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1 Swinburne Researh Bank Al-Abbas, A. H., Naser, J., & Bliblau, A. (2012). Computational fluid dynamis modelling of hemistry reation shemes in a lab-sale oxy-fuel furnae. Originally published in C. B. Solnordal, et al. (eds.). Proeedings of the 9th International Conferene on Computational Fluid Dynamis in the Minerals and Proess Industries (CFD 2012), Melbourne, Australia, Deember. Melbourne: CSIRO. Copyright 2012 CSIRO Australia. This is the author s version of the work, posted here with the permission of the publisher for your personal use. No further distribution is permitted. You may also be able to aess the published version from your library. The definitive version is available at Swinburne University of Tehnology CRICOS Provider 00111D swinburne.edu.au

2 Ninth International Conferene on CFD in the Minerals and Proess Industries Melbourne, Australia Deember 2012 Computational Fluid Dynamis Modelling of Chemistry Reation and NO x Formation Mehanisms in a Lab-Sale Oxy-Fuel Furnae Audai Hussein Al-Abbas, Jamal Naser *, and Aaron Bliblau Faulty of Engineering & Industrial Siene Department Swinburne University of Tehnology, Hawthorn 3122, AUSTRALIA ABSTRACT This paper presents a three-dimensional numerial investigation of pulverized dry lignite in a 100 kw oxy-fuel furnae. A hybrid unstrutured grid omputational fluid dynamis (CFD) ode was used to model and analyze: an air-fired, oxy-fuel OF25 (25 vol. % O 2 onentration), oxy-fuel OF27 (27 vol. % O 2 onentration), and oxy-fuel OF29 (29 vol. % O 2 onentration). Under oxy-fuel ombustion, the appropriate mathematial models with the related kinetis parameters were implemented to alulate the temperature distributions, speies onentrations (O 2 and CO 2 ), and NO x emission onentrations. The multi-step hemial reation mehanisms were onduted on the gas-phase and the solid-phase of oal reation in two-step and three-step reation shemes. The predited results showed a reasonably good agreement against the measured data for all ombustion ases. This numerial investigation of the oxy-fuel ombustion senarios might probably provide important information towards future modelling of a 550 MW large-sale brown oal oxy-fuel tangentially fired furnae. 1- Introdution Emissions of fossil fuel ombustion partiularly oal-firing have been highly inreased in the atmospheri zone in reent years. This inrease of greenhouse gas (GHG) emissions leads negatively to the global limate hange. Carbon dioxide (CO 2 ) and nitri oxides (NO x ) are being onsidered the main ontribution gases to the emission of greenhouse gases (GHG) from the energy prodution units (Ahmed et al. 2007; Ahmed and Naser 2011; Hart and Naser 2009). Reently, several CO 2 apture tehnologies have been developed for ontinuing use of fossil fuel soures suh as preombustion apture, post-ombustion apture, and oxy-fuel ombustion. The last ombustion tehnology has been extensively onsidered as one of the most ompetitive option to ontrol and redue several types of gaseous emissions suh as CO 2, NO x and SO x from pulverized oal (PC) power plants (Buhre et al. 2005; Kannihe et al. 2009; Wall et al. 2009). The basi priniple of oxy-fuel ombustion is to inrease the partial pressure of CO 2 in the exhaust gases in order to make its sequestration and ompression proesses hemially easier and more eonomial. This approah an be performed by using a mixture of pure oxygen (produes in air separation units) with part of reyled flue gas (RFG) (mostly CO 2 ) instead of air in the ombustion hamber in order to dilute the high ombustion temperature (Kakaras et al. 2007). In this ase of ombustion, a higher onentration of CO 2 an be ahieved in the flue gas stream, and therefore the higher ost of its apturing proesses an be avoided. In the oxy-fuel (O 2 /CO 2 ) ombustion, many hanges ould be happened inside the furnae in terms of flame temperature levels, speies onentrations, and radiation heat transfer with respet to the air-fired ase. These hanges on the ombustion harateristis are mainly due to the higher volumetri heat apaity of CO 2 relative to that of nitrogen in the air-fired ase, radiative properties of gas mixture, and other gas properties suh as kineti visosity, thermal diffusivity, and gas phase hemistry (Al-Abbas et al. 2011; Al-Abbas and Naser 2012). The oal ombustion is onsidered as a omplex proess with respet to the ombustion of liquid and gaseous fuels beause it inludes several omplex physial and hemial proesses (Ahim et al. 2009; Dodds et al. 2011; Dodds and Naser 2012). During the thermal deomposition of the pulverized oal partiles the volatile matter (VM) and moisture ontent (MC) are released, and the har is stayed as a solid fuel in this pyrolysis proess. As a result, in the gas-phase