Centrifuge

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How does a centrifugal compressor work? Generally speaking, the main objective of increasing gas pressure is to increase the number of gas molecules per unit volume; in other words, to reduce the distance between gas molecules. To achieve this, gas dynamics methods are employed: mechanical work elements (such as high-speed rotating impellers) are used to do work on the gas, thereby increasing its pressure under centrifugal action. At the same time, the kinetic energy of the gas also increases significantly. Subsequently, within the diffuser channel, this kinetic energy is converted into static pressure energy, further raising the gas pressure. This is how a centrifugal compressor operates. 3. What are the common prime movers for centrifugal compressors? Common prime movers for centrifugal compressors include electric motors, steam turbines, gas-fired turbines, etc. 4. What are the auxiliary equipment of centrifugal compressors? The operation of the centrifugal compressor unit is dependent on the proper functioning of the auxiliary equipment, which includes the following aspects: • Lubricating oil system. • Cooling system. • Condensate water system. • The electrical instrumentation system is the control system. • Dry gas seal system. 5. What types of centrifugal compressors are there based on their structural characteristics? Based on their structural characteristics, centrifugal compressors can be classified into types such as horizontally split type, vertically split type, isothermal compression type, and combined type. 6. What components does the rotor consist of? The rotor includes a main shaft, impeller, shaft sleeve, shaft nut, spacer sleeve, balance disk, and thrust disk. 7. What is the definition of grade? The stage is the basic unit of a centrifugal compressor, consisting of an impeller and a set of fixed elements that work in conjunction with it. 8. What is the definition of a paragraph? Each stage between an inlet and an outlet constitutes a section, and a section is composed of one or several stages. 9. What is the definition of a cylinder? The cylinder of a centrifugal compressor is composed of one or several sections; a single cylinder can accommodate a minimum of one stage and up to ten stages. 10. What is the definition of a column? High-pressure centrifugal compressors sometimes require two or more cylinders; one or several cylinders arranged on the same axis form a row of centrifugal compressors. Different rows have different rotation speeds, with the high-pressure rows rotating faster than the low-pressure rows. For rows with the same rotation speed (on the same axis), the impeller diameter of the high-pressure rows is larger than that of the low-pressure rows. 11. What is the function of the impeller? What are the types based on structural characteristics? The impeller is the only component in a centrifugal compressor that does work on the gas medium. Under the centrifugal force generated by the rapidly rotating impeller, the gas medium rotates together with the impeller, thereby gaining kinetic energy; this energy is then partially converted into pressure energy in the diffuser. Driven by centrifugal force, the gas is expelled from the impeller outlet and flows through the diffuser, bends, and return vessels to reach the next stage of impellers where further pressurization occurs, until it is finally discharged from the compressor outlet. Based on their structural characteristics, impellers can be divided into three types: open, semi-open, and closed. 12. What is the maximum flow condition of a centrifugal compressor? The operating condition in which the flow rate reaches its maximum is known as the maximum flow condition. There are two possible reasons for this condition: 1. The airflow at the throat of a certain flow channel within the stage reaches a critical state; at this point, the volumetric flow rate of the gas is already at its maximum value. No matter how much the back pressure of the compressor decreases, the flow rate cannot increase any further. This condition is also referred to as a \"blocked\" condition. 2. The flow channel has not reached a critical state; in other words, a \"blocking\" condition does not occur. However, at high flow rates, the flow losses within the compressor are very large, and the exhaust pressure it can generate is extremely low, almost approaching zero. This pressure is sufficient only to overcome the resistance in the exhaust pipes and maintain such a high flow rate. This represents the maximum flow rate condition for a centrifugal compressor. 13. What is surge in a centrifugal compressor? During operation, centrifugal compressors can sometimes experience sudden intense vibrations. The flow rate and pressure of the gas medium also fluctuate significantly, accompanied by periodic low-frequency \"humming\" sounds, as well as loud \"whooshing\" noises caused by the fluctuations in airflow within the piping system. This phenomenon is known as surge condition in centrifugal compressors. The compressor cannot operate for long periods under surge conditions; once it enters such conditions, the operator must immediately take corrective actions by reducing the outlet pressure, or increasing the inlet or outlet flow rate, in order to help the compressor quickly exit the surge zone and achieve stable operation. 