Gas Turbines - Gas Pressure Drops

There is a pressure drop along any pipe that is related to the rate of flow inside.

When you fully load the turbines they use more gas, so greater flow, so more pressure drop.

Using larger bore pipes will make the problem go away.

What is a barg?

Dear thanks for your reply, to start with, barg means its unit of pressure (bar guage).Secondly as per your opinion if the pipe size was the problem then further to the same there are three gas turbines installed in site which have been running on HSD for last three years & now they have been converted to Natural gas, secondly I had the same problem last week on GTG 1, but when I went site suddenly without any reason the problem on GTG 1 disappeared & it was loaded till 5.0 mw & stable, now when we are commissioning the second GTG we are having similar problems and the GTG is not been able to be loaded beyond 2.0 mw as the GTG Pressure inside the gas trubine is dropping to 12 barg whereas the Pressure on the Gas fuel treatment skid is still showing at the same time 25.0 barg. Please advice…Awaiting your inputs.

Regards

It seems that your gas pipeline size is smaller than the required size. As you know pressur e is not only criteria for operation of gas turbine beside pressure you certain flow /volume of gas. So my suggestion is to check size of your gas pipeline. khurshid

First of all you should know that by reduction of pressure you will get power. I presume that your turbine is rated for 5 MW (as you are able to get for GTG-1). I also presume that You tried to run GTG-1 & 2 parallaly. How much pressure you are getting at GTG-1 at the same point you are getting 12 barg for GTG-2?

With the limited information you have provided, all I can say is that you are not getting enough gas for GTG-2 when GTG-1 is also in operation. Please check the inlet piping size whether it is designed to feed at least two turbines? HSD may require smaller size pipes. Also check piping configurations for GTG-1&2. Try to run only GTG-2 and see the performance.

Hi Sunil

This looks a curious one, but I think a few things need to be cleared up

The GTGs were running on HSD - umm what is HSD? My best guess is Hi Sulphur Diesel but I don't think thats the case here.

What is the rated power of the Turbine - both on original fuel and new fuel (Natural Gas)

There are a few things I am not sure on so I will just witter with how I see it and hopefully come out the other side

You are providing a gas line to the GTGs and under ALL circumstances this fuel gas supply line shows a pressure > 25barg (I think they use kPa in Oz for pressure which I find a most benighted unit)

I assume you have sized the supply line so if all three GTGs are at full power you can supply enough gas to fire the GTGs at 25barg

So at the skid limit for the GTG you have 25barg.

Then you start winding the power generation up and as the power delivered increases the pressure in the gas turbines drops to 10 barg.

Now what you don't say is where are you measuring this 10 barg. If it is the firing chamber that might be the right number, if it is upstream of the flow control valve for the GTG then you have a problem (I think - I am not a GTG expert)

Clearly you are getting a big pressure drop. As other people have said pressure drop is proportional to flow squared so there is something between the skid edge and the pint where you measured the 10 barg that causes this pressure drop.

Have you checked all the obvious - all valves open, filters clean and unclogged, control valves operating properly, shutdown valves in fully open position?

The other thing that occurs is that when the GTG was modified for the new fuel was anything changed on the skid in terms of piping. Nat Gas has a fairly high energy density (MJ calorific value per volume) so tends to need smaller pipes than many fuels but if you were firing the gas on pure hydrogen then the pipes would be too small for the Nat Gas supply required.

Alternatively seeing as the problem is on the skid can you get the company who modified the GTGs back in to fix it as they clearly didn't do a proper job or forgot one key facet of the job.

The problem it seems has to be pressure drop related and the thing causing the pressure drop has to be on the skid bit do check what the pressure should be where you are measuring the 10 barg.

Your measurement location and demand parameters pressure do not seem to be proper.

If you will tell the machine size MW etc, Secondly at GT input pipe size is Okay is Given by G.T. Manufacturer.

Your Fuel line is feeding three GT. Has been sized for that.

You may provide Full load Data and machine details you will know the problem yourself.

From the infomration you have provided I would suggest you have a leak in you piping. As thermal expansion and stresses are introduced into the piping it is creating a leak to prevent the gas from getting where it should.

Speculation on the unit that came into line is, the stresses were relieved on the piping after it was operated for a period of time and the leak reduced or eliminated.

Not sure of the flows being porvided to the unit, but based on the pressure I would expect you would easily identify a leak unless it was internal to the machine and going our the exhaust of the unit. As the previous fuel was heavier it may have been present previously but negligable.

Check all connections for leaks from where you identify 25 Barg can be measured to the point where you are measuring the 10 Barg.

Sounds to me like the main gas valve on the turbine is not responding properly. There may be a problem with a flowmeter. There may be a problem with the valve itself, maybe a sticky stem or torn diaphragm. Verify the controls first before putting a wrench on anything. If feedback and control mechanisms are not working reliably, the valve won't work either. A good ICE tech will set you straight quickly.