What are the requirements regarding material usage and container manufacturing for cold dryers using biogas as a medium?
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Dear Haiyou, there is currently a cold dryer using biogas as its medium. The design pressure is 1.6 Mpa, and the operating pressure is 1.3 Mpa ； The design temperature is 90°, with an operating temperature of ≤45°. May I ask Haiyou: Should wet H2S corrosion be taken into account for biogas? ； What standards are available for reference on wet H2S corrosion? What should be taken into account in materials and manufacturing processes? Thank you all!
Biogas is essentially a convenient, clean, high-quality gas fuel that results from the fermentation of organic materials such as human and animal excreta, domestic wastewater, and plant stems and leaves under specific conditions of moisture, temperature, and anaerobic environment by anaerobic microorganisms. It can be used directly for cooking and lighting, as well as for heating, drying, and storing grain. Physical and chemical properties of biogas: Biogas is a colorless and transparent mixed gas, whose main components are methane (CH4), carbon dioxide (CO2), along with small amounts of hydrogen sulfide (H2S), hydrogen (H2), carbon monoxide (CO), nitrogen (N2), and other gases. Methane accounts for about 50–70%, carbon dioxide accounts for about 30–40%, while the amounts of other components are relatively small. There is a slight smell of rotten eggs, but this smell disappears after burning. Compared to air, the specific gravity of biogas is 0.55. The average critical temperature is 37°C, and the average critical pressure is 56.64×105 Pa. Under normal temperature and pressure, biogas can exist only in gaseous form; therefore, it is usually transported through pipelines. The main component of biogas, methane, has the molecular formula CH4 and a molecular weight of 16.04. Its vapor pressure is 53.32 KPa at -168.8°C; its flash point is -188°C, and its melting point is -182.5°C. It is slightly soluble in water but soluble in alcohol. Hazardous properties: Methane is flammable and explosive, and is primarily used as a fuel and chemical raw material. One volume of biogas requires 6–7 volumes of air to burn completely; upon complete combustion, it produces CO2 and water. The chemical equation is: CH4 + 2O2 = CO2 + 2H2O + heat.
If the diameter is not large, it is recommended to use stainless steel； If the diameter is large, check whether it should be made of composite material ； Finally, consider manufacturing with carbon steel; at this point, pay attention to the various factors related to stress corrosion, as well as the selection of the corrosion margin value.
Thank you for your reply. Regarding the small amount of H2S in biogas, is it necessary to consider the corrosion issue caused by wet H2S?
The corrosion issue caused by wet H2S should be considered, and the use of HIC-resistant steel is recommended.