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Hydrogen sulfide removal from biogas with a fixed bed of rusted iron turnings Canas, Carlos Gonzalo

Abstract

Biogas produced at farm level has many applications, however the hydrogen sulfide must be eliminated from the biogas to prevent any possible damage to equipment, users and operators, and the environment. Among the various options available to the farmer to clean hydrogen sulfide from biogas a fixed-bed of rusted iron turnings seems appropriate. This study investigated the effectiveness of a fixed bed of rusted iron turnings in eliminating hydrogen sulfide. For that purpose, dynamic bench scale test were done to study the effects of flow rate (0.5 l/min, 0.75 l/min and 1.0 l/min) and hydrogen sulfide concentration (100 ppm and 200 ppm). The gas used was a mixture of saturated carbon dioxide and hydrogen sulfide. The iron turnings were made with a uniform thickness and width and allowed to oxidize under atmospheric conditions for 8 weeks. The resulting breakthrough curves were well described by sigmoidal curves. The breakpoint time was affected by flow rate and hydrogen sulfide concentration. At the higher flows and concentrations the breakpoint times were smaller. In contrast, the mass of hydrogen sulfide removed up to breakpoint time was independent of flow rate and hydrogen sulfide concentration (0.83 g). Nevertheless, the maximum removal capacity was independent of hydrogen sulfide concentration but dependent on flow rate. The rate data conformed well to a surface rate model, however the calculated pseudo-rate constants were different for the flow rates and hydrogen sulfide concentrations used in this study. Thus it was not possible to define a mechanism control for the rate of reaction. The fixed-bed was able to eliminate hydrogen sulfide from the gas mixture, however only 30 to 44% of the iron oxide reacted.

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