Atomizing Air Booster problem


Thread Starter


Hi guys,

Our plant has GT MS9001E by GE. Recently we tried starting the GT on distillate (gas = primary fuel; distillate = secondary fuel) but failed. The AA booster compressor was functioning but there was no pressure reading on the AA manifold pressure gauge. The indicator needle did not even move even a whisker. We suspected the check valve right after the AA booster compressor to be stucked.

But after we rectified it, it still failed to start on distillate. According to the GE manual, there should be about 12psig = 0.7 bar. Subsequently, we opened the venting valve which is normally close during normal operation, to check if there was suction or discharge of air. The motor was rotating CCW. Surprisingly, there wasn't any suction. The air was discharging through the venting valve. We swapped the cable terminal for the motor and tested again. There was suction.

We did not try starting on distillate since then. Will do if we get the opportunity. I double checked the manual. It is stated that the AA motor should be rotating CCW if view at the drive end. But the actual situation required us to change the rotation to CW. My only suspicion would be the impeller in the compressor is installed wrongly.

We discussed among us alternative ways to bypass the AA booster compressor. One of them is to tap an external air pressure. The only problem is that we do not know at what pressure should we regulate it to. I tried checking when was the last time we ran on distillate but to no avail. Coz we rarely or did not start up on distillate.

I wonder if you guys have experienced similar problems. Appreciate the feedback.

thank you.
Are there any Process- or Diagnostic Alarms being annunciated during the liquid fuel start attempts?

What makes you believe the problem is only lack of sufficient AA pressure from the Booster AA Compressor? Have you eliminated other potential problems? If so, can you describe what you've done and the results?

It's very difficult to read pressures near zero on a gauge that's rated for 15 or 20 bar. If you want to accurately measure Booster AA Compressor discharge pressure you need to install a temporary gauge rated for 2 or 3 bar on the outlet of the compressor, and put an isolation valve between the piping and the gauge. You will need to manually close the isolation valve during start-up once flame is established to protect the gauge against over-pressurization after flame is established to prevent damaging the gauge. But this is about the only way to reliably measure the Booster AA Comp discharge pressure.

Most of the Booster AA Compressors I have seen have been roots-type, positive displacement blowers and if operated "backwards" even for a couple of seconds (if that) they draw extreme amounts of current, usually tripping the motor starter's incoming circuit breaker. So, this must not be a roots-type blower, or else something is wrong with the breaker trip element.

Another good way to determine if the Booster AA Compressor is working properly is to use a clamp-on ammeter on the motor leads when it's running, and comparing the reading to the motor's nameplate and the compressor's nameplate.

Have you checked the Tell-tale Leak-off for fuel during firing? If so, then one or more of the Purge Air Check valves are leaking, presuming they are the typical spring-loaded poppet-style check valves. (Usually, the only way to tell which one is leaking is to remove them all and test them.)

Are there any white vapors coming out of the exhaust during or after the failed start attempt?

Have you tried starting on gas fuel, transferring to liquid fuel at FSNL, shutting the unit down, then starting on liquid fuel?

Are you certain the liquid fuel supply pressure is adequate (per the Device Summary) and stable?

Are you sure there is no air trapped in the tops of the liquid fuel filter canisters?

Is liquid fuel flow through the flow divider steady and equal to the reference during the firing period?

Have you monitored the liquid fuel pressures to each fuel nozzle using the manual selector valve downstream of the liquid fuel flow divider to see if the pressures are all fairly equal and above the Liq. Fuel Check valve cracking pressure? (Again, this is presuming the Liq. Fuel Check Valves are the spring-loaded poppet-style check valves.) Any large difference in pressure can mean a failed or failing Liq. Fuel Check Valve or a problem with the liquid fuel nozzle.

If you haven't checked any other possibilities but are simply focusing on the Booster AA Compressor, then it's probably a good idea to widen the focus of your troubleshooting whilst trying to confirm the problem is the Booster AA Compressor, or eliminating it. Liquid fuel systems are quite complicated systems especially given the fact that many of the variables are neither monitored nor controlled by the Speedtronic (presuming the control system is a GE Speedtronic control system).

