62 Compressor Questions: Read and Become an Expert!

Compressor is a passive fluid machinery that boosts low - pressure gas to high - pressure gas. Today, the editor has collected 62 questions about compressors. Let's see how many you can answer.

Proportional adjustment refers to the adjustment that keeps the pressure ratio unchanged (such as anti - surge adjustment), or keeps the volume flow percentage of two gas media unchanged.
20. What is a pipeline network? What are its components?
A pipeline network is a pipeline system through which a centrifugal compressor transports gas media. The pipeline located before the compressor inlet is called the suction pipeline, and the pipeline located after the compressor outlet is called the discharge pipeline. The sum of the suction and discharge pipelines, a complete pipeline system, is usually called the pipeline network.
A pipeline network generally consists of four elements: pipelines, pipe fittings, valves, and equipment.
21. What are the hazards of axial force?
For a high - speed running rotor, there is always an axial force acting from the high - pressure end to the low - pressure end.
Under the action of the axial force, the rotor will generate an axial displacement along the direction of the axial force. The axial displacement of the rotor will cause relative sliding between the journal and the bearing bush.
Therefore, it is possible to scratch the journal or the bearing bush. More seriously, due to the displacement of the rotor, friction, collision, and even mechanical damage between the rotor components and the stator components may occur. Since the axial force of the rotor may cause friction, wear, collision, and even damage to the machine, effective measures should be taken to balance it to improve the operational reliability of the unit.
22.

What are the methods of balancing axial force?
The balance of axial force is an important issue to be considered in the design of multi - stage centrifugal compressors. Currently, the following two methods are generally used:
? Opposed arrangement of impellers (the high - pressure side and the low - pressure side of the impellers are arranged back - to - back).
The axial force generated by a single - stage impeller is directed towards the impeller inlet, that is, from the high - pressure side to the low - pressure side. If multi - stage impellers are arranged in sequence, the total axial force of the rotor is the sum of the axial forces of each stage of impellers. Obviously, such an arrangement will result in a large axial force on the rotor. If multi - stage impellers are arranged in an opposed manner, the impellers with opposite inlets will generate an axial force in the opposite direction, which can balance each other. Therefore, the opposed arrangement is the most commonly used method for balancing the axial force of multi - stage centrifugal compressors.
? Installation of a balance disc. The balance disc is a commonly used axial - force - balancing device for multi - stage centrifugal compressors. The balance disc is generally installed on the high - pressure side. A labyrinth seal is provided between its outer edge and the cylinder, so that a certain pressure difference is maintained between the high - pressure side and the low - pressure side connected to the compressor inlet. The axial force generated by this pressure difference is in the opposite direction to the axial force generated by the impeller, thus balancing the axial force generated by the impeller.
23. What is the purpose of balancing the axial force of the rotor?
The purpose of rotor balancing is mainly to reduce the axial thrust and relieve the load on the thrust bearing. Generally, 70% of the axial force is eliminated by the balance disc, and the remaining 30% is borne by the thrust bearing. Production practice has proved that retaining a certain amount of axial force is an effective measure to improve the stable operation of the rotor.
24. What are the reasons for the increase in the temperature of the thrust bearing bush?
Unreasonable structural design, the bearing area of the thrust bearing bush is small, and the load per unit area exceeds the standard.
The inter - stage seal fails, causing the gas at the outlet of the next - stage impeller to leak to the previous stage, increasing the pressure difference on both sides of the impeller and forming a large thrust.
The balance pipe is blocked, and the pressure in the negative - pressure chamber of the balance disc cannot be relieved, so the function of the balance disc cannot be exerted normally.
The seal of the balance disc fails, the pressure in the working chamber cannot be maintained normally, the balancing ability decreases, and the decreased part of the load is transmitted to the thrust bearing bush, causing the thrust bearing bush to operate over - loaded.
The throttle hole diameter of the oil inlet of the thrust bearing is small, the flow rate of the cooling oil is insufficient, and the heat generated by friction cannot be completely carried away.
The lubricating oil contains water or other impurities, and the thrust bearing bush cannot form a complete liquid lubrication.
The oil inlet temperature of the bearing is too high, and the working environment of the thrust bearing bush is poor.
