LIU Siqi;NIU Yanqing;WEN Liping;YAN Bokang;WANG Denghui;HUI Shien;

• 1:School of Energy and Power Engineering
• 2:Xi'an Jiaotong University

Abstract：

In order to control the emission of particulate matter( PM) from coal combustion,it is necessary to have a thorough understanding of the emission rule and formation mechanism of PM. During pulverized coal combustion,PM can be divided into three formation modes: coarse mode,fine mode,and ultrafine mode.Compared to the coarse mode,the fine mode particles account for a larger proportion,and affect human health and atmospheric environment due to their small sizes and enrichment characteristics.Besides,the systemic summary of formation mechanism and research progress on fine mode PM are relatively lacking,compared with that of ultrafine mode,and it is difficult to suppress the emission of the fine mode PM.In this paper,the formation mechanisms of fine mode PM( char fragmentation,mineral melt coalescence,exterior mineral fragmentation and ash shedding) as well as the main influencefactors were analyzed.The research progress of simulationwere discussed and the research emphasis in future was pointed out.The particle size distribution of PM in coal ash turns out to be the result of competition between the char fragmentation and mineral aggregation. The fragmentations results in the increase of amount and the decrease of particle size of fine mode PM,while mineral aggregation leads to the amount decrease of PM,which is conducive to the formation of coarse mode PM.The main factors affecting the formation of PM arepore structure,combustion mode and char particle size.With relatively higher porosity,char cenospheres are more likely to broken up into more fine mode PM than other chars.Both increasing temperature,oxygen content and decreasing particle size are helpful to the formation of PM,but the aggregation of ash particles at higher temperature may lead to the particle size distribution towards coarse mode PM.The simulation of coke combustion characteristics by fragmentation behavior is mainly divided as population balance model and percolative fragmentation model. On the basis of the formation mechanism and influencing factors of fine mode PM,the percolative model is more suitable for simulating the char fragmentation,which takes the porous char structure into account.Therefore,the combination of kinetics combustion model and percolative fragmentation model is the key for the accurate prediction on the ash particle size distribution,which is the next research focus.

Key Words： coal char combustion;fine mode particle matter;formation mechanism;percolative model

Abstract:

Keywords:

Foundation: 国家自然科学基金面上资助项目(51776161);; 陕西省自然科学基础研究计划资助项目(2018JQ5010)

Authors: LIU Siqi;NIU Yanqing;WEN Liping;YAN Bokang;WANG Denghui;HUI Shien;

