Removal of H/sub 2/S from geothermal steam. Final report

Abstract

The use of solid sorbents to remove hydrogen sulfide from geothermal steam was studied. Tasks consisting of a literature review, thermodynamic study of candidate sorbents, preparation of sorbents, obtaining sorbents from commercial sources, setting up sorbent screening and evaluation apparatus, screening of candidate sorbents and evaluation of screened sorbents under simulated geothermal steam conditions were carried out. No process, so far, has been developed commercially to remove H/sub 2/S from steam. Zinc oxide was verified as a good candidate by literature search and laboratory experiments. However, regeneration of sulfided sorbent proved to be difficult. Mixed metal oxide sorbents were prepared. Some of these sorbents reacted with hydrogen sulfide in a H/sub 2/S-air system; however, they show no activity to hydrogen sulfide in steam. Impregnation of catalyst support with organic compounds, such as diethanolamine was attempted. Diethanolamine was leached out of the impregnated sorbent upon contact with steam, and the sorbent failed to remove H/sub 2/S from steam. Solid organic sorbents were evaluated; one of these sorbents, Sorbent-0091 showed good potential. The sorbent reacted with H/sub 2/S under simulated geothermal conditions and could be regenerated easily by purging the spent sorbent with superheated steam. The high pressure drop through packed bedsmore » and excessive steam required for regeneration are major problems in the practical application of this particular material.« less