25. How to deal with the excessive temperature of the thrust bearing bush?
Check and verify the pressure on the thrust bearing bush, appropriately expand the bearing area of the thrust bearing bush, so that the load borne by the thrust is within the standard range.
Disassemble and inspect the inter - stage seal, and replace the damaged inter - stage seal parts.
Check the balance pipe, remove the blockage, so that the pressure in the negative - pressure chamber of the balance disc can be relieved in a timely manner, ensuring the exertion of the balancing ability of the balance disc.
Replace the sealing strip of the balance disc, improve the sealing performance of the balance disc, maintain the pressure in the working chamber of the balance disc, and reasonably balance the axial thrust.
Enlarge the diameter of the throttle hole of the bearing oil inlet, increase the amount of lubricating oil, so that the heat generated by friction can be carried away in a timely manner.
Replace with new qualified lubricating oil to maintain the lubricating performance of the lubricating oil.
Open the inlet and return water valves of the cooler wider, increase the amount of cooling water, and reduce the oil supply temperature.
26. What should the personnel of the combined compressor do when the synthesis system is severely over - pressured?
Inform the on - site personnel of the synthesis unit to open PV2001 for pressure relief.
Inform the on - site inspection personnel of the combined compressor to open the manual vent at the outlet of the second stage of the compressor for pressure relief (in case of emergency), and pay attention to the supervision of the operators and take anti - poisoning measures.
27. How does the combined compressor circulate for the synthesis system?
Before the start - up of the synthesis system, nitrogen needs to be filled and the temperature needs to be raised in the synthesis system under a certain pressure. Therefore, it is necessary to start the syngas compressor to establish a cycle for the synthesis system.
Start the steam turbine of the syngas compressor according to the normal start - up procedure, and operate it at no - load until it reaches the normal rotational speed.
Maintain a certain amount of gas return from the outlet of the anti - surge cooler to the inlet of the first stage. The return flow should not be too large, and pay attention not to over - heat.
Control the gas volume and pressure entering the synthesis system with the anti - surge valve of the circulation section, and maintain the temperature of the synthesis tower.
28. When the synthesis system needs to cut off the gas urgently (the compressor does not stop), how does the combined compressor operate?
The combined compressor needs to perform an emergency gas - cutting operation:
Report the emergency gas - cutting of the combined compressor to the dispatching room, switch the primary seal to medium - pressure nitrogen, vent the gas at the inlet of the combined compressor (outlet of the purification unit), and pay attention to maintaining the pressure.
Open the anti - surge valve of the fresh section to reduce the amount of fresh gas, and open the anti - surge valve of the circulation section to reduce the amount of circulating gas.
Close XV2683, close XV2681 and XV2682.
Open the discharge valve PV2620 at the outlet of the second stage of the compressor and relieve the body pressure at a rate of ≤ 0.15 Mpa/min. The syngas compressor operates at no - load; the synthesis system is depressurized.
After the accident handling of the synthesis system is completed, fill nitrogen into the synthesis system from the inlet of the combined compressor for replacement, carry out circulation, and maintain the temperature and pressure of the synthesis system.
29. How to increase the amount of fresh gas?
Generally, the inlet valve XV2683 is in a fully open state. Controlling the amount of fresh gas can only be achieved through the anti - surge valve of the fresh section after the anti - surge cooler. By closing the first - stage anti - surge valve to reduce the amount of return gas, the purpose of increasing the amount of fresh gas can be achieved.
30. How to control the space velocity through the compressor?
Controlling the space velocity with the syngas compressor is achieved by increasing or decreasing the circulation volume, so that the space velocity can be changed. Therefore, when the amount of fresh gas is constant, increasing the circulation volume of the synthesis will correspondingly increase the space velocity. However, the increase in space velocity will have a certain impact on the methanol synthesis reaction.
31. How to control the synthesis circulation volume?
Restrict it through the throttling of the anti - surge valve of the circulation section.
32. What are the reasons why the synthesis circulation volume cannot be increased?
The amount of fresh gas is low. When the reaction is good, the volume shrinks and the pressure drops too fast, resulting in a low outlet pressure of the tower. At this time, it is necessary to increase the space velocity to control the synthesis reaction rate.
