7FA Operating in Venezuela on Liquid Fuel. And operating at 70 MW with no water injection. At this time the IBH is about 22 to 24% open, flow rate 14.2, and if we go to Base Load of course IBH goes closed. Ambient Temp here is in the high 80's most of the year. My question is do we have to have the Inlet bleed heat in service? I have heard that some plants have decided to keep IBH off if ambient inlet temps are hot. What if we had Inlet Cooling is IBH off then?

Thanks.

 

Tom Murphy,

IBH is necessary if the IGV angle is less than approximately 57-62 DGA. It's necessary to protect the compressor against stall/surge when the IGVs are closed to less than compressor design minimum operating angle (which most F-class machines are during start-up and low load operation).

Inlet air cooling is only usually permitted when the load and IGV angle are near maximum, and IBH would be off by then.

IBH is a TERRIBLE name for the function it provides--it really has little (2 to 5 deg F, depending on ambient, usually) affect on the compressor inlet air temperature, but it does lower the density of the air. And, by recirculating a portion of the axial compressor discharge it reduces the "back-pressure" on the compressor, which will increase CPD, but which doesn't have much affect on performance when the IGVs are not full open, anyway.

If you own the machine and it's not under any kind of CSA or LTSA then you can do what you want with the machine--as long as you're willing to live with the consequences. I would say you could run a test by selecting a time of day when the ambient temp is fairly stable (afternoon/early evening?) and recording the output and fuel flow-rate (fuel flow-rate is IMPORTANT) and then selecting IBH OFF (if that's even available; it may be necessary to force it off--in which case the sequencing might trip the machine, or, it might not....) and then once things stabilize (15-30 minutes or so) take another set of data. Do this with Pre-Selected Load OFF (you'll be surprised at how little the load will actually change presuming the frequency is relatively constant). Again, the fuel flow-rate is most important.

Compare the heat rate of the turbine when IBH was off compared to when it was on, and that will tell you if the unit is more efficient--and by how much, to tell if the effort is worth the trouble.

Gas turbines at Part Load are not very efficient anyway. It may, or may not, be more advantageous if the IBH control valve is only at 22-24% open....

And, IBH isn't as much about heating the air as it is about protecting the axial compressor when IGVs are closed below compressor design minimum angles (again, approximately 57-62 DGA, depending on the vintage of the axial compressor).

So, the answer is not as simple as you might think, and the possible side-effect may be more dangerous than thought, too.

 

Tom just to echo what CSA had to say.

What you all do with the machine is your choice. IMHO even if you had an LTSA or CSA with GE, if you choose to break the machine, they will be glad to charge you to fix it. Right?

But seriously as far as inlet bleed heat(IBH) goes, its there for two main purposes. First is to protect the compressor at lower loads and IGV angles. Second is to further control compressor airflow(along with IGV angle) to help with emissions during part load operation. In your case I do not think you guys are too worried about emissions, especially since you are running liquid fuel.

I did want to point out a possible typo from CSA? I think his statement from his last post should say,

"And, by recirculating a portion of the axial compressor discharge it reduces the "back-pressure" on the compressor, which will DECREASE CPD.

This decrease in CPD reduces the efficiency of the machine which I think is what you guys might be after? But basically in my opinion I really doubt that you will see much of an improvement in efficiency with IBH off.

Please write back if we did not completely answer your question. Hope all is well there, it would be something to see the place again.

 

<b>>>CORRECTION<<</b>

The following statement is <b>INCORRECT:</b>

>And, by recirculating a portion of the axial
>compressor discharge it reduces the
>"back-pressure" on the compressor, which
>will increase CPD, but which doesn't
>have much affect on performance when the
>IGVs are not full open, anyway.

It <b>should have</b> read:

Recirculating a portion of the axial compressor discharge pressure which reduces the "back-pressure" on the compressor, <b>decreases</b> CPD, which doesn't have the same affect as decreasing CPD when the IGVs are fully open.

Unfortunately, this is really a question for the OEM. But, the OEM is likely going to give the stock "No," answer without qualifying or looking at the machine characteristics, ambient data, etc., unless the site is covered under a CSA or LTSA with the OEM. And even then, your response is likely going to be a function of how well your CPM is acting as an advocate for your site, and who your CPM knows at the OEM.

With F-class machines there is just not a lot of margin built into the physical machine--meaning they are flat-out running at the limits of the materials of the machine with little or no margin for error. And, there are SO many variations of compressor designs and compressor blading (inlet, stationary, rotating) that without careful consideration by the OEM of the actual physical components and design of any particular machine it's really difficult to say what is or isn't possible.

It sounds as if from what you've heard that some sites have either had good assistance from the OEM about operating outside the normal conditions, or some sites have just decided to try their luck with operating outside the normal conditions. It would be best if you knew a LOT more about the background of any site with F-class machines making decisions to operate outside normal conditions before making a decision for yourself.

Or just run a short test (again, when ambient temperature conditions are not likely to change very much during the duration of the data-gathering) and compare the heat-rate for the two operating conditions. You're not going to get any MW with this change; it's only going to affect the amount of fuel being burned for the MW being produced (heat-rate), and at low loads with the IGVs not fully open the affect may be marginal at best and not worth the risk of continued operation without IBH.

But I would definitely not recommend doing any kind of test if the IGVs are below 57-62 DGA, because that's when the compressor is most likely to exceed a limit and experience damage.

And, please write back to let us know how you proceed, and what the results of any test are.