A compressor is a driven fluid machine that boosts low-pressure gas into high-pressure gas. Today, we have compiled 62 frequently asked questions about compressors. Let’s see how many you can answer!
What are the characteristics of centrifugal compressors?
The centrifugal compressor belongs to turbocompressors. It features large gas handling capacity, compact structure, stable operation, convenient maintenance, zero oil contamination of process gas, and compatibility with various driving modes.
Working principle of centrifugal compressors?
Generally speaking, the core objective of increasing gas pressure is to raise the quantity of gas molecules per unit volume, i.e., shorten the distance between gas molecules. To achieve this goal, aerodynamic principles are adopted: mechanical working components (high-speed rotating impellers) impart work to gas. Under centrifugal action, gas pressure rises and kinetic energy increases significantly. Subsequently, such kinetic energy is converted into static pressure energy inside diffuser passages for further gas pressure elevation. This is the working principle of centrifugal compressors.
What are the common prime movers for centrifugal compressors?
Common prime movers include electric motors, steam turbines, and gas turbines.
What are the auxiliary equipment of centrifugal compressors?
The stable operation of the main compressor unit relies on normal operation of auxiliary systems, including:
Lubricating oil system
Cooling system
Condensate system
Electrical instrument & control system
Dry gas seal system
Classifications of centrifugal compressors based on structural features?
Centrifugal compressors are categorized as horizontally split, vertically split, isothermal compression, and combined types.
Components of a rotor?
The rotor consists of main shaft, impellers, shaft sleeves, shaft nuts, spacing sleeves, balance drum and thrust disk.
Definition of a Stage?
A stage is the basic unit of a centrifugal compressor, composed of one impeller and a set of matched stationary components.
Definition of a Section?
Stages between one suction port and discharge port form a section; one section consists of one or multiple stages.
Definition of a Casing?
A casing of centrifugal compressor contains one or multiple sections. A single casing can accommodate a minimum of 1 stage and a maximum of 10 stages.
Definition of a Train?
High-pressure centrifugal compressors sometimes consist of two or more casings. One or multiple casings arranged on a single shaft form a train of centrifugal compressor. Different trains operate at different rotational speeds; high-pressure trains run faster than low-pressure trains. For trains sharing identical rotational speed (coaxial), impellers of high-pressure trains have larger diameters than those of low-pressure trains.
Functions of the impeller and its structural classifications?
The impeller is the sole component that transfers work to gas medium in centrifugal compressors. Driven by centrifugal force from the high-speed rotating impeller, gas rotates together with the impeller and gains kinetic energy. Part of the kinetic energy is converted into pressure energy via the diffuser. Gas is thrown out from the impeller outlet, flows through diffuser, bend and return channel into the next-stage impeller for further pressurization until discharged from the compressor outlet.
Impellers are classified into three types by structure: open, semi-open and closed impellers.
What is the maximum flow operating condition of centrifugal compressors?
The operating condition at maximum volumetric flow is defined as maximum flow condition. Two scenarios may lead to this condition:
Gas flow at the throat of a flow passage within a stage reaches critical state. At this time, volumetric flow reaches the upper limit. No further flow increase can be achieved even if compressor backpressure continues to drop. This condition is also known as the choking condition.
Critical flow state (choking) does not occur inside the passage. However, under large flow rate, internal flow loss is extremely high, and the achievable discharge pressure is very low, nearly zero energy head, only sufficient to overcome resistance of discharge pipelines to sustain such large flow. This is the maximum flow condition of centrifugal compressors.
What is surge of centrifugal compressors?
During operation, centrifugal compressors may suddenly generate violent vibration, accompanied by drastic fluctuation of gas flow and pressure, periodic low rumbling noise, and heavy huffing noise triggered by airflow oscillation in pipe networks. This phenomenon is called surge condition of centrifugal compressors.
Long-term operation under surge condition is prohibited. Once surge occurs, operators shall immediately take regulating measures to reduce discharge pressure or increase inlet/outlet flow, so as to pull the compressor out of the surge zone and restore stable operation.
Characteristics of surge phenomenon?
Once surge occurs in centrifugal compressors, the unit and pipe network exhibit the following features:
Dramatic variation of discharge pressure and inlet flow, and possible reverse gas flow, where gas flows backward from compressor discharge side to inlet side — this is a hazardous operating condition.
Periodic vibration of pipe network with large amplitude and low frequency, accompanied by periodic roaring noise.
