Auxiliary machine talks about the thermal calculation of compressed air refrigerating dryer Jiang Qiang, Han Wei, Chen Wencai, Teng Fei, Wu Hui (Dongfeng Motor Corporation Equipment Management Department Compressed Air Purification Countermeasures Group, Hubei Shiyan 402) Commented.
92 Document identification code: B In recent years, "Compressor Technology" magazine published the relationship between the actual processing capacity of the freeze dryer and the state of compressed air (refer to article 1) and the analysis of the preheater heat exchange process in the freeze dryer (refer to article 2) . At present, as the cold-drying machine industry in China's emerging industries is at a critical juncture in market competition, the authors of the article can express the calculation formulas and calculation data that are closely related to the core technology of their products to the experts, and undoubtedly improve the dryer. The design level of the industry, product quality and how the industry faces the WTO has a profound impact.
In 1999, inspired by the article 1, Dongfeng Motor Corporation's Compressed Air Purification Countermeasures Group referred to the book "Piston Compressor Design", "Air Conditioning Design Manual", "Refrigeration Accessories" and "Heat Exchanger Design Manual". The formula is used for thermal calculation of the XLG type cold storage type cold dryer, and the prototype is designed and manufactured using the calculated data.
Through field tests, it was found that the heat exchange area calculated by the formula of the cooler design in the "Piston Compressor Design" book, the thermal parameters and the resistance loss value of the compressed air at the inlet and outlet of the evaporator and the precooler are the same as the measured data. Proximity, this is probably because the compressor's cooler and the dryer are cooled by compressed air. In order to further explain the situation, the formula and calculation data used in the calculation of the thermal load of the evaporator of the dryer 1 are compared with the formulas and calculation data used in the design of the piston compressor, as shown in Table 1. For the sake of comparison, the symbols of the parameters and their physical meanings are consistent with the article 1, and the selected parameters are: the compressed air rated treatment capacity of the dryer (M / min) (the volume flow rate converted to the standard state) rated pressure p rated intake air temperature T = 40 ° C converted to the air compressor inlet standard state air p serial number design in the vicinity of atmospheric pressure on the thermal calculation of the air according to the "piston compressor design" cooler design for compressed air The calculation formula of the heat is based on the inlet air temperature of the evaporator t = 32 ° C. Check the wet air. The partial pressure of the steam is obtained. The ventilator outlet air temperature is t. The evaporator inlet air temperature t is the evaporator outlet compressed air temperature. The moisture content of the outlet air is determined by the evaporator inlet and outlet compressed air moisture content. The technical number of the compressor is designed to calculate the heat of the air near the atmospheric pressure. According to the design of the cooler in the "Piston Compressor Design" Calculate the air enthalpy of the inlet and outlet of the evaporator by using the compressed air as the thermal calculation formula. Find the heat released by the dry compressed air after cooling by the evaporator. 1 Nm / min air dryer dryer (including refrigeration system) bears the heat load to reduce the water vapor in the compressed air to cool and partially condense into the heat released by the water Q 2 steam evaporator to bear the heat load steam 1 steam 2 Steaming From the above table, it can be seen that the heat load of the evaporator of the dryer is calculated by the two formulas, that is, the cooling capacity required by the refrigeration system is a small heat load to select the refrigeration compressor, and the actual heat load is required. It is closer to 601?85 kcal/h. The temperature of the compressor can reach the outlet air of the evaporator at a temperature of 2.22 °C higher than the 5 °C selected by the original design. It is impossible to suspend the evaporator from the compressed air. The condensed water particles 100 are separated, so that the actual dew point of the compressed air at the exit of the dryer will be 2 to 3 ° C or higher than 7.22 ° C. The performance of such a dryer does not meet its design requirements and national standards. JB/JQ209010 88 requirements. The reason for the difference between the two formulas is mainly due to the relative humidity φ in the calculation formula of the moisture content d. Under the condition of the selected parameters of the above design, the moisture content d in the compressor air should be calculated as φ=1. When calculating the moisture content of the compressed air at the air conditioner design or the intercooler inlet of the air compressor, φ Take the relative humidity of the atmosphere or the relative humidity of the air compressor suction environment. It should be noted that the author of the article 1 is clear about the concept of the above φ value. In the article 2 published in 2000, the calculation process of the calculated values ​​of the parameters of the dryer at different t temperatures has taken this factor into account. It is.
Article 2 presents a very striking assertion: in theory, the final temperature of the cold fluid in the reverse heat transfer can be less than, equal to or even greater than the final temperature of the hot fluid. Therefore, in large and medium-sized cold dryers, the precooler is mainly countercurrent heat transfer (Figure 3). However, due to the limitation that the cold capacity utilization cannot exceed 100, the exhaust gas temperature of the dryer can not be raised even in the countercurrent heat exchange. For example, under the above conditions, the exhaust gas temperature of the dryer is limited to 28 °C.
