Henk Jan Panneman, Cornelis W. Koreman, Sjoerd Toonstra, Floris Huijsmans
THE USE OF ULTRASONIC GAS FLOW METERING TECHNOLOGY FOR THE DEVELOPMENT OF ACCURATE ENERGY METERS FOR NATURAL GAS
Gasunie Research gained their years of experience in efficient energy utilization, gas transport and gas measurement as the in-house laboratory for N.V. Nederlandse Gasunie. This company, which was an integrated gas transport and trading company until the beginning of 2002, has been one of the largest gas suppliers in Europe for several decades. As part of this company, Gasunie Research has always striven to guarantee the continuity of the gas supply, to ensure the safety of gas transport and to enhance the added value of natural gas as a fuel. Gasunie Research developed a wealth of new technology for domestic, commercial and industrial end users, and for the energy sector itself. The expertise that Gasunie Research has acquired through these activities and the years of practical experience is now made available to third parties.
Energy measurement is one of the main tasks of gas transport companies. New challenges in the gas world confront gas transport companies with new requirements regarding energy measurement. (e.g. the variation in gas composition will be larger and will occur more frequently). These changes are the driving force for a number of new developments in energy metering. Present energy measurement systems for natural gas comprise of volume metering, volume conversion from field conditions to reference conditions and calorific value determination at reference conditions. The calorific value, HSR , is mostly determined by compositional assay using a process gas chromatograph. The volume is commonly measured by a turbine flow meter, an ultrasonic flow meter or an orifice plate. The volume conversion factor is mostly determined from thermal equations of state, using the gas composition or some gas properties as input. The cost of ownership for accurate energy meters based on process gas chromatographs is high. These high costs were the main reason for Gastransport Services (the transportation company of N.V. Nederlandse Gasunie) and Ruhrgas AG to join forces on the development of new energy flow measurement methods.
These new methods are based on the measurement of three suitable properties (e.g. physical properties or component concentrations) and an accurate correlation between these properties and the gas composition. The inferred gas composition is used to compute a variety of gas properties like the superior calorific value, the density, the compression factor under reference and field conditions and the Wobbe-Index.
Within the joint project Gasunie Research focussed on the development of an energy meter based on velocity of sound measurements. The new meter is based on the measurement of the velocity of sound at high pressure (VOShigh), the velocity of sound at low pressure (VOSlow), and the molar fraction carbon dioxide (XCO2). This combination is particularly suitable for stations with high pressure gas available (P > 40 bar).
In this paper results for the superior calorific value of natural gas obtained with both a dedicated double velocity of sound meter and with velocity of sound measurements obtained by an ultrasonic gas flow meter will be discussed.