The calculation and analysis of the capacity of Dafa 101J air compressor Chen Chenhua Zhang Yading Chen Yanfeng Wu Long (Tianhua Chemical Machinery and Automation Research and Design Institute) (Ningxia Chemical Plant) carried out a series of calculations and analysis, analyzed the actual air pumping of the air compressor The reasons for the lack of capacity, and pointed out the defects and deficiencies of the original design.
1 Introduction A chemical fertilizer plant in a factory was purchased from the Lamton plant in Canada in 1992 to rebuild a second-hand large-scale fertilizer plant. The daily output of synthetic ammonia is about 1000t, which is the Kellogg process. Because the device was designed and built in the 1960s, and the cooling water temperature, meteorological conditions, natural gas conditions, etc. of the plant are obviously different from those in Canada, the production capacity of the second chemical fertilizer plant of the plant is less than 907tN H /d original design requirements. .
Among them, the lack of capacity of 101J air compressor is one of the main bottlenecks limiting the production of ammonia. In order to increase the output of the plant, the plant intends to introduce a feed of about 5000 Nm / h of air from a chemical fertilizer into the inlet of the 101J air compressor high pressure cylinder. To do this, it is necessary to perform capacity calculation on the 101J air compressor.
2 101J Air Compressor Features The main function of the 101J air compressor is to supply process air (source in NH) to the process gas and instrument air to the pneumatic instrument. Its main features are: (1) Driven by steam turbine 101JT, gear speed increaser 101 JG speed increase, the whole unit shares a common base.
(2) Two horizontal split type cylinders are used, of which the low pressure cylinder is 4 sections and 11 stages.
(3) The high and low pressure cylinder impellers adopt a aligning structure, and the balance disc balances the axial force.
(4) Impeller structure Except that the first stage is a semi-open type ternary impeller, the other 10 stages are closed type binary impellers (the second and fourth arc blades).
(5) The aerodynamic design uses a one-dimensional design method.
(6) A vaneless diffuser is used, the width of which is smaller than the width of the impeller exit vane.
(7) All gas seals and shaft seals are sealed with a labyrinth.
(8) Use tilting pad bearings to force oil lubrication.
Air compressor capacity calculation In order to accurately calculate the design capability of the 101J air compressor, it is necessary to understand its original design performance parameters, geometric parameters, actual operating parameters, and must also know its actual performance parameters such as variable efficiency, power and pressure ratio. Therefore, a series of calculations and conversions are required.
3. 1 main design characteristics of the unit 101J/JT air compressor unit mainly by 101J air compressor, air compressor drive turbine, 101JG gear speed increaser, oil Chen Zonghua, male, born in October 1965, master, senior engineer . Lanzhou City, 730060.
System, cooler, separator, etc., its configuration diagram is shown in Figure 1. The main design characteristics of the main unit of the unit are as follows: (1) 101J air compressor design characteristic parameters () 101 J air compressor design characteristics parameters cylinder low pressure cylinder high pressure cylinder model segment number medium air relative humidity / compression factor import molecular weight Constant entropy index inlet pressure inlet temperature / °C outlet pressure outlet temperature / °C variable energy head mass flow inlet volume flow standard volume flow power / kW Note: no pumping is 46450. 338kg / h, a factory is not pumping.
(2) 101JT drive turbine design characteristic parameters (see table steam turbine design characteristics parameter model number design power / kW rated power / kW steam temperature / ° C steam flow / kg h ( 3) 101 JG gear speed increaser design characteristics Parameters (see Table 101JG gear speed increaser design characteristic parameter input speed / r min rated power / kW output speed / r min power loss / kW increase rate ratio 3.2 actual operating parameters for the calculation and comparison, now a factory The actual operating parameters of the air compressor unit in May 2001 are listed in Table 4. Compared with Table 1, it can be seen that the operating flow is reduced and the outlet pressure is low, which indicates that the compressor design capability is low.
Air compressor actual operating parameter name 1st paragraph 2nd paragraph 3rd paragraph 4th stage inlet pressure p inlet temperature t outlet pressure p outlet temperature t inlet volume flow q outlet volume flow q mass flow q Note: a local atmospheric pressure of a factory is 0 089M Pa, three cooler pressure losses are not pumped before the inlet of the fourth section of a plant.
