The Lime Industry, a Potential Business Area for Kanthal

UPTEC Q10 001 Examensarbete 30 hp Mars 2010

The lime industry, a potential business area for Kanthal

Jesper Ejenstam Abstract The lime industry, a potential business area for Kanthal Jesper Ejenstam

Teknisk- naturvetenskaplig fakultet UTH-enheten The subject of this M.Sc. thesis is to find out whether the lime industry is a possible business area for Kanthal AB. The lime industry is one of the biggest chemical Besöksadress: industries in the world and it is very energy demanding. In the process of making Ångströmlaboratoriet Lägerhyddsvägen 1 quicklime, calcium oxide, a lot of energy is needed as the dissociation of limestone, Hus 4, Plan 0 which consists mainly of calcium carbonate, takes place in the temperature span between 900°C and 1300°C. The total production of quicklime was in 2009 about Postadress: 280 million tonnes, and the selling price was about $100 per ton. Today, all limekilns Box 536 751 21 Uppsala are driven by fossil fuels, i.e. oil, coal and gas. The increasing demand on lowering the emissions of carbon dioxide strongly affects the industry, as it is responsible for about Telefon: 2 % of the total emissions of carbon dioxide. The industry itself claims that the 018 – 471 30 03 emissions may only be reduced about 10 %, although at very high costs. Kanthal AB

Telefax: produces electric heating solutions that may be suitable for lime production. 018 – 471 30 00 However, the lime industry is conservative and the use of electricity for lime production is not economically feasible today. Most of the electricity comes from coal Hemsida: power plants and therefore the use of electricity would not be more environmentally http://www.teknat.uu.se/student friendly in most countries. New limekilns, which are more environmentally friendly, are on the way. These kilns do not necessarily have to use fossil fuels, provides a purer end product and the emission of carbon dioxide is minimized. The size of the production is also much lower, but the end products might be used in more demanding areas, e.g. the pharmaceutical industry, and be sold at a higher price. It is this area Kanthal has to focus on if going to enter the lime industry at this point.

Handledare: Gustaf Lorenzson Ämnesgranskare: Håkan Engqvist Examinator: Åsa Kassman Rudolphi ISSN: 1401-5773, UPTEC Q10 001 Sponsor: Kanthal AB Kalkindustrin, en möjlig marknad för Kanthal

Jesper Ejenstam

Bakgrund och syfte

Kalkindustrin är en av världens största kemikalieindustrier, näst störst efter svavelsyraindustrin. Tekniken som används är ungefär densamma som för 100 år sedan, dock har den optimerats en hel del. Industrin hävdar att metoderna är så pass utvecklade de kan bli, vilket är ett problem eftersom effektiviteten ligger mellan 30 och 80 %. 2009 producerades ca 280 miljoner ton bränd kalk, varav Kina stod för ca 180 miljoner ton, och det ungefärliga priset ligger på 100 dollar per ton.

Kanthal AB vill med det här examensarbetet få svar på frågan om kalkindustrin kan vara ett möjligt affärsområde. Därför syftar examensarbetet till att vara kunskapsbyggande och ska kunna ligga som underlag vid ett eventuellt ”business case” om Kanthal bestämmer sig för att satsa på kalkindustrin.

Bränd kalk

Kalksten har används av människan i tusentals år. Ett exempel på det är pyramiderna i Egypten som består av kalksten. Kalksten består i huvudsak av kalciumkarbonat och det finns mycket god tillgång till mineralen över hela världen. När kalciumkarbonat upphettas till ca 900°C sönderdelas det till ungefär lika stora delar kalciumoxid och koldioxid . Kalciumoxid, även kallat bränd kalk, är en viktig ingrediens i många andra processer, till exempel stålframställning där det används som slaggbildare. Idag används framförallt två typer av ugnar för framställning av bränd kalk, roterugnar och schaktugnar. En roterugn består av en enorm lätt sluttande cylinder med en längd på ca 100 m och en diameter på ca 3-4 m. I ena änden finns en brännare som drivs med fossila bränslen såsom olja eller kol. I andra änden matas kalksten in i cylindern och när cylindern sätts i rotation transporteras kalkstenen mot brännaren där bränd kalk bildas. En schaktugn består av ett högt torn på ca 30 m, med en diameter på 4-5 m. Kalksten matas in i toppen av schaktet, i mitten bränns den och i botten plockas den brända kalken ut. I och med att brännarens låga är i direkt kontakt med kalkstenen i bägge dessa kalkugnar är en viss förorening av slutprodukten oundviklig. Detta medför att kvalitén på den brända kalken blir något sämre, vilket påverkar priset.

Energi och miljöaspekter

Eftersom det går åt mycket energi att framställa bränd kalk, och att fossila bränslen används som energikälla, är stora utsläpp av koldioxid oundvikligt. Kalkindustrin står för ca 2 % av världens totala koldioxidutsläpp, där upp till 40 % kan kopplas till förbränningen av fossila bränslen. Miljöskatter, såsom koldioxidskatt, påverkar industrins resultat kraftigt. Enligt representanter från kalkindustrin skulle utsläppen kunna minskas med 7 till 10 %, fast till mycket höga kostnader. Detta är långt ifrån tillräckligt och nya produktionsmetoder måste till. I dagsläget skulle en kalkugn inte kunna drivas av elektricitet eftersom elpriset är så högt i förhållande till fossila bränslen. Dessutom produceras stora delar av världens elektricitet idag genom förbränning av fossila bränslen, framförallt kol. Detta medför att elanvändning inte skulle vara mer miljövänlig i dagsläget, utan endast flytta problemet till den energiproducerande sektorn. Dock tar koldioxidneutrala energikällor, såsom kärnkraft, vindkraft, vattenkraft och solenergi, hela tiden nya marknadsandelar. Detta faktum, kombinerat med ett ökat pris på fossila bränslen, gör att många vetenskapsmän tror att el som energikälla kan vara konkurrenskraftig runt 2050.

Ny teknik

På senare år har nya förslag på kalkugnar presenterats av forskarlag och kalkföretag. Gemensamt för alla dessa prototyper är att slutprodukten ska bli mycket renare och därför kunna användas inom nischade produktområden, till exempel inom läkemedelsindustrin. Detta beror framför allt på att den brända kalken aldrig förorenas av en öppen låga, vilket är ett av problemen idag. Stort fokus ligger även på energifrågan, och ett forskarlag har tagit fram en idé där koncentrerade solstrålar är värmekälla. Gemensamt för de nya teknikerna är att slutprodukten blir dyrare än den är i dagsläget, storleken på produktionen blir mindre men slutprodukten blir mycket renare.

Slutsats I dagsläget är det inte ekonomisk lönsamt att storskaligt producera bränd kalk med elektricitet som energikälla. Det skulle heller inte bidra till minskade utsläpp av växthusgaser. Däremot kan produktion av bränd kalk i mindre skala kunna vara ett intressant område för Kanthal. Flera forskargrupper har presenterat goda resultat och ett intresse från bland annat läkemedelsindustrin finns. Detta är det område som Kanthal idag bör satsa på, vilket även ger större inblick i industrin. Förslagsvis ska Kanthal delta på internationella kalkkonferenser där kontakter med kalkföretag och ugnsbyggare kan skapas. Dessutom diskuteras energiproblem och ny teknik vilket är områden där Kanthal kommer in i bilden.

Examensarbete 30 hp på civilingenjörsprogrammet Teknisk fysik med materialvetenskap Uppsala universitet, mars 2010 The lime industry, a potential business area for Kanthal

Contents

1Introduction 1 1.1 Background ...... 1 1.2 Basic deﬁnitions and notiﬁcations ...... 3 1.3 Purpose ...... 3

2Methodology 4

3Limestone 5 3.1 History...... 5 3.2 Formation of limestone ...... 6 3.3 Properties ...... 6 3.4 Quarrying ...... 7 3.5 Limestone preparation ...... 7 3.6 Environmental aspects of limestone quarrying ...... 7

4Quicklime 9 4.1 Properties ...... 9 4.2 Theory of calcination ...... 9 4.2.1 Calcitic quicklime ...... 9 4.2.2 Dolomitic quicklime ...... 10 4.2.3 Stages of calcination ...... 11 4.2.4 Dissociation of calcite ...... 11 4.2.5 Sintering of high calcium quicklime ...... 14 4.3 Production of quicklime ...... 15 4.3.1 Shaft kiln ...... 15 4.3.2 Rotary kiln ...... 17 4.3.3 Distribution of kiln types ...... 18 4.3.4 Environmental aspects of lime burning ...... 18 4.4 Slakedlime ...... 19 4.5 Largest quicklime producing countries ...... 20 4.6 Usesofquicklime ...... 21 4.6.1 Agriculture ...... 21 4.6.2 Glass ...... 22 4.6.3 Metal reﬁning ...... 22 4.6.4 Pulp and Paper ...... 23 4.6.5 Caustic soda ...... 23 4.6.6 Soil stabilization ...... 23 4.6.7 Steelmaking ...... 23 4.6.8 Sugar ...... 24 4.6.9 Water treatment ...... 24 4.6.10 Flue gas desulphuration ...... 25 The lime industry, a potential business area for Kanthal

