Nitrogen and vacuumizing combined pre-startup replacement method for pressure swing adsorption decarbonizing device

The invention relates to a pre-startup replacement method for a pressure swing adsorption device after installation or maintenance is finished. After pipes are purged by compressed air and leakage test and pressure test are qualified, towers are fully filled with air. The method includes: step one, opening program control valves of adsorption towers and program control valves of pressure equalizing equipment, vacuumizing until the pressure is smaller than or equal to -0.07MPa, and closing all vacuumizing program control valves; step two, feeding nitrogen by nitrogen pipelines on outlet main pipes at tops of the adsorption towers through all open outlet program control valves from the outlet main pipes of the adsorption towers until the pressure is 0.005MPa, emptying replacement outflow gas through emptying pipes arranged at feed gas inlets, stopping feeding nitrogen, and closing nitrogen valves, wherein the gas emptying volume accounts for 10%-20% of the total volume of each vessel, the oxygen content of each