The standard air density (molecular weight 28.4) density is 1. 2671kg / m. It should be noted that the standard volume flow parameters in the measurement parameters are obviously wrong. Because there are internal leakage and external leakage in the compressor, a small amount of water is separated after the intermediate cooling, so the standard volume flow rate of the compressor outlet is necessarily smaller than the inlet standard volume flow. When calculating, we take the import standard volume flow of 35500Nm as the basis for mass flow calculation.
3. 3 main geometric parameters (see Table 5) Large chemical fertilizer 101J air compressor capacity accounting and analysis Air compressor main geometric parameters cylinder low pressure cylinder (4C K high pressure cylinder (7C K segment inlet flange line inner diameter D measured) Mm outlet flange line inner diameter D measured mm level impeller inlet diameter impeller inlet outer diameter impeller blade inlet disk side diameter impeller blade inlet wheel cover side diameter D impeller blade inlet diameter D impeller blade inlet width b impeller blade inlet blade angle U impeller blade Number of imported blades Z / piece Impeller blade inlet thickness W Impeller blade inlet edge angle V / (°) Wheel cover sealing clearance s / mm Wheel cover sealing diameter D wheel cover sealing teeth number z / Impeller blade outlet diameter D Impeller blade outlet width impeller Blade exit blade angle U impeller blade exit blade number / piece impeller blade exit thickness W bladeless diffuser inlet diameter D bladeless diffuser inlet width b bladeless diffuser outlet diameter D bladeless diffuser outlet width b reflow Inlet diameter D reflow inlet width b reflow inlet vane angle U reflow inlet vane number Z / piece reflow blade inlet thickness W reflow outlet diameter D reflow outlet width b reflow outlet Blade angle U recirculator outlet blade number / piece reflow blade blade exit thickness W 3. 4 Multivariable efficiency calculation Multivariable efficiency is one of the most important parameters in the centrifugal compressor characteristic parameters, and its numerical value reflects both centrifugal compression The level of machine design directly determines the actual energy consumption of the centrifugal compressor [2]. In the specific calculation, we use the computer-aided design and analysis of centrifugal compressor developed by our institute to calculate the variable efficiency in large software packages. The calculation program is carried out. From the results of multivariate efficiency calculation, the design of the first stage of the design parameters is unreasonable (the efficiency is too high, the efficiency of the semi-open impeller and the binary closed impeller of the early design will not be very high. The efficiency is also high. There is a large error in the measured value of the second segment of the operating parameters (the third segment also has an error).
3. 5 Performance parameters Calculation performance parameters mainly refer to flow rate, pressure ratio (or exhaust pressure), efficiency, power, energy head, temperature rise, etc., which reflect the performance of the centrifugal compressor. The calculation of performance parameters is carried out by computer-aided design and analysis of centrifugal compressors. The performance parameters of the large-scale software package are calculated. 7 The design conditions of 101 J air compressor and the performance of a factory operating 101 J air compressor are listed. Parameter calculation result name 1st paragraph 2nd paragraph 3rd paragraph 4th paragraph entropy index k molecular weight_compression factor z inlet pressure p inlet temperature t outlet pressure p outlet temperature mass flow pressure ratio X variable compression work variable efficiency Z Power N Note: The total internal power is 6406. 32kW, and the average multi-variable efficiency of the whole machine is 77.
101 J air compressor operating conditions performance parameter calculation result name 1st paragraph 2nd paragraph 3rd paragraph 4th paragraph entropy index k molecular weight_compression factor z inlet pressure p inlet temperature t outlet pressure p outlet temperature t mass flow q volume The flow rate q pressure ratio X multi-variable compression work multi-variable efficiency Z internal power N Note: total internal power 6203. 24kW, the average multi-variable efficiency of the whole machine is 76. 9392.
The performance parameters calculated under the conditions. From the operating pressure ratio data, the second stage pressure ratio is high, and the third stage pressure ratio is low, and it also shows that the high pressure cylinder (especially the third stage) has a low design capability. From the operating temperature point of view, the second stage outlet temperature is high, and the third stage outlet temperature is low (and the inlet temperature is high).
