There are three methods for plate cleaning of plate heat exchanger, namely backwashing (no disassembly cleaning), manual cleaning (disassembly cleaning), and chemical cleaning (no disassembly cleaning). 2. Cleaning method (1) manual cleaning. When the scaling thickness of heat exchange plate is very thin and insoluble in water, it can be disassembled. The pressure water (0.1-0.2mpa) or low-pressure steam with water shall be used for jet washing treatment. For sediment which is difficult to wash with water, soft fiber brush and bristle brush can be used for cleaning（ 2) Chemical cleaning. The hard sediment (oxide or carbide) is found on the surface of heat exchange plate, especially at the dead corner of medium flow. It is difficult to solve by manual cleaning. Different chemical solvents can be used to clean the plate according to the material of the heat exchange plate. Photo 2. The selection of cleaning agent is generally pickling, which includes organic acid and inorganic acid. Organic acids are mainly oxalic acid, formic acid, etc. Inorganic acids are mainly hydrochloric acid, nitric acid, etc. 3. Cleaning process (1) flushing: before pickling, the heat exchanger shall be washed open to make sure that there is no mud, scale and other impurities in the heat exchanger. This can not only improve the effect of pickling, but also reduce acid consumption of pickling（ 2) Pour the cleaning liquid into the cleaning equipment and then inject it into the heat exchanger（ 3) Pickling: soak the heat exchanger filled with acid solution for 2 hours. Then, the dynamic cycle was continuously for 3-4 hours. Every 0.5h. Carry out positive and negative alternating cleaning. After the acid cleaning, if the pH value of acid solution is greater than 2, the acid solution can be reused. Otherwise, the acid washing solution shall be diluted and then dropped（ 4) Alkali washing: after the acid cleaning, NaOH, Na, Po and softened water are prepared in a certain proportion. The heat exchanger is alkaline washed by dynamic circulation to reach acid-base neutralization so that the plate of heat exchanger will not be corroded（ 5) Water washing: after the alkali washing, use clean softened water. Wash the heat exchanger for 0.5 hours repeatedly, and thoroughly wash the residue in the heat exchanger（ 6) Record: during cleaning, the time of each step shall be strictly recorded to check the cleaning effect. In short, after cleaning, the heat exchanger shall be pressure tested. Only qualified can they be used. 4. Measures to prevent scaling (1) strictly control the water quality during operation, and strictly test the water quality of the water in the system and softened water in the softening tank, and then inject it into the pipe network after passing the qualification（ 2) When the new system is put into operation, the heat exchanger and the system shall be separated, and then the heat exchanger shall be connected to the system after a period of circulation to avoid impurities entering the heat exchanger in the pipe network（ 3) In the whole system, the decontaminator and filter shall be cleaned irregularly, and the cleaning in the pipe network shall be kept to prevent the heat exchanger from blocking.