As a kind of heat exchange equipment, plate heat exchanger has been widely used in many fields in our country and has brought great economic benefits. However, various failures and damages of plate heat exchangers also cause certain economic losses to users. The reasons are various. It is related to the short application history of plate heat exchangers in our country and insufficient experience in design, use, maintenance and maintenance.
1. seal failure
1.1 pressure When the detachable plate heat exchanger is used within the rated working pressure, leakage occurs, which is mainly related to abnormal impact load (water hammer and air hammer) in the system besides the quality factors of equipment in manufacturing and assembly. This is a phenomenon that is not easy to be observed by ordinary operators. The instantaneous pressure peak caused by impact is usually 1-3 times higher than the normal working pressure, which causes the rubber gasket installed in the plate heat exchanger to shift, leading to seal failure. As the heat transfer element of this equipment is made of stainless steel sheet (thickness is 0.5-0.8), its sealing rigidity is relatively poor and its sealing periphery is very long, so its impact pressure resistance is much lower than that of shell-and-tube heat exchanger. Precautions: ① Considering the structural characteristics of the plate heat exchanger and depending on the operating pressure, increase the design pressure of the equipment by 1.5-2 times. (2) The impact phenomenon in the system should be avoided as much as possible during use. (3) In applications where such accidents have occurred, measures can be taken to increase the plate thickness depending on the situation, with obvious effect.
1.2 Temperature Rapid changes in temperature can also cause seal failure. When the temperature changes too fast, the linear expansion coefficient of the rubber gasket does not match the elastic deformation and the sealing pre-tightening force, which reduces the sealing pre-tightening force and causes the bearing capacity of the equipment to be lower than the rated design pressure. The following methods can be adopted to solve this problem: ① The pressure rise and temperature rise should be slowed down as much as possible when operating the equipment. (2) A compression pre-tightening spring can be designed on the clamping stud to effectively compensate the change of the sealing pre-tightening force and prevent leakage.
2.1 Blocking The gap between the flow passages of plate heat exchangers is small (2.5 ~ 6 mm), and particle sundries with diameters larger than 1.5 ~ 3 mm are easy to block the passage of plates, causing the pressure drop of equipment to deteriorate sharply, leading to equipment failure due to blockage. According to needs, a coarse filtering or backwashing device can be arranged at the medium inlet, which can effectively prevent the equipment from being blocked.
2.2 Scaling Scaling can lead to the reduction of heat transfer coefficient of heat transfer equipment and block the plate passage in severe cases. The countermeasures are: ① Plate heat exchanger should not be used in dirty or easily scaling environment (unless effective other measures are added). (2) when using non-softened cooling water as cooling medium, the operating temperature should be controlled at about 50℃ or even lower to avoid the sensitive temperature of calcium and magnesium ions precipitation in the medium. For domestic hot water (bath water), it is necessary to design a special temperature control system to control the outlet water temperature (bath water is not allowed to be softened or treated by other chemical methods) in order to enable the normal use of the equipment.
The practice has proved that chlorine binding agent can effectively prevent stress corrosion.
3.Conclusion
Knowing and understanding the main influencing factors of plate heat exchanger failure, correctly selecting, operating and maintaining equipment can give full play to the characteristics of high efficiency and energy saving of plate heat exchanger safely and reliably, thus obtaining better economic benefits.