TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Method: The preprocessing step comprises (a) absorbing the raw material gas (C5+) hydrocarbon impurities in the pre-adsorption tower at room temperature, then saturating, and transferring into regeneration process; (b) reverse discharging process: discharging the pressure of the pre-adsorption tower in reserve manner, reducing the pressure, and discharging the raw material gas into buffer tank; (c) thermal desorption of impurities: using nitrogen gas as source of regeneration gas, heating to 200 degrees C, blowing against absorption direction of the absorption layer, carrying out of adsorption and desorption of impurities to be completely under heating condition, and cooling the regenerated gas after separation of discharged hydrocarbon; (d) cooling the adsorbent: after completing desorption, stopping heating of the regeneration gas, blowing the regeneration gas against the air inlet direction adsorbent bed layer at room temperature to make it cooling to absorption temperature, cooling and blowing out the desorbed gas; and (e) boosting process: using adsorption bed gas at the top of the pre-adsorption tower to be boosted, equalizing the pressure, and converting into secondary adsorption preparation, where the preprocessing step adopts at least one pre-adsorption tower in the regeneration state, and at least one pre-adsorption tower in the adsorption state. The decarburization process comprises (a) pressure equalization and releasing process: after the adsorption process, completing the process of regeneration along the direction of higher pressure adsorption tower into the other gases having lower pressure in the adsorption tower, where the process comprises the three times of continuous pressure equalizing and releasing process; (b) reverse discharging process: when the mass transfer area reaches the edge of the bed layer outlet, then countering the adsorption direction to the pressure below the adsorption tower close to atmospheric pressure, at this time, desorbing the absorbed carbon dioxide from the adsorbent in large quantities, and emptying the desorbed gas; (c) after completing reverse discharging process, using the vacuum pump for vacuumizing, further reducing the partial pressure of adsorbate components and desorbed adsorbate, and air emptying; (d) boosting equalizing process: after completing the vacuum process, sequentially boosting the adsorption tower from the other high pressure gas to the adsorption tower, where the process comprises a total of three consecutive boost pressure equalization process; and (e) product gas boosting process: completing three time voltage boosting process, slowly and stably raising the adsorption pressure of methane-enriched gas by the boost valve, adopting multiple absorption towers for adsorption, performing regeneration operation, and there is always an adsorption tower in the adsorption mode to achieve the secondary gas carbon dioxide removal. The PSA denitrification process comprises (a) forward discharging process: reducing the lower end of adsorption pressure along the lower end of the adsorption, conveying the gas into the raw material gas buffer tank, and processing forward discharging of high-concentration nitrogen; (b) equalizing and decreasing pressure process: after completing the adsorption process, completing the process of regeneration along the direction of higher pressure adsorption tower into the other gases having lower pressure in the adsorption tower, where the process comprises three times of continuous pressure equalizing and releasing process; (c) backwashing: after completing pressure reduction process, completing equalizing and releasing pressure for second time, subjecting methane product of absorption bed to backwashing to improve methane concentration; (d) reverse discharging process: when the mass transfer area reaches the edge of the bed layer outlet, then countering the adsorption direction to the pressure below the adsorption tower close to atmospheric pressure, at this time, desorbing the absorbed methane from the adsorbent in large quantities, and conveying the desorbed gas to the air buffer tank; (e) vacuum process: completing reverse discharging process, in order to obtain complete regeneration of the adsorbent, using the vacuum pump for vacuumizing, further reducing the partial pressure of adsorbate components and desorbed adsorbate, and conveying desorbed gas to a vacuum buffer tank; (f) backwash process: backwashing gas by using the adsorption bed for boosting, and fully recovering methane; (g) pressure equalizing and boosting process: after the completing the backwash process, conveying higher pressure gas from the absorption tower to the other absorption tower, where the process includes a total of three consecutive boosting and pressure equalizing process; and (h) product gas boosting process: completing three consecutive boosting and pressure equalizing process, slowly and stably raising the adsorption pressure of nitrogen-enriched gas by the boost valve, adopting multiple absorption towers for adsorption, performing regeneration operation, and there is always an adsorption tower in the adsorption mode to achieve the secondary gas methane removal.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The preprocessing adsorbent is activated carbon adsorbent, the decarbonization adsorbent is silica gel adsorbent, and the denitrification adsorbent is activated carbon-based adsorbent.