5ResearchandDevelopment 26 5.1 Solar reactors for quicklime production ...... 26 5.2 Indirect ﬁred limekiln ...... 29 5.3 Energy source outlook ...... 30 5.3.1 Fossil fuels ...... 30 5.3.2 Renewable energy sources and Nuclear energy ...... 31

6Ideaforanalternativeheatingsolutionsforlime-burning32 6.1 Background ...... 32 6.2 Kanthal APMT ...... 32 6.3 Radiant tubes ...... 32 6.3.1 Tubothal ...... 33 6.3.2 Ecothal ...... 34 6.4 Prototype proposal ...... 35

7InvestigationoftheimpactofthecalcinationprocessonKanthal APMT 37 7.1 Background ...... 37 7.2 Experimental ...... 37 7.3 Results...... 38 7.3.1 Visual observations ...... 38 7.3.2 Light Optic Microscopy ...... 38 7.3.3 Scanning Electron Microscopy ...... 39 7.3.4 Summary ...... 41

8Discussion 43 8.1 Quicklime production ...... 43 8.2 The market potential ...... 43 8.3 Energy sources and environmental aspects ...... 43 8.4 Eﬀects of limestone calcination on Kanthal APMT ...... 44 8.5 The alternative limekiln prototype ...... 44 8.6 Other proposed prototypes ...... 45

9Conclusions 46

10 Future work 47 10.1 Porcupine heating cassettes as pre-heaters in cement production . . . 47 10.2 Alloys as construction material in lime and cement facilities . . . . . 47 10.3 Lance tubes for quicklime shaft kilns ...... 47

11 Acknowledgments 49

References 50 The lime industry, a potential business area for Kanthal 1

1Introduction

1.1 Background The lime industry is one of the largest chemical industries intheworld.Everyyear, about 280 million tons of quicklime (calcium oxide) is produced. The lime products are very versatile, whereas many areas of usage have been defined. Quicklime is produced in large kilns, which often have poor efficiency. The kilns also use fossil fuel and are one of the largest contributors of green house gases, such as carbon dioxide. The burner in conventional limekilns does also affect the product. The flame of the burner is in direct contact with limestone and therefore the end product will be polluted. This reduces the selling price of the product, which is already low from the beginning. It also decreases the areas of use of quicklime. Because quicklime is a fairly cheap chemical, about $ 100 per ton, many producersarestrugglingto survive. Thus, long range exporting of the products is just not economically feasible. Therefore a lime plant often only supplies the local industries near by. The high fuel prices, emission-taxes and low efficiency of the kilns force the producers to find new ways of lime production. A lot of work has been done insmallexper- imental setups, but as the lime industry is very conservativethedevelopmentof new solutions is progressing slowly. The whole lime production cycle is very large and therefore the main focus in this report will be at the calcining processes, figure 1.

Quicklime is produced by dissociation of calcium carbonate (CaCO3)tocalcium oxide (CaO)andcarbondioxide(CO2). The process takes place at high temperatures, about 900◦Cto1300◦Cdependingonwhichpropertiesarerequested.Some of the processes that are common today have large energy and heat losses and this problem may be solved by modiﬁcations or using other heating techniques.

Kanthal AB is producing and selling heating solutions and is constantly looking for new market areas where their products may ﬁt in. The lime industry is new ground for Kanthal AB that are hoping their products can make adiﬀerenceinthis area. The lime industry, a potential business area for Kanthal 2

Figure 1: Schematic ﬁgure of the lime production process. This report focuses on the calcining process, which is illustrated in the square [1]. The lime industry, a potential business area for Kanthal 3

1.2 Basic definitions and notifications The phrase lime is often used rashly by representatives and people connectedto the lime industry. This may lead to misunderstandings, as thewordlimeimplicates both quicklime and slaked lime. However, this does not mean that these products have the same properties. Unfortunately this misleading phrase is commonly used and the reader has to know the differences. Beneath, the commonwordsarelisted together with a short explanation [2].

• Limestone is a mineral that occurs naturally in the nature, and consistsmostly of calcium carbonate (CaCO3). It occurs all over the world and is one of the most important minerals known to mankind.

• Quicklime consists almost entirely of calcium oxide (CaO), and is produced by thermal dissociation of limestone.

• Slaked lime is produced by adding water to quicklime. This is an endothermal reaction where calcium hydroxide (Ca(OH)2)istheendproduct.

1.3 Purpose Kanthal AB wants to know whether quicklime processing can strengthen its business, and if the company can contribute to the industry. Thereisaneedtoknow more about lime and lime production, what furnace types are used, energy usage and research done in the area, and also to get an estimate of howbigthemarket potential is.

Kanthal also wants to ﬁnd new systems for quicklime processing, by renewable energy or with higher eﬃciency. If it turns out to be possible for Kanthal to enter this industry, ideas of a prototype limekiln, using Kanthal products are wanted.

This M.Sc. thesis is supposed to be the base for an upcoming business case. The lime industry, a potential business area for Kanthal 4

2Methodology

This M.Sc. thesis is mainly a literature study of the lime industry and information has been gathered from scientiﬁc reports, books and web pages. To further understand the processes, technology and important factors oflimeproduction,lime facilities were visited. Experts in interesting areas, who had great importance to the conclusions in this report, have been interviewed and cited.Theliteraturestudyis presented in Chapters 3-5. Aprototypeproposal,usingKanthalheatingsystem,ispresented in Chapter 6. AsmallexperimentalworkwascarriedouttoexaminewhetheraKanthalalloy was aﬀected by the calcination when getting in direct contactwithquicklime.This work is presented in Chapter 7. The lime industry, a potential business area for Kanthal 5

3Limestone

3.1 History Limestone has been used for thousands of years. One proof is the pyramids in Giza, ﬁgure 2 [3], which are about 5000 years old. Also the ancient Greeks and Romans used limestone as construction material long time before thebirthofChrist(BC)[2]. Moreover, in Yugoslavia, excavations have found limestone constructions that have been dated to 5-6000 years BC. In addition to limestone, excavations have shown that quicklime was also used in mortar to strengthen buildings. During the 19th and 20th century several cities in USA and Canada were built inpurelimestone. An example is Kingston in Canada, where several buildings consist of limestone. Hence, the city is known as the ”Limestone City”. These are just a few examples of how important limestone has been to mankind throughout theyears,andeven today limestone is an essential part of construction materials [2, 4].

Figure 2: Cheops pyramid in Giza, an early example that limestone has been used as a construction material a long time. The lime industry, a potential business area for Kanthal 6

3.2 Formation of limestone Limestone is formed mainly in warm, shallow and still waters.Itisintheseenvi- ronments where organisms, which form shells and skeletons, flourish. The limestone is in fact formed when these organisms die and accumulate ontotheseabed.What kind of organisms that flourishes in a certain area highly affects the composition of the limestone. Apart from the organism, the environment itself at a certain area affects the formation of limestone as well. This is why there are different types of limestone at different places throughout the world. The formation is a very slow process, which takes several million years to complete [2, 4]. Limestone is also formed when water evaporates. Water often consists of some amount calcium, which is transferred to the ground when watereitherabsorbsto the ground or evaporates.

3.3 Properties

Limestone is a sedimentary rock that consists primarily of CaCO3,butMgCO3 and several other minerals are also to be found within the rock. Itcanbebothcrystalline and amorphous, but the structure mainly depends on the age of the rock. Very old limestone, typically more than 600 million years old, tends to be crystalline whereas younger limestone often is amorphous. This property, among others, is the reason that a classification system for different limestone types hasbeeninvented.The limestone classification depends on microstructure, texture, impurities, age, grain size and CaCO3-content. This system has been constructed because of the wide use of limestone and different uses have different demands. Forexample,when burning limestone the temperature of the process depends of the composition of the limestone. Further on, the temperature affects the resultingproduct.Theamount of a certain impurity can be crucial to one process, but is devastating to another. The properties of limestone therefore depend very much on where, when and how it was formed [2]. The color varies from white to grey, but can be slightly red or yellow depending of what kind of impurities are present at a certain quarry. Thecrystalstructure can be orthorhombic (aragonite), hexagonal (vaterite) or rhombohedral (calcite). Aragonite is semi stable, which means that it slowly convertstocalciteinpresence of water or at temperatures above 400◦C. The same implies for vaterite, although it is even less stable than the aragonite and converts into calcite at temperatures above 60◦C[2,4]. CaCO3 has a molar mass of 100.09g/mole.Thedensityvariesfromabout 1.5g/cm3 to 2, 9g/cm3,dependingofthecompositionofthelimestone.Limestone has a hardness of about 2-4 Mohs, a scale from 1 to 10 where diamond has the highest value. Specific heat capacity is about 0.22cal/g,andthepHisabout9[2]. The lime industry, a potential business area for Kanthal 7

3.4 Quarrying Limestone is one of the most common minerals in the crust of theearth,andcan be found all over the world as it covers about 10 % of the surfaceoftheearth. It is a relatively young mineral and therefore it can be found near the surface. Limestone quarries are often open quarries, i.e. it is deposited from the surface and down. Limestone mines are not feasible from an economic pointofview,aswallsof limestone would have to be left behind. The quarrying can be divided into five steps; overburden removal, drilling, blasting and transportation. First of all, the limestone has to be exposed. It can be found less than 1 m to tens of meters down in the ground. This is done byconventional excavators and is considered to be the most demanding part of the quarrying. When this is done, blasting holes are drilled. They are drilled with a twenty-degree angle, which has been shown to be most effective. Further on, the limestone is loaded onto lorries using excavators or rolling hoops. All steps in the quarrying have over the years been accurately developed to ensure as high profit as possible [2]. In Sweden, limestone is quarried at several places but the largest quarry is found near Slite, Gotland. The largest limestone quarry in the world is found near Roger’s city in USA, and is owned by Michigan Limestone and Chemical company [2].

