TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Method: In the process, the mixed gas enters from the bottom side of an absorption column (T1) and the absorbing tower is added with excessive amount of water to mix and absorb hydrogen chloride in the packed column and bubble-cap tower, the bottom of the absorption column is connected with a hydrochloric acid circulation pump to form a circulation loop, hydrochloric acid composted and absorbed in the packed column absorbs hydrogen chloride in the rising mixed air circularly to increase the concentration; when the concentration of the hydrochloric acid comes to a certain standard, it is recovered through the bottom of absorption column and the unabsorbed hydrogen chloride rises to the upper bubble-cap column to be absorbed completely. The mixed gas gets into the strong sulfuric acid drying tower through its bottom side, and at the same time, the packed column is saturated with concentrated sulfuric acid to mix and absorb the moisture in the risen air mixture; after the moisture in the risen air mixture has been fully mixed and absorbed, the concentrated sulfuric acid becomes diluted gradually and when the concentration of the concentrated sulfuric acid comes to a certain standard, the diluted sulfuric acid is recovered through the bottom side of drying column (T2) and then re-injecting with adequate concentrated sulfuric acid. In the process, vacuum variable pressure adsorption system is composed with at least two absorbing tower device, where each of the absorption is filled with the same amount of the absorbents using the same way; the raw material gas gets chloride with high purity after the processes of being absorbed, pressed, substituted and vacuum analyzed; vacuum variable pressure adsorption system is composed with at least two absorbing tower device, where each of the absorption is filled with the same amount of the absorbents using the same way; the raw material gas gets chloride with high purity after the processes of being after the processes of being absorbed, pressed, substituted and vacuum analyzed. The absorption of the absorption columns' absorption pressure is 0.1-1 MPa and absorption temperature is the room temperature. The vacuum desorption step before adding the cleaning operation to with the purity of the solution into, is connected with for the product of gas washing.