14. What are the characteristics of surge phenomenon? Once surge occurs during the operation of a centrifugal compressor, the operation of the unit and the piping system exhibits the following characteristics: • The exit pressure and inlet flow rate of the gas medium change significantly, and sometimes gas backflow may also occur. It is a dangerous operating condition when the gas medium flows from the compressor outlet back toward the inlet. • The pipeline network experiences periodic vibrations with large amplitudes and low frequencies, accompanied by a periodic \"roaring\" sound. • The compressor casing vibrates intensely; the casing and bearings experience severe vibration, along with a loud, periodic airflow noise. Due to these intense vibrations, the lubrication conditions of the bearings are compromised, the bearing bushes can be damaged, and even the shaft may break. Friction and collisions between the rotor and stator occur, and the sealing elements suffer serious damage. 15. How to perform anti-surge control? The hazards of surge are extremely severe, but it has not yet been possible to eliminate it through design; instead, efforts must be made during operation to prevent the unit from entering a surge condition. The principle of surge prevention involves addressing the causes of surge, and by increasing the compressor’s flow rate immediately when surge is about to occur, ensuring that the unit operates outside the surge zone. There are specifically three methods to prevent surge: • Partial gas bypass method. • Partial gas reflux method. • Method of changing the compressor’s operating speed. 16. What are the reasons why the compressor operates below the surge limit? • The outlet backpressure is too high. • The valves in the inlet pipeline are throttled. • The valve on the outlet pipeline is throttled. • The anti-surge valve is defective or not adjusted correctly. 17. What are the methods for adjusting the operating conditions of centrifugal compressors? Since process parameters in production inevitably change, it is often necessary to manually or automatically adjust the compressor so that it can operate under varying conditions to meet production requirements and maintain the stability of the production system. There are generally two types of regulation for centrifugal compressors: one is isobaric regulation, which involves adjusting the flow rate while keeping the back pressure constant ； Another method is constant-flow regulation, which involves adjusting the exhaust pressure of the compressor while maintaining a constant flow rate. Specifically, there are five such adjustment methods: • Outlet flow regulation. • Import flow regulation. • Change the speed adjustment. • Adjust by rotating the inlet guide vanes. • Partial venting or backflow regulation. 18. What is the impact of rotational speed on the performance of a compressor? The speed of the compressor enables the modification of its performance curve, while the efficiency remains unchanged; therefore, it represents the best form of compressor control method. 19. What do equal pressure control, equal flow control, and proportional control mean? • Isobaric regulation refers to a control method that maintains the exhaust pressure of the compressor constant while only changing the gas flow rate. • Constant flow regulation refers to a control method that maintains the flow rate of the gas medium delivered by the compressor unchanged, while only altering the discharge pressure. • Proportional control refers to regulation that maintains a constant pressure ratio (such as anti-stall control), or maintains a constant percentage of volumetric flow rate for the two gas media. 20. What is a pipeline network? What are its components? The piping system is the pipeline network used by centrifugal compressors to transport gaseous media. The pipeline located before the compressor inlet is called the suction pipe, while the one located after the compressor outlet is called the discharge pipe. The combination of the suction pipe and the discharge pipe constitutes a complete piping system, which is commonly referred to as the piping network. Piping systems generally consist of four elements: pipes, fittings, valves, and equipment. 