| Abstract |
No well-defined standard exists for the measurement of combined steam-NCG flows specifically for use by the geothermal power industry. The primary challenge in measuring geothermal steam flow is in defining the density of the combined steam-NCG mixture based upon the measured pressure, steam quality (or degrees of superheat), and the non-condensible gas constituents. The purpose of this paper is to define a standard procedure for calculating the density of geothermal steam for steam flow metering. Typically, a high quality steam venturi is used to measure the main steam flow. This meter is critical because it is used not only to measure the plant performance but, in some cases, serves as a custody transfer billing meter between the steamfield operator and the power plant. This meter is also usually used to demonstrate during plant acceptance testing that the guaranteed performance objectives are met. The plant performance is typically expressed as a “steam rate” in units of kg/kWh, which is simply the main steam flow divided by the net plant electrical output. The U.S. standard for differential pressure flow metering is ASME MFC-3M-1989 Measurement of Fluid Flow in Pipes Using Orifice, Nozzle, and Venturi. This standard is consistent with and technically equivalent to the corresponding international standard, ISO 5167. The book Flow Measurement Engineering Handbook (ISBN 0-07-042366-0) written by the chairman of this ASME committee, Dr Richard Miller, is widely regarded in the differential pressure flow metering industry as the reference of choice. These are the two recommended sources that should be referenced when developing a flow measurement system. |