3.5 Limestone preparation Before the limestone can be transported to the lime facilities for processing, it has to be crushed and screened in diﬀerent fractions. In some cases washing is necessary as well. When crushing limestone, two diﬀerent methods are used, impact crushers and compression crushers. Impact crushers have the advantage of producing cubical fractions, although a lot of powder is obtained as well. The compression crushing obtains a more even fraction distribution, but the limestonetendstobeslightly rounded. Washing of limestone is often not necessary, as mostlimestonequarries have very clean limestone that is not contaminated by clay anddirt.However, for some areas, which demand extra clean limestone, washing is needed to achieve required purity. Washing in rotating barrels is also used to reduce fractions size, when fractions smaller than 10 mm are necessary [2].

3.6 Environmental aspects of limestone quarrying The environmental eﬀects of lime production start with the limestone quarrying. The limestone quarries are large areas, which looks like giant craters. This results in a disturbance in the wildlife of the area. The quarrying companies have a big responsibility to ensure that the wildlife is not disturbed too much in the area, and a plan has to be made how to restore the area when the quarry has served its purpose. Another environmental eﬀect of quarrying is the dust, which the process creates. The dust mainly originates from crushing of the quarried limestone. There is always The lime industry, a potential business area for Kanthal 8 ariskthatthedustisspreadbythewindandcausesover-fertilization of lakes, forests and agricultural land. The dust is unhealthy when inhaled as well. Huge industrial machinery is used in the process and these generate noise, vibrations and exhaust gases. Although noise is mainly from theexplosivesthatare used when large pieces of limestone are being quarried. This is the main source of vibrations as well, which may cause damage to near-by buildings [2, 4]. The lime industry, a potential business area for Kanthal 9

4Quicklime

4.1 Properties Quicklime is a porous rock, which often appears white or slightly discolored due to impurities. Impurities may be found naturally within the limestone or may come from the burning of fossil fuels while burning the limestone [4]. To the naked eye, CaO appears like an amorphous material, although this is not the case. It consists of many small crystals in NaCl structure with the lattice constant of 4.81A.˚ The melting point is about 2850◦C. Quicklime is a very reactive substance that reacts strongly with water, thus gen- erating a large amount of heat, about 1140kJ/kg, and calcium hydroxide (Ca(OH)2) [2, 4, 5].

4.2 Theory of calcination To produce quicklime, limestone is heated to a temperature over the dissociation temperature. The dissociation temperature depends on the type of limestone that is used, and cannot be generally defined. This is because the limestone differs from quarry to quarry, and experiments have to be carried out to findtheoptimalcalcining temperature for each limestone. Limestone can be divided in two subgroups, calcite and dolomite.

4.2.1 Calcitic quicklime

Calcite consists mostly of CaCO3 and is the type of limestone that is most widely used in the lime industry. This is because of the fact that mostcustomerswanta high level of pure CaO as possible in their processes. The decomposition of high calcium limestone is expressed in reaction 1 [2, 4, 5].

CaCO3 + heat ! CaO + CO2 (1) 100g 56g 44g

At atmospheric pressure, it has been shown that CaCO3 decomposes to CaO around 900◦C. The amount of heat that is needed for the reaction has been closely investigated through the years and values from 695 kcal/kg ofCaOto834kcal/kg of CaO have been reported. These values have been calculated relative an ambient temperature of 25◦C. This is not entirely correct due to the fact that heat, which is needed to raise the temperature from 25◦Cto900◦C, has to be taken into con- ◦ ◦ sideration. Furthermore, when CaO and CO2 are cooled from 900 Cto25C, some energy is gained by exothermic reactions. The net sum of the total required heat is therefore a little lower than for the heat required for the decomposition. With respect to this, values from 698 kcal/kg of CaO to 723 kcal/kg of CaO have been reported [2, 4, 5]. The lime industry, a potential business area for Kanthal 10

4.2.2 Dolomitic quicklime

Dolomite is a magnesian limestone, which consists of both CaCO3 and MgCO3. When dolomite decomposes, it can be done in a two-stage decomposition, a direct decomposition or by a mix of these reactions [2, 4, 5].

MgCO3 · CaCO3 + heat ! CaCO3 · MgO + CO2 (2) 184g 140g 44g

CaCO3 · MgO + heat ! CaO · MgO + CO2 (3) 140g 96g 44g

MgCO3 · CaCO3 + heat ! CaO · MgO +2CO2 (4) 184g 96g 88g

The diﬀerent reaction stages depend on the starting temperature of the calcination. At low temperatures, the two-stage reaction, 2 + 3, has been reported whereas reaction 4 has been reported for temperatures around 900◦C. The heat of dissociation of dolomite has been reported to be about 700 kcal/kg of (CaO · MgO), i.e. about the same as for calcitic limestone [2, 4, 5]. The lime industry, a potential business area for Kanthal 11

4.2.3 Stages of calcination Throughout the years, the calcination process has been closely studied. The process can be divided in ﬁve steps [2].

1. Limestone is preheated to about 800◦Cbyusingexhaustgasesfromthemain process.

◦ 2. When the limestone reaches 800 C, the pressure from the dissociated CO2 equals the pressure of the hot gases in the limekiln. The surface of the limestone starts to dissociate even faster and when the temperature reaches about 900◦C, the layer of quicklime is about 0.5 mm thick for a limestone lump of about 25 mm radius.

3. When the temperature rises above 900◦C, which is about the optimal dissociation temperature, the partial pressure within the lump surpasses the atmospheric pressure and the dissociation proceeds beneath the surface layer.

4. The dissociated limestone begins to sinter after some time, which corresponds to the temperature in the furnace. A higher temperature implies a faster sintering. The sintering process results in less reactive quicklime due to a smaller surface area.

5. The quicklime leaves the calcination zone and is cooled by air.

4.2.4 Dissociation of calcite The disassociation of high calcium limestone, calcite, always starts from the surface of the limestone and proceeds gradually into the core. As earlier mentioned, the dissociation process starts at the surface of the limestone at temperatures slightly below the calcining temperature, whereas a quicklime shell encapsulates it. At temperatures higher than the calcining temperature, the CO2-pressure is higher inside the limestone than outside that forces CO2 to escape. This implies that greater radius of the limestone will require a higher temperature to fully calcine it. For some types of limestone the dissociation temperature canvary150◦Cto350◦C from the surface to the center of the limestone. In addition tohighertemperatures, there is often a longer calcining time for larger fractions oflimestone.Thevariation of the calcining time with respect to the temperature and radius is shown in ﬁgure 3[5]. The lime industry, a potential business area for Kanthal 12

Figure 3: The variation in calcining time with temperature and lump diameter. a.) 150 mm, b.) 125 mm, c.) 100 mm, d.) 75 mm and e.) 50 mm.

The dissociation of calcitic limestone, illustrated in ﬁgure 4 [5], can be summarized as:

(a) Heat is transferred from the hot ambient to the surface of the limestone

(b) Heat is conducted through the decomposed layer into material, which is yet to be dissociated.

(d) CO2 migrates from the inside of the limestone through the decomposed layer.

(e) CO2 migrates from the surface limestone. The lime industry, a potential business area for Kanthal 13

Figure 4: A schematic of the calcination process of high calcium limestone.

The processes (a), (b) and (c) are well known as they are relatively straight for- ward. However, (d) and (e) are more complex as the properties of the decomposed layers will change due to sintering of CaO,slaggingofthesurfaceandabsorption of sulfur dioxide [2, 5].