21. What are the hazards of axial force? High-speed rotating rotor. An axial force directed from the high-pressure side to the low-pressure side is always present. Under the action of axial force, the rotor will undergo axial displacement in the direction of that force. This axial displacement of the rotor causes relative sliding between the shaft journal and the bearing shells. Therefore, it is possible for the journal or bearing shells to be scratched. More seriously, due to rotor displacement, friction and collision between rotor components and stator components can occur, leading to mechanical damage. The axial force exerted by the rotor can also cause friction, wear, collision, and even destruction of the machinery. Hence, effective measures must be taken to achieve balance in order to improve the operational reliability of the unit. 22. What are the methods for balancing axial forces? The balance of axial forces is a critical issue that must be taken into consideration in the design of multi-stage centrifugal compressors. Currently, two main methods are generally used: ❶ Opposite arrangement of impellers (with the high-pressure and low-pressure sides of the impellers facing each other). The axial force generated by a single-stage impeller points toward the inlet of the impeller, that is, from the high-pressure side to the low-pressure side. If multiple impellers are arranged in this sequential manner, the total axial force on the rotor is the sum of the axial forces of each individual impeller; obviously, such an arrangement results in a very large axial force on the rotor. If multi-stage impellers are arranged in opposition, the impellers on opposite sides generate axial forces in opposite directions, which can balance each other out; therefore, this opposed arrangement is the most common method for balancing axial forces in multi-stage centrifugal compressors. ❷ Installation of a balance drum: The balance drum is a commonly used device for balancing axial forces in multi-stage centrifugal compressors. It is typically installed on the high-pressure side. A labyrinth seal is provided between its outer edge and the cylinder, thereby maintaining a certain pressure difference between the high-pressure side and the low-pressure side connected to the compressor inlet. The axial force generated by this pressure difference acts in the opposite direction to the axial force produced by the impeller; thus, it balances out that axial force. 23. What is the purpose of balancing the axial force on the rotor? The purpose of rotor balancing is primarily to reduce axial thrust and lessen the load on the thrust bearings. In general, 70% of the axial force is eliminated through the balance disc, while the remaining 30% is borne by the thrust bearings. Production experience has shown that maintaining a certain amount of axial force is an effective measure to ensure the smooth operation of the rotor. 24. What are the reasons for the increase in the temperature of thrust bearings? • The structural design is unreasonable; the bearing area of the thrust pads is small, resulting in an excessive load per unit area. • The inter-stage seal fails, allowing the gas exiting the impeller of the subsequent stage to leak into the preceding stage, thereby increasing the pressure difference on both sides of the impeller and generating a significant thrust. • The balance tube is blocked, preventing the pressure in the balance disc’s secondary pressure chamber from being released, and as a result the balance disc cannot function properly. • The balance disc seal fails, preventing the pressure in the working chamber from remaining at normal levels; as a result, the balancing capacity decreases, and part of the increased load is transferred to the thrust bearings, causing them to operate under excessive load. • The throttle orifice for oil supply to the thrust bearing is small, resulting in insufficient flow of cooling oil; as a result, the heat generated by friction cannot be completely removed. • If the lubricating oil contains water or other impurities, a complete liquid lubrication layer cannot be formed on the thrust bearings. • The oil inlet temperature of the bearing is too high, resulting in an unfavorable working environment for the thrust bearings. 25. How to deal with excessively high thrust bearing temperatures? • Check the compressive pressure on the thrust bearing pads, and appropriately increase their load-bearing area to keep the thrust load within the standard range. • Inspect the inter-stage seal for damage and replace any faulty parts of the inter-stage seal. • Inspect the balance tube, remove any blockages, so that the pressure in the pressure chamber of the balance disc can be released in a timely manner, thereby ensuring the proper functioning of the balance disc’s balancing capability. • Replace the balance disk seal strip to improve its sealing performance, maintain the pressure in the balance disk’s working chamber, and ensure that the axial thrust is properly balanced. • Increase the diameter of the oil inlet hole in the bearing and raise the amount of lubricating oil, so that the heat generated by friction can be removed promptly. • Replace it with new, qualified lubricant to maintain its lubricating properties. • The Kaidai has inlet and outlet valves for the coolant, which increase the amount of coolant flow and reduce the oil supply temperature. 