Lastly, GE recommends periodic and even "frequent" operation of a dual fuel unit on liquid fuel in order to keep all of the lines free and clear of air and to keep all of the check valves working properly. If you haven't operated the unit on liquid fuel for some time, then it's a good bet that one or more of the check valves aren't working properly, or that something else is amiss in the system. AA pressure is important during firing, but it's not the only possible problem, especially if the unit hasn't been operated on liquid fuel for some time.
Thanks for the feedback CSA. Appreciate it a lot.

Back to the topic. We have just confirmed that the motor rotation is wrong. On the nameplate, it is written that the drive end of the pump and motor to be CCW. But when we turned on the AA booster pump manually via mcc, we did not feel any suction from the venting vent above the AA booster pump. Instead we felt blow out of air. We changed the motor cable terminal and got the suction as expected.

For your information, we have tested starting up on distillate yesterday but failed. We have already eliminated the AA as the culprit after checking the two check valves, VA 22, VA 18 and AA motor. When we tested yesterday, there was flow on HMI (FQL reading) but there wasnt any pressure on the flow divider at any line from 1-14. The subsequent alarms which were annunciated were, low hydraulic supply pressure, wheelspace temperature differential high. Oh yeah, when we were coasting down to shut down, at load 35MW we tried to perform a changeover from distillate to gas (we ran on distillate the entire day yesterday),we failed due to fuel gas nozzle purge valve failed to close.

Whenever there is a shutdown opportunity, we will perform the start up on distillate again. We will also change the AA gauge to a smaller range gauge bout 2-3 bars to trend the rise in pressure as the unit goes up. Besides, we will check the fuel forwarding pump, liquid fuel supply pressure, liquid fuel pressure right after the low pressure filter and flow divider pressure. During normal running on distillate, the pressure after the low pressure filters is 3.4 kg/cm2. We all also check the liquid fuel bypass valve,smoke from chimney, hydraulic pressure during start up and AOP. Will keep you posted on the results.

On whether we have checked the tell-tale leak-off for fuel during firing, is there a way to check when the unit is running? we dont suspect the purge air line at the moment unless all else fails.

We have tried starting on gas fuel, transferring to liquid fuel at FSNL,shutting the unit down, then starting on liquid fuel but failed due to failed to ignite problem.

The filters should not be a problem right? since the dp is low and unit was running smoothly after changeover from gas to diesel till we shut down yest. the liquid fuel flowing through the flow divider is normal during firing. i have already checked. the pressure is at 34 kg/cm2.
I would like to contribute to the cause of the failure to ignite when you start on gas, shut down and try starting on liquid fuel. This could be caused by coking of the liquid fuel nozzles when you start and run on Gas.

Either the liquid fuel nozzle purging is not effective ( i.e from VA 19) or you have not performed nitrogen purging well in previous change over from liquid fuel to gas.)

I would like to add that coking of the fuel nozzles is definitely a possibility if the unit doesn't run on liquid fuel very often. And, it has been a problem on many Frame 9Es that one or more of the liquid fuel check valves leak in the reverse direction when running on liquid fuel and cause coking of the fuel nozzles in spite of the purge air system.

And, this has also been demonstrated to cause air to collect in the tops of filter canisters. It has even been demonstrated to cause the liquid fuel stop valve to open from CPD.

So, it could still be failed liquid fuel check valves (one or more), and the fact that you weren't able to read any pressure on the liquid fuel lines with the manual selector valves also points to them as a possible problem. The liquid fuel check valves have a cracking pressure of more than 100 psig which helps to atomize the fuel as it passes through the nozzles. So, the fuel pressure must be above the check valve cracking pressure (stamped on the check valve) during firing.

Still awaiting more troubleshooting information.

And, not every Frame 9 (E or F-class) has nitrogen purge of the liquid fuel nozzles.
I will get back to you guys regarding the results of the test. The test was not done last weekend due to insufficient time. We needed to start up the unit earlier than expected. Will continue with the test whenever opportunity arises. I will keep all the points in mind too. Thank you louis and CSA
Hi there guys,

We had an opportunity to test to start up GT1 on diesel last night. Before the test, we changed the AA pressure gauge to a 3 bars gauge. We turned on the AA booster manually to observe if there was any suction. The suction was weak and there wasn't any pressure reading.

