Comparative study on orifice versus turbine meter for gas flow measurement

Abstract

In Titas gas system Orifice and Turbine meters are most widely used for gas flow measurements in bulk customer’s RMS, CGS, TBS and DRS. Generally at the purchase points, Orifice meters are used in gas delivery line. The total gas input measurement that made by production companies depend on Orifice meters reading. About 1300MMSCFD gas is purchased from the production companies and delivered to the customer end through the Orifice and Turbine meters in Titas franchise area, so it is apparent that accurate measurement is very important for companies. This project aims to perform a comparative study on measuring principle, measuring devices, Operation & installation standards, metering accuracy and uncertainty analysis of Orifice & Turbine meters. As Titas Gas Company has to procure and install a large number of meters for gas flow measurement for various load applications and operating conditions, therefore, selection of meters for various types of customers is one of the major objectives. In this project Calibration method of Orifice meter with secondary devices have been studied and analyzed the calibration results to determine what affect the accuracy of gas flow measurement. For an Orifice meter due to differential pressure measurement deviation, it has been found that 4.7% flow measurement error occurs at minimum flow rate and 1.5 – 2.0% error occurred in normal operating range (range of customer demand).Similarly, from the test results of Turbine meters, it has been observed that Turbine meters with higher capacities, show below 0.5% error and Turbine meters with lower ranges perform below 1% error with respect to reference/standard meter. Analyzing the uncertainty of Orifice meter with 0.71439 beta ratio, 1.06% measurement uncertainty have been found. For Turbine meter the measurement uncertainty value is 0.68%. If two Orifice meters are installed in series in Titas Gas Transmission system for counter measurement, a significant flow difference have been found in gas flow measurement by two Orifice meters. The comparison of flow measurement between Orifice and Turbine meters have been made by considering measured variables data over 15 months when the two meters installed in series. From that analysis, it shows that Turbine meter measurement is 1.992% better than that of Orifice meter with considering calibration and uncertainty analysis.