Thermodynamic Model for Relating Volumetric to Mass Flow Rate for Natural Gas

This project presents a method of measuring mass flow rate of natural gas using a reliable
Equation of State (EOS) to eliminate the use of expensive coriolis meter. Natural gas is
an alternative vehicle fuel that has long been proposed as a way to provide significant air
quality benefits over petroleum fuels. Unlike gasoline or diesel gas that can be measured
in volumetric flow rate, natural gas needs to be measured in mass flow rate. Only coriolis
meter is available in the market that can give the reading in mass per unit time while the
other flow meters give the volumetric reading. However, the high cost of coriolis meter
has led to the research of finding another alternative to measure mass flow rate of natural
gas. The method considered in the study is to have the volumetric flow rate measured,
prior to converting it to mass flow rate using a suitableEquationof State (EOS).
In orderto complete this project, there are four critical stages involved. The first stage is
to conduct several experiments using a Test Rig Dispenser to obtain Pressure-Volume-
Temperature (PVT) relation of natural gas. These data are then being used for the
purpose of performing computation of errors for the tested EOSs. Errors for all of the
EOSs are then compared to determine the EOS that gives the smallest error percentage.
After that, another stage to validate the obtained EOS is done. In this stage, the EOS is
used along with PVT data to compute mass flow rate of the natural gas dispensed. This
mass flow rate from the computation is then being compared to the measured value of
coriolis meter.
From the results of dynamic experiment, it is observed that ideal gas law gives smallest
error percentage followed by SRK, Lee-Kesler, Peng-Robinson, Van der Waals and
Virial equation of state. However, from the static experiment, SRK gives the smallest
error followed by Lee-Kesler Plocker, Peng-Robinson, Van der Waals, Virial, and ideal
gas equation. The static experiment gives more accurate result since all thermodynamic
properties are taken at their steady state condition.