Abstract: A process for selectively absorbing H.sub.2 S from gas mixtures which contain CO.sub.2 and H.sub.2 S in a molar ratio of 4:1 or greater and in which the gas flow rate varies substantially. Alkali metal carbonate solutions are used with absorption under pressure and at an elevated temperature and desorption by steam stripping at about atmospheric pressure. The degree of selectivity of H.sub.2 S removal is maintained constant despite substantial variations in the gas flow rate by maintaining a constant stripping steam/gas ratio selected to provide the desired partial pressure of H.sub.2 S in the purified gas and by adjusting the solution/gas ratio to a value in the vicinity of that at which the partial pressure of H.sub.2 S in the purified gas remains at said selected value while the difference between the partial pressures of CO.sub.2 and H.sub.2 S in the purified gas reaches a maximum value, and by then maintaining such solution/gas ratio as the gas flow rate varies.
Abstract: A process for removing acid gases such as CO.sub.2 and H.sub.2 S from gas streams using an aqueous alkaline scrubbing solution which is circulated between an absorption and regeneration stage wherein the stripping steam for regeneration is derived at least partly from the hot feed gas to be purified. The thermal efficiency of the process is substantially improved by first heat-exchanging the hot feed gas with the scrubbing solution to raise stripping steam and then heat-exchanging the hot feed gas with water (which is preferably condensate water produced in the scrubbing process) in a second heat exchanger operating under reduced pressure, thus recovering additional low-level heat from the feed gas and producing low-pressure steam which is compressed and then utilized as additional stripping steam.
Abstract: An improved ammonia synthesis train utilizing hydrocarbon starting materials which are converted to hydrogen under superatmospheric pressure in a series of steps which include conversion of the hydrocarbons to hydrogen-carbon monoxide mixtures, shift conversion of the carbon monoxide to hydrogen and CO.sub.2, and removal of the CO.sub.2. In such a system, reduction in process gas losses is achieved through an improved arrangement and integration of the shift conversion and CO.sub.2 removal steps. The carbon monoxide is first shifted in a series of shifts including a final low temperature shift; the bulk of the CO.sub.2 is removed by an essentially isothermal hot potassium carbonate CO.sub.2 removal system; the small residual amount of carbon monoxide is shifted to very low levels in a final low temperature shift; and the small amount of residual CO.sub.2 is then removed to very low levels in a second non-isothermal scrubbing system employing an aqueous solution of a chemical absorbent.