Articles & Case Studies

KROHNE's precise flowmeters improve the efficiency of power plants

Posted: Friday 30th May 2008

For the improvement of the efficiency of the Japanese nuclear power plants the National Metrology Institute ofJapan(NMIJ) has put the world's most accurate research and test facility into operation for the measurement of ultra-large flows. The heart of this facility includes four ALTOSONIC V ultrasonic flowmeters from KROHNE which are arranged in series each with one electromagnetic OPTIFLUX flowmeter from KROHNE for the technology-independent plausibility checking.

The energy demand growing globally and the discussion about climatic change have placed the power engineering sector increasingly in the focus of public interest. New technologies are in demand in order to use the resources used for electricity generation more effectively and with less harm for the environment. A new research facility in Japan now shows that with the help of ultramodern measuring technology from KROHNE one has come quite a bit closer to this goal. The research results of this project that was called into being for the Japanese nuclear power industry, can also be transferred to conventional power plants operating on the basis of fossil energy sources.

Apart from the energy source used, the basic circuit in nuclear power plants and conventional coal-fired power plants is the same. In a reactor or boiler water is, by being heated up, converted into water vapour/steam which is under high pressure and at a high temperature.

The steam is passed through a turbine which in turn drives the generator producing steam. To produce the necessary pressure difference there is a condenser located downstream of the turbine, in which the steam is cooled down sharply. In the next step, the water is passed to a feedwater tank, from where it is conveyed by means of the feedwater pump back into the reactor or boiler for renewed heating-up.

Process control with the help of the feedwater flowmeter

Downstream of the feedwater tank and the feedwater pump a flowmeter is arranged which is referred to as the 'feedwater flowmeter'. It is of particular importance for control of the process, as with the flow rate measured here in conjunction with a temperature measuring system the output of the reactor or boiler is determined and the meeting of the maximum degree of capacity utilisation is monitored. This flow measurement is where NMIJ's research facility starts from.

The inaccuracy of this flow and temperature measurement so far amounts to a total of 2 to 3 percent, about 90 percent of the inaccuracy originating from the flowmeter. For safety reasons the whole circuit is naturally controlled in such a way that the measuring accuracy is taken into account and the maximum utilisation of the plant is reduced by 2 to 3 percent. The undesirable effect of this way of proceeding is hence a reduction of the plant efficiency by a total of 2 to 3 percent due to the uncertainty of the measurement.

It is now the aim of the NMIJ project to reduce the inaccuracy if this measurement to 1 percent and to increase the efficiency accordingly. For this purpose, the test facility was built in which flow rates are generated corresponding to those in a nuclear power plant. By the use of the ALTOSONIC V ultrasonic flowmeters from KROHNE the world's most accurate research and test facility for very high flow rates has been produced.

For the entire project, the NMIJ has estimated a period from 2004 to 2008 and a capital expenditure volume of approximately 3 billion yen, i.e. about 18 million euros. Ultimately the gain will be enormous. With the insights gained, not only the effectiveness of all nuclear power plants, but of all thermal power plants worldwide can be improved by 1 to 2 percent. 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 tonnes of CO2 emissions per annum.

Announcements of interest in the Japanese project have already been received from different countries. In Japan starting from the local conditions the main focus so far has been on the utilisation of the research results for nuclear power plants. However, it seems in principle that a transfer to other power plant types is possible. In that way the ALTOSONIC V ultrasonic flowmeters from KROHNE will very soon become the standard for feedwater flowmeters and help to considerably reduce the worldwide output of CO2.

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