DOI: 10.13226/j.issn.1006-6772.19011803

References：

• [1] BP.BP energy outlook[R].London:BP Energy Economics,2018.
• [2] YAO Q,LI S Q,XU H W,et al.Reprint of:Studies on formation and control of combustion particulate matter in China:A review[J].Energy,2010,35(11):4480-4493.
• [3] MCELROY M W,CARR R C,ENSOR D S,et al.Size distribution of fine particles from coal combustion[J].Science,1982,215:13-19.
• [4] DAMLE A S,ENSOR D S,RANADE M B.Coal combustion aerosol formation mechanisms:A review[J].Aerosol Science and Technology,1982,1(1):119-133.
• [5] NEVILLE M,QUANN R J,HAYNES B S,et al. Vaporization and condensation of mineral matter during pulverized coal combustion[J]. Symposium on Combustion,1981,18(1):1267-1274.
• [6] LINAK W P,MILLER C A,SEAMES W S,et al.On trimodal particle size distributions in fly ash from pulverized-coal combustion[J].Proceedings of the Combustion Institute,2003,29:441-447.
• [7] SEAMES W S.An initial study of the fine fragmentation fly ash particle mode generated during pulverized coal combustion[J]. Fuel Processing Technology,2003,81(2):109-125.
• [8] YU Y X,XU M H,YAO H,et al.Char characteristics and particulate matter formation during Chinese bituminous coal combustion[J].Proceedings of the Combustion Institute,2007,31(2):1947-1954.
• [9] YU D X,XU M H,YAO H,et al.Mechanisms of the central mode particle formation during pulverized coal combustion[J]. Proceedings of the Combustion Institute,2009,32(2):2075-2082.
• [10] YU D X,XU M H,YAO H,et al.A new method for identifying the modes of particulate matter from pulverized coal combustion[J].Powder Technology,2008,183(1):105-114.
• [11] TIAN C,LU Q,LIU Y,et al. Understanding of physicochemical properties and formation mechanisms of fine particular matter generated from Canadian coal combustion[J]. Fuel,2016,165:224-234.
• [12] WEN C,XU M,YU D,et al.PM10formation during the combustion of N2-char and CO2-char of Chinese coals[J].Proceedings of the Combustion Institute,2013,34:2383-2392.
• [13] QUANN RJ,NEVILLE M,JANGHORBANI M,et al.Mineral matter and trace-element vaporization in a laboratorypulverized coal combustion system[J]. Environmental Science&Technology,1982,16(11):776-781.
• [14] NIU Y,LIU X,WANG S,et al.A numerical investigation of the effect of flue gas recirculation on the evolution of ultra-fine ash particles during pulverized coal char combustion[J]. Combustion and Flame,2017,184:1-10.
• [15] NIU Y,WANG S,SHADDIX C R,et al.Kinetic modeling of the formation and growth of inorganic nano-particles during pulverized coal char combustion in O2/N2and O2/CO2atmospheres[J].Combustion and Flame,2016,173:195-207.
• [16] NIU Y,YAN B,LIU S,et al.Ultra-fine particulate matters(PMs)formation during air and oxy-coal combustion:Kinetics study[J].Applied Energy,2018,218:46-53.
• [17] GRAY V R.The role of explosive ejection in the pyrolysis of coal[J].Fuel,1988,67(9):1298-1304.
• [18] ZYGOURAKIS K.Effect of pyrolysis conditions on the macropore structure of coal-derived chars[J].Energy&Fuels,1993,7(1):33-41.
• [19] DACOMBE P J,HAMPARTSOUMIAN E,POURKASHANIAN M.Fragmentation of large coal particles in a drop-tube furnace[J].Fuel,1994,73(8):1365-1367.
• [20] BUHRE B,HINKLEY J,GUPTA R,et al.Fine ash formation during combustion of pulverised coal–coal property impacts[J].Fuel,2006,85(2):185-193.
• [21] XU M,YU D,YAO H,et al.Coal combustion-generated aerosols:Formation and properties[J]. Proceedings of the Combustion Institute,2011,33(1):1681-1697.
• [22] HELBLE J J,SAROFIM A F.Influence of char fragmentation on ash particle-size distributions[J]. Combustion and Flame,1989,76(2):183-196.
• [23] MITCHELL R E,AKANETUK A E J.The impact of fragmentation on char conversion during pulverized coal combustion[J].Symposium on Combustion,1996,26(2):3137-3144.
• [24] KANG S G,HELBLE J J,SAROFIM A F,et al. Time-resolved evolution of fly ash during pulverized coal combustion[J].Symposium on Combustion,1989,22(1):231-238.
