Introduction to heat exchangers
Refining chemical projects several common heat exchanger introduction
Table of Content
隐藏
1. All-welded plate and shell heat exchanger
Refining PX combined unit, reforming, disproportionation, isomerization unit feed heat exchanger heat load is quite large, if the use of vertical shell and tube heat exchanger, so there is a single volume is too large, heavy, the current technical means can not be achieved; if made into multiple units, there is a large footprint and uneven distribution of logistics between each unit and other issues. The AXENS process package patent requires the use of an all-welded plate and shell heat exchanger, whose equipment parameters are based on the heat transfer calculations of the Pachino plate exchange.
At present, the vast majority of domestic PX combined units use all-welded plate (shell) exchange, and Alfa Laval-Pachino’s all-welded plate exchange and the absolute advantage, in recent years, with the continuous improvement of Lanke’s all-welded plate exchange technology, the occupancy rate is also on the rise.
1.1 All-welded plate and shell heat exchanger structure
All-welded plate and shell heat exchanger is mainly composed of pressure vessel shell, heat transfer plate bundle, fluid distributor, logistics collection receiver, expansion joint, oil spray bar and other parts. The role of the pressure vessel shell is to withstand the strength (or withstand the operating pressure). The heat transfer plate bundle is the core component of the welded plate heat exchanger. The plate bundle consists of many stainless steel plates welded together, each obtained through a patented technology – underwater explosion forming, and the runners of the plates are designed to be arranged in a corrugated shape. Heat is transferred by counterflow. The tube box and the surface of the plate bundle are also welded together to form a closed elastic combination.
Ø The overall structure is shown in Figure.
The circulating hydrogen enters the cavity inside the shell and plate bundle from the lower flange of the plate changer (all filled with hydrogen), goes upward into the narrow venturi members on both sides of the lower end of the plate changer (similar to the shape of a trough and weir) and then goes upward through the distribution grille net and then around the horizontally arranged oil spray bar, mixes fully with the oil coming out of the spray holes of the oil spray bar and other parts and then enters the open flow channels of the outer plates on both sides of the lower end of the plate bundle and follows the texture of the plate corrugations Upward flow
Cold side fluid from the lower side wall of the heat exchanger is inserted vertically into the plate shell, sprayed by the horizontal arrangement of the spray bar, fully mixed with the circulating hydrogen from the bottom of the heat exchanger into the flow channel of the plate bundle, with the hot side of the flow channel at the interval of the full heat exchange medium, downstream, still from the openings on both sides of the plate end out, into the cold flow port collection tank of the fluid distributor on both sides of the upper end of the plate bundle, and then Through the collection tank welded on the no receiver, expansion joint, through the shell of the receiver out of the external plate into the process pipeline of the large elbow.
Note that the upper end of the plate bundle has two layers of fluid collection tank, the outermost volume of the collection tank for cold flow of oil and gas mixture material, the inner layer of small volume of hot flow.
And the opposite of the hot side of the fluid from the upper part of the shell into the expansion joint, after the receiver into the fluid distributor of the hot flow port dispersion, into half of the hot side of the fluid channel, convection downward, into the heat exchanger shell in the lower fluid distributor in the hot side of the fluid outlet end of the collection, after the receiver, expansion joint out of the lower part of the shell.
1.3 All-welded plate for the main materials.
Plate bundle: stainless steel 321 or 304 or 316; plate thickness: 0.8-1.5 mm.
Bellows: Inconel 625 for the cold flow side; Incoloy 800 or 825 for the hot flow side.
Pressure-bearing shell: Cr-Mo steel 1.25Cr-0.5Mo,,2.25Cr-1Mo, or stainless steel, carbon steel
1.4 All-welded plate exchange advantages: (compared to shell and tube heat exchanger)
Has the following advantages.
① High heat transfer efficiency. Because the heat transfer plate bundle is composed of hundreds of corrugated plate thickness of 0.8mm, can provide high turbulence of fluid, high heat transfer efficiency, both sides of the fluid heat transfer film coefficient of about 2 to 3 times the shell and tube heat exchanger; fluid distribution is uniform, basically no dead space, there is no leakage; pure countercurrent heat transfer, so that the hot end of the approach temperature to reach a minimum △ t < 51 ℃, which can not be achieved by shell and tube heat exchanger.