The following list roughly rates the most important factors of limestone calcination [2, 5]. 1. Characteristics of the limestone. 2. Particle size distribution. 3. Shape of particles. 4. Temperature profile of the calcining zone. 5. Rate of heat exchange between the gases and the particles. Because different limestone types have slightly different properties, each type must be properly investigated. The optimum temperature cycle may vary between types, whereas it is important to characterize the limestonetypepropertiesindivid- ually, with respect to the optimal calcining temperature cycle. The heating cycle have great impact on lime quality, shrinkage and reactivity.Experimentshaveshown that a gradual increase of temperature, rather than shock heating, gives the best quicklime quality. However, little is investigated in this area and perhaps even better quicklime could be produced with better understanding oftheimpactofthe temperature cycle [5]. The lime industry, a potential business area for Kanthal 14

4.2.5 Sintering of high calcium quicklime One process that may disturb the calcining process is sintering. When high calcium limestone is heated, the volume increases due to thermalexpansion.At,and above, the calcining temperature small crystals of CaO are formed. This process proceeds until the whole limestone has been converted into CaO,whichconsistsof several small crystals at this point. This leads to an extremely large surface area, and therefore highly reactive quicklime, due to the large amount of small crystals. When the furnace temperature is higher than the calcining temperature, these small crystals starts to unitize and larger crystals are formed. This leads to shrinkage of the material due to the settle up of the CaO-crystals. Another eﬀect of to high calcining temperature is when the surface of the material hasbeenseveredsintered it may disrupt the continuous dissociation of limestone core, and stops it. When this happens, so called dead burned quicklime is formed. On the other hand, the sintering process that occurs after completion of the calcination is very common and useful. Soft, medium and hard burnt quicklime are common products, and refers to the level of sintering of the material. Soft burnt quicklime is very reactive but may contain small amounts of CaCO3,asthecalcinationprocesswasstoppedtoensure small crystal sizes in the material. Therefore a full calcination of the core has to be sacriﬁced. Hard burnt lime has a high CaO-content but is not as reactive as soft burnt quicklime due smaller total surface area because of fewer grains. What type of quicklime is requested depends on the buyer’s processes. Some processes require highly reactive lime, while others require not so reactive lime [2]. The lime industry, a potential business area for Kanthal 15

4.3 Production of quicklime 4.3.1 Shaft kiln The shaft kiln, ﬁgure 5 [6], is a vertical furnace, in which thelimestoneisinserted from the top, and passes down through the kiln during the process. The top of the kiln works as a preheating stage where the limestone is heatedandpartlycalcined. This is due to the hot exhaust gases created by the calcining burners. In the middle of the kiln, the calcining zone is found. The limestone is heated with a ﬂame, which is led into the limestone through pipes. The bottom of the kilnisthecoolingarea. Cooled air is blown into the kiln, which help cooling the limestone. The air is then heated in the calcining zone and travels upwards in the kiln and helps preheating the incoming limestone.

Figure 5: Schematic of shaft kiln.

Atypicalshaftkilnisabout30metershighandhasadiameterof 2 to 7 meters. Firebricks build up the walls, which have a thickness ofabout400mm.The most common shaft kiln has two shafts connected to each other,calledparallelflow regenerative (PFR), to acquire as high efficiency as possible.Theideaistolethot The lime industry, a potential business area for Kanthal 16 exhaust gases travel through as much limestone as possible before leaving the furnace, figure 6. As there are two shafts in a PFR, the hot exhaust gases from the active shaft are used to heat the limestone in the passive shaft. In the next cycle, the active and passive shaft shifts. This solution makes the shaft kiln the most efficient limekiln today. The down side is that a maximum temperature inthefurnaceis about 1000◦C, due to the thick limestone mass. The ”low” temperature implies to ahighsulphurcontentinthequicklimeasthetemperatureisto low for formation of SO2.Thisfactreducesthenumberofpossibleusers,e.g.stainless steel producers. On the other hand, the low temperature leads to a low levelofsinteringand therefore highly reactive quicklime is obtained. The production capacity of modern PFR shaft kilns is about 100 to 600 tones per day. Today the shaft kiln is the most common lime-burning furnace, mainly because of the high efficiency. The efficiency of a PFR shaft kiln is about 80 % [7], and the consumed heat is about 4 MJ per kg quicklime [2, 6].

Figure 6: The heat ﬂow in a PFR shaft kiln. The lime industry, a potential business area for Kanthal 17

4.3.2 Rotary kiln The rotary kiln, figure 7, is the other major type of lime-burning furnaces. It was invented in the beginning of the 20th century, and at that timetherotarykiln was superior all other kilns. The reason to the success was because wider range of limestone fractions could be calcined, from very fine fractions and upwards. Another advantage of the rotary kiln was the possibility to remove sulphur from the quicklime. Quicklime is used in the metallurgical process as a slag remover. If high levels of sulphur contaminate the stainless steel, the corrosion resistance is affected as the sulphur makes passivation of the steel surface difficult [8]. The reason that sulphur can be removed is because of the high operating temperatures,whichispossibleto achieve in the kiln. At these temperatures, sulphur complexes dissociate and leave the limestone as sulphur dioxide is transported out of the kiln with the exhaust gases. A typical rotary kiln produces about 1000 tones of quicklime per day. The theoretical heat requirement for dissociation of CaCO3 is about 3,15 MJ per kg of lime. The rotary kiln consumes about 8 MJ per kg of lime, which gives an approximate efficiency of 40 % [7]. The burners is often of flexible fuel type, i.e. gas, coal, oil or waste can be burnt individually or simultaneously. The power of the burner is decided by the heat exchange of the fuel that is burnt, but has an average power of 50 to 100 MW [7]. In contrast to shaft kilns, the rotary kiln has a much higher operating costs. This is mainly due to the higher fuel cost due to poor heat exchange. Some modern rotary kilns have a pre-heating system that uses the heat fromtheexhaustgasesto heat the limestone before it enters the kiln. The loss of heat in the rotary kiln system is another problem. The shell is built up of firebricks and a thin steel mantle, which have the combined thickness of about 250 mm. There are rotary kilns of all sizes, longer with smaller diameter as well as shorter with greater diameter. A modern kiln is about 100 m long with a diameter and about 4-5 meters. The weight varies between models, but is often greater than 1000 tonnes. The rotary kiln also has a small gradient, which is needed for transportation of limestone through the kiln. Rotary kilns have a few support points, called riding rings, which also are the points where the rotating motion is created. The rotating motion is needed to move the limestone through the kiln during the process. The lengthofthekilndecides the number of support points that are needed. Riding rings aremachinedtoobtain as smooth surface as possible. This is to ensure that the friction is low between the riding rings and the kiln. The rotation speed of the kiln istypically4to5rpm and a drive gear creates the motion. To start the rotating motion a strong electric engine, of about 800 kW, is used. The engine has a variable speed drive, which is needed, as the rotation speed of the kiln is proportional to the flow of lime trough the furnace. These days the rotary kiln is the standard furnace type in manyapplications, not only for lime burning. Other products made by rotary kilnsare;cement,iron ore pellets, alumina silicate, titan dioxide, vermiculite.Rotarykilnsarealsoused for roasting sulfide ores [2, 9]. The lime industry, a potential business area for Kanthal 18

Figure 7: Schematic ﬁgure of a typical rotary kiln. The limestone is transported through the kiln due to the rotating motion and the small gradient of the kiln.

4.3.3 Distribution of kiln types Because of the higher eﬃciency of PFR-kilns, they have becomethemostcommon kiln type, ﬁgure 8 [10]. In China, which is the largest lime producing country, there are lots of unknown types of limekilns. This is due to many locally constructed kilns and a rapid expansion of the lime industry within China.InJapan,several smaller alternative limekilns have been developed during the past years, mainly for experimental work [7, 10].

Figure 8: Chart showing the distribution of limekilns used intheworld.

4.3.4 Environmental aspects of lime burning During the calcining process, a lot of greenhouse gases are emitted, especially nitrous gases and carbon dioxide. The chemical process itself gives rise to carbon dioxide, which constitute about half the mass of CaCO3.ThispartoftheCO2-emission should not be calculated as a true emission of carbon dioxide as CaO want to convert into CaCO3 again, and for this process CO2 is needed. The lime industry, a potential business area for Kanthal 19

During the process of making quicklime, a large amount of CO2 is created. The industry is responsible for almost 2% of the global CO2 emissions. Up to 40% of these emissions is derived from the fuel, burnt in the process. The total sum of the emitted CO2 by mankind is about 29 billion tons per year. Up to about 220 million tons are directly derived from the usage of fossil fuels [5], ﬁgure 9. The global warming rate is estimated to about 0.2◦Cevery10year,andduringthe20thcentury the mean temperature in Europe have risen about 0.95◦C. Reports are showing that in about 100 years the mean temperature will rise about 2.0 - 6.3◦C, due to global warming [11]. However, this is lively debated and some scientists claims that the global mean temperature actually are decreasing.

Figure 9: Distribution of CO2-emissions within the lime industry (in million tonnes).

4.4 Slaked lime

Slaked lime consists of calcium hydroxide (Ca(OH)2)andisobtainedwhenCaO reacts with water in an exothermal reaction; see reaction 5. Slaked lime is often used for several lime products consisting Ca(OH)2 such as hydrated lime, milk of lime and lime putty. In this section, only hydrated lime will be considered. The other products are basically variations of the hydrated lime. At temperatures lower than 350◦C, CaO reacts with water, and heat is released. About 276 kcal/kg of CaO have been reported for this process [2]. However, if the temperature exceeds 350◦C, the counter-reaction occurs.

CaO + H2O ! Ca(OH)2 + Heat (5) 56 1 . g 18g 74.1g The lime industry, a potential business area for Kanthal 20

For dolomitic lime, with high magnesium content, the processisdoneslightly diﬀerent. The reaction is similar to the reaction of CaO and water; see reaction 6, although under steam pressure at temperatures above 100◦C. The released heat has been reported to 211 kcal/kg of CaO [2].

MgO · CaO +2(H2O) ! Ca(OH)2 · Mg(OH)2 + Heat (6) 96.4g 36g 132.4g

An interesting thing to notice is the low solubility of Ca(OH)2 in water, which is 1.28 g/l at 50◦Cand0.71g/lat100◦C. Magnesium hydroxide hardly solute in water, only 0.01 g/l has been reported [2].