• [25] KANG S G.Fundamental studies of mineral matter transformation during pulverized coal combustion:Residual ash formation[D].Cambrige:Massachusetts Institute of Technology,1991.
• [26] YAN L.CCSEM analysis of mineral in pulverized coal and ash formation modeling[D]. Newcastle:The University of Newcastle,2000.
• [27] RAASK E.Mineral Impurities in coal combustion:Behavior,problems,and remedial measures[M]:New York:Hemisphere Publishing,1985.
• [28] YAN L,GUPTA R P,WALL T F.A mathematical model of ash formation during pulverized coal combustion[J]. Fuel,2002,81(3):337-344.
• [29] KANG S W,SAROFIM A F,BER J M. Particle rotation in coal combustion:Statistical,experimental and theoretical studies[J].Symposium on Combustion,1989,22(1):145-153.
• [30] MONROE L S.An experimental and modeling study of residual fly ash formation in combustion of a bituminous coal[D].Cambrige:Massachusetts Institute of Technology,1989.
• [31] YU J,LUCAS J A,WALL T F.Formation of the structure of chars during devolatilization of pulverized coal and its thermoproperties:A review[J].Progress in Energy and Combustion Science,2007,33(2):135-170.
• [32] FLETCHER T H. Swelling properties of coal chars during rapid pyrolysis and combustion[J].Fuel,1993,72(11):1485-1495.
• [33] GADIOU R,BOUZIDI Y,PRADO G.The devolatilisation of millimetre sized coal particles at high heating rate:The influence of pressure on the structure and reactivity of the char[J]. Fuel,2002,81(16):2121-2130.
• [34] GALE T K,FLETCHER T H,BARTHOLOMEW C H.Effects of pyrolysis conditions on internal surface-areas and densities of coal chars prepared at high heating rates in reactive and nonreactive atmospheres[J].Energy&Fuels,1995,9(3):513-524.
• [35] HAN X,JIANG X,YAN J,et al. Effects of retorting factors on combustion properties of shale char.2:Pore structure[J].Energy&Fuels,2011,25(1):97-102.
• [36] LEE C W,SCARONI A W,JENKINS R G.Effect of pressure on the devolatilization and swelling behavior of a softening coal during rapid heating[J].Fuel,1991,70(8):957-965.
• [37] LIGHTMAN P,STREET P J.Microscopical examination heat treated pulverized coal particles[J].Fuel,1968,47(1):7-28.
• [38] NSAKALA N Y,ESSENHIGH R H,WALKER P L.Characteristics of chars produced from lignites by pyrolysis at 808℃following rapid heating[J].Fuel,1978,57(10):605-611.
• [39] YU J,LUCAS J,WALL T,et al.Modeling the development of char structure during the rapid heating of pulverized coal[J].Combustion and Flame,2004,136(4):519-532.
• [40] ZENG D,CLARK M,GUNDERSON T,et al.Swelling properties and intrinsic reactivities of coal chars produced at elevated pressures and high heating rates[J]. Proceedings of the Combustion Institute,2005,30(2):2213-2221.
• [41] BAILEY J G,TATE A,DIESSEL C F K,et al.A Char morphology system with applications to coal combustion[J]. Fuel,1990,69(2):225-239.
• [42] BENFELL K E,LIU G S,ROBERTS D G,et al. Modeling char combustion:The influence of parent coal petrography and pyrolysis pressure on the structure and intrinsic reactivity of its char[J]. Proceedings of the Combustion Institute,2000,28(2):2233-2241.
• [43] SIMONS G A.The role of pore structure in coal pyrolysis and gasification[J]. Progress in Energy&Combustion Science,1983,9(4):269-290.
• [44] WEBB P A,ORR C.Analytical methods in fine particle technology[M]. Norcross,GA:Micromeritics Instrument Corporation,1997.
• [45] ROUQUEROL J,AVNIR D,FAIRBRIDGE C W,et al. Recommendations for the characterization of porous solids[J].Pure and Applied Chemistry,1994,66(8):1739-1758.
• [46] KANG SG,SAROFIM AF,BER J M.Effect of char structure on residual ash formation during pulverized coal combustion[J].Symposium on Combustion,1992,24(1):1153-1159.
• [47] KANTOROVICH I I,BAR-ZIV E.Role of the pore structure in the fragmentation of highly porous char particles[J]. Combustion and Flame,1998,113(4):532-541.
