Analysis of four types of heat exchangers (partition-wall hybrid regenerative ceramics)

A heat exchanger is a device that transfers part of the heat of a hot fluid to a cold fluid, also known as a heat exchanger. Heat Exchangers play an important role in chemical, petroleum, power, food and many other industrial productions. In chemical production, heat exchangers can be used as heaters, coolers, condensers, evaporators and reboilers, etc., and are widely used. .

Partition

Jacketed Heat Exchanger:

This heat exchanger is made by installing a jacket on the outer wall of the container, and has a simple structure; however, its heating surface is limited by the container wall, and the heat transfer coefficient is not high. In order to improve the heat transfer coefficient and make the liquid in the kettle evenly heated, a stirrer can be installed in the kettle. When cooling water or a heating agent without phase change is introduced into the jacket, a spiral baffle or other measures to increase turbulence can also be set in the jacket to improve the heat supply coefficient on one side of the jacket. In order to supplement the lack of heat transfer surface, coils can also be installed inside the kettle. Jacketed heat exchangers are widely used for heating and cooling of reaction processes.

Immersion coil heat exchanger:

This heat exchanger is a metal tube that is bent into various shapes suitable for the container and immersed in the liquid in the container. The advantage of the coil heat exchanger is that it has a simple structure, can withstand high pressure, and can be made of corrosion-resistant materials; its disadvantage is that the liquid turbulence in the container is low, and the heat supply coefficient outside the tube is small. In order to improve the heat transfer coefficient, a stirrer can be installed in the container.

Spray heat exchanger:

This type of heat exchanger is to fix the heat exchange tubes on the steel frame in rows, the hot fluid flows in the tubes, and the cooling water is evenly sprayed from the upper spray device, so it is also called a spray cooler. The outside of the tube of the spray heat exchanger is a layer of liquid film with a high degree of turbulence, and the heat supply coefficient outside the tube is much larger than that of the immersion type. In addition, most of these heat exchangers are placed in the place where the air circulates, and the evaporation of the cooling water also takes away part of the heat, which can reduce the temperature of the cooling water and increase the driving force of heat transfer. Therefore, compared with the immersion type, the heat transfer effect of the spray type heat exchanger is greatly improved. Sleeve Heat Exchanger The Sleeve Heat Exchanger is a concentric sleeve made of straight pipes of different diameters and connected by a U-shaped elbow. In this heat exchanger, one kind of fluid goes in the tube and the other kind of fluid goes through the annular gap, both of which can get a higher flow rate, so the heat transfer coefficient is larger. In addition, in the casing heat exchanger, the two fluids can be pure countercurrent, and the logarithmic average driving force is large. The casing heat exchanger has a simple structure, can withstand high pressure, and is convenient to use (the number of pipe sections can be increased or decreased as required). Especially because the casing heat exchanger has the advantages of large heat transfer coefficient, large heat transfer driving force and ability to withstand high pressure.

Plate Heat Exchanger:

The most typical partition heat exchanger, its application in industry has a long history, and it still dominates all heat exchangers today. The main structure is composed of heat exchange plates and rubber strips between the plates. It has dominated the market for a long time, but its volume is large, the heat exchange efficiency is low, and the replacement of the rubber strip is expensive (the replacement cost of the rubber strip accounts for about 1/3-1/2 of the entire process). It is mainly used for heat exchange between liquid and liquid, which is often called water-water heat exchange in the industry, and its heat exchange efficiency is 5000w/m2.K. In order to improve the heat transfer coefficient of the fluid outside the tube, a certain number of transverse baffles are usually installed in the shell. The baffle plate can not only prevent the short circuit of the fluid and increase the fluid velocity, but also force the fluid to cross-flow through the tube bundle multiple times according to the specified path, which greatly increases the degree of turbulence. The commonly used baffles are circular and disc-shaped, and the former is more widely used. . Due to the launch of China's new version of GMP, plate heat exchange will gradually withdraw from industries with high hygiene levels such as food, beverage, and pharmaceuticals.

Shell And Tube Heat Exchanger:

Shell-And-Tube Heat Exchanger (also known as shell-and-tube type) is a shell-and-tube heat exchanger mainly composed of shell, tube bundle, tube sheet and head. , both ends of the tube bundle are fixed on the tube plate. Two kinds of fluids for heat exchange in the shell and tube heat exchanger, one flows in the tube, and its stroke is called the tube side; the other flows outside the tube, and its stroke is called the shell side. The wall of the tube bundle is the heat transfer surface. The types of pipes are different, the process is generally 16mm, 20mm or 25mm in diameter, and the thickness of the pipe wall is generally 1mm, 1.5mm, 2mm and 2.5mm. The imported heat exchanger has a minimum diameter of 8mm and a wall thickness of only 0.6mm. The heat exchange efficiency has been greatly improved, and since 2012, it has been gradually promoted in the domestic market. Shell and tube heat exchanger, spiral tube bundle design, can maximize the turbulent flow effect and increase the heat exchange efficiency. The asymmetric design of the inner shell layer and the tube layer can reach a maximum of 4.6 times. This asymmetric design determines its wide application in the field of steam-water heat transfer. The maximum heat exchange efficiency can reach 14000w/m2.k, which greatly improves production efficiency and saves costs. At the same time, since shell-and-tube heat exchangers are mostly metal structures, with the introduction of China's new version of GMP, heat exchangers with stainless steel 316L as the main body will become a must for beverage, food, and pharmaceutical industries.