3. 6 performance conversion Because the operating conditions (import pressure, inlet temperature, speed, etc.) of a certain plant are obviously different from the design conditions of the Lambton plant in Canada, in order to clarify the actual working capacity of the 101J air compressor, it is necessary to The plant operation data is converted into data under design conditions. To this end, we use the centrifugal compressor computer-aided design and analysis and calculation of the variable operating conditions performance conversion program in large software packages for performance conversion (see Table 8) Table 8 air compressor performance conversion results name paragraph 1 paragraph 2 3rd paragraph 4th inlet pressure p inlet temperature t outlet pressure outlet temperature mass flow rate power variable efficiency Z pressure ratio X Note: total internal power? N Obviously, compared with the design data of Table 1, the first and second stages of the converted mass flow are higher than the design flow, and the third and fourth stages are lower than the design flow. The mass flow rate in the third paragraph is much lower, which indicates that the design flow in the third paragraph is low, and the third paragraph is the bottleneck restricting the flow.
It is emphasized here that there is an error in the conversion result due to the error in the measurement result of the operation data.
3. 7 Pneumatic recalculation Pneumatic recalculation is based on the geometric parameters of the compressor air flow channel to calculate the aerodynamic thermal parameters and the performance parameters of the compressor flow path. The specific calculation uses the computer-aided design and analysis of the centrifugal compressor to calculate the pneumatic recalculation program (efficiency method) in the large software package. Tables 9 and 10 respectively list the main results of the pneumatic recalculation under the design conditions and operating conditions. In view of the deviation between the design data and the operation data, the calculation and analysis of the capacity of the large fertilizer 101J air compressor is based on the calculation, operation, experience and other comprehensive considerations. In addition, there are errors in the geometric data of the survey (for example, the sixth part of the theoretical design) 7 should be the same, the 9th and 10th grades should be the same, but the measured results are different. It will inevitably lead to some deviation in the calculation results.
From the calculation results under the design conditions, the outlet pressure and outlet temperature of the first and second sections are almost the same as the design values. The outlet pressure and outlet temperature of the third and fourth sections are lower than the design value, indicating the high pressure cylinder. The design ability (gas volume, pressure ratio) is low and the power in the third and fourth sections is low, resulting in low internal power calculation, indicating that the high-pressure cylinder design is low in function (the geometric parameters are problematic).
From the calculation results under operating conditions, the outlet pressure and outlet temperature of the first stage are almost the same as the measured values. The second stage outlet pressure and outlet temperature are lower than the measured value. The third stage outlet pressure is low and the outlet temperature is high. The outlet pressure and outlet temperature of the 4 sections are lower than the measured value, indicating that the design capacity of the low pressure cylinder is sufficient, the design and measurement deviation of the high pressure cylinder geometry parameters, and the outlet pressure and outlet temperature of the second and third sections are also large. The measurement error, that is, the second section of the outlet pressure and the outlet temperature measurement value is too high, and the third section of the outlet pressure and the outlet temperature measurement value are low.
In addition, from the perspective of design optimization, the pneumatic recalculation results also indicate that the 101J air compressor has the following design defects and deficiencies: (1) The impeller inlet airflow velocity c is not designed according to the principle of decreasing step by step, of which 2, 4, 6, 11 grade c is high (the cross-sectional area of ​​the impeller inlet airflow passage is too small, which affects the impeller flow capacity) (2) Impeller blade inlet angle of attack i (3) Impeller blade inlet installation angle U is not designed according to the optimal angle of 30°～35° (4) Impeller blade inlet relative width b is not (5) Impeller diffusing degree W is large at the 2nd and 5th stages (6) Flow coefficient h is too large, and the 3rd, 6th, and the values ​​are not suitable (7) ) Diffuser width b design is not suitable (3rd, 4th, 6th, according to design is not optimal) (8) Curved inlet and outlet width ratio b is too large (9) Reflower blade inlet angle of attack i (10) 5th The stage outlet b width design is too small. The outlet diameter D is unreasonable. (12) The sixth and seventh, the ninth and the tenth are respectively designed to be unreasonable. (13) The first multivariate efficiency value High (14) The pressure ratio distribution of each section is unreasonable (not allocated according to the optimal pressure ratio).
