Turbine plant systems

British Electricity International, in Turbines, Generators and Associated Plant (Third Edition), 1991

6.2.3 AC and DC motor-driven auxiliary oil pumps

The AC and DC auxiliary oil pumps which supply oil to bearings under start-up and normal shutdown, or under emergency shutdown respectively, are centrifugal pumps with a submerged suction. They are also suspended from the tank top and their arrangement is very similar to Fig 2.56, but with an AC or DC motor replacing the oil turbine. The AC pump delivers oil to the lubricating oil pipework feeding the oil filters and coolers at around 3 bar, and primes the main oil pump. The DC pump feeds either the same pipework system as the AC pump, or the pipework which feeds oil directly to the bearings at around 1.5 bar. Each pump has a capacity of around 70-120 litres/s.

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Major Process Equipment Maintenance and Repair

In Practical Machinery Management for Process Plants, 1997

Routine Startup, Pressure Lubricated Turbines

1.

Check the oil reservoir for proper oil level. Start the auxiliary oil pump (if provided) and circulate oil through the system.

2.

Ensure that the oil temperature is 50°F to 70°F (10°C to 20°C) before operating the turbine.

3.

Place all controls, trip mechanisms and other safety devices in their operative positions. Open hand nozzle valves (1, Figure 8-6), if furnished.

4.

Open all drains from steam lines, turbine casing and steam chest.

5.

If condensing, close all drain valves when drain lines indicate the system is free of water.

6.

Open the turbine exhaust valve. If condensing, start the condensing equipment.

7.

Open the inlet steam shutoff valve and bring the turbine up to rated speed. If noncondensing, close the drain valves when the system is free of water. If condensing, admit sealing steam to the packing cases when the rotor shaft begins to rotate.

8.

Make necessary governor adjustments to attain desired speed as load is applied.

9.

Observe bearing temperatures and introduce sufficient cooling water to the oil cooler to maintain bearing oil temperatures of 140°F to 190°F (60°C to 88°C).

10.

Check the overall operation to determine all conditions to be satisfactory.

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Flushing of Lube Oil Piping System

Dipak K. Sarkar , in Thermal Power Plant, 2017

7.6.2 Oil Circulation

The flushing medium must be circulated with the help of the starting oil pump or auxiliary oil pump or temporary flushing oil pump to establish the requisite flow as recommended by the manufacturer. Each lubricating oil pump and auxiliary pump should be used during the flushing period. Put the vapor exhausters and oil heaters of the MOT in service. Raise temperature of oil to 343–353  K, then stop heating the oil. Heating of oil may be recommenced once oil temperature drops to 313–323   K. The circulation shall be generally continuous with stopping from time to time for inspection and cleaning of temporary strainers. Experience reveals that almost all of the foreign matter is collected in the filters or temporary strainers during the first few hours of flushing. During this time, whenever a noticeable increase in pressure drop across the strainers is observed, the strainers should be cleaned and replaced. This may occur as frequently as every 15   min at the beginning (Clause 7.7.2 [4]).

To facilitate dislodging of debris, rust, weld beads that may have adhered to inner surface of piping, particularly at joints and flanges, and other loose materials inside piping, as well as to make removal of debris along with the flushing oil flow easier, it is recommended to pound the oil lines with a rawhide hammer, rubber mallet, or pneumatic vibrator along the direction of the oil flow so that it is just sufficient to initiate some vibration and thermal shock in the pipe section without causing any indentation. The pounding shall continue for a few hours on each section while maintaining as high rate of flow as possible through this section.

In the event any scale is retained in the pipe line even after chemical cleaning, this scale is dislodged by allowing the oil temperature to drop by 28–32   K for 2–3   h during flushing to allow for pipe contraction (Clause 7.7.4 [4]). Repeat the circulation process with proper heating of oil.

During the flushing operation, it may be required to remove the top housing of bearings to permit hosing of journals if it is suspected that damage by abrasive matters might otherwise occur. On completion of oil flushing, it would suffice to examine two or three bearings to determine whether any extraneous matter will have to be removed manually.