Severe vibration of compressor casing, casings and bearings, together with strong periodic airflow noise. Severe vibration will damage bearing lubrication, cause burnt thrust pads, even shaft rupture, friction and collision between rotor and stator, and severe damage to sealing components.
How to implement anti-surge regulation?
Surge brings severe hazards and cannot be eliminated completely via design. Only operational measures can prevent the unit from entering surge condition. The anti-surge principle is to rapidly increase compressor flow once surge is imminent, pulling the unit away from the surge zone.
Three typical anti-surge methods:
Partial gas venting method
Partial gas recirculation method
Rotational speed adjustment method of compressor
Causes of compressor operation below surge limit?
Excessive discharge backpressure.
Throttling of inlet pipeline valve.
Throttling of discharge pipeline valve.
Defective or improperly adjusted anti-surge valve.
Regulation methods for centrifugal compressor operating conditions?
Process parameters inevitably fluctuate during production, so manual or automatic regulation is often required to adapt compressors to variable operating conditions and stabilize the whole production system.
Two major regulation types for centrifugal compressors: constant pressure regulation (adjust flow under constant backpressure), and constant flow regulation (adjust discharge pressure under constant flow). Five specific regulation approaches are listed below:
Discharge flow regulation
Inlet flow regulation
Rotational speed adjustment
Inlet guide vane rotation regulation
Partial venting or recirculation regulation
Influence of rotational speed on compressor performance?
Rotational speed changes the compressor performance curve while efficiency remains unchanged. Therefore, speed adjustment is the optimal regulation method for compressors.
Definitions of constant pressure regulation, constant flow regulation and proportional regulation?
Constant pressure regulation: maintain constant compressor discharge pressure while adjusting gas flow rate.
Constant flow regulation: maintain constant gas delivery flow while adjusting compressor discharge pressure.
Proportional regulation: maintain constant pressure ratio (e.g., anti-surge regulation), or maintain constant volumetric flow percentage of two gas media.
What is a pipe network and its constituent elements?
A pipe network is the piping system for gas transportation by centrifugal compressors. Piping upstream of the compressor inlet is the suction pipeline; piping downstream of compressor outlet is the discharge pipeline. The combination of suction and discharge pipelines forms a complete piping system generally referred to as pipe network.
A pipe network normally consists of four elements: pipelines, pipe fittings, valves and equipment.
Hazards of axial thrust?
Axial thrust continuously acts on the high-speed rotating rotor, pointing from the high-pressure end toward the low-pressure end.
Under axial thrust, the rotor generates axial displacement along the thrust direction, leading to relative sliding between journal and bearing shell.
This may scratch journals or bearing shells. Worse still, rotor displacement will trigger friction, collision and mechanical damage between rotor and stator components. Effective balancing measures must be adopted to counteract axial thrust and improve unit operational reliability.
Balancing methods for axial thrust?
Axial thrust balancing is a key design consideration for multi-stage centrifugal compressors. Two widely adopted methods are shown below:
(1) Opposed arrangement of impellers (back-to-back arrangement of high-pressure side and low-pressure side of impellers)
Axial thrust generated by a single-stage impeller points toward the impeller inlet (high pressure to low pressure). If multi-stage impellers are arranged sequentially, total rotor axial thrust equals the sum of axial thrust of each stage, resulting in huge overall thrust. Opposed arrangement makes impellers with opposite inlet directions generate counteracting axial thrust for mutual balancing. Therefore, opposed arrangement is the most common axial thrust balancing method for multi-stage centrifugal compressors.
(2) Installation of balance drum
Balance drum is a common axial thrust balancing device for multi-stage centrifugal compressors, usually installed on the high-pressure side. Labyrinth seal is arranged between the outer rim and casing to maintain a specific pressure difference between the high-pressure side and low-pressure side connected to compressor inlet. The axial thrust generated by such pressure difference acts opposite to the thrust from impellers, balancing the axial force produced by impellers.
Objectives of rotor axial thrust balancing?
The main objective of rotor balancing is to reduce axial thrust and lower the load on thrust bearings. Normally, approximately 70% of axial thrust is counteracted by the balance drum, and the remaining 30% is borne by thrust bearings. Production experience proves that retaining a certain amount of residual axial thrust is an effective measure to ensure stable rotor operation.
Causes of rising thrust pad temperature?
Unreasonable structural design with insufficient bearing area of thrust pads and excessive load per unit area.
Failure of interstage seal leads to gas leakage from outlet of rear-stage impeller to the preceding stage, increasing pressure difference on both sides of impeller and generating excessive thrust.
