Bleed valve function

this is normal, as every machine had different behavior, this is related t the efficiency of each machine? You try to calculate it as per your machine OEM .

you did not mention about other measurements such as inlet air mass flow in m3/hr, you measured pressure and temperature pnly which is not enough.

One factor may affect the efficiency the mass flow is the inlet filter pressure drop (delta p) you check this point as well.

Also both compressors cleanness is a major factor .
Good luck


 
M

Mohsin Hasan

>Compressor bleed valves are generally closed
>during normal operation (with the previous exception) since
>"dumping" axial compressor discharge into the exhaust
>reduces efficiency

How does it reduces efficiency? If they are opened during normal operation, what would be the impact?
 
Two turbines are of same manufacturer, same model and same name plate data installed at same site. Filter DP across inlet air filters and inlet vacuum is also almost same, however we do not have any direct means to measure inlet air flow rate. We also have changed the entire turbine rotor but power difference between two turbines still persists..
 
hello,

I want to know. if the bleed valve keeping open after her function, what would happen?

.......thanks
 
What should be the expected "Operational Time" to fully close or to fully open? (W251B11; 50MW).

Thank you.
 
I want to know about SGT600 bleed valves discharge location. In old package they discharge into inlet plenum (intake system), but in new gas turbine package they discharge into exhaust.

I want to know that, It is just for arrangement concern and enclosure limitation or it is related to other aspects such as engine parameters.

Best Regards
 
> What to do if surge/stall condition occur in axial
> compressor at rated speed?

The axial compressor bleed valves of a GE-design heavy duty gas turbine offer no protection against surge/stall at rated speed. And, most newer GE-design heavy duty gas turbine control systems monitor operation and annunciate a Process Alarm when the axial compressor is approaching the limits of operation that, if exceeded, could result in surge/stall. On some GE-design heavy duty gas turbines, the turbine control system will actually limit output to protect against damaging the compressor.

But, if one occurs, well, about the best thing one can hope for is that the damage is minimal and the cost to repair is minimal and the lost production is minimal.
 
>The axial compressor bleed valves of a GE-design heavy duty
>gas turbine offer no protection against surge/stall at rated
>speed. And, most newer GE-design heavy duty gas turbine
>control systems monitor operation and annunciate a Process
>Alarm when the axial compressor is approaching the limits of
>operation that, if exceeded, could result in surge/stall. On
>some GE-design heavy duty gas turbines, the turbine control
>system will actually limit output to protect against
>damaging the compressor.

Which process alarm gets triggered when approaching stall exactly?? I have seen significant damage to axial compressor of a GE 9FA turbine when "Compressor stall detected " "loss of compressor discharge pressure bias" alarm appeared while running at about 90% load and IBH closed. The unit had been running normally for the past many days. Unfortunately, everything happened within fraction of seconds without any warning or associated process alarm that could have provided even 10 seconds for operator to react. No foreign object, no damage at filter house or screen thereafter was observed even though IGV also suffered significant damage. Although the enquiry and RCA is over, people have been secretive and not disclosed much as huge losses were incurred. I will post the details when I get to know, nowhere sooner of course, but was really really surprised with the event.

I ALWAYS THOUGHT GAS TURBINE DESIGN IS SO GREAT THAT NOTHING CAN HAPPEN WITHOUT ALARM !!
 
The compressor protection is usually accomplished in two places--the sequencing, or application code, running in the control processors (<R>, <S> & <T>) and in the firmware on one of the I/O cards (depends on the version of Mark*).

The protection in the sequencing/application code runs at the scan rate of the the control processors. The protection in the firmware on the I/O cards runs at 128 Hz or 100 Hz (again, depending on the version of Mark*).

The quality of the maintenance of the instrumentation is critical to the sensing and alarming/protection.

A LOT of GE-design Frame 9 F-class heavy duty gas turbines are operated in parts of the world where the frequency control is not so good. Off-frequency operation of these machines is not good for them, and they were designed for Base Load operation, with few starts. And trips from load, in addition to starts, decrease parts life more than previous designs.

GE F-class gas turbines were designed at the very limits of materials and technology with very little engineering margin--unlike B/E-class gas turbines, including Frame 3s and Frame 5s. B/E-class gas turbines were designed and built with large engineering margins and could "take a licking and keep on ticking" (a reference to an ability to withstand heavy use and even abuse for decades). They could withstand trips and off-frequency operation and frequent start/stop operation.

So, your statement is very accurate for the majority of the GE-design heavy duty gas turbine fleet. But, operating F-class gas turbines in frequent start/stop cycles, and, worse, at off-frequency conditions is not how they were designed to be operated. GE has designed and extensively tested their new HA-class gas turbines to operate in frequent start/stop operation, and in off-frequency applications in a return to the tradition of previous designs.

So, without knowing a <b>LOT MORE</b> about how the unit was operated prior to the event, how it was being operated at the time of the trip, the time since the last planned maintenance outage, what kind of parts were used in the last maintenance outage, the number of starts/stops and trips, the age of the machine, and ambient conditions as well as grid conditions it's really difficult to say more. Your instrument technician should be able to to look at the Process Alarm list for the unit and tell you what alarms are used for the machine at your site.

