Mechanism and prediction of bed agglomeration during fluidized bed combustion of a biomass fuel: Effect of the reactor scale

The fluidized bed combustion of a biomass residue (pine seed shells) was investigated both in a bench-scale and in a pilot-scale reactor. Extensive bed agglomeration problems were experienced during combustion of this fuel, as a consequence of the high content of alkali species in the ash. The focus of the study was the effect of the combustor scale and of the operating conditions on the characteristic time and the extent of bed agglomeration during combustion. Bed defluidization times as well as the extent of ash accumulation in the bed were measured at different operating conditions in the two reactors. Results indicated that sand size, combustor size, and presence of internals had a significant influence on the agglomeration phenomenon. SEM/EDX analysis on agglomerate samples discharged from the bed after defluidization confirmed that bed agglomeration is a consequence of potassium and sodium enrichment on the sand particle surface, in conjunction with high temperature spots near burning char particles. The competition between formation of stable bonds between bed particles and the breaking of the agglomerates by inertial forces is the key mechanism leading to bed agglomeration. In addition, a previously developed diagnostic tool based on the measurement of the dynamic pressure signal inside the bed was successfully tested with the present biomass fuel and at both combustor scales for its capability to predict the bed defluidization onset.

[1]  F. Scala,et al.  Fluidized bed combustion of alternative solid fuels , 2004 .

[2]  Simeon N. Oka,et al.  Biomass FBC combustion -- Bed agglomeration problems , 1995 .

[3]  P. Salatino,et al.  The influence of fine char particles burnout on bed agglomeration during the fluidized bed combustion of a biomass fuel , 2003 .

[4]  E. Anthony.  Fluidized bed combustion of alternative solid fuels ; status, successes and problems of the technology , 1995 .

[5]  P. Salatino,et al.  The relevance of attrition to the fate of ashes during fluidized-bed combustion of a biomass , 2000 .

[6]  C. K. Jotshi,et al.  Fluidized-bed incineration of waste materials , 1994 .

[7]  Fabrizio Scala,et al.  On the Relevance of Axial and Transversal Fuel Segregation during the FB Combustion of a Biomass , 2004 .

[8]  T. Kodas,et al.  The ash formation during co-combustion of wood and sludge in industrial fluidized bed boilers , 1998 .

[9]  P. Salatino,et al.  Fluidized bed combustion of a biomass char (Robinia pseudoacacia) , 2000 .

[10]  Fabrizio Scala,et al.  Characterization and Early Detection of Bed Agglomeration during the Fluidized Bed Combustion of Olive Husk , 2006 .

[11]  Mikko Hupa,et al.  Characterization of the sintering tendency of ten biomass ashes in FBC conditions by a laboratory test and by phase equilibrium calculations , 1998 .

[12]  P. Salatino,et al.  Fluidized-bed combustion of a biomass char: The influence of carbon attrition and fines postocombustion on fixed carbon conversion , 1998 .

[13]  B. Jenkins,et al.  Combustion properties of biomass , 1998 .

[14]  A. Lyngfelt,et al.  Ash behaviour in a CFB boiler during combustion of coal, peat or wood , 1998 .

[15]  Anders Nordin,et al.  Bed Agglomeration Characteristics during Fluidized Bed Combustion of Biomass Fuels , 2000 .

[16]  J. Werther,et al.  Combustion of agricultural residues , 2000 .

[17]  R. C. Brown,et al.  Bed material agglomeration during fluidized bed combustion , 1993 .

[18]  A. Rao,et al.  Experimental determination of bed agglomeration tendencies of some common agricultural residues in fluidized bed combustion and gasification , 1998 .

[19]  Fabrizio Scala,et al.  Modelling fluidized bed combustion of high-volatile solid fuels , 2002 .