Application and maintenance of plate heat exchanger in chlor-alkali production
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The plate heat exchanger is a compact and efficient heat exchange device. Compared with the tube heat exchanger: its footprint is only about 20% of the tube heat exchanger. Due to the increased disturbance, heat transfer is enhanced and the heat transfer efficiency is increased by 4 to 5 times. It has flexible assembly, low heat loss, no need for insulation layer, light weight, convenient disassembly and maintenance, and is widely used in various industrial production.
1 Working principle and performance comparison In the plate heat exchanger, the plate is a heat transfer element, suspended on the guide bar, and the plate is also covered with a sealing gasket, and the plate is assembled and pressed according to design requirements. The flow of fluid in the plate heat exchanger enters the plate passage through the angular holes in the plate, and the heat exchange between the hot and cold fluids is achieved. Ordinary plate heat exchangers are mainly used for non-phase-change heat exchange applications, as well as condensing plate heat exchangers for gas condensation and welded plate heat exchangers with high pressure resistance.
The performance comparison between plate heat exchanger and shell-and-tube heat exchanger is shown in Table 1. 
2 chlor-alkali plant use procedures in the chlor-alkali plant, in addition to the evaporator heating chamber and concentrated alkali cooler can not use the plate heat exchanger due to the presence of crystalline salt, other processes that can use heat exchangers, plate heat exchangers Can work well.
2.1 Silicon Rectification Process The two heat exchangers of the silicon rectification process belong to liquid-liquid heat exchange. The oil cooler of the transformer can use aluminum brass plate material and oil-resistant nitrile rubber gasket plate heat exchanger; the pure water cooler of the rectifier cabinet can use the plate material of 1Cr18Ni9Ti and the plate type of nitrile rubber gasket. Heater.
2.2 brine process brine preheater belongs to gas-liquid heat exchange, and due to the electrochemical corrosion of brine medium, the plate material must use 1Cr18Ni9Ti or more austenitic stainless steel, and the gasket is a condensed plate heat exchanger of nitrile rubber.
2.3 Chlorine gas treatment process In the chlorine gas treatment process, the titanium tube cooler plate can be made of TA2 titanium material. Because the chemical corrosion of wet chlorine gas is heavier, the oxidation resistant EPDM rubber gasket is used, and there is chlorine water at the same time. Condensation, condensed plate heat exchanger must be used; the same chlorine water cooler can use plate heat exchanger with plate material of TA2 and gasket for EPDM; cycle acid of Nessler pump and acid exchange of each column The heat exchanger plate can be made of Harbin-type alloy C-276 and fluorine rubber gasket which are resistant to concentrated sulfuric acid and chlorine gas.
2.4 Liquid chlorine process In the liquid chlorine process, whether using ammonia refrigeration or Freon refrigeration, the liquefaction of the refrigerant can use a plate heat exchanger with a plate material of 1Cr18Ni9Ti. Since the gas pressure after compression is high, this plate type The heat exchanger must be welded. Although the plate cannot be dismantled, the service life is still more than 8 years due to the weak corrosiveness of the medium.
The chlorine gas liquefier can use a condensed plate heat exchanger with a plate material of 1Cr18Ni9Ti, and the gasket is made of EPDM rubber like the titanium tube cooler.
2.5 Electrolysis process Because the corrosion of the electrolyte includes pitting corrosion, alkali brittleness and electrochemical corrosion of chloride ions, the electrolyte preheater must use austenitic stainless steel sheet material of 1Cr18Ni9Ti or Mo2Ti, and the gasket is selected to be strong alkali resistant. Base rubber.
3 Problems to be noted in use (1) When the heat exchange medium contains solid particles or fibrous substances, such as primary water or circulating water, a filter should be installed in front of the heat exchanger.
(2) When the plate heat exchanger is put into use, the high temperature medium inlet valve should be slowly opened to fill the high temperature side plate, and then the inlet valve of the low temperature medium is opened. It is strictly forbidden to change the pressure and temperature drastically.
(3) By analyzing the composition of the medium or judging the pressure change, it is found that when there are two kinds of media colliding, stop immediately and find and replace the damaged plate.
(4) Strictly control the use temperature and pressure below the allowable value, otherwise it will accelerate the aging of the gasket and cause serious leakage.