3. 8 performance prediction is different from pneumatic recalculation. The performance prediction is calculated by the flow path loss method. The aerodynamic thermal parameters on the characteristic sections of the compressor flow passage are calculated by giving all the geometric parameters of the compressor flow path, and the compression is estimated. Machine operating conditions characteristics and performance curves. Table 101J Air compressor design performance prediction result name 1st paragraph 2nd paragraph 3rd paragraph 4th stage inlet pressure inlet temperature outlet pressure outlet temperature t speed mass flow q variable efficiency Z pressure ratio X internal power N Note: total The internal power is 5823. 86kW.
101J air compressor operating conditions performance prediction results name 1st paragraph 2nd paragraph 3rd paragraph 4th stage inlet pressure p inlet temperature t outlet pressure p outlet temperature t mass flow q variable efficiency Z pressure ratio X internal power Note: total The internal power is 5865. 75kW.
11. Table 12 lists the main results of performance prediction under design conditions and operating conditions. Airflow obstruction occurred at the 5th, 6th, and 9th stages of the high-pressure cylinder during the calculation, which proved that their design flow was low. Obviously, the performance prediction results are very close to the aerodynamic reset results.
The above calculation results show that the design capability of the 101J air compressor high pressure cylinder is insufficient, and the third section of the flow is the bottleneck.
It must be pointed out that due to the large measurement error of the geometric parameters and operating parameters of the 101J air compressor of a certain plant, the calculation and analysis work has increased the difficulty and the accuracy of the calculation results.
Air compressor refueling calculation According to the actual air pumping capacity under the existing operating conditions of a factory, the capacity of 101 J air compressor can not meet the requirements of 1,000 tons of synthetic ammonia per day. There are three main reasons for this: First, the local atmospheric pressure of a factory is low and the temperature of the cooling water is high. The machine casing is severely deformed, and there is a large leakage. The third is that the machine is designed and manufactured earlier, and the design capability is insufficient. In order to increase the production of synthetic ammonia, a plant intends to introduce a 5,000 Nm air from a chemical fertilizer into the inlet of the high-pressure cylinder of the 101J air compressor (3 sections of imports). Let's analyze the problems of whether it can be added, how much can be added, and the effect on the low pressure cylinder of the 101J air compressor.
4. 1 Calculate the amount of gas filling to the high pressure cylinder. If the high pressure cylinder is not the bottleneck of the flow design, the high pressure cylinder can theoretically be refilled, and the gas filling amount should be the difference between the maximum air volume of the high pressure cylinder and the existing air volume. After calculation and analysis, the high-pressure cylinder has a gas filling capacity of about 500 Nm under the current operating conditions. The following two aspects are considered: one is the conversion of the existing operating capacity to the design capability, and the second is the airflow that occurs when the refueling amount is increasing. Blocking and performance analysis. Since there are large measurement errors in both the operating parameters and the geometric parameters, the gas filling amount is the maximum gas filling amount calculated under the current conditions.
4. 2 Axial force calculation Adding gas to the high pressure cylinder is equivalent to increasing the blockage of the low pressure cylinder. The operating point of the low pressure cylinder moves along the performance curve to the direction of small flow, that is, the exhaust flow of the low pressure cylinder is reduced, and the exhaust pressure is increased. Large, resulting in an increase in axial force. When calculating the axial force, the computer program-assisted design and analysis of the centrifugal compressor are used to calculate the axial force calculation program in the large software package. 5之间。 The design of the low-pressure cylinders, the high-pressure cylinders of the axial force were respectively increased under the operating conditions of the axial force of the cylinder increased by 1. 7N, 84. 5N, respectively, before the addition of gas increased by 5.2 and 31.
Because the amount of air is not large, the axial force of the low-pressure cylinder does not change much, from 27,342 N before refueling to 28,759. 7N after refueling, only increased by 5. 2. The axial force of the high-pressure cylinder after refueling increases greatly. The main reason is the error in the measurement of the geometric parameters of the high-pressure cylinder and the change of the inlet pressure and the inlet temperature after the gas filling.
