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.)−58−Synthesiology - English edition Vol.3 No.1 (2010) standard. Here, the calibration capacity is presented quantitatively by the uncertainty based on the international comparison conducted under the Convention du Mètre. This can be considered the evaluation result of the most authoritative national standard, where all the participating institutes agree to the technological basis of the uncertainties that are presented by each other. In the calibration of the hydrocarbon flowmeter in overseas national standards, the liquid flow method using the volume pipe and the stop method using the volume tank are used frequently. However, as mentioned earlier, these methods have several technological issues in achieving the high level of uncertainty. Also, in the standing method, the transient state of the flow may become a major source of uncertainty, depending on the type of the flowmeter. In some calibration methods, the type of the flowmeter to be calibrated may be limited. On the other hand, the gravimetric method with flying start and stop using the diverter, which is frequently employed in the calibration facilities for water flowmeter, is rarely employed for petroleum products since they are hazardous materials with risk of explosion due to static electricity. If this point can be overcome, there is high possibility for achieving small uncertainty. Therefore, AIST selected the “gravimetric method with flying start and stop using the diverter” as the calibration method of the national standard facility, to realize a national standard with the highest accuracy in the world, and developed the elemental technologies to achieve the high accuracy and took measures to ensure safety.5 Construction of the hydrocarbon flow standard5.1 Calibration facility for hydrocarbon flow Since this facility will store and use large amounts of kerosene and light oil, it must be designed in accordance with the Fire Service Law as a place for handling hazardous materials. Also, a safety management system must be established, and measures to prevent the leakage or outflow of the test liquid are required in consideration of the surrounding environment. Because the risk factor increases, as mentioned in the previous chapter, in the “gravimetric method with flying start and stop using the diverter,” it is mandatory to take sufficient safety measures. In Japan, there were almost no cases of a large indoor facility where a large amount of petroleum products, which are hazardous materials, was allowed to flow, but its construction was approved by the fire service authority because of its importance as a national standard and the implemented special safety measures. Figure 3 shows the safety measures and the relationships to the elemental technologies for uncertainty.To prevent leakage of oil, dual measures were taken where the entire facility was surrounded by an oil dike, and a pit and an oil-water separator were installed around the building. The roof was made of light corrugated sheets with an explosion-release structure to release the pressure upward in case of an explosion, but had insulation to improve the temperature stability in the building. The hazardous area containing the test line through which the petroleum products will circulate and the nonhazardous area such as the operating room where the control computer will be installed were clearly demarcated. The test line would be monitored from the operating room, and a refractory glass and refractory shutters were installed to enable quick response in case of emergency. In the hazardous area, oil-proof floor was installed to prevent underground permeation of oil, the two 43 m3 storage tanks were placed in the underground pit, and the weighing tank was installed in the room with the underground pit, to prevent leakage to exterior environment in case of any accident.Figure 4 shows the diagram of the hydrocarbon high-flow calibration facility[5] which is a real-flow calibration facility for hydrocarbon flowmeter, and Table 2 shows the sources of uncertainty[6][7]. This calibration facility is composed of two test lines for kerosene and light oil, and the flow range Employ gravimetric method with flying start and stop using a diverter Bubble removal: multistage screen mesh inside the storage and collection tanksElemental technologies related to uncertaintySafety measuresSteam evacuation deviceGeneration of mist, vapor, and bubblesPossibility of leakage from the weighing tankMeasures by interlockOil leak measuresExplosion-proof air conditioning (all-fresh 24-hour air conditioning)Explosion-proof devices, fire extinguishing facility (foam extinguisher, etc.)Ideal calibration environment with stable room temperatureWeighing scale with standard dead weightsHigh-precision temperature adjustment system: stable liquid temperatureLong, straight pipe installed upstream of the flowmeter to be calibratedConstruction of flow stabilization systemDevelopment of a new diverterWhole facility acts as an oil dikeDouble prevention: pits installed around the buildingStorage tank (43 m3 × 2) placed in underground pitFig. 3 Elemental technology developed for hydrocarbon high-flow standard.

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