cause

(1) The 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 Some gaskets are separated from the sealing groove, the main sealing surface of the gasket has dirt, the gasket is damaged or the sealing gasket of the plate heat exchanger is aging. (3) The cushion plate is deformed, and the assembly dislocation causes the cushion to run. (4) There are cracks in the sealing groove or secondary sealing area of the plate. For example, many thermal power stations in Beijing, Qinghai and Xinjiang 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, resulting in steam leakage.

job operation

(1) In the pressureless state, re-clamp the equipment according to the clamping size provided by the manufacturer. The dimensions shall be uniform, and the deviation of clamping dimensions shall not be greater than 0.2n (mm) (n). For the total number of plates), the parallelism between the two pressure plates should be kept within 2 mm (2) Mark the leakage parts, then disassemble the heat exchanger and solve them one by one, reassemble or replace the gaskets and plates. ③ Dismantle the heat exchanger and repair or replace the deformed plate. When the plate has no spare parts, the deformed plate can be temporarily removed and reassembled for use. ④ When reassembling the disassembled board, clean the board surface to prevent dirt from adhering to the gasket sealing surface.

Liquid string

cause

(1) Due to improper plate selection, plate corrosion leads to cracks or perforations. ② The operating conditions do not meet the design requirements. (3) Residual stress after cold stamping and stress corrosion caused by too small clamping size during assembly. (4) there is slight leakage at the leakage groove of the plate, which makes harmful substances (such as C 1) in the medium corrode the plate and form cross flow. Example: The 1 BR03 plate heat exchanger with the medium plate material of 254 SMo in the sulfuric acid system of an aluminum company was operated for 5 months, and the carbon steel nozzle on the cooling water side was corroded and leaked, and the acid solution leaked to the cooling water side. It is found that there are serious corrosion and cracking in the acid inlet and shunt areas of the plate. Field analysis shows that the operating temperature, flow rate and concentration of the system are beyond the design conditions, and the operating temperature is far beyond the applicable range of materials. Plate heat exchanger with saturated steam as the main heat source is prone to plate corrosion during operation, which leads to cross-flow of products. This is because the steam temperature is high, which easily causes the rubber pad to fail at high temperature during the operation of the equipment, resulting in steam leakage and rapid condensation in the secondary sealing area. With the continuous leakage, the condensation residue accumulates more and more, and the area with high cl mass concentration is formed locally, reaching the corrosion condition of destroying the passivation layer on the board surface. At the same time, due to the large internal stress formed by cold stamping of plates in this area, when the surface passivation layer is destroyed, the internal stress will lead to stress corrosion.

job operation

(1) Replace the cracked or perforated plate, and find the plate crack by light transmission method on site. ② Adjust the operation parameters to meet the design conditions.

(3) The clamping size of the heat exchanger during maintenance and assembly should meet the requirements, and the smaller the better. ④ Reasonable plate matching of plate heat exchanger.

Excessive pressure drop

cause

(1) The pipeline of the operating system is not purged normally, especially a lot of dirt (such as welding slag, etc. ) into the interior of the plate heat exchanger. Due to the narrow cross-sectional area of the flow channel of the plate heat exchanger, the sediment and suspended matter in the heat exchanger gather in the corner hole and the diversion area, which leads to the greatly reduced flow channel area and the main pressure loss in this part.

② The area of plate heat exchanger is small when it is selected, which leads to high flow velocity and large pressure drop between plates.

(3) After the plate heat exchanger runs for a period of time, the pressure drop is too large due to scaling on the plate surface.

Example: In 2000, our factory provided BR 10 plate heat exchanger for Xinjiang users, which was used in the central heating system for water-water heat exchange. The design temperature of primary water supply is 130℃. In the design and selection of heat exchanger, the heat transfer derivative is high, close to 5500 W/(RN K), but it should actually be 3500 W/(RN K). At the same time, when the design unit selects the pump, the flow margin is too large, which leads to the flow velocity between the medium plates on the secondary side of the heat exchanger exceeding 1 m/s, and the actual operating pressure drop is 0.2~0.3 MPa, which makes the hydraulic balance of the secondary network seriously out of balance.

job operation

(1) Remove the dirt or plate scale in the heat exchanger flow channel, and clean the newly operated system once a week according to the actual situation. When cleaning the scale (mainly CaCO3) on the board surface, choose 0.3 sulfamic acid solution or 0.8 nitric acid solution containing 0.3 urotropine, 0.2 aniline and 0. 1 potassium thiocyanate as cleaning solution, and the cleaning temperature is 40 ~ 60℃. When cleaning the equipment by chemical soaking, the inlet and outlet of the cold medium of the heat exchanger must be opened, or DN25 cleaning port should be installed on the nozzle of the medium inlet and outlet when installing the equipment, and the prepared cleaning solution should be injected into the equipment. After soaking, the residual acid should be cleaned with clear water to make the pH≥7. When dismantling and cleaning, soak the plate in cleaning solution for 30 min, then lightly brush it with a soft brush to remove dirt, and finally clean it with clear water. Avoid damaging the printing plate and rubber pad when cleaning. If the mechanical backwashing method without disassembly is adopted, a nozzle should be connected to the medium inlet and outlet pipeline in advance, the equipment should be connected to the mechanical cleaning vehicle, and the cleaning liquid should be injected into the equipment in the opposite direction of the medium flow. The circulating cleaning time is 10 ~ 15 min, and the medium flow rate is controlled at 0.05 ~ 0.15 m/s. Finally, the clean water is circulated several times, and the mass concentration of Cl in the clean water is controlled below 25 mg/L. ..

(2) It is best to use softened soft water for secondary circulating water. Generally, it is required that the mass concentration of suspended solids in water is not more than 5 mg/L, the diameter of impurities is not more than 3 mm, and the pH value is not less than 7. When the water temperature is not more than 95℃, the concentration of calcium and magnesium should be not more than 2 mmol/L; When the water temperature is greater than 95℃, the concentrations of calcium and magnesium should not be greater than 0.3 mmol/L, and the mass concentration of dissolved oxygen should not be greater than 0.1mg/L.

(3) For the central heating system, the method of primary or secondary water supply can be adopted.

The heating temperature can't meet the requirements.

cause

(1) Insufficient medium flow on the primary side leads to large temperature difference and small pressure drop on the hot side.

② The cold end temperature is low, and the cold and hot ends are low.

③ The flow distribution of multi-plate heat exchangers running in parallel is uneven.

④ The scale inside the heat exchanger is serious.

job operation

① Increase the flow rate of heat source or increase the diameter of heat source medium pipeline.

② Balance the flow of multiple plate heat exchangers running in parallel.

③ Dismantle the plate heat exchanger to remove the scale on the plate surface.