MECHANISMS OF BED MATERIAL AGGLOMERATION IN A PETROLEUM COKE-FIRED CIRCULATING FLUIDIZED-BED BOILER

Petroleum coke firing in a circulating fluidized bed boiler has someti mes been reported to be associated with cyclone deposit problems and r eturn leg plugging. In this paper we present data which indicate that some of these problems may be due to the calcium-rich bed material use d during the firing. We have earlier shown that calcium oxide may reac t with the flue gas components SO2 or CO2, causing neck growth between the solid particles. This neck growth between particles may lead to b oth deposits in the cyclone and plugging of the cyclone return leg. In this study we made use of a sintering testing method, based on compre ssive strength tests of heat-treated cylindrical pellets. Laboratory-p repared petroleum coke ash was mixed with two potential bed materials, limestone and dolomite, and sintering tests were performed in three d ifferent gas atmospheres. Significant differences were found between t he mixtures as a function of both the gas atmosphere and temperature. We also performed thermogravimetric analyses on one of the bed materia ls, the limestone. Based on these results a mechanism for the formatio n of cyclone deposits and bed material agglomeration in the return leg was suggested.