Sustainability measures in quicklime and cement clinker production Matias Eriksson

Thermochemical Energy Conversion Laboratory Department of Applied Physics and Electronics 901 87 Umeå Umeå 2015

Copyright© Matias Eriksson ISBN 978-91-7601-392-2 Cover illustration: Matias Eriksson Printed by: Print & Media, Umeå, Sverige 2015

Ett stort tack.

Table of Contents �

Abstract� ��

Populärvetenskaplig sammanfattning� ���

List of Papers� ����

Author contributions� ���

The context of the papers in this thesis� ��

1� Introduction� ��

1.1� Limestone and limestone based products� ��

1.2� Quicklime products and quicklime production� ��

1.3� Cement clinker and cement clinker production� ��

1.4� Calcite and calcination� ���

1.4.1� Calcination or the thermal decomposition of CaCO3� ���

1.4.2� On the kinetics of CaCO3 decomposition� ���

1.5� Sustainability concerns related to quicklime and cement clinker production� ���

1.5.1� Carbon dioxide emissions from quicklime and cement clinker production� ���

1.5.2� Reducing carbon dioxide emissions� ���

1.5.3� Near zero emission production of quicklime and cement clinker� ���

1.5.3.1� Post-combustion capture of CO2� ���

1.5.3.2� CO2 capture through oxyfuel combustion� ���

1.5.3.3� CO2 capture and storage through mineral carbonation� ���

2� Methods� ���

2.1� Calculating fuel properties and analyzing the effect on rotary kiln production� ���

2.2� Predictive process simulations through multicomponent chemical equilibrium calculation���

2.2.1� Development and validation of the simulation tool� ��

2.3� Thermogravimetric analysis� ���

3� Results and discussion� ���

3.1� Calculated effects of fuel properties on rotary kiln production� ���

3.2� Process simulations of changes to the fuel mix in quicklime production� ��

3.3� Process simulation of oxygen enrichment in quicklime production� ���

3.4� Process simulation of oxygen enrichment in cement clinker production� ���

3.5� Simulation of CO2 capture and storage through mineral carbonation applied to quicklime

production� ���

3.6� Process simulation of CO2 capture through oxyfuel combustion in quicklime production� ���

3.7� Process simulation of CO2 capture through oxyfuel combustion in cement clinker

production� ��

3.8� Dynamic rate thermogravimetry for lime kiln feed limestone characterization� ��

3.8.1� Effect of pCO2 on decomposition behavior of CaCO3� �

3.8.2� The effect of dynamic rate experimental settings� ��

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4� Conclusions� ���

5� Future work� ���

6� Acknowledgements� ���

7� References� ���

8� Appendices� ��

8.1� Appendix 1: Chemical quality requirements for industrial limestone� ��

8.2� Appendix 2: Development of simulation database, lists of compounds� ���

8.2.1� Selected gas phase compounds, Papers II - VI� ��

8.2.2� Selected pure solid compounds, Papers II and VI� ���

8.2.3� Selected pure liquid compounds, Papers II - VI� ���

8.2.4� Selected pure solid compounds, Papers III, IV and V� ���

8.2.5� Selected solid solution compounds, Papers III, IV and V� ���

8.2.6� Selected melt phase compounds, Papers II-VI� ���

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Abstract This thesis investigates sustainability measures for quicklime and cement clinker production. It is the aim of this thesis to contribute to the effort of creating a more sustainable modus of industrial production. The methods used comprises process simulations through multicomponent chemical equilibrium calculations, fuel characterization and raw materials characterization through dynamic rate thermogravimetry. The investigated measures relate to alternative fuels, co-combustion, oxygen enrichment, oxyfuel combustion, mineral carbonation and optimizing raw material mixes based on thermal decomposition characteristics. The predictive multicomponent chemical equilibrium simulation tool developed has been used to investigate new process designs and combustion concepts. The results show that fuel selection and oxygen enrichment influence energy efficiency, and that oxyfuel combustion and mineral carbonation could allow for considerable emission reductions at low energy penalty, as compared to conventional post-combustion carbon dioxide capture technologies. Dynamic rate thermogravimetry, applied to kiln feed limestone, allows for improved feed analysis with a deeper understanding of how mixing of different feed materials will affect the production processes. The predictive simulation tool has proven to be of practical value when planning and executing production and full scale campaigns, reducing costs related to trial and error. The main conclusion of this work is that several measures are available to increase the sustainability of the industry.

Key words: limestone, quicklime, cement clinker, sustainability, oxygen, carbon dioxide, thermal decomposition, dynamic rate thermogravimetry, predictive multicomponent chemical equilibrium calculations, mineral carbonation. �

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Populärvetenskaplig sammanfattning Kalksten är en bergart med många användningsområden. Kalksten används som sådan eller förädlad på olika sätt vid produktion av bl.a. papper, stål, plast, glas och betong. Därtill används kalkstensbaserade produkter i en rad miljöapplikationer såsom rökgasrening, jordförbättring och neutralisering av sura vattendrag. Detta arbete diskuterar olika metoder för att öka hållbarheten i industriell produktion av bränd kalk och cementklinker, två kalkstensbaserade produkter. Bränd kalk används i otaliga applikationer och cementklinker används vid produktion av cement. Gemensamt för dessa produkter är att produktionen omfattar upphettning av kalkstensråmaterialet till 1000°C och över, varvid den vid normala förhållanden stabila kalkstenen sönderfaller. Vid sönderfallet avgår koldioxid som en gas och den kemiskt aktiva kalciumoxiden återstår. Arbetet omfattar bränslekarakterisering, laboratoriestudier av kalkstenens beteende under upphettning och processmodellering. Målsättningen är att spara energi och minska koldioxidutsläppen. Arbetet studerar syrgasanrikning, där syrehalten i förbränningsluften höjs över det normala, som metod för att spara energi. Vidare studeras bränslets och askans inverkan på processerna, samt förbränning i ren syrgas, som metod för att rena koldioxid från rökgaser, och koldioxidlagring i mineral. Arbetet visar att bränsleegenskaper och processinställningar påverkar energieffektiviteten och att syrgasanrikning gör det tekniskt möjligt att spara energi. Den utvecklade metoden för brännegenskapskarakterisering av kalksten ger fördjupad förståelse av materialens egenskaper och kan användas för att optimera processerna. Modelleringsresultaten visar att förbränning i ren syrgas skulle producera en ren koldioxid gas som kan användas som produkt eller lagras för att minska utsläppen. Energibalanserna antyder att både förbränning i ren syrgas och koldioxidlagring i mineral skulle ha en lägre energiförbrukning än den konventionella koldioxidrening som idag sker med hjälp av svårhanterliga organiska vätskor. Det finns idag inga anläggningar för produktion av bränd kalk eller cementklinker där förbränningen sker ren i syrgas. Eftersom tekniken förutsätter en omställning av produktionsprocesserna måste den undersökas mer innan den kan tillämpas. Lagring i mineral har inte heller prövats i den skala som krävs för att tekniken skulle bli allmänt tillämpad. Det finns således ett flertal tekniker för industrin att minska koldioxidutsläppen, vilket ur hållbarhetssynvinkel är viktigt.

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List of Papers This Thesis is based on the following papers, which are separately appended and referenced by their corresponding roman numerals in the text. The papers are listed chronologically according to order of publication. Reprints have been included within this thesis with permission from the publishers. The contribution of Matias Eriksson and a discussion of the context of these papers in this thesis can be found below. I. Carbon dioxide storage by mineralisation applied to an industrial-

scale lime kiln Inês Romão, Matias Eriksson, Experience Nduagu, Johan Fagerlund, Licínio Gando-Ferreira, Ron Zevenhoven Proceedings of ECOS2012, Perugia, Italy, June 2012, 226, pp. 1-13

II. Improved process modeling for a lime rotary kiln using equilibrium

chemistry

Bodil Hökfors, Matias Eriksson and Rainer Backman

Journal of Engineering Technology, 2012, Vol. 29(1), pp. 8-18. III. Modelling the cement process and cement clinker quality

Bodil Hökfors, Matias Eriksson and Erik Viggh

Advances in Cement Research, 2014, Vol. 26(6), pp. 311–318 IV. Simulation of oxy-fuel combustion in cement clinker manufacturing

Bodil Hökfors, Erik Viggh and Matias Eriksson Advances in Cement Research, 2014, Vol. 27(1), pp. 42 –49

V. Oxyfuel combustion in rotary kiln lime production

Matias Eriksson, Bodil Hökfors, and Rainer Backman, Energy Science & Engineering, 2014, Vol. 2(4), pp. 204–215

VI. The Effects of Oxygen Enrichment and Fuel Composition on Rotary

Kiln Lime Production Matias Eriksson, Bodil Hökfors, and Rainer Backman, Journal of Engineering Technology, 2015, Vol. 32(1), pp. 28-39.

VII. Characterization of kiln feed limestone by dynamic heating rate

thermogravimetry Matias Eriksson, manuscript International Journal of Mineral Processing

Submitted: 2015-03-31; Revised 2015-11-11

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Author contributions

Paper I: Eriksson is responsible for the description of the quicklime process, the process integration concept and the collection of full scale process data. In addition Eriksson has contributed to materials selection and to the interpretation of the simulation results.

Paper II: The contribution relate to defining simulation setup, collection of process data including but not limited to fuels, raw materials and final product, validation of model by full scale tests, selection of relevant species used in the simulation, selection of input variables for simulations and interpretation of simulation results.

Paper III: The contribution relate to defining simulation setup, oxygen enrichment concepts, model validation based on full scale tests, and interpretation of simulation results.

Paper IV: Eriksson’s contribution relate to defining simulation setup, oxyfuel and recirculation concepts, and interpretation of simulation results. Matias Eriksson has also contributed by text editing.

Paper V: Matias Eriksson is the principal author and the further contribution comprises oxyfuel and recirculation concepts, defining simulation cases and interpretation of simulation results.

Paper VI: Eriksson is the principal author and the further contribution comprises combustion concept and fuel selection, defining simulation cases and interpretation of simulation results. Matias Eriksson was responsible the for full scale enrichment test utilized for model validation.

Paper VII: Matias Eriksson is the sole author of the paper and performed all experiments, result interpretation and writing.

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The context of the papers in this thesis The context of Papers I to VII is illustrated by Figure 1, where the measures investigated are put in relation to the kiln processes of quicklime and cement clinker production.

Figure 1 A simplified sketch describing the industrial process context of Papers I to VII. Paper I: mineral carbonation of flue gas CO2, Paper II: different fuel mixes for quicklime production, Papers III and VI: oxygen enrichment for improved energy efficiency and increased utilization of alternative fuels, Papers IV and V: recirculation of flue gases in oxyfuel combustion for CO2 capture, and Paper VII: raw material characterization. Three of the papers relate to quicklime production (Papers II, V and VI). The production technology studied is that of a 210 tpd rotary kiln. The fuels and the combustion technology is varied and a predictive multicomponent chemical equilibrium model, the simulation tool, is used to investigate the effects on process temperatures, product quality, flue gas composition, energy consumption, specific CO2 emission, process capacity and other process parameters. Although the limestone feed material remain the same, the chemical species considered increase when the simulation database is improved as the work progresses. The work comprises a full scale reference campaign, a full scale oxygen enrichment campaign and a co-combustion campaign burning coal and saw dust. The simulation tool has been used when planning campaigns and the campaign results have been used to validate the model. The material in sections 2.1, 2.2, 3.2, 3.3, and 3.6 relate to Papers II, V and VI. Two of the papers relate to cement clinker production (Papers III and IV). The production processes studied are dry processes with pre-heaters and pre-calciners, one 5350 tpd and one 2000 tpd. Again the fuels and the combustion technology is varied and the simulation tool is used to investigate the effects on key process parameters. Although the raw meal feed mix remain the same, the species considered increase as

Fossil carbon deposit

C

Limestone deposit

CaCO3

CO2

Biogenic carbon deposit

OceanCarbonate

deposit

Paper I

Paper VII

N2 + O2

O2

N2

Paper III and Paper VI

Paper IV and Paper V Paper II

Quicklime and

cement clinker

Geological storage of

CO2

CO2 based

products

Atmospheric emissions

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the simulation database is improved as the work progresses. The work comprises a full scale reference campaign and the data from a full scale oxygen enrichment campaign that has been available for validation. The material in sections 2.1, 2.2, 3.4 and 3.7 relate to Papers III and IV. Although the main focus of Paper VII is on quicklime production it is also relevant to cement clinker production. In this paper a new laboratory method of thermal analysis, dynamic rate thermogravimetry, is used to investigate thermal decomposition characteristics of different industrial limestone, the main component in both quicklime and cement clinker production. The thermal decomposition is one of the most energy consuming steps when producing quicklime and cement clinker and need to be controlled. Since the limestone properties usually vary within a quarry, the ability to create a chemically sound mix with controlled decomposition characteristics, can increase operational performance, product quality, and possibly allow for increased energy efficiency and production capacity through process optimization. The material in 2.3, 3.8 relate to Paper VII. The use of oxygen to enhance combustion and manipulate gas composition is a key question in this thesis. The utilization of concentrated oxygen is driven by the need to reduce environmental impact originating from the use of fossil fuels and raw materials. Oxygen combustion technologies have been shown to increase fuel efficiency, improve process stability and production capacity. Simulation results show the possibility to increase utilization of fuels with low flame temperatures, and the possibility to produce a pure carbon dioxide stream that after minor processing is readily available for transport to utilization, mineral carbonation or geological storage. In Paper I the suitability for mineral carbonation of two minerals, a serpentinite and a diopside, is investigated. The carbonation process is applied to the flue gases from quicklime production. If successfully applied a mineral carbonation process would effectively reduce the CO2 emissions. The material in section 3.5 relate to Paper I. Increasing sustainability, through reducing environmental impact, is the common theme of the papers in this thesis. Of the environmental concerns this work concentrates on CO2 emissions. Papers II, III, VI and VII investigate measures that allow minor reductions of CO2 emissions, while Papers I, IV and V investigates technologies that would allow major emission reductions.

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1 Introduction For thousands of years man lived on less than 2 dollars a day (Maddison 2006). The economy was a zero-sum game mainly conditioned by land and precious metals. The random harvest of the land, growing at a slower pace than the population, led to reoccurring starvation affecting the vast majority of people, most of which were living at subsistence level (Malthus 1798). With the bourgeoisie liberation starting in northern Europe in mid-18th century, and it’s spreading during the following centuries, improved living conditions were created (McCloskey 2006). The liberation produced a surplus of goods and food and thereby broke the Malthusian trap. Considering function, cost, quality and availability, the material goods and services the new society provided proved far more attractive than the old. Human resourcefulness, such as trade and innovation, would become the true wealth of nations (Smith 1776). However in the 20th century the full destructive capacity of the new technology was revealed. The bourgeoisie liberation and the technical development that followed had opened up for a wide range of possible futures unimaginable before, when only the Malthus option seemed to be available. Since then serious concerns have been raised by science of all fields as to the sustainability of our modern way of life (Union of concerned scientists 1992, Oscamp 2000, Crutzen 2002, Guinotte 2008, IPCC 2014, Steffen 2015, Gattuso 2015). This thesis considers the industrial production of the limestone based products quicklime and cement clinker. Through a chemical engineering approach, the aim is to contribute to the effort of creating a more sustainable modus of industrial production. Limestone is an abundant rock that constitutes approximately 5 % of the earth’s crust (Santos 2012, USGS 2015). The main elements in limestone are calcium (Ca), carbon (C) and oxygen (O). The elements occur as a carbonate compound with the molar ratio of 1:1:3, with only minor deviations in stoichiometry (Shukla 1979). Limestone deposits have formed over geological timescales through various mechanisms, e.g. sedimentation of biogenic skeletons or chemical precipitation (Harrison 1993). The key element of limestone is calcium. The most common element in the earth’s crust is oxygen at approximately 47 wt.-%. Calcium as the 5th most common element constitutes 3-4 wt.-% while carbon is only available at 200-300 ppm (Weast 1980, Wedelpol 1995, Yaroshevsky 2006). Due to the low availability of carbon in the crust it is obvious that calcium is widely available in other rocks as well. Other minerals rich in calcium are apatite, fluorite, anhydrite, diopside and

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wollastonite. However the concentration of calcium is relatively low in other rocks (< 6 %) leaving limestone as the main calcium ore (Weast 1980). Another significant source of calcium is the ocean. Seawater contains an estimated 5.5.1014 tonCa. However, the Ca concentration is low at approximately 400 ppm (Bearman 1995). Ca is also stored in the biosphere and probably every living organism requires Ca, e.g. Ca participates in low concentrations (10-5 M) in the operation of muscles (Mathews 1995). Compared to the oceans, the biosphere and other rocks the limestone deposit is a highly concentrated source of calcium. Limestone has been quarried or mined and processed into a large variety of products for centuries. Lime binders were used already 12000 BC (Elert 2002). Still today limestone based products are central for the modern quality of life. Quicklime and cement clinker are used in the production of products such as paper, steel and concrete. Limestone based products are used in the production of plastics, paints, ceramics, mortars and glass. A large volume of limestone products is used in ground construction, e.g. roads. Furthermore the properties of limestone allow for valuable environmental services; reduction of industrial sulphur emissions to the atmosphere, acid waste neutralization, restoration of acidified natural lake waters, and soil improvement in gardening and agriculture (Boynton 1980, Harrison 1993, Oates 1998, Schorcht 2013). The limestone based industry provides services to society. For production processes that rely on Ca, such as for iron and steel, limestone based products seem to provide a source of Ca with lower environmental impact and cost than any alternative source.