26. What should the personnel in charge of the combined compressors do when the synthesis system experiences severe overpressure? • Notify the personnel at the synthesis site to open PV2001 for pressure relief. • Notify the on-site compressor inspection personnel to open the manual vent at the second-stage outlet of the compressor for pressure relief (in emergency situations), and pay attention to having operators supervise the process and take precautions against exposure to toxic substances. 27. How does a combined compressor circulate fluid in the synthesis system? Before starting up the synthesis system, it is necessary to fill the synthesis vessel with nitrogen at a certain pressure and raise the temperature. Therefore, it is necessary to start the syngas compressor to establish a cycle in the synthesis system. • Start the syngas compressor turbine according to the normal operation procedure, and run it at no load until it reaches the normal speed. • Maintain a certain amount of post-cooler cooling; the cooled gas is then fed back into the first-stage inlet. The reflux volume should not be excessive, and care must be taken to prevent overheating. • The surge control valve in the circulation section is used to regulate the gas flow and pressure entering the synthesis system, thereby maintaining an optimal temperature in the synthesis tower. 28. How should the combined compressor be operated when the synthesis system requires an emergency gas cut-off (without shutting down the compressor)? An emergency gas isolation operation is required for the combined compressor: • Report the emergency gas isolation of the combined compressor to the control room, switch the primary seal to medium-pressure nitrogen, and vent the combined compressor at the inlet section (purification outlet section), being careful to maintain pressure. • Open the surge prevention valve for the fresh section to reduce the fresh gas flow, and open the surge prevention valve for the circulation section to reduce the circulation gas flow. • Turn off XV2683, and turn off XV2681 and XV2682. • Open the compressor second-stage outlet vent valve PV2620 and relieve the pressure in the machine at a rate of ≤0.15 Mpa/min; operate the syngas compressor under no-load conditions ； The synthesis system is depressurized. • After the accident in the synthesis system has been resolved, nitrogen is introduced at the inlet of the combined compressor to purge the synthesis system, circulation is initiated, and the system is kept at a constant temperature and pressure. 29. How to increase the fresh air supply? Under normal conditions, the valve XV2683 in the inlet section is in the fully open position. Controlling the amount of fresh gas can only be achieved by using the anti-surge valve in the fresh gas section, which is located after the anti-surge cooler. By closing this anti-surge valve, the amount of backflow gas is reduced, thereby increasing the amount of fresh gas. 30. How to control the air velocity using a compressor? Controlling the space velocity using a syngas compressor is achieved by increasing or decreasing the circulation volume, thereby altering the value of the space velocity. Therefore, with a constant amount of fresh gas, an increase in the amount of syngas circulating will result in an increase in the space velocity; however, this increase in space velocity has a certain impact on the methanol synthesis reaction. 31. How to control the synthesis cycle volume? Throttling limitation through the anti-surge valve in the circulation section. 32. What are the reasons why the synthesis cycle volume cannot be increased? • The amount of fresh gas is low; when the reaction is proceeding well, the volume decreases and the pressure drops too rapidly, resulting in a low pressure at the outlet of the tower. In such cases, it is necessary to increase the space velocity in order to control the rate of the synthesis reaction. • The vent volume of the synthesis system (relief gas volume) is too high, resulting in a high PV2001 value. • The opening of the recirculation gas anti-surge valve is too large, resulting in significant backflow of gas. 33. What are the interlocks between the synthesis system and the combined compressor? • The low limit for the drum liquid level is ≤10%, and it is interlocked with the combined compressor; XV2683 closes to prevent the drum from drying out. • The high liquid level limit for the methanol separator is ≥90%, and it is interlocked with the combined compressor for shutdown protection; XV2681, XV2682, and XV2683 are turned off to prevent liquid from entering the cylinders of the combined compressor and damaging the impellers. • The maximum allowable hot spot temperature in the synthesis tower is ≥275°C, triggering an interlock shutdown in conjunction with the combined compressor. 