Recently in one of our Frame5 gas turbine due to high lube oil temperature the unit could not generate power to its full capacity. The lube oil cooler has been cleaned manually as much as possible, the oil has been tested in a laboratory,and found ok. The cooling water line circuit has been checked thoroughly and found no abnormality. The problem is deteriorating day by day. If you have any idea to solve the problem, pls suggest.

 

Why would high lube oil temperature cause a combustion turbine to incapable of producing full output?

Is there some logic in the control system that is limiting the power output based on lube oil temperature?

If so, that would be pretty unusual. Typically, when L.O. temperature is high (approximately 165 deg F), there is an alarm and if it's allowed to get higher (exceeding 175 deg F) then the turbine is tripped. The concept is that above approximately 175 deg F hydrocarbon lube oil vapors, particularly in the bearing housings, are approaching their flash point and could be ignited by an ignition source. But, I've never heard of load being limited by lube oil temperature through the control system.

Exactly how is the power output being limited or reduced? Is there a process alarm that says something like "L.O. TEMP HIGH - LOAD LIMITED"? Or something similar?

What kind of application is this: a generator drive or a compressor drive? What kind of lube oil is being used in the turbine: hydrocarbon (petroleum) based, or synthetic?

 

Not having seen the system, does it have a thermostat to bypass cooling water when starting the unit from cold condition? This device could be malfunctioning, in the sense that it might not be opening as required.

Regards,
Tomy Zacharia

 

It is highly uncommon to have heard of machine being incapable of loading on account of high lube oil temperature (particularly frame-V machines). Did you check the VTR functioning? Sometimes the sensing element fails and the valve gets locked at one end. What about the cooler, shell side cleaning and tube side cleaning on account of disturbed water chemistry (internal chocking). High header temperature would be a direct reflection of the high tank temperature and the values mentioned by CSA are exactly how they are.

Lastly, if post an maintenance stoppage there could be some blinded portion in CW line(just in case). Also what is the lube oil tank level? What about your LTBT... temperatures (they should be ideally not more than 80's). All said and done, but load limitation is an unheard phenomenon.

Please mention the alarm text that is being witnessed when the load on the machine gets inhibited from raise.

 

Thank you for your response.

It is correct that there is no logic in the control system which directly limits the load of the unit but we are actually forced to run the unit at a under rated load to avoid the unit tripping in high lube oil temperature. It has been seen that the temp of the L.O. goes on increasing along with the increase of load and also with the ambient temp. At present, we are spraying water on the heat exchanger which cools the L.O. cooling media (ie water) to maintain the L.O. temp. This is helping a little bit but we are still loosing 2 to 3 MW during this summer season with ambient temp around 38deg C. Moreover, with this spray system we could maintain the lube oil temp.of the unit around 67 deg C and the highest bearing metal temp of the load gear box around 95 deg C which are on the higher side. I have doubt whether running the unit continuously at these high temp would lead to pre mature failure of the bearings?

The temp setting of alarm and tripping for L.O.are same as you have mentioned.

Yes, the turbine is used here to drive a generator.

We are using hydrocarbon base lube oil with brand name Servo Prime 32T.

Regards
Aditya

 

Thanks for your kind words.

Actually there is no logic in the control system which limits the loading of the unit due to high lube oil header temperature. In fact the unit trips due to high lube oil temperature if we do not reduce the load of the unit. I have mentioned this in the reply to CSA.

As you have asked we have checked the VTR and found it working properly. The tube side cleaning of the cooler has been done but is it necessary to clean the shell side as the shell is filled with oil only.

Regarding blockage of CW line we have checked the doubted portion. The bearing drain temperature are around 80deg C.

The lube oil tank level is maintained more than half in the level indicator.

Regarding the alarm text the bearing metal temp (BTRGB1)high of load gear box also comes along with the L.O.bearig header temp high. We have checked the inlet and outlet water temp of the lube oil cooler and found 32deg C and 37deg C respectively. Is the heat transfer of the cooler is satisfactory?

Regards,
aditya

 

Are you certain the L.O. cooler transfer valve is working properly? You should not see a "spray" on the sight glass of the cooler which is not in service (and the transfer fill valve should be closed); of course, this is presuming there is a duplex cooler, which most units have, especially in hot environs. If the coolers are duplex, are both coolers experiencing the same problem?

If the coolers are duplex, beware of trying to put the transfer valve in the mid position; it can damage o-rings used in the valves if left in that position for extended periods.

Where does the cooling water come from? An on-base or off-base skid? Or from some other source?

