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J
Our GE- Frame -9E was converted from single to dual fuel and ever since the conversion, we encounter frequent failure of main atomizing air compressor driver coupling shaft. What probably are the causes?
What have you done to troubleshoot the problem?
Have you contacted the company that performed the conversion for their assistance?
We'll presume the main atomizing air compressor is driven by an output shaft of the Accessory Gear Box.
Are you confident of the alignment of the compressor to the gear box?
Is there excessive vibration of the compressor?
Do the failures usually occur shortly after start-up on liquid fuel or shortly after transfer to liquid fuel while running? Or during operation on gas fuel? Or shortly after transfer to gas fuel?
Are you confident the temperature of the main atomizing air compressor inlet air is consistently less than the manufacturer's maximum (which is usually approximately 150 deg C)? If the inlet temperature exceeds the rating of the compressor, then the internal clearances can decrease and cold cause mechanical rubs. If I recall correctly, these compressors can operate at 44,000 RPM, or thereabouts. Reduced internal clearances can be catastrophic at worst.
There is usually an atomizing air pre-cooler and temperature regulating valve to control the main atomizing air compressor inlet temperature. That temperature regulating valve is typically a self-actuated device, with a remotely-mounted bulb connected to a bellows by a capillary. The setpoint for the control valve is usually 107 deg C. When the turbine is started from a cold condition, the air temperature is ambient, and so the temperature regulating valve will be closed, to try to make the air temperature equal to the setpoint. These valves are slow to react to temperature changes, and during start-up it's very common for an AA Compressor Inlet Temp High alarm to be annunciated (setpoint is usually 135 deg C). In a few minutes the valve will usually be able to open sufficiently to get the temperature down below the switch setpoint. But, during this time, the air entering the main atomizing air compressor will be higher than normal, possibly much higher since the air comes from the axial compressor discharge.
Another possible problem could be that the temperature setpoint of the temperature regulating valve is set too low causing condensation to occur and when moisture enters the main atomizing air compressor damage can also occur. It's not uncommon for people to try to lower the setpoint of the temperature regulating valve to try to avoid the high temp alarms during start-up, but inadvertently cause another problem. The main atomizing compressor inlet air temperature is very critical and must remain above boiling point (to prevent condensation) and below the compressor's maximum to ensure longevity of the compressor, and possibly the drive.
If I recall correctly, there should be a continuous blowdown (a very small, permanently open orifice) in the low point of the piping between the outlet of the atomizing air pre-cooler and the inlet of the main atomizing air compressor to allow any condensation which might accumulate during shutdown or operation to be drained from the piping. It's very common for these to be capped in the belief that they are "leaks" when they are not.
Have you confirmed the coupling/shaft is the proper one for the application by consulting the manufacturer? In my recollection, the coupling as a splined shaft inserted into the Accessory Gear and also into the input of the compressor. But, that was a Frame 5 many years ago, which is similar, but not always identical to larger machines, and the designs do change over time and with different Frame sizes.
It could also be that the inlet- and/or outlet piping are causing undue stress and misalignment when they heat up during normal operation.
If that is supposed to be a lubricated coupling, are you sure it's being properly and/or adequately lubricated?
Have you contacted the company that performed the conversion for their assistance?
We'll presume the main atomizing air compressor is driven by an output shaft of the Accessory Gear Box.
Are you confident of the alignment of the compressor to the gear box?
Is there excessive vibration of the compressor?
Do the failures usually occur shortly after start-up on liquid fuel or shortly after transfer to liquid fuel while running? Or during operation on gas fuel? Or shortly after transfer to gas fuel?
Are you confident the temperature of the main atomizing air compressor inlet air is consistently less than the manufacturer's maximum (which is usually approximately 150 deg C)? If the inlet temperature exceeds the rating of the compressor, then the internal clearances can decrease and cold cause mechanical rubs. If I recall correctly, these compressors can operate at 44,000 RPM, or thereabouts. Reduced internal clearances can be catastrophic at worst.
There is usually an atomizing air pre-cooler and temperature regulating valve to control the main atomizing air compressor inlet temperature. That temperature regulating valve is typically a self-actuated device, with a remotely-mounted bulb connected to a bellows by a capillary. The setpoint for the control valve is usually 107 deg C. When the turbine is started from a cold condition, the air temperature is ambient, and so the temperature regulating valve will be closed, to try to make the air temperature equal to the setpoint. These valves are slow to react to temperature changes, and during start-up it's very common for an AA Compressor Inlet Temp High alarm to be annunciated (setpoint is usually 135 deg C). In a few minutes the valve will usually be able to open sufficiently to get the temperature down below the switch setpoint. But, during this time, the air entering the main atomizing air compressor will be higher than normal, possibly much higher since the air comes from the axial compressor discharge.
Another possible problem could be that the temperature setpoint of the temperature regulating valve is set too low causing condensation to occur and when moisture enters the main atomizing air compressor damage can also occur. It's not uncommon for people to try to lower the setpoint of the temperature regulating valve to try to avoid the high temp alarms during start-up, but inadvertently cause another problem. The main atomizing compressor inlet air temperature is very critical and must remain above boiling point (to prevent condensation) and below the compressor's maximum to ensure longevity of the compressor, and possibly the drive.