34. How should high temperature of the synthetic cycle gas be addressed? • Monitor whether the temperature of the circulating gas in the synthesis system rises; if it exceeds the specified value, reduce the circulation volume or inform the dispatch team to increase the water pressure or lower the water temperature. • Check whether the return water temperature of the anti-surge cooler has increased; if it has, an excessive amount of gas is returning, resulting in poor cooling performance, and in such cases the circulation rate should be increased. 35. How to alternately add fresh gas and recycled gas during the start-up of synthesis? During the start-up of synthesis, due to the low temperature of the gas and consequently the low temperature at the catalyst hot spots, the synthesis reaction is restricted. At this time, the increase in gas flow rate should be aimed at stabilizing the temperature of the catalyst bed. Therefore, before increasing the flow rate of fresh gas, the circulation volume should be increased first (usually, the circulation gas volume is 4 to 6 times that of the fresh gas), and only then should the fresh gas flow rate be increased. The increase in gas flow rate must be done gradually, with appropriate time intervals between adjustments (depending mainly on whether the temperature at the catalyst hot spots can be maintained and show an upward trend). Once the gas flow rate reaches a certain level, it may be possible to reduce the amount of steam used in the synthesis process. Reduce the fresh gas flow rate by closing the anti-surge valve for fresh gas. Reduce the flow rate of circulating gas to the anti-surge valve in the low-cycle section. 36. How to use a compressor to maintain temperature and pressure during the start-up and shutdown of a synthesis system? Nitrogen is introduced at the inlet of the combined compressor to purge and pressurize the synthesis system; circulation is established between the combined compressor and the synthesis system. System venting is generally determined based on the pressure in the synthesis system, and the space velocity is used to maintain the temperature at the outlet of the synthesis tower. Startup steam is used to supply heat, allowing the synthesis system to operate in a low-pressure, low-speed cycle for heat retention. 37. How to increase the pressure in the synthesis system when it is started up? What is the pressure increase speed control set at? The pressure increase in the synthesis system is primarily achieved by increasing the amount of fresh gas and raising the pressure of the recycle gas; specifically, reducing the anti-surge setting in the fresh gas section helps to increase the amount of fresh gas used in synthesis ； Closing the anti-surge valve in the low-cycle section can control the synthesis pressure. During normal operation, the pressure rise rate in the synthesis system is generally controlled at 0.4 MPa/min. 38. When heating the synthesis tower, how can a combined compressor be used to control the heating rate of the synthesis tower? What is the control index for the heating rate? When heating up, on one hand, start-up steam is introduced to provide heat, thereby driving the circulation of boiler water and raising the temperature of the synthesis tower ； On the other hand, the combined compressor is started to utilize the gas added in the circulation section and the syngas exhaust gases for the gas circulation in the synthesis system, thereby controlling heat and stabilizing the temperature rise of the tower; hence, during the heating process, the temperature increase of the tower is mainly regulated by adjusting the circulation volume. The control index for the heating rate is 25°C/h. 39. How to adjust the anti-surge gas flow rate for the fresh section and the recirculation section? When the operating conditions of the compressor approach those of surge, anti-surge control measures must be taken. Before making such adjustments, in order to prevent excessive fluctuations in the system’s gas flow, it is first necessary to identify which section of the system is approaching surge conditions; thereafter, the anti-surge valve corresponding to that section should be opened slightly to eliminate the surge. It is also important to monitor the fluctuations in the system’s gas flow (striving to maintain stability in the gas flow entering the tower), but two anti-surge valves should not be activated simultaneously to address surge. 40. What are the reasons for liquid presence at the compressor inlet? • The process gas delivered by the previous system was at a high temperature, so it was not completely condensed; moreover, the gas delivery pipes were too long, resulting in liquid present in the gas after condensation within the pipes. • The temperature in the process system is high, causing the components with lower boiling points in the gaseous medium to condense into a liquid. • The separator level is too high, resulting in gas-liquid entrainment. 41. How to deal with liquid at the compressor inlet? • Contact the previous system to adjust the process operations. • This system appropriately increases the number of liquid discharge cycles of the separator. • Reduce the liquid level in the separator to prevent gas-liquid entrainment. 