Process for separating gases

摘要

Carbon dioxide is separated from gas mixtures by passing a stream of the gas through an absorbtion tower or column wherein the carbon dioxide is absorbed by a 2N to 8N ammoniacal solution lean in CO2, to produce a solution rich in CO2, passing the resulting solution through a heat exchanger under a pressure of at least 3, and preferably 5, atmospheres absolute, flashing the solution into a regenerator where the solution is heated indirectly to regenerate lean solution, passing this regenerated lean solution through the heat exchanger to heat the incoming rich solution, without coming into direct contact therewith, and thereafter returning the lean solution to the absorbtion column. Preferably the CO2: NH3 molar ratio in the liquor employed in the washing step is 0,6, and is regenerated when the ratio reaches 0,8. The gas mixture may be one which has undergone a shift reaction to convert carbon monoxide to carbon dioxide. Fig. 1 illustrates a suitable plant for carrying out the process of the invention, in which combustible gases which have undergone a shift reaction to convert carbon monoxide to carbon dioxide enter the plant at atmospheric pressure at point 10, and are forced by a booster 11 via a washer cooler 12 into the absorption column 13 and then via a washer 14, where ammonia is removed, to further stages in town gas manufacture. Ammoniacal liquor is supplied from 15, and the effluent from 13 is stored in 17. This effluent is pumped by pump 18 and split into two streams, one of which is passed through heat exchanger 19 into preheater 20 from where it is flashed into flash chamber 22 via reducing valve 21. Some CO2 is released in 22, and more is expelled in reboiler 23. The liquor from 23 is cooled in heat exchanger 19 and cooler 29, and returned to 15. The second stream of effluent is cooled in cooler 24 and passed to the top of scrubber 25 to remove ammonia from the gases leaving the regenerator. Final traces of ammonia are removed in acid scrubber 26.