GB653317A - Improvements relating to the removal of hydrogen sulphide from industrial gases - Google Patents

Abstract

<PICT:0653317/III/1> <PICT:0653317/III/2> In a process for the removal of H2S from gases by treating the gases in a purification zone with an excess of SO2 in the presence of a solid adsorbent for the H2S and SO2, e.g. activated alumina or carbon, which acts also as a catalyst in the reaction of H2S with SO2 resulting in the deposition of S on the adsorbent, the catalytic and adsorptive properties of the adsorbent are maintained at a high level by continuous withdrawal from the purification zone and continuous replenishment of the zone with freshly regenerated adsorbent. In Fig. 2 unpurified gas from the main 1 is mixed with SO2 from the pipe 10 and passed to the bottom of a purifier chamber 3 containing a descending mass of adsorbent solids, preferably in granular form, which is constantly replenished from a hopper 5. The purified gas passes out at 4. The bottom of the purifier may be warmed by any suitable means, a temperature up to 80 DEG C. being maintained. The fouled adsorbent solids pass into a desorption vessel 7 in which adsorbed gases, particularly the excess of SO2, but including moisture, vapours of benzole or similar oils if the original gas included these, are liberated by heat supplied by a pipe system as described below, a final temperature of 160-180 DEG C. being reached, a purging gas admitted by the pipe 8 and preferably being the original unpurified gas stripping the final traces of SO2 from the adsorbent. The stripping gas SO2 &c. pass through a pipe 9 to a condenser 20, 22 for removing benzole, water, &c. and then through the pipe 23 to the main 1. The adsorbent solids pass from the vessel 7 to the regenerator 12 which is supplied by a pipe 13 with air for the oxidation of the sulphur. The SO2 thus generated is led off through a pipe 19 and some may be passed directly back to the main 1 by the pipe 10. The SO2 may be adsorbed in regenerated adsorbent which is returned to the purifier chamber 3 or the SO2 may be supplied from SO2 liquefied after the process or from an external supply. The reaction in the regenerator 12 is isothermic and is controlled by a heat-transfer medium which flows, in pipes, in counterflow to the adsorbent. The adsorbent entering the regenerator 12 is thus heated by the heat-transfer medium, and the material at the bottom of the chamber is cooled. Temperatures of from 280-500 DEG C. are used in the regenerator 12, although the latter temperature should not be used with a carbon adsorbent. The heat transfer pipes may pass upwardly into the desorption vessel 7 to provide the necessary heat in that chamber. The regenerated adsorbent passes through a valve 14 to a receiver 15 from which it is returned by compressed air supplied at 16, to the hopper 5. The pressures in different parts of the plant are adjusted to prevent undesired flows of gases, e.g. a flow from the purifier 3 to the pipe 9. By limiting the air supplied at 13, some of the S may be carried off as vapour with the SO2 and N and recovered in solid form. In operation, the mass at the bottom of the purifier rises in temperature, and adsorbed SO2 is consequently released to be adsorbed by cool adsorbent coming from the hopper 5. This effect is cumulative and the cool adsorbent may become saturated as regards SO2, allowing SO2 to reach the pipe 4. To avoid this, a part of the cool adsorbent may be byepassed directly to the desorption vessel 7, around the warm zone in which the initial adsorption is effected, the warm zone being situated in an open-ended vertical casing concentric with, and within, the walls of the purifier 3, the byepass being provided by the annular space between the casing and the purifier. Alternatively, a byepass pipe external to the purifier may be provided. In Fig. 5 the initial adsorption is effected in a vessel B which, as regards gas flow, is in series with a vessel C through which cool adsorbent passes directly to the desorption vessel 7. A parallel supply of adsorbent passes through the vessel B. In some cases it is necessary to have a desorption rate in the vessel 7 which is greater than the required regeneration rate in the regenerator 12. In this case a part of the desorption material may byepass the chamber 12, being led directly from the vessel 7 to the receiver 15. Specifications 207,196, [Class 90], and 369,913 are referred to.