Subsequently, we proceeded to start up GT on diesel. Field operators were assigned to observe several parameters:

1. Fuel forwarding pump running or not

2. Outlet pressure of the liquid fuel in fuel forwarding pump

3. hydraulic pressure (just to make sure the auxiliary motor was running fine and in time) at 100 bars

4. flow divider pressure

5. white smoke from the chimney

6. fuel stop valve

When operator selected start on diesel, hydraulic pressure went up to 100bars almost immediately. Fuel stop valve opened after a while. Pressure on the flow divider was at 10 kg/cm2. only #14 was at 8kg/cm2. There was white smoke from the chimney. The outlet pressure of fuel forwarding pump was at 8bars. After a few minutes, failure to ignite alarm was annunciated and subsequently failure to start up on distillate.

What we suspect was that, combustion did happened which was indicated by the white smoke from the chimney but maybe the distillate wasnt properly atomized. The pressure build up of the AA was way too weak. My question is that, failure to ignite annunciated although white smoke was visible, is that possible? Could there be problems with the spark plugs that gave the wrong signal?

We are gonna install the pressure gauge directly at the discharge of the AA booster in the next test during online. If the pressure build up by AA booster is insignificant, maybe an external instrument air pressure can be installed on the booster pump. Anybody know what kinda pressure should we be regulating the air pressure? Thanks for the feedback. appreciate it alot.
Thanks for the feedback.

I'm going to go back to what I said earlier about Booster Atomizing Air Compressors: Most are roots-type blowers, and when operated in reverse draw excessive current which usually trip the breaker of the motor starter.

You have said on repeated occasions that you have reversed the rotation of the compressor and that it has been run (for extended periods of time) in the reverse direction with no apparent problems, meaning that the motor starter thermal overload relay didn't actuate and the motor starter breaker's thermal overload device didn't trip the breaker.

To me this says that there is something catastrophically wrong with the Booster Atomizing Air Compressor--presuming that it IS a roots-type blower (which you have never confirmed, by the way). <b>What is the Booster Atomizing Air Compressor manufacturer's name, and what kind of "compressor" is it--centrifugal or roots (lobe) or???</b>

You failed to indicate if there was any flame indication/intensity, or if there was any exhaust temperature increase during the firing. I'm also <b>VERY</b> concerned when you say that "firing" continued for several minutes before a failure to ignite alarm was annunciated! Fuel should only be admitted with the spark plugs energized for about 60 seconds during the process called firing. Continuing to "dump" liquid fuel into the machine for more than 60 seconds with the spark plugs energized is just asking for trouble--big bang trouble if flame is finally established and unburnt fuel has collected in the turbine and exhaust.

If there was combustion, there would have been an increase in exhaust temperature, at least on some of the exhaust T/Cs. <b>Did any of the exhaust T/Cs indicate an increase in temperature?</b>

When a unit is trying to start on liquid fuel and there is liquid fuel flowing into the combustors, there will be white "vapor" coming out of the exhaust stack--which is atomized liquid fuel which hasn't been burned. The vapor is kind of like steam, wispy and "thin" and usually evaporates fairly quickly.

If there is white <b>smoke</b>, billowy and cloud-like white smoke, that indicates that some of the combustors have established flame and that the heat from those combustors where flame has been established is trying to ignite unburnt fuel from other combustors and this makes cloud-like white smoke.

The two "smokes" are very distinct from each other.

If you get the Booster Atomizing Air Compressor nameplate data, you can likely determine how much air and the pressure which would be required. I think you will find it will be a fairly significant air flow at a relatively low pressure.

You may have been correct all along about the problem being the Booster Atomizing Air compressor. By not responding to the indirect question about the type of compressor and not providing any information about the current being drawn by the compressor's motor, you have not properly troubleshot the compressor.

I have seen two Booster Atomizing Air Compressors damaged by trying to operate them in reverse. I say trying, because on both occasions the motor starter breaker tripped very quickly when the motor was started. And, on both occasions someone was stationed to manually try to keep the breaker closed when the motor was started. One motor starter caught on fire and the breaker on the other one blew up. Fortunately, no one was hurt in either incident. Operating a roots-type blower in the reverse direction is like and infinite load on the motor, which draws high and excessive current. Which usually trips the motor starter's incoming power breaker.

