National Service Hotline:
Zibo Taylor Heat Exchange Equipment Co., Ltd.
Address: Boshan District, Zibo City, Shandong Province
Contact: Gao Qing
Mobile phone: 13409069825
Chapter I Status and Prospects of the Development of Plate Heat Exchangers
Development Status of Section I Plate Heat Exchanger
I. Development status of plate heat exchangers:
In recent decades, plate heat exchangers have developed rapidly, mainly in the following aspects.
越来越 There are more and more types of plate heat exchangers, the technical performance is getting better and better, and the application range is getting wider and wider.
① Type of plate heat exchanger:
From the connection mode of plate heat exchangers: from detachable plate heat exchangers to brazed plate heat exchangers. From semi-welded and fully welded to plate and shell heat exchangers.
From the form of the plate: from symmetric to asymmetric.
From the flow path of the plate: from symmetrical flow path to wide and narrow flow path, wide and wide flow path.
From the depth of the plate corrugation: from a general plate with a wave depth of 3 to 5 mm to a shallow dense corrugated plate with a wave depth of 2 to 2.5 mm.
② The technical performance of plate heat exchangers is getting better and better
Design temperature and design pressure range of plate heat exchanger.
The operating temperature has evolved from a removable 260 ¡ã C to a plate and shell 1000 ¡ã C.
The working pressure has developed from a removable 2.5 MPa to a plate and shell 8.0 MPa.
The heat transfer coefficient has developed from 2000W / m2 ¡¤ k to 12000W / m2 ¡¤ k.
The maximum equivalent diameter is 28mm.
The largest removable single plate heat exchange area is 4.75m2.
The maximum heat exchange area of welded veneer is 18m2.
The minimum heat exchange area of brazed veneer is 0.006m2.
The largest removable single heat exchange area is 2500m2.
The largest fully welded single unit heat exchange area is 10000m2.
The maximum takeover size is 500mm.
③ The application range of plate heat exchanger is getting wider and wider (see Table 1-1).
Table 1-1 Application scope of various types of plate heat exchangers
板 The plate heat exchanger is developing towards large size, miniaturization, specialization, diversification and installation.
Large plate heat exchangers are mainly used in the central cooling system (hereinafter referred to as CCS), which centrally cools the cooling water used in various factories and serves as a cooler for the bearing cooling water in power plants. The capacity of the plate heat exchanger is related to the size of the plant and the process. The necessary cooling water volume ranges from thousands to tens of thousands of m3 / h. Large plate heat exchangers can reach hundreds of thousands of m3 / h. CCS hopes to use as much as possible Large number of plate heat exchangers are required for processing. In recent decades, many world-scale LNG plants have been built in the Middle East. The cooling method using the previous cooling tower cannot ensure the make-up water, so I hope to change to CCS method using plate heat exchanger. In the past, power plants used S & T bearing cooling water, but performance evaluation showed that plate heat exchangers have obvious advantages in terms of cost, heat transfer performance, miniaturization and maintainability, so they need to be replaced with plate heat exchangers. Way. For example, the energy system of the Barcelona Forum area uses waste (anaerobic analysis of garbage collected in the urban area of Barcelona to produce artificial gas), waste heat power generation (gas-fired steam boilers generated by waste, drive gas turbine generators, Power supply from the urban power grid), power generation waste heat refrigeration (high-pressure steam decays to low-pressure steam after power generation, and is sent to an absorption refrigerator manufactured by Yuanda Air Conditioning to heat the lithium bromide solution for cooling), and seawater cooling. Equipment design capacity: absorption refrigerator 4 ¡Á 4500 kW; steam-water plate heat exchanger 4 ¡Á 5000 kW; cold storage tank 5053m3; seawater plate heat exchanger 4 ¡Á 12000 kW (flow of 961m3 / h per seawater plate heat exchanger) , Pressure drop 58kPa), the plate material is titanium. Seawater cooled plate heat exchanger (see photo 1-1).
A common feature of the above uses is that seawater is used as a water source for cooling water, and one of the problems in using seawater in a plate heat exchanger is antiscaling. In the future, with the increasing requirements of plate heat exchangers for coolers in CCS and power plants, it is necessary to study the degree of influence of marine organisms on the heat transfer performance after attaching to the plates and understand the corrosion resistance of the plates.
a. Seawater resistance
Antifouling when using seawater. Currently, as a method for preventing the attachment of marine organisms, there is a method of continuously injecting seawater into the seawater to obtain sodium hypochlorite (NaClO) by an electrolysis method. The actual operation shows that the measurement is performed after continuous injection of sodium hypochlorite (0.9 ppm) in a plate heat exchanger using seawater. After 3 months of operation, the total heat transfer coefficient does not change. In the summer when seaweed and shellfish are prone to breeding, continuous infusion of sodium hypochlorite can also ensure the same heat transfer performance. There are other methods. From the perspective of environmental preservation, the use of ozone and hot water to prevent pollution is also effective, but no experimental verification and corresponding technical methods have been established.
