Natural gas is one of today’s most important energy carriers in many factory processes, with sales constantly increasing. In many companies and plants it is an easy to handle fuel without which operation is virtually unimaginable. Although the current price is relatively low there are considerable costs that come to bear in practice. For example, in a DN 100 natural gas pipe at 25 bars of pressure, 35 million euros flow through the pipe per year. In this case, it is worth investing in precise measuring equipment, especially if internal balancing of energy consumption is a goal.
In this application, a vortex flowmeter such as Krohne’s Optiswirl 4070 C provides high accuracy at minimal investment cost. In order to check the characteristics of the flowmeter when measuring natural gas, Krohne had a production model tested under practical conditions at the pigsar testing facility in Dorsten.
The high pressure gas meter testing facility operated by EON Ruhrgas is the national standard for the Federal Republic of Germany and as such is responsible for maintaining the reference value for unit of volume for high pressure natural gas and passing on this reference value to other laboratories. In association with, and under the control of, the Federal Institute of Physics and Metrology (PTB), pigsar conducts calibrations and verifications as an independent laboratory.
An Optiswirl 4070 C DN150 PN40 featuring integrated pressure and temperature compensation was used as a test device. The purpose of the test was the volumetric measurement (standard cubic metres) of natural gas routed directly to the calibration rig from the EON Ruhrgas operating network. Results were then compared to those of the turbine-type meters used as reference devices.
Two series of tests at 16 and 41 bars of pressure were run as these are representative of the prevailing pressure range of 16-40 bar in practice. The result did not only confirm the specified measuring accuracy – it exceeded it considerably: at 16 bar of pressure, the measuring accuracy of the meter only deviates an average of ±0,24% from the turbine, while measuring uncertainty is at ±0,15%. At the higher pressure, the values were even better with the same measuring uncertainty, measuring inaccuracy was ±0,135%. This puts the device clearly above the standard specified accuracy of 1% for gases in both tests.
For the user, improved measuring accuracy means more precise monitoring, which in the case of internal balancing means more accurate billing: In the example cited, 0,1% measuring accuracy corresponds to a sum of 35 000 EUR. The price of an Optiswirl (size DN150) is considerably less than this.
For more information contact Mahendra Rajcoomar, Krohne South Africa, +27 (0)31 266 9270, [email protected], www.krohne.com
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