Process conditions for methane-water vapor conversion
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Pressure: A compression pressure of 3–4 MPa is used； Temperature: The reaction temperature in the first stage of the converter is 700–800°C, while the exit temperature of the second stage furnace is around 1000°C ； A water-to-carbon ratio of 3–4 in the raw materials is appropriate ； Space velocity: It indicates the catalyst’s ability to process feed gas; the higher the catalyst activity and the faster the reaction rate, the higher the space velocity can be.
For the methane-water vapor conversion reaction catalyst, nickel is the most effective catalyst; it exists in the form of NiO, with a concentration of 4–30%； Catalysts are required to be heat-resistant, highly active, strong, and have excellent resistance to carbon deposition ； Al2O3, MgO, CaO, K2O, etc. are commonly used as carriers, with promoters such as Cr2O3, TiO2, La2O3, etc. added ； Nickel catalysts can be prepared by co-precipitation, mixing, impregnation, and other methods, followed by high-temperature calcination ； The catalyst must be reduced before use; common reducing agents include hydrogen with steam or methane with steam ； Reduced active nickel catalysts are sensitive to poisons such as sulfur, halogens, and arsenic.
Carbon deposition in the methane-water vapor conversion process and its treatment. Hazards of carbon deposition: It covers the catalyst surface, blocks the micropores, reduces the methane conversion rate, causes overheating in certain reaction areas thereby shortening the service life of the reaction tubes, and leads to the fragmentation of the catalyst, increasing the resistance in the bed. The main measures to prevent carbon deposition are: appropriately increasing the amount of steam used, selecting suitable catalysts and maintaining their good activity, and controlling the preheating temperature of hydrocarbon-containing feedstocks from being too high. Eliminate carbon deposits: Take measures such as increasing the amount of steam used and reducing pressure ； If carbon deposition is severe, stop feeding the feed gas, retain steam, increase the bed temperature, and use the reaction H2O+C=CO+H2 to remove carbon; a mixture of air and steam can also be used to \"burn away\" the carbon.