In the methane conversion reaction, when H2 contains no water vapor, the reaction forms SiO gas to escape, resulting in weight loss of the refractory material; when the temperature is lowered, SiO is reoxidized to SiO2 to form a deposit. This is called "SiO2 migration." When water vapor is contained, the reaction is suppressed but it cannot be completely eliminated.
When H2 contains water vapor, SiO2 is distilled from the refractory material to form gaseous hydrates. Fe3O4, FeO, and metallic elemental Fe can be formed depending on the temperature, and the refractories are destroyed along with the volume change. The CO first penetrates into the pores of the refractory, and then forms a char deposit under the catalysis of Fe2O3, causing the refractory to bulge and crack.
The methanation device is a medium pressure device. The refractory lining must be able to withstand radial pressures of 3 to 4 MPa during use. Therefore, the compressive strength of the refractory material must be high. The heat insulation layer withstands the pressure transmitted from the refractory layer, and its compressive strength must be greater than 4 MPa.
Fire-resistant layer materials work under high-pressure medium flow for a long time, and their wear resistance is better. Once the wear is severe, the outer wall will be overheated, and the broken particles will block the tubes of the waste heat system, resulting in reduced efficiency and affecting normal operation. In order to ensure the integrity and hermeticity of the lining, it is necessary to make a monolithic poured cast lining. The smaller the rate of change of the lining material after burning, the higher the volume stability and the more stable it is at high temperatures.
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