In 9e gas turbine


After major inspection which is done by GE company, we got issue from mist eliminator , the issue is continuously too much vapor come out from the vent while all the bearing temperature and lube oil tank temperature is normal , what could be a reason ??

 

What's the vacuum on it?

 

What's the vacuum on it?

Vacuum pressure is -160 mmH2O and we try to adjust but not affected, while other units vacuum pressure around -75 mmH2O.

 

@Rova,

I'm presuming you are referring to the L.O. Tank vacuum--and the main L.O. Mist Eliminator. Some machines with air-cooled generators have a separate L.O. Mist Eliminator for the generator bearing cavities/drains, and sometimes these have been known to have excessive vapor discharge, also. We don't know anything about the machines at your site (age of installation/commissioning; what maintenance outage was just completed and what work was done on the L.O. Mist Eliminator (if any). We don't know anything at all about the machine--except it's a Frame 9E GE-design heavy duty gas turbine, most likely driving a generator. The more information you can provide in your original post the more likely you will receive a more concise reply about the cause(s) of the problem.

NOTE: The purpose of all the questions below is to discuss most of the possible causes that have happened over decades at other sites. Since we didn't get a lot of information about the machine and the recent maintenance outage (completed by GE...) all we can do is try to ask questions and hope that one or more of them weren't considered and may help you to find and resolve the problem(s) (there may even be multiple issues contributing to this problem). Again, the more information you can provide the better the responses you will receive. EVERY TIME. GUARANTEED. As you can see, even with something as simple as the L.O. Mist Eliminator there are multiple conditions--none of which are controlled (typically) by the Mark* turbine control system and require manual inspection and verification during reassembly and if necessary after reassembly to eliminate them as a source of the problem or to find and resolve them when found to be incorrect. So, please don't be offended by the questions--we need more information to be of better help. AND, when you find and resolve the problem please write back to let others know what you found and how you resolved the problem. (A LOT of people read these threads--not just now, but in the future, also....)

Usually there is a NOTE on the L.O. system P&ID that specifies the vacuum to be present at the L.O. tank and at what load that vacuum should be present. What does your L.O. System P&ID say about the specified vacuum at the L.O. tank and when that measurement should be taken?

Please explain how you tried to adjust the vacuum on the L.O. tank.

Is there a pressure transducer providing the L.O. tank vacuum reading? Or is this reading coming from a gauge somewhere? If it's coming from a gauge, when (at what load) was this vacuum reading measured?

Is the gauge or pressure transducer a zero-centered device (meaning it shows or registers both pressure and vacuum? Was this device being used to measure L.O. tank vacuum "calibrated" during the maintenance outage?

What is the vacuum reading of the L.O. Tank when the machine is running at FSNL? What is the vapor discharge situation from the discharge of the L.O. Mist Eliminator at FSNL?

What is the vacuum reading of the L.O. Tank when the machine is running at 50% load? What is the vapor discharge situation from the discharge of the L.O. Mist Eliminator at 50% load?

What is the vacuum reading of the L.O. Tank when the machine is running at Base Load? What is the vapor discharge situation from the discharge of the L.O. Mist Eliminator at Base Load?

(In other words does the vacuum change when the load changes? And, does the amount of vapor discharge from the L.O. Mist Eliminator change when the load changes?)

When (at what load) were the other units' vacuum readings taken? Was an adjustment made to the as-found calibration adjustment of the device when the operation of the device was being "calibrated"?

There could be a problem with the assembly of the #2 Bearing Vent line after the maintenance outage. There could be too much pressure on the L.O. tank because of a misplaced or missing orifice in a Cooling & Sealing Air system line, probably suppling air to one of the turbine bearings.

There is supposed to a loop-seal drain between the bottom of the L.O. Mist Eliminator that is filled with oil to provide a seal between the L.O. Mist Eliminator vessel and the L.O. tank (where the condensed oil vapors are drained to). There is (or should be) a sight glass in this loop seal drain to prove there is oil in the piping of the loop seal.)