• [48] AARNA I,SUUBERG E M.Changes in reactive surface area and porosity during char oxidation[J]. Symposium on Combustion,1998,27(2):2933-2939.
• [49] ADAMS K E,GLASSON D R,JAYAWEERA S A A.Development of porosity during the combustion of coals and cokes[J].Carbon,1989,27(1):95-101.
• [50] WU H W,WALL T,LIU G S,et al.Ash liberation from included minerals during combustion of pulverized coal:The relationship with char structure and burnout[J]. Energy&Fuels,1999,13(6):1197-1202.
• [51] WALL T F.Mineral matter transformations and ash deposition in pulverised coal combustion[J].Symposium on Combustion,1992,24(1):1119-1126.
• [52] ZHANG X,DUKHAN A,KANTOROVICH I I,et al. Structural changes of char particles during chemically controlled oxidation[J].Symposium on Combustion,1996,26(2):3111-3118.
• [53] KERSTEIN A R,NIKSA S.Fragmentation during carbon conversion:Predictions and measurements[J]. Symposium on Combustion,1985,20(1):941-949.
• [54] REYES S,JENSEN K F.Percolation concepts in modeling of gas solid reactions.1:Application to char gasification in the kinetic regime[J].Chemical Engineering Science,1986,41(2):333-343.
• [55] REYES S,JENSEN K F.Percolation concepts in modeling of gas solid reactions.2:Application to char gasification in the diffusion regime[J]. Chemical Engineering Science,1986,41(2):345-354.
• [56] MARBAN G,FUERTES A B. Influence of percolation on the modification of overall particle properties during gasification of porous solids[J]. Chemical Engineering Science,1997,52(1):1-11.
• [57] FIX G,SEAMES W,MANN M,et al. The effect of combustion temperature on coal ash fine-fragmentation mode formation mechanisms[J].Fuel,2013,113:140-147.
• [58] LIU X,XU M,HONG Y,et al.Effect of combustion parameters on the emission and chemical composition of particulate matter during coal combustion[J].Energy&Fuels,2007,21(1):157-162.
• [59] ZHANG P A,YU D,LUO G,et al. Temperature effect on central-mode particulate matter formation in combustion of coals with different mineral compositions[J].Energy&Fuels,2015,29(8):5245-5252.
• [60] KRAMLICH J C,NEWTON G H.Influence of coal properties and pretreatment on ash aerosol yield[J]. Fuel,1994,73(3):455-462.
• [61] NINOMIYA Y,ZHANG L,SATO A,et al.Influence of coal particle size on particulate matter emission and its chemical species produced during coal combustion[J]. Fuel Processing Technology,2004,85(8/9/10):1065-1088.
• [62] BAXTER L L.Char fragmentation and fly-ash formation during pulverized-coal combustion[J].Combustion and Flame,1992,90(2):174-184.
• [63] LIAW S B,CHEN X,YU Y,et al.Effect of particle size on particulate matter emissions during biosolid char combustion under air and oxyfuel conditions[J].Fuel,2018,232:251-256.
• [64] TILGHMAN M B,MITCHELL R E.Characterizing char particle fragmentation during pulverized coal combustion[J]. Proceedings of the Combustion Institute,2013,34:2461-2469.
• [65] MICCIO F.Modeling percolative fragmentation during conversion of entrained char particles[J]. Korean Journal of Chemical Engineering,2004,21(2):404-411.
• [66] MICCIO F,SALATINO P.Monte-carlo simulation of combustioninduced percolative fragmentation of carbons[J]. Symposium on Combustion,1992,24(1):1145-1151.
• [67] KUROSE R,MAKINO H,MATSUDA H,et al.Application of percolation model to ash formation process in coal combustion[J].Energy&Fuels,2004,18(4):1077-1086.
• [68] KUROSE R,MATSUDA H,MAKINO H,et al.Characteristics of particulate matter generated in pressurized coal combustion for high-efficiency power generation system[J]. Advanced Powder Technology,2003,14(6):673-694.
• [69] SUZUKI A,YAMAMOTO T,AOKI H,et al.Percolation model for simulation of coal combustion process[J]. Proceedings of the Combustion Institute,2003,29:459-466.
• [70] SANDMANN CW,ZYGOURAKIS K.Evolution of pore structure during gas-solid reactions-discrete models[J]. Chemical Engineering Science,1986,41(4):733-739.