The finished product is collected at the bottom of the drying tower, and the superheated gas is discharged through the circulation fan below the drying tower and separated by the solid-gas separator. The fine powder material entrained in the superheated air is settled to the bottom of the separator by the cyclone action of the solid-gas separator. The superheated gas is blown back through the nitrogen dust collector twice to realize the collection of the dust material entrained in the gas. The waste heat gas enters the condenser and passes through the condenser cooling medium (condensation temperature is 3℃). Condensate to dew point to achieve recovery of organic solvents. The circulation system is supplemented by nitrogen to achieve the continuity of a new round of nitrogen closed-circuit drying production, so as to meet the above-mentioned industrial requirements for industrial production.