After completion of the reaction in the cracking furnace, ketene gas generated during cracking, unreacted acetic acid vapors and exhaust gases generated as a result of a side reaction quickly pass through a condensation cooler, where they are first cooled with process water and then with frozen brine. The cooled mixture then enters a gas-liquid separator to separate gas and liquid. After separation, the gas enters the absorption system and is absorbed by acetic acid (99%) to form crude acetic anhydride, and diluted acetic acid enters the intermediate container for diluted acetic acid.