Patent GB-1077324-A (GB)
Title: Improved method for the regeneration of cooking liquor from waste liquor obtained from cooking cellulose containing fibre materials
IPC: D21C11/00
Filed: 1965-01-29
Abstract: In the regeneration of pulp cooking liquors which contain a mixture of Na2SO3 or Na2SO3/NaHSO3 and NaHCO3 and/or Na2CO3, waste pulp liquors are evaporated and the smelt soda produced, mainly Na2CO3 + Na2S, dissolved in water.  The solution obtained is treated with pure CO2 to drive off H2S and produce a NaHCO3/Na2CO3 solution, a portion of which is removed for use in preparing fresh pulp liquor, the remainder being treated with SO2 or NaHSO3 solution to decarbonate it, giving CO2 for use in the sulphide removal step and a Na2SO3 and/or NaHSO3 solution at least part of which is used in the preparation of fresh pulp liquor.  The CO2 removed from the regenerating cycle in that portion of the Na2CO3/NaHCO3 solution which is used as pulp liquor is replaced by feeding additional CO2 into the regenerating cycle.  This addition of CO2 is preferably accomplished by treatment of the smelt soda solution in a pre-carbonating step with a suitably SO2-poor, CO2-containing gas in such restricted quantity as to avoid release of H2S.  Said SO2-poor, CO2-containing gas is preferably produced by leading waste gases formed in the combustion of the waste liquor through a solution containing Na2SO3, preferably that formed in the decarbonating of the residual portion of the Na2CO3/NaHCO3 solution in the regeneration cycle.  As in the prior art, the H2S containing gas from the smelt soda solution treatment may be reacted with SO2 in a contact furnace to remove the H2S and form S, the CO2-containing gases formed being used in the smelt soda solution carbonating step.  The S formed may be burned to produce the SO2 necessary in the regeneration cycle.ALSO:In the regeneration of pulp cooking liquors which contain a mixture of Na2SO3 or Na2SO3 /NaHSO3 and NaHCO3 and/or Na2CO3, waste pulp liquors are evaporated and the smelt soda produced, mainly Na2CO3+Na2S, dissolved in water.  The solution obtained is treated with pure CO2 to drive off H2S and produce a NaHCO3/Na2CO3 solution, a portion of which is removed for use in preparing fresh pulp liquor, the remainder being treated with SO2 or NaHSO3 solution to decarbonate it, giving CO2 for use in the sulphide removal step and a Na2SO3 and/or NaHSO3 solution at least part of which is used in the preparation of fresh pulp liquor.  The CO2 removed from the regenerating cycle in that portion of the Na2CO3/NaHCO3 solution which is used as pulp liquor is replaced by feeding additional CO2 into the regenerating cycle.  This addition of CO2 is preferably accomplished by treatment of the smelt soda solution in a pre-carbonating step with a suitably SO2-poor, CO2-containing gas in such restricted quantity as to avoid release of H2S.  Said SO2-poor, CO2-containing gas is preferably produced by leading waste gases formed in the combustion of the waste liquor through a solution containing Na2SO3 preferably that formed in the decarbonating of the residual portion of the Na2CO3/NaHCO3 solution in the regeneration cycle.  As in the prior art, the H2S containing gas from the smelt soda solution treatment may be reacted with SO2 in a contact furnace to remove the H2S and form S, the CO2-containing gases formed being used in the smelt soda solution carbonating step.  The S formed may be burned to produce the SO2 necessary in the regeneration cycle.