Finally, a stall/surge event can occur very suddenly. While GE has done a very good job of developing protection and detection algorithms I visit too many sites where any alarm is a nuisance and alarms are ignored--even if the unit has tripped. Any review and analysis would have to include alarms prior to the event, also.

Hope this helps! If you can share complete information, that would be great--but there can be many factors and contributors to an event like the one at your site. If you can share the full, final report that would be great; anything less could be misleading.
 
hello,

I want to know. if the bleed valve keeping open after her function, what would happen?

.......thanks
You got any answer/solution to above problem ? If yes, kindly share .
We are currently facing same problem ie bleed valve keeping open during normal running of Gas turbine.
 
You got any answer/solution to above problem ? If yes, kindly share .
We are currently facing same problem ie bleed valve keeping open during normal running of Gas turbine.
Can you tell us :

Frame type
Controls systems
Combustion mode
"Open" "Simple"/combined cycle

A bried description of the problem would be better way for us to have a picture of whats goig on a your site
 
Var.i,

Most axial compressor bleed valves are designed to fail in the open position/condition to protect the machine. This means the valve actuator must have a force applied to it to close the valve and keep the valve closed. Many actuators use compressed air to close the compressor bleed valve and to keep them closed. The compressed air supply to the actuator is usually controlled by another valve, often a solenoid-operated valve which can fail and cause the actuator to lose air pressure and allow the bleed valve to open when it should be closed.

So, if the compressor bleed valve on the unit at your site is not remaining closed, to troubleshoot the problem it would be necessary to understand how the valve actuator closes the valve and keeps the valve closed. There should be a P&ID (Piping or Process & Instrumentation Diagram) for the unit which clearly shows the bleed valves and their actuators and the motive force (such as air pressure) and the method for controlling the application of the motive force to the actuator (such as a solenoid-operated valve).

If the motive force is compressed air, there may be a pressure regulator in the air supply to the bleed valve actuator which is not allowing sufficient flow and pressure to fully close the bleed valve or to keep the bleed valve closed. Or the bleed valve actuator may need repair or replacement.

But the best place to start investigating the problem is to obtain the system P&ID drawing to understand how the bleed valves are operated and maintained in a closed position and then start checking each component to ensure it is working correctly to close the valves fully and completely and to keep them closed when they should be closed. A loose wire or a loose termination in the circuit that applies voltage and current to the solenoid-operated valve could be the problem that requires a simple fix. Or a failed or failing air pressure regulator.

It’s also very helpful to know when the problem started. For example, if it started soon after a maintenance outage where some work was done on the bleed valves or in the area of the bleed valves then they could have been improperly or incompletely reinstalled or something might have been not properly recommended—such as a wire or termination or compressed air tubing fitting or something like that.

But, find and use the system P&ID for the bleed valves. Use the Operations & Maintenance Manuals for more information. This is the proper method for troubleshooting.

In the future, if you write to a World Wide Web for help or information you will get a better response—and probably a quicker response—if you provide more information about the equipment you are working on. We are not on your site with you; we can’t see what you see or know what you know about the equipment—without more information we can only guess at how the equipment works and what might have been done to try to resolve the problem, or when the problem started. Help us to help you by providing more information—and provide any requested information—and we can be more helpful.

Please write back to let us know how you resolve the problem!

Best of luck.
 
var.i,

A couple of colleagues have written me to let me know, in their opinion, I didn’t answer your “question.” In my opinion, your question is very unclear. Do you mean when the bleed valve doesn’t close and remain closed when it should be closed?

OR, did you mean when bleed valve doesn’t open when it should open?

In the first case,if the bleed valves don’t close and remain closed when they should be closed the axial compressor discharge pressure will be less than it would normally be—which means the power produced by the turbine will be less than normal. If the turbine is a GE-design heavy duty gas turbine equipped with a DLN-I combustion system the turbine control system might trip the turbine on low axial compressor discharge pressure. (Some machines may continue to run—just at a low power output; others might trip because the axial compressor discharge pressure is less than some setpoint. The standard is: There is no standard, and it is an evolving control philosophy.)

If it’s the latter, and the bleed valves aren’t or don’t open when they should be open the unit can’t be started. If the bleed valves don’t open during shutdown or tripping from rated speed load the axial compressor may suffer mechanical damage, up to and including catastrophic damage.

Hope that helps (my colleagues, at least….)
 
I am working with SGT700, the Compressor has two Bleed Valves, BV1 & BV2. BV1 being near the suction end, and BV2 near the discharge end of the compressor. The description I gather from the discussion is very accurate. During start both are fully open. while accelerating, BV2 starts closing first there by pushing air towards the turbine, hence accelerating.
BV1 though, stays open untill 1MW of generation and then starts closing. While shutting down BV2 starts opening first, and when the load remaining is around 1.5 MW BV1 starts opening.

It would be of great help if someone can help me visualize how BV1 is helping here?

initially it is venting out air from the LP side of the compressor, how does it help avoid surge? and this would mean very little air reaching the HP side? if some one could break it down further...
 
Top