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keywords] Large plate and shell heat exchanger, reformer, application summary] introduced * * The application of large-scale welded plate and shell heat exchangers in reforming units summarizes the advantages and economy of welded plate and shell heat exchangers in use. The structural form of the plate and shell heat exchanger is between the shell and tube heat exchanger and the plate heat exchanger. It combines the advantages of these two heat exchangers and is widely used in the food, chemical, light industry, medicine and power industries. However, because most of the heat exchange equipment used in the oil refining unit is under high temperature and high pressure conditions, and the operating conditions fluctuate greatly, it has not been widely used in the oil refining industry. Since the 1980s in Europe and the United States * * Started to develop plate and shell heat exchangers for use in the refining and chemical industry. Among them, the new plate welded heat exchanger developed by the French company PACKINOX has been widely used in refining equipment such as reforming and hydrogenation. In China, in the 1990s, the Lanzhou Petroleum Machinery Research Institute and the Sinopec Beijing Design Institute jointly developed large plate and shell heat exchangers based on the requirements of domestic production equipment in the refining and chemical fields. 1. Introduction to large welded plate and shell heat exchangers North China Petrochemical Company 300,000 tPa In the catalytic reforming unit, the mixed hydrogen feed P reaction product heat exchanger (E202) in the second stage of reforming is a welded plate and shell heat exchanger produced by Lanzhou Petroleum Machinery Research Institute. The specifications of the heat exchanger are shown in Table 1. The heat exchanger consists of a plate bundle and a shell. The structure is shown in Figure 1. The cold flow enters the plate bundle side from the bottom of the equipment and flows out from the top of the equipment; the hot flow enters the plate bundle shell side from the upper opening of the equipment and flows out from the lower side opening of the equipment. The two fluids are fully counter-current heat exchange in the plate bundle. An expansion joint is set at the lower end of the plate bundle to solve the thermal expansion problem. The heat exchanger plate bundle (6m long) is made of 0.8mm The stainless steel plates are pressed and welded by the mold. Longitudinal welds on both sides of the plates are welded using program-controlled automatic argon arc welding to form plate tubes. The number of plates and tubes required by the design are then superimposed to form a plate bundle. The transverse welds between the plate tubes and the plate tubes are welded at both ends of the plate bundle. Finally, the plate bundle is welded to the dividing connecting plate. The structure of the heat exchanger plate bundle is shown in Figure 2. The plate and shell heat exchanger uses corrugated plates as heat transfer elements, and the material passes through the gap between the two corrugated plates. These corrugations cause the fluid to continuously change the flow direction, produce rotation and torsion, and form many fine vortices, which causes the particles in each part of the fluid to continuously and rapidly transfer, allowing heat exchange to proceed quickly. The corrugated surface also increases the actual heat exchange area. These factors significantly enhance the heat transfer process. Generally, the critical Reynolds number is 400. Strong turbulence can be achieved when the heat transfer efficiency is 2-3 times that of shell and tube heat exchangers. The plate and shell heat exchanger produced by Lanzhou Petroleum Machinery Research Institute pioneered a detachable structure and is easy to maintain. The main differences with the heat exchangers of foreign PACK2INOX companies are shown in Table 2. 2. The use of plate and shell heat exchangers in reforming units. The brief process flow of the 300,000 tPa catalytic reforming unit of North China Petrochemical Company is shown in Figure 3. This heat exchanger has been in use since April 2003. Since the monthly reforming unit was put into operation, it has been running well. The process parameters of the heat exchanger are shown in Table 3. After more than a year of use, due to the small processing capacity of the unit, the design load of the heat exchanger has not been reached, but the effect is good from the operating conditions. The plate and shell heat exchanger has the following characteristics: 1. High heat transfer efficiency. Due to the use of corrugated plates as heat transfer elements, its heat transfer coefficient is several times higher than that of ordinary tubular heaters. In addition, plate and shell heat exchangers can achieve true "pure countercurrent" heat exchange. Compared with shell and tube heat exchangers, the temperature difference between the cold end and the hot end can be reduced from the usual 50-80 ℃ to 12-30 ℃, which can recover more heat. * * It saves the operating cost of the device. 