proess, several radial speies an be formed in the reation zone suh as total hydroarbon (THC), hydrogen yanide (HCN), ammonia (NH 3 ), N, CO, H 2 et. These intermediate speies need speial treatments in the ombustion zone. This an be pratially performed by applying multi-steps hemial reation mehanism on these aforementioned speies and residual har in order to predit the important speies and thermodynami equilibrium temperature aurately enough. This multi-step reation mehanism is not only important for the volatile and har ombustion, but also for the detailed information of thermal and fuel nitri oxides (NO x ) formation. Up-to-date there is very little researh work onduted on the dry lignite oxy-fuel ombustion using multi-steps reation shemes in detail for volatile and residual har ombustion, and global NO x formation mehanism in numerial simulation fields. The gaseous and solid phase hemistry mehanisms were presented and disussed in this paper. Multi-steps hemial reation mehanisms and nitri oxides formation mehanisms were performed in four different ombustion senarios on a labsale 100 kw firing lignite unit (Chalmers furnae). Air-fired (referene ombustion ase) and three different oxy-fuel ombustion ases (known as OF25, OF27, and OF29) were modelled by using AVL Fire CFD ode. The temperature distributions and speies onentrations inside the furnae were presented and validated against the measurements of Andersson (2007). 2- Multi-step reation shemes In this setion, eight speies fuel (volatile and har), O 2, N 2, CO 2, CO, H 2, and H 2 O were onsidered and taken into aount in one- (single-), two-, and three-step hemial reations. Although, there were some good preditions in term of temperature distributions and speies onentrations in a single -step reation sheme, some disrepanies were visible in those numerial results against the experimental data (Al-Abbas et al.

3 2011). As desribed previously, those disrepanies in the predited results might have been aused due to the usage of a single-step hemial reation. Therefore, it is appropriate to onsider these speies, espeially in the flame envelope zone (hottest region in the furnae) in order to predit the important intermediate speies suh as CO and H 2, and thermodynami equilibrium temperature aurately enough. In addition, the one-step hemial mehanism used to desribe the fuel onversion annot apture the CO 2 /CO ratio and equilibrium between H 2 and H 2 O. Moreover, regarding the har burn-out, these multi-step hemial reation mehanisms an provide good information to larify the onnetion of the order of reation of har ombustion rate and CO/CO 2 prodution rate with the temperature and oxygen partial pressure (Nikolopoulos et al. 2011; Hurt and Calo 2001). During the oxy-fuel ombustion, the following hemial equations of one-, two-, and three-step reation shemes were onsidered as shown below. The hemial equation for devolatilized methane burned with oxygen (homogenous phase) an be expressed as follows: CH 4 + 2O 2 CO 2 +2H 2 O (1) The hemial equation for har burned with oxygen (heterogenous phase) an be expressed as follows: C har + O 2 CO 2 (2) The heats of ombustion ( H) of the methane and residual har are onsidered and taken into aount of the ombustion model are equal to kj/kmol. and kj/kmol., respetively. Due to the limitation of single-step reation mehanism on the important intermediate speies (CO) and flame temperature, two-step reation sheme an be partially provided information on the arbon monoxide (CO) in the hydroarbon reation and har burn-out shemes whih are based on the following reations: The hemial equation for devolatilized methane burned with oxygen an be expressed in the two hemial reations: CH 4 + 3/2O 2 CO+2H 2 O (3) CO + 1/2O 2 CO 2 (4) While the hemial equation for har burned with oxygen an be expressed in the following hemial reation: C har + 1/2O 2 CO (5) From the interesting point of investigation, the reverse hemial reation of Eq. (4) has a signifiant effet on the equilibrium onentration of CO and heat release intensity in the flame envelope, whih onsidered the higher temperature level inside the furnae. The heats of reation of first and seond equations in the two-step reation sheme are kj/kmol and kj/kmol, respetively. Three-step reation mehanism has the ability to predit well these speies (CO and H 2 ), as well as the aforementioned main speies. Therefore, the hydroarbon fuel (methane) and residual har (C har ), in this reation mehanism, are presented in threestep hemial reation in order to aurately explain the dissoiation proesses, as illustrated in the following hemial equations. The hemial equation for devolatilized methane burned with oxygen an be expressed in the three hemial reations: CH 4 + O 2 CO+H 2 +H 2 O (6) CO + H 2 O CO 2 +H 2 (7) O2 + 2H 2 2H 2 O (8) The heats of reation of first, seond, and third hemial equations in the three-step reation sheme are kj/kmol, kj/kmol, and kj/kmol, respetively. Detailed numerial information regarding multi-step reation shemes an be found in the reent numerial simulation work (Al- Abbas and Naser 2012). The hemial equation for har burned with oxygen an be expressed in the three heterogenous hemial reations: C har + 1/2O 2 CO (9) C har + CO 2 2CO (10) C har + H 2 O CO+H 2 (11) The heats of ombustion ( H) of the above-mentioned speies are taken into aount and inorporated as a soure term in the enthalpy equation for all ombustion ases as separate subroutines. 