② Underwater blast forming of each plate, not using the usual metal extrusion molding. Blast forming not only has a smooth surface (which can significantly reduce clogging) and avoids the cold work-hardening phenomenon of mechanical extrusion forming, but also fundamentally eliminates the stress during forming, substantially reducing stress corrosion.
③ The sawtooth and herringbone grooves of the corrugated plate form tens of thousands of plate-to-plate contact points, making the plate bundle not vibrate at any flow rate.
④ Uniform fluid distribution and continuous mixing of two-phase (gas and liquid) fluids form a uniform temperature distribution over the entire plate bundle, reducing the thermal stress caused by inter-phase delamination.
⑤ The corrugated plate is subjected to a lower mechanical pressure. Because the plate bundle is suspended vertically from a unique header box support system, it allows each plate to carry almost only its own weight.
⑥ The pressurized shell is subjected to the same pressure as the reaction medium pressure, and the circulating hydrogen in the reaction medium is introduced into the shell with the purpose of reducing the pressure difference between the inside and outside of the plate bundle (△P is almost equal to 0), so that it is very safe to operate even at high temperature and pressure. The shell is equipped with huge flanges and tube plates to eliminate the main external leakage points and to avoid internal leakage due to the failure of the tube plate connection.
2. High flux tube heat exchanger
The technology is patented by UOP, which is characterized by superb boiling evaporation, boiling when the temperature difference between inside and outside the tube is equal to 2°F. Its total heat transfer efficiency is 3~4 times that of common light tubes. In addition, even now using high flux tube heat exchanger, which has several bit number of heat exchanger, its diameter has reached 2700mm, such as the use of conventional U-tube heat exchanger design, the shell diameter will be very large, a single manufacturing process, maintenance and test pressure will be very difficult, after a comprehensive comparison of the final determination of the use of high heat flux tube heat exchanger.
High flux heat exchanger tube is the use of powder alloy using metallurgical methods in the ordinary heat exchanger light tube (boiling side) inside and outside (or inside and outside at the same time) surface sintering (spraying) a thin layer of metal, with a specific structure of the porous surface of the high-efficiency heat exchanger tube, the surface porous layer of pits and pores are connected to each other, can significantly strengthen the boiling heat transfer, heat transfer effect can theoretically increase by more than 20 times. The thickness of the coating layer is 5~15mils, equivalent to 0.127~0.381mm. for vertical heat exchangers are also processed in the outer wall of the tube to facilitate the flow of liquid grooves (when the outer wall is not sprayed). The coating layer is so firmly bonded to the substrate that it can withstand the stresses of the U-bend. In contrast to other shell and tube heat exchangers, high flux tube heat exchangers only use sintered tubes instead of the traditional bare tubes, but nothing else is different, so high flux heat exchangers can be used to make all kinds of heat exchangers just like ordinary heat exchangers.
High heat flux tube is the highest heat transfer coefficient tube heat transfer element so far, especially for alkanes, olefins, aromatics, alcohols, water, Freon, liquid nitrogen and other media. At present, only the patented technology developed by the U.S. UOP company is being applied internationally, and the domestic East China University of Science and Technology has mastered the industrialization technology of sintered high flux heat transfer tube and its heat exchanger. (The achievement passed the expert appraisal organized by the Science and Technology Development Department and Major Equipment Localization Office of Sinopec Corporation (Sinopec Appraisal No. 222 [2002], No. 92 [2007], [ 2008] No. 213): “Boiling heat transfer coefficient is increased by 5~15 times, which is better than the performance of similar foreign products. Fill the gaps in the country, the technology has reached the international advanced level, it is recommended to promote the application in the petrochemical industry.”) Has been put into the market by joint Wuxi Chemical Manufacturing, other companies such as Beijing Guangsha and other manufacturers, because of technical confidentiality reasons, its sintering tube process, technology can not be known, the application performance has not seen a positive confirmation, can not verify the effect. Overall: domestic sintering technology and coating surface molding and UOP intuitive comparison or some gap, the long-term use of the effect is still to be verified.
The working characteristics of the high flux tube are shown in the figure below, and the upper end shows the surface of the light tube. On the surface of the light tube, bubbles are usually generated in the small dents and scratches on the surface. The lower end shows the high flux heat exchanger tube surface, where the good thermal conductivity of the porous surface and substrate, the large microporous surface area and the numerous contact points of the porous layer ensure the formation of a large number of stable bubble nuclei. Compared with ordinary optical tubes, sintered surface porous tubes have the following advantages.