In both occasions, someone was looking at the manual instead of the compressor to determine the direction of rotation of the motor driving the compressor, and in both cases the manual was wrong.

So, while it's good that you have been looking at all aspects of liquid fuel firing operation, you have not confirmed nor eliminated the Booster Atomizing Air Compressor as the cause of the problem. Frame 9Es do require atomizing air flow from a Booster Atomizing Air Compressor to establish flame. And it sounds like you have sufficient pressure at the combustors, but you don't know if the Booster Atomizing Air Compressor is working properly. You can probably use a clamp-on ammeter to check the motor currents (of each phase) to see how much current is being drawn when the motor is operating in the proper direction, and then, because you have said it operated "fine" in the reverse direction, you can check it then, also.

If the motor isn't drawing near nameplate rated amps when rotating in the proper direction, then it's probably not moving much air. If the current is much less than nameplate rating, then it's probably not moving any air to speak of. (Current draw is directly proportional to torque, and torque is required to move air. Moving more air requires more torque.)

If the motor is not drawing excessive current (in excess of motor nameplate) when it's running in the reverse direction, then my money says the compressor isn't working properly--even in the forward direction.

You can use your favorite search engine to research roots blowers, or roots superchargers. Wikipedia has a pretty good article on them.

You also haven't told us if you've checked the spark plugs to see if they are working properly, and if they are "wet" after a failure to ignite on liquid fuel. Just because the work with gas fuel doesn't mean they will work properly with liquid fuel, expecially if they get wet during firing.

We look forward to hearing the answers to the above questions.
Thanks for the feedback CSA.

The Atomizing Air Booster Compressor manufacturer's name is cyclo blower and its a Rotary Lobe Axial Flow Compressor. We have not encountered any tripping on AA booster compressor when we tried to start on diesel which failed up until now.

In the previous test, we tapped the external air pressure at the suction of the main AA compressor at 1 bar and tried to start on diesel. The exhaust spread temp did not rise at all. They maintained at about 105-110 C (from the cranking until firing until the alarm "failure to ignite" was annunciated). There wasn't any loss of flame alarm to indicate that there was flame but it did not last. We also tracked the movement of solenoid 20FD-1 and liquid fuel stop valve. They were both energized (20FD-1 open, liquid fuel stop valve open) a few seconds b4 firing status was achieved. Flow divider pressure was at 10kg/cm2.

The white vapor that came out of the exhaust stack was a thin and quick evaporated one indicating that the combustion did not happen at all and supported by the exhaust temp maintained at bout 105-110 C.

The AA booster compressor has a rating of inlet pressure 14.7psig and outlet 12psig. We also tried at 3 bars of external air pressure but failed. The only alarm that we got prior to the incident was hydraulic filter dp low and hydraulic supply pressure low and of course the failure to ignite alarm. We checked the hydraulic when we started on diesel. The auxiliary hydraulic motor started on time giving us the hydraulic pressure of 100kg/cm2. So, i am not sure why did we get the alarm. The fuel bypass also closed bout 50% when fuel stop valve was open.

After 3 tries, we discontinued the test to further discuss the problems. We tried raising the ext air pressure at 8bars just to see if the AA pressure gauge would show any reading but it did not. (we did not start at 8 bars, just wanted to observe the reading)

We have not checked the motor current as of now. Ext air was tapped in at one bar. Even if the AA is working perfectly as rated, i dont think we wud succeed. I do suspect the functionality of spark plugs. How do i check the spark plug whether it functions well with diesel or not? We have performed change over from gas to diesel and we have no problems. It shows that the spark plug is working fine rite? What further test should i do on the spark plug? the amp of the AA motor is 25.7/27.4 amp. Appreciate the feedback. we hope to tackle this issue asap to give us the ease of mind when instructed to start on diesel.
Okay; we're getting somewhere now. Slowly, but we're making forward progress. We have light, wispy vapors (not smoke), and no exhaust temperature increase or spread. Most Frame 9Es have four flame detectors, and fourteen combustors, so it's entirely possible for there to be flame in some cans without flame detectors but not in cans with flame detectors. Not likely, but possible, especially since the spark plugs are not usually located in cans that also have flame detectors mounted on them.

