Presentation of a dry black liquor gasification process with direct causticization

摘要

In a new black liquor gasification process,black liquor is injected into a circulating fluidized bed,with sodium titanate (Na_2O centre dot (TiO_2)_3) as the fluidizing medium.The organics are gasified mainly by steam reforming because the temperature is relatively low (below 870 deg C) and the water content of the black liquor is relatively high (>20% water).The black liquor inorganics consist mainly of sodium carbonate and sodium sulfate.In the reactor,sodium carbonate is converted into Na_2OTiO_2,which is removed from the bed and dissolved in water to give 4 NaOH + Na_2O(Ti0_2)_3.After dewatering,this material is reinjected into the fluidized bed.The sulfate is reduced to Na_2S,and most of the sulfur is evaporated as H_2S after Na_2S reacts with CO_2 + H_20.In a scrubber,the H2S is selectively absorbed without CO_2.The direct causticization makes the lime kiln unnecessary.The gas is reheated after dust is removed and then combusted in a gas turbine/steam turbine cycle,to produce 2-3 times more electricity than produced in steam cycles with conventional recovery boilers.