Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Carbon dioxide or hydrogen sulfide component
Patent
1990-01-19
1992-07-28
Straub, Gary P.
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Carbon dioxide or hydrogen sulfide component
423228, 55 73, 422168, C01B 1716
Patent
active
051339498
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process for the removal of H.sub.2 S present at low concentration in a gas which also contains a large quantity of water vapour. It also relates to a device for making use of this process.
Gases containing H.sub.2 S at low concentration, namely in a concentration ranging from 10 volumes per million to 10% by volume, and also containing a quantity of water vapour ranging from 5 to 60% by volume are frequently encountered in industry. This is particularly the case with certain residue gases and especially residue gases of a sulphur plant, which have been subjected to a hydrogenation and hydrolysis treatment to bring all the sulphur compounds which they contain into the single H.sub.2 S form, or else synthetic gases which are obtained, for example, by hydrogenation or cracking of carbonaceous products such as coal, wood or petroleum residues
Such gases are generally subjected to a treatment for the removal of the H.sub.2 S which they contain either, when synthesis gas is involved, to prevent this compound from perturbing the synthesis reactions in which these gases are to take part, or, in the case of residue gases, to bring these gases within the standards imposed by legislation concerning atmospheric pollution before they are discharged into the atmosphere.
In a known process (FR-A-2,101,724), which is employed for the treatment of residual gases orieinating from a Claus sulphur plant and which primarily comprises stage of hydrogenation and hydrolysis of sulphur compounds other than H.sub.2 S which are present in the said residue gases to bring these sulphur compounds into the single form of H.sub.2 S, the gas stream resulting from the said hydrogenation and hydrolysis stage, which has an H.sub.2 S content of less than 5% by volume and water vapour concentration of the order of 30% by volume, is cooled to a temperature below the dew point of the water which it contains, to condense virtually all this water. The water-free gas stream is then scrubbed countercurrentwise, be operating at a temperature below 50.degree. C., with a regenerable solvent binding H.sub.2 S, for example an aqueous solution of a secondary or tertiary alkanolamine, and the scrubbed gas stream is then subjected to an incineration to convert into SO.sub.2 the last traces of H.sub.2 S which it may still contain, and is then discharged into the atmosphere.
In a process of this kind, the water condensed during the stage of cooling the hydrogenated gas stream is an acidic water saturated with H.sub.2 S, which must undergo a specific purification treatment to be capable of being reemployed in the process or discharged as waste water, a treatment of this kind being complex and by the same token costly, especially because of the large volumes of water to be treated.
To avoid the disadvantages due to the condensation of water, reference FR-A-2,425,886 proposes to do away with this condensation by permanently maintaining the temperature of the gas stream at all points of the plant at a value above the dew point of the water contained in the said gas stream.
When operating in this way, it is necessary for the contact between the hydrogenated gas stream and the regenerable solvent to be brought about at higher temperatures, namely between 65.degree. C. and 85.degree. C., and, furthermore, all the water vapour is present in the gas stream when this contact takes place. These operating conditions result in the use of a markedly higher solvent flow rate, namely approximately three times more, to obtain the same degree of removal of H.sub.2 S.
In the process of reference FR-A-2,449,470, the stage of condensation of the water contained in the gas stream to be treated originating from the hydrogenation is maintained, before the said gas stream is brought into contact with the regenerable solvent, but the condensed water is injected into the circuit of the said solvent and the temperature of this solvent is adjusted to a suitable value of the order of 70.degree. C. when it is injected into the zone for bringing into contact with
REFERENCES:
patent: 4308243 (1981-12-01), Castel
patent: 4452763 (1984-06-01), van de Kraats
patent: 4869884 (1989-09-01), Riggs
European Patent Application 0,124,835 by Edwards Nov. 14, 1984.
Elgue Jean
Tournier-Lasserve Jacques
Societe Nationale Elf Acquitaine (Production)
Straub Gary P.
Vanoy Timothy C.
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