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What is the quantity of 1% FQL in gas turbines?
What is the meaning of 1% FQL, and how much quantity of fuel it indicates?
By chiru4433 on 21 May, 2019 - 6:44 am

We have frame 5 machines running with liquid fuel. I want to know what is the value of 1% fql, and why it is indicated/controller in % but in terms of any SI units? We have frame 5 BHEL gas turbines..

can anyone please explain?

By chiru4433 on 23 May, 2019 - 6:43 am

Can you please help on this?

It's been a while since I've seen 'fql' expressed as a percent, but, things are always changing....

I believe if you find 'fql1' in the application code (I'm presuming you have either a Mark VI or a Mark VIe) using Finder, you will see that it comes from the liquid fuel flow divider's pulse rate (speed) feedback inputs to the Mark*. You should be able to find the I/O Configuration for the pulse rate inputs, and if the Requisition
Engineer was nice enough you will find that there is a note on the 'PRScale' configuration Description field. It might say something like "Scaling: Hz to Engineering Units; e.g., 0.1 converts 1000 Hz to 100 Units" (e.g., is a Latin (I believe) abbreviation for "for example").

The Mark puts out a reference, FQR, which is in percent of a maximum flow-rate. (I've never quite understood how they calculate the "maximum.") The reference, in percent, is compared to the feedback, which is in percent, and the liquid fuel control valve position is adjusted to make the feedback equal to the reference (which, again, are both in percent). That's how it usually works.

I believe the "maximum" flow-rate is chosen based on the maximum flow-rate of the liquid fuel control valve, which should be more than the maximum expected fuel flow-rate on the coldest expected day for a new and clean machine (turbine and axial compressor). In other words, the maximum expected fuel flow-rate is a value which is calculated based on the machine's rating and known operating characteristics and the coldest expected day for the site where the turbine is located. The output of the unit would be slightly more than the turbine nameplate rating, and that means the fuel flow-rate would be slightly more than the fuel flow-rate at the turbine nameplate conditions. And, so the fuel control valve would not be at maximum opening the fuel control valve is chosen so that it will not be 100% open at the maximum expected fuel flow-rate on the coldest possible day.

I believe if you follow 'fql1' in the application code you will find a place where it converted into mass flow-rate per second (pounds-per-second, or kg-per-second). Usually, that signal name is something like 'fqlm' or 'fqlm1.'

But, this question--by itself--is a little odd. If one of the units is experiencing problems with liquid fuel operation, one needs to be sure that the PRScale valve is what it should be, per the Control Specification which is supplied with the unit control system. Or, if one or all of the other units is/are NOT experiencing problems, then one needs to compare the settings of the unit which IS experiencing problems to a unit which IS NOT experiencing problems.

But, we don't know what the context of this question is. If you be more specific about why you need to know what this particular signal means in reference to some issue or problem or something you are trying to determine, we might be able to be of more help.

BHEL should have provided a document called the "Control Specification." Section 5.01 of the Control Specification document is related to liquid fuel. There is usually a table in that section called something like 'Expected Fuel Characteristics.' In that table, there are usually rows for FIRING, FSNL, 1/4 LOAD, 2/4 LOAD, 3/4 LOAD,
RATED LOAD, PEAK LOAD (if the unit has PEAK firing capability), and MAX LOAD (which would be the maximum expected load on the coldest possible site day for a new and clean unit). Each row usually lists an expected FSR (in percent--which would be FQR when running on liquid fuel), and a fuel flow-rate (in #/sec (pounds/per-second) or kg/sec). I have seen some Control Specifications which listed the mass fuel flow-rate for each condition, also.

There may also be another sub-section in Section 5 which lists some information about the scaling of the liquid fuel flow divider speed (pulse rate) feedback. It may have more specific information that may be of help to you.

But, without more information about the context of the question, all we can say is: 'fql1' is a percentage of some maximum fuel flow-rate. It is usually compared to the liquid fuel flow-rate reference, usually signal name 'FQR,' and the liquid fuel control valve is adjusted to make 'fql1' equal to 'FQR.'

Again, if one of the unit is having an issue, please describe the issue and perhaps we can help. There should be at least two (2) speed pick-ups on the liquid fuel flow divider, providing the pulse rate input to the Mark*. Usually, the higher of the two pulse-rates is selected and used to drive 'fql1.' If the flow divider is a horizontal style, the shaft of this type of flow divider has been known to break, and cause problems with the liquid fuel flow-rate (pulse rate) feedback. Sometimes, the speed pick-ups are mounted on the ends of the flow divider, meaning that if the shaft is broken the inputs from the two ends of the flow divider can be VERY different.

The purpose of the liquid fuel flow divider is to evenly divide the flow-rate coming out of the liquid fuel control valve into ten (10) equal flow-rates to each combustor's fuel nozzle. By having the exact same amount of fuel flowing into each combustor's fuel nozzle, the temperatures of the hot gases exiting each combustor and entering the first stage turbine nozzles should all be the same or very nearly the same. This would mean even combustion in all the cans, and even exhaust temperatures. This is the optimum operating condition--uniform hot gas temperatures in all the combustors when the unit is operating. The hot gas path parts last longer when they are experiencing the same temperatures.

Hope this helps! Again, by itself--without understanding the reason for the question--the original question is unusual. And, difficult to answer. When you write to any World Wide Web-based forum for help or information, the more information you can provide you will almost always find the quality and conciseness of the response will be better. Help us to help you by providing as much information as you can (in this case, the reason for the question would have been very helpful) and we will do our best to respond as quickly and concisely as possible!

If you can find the Control Specification which was should have been supplied with the control system(s), you may find more information which may be of more help, also.