I have needed following information about GT. I am at new power project CCPP under erection. This is My first experience on GT.

GT is dual fuel type, Mark-VI, Starting at fuel oil (HSD), Atomising Air system main components are, Cooler, Main and accessory compressor, control valves.

1- What is Atomising air normal pressure and temperature
How pressure is controlled?
2- What is Atomising air conditions (Temp. and Press.) during start up and shut down

3- What affect of increasing/Decreasing pressure/Temp.

4-What can be reason of increasing/decreasing pressure/temperature

 

Hello,

There should be a document that is provided with the unit and control system called the Device Summary. You need that document, along with the Piping Schematic drawings (P&IDs) to answer most of these questions.

You should find there is a temperature regulating valve in the Atomizing Air System, that controls the temperature of the air entering the Main Atomizing Air Compressor. If the Main AA Compressor is typical of most Frame 9Es it will be driven by the Accessory Gear and there is a speed increaser which spins this centrifugal compressor at very high speeds. Some Main AA Compressors operate at 14,000 RPM, some at even higher speeds. So, the temperature of the air entering the compressor is very critical to maintain proper clearances inside the compressor. Excessively high temperatures will cause catastrophic failure of the Main Atomizing Air Compressor. I believe the Device Summary will list the setpoint of the Atomizing Air Pre-Cooler Temperature Regulating Valve as 225 deg F, or approx. 108 deg C. There is usually a temperature switch, 26AA-1, which will alarm if the temperature of the air entering the Main AA Compressor exceeds approximately 275 deg F. And, the Main AA Compressor manufacturer (typically Atlas-Copco) usually states that the entering air temperature must be less than 300 deg F. So, it's vitally important to keep the temperature of the air entering the Main AA Compressor controlled, hopefully to 225 deg F, and in all cases, less than 300 deg F.

There is a Booster Atomizing Air Compressor, used for providing atomizing air during starting and initial acceleration. The presence of atomizing air during starting and acceleration is very critical to establishing flame and reducing smoking during starting and acceleration. So, this compressor is critical to start-up.

There is no direct control of Atomizing Air pressure; none. At least not on any GE-design heavy duty gas turbines that I've ever worked on. There is an orifice in the AA piping that is used to control pressure and flow based on empirical data. There are some typical parameters that are followed, but you didn't tell us if the unit has conventional combustors or DLN (Dry Low NOx) combustors.

AA pressure on units with conventional combustors usually isn't monitored with a pressure transmitter (or multiple transmitters) since it's not controlled (it just is what it is). Having said that, some of the turbine packagers have begun adding an AA pressure transmitter since it's good to be able to monitor it from the HMI (since most operators are loathe to go to the Gauge Cabinet and look at a gauge). For conventiona combustor-equipped units, I believe the absolute pressure ratio for AA-to-CPD is somewhere around 1.2:1, but I may be a little high on that (hopefully someone will correct me if I'm wrong!). I don't know what it is or should be for DLN combustor-equipped Frame 9Es.

During start-up, it's usually very difficult to see much, if any, pressure increase because the pressure during firing and early acceleration is very low with respect to the range of the gauge and/or transmitter. But, rest assured: if there's not sufficient atomizing air for firing from the Booster Atomizing Air Compressor the unit will not light, and even if it does (which it likely will not) there will be a LOT of smoking (not that all smoking during firing and acceleration is a function of AA pressure; it's not!).

Too much AA will potentially blow the flame out; and too little will result in excessive, billowing white smoke coming from the exhaust.

There isn't much reason for changes in AA pressure, during steady-state operation, because it's a function of IGV angle and load, primarily. Air is extracted from the axial compressor discharge and fed to the AA Pre-cooler, then to the suction side of the Main AA Compressor. Again, none of the GE-design Frame 9Es I've ever seen or worked on had any kind of control for AA pressure, nor for the temperature of the Main (or Booster) AA Compressor(s). The temperature and pressure are what they are at the discharge of the compressors. The only real "control" is the temperature of the air entering the Main AA Compressor, and it's pretty critical.

If the temperature regulating valve to be used for the AA Pre-Cooler is made by Robertshaw, be sure to read the instructions from the valve manufacturer before attempting to adjust the valve's setpoint. Also, you can't adjust the setpoint unless the unit is running, and any adjustment you make will take several minutes for the change to stabilize so patience is key! Along with knowing how to change the setpoint (it's not intuitively obvious on the Robertshaw valves).

