McCrometer's V-Cone Flowmeter Solves Wet Gas Measurement Problems for the Oil & Gas Industry

N/A plates have historically been used to measure the vast majority of natural gas flow around the world. The experience and data of orifice plate measurements has been based on dry gas calibrations. However, when it comes to the effects of wet gas on orifice plate measurement, there is a general consensus that wet gas affects meter accuracy. Experts agree that more research should be done to quantify the effects of wet gas, and how other technologies such as <%=company%>'s V-Cone Flowmeter have been able to overcome potential measurement discrepancies.

The Southwest Research Institute (SwRI; San Antonio, TX) developed a wet gas-testing loop using nitrogen gas and water. <%=company%> contracted with SwRI to conduct a series of tests to evaluate the performance of their flagship product, the V-Cone flowmeter (see Figure), in wet gas applications. The tests were designed to address the oil and gas industry's need for accurate measurement of wet gas without liquid build-up in the meter section.

"With the introduction of liquid into a gas flow line, the data and parameters that the orifice calculations are based on become less accurate. One of the effects of wet gas on an orifice plate meter is the holding of liquid before or after the plate," says Stephen Ifft, <%=company%>'s Flow Measurement Technology Manager. "Most people assume an orifice plate holds liquid before the plate like a dam. At higher velocities, however, more liquid is held downstream."

An Alternative Metering Technology
The geometry of the V-Cone provides a clean measurement of wet gas without liquid build up before or after the meter section. Until now, no research had been formally completed to analyze the effect of wet gas on the accuracy of the V-Cone. By testing it, <%=company%> wanted to prove that the V-Cone held no water either upstream or downstream of the cone section.

"<%=company%> introduced the V-Cone differential pressure meter in 1986 as an alternative metering technology," says Ifft. "The design of the V-Cone improves the performances of the meter in less than ideal conditions." Unlike other traditional differential pressure devices where the restriction comes from the pipe wall, the V-Cone is designed with a centrally-located cone as a restriction. The V-Cone leaves an annular opening around the cone. "In wet gas," Ifft continues, "any free running liquid along the pipe wall would simply pass through, without touching the cone." According to Ifft and the <%=company%> team, these facts make the V-Cone well suited for wet gas applications.

Recirculating Flow Loop Test
At SwRI, the tests were conducted on a recirculating flow loop to determine the effect of liquid on the V-Cone's measurement accuracy. It consisted of a recirculating Roots-type compressor with variable speed motor, compressor suction and discharge bottles to eliminate compressor pulsations, and a heat exchanger and chiller to control the gas temperature. The V-Cone was installed in the test facility in a 4-inch diameter horizontal pipe section that was located downstream of a sonic nozzle bank. The sonic nozzles were used as the reference gas flow meters for the tests. No flow conditioner was installed directly upstream of the V-Cone flowmeter. A pump recirculated the liquid from the scrubber back to the liquid injection port.

Gas and liquid injected upstream of the V-Cone meter were allowed to mix for 59 pipe diameters before it entered the flowmeter. The two-phase flow was established by the mixing in its natural flow regime, independent of the water injection method.

With a constant gas flowrate, seven different nominal liquid loadings were tested. In addition to the performance testing, SwRI also installed a <%=company%> supplied "clear" V-Cone made with acrylic pipe. This clear meter, under low pressure, allowed a visualization of the flow of wet gas through the meter. Still photography and video cameras were used to capture several combinations of gas flow and water loading.

The Results
Three meters were tested with beta ratios of 0.45, 0.59., and 0.67. The beta ratio of the V-Cone equates to the same open area in the meter as an orifice of similar beta ratio. SwRI tested at two different pressures, with three flowrates at each pressure. The liquid loadings varied between 0 to 5% by mass in seven increments.

The errors in indicated gas flow were nearly always positive. For the two smaller beta ratios, the error reaches a maximum of 1.0%. At the lower pressure, the beta 0.45 error stayed within -0.25% to 0.5%. For the higher pressure, the beta 0.59 performed best with errors between 0 and 0.5%. The largest errors of 1.5% were measured with the beta 0.67 meter at both pressures.

Expectations Surpassed
The results of these tests amply met <%=company%>'s expectations: the V-Cone held no water either upstream or downstream of the cone section. More importantly, the test proved that the V-Cone not only matches traditional orifice plate measurement, but surpasses it.

Both the report and video recording of the tests are available on CD-ROM.

The patented V-Cone flowmeter offers an advanced, differential pressure flow technology that acts as its own flow conditioner. Its unique design enables the V-Cone to provide outstanding performance without the straight pipe runs of other flowmeters. It has an accuracy of up to ±0.5% of reading, ±0.1% repeatability, and flow range of 10:1 or greater, along with installation flexibility and low maintenance. It is ideal for retrofits and limited-space applications. The V-Cone can be sized for line diameters of 0.5 in. to over 120 in.

For more information:

<%=company%>
3255 West Stetson Ave.
Hemet, CA 92545
Tel: 909 652 6811
Fax: 909 652 3078