Vol.3 No.1 2010

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Research paper : Development of primary standard for hydrocarbon flow and traceability system of measurement in Japan (T. Shimada et al.)−60−Synthesiology - English edition Vol.3 No.1 (2010) of the test liquid, it is necessary to stabilize the temperature of the test liquid. Sufficient temperature stability of the test liquid (± 0.05 ºC or less) was obtained by devising ways to reduce the time change of the load on the heat exchanger, such as maintaining a stable room temperature using the explosion-proof air conditioning facility, and keeping the constancy of flow that passes through the heat exchanger that controls the temperature of the test liquid. As a result of such technological developments, the uncertainty of “5) Density measurement of test liquid in the flowmeter” and “2) Mass change rate in the connecting pipe” in Table 2 were minimized[6].For the purpose of checking the reproducibility of the calibration system, a servo positive displacement (PD) flowmeters with excellent reproducibility[9] were developed, and three of them were installed permanently in the test line for kerosene and light oil. The adequacy of the calibration could be checked at all times by calibrating the servo PD flowmeter while calibrating the flowmeter, and then comparing the result with the past calibration values.As an assumption of calibration, the check of residual gas in the pipe and the check of leakage of the test liquid that occurs from the valve at the branch pipe are incorporated in the calibration routine.By incorporating the above safety measures and elemental technologies for reducing the uncertainty, the calibration uncertainty of the volume flow was 0.03 %, which was superior than the goal value 0.04 %. The world’s highest accuracy of 0.02 % was achieved for mass flow[5].5.2 Verification of the validity of the developed flow standards The developed hydrocarbon high-flow calibration facility is designated as the specific standard for hydrocarbon flow by the Measurement Law. It is extremely important to verify the validity of the absolute value and the uncertainty of the value of the hydrocarbon flow to be calibrated, and to check the international equivalency, to guarantee the reliability of the hydrocarbon flowmeter of Japan.As a result of conducting bilateral international comparison with the SP Technical Research Institute of Sweden (SP) (see Table 1), the calibration results at the calibration facilities of NMIJ and SP matched in the range of each other’s uncertainties[5]. We also participated in the international comparison test for hydrocarbon flow conducted under the Convention du Métre, with National Engineering Laboratory (NEL) of U.K. as the officiating country[10]. The initial participants included five European countries, two Asian countries (including Taiwan), and two North American countries, a total of nine nations. Since a flowmeter for international comparison with excellent reproducibility and flow characteristic was damaged during transportation, the comparison was carried out over a two-year period from 2005 to 2007. The calibration values of the flowmeters of all participating countries are shown in Fig. 5. The calibration values of the two countries, Mexico and Canada that were dropped midway in the comparison, were greatly divergent from the values of other countries. For these two countries, the calibration was conducted by transporting the calibration device using the pipe prover (small volume prover) or the volume tank to external facilities (such as the petroleum company). This implies that it is technologically difficult to set up a highly accurate flow standard just by maintaining the traceability for individual measurement devices such as the volume tank, as mentioned before, and it is necessary to reduce the uncertainty source of the entire calibration device including the calibration environment. The Japanese national standard values are distributed in the center of the overall calibration values, as can be seen in Fig. 5. Moreover, it was confirmed that the Japanese values match within the range of the internationally agreed values and uncertainties obtained by statistic analysis[10].6 Effort to create an efficient JCSS traceability systemTo respond to the demands of industry that uses the flowmeter for diverse petroleum products at wide flow range, it is necessary to expand the flow range and the range of liquid types from the national standard through the Japan Calibration Service System (JCSS). Therefore, in a government-supported research project[11], we developed the technology to enable easy expansion to different liquid types by adding an advanced analysis to the characteristic of the flowmeter that is dependent on the liquid viscosity, and the technology to extend the flow range by the parallelization of the flowmeters[11][12]. Figure 6 shows Flow rate (L/s)0510152025303516.8416.8316.8216.8116.800.1 %16.7616.7716.7816.79Calibration factors of the flowmeter K-Factor (P/L)NEL May 2005SP Jun 2005CMI Jul 2005NMi Sep 2005Force Jan 2006CMS Mar 2006NMIJ Apr 2006CENAM Jun 2006MC Aug 2006NEL Nov 2006NMi Feb 2007Force Feb 2007SP Mar 2007NEL Jul 2007Fig. 5 Measurement results of the international comparison for hydrocarbon flow.The participating organizations and countries are: NMIJ: Japan, NEL: UK, SP: Sweden, CMI: Czech Republic, NMi: The Netherlands, Force: Denmark, CMS: Taiwan, CENAM: Mexico, and MC: Canada. The data in Fig. 2 of the International Key Comparison[10] were re-plotted.

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