Henan Chemical Analysis of the Causes of Insufficient Air Volume of B Set of Centrifugal Air Compressors and Treatment Cao Qingliang (Henan Gas (Group) Co., Ltd. Yima Gasification Plant, Henan Yima 472300)-2 (2951) Centrifugal Air Compressor In the operation, the problem of insufficient air pumping capacity is obvious. The effect of repairing the transformation is very obvious. The compressor air pumping capacity is greatly improved, and the technical indicators meet the original design requirements, which meets the load requirements of the plant's product structure adjustment for the air separation unit.

1 Project Background-2 (2951) centrifugal air compressor, designed and produced by Shenyang Blower Group, adopts a new structure of single-axis isothermal type, the compression process is close to isothermal compression, so its efficiency is high, the compressor is single cylinder, isothermal, Four-stage and five-stage centrifugal compressors, horizontally split cylinders, round cast outer diaphragms and square welded inner partitions. There are five stages of compression and four internal intermediate coolings. The compressor prime mover is condensing. Turbine, the unit is lubricated by centralized oil supply, and the air is directly sucked from the atmosphere. After compression, the pressure is increased to 0.56 MPa (design pressure), and the pre-cooling system and purification system enter the fractionation tower. Since it was put into operation in 2001, the mechanical operation of the unit has been relatively stable. After 2006, with the increase of the production load of the plant, it was found that the operating conditions of the compressor deviated greatly from the design conditions. The design flow rate is: 38500Nm3/h, the actual operating flow minimum is 30587Nm3/h in summer, the flow rate is about 80% of the design flow rate, the design outlet temperature is °112°C, and the actual outlet temperature is 137°C, which is quite different from the design. Because of the product structure adjustment of the plant, there is a high requirement for the load of the air separation unit, and to achieve full load, the compressor needs to be repaired and modified.

2 Analysis of the reasons for insufficient air pumping 2.1 Factors affecting the amount of air blown by the compressor 1 The suction filter of the compressor suction system is blocked or the resistance increases, causing the suction pressure of the compressor to decrease. When the outlet pressure is constant, the compressor pressure ratio is increased and the power consumption is reduced. According to the performance curve of the compressor, when the pressure ratio is increased, the amount of pumping is reduced.

2 Compressor exhaust system blockage, increased resistance or valve failure, causing air compressor exhaust pressure to rise. Under the condition that the suction pressure is constant, the pressure ratio increases the power consumption, resulting in a decrease in the amount of air pumping.

3 Compressor intercooler is blocked or the resistance is increased, causing a decrease in the amount of air blow. Blocking at different positions, the situation is different: if the gas side resistance of the cooler increases, it only increases the internal resistance of the machine, so that the efficiency of the compressor decreases, and the amount of air blows decreases; if it is the water side resistance booster, the amount of circulating cooling water Decrease, so that the gas does not cool well, the temperature rises, affecting the lower stage suction, and reducing the pumping amount of the compressor.

4 The seal is not good and causes gas leakage. Including: internal leakage, that is, helium between stages. The compressed gas is poured back and the second compression is performed. It will affect the working conditions at all levels, so that the low pressure stage pressure ratio will increase, the high pressure stage pressure ratio will decrease, the whole compressor will deviate from the design working condition, and the air pumping capacity will decrease; the external leakage, that is, the air leakage from the shaft end seal to the outside of the casing . Although the amount of inhalation does not change, the portion of the compressed gas that leaks out naturally causes a decrease in the amount of air pumping.

5 cooler leaks. If the first stage leaks, because the water side pressure is higher than the gas side pressure, the cooling water will enter the gas side passage and be further entrained by the air flow into the impeller and the diffuser. After a certain period of time, scaling and clogging are caused, and the air flow is reduced. If the second and third stage coolers leak, because the gas side pressure is higher than the water side, the compressed air will leak into the cooling water and run away, so that the amount of gas is reduced.

6 The prime mover's speed decreases and the amount of air pumping decreases.

7 In the five-stage compression, the inhalation temperature rises and the gas density decreases, which also causes the inspiratory volume to decrease.

-), male, assistant engineer, engaged in equipment management of coal chemical enterprises, telephone Henan Chemical 8 compressor intercooler cooling effect is poor, resulting in reduced air volume. The air compressor intercooler is a plate structure, the pipe is circulated water, and the air is cooled between the pipes, and the heat is exchanged through the fluid inside and outside the pipe to cool.

The reasons that affect the cooling effect of the compressor intercooler are: insufficient cooling water. The heat of the air is not enough to be carried away by the cooling water, causing the lower inhalation temperature to rise and the gas density to decrease, eventually resulting in a decrease in the amount of gas. Therefore, the water supply pressure of the cooling water should be closely monitored during operation to control the water supply. The process usually controls the cooling water pressure to be greater than 0.4 MPa. The circulating cooling water temperature is too high. The high water temperature reduces the temperature difference between water and gas, and the heat transfer and cooling effect is reduced. Even if the amount of circulating cooling water is not reduced, the temperature of the gas is still high after cooling.

