Application and maintenance of plate heat exchanger in chlor alkali production

As we all know, chlor alkali production is a high energy consumption industry In recent years, with the increasing production scale of chlor alkali plant, the total energy consumption is also increasing Because the energy consumption and investment of heat exchanger account for a high cost of caustic soda, it is more and more important to use new heat exchanger in the expansion of chlor alkali enterprise Plate heat exchanger is a kind of heat exchanger with compact structure and performance Compared with the tubular heat exchanger, its floor area is only about 20% of that of the tubular heat exchanger Due to the increase of disturbance, the heat transfer is strengthened and the heat transfer efficiency is increased by 4-5 times The utility model has the advantages of flexible assembly, small heat loss, no need of thermal insulation layer, light weight, convenient disassembly and maintenance, and is widely used in various industrial production 1 Working principle and performance comparison in plate heat exchanger, the plate is a heat transfer element, suspended on the guide rod, and the plate is also pasted with sealing gasket, and the plate is assembled according to the design requirements and then compressed The flow of fluid in the plate heat exchanger is through the corner hole on the plate to enter the plate channel, and the hot and cold fluid can exchange heat Ordinary plate heat exchanger is mainly used for heat exchange without phase change, and condensation plate heat exchanger is used for gas condensation, as well as welding plate heat exchanger with high pressure resistance See Table 1 for performance comparison between plate heat exchanger and shell and tube heat exchanger 2 In chlor alkali plant, except for the heating chamber of evaporator and concentrated alkali cooler, plate heat exchanger can not be used due to the existence of crystal salt, other processes that can use heat exchanger, plate heat exchanger can work well 2.1 the two heat exchangers of silicon rectification process belong to liquid-liquid heat exchange Among them, the oil cooler of the transformer can use the plate heat exchanger made of aluminum brass plate and oil-resistant NBR gasket; the pure water cooler of the rectifier cabinet can use the plate heat exchanger made of 1Cr18Ni9Ti plate and NBR gasket 2.2 the brine preheater in brine process belongs to gas-liquid heat exchange At the same time, due to the electrochemical corrosion of brine medium, the plate material must be austenitic stainless steel above 1Cr18Ni9Ti, and the gasket is a condensation plate heat exchanger of NBR 2.3 chlorine treatment process in chlorine treatment process, TA2 titanium material can be used for plate of titanium tube cooler Due to the heavy chemical corrosion of wet chlorine, the oxidation-resistant EPDM rubber gasket is selected, and the condensation of chlorine water occurs at the same time The condensation plate heat exchanger must be used; In the same way, plate heat exchanger with TA2 plate material and EPDM gasket can be used for chlorine water cooler; the plate of circulating acid heat exchanger of Nessler pump and each tower can be made of Harbin alloy C-276 with strong sulfuric acid and chlorine corrosion resistance and fluorine rubber gasket 2.4 liquid chlorine process in liquid chlorine process, whether ammonia refrigeration or freon refrigeration is used, the plate heat exchanger with 1Cr18Ni9Ti plate material can be used for refrigerant liquefaction Because of the high compressed gas pressure, the plate heat exchanger must be welded Although the plate cannot be disassembled for inspection, the medium is less corrosive, The service life is still more than 8 years The condensing plate heat exchanger with 1Cr18Ni9Ti plate material can be used for chlorine liquefier, and its gasket is the same as that of titanium tube cooler 2.5 in the electrolysis process, due to the corrosion of electrolyte, including the hole corrosion, alkali embrittlement and electrochemical corrosion of chloride ion, the austenitic stainless steel plate material of 1Cr18Ni9Ti or mo2ti must be used for the electrolyte preheater, and the butyl rubber with strong alkali resistance shall be selected as the gasket 3 Precautions in use (1) when the heat exchange medium contains solid particles and fibrous substances, such as primary water or circulating water, a filter shall be installed in front of the heat exchanger (2) when the plate heat exchanger is put into use, the inlet valve of high-temperature medium shall be opened slowly to make it full of high-temperature side plate process, and then the inlet valve of low-temperature medium shall be opened Sharp changes in pressure and temperature are strictly prohibited (3) by analyzing the composition of the