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Start-Up and Shut-Down

Dipak K. Sarkar , in Thermal Power Plant, 2015

12.6 Normal Shut-Down of Steam Turbine

1.

Inform the boiler house that the turbine is being shut down

2.

Ensure auxiliary oil pump and emergency oil pump are available and are ready for operation

3.

Ensure the HP-LP bypass controllers are ON

4.

Check for non-seizure of ESVs and IVs

5.

Unload the turbine by gradually closing the control valves; the unloading should be carried out at a rate determined by the manufacturer's guidelines

6.

During unloading always keep watch on the following parameters to ensure they remain within the permissible limits:

i.

Differential contractions of turbine, especially of HP rotor

ii.

Bearing vibration

iii.

Steam-metal differential temperature margin

iv.

Differential temperature between upper and lower halves of turbine casing

7.

For minimizing the contraction of the HP rotor during shut-down admit main steam to HP front gland, if recommended by the manufacturer

8.

Start the auxiliary oil pump and ensure that oil pressure in lube oil system is normal

9.

Maintain lube oil temperature

10.

After unloading the turbine to no load, trip the turbine manually

11.

Ensure the ESV, IV, and control valves get closed

12.

Ensure the extraction steam line block valves closed

13.

Ensure the non-return valves at the HP turbine exhaust are closed

14.

Ensure the generator is isolated through reverse power/low forward power relay

15.

Verify that the field breaker is switched off

16.

With the tripping of generator circuit breaker the HP-LP bypass system becomes operative; this may be used to stabilize boiler conditions and maintain steam flow through reheater until the boiler is shut down

17.

Start jacking oil pump

18.

When rotor speed falls to a predetermined low value, put the rotor on turning gear manually or turning gear may cut-in automatically. The rotor should remain on turning gear till temperature of HP casing falls below a recommended limit

19.

Stop jacking oil pump

20.

Follow the manufacturer's guidelines to open drain valves as follows:

i.

HP turbine casing

ii.

Before-seat and after-seat drain valves of non-return valves on turbine extraction steam lines

iii.

Warm up drain valves for emergency stop valve/s and control valves

21.

Close the HP-LP bypass valves

22.

Stop the boiler firing per the recommendation of the boiler manufacturer and bottle up the boiler

23.

Break the condenser vacuum once the fire in the boiler is killed

24.

When the vacuum falls to zero, stop the gland steam supply

25.

Stop the condensate extraction pump

26.

The CW pump may be stopped when the temperature of the exhaust part of the LP turbine falls to 328   K or to a value recommended by the manufacturer

27.

Open the drain valves on main steam piping

28.

Open drain valves on cold and hot reheat piping

29.

As the unit cools down and water shrinks, add make-up water intermittently to the boiler to prevent the drum level from dropping below the visibility limit of drum level gauge glass.

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Dynamic compressors

Maurice Stewart , in Surface Production Operations, 2019

8.6.7 Lube and seal oil systems

The lubrication of centrifugal compressors is normally handled by a pressurized system, which also provides the seal oil and control oil in some cases. One system usually supplies all machines in a given train (such as the compressor, any gears, and the driver).

A basic pressurized lube system consists of a reservoir, pumps, coolers, filters, control valves, relief valves, instrumentation, and other auxiliaries specific to the application.

Seal oil may be provided from a combined lube and seal oil system, or from a separate seal oil system. Generally, combined systems are selected for sweet gas services. Separate seal oil systems are generally selected for compressors in services that contain hydrogen sulfide or other corrosive or toxic gases. In either type of system, the inner (called "sour") seal oil leakage is not returned to the reservoir. The outer (called "sweet") is returned to the reservoir. Under certain conditions, it is possible for sour gas to migrate into the outer seal oil stream that is returned to the reservoir. Having a separate system positively avoids contamination of the lubricating oil and subsequent corrosive attack of Babbitt-lined bearings and other components served by the lubricating oil system.

