The influences of coal type on in-bed desulphurization in a PFBC demonstration plant

Desulphurization features of Blair Athol (BA), Witt Bank (WB), Nang Tong (NT) and Drayton (DT) coals were investigated in a 71 MW demonstration plant PFBC boiler operated at bed temperature of around 850 °C, Ca/S molar ratios in feeds of above three, partial pressure of CO₂ at combustion boiler outlet of around 0.9 kg/cm² and boiler load of 50%, to clarify the influences of coal type on the in-bed desulphurization achievement. Bed materials (BM) and fly ashes (FA) were characterized to describe their roles in the desulphurization. SO₂ emission in the stack was found 3, 2, 41 and 27 ppm in the respective combustion of BA, WB, NT and DT. The desulphurization efficiencies were determined by their Ca/S molar ratio of the fine sorbent formed by attrition. The ratios were 1.51, 2.98, 0.79, and 0.67 for BA, WB, NT and DT, respectively. Calcination in the bed increased the attrition rate of the sorbent to allow a better desulphurization in PFBC. However, the very high attrition rate yielded a large amount of unreacted sorbent which was entrained out from the bed, lowering the calcium utilization efficiency.