated water is still contaminated with heavy The regeneration process for recovering under the assumption that it would probably metals. the caustic soda solution takes place in a be disposed of in landfills. This assumption The results from the Hobro demonstra- separate plant and therefore has no in- was made on the basis of the quantity pro- tion plant were promising from the begin- fluence on the availability of the scrubber duced in a waste incineration plant usually ning, and gypsum suitable for Class I landfil- and the chemical reactions. Oxidation of the being much smaller than the amount pro- ling could be produced immediately and remaining sulfite to sulfate takes place in a duced, for example, in a coal-fired power without problems. The requirements for separate oxidation tank located in the outlet of the scrubber’s SO2 stage. Complete oxidation is easily achieved since both the Separation of sulfur dioxide with the ABB spray scrubber 4 sulfite and the sulfate are present in the (N.tr. = standard condition, dry gas) dissolved state. Green SO2, inlet Red SO2, outlet Blue SO2, theoretical equilibrium

2Na2SO3 + O2 ––> 2Na2SO4 mg/m3, N.tr. 600

Control of this process is also easy. The 1500 dose rate for the regenerated NaOH sol- 500 ppm,tr. ution passed back to the scrubber is con- trolled via the pH value in the scrubber cir- 400 cuit, while the amount to be drawn off is 1000 regulated according to the level of the liquid 300 in the system. Control of the lime feed rate is also relatively simple, regulation taking SO2 place in direct proportion to the amount of 200

SO2 separated. This is possible due to the 500 stoichiometric ratio being close to unity. 100 In terms of operating reliability, the com- bination of NaOH scrubber and dual- 0 alkali system offers good flexibility due to 6.1 6.3 6.5 6.7 separate stages being used for scrubbing, pH oxidation and NaOH recovery (with precipi-

ABB Review 1/1996 33 WASTE INCINERATION

Additional optimization of the scrubber was not necessary. The principal lesson Hobro has taught is therefore that scrubber operation is not affected at all by the oper- ation of the dual-alkali system. From this it can be concluded that all sodium-based ABB scrubbers can be retrofitted with a dual-alkali system. As a rule, other, non- ABB scrubbers using a caustic soda sol- ution can also be brought up to the stan- dard required for retrofitting with an ABB dual-alkali system. The demister flushing system in the Hobro plant was shut down completely for several weeks, during which time no trace of sedimentation could be detected. Like- wise, there were no signs of incrustation in the scrubber. This shows how effective the soda is at softening the regenerated caustic soda solution.

Dual-alkali system The experience gained in the Hobro inciner- ation plant mainly concerns the dual-alka- li system, in which the entire liquid flow from the scrubber is treated. The tests have shown that the scrubber and regeneration system can handle all the operating con- ditions that could arise in practice. Full-scale operation was especially important for the way it helped with the design and fine-tun- ing of the control system. Operation on this scale is also necessary Filsorption stage with scrubber using a solution, 5 to obtain reliable mass balances for the as retrofitted recently in the waste incineration plant at Zirndorf in Germany combined scrubber and regeneration system. Tests were carried out both with dry construction-quality gypsum could also be Operating experience in slaked lime and lime milk. fulfilled from the start. At about the same the Hobro waste incineration plant Full-scale trials are also important as they time, several countries began to require provide experience with operation of the in- waste incineration plants to produce recy- Scrubber dividual components. The only component clable end-products only. In view of this, The scrubber, which uses a caustic soda that has had to be replaced during the pro- special emphasis was placed on demon- solution, is a proven ABB design with more gramme is the gypsum dewatering system. strating the Hobro plant’s capability for pro- than 65 modules; 15 of these are part of the Because the gypsum crystals obtained with ducing construction-quality gypsum (eg, for waste incineration flue-gas cleaning pro- the new system are considerably larger than wall-board). cess. Since the scrubber was optimized for those obtained with similar systems and Tables 2 and 3 compare the achieved this application from the start, emission with the pilot installation in the ABB re- gypsum quality with the requirements for values are very low 4 . Features that make search center in Växjö, Sweden, the drum Class I and II landfilling as well as for wall- a decisive contribution to the good results filter had to be replaced by a band filter. The board manufacture. It can be seen that all include the design of the nozzle lances and advantage of the larger crystals in terms of the requirements are easily satisfied. the intermediate bottoms. dewatering, washing properties and gyp-

34 ABB Review 1/1996 WASTE INCINERATION

sum purity were recognized at an early stage and subsequently put to good use, as Table 2: the gypsum quality data given in Tables 2 Eluate analysis for gypsum: requirements and results at Hobro waste incineration plant, Denmark and 3 show. Hobro Requirements, Requirements, The trend to zero emissions results Class I Class II landfill

