Sodium sulphate removal from sulphur dioxide absorption medium - by treatment with dry gas contg. sulphur dioxide to reduce sodium loss

摘要

Removal of SO2 from a gas is achieved by absorption in an aq. Na2SO3 soln. forming NaHSO3, followed by desorption of SO2 to regenerate the absorbent, Na2SO4 being formed in the system. The Na2SO4 is removed by contacting (part of) the aq. medium contg. NaHSO3 less Na2SO4 and less or no Na2SO3 with a gas contg. SO2 and (at least 50%) unsatd. with water vapour, so that enough water evaporates to ppte. up to 20, pref. 1-10, esp. 3-7 wt % of the solids from the soln. The ppte. contg. Na2SO4 and soln. contg. NaHSO3 are then sepd. the soln. pref. being recycled to the SO2 desorption stage. The Na2SO4 formed as by-prod. is sepd. without excessive loss of valuable Na cpds. from the system. The soln. treated with the gas is the spent absorption soln. so that the ratio of the wt. of Na2SO4 to the sum of the wts. of Na2SO4, Na2SO3 and NaHSO3 in the ppte. is greater than and pref. at least twice as great as that of the absorption-desportion medium. Treatment is carried out at 40-70 degrees C. Desorption is carried out with a suspension of NaHSO4 soln. contg. 25% undissolved solids.