CHEMISTRY OF DEPOSIT FORMATION IN A COAL-GASIFICATION SYNGAS COOLER

During entrained slagging coal gasification utilizing syngas coolers (waste heat boilers), submicrometre to 10 mum spherical ash particles can be deposited as a fouling layer on the water wall tubes. Unlike conventional pulverized-coal-fired boilers, the conditions within the gasification process are reducing (P(O2) = 10(-11); P(S2) = 10(-5) atm). Metal sulfides along with fluoride and chloride compounds have been identified on the water wall and on the outer surfaces of the fly-ash particles, whereas alkali sulfates and iron oxide compounds are commonly repeated in layers responsible for fouling in the convection and superheater sections of coal-fired boilers. Once the initial fouling layer is formed, fly ash can adhere to it if an improper soot blowing design is chosen. The hardness and size of the deposit is a function of ash chemistry and fluid dynamics.