Measurement of Forward and Reverse Natural Gas Flows in Closed Conduits by Differential Pressure Cone Flow Meters and Ultrasonic Meters

摘要

The use of differential pressure type meters to measure accurately a bi-directional gas flow in a pipeline can have major measurement uncertainty issues due to the geometric difference in the differential producer element shape when used in the reverse direction. Meter discharge coefficient's may be different in these particular cases for geometric devices such as concentric, square edged and flange tapped orifice flow meters and Venturi meters. Current national and international measurement standards state that bi-directional flow measurement is not permitted using orifice plate type flow meters for a "good measurement uncertainty" and that meter runs dedicated for each direction must be used in this application. This paper details the recent experience and testing of differential pressure cone meters used to measure high pressure natural gas to custody transfer standards and as check meters for the CTM Gas Ultrasonic Meters (USM"s) at a natural gas storage and transmission facility in New Mexico USA The cone meters mentioned in this paper were supplied for the field application, and were independently tested using High Pressure Natural Gas Product at a nationally certified test facility in the USA. The provisional testing and a feasibility study was done on smaller diameter meters with water to demonstrate and prove the application at an international certified independent laboratory in the far east. A user in-field data set comparison will be shown between the bi-directional cone meters and the bi-directional ultrasonic meters used for the custody transfer measurement on the site. The resulting test and installation data demonstrates that the use of cone meters in a bi-directional configuration works well and is a "real world" cost effective alternative method to an old issue. The paper will not mention any trade names and will only use' generic names and terminology The data set from the operation in the field shows a better than expected repeatable result over the time the data was collected. The cone meters have performed exceptionally well and held the system balance within values better than the contract uncertainty. Mr. Larry Whitaker ENSTOR Inc Houston is available for comment by e-mail regarding the fidelity of the system data and its operational success. The cone meter design utilizing a welded cantilever support assembly invented and pioneered by Engineer Mr. Floyd McCall of California circa 1985 is now available to be produced by any company whom has the knowledge and tooling to manufacture it because of the patent expiration some years ago. The differential pressure cone meter is an excellent meter and a tribute to Mr. McCall's ingenuity and forward thinking. The 6 inch diameter cone meters shown in this paper appear to be able to match with good measurement uncertainty the other meter types that have been standardized (API-ISO-AGA) and used for fiscal or custody purposes. We will have to see if further standardization occurs in the future alongside the current API chapter 22.2 Test Protocol for this worthy measurement device.