Digital users of engineering technology talk about the thermal calculation of compressed air refrigerating dryer Zhou Wei (412002 China Aerospace Power Machinery Research Institute, Zhuzhou, Hunan) is also getting higher and higher requirements. Therefore, a compressed air refrigerating dryer has been introduced. In this paper, the working principle of the compressed air refrigerating dryer is briefly introduced. Secondly, the thermal calculation of the compressed air refrigerating dryer is introduced from the aspects of thermal calculation in the process of compressed air treatment and thermal calculation of the refrigeration system.
With the rapid development of modern industry, there are more and more applications of compressed air. When using compressors in the textile industry, petroleum and steel production, if there is some moisture in the air entering the compressor inlet. More, this can lead to failure of production equipment or poor quality of products.
Therefore, with the continuous development of science and technology, the requirements for the degree of drying of compressed air are also increasing. Because the compressed air refrigerating dryer has a stable pressure dew point, it can carry out continuous work and does not need to consume a part of gas for regeneration and many other advantages, and has been widely used at home and abroad.
First, the working principle of compressed air refrigerating dryer The working principle of compressed air refrigerating dryer is to exchange heat with compressed air and compressed air to cool the compressed air to 210 ° C, so as to compress the moisture in the air or It is the removal of steam components to achieve the purpose of drying compressed air. It consists of two main processes, one is the compressed air process and the other is the refrigerant process.
(1) Compressed air flow The compressed air that has been dried into the compressed air refrigerating dryer first enters the pre-cooler and exchanges heat with the already dried low-temperature cold air present in the evaporator in the pre-cooler. When the temperature, enthalpy or moisture content decreases, the dried compressed air coming out of the pre-cooler has lowered the pressure dew point, and the vapor-water mixture in the evaporator exits the evaporator and enters the gas-liquid separator, and The moisture is separated in the gas-liquid separator, where the dry air enters the pre-cooler and exchanges heat with the hot air in the compressed air refrigerating dryer, and after the temperature is raised, it is discharged into the compressed air to be freeze-dried. machine.
(2) The high-pressure high-temperature refrigerant air discharged from the refrigerant flow compressor and let it enter the condenser, while releasing heat, and after condensing into a liquid, the liquid refrigerant discharged from the condenser is cooled and depressurized by the throttling mechanism. The vapor-liquid two-phase state, which then becomes a low temperature, enters the evaporator and is exchanged with the air that has been dried in the evaporator to vaporize it, and the superheated gas exits the evaporator and then enters the compressor. Thus the next round of cycles.
Second, the compression calculation of the compressed air refrigerating dryer The compressed air refrigerating dryer is actually composed of a series of refrigeration systems and pre-coolers, and the thermal calculation of the compressed air refrigerating dryer includes two parts of the calculation content, respectively Thermal calculations for compressed air processing and thermal calculations for refrigeration systems. In general, the thermal calculation of the second partial refrigeration system is performed on the basis of the thermal calculation in the first partial compressed air, thereby further determining the condenser load of the compressed air refrigeration dryer and the compression power of the compressor.
(I) Thermal calculation during compressed air treatment The main purpose of thermal calculation during compressed air treatment is to determine the amount of refrigeration required for compressed air treatment.
The compressed gas from the air compressor is humid air, which is composed of water vapor and dry air, while dry air can be regarded as ideal air, and because the water vapor content in the humid air is small, The capacitance is large but the partial pressure is reduced. Therefore, under certain circumstances, it can also be regarded as an ideal gas. Therefore, the relationship between various state parameters can be expressed by the relationship between the state parameters of the ideal gas.
The thermal calculation steps in the compressed air treatment process are as follows: 1. Determine the mass flow rate of the compressed air.
2. Calculate the inlet compressed air in the refrigerated dryer and the ç„“h. in the evaporator where the treated air exits the evaporator, where t refers to the temperature of the air and d refers to the moisture content of the air.
Whereas 622<7, wherein the purpose is relative humidity, which is 100% under saturation; and P refers to the pressure of compressed air, and P refers to the partial pressure of saturated water vapor at the corresponding temperature.
3. Calculate the load e of the pre-cooler of the compressed air refrigerating dryer and the load in the evaporator a. Among them, Jiang Qiang, Han Wei, Chen Wencai, Teng Fei, Wu Hui, talk about the heat of the compressed air refrigerating dryer Calculation, Compressor It, 2001 (01).
Huang Hu, Thermal Calculation and Experimental Verification of Working Process of Compressed Air Freeze-Drying System, Journal of Nanjing Normal University (Engineering Technology Edition), 2004 (01 Chen Yunguang, Yuan Xiuling, Zhang Xingqun, Huang Dong, Jiang Zenghui, Yang Yifan, Ma Jun, Compressed Air Refrigeration The performance of the dryer is calculated and graphically, and it can be intuitively observed that the wave shape of the steel strip is determined by the positive and negative forces of the force applied to each zone to determine the small difference in the thickness of the steel strip in the zone.
Third, the compensation mode inside the ABB shape meter In the rolling process, in order to make the displayed shape curve load the actual strip shape, the measured value needs to be compensated to correct. Several necessary compensation modes have been written into the ABB shape control system to establish the model. The following describes the target compensation function.
Target shape curve (1) Target model flatness target The shape curve model depicts the pre-set target shape of the strip to be rolled (as shown), and the shape of the plate is rolled by the operator according to the needs. To select, in the process of rolling, the shape of the plate we measured and the target shape curve are displayed on the page at the same time, which can be intuitively compared for easy control by the operator.
(II) Target compensation During the strip rolling process, various data quantities are changed, such as temperature, strip crown, edge and other factors, which are selected by the operator. The purpose of the target compensation is to eliminate the influence of the above factors on the shape of the plate by dynamic adjustment during the rolling process to achieve the desired shape of the plate. The temperature compensation and crown compensation are introduced below: 1. Temperature compensation During the rolling process, the temperature of the strip surface is distributed along the width direction. However, our requirements for the shape of the plate are very precise, and the temperature difference will be This leads to a change in the length direction of the strip, so that the shape of the product will be deviated. In order to compensate for the high temperature in the local area, low-stress rolling is required in the high temperature region. This function can be achieved by selecting temperature compensation.
2. The crown compensation of the strip will be over-stressed when the strip is wound on the coiler, causing the strip to have a partial extension on the coiler, resulting in a change in crown, while the strip has passed the shape of the plate. The roller, which affects the plate-shaped roller, cannot be detected, so that the compensation amount of this corresponding region is added to the shape meter system, which changes correspondingly with the change in the crimp diameter of the strip.
ABB's plate type control system uses the principle of piezomagnetic to detect the plate type of the strip. It has high detection precision and stable working system, and it is not affected by the strip material. It adapts to the harsh working environment and is easy to maintain. Reliable and widely used in the metallurgical industry.
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