Fouling of heat exchanger is an urgent problem related to the national economy and many industries, and it is also one of the main problems not really solved in the field of heat transfer. It is concerned by the scientific and engineering circles all over the world. The economic losses caused by scale formation (excluding water cooling, air cooling and boiler scale) due to the treatment of hydrocarbon materials in some refineries in the United States and the world are investigated. The results show that the economic losses caused by scale formation in refineries in the United States amount to 1.36 billion US dollars every year, and the total economic losses in the world amount to 4.4 billion US dollars. According to relevant reports in China, for heat exchange equipment, the energy consumption per cubic meter of scale is 7% ~ 9% more, and the thermal efficiency is reduced by 10% ~ 20%. There are about 420000 industrial boilers in China, and about 1750000 tons of raw coal are wasted every year due to scale. Due to improper management of boiler water quality, scaling will lead to local expansion deformation and corrosion under scale, which directly affects the safety of chemical production. Classification of fouling from the perspective of fouling mechanism, liquid side fouling can be divided into the following six categories: it should be pointed out that the usual fouling formation process may be the result of the joint action of several fouling formation mechanisms. The most common cleaning methods are chemical cleaning and physical cleaning. Selection of cleaning agent cleaning agent mainly refers to acid cleaning agent, commonly used inorganic acid and organic acid. Picture selection cleaning agent should generally grasp the following principles. 1) On the premise of ensuring a certain time to dissolve the scale, the cleaning agent with low concentration, normal temperature, safety and economy should be selected. 2) The cleaning agent used in the test should be determined according to the material of the equipment, the condition and composition of the scale sample. It should be emphasized that hydrochloric acid is not allowed for the cleaning of stainless steel equipment, because the residual chloride ion in hydrochloric acid pickling will cause stress corrosion and intergranular corrosion cracking of stainless steel. 3) Generally, two kinds of cleaning agents can be selected, and each cleaning agent has two different concentrations, high and low, which are commonly used in cleaning. There are four kinds of cleaning agents in total. 4) For some complex and special scale samples, the selection range should be wide, and more cleaning agents can be selected for the test. For some complex organic scale samples, special and targeted cleaning agents should be selected. According to the selection principle of cleaning agent, and combined with the actual situation to determine the cleaning agent. Generally speaking, the shorter the scale dissolving time is, the better the scale dissolving performance of the cleaning agent is. Therefore, the cleaning agent with the shortest scale dissolving time should be selected. If the scale dissolving time is not different, when considering the scale dissolving time, it is mainly measured from the selection principle of cleaning agent and the difficulty of operation. After comprehensive analysis, the appropriate cleaning agent is determined. After determining the cleaning agent formula, the last test work is the selection of corrosion inhibitor, which is an important step in determining the cleaning solution formula. An ideal cleaning solution can not only remove the scale, but also can not damage and destroy the cleaned equipment, otherwise the cleaning itself will lose its significance. The selection range of corrosion inhibitor is usually determined according to the type, temperature and concentration of cleaning agent, and then the type and concentration of corrosion inhibitor are determined according to the test results, combined with various factors and actual situation. After the above steps, the formula of cleaning solution can be determined scientifically, that is, the type and concentration of cleaning agent and the type and concentration of corrosion inhibitor can be determined. Backwash pickling of plate heat exchanger