Gas Turbine Fuel Consumption

<...how to covert this amount of NM3 to BTU?...>

The calorific value of the gas will be found on the supplier's invoices.

Then convert it into MW. Take average efficiency of GTG set at 35-40% (without co-generation) and then reverse calculate how much you need per MW. But that is assuming you are working at a proper frame - not 1MW

"or standard NM3 of gas"

Get down to basics, gas is a pretty vague term as you can burn a whole range of "gases" in these things.

Once you know what gas you are using (calorific value) or intend to use then you look up the Heat Rate of the specific GT. This will be given in kJ/kW.hr.

You can then work out very simply what your fuel consumption is likely to be, but remember that the Heat Rate (heat energy put into the machine in the form of fuel to produce power at the output shaft) is given for ISO standard conditions and must be corrected for altitude, temperature, humidity and inlet and exhaust conditions.

Heat rates vary by size, manufacturer and GT type from around 8000 to 12000 with some machines as high as 17000 kJ/kW.hr

After 30 years working in gas Turbine Power plants, just completed a heat rate tests as per our contract with the utility. This is how I do it:

Just to mention, the ASME standard for Gas Turbine performance test including heat rate and efficiency is PTC 22, last revision I have is 1985.

The calculations can be expressed in SI e.g. M³ or imperial units e.g. ft³

This will depend on what engineering units your start the metering process with , i.e. is your instantaneous and totalized flow in SCF( standard cubic feet) or SM³standard metre cube.

In which case your LHV and HHV should be in BTU/ft³ or KJ/m^{3 .}

The flow calculation we used is by the American gas association ( AGA3).

Your fuel gas flow meter should be able to show instantaneous gas flow ( if you want to get on-line efficiency readings) or totalized flow over a period of time .

Common practice is to take the totalized fuel gas volume flow over a 24 hour , midnight to midnight period. Same for electrical energy delivered.

Your generator metering system would show instantaneous power9 KW for smaller machines and MW for larger machines).

It will also totalize the energy delivered in kWHrs or MWHrs depending on the size of the machines.

If you are conducting a heat rate test , PTC 22 specifies test periods or 30 minute intervals.

A very important factor when testing is to ensure that your ambient temperature change from start to end of test does not exceed 4 def F. Gas turbines are very sensitive to ambient temperature, and to a lesser degree to atmospheric pressure and humidity.

If that is the case you should stick to one set of engineering units, than you will need to know the heating value of your fuel gas, expressed as Lower heating value (LHV) or Higher heating value (HHV).

Conservative practise is to calculate at LHV.

Having the total energy in the gas and the electrical energy delivered , you can then calculate the heat rate (kJ/KwHr) and machine efficiency (%).

Just to give you an idea, our natural gas fuel has a specific gravity of 0.5817 and heating values of :

By volume:

(cubic ft referred to is taken as standard cubic feet , i.e. measured flow corrected for flowing pressure and temperature.)

(LHV ) or commonly referred to as :Net (dry) 939.2 BTU/ft³ 34,961.52 kJ/m³

(HHV) or commonly referred to as :Gross 1042.2 BTU/ft³ 38831.30 kJ/ m³

By mass:

(LHV ) or commonly referred to as ;Net 21156.1 BTU/lb 10,145.85 kJ/kg

(HHV) or commonly referred to as: Gross 23476.7 BTU/lb 11,258.74 kJ/kg

And the machines which we tested recently 108MW base load rating for site conditions had a heat rate of 10605 BTU/kWhr at LHV

11,189 kJ/kWHr at LHV

If you need to cross calculate from one engineering units to another, this website has a very good engineering units converter/calculator.

1 BTU = 1.055056 kJ

Hi,

Can you please advise me my consumption. I got 13.2 GJ/KW HR Heat Rat and Calorific Value is 37 MJ/M3.

Regards,

Jigar

A means to estimate change in fuel flow for heating value and ambient condition is to calculate the corrected fuel flow:

WFC = (WF/del*theta^C)*(LHV/LHV0)

where

WFC = corrected fuel flow [ mass / time ]

WF = actual fuel flow [ mass / time ]

del = ambient pressure / standard pressure

theta = ambient temperature / standard temperature

C = empirical coefficient, use 0.5 if unknown, otherwise adjust based on data

LHV = fuel heating value

LHV0 = baseline fuel heating value

Using this equation, the manufacturer's information at standard conditions and specified fuel can be converted to actual installation conditions and used fuel. Basically, calculate WFC from the manufacturer's information. In most cases, the manufacturer's WFC will be equal to the quoted flow rate since del, theta, and LHV/LHV0 are all equal to one at standard conditions and specified fuel heating value. Next, at the same power condition, the actual fuel flow can be back calculated based on existing conditions and the used fuel.

However, a word of caution: the WFC approach assumes similar combustion efficiency between conditions. As long as sticking to the same fuel class (i.e. comparing one natural gas to another, or one jet fuel to another jet fuel), the assumption is generally good. But if there is some significant engine performance difference due to fuel quality, source, or phase, then the assumption may not hold.

Hopefully the above helps.

Thank you all

best regards

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