4.5 Largest quicklime producing countries In 2009, the world production of lime was estimated to about 280 million tonnes. This was a decrease in production from 2008 with about 5 %, due to the world wide financial crisis. However, the price of quicklime continued to increase, which it has done every year. In 2009, the quicklime price increased with about $11 per ton to $ 101 per ton. The increasing price is mainly because of increasing production costs. Earlier years the increasing fuel costs, and taxes, stronglyinfluencedthepriceof quicklime. In 2009, the fuel prices decreased dramatically but the lime companies still struggled with increasing production costs. China is today, by far, the largest lime-producing country in the world with more than 50 % of the total production, see figure 10 [12]. The lime industry, a potential business area for Kanthal 21

Figure 10: Countries with 90 % of the total world lime production (in million tonnes).

4.6 Uses of quicklime Quicklime is one of the most versatile chemicals known to man and the areas of use are almost countless. It is also one of the largest chemical industries in the world [4]. The areas that consume the most tonnage of lime will be presented in this section, but remember that there are other areas of use as well. Many areas of use may not even have seen the light of the day at this point.

4.6.1 Agriculture Agricultural lime, mostly slaked lime, is mainly used to neutralize the pH-value of soil to improve vegetation. It also improves the stability ofthesoilbydecreasing crusting of the surface and therefore reducing soil erosion.Anothereﬀectisthat the water penetration, of the soil, is improved. Other important minerals, such as magnesium, phosphorous, nitrogen and potassium, can be added to the agricultural lime to improve the fertility of the soil. If the soil has high levels of iron and aluminum, the lime helps to neutralize those elements. Agricultural lime can also be used to prevent spreading of diseases among plants and animals. By increasing the pH-value of the treated soil, spreading of bacteria is prevented [2, 13]. The lime industry, a potential business area for Kanthal 22

4.6.2 Glass Soda-Lime glass is one of the most common types of glass. It is mostly used for glass containers, such as coca cola bottles, and windowpanes. The glass is made by melting and mixing of quicklime, limestone, sodium carbonate, silicon dioxide, aluminum dioxide, and ﬁning agents at a temperature of about 1700◦C. For glass containers, limestone is mainly used, but for windowpanes high calcium quicklime is used. This is because high calcium quicklime improves the transparency of the glass within the wavelengths of visual light [2, 13].

4.6.3 Metal reﬁning Quicklime is a very important ingredient when reﬁning non-ferrous metal ores. The quicklime controls the pH value of the solution and acts depressant that is necessary to extract pure metals, such as gold, silver and nickel from cyanide extraction. Quicklime also enables copper pyrites (Cu2S)tobeseparatedfromarsenopyrite (As2S5).

When producing magnesium, dolomitic quicklime is used to reduce magnesium oxide with ferrosilicon (FeSi). The process takes place at temperatures above 1200◦C and at low pressures, about 13 to 670 KPa. When the magnesium oxide has been reduced, gaseous magnesium is obtained that condensates at about 450◦C.

2CaO +2MgO + Si → 2Mg + Ca2SiO4 (7)

Pure calcium is another metal that is produced by thermal reduction. High calcium quicklime is mixed with aluminum, and heated to about1200◦ at about 0,1 Pa.

3CaO +2Al → Al2O3 + Ca (8)

Mercury is produced by a similar process and the mineral that is used is cinnabarite (HgS). Cinnabarite is reduced in presence of oxygen, but can be reduced in absence of oxygen as well, see reaction 9 and reaction 10. There are twowaysofreducing cinnabarite, with or without presence of oxygen. Both processes take place at about 300◦C[2,13].

4HgS +4CaO → 3CaS + CaSO4 +4Hg (9)

HgS + CaO +1, 5O2 → CaSO4 + Hg (10) The lime industry, a potential business area for Kanthal 23

4.6.4 Pulp and Paper In the paper industry, slaked lime is used in the sulfate process or the Kraft-process as it is called. In this process, wood is converted into wood pulp that consists mostly of cellulose fibers. Kraft is called ”black liquor” andisdehydratedandburnt to produce a mix of sodium carbonate and sodium sulfide. This smelt is then mixed with slaked lime, which has a caustic effect, and calcium carbonate and sodium hydroxide liquor is obtained. The calcium carbonate is filtered from the solution and is later re-calcined in a kiln and can therefore be recycled. The same implies for the sodium hydroxide. About 250 kg of slaked lime is used inthisprocess. Alotofslakedlimewasearlierusedinthesulfitepulpprocessaswell,buthas now been exchanged for other alkalis that are easier to handlethanlimeproducts [2].

4.6.5 Caustic soda Slaked lime and soda ash converts into caustic soda and calcium carbonate, when mixed. Caustic soda is an essential ingredient in many products such as soap and detergents, bleach, aluminum, petroleum products and in several chemical processes [13].

4.6.6 Soil stabilization Quicklime and slaked lime are commonly used at building sitestodrywetsoiland increase the stability of the ground. This is necessary when heavy machinery is used at these sites. By stabilizing the soil, building time is reduced and money is saved. The soil is stabilized because quicklime modiﬁes clay, due totheexchangeof cations from the calcium and the minerals the clay consists of. The result is swelling, hardening and drying of the clay. Because both quicklime and slaked lime are relatively cheap chemicals, this area of use has been very popular as it is very cost eﬀective [2, 13].

4.6.7 Steelmaking There are two different methods commonly used in steel production today, the method of Basic Oxygen Steelmaking (BOS) or re-melting steelscrap.Whenpro- ducing steel with BOS, oxygen are blown through the melted pigirontoreduce the high level of coal in the melt. At the same time, quicklime is mixed into the melt. This is done to remove impurities, such as phosphor, sulphur and silica, by forming slag. Typically 30 to 50 kg CaO is used per ton produced steel. About 30 to 50 % of the lime is dolomitic lime, high magnesium content, which is added for two reasons. First of all, magnesium oxide help produce certain slag products that calcium oxide is unable to elaborate. Secondly, magnesium oxide slag products protect the furnace, increasing refractory lining lifetime. Steel can also be produced by scrap melting. This is very common today, whereas lots of steel is recycled. The The lime industry, a potential business area for Kanthal 24 steel-scrap is often melted in blast furnaces, and lime is once again used for impurity removal through slag forming. The used quicklime is often in form of lumps, but some modern steel plants uses quicklime powder as it has showntobemoreeffective in modern refractories. When producing ultra pure steel, a secondary refining is oftennecessary.Inthis production step, quicklime is used for further impurity removal, but also to adjust the temperature and the chemistry of the steel-melt [14, 15].

4.6.8 Sugar Sugar can be produced from either sugarcanes or sugar beets. When using sugarcanes, slaked lime is used in both the production and reﬁning of the sugar. When the canes are harvested they are treated with water, which lowers the pH to about 4to5.SlakedlimeisaddedtoraisethepH,whichisneededtodestroy enzymes, e.g. invertase. Further on, slaked lime is also used to removeinorganicandorganic compounds by forming insoluble calcium salts. These salts are then ﬁltered from the solution.

When producing sugar from sugar beets, quicklime is used instead of slaked lime. The sugar beet is washed in hot water to extract the sugar, which also contains col- loidal, suspended and dissolved compounds. At this point theextractistreated with quicklime to raise pH and to create deposits of calcium salts and ”carbonation sludge” that are ﬁltered from the solution.

When producing sugar from canes, about 3 kg of slaked lime is used to produce 1tonofsugar.Sugarfromsugarbeetsrequiresabout200kgofquicklime per ton produced sugar. The latter industry often has its own quicklime production close to the sugar reﬁnery [2, 13].

4.6.9 Water treatment Lime is essential in water treatment. In municipal wastewater treatment, lime is used to remove nitrogen and phosphor. This is because of the high pH caused by lime. The result is that nitrogen and phosphor are precipitated and can be removed from the wastewater. Due to this, algae growth can be prevented. Lime also acts as aﬁlter,inwhichsludgeisremoved.Inindustrialwatertreatment, lime is used to neutralize acids and to remove heavy metals by precipitation. For drinking water treatment, lime is used for softening, pH adjustment, removal of impurities (e.g. arsenic) and to kill bacteria and viruses. The latter is done by raising the pH of the water to about 11 for about 1 to 3 days [2, 13]. The lime industry, a potential business area for Kanthal 25

4.6.10 Flue gas desulphuration

When fossil fuels and waste are burnt, sulphur dioxide (SO2)isformed. SO2 is responsible for the formation of acid rain, which affects the environment negatively due to acidifying of lakes and grounds. Use of lime prevents large emissions of SO2. Exhaust gases, which consist partly of SO2 is filtered through lime and calcium sulfite (CaSO3). This can be achieved through wet or dry filtering. Wet filtering of SO2 is done by using slaked lime, reaction 11, and dry filtering, reaction 12, by using quicklime. The resulting product, CaSO3,iscommonlyusedasapreservative.Itis also used to produce gypsum, which is done by adding water and oxygen to CaSO3, see reaction 13. Then the solution is dried and gypsum plates are formed, which are used in constructions etc [2].

