Best 50MW range Gas Turbine for existing 2x1 combined cycle plant to improve heatrate

[asifhdd]

We are looking to add one GT/HRSG package in our existing 150MW supplementary fired CC plant in order to stop duct firing and use the 3rd GT/HRSG to supply about 160-170 kpph (~75ton/hr) HP steam presently coming by Duct firing. Maximum Steam pressure for ST is @ 1470psi (100bar) & steam inlet temperature is 930F (500C). Since we are limited by our Electrical Power Evacuation limit, therefore only 50-55MW GT model will be compatible. Exhaust Temp. of new GT shall be > 970F and HRSG shall be Single Pressure (HP drum only) because LP steam is already on maximum limits. I am asking for the best GT model suitable for integration which provides the best efficiency at minimum cost. In my view Siemens SGT800 or GE 6F.01 are the only proper candidates. I would appreciate any detailed views from engineering community. Also what will be approximate cost of of this addition. it may be noted that ST, Condenser & Cooling Tower are not needed because overall steam requirements will not change.
Regards,
Asif, Operations Manager

 

[ScottyUK]

You've listed two frame machines as 'the only proper candidates', yet the power range you're interested in is well within the capability of the larger aero-derivatives which would give you a considerable improvement in efficiency straight away.

 

[asifhdd]

Scot as i mentioned that we are restricted by the POWER EVACUATION LIMIT (transmission line of utility company is not capable of carrying more than 200 MW load), so adding a 50 MW range GT to our present generation capacity 150 MW means we stop about 20 MW duct firing and use steam from added HRSG to compensate in addition to 50+ from new GT. This leaves us getting only around 50 MW GTs. Do you know any other good GT besides GE/Siemens having 970+ exhaust temperatures?

 

[ScottyUK]

I apologise - the Trent and the LM6000 both fall slightly short of the 970°F EGT requirement, although the LM6000 isn't far away. My mental conversion of °F to °C wasn't as accurate as I thought it was.

Are you intending to use the HRSG to raise HP steam rather than just IP and LP steam? I'm guessing this is the reason for the relatively high minimum EGT?

 

[asifhdd]

Exactly the HP steam only. There is no IP steam while LP Induction steam is already at the maximum limit. We have very hot summer days. Temperatures usually touch 45C from May to September everyday almost. I have temperature vs output/heatrate curves of Siemens SGT-800 (50MW) but I need GE 6F.01 Temperature - Output & Heatrate curve for comparison to select the better one without INLET COOLING for hot ambient conditions. Site yearly mean temperature is 25C with average relative humidity about 60%.

 

[ScottyUK]

Have you had a look at Mitsubishi's H-50 series? It's in the same size range as the SGT800. I don't have any direct experience of the H-50, but from experience MHI's larger M-701 machines were well-built and pretty reliable.

 

[asifhdd]

yes, i did some search but couldn't find any references or useful information. The first H-50 will probably come in commercial operation sometime in 2016. So only 6F.01 & SGT800 are in contention at the moment.

 

[davefitz]

You will need to model the entire plant to confirm that no other components or systems will exceed their design or permitted limits. It only takes one component to limit the entire plant. Everything has to be reviewed , from A to Z.
- condenser
-cooling tower
-condensate pumps
-water treatment
-need to add double block and bleed valves on boilers as they will be on a "header system"
- steam turbine blade and path review, thrust calcs, etc
-transformers and electrical buses
-fuel gas flow element , press reducing station or compressor
-financial calcs- all of this investment is aimed at improving heat rate to reduce the fuel charge, but at historically low fuel gas costs it may be difficult to prove a adequate rate of return.






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