Acetylene low-pressure dryer is used to reduce the water content in acetylene gas, so as to improve the service life of chemical purification agent and thus increase the output of acetylene compressor. Anhydrous calcium chloride is generally used as desiccant, and its consumption index is about 0.034 kg / m3 acetylene. The quantity and discharge time of the low-pressure dryer can be adjusted according to the size of the air flow.