The vent volume (bleed gas volume) of the synthesis system is too large, and PV2001 is too large.
The opening of the anti - surge valve of the circulating gas is too large, resulting in a large amount of gas reflux.
33. What are the interlocks between the synthesis system and the combined compressor?
When the low - limit level of the steam drum is ≤ 10%, it is interlocked with the combined compressor, and XV2683 is closed to prevent the steam drum from running dry.

When the high - limit level of the methanol separator is ≥ 90%, it is interlocked with the combined compressor for trip protection. XV2681, XV2682, and XV2683 are closed to prevent liquid from entering the cylinder of the combined compressor and damaging the impeller.
When the high - limit hot - spot temperature of the synthesis tower is ≥ 275℃, it is interlocked with the combined compressor for trip.
34. How to deal with the excessive temperature of the synthesis circulating gas?
Observe whether the temperature of the circulating gas in the synthesis system rises. If it is higher than the standard, reduce the circulation volume or inform the dispatcher to increase the water pressure or lower the water temperature.
Observe whether the return water temperature of the anti - surge cooler rises. If it does, the large gas return volume causes poor cooling effect. At this time, the circulation volume should be increased.
35. During the start - up of the synthesis, how to alternately increase the amount of fresh gas and circulating gas?
During the start - up of the synthesis, due to the low gas temperature and the low hot - spot temperature of the catalyst, the synthesis reaction is restricted. At this time, the increase in volume should mainly focus on stabilizing the temperature of the catalyst bed. Therefore, before increasing the amount of fresh gas, the circulation volume should be increased first (generally, the circulation volume is 4 - 6 times that of the fresh gas volume), and then the amount of fresh gas is increased. The process of increasing the volume should be slow, and there should be a certain time interval (mainly depending on whether the hot - spot temperature of the catalyst can be maintained and shows an upward trend). After the gas volume is increased to a certain extent, the synthesis unit can be required to close the start - up steam slightly.
Close the anti - surge valve of the fresh section to increase the amount of fresh gas. Close the anti - surge valve of the circulation section to increase the circulation volume.
36. During the start - up and shutdown of the synthesis system, how to maintain the temperature and pressure with the compressor?
Fill nitrogen into the synthesis system from the inlet of the combined compressor for replacement and pressurization. The combined compressor and the synthesis system are put into circulation. Generally, the system venting is determined according to the pressure of the synthesis system. The space velocity is used to maintain the outlet temperature of the synthesis tower. The start - up steam is turned on to provide heat, and the synthesis system is circulated at low pressure and low speed to maintain the temperature.
37. During the start - up of the synthesis system, how to increase the pressure of the synthesis system? What is the pressure - increasing rate control?
The pressure increase of the synthesis system is mainly achieved by increasing the amount of fresh gas and the pressure of the circulating gas. Specifically, closing the anti - surge valve of the fresh section can increase the amount of fresh gas for synthesis; closing the anti - surge valve of the circulation section can control the synthesis pressure. During normal start - up, the pressure - increasing rate of the synthesis system is generally controlled at 0.4 MPa/min.
38. When the synthesis tower is heated up, how to control the heating - up rate of the synthesis tower with the combined compressor? What is the control index of the heating - up rate?
During heating - up, on the one hand, turn on the start - up steam to provide heat and drive the furnace water circulation to increase the temperature of the synthesis tower. On the other hand, start the combined compressor, use the gas - adding of the circulation section and the gas discharge of the syngas to carry out the gas circulation of the synthesis system, control the heat, and stabilize the heating - up range of the tower. Therefore, during the heating - up operation, the temperature rise of the tower is mainly adjusted by adjusting the circulation volume. The control index of the heating - up rate is 25℃/h.
39. How to adjust the anti - surge gas flow of the fresh section and the circulation section?
When the operating condition of the compressor is close to the surge condition, anti - surge adjustment should be carried out. Before adjustment, to prevent excessive fluctuations in the system gas volume, first judge and determine which section is close to the surge condition, and then appropriately open the anti - surge valve of that section to eliminate it. Pay attention to the fluctuation of the system gas volume (try to maintain the stability of the gas volume entering the tower), but do not open two anti - surge valves simultaneously to eliminate surge.