AGAIN, the fact that you have NOT encountered any tripping of the Booster AA Compressor motor starter is a red flag--for me. You say you have found the motor rotating in the opposite direction, have reversed it, and have tried rotating it both directions since then, and there has been no tripping. My understanding of and experience with roots-type blowers is that if rotated in the opposite direction of the intended rotation that it creates an infinite load on the motor, and that causes the motor starter breaker to trip very quickly. In some cases, this is before the thermal overload relay on the motor starter will actuate.

It's very important that you obtain running current data for the motor, because THAT will tell you if the blower is working properly. The amount of current being drawn by the motor is directly proportional the amount of torque being produced by the motor which a function of the amount of air being moved by the blower. If the current draw is low, then there's not much air moving. If the current draw is about equal to the motor nameplate rating, then the blower is probably working fine.

That's one check that's still not been done.

And, if you can operate the motor such that the blower is running in the opposite direction from the intended rotation and get current data, that would be helpful, very helpful, as well.

The spark plugs <b>do not</b> operate after the firing timer has expired during starting. Unless this unit has DLN combustors (which you haven't indicated.!.!.!) then the spark plugs are de-energized at all times after the firing timer has expired, even if flame has been detected.

Gas turbines are not like reciprocating engines; they don't need a spark to keep the flame burning once established. They only need a spark to establish flame during starting, and after the firing timer has expired (L2F equals logic "1") the spark plugs are de-energized.

In the unit has conventional combustors, the spark plugs will have a spring that should push the plug tips into the combustor when the unit is shut down, and when flame is established and the axial compressor discharge pressure is building up in the unit it (the pressure) will push the plug tips out of the combustor to prevent them from being damaged by the heat of the flame and combustion gases. And, when the unit is shutting down and axial compressor discharge pressure is falling this will cause a spring in the plugs to push the tips back into the combustors in preparation for the next start attempt.

So, the first thing to check is to see if the plugs have "retracted" properly into the combustor during shutdown. One can pull the visible end of the plug (where the spark plug cable attaches) out and test the spring action. DO NOT release the plug and let it slam back into the combustor! You can damage the ceramic material inside the plug body by doing so. Just reduce the force you are applying to the plug end and allow the spring to pull the plug back into the combustor. If it binds up being pulled out or when going back in, that could indicate some problem which should be resolved.

Before removing the plugs, you should make sure that the power to the plugs is isolated (for personnel safety).

The plugs are usually held in place by four bolts (each), and the four bolts can usually be easily removed, and then the plug assembly can be removed from the combustor (it's not usually necessary to disconnect the spark plug cable to do this).

Lay the plugs on a metal surface and be sure they are grounded. If the metal surface is painted, scratch the paint directly underneath the plug body to ensure there is good contact with earth. Watching from a safe distance (approximately 1 m) with safety glasses in place, have someone restore the power to the spark plug circuit and then force the logic signal that energizes the spark plug transformers to a logic "1". That signal name is usually L2TVX, but you need to look in your I/O Report or CSP to be sure about that.

When the spark plugs are energized, you should see a spark at a fairly constant rate on each of the two plugs. It should be bright, but you don't need sunglasses (it's not that bright), and it should be steady. The plugs can stay energized for a couple of minutes, if necessary, just be sure to have people mind their approach and presence in the area when they are energized. (Usually, MANY people want to come and see the spark plugs.) Another important thing to note is that the two plugs should be firing with the same brightness; if not, then the dimmer of the two may have some issue(s). And, both of them should be sparking reasonably well, not just faintly. Again, it's not a bright spark, but it should be visible inside the turbine compartment in indirect light (if the sun is bright, it might be difficult to see).

When firing, the plugs also usually make a buzzing or sometimes a slight "crackling" sound, as electricity is wont to do when jumping across an air gap and ionizing the air in the process.

Once you have proven the plugs are working correctly (or not, and resolved any issue(s)) you can then re-install them (minding the safety precautions).