Blockage of balance pipe prevents pressure relief of the secondary pressure chamber of balance drum, disabling normal function of balance drum.
Failure of balance drum seal cannot sustain normal pressure in working chamber, reducing balancing capacity and transferring extra load to thrust pads, resulting in overload operation of thrust pads.
Small throttling bore for bearing oil supply leads to insufficient cooling oil flow, failing to completely remove heat generated by friction.
Water or impurities contained in lubricating oil prevent formation of complete hydrodynamic lubrication film on thrust pads.
Excessive temperature of bearing supply oil creates poor operating environment for thrust pads.
Solutions for excessive thrust pad temperature?
Check bearing pressure of thrust pads; properly expand bearing area to keep thrust load within standard range.
Disassemble and inspect interstage seals, replace damaged sealing components. Inspect balance pipes and remove blockages to ensure timely pressure relief of secondary pressure chamber of balance drum and restore balancing capacity. Replace sealing strips of balance drum to improve sealing performance, maintain pressure inside balance drum working chamber and realize reasonable axial thrust balancing.
Enlarge throttling bore of bearing oil supply to increase lubricating oil flow and timely remove friction heat. Replace with qualified fresh lubricating oil to guarantee lubrication performance. Fully open inlet and return cooling water valves of oil cooler to increase cooling water flow and reduce supply oil temperature.
Operating actions for combined compressor during severe overpressure of synthesis system?
Notify on-site synthesis operators to open PV2001 for pressure relief.
Notify patrol operators of combined compressor to open manual vent valve at secondary-stage outlet of compressor for emergency pressure relief; ensure operator supervision and toxic gas protection.
How does the combined compressor establish circulation for the synthesis system?
Before startup of synthesis system, nitrogen charging and heating are required under designated pressure. Therefore, the syngas compressor needs to be started to build circulation for the synthesis system.
Start the steam turbine of syngas compressor following normal startup procedure, run under no-load condition until reaching rated speed.
Maintain gas recirculation after anti-surge cooler flowing into primary-stage suction; avoid excessive recirculation flow and prevent overtemperature.
Control gas flow and pressure entering synthesis system by adjusting circulation-stage anti-surge valve and stabilize temperature of synthesis reactor.
Operation of combined compressor for emergency gas cut-off (compressor remains online)?
Implement emergency gas cut-off operation for combined compressor:
Report emergency gas cut-off of combined compressor to control room; switch primary seal gas to medium-pressure nitrogen; vent combined compressor inlet stream (purification outlet stream) while maintaining pressure.
Open fresh gas section anti-surge valve to reduce fresh gas flow; open circulation section anti-surge valve to reduce circulating gas flow.
Close XV2683, XV2681 and XV2682.
Open vent valve PV2620 at secondary-stage outlet of compressor and relieve unit pressure at a rate ≤0.15 MPa/min; the syngas compressor operates under no load, and the synthesis system undergoes pressure relief. After troubleshooting of synthesis system, charge nitrogen from combined compressor inlet to purge the synthesis system, establish circulation and maintain temperature and pressure of synthesis system.
How to increase fresh gas flow?
Normally, inlet stream valve XV2683 is fully open. Fresh gas flow can only be regulated via the fresh gas section anti-surge valve downstream of anti-surge cooler. Gradually close the primary-stage anti-surge valve to reduce recirculation flow and increase fresh gas feed.
Control of space velocity via compressor?
Space velocity is adjusted by increasing or decreasing circulating gas flow through the syngas compressor. With fixed fresh gas flow, higher synthesis circulating gas flow leads to higher space velocity, which imposes certain influence on methanol synthesis reaction.
Regulation of synthesis circulating gas flow?
Throttling control via circulation-stage anti-surge valve.
Reasons for insufficient increase of synthesis circulating gas flow?
Low fresh gas flow. When reaction proceeds efficiently, volume contraction and rapid pressure drop lead to low reactor outlet pressure; higher space velocity is required to control synthesis reaction rate.
Excessive venting flow (purge gas flow) of synthesis system, excessive opening of PV2001.
Excessive opening of circulating gas anti-surge valve, causing massive gas recirculation.
Interlock logic between synthesis system and combined compressor?
Low liquid level interlock of steam drum (≤10%): interlock with combined compressor, automatically close XV2683 to prevent dry-out of steam drum.
High liquid level interlock of methanol separator (≥90%): trigger trip protection of combined compressor; close XV2681, XV2682 and XV2683 to prevent liquid from entering compressor casing and damaging impellers.