Lastly, know that when the AA Pre-cooler Temp Regulating valve is set for 225 deg F, that when the unit is shut down and the line is at ambient temperature, the valve will be CLOSED because ambient is much less than the setpoint! So, when the unit starts up, it will take some time (because the Robertshaw valves are very slow-acting, but they do work well!) for the valve to open and there is a risk of a high AA temp process alarm while the valve is opening. PATIENCE is key here, as well as a good understanding of how the valve works.

Of course, if the unit does not use Robertshaw temperature regulating valves, then the above is not relevant. But, we don't know what is to be used at your site.

Hope this helps!

The best thing you can do to get familiar with the turbine and it's operation is to get your own copies of the Piping Schematics (P&IDs) and Device Summary and start studying them and commit them to memory. You should make notes with a pencil and highlighters all over the drawings about the setpoints for devices and any pertinent information you have learned about the systems.

Finally, all of the Piping Schematic drawings have notes on them. READ THE FINE NOTES!!!! There is invaluable information in the Notes on each of the Piping Schematic drawings.

No one can be a good operator or a good technician unless they understand and can read and interpret the Piping Schematics (P&IDs), and that includes the Device Summary (which as the setpoints and calibration information for most of the devices and instruments on the drawings). Make sure you know where all of the field devices and instruments are located, because there's not generally one drawing which depicts the locations of all the devices and instruments, and when you need to find one, you need to know where it is to find it!

Good luck with your training. Let us know if we can provide any more information.

And, remember: Feedback is the most important contribution!"(c) here at control.com. There has been a lot of information written and shared here on control.com over the last few years, and the 'Search' feature can be very helpful in finding answers to questions which likely have already been asked. And, when you use the 'Search' feature you should notice that most people have responded to say if they found the information helpful or useful, which is the feedback which lets others know if the information was truly helpful--or not. If you can take a few minutes to ask a question or ask for help, you can take a few minutes to write back and let others know if you received the information you needed or if the help was instrumental in resolving your problem. Without that kind of feedback, it's virtually impossible for others reading the posts in the future to know if the information in the post is good or not.

So, help up to keep our tradition going, of responding to let others know if you found what you were looking for in the responses provided!

 

Dear sir,

Thanks for your response
Your reply was more explanatory, even more than my expectations, I really appreciate.

Moreover,Our site GT is Conventional combustion system, not DLN.
I checked device summary anbd also logics. CA1 inlet temp, ranges are Low:194F, High:270F. while differential pressure setting for CA1 is Low:6PSI. I have seen at nameplate of Main AA compressor
Rated RPM are 50100

Is it true?

Gear box shaft at which Compressor is installed,its rpm are 6600
I could not find compressor pinion and gear speed ratio any where

after that from precooler there is a line installed mesh silencer and a hand valve that is for blowing or purging, that's for what purpose
also a .08mm hole in a plug after booster compressor discharge, That is also for purging,for??

A bypass valve VA18-1
that is open at gas fuel operation and close at fuel oil operation,That is ok, make sense
But when I see logic for that valve
During fuel transfer oil to gas, this will remain open,after transfer close for 33sec,then again open
this sequence stand for what

an orifice is installed at by pass line after VA18-1 but no thing on main line to control flow or pressure as you mentioned in reply

And another question, If there is any trouble with booster compressor can we go for startup? is it possible

After atomizing air I have also few actual issues existing at our site
Thanks

 

Yes; it's true. 50100 RPM sounds like a reasonable speed for the Main AA Compressor (CA1). They usually have their own speed-increasing gear box. The Accessory Gear Box on which CA1 is mounted should have its own nameplate, and the speed of the various output shafts should be listed on the nameplate, or on some document in the Instruction Manuals provided with the unit.

The temperature of the inlet air is important. If it's too high then the compressor can fail; if it's too low then liquid from condensed moisture in the air might make its way into the compressor which can also make it fail. The internal clearances in the compressor are very critical to the compressor's performance, and so they are very small. High temperature inlet air and moisture in the inlet air are the two main causes of failure of the Main AA Compressor. So, the proper setting of the Atomizing Air Pre-cooler Temperature Regulating Valve is very important. It must be set so that the air temperature doesn't exceed the 270 deg F inlet maximum, nor the 194 deg F inlet minimum (during operation at rated turbine speed).