API 614, "Lubrication, Shaft-Sealing, and Control Oil Systems for Special Purpose Applications" cover the design, manufacture, and testing of the overall system, as well as individual components. Used as a reference, they provide guidelines based on user experience which can easily be scaled down or tailored to fit any requirement.

The system may be designed either as a console or baseplate-mounted package, with all components mounted on a single baseplate, or alternatively as a multiple-package arrangement, with system components separated into individually packaged units. In this case, the individual component packages are piped together in the field.

Oil return lines must slope toward the reservoir(s) to allow gravity draining. This is often overlooked when piping is being laid out. Also, one must be careful to avoid "head knockers" when laying out pipe.

Offshore installations may require a system mounted integrally with the compressor/driver baseplate, with off-mounted air coolers.

The console arrangement, because of its compact layout, may limit or restrict access to various components making maintenance difficult. The multiple-package arrangement allows greater flexibility in locating the individual packages for improved maintenance access. A major disadvantage of the multiple-package arrangement is that the complete system is seldom shop tested and therefore performance is not verified prior to arrival on site.

Careful attention at all phases from initial specification through installation and start-up will contribute significantly to trouble-free compressor train start-up and operation. Historical maintenance data from many compressor installations indicate approximately 20%–25% of centrifugal compressor unscheduled downtime results from instrument problems (many of these associated with operation and control of the lube and seal system).

When designing or modifying a system, obtain specific input from field personnel regarding site requirements, preferences, and operating experience. Field personnel may have already modified the basic system to correct problems experienced, found a particular type or brand of instrument that functions better under their site conditions, or standardized on components to reduce spare parts inventories, and so on.

The following highlights areas requiring special attention:

•

For critical or nonspared equipment, include a main and an identical full-sized auxiliary oil pump (not to be confused with an emergency oil pump which is normally of much smaller capacity, sized only to handle lube and seal requirements during coast-down). A popular drive arrangement for turbine-driven compressors is a steam-turbine-driven main oil pump with an electric motor-driven auxiliary. This arrangement has the advantage that auto-start control of the electric-motor driven unit is relatively simple and reliable with rapid acceleration to full speed and rated pressure output. For installations where steam is not available, several alternative drive combinations are used, including motor, shaft driven, and in a few cases air or gas expanders. With motor-driven main and auxiliary pumps, each should be supplied by an independent power source.

•

Consider adequate oil flow to bearings and seals during coast-down following a trip of the auxiliary pump. The two approaches used most often involve either an emergency oil pump or overhead rundown tanks. Overhead rundown tanks are typically located to provide an initial pressure (head) equal to the low oil pressure trip pressure. API requires capacity to be sufficient to supply oil for a minimum of three minutes. In the majority of cases this is adequate. A second method is an emergency oil pump. This pump would probably be direct current (DC) motor driven, with power supplied by a battery-backed UPS system.

•

Manufacturers often insist that the response time of a motor-driven auxiliary pump is sufficient to avoid pressure decay tripping the main unit, and therefore accumulators are not required. However, several tests have shown this not to be the case. The option should always be held open so that accumulator requirements are based on the system demonstrating acceptable stability during the prescribed testing.

•

The system rundown tanks and the accumulators are sometimes confused. The rundown tanks provide lubrication and cooling to bearings and seals during coast-down. The accumulator is designed to maintain system pressure within specified limits during transient conditions or upsets, thus avoiding machinery trips.

•

When oil seals are used, the manufacturer is normally asked to guarantee a maximum value for this inner seal oil leakage. The guaranteed value is often found to be considerably lower than actual leakage on test or following start-up. Since size of the degassing tank is based on this leakage rate, the tank often ends up being undersized. API specifies that the degassing tank be sized for a minimum of three times the guaranteed inner seal oil leakage. Actual machine be shutdown. Leakage, however, has in some instances exceeded quoted values by more than 10 times. The manufacturer's sizing criteria should be verified based on review of leakage rate tests for similar seals.

•

For centrifugal lube oil pumps, the pump head should be compared to the maximum allowable filter pressure drop (of dirty filters) to ensure that sufficient oil flow is provided to the machinery as the filters become dirty.