High hot spot temperature interlock of synthesis reactor (≥275°C): trigger trip of combined compressor.
Treatment measures for excessive synthesis circulating gas temperature?
Monitor circulating gas temperature of synthesis system; reduce circulation flow or notify control room to increase cooling water flow or lower cooling water temperature if temperature exceeds set index.
Check return water temperature of anti-surge cooler. Rising return water temperature indicates excessive gas recirculation flow and poor cooling efficiency; increase circulation flow in this case.
Alternate flow increase of fresh gas and circulating gas during synthesis system startup?
During synthesis startup, low gas temperature results in low catalyst hot spot temperature and restricted synthesis reaction. Flow increase shall prioritize stabilizing catalyst bed temperature. Therefore, circulating gas flow shall be increased first before fresh gas flow (circulating flow is generally 4~6 times fresh gas flow). Flow increase shall be slow with proper intervals, mainly depending on whether catalyst hot spot temperature can be maintained and show an upward trend. After gas flow reaches designated level, request synthesis unit to reduce startup steam supply.
Close fresh gas section anti-surge valve to increase fresh gas flow; close circulation section anti-surge valve to increase circulating gas flow.
Temperature & pressure maintenance of synthesis system by compressor during startup and shutdown?
Charge nitrogen from combined compressor inlet for purging and pressurization of synthesis system; establish circulation between combined compressor and synthesis system. Adjust system venting according to synthesis system pressure, maintain synthesis reactor outlet temperature by space velocity, supply heat via startup steam, and realize low-pressure low-speed circulation for heat preservation of synthesis system.
Pressure buildup of synthesis system during startup and specified pressurization rate?
Pressure buildup of synthesis system is realized by increasing fresh gas flow and circulating gas pressure. Specifically, closing fresh gas section anti-surge valve raises fresh gas flow into synthesis unit; closing circulation section anti-surge valve controls synthesis system pressure. During normal startup, the pressurization rate of synthesis system is generally controlled at 0.4 MPa/min.
Control of synthesis reactor heating rate by combined compressor and specified index?
For reactor heating: startup steam is activated to supply heat and drive furnace water circulation to raise reactor temperature. Meanwhile, start combined compressor, utilize gas feeding of circulation section and gas discharge from synthesis reactor to build gas circulation of synthesis system, regulate heat load and stabilize reactor heating amplitude. Therefore, heating rate is mainly adjusted by controlling circulation flow. The specified heating rate is 25°C/h.
Flow regulation of anti-surge gas for fresh gas section and circulation section?
When compressor operating condition approaches surge zone, anti-surge regulation shall be implemented. Before adjustment, judge and confirm which section is close to surge to avoid violent system flow fluctuation. Appropriately open the anti-surge valve of the corresponding section to eliminate surge. Monitor system flow variation (stabilize gas flow into reactor as much as possible). Do not open two anti-surge valves simultaneously for surge elimination.
Causes of liquid entrainment at compressor inlet?
High temperature of process gas delivered from upstream unit leads to incomplete gas condensation. Long gas transportation pipelines cause liquid condensate inside gas after pipeline cooling.
High temperature of process system condenses low-boiling components in gas medium into liquid.
Excessive liquid level inside separator triggers gas-liquid entrainment.
Treatment for liquid entrainment at compressor inlet?
Coordinate with upstream unit to adjust process operation.
Increase liquid draining frequency of separators in local system.
Lower separator liquid level to avoid gas-liquid entrainment.
Causes of performance degradation of combined compressor unit?
Severe damage of interstage seal reduces sealing performance and increases internal gas recirculation.
Heavy impeller wear degrades rotor performance; gas cannot obtain sufficient kinetic energy.
Blockage of steam filter screen of steam turbine obstructs steam flow, reduces flow rate and raises pressure drop, lowering turbine output power and unit performance.
Vacuum degree fails to meet specification, hindering turbine exhaust.
Steam temperature and pressure parameters below operating index reduce steam internal energy and fail to satisfy unit operation requirements.
Occurrence of surge operating condition.
Main performance parameters of centrifugal compressors?
Main performance parameters include flow rate, discharge pressure or pressure ratio, power, efficiency, rotational speed, and energy head.
Performance parameters are fundamental data reflecting structural characteristics, handling capacity and operating environment of equipment, serving as important guidelines for equipment procurement and planning.
Definition of efficiency?
Efficiency reflects the utilization level of energy transferred from centrifugal compressor to gas. Higher utilization level corresponds to higher compressor efficiency.
