Process for co-producing and synthetic natural gas and food-grade carbon dioxide by using calcium carbide furnace gas

The invention discloses a process for co-producing synthetic natural gas and food-grade carbon dioxide by using calcium carbide furnace gas. The process sequentially comprises the steps that after purified calcium carbide furnace gas is pressurized and mixed with medium-pressure steam and then the obtained mixture enters a shift-converter to carry out shift-conversion, the obtained gas enters a methanation reactor to carry out methanation, and then enters a decarbonization system to remove CO2; the gas subjected to CO2 removal is dried, and then enters a methane concentration system to carry out concentration, thereby obtaining synthetic natural gas; and the removed CO2 is prepared into food-grade CO2 through a recovery unit. The decarbonization system can adopt a PSA (pressure swing adsorption) dry decarburization process, and also can adopt a wet decarburization process. The wet decarburization is implemented by removing CO2 by using a thermokalite method or MDEA washing. A CO2 recovery unit has the functions of CO2 collecting, purifying, and purification by flash distillation. The methane concentration can be implemented by concentrating methane by using a PSA method, and also can be implemented by concentrating methane through low-temperature separation. The process disclosed by the invention is a packaged technology for co-producing synthetic natural gas and food-grade carbon dioxide by using calcium carbide furnace gas, which is suitable for industrial scale applications.