•

Shaft-driven main lube oil pumps are not recommended, since any maintenance or repair of this pump requires the machine to be shutdown.

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Maintenance of Electric Motors

K.C. Agrawal , in Industrial Power Engineering Handbook, 2001

Additional checks for large motors

•

Check for proper connection and circulation of fluid or gas in the coolant circuit (Section 1.16).

•

Check for satisfactory operation of auxiliary oil pump and fan.

•

Check all safety devices such as temperature sensors in the windings and the bearings, PTC thermistors, vibration probes, space heaters and coolant circuit, for their correct fitting, wiring and functioning of the alarm, annunciation and tripping circuit of the protective switchgear (Section 12.8).

•

Check for satisfactory functioning of all gauges, indicators and recorders.

•

Check for bearing insulation (dealt with separately in Section 10.4.5).

•

Check for bearing housing grounding.

•

Check for winding insulation by polarization index (Section 9.5) and dissipation factor, tan Δ (Section 9.6)

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Application of Hot Gas Turboexpanders

Heinz P. Bloch , Claire Soares , in Turboexpanders and Process Applications, 2001

Lube Oil Units

Lube oil units are typically available in two versions: the manufacturer's standard or in accordance with AP1 Standard 614. The major components of a unit are the oil tank, auxiliary oil pump, double filter and, selectively, one or two oil coolers. All components of the smaller units are mounted on a common bedplate, separated from the other components. The oil can be heated by an electrical or steam-powered heating unit. The necessary instrumentation is a standard supply item and, if requested, the switches and motors can be prewired. The main and auxiliary oil pumps are driven by different types of drivers (e.g., one by an electric motor and the other by either a small steam turbine or by direct connection to the shaft end of a major machine casing in the turbotrain).

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Lube and Seal Oil System Key Safety and Reliability Issues

William E. Forsthoffer , in Forsthoffer's Proven Guidelines for Rotating Machinery Excellence, 2022

Awareness information

Check system transient functions (pump transfer) immediately before turnaround. I recommend that the following procedure be followed immediately before each scheduled shutdown of critical (unspared) machinery units:

1.

Confirm auxiliary oil pump start switch or transmitter actuates at the proper setting and starts the auxiliary oil pump.

2.

Put auxiliary oil pump in auto start mode and station an operator at auxiliary oil pump with instructions to immediately manually start auxiliary oil pump if compressor unit trips.

3.

Trip main oil pump and observe the following (with strip charts, if possible):

A.

Auxiliary oil pump starts without unit trip

B.

Lowest tube oil pressure during transient

C.

Lowest control oil pressure during transient

D.

That all control valves remain stable

The previously mentioned procedure is the only way to assure that the transient response of the oil system will not cause a trip during operation. The amount of oil taken by the machinery components during operation is more than during the stationary unit case (when the unit is not operating). Performing the transient check just prior to the turnaround will allow ample time for any corrective action. Most functional oil system checks are performed at turnarounds with the unit offline only to find during operation that the system cannot respond to a transient event without a unit trip.

Functional testing

All auxiliary equipment should be functionally tested, and all instruments and controls checked for proper setting prior to operation of equipment after a TA. I strongly recommend that this functional test be also be performed while the unit is in operation prior to a planned shutdown. A functional test outline is included in the back of this section. We will highlight the major considerations of the procedure at this time.

It is recommended that the console vendor and/or the equipment purchaser prepare a detailed field functional test procedure and calibration check form. The format of this procedure can follow the factory test procedure if it was acceptable. As a minimum, the auxiliary system, bill of material, and schematic should be thoroughly checked in order to include the calibration and functional test of each major component in the auxiliary system. That is, components on consoles, and up at unit interfaces. A detailed record should be kept of this functional test procedure. This will help significantly during the operation of the unit. The functional test procedure should be accomplished without the critical equipment running initially and then with the auxiliary system at design operation conditions as closely as possible.

