How to clean the heat exchanger, the plate heat exchanger cleaning plate heat exchanger in the process of use, because of the improper operation of water treatment equipment; The unqualified softened water is injected into the system, which makes the calcium, magnesium and carbonate in the water decompose into calcium carbonate and magnesium hydroxide precipitates after heat treatment to bind on the heating surface of the heat exchanger, forming a hard scale. Because of the poor thermal conductivity of scale, the heat exchange efficiency of heat exchanger is reduced and the heat energy is wasted seriously. Thus, the effect of heat transfer is affected. The cleaning method of fouling in plate heat exchanger 1. The choice of cleaning agent is 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. According to the analysis of fouling and process, material and scale composition of the heat exchanger, it is concluded that: 1) the flow area of the heat exchanger is small, the internal structure is complex, and the cleaning solution is not easy to discharge if the precipitation is produced. 2) The heat exchanger is made of Ni Ti alloy and hydrochloric acid as cleaning solution. It is easy to produce strong corrosion on plate and shorten the service life of heat exchanger. Through repeated experiments, it was found that the best effect was formic acid as cleaning solution. The results show that the corrosion of the cleaning solution to the plate can be reduced by adding buffer and surfactant into the formic acid cleaning solution. The chemical test of scale samples shows that formic acid can effectively remove the scale. The results show that formic acid can effectively remove the scale attached to the plate, and its corrosion effect on the plate of heat exchanger is also very small. 2. The basic principle of removing scale 1) dissolution: acid solution is easy to react with calcium, magnesium and carbonate scale, and to form soluble compounds to dissolve the scale. 2) Stripping: acid solution can dissolve oxide on metal surface. Destruction and scale combination. Thus, the scale attached to the surface of metal oxide is stripped. And fall off. 3) Gas lift: acid solution reacts with calcium, magnesium and carbonate salt water scale, and produces a large amount of carbon dioxide. Carbon dioxide gas is in the process of spilling. For the scale layer which is difficult to dissolve or dissolve slowly, it has certain lifting power, which makes the scale fall off the heating surface of the heat exchanger. 4) Loose action: for the scale mixed with silicate and sulfate, the remaining scale will become loose and easily washed down by flowing acid solution due to the dissolution of oxides of calcium, magnesium, carbonate and iron in acid solution. 3. The process requirement of cleaning scale 1) pickling temperature: raising the pickling temperature is conducive to improving the scale removal effect. If the temperature is too high, the corrosion of pickling solution to the plate of heat exchanger will be intensified. Through repeated tests, it is found that it is appropriate to control the pickling temperature at 60-e. 2) Acid pickling solution concentration: according to repeated test, the pickling solution should be prepared according to the concentration of 81.0% formic acid, 17.0% water, 1.2% buffer and 0.8% surfactant, and the cleaning effect is excellent. 3) Pickling method and time: pickling method shall be carried out by combining static immersion and dynamic cycle. The pickling time is static immersion for 2 hours, then dynamic cycle for 3-4 hours. The pickling concentration should be sampled and tested frequently during the pickling process. When the difference between the two adjacent tests is less than 0.2%, the acid washing reaction is considered to be over. 4) Passivation treatment: after pickling, most of the scale and metal oxide on the surface of plate heat exchanger are dissolved and shed, exposing new metals, which are very easy to corrode. Therefore, after pickling, passivation treatment is carried out for the plate of heat exchanger. 4. Cleaning the scale: 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 the 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. During the period, the positive and negative cleaning should be conducted every 0.5 hours. 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. 5. Measures to prevent fouling of plate heat exchanger 1) strictly control the water quality during operation. The water in the system and softened water in the softening tank must be tested strictly. Only after passing the test can the water be injected into the pipe network. 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. It is an important guarantee for normal operation of production to clean strictly according to the cleaning method of plate heat exchanger