This system is applicable to hydrochloric acid of any concentration. An extractant calcium chloride (CaCl₂) is added into the acid to break the chemical equilibrium, so that hydrogen chloride gas can be separated via extractive distillation. The diluted calcium chloride solution flows into the concentration system for recycling.

If impurities contained in the acid tend to react with the extractant, the differential pressure distillation process is recommended for hydrogen chloride gas recovery.