5 Calculation results analysis After a series of calculations such as multivariate efficiency calculation, performance parameter calculation, performance conversion, pneumatic recalculation, performance prediction, axial force calculation, etc., the results show that: (1) There is an impeller inlet for the 101J air compressor design of a factory. The speed c is high (levels 2, 4, 6, and 11), the impeller inlet angle i is too large, and the impeller blade inlet design is unreasonable (the blade inlet angle, the blade inlet relative width b is not designed according to the optimal value), and the impeller is expanded. The pressure W is too large (levels 2 and 5), the flow coefficient h is too large (and the values ​​of the 3rd, 6th, and 8th stages are not suitable), the diffuser width b, and the curve exit width b are not optimal. Design, the inlet angle of the inlet of the return vane i is too large, the width of the outlet of the 5th stage returner is unreasonable. The design of the diameter D of the impeller blade is unreasonable, and the value of the first section is high, and the sixth, seventh and ninth, The 10th grades are designed to be unreasonable, and the pressure ratios of the sections are not distributed according to the principle of optimal pressure ratio distribution.
(2) The outlet pressure, outlet temperature and internal power of the two sections of the low-pressure cylinder are in accordance with the design values. The outlet pressure, outlet temperature and internal power of the two sections of the high-pressure cylinder are smaller than the design values, indicating the design capability of the high-pressure cylinder ( The amount of air pumping, pressure ratio, etc. is insufficient, and the third pumping volume is the bottleneck.
(3) There is a large error in the measurement of operating parameters. For example, the capacity calculation of the second largest fertilizer 101J air compressor and the outlet pressure and outlet temperature of the analysis section are both high, and the outlet pressure and outlet temperature of the third section are both low.
(4) There is a large error in the measurement of geometric parameters (especially high pressure cylinders).
(5) The three methods of performance conversion, pneumatic recalculation and performance prediction are used to calculate the air volume of the compressor, and the calculation results are basically the same.
6 Conclusions (1) The design capability of the high-pressure cylinder of the 101J air compressor of a chemical plant is insufficient, and there are many design defects and deficiencies in the design of the whole machine.
(2) The actual operation capacity of a chemical fertilizer 101J air compressor in a factory is insufficient, mainly caused by factors such as low atmospheric pressure, high cooling water temperature, leakage, and insufficient design capability.
(3) The design flow of the third section of a 101J air compressor in a factory is low, which is a bottleneck restricting the air volume of the compressor.
(4) The calculation of the existing conditions shows that the gas filling amount to the third stage (high pressure cylinder inlet) is about 500 Nm / h, and this gas has little effect on the performance and axial force of the low pressure cylinder (sections 1 and 2).
(5) There is a large measurement error in the geometric parameters and operating parameters of a 101 J air compressor in a factory.
7 Recommendations (1) Since the amount of gas that can be added is too small, it is recommended not to construct (from a fertilizer auxiliary pipeline to a second fertilizer 101J air compressor).
(2) It is recommended to improve the cooling effect of each intercooler of 101J air compressor (such as cleaning, increasing heat exchange area, adopting new high efficiency heat exchanger, etc.).
(3) It is recommended to carry out the energy expansion technical transformation of the 101 J air compressor to significantly increase the ammonia production and reduce the energy consumption of the unit.
1 Chen Zonghua. Ningxia Chemical Plant II Fertilizer 101J air compressor capacity accounting report.
Chemical Machinery Research Institute, Ministry of Chemical Industry, 2001.
2 Xu Zhong. Principle of centrifugal compressors. Beijing: Mechanical Industry Press, 1990.
3 Chen Zonghua and so on. Computer aided design system for centrifugal compressors. Chemical machine 4 Chen Zonghua and so on. Capacity calculation and software development of centrifugal compressors. Thermal recovery of piston compressors Cai Kexia Bao Xiaojun Wang Yi (Department of Mechanical Engineering, Ningxia University) (Northwest Bearing Co., Ltd.) In the process of actually using piston compressors, this situation is often encountered: When the compressor of the working condition (the structure size has been determined) has a large change in the working condition, the interstage pressure and temperature of the compressor, as well as the power and displacement of the compressor, will be changed, in order to grasp the change. To the extent, it is necessary to perform the calculation of the thermodynamic calculation. The first is to calculate the pressure between the stages. In addition, production often encounters the use of some off-the-shelf compressors to compress non-originated gases or non-rated conditions, and should also be recalculated. For another example, in the process of designing the thermal calculation of the compressor, the rounding cylinder diameter also needs to be recalculated. Cai Kexia, female, born in February 1967, associate professor. Yinchuan City, 750021.
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