42. What are the reasons for the decline in the performance of combined compressor units? • The inter-stage seal of the compressor is severely damaged, resulting in reduced sealing performance and increased backflow of the gas medium. • The impeller is severely worn, the rotor’s performance declines, and the gas medium does not receive sufficient kinetic energy. • The steam filter in the turbine is clogged, which hinders steam flow; as a result, the flow rate is low and the pressure difference is high. This affects the turbine’s output power and reduces the performance of the unit. • The vacuum level is below the specified requirement, causing obstruction in the turbine exhaust. • The steam temperature and pressure parameters are below the operational specifications; the internal energy of the steam is low, and it cannot meet the requirements for the operation of the unit. • A surge condition occurs. 43. What are the main performance parameters of centrifugal compressors? The main performance parameters of a centrifugal compressor include: flow rate, outlet pressure or compression ratio, power, efficiency, speed, and energy head. The main performance parameters of a device are the basic data that characterize its structural features, operating capacity, operating environment, etc.; they serve as important guiding materials for users when selecting devices and formulating plans. 44. What is the meaning of efficiency? Efficiency is a measure of the degree to which the energy transferred by a centrifugal compressor to the gas is utilized; the higher this degree of utilization, the greater the efficiency of the compressor. Since gas compression involves three processes: polytropic compression, adiabatic compression, and isothermal compression, the efficiency of compressors is also divided into polytropic efficiency, adiabatic efficiency, and isothermal efficiency. 45. What does the compression ratio mean? The compression ratio we are referring to is the ratio of the pressure of the gas discharged by the compressor to the intake pressure; therefore, it is sometimes also called the pressure ratio. 46. What components does the lubricating oil system consist of? The lubricating oil system consists of a lubricating oil station, a high-level oil tank, intermediate connection pipelines, as well as control valves and monitoring instruments. The lubricating oil station consists of an oil tank, an oil pump, an oil cooler, an oil filter, a pressure control valve, various monitoring instruments, as well as oil pipelines and valves. 47. What is the function of a high-level fuel tank? The high-level oil tank is one of the safety measures for the unit. During normal operation, the lubricating oil enters from the bottom and exits from the top to return to the oil tank. In the event of a power outage that causes the unit to stop, if the auxiliary oil pump cannot start in time to supply oil, the lubricating oil in the high-level oil tank will flow through various lubrication points via the inlet pipelines before returning to the oil tank, thereby ensuring an adequate supply of lubricating oil during the unit’s coasting phase. 48. What safety protection measures does a combined compressor unit have? • High-level fuel tank • Safety valve • Accumulator • Quick-shut valve • Other interlock devices 49. What is the principle of sealing action of a labyrinth seal? By converting potential energy (pressure) into kinetic energy (flow velocity), and then dissipating that kinetic energy in the form of vortices. 50. What is the function of a thrust bearing? Thrust bearings serve two purposes: to bear the thrust force of the rotor and to axially position the rotor. The thrust bearing bears the portion of the rotor’s thrust that has not been balanced by the balancing piston, as well as the thrust transmitted by the gear coupling; the magnitude of these thrusts is primarily determined by the load on the steam turbine. Additionally, the thrust bearing also serves to fix the axial position of the rotor relative to the cylinder. 51. Why is it necessary to relieve the pressure in the compressor housing as quickly as possible when shutting it down? Since the compressor stops operating under pressure for an extended period of time, if the inlet pressure of the primary seal gas does not exceed the compressor’s inlet pressure, the unfiltered process gas inside the compressor can penetrate the seal and damage it. 52. What is the function of sealing? To achieve good operational performance, a centrifugal compressor must maintain a certain gap between the rotor and the stator, in order to prevent friction, wear, as well as collisions and other types of damage. At the same time, the presence of gaps inevitably leads to leakage between stages and at the shaft ends. Such leakage not only reduces the efficiency of the compressor but also causes environmental pollution and may even result in explosion accidents. Therefore, leakage must not occur. Sealing is an effective measure to prevent leakage between compressor stages and at the shaft ends, while maintaining an appropriate gap between the rotor and the stator. 