BED MATERIAL COHESION AND LOSS OF FLUIDIZATION DURING FLUIDIZED-BED COMBUSTION OF MIDWESTERN COAL

Tests were conducted in a laboratory-scale fluidized bed combustor to determine the factors and mineralogical reactions that initiate agglomeration of bed particles and lead to defluidization of fluidized bed combustors. Combustion products from these tests were analysed using X-ray fluorescence (XRF), X-ray diffraction (XRD), and petrographic relationships were determined from polished thin sections using transmitted polarized microscopy and scanning electron microscopy with an energy-dispersive X-ray detector (SEM-EDX). Loss of bed fluidization resulted when a cohesive aluminosilicate material wetted the surface of bed particles. This occurred when the combustion air was below 100% of theoretical values for complete combustion. Reduced iron may have acted as a flux to promote the flow of aluminosilicate particles. Solid-solid reactions involving calcium oxides and silicates (aluminosilicate cohesive material and quartz grains) also contributed to the bonding of bed particles and loss of fluidization. Reaction products produced without limestone included pyroxene and amphibole; with limestone, wollastonite was ubiquitous.