Separation of carbon dioxide from gaseous mixtures

摘要

CO2 is recovered from gaseous mixtures containing it together with H2, N2, O2, CO, H2S, hydrocarbons, moisture and air by absorption at superatmospheric pressure in a countercurrent stream of glycerol triacetate, reduction of the pressure to flash off the CO2 and subsequent recycling of the lean triacetate solution for further CO2 absorption. A gaseous mixture containing CO2 under a partial pressure of CO2 of 40-600 p.s.i.a., preferably 60-600 p.s.i.a., and a temperature of 30 DEG -130 DEG F., preferably 70 DEG -120 DEG F., enters the base of a packed or tray-filled absorption tower 11 through line 10 and flows in counter-current to a descending stream of glycerol triacetate cycling in the system and entering the tower through line 12. Undissolved gases are vented through line 13 to a suitable receiver 14. Rich triacetate solution containing absorbed CO2 leaves the base of the absorption tower through line 15 and passes either directly through line 15, valve 17 and line 15a to flash-off chamber 18 or indirectly through cooler 16 which removes the excess heat of solution. Solution passing through valve 17, which may be a turbine, into chamber 18 undergoes controlled pressure reduction, usually to atmospheric pressure, to effect dissolution of absorbed CO2 which is vented through 19. Lean triacetate solution may by recycled direct to the absorption tower by pump 20 through lines 21 and 12 or some or all may be subjected to gas stripping in tower 23 to remove final traces of absorbed CO2. Tower 23 receives stripping gas, e.g. air or inert gases, through line 24 usually at the rate of 1-4 SCF/gallon of triacetate solution, and vents stripping gas and desorbed CO2 through an overhead line, triacetate solution passing out through line 25 back to the absorption tower. Stripping of final traces of absorbed CO2 may also be effected by application of a vacuum in tower 23. Moisture absorbed by the rich triacetate solution from the feed gas will be flashed off with the CO2. In a modification of the above process (not shown) wherein CO2 is removed from gases comprising hydrocarbons which normally cause problems by solution in the glycerol triacetate, the rich triacetate solution is removed from the absorption zone of the tower and passed into a lower medium pressure flash-off chamber forming the bottom of the tower, where the pressure is reduced to between that existing in the absorption zone and the vapour pressure of the CO2 in the rich triacetate solution at the temperature of operation. Flash-off gas comprising mainly hydrocarbon is removed from the chamber and may be compressed and coded and recycled to the absorption tower for recovery with the other undissolved gas or be used independently as a fuel. The remaining partially regenerated solution is passed to the final flash-off chamber 18 as before.