Plate heat exchanger is a new type of high-efficiency heat exchanger made up of a series of metal sheets with a certain corrugated shape. Thin rectangular channels are formed between the various plates, and heat exchange is carried out through the half plates. Plate heat exchangers are ideal equipment for liquid-liquid, liquid-vapor heat exchange. It has the characteristics of high heat exchange efficiency, low heat loss, compact and lightweight structure, small footprint, convenient installation and cleaning, wide application, long service life and so on. Under the same pressure loss, its heat transfer coefficient is 3-5 times higher than that of the tube heat exchanger, covering an area of ​​one third of that of the tube heat exchanger, and the heat recovery rate can be as high as 90% or more. As a compact and efficient heat exchange equipment, plate heat exchangers have been widely used in many industrial fields in our country and have achieved huge economic benefits. However, the failure of the plate heat exchanger also causes certain economic losses for our users. The main reasons are seal failure, fouling, clogging, and corrosion, which make the heat exchanger ineffective.

 1. Analysis of reasons for seal failure and related preventive measures 　　

1. Pressure

The main causes of seal failure are pressure, temperature, time and operating conditions.  　　　　

Plate heat exchanger types are detachable, sealed, etc., such as plate detachable heat exchangers used under rated working pressure, leaks, in addition to the quality of equipment manufacturing, mainly due to abnormalities in the system The impact load is related, which is not easy for the operator to find. The impact causes an instantaneous pressure increase, and the pressure may be 1 to 3 times higher than the normal pressure, displacing the sealing gasket installed in the plate heat exchanger, resulting in sealing failure. And because the heat transfer elements of the equipment are made of thin plates at one time, with a thickness of 0.5-0.8mm, the rigidity and endurance of the seal are relatively poor, and some heat exchange plates have a long periphery, and the impact resistance is relatively poor. It is much worse than other heat exchangers such as tube type.

In this regard, corresponding precautions should be taken: depending on the operating pressure, increase the design pressure of the equipment to 1.5 to 2 times the operating pressure; try to avoid impact in the system during use; increase the thickness of the plate under special circumstances Measures.  　　

2Temperature 　　

A sharp change in temperature also caused seal failure. When the temperature changes too fast, the expansion coefficient of the gasket does not match the elastic deformation and the pre-tightening force of the seal, which reduces the pre-tightening force of the seal, causing the equipment to withstand lower than the rated working pressure.  　　The following measures should be taken to solve this problem: the pressure rise and temperature rise should be as slow as possible when operating the equipment; a compression preload spring is designed on the clamping bolt to compensate for the change of the preload.  　　

3 time 　　

The use time of the plate heat exchanger, as the use time increases, the material of the sealing gasket will also deteriorate. Cause the sealing effect and affect the sealing effect of the plate heat exchanger. In this regard, according to the characteristics of the material, the sealing gasket of the appropriate material should be selected, and different sealing gaskets should be used according to the different conditions of use.  　　

4 Operating conditions 　　

Different process media conditions can also cause seal failure. The supersaturated steam as the temperature will cause the sealing sheet to fail in a short time. The saturated steam at the same temperature can form a water film on the surface of the gasket, which can protect the gasket.  According to the operating conditions, selecting the appropriate process medium is also a way to ensure that the plate heat exchanger is prevented from failing.  　　

Second, the cause analysis of blockage and scaling failure and the corresponding preventive measures 　　

1 Blocked 　　

The circulation gap of the plate heat exchanger is small, about 2.5-6mm. Particles with a diameter greater than 1.5-3mm can easily block the channel, causing the pressure drop of the equipment to change sharply, the flow rate is reduced, and the heat exchange effect is reduced. The device fails. Preventive measures can be set up at the inlet of the medium filter or flushing device, regular cleaning or treatment.  　　

2 Scaling 　　

After the plate heat exchanger is used, fouling occurs due to the heat transfer or cooling medium, which can cause the heat transfer coefficient of the plate heat exchanger to decrease, and in severe cases, it will block the plate passages. The plate heat exchanger is designed with a large number of supporting contacts, which are designed to support the flow of the medium. The side effect is that the fluid forms a local stagnant flow and forms dirt. With time and at a suitable temperature , The calcium and magnesium ions in the cooling water are precipitated and increase continuously, forming honeycomb scales.  　　

Although the causes of clogging and fouling are different, the effects are the same. The preventive measures are: plate heat exchangers should not be used in dirty or fouling materials; do not use unsoftened water as the cooling medium, and the temperature should have relevant requirements to avoid the sensitive temperature zone where calcium and magnesium ions are precipitated . Moreover, when the new system is put into operation, the heat exchanger should be separated from the system, and cycled for a period of time before putting the heat exchanger into use in the system.  　　

3 Cause analysis of corrosion failure and preventive measures 　　

Corrosion failure types of plate heat exchangers are pitting corrosion, crevice corrosion, stress corrosion cracking, uniform corrosion and other corrosion failures. Corrosion is a complex chemical phenomenon, such as pitting corrosion of rust or scale on the surface of the plate; Crevice corrosion caused by sealing gasket groove bottom or plate closure; uniform corrosion in which all or most of the metal surface in contact with the medium is corroded. In this regard, the following effective preventive measures should be taken: the correct selection of plate materials; regular cleaning of dirt to destroy the conditions and development of corrosion; selection of non-chlorine-containing binders.  　　

4 Reason analysis and measures for design, manufacturing and installation. Due to the high efficiency and energy saving characteristics of plate heat exchangers, they are widely used in many fields and deal with a variety of media. In the production process, there are more conditions and more Variety. The selection of the gasket is the key. If the selection is not appropriate, the material cannot meet the physical properties of the process medium, and the elasticity is not good. During use, the gasket may come off, elongation, deformation, aging, fracture, etc. During the manufacturing process of the plate, the residual stress generated during stamping will cause stress corrosion when used in a corrosive environment, which will directly damage the plate. The surface of the plate is uneven, and the equipment is not easy to install and center during installation, use, and maintenance, which makes the pressing force uneven, affecting the seal and causing leakage. In this regard, during installation, the center should be installed as much as possible to make the pressing force uniform, so that it can be kept pressed tightly during use and does not leak.  　　

5 Conclusion 　　

Analyzed the reasons for the failure of the plate heat exchanger, and proposed corresponding preventive measures. During the use process, corresponding maintenance and preventive measures should be formulated for the use of various plate heat exchangers to make them play Its due role.