If the internal elements of the L.O. Mist Eliminator were not installed properly that could be a reason for excessive vapors discharging from the L.O. Mist Eliminator.

Sometimes, even when the proper vacuum at the L.O. tank is present at the specified load when the machine is running at low load or FSNL (Full Speed-No Load) the vacuum at the L.O. tank will be higher than at a much higher load and that can lead to issues with excessive vapors discharging from the L.O. Mist Eliminator.

That's a LOT of possibilities--and all of them have occurred at one time or another at most sites. A common reason sometimes is that manual valves were moved during the maintenance outage and not returned to the normal running position(s) prior to the re-start of the machine. Also, calibration errors can cause improper readings. Review BOTH the L.O. system and Cooling & Sealing Air system P&IDs to look for information about required vacuum readings, and orifice sizes. It may be necessary to shut the machine down to check the orifice sizes to be sure they were installed and sized correctly after the reassembly. And, at the same time, check the internal element arrangement of the L.O. Mist Eliminator to be sure everything is correct, and there is oil present in the loop seal between the L.O. Mist Eliminator and L.O. tank.

Best of luck; if you want more help--remember, we need more information.

 

Thank you for your valuable reply.

Our generator is an air-cooled type and does not have a separate mist eliminator for the generator.
GE has already carried out a major inspection.
However, our team replaced the mist eliminator filter with a new one.
We took measurements while the unit was operating at base load, but the vapor level remained the same across all load conditions—it did not decrease.
The readings were taken from the transducer.
We are currently unable to confirm whether an orifice is installed or not.
However, from the lube oil return line, we can observe oil flow, although it shows slight fluctuations (turbulent flow).

Please let us know if you have any further suggestions or recommendations. Your support is highly appreciated.

 

@Rova,

I'm presuming you are referring to the L.O. Tank vacuum--and the main L.O. Mist Eliminator. Some machines with air-cooled generators have a separate L.O. Mist Eliminator for the generator bearing cavities/drains, and sometimes these have been known to have excessive vapor discharge, also. We don't know anything about the machines at your site (age of installation/commissioning; what maintenance outage was just completed and what work was done on the L.O. Mist Eliminator (if any). We don't know anything at all about the machine--except it's a Frame 9E GE-design heavy duty gas turbine, most likely driving a generator. The more information you can provide in your original post the more likely you will receive a more concise reply about the cause(s) of the problem.

NOTE: The purpose of all the questions below is to discuss most of the possible causes that have happened over decades at other sites. Since we didn't get a lot of information about the machine and the recent maintenance outage (completed by GE...) all we can do is try to ask questions and hope that one or more of them weren't considered and may help you to find and resolve the problem(s) (there may even be multiple issues contributing to this problem). Again, the more information you can provide the better the responses you will receive. EVERY TIME. GUARANTEED. As you can see, even with something as simple as the L.O. Mist Eliminator there are multiple conditions--none of which are controlled (typically) by the Mark* turbine control system and require manual inspection and verification during reassembly and if necessary after reassembly to eliminate them as a source of the problem or to find and resolve them when found to be incorrect. So, please don't be offended by the questions--we need more information to be of better help. AND, when you find and resolve the problem please write back to let others know what you found and how you resolved the problem. (A LOT of people read these threads--not just now, but in the future, also....)

Usually there is a NOTE on the L.O. system P&ID that specifies the vacuum to be present at the L.O. tank and at what load that vacuum should be present. What does your L.O. System P&ID say about the specified vacuum at the L.O. tank and when that measurement should be taken?

Please explain how you tried to adjust the vacuum on the L.O. tank.

Is there a pressure transducer providing the L.O. tank vacuum reading? Or is this reading coming from a gauge somewhere? If it's coming from a gauge, when (at what load) was this vacuum reading measured?

Is the gauge or pressure transducer a zero-centered device (meaning it shows or registers both pressure and vacuum? Was this device being used to measure L.O. tank vacuum "calibrated" during the maintenance outage?

