Heating value has nothing to do with the heat to heat something substances. Heating value is the value of the heat generated from the complete combustion of a substance at a given temperature.
Hydrocarbon combustion reactions like this:
CxHy + (x + y / 4) O2 ---- x CO 2 + y / 2 H2O
By definition the heat of combustion is calculated as if the reactants and reaction products have the same temperature. Usually the standard conditions used for the calculation of heating value is 25 ° C and 1 atm. As we all know at 25 ° C and 1 atm H 2 O has a liquid phase, the calculations assume HHV H2O combustion condensed into liquid phase, so in addition to the heat obtained from combustion, energy is also obtained from the heat of condensation of H2O. If the calculation of LHV is assumed that H 2 O remains in the gas phase at 25 ° C. So the difference between HHV and LHV is the heat of condensation of H2O at standard temperature and pressure.
It should be noted that the HHV and LHV is a theoretical notation, only used for indication and do not show the actual conditions in practice. The reason for the fuel and gas combustion products have never been at the same temperature according to the assumptions used to calculate the HHV and LHV. In practice, we can get energy from burning fuel will always be smaller than the HHV or LHV, because there is energy in the form of heat is carried away by the gases of combustion. That is why the energy conversion efficiency of all engines (steam power plants, internal combustion engines, gas turbines) can never be 100%.
So HHV and LHV absolutely nothing to do with the phases of the fuel, either solid or liquid fuels, both had HHV and LHV. If it's easy or hard it burns, it also has nothing to do with HHV & LVH. Remember! Combustion process is exothermic, so do not take the heat (energy) from the environment it provides heat to the environment. Actually that can be burned it is the gas phase, if any liquid fuel, then there must be enough steam on the surface in order to initiate combustion. If we start from ambient temperature, to a certain liquid fuels such as diesel oil, must be given sufficient temperature to a high enough vapor pressure to form a vapor phase that can be burned (hence the term flash point). But once been burned, the heat of combustion will always provide enough energy to produce a vapor phase that is ready to be burned.
The higher the carbon number, heating value in kJ / kmol (but not within kJ / kg!) Is also higher. For gas, heating value is usually expressed in Btu / MMSCF, and we know that it is proportional to the gas mole to volume, so for the more natural gas weight fraction higher volumetric heating valuenya the base.
Please note, the unit which states the value of LHV / HHV also, that the value of LHV / HHV enlarge as certainly increase the amount of carbon to units of Btu / lbmol (kJ / kmol). Because if the units used are mass-based, LHV / HHV of methane is greater than the longer chain (because MWnya vanishingly small).
Determining the gross heating value instead of passing through the GC but numerical computation (which is generally already in its soft machine that took GC composition data peaknya GC). Why? Because we have to input the properties of natural gas at 14.7 psia and 60 oF.
Essentially, the GC is not limited to the measurement of C9 alone, could be more depending on the setting / instruments and standard methods are implemented.
GHV is not a direct measure of the GC kayaks from pressure transmitters measure the pressure, but there is a computation of the GC after the gas composition obtained.
It can calculate the carbon chain until the weight, but usually is not accurate, after all, in fact fractions are also very small compared with the fraction C1 (which is usually used as the standard specification of the gas to sales), so if there is a small change of the composition of the carbon chain weight gives only a small impact on the value of GHV.
GC can perform calculations GHV. Performed by GC is to see the gas composition based on chromatogram peak. Then based on the standards used, whether it is GPA-2172, or ISO 6976, GC will calculate GHV mol% based on the input data of the measured gas itself, the base pressure and base pressure measurements are used. In some places this is not usually done because the GC does not measure the value of the composition of H2O and H2S, and several other componen not detected by GC. So are wont to do is to give all this information into the data flow computer (GC data and H 2 O and other components required), and the flow computer will calculate the gross heating value.
For the ISO6976 standard, we can not choose the standard pressure is used, it is not specified by the standard. Output unit of the ISO6976 standard is MJ/Sm3 for volume calculation. ISO6976 provides the option to calculate GHV in some combustion / metering temp. That is quite commonly used (15.15) and (20.20). All inputs and outputs of ISO6976 is in the form of the metric.
For the GPA standard 2172, we can choose the GHV would be calculated on how much pressure is up to us. The commonly used is 14.73 psia. Standard calculations use a pressure GPA2172 14,696. However, GPA 2172 does not provide options for the calculation of the temperature input is always considered for the standard temperature 60 degF. Another input required is the value of Compressibility of gas at standard pressure (14.73 in this case) are usually obtained from AGA 8 calculations.
For the measurement of the gas itself, which is the weight fraction fiscal gas measurement value is quite small, but if there is miscalculate will provide a significant difference because the weight fraction has a heating value of the greatest value. If for example the value of the gas which should read 0.01% 0.1%, it is enough to give an error of about 0.4% error which, when cashed would give a figure of about several hundred thousand dollars per year depending on the amount of gas flowing.
C1 - C4 has a greater contribution to HHV, because among other C heating value of C1 - C4 bigger. As a reference in Perry's chemicals in Engineers Handbook 6th edition, table 3-207. Heating value listed there for each component:
- C1 == 21.502 (BTU/lb)
- C2 == 20.416 (BTU/lb)
- C3 == 19.929 (BTU/lb)
- iC4 == 19.614 (BTU/lb)
- nC4 == 19.665 (BTU/lb)
- iC5 == 19.451 (BTU/lb)
- nC5 == 19.499 (BTU/lb)
- nC6 == 19.391( BTU/lb)
C3 == 47.739 BTU / Kg == 2516.2 BTU / SCF
i-C4 == 46.808 BTU / Kg == 3252.0 BTU / SCF
n-C4 == 46.958 BTU / Kg == 3262.4 BTU / SCF
i-C5 == 46.394 BTU / Kg == 4000.9 BTU / SCF
n-C5 == 46.484 BTU / Kg == 4008.7 BTU / SCF
n -C6 == 46.174 BTU / Kg == 4756.0 BTU / SCFThere is a 'measure' the other of the heating value of the volume, with units of Btu / scf. Usually when we talk with on line gas chromatograph metering the heating value measurement is based on this volume, Btu / scf, so the total energy that passes through the meter (Btu per hour or per day) is the multiplication of the volume, mmscfd and heating value of this value (Btu / scf). If the heating value is calculated based on the volume then logically heating value of C2 will be higher than C1 and C3 is higher than the C2 and so on because the molecular weight of more than C1 C2 etc., is based on the principle that the volume of 1 mole of C1 will be equal to the volume of a mol C2 (about 379 scf / mol).
GHV can be measured based on the Mass and the Volume, if based on the Mass (BTU / Kg), C Higher Heating Value will contribute to lower and lower, whereas if it is based on Volume (BTU / SCF), the opposite C higher contribution Heating Value is higher.
Of GPA 2145 of 2003, Physical Constants for Hydrocarbon. If the LNG component in the molar fraction, the GHV at 60 F as an ideal gas is:
C1 == 52.673 BTU / Kg == 1010.0 BTU / SCF
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