Sintering tendency of different fuel ashes in combustion and gasification conditions

摘要

Ash sintering in two different cases, in bed agglomeration of fluidized bed combustion/gasification processes and in the case with fireside deposit formation on boiler heat exchanger surfaces were studied. The sintering processes involved in bed agglomeration has been studied in circulating fluidized bed combustors and fluidized bed gasifiers while ash sintering as a cause for fouling has been studied in a pulverized coal-fired boiler with limestone injection for sulphur dioxide removal and in boilers burning pulping process spent liquor, in the black liquor recovery boilers. The study has made use of both laboratory experiments and full-scale measurements. The main laboratory method used is a sintering test based on compression strength measurements of heat treated cylindrical ash pellets. In the full-scale tests, air-cooled probes have been used for collecting short term deposit samples. In the bed agglomeration studies the sintering test was at first used as a predictive tool to forecast possible bed agglomeration problems in fluidized bed boilers. Three sintering mechanisms were identified to be able to cause bed agglomeration in fluidized bed processes: sintering caused by partial melting, sintering due to viscous flow of the glassy silicate phase in the ash, and sintering caused by chemical gas-solid reactions. The sintering tendency of the coal ashes was also tested under typical fluidized bed gasification conditions. In the fouling studies of black liquor recovery boilers, the effect of chlorine, potassium and carbonate on the fluegas dust sintering were examined