API TR 2571-2011 pdf download.Fuel Gas Measurement.
1 Scope This Technical Report (TR) provides guidance in the following areas to allow the user to achieve a targeted uncertainty of measurement: — selection of flow meter type; differential pressure (DP), displacement, ultrasonic, Coriolis, vortex, turbine, thermal, and others; — associated instrumentation for measuring fluid properties and flowing conditions, such as pressure and temperature transmitters, densitometers, gas chromatographs; — obtaining and use of gas composition or other analytical data; — design and installation requirements of the measurement system; — inspection, verification and calibration practices of flow meters and their associated accessory instrumentation; and — simplified uncertainty calculations with examples to illustrate the methodology. 2 Terms and Definitions For the purposes of this document, the following definitions apply. 2.1 accuracy The ability of a measurement instrument to indicate values closely approximating the true value of the quantity measured. 2.2 bias Any influence on a result that produces an incorrect approximation of the true value of the variable being measured. Bias is the result of a predictable systematic error. 2.3 calibration The process or procedure of adjusting an instrument so that its indication or registration is in satisfactorily close agreement with a reference standard. 2.4 carbon content The fraction of carbon in the fluid expressed as percent by weight. 2.5 compensation The adjustment of the measured value to reference conditions (e.g. pressure compensation). 2.6 fuel gas Typically a mixture of light hydrocarbon and other molecules (e.g. H 2 , N 2 ) in a gaseous state that are consumed in fired heaters. Fuel gas is often a mixture of recovered gaseous molecules from plant operations and purchased natural gas.
2.7 flowing density The density of the fluid at actual flowing temperature and pressure. 2.8 flowing compressibility The compressibility of the fluid at actual flowing temperature and pressure. 2.9 higher heating value The high or gross heat content of the fuel with the heat of vaporization included. The water is assumed to be in a liquid state. 2.10 influence parameter Any factor that impacts the performance of the measuring device, hence the uncertainty and accuracy of the measurement. Examples are process temperature, pressure, fluid composition, upstream straight length, etc. 2.11 inspection A visual assessment or mechanical activity (e.g. instrument lead line blow down or orifice plate cleanliness) that does not include comparison or adjustment to a reference standard. 2.12 metering or measurement system A combination of primary, secondary and/or tertiary measurement components necessary to determine the flow rate. 2.13 meter condition factor An estimate of additional uncertainty based on a technical judgment of the physical condition of the meter in lieu of the ability to inspect. 2.14 performance The response of a measurement device to influence parameters such as operating conditions, installation effects, and fluid properties. 2.15 range of uncertainty The range or interval within which the true value is expected to lie with a stated degree of confidence. 2.16 verification The process or procedure of comparing an instrument to a reference standard to ensure its indication or registration is in satisfactorily close agreement, without making an adjustment. 2.17 uncertainty Describes the range of deviation between a measured value and the true value, expressed as a percentage. For example, a device with an accuracy of 2 % would have an uncertainty of ±2 %.
3 Performance Characteristics and Measurement by Meter Type 3.1 General The primary purpose of a fuel gas meter for any application is to measure the flow. The uncertainty of measurement depends on the measurement equipment selected for the application, proper installation of the equipment, the ability to inspect, verify, or calibrate the various measurement system components, and the frequency of those maintenance activities. The performance of the meter may also depend on the piping configuration and compensation for variability of operating pressure, temperature, and fluid composition. It is important to recognize individual influence parameters and their effect on the measurement. Since the principle of operation and differing influence parameters have varying degrees of influence by meter type, it is important to identify and define the significant influence factors for the meter to determine the total or combined measurement uncertainty.