cameron compressor operation

Engineering Specification AAIL-2861

Revision 01: January 20, 2010

Compressor Operation

Compressor Operation (IL-2861) of 13

Table of Contents:

Principles of Operation .......................................................................................................................... 3

Compressor .................................................................................................................................. 3

Lubrication .................................................................................................................................... 4

Surge Control Line Theory ........................................................................................................... 5

Compressor Safety Guidelines ............................................................................................................. 6

Routine Startup ...................................................................................................................................... 7

Routine Shutdown .................................................................................................................................. 8

Special Requirements for Elevated Inlet Pressures ........................................................................... 9

Operation Restriction .................................................................................................................... 9

Design Criteria .............................................................................................................................. 9

Compressor Safety Mechanisms ........................................................................................................ 10

Operating Principle ..................................................................................................................... 10

Recommended Measurement Points ......................................................................................... 10

Alarm and Trip Conditions .......................................................................................................... 10

The Operating Data Record ................................................................................................................. 11

Revision History ................................................................................................................................... 13

NOTE: The intent of this specification is to provide general operating guidelines for centrifugal compressors, surge line control theory, and routine startup and shutdown procedures. This document does not incorporate all operating scenarios, and any questions regarding the compressor operation should be directed to Cameron.


Principles of Operation

Compressor Cameron’s centrifugal line of multi-stage gear (MSG) compressors utilize dynamic compression to

generate the necessary pressure and flow requirements of air, nitrogen, or a specific process gas. The

centrifugal compressor consists of a low speed increasing gear (bullgear) which rotates high speed

output shafts (pinions) and mounted impellers. A typical compressor gearbox can have one to three

high speed output shafts as well as a total of one to six impellers, or stages of compression. Depending

on the customer’s requirements, a compressor package may have multiple processes on the same

gearbox, or even multiple interconnected gearboxes.

Gas enters each stage axially, where the high speed rotating impellers greatly increase the velocity of

the gas, through the principle of centrifugal force. As the high velocity gas leaves the impeller, it enters

the small space of the diffuser. The non-rotating diffuser surrounds the impeller, reducing the velocity

of the gas, causing the gas’s pressure and temperature to increase.

A scroll or volute casing surrounds the diffuser, providing a smooth exit path with minimal pressure

loss. If higher pressure is required for the process, the gas goes through an intercooler where heat is

removed from the gas before continuing to the next stage(s) of compression, until the necessary

process conditions are achieved.

Figure 1 – A typical three stage compressor


Lubrication The lubrication system provides a constant supply of cooled and filtered oil to the compressor bearings

and gear sprays. Unlike some other types of rotating equipment, high speed, integrally geared

compressors cannot operate, even for very brief periods, without adequate lubrication. No interruption

can be permitted in the lube oil supply.

Before startup, the electrically driven auxiliary oil pump is started to provide lubrication to the bearings

and gearing, and to obtain a permissive start signal. During startup, the mechanically driven main oil

pump comes up to speed and takes over the function of providing oil flow and pressure. The auxiliary

oil pump is signaled to switch off and remains off during normal operation.

During normal operation, oil is drawn from the reservoir by the main oil pump. Oil is prevented from

being pumped back in the reservoir through the auxiliary pump by a check valve. Another check valve

blocks the oil flow through the main pump when the auxiliary pump is operating. Cooling water flowing

through the oil cooler removes heat from the oil. Regulating the oil flow through the oil cooler maintains

the operating temperature of the oil. The oil filter removes particulate, which could be harmful to

compressor bearings and gearing. Oil temperature and pressure are sensed using pressure

transmitters and RTDs. The proper operating pressure is maintained by a pressure regulator, which

takes place before the oil enters the compressor gearbox and returns excess oil to the reservoir. The

oil entering the manifold of the compressor gearbox is distributed through oil passages to the journal

bearings and thrust bearings. The oil is also distributed to nozzles, which are positioned to direct a

constant spray of oil at the gear mesh to lubricate and cool the gearing.

Should a malfunction result in loss of oil pressure, it will be detected by the oil pressure transmitter,

activating an alarm and starting the auxiliary pump. Normal oil pressure will be restored by the auxiliary

pump, and the compressor will continue operating. If the oil pressure continues to decrease to the trip

set point, the compressor driver will be automatically shutdown.