1.1 Limestone and limestone based products The main component in limestone is calcium carbonate (CaCO3). Six different phases have been reported; amorphous CaCO3, ikaite, monohydrocalcite, vaterite, aragonite and calcite (Zhang 2012). All phases except calcite are unstable at ambient temperature and pressure (Jamieson 1953, Simmons 1963, Brecevic 2007, Demichelis 2013, Demichelis 2014). Although aragonite can be found in natural limestone, the limestone of industrial interest consists mainly of calcite. Many limestones contain significant amounts of dolomite (CaMg(CO3)2) and the two fundamental types, high calcium limestone and dolomitic limestone are identified by their magnesium (Mg) content. There are several methods and systems for the further classification of limestone. In this work the chemical classification originally by Cox will be used (Cox 1977, Harrison 1985, Mitchell 2011), see Table 1. Limestone can also be classified for example according to grain type and grain size (Folk 1959) or by depositional texture (Dunham 1962).

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Table 1 Classification of high calcium limestone.

[wt.-%] CaCO3 CaO MgO SiO2 Fe2O3 Very high purity > 98.5 > 55.2 < 0.8 < 0.2 < 0.05

High purity 97.0 - 98.5 54.3 - 55.2 0.8 - 1.0 0.2 - 0.6 0.05 - 0.1 Medium purity 93.5 - 97.0 52.4 - 54.3 1.0 - 3.0 0.6 - 1.0 0.1 - 1.0

Low purity 85.0 - 93.5 47.6 - 52.4 > 3.0 < 2.0 > 1.0 Impure < 85.0 < 47.6 > 3.0 > 2.0 > 1.0

The production of limestone through quarrying comprises several steps; planning, overburden removal, drilling, blasting, loading and hauling to the processing plant. The processing covers operations such as crushing, grinding, sizing, washing, sorting, and scalping before product storage. The whole production process requires rigorous sampling and quality control. Limestone properties can vary significantly within a deposit, e.g. concerning the local concentration of iron (Fe), silicon (Si), sulphur (S) or Mg (Harrison 1985). To increase the high value utilization, such as quicklime production, the mixing of different property limestone within a deposit is of interest. The mixing can be made based on chemical properties but also for example on physical fraction or color. Quarry fines are usually of low value and increasing the utilization of fines will have positive environmental and economic consequences (Mitchell 2009a). A summary of limestone product applications can be seen in Table 2 (Harrison 1993, Oates 1998, Schorcht 2013). The average limestone is impure and is estimated to contain 77 wt.-% CaCO3 (Weast 1989). Industrial applications, with some exceptions, require a significantly higher purity. Product data for some commercial limestone products can be found in Table 3. Additional quality requirement for limestone products can be found in Appendix 1. The typical trace elements in limestone can be seen Table 4 (Mitchell 2009b).

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Table 2 Limestone product applications.

Massive Crushed stone Coarse to medium

ground Fine to ultrafine ground

Dimension Aggregate Chemical

use

Low value fillers

Medium value non-

functional fillers

Medium value

functional fillers

High value powders,

coated/uncoated ultrafine

Fillers/pigments Building

stone Concrete

Iron smelting

Asphalt filler

Carpet backing

Household products

Paper

Monuments Road stone Glass Agriculture Plastic floor

tiles Adhesives Paint

Slabs Construction

fill Ceramic

tiles Mine dust Sealants Rubber

Paving Drainage materials

FGD Poultry grit Paper filler Plastics

Filter stone Quicklime Mineral

food

Low cost paints

Pharmaceuticals

Table 3 Commercial limestone products, n = number of products.�

[wt.-%] CaCO3 CaO MgO SiO2 Fe2O3 Reference

Paint (n = 100)

92 - 99.35 51.55 - 55.67 0.15 - 1.2 0.05 - 4.5 0.01 - 0.1 Mitchell 2011

Paper (n = 35)

96 - 99.35 53.79 - 55.76 0.15 - 1.2 0.05 - 0.4 0.01 - 0.1 Mitchell 2011

Plastic (n = 88)

92 - 99.35 51.55 - 55.67 0.15 - 1.2 0.05 - 4.5 0.01 - 0.1 Mitchell 2011

Food & Pharmaceuticals (n = 34)

97 - 99.5 54.35 - 55.75 0.24 - 0.42 0.1 - 0.12 0.011 - 0.1 Mitchell 2011

Ceramic (n = 14)

98.8 - 99.35 55.36 - 55.67 0.22 - 0.38 0.06 - 0.12 0.02 - 0.044 Mitchell 2011

Rubber (n = 51)

92 - 99.35 51.55 - 55.67 0.15 - 1.2 0.05 - 4.5 0.01 - 0.1 Mitchell 2011

Adhesives & sealants (n = 65)

92 - 99.35 51.55 - 55.67 0.15 - 1.2 0.05 - 4.5 0.01 - 0.1 Mitchell 2011

Agriculture & animal feed (n = 14)

92 - 99.35 51.55 - 55.67 0.22 - 0.96 0.06 - 4.5 0.037 - 0.1 Mitchell 2011

Functional filler (n = 1)

96.4 54 0.3 0.1 0.04 Nordkalk 2015

Metallurgy (n = 1)

97.6 54.7 Carmeuse 2015

Roofing shingles (n = 1)

> 90 > 50.4 Carmeuse 2015

Animal feed (n = 1)

> 95 > 53.2 Carmeuse 2015

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Table 4 Typical trace elements in limestone.

Component

[wt.-%]

Al2O3 BaO Cr2O3 CuO K2O Mn3O4 Na2O NiO

< 0.3 < 0.1 < 0.1 < 0.1 < 0.1 < 0.1 < 0.1 < 0.1

P2O5 PbO SO3 SrO TiO2 ZnO ZrO2

< 0.1 < 0.1 < 0.5 < 0.2 < 0.1 < 0.1 < 0.1

The most significant flows in the limestone based products value chain is shown in Figure 2. From the viewpoint of this thesis three main value chains can be identified; the quicklime based value chain, including slaked lime products and precipitated calcium carbonate (PCC), the cement clinker value chain, including cement and concrete, and the limestone product value chain, including ground calcium carbonate (GCC). There are difficulties in determining the actual volumes of limestone quarried and used (Brown 2013, Chen 2015). Reliable world limestone production data has not been found. For 2007 the USGS estimates world production of industrial limestone to 11000 – 22000 Mton (USGS 2012).

Figure 2 The three main value chains of limestone based products. This work focuses on quicklime and cement clinker production, where the processing includes the thermal decomposition of limestone with the subsequent release of gaseous CO2 (highlighted). Based on the data available the main use of limestone is estimated to be within construction (Harrison 1993, Harrison 2006, Willet 2012). These are limestone products screened to pre-defined fractions and used e.g. when building roads. The value of the limestone product varies between 4-20 USD/ton, depending on quality and use (Willet 2012). The specific use of limestone per ton of product for some industrial applications can be seen in Table 5.

Limestone quarry and pretreatment

plant

Quicklime production plant

Slaked lime production plant

Precipitated calcium carbonate (PCC) production plant

Quicklime shipping and sales

Slaked lime shipping and sales

PCC shipping and sales

Ground calcium carbonate (GCC) production plant

Limestone shipping and sales

GCC shipping and sales

Cement clinker production plant

Cement production plant

Clinker shipping and sales

Cement shipping and sales

Concrete production plant

Wet concrete and cast concrete

shipping and sales

Limestone beneficiation plant

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Table 5 Use of limestone based product in industrial applications, EAF = electric arc furnace, OHF = open heart furnace, BF = blast furnace, BOF = basic oxygen furnace, ADt = air dry ton of pulp.

Product

Limestone consumption [ton/tonproduct] Reference

Quicklime 1.4 - 2.2 Schorcht 2013 Cement clinker 1.27 - 1.57 Schrocht 2013 Hydrated Lime 1.3 Stochiometric Expanded clay aggregates 0.5-3.0 adapted from Scalet 2013 Sinter A 0.025 Kasai 2001 Sinter B 0.034 Kasai 2001 Sinter for iron 0.00204 Remus 2013 Sinter plant A 0.0583 Kasai 2001 Crude steel (EAF) 0.064 World steel 2012 Crude steel (BF-BOF) 0.3 World steel 2012 Sinter for iron, Limestone/dolomite 0.131 Remus 2013 Textile fiber glass 0.12 Ruth 1997 Sinter plant B 0.1090 Kasai 2001 Pelletisation plant (pellet for BF) 0-0.005 Remus 2013 Hot metal (BF) 0-0.08 Remus 2013 Crude steel (BOF) 0.06-0.134 Remus 2013 Crude steel (EAF) 0.05-0.28 Remus 2013 Sinter 0.12 Oates 1998 Pig iron (BF) 0.16 Oates 1998 Hot metal (OHF) 0.025 Oates 1998 Flat/float glass 0.24 Ruth 1997 Glass wool 0.19 Ruth 1997 Container glass 0.19 Ruth 1997 Domestic glass (soda-lime) 0.3-0.42 Scalet 2013 Domestic glass (crystal and lead crystal) 0.08-0.20 Scalet 2013 Borosilicate glass tubes 0.018-0.022 Scalet 2013 Glass lamp bulbs (soda-lime) 0.1-0.4 Scalet 2013 Copper cathodes 0.027-0.038 EC 2014b Waelz oxide 0.42 EC 2014b CaSi (calcium silicon alloys) 0.9 EC 2014b Unbleached kraft pulp (ADt) 0.011-0.022 EC 2013 Bleached kraft pulp (ADt) 0.011-0.022 EC 2013 Fine paper (filler) 0.387 EC 2013 Chemical stabilization of primary waste sludge 0.47-2.65 EC 2014a Chemical stabilization of activated waste sludge 0.55-5.59 EC 2014a Chemical stabilization of aerobically digested mixed sludge

2.18-4.55 EC 2014a

Chemical stabilization of septage sludge 0.23-5.97 EC 2014a

Roofing shingles 0.5-0.7 Carmeuse 2015

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1.2 Quicklime products and quicklime production The limestone flow in the quicklime value chain is schematically described by Figure 3 displaying typical unit operations involved. From a sustainability viewpoint, the lime kiln, where the thermal decomposition takes place, is of special relevance.

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Figure 3 The limestone flow in the quicklime value chain. The focus of this work is on the lime kiln where the thermal treatment takes place (highlighted).

In quicklime production the limestone is heated in an industrial kiln. During heating carbon is released from the limestone as carbon dioxide gas. Quicklime containing mainly CaO remains as the solid product. The thermal decomposition, or calcination, can de described by reaction (1).

CaCO3 (s) � CaO (s) + CO2 (g) ∆H = +177.8 kJ/mol (1)

Shaft kilns and rotary kilns are the dominating technologies. The energy consumption for different kiln technologies are presented in Figure 4 (Schorcht 2013). The theoretical energy consumption for calcination according to reaction (1) is 3.2 GJ/tonCaO. This work is mainly concentrated on rotary kilns and other technologies are not discussed. In rotary kiln production the kiln feed limestone enters the kiln in the upper end. A small inclination (Θ) forces the feed down through the kiln during rotation. The fuel and combustion air enters the kiln in the lower end and the hot gases travelling upwards heats the limestone feed as illustrated in Figure 5.

Limestone quarry

Crushing

Blasting

Limestone beneficiation plant

Screening

Grinding

Scalping

Washing

Sorting

Limestone product storages

Quicklime production plant

Lime kiln

Screening

Screening

Milling

Quicklime cooler

Compacting

Crushing

Quicklime product storages

Mixing with additives

Slaked lime production plant

Slaking

Slaked lime storage

Precipitated calcium carbonate (PCC) production plant

Carbonation

PCC storage

Dewatering

Coating

Milling

Quicklime shipping and sales

Slaked lime shipping and sales

PCC shipping and sales

Limestone shipping and sales

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Figure 4 Thermal energy consumption span for quicklime production with different kiln technologies.

Figure 5 Simplified schematics of a rotary kiln with satellite coolers /VI/. Quicklime is used in many applications. As such or through the further processing by slaking and carbonation. The use can be divided into four main areas: (i) construction, (ii) chemical and industrial, (iii) environmental and (iv) metallurgical. In 2004 in the EU-27 metallurgy was the biggest sector (30-40 %), followed by environmental use (30 %), construction (15-20 %), and chemical and industrial use (10-15 %) (Schorcht 2013). In the US the situation is similar. For the period 2002-2013 metallurgy was the biggest sector (31-38 %), followed by environmental use (27-35 %) and chemical and industrial use (21-25 %). Here construction was the smallest sector (8-14 %) (Miller 2014, USGS 2014a). Quicklime production is largely dominate by China. Since 2009 an estimated 61-65 % of global production is located in China. The second biggest producer is the US followed by India (Miller 2014). Accurate world data for production of quicklime is not readily available and the data found contain many estimates, e.g. for 2006 the

3 4 5 6 7 8 9 10

Other kilns

Long rotary kilns (LRK)

Rotary kilns with preheater (PRK)

Mixed feed shaft kilns (MFSK)

Annular shaft kilns (ASK)

Parallel flow regenerative kilns (PFRK)

Thermal energy consumption [GJ/ton quicklime]

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world production estimates range from 172 - 278 Mton (Schorcht 2013, USGS 2014a).

1.3 Cement clinker and cement clinker production The limestone flow in the cement clinker value chain is schematically described in Figure 6 displaying typical unit operations involved. From a sustainability viewpoint the thermal decomposition is of special relevance. In cement clinker production the thermal treatment starts in the cyclone tower and ends with cooling of the final product.

Figure 6 The limestone flow in the cement clinker value chain. This work focuses on the thermal processing, i.e. the cyclone tower, pre-calciner, rotary kiln and the clinker cooler (highlighted). Although clinker and cement are sold as such, in the end virtually all clinker is used to produce cement and all cement is used to produce concrete. The cement clinker raw material is a mix of limestone, quartz and clay. The quarried materials are mixed and co-grinded to a fine raw meal. Different finenesses are reported, e.g. less than 2 wt.-% larger than 200 �m and less than 15 wt.-% larger than 90 �m (Wilck 1987, Koskinen 2000). Homogenization of the raw meal is essential. There are several possible process layouts adapted to the water content in the raw meal. Today the dry processes are the dominating technology. A simplified schematic of a dry process with two-string five stage cyclone suspension heaters and pre-calciners can be seen in Figure 7. The homogenized and grinded raw meal enterers the cyclone heaters, travels through the pre-calciners into the kiln were the main clinkering reactions occur. The clinker product exits through the cooler. The main gas

Limestone quarry

Crushing

Blasting

Cement clinker production plant

Raw meal mill

Cyclone tower

Pre-calcinator

Rotary kiln

Clinker cooler

Homogenization of raw materials

Clinker storage

Cement production plant

Cement mill

Mixing additives and clinker

Cement storage

Clinker shipping and sales

Cement shipping and sales

Concrete production plant

Mixing additives and cement

Casting of concrete elements

Wet concrete and cast concrete

shipping and sales

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flow enters through the cooler and successively heats the condensed material traveling in the opposite direction. The fuel is fed through the main burner in the rotary kiln and to the pre-calciners. In the pre-calciners the temperature is raised to 1000°C to release CO2 and form the reactive CaO. In the rotary kiln the temperature is further increased to 1450°C to form the desired clinker mineral alite (3CaO.SiO2). The fuel ash is incorporated in the product and needs to be accounted for, e.g. phosphorous, readily available in biofuel ashes, inhibits the formation of alite (Hökfors 2015). The cooling need to be fast for the alite to remain intact.

Figure 7 Simplified schematics of a dry process for cement clinker production.

The raw meal mix is controlled by three main indicators, the lime saturation factor (LSF), the silica ratio (SR) and the alumina ratio (AR). The indicators are calculated from the chemical analysis of the raw material feed expressed in wt.-%, see Table 6. The typical composition of a clinker raw material, at LSF = 0.96, SR = 2.46 and AR = 2.56, can be seen in Table 7 (Hewlett 2004).

Table 6 Clinker quality indicators (wt.-%). �

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Table 7 Typical clinker raw meal composition.

Component [wt.-%] CaCO3 77.1 SiO2 14.0 Al2O3 4.1 Fe2O3 1.6 Other 3.2 Total 100.0

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The chemical composition, mineralogy and the finesses of the raw materials can be utilized to estimate the thermal behavior of the raw meal and the energy consumption of the thermal processing (Chatterjee 1983, Hills 2002). A fine raw material need less energy for the thermal processing, but more energy for raw material preparation, i.e. grinding. Already at low temperatures, before the calcination reaction (1) commences, minor phases of calcium silicates are formed when reactive SiO2 displaces CO2 in CaCO3; wollastonite (CaO.SiO2), rankinite (3CaO.2SiO2) and belite (2CaO.SiO2). During calcination the reactive CaO is formed, whereafter the temperature is increased and the main clinkering reactions follow. Although the chemistry is complex and not fully known the main clinker reactions can be simplified by reactions (2)-(5) (Taylor 1972, Hills 2002, Telschow 2012).

2 CaO (s) + SiO2 (s) � 2CaO.SiO2 (s) (2)

3 CaO (s) + Al2O3 (s) � 3CaO.Al2O3 (s) (3)

CaO (s) + 3CaO.Al2O3 (s) + Fe2O3 (s) � 4CaO.Al2O3.Fe2O3 (s) (4)

CaO (s, l) + 2CaO.SiO2 (s, l) � 3CaO.SiO2 (s) (5)

When appropriate the following abbreviation will be used to describe the main clinker compounds; C = CaO, S = SiO2, A = Al2O3 and F = Fe2O3. And for the corresponding clinker minerals; alite: C3S = 3CaO.SiO2, belite: C2S = 2CaO.SiO2, tricalcium aluminate: C3A = 3CaO.Al2O3, calcium aluminoferrite: C4AF = 4CaO.Al2O3

.Fe2O3. The reaction paths are not fully known but the chemical events in clinker production can be described through equilibrium compositions, as in Figure 8. Above 1200°C an oxide melt is formed. CaO dissolve into the melt and the desired alite is formed. As mentioned product cooling is central and need to be controlled. In Figure 9 a modelled cooling procedure describes the events. The C3S present at 1500°C remain and aluminate and ferrite phases crystallize out of the melt. The final clinker product usually contain 50-70 wt.-% alite, 15-30 wt.-% belite, 5-10 wt.-% tricalcium aluminate and 5-15 wt.-% calcium aluminoferrite (Telschow 2012).