(1) It can significantly enhance boiling heat supply and reduce the required heat transfer area by about half, which is promising for application in chemical and petrochemical plants such as large ethylene and large aromatics.
(3) The critical heat load is more than 50% higher than that of ordinary tubes.
(4) It has good scale inhibition performance.
High flux tube material
Base tube material: copper, copper-nickel alloy, carbon steel, heat-resistant steel
Porous layer: inner surface, outer surface
Alloy powder: copper-based, copper-nickel alloy-based, iron-based alloy
Translated with www.DeepL.com/Translator (free version)
Surface porous tube heat transfer enhancement mechanism.
Main advantages of surface porous tube.
3. Double tube and plate shell and tube heat exchanger
Double tube plate shell and tube heat exchanger is a tube plate at the end of the heat exchanger tube bundle, called the outer tube plate (tube process tube plate), which also serves as the equipment flange, and the heat exchanger tube and tube box flange to connect. There is also a tube plate at a location closer to the end of the heat exchanger tube, called the inner tube plate (i.e. shell process tube plate), which is connected with the heat exchanger tube and shell process. There is a certain distance between the outer tube plate and the inner tube plate, this part of the space can be an open structure, but also can be closed with a short section and the outside world, forming an isolation cavity, called the liquid collection tube. The high point of the liquid collecting cylinder is equipped with exhaust and the low point is equipped with liquid discharge. Among them: the inner tube plate can only use strength expansion (mechanical or hydraulic expansion), the outer tube plate is usually used strength welding + paste expansion (or strength welding + strength expansion).
Structural features.
3.1 Double tube plate to solve the main problem
A, conventional heat exchangers exist at the tube plate head weld failure leads to media mixing (accounting for most), tube leakage leads to mixing (accounting for a minority) of the two cases. The double tube plate is only a structural solution to the tube plate at the head weld failure to ensure that the tube / shell process media completely separated from each other can not be colluded. But the internal heat exchanger tube failure mixing problem is not solved.
B. The failure of tube process tube plate joint and shell process tube plate joint will only leak out and not mix material.
C, can be quickly judged by visual inspection or leak detection drainage tube whether there is leakage
3.2 The choice of double tube plate structure
★ single plate heat exchanger most of the failures are in the tube and tube plate connection head weld part of the leak, resulting in the tube / shell media mixed with each other, in order to avoid string material here, there is a double tube plate type.
★ tube / shell process when the medium does not contact no corrosion, leaks when mixed materials, will cause serious corrosion of equipment.
★One side is highly toxic media leakage to the other side, highly toxic substances will spread to a large area, may cause personal injury, environmental pollution and other situations.
★Mixing or contacting fluids on both sides can cause combustion or explosion.
★After mixing the fluids on both sides, chemical reaction is generated, forming sticky dendrites or polymer and other dirt.
★Chemical reaction with catalyst or change the performance of catalyst after mixing and changing fluids on both sides.
★After contacting fluids on both sides, it leads to chemical reduction reaction, which restricts or changes a chemical reaction.
★After contacting fluids on both sides, it may contaminate the product and reduce the product quality.
3.3 Status of double-tube plate heat exchanger
A. Conventional single-tube plate heat exchanger failure is usually 4 parts.
① Leakage at the weld of the heat exchanger tube joint on the tube plate (mixed material)
② Internal tube leakage (mixing).
③ shell process and tube plate flange leakage outside (shell process media)
④ External leakage of pipe box and pipe plate flange (pipe process medium)
⑤ Leakage of other orifice flanges on the equipment.
In the above ① ② leakage will lead to the mixing of tube process and shell process media, where the failure rate of ① is much greater than ② in actual use. While ③ and ④ usually outside the external leakage, will not mix materials.
The double tube plate heat exchanger only solves the previous problem of ① tube plate at the mouth weld failure, but does not solve the problem of ② internal tube leakage itself (corrosion, vibration fracture, etc.), theoretically there is still a leak after the tube shell / process mixing potential problems. At the same time derived from the inner tube plate tube joint strength expansion may fail external leakage, the problem of
If the welding structure without core extraction can also solve the shell process media leakage problem of ③. But no matter what kind of structure can not solve the possibility of ④ tube process leakage.
B, double tube plate heat exchanger in polysilicon, silicone industry applications more, the use of aromatics device performance is relatively small, in the reboiler application is even less, in the steam generator (vapor-liquid two-phase, multi-issue vibration) on the application of basic no.