3- NO x modelling The nitri oxides (NO x ) formation an be simulated via three prinipal soures: Thermal NO that is formed by the dissoiation of the moleular air-nitrogen, Prompt NO that is formed from the attak of hydroarbon fragments on the airnitrogen, and Fuel NO that is formed from nitrogen ontaining omponents in the oal for both the volatile matter and residual har. In the present study, the only main soures of NO x formation (Thermal NO and Fuel NO) were used, whilst the Prompt NO formation was ignored beause it is only important at low temperature (below 1000 K), and in fuel-rih mixtures (Díez et al. 2008). The NO x model involved solving extra three transport equations for the mass fration of NO, HCN, and NH 3 as soure term values (kg/m 3 se) in the transport equation as S NO, S HCN, and S NH3. respetively. Regarding thermal NO formation, the extended Zeldovih mehanism is used as follows: N 2 + O NO+N (12) N + O 2 NO+O (13) N + OH NO+H (14) In the fuel-lean zones, a quasi-steady state onsumption and formation of free nitrogen atoms an be established, partiularly when there is an adequate amount of oxygen in the ombustion zones. Therefore, the overall NO formation rate for the three above-mentioned Eqs. (12)- (14) an be written as follows:

4 d dt NO 2 K 1 f O N2 1 K1 b K 2b 1 K1 f N K 2 K1 b NO K K 2 f O2 2 f 2 NO 3 f O2 OH (15) where is the onentration of the speies in mol/m 3, K 1 f, K 2 f, and K 3 f are the kineti rate onstants for the forward reations, and K 1 b, K 2 b, and K 3 b are the kineti rate onstants for the bakward (reverse) reations. The fuel nitrogen in the oal via both the volatile matter and har an be ontributed to the total NO x formed during the reation pathways. Although, the route leading to the formation/destrution of fuel NO x is still under investigating, the onversion of the fuel nitrogen to NO is highly dependent on two main onepts: the initial nitrogen-ontaining ompounds onentration and the loal ombustion harateristis. Generally, during the devolatilization proess of the pulverized oal partiles several seondary intermediate nitrogen speies are released into the gas phase suh as hydrogen yanide (HCN), ammonia (NH 3 ), nitrogen atom (N), et. The first two speies (HCN and NH 3 ) are ommonly onsidered the most dominant speies from the thermal deomposition of the oal partiles in the reation zone. However, the following five simplified models of oxidation and redution proesses an suffiiently simulate the NO x model: ontrast to the two latter ombustion ases, the flame shapes of OF27 and OF29 are obviously shorter and more onfined in the near-burner region. Moreover, the flame diameters of OF27 and OF29 are larger omparing to the air-fired and OF25, as showed at ports 2 and 3 for all ombustion senarios. Regarding the flame temperature level, there are obvious differenes that ould be distinguished among the ombustion ases. It was notied that the OF29 and OF27 have the higher temperature levels with respet to the air-fired and OF25. The OF25 ase is loser to that of the air-fired ase, but OF27 ase is marginally lower than that of OF29 ase. However, the maximum temperature values of these four ombustion senarios were 1601 (K), 1586 (K), 1638 (K), and 1660 (K) for the air-fired, OF25, OF27, and OF29 ombustion ases, respetively. The main two reasons for these differenes in the flame temperature levels are the inrease of the oxygen onentrations in the feed oxidizer gases and the redution in the RFG amount via both the primary and seondary registers of the burner. HCN O 2 NO+CO+0.5H 2 O (16) HCN NO 1.25N 2 +CO+0.5H 2 O (17) NH O 2 NO+1.5H 2 O (18) NH NO 1.5N H 2 O (19) C har + NO 0.5N 2 +CO (20) As for the above reations mehanism, Eqs. (16)-(20) represent the oxidation and redution proesses and the depletion rates of HCN and NH 3 are given below aording to De Soete (1975). Whilst Eq. (20) represents additional heterogeneous redution of NO to N 2 due to reating between the har partiles and nitri oxide, and its reation rate is approximately equivalent to the arbon onsumption rate that is given by Levy et al.(1981). 