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Figure 8 Modelled results for main clinker phases during heating. Input 100 g raw meal containing Ca, Si, Al, Fe, Mg, K, Na, S, P, Cl, F, Zn, Ti, C, H, and O, at LSF = 0.925, SR = 2.9, AR = 1.5 (Hökfors 2014).

Figure 9 Modelled results for main clinker phases during cooling. Input 100 g raw meal consisting of CaO, SiO2, Al2O3 and Fe2O3, with LSF = 0.925, SR = 2.9 and AR = 1.5 (Hökfors 2014).

The moisture content of the raw meal, bypass operation, fuel properties and plant capacity determines the thermal energy use of the cement clinker process. It has been suggested that the best way to reduce energy consumption is to increase the kiln size (Schneider 2011). The theoretical energy consumption for cement clinker production is 1.7 - 1.8 GJ/tonclinker. At best a dry process equipped with multistage pre-heaters and pre-calciners can achieve an actual energy consumption of 2.9 – 3.3 GJ/tonclinker (Schorcht 2013). Energy consumption for different production paths can be seen in Figure 10 (Gielen 2007, Schorcht 2013).

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Figure 10 Thermal energy consumption spans for different clinker production technologies.

2 3 4 5 6 7 8

Wet process

Shaft kilns and for the production of special cements

For the semi-dry/semi-wet processes (Lepol kiln)

Long dry process

1 stage cyclone pre-heater

2 stage cyclone pre-heater

4 stage cyclone pre-heater

4 stage pre-heater + pre-calciner

5 stage pre-heater + pre-calciner

6 stage pre-heater + pre-calciner

Thermal energy consumption [GJ/ton cement clinker]

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All cement clinker is used to produce cement. In 2003 the clinker ratio (tonclinker/toncement) was on average 0.85 (Harder 2006). Clinker substitution has reduced the clinker ratio to 0.77 in 2010 (Schneider 2011). In 2008 the world limestone consumption for clinker production was estimated to 2500 Mton (Damtoft 2008). Assuming 1.77 ton raw materials per ton clinker (Worrell 2007) and approximately 80% of the raw meal being limestone, the Damtoft data indicate a world production of clinker at 1766 Mton/a. USGS data report world cement production at 3830 Mton in 2012 (USGS 2014b). At an estimated clinker to cement ratio of 0.77 this would indicate a clinker production of 2926 Mton/a. The USGS estimates world clinker production capacity to be 3400 Mton for 2013 (van Oss 2014). At a clinker ratio of 0.77 USGS production and capacity data gives an estimated clinker production of 2618 Mton. “World” production of cement clinker, as reported by the GNR project, is around 650 Mton/a (GNR 2015). The GNR data is reported to cover only an estimated 21% of total cement production, giving a total production volume at 3095 Mton clinker.

1.4 Calcite and calcination Calcite has five structures, calcite I-V. At ambient pressure, CaCO3 is expected to be found as calcite I up to 800°C and as calcite IV above 800°C (Mirwald 1976). At ambient temperatures CaCO3 is expected to be found as calcite I up to 4 kbar. Calcite II and III phases require higher pressures. The phase transitions are difficult to determine and phases are reported to co-exist (Crawford 1964, Fiquet 1994, Redfern 1999, Kawano 2009a).

1.4.1 Calcination or the thermal decomposition of CaCO3

The decomposition event evolves along a reaction zone. The reaction zone starts at the surface of the CaCO3 particle moving towards the center, usually described as a “shrinking core” (Garcia-Labiano 2002), a “contracting sphere” (Haines 1995) or an “unreacted core” (Ar 2001). The CO2 gas migrates through the CaO layer and is released to the atmosphere. The event can be seen in Figure 11, showing the un-calcined core in a piece of quicklime. Several processes are involved in the decomposition, as illustrated by Figure 12. The consecutive processes of the decomposition are: heat transfer to the particle surface and through the CaO and CaCO3 layers to the reaction zone (Q1

�, Q2� and

Q3�), the chemical reaction (R), and the mass transfer of CO2 through the CaO layer

and away from the particle surface (m1�

CO2 and m2�

CO2) (Wang 1995, Oates 1998, Garcia-Labiano 2002, Cheng 2006). Mass transfer and chemical reaction are usually considered as the rate-limiting steps of decomposition (Garcia-Labiano 2002).

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Figure 11 Split lump lime from shaft kiln (approximately 90*50*50mm).

Figure 12 Schematic process illustration of limestone decomposition.

The CaCO3 decomposition behavior varies with atmosphere conditions. Important parameters are the total pressure and the product gas partial pressure. The pCO2 in the reaction atmosphere has a significant effect on the decomposition. At high pCO2 the full decomposition equilibrium occurs at a higher temperature and at low pCO2 CaCO3 decomposes at lower temperatures, as illustrated by Figure 13.

Figure 13 Equilibrium temperature as a function of pCO2 for CaCO3 decomposition (FactSage 2011).

1.4.2 On the kinetics of CaCO3 decomposition

To quote the president of the Scientific Committee on Kinetics of the International Confederation for Thermal Analysis and Calorimetry and Professor at the Chemistry Department at the University of Alabama at Birmingham (ICTAC 2015), Sergey Vyazovkin “there is no adequate theory of solid state kinetics” (Vyazovkin 2003).

600

650

700

750

800

850

900

950

1000

0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 4,0 4,5

Tem

pera

ture

[�C

]

pCO2 [bar]

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Many in the field agree and the situation has been acknowledged for a long time (Stern 1969, Brown 1997, L’vov 2001 and Galwey 2012). The kinetics of thermal decomposition of CaCO3 and the interpretation of thermogravimetric data, usually utilized to investigate these kinetics, has been widely debated (references above and Sharp 1969, Johnson 1972, Zsakó 1973, Elder 1986, Khinast 1996, Roduit 2000, Burnham 2000, Brown 2000, Czarnecki 2000, Vyazovkin 2000, L’vov 2002a, L’vov 2002b, Stanmore 2005, Khawam 2006, Cheng 2006, Vyazovkin 2011, Vyazovkin 2014, L’vov 2015). Usually the kinetics of CaCO3 decomposition is expressed as the rate of decomposition, described as the extent of reaction (α) as a function of time (t). The rate is parameterized by three variables; temperature (T), extent of conversion (α) and pressure (P) (Vyazovkin 2011):

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The Arrhenius equation for homogenous reactions is applied to describe the temperature dependency, k(T), where A and E are kinetic parameters, T is the temperature and R the universal gas constant:

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If there is knowledge of the reaction mechanism involved a model fitting method can be applied. A reaction model is then created to fit the function of extent of conversion f(�), e.g. the contracting sphere:

���� � ��� # ��&'( Other models and the fitting of experimental data has been extensively discussed (Vyazovkin 1999, Han 2014). Options to the model fitting method are the invariant kinetic methods and a wide range of model free methods, e.g. isoconversional methods. For a further discussion of methods see Han and references within (Han 2014). Usually the kinetic result is the tabulation of experimentally determined A and E parameters and the fitted reaction model f(�), called the kinetic triplet. The kinetic parameters will vary with the material, experimental method, temperature, gas composition, analytical method chosen etc. For example E from identical data on CaCO3 decomposition is reported to vary between 89 and 262 kJ/mol, even “after the removal of extreme results” (Maciejewski 2000).

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Another approach is the so called third-law method (L’vov 2002a). Here the thermal decomposition is described as the decomposition of CaCO3 to gaseous CO2 and gaseous CaO with the simultaneous condensation of the low volatile CaO (L’vov 2002b).

CaCO3 (s) � CaO (g) � + CO2 (g) (6) The method separates decomposition conditions as equimolar, in absence of product gas, or isomolar, in presence of product gas. For example at equimolar conditions the method gives the theoretical value Ee = 253 kJ/mol, and reported experimental values range from 237 to 271 kJ/mol (L’vov 2002b). It has also been suggested that the decomposition involves the formation of metastable calcium oxide, CaO* (Hyatt 1958, Valverde 2015a, Valverde 2015b). The reaction path involves the chemical decomposition of CaCO3 into metastable CaO* and CO2 gas. The CO2 is physically adsorbed by van der Waals interaction with the solid matrix. This step is followed by desorption of CO2 gas and the exothermal structural transformation of CaO* to CaO.

CaCO3 (s) � CaO*(s) + CO2adsorbed (g) (7)

CaO*(s) + CO2adsorbed (g) � CaO(s) + CO2 (g) (8) The theory predicts an Arrhenius law behavior at low temperatures (< 850°C). When increasing the temperature a critical temperature is reached where the activation energy E decreases and eventually becomes negative.

1.5 Sustainability concerns related to quicklime and cement clinker production

The intention to aim for a sustainable society was formulated by the Bruntland report of the World Commission on Environment and Development: “Humanity has the ability to make development sustainable to ensure that it meets the

needs of the present without compromising the ability of future generations to meet

their own needs.” (Section 3, §27, Bruntland 1987)

Nine environmental global control variables have been suggested (Rockström 2009a, Rockström 2009b, Steffen 2015): (1) biosphere integrity, (2) novel entities, (3) stratospheric ozone depletion, (4) atmospheric aerosol loading, (5) biochemical flows, (6) freshwater use, (7) land-system change, (8) climate change (9) ocean acidification. Industrial sites, such as limestone quarries and quicklime and cement clinker plants, influence the environment it operates in. The impact comes through the use of land

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and input of resources, but also through the output, e.g. noise, light, and emissions to air, land and water. These effects can be related to control variables (1) - (7). For many of these there are commercially available abatement technologies. Like many other limestone based processes, quicklime and cement clinker production include thermal decomposition of minerals in the limestone followed by the release of gaseous CO2 to the atmosphere. If the fuel used to generate the heat is carbon carrying, additional CO2 will be released. Biofuels are considered carbon neutral and excluded from emissions trade legislation (EU 2003). Although there is an increase in non-fossil fuel utilization in quicklime and cement clinker production fossil fuels are still dominating (Schorcht 2013). Of all the greenhouse gas emissions that have been identified to contribute to climate change, CO2 is described as the dominant one (IPCC 2014). Today the CO2 concentration in the atmosphere is increasing at 2.1 ppm/a (Feldman 2015). Climate modelling indicate that CO2 mitigation is not substitutable and should be prioritized (Strassmann 2009). It has been estimated that on the short term approximately 40-50% of the anthropogenic CO2 remain in the atmosphere, while the rest is stored in the oceans and in the terrestrial biosphere (Sabine 2004). In the longer term more than 90% of the CO2 will be dissolved in the oceans contributing to acidification (Archer 1998). The environmental effects of quicklime and cement clinker production can therefore also be related to parameters (8) and (9). As per today no full scale abatement technology for CO2 emissions has been deployed on quicklime or cement clinker production.

1.5.1 Carbon dioxide emissions from quicklime and cement clinker production

In 2010 all in all 13.14 GtonCO2 was emitted from industrial processes (Fischedick 2014). Industrial emissions of CO2 are categorized as direct, indirect and process emissions. The categorization is of relevance for quicklime and cement clinker production. For quicklime and cement clinker production the direct emissions, or combustion emissions, emerge from the use of carbon carrying fuels used in the kilns and calciners. The process emission relate to CO2 emitted from non-combustion processes, here the decomposition of carbonate minerals. Indirect emission relate to the generation of utilities, e.g. electricity, used all through the value chains. From a regulatory stand point the indirect emissions are allocated to the source, i.e. the power plant, not to the quicklime or cement clinker processes. For quicklime production an estimated 68-80 % of the CO2 emissions are process emissions. The rest 20-32% are combustion emissions (Schorcht 2013). These emission all originate in the lime kiln, compare Figure 3. Besides the carbon content of the fuel used the large the variation in fuel efficiency, as described in Figure 4, gives the wide spread in the shares of the direct emissions. For clinker production approximately 62 % are process emissions and 38 % combustion emissions (Schorcht 2013). These emissions originate from the thermal treatment highlighted in Figure 6.

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Since the combustion emissions vary with the energy consumption, energy efficiency measures will reduce emissions. The production technology influences the energy consumption as seen in Figure 10. At a given raw material the process emissions are constant with the production volume. Changing the raw material will affect the emissions. On a global level the 13.14 GtonCO2/a of industrial emissions comprises 5.27 GtonCO2 direct energy-related emissions, 5.25 GtonCO2 indirect emissions from electricity and heat production, 2.59 GtonCO2 from process emissions and 0.03 GtonCO2 from waste/wastewater. Of the total 2.59 GtonCO2 process emissions the value chains for quicklime and cement clinker together constitute 1.594 GtonCO2 or 62 % (Fischedick 2014). The specific emission (tonCO2/tonproduct) is used to evaluate process performance. The European Union Emissions Trade System has set the product benchmarks for quicklime to 0.954 tonCO2/tonproduct and for cement clinker to 0.766 tonCO2/tonproduct (EC 2011a). Quicklime and cement clinker is easily shipped and large volumes are imported and exported (Brown 2013). The trade intensity, together with the cost for compliance, are the evaluation criteria for being exposed to the risk of carbon leakage (EC 2010). Carbon leakage meaning that a stringent environmental legislation is expected to move production to regions with a less stringent legislation, thus redeeming the environmental gain from the legislation. Both quicklime and cement clinker production are today classified to be at risk of carbon leakage. To counteract the risk alleviations have been made. In EU a predefined amount of allowances are distributed within the cap-and-trade system free of charge to the producers. In 2013 the free allocation was 80 % of the benchmark and the legislation indicate a plan to reduce the free allocation to 30 % 2020 and 0 % in 2027 (EC 2011a). Through the UN Framework Convention on Climate Change member states commit to emission reductions, called Intended Nationally Determined Contributions or INDCs. As of today (2015-10-05) 119 INDC submissions are registered (UN 2015). The commitments are in the range of 30 - 40 % reduction by 2030. An independent analysis by the organization Climate Action Tracker indicate that the INDCs now cover 65 % of global emissions in 2010 (CAT 2015).

1.5.2 Reducing carbon dioxide emissions

There are several possibilities to reduce CO2 emissions. In this work alternative fuels and O2 enrichment as an energy efficiency measure are investigated in papers II, III and VI. Oxygen enrichment is the practice of increasing the O2 content above the ambient 21 vol.- % during combustion, illustrated for quicklime and cement clinker production in

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Figure 14. The combustion air feed is reduced and compensated by concentrated O2 whereas the nitrogen (N2) load on the kiln will be reduced, resulting in less heat lost by heating of N2 and a smaller flue gas stream. Oxygen is usually produced from air. In this work the energy consumption of 1.044 GJ/tonO2, at 99.5 vol.-% O2 purity, will be used as a reference value in the further discussion (Göttlicher 2014). Other consumption figures have been presented (Bolland 1992, Zeman 2008).

Figure 14 Simplified schematics of O2 enrichment in quicklime and cement clinker production. To achieve major reduction targets, such as the EU indication of 80 - 95 % reduction by 2050 compared to 1990 (EC 2011b), a readjustment or a slow-down in industrial production will be necessary. Reducing emission by 95 % while maintaining production volumes would imply a near-zero emission production modus. In this work technological concepts for ambitious reduction of CO2 emissions from quicklime and cement clinker production is investigated in papers I, IV and V. Other means to reduce CO2 emissions comprises energy efficiency measures from switching production technology, compare Figure 4 and Figure 10, and increasing automation. Several solutions related to process control and automation are available. Reduced energy consumption in the range of 5 - 8 % is reported (Hagemoen 1993, Pearson 1999, Järvensivu 2001a, Järvensivu 2001b, Williamson 2008, Stadler 2011). For cement clinker production substitution of limestone in the raw material can also reduce emissions. Although many secondary industrial products have been suggested (Gartner 2004, Damtoft 2008, Baeza 2013), significant limestone substitution has yet only been achieved with blast furnace slag and some fly ashes (Class C fly ash, ASTM C618 - 12a, Damtoft 2008, Hower 2012). Furthermore a wide range of materials have been identified as having the potential to substitute clinker in cement production (Harder 2006, IEA 2008, Baeza 2013). However, clinker substitution is out of the

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scope of this thesis, and will not be further discussed. For quicklime no raw material substitution has been found. Pre-combustion capture of CO2 aim to concentrate and remove CO2 prior to combustion. The method is based on fuel preparation. A partial oxidation of the fuel results in a synthetic gas high in CO and H2, called syngas. After water-gas shift reaction of the syngas CO2 is separated and H2 is the product fuel gas (Jansen 2015). In quicklime and cement clinker production the utilization of carbon free fuels, such as H2, would reduce combustion emissions, but not process emissions.

1.5.3 Near zero emission production of quicklime and cement clinker

The concept of CCS, or Carbon dioxide Capture and Storage, implies the separation or concentration of gaseous CO2 with the aim to permanently store CO2 away from the atmosphere. The technology allows for continued use of (fossil) carbon carrying fuels in energy and industrial production while cutting CO2 emission virtually to zero. If applied to non-fossil carbon the emission would be negative, the CO2 storage acting as a carbon sink. In the IEA emission reduction scenarios toward 2050 CCS technology is calculated to stand for 14 - 19 % of the total emission reduction. The development of these technologies is considered important if the ambitious emission reductions targets are to be achieved (IEA 2008, Deetman 2013). For the separation of CO2 three technological paths have been identified; pre-combustion capture, post-combustion capture and capture through oxyfuel combustion. The permanent storage of CO2 has been suggested to be achieved through injection in deep saline aquifers, in depleted oil and gas fields, in unminable coal seams, in geological shale formations or through mineral carbonation (Hendriks 1995, IPCC 2005, Liu 2013). As per today there are two types of commercial CCS value chains in operation, one where CO2 is stored in deep saline aquifers and one where CO2 is utilized for enhanced oil recovery and simultaneously stored in the oil field (CCS Institute 2015). Even though CCS is a part of the cement sector roadmap to CO2 emission reduction no CCS technology has yet been applied to quicklime or cement clinker production (IEA 2011). There is however a demonstration project under construction in Norway, where post-combustion technologies will be evaluated on a cement clinker process (Norcem 2015). Pre-combustion capture of CO2 applied to quicklime and cement clinker, would not influence the process emissions. Thereby only 20 - 40 % of the emissions could be avoided, not allowing a near-zero production modus. Therefore pre-combustion capture was discussed as an emission reduction path in section 1.5.2.