C, in the design and manufacture of a certain degree of difficulty and skill, especially in the double tube plate and heat exchanger tube connection, tube bundle assembly sequence, testing requirements must be strictly guarded in order to design and manufacture a double tube plate heat exchanger can meet the requirements of use.
3.4 The use of double-tube plate heat exchanger may have problems
A, there are still internal tube leakage, tube and shell process media mixing. Usually minor leaks are difficult to detect, with the process may also enter the downstream adsorbent, the production department should pay attention to.
B, the inner tube plate tube joints can only be used strength expansion this only method, manufacturing process requirements are higher than other types of heat exchangers, especially in the manufacturing process of the subsequent welding of the liquid collector tube and tube plate, the operation of the tube plate local temperature is too high will cause thermal deformation of the tube plate, affecting the tube expansion rate, easy to cause leakage, and because of many factors such as processing and manufacturing tolerances cumulative unavoidable deviations lead to the actual Each tube expansion rate are different, so with the use of years and changes in working conditions, inevitably failure leakage, and expansion of good or bad and manufacturing workers’ skill level and responsibility has a lot to do with the process characteristics can be thoroughly eaten and many other factors determine the quality of expansion of the inner tube plate there are many uncertainties, may fail leakage, or even a large area of systematic failure problems.
C, due to the larger diameter of the equipment unit, the initial design of the tube plate thickness should be in between 80-150mm, relatively thin, the manufacturing process of machining, welding thermal effects and operation of the opening and closing, sudden changes in temperature and other operations may cause irreversible thermal deformation of the tube plate, this deformation is difficult to control and deal with.
D, the actual manufacturing of the expansion of a low rate of forming, the need to make up the expansion several times to do, the strength of the inner tube plate expansion in the actual operation of the site leak detection basically can not be achieved, it is not clear which tube; even if it is clear which tube leakage, do not know the original expansion of the original data (manufacturers do not provide the technical core), can not assess the expansion rate, so it can not make up the expansion, only to let it leak.
E, the isolation cavity of the all-welded liquid collection cylinder and double tube plate between the tube bundle thermal stress matching problem, in serious cases, may cause a large number of tube joints failure leak risk.
F, the evaporator special working conditions determine the existence of vapor-liquid two-phase easily caused by vibration caused by the risk of tube bundle wear fracture.
H, the tube bundle single large, heavy, maintenance of the extraction and installation of the core process a little careless, card, hit, forced pulling and pushing may cause tube bundle deformation, may have an impact on the strength of the inner tube plate expansion joint, there is caused irreversible fatal damage.
G, such as the use of tube bundle and shell welding structure, the future replacement of the tube bundle need to cut the barrel, replace the new tube bundle after re-welding, maintenance is time-consuming, and also need to carry out pressure vessel supervision and inspection to pass the inspection.
H, the tube plate may produce damage caused by fouling, various corrosion, erosion and cavitation.
3.5 The use of double tube plate type heat exchanger recommended matters
A. Regardless of whether or not a core extractable structure is used, core extraction should be avoided as much as possible. If the core must be drawn, it must be done carefully.
B, the design can be considered on the basis of standard specifications to enhance the design level of the plate a grade, the use of reasonable special tooling in the manufacture and operation of temperature control and other reasonable operating methods to reduce the probability of deformation of large diameter tube plate.
C, such as the use of isolation cavity (liquid collection cylinder) all-welded structure, if necessary, increase the expansion joint to compensate for the matching stress problem, or the use of incomplete closure or open structure.
D, in the RFQ stage to the design institute to make recommendations: the existence of vapor-liquid two-phase conditions of the heat exchanger whether it is necessary to strengthen the design, clear requirements: on the basis of conventional design to increase the number of support plates, thickness, improve the accuracy of tube hole processing, improve the level of tube manufacturing accuracy, reduce the cumulative deviation and other methods to minimize the potential hidden risks of expansion joint failure.
E, the heat exchanger for finite element analysis (especially the tube plate, flange and cone shell) and vibration analysis, analysis of the flow field on the temperature, the impact of forces, etc..
F. Strictly control the metallurgical components of raw materials, improve the grade of welding materials, and carefully audit subcontractors.
G. The key points of the manufacturing process must be strictly enforced to stop the witnessing system and be qualified before moving to the next step of the process. Resolutely put an end to non-standard construction.
