New Japanese Research Facility Measures High Performance Flowmeters

In a study of higher performance flowmeters to improve the efficiency of Japanese nuclear power plants, the National Metrology Institute of Japan (NMIJ) has put one of the world’s most accurate research and test facilities into operation for the measurement of ultra-large flows.

At the heart of the facility are four Krohne Altosonic V flowmeters arranged in series, each with one electromagnetic Krohne Optiflux flowmeter as a technology-independent plausibility check.

Inaccuracy of flow and temperature measurement amounts to a total of 2 percent to 3 percent, with about 90 percent of the inaccuracy originating from the flowmeter due to the uncertainty of the measurement. The NMIJ project’s goal was to reduce the inaccuracy of this measurement to a more acceptable 1 percent, thereby increasing the overall efficiency of the reactor.

The NMIJ test facility was built to simulate flow rates that would typically be found in a functioning nuclear power plant. Construction of the facility, whose water tower supplies 12,000 cubic meters of water per hour, began in 2004. The entire program is expected to represent a total capital investment of approximately 3 billion yen (US$33.3 million). With the insights gained, the effectiveness of all nuclear power plants and thermal power plants could be improved by 1 percent to 2 percent.

By using five parallel paths, the Altosonic V provides a good representative sample of the mean flow velocity distribution throughout the cross-sectional area. To ensure a constant cross-sectional area, the Altosonic V is machined from a single block of steel for resistance to expansion due to line pressure. To compensate for thermal expansion and contraction, a temperature sensor is located in the meter body, allowing for corrections.

The specified accuracy of the Krohne Altosonic V flowmeter is +/-0.15 percent of the measured flow rate. Additional uncertainties occur in the high temperature regimen, due mostly to the inability to calibrate at the elevated operating Reynolds Numbers. The target is the industry requirement of +/-0.25 percent of the measured flow rate on the flow element and it allows for an additional +/- 0.05 percent on the differential pressure measurement or a combined uncertainty of +/- 0.3 percent. Whether or not this performance is actually being achieved with the traditional flow solution has been questioned throughout the industry.

The Krohne Altosonic V ultrasonic flowmeters have no obstructions or moving parts in the pipe, which ensures no wear or pressure loss. This, in combination with larger meter sizes, permits simplified configuration of metering systems. No strainers and fewer parallel lines are required. Operation of the flowmeters is maintenance- free and no periodic calibration is required. —Krohne

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