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1.5.3.1 Post-combustion capture of CO2

The separation of CO2 from flue gases is described as post-combustion capture. The technology usually utilize a solvent or a sorbent, that selectively binds and releases CO2. This allows for recycling of the solvent or re-use of the sorbent. Cryogenic distillation and selective membranes have also been suggested (IPCC 2005). The principle is illustrated in Figure 15. The solvent based technology predates the concept of CCS and is a mature commercial technology. There are numerous solvents and the regeneration is usually achieved through heating. Current technology energy requirement is 2.6 GJ/tonCO2. The technology has been recently reviewed (Idem 2015, Liang 2015). Several solid sorbents are available and regeneration is usually controlled by temperature and/or pressure. Limestone and dolomite have also been proposed as a sorbents for CO2 (Abanades 2002, IPCC 2005). Post-combustion technologies with the aim for application to quicklime production has been reviewed in earlier work (Eriksson 2009b).

Figure 15 Simplified schematics for post-combustion capture of CO2 applied to a quicklime or cement clinker production unit.

1.5.3.2 CO2 capture through oxyfuel combustion

Oxyfuel technology, investigated in papers IV and V, implies the use of pure O2 instead of air in combustion processes. Flame temperature is controlled by recirculation of flue gases. The product gas is high in CO2 and low in N2. The concept of oxyfuel applied to quicklime and cement clinker production is illustrated by Figure 16.

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Figure 16 Simplified schematics for oxyfuel combustion applied to quicklime or cement clinker production. There are several applications of oxyfuel technologies, like converters and pit furnaces (Vesterberg 2006). These are not CCS applications but are mainly applied to achieve increased production capacity and improvements in energy efficiency. As a CCS concept the technology has been demonstrated for power production (Strömborg 2009, Stanger 2015). The application to blast furnace production has also been suggested (Danloy 2009). It can be noted that the formation of NOx is expected to be reduced in an oxyfuel combustion modus (Manickam 2009). To date there are no full scale CCS oxyfuel plants in operation. Research on oxyfuel in quicklime production has not been published before paper V, but the concept has been related to cement clinker production (Zeman 2008, ECRA 2009, Zeman 2009, Granados 2014).

1.5.3.3 CO2 capture and storage through mineral carbonation

Natural weathering processes allow for carbonation of silicate minerals. It has been suggested that through mimicking and enhancing these weathering processes CO2 could be permanently stored (Seifriz 1990). Natural minerals such as serpentine (Mg3Si2O5(OH)4), olivine (Mg2SiO4), and wollastonite (CaSiO3) have been suggested for carbonation (IPCC 2005). Also secondary industrial products, such as metallurgical slags, fly ashes and cement kiln dusts, have been suggested for carbonation processes (Fernández Bertos 2004, Eloneva 2008, Gunning 2010, Eloneva 2012, Mattila 2012). To date no full scale CCS mineral carbonation plants are in operation. The technology have been revived (Huijgen 2003, Huijgen 2005, Sipilä 2008, Olajire, 2013, Sanna 2014, Romanov 2015). In paper I the mineral carbonation path, described first by Nduagu, is investigated as applied to a rotary lime kiln (Nduagu 2008, Romão 2010, Romão 2011, Fagerlund 2011, Nduagu 2012a, Nduagu 2012b).

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2 Methods

2.1 Calculating fuel properties and analyzing the effect on rotary kiln production

A wide range of fuels are used in quicklime and cement clinker production. In 2003 in the EU-27 more than 90 % of the fuel used was fossil (Schorcht 2013). Introducing new fuels and mixing fuels requires characterization of fuel properties. Fuels have many relevant properties but in this work main focus is on the adiabatic flame temperature and the amount and composition of the ash. In the rotary kiln radiation from the flame to the bed is the main heat transfer mechanism driving the calcination reaction and the clinker mineral reactions. The radiation that reaches the refractory is partially reflected and partially absorbed. All in all only a small fraction of the flame radiation reaching the refractory is lost through the shell (Boateng 2008). The heat transfer of the rotary kiln is illustrated by Figure 17.

Figure 17 Heat transfer Q� in rotary kilns, A = Ambient surroundings, B = bed, G = Gas, R = Refractory, and S = Shell.

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For a simplified case the heat transfer through radiation from a flame is calculated according to:

Q = � � A (T4 - TS4)

Where Q = rate of heat transfer in J/s, � = emissivity = (0.0 – 1.0), � = Stefan-Boltzmann constant 5.676 10-8 J/sm2K4, A = area available for heat transfer in m2, T = flame temperature in K, TS = ambient temperature in K. The impact of flame emissivity on the total radiant heat transfer between the flame and the bed solids in a rotary kiln is limited. High emissivity flames have high direct radiation, but have less radiant heat transmitted from the refractory walls to the bed solids, while low emissivity flames have lower direct radiation, but higher transmission of radiation from refractory walls. Therefore the net result is that kiln performance is not very sensitive to flame emissivity (Gorog 1983, Adams 2008). Throughout this work, � = 1.0, is used. The adiabatic flame temperature (AFT) is a theoretical fuel property. It can be used as a description of an ideal flame. It indicates what temperature the fuel would generate in an imaginary reactor with no heat losses and no fixed volume. Studies on lime mud reburning in rotary kilns show that the adiabatic flame temperature of a fuel is the dominant factor in determining rotary kiln performance. A 5% change in AFT corresponds to a 5% change in kiln efficiency. Compared to a 50% change in flame length that also corresponds to a 5% change in efficiency (Adams 2008, Adams 2009). In this work the AFT is calculated for different fuels. The calculations are performed with FactSage 6.4 FactPS database at constant pressure with a synthetic air consisting of only N2 and O2. Lambda, λ, describes the ratio of O2 to the stoichiometric O2 required for complete combustion, and is varied to calculate the maximum AFT. Furthermore AFTs at different O2 concentrations in the oxidant gas is calculated. The chemical events within the production processes are dependent on the combustion process. AFTs are also calculated at O2 contents corresponding to process conditions. During quicklime production in a rotary kiln the O2 concentration of the kiln exit gas is usually kept at 1.0 - 3.0 vol.-%. In cement clinker production the rotary kiln exit gas optimally contain 0.5 - 1.5 vol.-% residual O2 (Manias 2004). �

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2.2 Predictive process simulations through multicomponent chemical equilibrium calculation

If one knows a reaction path, the kinetic reaction constant can be predicted for a certain concentration of a component at a given time. Since the chemical reaction paths for quicklime and cement clinker production are not fully known, kinetic models are difficult to use to predict the effect of changes to the processes, e.g. when changing the fuel mix. Another way is utilizing multicomponent chemical equilibrium calculation to predict the chemical composition of a mixture of species at a given temperature and pressure. The predictive simulation tool utilized in this work is a combination of commercially available software: AspenPlusTM V7.1 (AspenPlus 2011) and ChemAppTM (ChemApp 2011). AspenPlusTM is used for drawing the process scheme and iteratively solving the mass and energy balances. ChemAppTM is used to calculate the equilibrium chemistry. In addition, FactSage V6.1 (Bale 2002, FactSage 2011) is used as a source of thermochemical data for the system and to calculate fuel and feed properties. Besides papers II to VI the work with the chemical equilibrium tool and the database is also described by Hökfors (Wilhelmsson Hökfors 2008, Hökfors 2014). The model in this work is a continuation of the modeling work started by Kääntee, Zevenhoven, Backman and Hupa (Kääntee 2004). Different models for quicklime and cement clinker production in rotary kilns are available (Boateng 1996, Martins 2002, Modigell 2002, Schwertmann 2004a, Schwertmann 2004b, Ginsberg 2005, Georgallis 2005, Koukkari 2009). However, empirical factors are used in almost all of the models and it should be pointed out that if the model includes empirical factors it cannot be regarded as predictive in general.

2.2.1 Development and validation of the simulation tool

The simulation tool has been developed over time. More elements and fuels have been added to the database and the process schemes have been optimized and extended from the conventional setups to fit the simulation needs. The compound selection has also been extended and optimized over time. In papers II and VI the database comprise 11 elements: Al, C, Ca, Cl, Fe, H, K, N, S, Si and O. In papers III, IV and V the database was extended to 16 elements by including: Mg, P, Na, Ti and Zn. In papers II and VI 157 compounds were selected and in papers III, IV and V 251 compounds were selected. The number of elements and compounds included are listen in Table 8. The selected compounds for all phases are listen in Appendix 2.

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Table 8 Development of simulation tool: optimization and extension of database, number of elements and compounds included in papers II to VI. Compounds listed in Appendix 2.

Papers II and VI Papers III, IV and V

Elements 11 16

Compounds in gas phase 56 52

Compounds in pure solid phases 71 156 Compounds in solid solutions 0 21 Compounds in mixed melt phases 8 20 Compounds in pure liquid phases 22 2 Total number of compounds 157 251

Eight fuels have been defined in the database and used in the simulations. In paper II the simulations are performed with a coal (coal 2) and a converted fuel oil (in Swedish

KEO = Konverterad Eldnings Olja). The oil is a commercially available waste derived fuel oil. In papers III and IV the fuels used in the simulations are coal, petroleum coke and used car tires. The results in paper V are obtained with coal (coal 2) as the fuel. In paper VI the usage of a coal (coal 2), KEO and saw dust is simulated. The user defined fuels are presented in Table 9.

Table 9 Fuels defined in the process database, d.b. = dry basis, HHV = Higher Heating Value, AC = Light fuel based on recycled paint waste and solvents, MBM = Meat and Bone Meal, KEO = Converted fuel oil, a waste derived fuel oil.

[wt.-%] Coal Petroleum

Coke AC MBM KEO Rubber

tires Coal 2 Sawdust

Fuel d.b.

C 67.8 86.2 77.7 39.5 73.0 67.6 75.8 50.4 H 4.3 3.1 10.4 5.3 10.9 7.0 5.0 6.2 O 11.4 0.9 7.2 17.3 13.9 1.3 8.8 42.7 N 1.2 1.7 0.4 7.5 0.1 0.4 1.2 0.1 S 0.3 7.5 3.8 0.2 0.88 1.6 0.76 0.03 Cl 0.001 0.004 0.48 0.3 0.10 0.1 0.01

Ash: 15 0.6 0 30.0 1.1 21.9 8.4 0.6 Total fuel d.b.: 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0

HHV d.b. [MJ/kg]:

31.7 35.1 31.2 18.2 43.0 33.2 32.9 20.3

Moisture: 9.7 6.8 5.0 6.5 0.0 1.6 4.7 8.0

Ash:

CaO 3.43 17.8 95.8 0.0 1.3 8.8 4.2 SiO2 69.35 13.9 0.0 7.1 2.5 42.0 21.9 Al2O3 15.46 2.3 0.0 38.8 1.3 30.9 46.2 Fe2O3 6.87 32.5 0.1 5.9 94.3 8.5 2.4 K2O 2.23 0.1 0.4 0.0 0.0 2.4 13.4 Na2O 0.94 30.2 0.0 0.0 0.0 1.3 0.9 MgO 1.72 3.1 0.4 48.2 0.6 3.6 7.2 P4O10 3.2 1.2 3.9 TiO2 1.1

Total ash: 100.0 100.0 0.0 100.0 100.0 100.0 100.0 100.0

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In papers II, III, and VI comprehensive models of the quicklime and cement clinker processes was used. The Aspen schematics for the full quicklime model can be found in papers II and VI. The Aspen schematics for the full clinker model used in paper III, can be seen in Figure 18. In papers IV and V less complex and more generic models were developed. The aim was to increase applicability, improve convergence and achieve shorter simulation times. For the generic lime model the Aspen schematics can be found in paper V. The rotary kiln was modelled as three ChemApp equilibrium blocks. The option to recirculate flue gases from kiln exit to the combustion zone was included in the model. The reference case was simulated by defining recirculation to zero.

Figure 18 Aspen schematics for the full cement clinker model. The generic cement clinker model was built in two versions to allow for simulation of partial and full oxyfuel. The reference case was simulated with the full oxyfuel model by defining recirculation to zero. The full oxyfuel model and the more complex partial oxyfuel model contain 10 and 16 ChemApp equilibrium blocks respectively. The Aspen schematics can be found in paper IV. The model temperatures are controlled by heat losses. The heat losses are defined according to the reference cases and are based on process surface temperature measurements. The measured lime kiln surface temperatures have been published in paper II. The raw material properties used in the simulations are given in Table 10. The limestone elements do not fully correspond to the actual analysis, e.g. Mg and Na are

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present at small concentrations in the limestone. Since all elements were not present in the database at the time they were approximated as other elements. Here Mg and Na has been approximated as Ca and K. This simplification is further discussed in paper II.

Table 10 Raw material feed properties.

Compound [wt.-%]

Limestone Papers II, V and VI

Clinker raw meal Papers III and IV

CaCO3 97.41 77.97 SiO2 1.25 13.76

Al2O3 0.14 2.61 Fe2O3 0.58 1.67 FeSO4 0.33 K2O 0.24 0.77

CaCl2 0.05 0.06 MgO 1.74 P2O5 0.02 TiO2 0.15 Na2O 0.2 SO3 1.04 ZnO 0.01 Total 100.00 100.00

The simulation tool has been validated by full scale campaigns for both quicklime and cement clinker production. Interpreting equilibrium data and validating against actual process data can be challenging. It was concluded from the validation work that the models in the simulation tool describe the processes in a way accurate enough predict responses when process conditions are changed. The simulation results are validated against operational parameters, such as temperatures and flows, and chemical composition of the products. All modifications to the models have been validated against operational data. Validation data is found in papers II and III. Further validation data has been published by Hökfors and by Eriksson (Wilhelmson Hökfors 2008, Eriksson 2009a). An overall accuracy of the simulation tool has not been determined. Since the production processes in question are difficult to measure accurately the tool is often used to predict relative changes to specific parameters, as described in paper V. The tool has been of practical value when planning and executing full scale campaigns and production modes, reducing costs related to trial and error.

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2.3 Thermogravimetric analysis Measuring the mass of a sample by weighing is one of the basic quantitative techniques used in a laboratory. Using this technique in an analytical way is described as gravimetric analysis. Monitoring the effect of controlled temperature change, time and atmosphere on the mass of a sample is called thermogravimetry (TG), or thermogravimetric analysis (TGA). The TG result is a weight curve describing the weight as a function of time or temperature. The technology has evolved during the 20th century and today sophisticated apparatus with electrobalances, furnaces, purge gases, reaction gases, and advanced control and data acquisition devices are readily available and easy to use (Ozawa 2000). The samples and sample holders are small, the temperature sensors several and the instruments are easily calibrated for thermal changes within the apparatus, e.g. weighing beam growth and gas density variations. Thermogravimetry includes several different methods. Conventional methods are isothermal and constant heating rate thermogravimetry, where the sample temperature held constant or is constantly changed in a predetermined scheme set by the user. Other methods are e.g. constant reaction rate TG and dynamic heating rate TG. In constant reaction rate TG a certain predetermined weight change (%/min or %/°C) is achieved by continuously adjusting the experimental temperature according to the weight change of the sample. In dynamic heating rate TG the temperature change varies in a non-predetermined way. The method adjusts the heating rate, through sensitivity and resolution settings, related to the sample weight change (Gill 1992). In this work two thermogravimetric analyzers were set up in the laboratory, Q600 TA Instruments STD and Q500 TA Instruments HiResTM TG. The aim was to compare constant heating rate and dynamic heating rate methods applied to lime kiln feed limestone. Comparative studies of this kind can be found in literature, however no publications related to limestone or CaCO3 was found (Lever 1993, Berbenni 1999, Li 2000a, Masson 2005, Brozek 2007, Tobón 2010). Some publications are available on dynamic rate TG analysis of specific samples such as polymers, minerals, fillers, fuels and fuel additives (Bereznitski 1996, Li 1999a, Li 1999b, Gonzalez 2006, Li 2000b, Wang 2001, Zanier 2001, Frost 2003, Frost 2004, Kök 2008). No publications on the study of thermal decomposition of limestone or CaCO3 by dynamic rate TG have been found. The extrapolated onset temperature, experimental time, maximum decomposition rate and temperature at maximum decomposition rate was used for the comparison. The

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extrapolated onset temperature is defined as the point of intersection of the tangent drawn at the point of greatest slope on the leading edge of the peak with the extrapolated base line (IUPAC 2002). The maximum decomposition rate was determined at peak maximum of the 1st derivative weight change signal for the relevant reaction. Proper care was taken to secure instrument stability. The instruments are individually connected to instrumental N2 and CO2 gas. Gas flow is controlled by the instruments by means of adjustable mass flow meters. The samples were grinded by hand. Prior to the experiment the calibrations of the instruments were validated against the instrument suppliers’ pure calcium oxalate. The validation was repeated after the experiments. During these validations both instruments performed according to the specifications of the supplier. The complete experimental setup for the work can be found in paper VII. The Q600 TA instruments STD provides simultaneous thermogravimetric analysis and differential scanning calorimetry. The instrument has a horizontal furnace and balance design. It operates with dual beams up to 1500°C. The balance sensitivity is reported at 0.1 �g. The sample capacity is 200 mg and the heating rate from ambient to 1000°C can be set between 0.1°C/min and 100°C/min. The instrument is equipped with mass flow controllers for purge gas and reaction gas control. A purge gas of 100 mlN2/min was used. No reaction gas was used. TA instruments 90 �l ceramic alumina cups were used both for the sample and as reference. The sample mass was between 22.4 and 27.0 mg. The differential heat flow function was not utilized in this work. The Q500 TA instruments HiRes™ TG was used for the dynamic rate analysis. The instrument has a vertical furnace and balance design. It operates with a dual hanging holder up to 1000°C. The balance sensitivity is reported at 0.1 �g. The sample capacity is 1000 mg and the heating rate from ambient to 1000°C can be set between 0.01°C/min and 100°C/min. The instrument is equipped with mass flow controllers for purge gas and reaction gas control. A balance purge gas of 10 mlN2/min and a sample purge gas of 25 mlN2/min was used. No reaction gas was used. TA instruments 100 �l ceramic alumina cups were used both for the sample and as reference. The sample mass was between 20.3 and 28.2 mg. The dynamic rate TG, the Q500, operates with two mode specific parameters: the resolution and the sensitivity settings (TA Instruments 2001). The resolution setting determines at what reaction rate the heating rate is reduced. The sensitivity setting controls the response to changes in the reaction rate. The resolution setting can be set between -8.0 and + 8.0. With a negative setting the mode is constant reaction rate TG and with a positive setting dynamic rate TG. At resolution zero the instrument operates as a conventional constant heating rate TG.

