The demand for energy has been growing steadily, not just in the United States but globally. At the same time, concerns about climate change have placed the power engineering sector increasingly in the focus of public interest. New technologies are being actively pursued that will generate electricity more efficiently while reducing its environmental impact.
An impediment to achieving this goal, however, is the nature of the equipment used by the nuclear power industry, which too often is antiquated. The primary reason for the old machinery is simply that most plants were designed and built more than 20 years ago. Upgrading the equipment would require extensive cost. In addition, much of the equipment and technology no longer is supported by the original suppliers.
Now, a research facility in Japan is demonstrating that, with the help of measuring technology designed for the process industries from Krohne, headquartered in Duisburg, Germany, the goal of improved efficiency is substantially closer.
In a study of high performance flowmeters to improve the efficiency of Japanese nuclear power plants, the National Metrology Institute of Japan (NMIJ) has put a research and test facility into operation for the measurement of ultra-large flows. At the heart of the facility are four Krohne Altosonic V ultrasonic flowmeters arranged in series, each with one electromagnetic Krohne Optiflux flowmeter as a technology-independent plausibility check.
Flow measurements are necessary in the power plant because of the process by which electricity is produced. Inside the reactor, water is heated up and converted into water vapor (steam), which is under high pressure at an elevated temperature. The steam passes through a turbine, which in turn drives the generator and produces electricity. To produce the necessary pressure difference, a condenser is located downstream from the turbine, in which the steam is cooled down sharply. In the next step, the water passes to a feedwater tank from where it is conveyed by means of the feedwater pump back into the reactor or boiler for renewed heating.
The boilers in these facilities are producing higher and higher temperatures, so an accurate flow measure is required for calculation of the power plant's entire production - and that is the driving force for the NMIJ project. A critical part of the process is to measure the flow rate very accurately. The more accurate the measurement, the closer the reactor operator can get to the maximum output, which ultimately has a big impact on the plant's overall efficiency.
A flowmeter, positioned downstream from the feedwater tank and pump, helps control the process. The flow rate, measured at that point in the system and in conjunction with a temperature-measuring system, will determine the output of the reactor while helping the reactor achieve maximum capacity. This flow measurement is where the research conducted at the NMIJ facility begins.
The inaccuracy of this flow and temperature measurement amounted to a total of two to three percent, meaning that the maximum utilization of the plant was reduced by that percentage. About 90 percent of that inaccuracy originated from the flowmeter due to the uncertainty of the measurement. The aim of the NMIJ project was to reduce the inaccuracy of this measurement down to a more acceptable one percent, thereby increasing the reactor's overall efficiency.
"Traditionally, this crucial measurement has been done with what are called ASME [American Society of Mechanical Engineers] flow nozzles, which are basically differential pressure devices with significant technological limitations," says Jonathan Fiedler, a Krohne product specialist. "They offer limited accuracy, are prone to drift, and have limited self-diagnostics to allow verification of the measurement. While some of the inherent variations of this technology can be minimized by proper sizing, design, manufacture and installation, its precision as a flow measurement technology is as good as it can be with the ASME-specified flow nozzles."
Consequently, the NMIJ test facility was built to simulate flow rates that would typically be found in a functioning nuclear power plant. The Altosonic V flowmeters have contributed to the development of very high flow rates at the research and test facility. The absence of obstructions or moving parts in the pipe ensures no wear or pressure loss, and, in combination with larger meter sizes, permits simplified configuration of metering systems. No strainers and fewer parallel lines are required.
Flowmeter operation is maintenance-free. No periodic calibration is required, which cuts costs for on-site equipment and procedures. With the insights gained, not only the effectiveness of all nuclear power plants, but of all thermal power plants worldwide could be improved by one to two percent, according to Krohne. The NMIJ translates the gain in effectiveness for the 55 Japanese nuclear power plants into a saving of new fossil fuel-fired power plants and hence into a saving of 200,000 tons of CO2emissions annually.
Flowmeters Improve Nuclear Power Plant Efficiency
July 10, 2009