Plugs do require periodic maintenance. The gap between the electrode and the body can't be too large, and the electrode and the body "tips" can both erode over time. The ceramic insulator inside the body must be in place and not be cracked or broken. Also, many times when the plugs are removed and re-installed during maintenance outages the plug cable connectors can become damaged (though you don't seem to be having any trouble firing on gas fuel, so this particular problem shouldn't be an issue, but if the electrical connection isn't solid it could lead to a weak spark that might not ignite liquid fuel, so it's something to be checked as well since you're examining the plugs anyway!).

It would be very interesting to know what the plugs looked like on initial examination, and what they looked like after a failed start attempt. Again, if the plugs get "wet" from the liquid fuel flowing during starting, they won't work very well and can lead to a failed start attempt.

There are two plugs for redundancy purposes; only one plug needs to work to establish flame in a gas turbine, but it doesn't hurt if both are working. And, to answer your question, you can't know if one is not working when the unit is being started.

I'm a little concerned about these hydraulic pressure alarms. First, there's not usually an alarm on <b>low</b> hydraulic filter differential pressure. (I'm hoping that's just a "typographical" error.) Second, when you start the unit on gas fuel are the same hydraulic pressure alarms annunciated?

Do these alarms get annunciated, and then "clear" shortly after they are annunciated? If the hydraulic filter differential pressure is actually high, then that could be a cause for the problem.

Are there any Diagnostic Alarms being annunciated during liquid fuel firing?

Can you monitor the Liquid Fuel Bypass Valve servo current during firing to see what it is? The signal name is usually FAL.

Firing a gas turbine takes three or four things: Fuel, Spark, and Combustion Air, and when firing on liquid fuel, some Atomizing Air pressure--especially on Frame 9Es. It seems you have fuel flowing, based on the pressures, and on the vapors coming from the stack. The one thing we're not very sure about at this point is the atomizing air. Or, even that there is sufficient fuel flow for that matter. Please monitor FQROUT and FQLM or FQLM1. Those signals are the liquid fuel flow-rate reference and the liquid fuel flow divider feedback signals. The reference and the feedback should match if everything is working correctly.

You still haven't said if you've checked the Tell-Tale Leakoff drain to see if there is anything coming from it during firing. (It's usually located on the right side of the turbine compartment, under the walkway grating.)

I'm really leaning towards recommending you get someone knowledgeable to site to help with this problem. Based on the questions and the trouble this is causing and the urgency you seem to be exhibiting, this is a slow method to try to resolve the problem and there seems to be some basic unfamiliarity with gas turbines and turbine operation. Making this not impossible, but slow.

Please try to get as much information and reply to all of the questions! Troubleshooting can be very demanding, and sometimes requires a lot of simultaneous activities to solve a problem as quickly as possible.

I don't know if we've ever discussed this before, but, has this unit always had trouble firing on liquid fuel, or is this a relatively recent occurrence?
One more thing about using plant instrument air for Booster Atomizing Air during starting on liquid fuel. If you find the pump curve, I believe you will find that it's a fairly substantial flow that the pump provides to the AA piping. I don't think it's possible to take a 12mm or 15mm hose and drop the pressure to 0.7 barg and inject sufficient air (flow-rate) into the system through a pipe tap to have much of an effect on the liquid fuel atomization.

So, if the temporary gauge you have installed at the pump discharge (you have installed one, correct?) isn't indicating any pressure, then it's even more important that you take some running amp readings to see if the pump is actually producing any flow/pressure. Again, the AA gauge on the Acc. Gauge Cabinet isn't going to read less than 1 barg very well when the gauge is sized for more approximately 20 barg.
You might also consider removing one, or two, or three fuel nozzles to inspect them for coking. As Louis said in an earlier response, this could be a contributor to the problem. As you said, you didn't think you would succeed in the firing attempt even if the Booster AA Compressor was working properly.

The unit might run on liquid fuel when transferring from gas fuel, but if the coking is severe enough it might not allow for proper atomization during firing. You have already indicated can #14 has a lower pressure than the others, and if I'm not mistaken some Frame 9Es have a spark plug installed in can #14.

You have also never told us if there are high exhaust temperature spreads when running on liquid fuel after transferring from gas fuel. If there are high exhaust temperature spreads then that could indicate coking, or other problems.