There is much scale in the cooling water pipe or is blocked by sediment and organic matter, and water is analyzed after cooling on the gas side of the cooler. It cannot be discharged in time, which will affect the heat transfer area or heat transfer conditions and affect the cooling effect. The cooling effect is not good, so the temperature entering the lower stage is increased, affecting the performance curve of the lower stage, and reducing the outlet pressure and flow rate. In addition, when the amount of inhalation of the lower stage is reduced, the amount of gas that is pushed out of the front stage cannot all enter the lower stage, and it is easy to cause the work of the preceding stage to enter the surge zone where surge occurs. You can check the upper water temperature and water pressure and adjust it.

9 The effect of the compressor seal on the amount of air pumping. In order to reduce the leakage of air between the compressor rotor and the fixed element, a seal must be provided. The compressor seals can be divided into four types according to their positions: wheel cover seals, interstage seals, balance disc seals, and (front and rear) shaft seals. The sealed form uses a comb-tooth labyrinth seal.

The working principle of the labyrinth seal: When the airflow passes through the gap of the comb-shaped seal, the airflow is approximately subjected to an ideal throttling process, the pressure and temperature are decreased, and the speed is increased. When the airflow enters the cavity between the sealing sheets from the gap, the airflow forms a strong vortex due to the sudden enlargement of the cross-sectional area, so that the speed is almost completely disappeared, the temperature returns to the value before the sealing sheet, and the pressure cannot be restored. , keep the pressure equal to the pressure through the throttle gap. The air flow passes through each of the subsequent seal gaps and cavities, and the change in air flow repeats the above process. The difference is that as the mass of the airflow gradually increases, the airflow velocity and pressure drop across the gap become larger. It can be seen that when the airflow is sealed through the entire labyrinth, the pressure is gradually decreased, and finally it is close to the back pressure, thereby functioning as a seal.

The effect of the seal leakage of the centrifugal compressor on the pumping performance of the compressor. Leakage between the wheel cover seal and the interstage seal is an internal leak. Severe internal leakage will increase the energy loss of the compressor, the efficiency of the stage and the efficiency of the compressor will decrease, and the amount of air pumping will decrease. However, the mechanism of influence of the two is also different: the leakage of the wheel cover seal is to return the compressed gas to the impeller, and then the second stage of compression, so that the total power consumption of the stage is mainly increased; the leakage of the interstage seal is The helium gas between the stages will increase the pressure ratio of the low pressure stage, and the pressure ratio of the high pressure stage will decrease, resulting in a decrease in the air volume. The severe leakage of the balance disc seal has little effect on the performance of the compressor, but it is of great concern to the safe operation of the centrifugal compressor.

The leakage of the shaft seal is an external leak. External leakage means that the gas leaks from the seal to the outside of the casing. It goes without saying that a serious external leakage will directly cause a reduction in the amount of air pumping.

10 The effect of impurities in the air on the pumping capacity of the compressor. In addition to oxygen and nitrogen in the air, there are small amounts of water vapor, carbon dioxide, acetylene and other hydrocarbons, as well as a small amount of solid impurities such as dust.

The water vapor content per cubic meter of air is 4 to 40 g/m3 (varies by region and climate), the carbon dioxide content is 0.6 to 0.9 g/m3, and the acetylene content is 0.01 to 0.1 cm3/m3. The content of impurities is generally 0.005 ~ 0.15g / m3. Although the content of these impurities in the air per cubic meter is not large, due to the large amount of air per hour of air separation equipment, the total amount of compressors brought into the hourly Still considerable. Taking the 6000m3/h oxygen generator as an example, the amount of water that is brought into the air compressor with air per hour is about 11, and a lot of water will be deposited after passing through the air cooler and the nitrogen water precooler. Even so, the amount of water that is brought into the air separation plant per hour is 200 kg. The dust that is inhaled with the air every day amounts to 4.8 to 9.6 kg, or even more, and these impurities have an effect on the air volume of the air compressor.

2.2 Insufficient air blow-up of the compressor Main cause 1 Due to the long running time of the compressor, the casing and the baffle are deformed. In particular, the baffle is deformed greatly, and the gap between the upper and lower baffles is large. The circulation flow loss is very large. From the analysis of the disassembly and unloading of the compressor, the airflow scouring marks between the upper and lower partitions can confirm the cross-flow between the compressor separator stages, and the leakage at the gap between the upper and lower partitions is an internal leakage. , the compressor energy loss will increase, the stage efficiency and compressor efficiency will decrease, and the air pumping capacity will decrease. Leakage between the baffles causes the compressed gas to return to the impeller, and then a second compression, resulting in an increase in the total power consumption of the stage, an increase in the low pressure stage pressure ratio, and a decrease in the high pressure stage pressure ratio.

2 There is internal air leakage in the air compressor interstage cooler. The cooling effect is not good. Some of the gas is not cooled by the interstage cooler. The heat of the compressed air is not enough to be taken away by the cooling water, causing the lower inhalation temperature to rise. The density is reduced, which ultimately results in a reduction in compressor pumping.