When seawater is used, the plate is generally made of titanium. Titanium has excellent corrosion resistance to seawater. According to relevant corrosion resistance data, it is known that for seawater, titanium plates will not corrode even at 120 ¡ã C. In addition, sodium hypochlorite injected to suppress the adhesion of marine organisms also produces a strong, non-dynamic film, which improves the corrosion resistance of titanium plates. Using nitrile rubber as the gasket, even if the seawater temperature reaches 80 ¡ã C, it will not cause any corrosion. In terms of heat resistance, when the seawater temperature is lower than 60 ¡ã C, there is no thermal degradation phenomenon, and good sealing performance can be ensured for a long time.
c. Characteristics of large plate heat exchanger
¡¤ The processing flow of each plate heat exchanger is related to the diameter of the angular hole of the plate. The diameter of the angular hole of the large plate heat exchanger is Φ500, and the flow rate of each processing is 5000m3 / h. , The number of required units can be reduced by half. As a result, the initial investment in filters, installation engineering and piping for heat exchangers, maintenance costs such as plate cleaning and replacement of gaskets can be significantly reduced, and space can also be saved. The following example illustrates this. Comparison of large plate heat exchangers with previous large plate heat exchangers (see Table 1-2). From the number of units, only two mainframes are required, compared with 4 in the past. The investment of mainframe is about 10% larger than that of the mainframe in the past, but its filter investment is about 2/3 of Table 1-2 compared with the previous mainframe, and the installation project is about half. 30% reduction. From the installation space, it can reduce about 40%. Even if one standby machine is installed, the total cost can be reduced by 15%, and the space can be saved by 30%. In terms of decomposition and cleaning, due to the small number of plates, labor costs have also been reduced by about 30%.
• Treatment measures for seawater. When seaweed and shellfish in the seawater adhere to the inside of the board or are blocked near the corner holes, the flow of seawater will be reduced and cooling performance cannot be guaranteed. Therefore, when the seawater passes from the corner holes to the inside of the board, there should be no protrusions Obstacles make the flow path linear, which is one of the methods to prevent marine organisms from blocking the corner holes. In order to verify the above effect, a large plate heat exchanger passing through seawater was measured, and the test results proved that when a small amount of algae adhered near the corner hole, there was no effect on the performance of the flow path. However, in order to ensure the smooth flow path in the plate, foreign objects with a diameter larger than the plate spacing must not be allowed to pass, so a filter must be installed before entering the heat exchanger.
d. High performance
Compared with the previous plate heat exchanger, the uniform flow path without bias flow is the main way to maintain high performance. One of the measures is to set a bias flow suppression plate on the main heat transfer surface inside the plate to minimize the flow path at the liquid inlet, so that the main heat transfer surface is uniform (see Figure 1-2). Secondly, when designing the plate, the flow at the center of the plate should be increased, that is, the flow at the end should be prevented from increasing. As mentioned earlier, since the deflection prevention plate can reduce the pressure drop in the corner hole, its heat transfer performance is increased by about 15-20% compared with the previous large plate.
When selecting the size of the plate heat exchanger corresponding to the conditions of use, consideration must be given to issues such as initial investment and installation space. One of the market for plate heat exchangers is used for users who consume less energy, sterilize food and medical fluids, and heat / cool small amounts of fluids. For this reason, ultra-small plate heat exchangers must be developed to meet the requirements of product diversification, uneven production scale, and to meet the requirements of the thermal energy industry with low energy consumption. At present, ultra-small plate heat exchangers on the market have the advantages of miniaturization, low cost, high performance, light weight, and fast production.
a, the size of the heat exchanger, the largest plate is only equivalent to the size of A4 paper, each weighing about 20kg, can be installed on the wall.
b. The number of standard plates is 12, 24, 36, 48. The materials of the plates are SUS316 and titanium. The gaskets are two types of ethylene-propylene-diene rubber and silicone rubber.
a. The plate heat exchanger used in the process of heat sterilization and heating / cooling of food fluid must have the following three conditions: to improve productivity; to ensure hygiene; to ensure the stability of food quality.
b. The plate heat exchanger for food is a commercial plate heat exchanger developed in order to meet the above three conditions. It has been widely praised for its use as a sterilizer such as coffee, seasoning liquid, and soy sauce.
c. When designing a special plate heat exchanger for food, the flow velocity distribution in the plate should be uniform. For this reason, even on the plate surface, no liquid scale should be formed, and continuous operation can be performed for a long time. It is to achieve a uniform heating / cooling process, improve the quality of the product and ensure the stability of the quality. If CIP is used, all plates of the plate heat exchanger can be cleaned.
d. The gasket with inlaid structure is adopted to meet the requirements of new performance. The maintenance time is 1/2 ~ 1/3 of the original device.
a 、 Fully-welded plate heat exchanger
As we all know, the plate heat exchanger has many advantages, but because of the following problems, its application range and development are limited, the tightness is poor, and it is easy to leak. It is necessary to replace the gasket frequently, which is troublesome and has a low pressure resistance. About 1MPa; the temperature resistance is limited by the gasket material; the flow channel is small, which is not suitable for gas-to-air heat exchange or steam condensation; easy to block, not suitable for fluids containing suspended substances, etc. With the manufacture of plate heat exchangers, the emergence of plate materials and welded plates has overcome the above disadvantages and expanded the scope of application.