Many times these kinds of problems are not the result of just a single problem. You may be experiencing several problems at the same time. As has been said many times on Dual fuel (gas/liquid) GE-design heavy duty gas turbines should be operated regularly and periodically on liquid fuel in order for them to operate properly on liquid fuel when desired. There are so many components in the liquid fuel system that are **NOT** controlled or even monitored by the Speedtronic turbine control system, and they must all be working correctly in order for the turbine to operate properly on liquid fuel.
Dear CSA

While reading this thread, so many questions raised on my mind and along with this thread knowledge i have gone through CSP and P&ID as per that i understood that Compressor booster suction kept open (By VA22) Till compressor bleed valves close(At 95% TN), so once compressor bleed valve close the suction get blocked.

As per booster motor logic permissive it is running till machine reaches L14HC(60% TNH) with liquid fuel selection

Really i don't know about this atomizing air booster compressor function during liquid fuel operations but my curiosity made me to post this questions.

Our machine is GE 9E,MKV Controlled, Dual fuel machine (Gas primary, Distillate is secondary fuel)

while running in gas fuel VA18 is closed (L20AAX -1) and VA22 is opened (L20AB1X-1) and VA19-1 is closed to purge liquid fuel nozzle (L20PL1X-1)
Dear 4_20ma,

How nice to hear from you again, on a different topic (not that we know if you were "satisfied" with the responses to the last topic you wished to argue about).

Without being able to see the P&IDs and CSP for the unit at your site, I can't comment exactly on how each component works, and I don't presently have access to any gas-distillate P&IDs for a Frame 9E.

The Booster AA Compressor serves to provide some atomizing air to help with breaking up the liquid fuel being sprayed into the combustor during initial firing and acceleration. This is because the Main AA Compressor gets its suction from the axial compressor discharge, and at 10% speed (during firing) there ain't much air pressure or flow from the axial compressor. Combine that with the fact that the Main AA Compressor is Accessory Gear-driven, and that during firing the unit is running at 10% speed, the Main AA Compressor is also running at 10% of rated speed so there just ain't very much air flowing out of the Main AA Compressor, either, at firing. So, the designers decided to use a Booster AA Compressor to assist with starting on liquid fuel.

When the unit is running on gas fuel, it's not necessary to have full Atomizing Air flow, so, usually there is a bypass around the Main AA Compressor to reduce the energy consumed by the Main AA Compressor since full flow isn't required when running on gas fuel. It is desired to have some "purge" air flow through the AA passages, to keep hot combustion gases from back-flowing into the AA manifold and to cool the fuel nozzles, as well, so there needs to be some air flowing through the AA passages when running on gas fuel, just not the same amount required as when running on liquid fuel.

And, to prevent any "back-flow" of air through the Booster AA Compressor, there is usually an air-operated valve in addition to a gravity-operated (sometimes spring-assisted) check valve on the discharge and suction lines, respectively, of the Booster AA Compressor (if I remember correctly).

There should be a written, though brief, System Description for each of the systems for which there is a P&ID in the manuals provided with a GE-design heavy duty gas turbine. These can be a good source of very basic information and helpful when trying to learn and/or understand the various systems. Please refer to them for more assistance with your learning.
I have one more <b>very important</b> question:

<b>At what speed is firing occurring?</b>

In other words, when (at what speed, in percent of rated) does the operator interface indicate "FIRING" and the Liq. Fuel Stop Valve open and the spark plugs get energized?

Is it 10% speed? Or 12% speed? Or 15% speed?

Because if firing is occurring at a high speed while on liquid fuel, this may be part of the problem.

Most Frame 9Es with adjustable torque converters (and we don't know exactly what you have at your site) usually fire at about 10% speed. On gas fuel, it's usually easier to fire at a higher speed, but not so on liquid fuel.

So, please tell us at what speed firing is occurring!
Dear CSA
Thank you for your reply. Our firing speed 18% TNH in GAS fuel, but really i don't know about liquid fuel (This is one of the great thing which i have learned and understood TODAY), i will study and come back to u regarding Liquid fuel starting FSR.

Yes we have 9E with adjustable torque converter.

Again Thank you so much for your reply.

