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In 1998, the construction of a wet-gas research loop at the laboratory facilities of CEESI was completed. The research loop was designed for two-phase flow studies consisting of natural gas and hydrocarbon liquids. An initial Joint Industry Project (JIP) was formed to study wet-gas effects on single-phase flow meters, and a large amount of experimental data has been collected. The data collected for the JIP is proprietary to the members of the JIP. However, the types of flow meters tested include single-phase flow meters such as orifice plates and venturi meters, and proprietary meters such as ultrasonic, vortex, and specially designed differential pressure meters. The data collected for the JIP program is being reviewed by the member companies, and will be made public at a future date.
The picture to the left is a simplified block diagram that shows the major components of the wet-gas research loop. Lean natural gas is brought into the CEESI complex at a low pressure near 0.3 Mpa (50 psi). A charging compressor is used to pressurize the research loop to the desired operating pressure for the test being conducted. The normal operating pressure range is between 0.7 to 9.9 Mpa (100 to 1440 psi). Once the loop is pressurized, any combination of the four positive displacement compressors can be used to circulate the natural gas around the research loop at the desired velocity. Gas velocities of 7 to 90 ft/sec (2 to 27 m/s) can be obtained in a 4" (100mm) pipe. The obtainable velocities in other size pipes vary inversely with the pipe area.
Both a turbine meter and a subsonic venturi measure the mass flowrate of the natural gas. The difference in mass flowrate between these two meters is monitored; and if the difference exceeds a specified amount, the data is scrutinized for detrimental effects such as pulsation. If the difference is within tolerance, than all other meters installed in the research loop can be compared to the natural gas mass flowrate as measured by the turbine meter.
The hydrocarbon liquid, which resides in the liquid storage vessel, can be injected into the gas stream by positive displacement pumps (triplex pumps). Coriolis meters measure the liquid mass flowrate and the density of the injected liquid. The gas stream carries the liquid through the meter test locations to the horizontal separator where it is then returned to the liquid storage vessel. Coriolis meters again measure the mass flowrate rate and the density of the returned liquid. When the injected liquid mass flowrate is equal to the return liquid mass flowrate and all pressures and temperatures within the loop are constant with time; the system is at a steady state condition where data can be acquired. At this condition, the liquid "hold-up" within the piping sections has occurred.
Once the steady state conditions exist within the research loop, the effect of liquid entrained in the gas stream upon the flow meter can be determined.
To the right is a photograph showing a partial view of the wet-gas research loop. This photograph was taken when a large horizontal liquid separator was being installed to increase the liquid separation efficiency. A vent stack can be seen at the left-hand portion of the picture along with a small building that contains a gas chromatograph capable of C9+ analysis. The density of the flowing natural gas at any test location is calculated by the measured pressure and temperature at that location, and the composition of the natural gas stream per the procedures in AGA8.
A portion of the meter test locations can also be seen in the left and center part of the photograph. The two long horizontal pipe sections shown near the right side of the photograph are the storage vessels for the liquid hydrocarbons that are injected into the natural gas stream. The positive displacement compressors that circulate the natural gas are just out of view at the 3 o'clock position. Data from all instruments are transmitted into the control room from where this picture was taken. As can be seen, the operator has a good view of the research loop, and a detailed program is always followed to maintain the safety of the personnel and the equipment.
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