GB927929A - An improved method of removing carbon dioxide from gaseous mixtures - Google Patents

Abstract

CO2 is at least partially recovered from aqueous alkaline solutions containing arsenite ions which have been employed, according to the process of the parent Specification, to absorb CO2 from gaseous mixtures containing it by passing a desorbing gas, e.g. air, through the solution which is at a temperature below the boiling point at atmospheric pressure and not more than 15 DEG C. above the temperature of the absorption. A converter gas containing, for example, 16-18% by volume CO2 is scrubbed with say an aqueous solution of potassium carbonate containing <PICT:0927929/III/1> dissolved arsenious oxide in varying proportions up to that required to yield a solution corresponding to potassium orthoarsenite preferably at superatmospheric pressure, e.g. 11 atmospheres. Spent absorption solution is expanded and regenerated, CO2 being desorbed by contacting the solution with air at temperatures below the boiling point of the solution at atmospheric pressure, i.e. below 100 DEG -105 DEG C., e.g. ambient temperature or 60 DEG -75 DEG C. The heat required, if any, for the regeneration step may be supplied by recovery or dead steam, or any steam of low thermal content, e.g. discharge steam from power plants or other industrial processes. In a modification of the above process, regeneration may be effected in two stages, the first by boiling the solution to effect partial CO2 desorption, and the second by passing desorbing air through the solution at a lower temperature. CO2-containing gases are scrubbed with absorption solution in tower 1 under superatmospheric pressure. The solution is expanded and passes in part through heat exchanger 2, where it is heated by partially regenerated solution from tower 3, and in part through line 9 to tower 3, where it is heated to its boiling point, indirectly by steam in coil 4, or directly by steam entering through 8. Desorbed CO2 escapes from the top of tower 3. Partially regenerated solution passes through heat exchanger 2 to the top of tower 5, and down therethrough in countercurrent to air blown in from 6 completing regeneration, and lowering its temperature to that for absorption, before reintroduction into tower 1 through pump 7. Arsenate formed by oxidation of arsenite in the solution is converted to arsenite by action of a reducing agent at above 150 DEG C. Sulphuretted arsenic compounds formed by H2S in the gases are removed by treatment with alkali metal cyanides, or as insoluble sulphides by action of metal salts, e.g. lead carbonate. Specifications 786,669 and 873,462 also are referred to.