H, evaporator working conditions necessary to use strength expansion + strength welding (when working conditions are harsh).
I, heat exchanger tube head weld RT detection when necessary.
J. After the installation of the equipment, all pressure test to ensure that no major problems occur when the material is put into operation.
K. Consider using coating treatment for pipe plate if necessary to retard erosion.
L. If necessary, select more than 2 meters of large diameter pipe plate, in use for more than 5 years of the user 2-3, go to research, to grasp the actual in use first-hand information, in order to facilitate decision-making.
3.6 Double tube plate structure heat exchanger picture
4. spiral folded plate heat exchanger
4.1 The schematic sketch of the structure is as follows.
In shell and tube heat exchangers, the shell process is usually a weak link. Usually the common bow-shaped folding plate can cause a zigzag flow system (zigzag flow path), which can lead to large dead space and relatively high return mixing. These dead spots in turn can cause increased fouling in the shell process, which is detrimental to heat transfer efficiency. The re-mixing can also distort and reduce the average temperature difference. As a consequence, the bowed plate reduces the net heat transfer compared to the piston flow. Superior bowed plate shell and tube heat exchanger is difficult to meet the requirements of high thermal efficiency, so often replaced by other types of heat exchanger (such as compact plate heat exchanger). The improvement of the geometry of the common folded plate is the first step in the development of the shell process. Although the introduction of seals and additional measures such as deflecting the folding plate and other measures to improve the performance of the heat exchanger, but the main drawbacks of the ordinary folding plate design still exists.
For this reason, the United States has proposed a new scheme that suggests the use of a spiral folding plate. This design has been advanced for the fluid dynamics research and heat transfer test results confirmed, this design has been patented. This structure overcomes the main drawbacks of the common folding plate. The design principle of the spiral folding plate is simple: a special plate of circular cross-section is installed in the “proposed spiral folding system”, each folding plate accounts for one-fourth of the cross-section of the heat exchanger shell process, its inclination toward the axis of the heat exchanger, that is, to maintain an inclination with the heat exchanger axis. The perimeter of adjacent folding plates meet and become a continuous spiral with the outer circle. The axial overlap of the folding plates can also be obtained in a double helix design if the span of the supporting tubes is to be reduced. The spiral folding plate structure can meet relatively wide process conditions. This design has a lot of flexibility to choose the best helix angle for different operating conditions; either overlapping or double helix folding plate structure can be chosen for each case.
The plane of the traditional heat exchanger folding plate with the heat exchanger tube is perpendicular to the axial direction, the shell process media flow between the folding plate and the heat exchanger tube has several parts such as vertical and parallel. The spiral plate heat exchanger folding plate is an approximate spiral channel, shell process media from the shell process inlet into the spiral channel along the oblique forward, the traditional folding method into a longitudinal spiral folding method. Changed the most basic flow state of the traditional heat exchanger. It has the following characteristics.
(1) Shell process pressure is reduced. Media in the shell continuous smooth spiral flow, to avoid the serious pressure loss generated by the transverse fold. In the same flow conditions can make the pressure drop reduced by about 45%
(2) High shell flow rate. Compared with the bow-shaped folding plate, in the same shell process pressure drop, can make the shell process medium flow rate increased significantly, improving the flow state.
(3) Heat transfer reinforcement capacity is large (high heat transfer coefficient). As the shell process medium spiral forward, the speed gradient in the radial section, the formation of radial turbulence, will make the heat exchanger tube surface stagnant bottom layer thin, is conducive to improve the shell process heat transfer coefficient. In addition, the structure of no flow dead zone makes the utilization rate of heat transfer surface higher, and thus will obtain stronger heat transfer capacity. According to foreign literature, the heat transfer coefficient of the shell process under unit pressure drop is 1.8~2 times of that of the bow-shaped folding plate, and the total heat transfer coefficient under most working conditions can be increased by 20%~30%, especially when the spiral inclination angle is 25o~45o, the heat transfer effect is the best. Therefore, in the case of the same heat load can reduce the size and mass of the heat exchanger.
(4) No overhaul cycle is long, applicable to a wide range of media. As the spiral channel in the high-speed rotation of the media flow is conducive to flush away particles and precipitates in the shell process, eliminating the serious scaling of the delta dead zone, which is extremely beneficial to the improvement of heat transfer efficiency. Smooth flow channel does not exist in the dead zone, coupled with the use of higher flow rates, even if the media is very dirty, high viscosity, it is not easy to deposit the formation of surface fouling, will make the heat exchanger in a long-term low scale, efficient operation of the state. Heat exchanger in the entire life cycle of the total heat transfer coefficient decline is very small, in the late use of the device still has good operating performance, can extend the maintenance cycle.