SO2 + Ca(OH)2 → CaSO3 + H2O (11)

SO2 + CaO → CaSO3 (12)

2CaSO3 +4H2O + O2 → 2(CaSO4 · H2O)(13) The lime industry, a potential business area for Kanthal 26

5ResearchandDevelopment

5.1 Solar reactors for quicklime production Anton Meier, doctor at the Solar Technology Laboratory at thePaulScherrerIn- stitute, has during the last years been working, together with his team, on a solar reactor for quicklime production. The idea is to use mirrors to concentrate solar beams to calcine limestone. This would generate highly pure quicklime for special sectors, such as the chemical and pharmaceutical industry because no exhaust gases are polluting the end product. However, this is true for any indirect heated limekiln. Another advantage is the huge reduction of emitted CO2.Thissolutionisentirely CO2-free, in contrast to conventional limekilns that emit about2%ofthetotal global emissions. A solar lime reactor plant would thereforebeabletoreduceemis- sions up to 20 %. The fraction of limestone that the group focused on is in the range of 1 to 5 mm, and results showed that over 98% of the limestone were calcined. This was done in a laboratory kiln of about 10 kW, which managed to produce about 15 tones per day. Concentrated solar beams were not used in theexperiment,but silicon carbide (SiC)elementsfromKanthalAB,ﬁgure11.Theheatsourceitself does not inﬂuence the resulting quicklime, and therefore electric heating was used to produce reference samples of quicklime [1, 16].

Figure 11: SiC element from Kanthal AB was used to produce reference quicklime.

For industrial use A. Meier et. al., proposed three different solutions for solar beam lime burning [1, 16]. All of these solutions use mirrors to concentrate the solar beams, but some minor differences were introduced as allofthemhadtheir advantaged. The ”Top Tower” (TT), figure 12a, uses heliostat mirrors to focus the solar beam into the reactor, which is located in the top of a tower. The ”Beam down” (BD), figure 12b, is very similar but instead of having the reactor in the top of the tower, it is located in the bottom. In the top of the tower, a parabolic concentrator is mounted that collects the solar beams from the heliostat mirrors and focus the beam into the reactor. The reason for having two solutions is because of how much areal available at a certain location. The TT-solution may bethebestsolutionifthe areal is limited, although as the reactor is located in the topofthetowerhandling The lime industry, a potential business area for Kanthal 27 of the quicklime is an issue. The BT-solution makes quicklimehandlingeasier,but tends to be more expensive due to the extra parabolic concentrator [1, 16].

Figure 12: a.) Illustration of a tower top system (TT), b.) Illustration of a beam down system (BD).

The third solution, ﬁgure 13, is supposed to be applied at areas that are moun- tainous or where land area is limited. Heliostat mirrors are mounted on a south facing hill, natural of artiﬁcial, and the solar beams are concentrated into a vertical lime reactor [1, 16]. The lime industry, a potential business area for Kanthal 28

Figure 13: Illustration of a mountainside mounted solar limeplant.

Adisadvantageofthislimeburningsolutionisthegeographic areas, ﬁgure 14, where it can be applied, as the minimum solar insolation is 2000 kWh/m2.Solar beam produced lime have higher production costs than conventional lime, due to more expensive production equipment. The capacity of the plants is calculated to about 50 tones per day, which is notably less than a conventional kiln such as the shaft kiln. This leads to a cost of about $ 128 per ton to $ 157 perton,forsolar beam produced lime. The selling price for conventional lime is about $ 100 per ton, about 1 to 1.5 times less than solar produced lime. However, solar produced lime has far greater purity and therefore may be interesting in special sectors such as the pharmaceutical industry [1, 16].

Figure 14: Regions with annual solar irradiation of at least 2000 kWh/m2. The lime industry, a potential business area for Kanthal 29

5.2 Indirect fired limekiln At the international lime association congress in 2002, H.E.WillisofMerichem Company, USA presented an idea of an indirect fired limekiln [17]. He had been sketching on a horizontal limekiln, consisting of a ceramic tube, in which a ceramic screw was inserted. The screw was supposed to rotate slowly, and therefore move the limestone through the kiln while being calcined, see figure 15 [17]. The kiln is supposed to have three main advantages over conventional limekilns:

1. Possibility to calcine very ﬁne limestone lumps and powder.

2. CO2 decomposed from the calcination can be separated from exhaust gasses, and be recovered. 3. Any heat source can be used.

Figure 15: Schematic view of the indirect ﬁred limekiln.

H.E Willis, Yoshizawa lime industry, JP Steel Plantech and Haldenwanger started collaboration and a prototype kiln was constructed. The prototype was of semi- industrialized size and was finished in 2003. The total lengthofthekilnwas5.4 m, in which the ceramic tube, consisting of six sections, withlengthof0.9mand diameter of 0.3 m, was mounted. Inside the ceramic tube, the ceramic screw was inserted. In figure 16, a cross section sketch of the prototypecanbeobserved.Early in the project they were able to produce quicklime with quality equal to conventional quicklime. However, some problems occurred. The limestone had ambient temperature when entered the kiln. This caused thermal stress to the first ceramic tubes, which broke. There was not enough room for a limestone pre-heater so the solution was to change the first two ceramic tubes to metallic tubes. Further testing showed that the prototype were able to calcine very fine limestone powder with good results. This cannot be done in conventional limekilns today. However, fine lime powder tended to aggregate and adhered to the ceramic screw. This caused the rotation torque to increase and less limestone could be calcined due to less space in the kiln. The result was that the calcination capacity of the kiln decreased from 150 kg per hour, to about 100 to 120 kg per hour [17]. The lime industry, a potential business area for Kanthal 30

Figure 16: Cross sectional view of the indirect ﬁred limekiln.

The conclusion was that the indirect limekiln prototype is very successful. Fur- ther work is to be carried out with a goal to commercialize the prototype kiln. The ceramic tube is very sensitive to thermal stress whereas other materials were considered, such as aluminum oxide, which can withstand higher temperatures. This would also open for other high temperature applications, such as high temperature treatment of inorganic materials etc [17].

5.3 Energy source outlook 5.3.1 Fossil fuels Fossil fuels have been the major energy source the last centuries, but now new energy sources must be invented. There are two major reasons for this, the environmental impact and the fact that oil fields and natural gas resources are starting to peter. Coal findings, however, do not show signs of declination [18].Fossilfuelshave lately become the topic of conversation all over the world, due to the environmental aspects. The majority of emitted CO2 originates from burning of fossil fuels, and scientists claims that this is one of the reasons why the temperature of the earth is rising. One attempt to reduce the use of fossil fuels has been to introduce the CO2-tax, where companies, which emit large amounts of CO2,havetopayacertain fee. However, companies have been allocated a certain amountofCO2 that they can emit without being charged with any taxes. Companies, which have reduced their emissions, can sell emission rights to other companiesthathaveexceeded their amount of allocated CO2.Duetothis,thesecompaniesgetslowerCO2-tax. However, every year the allocated amount of ”free” CO2 is reduced and the CO2- tax increases [19]. The reason for this system is to force the companies that use fossil fuels, as their main energy source, to find other more environmentally friendly solutions. However, the associates of the lime industry claims that the processes The lime industry, a potential business area for Kanthal 31 used today are as optimal as they can be. The emissions can onlybereducedabout 10 %, but this would cost a lot [20].

5.3.2 Renewable energy sources and Nuclear energy Renewable energy sources, such as wind, solar, wave, and hydroelectric power have been increasing their market shares the last decades. Today,electricityfromre- newable energy sources have about 15 % of the total energy market but is rapidly increasing 17 [21]. Nuclear energy has always been controversial due to the security issues because of the accidents in Harrisburg 1979 and in Chernobyl 1986. The threat of nuclear weapons and the issue of handling of nuclearwasteproductshave also infected the debate around nuclear energy. The need of CO2-free energy, and the highly eﬀective nuclear energy have overcome many obstacles and today the development of nuclear power is very intense. New reactors are invented, which aims at reducing the half-life of the nuclear waste from some hundred thousand years to about 500 years [22]. Today, about 30 % of the produced electricity in the world comes from nuclear energy and this ﬁgure is increasing every year [21].

Figure 17: Distribution of energy sources for electricity production, within the Kyoto member countries. The lime industry, a potential business area for Kanthal 32

6Ideaforanalternativeheatingsolutionsforlime- burning

6.1 Background One part of this M.Sc. thesis was to propose a prototype lime-burning kiln, using a Kanthal heating system. The design, which is presented in this section, was chosen after a company visit where a similar furnace was studied. Thecompany,HASopor, produces foam glass for ground stabilization in a furnace where their product is applied on a rolling hoop and is heated as the hoop slowly movesthroughthe furnace. Electric radiant tubes are used, beneath and over the hoop, to heat the product to about 900◦C. The glass foam that HASopor produces has no resemblance with quicklime what- soever but the heating solution may be used successfully in both processes.

6.2 Kanthal APMT Kanthal APMT (Advanced Powder Metallurgical Tube) is an alloy consisting mostly of iron, chromium and aluminum. It oﬀers high strength and corrosion resistance, together with a long working life. In contrast to nickel-chromium alloys, Kanthal APMT withstands higher temperatures. Kanthal APMT also oﬀers high creep resistance, a property that can be derived to the high corrosionresistance.Corrosion reduces strength, due to local or general undermining of the material. Another as- pect of the creep resistance of Kanthal APMT is the linear deformation behavior over time and temperature. The high corrosion resistance of Kanthal APMT is due to the protective aluminum oxide (Al2O3), which is formed on the surface when the alloy is heated. This oxide is thermodynamically stable, hasgoodadhesiontothe bulk material and has a slow growth rate. The slow growth rate is important to ensure a long-term protection of the material. Due to the protective oxide, Kanthal APMT can be used in troublesome environments such as high carbon atmospheres and sulphur atmospheres. Kanthal APMT is recommended in temperatures from 600◦Cupto1250◦Ctoensureevenandgoodperformance,howeveritcanwithstand even higher temperatures [23].