40. What are the reasons for liquid carry - over at the compressor inlet?
The process gas transported from the previous system has a high temperature, and the gas is not completely condensed. The gas transportation pipeline is too long, and after condensation in the pipeline, the gas contains liquid.
The temperature of the process system is high, and the components with a lower boiling point in the gas medium are condensed into liquid.
The separator level is too high, resulting in gas - liquid entrainment.
41. How to deal with liquid carry - over at the compressor inlet?
Contact the previous system to adjust the process operation.
Increase the liquid - discharging frequency of the separator appropriately in this system.
Lower the liquid level of the separator to prevent gas - liquid entrainment.
42. What are the reasons for the performance decline of the combined compressor unit?
The inter - stage seal of the compressor is severely damaged, the sealing performance is reduced, and the internal gas reflux increases.
The impeller is severely worn, the function of the rotor is reduced, and the gas medium cannot obtain sufficient kinetic energy.
The steam filter of the steam turbine is blocked, the steam flow is blocked, the flow rate is small, and the pressure difference is large, affecting the output power of the steam turbine and reducing the unit performance.
The vacuum degree is lower than the required standard, and the exhaust of the steam turbine is blocked.
The steam temperature and pressure parameters are lower than the operating indicators, the internal energy of the steam is low, and it cannot meet the production and operation requirements of the unit.
A surge condition occurs.
43. What are the main performance parameters of a centrifugal compressor?
The main performance parameters of a centrifugal compressor include flow rate, outlet pressure or compression ratio, power, efficiency, rotational speed, energy head, etc.
The main performance parameters of the equipment are basic data characterizing the structural characteristics, working capacity, working environment, etc. of the equipment, and are important guiding materials for users to purchase equipment and make plans.
44. What is the meaning of efficiency?
Efficiency characterizes the utilization degree of the energy transferred to the gas by the centrifugal compressor. The higher the utilization degree, the higher the efficiency of the compressor.
Since there are three processes of gas compression: polytropic compression, adiabatic compression, and isothermal compression, the efficiency of the compressor is also divided into polytropic efficiency, adiabatic efficiency, and isothermal efficiency.
45. What is the meaning of compression ratio?
The compression ratio we mentioned refers to the ratio of the pressure of the gas discharged from the compressor to the inlet pressure. Therefore, it is sometimes also called the pressure ratio.
46. What parts does the lubricating oil system consist of?
The lubricating oil system consists of the lubricating oil station, high - level oil tank, intermediate connecting pipelines, control valves, and detection instruments.
The lubricating oil station consists of an oil tank, oil pump, oil cooler, oil filter, pressure regulating valve, various detection instruments, as well as oil pipelines and valves.
47. What is the function of the high - level oil tank?
The high - level oil tank is one of the safety protection measures for the unit. During normal operation of the unit, the lubricating oil enters from the bottom and is discharged from the top directly back to the oil tank. In case of a power failure and shutdown accident, if the auxiliary oil pump cannot start to supply oil in time, the lubricating oil in the high - level oil tank will flow through each lubrication point along the oil inlet pipeline and then return to the oil tank, ensuring the need for lubricating oil during the coast - down process of the unit.
48. What are the safety protection measures for the combined compressor unit?
High - level oil tank, safety valve, accumulator, quick - closing valve, other interlock devices
49. What is the sealing principle of the labyrinth steam seal?
It converts potential energy (pressure) into kinetic energy (flow velocity) and then dissipates the kinetic energy in the form of eddy currents.
50. What is the function of the thrust bearing?
The thrust bearing has two functions: bearing the thrust of the rotor and axially positioning the rotor. The thrust bearing bears the part of the rotor thrust that has not been balanced by the balance piston and the thrust transmitted from the toothed coupling. The magnitude of these thrusts mainly depends on the load of the steam turbine.
In addition, the thrust bearing also plays a role in fixing the axial position of the rotor relative to the cylinder.
51. Why should the body pressure of the combined compressor be relieved as soon as possible during shutdown?
Because if the compressor is shut down with pressure for a long time, and if the inlet pressure of the primary seal gas cannot be higher than the inlet pressure of the compressor, the unfiltered process gas in the machine will leak into the seal and damage the seal.