(5) Fluid-induced vibration damage of the tube bundle. Spiral folding plate on the heat exchanger tube restraint is stronger than bow folding plate, spiral flow on the tube bundle impact is also different from bow folding, (bow folding plate notch area twice the normal folding plate spacing of the support length is the main cause of tube vibration. Spiral plate heat exchanger by choosing the right angle, to get a uniform avoidance of tube vibration frequency support length, to solve the problem of vibration damage to the tube bundle) the result will reduce the tube bundle vibration, in mechanical terms can extend the operating life of the equipment. Especially suitable for medium flow fluctuations or vapor-liquid two-phase working conditions
(6) Enhanced shell-side condensing heat transfer. The spiral folding plate can play a role in diverting the condensate on the shell side, reducing the coverage of the condensate on the lower discharge tube, thus improving the condensation heat exchange effect.
(7) Easy tube bundle modification. Spiral folding plate heat exchanger and ordinary heat exchanger is only the difference in the structure of the folding plate. The appearance of the tube bundle shape, tube bundle and shell with the same size, in the maintenance and renovation of the tube bundle can be easily replaced with a spiral folding plate core bow-shaped folding plate type. In general, replacing the tube bundle can increase the heat transfer capacity by more than 30% or reduce the pressure drop by about 30%. The effect is even more significant when the spiral folded plate is used together with a tube type such as a scaled tube.
Disadvantages: spiral folding plate and fixed distance tube processing more difficult than the bow folding plate heat exchanger, the need for special processing tire, therefore, the price is slightly higher than the bow folding plate heat exchanger.
4.3 The development of spiral folded plate heat exchanger
Spiral folded plate heat exchanger technology is LUMMUS (LUMMUS) patented technology, the technology has a history of more than 30 years, which is characterized by each circle of its spiral channel consists of four discontinuous flat. Because of its good effect, it has been adopted by major companies in the world such as Shell, MEF, Total, Exxon, etc. At present, there are more than 2000 heat exchangers in use. Since the first application of spiral folded plate heat exchanger in China by PetroChina Fushun Petrochemical Company in 1997, spiral folded plate heat exchanger has been rapidly promoted to chemical refineries, and hundreds of spiral folded plate heat exchangers have been applied to dozens of refineries and dozens of units.
Lumos is mainly engaged in the upgrading of the technology and the research of the process calculation method, and the manufacturing of the equipment is all undertaken by its approved patent manufacturers, and there are more than 20 patent manufacturers worldwide. At present, there are many manufacturers in China who are developing the technology, but because of the large gap between the process calculation and foreign countries, there are often many problems in the promotion. Among the varieties developed in China, the continuous channel spiral baffle has a great advantage in structure. This has proven to be an alternative product with considerable advantages over traditional vertical bow plate folded flow and rod folded flow heat exchangers.
Note: The difference between spiral folded plate heat exchanger and spiral plate heat exchanger and spiral tube heat exchanger.
5. Winding tube heat exchanger
5.2 Advantages.
Ø compact structure unit volume with a large heat transfer area; heat exchanger easy to achieve large-scale.
Ø small temperature difference between the hot and cold ends, high heat transfer efficiency, high heat transfer coefficient.
Ø self-compensating thermal expansion effect .
ØVibration resistance, good performance of high temperature difference resistance.
ØHigh sealing reliability and high medium pressure.
ØThe medium is smooth and there is no heat transfer dead zone.
ØSimultaneous processing of multiple fluid heat transfer, multiple media involved in heat transfer at the same time, and small flow resistance, no pressure difference between different media requirements。
6 threaded ring locking seal structure high-pressure heat exchanger
Threaded ring locking seal structure high-pressure heat exchanger was first developed by the U.S. Chevron Corporation and Japan’s Chiyoda Company, the first domestic manufacturers to introduce and manufacture this heat exchanger is the Lanzhou Petrochemical Machinery Plant, now more mature Lanzhou Petrochemical Machinery Plant and Fushun Petrochemical Machinery Plant. Threaded locking ring heat exchanger is the current world advanced level of heat exchange equipment, large domestic and foreign oil refining enterprises in hydrocracking and heavy oil hydrodesulfurization units are generally used in this form of heat exchanger. China now has a new hydrogenation unit basically use this heat exchanger. Its basic structure is shown in the figure.