My most recent reply was not directed at your question; it was directed at the original poster, RY.

However, your post intrigues me (though I'm sure I'm going to regret asking).

What is the value of TNK14HM1 and TNK14HM2 at your site? These are the pick-up and drop-out values of the HP shaft minimum firing speed.

Most of the Frame 9E machines with conventional combustors I have worked on accelerate to *approximately* 20% speed for purging with the torque adjustor at "purge" speed setting. (The unit is purged at a higher speed in order to reduce the time it takes to purge the machine and exhaust of combustible gases prior to admitting fuel and energizing the spark plugs.)

Then when the purge timer expires, the unit decelerates to TNK14HM2 dropout, and during deceleration the torque adjustor is reduced to "firing" speed setting, and when the shaft speed drops below TNK14HM2 the torque converter is re-pressurized and the shaft should begin to accelerate slowly through TNK14HM1 pick-up, at which time firing should begin (fuel admitted and spark plugs energized).

WITHOUT BEING ABLE TO EXAMINE THE SEQUENCING OR APPLICATION CODE RUNNING IN EITHER MACHINE (yours or the original poster's) it's very difficult to say for certain exactly how the machines operate. Not all GE-design heavy duty gas turbines are the same; there are some very simple, but critical, differences in machines--even machines of the same Frame size.

When a unit is being started, the fuel valve is set to a particular position, usually defined by Control Constant FSKSU_FI. And for machines which can be started on either gas fuel or liquid fuel, sometimes there are different firing FSR values, and logic selects between them depending on which fuel is selected during starting. Sometimes, the Control Constants are FSKSU_FI_GAS and FSKSU_FI_LIQ.

<b>BUT</b>, the purging and firing sequence doesn't change--only the amount of fuel being admitted (gas fuel or liquid fuel) changes. The unit still accelerates to purging speed, then decelerates to below firing speed, then slowly accelerates to firing speed at which time fuel is admitted and spark plugs are energized. The only thing that might change is the amount of fuel, depending on which fuel is being burned during starting; the purging and firing sequence remains the same.

Shortly after flame is established, then the fuel is cut back to warm-up (FSKSU_WU) and shortly after the fuel is reduced the torque converter is usually pulsed to the "acceleration" setting, which starts accelerating the turbine-generator shaft. Approximately 60 seconds after flame is established, then fuel is ramped up slowly to assist with accelerating the unit.

At approximately 60% speed most Frame 9Es de-pressurize the torque converter and then the unit is accelerated completely with fuel up to FSNL.

So, my question to you, 4_20ma, is: What are the Firing Speed pick-up and drop-out values for your machine? And what are the firing FSR values for your machine?

Please don't confuse the engineering units for TNH and FSR. TNH is expressed in %, percent of rated speed. FSR is also expressed in %, but it's percent of rated fuel stroke (position). So, in this case % TNH does not equate to % FSR.
CSA, i must say i really appreciate the patience and the relentless guidance to all the people who need help. You are a consistent tutor which is something all other forum members can definitely learn from.

With regard to the topic, i am still waiting for an opportunity to test the GT start up on diesel. This time, i am more equipped. I believe i have planned all the parameters to be monitored and also delegated the task to maintenance department. Once the opportunity arises, i will keep you guys posted as soon as possible. Thanks again.

Please ensure you "capture" the speed at which the unit is running when the Liquid Fuel Stop Valve opens and fuel starts flowing and the spark plugs are energized.

Also, it would be very helpful to know the values of TNK14HM1 and TNK14HM2 for the GE-design Frame 9E at your site. So, please include this information, as well, when you report the details of the next firing attempt. (These values are Control Constants, and they can be viewed from the Control Constant Adjust Display, or temporarily placed on any Demand (User Defined) Display or a Logic Forcing Display.)
Dear CSA
The following values i have found in my Unit's control constants
TNK14HM1- 10 %
TNK14HM1- 9.5 %
FSKSU_FI-19.8 %

There is no control constat defined as FSKSU_FI_GAS and FSKSU_FI_LIQ

Our unit's FSKSU_WU- 11 %

I found that our unit fired at 18 % of TNH from old real time trend.

I am looking forward to read from you.

Thank you