Gas Consumption Calculation

Please explain what help is needed. Help the forum to help out!

Please be consistent and rigorous with labelling units. For example 1kW ≠ 1kWh as the first is a quantity and the second is a rate. Which is which in the original post?

can i understand any relationship between GCV= 1010.92 BTU/SCF then what is in MJ/KG

what if i say 1010.92 GCV has 35769 BTU ?

Other way round. First, kW is a rate, second, kWh is a quantity.

Oops.

Ask your supplier for enlightenment.

You need to explain better what your problem is.

I’m not aware of gas meters that read directly in heat units, only volume. For one thing, gas CV can vary, but perhaps you have them where you are.

I assume it’s for power generation. If you generate 35415336 kWh, why would you multiply that by the gas component price is 3.9/kWh? (putting in the correct units)

If MMBTU = Cubic meters/28.17385, CV = MMBTU/(28.17385m³) = 37.45MJ/m³.

1010.92 BTU/SCF = 37.67MJ/m³, so you have two approx equal ways to express the CV, why? Fairly typical for GCV of natural gas, perhaps a little on the low side.

If the Real Relative Density Gas = 0.6282 (real as opposed to what?), actual density = 0.6282*1.2 = 0.754 kg/Sm3 (std 20°C).

Test report figure 44.5 MJ/kg gives 44.5*0.754 = 33.55MJ/m3. My guess is the test report figure is NCV.

Bear in mind that natural gas is not pure methane, it contains higher mol. wt. hydrocarbons, so the density is higher (as you can see from the figures), the CV/m³ is higher, but the CV/kg is lower, than pure methane.

Why would you say 5800 kWh/kg? That’s over 20000MJ/kg. Cold fusion or something?

thanks codemaster, your real grue,

sir my boss killing ;) me due to higher gas consumption reflected on gas meters in terms of MMBTU

i still cant figure out why , even all generators running or OEM specification gas consumption in terms of KGs/h at rated MWh output,

i am confused , is there any relationship i can find in between to MMBTU with kg gas consumption so that i can verified the bill in-terms it is high or low or my plant efficiency not up to the mark , by the way how to calculate efficiency if i have MMBTU input or Kwh generation output in 31 days.

1MJ = 947.8 BTU, so 44.5MJ/kg (your test figure) = 44.5*947.8/10^6 = 0.0422 MMBTU/kg. So just multiply your kg consumption by 0.0422 to get MMBTU.

The other way round, 1 kWh = 3.6 MJ, so 1 kWh = 3.6*947.8/10^6 = 0.00341 MMBTU. That gives your electric output in MMBTU. Divide that by input MMBTU (in the gas) to get efficiency.

Your problem is not uncommon; when two types of metering (Therms and Kg) are used for the same apparent fuel amount, there will almost always be a discrepancy between the two readings. Further complicating the matter is the fact that you are dealing with a natural product whose GCV (Gross Caloric Value) varies over time.

The supplier's meter is calibrated in Therms at a particular temperature and pressure, but knows nothing about the amount of moisture or the actual heating value of the fuel. It is up to the supplier to provide a guaranteed minimum heating value during the billing period, and the customer has to rely on (trust) those numbers, or provide his own real-time analysis if there is a dispute.

Your check meter(s) integrate the mass (kG) of fuel that passes through them, but have no way to know the amount of moisture that may contribute to that mass, nor the actual time-varying heating value of the mixture passing through it; therefore, there will always be a discrepancy between their measurements and yours.

For the above reasons, all you can do is track the monthly readings, run statistics on them, and see how closely match up to what you expect (aka "the bogey") over many averaged billing cycles. There is no direct fixed mathematical equation that will always be correct since the fuel quality is not deterministic.

Similarly for calculating the overall Heat Rate (British thermal units (Btu) per net kWh generated) of the plant, because it relies on those same statistically varying values.