Three gas compression processes exist: polytropic compression, adiabatic compression and isothermal compression. Accordingly, compressor efficiency is classified into polytropic efficiency, adiabatic efficiency and isothermal efficiency.
Definition of compression ratio?
Compression ratio refers to the ratio of compressor discharge gas pressure to suction pressure, also called pressure ratio.
Composition of lubricating oil system?
The lubricating oil system consists of lubricating oil station, overhead oil tank, connecting pipelines, control valves and measuring instruments.
The lubricating oil station comprises oil tank, oil pumps, oil coolers, oil filters, pressure regulating valves, various measuring instruments, oil pipelines and valves.
Functions of overhead oil tank?
The overhead oil tank is one of unit safety protection measures. During normal operation, lubricating oil enters from the bottom and flows back to the main tank directly from the top outlet. In case of power failure and unit shutdown where auxiliary oil pump cannot start oil supply timely, lubricating oil from overhead oil tank flows through oil supply pipelines to all lubrication points and returns to the tank, guaranteeing oil supply during unit coast-down.
Safety protection measures for combined compressor unit?
Overhead oil tank
Safety relief valve
Accumulator
Emergency stop valve
Other interlock devices
Sealing principle of labyrinth steam seal?
Convert potential energy (pressure) into kinetic energy (flow velocity), then dissipate kinetic energy in the form of eddy current.
Functions of thrust bearing?
Thrust bearing has two functions: withstand rotor thrust and realize axial positioning of rotor. It bears residual rotor thrust unbalanced by balance drum and thrust transmitted from gear coupling, whose magnitude mainly depends on steam turbine load.
In addition, thrust bearing fixes the axial position of rotor relative to casing.
Reason for rapid pressure relief of combined compressor during shutdown?
Long-time shutdown under pressure. If primary seal gas supply pressure cannot exceed compressor inlet pressure, unfiltered process gas inside the unit will intrude into seals and damage sealing components.
Functions of seals?
For stable operation of centrifugal compressors, proper clearance must be retained between rotor and stator to avoid friction, collision and mechanical damage.
Nevertheless, such clearance inevitably causes interstage and shaft-end leakage. Leakage reduces compressor efficiency, triggers environmental pollution and even explosion accidents.
Therefore, leakage must be prohibited. Seals are effective solutions to prevent interstage and shaft-end leakage while maintaining appropriate clearance between rotor and stator.
Structural classifications of sealing devices and selection principles?
Different structural types of sealing devices are selected according to compressor operating temperature, pressure and hazard level of gas medium.
Sealing devices are divided into five types by structure: extraction type, labyrinth type, floating ring type, mechanical type and spiral type.
Floating ring, mechanical, spiral or extraction type seals shall be adopted for toxic, hazardous, flammable and explosive gas. Labyrinth seals can be selected for non-toxic gas under low pressure rise.
Definition of gas seal?
Gas seal is a non-contact seal using gas medium as lubricant. Optimized structural design of sealing components minimizes leakage.
Features and sealing principle:
Seal housing is relatively fixed with the rotor.
Seal blocks and sealing dams are arranged on the end face (primary sealing surface) where seal housing mates with primary ring.
Seal blocks vary in dimension and shape. During high-speed rotation of rotor, pressure is generated on gas injected into the clearance, pushing the primary ring away to form gas lubrication, reduce wear of primary sealing surface and limit gas leakage to minimum level. Sealing dams prevent gas escape during unit shutdown.
This type of seal requires stable sealing gas source, which can be process gas or inert gas. In any case, the gas must be filtered clean gas.
Selection guidelines for dry gas seals?
Series dry gas seal with intermediate gas injection shall be adopted for working conditions prohibiting both process gas leakage to atmosphere and barrier gas intrusion into compressor casing.
Conventional series dry gas seal applies to conditions allowing minor process gas leakage to atmosphere; the atmospheric-side primary seal serves as backup safety seal.
Primary functions of primary seal gas?
Primary seal gas prevents contaminated internal gas of combined compressor from polluting primary sealing faces.
As the compressor rotates at high speed, gas is pumped to primary seal vent flare cavity via spiral grooves on primary sealing faces, forming a rigid gas film between sealing faces for lubrication and cooling. Most gas flows into compressor casing through shaft-end labyrinth seal, and only a small fraction passes through primary sealing faces into flare vent cavity.
Primary functions of secondary seal gas?