53. How are sealing devices classified according to their structural features? What are the selection principles? Depending on factors such as the operating temperature and pressure of the compressor, as well as whether the gas medium is hazardous, different structural forms of seals are used, which are collectively referred to as sealing devices. Sealing devices can be classified into 5 types based on their structural features: vacuum-type, labyrinth-type, floating-ring type, mechanical type, and spiral type. For generally toxic, harmful, flammable, and explosive gases, floating-ring, mechanical, spiral, and vacuum-type sealing devices should be used ； If the gas is non-toxic and harmless and the pressure rise is low, a labyrinth seal can be used. 54. What is gas sealing? Gas sealing is a non-contact seal that uses a gas medium as a lubricant; through the clever design of the sealing element’s structure and the optimization of its performance, leaks can be reduced to a minimum. Its characteristics and sealing principle are as follows: ❶ The sealing seat is fixed relative to the rotor; sealing blocks and sealing dams are designed on the end face of the sealing seat that faces the primary ring (the primary sealing surface). Sealing blocks come in various sizes and shapes. When the rotor rotates at high speed, it generates pressure in the gas introduced during injection, thereby pushing back the primary ring and creating gas lubrication. This reduces wear on the primary sealing surface and minimizes the leakage of the gas medium. The sealing dam is used to prevent gas from escaping when the machine is stopped. ❷ This type of sealing requires a stable source of sealing gas, which can be either process gas or an inert gas; in either case, the gas must be filtered to be clean. 55. How to select a dry gas seal? For applications where it is required that neither process gas escapes into the atmosphere nor seal gas enters the machine, a series dry gas seal with intermediate gas inlet is used. A conventional series dry gas seal is suitable for situations where a small amount of process gas leaks into the atmosphere, with the primary seal on the atmospheric side serving as a backup seal. 56. What is the main function of the primary seal gas? The main function of the primary seal gas is to prevent unclean gases inside the combined compressor from contaminating the primary seal face. At the same time, as the compressor rotates at high speed, fluid is pumped through the spiral grooves on the primary seal face into the primary seal vent flare chamber, thereby creating a rigid air film between the seal faces that serves to lubricate and cool them. The vast majority of this gas enters the machine through the shaft-end labyrinth, with only a small portion entering the vent flare chamber via the primary seal face. 57. What is the main function of the secondary sealing gas? The main function of the secondary seal gas is to prevent the small amount of gas that leaks from the primary seal surface from entering the secondary seal surface, thereby ensuring the safe and reliable operation of the secondary seal. Most of this gas, along with the small amount of gas that leaks from the primary seal surface, enters the vent flare line through the vent flare chamber of the primary seal; only a small portion of the gas enters the secondary seal vent chamber via the secondary seal surface and is then vented at a higher point. 58. What is the main function of the rear isolation gas? The purpose of the rear isolation gas is mainly to prevent the secondary sealing surface from being contaminated by the lubricating oil of the combined compressor bearings. A portion of this gas is vented through the comb-tooth labyrinth on the inside of the rear seal, along with the small amount of gas that leaks from the end face of the secondary seal ； The other portion of the gas is discharged through the outer comb-shaped labyrinth of the rear seal, via the bearing lubricating oil discharge port. 59. What are the precautions for operating the dry gas seal system before it is put into use? • Introduce the back isolation gas 10 minutes before starting the lubricating oil system. Similarly, the rear isolation gas can be shut off only 10 minutes after the oil is stopped. Once oil transportation begins, the back isolation gas cannot be stopped, otherwise it will cause damage to the seal. • When putting the filter into use, the upper and lower ball valves of the filter should be opened slowly to prevent sudden pressure spikes from damaging the filter elements due to too rapid opening. • When putting the flow meter into use, the upper and lower ball valves should be opened slowly to maintain a stable flow rate. • Check the pressure of the air supply for the primary seal, as well as that of the air supplies for the secondary seal and the rear isolation, to ensure it is stable, and verify that the filters are not clogged. 