2. The pressure drop is small. Since the tube bundle is straight through, there is no need to set up baffles, and the pressure drop of the heat exchanger is generally less than 0. 05MPa. In addition, in the presence of gas and liquid two-phase flow, it also overcomes the gas and liquid two-phase separation caused by the "turnover" of the medium baffle in the shell and tube heat exchanger. 3. The strong turbulence of the fluid also reduces the deposition and scaling of suspended particles on the heat exchange surface. In addition, there are no dead corners in the structure, making the maintenance and cleaning of the equipment very convenient. 4. Compact structure. Due to the high heat transfer coefficient, when completing the same heat exchange task, the plate and shell heat exchanger is small in size. It is light in weight and consumes less metal, so it can * * Save the user's equipment installation space and installation costs. 5. Safe and reliable. Like the shell and tube heat exchanger, in addition to being limited by the design level of the pressure vessel, the use pressure of the plate and shell heat exchanger has no absolute limit. In addition, the use of welded structure eliminates some static sealing points, reduces the occurrence of leaks, and improves the equipment safety factor. At present, the plate and shell heat exchanger of the reforming unit has experienced continuous operation for 10 years without failure. 3. Economic analysis of plate and shell heat exchangers. First, save the initial investment in equipment. Taking the company's 300,000 tPa catalytic reforming unit two-stage mixed hydrogen heat exchanger E202 as an example, compared with using shell and tube heat exchangers, the heat transfer area is saved by 168m2, the total height is reduced by 7m, and the weight of the equipment itself is reduced by 13t. The data is shown in Table 4, which can save equipment investment of 325,000 yuan. Due to the reduced volume and weight of the equipment, the installation costs of the corresponding steel structure and auxiliary pipelines and equipment installation costs have been reduced. Due to the high heat exchange efficiency of the equipment, the heat load of the heating furnace and the aftercooler can be reduced accordingly, and the equipment investment in the heating furnace and the aftercooler can be reduced. Secondly, the equipment operation efficiency is improved and the maintenance cost is reduced. Since the plate and shell heat exchanger has a higher heat transfer efficiency than the riser type heat exchanger, the heat outflow outlet temperature of the 300,000 tPa reforming device is reduced by 10 Calculated at ℃, more heat can be recovered by 357925kJ, correspondingly reducing the heat load of the heating furnace and the aftercooler. According to the low calorific value of the heating furnace fuel 33528kJPkg, the fuel saving is 10.7kg per hour. Calculated based on the annual operating time of 8400h and the fuel cost of 830 yuan per ton. Compared with the shell and tube heat exchanger, the plate heat exchanger saves 90t of fuel per year and saves 7.47 fuel costs per year. Ten thousand yuan. The electricity cost of the air cooler is saved 40,000 yuan every year. In addition, the pressure drop of the plate and shell heat exchanger reduces the power loss of the circulating hydrogen compressor, which can correspondingly increase the processing capacity of the device under the same circumstances. 4. Conclusion The plate and shell heat exchanger has been used in the device for more than a year, with good results and good economic benefits. With the enlargement of domestic refining and chemical plants and the increasing requirements for efficiency and energy saving of key heat exchange equipment, especially for the feed and reaction product heat exchangers in catalytic reforming and hydrogenation units, due to the large temperature difference between the hot and cold flow inlets (about 400 ℃) , with large flow and high heat load, the application of plate and shell heat exchangers can reduce device energy consumption, save investment and reduce operating costs. Foreign plate and shell heat exchangers have become standard equipment in catalytic reforming, hydrogenation and aromatic hydrocarbon workshops in refineries. The maximum size of a plate and shell heat exchanger produced by Packinox can reach 1400mm Plate and shell heat exchangers have been successfully used in reforming units.