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Increasing the resolution setting increases the resolution between consecutive reactions. The resolution setting influences the detected transition temperature. A high resolution lowers the temperature at which a transition is detected, bringing it closer to the theoretical decomposition temperature. A high resolution also increases the experimental time. Increasing the resolution by a whole number, e.g. from 3.0 to 4.0, generally increases the experimental time by a factor of between 2 and 5. The sensitivity can be set between 1.0 and 8.0. At a high sensitivity setting the method is more sensitive to small changes in reaction rate, increasing experimental resolution and experimental time. The sensitivity setting is designed to be used to further increase the experimental resolution when the optimal resolution setting has been found. The sensitivity setting can increase the experimental resolution by narrowing the range over which the heating rate is varied. The impact of the sensitivity setting on the range in %/minute at resolution 3.0 and 4.5 can be seen in Figure 19.

Figure 19 Approximate influence of sensitivity setting on rate of weight change (%/minute) at resolution setting 3.0 and 4.5.

0

2

4

6

8

10

12

14

16

18

20

1 2 3 4 5 6 7 8

Sam

ple

wei

ght

chan

ge [

%/m

in]

Sensitivity setting

Resolution setting 3.0

Resolution setting 4.5

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3 Results and discussion

3.1 Calculated effects of fuel properties on rotary kiln production In addition to the fuels defined in the database, Table 9, the adiabatic flame temperatures of H2, CH4 and elementary carbon has been calculated at different conditions. The calculated heat transfer as a function of AFT can be seen in Figure 20. The results related to H2, CH4 and C at different conditions can be seen in Figure 21, Figure 22, and Figure 23. The results for the fuels in the simulation database can be seen in Figure 24 and Figure 25. In paper VI a coal flame is compared to a flame from co-combustion of coal and KEO. AFT is calculated at different O2 levels. The results are shown in Table 11.

Figure 20 Radiation heat transfer at different AFT and surface temperature (Ts1 = 800°C, Ts2 = 25°C), constant surface (A = 1 m2) and constant emissivity (ε = 1).

0

2 000 000

4 000 000

6 000 000

8 000 000

10 000 000

12 000 000

1000 1500 2000 2500 3000 3500

Rad

iatio

n he

at tr

ansf

er [

J/s]

Adiabatic flame temperature [�C]

TS = 800°C

TS = 25°C

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Figure 21 AFT at 21 vol.-% O2 for C, H2 and CH4 as a function of λ.

Figure 22 AFT at 21 vol.-% O2 for C, H2 and CH4 as a function of residual O2 in the combustion flue gas.

��� λ = 0,94

AFT = 2125�C

CH4: λ = 0,94AFT = 2080 �C

C: λ = 0,94AFT = 2045�C

1900

1950

2000

2050

2100

2150

0,5 0,6 0,7 0,8 0,9 1,0 1,1 1,2 1,3

Ada

iaba

tic

flam

e te

mpe

ratu

re [�C

]

λ

H2

CH4

C

1900

1950

2000

2050

2100

2150

0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5

Ada

iaba

tic f

lam

e te

mpe

ratu

re [�C

]

O2 in flue gas [Vol.-%]

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Figure 23 AFT profiles for C, H2 and CH4 at different λ and O2 concentrations (21 vol.-%, 23vol.-% and 25 vol.-%).

Figure 24 AFT at 21 vol.-% O2 for fuels in database, ash free and with ash at Tmax and at process conditions with 2.0 vol.-% residual O2 in the combustion flue gas.

21%23%25%

21%23%

25%

21%23%25%

0

500

1000

1500

2000

2500

0,0 0,5 1,0 1,5 2,0

Adi

abat

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mpe

ratu

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]

λ

��

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Coal Petcoke AC MBM KEO Tyres Coal 2 sawdustNo ash, Tmax 2257 2100 1704 1914 2231 2101 2158 1968With ash, Tmax 2215 2099 1704 1872 2228 2070 2143 1967With ash, 2 vol% residual O2 2146 2013 1586 1761 2135 1985 2066 1879

0

500

1000

1500

2000

2500

Adi

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ratu

re [�C

]

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Figure 25 AFT with ash, Tmax for fuels in database at different O2 concentrations.

Figure 26 Change in heat transfer by radiation for fuels in database as a function of O2 concentration in combustion air at Tmax with ash.

CoalPetcoke

ACMBM

KEO

TyresCoal 2

Sawdust

1600

1800

2000

2200

2400

2600

2800

3000

20 30 40 50 60 70 80 90 100

Adi

abat

ic f

lam

e te

mpe

ratu

re [�C

], w

ith a

sh, T

max

Oxygen [Vol.-% O2]

Coal

Pet coke

AC

MBM

KEO

TyresCoal 2Sawdust

0%

10%

20%

30%

40%

50%

60%

20 30 40 50 60 70 80 90 100

Cha

nge

in h

eat f

low

by

radi

atio

n [%

]T

max

, with

ash

O2 in combustion air [vol.-%]

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Table 11 AFT and change in heat transfer, as compared to coal at 21 vol.-%, for coal and co-combustion of coal and KEO at different O2 concentrations.���

Fuel mix: 100 % Coal 90 % Coal + 10 % KEO

Combustion air [vol.-% O2]

AFT [°C]

Change in heat transfer [%]

AFT [°C]

Change in heat transfer [%]

21 2090 0 2100 + 2

23 2160 + 12 2175 + 15 25 2220 + 24 2230 + 26

Discussion

The radiation heat transfer equation shows that increasing flame temperature (T) is an effective way to increase radiation and thereby heat transfer to the bed. Increasing the radiation heat transfer from the flame influences the heat load profile over the whole kiln length. If the kiln exit gas temperature declines the bed will have a lower temperature entering the flame zone. As can be seen in Figure 20 though, the effect of the bed temperature is not significant, AFT dominates the heat transfer. H2 is relevant as a carbon free fuel and as the product gas from processes of pre-combustion capture of CO2. CH4 is relevant due to the low carbon content, availability and wide use in industry, not least in quicklime production. Elementary carbon is calculated as a reference. The result, in Figure 21, show that H2 and CH4 are superior fuels, with high AFT. If the O2 concentrations is too low, e.g. at Tmax λ = 0.94, significant amounts of products of incomplete combustion such as CO enters the flue gas system posing explosion risks. Incomplete combustion also reduces the energy efficiency of the kiln and influences product quality. In addition, reducing conditions influence the vaporization and condensation of volatile components, such as sulphur, which affects process stability (Cortada Mut 2015). On the other hand, if the residual O2 is high the heat losses with flue gases will increase and the AFT will decline, and with it the radiation heat transfer. The calculated AFT for H2, CH4 and C as a function of residual O2 in the combustion flue gas can be seen in Figure 22. At process conditions (λ > 1.0) the AFT decreases from the maximum value. This is especially the case for the quicklime rotary kiln, with up to 3.0 vol.-% residual O2, and but also for the cement clinker rotary kiln, at 0.5 - 1.5 vol.-% residual O2. Oxygen enrichment influences the AFT. In Figure 23 the temperature profile at different λ and O2 concentrations (21 vol.-%, 23 vol.-% and 25 vol.-%) is shown. The

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maximum concentration of CO can be seen in the lean area at λ � 0.50 for C and at λ � 0.34 for CH4. At process conditions, λ > 1.0, increasing O2 increases AFT for all fuels. For the simulation tool eight fuels, Table 9, are included in the process database. The fuels are defined as containing the following elements; C, H, N, O, S and Cl. The ash has been added in order to resemble the actual case. Although the components in the fuel, that eventually will remain as the inorganic residue, the ash, will participate in combustion events, the results in Figure 24 show that adding the ash will lower the adiabatic flame temperature. Figure 24 shows a comparison of (i) the AFT for the ash free fuel at Tmax (λ < 1.0), (ii) the AFT Tmax with ash and (iii) the ATF with ash at process conditions of 2.0 vol.-% residual O2 in the combustion flue gas. The AFT and the heating value of a fuel are not directly correlated and therefore the AFT cannot be determined directly from the analysis data usually provided by the fuel supplier but needs to be calculated from the fuel composition. The effect of O2 concentration in the combustion oxidant on the AFT for the fuels in the database can be seen in Figure 25. All AFT increase with increasing O2. The increase in AFT increases the heat transfer. The effect is largest on the AC fuel, a waste derived fuel based on recycled paint waste and solvents, where combustion in pure O2 would theoretically increase the heat transfer with more than 55 %, see Figure 26. Even though it is not always practiced by plant operators (Mokrzycki 2003), AFT is a key fuel property and utilizing it, e.g. when changing a fuel mix, can be beneficial. Of course also other fuel properties need to be accounted for, e.g. chemical composition, heating value, particle size, and moisture content. The process can be adjusted to the new fuel mix by calculating the AFT at normal process conditions, e.g. at 100 wt.-% coal and 2 vol.-% residual O2 in the flue gas, and adjusting the combustion air feed so that the new fuel mix comes as close to the original AFT as possible. The results in Table 11 show that introducing KEO at 10 % of total energy input marginally increase the AFT and the heat transfer. The change from coal to co-combustion of coal + KEO should therefore not significantly affect the process. On the other hand oxygen enrichment has a significant affect and will alter the process. When evaluating new fuels one might find that the AFT of the new fuel mix does not reach the original temperature. The temperatures required can then be reached by O2 enrichment. Increasing the fuel load will not increase the AFT. Hydrogen and methane fuel gases have no ash and high AFTs, see Figure 21. As a fuel for quicklime and cement clinker production H2 and CH4 would be good fuels. Both H2 and CH4 have lower carbon content than coal witch would reduce CO2

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emissions. If CH4 would have a biogenic origin it would be considered carbon neutral, and if applied within a CCS system the emissions would be negative. In cement clinker production, where the composition of the ash need to be considered as part of the raw materials mix, the absence of ash must be taken into account. As noted in papers II and VI, quicklime product quality will benefit from low-ash and no-ash fuels.

3.2 Process simulations of changes to the fuel mix in quicklime production

The simulation tool was utilized to investigate the effect of different fuels and ashes. Paper II studied the combustion of coal, KEO and the co-combustion of coal and KEO. The main simulation input data is shown in Table 12. The main results are shown in and Figure 27. Further results are found in paper II. In paper VI the effect of a wider fuel mix on quicklime production was investigated. KEO and Sawdust was added to coal at 10 % of total energy content. The main results are shown in Table 14.

Table 12 Input parameters for simulation of quicklime production with coal and/or KEO at constant limestone and air feeding rates.

Fuel mix [% of energy input]

Coal [MJ/h]

KEO [MJ/h]

Ash load [ton/h]

Moisture load [ton/h]

100 % coal 75059 0 0.199 0.467 80 % coal + 20 % KEO 60047 15012 0.163 0.443 60 % coal + 40 % KEO 45035 30024 0.127 0.420 40 % coal + 60 % KEO 30024 45035 0.092 0.397 20 % coal + 80 % KEO 15012 60047 0.056 0.373

100 % KEO 0 75059 0.020 0.350

Table 13 Simulated results for quicklime production with coal and/or KEO.

Kiln exit gas

[m3/h]

Process temperatures

Fuel mix [% of energy input]

Production [ton/h]

Burn zone [°C]

Calcination zone [°C]

Kiln exit [°C]

100 % coal 9.999 38368 1000 850 400 80 % coal + 20 % KEO 9.966 38441 999 852 402 60 % coal + 40 % KEO 9.931 38586 999 855 405 40 % coal + 60 % KEO 9.897 38591 998 857 407 20 % coal + 80 % KEO 9.863 38663 996 858 408

100 % KEO 9.830 38739 996 862 412

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Figure 27 Simulated results of influence on quicklime product quality related to coal and KEO combustion. �

Table 14 Simulation results for coal, KEO and sawdust combustion in quicklime production and relative change as compared to coal reference, QL = Quicklime.

Fuel mix (in 21 vol.-% O2)

100 % coal

90 % coal + 10 % KEO

90 % coal + 10 % sawdust

Result Result Change Result Change

Production [tonQL/h]

9.999 9.984 -0.2 % 9.297 -7,0 %

Free CaO in product [wt.-%]

84.7 85,0 0.4 % 84.7 0.1 %

Flue gas CO2 [wt.-%]

20.2 19.9 -1.2 % 19.5 -3,0 %

Flue gas CO2 [tonCO2/tonQL] 1.39 1.38 -1,0 % 1.45 4.3 %

Flue gas CO2 [tonCO2/tonfreeCaO]

1.64 1.62 -1.4 % 1.71 4.2 %

Energy consumption [GJ/tonQL]

7.507 7.518 0.2 % 8.073 7.5 %

Energy consumption [GJ/tonfreeCaO]

8.868 8.843 -0.3 % 9.531 7.5 %

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Discussion

There is some discrepancy between the simulated results and the operational results related partly to the nature of the predictive simulation tool and partly to difficulties and inaccuracies in the full scale process measurements. The simulated product flow is usually higher than the operational data, e.g. 227 ton/h and 223 ton/h as in paper III. This discrepancy can be attributed to difficulties measuring clinker flows and to fact that no dust entrained in gases can be simulated while in the real case a significant amount of dust is transported with the gas. Furthermore in the simulations the ash is fully incorporated in the condensed product phase, while in e.g. rotary kiln quicklime production some ash probably exits the kiln entrained in the gas phase. There are also other build-ups in the kiln systems that are difficult to define and measure, but influences the full scale measurement results. There are discrepancies related to product quality as seen in paper II, where the simulated CaO content is 85 wt.-% while the operational result show 96 wt.-%. With the simulation tool all composition is described through equilibrium conditions while in the actual production processes full equilibrium is not reached. Therefore the actual quicklime product contains different phases than the simulation indicates. Here the operational data contain a SiO2 phase while in the simulation the SiO2 is fully reacted with CaO to C2S and C3S. For other parameters the validation results are better. In paper II the calculated flue gas stream at 48.59 ton/h differ by 0.98 ton/h (2.1 %) from operational data and the calculated product flow of 9.99 ton/h differ by 0.24 ton/h (2.3 %). In paper III the calculated burn zone temperature of 1399°C differs by 29°C (2.3 %) from operational data and the calculated kiln exit gas O2 concentration at 2.3 vol.-% differs with 0.1 vol.-% (4.2 %) from operational data. The results show that the temperature profile or other process conditions do not significantly change when substituting coal with KEO. The variations are within normal process fluctuations. Fuel efficiency and production capacity remain essentially unchanged. The nature of the equilibrium method is clearly shown in Table 13, where an increased ash load increases the product flow. The reduced ash load with increasing KEO feed gives an increase in product quality (+0.4 %) and the high hydrogen content of KEO decreases the CO2 concentration in the flue gas (-1.4 %). The fact that the coal has an ash high in SiO2 and Al2O3 explains the high amount of α´-C3S and C3A in the product, seen Figure 27. If, on the other hand, the ash would be low in SiO2 and Al2O3, such as the meat and bone meal ash, the effect on product quality would be different. The meat and bone meal contains insignificant amounts of SiO2 and Al2O3 which would reduce the amount of α´-C3S

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and C3A. However the meat and bone meal contains phosphorous and the quicklime product would be likely to contain an increased amount of Ca3(PO4)2 instead. The low AFT of sawdust, see Figure 24, has a significant impact on key properties of the process. The results in Table 14 show that at normal conditions, i.e. at 21% O2, the sawdust reduces production capacity (- 7.0 %) and energy efficiency (-7.5 %). On the other hand the low ash content has a positive effect on simulated product quality. The high moisture content of the sawdust increases the water content in the flue gas, which decreases the CO2 concentration as compared to the reference case. The specific emission of CO2 per ton of product increases (+ 4.3 %), but one must bear in mind that the sawdust is classified as 100 % biogenic, and 0 % fossil. Again, introducing KEO does not significantly impact key process parameters.�

3.3 Process simulation of oxygen enrichment in quicklime production In paper VI the effect O2 enrichment on the quicklime process is investigated with the simulation tool. Nine cases are simulated and the results are summarized in Table 15. In addition to the reference case two co-combustion scenarios are simulated, a fuel mix of coal and KEO, and one of coal and sawdust. The overall energy consumption is shown in Table 16.