60. How to guide the fluid in freezing stations V2402 and V2403? Before starting the machine, normal liquid levels should be established for V2402 and V2403. The specific steps are as follows: • To establish the liquid levels, open the drain valves for V2402 and V2403 leading to the pipeline of V2401 in advance; ensure that the \"8\"-shaped blind valve on the pipeline has been switched; confirm that the drain valve leading into V2401 is closed; ensure that LV2420 and the check valves before and after it are fully open; and ensure that FV2401 and FV2402 are fully open ； • The introduction of propylene into V2402 is achieved based on pressure differences; the outlet main valve of V2401, XV2482, the valves from V2401 to V2402, LV2421, and the check valves before and after it are gradually opened to slowly raise the propylene level in V2402. • Due to the pressure equilibrium between V2402 and V2403, propylene can only be introduced into V2403 through the liquid level difference. • The liquid guiding process must be carried out slowly to prevent overpressure in V2402 and V2403. Once normal liquid levels are established in V2402 and V2403, LV2421 as well as the check valves before and after it should be closed. The valves that allow liquid to flow from V2402 and V2403 to the pipeline connected to V2401 should also be closed, and the blind flanges should be reinstalled. (Welcome to follow \"Chemical Equipment Management and Training\", the favorite media outlet in the chemical equipment management industry. It aims to deliver value and share experiences, enabling everyone to improve themselves on an equal footing. Let’s make progress a little bit every day!) ) 61. What are the emergency shutdown procedures for the freezing station? The compressor shuts down urgently in the event of faults such as power supply issues, oil pump problems, explosions, fires, water supply interruptions, instrument air shortages, or inability to eliminate compressor surge. In the event of a system fire, the propylene supply should be quickly cut off and the system pressurized by filling it with nitrogen. • Shut down the compressor urgently on-site or from the control room; if possible, measure and record the coasting time. Switch the primary seal of the compressor to medium-pressure nitrogen. • If the oil circulation continues to operate (without a power outage and with a supply of low-pressure nitrogen), turn the rotor manually immediately after it stops rotating ； In the event of a power outage across the entire plant, the control buttons for the feedwater pumps, condensate pumps, and oil pumps should be turned to the off position promptly, to prevent the pumps from starting automatically once power is restored. • Close the compressor second-stage outlet valve. • Close the large propylene valve for entering and exiting the refrigeration system. • Stop the water pump and the shaft seal steam when the vacuum level approaches zero. • Pay attention to adjusting the recirculation volume; if necessary, slightly open the make-up demineralized water valve. Stop the condensate pump once the intake valve of the exhaust pump is closed. • Find out the cause of the emergency shutdown. 62. What are the emergency shutdown steps for a combined compressor? The compressor shuts down urgently in the event of faults such as power supply issues, oil pump problems, explosions, fires, water supply interruptions, instrument air shortages, or inability to eliminate compressor surge. In the event of a system fire, the propylene supply should be quickly cut off and the system pressurized by filling it with nitrogen. • Shut down the compressor urgently on-site or from the control room; if possible, measure and record the coasting time. • If the oil circulation continues to operate (without a power outage and with a supply of low-pressure nitrogen), turn the rotor manually immediately after it stops rotating ； In the event of a power outage across the entire plant, the control buttons for the feedwater pumps, condensate pumps, and oil pumps should be turned to the off position promptly, to prevent the pumps from starting automatically once power is restored. • Switch the primary seal to medium-pressure nitrogen in a timely manner, and ensure that XV2683, XV2682, and XV2681 are closed. In the control room, open PV2620 and control the pressure release rate to ≤0.15 Mpa/min in order to relieve the pressure in the compressor system. In the event of a power outage or a loss of instrument air, XV2681 will automatically shut down; in such cases, the personnel responsible for the compressor should be informed to open the outlet valve on the second stage of the compressor in order to relieve pressure manually. • Stop the water pump and the shaft seal steam when the vacuum level approaches zero. • Pay attention to adjusting the recirculation volume; if necessary, slightly open the make-up demineralized water valve. Stop the condensate pump once the intake valve of the exhaust pump is closed. • Find out the cause of the emergency shutdown.