In my experience, there is not a high temperature differential on the cooling medium (the cooling water) on GE systems, either through the coolers or through the finned coolers.

If the cooling water system is self-contained, such as the typical one provided by GE or one of it's packagers, are you certain that the Cooling Water pump suction strainers are clean?

Did this problem start after some maintenance outage? Sometimes there is an orifice in the cooling water piping which is there to maintain flows to achieve desired temperature differentials. I've seen sites where, when the orifice was removed, the system was incapable of maintaining L.O. temperature.

If the cooling water comes from another source (that is, not from a self-contained cooling water system provided by the turbine packager), has there been any change to that system or to the temperature of the cooling water?

It's a fine balancing act with these self-contained systems. Too much flow is just as bad as too little flow. The typical cause is too little flow, usually because of blocked pump suction strainers. The orifice dimension should be stated on the cooling water piping schematic (P&ID), or the expected flow-rate should be stated there if the cooling water comes from a source other than a self-contained, packager-provided cooling water system.

It's possible to rent portable ultrasonic flow measuring systems which strap to the pipe, but an instrument orifice with a differential pressure gauge is best. Most systems provided by GE have tapped flanges just for installing an orifice (it doesn't come with the system...) and easily measuring the differential to calculate a flow.

Have you measured the L.O. Tank temperature to see what kind of L.O temperature differential you're getting through the cooler?

What kind of cooling "water" are you running? In other words, is it just straight water or is there some anti-freeze, which usually helps to also improve heat transfer capability of the water? Has this "composition" changed recently?

Have you considered contacting the cooler manufacturer for some assistance with the problem? Sometimes, with good data (given in the beginning of the request), they will be able to make recommendations or pinpoint problems very easily. Try to provide as much data as you think they might ask for; anticipate their possible questions. The more information you can provide them in your original request, or in the first transmittal of data when you contact them, the better the response you will likely get.

High L.O temperatures, within reason, are not going to cause damage to the bearings. Again, GE's philosophy in choosing the settings is to prevent possible ignition of L.O. vapors because they are near or at their flashpoint.

 

Hi Aditya,

have you found solution to your high lube oil temperature problem yet? We are facing the same problem here in our plant. We've cleaned the tube and shell side. Changed oil. Cleaned oil sump. But still we have the high lube oil temperature. And yes, we also tried the water spray to the cooler but that method not practical enough as it doesn't really bring down the temperature. It only helps in maintaining the temperature by not going any higher.

We have the design data from the manufacturer and it seems there's no problem with the design. So now we are thinking of either getting a new cooler with bigger surface area or having and additional cooler. But still haven't finalise yet. More study need to be done as we don't want after we change the cooler, we still be facing the same problem.

Lina T.

 

Lina T.,

Is this problem you are experiencing something that has developed over time or has it been ongoing since commissioning?

How high is your L.O. header temperature?

It would seem that you have some kind of water-to-air heat exchanger that you have tried spraying water on. Is this located above the Accessory Module or is it an off-base "skid"?

If this is something which has developed over time or which started relatively quickly after some time of operating without a problem, then it's likely some "mechanical" problem, not a controls problem.

Have you tried manually opening the VTR1-1 L.O. Header Temperature Regulating Valve fully to see what happens?

If you have an off-base cooling water module with pump(s) and a strainer, are you sure the strainer is clean?

Is the system filled with the recommended fluid (demineralized water, and/or ethylene-glycol? "Antifreeze" as it's sometimes called, helps to raise the boiling point of the water, and can help with heat transfer from the L.O. Coolers and in the water-to-air heat exchangers. Some people think they don't need "antifreeze" in some climates, but it's not just for freeze protection. I believe there are even formulations just for high-temp applications.

In any case, is the system filled with the proper fluid(s)?

Again, if this is something that has persisted from the original commissioning, then it might be a system design problem. But, if it's something that just started or has gotten worse over time, then it's probably a "mechanical" problem. I have seen some very poorly coated galvanized pipe, with large "gobs" of galvanic coating inside (covering debris not removed from the pipe prior to treatment) that served to catch debris in the pipe and eventually restrict flow. So, it might not just be a component problem (valves, pumps, heat exchangers); it could be a piping problem.

I've also seen some very poorly manufactured pumps come out of a certain region of the world which did not move the proper volume of fluid.

Lastly, there is sometimes an orifice that is supposed to be installed in the cooling water system piping; look at the Cooling Water Piping Schematic drawing (P&ID) to see if one is supposed to be installed, and what size it is supposed to be. Lack of an orifice can be as big a problem as an incorrectly sized orifice. Flow rate in these systems is as important heat exchanger efficiency/effectiveness.

