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The SO2 gas drawn from the outlet of the waste heat boiler in sulfuric acid production is cooled by a shell-and-tube cooler before entering the pickling tower. The SO2 gas entering the pickling tower comes into countercurrent contact with 95% sulfuric acid sprayed from above in the packed tower, thereby removing impurities such as SO3. 95% sulfuric acid in the pickling tower flows by gravity from the bottom of the tower to the 95% sulfuric acid production circulation tank. The acid-washed raw gas enters the bottom of the primary absorption tower from the top of the acid-washing tower, where it comes into countercurrent contact with the absorption liquid sprayed from the top of the tower within the primary absorption packed tower for absorption. The absorbed rich liquid flows by gravity from the bottom of the primary absorption tower to the desorption circulation tank. The absorbed gas enters the bottom of the secondary absorption tower from its top to be absorbed again. The absorption liquid goes from the bottom of the secondary absorption tower to the primary absorption circulation tank. The absorbed exhaust gas is sent from the top of the secondary absorption tower to the sulfurous exhaust gas absorption tower for treatment before being released. After the absorbed rich liquid from the desorption tank is pumped up by a self-priming pump, it first undergoes heat exchange with the desorbed high-temperature lean liquid in a heat exchanger, then enters a heater where it is further heated to 90°C–100°C before entering the packed desorption tower from the top for desorption. The desorption liquid enters the desorption vessel from the bottom of the tower, is indirectly heated by steam, and then undergoes further desorption. After the desorbed lean liquid is cooled to 30°C–40°C through a heat exchanger, cooler, and re-cooler, it enters the secondary absorption circulation tank to recycle and absorb SO2 gas. The SO2 gas desorbed from the desorption vessel and desorption tower is, under vacuum, sent to the condensation separator and gas-liquid separator for gas-water separation. After further drying with first and second-stage sulfuric acid, and defoaming using a vacuum-wrapped mesh, it is pumped by a vacuum pump to a compressor for compression; after cooling, it enters the storage tank for liquid sulfur dioxide product.