Leakage of plate heat exchanger
Cause
①The clamping size is not in place, the size is uneven everywhere (the size deviation should not be greater than 3 mm) or the clamping bolt is loose. ② Part of the gasket is out of the sealing groove, the main sealing surface of the gasket is dirty, the gasket is damaged or the plate heat exchanger gasket is aging. ③ The plate is deformed, and the assembly misalignment causes the running mat. ④ There are cracks in the sealing groove of the plate or the second sealing area. Example: Many thermal stations in Beijing, Qinghai, Xinjiang and other places use saturated steam as the primary heat source for heating. Due to the high steam temperature, when the system is unstable at the initial stage of equipment operation, the rubber gasket fails at high temperature, causing Steam leaks.
Treatment method
① In the no-pressure state, re-clamp the equipment according to the clamping size provided by the manufacturer. The size should be uniform, and the deviation of the compaction size should not be greater than ±0.2N (mm) (N. is the total number of plates), two The parallelism between the compression plates should be kept within 2 mm. ② Make a mark on the leaking parts, then disassemble the heat exchanger and investigate and solve them one by one, and reassemble or replace the gaskets and plates. ③ Disassemble the heat exchanger, repair the deformed part of the plate or replace the plate. When there is no spare part for the plate, the plate at the deformed part can be temporarily removed and then reassembled for use. ④ When reassembling the disassembled plates, clean the plate surface to prevent dirt from adhering to the gasket sealing surface.

String liquid
Cause
① Due to improper plate selection, cracks or perforations are caused by plate corrosion. ②The operating conditions do not meet the design requirements. ③ The residual stress after cold stamping of the plate and the clamping size during assembly are too small to cause stress corrosion. ④ There is a slight leakage in the plate leakage groove, which causes the harmful substances in the medium (such as C1) to concentrate and corrode the plates, forming a stream of liquid. Example: A BR03 plate heat exchanger with a plate material of 254 SMo in a sulfuric acid system of an aluminum industry Co., Ltd. experienced corrosion leakage of the carbon steel pipe on the cooling water side after 5 months of operation, and the acid leaked to the cooling water side. The inspection found that there was serious corrosion and cracking at the plate acid inlet and diversion area. On-site analysis found that the system operating temperature, flow rate and concentration and other process parameters are beyond the design conditions, and the use temperature far exceeds the applicable range of the material. Plate heat exchangers that use saturated steam as the primary heat source are prone to plate corrosion during operation, resulting in product leakage. This is because the steam temperature is high, and it is easy to cause the rubber gasket to fail at high temperatures during the operation of the equipment, causing the steam to leak out and rapidly condense in the second sealing area. As the leakage continues, the condensed residual liquid will accumulate more and more, locally forming areas with higher cl mass concentration, and reaching the corrosion conditions that destroy the passivation layer on the surface of the plate. At the same time, since the internal stress formed by cold stamping of the plate in this area is relatively large, when the surface passivation layer is destroyed, the internal stress causes the occurrence of stress corrosion.
How to deal with
① Replace the cracked or perforated plate, and use the light transmission method to find the crack of the plate on the spot. ②Adjust the operating parameters to meet the design conditions.
③The clamping size of the heat exchanger should meet the requirements during maintenance and assembly, not as small as possible. ④The plate heat exchanger plate materials are reasonably matched.

Excessive pressure drop
Cause
①The pipeline of the operating system is not normally purged, especially when many dirt (such as welding slag) in the pipeline of the newly installed system enters the inside of the plate heat exchanger. Due to the narrow cross-sectional area of ​​the plate heat exchanger, the heat exchange The sediment and suspended matter in the vessel gather at the corner hole and the diversion area, which causes the flow channel area to be greatly reduced, causing the main pressure loss in this part.
② When the plate heat exchanger is selected for the first time, the area is too small, resulting in excessively high flow velocity between the plates and large pressure drop.
③ After the plate heat exchanger has operated for a period of time, the pressure drop is too large due to scaling on the plate surface.
Example: In 2000, our factory provided a BR10 plate heat exchanger for users in Xinjiang, which is used in a water-to-water heat exchange central heating system. The design temperature of the primary water supply is 130℃. In the design and selection of heat exchangers, the heat transfer coefficient is relatively high, close to 5 500 w/(rn · K), but actually should be 3 500 w/(rn · K). At the same time, when the design unit selects the water pump, the flow margin is too large, causing the flow velocity between the medium plates on the secondary side of the heat exchanger to exceed 1 m/s, and the actual operating pressure drop is 0.2 to 0.3 MPa, which makes the hydraulic balance of the secondary network serious. Imbalance.
How to deal with
① Remove the dirt or plate fouling in the flow channel of the heat exchanger. For the newly operating system, clean it once a week according to the actual situation. When cleaning the scale on the surface of the plate (mainly CaCO3), use 0.3 sulfamic acid solution or 0.8 xiao acid solution containing 0.3 **, 0.2 aniline, and 0.1 potassium thiocyanate as the cleaning solution, and the cleaning temperature is 40 ~ 60 ℃. When not disassembling the equipment for chemical immersion cleaning, open the cold medium inlet and outlet of the heat exchanger, or install DN25 cleaning ports on the medium inlet and outlet pipes when installing the equipment, inject the prepared cleaning solution into the equipment, and clean with water after soaking Clean the residual acid and make pH≥7. When disassembling and cleaning, soak the plate in the cleaning solution for 30 minutes, then use a soft brush to lightly brush the scale, and finally clean it with clean water. Avoid damaging the plates and rubber pads during the cleaning process. If the mechanical backwashing method without disassembly is used, a nozzle should be connected to the medium inlet and outlet pipes in advance, the equipment is connected with the mechanical cleaning vehicle, and the cleaning fluid is injected into the equipment in the opposite direction of the medium flow. The cycle cleaning time is 10-15 min. , The flow rate of the medium is controlled at 0.05～0.15 m/s. Finally, circulate the clean water several times to control the Cl mass concentration in the clean water below 25 mg/I.
② It is better to use softened water for the secondary circulating water. Generally, it is required that the suspended solids concentration in the water is not more than 5 mg/L, the impurity diameter is not more than 3 mm, and the pH is 7. When the water temperature is not more than 95℃, the concentration of Ca and Mg should not be more than 2 mmol/L; when the water temperature is more than 95℃, the concentration of Ca and Mg should not be more than 0.3 mmol/L, and the mass concentration of dissolved oxygen should not be more than 0. 1 mg/L.
③For the central heating system, the method of supplementing water once and twice can be used.

Insufficient temperature
Cause
① The medium flow on the primary side is insufficient, resulting in a large temperature difference on the hot side and a small pressure drop.
② The temperature of the cold side is low, and the temperature of the cold and hot ends is low.
③ Uneven flow distribution of multiple plate heat exchangers operating in parallel.
④The internal scale of the heat exchanger is serious.
Treatment method
① Increase the flow of the heat source or increase the diameter of the heat source medium pipeline.
② Balance the flow of multiple plate heat exchangers operating in parallel.
③ Disassemble the plate heat exchanger to clean the surface of the plate fouling.