I believe there is also some flow-rate data on the system drawing. One can install some means of monitoring flow and check to see if the proper flow-rate is being achieved. I have seen some sites use ultrasonic flow-measuring equipment, but it can be very difficult to install because of the requirements for straight runs of pipe before and after the instrument. Sometimes, the design of the system does not have such straight runs of pipe available. So, an orifice plate with differential pressure measurement is necessary; of course, that has it's own requirements but usually not as much as the ultrasonic equipment.

 

I have thoroughly read all issues related to the high lube oil temperature. We have a similar high lube oil temperature where we reduced load and it brought the temperature down. 50MW TO 68derees,Bearing metal temperature 109 degrees then 90MW T0 72degrees,Bearing metal temperature 115degrees. The pump pressure is 80psi at 150A.

This problem of high temperature lube oil happened when we re-routed the cooling water pipe underground to surface. This surface routing of piping came about when we had the underground piping leaking. After the construction of the pipes, thoroughly flushing of the pipes were done. The system was bled to expel all air trapped.

After all checks done, gas turbine started and the above problem happened high lube oil temperature.

We are still investigating to rectify the problem. Also looking at the temperature regulating valve for its function.

Please can this issue be discussed further and the probable causes which needed to be rectified.

 

Joseph K. Amoah... what are the associated thrust bearing temperatures?

Regards, Phil Corso

 

If this unit has an off-base cooling water module, there is usually an orifice in the piping between the cooling water module and the turbine. It should be shown on the Cooling Water Piping Schematic (P&ID), and it very necessary for proper operation of the system.

Is this orifice installed in the new piping?

The purpose of the orifice is to regulate the flow to the specifications shown on the same drawing, so, if piping size was changed from what was in-ground you may need to re-size the orifice taking any pressure drop in the new piping into account and install a new orifice.

Are you sure all valves are in the proper positions?

Presuming the unit has the typical Robertshaw L.O. Temperature Regulating Valve, have you tried using the manual crank to put the valve in full flow to the cooler (only one cooler should be in service at a time!)?

If the problem began after the new above-ground piping was installed (and flushed), then it's most likely related to something to do with the new piping.

 

If this problem was slow to develop one thing I would check is the wear-ring clearance in the shaft driven cooling water pump. Your turbine manual should have the acceptable tolerances.

Also it would be helpful to know the cooling water header pressure. From what I have seen 50 to 60 psi is normal for the frame 5s I have been around.

Thanks
Mark Allen

 

We had a similar kind of problem in our GT some time back. L.O temperature kept increasing day by day with load.

Actually while running mist eliminator some amount of oil was sucked into the mist eliminator piping. We stopped mist eliminator for some days because of oil suction. During this time, lube oil vapours started accumulating in MOT since it didn't have any path to vent out as the mist eliminator pipings contained oil and coalescer filter drum was also filled with oil. Lube oil started oozing out from AGB, LGB, generator bearing seals. The MOT pressure had become >+50mmWC.On opening MOT manhole lot of lube oil fumes where coming out and MOT pressure reduced to 0mmWc, and slowly lube oil temperature and its associated parameters like bearing drain temperatures, bearing metal temperatures etc came down.

So just open you MOT manhole or check the MOT vacuum.

 

We are also facing the problem of high lube oil temperature at our Frame5 gas turbine.

We want to fully open VTR-01 by manual crank, but we don't know, how to perform it on running turbine. Kindly provide me some guidelines about operating the valve on manual crank.

 

It's pretty likely you have a Robertshaw Model RT-1010A. This fine manual is available for download and reading from this URL:

http://www.robertshawindustrial.com/manuals/rflevel/MAN160_RT1010.pdf

(remove any spaces inserted by the control.com software before pasting into your web browser)

There should be nothing more to adjusting the valve plug position manually than turning the valve handle in the proper direction. The indicator should move to the OPEN position and the mechanism should move the plug to the open position.

You should already be able to see if the plug is fully open from the indicator (which is the L.O. Temp is above the regulator valve setting it should be--providing the automatic bellows, capillary and sensing bulb are all intact).

If you're worried about manually operating the valve, just do it one-half turn at a time over several minutes or a half-hour or a one hour time period and see if the L.O. Temp goes up. If it does, then something would seem amiss.

Best of luck. Let us know how you fare.