3 Because the compressed air of the compressor contains a certain amount of moisture, and has a certain humidity, the compressed air flows under the condition of high pressure and low temperature after flowing out of the intercooler, under which the gaseous water in the air easily condenses into liquid water. The liquid water is collected by a stainless steel water-repellent sheet placed in the compressor of the Henan chemical compressor, and then discharged out of the compressor through the interstage steam trap. Due to the damage of the interstage cooler fins, the hydrophobic effect is poor, causing some moisture to condense on the inner wall of the compressor runner. In the presence of moisture and oxygen, the inner wall of the compressor runner is prone to oxidative corrosion and iron oxide powder. Long-term accumulation, there will be corrosion and peeling of the inner wall of the compressor. The falling rust is trapped in the air flow, which will block the air passage on the air side of the intercooler, and will also adhere to the inner surface of the interstage cooler gas side, reducing The gas side air heat exchange efficiency, the end result is to reduce the compressor pumping capacity.

There are obstructions and valve failures in the 4 gas pipelines, the pipelines of the equipment system are blocked, the resistance is increased, or the leakage valve in the bypass valve is not open, causing the exhaust pressure of the air compressor to rise. Under the condition that the suction pressure is constant, the pressure ratio increases, causing the compressor to reduce the amount of air.

In order to ensure that the air separation plant after the product structure adjustment of the plant can meet the requirements of the subsequent system, the analysis of the cause of insufficient air pumping capacity of the sic75-n centrifugal air compressor of the b air separation unit is carried out.

3Rehabilitation measures According to the lack of air volume check and analysis of the compressor, the compressor is repaired and modified. The specific implementation is as follows: 1 The deformation of the casing and the partition is used, especially the deformation of the diaphragm is large, and the gap between the upper and lower partitions Large, tightly sealed, inter-stage gas caused a large loss of internal circulation flow, internal leakage at the gap between the upper and lower partitions, the compressor energy loss increased, the stage efficiency and compressor efficiency decreased, and the air volume decreased. Leakage between the baffles causes the compressed gas to return to the impeller, and then a second compression, resulting in an increase in the total power consumption of the stage, an increase in the low pressure stage pressure ratio, and a decrease in the high pressure stage pressure ratio.

The following modifications are made to the deformation of the partition and the casing: a. Disassemble the compressor, take out the partition, and measure the deformation of the upper and lower casings and the gantry bed on the rotor; b. Re-repair the casing according to the deformation of the casing ; c, detecting the deformation of the bearing area of ​​the casing; d, according to the size of the machined casing, re-manufacturing and manufacturing new partitions and gas seals (to ensure that the original design dimensions of the gas seals remain unchanged, so that the previous gas seal spare parts can continue to be used) .

2 After the processing, the casing and the partition, the gas seal and the rotor are reassembled. The repair is as follows: a. The sealing gap value after the assembly is controlled within the technical requirements; b. The gap value and the axial dimension value of each part of the rotor and the casing are controlled.

3 For the interstage cooler, the hydrophobic sheet has poor hydrophobic effect, which causes some moisture to condense on the inner wall of the compressor flow passage. In the presence of moisture and oxygen, the inner wall of the compressor runner is prone to oxidative corrosion and iron oxide powder is formed. Long-term accumulation, there will be corrosion and peeling of the inner wall of the compressor. The falling rust is trapped in the air flow, which will block the air passage on the air side of the intercooler and also adhere to the inner surface of the gas side of the interstage cooler. Reduce the heat exchange efficiency of the air side air, repair the hydrophobic sheet damaged by the interstage cooler to improve the hydrophobic condition, replace the 16 stainless steel steam traps of the cooler to ensure the hydrophobic effect after the cooling gas between the stages is cooled.

4 For the internal leakage of the interstage cooler and the shell with the sealing surface, some of the gas is not cooled by the interstage cooler, and the lower suction temperature is increased, the gas density is reduced, and the compressor pumping amount is reduced. The original cooler seal strip structure was designed and modified, and the original rubber seal strip was changed into a flexible titanium alloy seal strip, which eliminated the defect of air leakage between the interstage cooler and the housing.

5 Flush the pipe on the pipeline, check the condition of the valve, replace the bypass valve of the internal leakage, repair the defect of the outlet valve, and eliminate the problem on the pipeline.

6 The rotor is dynamically balanced to eliminate the vibration caused by the rotor imbalance and the effect on the gas seal.

4 After the repair, the effect of the compressor repair and transformation is very obvious, the air pumping capacity is greatly improved, reaching 38110Nm3/h, about 99% of the design flow rate, the exhaust temperature of the stage is reduced, and the exhaust temperature of the final stage is lowered. 110 ° C, less than the designed 112 ° C, the compressor efficiency is improved, the shaft power is reduced under the condition of increased air pumping, saving energy consumption, various technical indicators meet the original design requirements, and meet the product structure adjustment of the plant. The load requirements of the air separation unit.

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