6.3 Radiant tubes Radiant tubes, figure 18 are extruded from a powder metallurgical (PM) base material, which gives benefits over traditional tubes, e.g. higher mechanical strength due to dispersion strengthening. Kanthal offers two PM materials, Kanthal APM and Kanthal APMT. Kanthal APMT is a further development of Kanthal APM, with higher strength [23]. The lime industry, a potential business area for Kanthal 33

Figure 18: Kanthal radiant tubes.

6.3.1 Tubothal Tubothal, figure 19, is an electric heating solution from Kanthal, which offers high power, low weight and long lifetime. The heating elements that are made from a Kanthal alloy are inserted into a radiant tube. The system hasanoperatingtem- perature interval of 600◦Cto1250◦C, and the temperature can be easily controlled. Ability to fine tune the temperature in the furnace gives Tubothal a big advantage in processes where temperature cycling is of great importance. Another advantage is that the elements can easily be replaced, without having toremovetheradiant tubes and therefore the process does not have to be interrupted [23]. The lime industry, a potential business area for Kanthal 34

Figure 19: Kanthal Tubothal.

6.3.2 Ecothal The Ecothal Single-Ended Recuperative burner (SER), figure 20, was designed for high efficiency, reliability and low emissions. It has an efficiency of about 80 % and has been shown to be about 10 % more effective than other commercial burners. The design of the Ecothal makes it the cleanest burner on the market, due to the well-defined combustion. This leads to lower emissions of green house gases and lower operating costs. The high efficiency and low emissions are obtained when the exhaust gases heat the gas at the inlet, and therefore a more effective burning of the gases is achieved. The Ecothal is mounted into a Kanthal APMT radiant tube, and therefore the burner offers indirect heating through the radiant tube [23]. The lime industry, a potential business area for Kanthal 35

Figure 20: Kanthal Ecothal.

6.4 Prototype proposal The prototype, figure 211,proposalthatwasdiscussedduringthisM.Sc.thesis has some advantages. The magnitude of the lime production caneasilybedecided, and the amount of power needed depends on how many radiant tubes are fitted inside the furnace. Tubothal or Ecothal heaters could be used, which gives the user the ability to use either electricity or gas as energy source.OtherKanthalheating solutions may be of interest as well, but these two options seem to be the most appropriate at the time. The throughput of lime also depends on the width of the conveyor belt, and for large quantities this may be a problem as the hoops often are around 1 m in width. However, in such case several parallel systems may be used to increase quicklime output. The system can also be divided into different heating zones, as each radiant tube is individually controlled. Thisgivestheproducerthe opportunity to fine-tune the optimal heating cycle for their process. The prototype is designed for temperatures of about 900◦Cto1000◦C, as this temperature is used in about 60 % of the conventional limekilns today. For higher temperatures, other heating elements may be of use. However, problems with the rolling hoop may also occur at higher temperature as the common materials does not withstand those

1Figure by Per Kruse, Kanthal AB The lime industry, a potential business area for Kanthal 36 temperatures.

Figure 21: Prototype sketch, using Kanthal radiant tubes. The lime industry, a potential business area for Kanthal 37

7Investigationoftheimpactofthecalcination process on Kanthal APMT

7.1 Background If used in the lime industry, the Kanthal alloy may be exposed to highly reactive quicklime. In theory this would not happen, as the heating system would never be in contact with lime or limestone. However, if direct contact would occur, the heating system must not be severely damaged.

7.2 Experimental Test samples of Kanthal APMT (Advanced Powder MetallurgicalTube),analloy consisting of mostly iron, chromium and aluminum, were exposed to a powder consisting of crushed calcitic limestone, which has high calcium content greater than 95 %. The limestone powder was applied on the test samples, whichthenwereplaced inside an electric furnace for about one hour. During this hour, the limestone powder calcined, and quicklime was obtained. After one hour, thetestsampleswere taken out of the furnace, the quicklime was removed and new limestone powder was applied. This was repeated eight times for every test sample. Four experiments were conducted, table 1. Two test pieces were pre-oxidized in 1050◦Cfor8hours,toensurethattheywereprotectedwithacovering layer of aluminum oxide when exposed to the lime. The other two test pieces were not pre- oxidized. Two different temperatures were chosen, 950◦Cand1250◦C. These two temperatures were chosen, as they are about the same temperatures that are used in conventional kilns. The working temperature in a shaft kiln is around 900◦Cto 1000◦C, and around 1200◦Cto1300◦Cinarotarykiln. Afinalfurnacecyclingtestwaspreformedtofindoutwhetherthe alloy would heal if affected to lime, and form a protective aluminum oxide.Thetestwaspre- formed in a special furnace where the samples were kept in the furnace chamber for 1hourat1200◦Candwherethenkeptinroomtemperaturefor1hour.Thiscycle was all automatic, and was repeated 24 times. The total cycle time was therefore 48 hours.

Table 1: Overview of the test samples and their conditions

APMT sample Temperature Pre-oxidized 1950◦CYes 2950◦CNo 31250◦CYes 41250◦CNo The lime industry, a potential business area for Kanthal 38

7.3 Results 7.3.1 Visual observations The non-oxidized samples 2 and 4 were severely affected by the calcination process, figure 22. Visual inspection of the pre-oxidized samples 1 and3didnotshowany signs of being affected.

Figure 22: Visual observation of sample 4 after eight calcination cycles.

7.3.2 Light Optic Microscopy Using a Leica stereomicroscope, it could be seen that the non-oxidized samples 2 and 4 were affected by the calcination, figure 23. Sample 2 was less affected than sample 4, probably due to lower temperature during the calcination.

(a) Sample 2 (b) Sample 4

Figure 23: Close-up on the damaged areas of sample 2 and sample4. The lime industry, a potential business area for Kanthal 39

7.3.3 Scanning Electron Microscopy The pre-oxidized samples, 1 and 3, did not show any signs of being affected even at very high resolutions, when examined with the Zeiss ScanningElectronMicroscope (SEM). The protective aluminum oxide was all there, and no aluminum nitrides had been formed. The lighter areas, figure 24, were identified as aluminum oxide, using Energy-Dispersive x-ray Spectroscopy (EDS).

Figure 24: SEM-picture showing lighter and darker areas of aluminum oxide on sample 1.

The non-oxidized sample 4 was also examined. EDS-analysis identiﬁed the composition of the damages areas as aluminum oxide, iron oxide, chromium oxide and bulk alloy, ﬁgure 25. The lime industry, a potential business area for Kanthal 40

Figure 25: The surface of sample 4. 1.) Iron oxide, 2.) Bulk alloy, 3.) Chromium oxide, 4.) Aluminium oxide.

Cross-sectional analysis of the pre-oxidized samples 1 and 3didnotshowany signs of inﬂuence of the calcination, while in the non-oxidized samples 2 and 4, aluminum nitrides were found, ﬁgure 26. The number of aluminum nitrides in sample 4 was far greater than in sample 2. The lime industry, a potential business area for Kanthal 41

Figure 26: Cross-sectional view, showing aluminum nitridesunderthesurfaceof sample 4.

7.3.4 Summary The results of the experimental work are summarized in table 2. The importance of pre-oxidation of the alloy is clearly noticed.

Table 2: Overview of the results of the experimental work

Sample Temperature Pre-oxidized Iron oxides Aluminum nitrides 1950◦CYesNoNo 2950◦CNoYesYes 31250◦CYesNoNo 41250◦CNoYesYes The lime industry, a potential business area for Kanthal 42

The ﬁnal furnace cycling test did give a positive result. The healing eﬀect of Kanthal APMT had rebuilt the aluminum oxide, and the samples were at this point covered with an aluminum oxide. No further growth of aluminumnitrideswas noticed. The lime industry, a potential business area for Kanthal 43

8Discussion

8.1 Quicklime production Future limekilns do not have to look like the kilns used today.Toproducequicklime, heat is needed and only heat. However, to produce quicklime ofreallygoodquality one has to be able to control the heat very carefully. The most suitable temperature cycle should be investigated very carefully as the calcination of limestone is sensitive to correct heat treatment. There are some different quicklimequalities,whichhave different properties depending on at what temperature they have been processed. This is desirable as some customers are looking for qualitiesthatareformedat higher temperatures, and others are looking for qualities that are formed at lower temperatures. It is also important to minimize the energy losses in the process. Quicklime is a relatively cheap product, about $ 100 per ton, and therefore energy losses are directly affecting the profit.

8.2 The market potential The market potential for lime products is huge. There are endless of areas where lime is used or may be used in the future. The production has increased over the years, and China is the main lime producing country today. Themarketisover heated as it is, and it is very tough to introduce a new type of limekilns, as it would be too costly. The economy of the producers is not good enough to let them try new solutions. In 2009, a lot of producers had to shut down their businesses due to high production costs that undermined most of the proﬁts. The use of lime in pharmaceutical areas or as a part of a biomaterial could be a future market where new types of kiln may ﬂourish. In these areas the need for extremely pure lime is increasing. The tonnages are and will be very small, but the price of the extremely pure lime is a lot higher than of conventional lime. Another view of the market potential is to look at the amount of consumed energy, which isabout2.4TWhper year based on an annual production of 280 million tonnes of lime. This gives an indication of the potential market for future electrical limekilns.