BEFORE you put the valve back in Automatic Control please have a read of the fine manual to understand how to make any adjustment to the Automatic setting. Many people falsely believe that all adjustment (Automatic and Manual) is done with the handwheel on the side, and that's simply not true. One puts the manual handwheel on the side in a "neutral" position and then makes adjustments to the triangular-shaped brass piece beneath the bellows to change the spring tension.

But that's all covered in the fine manual, a copy of which should also be in the 'Cooling Water System' tab of the manuals provided with the unit when originally installed.

 

We have the same problem on our F5 unit.

Have anyone find out the reason of such high oil temperature??
We have had to install a temporarily external shell and tube heat exchanger to cool down the water of cooling system.

Here is some of our unit details I've picked out of the log sheets:
Grease main pump outgoing pressure ~ 55 psi
Cooling water pressure ~ 70 psi
Compressor air pressure ~ 88.2 psi

There are 10 air radiators, 5 in left and 5 in right section of the unit. It's also interesting that left radiator cools down the water about 4C while the right ones do it about 2C!

There are 2 F5 units in the plant and both have the same problem.

Please assist.

 

Mos,

Exactly what "same" problem are you having?

When did this problem start? Or, has it been on-going for a long time?

From the sounds of it, you have older units with roof-mounted heat exchangers. Even if not, when was the last time the heat exchangers were cleaned with a pressure washer?

You say one side of both turbine's coolers has a higher temperature drop than the other? Is this consistent throughout the day? Or, is the difference predominantly in the heat of the afternoon? Are the sides experiencing the lower temperature drop facing the afternoon sun? Are the sides experiencing the higher temperature drop the beneficiary of prevailing winds? And, prevailing winds can be cooling, or can blow exhaust from nearby units or equipment into the radiators, so the winds may actually be negatively impacting the heat exchanger's ability to cool.

Another poster to this thread mentioned problems with the ceramic seals on gear-driven cooling water pumps. There are easily damaged by sand or dirt in the cooling water and the efficiency of the pump is greatly decreased. My experience has been that flushing the system and then using demineralized water with ethylene glycol is best.

Some systems used plate orifices to control flow-rates. Over time, these orifices can wear out, and I've even seen them discarded or not replaced during outages, leading to problems with cooling.

Lastly, many of the roof-mounted heat exchangers I've seen use motors with double-ended shafts and fans on each end. A couple of sites had experienced loose fan couplings which contributed to cooling problems.

Please write back with the answers to the questions (all of them), and any solution you arrive at.

 

I've found a 90 degree branch before the air coolers which is the flow divider.

Fluent simulation shows that 80% of fluid will go through the main branch (right radiators) and 20% of the fluid will go to the 90 degree branch (left radiators). This can be the reason of low air cooler performance and then high lube oil temperature.

 

I presume by '90 degree branch' you are referring to a tee connector that in intended to split the fluid flow between two sets of water-to-air heat exchangers (radiators).

I repeat probably the single most important question when troubleshooting any problem:

<b>WHEN DID THIS PROBLEM START?</b>

If this problem has been on-going since commissioning (original installation), then it might be that the tee was improperly sized or improperly installed or something similar.

Most of the air-cooled heat exchangers I've seen that were provided by the OEM or a licensed packager were designed such that the pressure drop across each bank, or set, of heat exchangers was equal. This meant that the flows through the heat exchangers downstream of a tee connection or a "manifold" would be relatively equal. Where necessary, an orifice was used to help balance the flows through the heat exchangers.

Any fluid simulation would require measured or assumed pressure drops and flow-rates to be accurate. I've seen some detailed Cooling Water P&IDs, but none with that kind of detail (piping losses, pressure drops in piping and across heat exchangers, etc.).

Unless the '90 degree branch' or tee connectors had different sized connections (say, two were 4-inch, and one was 6-inch) and the device was installed incorrectly, it's pretty hard to imagine how the flow through the device could be so unbalanced.

If the heat exchangers (radiators) are not the same size, that could be part of the problem.

But simply to say that a '90 degree branch' suddenly, or even over some period of time, caused an imbalanced flow that has resulted in high L.O. temperature. Unless some something has lodged inside the device that is blocking the flow to one of the radiators (which is presumed is the same size as the other radiator).

There were several other questions asked earlier which you did supply the answers to, such as when was the last time the heat exchangers were cleaned (internally and externally); which set of coolers is exposed to mid-day/afternoon sun; have you verified the presence of any orifices shown on the P&ID, and the ID of any orifice found, etc.

But, the most important question is: When did this problem start? Or has it been ongoing since commissioning?