Plate heat exchangers are also called plate heat exchangers. In addition to overhauls under special circumstances, they should also be regularly maintained. Because plate heat exchangers are easy to disassemble and assemble, and simple to maintain, they generally do not require special tools and equipment. Different methods can be used according to different situations. If there is no leakage in the equipment, but only the K of the heat transfer system has decreased, the heat exchanger can be left unassembled, and a closed-circuit system can be used to inject descaling liquid into the equipment for circulation for several hours. If there is no such condition on site, and if the equipment is disassembled or the scaling is not too serious, the plates can be directly rinsed with water without removing them, and a soft brush can be used to scrub them. Let's take a detailed look at the maintenance steps below!
1. Shut down the heat exchanger
When shutting down the heat exchanger for overhaul, first slowly close the fluid valves on both sides of the heat exchanger to slowly reduce the pressure on both sides at the same time, and then loosen the tension nut after draining the residual liquid. When removing the tie rod, it must be done after the temperature drops to room temperature and the residual liquid is drained as much as possible.
2. Plate cleaning
A clean plate surface without oxides is a necessary condition to ensure tightness. When the thermal efficiency of the plate heat exchanger is significantly reduced and the pressure drop changes significantly, the scale is serious. The plate should be disassembled, laid flat and cleaned. Using a steam bubble tank and chemical cleaning method is an effective way to obtain high-quality surface quality. When cleaning, first soak the plate in an alkaline solution tank at a temperature of 57-60oC (better if the temperature is 70-80oC) for 48 hours, and use the high temperature of the alkaline solution to soften the sealant and scale attached to the plate. Then, soak the plate in an acid tank for 2 hours to allow the scale to fully react with the acid. After the plate is soaked, brush it with a soft brush on the platform. Steel brushes are prohibited.
When cleaning the sealing groove, use a screwdriver to lift the gasket, gently remove it (or lightly bake it on the back with fire, but avoid metal discoloration), and then tear it off. Use acetone methyl liquid or other ketone organic solvents to clean the sealing groove.
After cleaning, rinse the plate with clean water first, then wipe it dry with a clean cloth. No foreign particles and fibers are allowed to remain on the plate surface. The chloride ion content of the cleaning water is ≤25pp.
3. Check and determine the workload After cleaning, carefully check the plate. There are three inspection methods:
1) Coloring method: check with colorant;
2) Transparent method: a light source is placed on one side of the plate, and people check on the other side;
3) Single-side pressure test method: test the pressure of one side with water to 0.35MPa (gauge pressure). If there is water at the lowest point on the other side, quickly check the wet part of the plate. We choose the transparent method for inspection. The advantages of this method are convenience and low cost. It is applicable to the inspection of new and old plates. However, it requires a high sense of responsibility for maintenance personnel.
According to the inspection of the plate, determine the workload, there are three main types:
- Replace all plates and gaskets;
- Replace only gaskets;
- Replace gaskets and some damaged and severely deformed plates.
4. Gasket Pasting
Use adhesive or strong adhesive to evenly apply a layer on the bottom of the sealing groove, then put the gasket into the sealing groove, fit evenly, pressurize, dry naturally, or heat to 100℃-120℃ for two hours and then dry. Check whether the fit is even, and remove excess adhesive.
5. Assembly
The characteristics of the flow combination of plate heat exchanger are: if the fluid enters from the left corner hole of the plate, it always exits from the left corner hole of the plate, and vice versa. When assembling, it is necessary to correctly distinguish between A plate and B plate, that is: take the side of the plate adhesive pad as the front, distinguish according to the direction of the guide groove, and define the plate with the guide groove in a certain direction as A plate, and the plate with the guide groove in another direction as B plate, but do not mark on the plate.
6. Water pressure test
Make four blind plates according to the size of the pipe flange, weld them at the inlet and outlet, and weld pipes on the plate to connect the compressor and the heat exchanger. A pressure gauge that has been calibrated and is within the validity period is installed at each inlet and outlet. The pressure gauge range should be twice the test pressure. The test pressure is 1.5 times the working pressure.
1) The inspection and maintenance are strictly carried out according to the above requirements. The quality fully meets the design requirements. There is no leakage during the 72-hour load test. The temperature measurement results of the heat exchange liquid: the inlet of alumina mother liquor is 45.2oC and the outlet is 84.6oC; the inlet of alumina concentrate is 97.0oC and the outlet is 78oC, which meets the normal operation requirements.
2) Save costs. Since the plate material is ultra-thin Crl7Nil3Mo2Ti stainless steel, the gasket is also special, and the cost of replacing all new plates is very high. After cleaning and inspection, reuse, a single plate heat exchanger can save 250,000 to 450,000 yuan.