4- Results and disussion The visualizations of the flame envelope strutures for the airfired, OF25, OF27, and OF29 ombustion senarios are presented in Figure 1, on the vertial ut along the furnae axis and at the horizontal uts through four different loations (ports 1, 2, 3, and 4) from the burner exit plane. In Fig. 1, it an be seen that the length of the flame was higher for the air-fired ase ompared to the oxy-fuel ombustion ases. In general, the flame struture of the OF25 ase showed some similarities to the referene firing ase, partiularly in the starting point of ombustion, in the near-burner region, and in the width of the flame at ports 1, 2, and 3, but it is somewhat shorter than the air-fired flame, as plotted at port 4 in both ombustion ases. In Fig. 1 Flame temperature distributions (K) on the vertial ut along the furnae axis and at the horizontal uts through four different loations (ports 1, 2, 3, and 4) from the burner exit for the air-fired, OF25, OF27, and OF29 ombustion senarios. Figures 2a and 2b presents the omparison of the temperature distributions (K) at port 1 of the furnae using one-, two-, and three-step hemial reations for the air-fired and oxy-fuel (OF29) ombustion senarios, respetively. As shown in Figs. 2a and 2b, ompared to the single-step reation results, the twoand three-step reation shemes yield better preditions of temperature profiles lose to the boundary walls. The reasons for this an improvement an be explained as follows: First this region (from 200 to 400 mm, in the radial diretion) is also showed an improvement of the O 2 onentration profiles for multi-step reations, as shown in the next disussion of speies onentrations (i.e. it showed a good improvement in the ombustion onditions in this region). Seondly, the aforementioned region of the furnae is relatively less aerodynami effet (swirl effet) by the primary and seondary registers than the entral axis in the near-burner region. These improvements in the temperature distributions in the two latter hemistry mehanisms ould be aused due to the formation of CO and H 2 as intermediate speies. Therefore, the ombustion heat is slowly released ausing a drop in the maximum flame temperature.

5 (a) (a) (b) (b) Figs. 2a and 2b Temperature distribution (K) profile at port 1 of the furnae in one-, two-, and three-step hemial reations for the air-fired and oxy-fuel (OF29) ombustion senarios, respetively. Figures 3a and 3b. shows the omparisons of oxygen mass fration (kg/kg) profiles at port 1 of the furnae for the air-fired and OF25, ombustion senarios, respetively for one-, two-, and three-step reation shemes. In the near-burner region (lose to port 1), the oxygen onentrations have an important influene on the ombustion harateristis, espeially on the ignition onditions and fuel onsumption. Therefore, two- and three-step hemistry models are highly reommended in order to ahieve better numerial results at that given loation of the furnae. In Figs. 3a and b, there is an improved agreement between the results of two- and three-step models and experimental data. The improvements are due to O 2 reation with CO (in two-step reation) and H 2 (in three-step reation) as extra intermediate reations in the oal partile ombustion. In addition, the predited results with the three-step reation mehanism showed a omprehensive improvement at port 1 of the furnae relative to the two-step reation sheme. This an be explained due to the neglet of produed CO 2 in the har ombustion, whih affets both O 2 onentration and temperature distribution in terms both of reation paths and radiation model. Figs. 3a and 3b. Oxygen mass fration (kg/kg) profiles at port 1 of the furnae for a) air-fired and b) oxy-fuel (OF25) ombustion senarios in one-, two-, and three-step reation shemes. In this study, Figure 4 is learly showed the inrease in CO 2 onentration for all oxy-fuel ombustion senarios (OF25, OF27, and OF29) with respet to the air-fired ase. These results were obtained with the three-step hemistry mehanism. As seen, the maximum mass fration value of CO 2 onentration was about % (kg/kg) for the air-firing, while for oxy-fuel ases was, in general, about % (kg/kg) due to usage of dry flue gas reyled, as implemented in the experimental study of Andersson (2007). However, the purity of oxygen (99.5% pure oxygen used in the experiments) and leakage in the furnae are relevant parameters to derease CO 2 onentration, and therefore they should be taken into onsideration in design any oxy-fuel ombustion boiler. Although, the numerial results of these speies are in reasonable qualitative and quantitative agreement with the experimental data, further hemistry reation models are required in order to desribe the thermal pyrolysis of oal partiles and related intermediate speies more preisely.

