Wastage rate of water walls in a commercial circulating fluidized bed combustor

Abstract

Wastage rate profiles of water walls were determined in a large (200 tonnes steam/h, 4.97 m x 9.90 m x 28.98 rn tall) commercial circulating fluidized bed furnace by measuring tube thickness with an ultrasonic thickness gauge. The wastage rate was most significant in the region just above the refractory lining on all water walls, decreasing with increasing height. Wear in this region was enhanced at the centre of the sidewalls, on some sidewall tubes near the front wall, and on outer areas of the front and rear walls. The wear pattern was complex around the gas exit level. Wastage increased with increasing height on the front wall below the gas exit. Wastage decreased, then increased, with increasing height at the top of the front wall. Above the gas exit level, the wastage on the rear wall was less than on the front wall. Tubes just below the gas exit were subject to appreciable wear on the rear wall. High wastage rates also occurred on some tubes near the centre of the sidewalls at the gas exit level. On all wing walls the wastage rate decreased, then increased, with increasing height. The wastage rate of many tubes below 7 m on all water walls exceeded the maximum acceptable wear rate for steel boiler tubes in a coal-fired utility plant, while for some tubes at the gas exit level on all walls it was close to the maximum acceptable rate.