How to clean the plate heat exchanger without disassembly

4.1.1 connection of chemical cleaning cycle circuit

First, close the inlet and outlet valves of the hot medium of the plate heat exchanger, and then close the inlet and outlet valves of the cold medium to drain the medium (generally water or steam). Take the inlet and outlet of cold and hot medium as the water inlet of cleaning solution, and the outlet and outlet of water as the water outlet of cleaning solution (if there is no sewage outlet, add valves). According to the sequence of hot medium inlet hot medium outlet cold medium inlet cold medium outlet, the chemical cleaning circulation system is composed of cleaning pump, cleaning tank and plastic pipe.

4.1.2 implementation of chemical cleaning process

Inject water into the cleaning tank to check that the circulation of the system is normal, and then add an appropriate amount of cleaning agent to start the circulation cleaning. According to the chemical cleaning process, the concentration of the cleaning solution in the cleaning tank should be detected every 1 h during the circulation process, so that the concentration of the cleaning solution is always kept in the effective range of 0.10 ~ 0.15 mol / L * *, and the cleaning agent should be added according to the measured data. Chemical cleaning without disassembly may take a long time, which can be combined with circulating cleaning and overnight soaking cleaning. When the cleaning agent concentration does not change for 2 hours or the change is small, the circulation can be stopped.

4.1.3 flushing

After chemical cleaning, due to the small internal flow aperture of plate heat exchanger, there is always dirt (especially dirt) adhering to the heat transfer plate, so it is necessary to use the circulating pump to wash the dirt repeatedly. Drain the waste liquid in the cleaning tank, fill it with clean water, wash it with circulating pump, drain the waste water, and then wash it repeatedly, and observe continuously until there is no more scale and slag in the plate heat exchanger.

4.2 neutralization and passivation treatment

Neutralization is to neutralize the residual acid in the equipment after cleaning without corroding the equipment; Passivation is the formation of an electron conducting film on the surface of a metal which can inhibit the dissolution process of the metal. The dissolution rate of the film itself in the medium is so small that it can keep the anodic dissolution rate of the metal at a very small value. Since several sections of pipes connected with plate heat exchanger are used for chemical cleaning without disassembly, the heat transfer plate is made of stainless steel and does not need neutralization and passivation treatment, but the pipe is made of steel. After cleaning, the scale and rust on the surface are removed, revealing the essence of steel. It is in a very active state and easy to rust. Therefore, neutralization and passivation treatment are needed to prevent secondary corrosion.

4.2.1 neutralization treatment

Neutralization treatment can be carried out with sodium hydroxide, sodium carbonate and other auxiliary neutralizing agents, and the dosage is 0.5%, that is, 1 t water plus 5 kg neutralizing agent, to neutralize the residual acid cleaning agent in the circulation system, so that the pH reaches 7 and the circulation stops.

4.2.2 passivation treatment

After neutralization treatment, passivation treatment is carried out. Appropriate amount of passivation pre filming agent is added to the circulation system. After the circulation is uniform, the pH value is controlled between 8 and 9. The amount of passivation pre filming agent is calculated according to the circulating water volume of cleaning agent. 1 t of water is added with 10 kg of passivation pre filming agent.

4.3 recovery

After passivation, remove the connecting pipe, close all drain valves, open the inlet and outlet valves of cold medium first, and then open the inlet and outlet valves of hot medium.