Figure 2 – A typical lubrication system for a compressor


Surge Control Line Theory Compressor surge is caused when the flow through the compressor is too low at a given pressure. At this point the impellers are compressing more gas than the process requires, and the gas flows through the compressor in the reverse direction. This is detected as an audible “whoomphing” noise from the compressor. Although surging a Cameron compressor on occasion is not a problem, repeated surging will cause the impellers to overheat and would eventually damage the impellers and/or the bearings. In order to prevent this condition, a blow-off valve is added between the compressor discharge and the check valve. When process requirements are reduced to a flow below the surge flow the blow-off/recycle valve is modulated open to prevent a surge from occurring. This will increase the flow through the compressor, while maintaining the required process flow, preventing a surge.

Figure 3 - Surge control line (pressure vs. flow)

Figure 3 above shows the pressure vs. flow relationship of the compressor. At start-up the compressor will begin to produce flow and the operating point will move along the flow axis until the process begins to produce a back pressure. The operating point then moves up the curved operating line. Which curved operating line it follows is dependent upon changes in IGV setting and process demands. This curved line is showing that while the pressure is increasing the flow is decreasing. If left unchecked, the pressure would increase and the flow decrease until the compressor surged. The dots on the figure represent the points at which the compressor surged. After locating four points, a line can be drawn as a best fit between these points. This is considered the surge line for the compressor. The compressor is considered in surge for all points to the upper left of this line. Points below the surge line are in the normal operating region. The surge line is dependent upon many factors including process conditions, such as inlet temperature. Therefore, the control line may need to be periodically redefined according to process changes and climate cycles.


Compressor Safety Guidelines

The compressor is a piece of high-speed rotating machinery. The same common sense precautions

should be observed as with any piece of machinery of this type. Carelessness in operation or in

maintenance could result in serious injury to personnel. Below are some typical safety precautions to

consider.

o Read and become familiar with the contents of the complete IOM (Installation, Operations, and

Maintenance Manual) before starting the compressor.

o Be certain that all electrical enclosures and components are correctly installed and grounded

according to any applicable national and local codes.

o Do not rewire the Cameron supplied control panels without express written consent from Cameron.

o Do not operate the compressor in areas where there is any possibility of it ingesting flammable or

toxic fumes.

o Do not use unfiltered discharge gas for breathing or for food processing, doing so could cause

severe injury or death.

o If gas from the compressor is to be used for breathing or food processing, first consult a filtration

specialist for additional filtration and treatment equipment to ensure that all applicable health and

safety standards are met.

o Wear appropriate eye and hearing protection when the compressor is operating.

o Do not operate the compressor at pressures exceeding the nameplate rating.

o Do not play with compressed gas or use it carelessly.

o Some surfaces of the compressor and motor have high surface temperatures. Keep hands and

other body parts away from those areas while the compressor is operating or recently shut down.

o Keep the area of compressor installation clean and tidy, and avoid leaving tools, rags, or loose

parts on compressor or drive parts.

o Do not attempt to service the compressor while the machine is operating.

o Do not remove the protective guards when the compressor is operating.

o Always close the discharge block valve or isolation valve and relieve the system of pressure before

removing any caps or plugs and/or before servicing the compressor.

o Since hot oil under pressure could cause injury, allow ten minutes of cooling time after the oil pump

is shut down before any service is conducted on the machine.

o Do not use flammable solvents for cleaning parts of the compressor.

o Periodically check all safety devices for proper operation.

Safety Disclaimer The owner or operator of the compressor is hereby notified and forewarned that any failure to observe

common safety precautions, whether stated herein or not, may result in damage or injury. Cameron

disclaims responsibility or liability for damage caused by failure to observe those specified, or other

common precautions or by failure to exercise ordinary caution, common sense and due care required in

operating or handling the compressor even though not expressly specified above.


Routine Startup

Use this procedure to start the compressor on a routine basis. Some steps may occur automatically as part of the control system start sequence.

WARNING Only fully trained personnel should be allowed to start and operate this

compressor. Failure to comply may result in serious injury or death.

1. Refer to the manufacturer’s instructions for the main drive controller (starter) and carry out the

recommended pre-starting procedures.

2. Check that the oil level in the oil reservoir sight gauge is above the center (normal operating level).

3. Apply instrument air to the control panel, control valves, transmitters, and buffered oil seals (if applicable).

4. Turn on the cooling water supply to the oil cooler, intercoolers, and aftercoolers.

5. Apply power to the compressor control system.

6. Apply air (or electrical power as needed) to the oil reservoir venting system and adjust appropriately to maintain the proper vacuum.

