Recoil pickling method for plate heat exchanger

Recoil pickling method for plate heat exchanger

26 Feb 2019

System composition of recoil - pickling method

For plate heat exchanger, mechanical cleaning is mainly to disassemble the heat exchanger, using artificial method to remove the scale layer on the heat exchange surface one by one, and then reassemble them. This method can only be used when the heat exchanger is completely separated from the heat exchange system. At the same time, the sealing gasket between heat exchangers is easy to damage, which is adverse to the maintenance of equipment.

System schematic diagram of recoil - pickling method
1.Primary circulation pump
2.Hot-water boiler
3.Heat exchanger cold inlet valve
4.Secondary pickling exit valve
5.Primary pickling exit valve
6.Heat exchanger hot inlet valve
7.Plate heat exchanger
8.Acid wash backwater valve
9.Acid-resisting vessel
10.Pickling pump
11.Drain pipe valve
12.Heat exchanger cold outlet valve
13.Secondary pickling inlet valve
14.Primary pickling inlet valve
15.Heat exchanger hot outlet valve
16.Heat consumer
17.Secondary circulation pump

The method can not only clean the heat exchanger without breaking away from the heat exchange system and avoid the trouble of disassembly, but also have the advantages of simple method, short cycle, quick effect and greatly reduced labor intensity.

The solid line in the picture is the entire pickling system. It consists of a acid-resisting vessel (9), a pickling pump (10) and its supporting pipes and valves. Backwash method is to use the pressure head generated by high pressure water to reverse impact the scale layer on the heat exchange surface and make it separate from the heat exchanger sheet, so as to discharge the circulation system.

Pickling method is the use of acid immersion, circulation to clean the heat exchange surface, remove dirt, improve the heat exchange effect.

2. The operation sequence of recoil - pickling method
Years of practice has proved that the secondary water flow of plate heat exchanger, that is, the side of cold inlet and cold outlet flow is easy to form scale, and the scale layer is thick, so we take the "recoil -- pickling method" as an example. The specific operation process is as follows:

When backwashing, first shut down the cold into the valve plate heat exchanger (3) and cold outlet valve (12), at the same time open the discharge drain pipe valve (11), when discharge all of the secondary water of the net plate heat exchanger (7), open the cold the valve (12), then the secondary water inside the heat exchanger form local reverse flow, using its impact pressure head to adhere to the scale layer on the surface of the heat transfer the relatively loose, and the adhesion which is not strong dirt out of the heat transfer surface and discharge system.

Pay attention when backwashing
Recoiling time should not be too long, and not too many times. It is advisable to take 1 minute every time for 3 to 5 times, until the discharged water is clear and transparent. If taking too many times, the recoil effect is not obvious, and the heat loss in the system is too much.

The pickling process is divided into ten steps
1. Closed process; Close all valves in the line while keeping the primary and secondary circuits clear.
2. Separation process: namely, the secondary cycle of the whole heat exchanger is separated from the heat exchange system. That is, close the cold inlet and outlet valves (3) and (12) of the heat exchanger.
3. Emptying process: open the drain pipe valve (11) and the secondary pickling inlet valve (13), and close the valve (11) after emptying the water storage in the heat exchanger.
4. Dosing process: start the pickling pump (10), and open the secondary pickling outlet valve (4) and pickling backwater valve (8); The acid in the pickling tank (9) is injected into the heat exchanger until the medicine liquid flows out of the pickling return pipe.
5. Sealing process: close the secondary pickling inlet valve (13), pickling pump (10), secondary pickling outlet valve (4) and acid wash backwater valve (8) successively and seal the secondary pickling pipeline.
6. Soaking process: the static soaking time is determined according to the acidity of the selected solution, and the second heat exchange surface of the heat exchanger is soaked statically.
7. Circulation process: open the secondary pickling outlet valve (4), pickling backwater valve (8), pickling pump (10) and secondary pickling inlet valve (13) successively to make the whole secondary pickling system circulate dynamically.
8. Discharge process: open the drain pipe valve (11) after the acid circulation for a certain period of time, drain the net residual liquid, and close the pickling system.
9. Neutralization process: add the prepared lye, usually Na3 PO4 or Na2CO3 solution, into the acid-resistant tank (9), and repeat steps 3 to 8.
10. Recovery process: slowly open the cold outlet valve of the heat exchanger (12) and the cold inlet valve (3) again to ensure the normal operation of the secondary circulation.