The raw biogas basically is split into two gas streams during biogas purification: the methane-rich bio-methane stream and the carbon-dioxide-rich, Hydrogen sulfide off gas stream. As no separation technology is perfect, this waste-gas stream still contains a certain amount of methane depending on the methane recovery of the applied technology. Whether this gas stream is legally permitted to be vented to the atmosphere or has to be further treated is depending on the methane content on the methane slip of the purification plant (amount of methane in the off gas related to the amount of methane in the raw biogas) and on the emission regulations at the plant site. Systems damage begins exhibiting itself when hydrogen sulfide in biogas exceed 100 ppm [1]. Oil and gas industries are faced with the severe corrosion effects of hydrogen sulfide in piping especially in wells operating in acidic conditions. To decrease costs in the transportation of oil and gas to refineries and utilities, removal of hydrogen sulfide and/or carbon dioxide is essential to create a low corrosion environment.A mechanistic model which would predict H2S corrosion of mild steel over time at pH 5.0–5.5 was reported [2]. The study observed that the corrosion rate increased with an increase in H2S gas concentration but the magnitude of the corrosion rate is lower after 24 hours compared to 1 hour because of the build-up of a protective iron sulfide film. It also studied the effect of H2S gas concentration at room temperature and had reported an increase in corrosion rate with increasing gas concentration.
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