Natural Gas CFM Into BTU/M Gas Composition Given

HI Guys;
I am hamad from pakistan and working in gas turbine compressor sets.
i want to know how we convert the flow in btu.
we measure the flow in cubic feet/h and want to convert into btu/hour.
the gas composition is as under
gross dry btu=914.47
gross sat btu=898.56
nitrogen=9.4550
co2=1.8590
ch4=87.1810
please help me on this issu
Thanks

[JohnS]

Originally Posted by javaboy

HI Guys;
I am hamad from pakistan and working in gas turbine compressor sets.
i want to know how we convert the flow in btu.
we measure the flow in cubic feet/h and want to convert into btu/hour.
the gas composition is as under
gross dry btu=914.47
gross sat btu=898.56
nitrogen=9.4550
co2=1.8590
ch4=87.1810
please help me on this issu
Thanks

Hi Hamad

Welcome. The two BTU figures given are per cubic foot. I am not entirely sure what is meant by dry and saturated btu. I am guessing dry means as analyzed after water vapor is removed, but that changes the volume. If saturated means water vapor is present at the saturated vapor pressure (for the temperature), that may understate the btu content. If you need a highly precise result, you need to know the actual water vapor content as supplied (and saturated vapor pressure) and interpolate between these two figures.

For a rough estimate, you could use a midpoint, assuming the gas is neither bone-dry nor saturated.

Thanks For Reply
i think dry gross btu=HHV or CV
then how i use this to convert CFM to BTU/M

[JohnS]

Originally Posted by javaboy

Thanks For Reply
i think dry gross btu=HHV or CV
then how i use this to convert CFM to BTU/M

I considered the possibility of HHV, LHV, but the two numbers are not far enough apart for that. I'm not entirely sure of your local engineering conventions so I am not sure which of the two figures to recommend: however, I believe both to be in units of BTU per standard cubic foot. I would use the midpoint for a rough, immediate number and seek clarification from your gas supplier, unless you know you are drying the gas before measuring flow.

Simply multiply by the flow in cubic feet per hour to get BTU/h

Unlike the metric system, the Imperial system (and US Customary) often use the Roman numeral M for thousand and MM for million. Is that what you meant by the M in your question?

Hi
Thx for reply
First we use M for thousands and MM for million.
Secondly the gas turbine engine test report from the manufacture shows the fuel flow value at full load is 37.01 mmBTU/HR while the gas composition is as under
Methane=94.4199
Eathane=1.0500
Propane=0.2800
I-Butane=0.0600
N-Butane=0.0600
I-Pentane=0.0300
N-Pentane=0.0200
Carbon dioxide=0.0200
Nitrigen=3.8900
Oxygen=0.1700
while they use LHV(BTU/SCF)=887.5
S.G=0.5816
and woob index at 60 farenhite is 1163.8
when we measure at site at the same load and speed the value is diffrent.
if we get 47.3 scf/HR then what will be BTU/HR in our case?
Can we calculate The LHV and HHV if gas composition knows if possible then how?
thanks for hep

[JohnS]

Originally Posted by javaboy

Hi
Thx for reply
First we use M for thousands and MM for million.
Secondly the gas turbine engine test report from the manufacture shows the fuel flow value at full load is 37.01 mmBTU/HR while the gas composition is as under
Methane=94.4199
Eathane=1.0500
Propane=0.2800
I-Butane=0.0600
N-Butane=0.0600
I-Pentane=0.0300
N-Pentane=0.0200
Carbon dioxide=0.0200
Nitrigen=3.8900
Oxygen=0.1700
while they use LHV(BTU/SCF)=887.5
S.G=0.5816
and woob index at 60 farenhite is 1163.8
when we measure at site at the same load and speed the value is diffrent.
if we get 47.3 scf/HR then what will be BTU/HR in our case?
Can we calculate The LHV and HHV if gas composition knows if possible then how?
thanks for hep

The value of 47.3 scf/hr looks far too low. At 887.5 BTU/scf, this is only 41978 BTU/hr. At full load, this is nearly 1000 to 1 below the turbine report. Is it possible that your units are hundreds or thousands of standard cubic feet (my natural gas to my home is metered in units of ccf, 100's of cubic feet, where "c" is used as Roman numeral). If it were ccf, that would be 4.2 MMBTU/hr, believable at light load. If MSCF, either the gas is lower quality than expected or the turbine is overloaded at 42 MMBTU/h.

LHV and HHV for a mixture like natural gas is calulated by taking the percentage of each gas,the HHV and LHV values for that gas and constructing a weighted average. In your data, you would only need to consider the methane through pentane, the remainder don't contribute.

The US Dept. of Energy has a fuels table which gives average data by fuel type. They give 1089 BTU/ft³ HHV and 983 BTU/ft³ LHV (these values are at 32 °F, or "normal" conditions in the metric system rather than "standard". Figure 94.6% of these values at 60 °F for "standard").

I don't have a reference for HHV and LHV of all the individual gases. I found a calculator on the web once, but lost the link.