I'm not sure about the silencer, but it might be possible that it's used to dampen pulsations in the line. When an Off-Line Water Wash is performed, there is a high likelihood of water entering the Atomizing Air Piping, so the manual valve is there to allow as much of the water to be drained from the piping as possible prior to re-start. This is very important. Valve positions during Off-line Water Washing are critical to proper operation and long life of the machine. You would do well to work closely with the commissioning personnel on site to develop a detailed procedure for Off-Line Water Washing, and then to paint the valve handles of the valves which must be manually operated during an Off-Line Water Wash so they can be quickly identified. A procedure is key to timely and safe completion of an Off-Line Water Wash, and marking the valve handles with uniquely colored (high-temperature) paint also helps tremendously. (The paint doesn't adversely affect turbine performance or the warranty of the unit--contrary to the statements of some Plant- and Operations Managers!)

You should have seen in the Notes on the Piping Schematic drawing that the 0.08mm orifice is for a continuous blow-down, which means that when the unit is running there will be a very small amount of air continuously blowing out that very small orifice, and with it should be any condensate or moisture which might be in the line. A lot of people think that "hole" is a "leak", and they cap it off; don't do that, it's very important, and it's very important that it be kept free and clear so it needs to be checked during maintenance outages.

Continuous blow-down orifices are typically used in various systems, and they are all very important. They are also supposed to be located in the lowest points of the piping systems, where any moisture/condensate might collect.

The time delay during transfer is likely for purging; without being able to see the Piping Schematic and the sequencing, it's difficult to say for certain.

If there is no orifice, then it's been determined that none is required, and the system has sufficient capacity and "restriction" without a need for any flow "control".

If there is a problem with the Booster Atomizing Air Compressor, and you need to start the unit on liquid fuel, then it's pretty likely the unit won't start. Or, if it does, it will likely be a very smokey start (lots of billowy, white smoke; high exhaust temperature spreads; and flickering flame indications). If it's an emergency situation and you needed to start the unit, it would be worth a try, but it likely wouldn't start. Fuel, spark, and air--combustion air and atomizing air--are what's required for starting on liquid fuel. Not enough of either, or too much of one with respect to the others is bad.

I've only seen a pressure switch used to indicate low atomizing air pressure when running on liquid fuel. And, I think it would be a differential pressure switch. Other than that, without being able to see the Piping Schematic and the sequencing, it would be difficult to say for certain.

Good questions. Don't forget to read the Notes on all of the Piping Schematic (P&ID) drawings! There is very important and useful information in those Notes. Some of it is "boiler-plate" (repeated) and common sense, but some of it is critical to proper configuration, operation and maintenance.

 

Haye
Dear sir

Silencer i I mentioned is installed at a small line (1" tube) taken from precooler. Thats also seems for continuous blowing.

And a isolation valve is available before cooler to isolate system during water washing, So no chance for water to reach at that location

During a start up I have seen that CPD at HMI appears one bar around 1600 rpm of GT. And Booster is stopped at 1800rpm.

So its mean is that in beginning atomizing air pressure will also very low,If there is trouble with booster compressor then if I arrange a external air supply after booster and before main compressor then would it assists the startup.

Can I send u P&I for easy discussion.
If I can then How?
Thanks

 

Hi,

Okay; makes sense about the silencer.

As for sending the P&ID, some people have posted drawings on some file-sharing websites (www.tinypic.com, for example) and then posted the URL here on control.com.

The likelihood of a failure of the booster atomizing air compressor, if properly maintained, is not very high. In other words, they are pretty reliable, if properly maintained.

You could always arrange another source of atomizing air, but it needs to be at the proper pressure and flow-rate, and I don't know how to tell you to determine that other than by examining nameplates and piping systems.

But, again, the likelihood of a problem with the booster atomizing air compressor increases in reverse proportion to the quality of the maintenance and operation. Don't maintain it; it will likely be a problem. Don't operate the liquid fuel system periodically, and it will most definitely be a problem when you need it.

Water can enter the atomizing air system by backflowing through the atomizing air passages of the fuel nozzles. Water can get everywhere it's not desired when Off-Line Water Washing. Best to get that procedure nailed down and those valves identified sooner rather than after the failure of some component.

Make sure all the continuous blow-downs are clear during every maintenance outage.

Maintenance and proper operation will do the most to ensure you don't need a secondary source of atomizing air for starting. And, keeping moisture out of places it doesn't belong, by keeping air temperatures at the proper values and properly performing Off-Line Water Washes, including draining the lines after washing, is also very important.

But, if you want to research and design a system to supply starting atomizing air, have at it! If reliable starting on liquid fuel is that critical, you have LOTs more potential sources of problems than the Booster AA Compressor! LOTS!

 

Hello

Mr. CSA can give brief which the function of this valve which i uploaded pic. to see in AA system. in Fact this valve location in AA booster.

http://i53.tinypic.com/1217g94.png

Thanks .