52. What is the function of the seal?
In order for a centrifugal compressor to achieve good operating results, a certain clearance must be maintained between the rotor and the stator to avoid accidents such as friction, wear, collision, and damage.
At the same time, due to the existence of the clearance, leakage between stages and at the shaft end will naturally occur. Leakage not only reduces the working efficiency of the compressor but also leads to environmental pollution and even explosion accidents.

Therefore, the leakage phenomenon is not allowed to occur. Sealing is an effective measure to avoid inter - stage leakage and shaft - end leakage of the compressor while maintaining an appropriate clearance between the rotor and the stator.
53. What types are the sealing devices classified into according to structural characteristics? What are the selection principles?
According to the working temperature, pressure of the compressor, and whether the gas medium is harmful or not, different structural forms of seals are adopted, and they are generally called sealing devices.
The sealing devices are classified into five forms according to structural characteristics: extraction type, labyrinth type, floating - ring type, mechanical type, and spiral type.
Generally, for toxic, harmful, flammable, and explosive gases, floating - ring type, mechanical type, spiral type, and extraction - type sealing devices should be selected. If the gas is non - toxic, non - harmful, and the pressure rise is low, the labyrinth - type sealing device can be selected.
54. What is gas seal?
Gas seal is a non - contact seal that uses gas medium as lubricant. Through the ingenious design of the structure of the sealing elements and the exertion of their performance, leakage can be reduced to the minimum.
Its characteristics and sealing principle are as follows:
The seal seat is relatively fixed to the rotor. On the end face (the primary seal face) opposite to the primary ring of the seal seat, seal blocks and seal dams are designed.
The seal blocks are of different sizes and shapes. When the rotor rotates at high speed, the gas injected into it generates a certain pressure, which pushes the primary ring away, forming gas lubrication, reducing the wear of the primary seal face, and minimizing the leakage of the gas medium. The seal dam is used to prevent gas from leaking out during shutdown.
This kind of seal requires a stable source of sealing gas. It can be the medium gas or an inert gas. Whichever gas is used, it must be filtered and clean.
55. How to select dry gas seals?
For the situation where neither the leakage of process gas into the atmosphere nor the entry of blocking gas into the machine is allowed, a tandem dry gas seal with intermediate gas inlet is adopted.
The ordinary tandem dry gas seal is suitable for the working condition where a small amount of process gas leaks into the atmosphere. The primary seal on the atmosphere side serves as a safety seal.
56. What is the main function of the primary seal gas?
The main function of the primary seal gas is to prevent the unclean gas in the combined compressor from contaminating the primary seal end face.
At the same time, with the high - speed rotation of the compressor, it is pumped to the primary seal vent flare cavity through the spiral grooves on the primary seal end face, and a rigid gas film is formed between the seal end faces, which plays a role in lubricating and cooling the end faces. Most of this gas enters the machine through the shaft - end labyrinth, and only a small part of the gas enters the vent flare cavity through the primary seal end face.
57. What is the main function of the secondary seal gas?
The main function of the secondary seal gas is to prevent the small amount of gas medium leaking from the primary seal end face from entering the secondary seal end face and to ensure the safe and reliable operation of the secondary seal. Most of this gas, together with the small amount of gas medium leaking from the primary seal end face, enters the vent flare pipeline through the primary seal vent flare cavity. Only a small part of the gas enters the secondary seal vent cavity through the secondary seal end face and is vented at the high - point.
58. What is the main function of the post - isolation gas?
The main function of the post - isolation gas is to ensure that the secondary seal end face is not contaminated by the lubricating oil of the bearing of the combined compressor.
Part of the gas is vented at the high - point through the inner comb - tooth labyrinth of the post - seal and the small amount of gas leaking from the secondary seal end face. The other part of the gas is vented through the outer comb - tooth labyrinth of the post - seal and the vent of the bearing lubricating oil.
59. What are the precautions before putting the dry gas seal system into operation?
The post - isolation gas should be put into use 10 minutes before the start - up of the lubricating oil system. Similarly, the post - isolation gas can be cut off 10 minutes after the oil is stopped. After the oil circulation starts, the post - isolation gas cannot be stopped, otherwise, it will damage the seal.
