The main cleaning methods are physical cleaning and chemical cleaning according to the different cleaning methods. 1. Chemical cleaning chemical cleaning is to produce some chemical reaction through chemical cleaning solution, which causes the scale and other sediment on the heat exchanger tube surface to dissolve, fall off or peel off. Chemical cleaning does not need to disassemble the heat exchanger, simplifies the cleaning process and reduces the labor level of cleaning. The disadvantage is that the chemical cleaning solution will be damaged by corrosion and damage to the substrate. Chemical cleaning method ◉ circulation method: use pump to force the cleaning liquid to circulate and clean. ◉ immersion method: fill the cleaning liquid with equipment and set it for a certain time. ◉ surge method: fill the cleaning liquid with the equipment, unload a part of the cleaning liquid from the bottom every certain time, and then install the discharged liquid back into the equipment to achieve the purpose of stirring and cleaning. Cleaning steps of chemical circulation method: picture schematic diagram of chemical cycle method (1) isolate equipment and discharge water from heat exchanger（ 2) Clean the pipeline impurities with high pressure water and close the system（ 3) The ball valve is installed between the isolation valve and the exchanger, connected with the delivery pump and the conduit, and the cleaning agent is pumped from the bottom of the heat exchanger and flows out from the top（ 4) Inject the cleaning agent needed and cycle again and again（ 5) Discharge gas and inject appropriate water at any time（ 6) The effectiveness of the cleaning agent was determined by pH test paper（ 7) Recycle the cleaning solution and rinse it with clean water repeatedly until pH is neutral. 2. Physical cleaning is to crush, separate and peel off the surface of the object by means of various mechanical external forces and energy, so as to achieve the effect of cleaning. Physical cleaning methods have one common point: high efficiency, no corrosion, safety, environmental protection. The disadvantage is that when cleaning the complex equipment, the force can not reach all parts evenly and then the dead angle appears. The common methods are ultrasonic descaling, pig pigging, electric field descaling, etc. Photo (1) high pressure water jet cleaning uses the high pressure water produced by the plunger pump to spray to the scale layer through special nozzle, which is thorough and efficient, but it has large water consumption and large installed container（ 2) Ultrasonic descaling mainly uses ultrasonic sound field to treat fluid, which makes the scale-forming substances of fluid species change a series of physical morphology and chemical properties under the action of ultrasonic field, which makes it disperse, crush, loose and loose without easy to attach the fouling formed by the pipe wall（ 3) The new type of moving scale removal equipment in the pipeline is of high efficiency and good quality. It is suitable for the descaling of oil and gas pipelines, chemical liquid and water pipelines. The typical moving scale removal equipment in the pipeline can be divided into: A. electric driven mobile scale removal equipment; B. Hydraulic driven movable scale removal equipment; C. Compressed air drives a mobile scale remover. 3. Mechanical cleaning is based on mechanical action to provide a force greater than the adhesion of dirt, so that the dirt from the heat exchange surface fall off. This method can remove the carbonized dirt and hard scale which cannot be removed by chemical method, but it usually takes 5-6 times to clean the scale layer in the pipe, sometimes up to 10 times, and the pigging efficiency is low and the quality is poor. 4. Microbial cleaning is a method to decompose the oil pollution attached to the surface of equipment by microorganisms, and convert it into non-toxic and harmless water-soluble substances. This kind of cleaning thoroughly decomposes pollutants (such as oil) and organic matter, which is a real environmental protection cleaning technology. Physical cleaning and chemical cleaning have their own advantages and disadvantages, and they are complementary. In the practical application, it is usually used by combining the two to get better cleaning effect. For chemical cleaning method, the choice of cleaning agent has a significant influence on the cleaning effect.