6 Fig. 4 Carbon dioxide onentration (kg/kg) in the upper half of the furnae for the referene air-fired ase (left hand sides) and oxy-fuel ombustion environments OF25, OF27, and OF29 (right hand sides) respetively, all dimensions are in mm. As shown in Figure 5, the NO x emissions distribution is presented on a vertial ut through the furnae axis for the airfired, OF27, and OF29 ombustion ases. The highest predited values of NO x onentration inside the furnae were 455 ppm, 374 ppm, and 421 ppm for the air-fired, OF27, and OF29 ases, respetively. The distribution of the NO x onentration inside the furnae was notieably different between the air-fired and oxy-fuel (OF27 and OF29) ases. For the air-fired ase, the onentration of NO x emissions started at about 400 mm in the axial distane from the burner exit plane. In ontrary to the airfired ase, the onentrations of NO x emissions for OF27 and OF29 ases were initiated further downstream in whih the predited emissions of NO x was started at about 800 mm and 900 mm from the burner exit plane for OF27 and OF29 ases, respetively. Figures 6a and 6b presents the omparisons and validations of the NO x emissions between the predited results and measured data at port 1 for the air-fired and OF25 ombustion senarios. Generally, the predited results of the NO x were in a good agreement with the measured data for all ombustion ases. As was disussed above in the speies onentration, in the airfired and OF25 ases, the O 2 onentration was higher than those of OF27 and OF29 ases along the entreline of the furnae. This higher value of oxygen affeted the NO x emissions in that region of the furnae. As seen in Fig. 6 a and b, the onentrations of NO x were higher at the entreline of the furnae ompared to the other loations along the port 1. The maximum differene of the predited results with the measured data at port 1 were around 14% and 7% for the air-fired and OF25 ases, respetively. These numerial differenes from the measured data an also be partially attributed to the unertainties of measured data or to the lak of measurements alibration. Finally, the predited results of the present modelling study ould apture the main qualitative and quantitative aspets of the measured data in all ombustion environments, espeially at that loation (port 1) of the furnae. (a) (b) Fig. 5 NO x emissions (ppm) on a vertial ut through the upper part of the furnae axis for the air-fired, OF27, and OF29 ombustion senarios, all dimensions are in mm. Figs. 6a and 6b. NO x onentration (ppm) profiles at port 1 of the furnae for the air-fired and oxy-fuel (OF25) ombustion senarios, respetively.