Secondary seal gas prevents a small amount of gas leaked from primary sealing faces from entering secondary sealing faces and ensures safe and stable operation of secondary seal. Most secondary seal gas mixes with leaked gas from primary faces and flows into flare pipeline via primary flare cavity; only a small portion passes through secondary sealing faces into secondary vent cavity for high-point venting.
Primary functions of separation gas (buffer gas)?
Separation gas ensures secondary sealing faces are free of contamination from bearing lubricating oil of combined compressor.
Part of separation gas flows through inner labyrinth teeth of rear seal and mixes with minor leaked gas from secondary sealing faces for high-point venting; the other part flows through outer labyrinth teeth of rear seal and vents via bearing oil drain port.
Pre-commissioning operation precautions for dry gas seal system?
Switch on separation gas 10 minutes before startup of lubricating oil system. Similarly, cut off separation gas 10 minutes after oil system shutdown. Separation gas cannot be interrupted during oil circulation, otherwise seal damage will occur.
Slowly open upper and lower ball valves when putting filters into service to avoid instantaneous pressure impact and damage to filter cartridges.
Slowly open upper and lower ball valves for flowmeters to maintain stable flow.
Check stability of gas source pressure for primary seal gas, secondary seal gas and separation gas, and inspect filter blockage status.
Liquid transfer operation of V2402 and V2403 in refrigeration station?
Normal liquid level of V2402 and V2403 shall be established before startup. Procedures are listed as follows:
Before liquid level establishment, open drain valves from V2402/V2403 to V2401 pipeline in advance, confirm the 8-shaped blind plate is switched, confirm drain valve to V2401 is closed, confirm LV2420 and its upstream & downstream isolation valves are fully open, confirm FV2401 and FV2402 are fully open.
Propylene is introduced into V2402 by pressure difference. Slightly open main outlet valve of V2401, XV2482, valve between V2401 and V2402, LV2421 and its upstream & downstream valves one by one, and slowly build propylene liquid level inside V2402.
Pressure balance exists between V2402 and V2403; propylene can only be transferred into V2403 via liquid level difference. Liquid transfer must be operated slowly to prevent overpressure of V2402 and V2403. After normal liquid level is achieved, close LV2421 and its upstream & downstream valves, close drain valves from V2402/V2403 to V2401 pipeline, and restore blind plate.
Emergency shutdown procedure for refrigeration station?
Emergency shutdown of the compressor shall be triggered upon faults including power failure, oil pump failure, explosion, fire, cooling water cutoff, instrument air loss, and irreversible compressor surge. In case of system fire, rapidly cut off propylene supply and maintain pressure via nitrogen purging.
Trip the compressor on-site or in control room; measure and record coast-down time if possible. Switch compressor primary seal gas to medium-pressure nitrogen.
Continue barring the rotor immediately after rotation stops if oil circulation remains operational (non-power failure and low-pressure nitrogen available). In case of plant-wide power failure, turn operation buttons of jet pump, condensate pump and oil pump to OFF position to avoid automatic startup upon power recovery.
Close secondary-stage outlet valve of compressor.
Shut off main propylene inlet and outlet valves of refrigeration system.
Stop jet pump and shaft sealing steam when vacuum degree approaches zero.
Adjust recirculation flow; slightly open supplementary desalinated water valve if necessary. Shut down condensate pump after closing air suction valve of ejector.
Investigate root cause of emergency shutdown.
Emergency shutdown procedure for combined compressor?
Emergency shutdown of the compressor shall be triggered upon faults including power failure, oil pump failure, explosion, fire, cooling water cutoff, instrument air loss, and irreversible compressor surge. In case of system fire, rapidly cut off propylene supply and maintain pressure via nitrogen purging.
Trip the compressor on-site or in control room; measure and record coast-down time if possible. Continue barring the rotor immediately after rotation stops if oil circulation remains operational (non-power failure and low-pressure nitrogen available). In case of plant-wide power failure, turn operation buttons of jet pump, condensate pump and oil pump to OFF position to avoid automatic startup upon power recovery.
Timely switch primary seal gas to medium-pressure nitrogen, confirm closure of XV2683, XV2682 and XV2681. Open PV2620 in control room and relieve compressor system pressure at a controlled rate ≤0.15 MPa/min. If power failure or instrument air loss occurs, XV2681 closes automatically. Notify compressor operators to open secondary-stage outlet valve for manual pressure relief.
Stop jet pump and shaft sealing steam when vacuum degree approaches zero.
Adjust recirculation flow; slightly open supplementary desalinated water valve if necessary. Shut down condensate pump after closing air suction valve of ejector.
Investigate root cause of emergency shutdown.