Inspection during the equipment manufacturing process includes inspection of raw materials, inspection between processes and pressure tests. The specific contents are as follows:
(1) Size and geometry of raw materials and equipment parts Inspection;
(2) Chemical composition analysis, mechanical property analysis test, and metallographic structure inspection of raw materials and welds, collectively referred to as destruction tests;
(3) Raw materials and welds For the inspection of internal defects, the inspection method is non-destructive testing, which includes: radiographic testing, ultrasonic testing, magnetic particle testing, penetrant testing, etc.;
(4) Equipment pressure test, including: hydraulic pressure test, medium test , air tightness test, etc.
Pressure test and air tightness test:
The completed heat exchanger should undergo a pressure test or increase the air tightness test on the connection joints of the heat exchanger tube plate, tube side and shell side. Tightness test and pressure test include water pressure test and air pressure test. Heat exchangers are generally subjected to hydraulic pressure testing. However, when liquid cannot be filled due to structural or support reasons or operating conditions do not allow residual test liquid, air pressure testing may be used.
If the medium is extremely toxic, highly hazardous or if trace leakage is not allowed between the tube and shell sides, an air tightness test must be added. The sequence of the heat exchanger pressure test is as follows:
For fixed tube sheet heat exchangers, the shell side pressure test is first performed, and the connection joints between the heat exchange tube and the tube sheet are checked at the same time, and then the tube side pressure test is performed;
U-shaped tube heat exchangers, kettle-type reboilers (U-shaped tube bundles) and stuffed function heat exchangers first use a test pressure ring to perform a shell side pressure test, check the joints at the same time, and then perform a tube side pressure test ;
For floating-head heat exchangers and kettle-type reboilers (floating-head tube bundles), first use test pressure rings and floating-head special tools to test the tube head pressure. Kettle-type reboilers should also be equipped with tube heads. A special shell is used for pressure test, then the tube side pressure test is carried out, and finally the shell side pressure test is carried out;
The pressure test of the overlapping heat exchanger joints can be carried out on a single unit. When the stages of each heat exchanger are connected, Pressure tests on the tube side and shell side should be carried out after overlapping assembly. The foundation for installing the heat exchanger must be sufficient to prevent the heat exchanger from sinking or causing the pipe to transmit excessive deformation to the heat exchanger nozzle. The foundation is generally divided into two types: one is a saddle-shaped foundation made of bricks. The heat exchanger does not have a saddle-shaped support and is placed directly on the saddle-shaped foundation. The heat exchanger and the foundation are not fixed and can expand as needed. Move freely. The other is a concrete foundation, and the heat exchanger is firmly connected to the foundation through saddle supports and anchor bolts.
Before installing the heat exchanger, strict inspection and acceptance of the foundation quality should be carried out. The main items are as follows: foundation surface overview; foundation elevation, plane position, shape and main dimensions, and whether the reserved holes are in compliance with reality. Requirements; whether the position of the anchor bolts is correct, whether the threads are in good condition, whether the nuts and washers are complete; whether the foundation surface on which the pads are placed is flat, etc.
After the foundation acceptance is completed, place pads on the foundation before installing the heat exchanger. The surface of the foundation where the pads are placed must be leveled so that the two can make good contact. The thickness of the pad iron can be adjusted so that the heat exchanger can reach the designed level. After the pad iron is placed, the stability of the heat exchanger on the foundation can be increased, and its weight can be evenly transferred to the foundation through the pad iron. Horn irons can be divided into flat horn irons, inclined horn irons and open horn irons. Among them, inclined shim irons must be used in pairs. There should be pads on both sides of the anchor bolts, and the installation of the pads should not hinder the thermal expansion of the heat exchanger.
After the heat exchanger is in place, a level must be used to level the heat exchanger so that each pipe can be connected to the pipe without stress. After leveling, the inclined pad iron can be welded firmly to the support, but it must not be welded to the flat pad iron or slide plate below. When two or more overlapping heat exchangers are installed, the upper heat exchanger should be installed after the lower heat exchanger is aligned and the anchor bolts are fully fixed. Before installing the pumpable tube bundle heat exchanger, the core should be pulled out for inspection and cleaning. When pumping out the tube bundle, attention should be paid to protecting the sealing surface and baffle plate. When moving and lifting the tube bundle, the tube bundle should be placed on a special support structure to avoid damage to the heat exchange tubes.
Depending on the form of the heat exchanger, sufficient space should be left at both ends of the heat exchanger to meet the requirements for condition (operation) cleaning and maintenance.
Sufficient space should be left at the fixed head cover end of the floating head heat exchanger so that the tube bundle can be withdrawn from the shell. At least one meter of space must be left at the outer head cover end to facilitate the assembly and removal of the outer head cover and the floating head cover.
