Dynamic purification of coal ash by a gas–solid fluidized bed

Fluidized bed filtration classified as granular bed filtration is a solution for removing particles from flue gas. Fine particles are captured by colliding with bed material. Binary mixtures including fines exist in the fluidized bed; the situation becomes more complex because the fines increases with time as particles enter continuously. Coal ash was put into the inlet gas of a gas–solid fluidized bed with silica sand and the variations in concentration with time was monitored, to elucidate the dynamic purification of fines by bed material and the interaction therewith. Water was injected into the inlet gas also to study the influence of water content on the removal of particles. Experimental results showed that the particle concentration rapidly increased with time until equilibrium was achieved. The outlet concentrations exceeded the inlet concentration (such that the removal efficiency was negative) at operating time between 26 and 30 min, yielding an efficiency as low as −35%. The removal efficiency increased with the relative humidity from 30% to 70%. The maximum cumulative collection ratios of particles (by mass) were 20%, 22% and 27% at humidities of 30%, 50% and 70%, declining to 7%, 13%, and 19% at the end.