The functional test procedure should first require that all instrumentation be properly calibrated before proceeding. Each specific functional test requirement should then be performed and results noted. If they do not meet specified limits as noted, testing should stop, and components should be corrected at this point. Each step should be followed thoroughly to assure each component meets all requirements. It is recommended that operators assigned to this particular unit assist in functional testing to familiarize themselves with the operation of the system. In addition, site training courses should be conducted prior to functional test to familiarize operators with system's basic functions. This training, again, significantly increases understanding of the equipment and assures unit reliability.

Satisfactory acceptance of a functional test then assures that the unit has been designed, manufactured, and installed correctly such that all system design objectives have been obtained and that equipment reliability is optimized.

One remaining factor to be proven is the successful operation of the system with the critical equipment unit in operation. During initial start-up, it is recommended that the functional test be reperformed with the unit operating. While this advice may seem dangerous, unless the unit operators are assured that the subject system has the ability to totally protect critical equipment while operating, auxiliary equipment will never be tested while the unit is in operation.

Remember, critical equipment is designed for 30   years or greater life. The components that comprise the auxiliary system are many and have characteristics that will change with time.

Therefore reliability of auxiliary systems can only be maintained if the systems are totally capable of online calibration and functional checks. The functional precommission procedure should be modified to include an online periodic functional checking procedure.

At this point, we can clearly see that the major determination of continued equipment reliability rests with the operation, calibration, and maintenance of the equipment. In order to assume maximum continued auxiliary equipment reliability, periodic online functional checks and calibrations must be performed. How can this be done? The only way is by convincing plant operations of the safety and reliability of the procedure for online checking. This can be reinforced during precommissioning by including operators in functional testing checks and on-site training sessions to show the function of the system. A site training course modified for the specific equipment would prove immensely valuable in achieving those results.

Only by involving unit operators in the prestart checkups can it be hoped to establish a field functional checking procedure that will be utilized and followed through. Remember, a pressure switch less than $400 in cost could cause equipment shutdown that could reduce on-site revenue on the order of one to two million US dollars a day. The pressure switch selected could be the best, the highest quality in the world, properly installed and set. If its calibration is not periodically checked, it could cause an unnecessary shutdown of equipment and result in this revenue loss.

Functional lube/seal system test procedure outline

Objective: To confirm proper functional operation of the entire system prior to equipment start-up
Procedure format: Detail each test requirement. Specifically note required functions/set points of each component. Record actual functions/set points and all modifications made.
Notes:
1.

All testing to be performed without the unit in operation for initial plant start-up or after modifications are made to the system.

2.

After the test is successful, the transient items of the test (auxiliary pump start, second pump started) should be retested with the unit in operation

3.

The test in item 2 should be repeated just before the unit is shutdown prior to each TA
I

Preparation

A.

Confirm proper oil type and reservoir level.

B.

Confirm system flush is approved and all flushing screens are removed.

C.

Confirm all system utilities are operational (air, water, steam, electrical).

D.

Any required temporary nitrogen supplies should be connected.

E.

All instrumentation must be calibrated, and control valves properly set.

F.

Entire system must be properly vented.

II

Test procedure

A.

Oil Reservoir

1.

Confirm proper heater operation.

2.

Check reservoir level switch and any other components (TIs, vent blowers, etc.).

B.

Main pump unit

1.

Acceptable pump and driver vibration.

2.

Absence of cavitation.

3.

Pump and driver acceptable bearing temperature.

4.

Driver governor and safety checks (uncoupled) if driver is a steam turbine.

C.

Auxiliary pump unit

Same procedure as item B.

D.

Relief valve set point and nonchatter check.

E.

Operate main pump unit and confirm all pressures, differential pressures, temperatures, and flows are as specified on the system schematic and/or bill of material.

F.

Confirm proper accumulator precharge (if applicable).

G.

Confirm proper set point annunciation and/or action of all pressure, differential pressure, and temperature switches.

H.

Switch transfer valves from bank "A" to bank "B" and confirm pressure fluctuation does not actuate any switches.

I.

