Improvements in Residence Time and Air Oxidation For H2S Abatement in The Geysers' Geothermal Power Plants With Direct-Contact Condensers and Crossflow Cooling Towers

Abstract

H2S abatement efficiency in geothermal crossflow cooling towers can be improved by increasing the reaction time and dissolved oxygen concentration in the circulating water (Ballantine, 1993). Additional efficiency is accomplished at Geysers? units with direct-contact condensers by raising the water level in the cooling tower hot water distribution trays and increasing aeration in the circulating water entering the tray. Cooling tower H2S emissions are abated at The Geysers by the addition of a chelated iron compound into the circulating water. The time allowed for the iron/ H2S abatement reaction to occur is limited to the duration that the circulating water/condensate mixture takes to leave the condenser and then drop through the cooling tower fill where any unreacted dissolved H2S is air stripped and emitted to the atmosphere. Increasing the depth of the water in the cooling tower hot water distribution trays was found to provide additional residence time for the iron/H2S reaction to occur. Furthermore, aeration of the water contained in the hot water distribution trays increased the circulating water dissolved oxygen concentration which re-oxidizes the iron contained in the water such that additional H2S abatement could be achieved with less iron solution added to the circulating water. The result is lower operating cost for H2S abatement. This paper explains how chelated iron usage can be reduced if cooling tower distribution deck water levels are increased or if cooling water on the hot deck is aerated, thereby allowing more time for the oxidation of H2S and decreased H2S emissions.