This document outlines the basics of the metering system design that this energy provider proposes to fit to all their Landfill Gas (LFG) and Coal Mine Methane (CMM) fuelled power generating sites. A description of the metering systems installation and operation, details of the equipment utilized and supporting information for ruling on the accuracy of the system has been included.
The consumption metering design consists of a methane analyser to measure the methane content of the gas supply by volume, a gas meter installed in the gas supply piping to the engines to measure volumetric flow rate, and a pressure and a temperature sensor installed immediately downstream of the gas meter to allow conversion to standard cubic metres per hour (SCMH). A dedicated flow computer is utilised to perform the required calculations for total consumption in energy units (Giga-Joule) and to store totalised values.
The ABB swirl flowmeter FS4000-ST was selected to measure the quantity of gas flowing to the gas engines. This flowmeter measures actual volume flow rate of LFG and CMM, independent of composition, at an accuracy of +/- 0.5 % and over a large range of flow. This specialized item of equipment, using proprietary technology, was identified to meet not only the accuracy and flow range requirements of the application, but also due to its lack of sensitivity to many external factors and thus robust operating characteristics. The volume flow rate is communicated to the flow computer via a pulsed signal output.