Trip main pump and confirm auxiliary pump starts without actuation of any trip valves or valve instability.

Note: Pressure spike should be a minimum of 30% above any trip settings.

J.

Repeat step I but slowly reduce main pump speed (if steam turbine) and confirm proper operation.

K.

Simulate maximum control oil transient flow requirement (if applicable) and confirm auxiliary pump does not start.

L.

Start auxiliary pump, with main pump operating and confirm control valve and/or relief valve stability Note: Some systems are designed to not lift relief valves during two-pump operation.

III

Corrective action

A.

Failure to meet any requirement in Section II requires corrective action and retest.

B.

Specifically note corrective action.

C.

Sign-off procedure as acceptable to operate.

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Centrifugal pumps

Maurice Stewart , in Surface Production Operations, 2019

3.11.6.4 Force-feed (pressurized) systems

As shown in Fig. 3.127, force-feed systems use a small rotary pump to move liquid from the bearing housing reservoir, through a cooler and then back to the bearings. Hydrodynamic lubricated bearings (sleeve bearings) may require a pressurized lube oil system. The pressurized lube oil system is normally designed to supply oil at a suitable pressure to the pump bearings, driver, and any other driven equipment, including gears and continuously lubricated couplings. Detailed requirements for a pump pressurized lube oil system are outlined in API Standard 610 and API Standard 614.

Fig. 3.127

Fig. 3.127. Schematic flow diagram of a typical pressurized lube oil system.

Steps in selection of a pressurized lube oil system are as follows:

1.

Determine bearing heat rejection and required oil flow for bearing size and speed.

2.

Select the shaft-driven oil pump and/or auxiliary oil pump. Select an oil pump of adequate capacity or rating for the appropriate rpm, including driver oil requirements, if specified.

3.

Select the heat exchanger. The heat exchanger must meet all heat transfer requirements, including driver requirements when specified.

4.

Select the filter to meet micron particle size and flow requirements for the pump and driver bearings.

5.

Select the reservoir (it should have a minimum of three minutes retention time). Divide the required oil flow, including driver requirements, into the reservoir capacity to obtain retention time.

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Turbo Generator Control System

Swapan Basu , Ajay Kumar Debnath , in Power Plant Instrumentation and Control Handbook (Second Edition), 2019

4.5.1 Turbine Oil Supply

This system provides pumping, bearing lubrication/cooling, jacking/lifting oil, turning gear operation, and vapor extraction of the system and control fluid. After getting the ON command, the following sequence starts:

1.

The AC auxiliary oil pumps (AOPs) and DC emergency oil pumps (EOPs) start at a per oil pressure setting and stop at a per pressure setting when the shaft-driven main oil pump (MOP) starts functioning.

2.

The temperature control loop for the turbine-bearing lube oil is activated and runs continuously as long as the turbine keeps running.

3.

Jacking oil pump (JOP) inlet valve is opened during startup and the JOP is started manually, and then the SLC of all JOPs are turned ON. The valve closes and the JOP stops when the TG set attains a sufficient speed of >   540   rpm (typically) to ensure adequate bearing lube oil. During turbine operation, the selected JOP(s) start (and valve opens) automatically if speed falls below 500   rpm (typically).

4.

The hydraulic turbine mechanism for shaft-turning gear starts when its inlet valve opens. The preconditions required are hydrogen pressure, seal oil hydrogen DP is adequate, SLC is ON, and JOP is adequate at >   130 bar (typically). During turbine operation, the turning gear starts (and valve opens) automatically if speed falls below 200   rpm (typically). The system will close automatically when the TG set begins to be driven by the steam, that is, the speed is typically >   250   rpm.

When the system gets the shutdown command, the following actions are taken. The selected JOP(s) start (and valve opens) when speed falls below 500   rpm. The turning-gear system inlet valve will be open so that the system is ON immediately when the turbine speed comes down to ∼   200   rpm during coasting down. It will stop operating automatically when the casing temperature settings permit it to do so. AOPs will again start and stop as per their pressure setting and shutdown command.

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