Sufficient space should be left at both ends of the fixed tubesheet heat exchanger to allow the tubes to be extracted and replaced. Also, when cleaning the inside of the pipe mechanically. Tubes can be scrubbed at both ends. The fixed head cover of the U-shaped tube heat exchanger should leave enough space to allow the tube bundle to be extracted, and enough space should be left at the opposite end to allow the shell to be disassembled.
The heat exchanger must not be operated under conditions exceeding those specified on the nameplate. The temperature and pressure drop of the tube and shell side media should be constantly monitored, and the leakage and scaling of the heat exchange tubes should be analyzed. Shell and tube heat exchangers use tubes to carry out heat exchange, cooling, condensation, heating and evaporation of materials inside and outside the tube. Compared with other equipment, the surface area in contact with other corrosive media is very large, and corrosion and perforation joints occur. The risk of loose leakage is very high, so the anti-corrosion and anti-leakage methods of the heat exchanger need to be considered more than other equipment. When the heat exchanger is heated with steam or cooled with water, the dissolved substances in the water will Most solubilities will increase, while calcium sulfate type substances will see little change. Cooling water is often recycled. Due to the evaporation of water, salts are concentrated, resulting in sedimentation or dirt. In addition, the water contains corrosive dissolved gases and chloride ions, which cause equipment corrosion. Corrosion and scaling occur alternately, intensifying the corrosion of steel. Therefore, cleaning must be performed to improve the performance of the heat exchanger. Since the difficulty of cleaning increases rapidly as the thickness or deposition of the scale layer increases, the cleaning interval should not be too long. It should be done regularly based on the characteristics of the production device, the nature of the heat exchange medium, the corrosion rate and the operating cycle. Perform inspections, repairs and cleaning.
A heat exchanger can be either a separate device, such as a heater, a cooler, a condenser, etc.; or it can be a component of a certain process equipment, such as a heat exchanger in an ammonia synthesis tower.
Due to the limitations of manufacturing technology and scientific level, early heat exchangers could only adopt simple structures, with small heat transfer area, large volume and heavy weight, such as snake-tube heat exchangers. With the development of manufacturing technology, a shell and tube heat exchanger has gradually formed. It not only has a large heat transfer area per unit volume, but also has a good heat transfer effect. It has long been a typical exchanger in industrial production. Heater. Plate heat exchangers appeared in the 1920s and were used in the food industry. Heat exchangers made of plates instead of tubes have compact structures and good heat transfer effects, so they have been developed into various forms. In the early 1930s, Sweden made the first spiral plate heat exchanger. Then the United Kingdom used brazing to create a plate-fin heat exchanger made of copper and its alloy materials, which was used to dissipate heat from aircraft engines. In the late 1930s, Sweden manufactured the first plate and shell heat exchanger, which was used in pulp mills. During this period, in order to solve the heat exchange problem of highly corrosive media, people began to pay attention to heat exchangers made of new materials.
Around the 1960s, due to the rapid development of space technology and cutting-edge science, there was an urgent need for various high-efficiency compact heat exchangers. Coupled with the development of stamping, brazing and sealing technologies, heat exchangers The manufacturing process of the heat exchanger has been further improved, thus promoting the vigorous development and widespread application of compact plate heat exchangers. In addition, since the 1960s, in order to meet the needs of heat exchange and energy saving under high temperature and high pressure conditions, typical shell and tube heat exchangers have also been further developed. In the mid-1970s, in order to enhance heat transfer, a heat pipe heat exchanger was created based on the research and development of heat pipes.
The relative flow directions of fluids in heat exchangers generally include downstream and countercurrent. When flowing downstream, the temperature difference between the two fluids is the largest at the inlet, gradually decreases along the heat transfer surface, and reaches the smallest temperature difference at the outlet. During countercurrent flow, the temperature difference between the two fluids along the heat transfer surface is distributed more evenly. Under the condition that the inlet and outlet temperatures of the cold and hot fluids are constant, when there is no phase change between the two fluids, the average temperature difference between the countercurrent flow is the largest and the downstream flow is the smallest.
Under the condition of completing the same amount of heat transfer, the use of counter flow can increase the average temperature difference and reduce the heat transfer area of ??the heat exchanger; if the heat transfer area remains unchanged, using counter flow can cause heating or cooling. Fluid consumption is reduced.