medium or judging the pressure change, if two kinds of medium are found to be in collusion, stop the machine immediately, find out 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) in case of leakage of heat exchange plate bundle during inspection, make marks so as to quickly find out the damaged plate and sealing gasket and replace them with new ones after the equipment is disassembled (6) at the beginning of operation, if the heat exchanger is found to be uneven in heat and cold, check whether there is air in the heat exchanger that is not completely discharged, then check whether the heat exchanger plate is wrongly added and whether the channel is blocked, and take corresponding effective measures for treatment (7) when the plate heat exchanger stops, the inlet valve of low-temperature medium shall be closed slowly, and then the inlet valve of high-temperature medium shall be closed slowly, then the outlet valve of low-temperature medium shall be closed, and then the outlet valve of high-temperature medium shall be closed No sharp change of pressure and temperature is allowed 4 Cleaning and maintenance 4.1 cleaning interval shall be determined according to the use of plate heat exchanger When the resistance of plate heat exchanger channel increases and the heat exchange effect decreases, it should be cleaned 4.1.1 backwash method when the flow resistance of the plate heat exchanger is light or the resistance drop suddenly increases, stop the machine and use the process medium 1.5 times higher than the operating pressure to backwash from the opposite direction of the flow channel 4.1.2 manual cleaning method if the flow resistance of the plate heat exchanger cannot be eliminated by back washing method, and the scale layer of the heat exchanger plate is very thin, according to the different strength, it can be washed with a soft fiber brush, and then washed with water with a pressure of 0.2MPa 4.1.3 chemical cleaning method: when the scale layer of the heat exchange plate is thick and the strength is high, and it is difficult to handle with the above two methods, the chemical cleaning method is used Generally, 10% nitric acid, 2% polymetaphosphoric acid and 5% ethylenediaminetetraacetic acid are used for cleaning, and 10% nitric acid and special inhibitor of Bluestar Cleaning Company are also used for cleaning Rinse Zui with clean water 4.2 maintenance when the plate heat exchanger is disassembled, inspected and cleaned, or the plate and gasket are damaged, the maintenance shall be carried out (1) before disassembling the plate heat exchanger, the compression length of the plate bundle shall be measured for use during reassembly (2) if the sealing gasket is stuck in the groove between the two plates, it shall be carefully inserted from the easily peeled part with tools, and then peeled along its periphery, and the plates and sealing gasket shall not be damaged (3) check whether the heat exchange plate is perforated, generally with a magnifying glass The austenitic stainless steel plate can be roughly inspected with a magnet first, and then inspected with a magnifying glass (4) if there is debris accumulation in the medium inlet and outlet and channel, it means that the filter is invalid, and the filter shall be cleaned in time (5) when the heat exchange plate is scabbed, do not use wire brush to wash, especially stainless steel plate to prevent the corrosion of the plate (6) when removing chlorine treated titanium sheet, it is forbidden to contact with open fire to prevent oxidation (7) check whether the sealing gasket has aging, crack and other defects It is forbidden to scratch the surface with hard objects (8) if one plate of plate heat exchanger is damaged without spare parts, the plate and adjacent plates can be removed at the same time, and then the clamping bolt can be tightened (9) during plate assembly, the sealant can be applied to the groove of the plate with a brush, and then the sealing gasket can be pressed in After Zui, the plate can be assembled Conclusion plate heat exchanger is a new type of heat exchanger with compact structure The application of new plate heat exchanger in chlor alkali production reduces the floor area by 80%, investment by 50% ~ 70% and heat transfer efficiency by 400% ~ 500% As the selected material is better, the safe and long-term operation of chlor alkali plant can be guaranteed as long as the operation is in accordance with the regulations At the same time, the plate heat exchanger is light in weight and does not need heat preservation outside the heat exchanger In use, if the resistance increases or scaling, cleaning is easier When the plate is damaged or the sealing gasket leaks, the disassembly and maintenance are also convenient Therefore, plate heat exchanger should be selected as much as possible in chlor alkali production.