When putting the filter into use, the upper and lower ball valves of the filter should be opened slowly to prevent the filter element from being damaged by the instantaneous pressure impact caused by opening too quickly.
When putting the flow meter into use, the upper and lower ball valves should be opened slowly to keep the flow stable.
Check whether the source pressures of the primary seal gas, secondary seal gas, and post - isolation gas are stable, and whether the filters are blocked.
60. How to drain liquid from V2402 and V2403 in the refrigeration station?
Before start - up, V2402 and V2403 should establish a normal liquid level in advance. The specific steps are as follows:
Before establishing the liquid level, open the valves on the pipeline from the drain of V2402 and V2403 to V2401 in advance. Confirm that the "8" - shaped blind flange on the pipeline has been switched, confirm that the valve of this drain into V2401 is closed, confirm that LV2420 and its front and rear stop valves are fully open, and confirm that FV2401 and FV2402 are fully open.
The introduction of propylene into V2402 is achieved according to the pressure difference. Slightly open the main outlet valve of V2401, XV2482, the valve from V2401 to V2402, LV2421 and its front and rear stop valves one by one, and slowly establish the propylene liquid level in V2402.
Since the pressure between V2402 and V2403 is balanced, propylene can only be introduced into V2403 through the liquid - level difference.
The liquid - draining process must be slow to prevent over - pressure in V2402 and V2403. After a normal liquid level is established in V2402 and V2403, LV2421 and its front and rear stop valves should be closed, the valves on the pipeline from the drain of V2402 and V2403 to V2401 should be closed, and the blind flange should be restored.
61. What are the emergency shutdown steps of the refrigeration station?
When failures such as power outage, oil pump failure, explosion, fire, water outage, instrument air outage, and non - eliminable compressor surge occur, the compressor is shut down urgently. In case of a fire in the system, the propylene gas source should be quickly cut off and purged with nitrogen to maintain pressure.
Trip the compressor to stop its operation on - site or in the control room. If possible, measure and record the coast - down time. Switch the primary seal of the compressor to medium - pressure nitrogen.
If the oil circulation continues to operate (in the case of no power outage and with a low - pressure nitrogen gas source), start barring immediately after the rotor stops rotating. If there is a power outage in the whole plant, the operation buttons of the condensate pump, ejector pump, and oil pump should be turned to the off position in time to prevent the pumps from starting automatically after the power is restored.
Close the outlet valve of the second stage of the compressor.
Close the large valves for propylene entering and leaving the refrigeration system.
When the vacuum degree is close to zero, stop the ejector pump and the shaft - end steam.
Pay attention to adjusting the recirculation volume. If necessary, slightly open the make - up demineralized water valve. Stop the condensate pump after the inlet valve of the ejector is closed.
Find out the cause of the emergency shutdown.
62. What are the emergency shutdown steps of the combined compressor?
When failures such as power outage, oil pump failure, explosion, fire, water outage, instrument air outage, and non - eliminable compressor surge occur, the compressor is shut down urgently. In case of a fire in the system, the propylene gas source should be quickly cut off and purged with nitrogen to maintain pressure.
Trip the compressor to stop its operation on - site or in the control room. If possible, measure and record the coast - down time.
If the oil circulation continues to operate (in the case of no power outage and with a low - pressure nitrogen gas source), start barring immediately after the rotor stops rotating. If there is a power outage in the whole plant, the operation buttons of the condensate pump, ejector pump, and oil pump should be turned to the off position in time to prevent the pumps from starting automatically after the power is restored.
Switch the primary seal to medium - pressure nitrogen in time, confirm that XV2683, XV2682, and XV2681 are closed. Open PV2620 in the control room and control the pressure - relief rate ≤ 0.15 Mpa/min to relieve the pressure of the compressor system. If there is a power outage or instrument air outage, XV2681 will close automatically at this time. The compressor operators should be notified to open the outlet valve of the second stage of the compressor to relieve pressure manually.
When the vacuum degree is close to zero, stop the ejector pump and the shaft - end steam.
Pay attention to adjusting the recirculation volume. If necessary, slightly open the make - up demineralized water valve. Stop the condensate pump after the inlet valve of the ejector is closed.

Find out the cause of the emergency shutdown.