The design principle of the spiral baffle is very simple: a special plate with a circular cross-section is installed in the "quasi-spiral baffle system". Each baffle occupies a quarter of the cross-section in the shell side of the heat exchanger, and its inclination angle is towards The axis of the heat exchanger maintains an inclination with the axis of the heat exchanger. The peripheries of adjacent baffles are connected and form a continuous spiral with the outer circle. By axially overlapping the baffles, a double helix design can also be obtained if the span of the supporting tubes is to be reduced. The spiral baffle structure can meet a relatively wide range of process conditions. This design has great flexibility and can select the best spiral angle for different operating conditions; overlapping baffles or double spiral baffle structures can be selected depending on the situation. The Swedish company Alares has developed a flat tube heat exchanger, often called a twist tube heat exchanger. Brown Company in Houston, USA, made improvements. The manufacturing process of spiral flat tubes includes two processes: "flattening" and "heat twisting". The improved twist tube heat exchanger is as simple as the traditional shell and tube heat exchanger, but has many exciting advancements. It has achieved the following technical and economic benefits: improved heat transfer, reduced fouling, true counterflow , reduced cost, no vibration, saved space, no baffle components.
Due to the unique structure of the tube, the tube side and shell side are in spiral motion at the same time, which promotes the degree of turbulence. The total heat transfer coefficient of this heat exchanger is 40% higher than that of conventional heat exchangers, while the pressure drop is almost the same. When assembling the heat exchanger, a mixture of spiral flat tubes and plain tubes can also be used. This heat exchanger is manufactured in strict accordance with ASME standards. This heat exchanger can be used wherever shell and tube heat exchangers and traditional devices are used. It can obtain the best values ??obtained by ordinary shell and tube heat exchangers and plate and frame heat transfer equipment. It is estimated to have broad application prospects in the chemical and petrochemical industries. spiral plate heat exchanger
Spiral plate heat exchanger
A heat exchanger in which the heat transfer element is composed of spiral plates.
The spiral plate heat exchanger is a high-efficiency heat exchanger equipment, suitable for steam-steam, steam-liquid, liquid-liquid, and liquid-to-liquid heat transfer. It is suitable for chemical, petroleum, solvent, medicine, food, light industry, textile, metallurgy, steel rolling, coking and other industries. According to the structural form, it can be divided into non-detachable (type I) spiral plate type and detachable (type II, type III) spiral plate heat exchanger
Structure and performance of spiral plate heat exchanger
1. This equipment is rolled from two sheets to form two uniform spiral channels. The two heat transfer media can flow in full countercurrent, which greatly enhances the heat exchange effect. Even if the two media have a small temperature difference, Can achieve ideal heat exchange effect.
2. The nozzle on the shell adopts a tangential structure, so the local resistance is small. Since the curvature of the spiral channel is uniform, the liquid flows in the equipment without major deflection, and the total resistance is small, so it can Increase the design flow rate to achieve higher heat transfer capacity.
3. The end face of the spiral channel of the I-type non-detachable spiral plate heat exchanger is welded and sealed, so it has high sealing performance.
4. The structural principle of the Type II detachable spiral plate heat exchanger is basically the same as that of the non-detachable heat exchanger, but one of the channels can be disassembled for cleaning, which is especially suitable for heat exchangers with viscous and precipitated liquids. exchange.
5. The structural principle of the Type III detachable spiral plate heat exchanger is basically the same as that of the non-detachable heat exchanger, but its two channels can be disassembled and cleaned, so it has a wide range of applications.
6. When a single device cannot meet the usage requirements, multiple devices can be used in combination, but the combination must comply with the following regulations: parallel combination, series combination, and the spacing between devices and channels is the same. Mixed combination: One channel in parallel and one channel in series. The variable sonic velocity booster heat exchanger is a two-phase flow jet heat exchanger and is widely used in various fields of steam-water heat exchange. Independently developed by China Luoyang Blue Ocean Industrial Co., Ltd. It uses steam as power, compresses and mixes steam and water to instantly increase the water temperature, and uses pressure shock wave technology to achieve the effect of supercharging without external force. The significant energy saving and supercharging features greatly reduce the user cost and can replace traditional heat exchange. device.
The variable sonic velocity booster heat exchanger is a type of mixed steam-water heat exchange equipment. The steam is introduced into the mixing chamber in a jet state through adiabatic expansion technology, and the heated water that has been membrane treated is impacted by the steam. It is uniformly mixed under the action of force to form a compressed mixture of steam and water with a certain calculated volume ratio. When its instantaneous compression density reaches a certain value, a two-phase fluid field phenomenon is formed. Under the intensification of the field state, the sound velocity value of the mixture undergoes a transitional transition that breaks through the critical sound barrier, and a large number of pressure shock waves erupt at the same time. The unidirectional conduction characteristics of the pressure shock wave cause hot water that instantly reaches the design temperature to appear in the constant cross-section pipe. The pressure increases without backflow. The variable sonic velocity pressurization heat exchange technology uses the orderly intensification of the two-phase fluid field to force the completion of the dual effects of "instantaneous heat exchange and no external force pressurization".