1, shell gasket; 2, tube plate; 3, gasket; 4, positioning bolts; 5, split ring; 6, tube box main gasket; 7, fixed ring; 8, pressure ring; 9, inner ring bolts; 10, tube box cover; 11, sealing disk; 12, threaded locking ring; 13, outer ring bolts; 14, inner sleeve; 15, internal bolts; 16, inner ring pressure ring; 17 split box; 18, outer ring pressure ring; 19, outer ring Top pin; 20 Inner ring top pin
The tube bundle of this heat exchanger mostly adopts U-tube type, and its unique structure lies in the tube box part. It is used in the case where the tube and shell process are both high pressure. The threaded locking ring heat exchanger has a compact structure, few leakage points, reliable sealing, small footprint, and material savings. Once a leak occurs during operation, there is no need to stop, tighten the inner and outer ring top tightening bolts to achieve sealing requirements.
In operation, if there is a series of leakage between the tube and shell process, through the inner ring bolt 9 exposed on the end surface and then tighten the force through the piece 8 → piece 11 → piece 14 → piece 17 → piece 2 to the shell process gasket (piece 1) and will be tightened to eliminate leakage. In addition, this structure because the tube box and shell is forged or welded into one, both to eliminate the heat exchanger like a large flange type heat exchanger open receiver directly
welded connection with the pipeline, reducing the leakage of these parts.
2）Easy disassembly and installation
Disassembly and installation can be completed in a short time. Because its bolts are small, it is easy to operate.
At the same time, when disassembling and assembling the tube bundle, there is no need to move the shell, which can save a lot of labor and time. Moreover, when disassembling and assembling, a specially designed disassembly frame is used, so that disassembly and assembly operations can be carried out smoothly. In general, from disassembly, inspection to reassembly, this heat exchanger requires more than one-third less time than the flange type.
6.2 Threaded locking ring type heat exchanger classification
Ø threaded locking ring heat exchanger according to the design pressure of the tube and shell process can be divided into tube process, shell process high-pressure type heat exchanger (high – high pressure type heat exchanger) and tube process high-pressure, shell process low-pressure type heat exchanger (high – low pressure type heat exchanger).
Ø threaded locking ring heat exchanger according to the shell process media flow direction can be divided into single-shell process heat exchanger and double-shell process heat exchanger.
6.3 Characteristics of each type of threaded locking ring heat exchanger
A.H-H type (tube process, shell process high-pressure type) features.
(1) tube box and shell group welding as one.
(2) the tube plate is designed for differential pressure, so the thickness of the tube plate is small.
3) There are two turns of compression bolts
4）There are more internal parts on the side of the tube box
5）The tube bundle can be withdrawn separately
B.H-L type (tube process high pressure, shell process low pressure type) features.
1）The tube box and the shell are flange connected and can be separated.
(2) tube plate and tube box group welding as one.
3) the tube process seal is separate from the shell process seal.
4) there is a ring of compression bolts.
5）The tube bundle and the tube box are connected as one.
C. Single shell process type features.
1) shell process side receiver a front and a back, up and down distribution, that is, the inlet and outlet are not in the same vertical line.
2) shell process medium, from one end of the shell to its other end.
3) No layered partition on the tube bundle.
4) lower heat transfer efficiency.
D. Double shell process type features.
1) shell process side pipes are distributed on the same cross-section, i.e., the import and export are on the same vertical line.
2) shell process medium is separated from the center of the shell, from the shell process inlet to the end of the shell, and then from the end of the shell to the shell process outlet.
3) A layered partition on the tube bundle.
4）Higher heat exchange efficiency
6.4 threaded locking ring heat exchanger sealing features
The main body of the threaded locking ring heat exchanger seal is mainly two major parts.
First, the tube side of the seal, it is through the threaded locking ring on the outer ring of bolts pressed on the sealing plate and gasket to complete the;.
The second is the shell side of the seal, it is the inner ring pressure bolt, through the ring, tube box sleeve pressed on the tube bundle tube plate and gasket to complete the seal, and can be threaded locking ring on the inner ring pressure bolt, indirect force, without disassembling the inner parts of the tube box, to solve the problem of internal sealing leaks.
