Cycle flue gas desulphurisation - using ammonium sulphite soln. with desorption by ammonium hydrogen sulphate melt regenerated by direct heating

摘要

Desulphurisation of flue gases from fossil fuels or other SOx-contg. waste gases using NH3 involves (a) washing the gas with solns. contg. NH4HSO3, (NH4)2SO3, (NH4)2SO4 and some (NH4)2S2O3 and (NH4)2S3O6 to sorb SO2, SO3, H2SO4 mist and opt. other S cpds.; (b) reaction by the soln. with a hot NH4HSO4 melt to desorb SO2 and crystallisation of the (NH4)2SO4 formed by evapn.; and (c) melting the (NH4)2SO4 by direct heating at 250-400 degrees C and decompsn. to NH4HSO4 or (NH4)2S2O7 and NH3, pt. of the NH4HSO4 or (NH4)2S2O7 corresp. to the increase in (NH)42SO4 in (a) being reduced to (NH4)2SO4 and SO2 by CO or other substances from the incomplete combustion of the fuel, sot hat the O2 excess in the combustion gas is regulated at 0.3 vol.% O2. The NH3 gas contg. So2 is recycled to (a), whilst the NH4HOS4 melt contg. (NH4)2SO4 from (c) is recycled for reaction according to (b). The use of the min. excess of air saves fuel and keeps the NH3 yield high. No special equipment or process stage is necessary for redn. of the NH4HSO4.