Combined Cycle Power Plant - GT and ST power output

[FelipeSC]

I'm trying to design a project of a combined cycle power plant with the two-on-one arranje, (2 GT, 2 HRSG and 1 ST).

Well, i got the results from the Aalborg (HRSG manufacturer) engineer.. he didn't show me the calculations, of course, but he returned the amount of steam that hrsg can deliver...

So, the Gas turbine is:

Gas Turbine Siemens SGT-300:
Power Output: 7.9 MW(e)
Fuel: Natural Gas
Frequency: 60 Hz
Electrical Eficiency: 31.2%
Heat Rate: 11,532 kJ/kWh
Rotation: 14,010 rpm
Gas Flow: 29.8 kg/s
Temperature: 537 °C

With that GT, the Aalborg HRSG can deliver 14.5 ton/h of steam with 25 bar pressure and 225 °C, and water on 105 °C.

With that information, i searched a way to estimate the power output of a steam turbine to be attached to this hrsg. I got from a Siemens presentation, that the preliminar perfomance calculation for industrial steam turbines is given by:

Power output (kw) = Steam Flow (kg/s) x Steam entalpy (kj/kg) x efficiencies (%), where

turbine efficiency (average) = 50-60% single-stage
75-89% multi-stage
reductor efficiency (approx) = 98.5%
generator efficiency (approx) = 98%
entalpy is taken from steam tables using the pressure of the steam used in the hrsg

So it means that ONE hrsg can run a steam turbine with:

power = 14.5 ton/h x 2802.2 kj/kg x 0.75 x 0.985 x 0.98

power = 8.17 MW

In the two-on-one arranje, there are 2 hrsg, the steam flow will be 29 ton/h and the power output of the gas turbine will be 16.34 MW.

Two Gas Turbine with total 15.8 MW can run a Steam turbine with 16.34 MW? Is that possible, or absurd?

I thought that combined cycle power plants usually have their steam turbines with approx. 1/3 of the total power, for example, 2 GT with 100 MW and 1 ST with 100 MW. The ST will have half power of the GT.

Can anyone please help me before i fall into despair???

Thank you very much..

Felipe

 

[MisterDonut]

Bilsko,

From what you describe, this sounds like a situation for a backpressure turbine. Efficiency will probably be around 50%, but confirm this with a vendor. Electrical output would be around 400 kWe with 27,500 lb/hr steam.

 

[Bilsko]

MisterDonut:
Thanks for confirming - I aslo plugged the data into the Katmar software and came up with just about the same figures.

RMW:
You're right it is definitely a confusing set of details. All of this equipment that I'm describing (GT, HRSG, BPT) would be new equipment.
I'm intrigued by the idea of the hybrid condenser/backpressure setup. That one will be a bit tricker to create a dispatch model for. It looks like their steam baseload rarely drops much below the 25-27mlb mark so it may not be necessary. Still, its good to keep it in mind as a potential configuration for a more detailed analysis later.

For now, I'm working with the assumption that I can get the 7500kW from the Taurus 70, 27.5mlbs of 150psi steam, and 400kW of BPT electrcity when its needed. The financials look pretty solid - assuming my estimates for capital and O&M costs are reasonable!. Next step is to run everything again assuming a Mars 90 and see if it still makes financial sense!