• Zhejiang Shengsong Heat Exchanger Co., Ltd
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Problems and countermeasures in the plate heat exchanger applications(Hits:) 
OriginShengsong AuthorMr Hu Add Time2012-02-03 fontSize: T|T
1 Introduction
                                     
        
The plate heat exchanger as a compact and efficient heat transfer equipment used in multiple sets of device in my company, and played a good value for money. The plate heat exchanger plates, gaskets, fixed head, activity head (bonnet), the clamping bolt, the composition of the rack rails, pillars, etc., it has a compact, high heat transfer efficiency, disassemble and clean overhaul advantages of convenience. However, various problems in the use of plate heat exchanger, but also have serious repercussions to the production, their are many reasons for it and design, use, maintenance and maintenance, etc..

        
2 device clogging and fouling

        
2.1 blockage

        
Plate heat exchanger flow channel gap smaller (2.5-6mm) diameter greater than 1.5 to 3mm particle debris easily blocked the channel of the plate, so that the sharp deterioration of the equipment, the pressure drop, resulting in equipment due to blockage of the heat transfer capacity significantly reduce serious cause the device to a continuous production disruptions. Circulating water of impurities, and similar devices E208/E209 has repeatedly blocked, resulting in frequent downtime device, some impact on the economic efficiency of enterprises. Later, the increase in the E208/E209 before easy to dismantle and clear the filter, to ensure the long-term operation of E208/E209. So according to the settings in the media at the entrance of the coarse filter or backwash device can effectively prevent the clogging of the plate heat exchanger.

        
2.2 scaling
                                     
        
Scaling can lead to reduced heat transfer coefficient of heat transfer equipment, so serious that it block the plate channel. The plate heat exchanger plate design there are a lot of the points of support to the media from the spoiler (medium turbulence to improve heat transfer coefficient) and the pressure supporting role, is easy-populated areas of solid debris and fiber The side effect is that the fluid and local stagnation and generate a dirt plot tumors, calcium and magnesium ions in the medium in the appropriate temperature precipitation is easy to plot tumor attached to grow up to form a honeycomb of dirt samples.

        
Clogging and fouling in Genesis are different, but on the plate heat exchanger is the same phenomenon. Can adopt the following countermeasures to alleviate the structural problems: (1) plate heat exchanger should not be used in dirty or fouling the environment (unless additional effective measures). (2) the use of cooling water for cooling medium without softening, the operating temperature should be controlled at 50 ℃ or less sensitive to temperature to avoid precipitation of calcium and magnesium ions in the medium.

        
3 seal failure

        
3.1 The pressure effect
                                     
        
Detachable plate heat exchanger within the rated working pressure leaks, non-normal impact, mainly related to the system in addition to the quality factor of the equipment in the manufacturing assembly loading (water hammer, hammer), which is generally The operator is not easy to observed phenomena. The impact caused by the instantaneous pressure peak is often higher than the normal working pressure of 1 to 3 times, installed in the plate heat exchanger rubber gasket shift, resulting in seal failure. Heat transfer components of the equipment manufacture of stainless steel sheet (thickness 0.5 ~ 0.8mm), sealed rigid relatively poor seal surrounding is very long, so the resistance to impact the ability of far below the shell and tube heat exchanger. Precautions: (1) In view of the structural characteristics of the plate heat exchanger according to the operating pressure in the selection of equipment to improve the design pressure of 1.5 to 2 times. (2) avoid the use of the system impact of the phenomenon. (3) applications of such an accident occurred, according to the situation can also take measures to increase the thickness of the plate, the effect is very obvious.

        
3.2 Temperature Effect
                                     
        
Sharp changes in temperature can also cause seal failure. When rapid temperature changes, the linear expansion coefficient and elastic deformation of the rubber gasket and seal preload does not match, so that the seal preload decreased, causing the device bearing capacity of less than the rated design pressure. This can be used as a solution: (1) to operate the equipment to boost warming should be as smooth as possible. (2) increase the preload spring clamping stud and effective compensation seal preload changes, to prevent leakage.

         
3.3 the influence of time

        
Use or idle equipment a few years, self-sealing material aging may affect the reliability of sealing, so should be used to overhaul the opportunity to replace them with new gasket.

        
4 Corrosion

        
Corrosion is a complex chemical phenomenon, the corrosion of austenitic stainless steel plate heat exchanger showed most of the Cl - caused by stress corrosion, often occurs in the bottom part of the bottom of the plate seal groove and after the formation of the dirt, the dirt, the main causes of : (1) stainless steel heat transfer plate formed by mechanical punching inevitably remnants of a certain amount of surface residual stress, non-molybdenum stainless steel sheet, the elimination of surface residual stress is very difficult, or even it is not feasible the. (2) plate assembly to form a multi-gap structures, such as the contact between the plate, sealing the bottom of the tank and other parts. While the gap is likely to cause Cl-enrichment of the local concentration is often far more than the stainless steel's own resistance to stress corrosion. (3) When the plate surface of the dirt is severe, the corrosion in the dielectric elements (Cl, S, etc.) may be a large number of attachment in the dirt, and the gap at the end of the scale enrichment. (4) the harmful elements are often in the sealed bottom of Cl due to the binder temperature to rise high temperature analysis out. Series of adhesive, such as neoprene, compressed asbestos (containing CaCl2), often in conditions of water and steam conditions, precipitation enrichment of Cl-and H + formation of HCl, so that the bottom of the gap at the severe stress corrosion cracking.

        
Slab cracks in the surface residual stress, Cl-concentration and temperature conditions, the gestation period, after a certain amount of corrosion, it is possible to stress corrosion cracking. In the selection of plate heat exchanger, seek to undermine the process of installation and use of any of these conditions, can effectively prevent or delay the corrosion takes place, the equipment safe and normal operation. The correct selection of materials on a regular basis to clear the dirt to destroy the corrosion formation conditions and the incubation period, the choice of a non-chlorine bonding agent, so to some extent, effective in preventing stress corrosion.

        
Other problems

        
(1) For the stainless steel plate heat exchanger, can not use hydrochloric acid (HCl) or hydrochloric acid class of cleaning agents and cleaning powder for chemical cleaning, which is not fully dissolved scale residue (containing residual chlorine) in the multi-gap structure is very difficult to rinse, alkali and can not be fully carried out. Can be used nitric acid and buffers or nitric acid cleaning agents, washing powder, cleaning, proper heating can improve the cleaning efficiency. (2) installation of equipment, piping, should avoid the wire to take the equipment, but should take on the plumbing pipes to prevent the wire current so that the contact plate at the breakdown. This problem have been frequent in the other company's equipment during the installation process. (3) steam superheat rubber gasket service life, the normal application of the rubber pressure pads 150 ℃ -180 ℃ saturated vapor, was about 3-5 years or longer, and used at about 130 ℃ life of only a few months of superheated steam. This is because the saturated vapor can be generated in the gasket surface layer of water film, and an effective protection at a high temperature gaskets. Therefore, the steam is used not only to pay attention to its temperature is applicable to the gasket, the superheat is also an important factor that can not be ignored.

        
6 Conclusion
                                     
        
Short by the correct selection, operation and maintenance, can effectively reduce the probability of failures in the use of the plate heat exchanger, to extend the operating cycle of the equipment, to maximize the advantages of energy efficient plate heat exchanger, for the company to obtain better economic benefits.
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