7. Start the auxiliary lube oil pump.

8. Check that the bypass valve or blow-off valve is open, and the inlet guide vane or throttle valve is

closed for compressor startup.

9. For compressors that operate at an elevated inlet pressure, vent the gas in the compressor so that no load is applied to the compressor during startup. No load is defined as 10% or less of the design mass flow. Alternative methods of reducing mass flow to the compressor must be approved by Cameron on an application specific basis.

10. Check the lube oil pressure and temperature. Normal operating pressure for the lubrication system

is 20 PSI (1.38 BAR, 0.14 Mpa). Normal operating temperature, measured at the gear case inlet, is 110°F to 130°F (43°C to 55°C). Minimum oil temperature for startup is 70°F (21°C).

11. Start the main drive motor and allow the compressor to come up to speed.

12. Put the compressor on line according to the instructions supplied with the control system.

CAUTION Unusual sounds or excessive vibration can indicate internal rubbing,

worn bearings, or shaft misalignment. Stop the compressor immediately if noise indicates a mechanical malfunction.


13. Check the compressor for gas or oil leaks.

14. Check that the inlet gas temperature is maintained within 10°F (5.6°C) of temperature listed in the data sheets for this compressor.

15. Check oil pressure and temperature; verify auxiliary oil pump shuts down.

WARNING DO NOT operate the compressor at pressures greater than the

nameplate rating. Doing so could result in equipment damage or personal injury.

Routine Shutdown Use the following procedure to shutdown the compressor under normal conditions. Some steps may occur automatically as part of the control system stop sequence.

1. Open the intercooler shell drains just prior to shutting down the compressor.

2. Unload the compressor according to the instructions previously provided (see startup step #8 and #9).

3. Press the stop button on the drive motor starter panel. This starts the auxiliary oil lube pump which

should be allowed to run for 30 minutes after the compressor shutdown to remove heat from the gearbox. Allow cooling water to continue circulating through the lube oil cooler. It is recommended that the auxiliary oil pump remain on during shutdown to prevent condensation and possible corrosion of compressor gearing if the compressor is outdoors or in ambient temperatures below 50°F (10°C).

4. Oil reservoir venting must remain on while the auxiliary oil pump is on and/or compressor is running, to prevent oil seepage from the oil seals.

5. Turn off the supply of instrument air to the control panel and control valves.

6. Allow the cooling water and oil to circulate to remove heat for at least 30 minutes after shutdown

and then turn off the water supply. During this time the oil reservoir venting system should remain running.


Special Requirements for Elevated Inlet Pressures

This section is applicable to all Cameron centrifugal compressors which are designed for inlet pressures substantially higher than atmospheric conditions. When multi-process compressors are involved, these criteria apply only to the portion with the elevated inlet pressure. Unless specifically designed for operation at specified off design conditions, operating for any extended period of time at off design conditions may result in failure and/or reduced operating life of the compressor.

Operation Restriction The compressor user/operator is required to provide inlet pressure protection to prevent over-pressurizing and/or overloading the compressor. Inlet pressure control is preferred to discharge pressure control because both over-pressure and overload protection is necessary. Without inlet pressure control, higher than desired mass flow could still pass through the machine. Cameron recommends that the inlet pressure not be allowed to exceed 110% of the design inlet pressure condition as stated on the compressor nameplate. After startup, the compressor must be brought to the design pressure ratio(s). This pressure ratio needs to be maintained during the loading and normal operation of the compressor. The compressor must be kept out of surge during the loading sequence and operation.

WARNING Failure to apply this method of operation may produce aerodynamic

instabilities in one or more stages with possible substantial increase in rotor vibration and subsequent compressor damage.

NOTE Brief excursions above the design inlet pressure are acceptable.

However, it is understood that these excursions are created by system upsets and time allotted is for control and adjustments only.

Design Criteria For every contract, unless otherwise specified, pressure containing components (scrolls, piping, seals, intercoolers, etc) and mechanical components (gearing, bearings, etc) are designed using an over-pressure tolerance of 10% above the specified design operating conditions. Any requirements in excess of 10% must be specified prior to the design of the compressor and may impact cost of the overall package. Surge recycle valves need to be sized to accommodate both normal and startup operation to prevent surging of the compressor.

WARNING Operation above the mechanical design limits will cause premature

wear and/or severe damage to the compressor.