7. Spiral flat tube heat exchanger
The manufacturing process of spiral flat tube includes “flattening” and “heat twisting” two processes. The manufacturing process is to first flatten the round tube, and then twist it into a spiral shape. The tube is arranged on the same side to form a tube bundle, the tube bundle without support, only rely on the outer edge of the spiral flat tube outside the contact point of the spiral line to support each other. In the tube process, the spiral flow of fluid increases the degree of turbulence, thinning the thickness of the inner layer of stagnant flow as the main heat transfer resistance, so that the heat transfer in the tube can be enhanced. In the shell process, because the spiral flat tube between the flow channel is also spiral, the fluid in its movement by the centrifugal force and periodically change speed and direction, thus enhancing the longitudinal mixing of fluid. In addition, when the fluid passes through the contact point of the spiral line of adjacent tubes to form a tail flow away from the wall, enhancing the degree of turbulence of the fluid itself, the destruction of the fluid in the wall of the heat transfer boundary layer, thus making the shell process of heat transfer can also be enhanced. Tube, tube outside the heat transfer at the same time to strengthen the results, so that its heat transfer effect than the ordinary shell and tube heat exchanger has increased substantially, especially for fluid viscosity, one or both sides are stagnant flow of heat transfer process, the effect is particularly prominent.
The improved twist tube heat exchanger is as simple as the traditional shell and tube heat exchanger and has the following advantages: improved heat transfer, small pressure drop, high heat transfer efficiency, reduced fouling, no fouling, true counterflow, no folding elements, reduced cost, no vibration, space saving. Overcome the shortcomings of the traditional heat exchanger, is currently the most ideal heat exchange equipment to extract low temperature waste heat, the heat exchanger applied to flush slag water effect is obvious, is the most ideal heat exchanger.
When assembling the heat exchanger can also be used spiral flat tube and light tube mixed way. The heat exchanger should be manufactured in strict accordance with ASME standards. Where shell and tube heat exchanger and traditional devices can be replaced by this heat exchanger, it can obtain the best value obtained by ordinary shell and tube heat exchanger and plate and frame heat transfer equipment, is expected to have a broad application prospects in the petrochemical industry.
8. Spiral plate heat exchanger
Spiral plate heat exchanger is a kind of high-efficiency heat exchanger equipment whose heat transfer element is composed of spiral-shaped plates. It is suitable for steam-vapor, steam-liquid, liquid-liquid, and liquid-to-liquid heat transfer, and is used in a variety of industries such as petrochemicals. According to the structure form can be divided into non-detachable (Type I) spiral plate type and detachable (Type II, Type III) spiral plate type heat exchanger.
① The equipment is rolled from two plates, forming two uniform spiral channels, two heat transfer media can flow in full countercurrent, greatly enhancing the heat exchange effect, even if two small temperature difference media, can also achieve the ideal heat exchange effect.
② The receiver on the shell adopts tangential structure, with small local resistance. Since the curvature of the spiral channel is uniform, the liquid flows in the equipment without a large turn, and the total resistance is small, thus the design flow rate can be increased to make it have a high heat transfer capacity.
③ Type I non-detachable spiral plate heat exchanger adopts welded seal on the end face of the spiral channel, and thus has high sealing performance.
④ Type II detachable spiral plate heat exchanger has the same structure principle as the non-detachable heat exchanger, but one of the channels can be disassembled for cleaning, which is especially suitable for heat exchange of viscous and sedimented liquids.
⑤ Type III detachable spiral plate heat exchanger has the same structure principle as the non-detachable heat exchanger, but its two channels can be detached for cleaning, which is applicable to a wider range.
⑥ Single equipment can not meet the requirements of use, you can use more than one combination, but the combination must comply with the following provisions: parallel combination, series combination, equipment and channel spacing is the same. Mixed combination: a channel in parallel, a channel in series.
9. Air cooler
In the petrochemical production, the most used cooler is the air cooler. Among them, the conventional one is mostly a silk plug type high-pressure air cooler. The air cooler is a device that uses ambient air as the cooling medium and sweeps across the finned tube to cool or condense the high-temperature process fluid inside the tube, referred to as “air cooler”, also known as “air-cooled heat exchanger”. Air cooler is also called fin fan, which is often used to replace the water-cooled shell-and-tube heat exchanger cooling medium.
Air coolers are generally composed of tube bundles, louvers, axial fans for cooling, and frame components.
