Ash transformation during co-firing coal and straw

Abstract Co-firing straw with coal in pulverized fuel boilers can cause problems related to fly ash utilization, deposit formation, corrosion and SCR catalyst deactivation due to the high contents of Cl and K in the ash. To investigate the interaction between coal and straw ash and the effect of coal quality on fly ash and deposit properties, straw was co-fired with three kinds of coal in an entrained flow reactor. The compositions of the produced ashes were compared to the available literature data to find suitable scaling parameters that can be used to predict the composition of ash from straw and coal co-firing. Reasonable agreement in fly ash compositions regarding total K and fraction of water soluble K was obtained between co-firing in an entrained flow reactor and full-scale plants. Capture of potassium and subsequent release of HCl can be achieved by sulphation with SO 2 and more importantly, by reaction with Al and Si in the fly ash. About 70–80% K in the fly ash appears as alumina silicates while the remainder K is mainly present as sulphate. Lignite/straw co-firing produces fly ash with relatively high Cl content. This is probably because of the high content of calcium and magnesium in lignite reacts with silica so it is not available for reaction with potassium chloride. Reduction of Cl and increase of S in the deposits compared to the fly ashes could be attributed to sulphation of the deposits.

[1]  B. Chadwick,et al.  Screening of potential mineral additives for use as fouling preventatives in Victorian brown coal combustion , 1999 .

[2]  Bo Sander,et al.  Properties of Danish biofuels and the requirements for power production , 1997 .

[3]  Peter Glarborg,et al.  Mechanism and modeling of the formation of gaseous alkali sulfates , 2005 .

[4]  K. Hein,et al.  Assessment of Chlorine−Alkali−Mineral Interactions during Co-Combustion of Coal and Straw , 2002 .

[5]  K. Iisa,et al.  Sulfation of potassium chloride at combustion conditions , 1999 .

[6]  Larry L. Baxter,et al.  Ash deposition during biomass and coal combustion: A mechanistic approach , 1993 .

[7]  Ole Hede Larsen,et al.  Cofiring coal and straw in a 150 MWe power boiler experiences , 2000 .

[8]  D. Chandra,et al.  Mineral Impurities in Coal Combustion , 1986 .

[9]  K. Dam-Johansen,et al.  Influence of deposit formation on corrosion at a straw-fired boiler , 2000 .

[10]  Larry L. Baxter,et al.  Deposition of potassium salts on heat transfer surfaces in straw-fired boilers: a pilot-scale study , 2000 .

[11]  Kim Dam-Johansen,et al.  Full-scale co-firing of straw and coal , 1996 .

[12]  H. Spliethoff,et al.  Legislative and environmental issues on the use of ash from coal and municipal sewage sludge co-firing as construction material. , 2001, Waste management.

[13]  Yuanjing Zheng,et al.  Laboratory Investigation of Selective Catalytic Reduction Catalysts: Deactivation by Potassium Compounds and Catalyst Regeneration , 2004 .

[14]  Mikko Hupa,et al.  Interaction of fuels in co-firing in FBC , 2005 .

[15]  Jan Erik Johnsson,et al.  Deactivation of V2O5-WO3-TiO2 SCR catalyst at a biomass-fired combined heat and power plant , 2005 .

[16]  Anders Nordin,et al.  Effect of Coal Minerals on Chlorine and Alkali Metals Released during Biomass/Coal Cofiring , 1999 .

[17]  Martti Aho,et al.  Preventing chlorine deposition on heat transfer surfaces with aluminium–silicon rich biomass residue and additive , 2004 .

[18]  A. Robinson,et al.  Pilot-Scale Investigation of the Influence of Coal−Biomass Cofiring on Ash Deposition , 2002 .

[19]  J. Ranogajec,et al.  Computerized thermodynamic analysis of reactions during sintering of CaOAl2O3SiO2 system , 1992 .

[20]  Kim Dam-Johansen,et al.  Deposit Formation in a 150 MWe Utility PF-Boiler during Co-combustion of Coal and Straw , 2000 .

[21]  Kim Dam-Johansen,et al.  Effects on SOx and NOx Emissions by Co-Firing Straw and Pulverized Coal , 1997 .