Compressor Safety Mechanisms Most control systems provide compressor protection to ensure correct and safe operation of all compressor systems by continuously monitoring vital functions. Whenever operating conditions diverge from predetermined safety parameters (set points or operational limits), the control system should automatically activate an appropriate system response.

Operating Principle Strategically located sensor devices provide measurements of the compressor’s vital operating parameters. A typical control system monitors these measurements and responds to specific changes that occur. The control system may provide a display of current readings for adjustment, data logging, trending, or other diagnostics. In the event of a condition that deviates from predetermined values, the control system may also display a log of events.

Recommended Measurement Points The table below lists the various standard measurements taken by the sensor devices described above. Subsequent tables list optional measurements or calculated conditions that may require additional sensors or other instrumentation.

Standard Measurements

System Gas Pressure (mode dependent)

Compressor Discharge Pressure (mode dependent)

Last Stage Inlet Gas Temperature

Stage Vibration

Oil Pressure

Oil Temperature

Main Drive Motor Current

Main Drive Motor Running Signal

Emergency Stop Signal

System Flow

Alarm and Trip Conditions Monitor points connected to the control system should be configured to activate safety mechanisms, when the measured value exceeds designated operating limits. The type of mechanism activated can be a warning signal (alarm) or an automatic protective action (trip). Records should be kept in the event of either occurrence.

Alarm: When an alarm condition occurs the compressor system continues to operate but the control panel automatically signals to the operator that an event has occurred. It is then the responsibility of the operator to acknowledge the alarm and determine the next course of action.

Trip: A trip condition is more extreme than an alarm event and initiates a complete compressor shutdown to protect vital components. Shutdown occurs if operating conditions exceed predetermined operational safety limits. Corrective action is necessary before the compressor can be put back into service.


The Operating Data Record Cameron recommends keeping an Operating Data Record, either manually or electronically. As part of an effective preventative maintenance program this record shows dates of inspections and a running log of operating data. A properly maintained record is invaluable as a trend analysis tool or to diagnose a major malfunction. This record should contain recorded values of the checklist items below along with spaces for the operator’s initials and the time and/or date. This ensures that each item or procedure receives attention at the recommended intervals. Maintaining the Operating Data Record is part of the Daily Inspection Checklist described in the Maintenance section. Cameron recommends recording the following values in the Operating Data Record. Some options shown may not be included on every unit.

Operating Data Record Information

Pressure Points: Vibration Points:

System Gas Pressure First Stage Vibration

Compressor Discharge Pressure Intermediate Stage(s) Vibration

Oil Pressure Final Stage Vibration

Inlet Filter Pressure Drop Inboard Motor Bearing Vibration

Oil Filter Pressure Drop Outboard Motor Bearing Vibration

Temperature Points: Additional Points:

Last Stage Inlet Gas Temperature Main Drive Motor Current

Oil Temperature Compressor Flow

Second Stage Inlet Gas Temperature Time

Inboard Motor Bearing Temperature Date

Outboard Motor Bearing Temperature Operators Initials

Motor Stator Temperature (A, B, C)


Operating Data Record

General Information

Serial Number: Total Running Time:

Model: Recorded By: Date:

Gas System

o System Gas Pressure:

o Compressor Flow:

o Inlet Gas Filter Pressure Drop:

o Inlet Gas Pressure (at Compressor):

o Discharge Gas Pressure:

o Discharge Gas Temperature:

o Stage 1 Inlet Temperature:





o Stage 6 Inlet Temperature: Vibration Levels

o Stage 1 Vibration:





o Stage 6 Vibration: Lubrication System

o Oil Temperature:

o Oil Pressure:

o Oil Filter Pressure Drop:

o Oil Tank Vacuum: Cooling System

o Coolant Temperature: (In / Out) /

o Coolant Pressure: (In / Out) /

Drive Motor

o Motor Current:

o Ambient Temperature:

o Motor Bearing Temperatures:

o Motor Stator Temperatures: Miscellaneous

o

o o


Revision History

Rev ID ECO Number Date Author Change Description 01 2433145 1/20/2010 N.Botkins Initial Release

Department Approval Date

Prepared By: N.Botkins / C.Impastato

Engineering

Reviewed By: N.Botkins / C.Impastato

Engineering

Approved By: C. Impastato

Engineering

Approved By:

Spec to be electronically distributed to CTC-MSG IL&EDR Distribution Listing in Global Contacts. Ref. DEP-1108

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