What is the vacuum reading of the L.O. Tank when the machine is running at FSNL? What is the vapor discharge situation from the discharge of the L.O. Mist Eliminator at FSNL?

What is the vacuum reading of the L.O. Tank when the machine is running at 50% load? What is the vapor discharge situation from the discharge of the L.O. Mist Eliminator at 50% load?

What is the vacuum reading of the L.O. Tank when the machine is running at Base Load? What is the vapor discharge situation from the discharge of the L.O. Mist Eliminator at Base Load?

(In other words does the vacuum change when the load changes? And, does the amount of vapor discharge from the L.O. Mist Eliminator change when the load changes?)

When (at what load) were the other units' vacuum readings taken? Was an adjustment made to the as-found calibration adjustment of the device when the operation of the device was being "calibrated"?

There could be a problem with the assembly of the #2 Bearing Vent line after the maintenance outage. There could be too much pressure on the L.O. tank because of a misplaced or missing orifice in a Cooling & Sealing Air system line, probably suppling air to one of the turbine bearings.

There is supposed to a loop-seal drain between the bottom of the L.O. Mist Eliminator that is filled with oil to provide a seal between the L.O. Mist Eliminator vessel and the L.O. tank (where the condensed oil vapors are drained to). There is (or should be) a sight glass in this loop seal drain to prove there is oil in the piping of the loop seal.)

If the internal elements of the L.O. Mist Eliminator were not installed properly that could be a reason for excessive vapors discharging from the L.O. Mist Eliminator.

Sometimes, even when the proper vacuum at the L.O. tank is present at the specified load when the machine is running at low load or FSNL (Full Speed-No Load) the vacuum at the L.O. tank will be higher than at a much higher load and that can lead to issues with excessive vapors discharging from the L.O. Mist Eliminator.

That's a LOT of possibilities--and all of them have occurred at one time or another at most sites. A common reason sometimes is that manual valves were moved during the maintenance outage and not returned to the normal running position(s) prior to the re-start of the machine. Also, calibration errors can cause improper readings. Review BOTH the L.O. system and Cooling & Sealing Air system P&IDs to look for information about required vacuum readings, and orifice sizes. It may be necessary to shut the machine down to check the orifice sizes to be sure they were installed and sized correctly after the reassembly. And, at the same time, check the internal element arrangement of the L.O. Mist Eliminator to be sure everything is correct, and there is oil present in the loop seal between the L.O. Mist Eliminator and L.O. tank.

Best of luck; if you want more help--remember, we need more information.

Thank you for your valuable reply.

Our generator is an air-cooled type and does not have a separate mist eliminator for the generator.
GE has already carried out a major inspection.
However, our team replaced the mist eliminator filter with a new one.
We took measurements while the unit was operating at base load, but the vapor level remained the same across all load conditions—it did not decrease.
The readings were taken from the transducer.
We are currently unable to confirm whether an orifice is installed or not.
However, from the lube oil return line, we can observe oil flow, although it shows slight fluctuations (turbulent flow).

Please let us know if you have any further suggestions or recommendations. Your support is highly appreciated.

Vacuum pressure is -160 mmH2O and we try to adjust but not affected, while other units vacuum pressure around -75 mmH2O.

 

@Rova,

So, the "vacuum pressure" is around -160 mmH2O for the machine with the problem, and the other machines have a vacuum pressure of around -75 mmH2O. And you report that the oil flow in the return line between the L.O. Mist Eliminator and the L.O. tank is "turbulent"--I presume this is viewed through the sight glass. And I ALSO presume the oil flow of the other machines is not as turbulent.

You didn't say what the L.O. system P&ID specified the L.O. tank vacuum pressure to be.

