For plate heat exchanger, mechanical cleaning is mainly to disassemble the heat exchanger, remove the scale layer on the heat exchange surface by manual method, and then reassemble. This method can only be used when the heat exchanger is completely separated from the heat exchange system, which not only takes time and effort, but also requires high clamping size of the heat exchanger when reassembling, and it is not easy to grasp; At the same time, the sealing gasket between heat exchanger plates is easy to damage, which is not good for the maintenance and maintenance of the equipment. The system schematic diagram of picture recoil pickling method is shown in the following figure: the method can not only make the heat exchanger be cleaned without separation from the heat exchange system, and can avoid the trouble of disassembly, but also has the advantages of simple method, time saving, short period, quick effect and greatly reducing labor intensity. The solid line in the figure is the whole pickling system. It is composed of a pickling tank (9), a pickling pump (10) and its supporting pipelines and valves. Backwashing is to use the pressure head produced by high pressure water to reverse impact the fouling layer on the heat exchange surface, so as to separate it from the heat exchanger plate, and then discharge the circulation system. Pickling is a method that uses acid immersion and circulation to clean the heat exchange surface, remove dirt and improve the heat exchange effect. The operation sequence of backwash pickling method has been proved for many years: the secondary water flow of plate heat exchanger is easy to scale on one side of cold inlet and cold out process and the scale layer is thick. Therefore, we take the "backwash pickling method" of secondary water process as an example. The specific operation process is as follows: when backwashing, first close the cold inlet valve (3) and cold out valve (12) of plate heat exchanger, open the drain valve (11) at the same time, when all the secondary water in the plate heat exchanger (7) is drained, then open the cold out valve (12), so that the secondary water will form local reverse flow in the heat exchanger, The scale layer attached to the heat exchange surface is impacted by the pressure head, which makes the loose and weak adhesion layer separate from the heat exchange surface, and then discharge the circulation system. When the picture is backwashing, we should pay attention to the time of backwashing should not be too long, and the times of each flushing should not be too many. One strand should be carried out for 3-5 times for 1 minute at a time until the water discharged is clear and transparent. Because the time is too long, too many times will lead to the effect of backflushing is not obvious, and the heat loss in the system is too much.