The present invention relates generally to the purification of steam produced by geothermal sources and more particularly to a process for abating, or removing, the hydrogen sulfide content of the steam.
In many areas of the world, geothermal steam is present at temperatures and pressures sufficient for utilization in turbines for the generation of electricity. Unfortunately, the geothermal steam contains a number of contaminating gases such as carbon dioxide, ammonia, nitrogen and hydrogen sulfide among others.
It has been widely recognized that in many instances, the hydrogen sulfide content of geothermal steam is sufficiently high to make discharge of the steam into the air environmentally unexceptable.
Therefore, it has been the object of many investigators to remove, or abate, the hydrogen sulfide in the geothermal steam in order to make release to the atmosphere an exceptable procedure.
Many methods for removing hydrogen sulfide from gases, have been developed. For example, gas containing hydrogen sulfide may be contacted with activated carbon to catalyze the oxidation of hydrogen sulfide to elemental sulfur and water. Some investigators, for example, see U.S. Pat. No. 4,330,307 issued to Coury in 1982, have developed methods to separate the geothermal steam into a usuable portion, having a low hydrogen sulfide content, and a vent portion or stream, containing the majority of the hydrogen sulfide, the latter being disposed of by reinjection into the ground. Reinjection of this vent portion is not desireable, however, because the H.sub.2 S may migrate and present itself in newly extracted steam.
The process described in U.S. Pat. No. 4,374,106 to Tipton is directed to a process for removing hydrogen sulfide from a geothermal steam by contacting the steam which is mixed with an oxygen containing gas, such as air, with iron oxide and wherein the molar ratio of oxygen to hydrogen sulfide in the steam and oxygen containing gas is at least 10.
It has now been discovered that hydrogen sulfide can be effectively removed from geothermal steam by mixing an oxygen containing gas with the geothermal steam to provide a molar ratio of oxygen to hydrogen sulfide less than 10 and contacting the mixture with iron oxide under specific process conditions. Further, it has been found that elemental sulfur can be recovered on a continuous basis from the geothermal steam after it is contacted with the iron oxide.
More specifically, the process is effective in removing high concentration, of hydrogen sulfide from geothermal steam such as concentrated in the vent stream of processes such as described by Coury (U.S. Pat. No. 4,330,307).
These results are unexpected and not anticipated by the prior art which has been extensively discussed in Tipton et. al. (U.S. Pat. No. 4,374,106).