8.3 Energy sources and environmental aspects The debate on future energy sources and environmental eﬀectsofusingfossilfuels has greatly inﬂuenced the lime industry, as it is one of the largest users of fossil fuel and therefore one of the largest emitters of CO2.TheCO2-tax was introduced in Europe as a result of the Kyoto protocol, which aims to lowertheemissionsof green house gases such as CO2.Thiswasalsothebeginningoftheemissiontrading experiment. The cost of exceeding the amount of emitted CO2 was about 40 Euro 2 per ton CO2 .Ifoneplayswiththethoughtthatallnoallocationsweregiven

2According to the Swedish environmental protection agency, 2006 The lime industry, a potential business area for Kanthal 44 to the lime companies, their total amount of about 560 milliontonnesofemitted CO2 would be charged for. In such a case, with the above-mentioned CO2-tax fee, about 22,5 billion Euros would be the final fine. This is more than the total profit for all produced quicklime in the world. The industry would not survive such a scenario. However, this is not going to be realized but is an indicator of how brittle the industry is. The natural step to take is to move towards ”green” energy in this industry as well. The world is seeing a big expansion of renewable energy sources and even in the nuclear power sector, which will provide CO2-free energy in the future. However, producing electricity from fossil fuels isstillthemajorsourcein production of electricity and will probably be in the near future. If renewable energy and nuclear power will be the main energy sources in 50 to 100 years nobody knows, but it is a time of change so it is not impossible as reports are showing decreasing oil and gas production and increasing development of ”green”energy.

8.4 Effects of limestone calcination on Kanthal APMT The radiant tubes in the prototype will not be in direct contact with limestone during the calcining process, although the experimental work showed the outcome if this would occur. The pre-oxidized APMT samples showed good resistance against the quicklime, which is very good as the radiant tubes are always delivered in this state. However, the oxide may spall offand in such case the bulkmaterialwould not be protected. A non pre-oxidized APMT sample that had beenindirectcontact with limestone, during eight calcination cycles, was severely affected. Brown-orange points could be seen where the quicklime had been lying. Thesedotswereidentified as iron oxide (Fe2O3). This oxide is porous and has not the protective properties, which aluminum oxide has, and therefore this was not very goodfromamaterial perspective. SEM-analysis discovered aluminum nitrides beneath the iron oxide, which partly explains why no aluminum oxide had been formed. It is also interesting to notice that even though the non pre-oxidized samples were severe affected by lime, they were able to heal when not exposed to lime. These results are interesting, but to further investigate the effects of limestone calcination on APMT more experiments are needed. For example, the APMT samples must be exposed to lime during the calcination process for a longer time.

8.5 The alternative limekiln prototype The limekiln prototype, which is proposed in this report, hassomeadvantagesand disadvantages. First of all, the prototype will be able to be used whatever the size of the lime production. It is just a matter of how many radiant tubes that are ﬁtted inside the kiln. This makes the kiln very versatile, and a growing lime company could easily expand their furnace. However, this is only in theory. Today it is too expensive to produce conventional lime, e.g. for the steel industry, in this way. The furnace may be suitable for lime companies that focus on special areas such as the The lime industry, a potential business area for Kanthal 45 pharmaceutical market. The fact that the kiln could be drivenwithbothTubothal and Ecothal makes it even more versatile. In areas where natural gas is cheap, the Ecothal solution may be more preferable. However, this is notthemostenviron- mentally friendly solution, which would be the Tubothal fed with ”green” energy, but the most environmentally friendly when it comes to gas solutions. The width of the rolling hoop is a disadvantage as it is often not more than about 1 m. To walk around this problem several prototypes could be installed side by side.

8.6 Other proposed prototypes There are several other prototypes, which have been developed at research institutes and at lime companies. Their purposes are to ﬁnd alternative ways to produce lime, and to be able to produce purer lime. In this report two prototypes, which are very interesting, have been presented. The solar reactor hasbeenshowntobe very successful, in theory. However, this solution could be usable for larger lime productions, as very large land area would be used. For applications, which require smaller amounts of lime than e.g. the steel industry, this method may be successfully used. Another drawback is that the solar reactors only can be used at some areas in the world, where the sunlight contains enough energy. The other kiln, which uses asiliconcarbidepipewithaninternalsiliconcarbidescrew, is also very interesting. Their purpose is the same as for the prototype proposed in thisreport.Theydonot say anything about a speciﬁc heat source, and Kanthal elements may be suitable. The kiln had a drawback with limestone sticking to the screw and with thermal induced stresses in the tube, but a part from that it is a very good solution. Both of these prototypes are interesting models, and will hopefullybenoticedbyassociates of the lime industry. The lime industry, a potential business area for Kanthal 46

9Conclusions

The purpose of this M.Sc. thesis was to find out whether the limeindustryis apotentialbusinessareaforKanthalornot.Twentyweekshave passed since the investigation started, and a lot of information has been gathered. However, a straight answer cannot be given because it depends on where in the lime industry the focus lies. If Kanthal wants to focus on the large producers and short-term profits, it is probably not a potential business area today. It is simply too expensive for the producers to change their furnaces and to use electricity as energy source. If Kanthal decides to focus on smaller areas, such as the special chemical industry that provide the pharmaceutical industry with lime, it could very much be apotentialbusiness area for Kanthal in the future. However, this would probably not generate profit for some time, as the focus would be at experimental setups in the beginning. Due to the complexity of the lime industry, a suggestion is that Kanthal should:

• Focus on small scaled lime production for special areas of lime, such as the pharmaceutical area (5 - 10 years)

• Extend the presence in the lime industry by starting to look atmoreconven- tional lime products (10 - 20 years)

• Develop a full-scaled lime kiln that has the potential of becoming the new conventional lime kiln (20 - 40 years)

To start with, Kanthal has to make business contacts within the lime industry, preferably at lime conferences held by lime associations such as European Lime Association (ELA), International Lime Association (ILA) orSvenskaKalkinstitutet. This is probably the best way to integrate with the lime industry and to ﬁnd out what is going on in the industry. The lime industry, a potential business area for Kanthal 47

10 Future work

During this investigation, some additional business areas have been found. If these areas could be improved with help from Kanthal, they would most certainly generate proﬁt in shorter terms than an introduction of Kanthal in the lime industry would do.

10.1 Porcupine heating cassettes as pre-heaters in cement production Producing cement has little resemblance with lime production, aside from rotary kilns as clinker burners. Clinker is a product, which is obtained when limestone and clay are heated to temperatures around 1450◦C. Then the clinker is crushed and gypsum is added to form cement. In this process, exhaust gasesfromthefurnace process is used to heat ingoing material in a pre-heating tower. This tower consists of some stages, so called cyclones, in which the limestone clay is heated in diﬀerent steps. When the clinker burners are using fuel with low energyvalue,forexample some biogases, a separate burner is needed to add heat to the pre-heating process. Instead adding a separate burner, a Kanthal porcupine heating cassette may be useful. The porcupine works like a large hair dryer, which heats air to about 900◦C. It is a very versatile product, which can be built after the customer’s demands.

10.2 Alloys as construction material in lime and cement facilities Rotary kilns for cement production uses a cooling system to cool the clinker and the gases in the end of the production lime. The gases are led from the kiln through acoolingsystembeforeitisusedinthepre-heatingsystem. These gases are hot and contain a lot of corrosive elements such as sulphur. Kanthal alloys have good resistance to sulphur attacks due to the protective aluminumoxide,andmaybe useful as construction material in a cement facility.

10.3 Lance tubes for quicklime shaft kilns In shaft kilns the heat source is several flames, which comes from so-called lace tubes, figure 27 [10]. In these lances, fuel (often oil) is transported into the kiln and ignites in the nozzle of the lances. As the lances are in direct contactoflimestone,some problems occur. First of all, the lance tubes are exposed to a lot of wear as they are in direct contact to limestone that continuously flows through the kiln. However, in modern shaft kilns the lances are often protected to minimizewear.Secondly,the environment inside is crude. Quicklime is very reactive and attacks the material of the lance tubes. In this harsh environment, Kanthal alloys may be useful. The lime industry, a potential business area for Kanthal 48

Figure 27: Lance tubes in a shaft kiln The lime industry, a potential business area for Kanthal 49

11 Acknowledgments

First of all I would like to thank Kanthal AB for giving me the opportunity to work with this project. I would like to thank my supervisor, Gustaf Lorenzson,who assisted me in my work from day one. Your positive attitude to the progress of my work has been very encouraging. I would also like to thank Fernando Rave for showing great interest in my work and providing assistance whenever I needed it. During my work, I have met many friendly people as well that assisted me. I would like to thank you all for making my time at Kanthal memorable and pleasant. Beside Kanthal AB, I would like to thank Nordkalk and SMA Mineral for helping me understand the lime industry and the processes involved bypatientanswermy questions and showing me the conventional production methods used today. The lime industry, a potential business area for Kanthal 50

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