Derating a gas turbine HP

[1969grad]

Can anyone direct me to methods to derate the std HP ratings of a gas turbine for altitude, ambient temperature and inlet/exhaust air pressure losses?

The purpose is to get reasonabily close prior to going out for bids for hydraulic, feasibility, etc. studies.

 

[gtsim]

For a given altitude you can get the ambient pressure.

Power(Alt)=Power(ISO)*Pamb(Alt)/Pamb(ISO)

Power(Alt) is the available at a given altitude
Power(ISO) is the ISO power rating
Pamb(Alt) is the ambient pressure a given altitude
Pamb(ISO) is the ambient pressure at ISO condition, usually 1.013Bar
(i.e. power output is proportional to ambient pressure.)

The effects of ambient temperature of power should be available from the manufacturers’ performance data sheets for your engine and normally given as a factor of ISO power. Multiply this factor with the Power(Alt) calculated from above

The effects of inlet and exhaust losses normally represent about a 2% decrease power in power output.

I trust this helps
Best wishes,
gtsim

 

[1969grad]

You are correct that this information is available on the manufacturer's data sheets supplied with the bid. However, I frankly get tired of calling the manufacturer and asking him what the site rating is BEFORE we go out for bids.

Typically we do the gas hydraulic studies which gives the HP requirements at each station. Then there is some adjustments based on a preliminary unit selection. We then move to a cost estimate and feasibility study which includes operating and fuel gas cost over a specified period of time.

It is not economic to make a preliminary unit selection that leaves HP on the table because of the pipeline MAOP limitations. So the HP often gets pushed downstream.

If the economics show there is a project we then move to the FERC permit stage which requires that we determine the amount of air emissions, etc. which is also based on the unit selected.

Does the bid process mean we end up with another manufactuere than the preliminary selection? Sure but some gas transmission companies are locked into a price agreement with a particular CA company and do not want to use any other source.

The point is that I want to determine my own destiny and be able to get the information when I need it and not hear that the manufacturer's rep is out of town or on vacation so I have to wait to get the information.

So if I can get the correlations to derate the HP for altitude, ambient temperture and duct loses to some reasonable level of accuracy then I can be in control of my own schedule.

I think that what you are telling me gtsim is that I could determine the mass rate of flow at the site conditions and then divide by the mass rate of flow at ISO conditions and get the impact of altitude and ambient temperature. But then what about the duct loses?

 

[gtsim]

I understand that you want to determine whether an engine you wish to select is suitable for your application with respect to power requirement. Let’s assume you are considering an engine whose ISO rating (zero inlet and exhaust losses) is 20MW. Let’s say your altitude is a 1000m and the ambient temperature 20 Celsius.

At 1000m meters the ambient pressure is about 0.7 Bars (from ISA). The loss in power due to altitude is:

20x0.7/1.013=14.18MW

At 20 degrees Celsius the power decreases by a factor of 0.97 and determined from the manufacturers performance data sheets. Therefore the decrease in power due to altitude and ambient temperature is:

14.182x0.97=13.76MW

Inlet and exhaust losses decreases this power output by another 2%. Therefore allowing for altitude, ambient temperature and inlet and exhaust losses we get the maximum power available for this engine as:

13.35MW

It is also advisable to allow for performance deterioration such as compressor fouling etc. This information should be available from the manufacturer.

 

[taylorg]

1969grad,

If you are doing this regularly then it would be worth looking at software to help you. The common one used for power plants is produced by Thermoflow:

http://www.thermoflow.com

Alternatively you could find someone who already has it to help you out!

 

[norzul]

Dear 1969grad,

Perhaps yu could download some info from this websites. It will give yu some estimated values for the derating factors. However, this is valid for this particular machine only.

http://www.gepower.com/prod_serv/products/tech_docs/en/all_gers.htm

Pls refer this doc : GER3567h : GE Gas Turbine Performance Characteristics

For software, perhaps yu can use GT PRO or GT Master

 

[norzul]

Based on my experience, we just procured 4 GTs + 1 ST for our cogen project. Each GT is sized +/- 25 MW. For the GT (gas turbine) we evaluated 3 bidders.

Bidder 1 : ISO Conditions (15C+60%RH) = 26.3MW. At our ambient temp (26.8C+84%RH) = 24.9MW (with steam injection)

Bidder 2 : ISO Conditions (15C+60%RH) = 27.5MW. At our ambient temp (26.8C+84%RH) = 26.5MW (with steam injection)

Bidder 3 : ISO Conditions (15C+60%RH) = 24.7MW. At our ambient temp (26.8C+84%RH) = 21.8MW (with steam injection)

For our evaluation, we also consider the power generated at worst case condition i.e. during the highest temp (36C). Degradation factor (mainly for compressor fouling), we consider 2.5%

 

[norzul]

correction, Bidder 3 : 21.8MW is without steam injection. They don't have the facilities...