Main Factors of Failure of Plate Heat Exchanger and Preventive Countermeasures
Plate heat exchanger is a new type of high efficiency heat exchanger assembled from a series of metal sheets with a certain corrugated shape. A thin rectangular channel is formed between the various sheets, and heat exchange is performed through the half sheets. The plate heat exchanger is a liquid & mdash; liquid, liquid & mdash; steam for heat exchange equipment. The utility model has the advantages of high heat exchange efficiency, small heat loss, compact and light structure, small occupied area, convenient installation and cleaning, wide application and long service life. In the case of the same pressure loss, the heat transfer coefficient is 3-5 times higher than that of the tube heat exchanger, and the floor space is one-third 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 China and have achieved great economic benefits. However, the failure of the plate heat exchanger also causes certain economic losses to our users. The main reasons are seal failure, fouling blockage and corrosion, which make the heat exchanger unable to use.
1. Analysis of the causes of seal failure and related precautions
The main reasons for seal failure are pressure, temperature, time and operating conditions.
plate heat exchanger type is detachable, sealed, etc., such as plate-type detachable heat exchanger used under the rated working pressure, leakage, in addition to the equipment in the manufacturing quality, mainly with There are abnormal impact loads in the system, which is not easy for the operator to find. The transient pressure is increased by the impact, and the pressure may be 1 to 3 times higher than the normal pressure, causing the sealing gasket installed in the plate heat exchanger to be displaced, resulting in failure of the seal. Moreover, since the heat transfer element of the device is manufactured by one-time forming of a thin plate, the thickness is 0.5-0.8 mm, the rigidity and the bearing capacity of the seal are relatively poor, and some heat exchanger plates have a long periphery and the impact resistance is relatively poor.
In this regard, appropriate precautions should be taken: depending on the operating pressure, increase the design pressure of the equipment to 1.5 to 2 times the pressure of use; in use, try to avoid the impact phenomenon in the system; Take measures to increase the thickness of the sheet.
A sharp change in temperature also causes 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, so that the pre-tightening force of the seal is lowered, and the bearing capacity of the device is lower than the rated working pressure.
The following measures should be taken to solve this problem: the boosting temperature should be as slow as possible when operating the equipment; the compression preloading spring is designed on the clamping bolt to compensate for the change of the preload.
The use time of the plate heat exchanger, as the use time increases, the material of the gasket will also age. The sealing effect is used, which affects the sealing effect of the plate heat exchanger.
According to the characteristics of the material, the gasket of the appropriate material should be selected, and different gaskets should be used depending on the conditions of use.
The difference in process media can also cause seal failure. A supersaturated steam like temperature will cause the seal to fail for a short time. The saturated steam of the same temperature can form a water film on the surface of the gasket to protect the gasket.
Selecting the right process medium for the operation, is also a way to ensure the failure of the plate heat exchanger.
2. Analysis of the cause of clogging and scaling failure and corresponding preventive measures
plate heat exchanger has a small flow gap, about 2.5 ~ 6mm, the particle debris larger than 1.5 ~ 3mm is easy to block the channel, so that the pressure drop of the device changes drastically, the flow is reduced, heat transfer The effect is reduced and the device is easily disabled. Precautions A filter or flushing device can be placed at the inlet of the media for regular cleaning or disposal.
After the plate heat exchanger is used, due to heat transfer or cooling of the medium, fouling occurs. The fouling can cause the heat transfer coefficient of the plate heat exchanger to decrease, and in severe cases, the plate will be blocked. aisle. The plate-type heat exchanger is designed with a large number of support contacts, which are intended to support the flow of the medium. The side effect is that the fluid forms a local stagnation and forms dirt, with time and at a suitable temperature. The calcium and magnesium ions in the cooling water are precipitated and continuously increase to form a honeycomb scale.
Although the cause of blockage and scaling is different, the impact is the same. The countermeasures against prevention are: plate heat exchangers should not be used in dirty or fouling materials; do not use unsoftened water as cooling medium, and temperature should have relevant requirements to avoid sensitive temperature zones 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 for a period of time, and then the heat exchanger should be put into the system.
3. Analysis of corrosion failure and preventive measures
The type of corrosion failure of plate heat exchangers is somewhat etched, crevice corrosion, stress corrosion cracking, uniform corrosion and other corrosion failures. Corrosion is a complex chemical phenomenon, such as rust or scale on the surface of the plate. Pitting corrosion; crevice corrosion at the bottom of the gasket groove or sheet closure; uniform or corrosion of all or most of the metal surface of the contact medium being corroded.
This should take the following effective precautions: the correct choice of sheet material; regular cleaning of dirt to destroy the conditions and development of corrosion; use non-chlorine-containing binder.
4. Analysis and measures for design, manufacturing and installation
Due to the high efficiency and energy saving characteristics of plate heat exchangers, it is widely used in many fields, and the processing media are various, and the conditions are different and varied in the production process. The choice of the gasket is the key. If the choice is not suitable, the material can not meet the physical properties of the process medium, the elasticity is not good, and the use of the padding, elongation, deformation, aging, breakage, etc. occurs.
During the manufacturing process of the sheet, the residual stress generated in the stamping is used in a corrosive environment, which will cause stress corrosion and directly damage the sheet.
The surface of the plate is not flat, the equipment is not easy to install and centered during installation and maintenance, which makes the pressing force uneven, affecting the seal and causing leakage.
In this regard, the alignment should be installed as much as possible in the installation, so that the pressing force is even, so that it can be kept tight during use and does not leak.