Table 15 Simulation results for oxygen enrichment in quicklime production with different fuel mixes, changes as compared to coal reference case at 21 vol.-% O2.

Fuel mix 100 % coal 90 % coal + 10 % KEO

90 % coal + 10 % sawdust

O2 in combustion air [vol.-%] 23 25 21 23 25 21 23 25

Change in calcination zone temperature (%) -6.7 -6.1 0.2 -6.7 -6.1 7.2 -6.7 -6.1

Change in kiln exit gas temperature (%) -16.0 -17.3 0.5 -16.3 -17.8 18.0 15.8 -17.0

Change in product quality as free CaO (%) 0.6 0.8 0.4 1.0 1.2 0.1 1.0 1.2

Change in fuel consumption per ton product (%)

-14.7 -23.5 0.2 -16.2 -24.4 7.0 -14.1 -22.3

Change in production capacity (%) 14.7 23.5 -0.2 16.2 24.4 -7.0 14.1 22.3

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Table 16 Overall energy consumption for quicklime (QL) production, different fuels and O2 enrichment, 1) electricity consumption 0.1116 GJ/tonQL estimated average for long rotary kiln production (Schorcht 2013), 2) 99.5 vol.-% O2 at 1.044 GJ/tonO2 (Göttlicher 2004).

Fuel mix 100 % coal 90 % coal + 10 % KEO

90 % coal + 10 % sawdust

O2 in combustion air [vol.-%]

21 23 25 21 23 25 21 23 25

Production [tonQL/h] 10.0 11.7 13.1 10.0 11.9 13.2 9.3 11.6 12.9 Enrichment [kgO2/tonQL] 0 6 12 0 6 11 0 6 12 Fuel consumption [GJ/tonQL]

7.5 6.4 5.7 7.5 6.3 5.7 8.1 6.4 5.8

Electricity consumption [GJ/tonQL](1

0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1

Energy consumption O2 production [MJ/tonQL](2

0 7 12 0 7 12 0 7 12

Total energy consumption [GJ/tonQL]

7.6 6.5 5.9 7.6 6.4 5.8 8.2 6.6 6.0

Discussion

On the whole the effects of O2 enrichment are positive increasing production capacity and reducing specific energy consumption, see Table 15. Since the energy consumption of oxygen production is low compared to the energy consumption of quicklime production, the overall energy requirement for the oxygen enriched quicklime process is lower than the for conventional production process, see Table 16. The results are discussed in more detail in paper VI. The results are in line with earlier published work. Together the enhanced heat transfer and reduced flue gas volume will enable increased energy efficiency and production capacity for a rotary kiln (Wrampe 1976, Kudrina 1979). The process and the enrichments results are similar to that of the pulp mill lime mud recovery kiln (Garrido 1982, Watkinson 1983).

3.4 Process simulation of oxygen enrichment in cement clinker production

Paper III investigates the effects of oxygen enrichment on the cement clinker process. Some key findings can be seen in Table 17 and Table 18.

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Table 17 Simulation results for oxygen enrichment in cement clinker, product quality.

Compound [wt.-%] Reference O2 enrichment C3S 65.2 66.5 C2S 11.7 10.7 C3AF + C3A 14.6 14.5 CaO 0.6 0.6 MgO 2.5 2.5 K2SO4 + Na2SO4 2.3 2.3 K2O + Na2O 0.6 0.5 CaSO4 1.7 1.6 CaTiO3 0.5 0.5 CaK2(SO4)2 0.4 0.4 Total 100.0 100.0 �

Table 18 Overall energy consumption for O2 enrichment in cement clinker production, CC = cement clinker, 1) at 1500 Nm3

O2/h, 2)�Estimated consumption of thermal energy 3.5 GJ/tonCC, 3)�Estimated consumption of electricity 72 kWh/tonCC (cement grinding excluded), 4) 99.5 vol.-% O2 at 1.044 GJ/tonO2 (Göttlicher 2004).

Reference O2 enrichment Production [tonCC/h] 223 262 O2 enrichment [tonO2/tonCC](1 0 0.01 Energy consumption [GJ/tonCC](2 3.50 3.09 Electricity consumption [GJ/tonCC](3 0.26 0.26 Energy consumption O2 production [GJ/tonCC](4 0 0.01 Total energy consumption [GJ/tonCC] 3.76 3.36

Discussion

The simulation results show that for a cement clinker process with a raw meal feed of 335.5 t/h the addition of 1500 Nm3/h of oxygen reduces the kiln exit gas temperature and allows for 8% more fuel to be added to the calciners. This in turn allows for an increase of raw meal feed without reducing product quality, see Table 17. The temperature profile of the process changes, the exhaust gas temperature decreases and consequently the heat losses are reduced. The results from the full-scale O2 enrichment test showed an increase of 20 % in production capacity. However, the specific energy consumption increased by 2 %. Lack of experience with O2 enrichment and the short test period may explain this unexpected result. The conclusion is that the process was not optimized during the test and that at stable operating conditions O2 enrichment would reduce the specific energy consumption.

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Overall the simulation results, showing increased production capacity and improved energy efficiency, are in line with published literature (Mayes 2001, Gotro 2001, Shafer 2001). Since the energy consumption of oxygen production is low compared to the energy consumption of cement clinker production, the overall energy requirement for the oxygen enriched cement clinker process is lower than the for conventional production process, see Table 18. The simulation tool utilized in this work does not fully account for events with substantial kinetic elements, such as NOx formation. Utilizing oxygen to increase flame temperatures will effect NOx emissions from both quicklime and cement clinker production (Mayes 2001). The application method, e.g. by lancing or by pre-mixed burner feeding, will affect the outcome. CFD simulation studies on O2 enrichment in cement clinker production have been conducted (Marin 2001). Marin also studied the effect on dusting in a rotary kiln producing cement clinker suggesting that oxygen enrichment might allow for an increase of dust insufflation through the flame for temperature control.

3.5 Simulation of CO2 capture and storage through mineral carbonation applied to quicklime production

In this work paper I considers the case of mineral carbonation applied to lime kiln flue gases. The raw material feed for the carbonation process is Hitura serpentinite rock, containing Mg3Si2O5(OH)4, FeO, and CaSiO3. In addition to the serpentinite rock, the suitability of a limestone quarry secondary product was evaluated for the carbonation process. The secondary product is diopside based and contains CaFeSi2O6, KAlSi3O8, NaAlSi3O8/CaAl2Si2O8, KAl2(AlSi3O10) (F, OH)2, and (Mg5Al)(AlSi3)O10(OH)8. The results summarized in Figure 28. The study also shows that the diopside has low reactivity, requires high extraction temperatures and has low CO2 capture capacity as compared to the serpentinite.

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Figure 28 Direct carbonation of lime kiln flue gases with an integrated serpentinite carbonation process /I/. Discussion

The capture process is designed as a retrofit in the flue gas system of the rotary kiln and would not influence the quicklime production process. AspenPlusTM was used to simulate an integration of the carbonation process and the lime kiln off gases to achieve, not maximum CO2 capture, but full utilization of lime kiln waste heat. The quicklime process was not simulated. The carbonation process comprise of a recoverable ammonium sulphate salt used to extract Mg from grinded serpentinite rock. The dissolution proceeds in several steps and the product Mg(OH)2 is carbonated to MgCO3 by the lime kiln flue gas CO2 in a pressurized fluidized bed reactor at 80 bar. The integration with the lime kiln allows for utilization of secondary heat and the energy consumption of 0.7 GJ/tonCO2 captured is related to crushing and grinding of the serpentinite and to the compression on gases. The results show that at full integration with the kiln process, 0.55 ton/h of serpentinite gives a capture potential of 0.19 tonCO2/h. As seen in Figure 28 the process produces 0.38 ton/h of MgCO3 and 0.34 ton/h of secondary products. The utilization of secondary products and the final use of the MgCO3 have not been solved though. Besides ground construction, cement clinker and iron production are possible

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recipients of the secondary products. The MgCO3 must be utilized in a way that does not cause decomposition followed by the release of the captured CO2. The results also show that the diopside raw material is not suitable to the proposed carbonation path. The main reason is the low reactivity and the low Mg content. Furthermore the high extraction temperature required, makes the relatively low gas temperatures of the lime kiln inadequate.

3.6 Process simulation of CO2 capture through oxyfuel combustion in quicklime production

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For quicklime production the effect of flue gas recirculation levels on the combustion with pure O2 instead of air, was studied in paper V. The main results are presented in Table 19, Table 20 and Figure 29. Furthermore the results show that the dry product gas consists of more than 94 vol.-% CO2.

Table 19 Simulation cases and temperature profile results for oxyfuel combustion in quicklime production.

Kiln temperatures

Case Energy input Recirculation

Burn zone [°C]

Calcination zone [°C]

Preheating zone [°C]

A 100 % 0 % 940 784 532 B 100 % 50 % 1 774 979 660 C 100 % 60 % 1 559 987 709 D 100 % 70 % 1 363 967 742 E 100 % 80 % 1 229 936 783 F 90 % 50 % 1 085 842 556 G 90 % 60 % 860 753 538 H 90 % 70 % 842 760 572 I 90 % 80 % 839 796 647

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Figure 29 Simulated results of quicklime product quality for different oxyfuel cases, main compounds in mol fraction.

Table 20 Overall energy consumption of an oxyfuel quicklime process, QL = Quicklime, 1) electricity consumption 0.1116 GJ/tonQL estimated average for long rotary kiln production (Schorcht 2013) 2) 99.5 vol.-% O2 at 1.044 GJ/tonO2 (Göttlicher 2004), drying and compression of CO2 gas not included.

Reference Oxyfuel Production [tonQL/h] 8.5 8.5 Energy consumption [GJ/tonQL] 7.0 6.3 Electricity consumption [GJ/tonQL](1 0.1 0.1 Oxygen feed [tonO2/h] 0 5.6 Energy consumption O2 production [GJ/tonQL](2 0.0 0.7 Total energy consumption [GJ/tonQL] 7.1 7.1

Discussion

The application of oxyfuel influences the temperature profile of the kiln, see Table 19. If the recirculation is too low the heat load on the kiln is too high and there will be a significant melt phase in the product stream, cases B and C, see paper V. If on the other hand the recirculation is too high the temperature in the kiln will drop to the extent that full product quality cannot be achieved, as for cases H and I in Figure 29. The results show that recirculating the hot flue gas increases the thermal energy efficiency of the kiln and allows full product quality with a 10 % reduction of fuel

A B C D E F G H ISiO2 (l) 0,00 0,03 0,01 0,00 0,00 0,00 0,00 0,00 0,00CaO (l) 0,00 0,09 0,06 0,00 0,00 0,00 0,00 0,00 0,00Al2O3 (s) 0,00 0,01 0,01 0,00 0,00 0,00 0,00 0,00 0,00C3A (s) 0,01 0,00 0,00 0,01 0,01 0,01 0,01 0,01 0,01C3S (s) 0,00 0,00 0,01 0,03 0,00 0,00 0,00 0,00 0,00C2S (s) 0,03 0,00 0,00 0,00 0,03 0,03 0,03 0,03 0,03CaCO3 (s) 0,00 0,00 0,00 0,00 0,00 0,00 0,00 0,04 0,11CaO (s) 0,96 0,87 0,90 0,96 0,96 0,96 0,96 0,92 0,85

0,75

0,80

0,85

0,90

0,95

1,00C

ompo

nent

s in

pro

duct

[m

ol f

ract

ion]

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energy input. If, however, the energy consumption of the oxygen production is included the overall consumption remain unchanged, see Table 20. This means that the CO2 is captured at close to zero energy penalty. The system has not yet been optimized for different O2 concentrations in the feed oxidizer gas. It is possible that optimization of the kiln process and the oxygen feed can further reduce the energy consumption. Lowering the concentration of the O2 in the feed gas will reduce the energy requirement for O2 production but increase the N2 load on the kiln and concentration in the flue gas, thus affecting energy efficiency and CO2 quality with regards to storage or utilization. The dry product gas consists of more than 94 vol.-% CO2, which is deemed suitable for storage or utilization. It is possible that the concentration of CO2 could be lowered, e.g. if utilizing low grade O2, and still be suitable for storage or utilization.

3.7 Process simulation of CO2 capture through oxyfuel combustion in cement clinker production

Oxyfuel in cement clinker production is investigated in paper IV. Full oxyfuel and partial oxyfuel scenarios are simulated at varied recirculation levels. Results from the full oxyfuel simulations can be seen in Figure 30, and from the partial oxyfuel simulations in Figure 31. The overall energy consumption of the simulated cases is presented in Table 21.

Figure 30 Simulation results of flue gas composition for different recirculation levels at full oxyfuel cement clinker production /IV/.

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Figure 31 Simulation results of flue gas composition for different recirculation levels at partial oxyfuel cement clinker production /IV/. �

Table 21 Overall energy consumption for oxyfuel in cement clinker production. CC = cement clinker, 1) 99.5 vol.-% O2 at 1.044 GJ/tonO2 (Göttlicher 2004), 2) Estimated 72 kWh/tonCC, cement grinding excluded (Schroht 2013), 3) drying and compression of CO2 gas not included. �

Reference Full

oxyfuel Full

oxyfuel Partial oxyfuel

Energy consumption production [GJ/tonCC] 3.0 3.0 3.0 3.1 Flue gas recirculation [%] 0 60 80 20 O2 feed [tonO2/tonCC](1 0 0.23 0.23 0.10 Electricity (GJ/tonCC)(2 0.26 0.26 0.26 0.26 Total energy consumption [GJ/tonCC] 3.3 3.5 3.5 3.5 CO2 captured [ton/h] 0 44.3 39.6 41.8 Energy consumption CO2 capture [GJ/tonCO2](3 0 0.01 0.01 0.01

Discussion

In the full oxyfuel scenario the clinker cooler is redesigned to a two-stage system, where air is used for the final cooling and then vented, having a negative effect on energy efficiency. The O2 is fed into the primary cooler and distributed with the

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recirculated flue gases to the burners. The reference case is illustrated by Figure 7, section 1.3, and the full oxyfuel is illustrated in Figure 32. For the full oxyfuel scenario recirculation is varied from 20 – 80 %. The influence on the product gas can be seen in Figure 30. The CO2 concentration increases when oxyfuel is applied and the dry product gas contains approximately 90 vol.-% CO2 independent of recirculation rate. At 20 % recirculation, which has the highest equilibrium temperature, the lowest content of C3S was obtained in the final product, see paper IV. The reason for this is expected to be the high temperature that destabilize C3S and increases the amount of oxide melt in the uncooled product. At 60 % recirculation the rotary kiln burn zone temperature is close to the conventional reference case. At 80 % recirculation the temperature seems to be optimal for this raw material, with the highest C3S and lowest free CaO concentrations.

Figure 32 Simplified schematics of full oxyfuel in cement clinker production. The partial capture scenario is motivated by the fact that retrofitting the cement clinker production process for full oxyfuel would be an extensive project with many uncertainties. The process is redesigned to separate the kiln burner and the pre-calciner burners. The tertiary air, recovering pre-heated air from the clinker cooler to the pre-calciners is cut off, reducing energy efficiency, see Figure 33. The kiln burner operates at normal air fired conditions and the N2 rich flue gas is directed directly into one of the suspension heater strings bypassing the pre-calciner. The pre-calciner burners are operated at oxyfuel conditions and the CO2 rich flue gases are separated

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in the second suspension heater string and recirculated to the pre-calciners. When the simulation input is iterated so that complete calcination is achieved in the pre-calciners and only the clinkering reactions take place in the rotary kiln, the process setup captures the CO2 from the pre-calciner fuels and the raw material carbonates, representing 84 % of the total CO2 emissions. The residual 16 %, originating from the kiln burner is vented with the N2 rich flue gases from the kiln. The results in Figure 31 show that the composition of the N2-string flue gases remain close to the reference case gases and that the CO2-string product gas is high in CO2. Again the recirculation level does not significantly influence the compositions and the dry product gas CO2 concentration is approximately 98 vol.-%.

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Figure 33 Simplified schematics of partial oxyfuel combustion in cement clinker production. Cutting off the tertiary air, recovering heat from the clinker cooler to the pre-calciners, has a negative effect on energy efficiency. At 20 % recirculation the specific energy consumption is 3.1 GJ/tonclinker, compared to 3.0 GJ/tonclinker in the reference case. Increasing the recirculation to 40 % increases the energy consumption to 3.3 GJ/tonclinker, see paper IV As seen in Table 21 the overall energy consumption increases for both full and partial oxyfuel operations. However the energy penalty related to CO2 capture is still low

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compared to conventional amine technology, which has an energy consumption of 2.6 GJ/ton of captured CO2.