Turbine bearings enclosures are usually slightly pressurized using air from the turbine Cooling & Sealing Air system. And the orifices used to limit the amount of air flowing into the bearing enclosures are usually shown on the Cooling & Sealing Air system P&ID. Often the orifices are small discs which are inserted between two halves of a threaded pipe coupling and can be easily misplaced during a maintenance outage (such as a MI (Major Inspection)) and forgotten when reassembling the machine after the outage. The pipes that supply the air flow to the bearing enclosures are usually about 1- or 1-1/2 inch in diameter. (I forget what they look like in the #2 bearing enclosure.) BUT, if in fact, the orifices were missing that usually means the vacuum pressure is very low--and not very high. So, this might not actually be the cause of the high vacuum pressure (negative pressure) reading you are describing.

Based on the information provided, my money is on the reassembly of the internal elements of the L.O. Mist Eliminator and/or the butterfly valve assembly usually used to adjust the vacuum on the L.O. tank. Now, GE Belfort like to make a lot of changes to what were standard designs used by GE for decades, and it's entirely possible they have some kind of automated L.O. tank vacuum control valve/mechanism--without being able to see the L.O. system P&ID we can't know for sure. BUT, if you are adjusting the vacuum pressure on the L.O. tank manually using a butterfly valve handle at the centrifugal fan mounted on the L.O. Mist Eliminator it certainly seems something is amiss with the butterfly valve mechanism OR the internal assemblies of the L.O. Mist Eliminator.

In general the purpose of the L.O. Mist Eliminator is to draw vapors from the L.O. tank through a vessel designed to cause the vapors to make several changes of direction and hopefully cause the majority of the oil vapors to condense and return to the L.O. tank through the return line between the bottom of the L.O. Mist Eliminator and the L.O. tank. And, in general the flow of oil in that return line is relatively "smooth" as seen looking at the sight glass in the line. (That should be confirmed by looking at the sight glasses of the other machines.) Also, there are filter elements which the uncondensed oil vapors are drawn through which capture the majority of the oil which also falls to the bottom of the L.O. Mist Eliminator vessel to return to the tank through the return line.

In general, when the flow of uncondensed oil vapors from the discharge of the fan assembly mounted on the L.O. Mist Eliminator are excessive it's either the result of excessive vacuum pressure on the L.O. tank or some problem with the internal assemblies of the L.O. Mist Eliminator not causing the entrained oil in the vapors being drawn through the L.O. Mist Eliminator to condense or be filtered out of the air flow.

Again, the above description is based on standard GE designs of L.O. Mist Eliminators used for decades on GE-design heavy duty gas turbines. GE Belfort is famous (or infamous) for changing tried-and-true design practices and schemes because they weren't invented in France. (Yes; that is the reason.) So, if the machines at your site have some different type of L.O. mist eliminator equipment then although the general purpose is still the same (to prevent oil vapors from discharging directly into the surrounding environment and contributing to air pollution as well as "greasing-up" the area) the method being used on your machine might be different.

You have chosen not to tell us how the vacuum pressure on the L.O. tank is measured on the machines at your installation or if the measuring means was calibrated during the MI. One of the poor aspects of the GE standard design for L.O. Mist Eliminators was that they didn't provide any means of measuring or monitoring the L.O. tank vacuum pressure--one had to be installed by the Customer or operations/maintenance people at the site. So, if GE Belfort has included some means of monitoring/measuring L.O. tank vacuum pressure on their standard design--that would be a welcome change. But, I haven't personally seen such a change though that doesn't mean they haven't implemented such a change.

Again, if there is some manual method for setting/adjusting the L.O. tank vacuum pressure that you are using to try to set and reduce oil vapors coming out of the L.O. Mist Eliminator fan discharge and that's not working at all, then something is truly amiss. I recall at a couple of installations there was a similar problem with excessive emissions from the L.O. Mist Eliminator during initial commissioning of the machines that were traced to lack of oil in the oil return line (specifically the loop seal of the oil return line). And, the sight glass in the oil return line did have some air bubbles flowing in it making the flow look turbulent. If the oil return line from the L.O. Mist Eliminator vessel to the L.O. tank was drained during the maintenance outage, that could be a very large part of the problem as without that loop seal being full it would be hard to control the L.O. Tank vacuum pressure.