Patent GB-1255201-A (GB)
Title: Improvements in or relating to separation of co2 and h2s from gas mixtures
Inventor: BENSON HOMER EDWIN
IPC: B01D53/14
Filed: 1969-03-18
Abstract: 1,255,201. Removing H 2 S and CO 2  from gas streams. H. E. BENSON, J. H. FIELD and W. E. EPES. 18 March, 1969 [22 March, 1968], No. 14280/69. Heading B1L. CO 2  and/or H 2 S are removed from gas streams, e.g. natural gas or gas from the shift reaction, by passing the stream by line 18 to absorber 10 which is operated at superatmospheric pressure. In zone A, the gas flows in countercurrent to scrubbing liquid which enters by line 11, and in zone B in countercurrent to liquid which enters by line 15, the purified effluent leaving by line 20, condenser 21 and line 23. Rich scrubbing liquid from zone A of absorber 10 passes by lines 13 and 28 to zone C of regeneration column 25, while that from zone B passes by lines 17 and 32 to zone D; zone C of column 25 is maintained at a higher temperature and pressure than zone D. In zones C and D, the rich liquid falls in countercurrent to steam which enters zone C by line 38 and zone D by lines 42 and 49. In the embodiment shown, the hot gas stream entering the process by line 43 is used to raise the steam in lines 38 and 42 by heat exchange in reboilers 35 and 39 with recycled portions of the regenerated scrubbing liquid obtained from sumps 29 and 33 respectively, before passing by lines 46 and 18 to absorber 10. Vapourladen effluent acid gases leave zones C and D by lines 54 and 58, passing to condensers 55 and 59 before being vented, condensate being returned to zones C and D by lines 56 and 60 respectively. Regenerated scrubbing liquid from sump 29 of zone C is passed by line 30 to vessel 47 where it is flashed to lower pressure, steam resulting therefrom being passed by line 49 to zone D of column 25. The flashed liquid is then returned from vessel 47 to zone A of absorber 10 by lines 51 and 11. Regenerated scrubbing liquid in sump 33 of zone D of column 25 is returned directly to zone B of absorber 10, by means of lines 34 and 15. In other embodiment, (a) where the gas to be treated is cool, the stream is passed directly to the absorber, steam is raised in the reboilers by heat exchange with steam, and the effluent scrubbing liquids in zones A and B are regenerated in zones D and C respectively (see Fig. 2, not shown); (b) regenerated scrubbing liquid, before entering absorbing zone B, is first heat exchanged with rich liquid leaving zone B and then cooled (see Fig. 3, not shown); (c) rich scrubbing liquid from zone A is regenerated in zone C which is sub-divided serially into separate sub-zones, each of which supplies regenerated liquid to a separate flash vessel, the most highly regenerated liquid which has passed through both sub-zones being returned to the head of zone B, regenerated liquid from zone D being returned to an intermediate point of zone B, and less highly regenerated liquid which has only passed through the upper of the two sub-zones of zone C being mixed with regenerated liquid from zone D and returned to the head of zone A (see Fig. 4, not shown); (d) regenerated liquid from zone C is in part passed to the head of zone B, while regenerated liquid from zone D is in part passed to an intermediate point of zone B, and in part mixed with part of the liquid from zone C and passed to the head of zone A (see Fig. 5, not shown); (e) zone B is divided, each sub-zone being supplied at the head with regenerated liquid from zone C, and each supply rich liquid for regeneration to zone C, rich liquid for regeneration from zone A passing to zone D (see Fig. 6, not shown); and (f) the absorber comprises 3 zones A, B, and C, while the regenerating column comprises 2 zones D and E the lower of which (E), operating at higher temperature and pressure, comprises 2 serial sub-zones, zone D receiving rich liquid from zone A and returning regenerated liquid to zone A, the upper sub-zone of zone E receiving rich liquid from zone B and returning regenerated liquid to zone B, and the lower sub-zone of zone E receiving rich liquid from zone C and returning regenerated liquid to zone C (see Fig. 8, not shown). In all these embodiments, flow in the absorber between gas being treated and scrubbing liquid is countercurrent. In Fig. 7 (not shown), a 3-zone absorber is illustrated in which gas and liquid flow in the first zone is co-current; but countercurrent in the second and third zones. The scrubbing solution is suitably aqueous potassium carbonate preferably containing diethanolamine; an alkali metal borate, arsenious oxide or an amino acid such as glycine may, however, also be included.