THE BEHAVIOR OF BED MATERIAL DURING FLUIDIZED-BED GASIFICATION - THE EFFECTS OF MINERAL MATTER INTERACTIONS

In the British Coal Topping cycle coal is partially gasified in a pressurized fluidized bed gasifier to give a char and ash. A study of eight UK coals has shown that under these conditions each coal produced an ash which has a much finer size distribution than the parent coal. Changes in ash composition with size fraction have been related to the mineral matter in each coal. Each ash showed a decrease in SiO2 and Al2O3 with decreasing size and an increase in Fe2O3 content. Fine pyrite particles have been observed to coat the surfaces of many of the larger clay particles. In instances where agglomeration between clay particles had occurred bonds of either Fe-S-O or an iron aluminosilicate glass were observed. Part washing one of the coals preferentially removed quartz, kaolinite and illite, thus enriching the remaining mineral matter in pyrite. The run-of-mine coal, although with a higher ash content, would be expected to show a lower propensity towards the formation of agglomerates.