Abstract
Hydrogen sulfide (H2S) is a corrosive trace gas present in biogas produced from anaerobic digestion systems that should be removed to reduce engine-generator set maintenance costs. This study was conducted to provide a more complete understanding of two H2S scrubbers in terms of efficiency, operational and maintenance parameters, capital and operational costs, and the effect of scrubber management on sustained H2S reduction potential. For this work, biogas H2S, CO2, O2, and CH4 concentrations were quantified for two existing H2S scrubbing systems (iron-oxide scrubber, and biological oxidation using air injection) located on two rural dairy farms. In the micro-aerated digester, the variability in biogas H2S concentration (average: 1938 ± 65 ppm) correlated with the O2 concentration (average: 0.030 ± 0.004%). For the iron-oxide scrubber, there was no significant difference in the H2S concentrations in the pre-scrubbed (450 ± 42 ppm) and post-scrubbed (430 ± 41 ppm) biogas due to the use of scrap iron and steel wool instead of proprietary iron oxide-based adsorbents often used for biogas desulfurization. Even though the capital and operating costs for the two scrubbing systems were low (<$1500/year), the lack of dedicated operators led to inefficient performance for the two scrubbing systems.
Highlights
Hydrogen sulfide (H2 S) is a corrosive gas that can corrode and damage, even in trace quantities, engine-generator sets (EGS) utilizing biogas from anaerobic digestion (AD) for electricity production.The produced H2 S can react with water vapor present in the biogas producing hydrosulfuric acid that can be further oxidized to sulfuric acid, which can cause corrosion
The objective of this study was to quantify the efficacy and costs associated with H2 S scrubber systems using units on dairy farms with AD systems
The unheated digester was exposed to ambient temperatures, which resulted in lower biogas production during winter months
Summary
Hydrogen sulfide (H2 S) is a corrosive gas that can corrode and damage, even in trace quantities, engine-generator sets (EGS) utilizing biogas from anaerobic digestion (AD) for electricity production. The produced H2 S can react with water vapor present in the biogas producing hydrosulfuric acid that can be further oxidized to sulfuric acid, which can cause corrosion. Hydrogen sulfide is toxic to living organisms under certain concentrations and can result in range of adverse health effects. Occupational Safety and Health Administration (OSHA) lists the acceptable ceiling concentration for human exposure to H2 S to be 20 ppm for an 8-h duration [1]. The total weighted average exposure limit is 10 ppm over 8 h. The acceptable peak concentration above the ceiling concentration is 50 ppm, but for a maximum time limit of 10 min.
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