The domestically produced cold-drying machine has only one company's cold-drying machine "Instruction Manual" which mentions whether there is a temperature difference between the hand and the air inlet and outlet (the normal temperature should be 10 to 17 °C). There is also a company in the country, the "Technical Instruction Manual" refers to the air temperature at the outlet of the reheater (the cold side of the pre-cooler) in the case of the rated air flow rate and the standard inlet air temperature. It is better than the cold-drying that the temperature difference between the inlet and outlet of the dryer is large or small, or it is not normal beyond the above range. This is to judge the technical performance and equipment technical condition of the dryer. Make it clear. However, it is clear that the inlet air temperature of the dryer is t'=40°C as specified in the article 2. The lower limit of the temperature difference between the inlet and outlet of the dryer is 10°C or 8.3°C. The exhaust temperature of the dryer is A diagnosis of 30 ° C or 31.7 ° C exceeds the limit of 28 ° C.
In the end, whether the diagnosis is correct or the temperature range of the inlet and outlet of the dryer is correct, this is another important issue that users of the dryer are urgently trying to figure out.
According to the national standard GB2588 81 "General Rules for the Calculation of Thermal Efficiency of Equipment", the thermal efficiency of equipment refers to the quantitative representation of the effective degree of supply energy utilization for the specific purpose of the thermal equipment, which is equal to the percentage of effective energy to the supplied energy. 4. Calculation of Effective Energy (QYX) ... 4.4 Heat absorbed by evaporating substances such as moisture in processes such as drying and evaporation. 5. Calculation of supply energy (GG) ... 5.3 The amount of heat transfer from the outside to the system. The dryer is a thermal device. Its specific purpose is to dry the compressed air according to the dew point of the dryer. The effective energy of the dryer (QYX) is the condensate that is actually discharged from the compressed air system of the dryer. Corresponding to the released heat, this heat is basically equal to the water vapor in the compressed air of the preheater heat flow side, the evaporator compressed air side, and the precooler cold flow side (reheater) according to the formula on the right side of Table 1. Cooling (reheating) and partial condensation (re-evaporation) of the heat released (absorbed) Q 2 pre-two steaming 2 and the algebra sum, the supply energy of the dryer (QGG) is the cooling system of the dryer to the compressed air system The amount of cold delivered, this amount of cooling is equal to the heat load on the compressed air side of the evaporator, that is, the steam calculated according to the formula on the right side of Table 1. Therefore, the calculation of the thermal efficiency η of the dryer should be carried out using the following formula 2: 2 steaming 2 and steaming In the proof-of-charge article 2, when the cooling capacity utilization Q is nearly 100 and the cooling and drying machine exhaust temperature reaches the limit value of 28 °C, the thermal efficiency of the cold-drying machine is only 51.7. The Dongfeng Motor Corporation's compressed air purification countermeasures research group and Shiyan State, Hubei Province this The XLG series of cold storage dryers jointly developed by Industry and Trade Co., Ltd. have been tested by the Hefei General Machinery Research Institute of the Ministry of Machinery. When the inlet temperature of the dryer is 40.3 °C, the exhaust temperature of the dryer reaches 38.3. °C, the temperature of the compressed air at the inlet of the evaporator is 16 °C. According to the above formula, the thermal efficiency of the XLG series cold storage dryer is 90. (The calculation in this paragraph is omitted) Li Shen. The relationship between the actual processing capacity of the freeze dryer and the state of compressed air [J].
Li Shen. Analysis of heat exchange process of precooler in freeze dryer [J]. Compressor technology Jiang Qiang, et al. Development of XLG series cold storage type dry dryer [J] . Compressor "Piston Compressor Design" writing group. Piston compressor design [M].
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Shenyang Gas Compressor Co., Ltd. developed a new hydrogen compressor passed the identification. Not long ago, China Petrochemical Corporation hosted the 4M80 30/22 200 BX new hydrogen compressor appraisal meeting. The meeting was held in Maoming Petrochemical Company and more than 60 experts attended the meeting.
The meeting heard the product development summary report of Shenyang Gas Compressor Co., Ltd., reviewed relevant technical documents and materials, conducted on-site inspections of the operation of the unit, and organized discussions and defenses. The appraisal committee composed of relevant experts has been seriously discussed: (1) The product identification technical information is complete, complete and accurate, and can guide the production. (2) The design of the machine is reasonable, and the structure is compact and advanced. Independently developed key components such as piston, cylinder, packing and double chamber spacer. The main transmission components adopt advanced technology of German BORSIG company, and the thermodynamic performance calculation, analysis and check of the compressor are carried out. (3) The machine is manufactured. In accordance with the ISO9001 quality system documents, the parts are manufactured with high precision and meet the requirements of relevant technical standards. Manufacturing process technology and processing equipment have the ability to manufacture large-scale reciprocating hydrogen compressors. (4) After operation practice and field test calibration, the unit has stable operation, low vibration and low noise, meeting design technical requirements and meeting process and production needs ( 5) This machine is the first large-scale reciprocating hydrogen compressor with 800 kN piston force developed by the state. It fills the domestic gap and is in the domestic leading position in technology. It has reached the level of international similar products and can replace imported (6) The unit will improve and perfect the high-pressure piston ring according to the on-site operation conditions to meet the long-term operation needs of the unit and further improve the auxiliary equipment level.
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