(5) When the inspection reveals that the heat exchanger plate bundle leaks, it should be marked so that after the equipment is disassembled, the damaged plates and gaskets are quickly detected and replaced with new heat exchange plates and gaskets.
(6) When starting the operation, it is found that the heat exchanger is uneven in temperature and heat. First check whether there is air in the heat exchanger and not clean it. Then check whether the heat exchanger plate is wrongly added, whether the channel is blocked, and take corresponding effective measures. Process it.
(7) When the plate heat exchanger is stopped, the low temperature medium inlet valve should be slowly closed, then the high temperature medium inlet valve should be slowly closed, then the outlet valve of the low temperature medium should be closed, and then the outlet valve of the high temperature medium should be closed. It is forbidden to change the pressure and temperature drastically.
4 Cleaning and maintenance 4.1 The interval between cleaning and cleaning should be determined according to the use of the plate heat exchanger. When the resistance of the plate heat exchanger passage increases, the heat exchange effect should be cleaned.
4.1.1 Backwashing method When the flow resistance of the plate heat exchanger is light or the resistance drop suddenly rises, stop, and in the opposite direction of the flow path, reverse flush with a process medium higher than 1.5 times the operating pressure.
4.1.2 Manual cleaning method If the flow path resistance of the plate heat exchanger cannot be eliminated by the backwashing method, and the fouling layer of the heat exchange plate is very thin, depending on the strength, the brush of the soft fiber can be used for scrubbing, and then the pressure is used. 0.2MPa of water is washed clean.
4.1.3 Chemical cleaning method When the fouling layer of the heat exchange plate is thick and the strength is high, when it is difficult to treat by the above two methods, the chemical cleaning method is used. It is generally cleaned with a mixture of 10% nitric acid, 2% polymetaphosphoric acid, and 5% ethylenediaminetetraacetic acid. It can also be cleaned with 10% nitric acid plus a special corrosion inhibitor from Bluestar Cleaning. Rinse with clean water after zui.
4.2 Maintenance When the plate heat exchanger is dismantled and cleaned or the plates and gaskets are damaged, it should be repaired.
(1) Before the disassembly of the plate heat exchanger, the compaction length of the bundle should be measured for use in reloading.
(2) If the gasket is stuck in the groove between the two plates, it should be carefully inserted into the easily peelable part with a tool, and then peeled off along the periphery, so that the plate and the gasket should not be damaged.
(3) Check whether the heat exchange plate has perforation, and generally check it with a magnifying glass. Austenitic stainless steel sheets can be roughly inspected with a magnet and then examined with a magnifying glass.
(4) If it is found that there is accumulation of debris in the medium inlet and outlet and the passage, the filter is invalid, and the filter should be cleaned in time.
(5) When the heat exchanger plate is crusted, it is forbidden to use a wire brush to wash the brush, especially the stainless steel plate, to prevent the corrosion of the plate.
(6) When disassembling the chlorine-treated titanium sheet, it is strictly forbidden to contact with open flame to prevent oxidation.
(7) Check the gasket for defects such as aging, cracks, etc. It is forbidden to scratch the surface with hard objects.
(8) When one plate of the plate heat exchanger is damaged without spare parts, the plate and the adjacent plates can be removed at the same time, and then the clamping bolts are tightened.
(9) When the plate is assembled, the sealant can be applied to the groove of the plate by a brush, and then pressed into the sealing gasket, and the plate can be assembled after being assembled.
5 Conclusion The plate heat exchanger is a new type of heat exchange equipment with compact structure and high efficiency. The application of the new plate heat exchanger in the production of chlor-alkali reduces the floor space by 80% compared with the tube heat exchanger, the investment is reduced by 50% to 70%, and the heat transfer efficiency is increased by 400% to 500%. Because the selected material is better, it can ensure the safe long-term operation of the chlor-alkali unit as long as it is operated according to the regulations. At the same time, the plate heat exchanger is light in weight and does not require heat preservation outside the heat exchanger. Cleaning is easier if the resistance increases or fouls during use. When the plate is damaged or the gasket leaks, it is convenient to disassemble and repair. Therefore, plate heat exchangers should be used as much as possible in the production of chlor-alkali.