7 5.-Conlusion The CFD ode was used to predit and analyze four different ombustion senarios (air-fired, OF25, OF27, and OF29), simulating the experiments on a 100 kw Chalmers lab-sale furnae. The temperature distributions, speies onentrations and NO x emission onentrations were investigated at different loations inside the furnae. The multi-step hemial reation mehanisms were arried out on the homogenous and heterogeneous reations of the pulverized lignite partiles in terms of single-, two-, and three-step reation shemes. The simplified approah of the hemial kinetis has been modelled to alulate the Fuel and Thermal NO formation, deoupled from the main fluid flow omputations. The present simulation results showed a very reasonable agreement with the measured results for all ombustion senarios, espeially with the threestep reation sheme. Generally, the predited results of the three-step hemistry reation mehanism illustrated improved agreement ompared to those of the one- and two-step reation models. The improvements were partiularly observed in the flame envelope zone and in the region lose to the furnae wall in terms of the temperature distributions and speies onentrations. This is obviously due to the adoption of thermal dissoiation of hemial speies in the three-step reation sheme. This is important and should be taken into onsideration during modelling the new oxy-fuel tangentially fired furnae. Aknowledgements The authors gratefully aknowledge the finanial support for this researh from Iraqi ministry of higher eduation and sientifi researh (MOHESR) during the sholarship period ( ) in Australia. REFERENCES: [1] G.G. De Soete, Overall reation rates of NO and N2 formation from fuel nitrogen, Symposium (International) on Combustion, 15 (1975) [2] J.M. Levy, L.K. Chan, A.F. Sarofim, J.M. Beér, NO/har reations at pulverized oal flame onditions, Symposium (International) on Combustion, 18 (1981) [3] R.H. Hurt, J.M. Calo, Semi-global intrinsi kinetis for har ombustion modeling, Combustion and Flame, 125 (2001) [4] B.J.P. Buhre, L.K. Elliott, C.D. Sheng, R.P. Gupta, T.F. Wall, Oxy-fuel ombustion tehnology for oal-fired power generation, Progress in Energy and Combustion Siene, 31 (2005) [5] S. Ahmed, J. Hart, J. Nikolov, C. Solnordal, W. Yang, J. Naser, The effet of jet veloity ratio on aerodynamis of a retangular slot-burner in the presene of ross-flow, Experimental Thermal and Fluid Siene, 32 (2007) [7] E. Kakaras, A. Koumanakos, A. Doukelis, D. Giannakopoulos, I. Vorrias, Oxyfuel boiler design in a lignitefired power plant, Fuel, 86 (2007) [8] L.I. Díez, C. Cortés, J. Pallarés, Numerial investigation of NOx emissions from a tangentially-fired utility boiler under onventional and overfire air operation, Fuel, 87 (2008) [9] D. Ahim, J. Naser, Y.S. Morsi, S. Pasoe, Numerial investigation of full sale oal ombustion model of tangentially fired boiler with the effet of mill duting, Heat and Mass Transfer/Waerme- und Stoffuebertragung, (2009) [10] J.T. Hart, J.A. Naser, P.J. Witt, Aerodynamis of an isolated slot-burner from a tangentially-fired boiler, Applied Mathematial Modelling, 33 (2009) [11] M. Kannihe, R. Gros-Bonnivard, P. Jaud, J. Valle- Maros, J.-M. Amann, C. Bouallou, Pre-ombustion, postombustion and oxy-ombustion in thermal power plant for CO2 apture, Applied Thermal Engineering, 30 (2009) [12] T. Wall, Y. Liu, C. Spero, L. Elliott, S. Khare, R. Rathnam, F. Zeenathal, B. Moghtaderi, B. Buhre, C. Sheng, R. Gupta, T. Yamada, K. Makino, J. Yu, An overview on oxyfuel oal ombustion--state of the art researh and tehnology development, Chemial Engineering Researh and Design, 87 (2009) [13] S. Ahmed, J. Naser, Numerial investigation to assess the possibility of utilizing a new type of mehanially thermally dewatered (MTE) oal in existing tangentially-fired furnaes, Heat and Mass Transfer/Waerme- und Stoffuebertragung, 47 (2011) [14] A.H. Al-Abbas, J. Naser, D. Dodds, CFD modelling of airfired and oxy-fuel ombustion of lignite in a 100 kw furnae, Fuel, 90 (2011) [15] D. Dodds, J. Naser, J. Staples, C. Blak, L. Marshall, V. Nightingale, Experimental and numerial study of the pulverised-fuel distribution in the mill-dut system of the Loy Yang B lignite fuelled power station, Powder Tehnology, 207 (2011) [16] N. Nikolopoulos, A. Nikolopoulos, E. Karampinis, P. Grammelis, E. Kakaras, Numerial investigation of the oxy-fuel ombustion in large sale boilers adopting the ECO-Srub tehnology, Fuel, 90 (2011) [17] A.H. Al-Abbas, J. Naser, Numerial Study of One Air- Fired and Two Oxy-Fuel Combustion Cases of Propane in a 100 kw Furnae, Energy & Fuels, 26 (2012) [18] D. Dodds, J. Naser, Numerial study of the erosion within the pulverised-fuel mill-dut system of the Loy Yang B lignite fuelled power station, Powder Tehnology, 217 (2012) [6] K. Andersson, Charaterization of oxy-fuel flames - their omposition, temperature and radiation, in, Chalmers University of Tehnology, Göteborg, 2007.