Double tube sheet heat exchanger is also called P-type heat exchanger:

In the heat exchanger, a tube sheet is added to each end of the shell and tube heat exchanger, which can effectively prevent the pollution caused by leakage. There are few domestic brands in the market, and the price is expensive, generally more than 100,000 yuan, and the import can reach hundreds of thousands. It is in line with the new version of GMP regulations. Although the price is expensive, it determines its broad market.

mixed type

Hybrid heat exchangers rely on direct contact between cold and hot fluids for heat transfer. This heat transfer method avoids the thermal resistance of the heat transfer partition and its sides. As long as the contact between the fluids is good, there will be greater heat transfer rate. Therefore, hybrid heat exchangers can be used wherever fluids are allowed to mix with each other, such as gas scrubbing and cooling, circulating water cooling, mixed heating between steam and water, steam condensation, and so on. It is used in chemical and metallurgical enterprises, power engineering, air conditioning engineering and many other production sectors. According to different uses, hybrid heat exchangers can be divided into the following different types:

(1) Cooling tower (or cold water tower) In this type of equipment, the water whose temperature has been raised in the production is cooled and cooled by means of natural ventilation or mechanical ventilation, and then recycled to improve the economic benefits of the system. For example, circulating water in thermal power plants or nuclear power plants, cooling water in synthetic ammonia production, etc., are recycled after being cooled by water cooling towers. This method has been widely used in practical engineering.

(2) The gas scrubber (or scrubber) is used in industry to scrub the gas for various purposes, such as absorbing some components in the gas mixture with a liquid, removing the dust in the gas, and increasing the increase of the gas. wet or dry etc. But its most widespread use is to cool gases, and the liquid used for cooling is mostly water. The spray room widely used in air conditioning engineering can be considered as a special form of it. The spray chamber not only cools the air like a gas scrubber, but also heats it. However, it also has shortcomings such as high water quality requirements, large floor space, and high water pump energy consumption: Therefore, in general buildings, spray booths are not often used or only used as humidification equipment. However, it is still widely used in textile factories and cigarette factories whose main purpose is to adjust humidity!

(3) Jet heat exchanger In this type of equipment, the fluid with higher pressure is ejected from the nozzle to form a high speed, and the low-pressure fluid is introduced into the mixing chamber to be in direct contact with the jet for heat transfer, and enters the diffusion together. tube, which is sent to the user after the outlet of the diffuser tube reaches the same pressure and temperature.

(4) Hybrid Condenser This type of equipment generally condenses steam by direct contact between water and steam.

Regenerative

The regenerative heat exchanger is used for equipment that performs regenerative heat exchange. Built-in solid filler to store heat. Fire lattices are generally made of refractory bricks (sometimes metal corrugated belts, etc.). The heat exchange is carried out in two stages. In the first stage, the hot gas passes through the fire grid and transfers heat to the fire grid for storage. In the second stage, the cold gas passes through the fire grid and is heated by the heat stored in the fire grid. These two stages alternate. Usually two regenerators are used alternately, i.e. when the hot gas goes into one, the cold gas goes into the other. Commonly used in the metallurgical industry, such as the regenerator of the steel-making open hearth. Also used in the chemical industry, such as air preheaters or combustion chambers in gas furnaces, regenerative cracking furnaces in artificial petroleum plants. Thermal heat exchangers are generally used in occasions where the requirements for medium mixing are relatively low.

ceramics

Ceramic heat exchanger is a new type of tubular high-temperature heat energy recovery device. The main component is silicon carbide. It can be widely used in metallurgy, machinery, building materials, chemical industry and other industries. High temperature flue gas waste heat to obtain high temperature combustion air or process gas.

The heat exchange element material of the developed device is a new type of silicon carbide engineering ceramics, which has excellent properties of high temperature resistance and thermal shock resistance. It is air-cooled from 1000 ℃ to room temperature and repeated more than 50 times without cracks; thermal conductivity Equivalent to stainless steel; good corrosion resistance in oxidizing and acidic media. In the structure, the thermal compensation and the gas sealing problem are solved successfully. The device has high heat transfer efficiency and remarkable energy-saving effect. It can be used to preheat combustion-supporting air or heat the process gas of certain processes, which can save primary energy, and the fuel saving rate can reach 30%-55%. production capacity. The production process of ceramic heat exchangers is basically the same as that of kiln furniture. Thermal conductivity and oxidation resistance are the main application properties of materials. Its principle is to place the ceramic heat exchanger near the flue outlet and where the temperature is high, so there is no need to mix cold air and high temperature protection. At 1300 °C, the waste heat recovered by the ceramic heat exchanger can reach 450-750 °C, and the recovered hot air is sent to the kiln to form a mixture with gas for combustion, which directly reduces production costs and increases economic benefits. Ceramic heat exchangers have been well developed under the limitations of the use of metal heat exchangers, because they better solve the problems of corrosion resistance and high temperature resistance. Its main advantages are: good thermal conductivity, high high temperature strength, good oxidation resistance and thermal shock resistance. Long life, small maintenance, reliable and stable performance, easy to operate.