3.8 Dynamic rate thermogravimetry for lime kiln feed limestone characterization

In paper VII the decomposition event of four industrial limestone is investigated by comparing conventional constant heating rate and dynamic rate thermogravimetric methods. The materials investigated are two very high purity high calcium limestone (samples A and D), one dolomitic limestone (sample B), one high calcium limestone with minor quartz and dolomite phases (sample C), and one dolomite with only a minor calcite phase (sample E). The results from XRD can be seen in Table 22. Experimental parameters are found in Table 23 and the results are summarized in Table 24. �

Table 22 Results from XRD analysis of samples A to E. �

Sample Phase A B C D E Calcite, CaCO3 99 88 97 99 0.5 Dolomite, CaMg(CO3)2 12 1 99.5 Quartz, SiO2 2 Sum: 99 100 100 99 100 �

Table 23 Experimental parameters for thermal analysis. DR = dynamic heating rate TG. CR = constant heating rate TG. DR with 100 µl Al2O3 crucibles with empty reference crucible. CR with 90 µl Al2O3 crucibles with empty reference crucible, No. = experimental run, S = sample, M = method.�

No. S M Mass [mg]

DR resolution

setting

Heating to 1000°C

[°C/min]

Isothermal at 1000°C

[min]

Purge gas Sample [/min]

Purge gas Balance [/min]

1 A DR 21.6 3 50 - 10ml N2 25ml N2 2 B DR 26.9 3 50 - 10ml N2 25ml N2 3 C DR 22.9 3 50 - 10ml N2 25ml N2 4 D DR 24.6 3 50 - 10ml N2 25ml N2 5 A CR 22.4 - 20 1 - 100ml N2 6 B CR 27.1 - 20 1 - 100ml N2 7 C CR 22.5 - 20 1 - 100ml N2 8 D CR 23.0 - 20 1 - 100ml N2 9 A DR 20.3 0.5 50 - 10ml N2 25ml N2

10 A DR 21.9 6 50 - 10ml N2 25ml N2 11 A DR 25.3 3 80 - 10ml N2 25ml N2 12 A DR 28.2 3 20 - 10ml N2 25ml N2 13 B DR 18.2 4 50 - 10ml N2 25ml CO2 14 B DR 18.0 4 50 - 10ml N2 25ml N2 15 E DR 6.4 4 50 - 10ml N2 25ml CO2 16 E DR 18.6 4 50 - 10ml N2 25ml N2

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Table 24 Summary of results for TG comparison of selected parameters for limestone samples A-D: S = sample, R = reaction: (1) CaCO3 (s) → CaO (s) + CO2 (g), (9) 2 CaMg(CO3)2 (s) � CaCO3 (s) + CaO (s) + 2 MgO (s) + 3 CO2 (g) and (10) CaMg(CO3)2 (s) � CaO (s) + MgO (s) + 2 CO2 (g). The dolomite decomposition is discussed in /VII/. No. = experimental run, DR = dynamic heating rate TG. CR = constant heating rate TG. Tonset = onset temperature of decomposition reaction [°C]. f’ = first derivative with regards to temperature (T) and time (t). Tmax = temperature at peak maximum. Rate = rate of decomposition event with regards to temperature [%/°C] and time [%/min]. End = end of experiment, Avg. = average, s.d. = standard deviation. �

f’(T) f’(t)

S R No. M Tonset [°C]

Tmax [°C]

Rate at Tmax [%/°C]

Tmax [°C]

Rate at Tmax [%/min]

tend [min]

A 1 1 DR 748 780 0.93 781 7.30 23 5 CR 757 818 0.51 825 9.92 43

B 1,

9-10 2 DR 745 777 0.81 780 6.96 24 6 CR 750 816 0.47 821 9.12 42

C 1,

9-10 3 DR 748 785 0.62 786 6.25 24 7 CR 756 822 0.42 824 8.35 43

D 1 4 DR 751 795 0.68 792 6.50 24 8 CR 752 835 0.43 837 8.56 44

A-D Avg. ± s.d.

1-4 DR 748 ± 2

784 ± 7

0.76 ± 0.12

785 ± 5

6.75 ± 0.41

24 ± 0.5

5-8 CR 754 ± 3

823 ± 7

0.46 ± 0.03

827 ± 6

8.99 ± 0.61

43 ± 1

Discussion

The kiln feed limestone properties varies with the geological formation from which it is quarried or mined. Usually there are also significant variations within a deposit. Characterization of feed properties is necessary to achieve an optimized production. Some of the samples contain both a dolomite and a calcite phase, see Table 22. At pCO2 = 0, as in these experiments, the dolomite decomposes simultaneously with the calcite. The simultaneous decomposition of dolomite and calcite is considered as a single event. The decomposition of dolomite is further discussed in paper VII. The results in Table 24 show that there are significant differences between the kiln feeds. At most the onset temperatures of the decomposition temperature varies between 748 °C and 757°C, sample A. For all samples the conventional TG onset at 754 ± 3°C is higher than the dynamic rate TG onset at 748 ± 2°C. The maximum reaction rates described as (%/°C) and (%/min) occur at higher temperatures for constant heating rate TG at 823 ± 7°C and 827 ± 6°C than for dynamic rate TG at 784 ± 7°C and 785 ± 5°C.

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Since the residence time of the lime kiln is easy to control the decomposition rate as a function of time is considered. Comparing maximum decomposition rates in (%/min), as in Figure 34, illustrates the different calcination properties.

Figure 34 The maximum decomposition rates and the corresponding temperatures for lime kiln feeds A-D /VII/. The results can be utilized when defining kiln feed fractions, when mixing different kiln feed or when preparing to switch between kiln feed. For example mixing the same fraction of feed A and D will result in a partly over burned and a partly unburned product stream. Decomposition of kiln feed A starts at a slightly lower temperature, 748°C as compared to D at 751°C. During decomposition feed A reaches a higher decomposition rate, 7.3 %/min, compared to D at 6.5 %/min. Furthermore feed A reaches the maximum decomposition rate at a lower temperature, 781°C, compared to D at 792°C. Applied to rotary kiln production the A and D fractions would be fully mixed and could not be separated to representable quicklime product samples. A key operational parameter in rotary kiln production is the residual CO2 content in the product stream. Kiln feed A will have a lower residual CO2 and a possibly a high degree of sintering and low reactivity, while kiln feed D will have a higher residual CO2 with less sintering and possibly a higher reactivity (Commandré 2007). To compensate the different calcination properties the fractions of the kiln feeds can be adjusted, so that the faster feed, here A, is fed as a coarser, e.g. 20 – 40 mm fraction and the slower feed, here D, is fed in a finer fraction e.g. 10 – 30 mm. �

0

2

4

6

8

10

12

770 780 790 800 810 820 830 840

Max

imum

rat

e [%

/min

]

Temperature at maxiumum rate [�C]

Dynamic heating rate TG

Constant heating rate TG

B

A

CD

A

B

C D

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3.8.1 Effect of pCO2 on decomposition behavior of CaCO3

In the kiln processes pCO2 will change with position. Therefore the equilibrium temperatures are calculated at increasing pCO2. The result can be seen in Figure 35. The partial pressure of CO2 also influences the type of decomposition reaction. A medium purity industrial grade limestone (96 % calcite) is analyzed by dynamic rate thermogravimetry in air and in CO2 atmospheres. The results can be seen in Figure 36 and Figure 37.

Figure 35 As the decomposition of CaCO3 (blue) proceeds the pCO2 (green) in the kiln atmosphere increases. The increasing pCO2 influences the equilibrium temperature so that a higher temperature is needed to further the decomposition reaction (FactSage 2011).

0,00

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90%

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200 300 400 500 600 700 800 900 1000

Mol

fra

ctio

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O2

in g

as p

hase

Wei

ght [

%]

Temperature [�C]

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Figure 36 Onset temperatures determined by dynamic rate TG for an industrial limestone in Air (solid lines) and CO2 (dotted lines) on time axis. Weight (green) and temperature (blue). �

Figure 37 Onset temperatures determined by dynamic rate TG for an industrial limestone in Air (solid lines) and CO2 (dotted lines) on temperature axis. Weight (green) and temperature (blue).

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Discussion

In quicklime production with rotary kilns the CO2 content in the gas phase increases from 400 ppm in the combustion and cooling air up to 41 vol.-% in the kiln exit gas. The increase is a result of CaCO3 and CaMg(CO3)2 decomposition and oxidation of carbon in the fuel. Leakage air then decreases the stack gas composition to, usually, around 20-30 vol.-%. The case is similar for the cement clinker process although there the calcination usually occur prior to the kiln. The effect can be illustrated by the calculated equilibrium temperatures, as in Figure 35. Initially solid phase is 100 wt.-% CaCO3 and pCO2 = 0. As the decomposition starts pCO2 increases whereas a new equilibrium composition for CaO-CaCO3-CO2 is achieved. As the pCO2 increases a higher temperature is required to further the decomposition. The thermogravimetric onset points of the decomposition, Figure 36, can be used to illustrate the phenomenon. The extrapolated onset temperatures are, 691°C in air (400 ppm CO2) and 899°C in CO2. The temperatures are higher than the equilibrium temperature in Figure 13 section 1.4.1. At pCO2 = 1 the TG onset temperature at 899°C is close to the equilibrium temperature at 893°C. The partial pressure of CO2 also influences the type of decomposition reaction. At low pCO2 the reaction proceeds with a gradual onset and at high pCO2 as a threshold reaction. The slope of the weight change curves in Figure 36 and Figure 37 show the reaction rate as the temperature is held near constant. At high pCO2 the rate is initially fast and at low pCO2 (Air) the rate is slow.

3.8.2 The effect of dynamic rate experimental settings

Since results from applying dynamic rate TG as a tool for limekiln feed characterization has not been published before the effects of different experimental settings are studied in more detail. The heating rate and resolution setting were varied in an experimental series with a very high purity high calcium limestone intended for quicklime production, sample A Table 22. The overall results can be seen in Figure 38 and Figure 39. The detailed results for varied heating rate at constant resolution, can be seen in Figure 40, and the detailed results for varied resolution at constant heating rate, can be seen in Figure 41. A summary of the result is presented in Table 25.

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Figure 38 Obtained temperature-time profiles at different dynamic rate TG experimental parameters, experimental runs No. 1, 9-12, see Table 23.

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Figure 39 Thermal decomposition of sample A at different experimental setup for dynamic rate TG, weight (green), 1st derivate of weight with respect to temperature (blue), experimental runs No. 1, 9-12, see Table 23.

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Figure 40 Dynamic rate TG at varied heating rate and constant resolution setting, experimental runs No. 1, 11 and 12, see Table 23, weight signal (blue) and temperature (green) on time axis, onset temperatures and time at onset. �

Figure 41 Dynamic rate TG at varied resolution setting and constant heating rate, experimental runs No. 1, 9 and 10, Table 23, weight signal (blue) and temperature (green) on time axis, onset temperatures and time at onset. �

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Table 25 Summary of results for variation of heating rate and resolution setting for dynamic rate TG. Sample A, decomposition reaction (1). Selected parameters. No = experimental run, see Table 23, Res. Setting = resolution setting, Tonset = onset temperature of decomposition reaction [°C]. f’ = first derivative with regards to temperature (T) and time (t). Tmax = temperature at peak maximum. Rate = rate of decomposition event with regards to temperature [%/°C] and time [%/min]. End = end of experiment.

f’(T) f’(t)

No Res. setting

Heating rate

[°C/min] Tonset [°C]

Tmax [°C]

Rate at Tmax

[%/°C] Tmax [°C]

Rate at Tmax

[%/min] tend

[min] 1 3.0 50 748 780 0.93 781 7.30 23 9 0.5 50 776 846 0.46 847 18.9 18

10 6.0 50 640 647 2.85 648 0.4 157 11 3.0 20 733 770 0.84 770 4.9 47 12 3.0 80 762 793 0.94 794 8.6 16

Discussion

To study the effect of dynamic rate TG experimental parameters the heating rate and the resolution setting were varied in an experimental series with sample A, experimental runs No.1 and No. 9-12, see Table 23. For further details se paper VII. The obtained temperature-time profiles at different experimental setup, seen in Figure 38, and decomposition event profiles, seen in Figure 39, show significant variation. At high resolution (No. 10) the temperature remains near constant for more than 120 minutes as the decomposition slowly progresses. At low resolution (9) the method comes close to constant heating rate TG. Shown in in Figure 40 three experiments were run at constant resolution 3.0 with different heating rates, 20, 50 and 80°C/min. Note that in dynamic rate TG the heating rate is constantly varied during the decomposition reaction and that the heating rate setting is the maximum heating rate applied, compare Figure 38. The results show that by varying the heating rate at constant resolution the onset temperature is affected. A low heating rate gives a lower onset temperature and increases the experimental time. Shown in Figure 41 three experiments were run at a constant heating rate setting of 50°C/min with different resolution, 0.5, 3.0 and 6.0. The experimental run at resolution 0.5 achieves near constant heating rate conditions all through the experiment. This is expected since the resolution setting 0.0 would correspond to the conventional constant heating rate TG. The results show that increasing the resolution setting increases the experimental time. The resolution setting has a significant effect on the extrapolated onset temperature, where a lower resolution gives a higher extrapolated onset temperature.

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4 Conclusions Limestone based products provides valuable services to society. It is the conclusion of this thesis that several measures are available to increase the sustainability of the industry. On a local level there are many potential sustainability issues that in general can be solved by commercially available technology. On a global level the main sustainability issue is the accelerated transport of carbon from the geosphere to the atmosphere, through emissions of fossil CO2, and its contribution to climate change and ocean acidification. Although many CO2 abatement technologies have been suggested none has been applied in full scale to quicklime or cement clinker production. Through a literature review, full-scale trials and the use of a predictive simulation tool the following paths to reduce the specific CO2 emission related to quicklime and cement clinker production have been discussed: fuels and co-combustion, oxygen enrichment, and CO2 capture through oxyfuel combustion. Furthermore mineral carbonation as a method for post combustion capture and storage of CO2 has been studied. In addition a new thermogravimetric method is evaluated for kiln feed characterization. The fuel has a significant impact on the production processes of quicklime and cement clinker. The adiabatic flame temperature together with the residual O2 content and temperature of the flue gas dominates the energy efficiency of the rotary kiln. The adiabatic flame temperature can be used to facilitate the successful application of new fuels and fuel mixes. The fuel ash interacts with the product influencing product quality and needs to be taken into account. In quicklime production a low fuel ash improves product quality while in cement clinker production the fuel ash can be utilized as part of the clinker product. Oxygen enrichment increases the flame temperature during combustion which enhances the heat transfer from the flame to the bed and thereby the energy efficiency of the kiln. The energy consumption is significantly reduced, even when the energy need for oxygen production is accounted for. Oxygen enrichment also decreases the nitrogen load on the kiln, contributing even further to an improved energy efficiency. Together these mechanisms allow for a significant increase in the production capacity of the kiln. Oxyfuel combustion applied to quicklime and cement clinker production will affect the energy efficiency of the processes. The outcome is dependent on process design. If a substantial amount of hot gas needs to be vented, e.g. from the product cooler, the

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energy consumption will increase, otherwise the recirculation of hot gases will improve the energy efficiency. The technology allows for near-zero emission production since the product gas is a highly concentrated carbon dioxide suitable for storage or utilization. When the energy requirement for oxygen production is accounted for the produced CO2 is captured at a significantly lower energy penalty, compared to the conventional post-combustion capture processes. If applied the flue gas circulation rate need to be controlled to ensure operating conditions. Mineral carbonation with a serpentinite raw material integrated to a lime kiln could allow for emission reductions. The process would produce a magnesium carbonate that cannot be allowed to decompose, if carbon storage is to be achieved. Optimized for partial capture of flue gas CO2 the process would sequester CO2 at a low energy consumption as compared to conventional post-combustion capture processes. Dynamic rate thermogravimetry can be used to characterize decomposition behavior of kiln feed materials. The characterization facilitates mixing of limestone feed fractions and qualities, while improving quicklime product quality. A controlled feed also improves kiln operations. By adjusting experimental parameters the method can be fitted to specific kilns. The results of this work contribute to the long-term development of the industry. If the new technologies are successfully implemented the limestone based industry moves towards increased sustainability and eventually towards near-zero emission production of quicklime and cement clinker. It must be noted that the economic viability of the studied measures will vary with location and over time, and have not been evaluated.

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5 Future work Future work comprise of further investigating the effect of O2 on the processes. The oxyfuel technology still needs assessment and optimization. In this work the oxygen feed has been of high purity. Since the energy cost for oxygen production decrease with decreasing purity the optimization of the purity of oxygen as regards to process parameters and flue gas composition is of interest. The technology has not been tested and pilot/demonstration will be required prior to deployment. It needs to be stressed that access to a CO2 storage network, not readily available today, will probably be required before full scale deployment. The process simulation tool will be utilized to study the impact of alternative raw materials. The high quality requirements increase the benefits of simulation prior to testing and full scale operation. Simulation can significantly reduce costs related to trial and error. Developing predictive features for dusting in the kiln processes would make the simulation results more accurate with respect to the actual process, furthermore valuable insight in kiln circulation phenomenon could be obtained. The mineral carbonation technology investigated is highly experimental and pilot scale demonstration will be required prior to deployment. The issue of the use of the primary and the secondary products also need to be addressed. The application of dynamic rate TG for kiln feed characterization has not been demonstrated at full scale. After full scale evaluation the technology is estimated to be ready for deployment.

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6 Acknowledgements I would like to thank my family Ella and Lise for adding light and joy to my life, and Ritva, Bo-Erik, Robert and Marita for all the love and support over the years. The following persons are gratefully acknowledged for their support and contributions: Rainer Backman, Bodil Hökfors and Dan Boström at Umeå University. Kjell Dahlberg at Nordkalk Oy Ab. Bo-Erik Eriksson, Stefan Sandelin, Erik Viggh, Anders Lyberg and Thomas Lind at Cementa AB. Jan Bida and Marianne Thomaeus at MinFo. Inês Romão, Johan Fagerlund and Ron Zevenhoven at Åbo Akademi University. Robert Eriksson is acknowledged for valuable discussions when finalizing this thesis. Additional support by Lars Backman and Lars Lövgren at Umeå University is acknowledged. The following persons need to be acknowledged for the valuable discussions and lessons provided relating industrial operations and limestone based processes, be it quicklime, cement clinker or other. The list is long but I have learned a lot. In no specific order: Kenneth Fjäder, Stig Nilsdorff, Jyrki Linke, Thomas Nyberg, Erja Kilpinen, Susanne Åhlström-Dahl, Mikael Wendel, Synnöve Hollsten, Tarmo Tuominen, Markus Fagervik, Sampsa Sysilä, Ulla Koponen, Kalevi Jernström, Roger Hellbom, Tua Welin, Gerhard Hakkarainen, Ola Thuresson, Riikka Hynynen, Vesa Laakso, Göran Sandström, Harry Jansson, Esa Tikka and Jarkko Kaplin at Nordkalk. Johan Larsson at Cementa. Risto Kiilakoski, Heikki Tuomikoski, Matti J. Rautio, Tarmo Flygare, Olavi Hailuoto, Nina Viirret, and Jaakko Kärjä at what was then Rautaruukki. Per Arne Nilsson at Panaware. Leif Norlander at SMA Minerals. Ziad Habib at Lhoist. Esa Suoninen and Eva-Katrin Lindman at Fortum. Marcel Magnusson at Mefos. Tommi Niemi at AGA. Hanne Markussen Eek, Sten Solum, Unni Nilsen Kristoffersen and Juan Rojas Ruiz at Franzefoss Minerals. Pertti Koukkari, Karri Penttilä, Sebastian Teir and Matti Nieminen at VTT.�Björn F. Möller at Eon.�Clas Ekström at Vattenfall� Erik Palmlöv and Torgny Berglund at OPAB. Freddie Linder at Preem. Kim Kärsrud at SSAB. Sture Boström and Kenneth Eriksson at ProcessFlow.� Stefan Grönkvist at KTH. Peter Backman at Åbo Akademi University. And last but not least, thanks to all the boys, who over the years have taught me a thing or two on how to burn limestone and operate limekilns: Jan-Erik Hinders and co. at the Pargas lime plant, Arto Aakko and co. at the Raahe lime plant, Marius Karlsaune and co. at the Verdal lime plant.

