Vol.3 No.1 2010

59/110

Research paper : Development of primary standard for hydrocarbon flow and traceability system of measurement in Japan (T. Shimada et al.)−56−Synthesiology - English edition Vol.3 No.1 (2010) demand for the calibration of devices that cannot be covered by method (2), including highly accurate flow measurement, measurement of diverse liquid types and flow ranges, and measurement that guarantees international integrity. Therefore, the combination of method (1) that achieves reliability and (2) that focuses on expandability was selected. This is a method where AIST provides the flow standard with high accuracy (small uncertainty) for core flow rates and liquid types, and the calibration lab extends the ranges of standard flow rates and expands the liquid types using the calibration device it already owns, by utilizing the JCSS. Figure 2 shows details of the division of labor between AIST and the calibration lab for the liquid types and flow ranges. Assuming the flow ranges of the flowmeter used for tanker shipment, 300 m3/h was set as the maximum flow rate in this national standard, and the liquid type was set as kerosene and light oil because their viscosity is of medium level. 4.2 Calibration method of the national standard and survey and comparison of the elemental technologiesWhen the calibration lab tries to expand the range of liquid types and flow rates, its calibration uncertainty increases compared to the uncertainty of the national standard on which it is based. To reduce the burden on the calibration lab in attempting to reduce the uncertainty, it is necessary to conduct calibration using the national standard at uncertainty as small as possible. The flowmeter used for measuring the quantities for taxation of the petroleum product must maintain an instrument error (deviation from the standard value) within 0.2 %[2]. Therefore, the goal value of the uncertainty of the national standard for hydrocarbon flow was set at 0.04 % or less for the volume flow standard. This is the highest-level goal value compared to the NMIs of other countries. Several technological challenges were expected, but we decided to overcome those challenges to establish the national standard.The calibration of the flowmeter is conducted by comparing readings of the flowmeter to be calibrated to the readings of the flowmeter through which the standard flow passes. The representative methods for calibrating the hydrocarbon flowmeter are categorized below[3][4]. The eliminated methods include: the comparison method in which the flowmeter is used to calibrate another flowmeter, because this necessitates the calibration of the flowmeter used as standard to be calibrated at a calibration facility; and the dynamic calibration method where the instant flow passing the flowmeter is measured because it is difficult to keep the uncertainty small.(1) Categorization by types of flow• Standing start and stop method: The method in which the flow of the flowmeter to be calibrated is stopped before and after the calibration. While the calibration facility can be constructed at relatively low cost, the transient state between the stop state and the flow state may affect the flowmeter.• Flying start and stop method: The method where the flow rate of the flowmeter to be calibrated is not changed between the calibrations. There is no effect of the transient state of the flow.(2) Categorization by types of reference standard• Volumetric method (volume tank): The method where the volume is measured by sending the test liquid into the volume tank equipped with preliminarily calibrated volume scale. While it has been used widely in general petroleum facilities, it is necessary to evaluate the effect of the test liquid that may remain on the inner wall of the volume tank, and to take highly accurate temperature measurement of the test liquid in the volume tank to reduce the effect of volume expansion by temperature.• Volumetric method (pipe prover): The method where the flowmeter is calibrated by calibrating the volume displaced by a piston moving inside the pipe. Calibration is then conducted using the conduit. Since there is no part open to the atmosphere (closed loop), the effect of evaporation does not have to be taken into account, and this has been used in many petroleum facilities. To achieve high accuracy, it is necessary to investigate the effects of the device to detect the position of the moving body, the temperature measurement in the measurement volume, the leakage between the moving body and the wall of the pipe, and the expansion/contraction of the moving body.• Gravimetric method (weighing scale): The method where the test liquid is introduced into the weighing tank, and the mass of the liquid is measured using a weighing scale. While high accuracy can be achieved, the scale may be affected by the impact of the test liquid when the test liquid is poured into the tank from a high place. It is also necessary to have a mechanism Fig. 2 Diagram for the work division according to liquid types and flow ranges between the national standard and the calibration labs.Flow rate (m3 / h)Viscosity (mPa ・s)Range of tax metersRange of tax metersExpansion and extension at calibration labs(Use of JCSS)Expansion and extension at calibration labs(Use of JCSS)Chemical plantsChemical plantsTankersTankersPetroleum refiningPetroleum refiningPetroleum stationsPetroleum stations0.10.1110100110100100010000NationalstandardKeroseneLight oilGasolineHeavy oil AHeavy oil B

※このページを正しく表示するにはFlashPlayer9以上が必要です