Graded oxygen regulating, explosion preventing and recycling system and method for liquid nitrogen wash tail gas

A graded oxygen regulating, explosion preventing and recycling method for liquid nitrogen wash tail gas, comprising the following steps:

• (a) liquid nitrogen wash tail gas entering a first-section heat exchanger (2) through a cold inlet (2-1) for heat exchange with first-section high-temperature exhaust gas from a bottom outlet (1-1-2) of a first-section catalytic combustion region 1-1;
• after the heat exchange, the liquid nitrogen wash tail gas entering a top inlet (1-1-1) of the first-section catalytic combustion region (1-1) through a heat outlet (2-2) and undergoing, in a layer-by-layer manner, first-section catalytic reaction on multiple layers of catalysts that are disposed in the first-section catalytic combustion region (1-1) at intervals to obtain first-section high-temperature exhaust gas, wherein in the process of layer-by-layer first-section catalytic reaction, the liquid nitrogen wash tail gas is mixed with air from an air flow guide pipe (6) above each layer of catalyst, and the first-section catalytic reaction is oxygen-deficient reaction;
• (b) discharging the first-section high-temperature exhaust gas from the bottom outlet (1-1-2) of the first-section catalytic combustion region (1-1) to a first-section heat exchanger (2) through a heat inlet (2-3) for heat exchange;
• after the heat exchange, the first-section high-temperature exhaust gas entering a top inlet (1-2-1) of a second-section catalytic combustion region (1-2) through a cold outlet (2-4) of the first-section heat exchanger (2) and undergoing, in a layer-by-layer manner, second-section catalytic reaction on multiple layers of catalysts that are disposed in the second-section catalytic combustion region (1-2) at intervals to obtain second-section high-temperature exhaust gas, wherein in the process of layer-by-layer second-section catalytic reaction, the first-section high-temperature exhaust gas is mixed with air from the air flow guide pipe (6) above each layer of catalyst, and the second-section catalytic reaction is oxygen-deficient reaction;
• (c) discharging the second-section high-temperature exhaust gas from a bottom outlet (1-2-2) of the second-section catalytic combustion region (1-2) to a second-section heat exchanger (3) through a heat inlet (3-3) for heat exchange with low-temperature exhaust gas discharged through a low-temperature exhaust gas outlet (4-1) of a pulverized coal drying section (4) in the second-section heat exchanger (3);
• after the heat exchange, discharging the low-temperature exhaust gas through a heat outlet (3-2) of the second-section heat exchanger (3) to the pulverized coal drying section (4) via a hot exhaust gas inlet (4-2), partially discharging the low-temperature exhaust gas through an exhaust gas discharge port (4-3);
• after the heat exchange, discharging the second-section high-temperature exhaust gas through a cold outlet (3-4) of the second-section heat exchanger (3) to a top inlet (1-3-1) of a third-section catalytic combustion region (1-3) for third-section catalytic reaction on a catalyst of the third-section catalytic combustion region (1-3) to obtain third-section high-temperature exhaust gas, wherein in the process of third-section catalytic reaction, the second-section high-temperature exhaust gas is mixed with air from the air flow guide pipe (6) above the catalyst of the third-section catalytic combustion region (1-3), and the third-section catalytic reaction is oxygen-rich reaction;
• (d) discharging the third-section high-temperature exhaust gas through a bottom outlet (1-3-2) of the third-section catalytic combustion region (1-3) to a boiler (5-1) via a heated gas inlet (5-1-1), transferring heat to soft water in a steam pocket (5-2) through the boiler (5-1), and delivering out medium-pressure steam formed from the soft water for use, wherein after transferring the heat, the third-section high-temperature exhaust gas is discharged from a heated gas outlet (5-1-2) of the boiler (5-1) to the pulverized coal drying section (4) via the hot exhaust gas inlet (4-2).