If I recall correctly, there should be a continuous blowdown (a very small, permanently open orifice) in the low point of the piping between the outlet of the atomizing air pre-cooler and the inlet of the main atomizing air compressor to allow any condensation which might accumulate during shutdown or operation to be drained from the piping. It's very common for these to be capped in the belief that they are "leaks" when they are not.
Have you confirmed the coupling/shaft is the proper one for the application by consulting the manufacturer? In my recollection, the coupling as a splined shaft inserted into the Accessory Gear and also into the input of the compressor. But, that was a Frame 5 many years ago, which is similar, but not always identical to larger machines, and the designs do change over time and with different Frame sizes.
It could also be that the inlet- and/or outlet piping are causing undue stress and misalignment when they heat up during normal operation.
If that is supposed to be a lubricated coupling, are you sure it's being properly and/or adequately lubricated?
J
Joseph K. Amoah
I am in agreement with the points you made in aiding the trouble shooting of the failure of the atomising air compressor coupling.
I am trying to investigate on the issues raised on the below points to ascertain the actual cause.
1. There is usually an atomizing air pre-cooler and temperature regulating valve to control the main atomizing air compressor inlet temperature. That temperature regulating valve is typically a self-actuated device, with a remotely-mounted bulb connected to a bellows by a capillary. The setpoint for the control valve is usually 107 deg C. When the turbine is started from a cold condition, the air temperature is ambient, and so the temperature regulating valve will be closed, to try to make the air temperature equal to the setpoint. These valves are slow to react to temperature changes, and during start-up it's very common for an AA Compressor Inlet Temp High alarm to be annunciated (setpoint is usually 135 deg C). In a few minutes the valve will usually be able to open sufficiently to get the temperature down below the switch setpoint. But, during this time, the air entering the main atomizing air compressor will be higher than normal, possibly much higher since the air comes from the axial compressor discharge.
2. Another possible problem could be that the temperature setpoint of the temperature regulating valve is set too low causing condensation to occur and when moisture enters the main atomizing air compressor damage can also occur. It's not uncommon for people to try to lower the setpoint of the temperature regulating valve to try to avoid the high temp alarms during start-up, but inadvertently cause another problem. The main atomizing compressor inlet air temperature is very critical and must remain above boiling point (to prevent condensation) and below the compressor's maximum to ensure longevity of the compressor, and possibly the drive.
3. If I recall correctly, there should be a continuous blowdown (a very small, permanently open orifice) in the low point of the piping between the outlet of the atomizing air pre-cooler and the inlet of the main atomizing air compressor to allow any condensation which might accumulate during shutdown or operation to be drained from the piping. It's very common for these to be capped in the belief that they are "leaks" when they are not.
We have two frame 9E gas turbines and they have the same problem, actually this problem came when we started running on dual fuel (natural gas and light crude oil)
What can be the probable causes of frequent failure even though I am still carrying out investigation on the above points.
I am trying to investigate on the issues raised on the below points to ascertain the actual cause.
1. There is usually an atomizing air pre-cooler and temperature regulating valve to control the main atomizing air compressor inlet temperature. That temperature regulating valve is typically a self-actuated device, with a remotely-mounted bulb connected to a bellows by a capillary. The setpoint for the control valve is usually 107 deg C. When the turbine is started from a cold condition, the air temperature is ambient, and so the temperature regulating valve will be closed, to try to make the air temperature equal to the setpoint. These valves are slow to react to temperature changes, and during start-up it's very common for an AA Compressor Inlet Temp High alarm to be annunciated (setpoint is usually 135 deg C). In a few minutes the valve will usually be able to open sufficiently to get the temperature down below the switch setpoint. But, during this time, the air entering the main atomizing air compressor will be higher than normal, possibly much higher since the air comes from the axial compressor discharge.
2. Another possible problem could be that the temperature setpoint of the temperature regulating valve is set too low causing condensation to occur and when moisture enters the main atomizing air compressor damage can also occur. It's not uncommon for people to try to lower the setpoint of the temperature regulating valve to try to avoid the high temp alarms during start-up, but inadvertently cause another problem. The main atomizing compressor inlet air temperature is very critical and must remain above boiling point (to prevent condensation) and below the compressor's maximum to ensure longevity of the compressor, and possibly the drive.
3. If I recall correctly, there should be a continuous blowdown (a very small, permanently open orifice) in the low point of the piping between the outlet of the atomizing air pre-cooler and the inlet of the main atomizing air compressor to allow any condensation which might accumulate during shutdown or operation to be drained from the piping. It's very common for these to be capped in the belief that they are "leaks" when they are not.
We have two frame 9E gas turbines and they have the same problem, actually this problem came when we started running on dual fuel (natural gas and light crude oil)
What can be the probable causes of frequent failure even though I am still carrying out investigation on the above points.
