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Natural Gas CFM Into BTU/M Gas Composition Given

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  • 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

  • #2
    Re: Natural Gas CFM Into BTU/M Gas Composition Given

    Originally posted by javaboy View Post
    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.

    Comment


    • #3
      Re: Natural Gas CFM Into BTU/M Gas Composition Given

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

      Comment


      • #4
        Re: Natural Gas CFM Into BTU/M Gas Composition Given

        Originally posted by javaboy View Post
        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?

        Comment


        • #5
          Re: Natural Gas CFM Into BTU/M Gas Composition Given

          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

          Comment


          • #6
            Re: Natural Gas CFM Into BTU/M Gas Composition Given

            Originally posted by javaboy View Post
            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/ft HHV and 983 BTU/ft 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.

            Comment

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