In the process of implementing energy conservation in all industrial industries, reducing fuel costs is an issue that enterprises need to solve urgently. Exhaust gas and waste water heat recovery is one of the important measures to save energy and reduce fuel costs. In order to adapt to this situation, a fully welded plate heat exchanger unit has been developed.
¡¤ Shape: There are two types of cross-flow type gas-air (air) heat exchangers with a fully welded structure combined with standardized ultra-thin flat plates, namely high temperature type and low temperature type.
¡¤ Characteristics: Unit combination, easy to expand, from small air volume to large air volume (60 ~ 300,000Nm3 / h), wide range of use; thin flat plate, high efficiency (temperature efficiency up to 80%); can be used at high temperature (1000 ℃) , High-pressure (30kPa) gas; Fully welded airtight structure, which will not mix with exhaust gas and odor; The structure is easy to maintain and clean; Choose the appropriate material according to the use temperature and the type of gas.
¡¤ Structure: In order to withstand the thermal stress under high temperature conditions, the sheet is processed into a hexagonal shape and assembled into a unit. The purpose is to disperse the thermal stress and form a high temperature resistant structure (see Figure 1-3).
¡¤ Material: S-TEN, S is suitable for units with temperature below 350 ℃; aluminum alloy plate is suitable for units with exhaust temperature below 500 ℃; SPCC is suitable for units with temperature below 200 ℃; SUS system should be based on temperature, The nature of the exhaust gas is selected from other non-ferrous metals, such as tin and copper.
¡¤ Thickness: 0.3 ~ 2.0mm (standard 0.8mm, 0.4mm for low temperature).
¡¤ Withstand voltage: 10kPa at 600 ¡ã C; 5kPa at 900 ¡ã C.
¡¤ Airtightness: T type is less than 0.001 of passing air volume for deodorization; N type is less than 0.1% of passing air volume for general use; S type is less than 1.0% of passing air volume.
¡¤ Pressure drop: The pressure drop is different between high temperature side and low temperature side. On the high temperature side (exhaust), the allowable value is 50 Pa or less under the conditions of the residual pressure outside the machine and the gravity of the chimney.
¡¤ Maximum operating temperature: It is related to the recovery temperature and operating pressure of the heated side, but it can reach 1000 ℃.
¡¤ Dust concentration in exhaust gas: When the exhaust path is a single flow, the heat transfer surface is a flat plate, so it is difficult to block, the dust concentration is about 0.1 ~ 0.5g / Nm3.
Flow direction (flow direction): In principle, it can be freely designed, and it can be negotiated with the user beforehand for the optimal design.
¡¤ Interchangeability: When the unit needs to replace some parts, the structure of the unit should be easy to replace.
¡¤ Layout: can be set vertically, horizontally or horizontally.
¡¤ Insulation: The appearance is convenient for heat preservation. Generally, plate heat preservation is adopted for easy maintenance. Recently, a low-pressure-loss unit device using exhaust gas to preheat boiler feedwater has been developed. At present, all-welded plate heat exchangers are used in steel, petroleum, boiler and other industries, and have achieved great results.
b. Plate type cross-flow heat exchanger
¡¤ The plate type cross-flow heat exchanger is a simple structure, with the advantages of elastic sealing, non-welding of heat transfer surface and wide application range.
¡¤ Principle structure: In the fixed frame of the steel structure, each heat transfer plate is overlapped one by one at 90 degrees. The exhaust gas passes through the heat transfer plate in a vertical direction and the air passes in a horizontal direction. (See Figure 1-4)
¡¤ Features: The heat transfer plate is assembled by elastic sealing, which can absorb thermal expansion freely, so it can meet the requirements of stress changes caused by temperature changes, and almost no leakage occurs; because the heat transfer surface is not welded, it can be based on the change of object temperature Many suitable materials are selected, ranging from low temperatures below the oxygen dew point to high temperatures around 1000 ¡ã C (see Figure 1-5); in order to prevent the wear and blockage caused by dust in the exhaust, many corresponding measures have been taken. Several to dozens can be combined, so the processing capacity is very large, and it can be used as a large-capacity air preheater.
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