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The following financial support is gratefully acknowledged: The Swedish Governmental Agency for Innovation Systems, Vinnova (No. 2014-04073 and 2015-02519), The National (Swedish) Strategic Research Program Bio4Energy, the Swedish Energy Agency (No. 2006-06679/30527-1), Cleen Oy Ab and the Finnish Funding Agency for Technology and Innovation, TEKES, for support via the CCSP project (2011-2015) and Nordkalk Oy Ab. The Swedish Mineral Processing Research Association (MinFo) is gratefully acknowledged for project support.

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8 Appendices

8.1 Appendix 1: Chemical quality requirements for industrial limestone

LS= limestone, LOI = loss on ignition, 1)H2O: 0.77 %, K2O: 0.33 %, Na2O: 0.05 %, TiO2: 0.06 %, 2)H2O: < 0.05 %, 3)K2O

< 0.3 %, Na2O: < 0.3 %, 4)K2O: < 3.5 %, Na2O: < 1.5 %, P2O5: < 0.8 %, TiO2: < 0.7 %, 5)K2O: < 0.01 %, Na2O: < 0.01 %,

6)CaCO3 equivalents > 80, 7)H2O: < 0.5 %, 8)CaO + MgO > 95 % and SiO2 + Fe2O3 + Al2O3 < 3 % at LOI = 0, 9) CaO +

MgO > 90 % at LOI = 0, 10) CaCO3 + MgCO3 > 97 %�

Compound [wt.-%] Al2O3 CaO Fe2O3 MgO SiO2 Reference Average limestone(1 0.81 42.57 0.54 7.89 5.19 Weast 1989 Blast furnace < 2.08 < 0.40 < 4.23 < 7.88 Murari 1984 Blast furnace < 2.49 < 0.41 < 4.95 < 8.62 Murari 1984 Blast furnace < 2.49 < 0.41 < 4.95 < 8.62 Murari 1984 Steel melting shop < 1.25 < 0.31 < 3.47 < 3.86 Murari 1984 Sinter < 2.86 < 0.41 < 4.30 < 9.34 Murari 1984 Blast furnace < 1.40 < 0.33 < 19.31 < 5.06 Murari 1984 Steel melting shop < 1.50 < 0.23 < 19.37 < 4.96 Murari 1984 Soda ash > 55.2 Harrison 1993 Sugar refining < 0.35 > 53.8 < 0.3 < 1 Harrison 1993 Glass > 55.2 < 0.07-0.18 Harrison 1993 FGD > 50.4 Harrison 1993 FGD < 0.05 > 53.2 < 0.15 < 0.15 Harrison 1993 Filler < 0.3 > 53.8 < 0.08 < 0.72 < 1.2 Övereng 1996 Filler marl > 53.2 < 1.43 Övereng 1996 Agriculture > 54.4 < 0.96 Övereng 1996 US glass < 0.08 > 54.9 < 0.12 < 0.62 < 0.15 Övereng 1996 PCC filler > 55.1 < 0.1 < 0.33 < 0.05 Övereng 1996 Shell sand 0.2 > 53.8 < 0.1 < 0.48 < 0.5-1.5 Övereng 1996 Quicklime < 0.12 > 55.4 < 0.04 < 0.5 < 0.34 Övereng 1996 Filler < 0.05 > 54.9 < 0.02 < 1.12 < 0.11 Övereng 1996 Filler chalk < 0.17 > 54.5 < 0.1 < 0.22 < 1.82 Övereng 1996 Filler calcite < 0.01 > 55.2 < 0.03 < 0.21 < 0.69 Övereng 1996 Pharmaceuticals > 54.9 < 0.05 Övereng 1996 Sugar refining > 55.2 Övereng 1996 Cement clinker > 36.4 < 4.0-5.0 Övereng 1996 Quicklime > 54.9 Övereng 1996 Plate glass(2 < 0.35 > 54.8 < 0.075 < 0.8 Övereng 1996 Portland-LS cement > 42.0 Tennis 2011 Portland-LS cement(3 < 1.50 > 50.0 < 0.80 < 0.8 < 5.0 Gudissa 2010 Cement clinker(4 0.1-20 20-55 0.2-5.9 0.2-6 0.5-50 Schorcht 2013 White cement clinker < 0.15 < 0.015 Schorcht 2013 Quicklime(5 0.27 54.94 0.09 0.91 0.3 Schorcht 2013 Glass 0.23 54.8 0.095 1.3 0.56 Freas 2006 Agricultural(6 44.8 ASTM C 602 Animal feed(7 > 44.8 < 1.0 ASTM C 706 Coal mines < 5.0 < 4 ASTM C 737 Sulfite pulp(8 > 95 < 3 ASTM C 911 Waste treatment(9 > 90 ASTM C 911 Cement 0.41 54.84 0.41 0.2 1.14 Khan 2004 Sugar refining Khan 2004 Ceramics Khan 2004 Pottery 0.3 Khan 2004 CaSi alloy 91-97 Oates 1998 Agricultural < 15 Oates 1998 Blast furnace(10 > 97 Oates 1998

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8.2 Appendix 2: Development of simulation database, lists of compounds

8.2.1 Selected gas phase compounds, Papers II - VI

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Compounds (56), Papers II and VI Al (g) Al2 (g) Al2O (g) AlCl (g) AlCl2 (g) AlCl3 (g) AlO (g) AlO2 (g) AlS (g) C (g) CH4 (g) CO (g) CO2 (g) COS (g) CS2 (g) Ca (g) CaCl (g) CaCl2 (g) CaO (g) CaOH (g) Ca(OH)2 (g) CaOH (g) CaS (g) Cl (g) Cl2 (g) Fe (g) FeCl (g) FeCl2 (g) FeO (g) Fe(OH)2 (g) FeS (g) H (g) H2 (g) H2S (g) H2SO4 (g) HCl (g) K (g) K2 (g) K2Cl2 (g) K2(OH)2 (g) K2SO4 (g) KCl (g) KOH (g) N2 (g) O (g) O2 (g) O3 (g) OH (g) S (g) S2 (g) SO2 (g) SO3 (g) Si (g) Si2 (g) SiCl (g) SiCl2 (g)

Compounds (52), Papers III, IV and V Al2O (g) AlO2 (g) C (g) Ca (g) CaCl2 (g) CaO (g) CH4 (g) Cl (g) Cl2 (g) CO (g) CO2 (g) COS (g) CS (g) Fe (g) (FeCl2)2 (g) (FeCl3)2 (g) FeCl (g) FeCl2 (g) FeCl3 (g) FeO (g) FeS (g) H2 (g) H2O (g) H2S (g) H2 (g) HCl (g) K (g) K2 (g) (KCl)2 (g) K2SO4 (g) KCl (g) MgCl2 (g) MgO (g) N2 (g) Na (g) Na2SO4 (g) NaCl (g) NaO (g) O (g) O2 (g) P (g) (P2O3)2 (g) (P2O5)2 (g) PO (g) PO2 (g) S (g) S2 (g) Si (g) SiO (g) SO (g) SO2 (g) SO3 (g)

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8.2.2 Selected pure solid compounds, Papers II and VI

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Compounds (71)

Al2Fe2O6 (s) Al2O3 (s) Al2S3O12 (s) Al2Si2O7 (s) Al2SiO5 (s)

Al6Si2O13 (s) AlCl3 (s) C (s) Ca2Al2SiO7 (s) Ca2Fe2O5 (s)

Ca2FeSi2O7 (s) Ca2SiO4 (s) �-Ca2SiO4(s) �’-Ca2iO4 (s) -Ca2SiO4 (s)

Ca3Al2O6 (s) Ca3Al2Si3O12 (s) Ca3Fe2Si3O12 (s) Ca3Si2O7 (s) Ca3SiO5 (s)

CaAl12O19 (s) CaAl2O4 (s) CaAl2Si2O8 (s) CaAl2SiO6 (s) CaAl4O7 (s)

CaCO3 (s) CaCl2 (s) CaFe2O4 (s) CaFe4O7 (s) CaFeSi2O6 (s)

CaO (s) CaSO4 (s) CaSiO3 (s) Fe2Al4Si5O18 (s) Fe2O3 (s)

Fe2S3O12 (s) Fe2SiO4 (s) Fe3Al2Si3O12 (s) Fe3O4 (s) FeAl2O4 (s)

FeCl2 (s) FeCl3 (s) FeO (s) Fe(OH)2 (s) Fe(OH)3 (s)

FeSO4 (s) FeSiO3 (s) K2Al12O19 (s) K2CO3 (s) K2Ca2(CO3)3 (s)

K2Ca2S2O12 (s) K2CaC2O6 (s) K2FeCl4 (s) K2O (s) K2SO4 (s)

K2SiO5 (s) K2Si4O9 (s) K2SiO3 (s) KAl9O14 (s) KAlCl4 (s)

KAlO2 (s) KAl(SO4)2 KAlSi2O6 (s) KAlSi3O8 (s) KAlSiO4 (s)

KCaCl3 (s) KCl(s) KFeCl3 (s) KFeCl4 (s) KOH (s)

SiO2 (s)

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8.2.3 Selected pure liquid compounds, Papers II - VI

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Compounds (22), Papers II and VI Al2O3 (l) CaAl2O4 (l) CaAl4O7 (l) CaCl2 (l) CaO (l) CaSO4 (l) Fe3O4 (l) FeCl2 (l) FeCl3 (l) FeO (l) H2O (l) H2SO4 (l) K2CO3 (l) K2O (l) K2SO4 (l) K2Si2O5 (l) K2Si4O9 (l) K2SiO3 (l) KAlO2 (l) KCl (l) KOH (l) SiO2 (l) Compounds (2), Papers III, IV and V H2O (l) CaSO4 (l)

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8.2.4 Selected pure solid compounds, Papers III, IV and V

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Compounds (156)

Al2(SO4)3 (s) Al2Fe2O6 (s) Al2O3 (s1) Al2O3 (s2) Al2O3 (s3)

Al2O3 (s4) Al2Si2O7 (s) Al2SiO5 (s1) Al2SiO5 (s2) Al2SiO5 (s3)

Al6Si2O13 (s) AlPO4 (s1) AlPO4 (s2) AlPO4 (s3) Ca2Fe2O5 (s)

Ca2FeSi2O7 (s) Ca2Mg2Al28O46 (s) Ca2MgSi2O7 (s) Ca2P2O7 (s1) Ca2P2O7 (s2)

Ca2SiO4(�) (s) Ca2SiO4(�’) (s) Ca2SiO4( ) (s) Ca3(PO4)2 (s1) Ca3(PO4)2 (s2)

Ca3Al2O6 (s) Ca3Al2Si3O12 (s) Ca3Fe2Si3O12 (s) Ca3MgAl4O10 (s) Ca3MgSi2O8 (s)

Ca3Si2O7 (s) Ca3SiO5 (s) Ca5HO13P3 (s) CaAl12O19 (s) CaAl2O4 (s)

CaAl2Si2O8 (s1) CaAl2Si2O8 (s2) CaAl2SiO6 (s) CaAl4O7 (s) CaCl2 (s)

CaCO3 (s1) CaCO3 (s2) CaFe2O4 (s) CaFe4O7 (s) CaFeSi2O6 (s)

CaMg2Al16O27 (s) CaMgSi2O6 (s) CaO (s) CaO6P2 (s) CaSiO3 (s1)

CaSiO3 (s2) CaSO4 (s1) CaSO4 (s2) Fe2(SO4)3 (s) Fe2Al4Si5O18 (s)

Fe2O3 (s) Fe2SiO4 (s1) Fe2SiO4 (s2) Fe2SiO4 (s3) Fe3Al2Si3O12 (s)

Fe3O4 (s1) Fe3O4 (s2) FeAl2O4 (s) FeO (s) FeO4P (s)

FeS2 (s) FeSiO3 (s1) FeSiO3 (s2) FeSiO3 (s3) FeSO4 (s)

K2Al12O19 (s) K2Ca(CO3)3 (s) K2Ca2(CO3)3 (s) K2Ca2(SO4)3 (s) K2CO3 (s1)

K2CO3 (s2) K2O (s) K2SiO5 (s1) K2SiO5 (s2) K2SiO5 (s3)

K2Si4O9 (s1) K2Si4O9 (s2) K2SiO3 (s) K2SO4 (s1) K2SO4 (s2)

K3Na(SO4)2 (s) KAl(SO4)2 (s) KAl9O14 (s) KAlO2 (s1) KAlO2 (s2)

KAlSi2O6 (s1) KAlSi2O6 (s2) KAlSi3O8 (s1) KAlSi3O8 (s2) KAlSi3O8 (s3)

KAlSiO4 (s1) KAlSiO4 (s2) KCl (s) Mg2Al4Si5O18 (s) Mg2SiO4 (s1)

Mg2SiO4 (s2) Mg2SiO4 (s3) Mg3Al2Si3O12 (s) Mg4Al10Si2O23 (s) MgCO3 (s)

MgO (s) Mg2SiO3 (s1) Mg2SiO3 (s2) Mg2SiO3 (s3) Mg2SiO3 (s4)

Mg2SiO3 (s5) Mg2SiO3 (s6) Mg2SiO3 (s7) MgSO4 (s) Na2Al12O19 (s)

Na2Ca2Si3O9 (s) Na2Ca3Si6O16 (s) Na2CaSi5O12 (s) Na2CO3 (s1) Na2CO3 (s2)

Na2CO3 (s3) Na2Fe2O4 (s) Na2Mg2Si6O15 (s) Na2MgSi4O10 (s) Na2O (s)

Na2Si2O5 (s1) Na2Si2O5 (s2) Na2Si2O5 (s3) Na2SiO3 (s) Na2SO4 (s1)

Na2SO4 (s2) Na2SO4 (s3) Na3(PO4) (s) Na4CaSi3O9 (s) Na4SiO4 (s)

Na6Si2O7 (s) Na6Si8O19 (s) NaAl9O14 (s) NaAlO2 (s1) NaAlO2 (s2)

NaAlSi2O6 (s) NaAlSi3O8 (s1) NaAlSi3O8 (s2) NaAlSiO4 (s1) NaAlSiO4 (s2)

NaCl (s) (P2O5)2 (s) TiO2 (s) SiO2 (s1) SiO2 (s2)

SiO2 (s3) SiO2 (s4) SiO2 (s5) SiO2 (s6) SO3 (s)

ZnO (s)

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8.2.5 Selected solid solution compounds, Papers III, IV and V

α-Belite (3)

Perovskite (Ca, Ti, O) (2) α-2CaO.SiO2

.Fe2SiO4 (ss) Ca2Ti2O6 (ss) α-2CaO.SiO2

.Ca2SiO4 (ss) Ca2Ti2O5 (ss) α-2CaO.SiO2

.Ca3(PO4)2 (ss) β-Belite (4) (Ca, K, Na)(SO4, CO3) (4) β-2CaO.SiO2

.Fe2SiO4 (ss) K2SO4 (ss) β-2CaO.SiO2

.Ca2SiO4 (ss) CaSO4 (ss) β-2CaO.SiO2

.Zn2SiO4 (ss) K2CO3 (ss) β-2CaO.SiO2

.Ca3(PO4)2 (ss) CaCO3 (ss) C3AF (Ca, Al, Fe) (2) (K, Na)(SO4, CO3) (4) 3CaO.Al2O3

.Fe2O3.Ca3Al2O6 (ss) Na2SO4 (ss)

3CaO.Al2O3.Fe2O3

.Ca3Fe2O6 (ss) K2SO4 (ss) Na2CO3 (ss) C2AF (Ca, Al, Fe) (2) K2CO3 (ss) 2CaO.Al2O3

.Fe2O3.Ca2Al2O5 (ss)

2CaO.Al2O3.Fe2O3

.Ca2Fe2O5 (ss)

8.2.6 Selected melt phase compounds, Papers II-VI

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Papers II and VI

Compounds (6) oxide melt phase Al2O3 (l) FeO (l) K2O (l) CaO (l) Fe2O3 (l) SiO2 (l) Compounds (2) salt melt phase KCl (l) K2SO4 (l)

Papers III, IV and V

Compounds (13) oxide melt phase

Al2O3 (l) FeO (l) Na2O (l) ZnO (l) CaO (l) Fe2O3 (l) SiO2 (l) CaSO4 (l) K2O (l) TiO2 (l) Ca3(PO4)2 (l) MgO (l) Ti2O3 (l) Compounds (7) salt melt phase CaSO4 (l) KCl (l) K2CO3 (l) K2SO4 (l) NaCl (l) Na2CO3 (l) Na2SO4 (l)