Operators of waste incineration plants pH 10.3 5.5 – 13 5.5 – 13 equipped with advanced flue-gas cleaning Conductivity µS/cm 2,000 < 10,000 < 50,000 Pb mg/l < 0.1 < 0.2 < 1 technology target zero emissions as their Cd mg/l < 0.05 < 0.05 < 0.1 operational goal. A prerequisite for this, be- Hg µg/l < 0.5 < 5 < 20 sides high-performance wet scrubbing and Zn mg/l < 0.1 < 2 < 5 F mg/l 4.8 < 5 < 25 catalytic reduction of the nitrogen oxides, is a filter with a ‘safeguard’ function. The de- scribed filsorption process performs this task in an ideal way. Considerable experience with the new Table 3: technology is available in Germany, es- Gypsum composition: requirements and results at Hobro waste incineration plant pecially with the systems installed in waste incineration plants in Ingolstadt, Zirndorf Hobro Requirements results for wall-board and Bonn. Other installations are currently under construction or at the planning Gypsum content % 96.8 > 95 stage. All existing German waste inciner- pH 7.6 5 – 8 Magnesium oxide % 0.005 < 0.1 ation plants have to comply with the 17th Potassium oxide % 0.0002 < 0.06 BImSchV decree by 1996. Chloride ppm 70 < 100 Calcium sulfite % 0.1 < 0.5 The plant in Zirndorf 5 is unique in a Aluminium oxide % 0.023 < 0.3 number of ways. For example, it is the first Iron (III) oxide % 0.031 < 0.15 Silicon dioxide % 0.11 < 2.5 one in Germany to feed the spent sorbent Ca and Mg carbonate % 0.91 < 1.5 from the filsorption stage back to the incin- erator. This procedure was approved by the authorities because the dioxins are de- stroyed in the furnace and the mercury is discharged from the acidic scrubber. As a Table 4: Clean-gas emissions at Zirndorf and Uppsala waste incineration plants result, an additional residual material has been avoided. Pollutants Zirndorf Uppsala Relevant limit The Zirndorf incineration plant [2] was flue-gas rate: flue-gas rate: in 17th 30,000 Nm3/h 200,000 Nm3/h BlmSchV shut down for a short time in 1990 because mg/m3 mg/m3 mg/m3 the dioxin values measured at the plant were too high. Installation of an NaOH Total carbon C < 2 nm* 10 Hydrogen chloride HCl < 1 < 1 10 scrubber and filsorption stage took about Sulfur dioxide SO2 < 2 10 50 four months, and the plant went back on Hydrogen fluoride HF < 0,1 < 0.1 1 stream in 1991. Nitrogen oxides NOx 425* nm* 200 September 1992 also saw a retrofitted fil- Mercury Hg < 0.006 < 0.001 0.05 sorption stage begin operating in the waste Cadmium and thallium Cd + Tl < 0.002 nm* 0.05 Residual heavy metals 0.011 < 0.02 0.5 incineration plant in Uppsala, Sweden. This Total dust < 0.6 < 1 10 plant is about seven times larger than the one in Zirndorf. Table 4 compares the gas ng/m3 TE ng/m3 TE ng/m3 TE emissions of the two plants with the limits Dioxins/furans PCDD/PCDF < 0.006 < 0.02 0.1 specified by the 17th BImSchV decree. * The retrofit made no provisions for reduction of this pollutant It can be seen that several of the values (nm = not measured) for clean gas (an exception is the NOx, due

ABB Review 1/1996 35 WASTE INCINERATION

München Süd, Germany’s first plant based on waste incineration to be equipped with the SCR denox system 6

to the Zirndorf installation only starting up in Waste incineration plants as References February 1995) lie considerably below the dioxin sinks [1] I. Joichi, J. Balg, C. Wieckert: Detoxifi- given limits, also that the scale-up did not Waste incineration plants have become a cation of municipal waste incineration resi- lead to any notable increase in the figures. permanent fixture of modern refuse disposal dues by vitrification. ABB Review 6/7-95, In the meantime, results from several programmes and are unlikely to be replaced 9–16. years of large-scale selective catalytic re- by alternative technologies. [2] G. Jungmann: Pollutant emissions re- duction of NOx in the waste incineration Since the 17th BImSchV decree, all the duced by retrofitting waste incineration sector have also become available. The first concerns about waste incineration plants plants. ABB Review 2/93, 15–20. plant in Germany to be equipped with this can be safely said to be no longer based on technology is the München Süd waste in- fact. Modern waste incineration plants emit Authors’ addresses cineration facility 6 , in which the flue-gas practically no dioxins; in fact, they act as Dr. Jürgen Gottschalk exits at a rate of 2 × 240,000 Nm3/h. In this dioxin sinks, since they destroy those dio- Dr. Peter Buttmann plant the NOx reduction takes place down- xins naturally present in waste. Also, by ABB Umwelttechnik GmbH stream of a dry flue-gas cleaning process making the organic part of landfilled waste P.O. box 260 with bag filter. Since being installed in 1990 inert they prevent chemical reactions from D-35510 Butzbach the SCR system has operated trouble-free occurring that could otherwise last dec- Germany and still works with its original catalysts. ades, possibly with pollutants escaping un- Telefax: +49 6033 60011 A guarantee value of 70 mg/m3 was given controllably into the environment. for the NOx emissions in the clean gas. State-of-the-art flue-gas cleaning tech- Torgny Johansson (This compares with a maximum value of nology for waste incineration plants is today ABB Fläkt Industri AB 600 mg/m3 in the raw gas.) In practice, the new benchmark by which all other in- S-35187 Växjö

3 NOx values of 50 to 60 mg/m are achieved dustrial sectors have to measure their clean Sweden for the clean gas. air performance. Telefax: +46 470 365 50

36 ABB Review 1/1996