Water-steam cycle in hard coal and lignite-fired power plants

Feed-water lines can reach 200°C/250 bar at sub-critical power plants while the steam parameters range up to 565 °C/220 bar. Ultra-Supercritical (USC) power plants achieve very high efficiencies of over 40% for the electricity production only at feedwater conditions of approximately 250°C/ 350 bar and steam temperatures and pressures up to 720°C/330 bar. Feedwater is fed via the FW-heaters and the economiser to the main steam turbine generator at high pressure. The main steam temperature is controlled by means of high pressure injection water. After leaving the high pressure (HP) turbine the steam is reheated by the reheater and further utilised in the intermediate pressure (IP) turbine and then in the LP turbine. The exploited steam is fed to the condenser where low temperatures and pressures maintain a good efficiency of the Rankine process. The condensate is led to the condensate system. The feed-water has tight limits for pH, conductivity, oxygen, silica, iron and other parameters to ensure safe and efficient operation and a long service life.

The feed-water flowmeters are of high importance for process control and safety and need to cope with the high temperatures and pressures, plus meet the accuracy and redundancy requirements. Typically Venturi tubes or flow nozzles installed in meter runs with redundant DP-transmitters according to ISO 5167 or ASME MFC-3M are used. The engineered KROHNE primary DP flow elements and meter runs are hot water factory calibrated at high Reynolds numbers. The state-of-the-art OPTIBAR DP 7060 C pressure transmitters are 100% 3D-calibrated over the entire temperature and static pressure range and are available with measurement capsules up to 700 bar line pressure. KROHNE supplies the complete flow solution with DP-flow element, DP-transmitter, pressure and temperature transmitter, process valves, engineering, calibration and documentation. A further new option here is the OPTISONIC 3400/4400 ultrasonic flowmeter series, suitable for these requirements of temperature, pressure, materials redundancy etc. KROHNE OPTISONIC units are drift and maintenance free, have no pressure drop and an extremely wide turndown ratio which enables very good low-end accuracy. Also for steam, reheat, condensate, injection water and other typical flow applications, KROHNE OPTIBAR DP and OPTISONIC ultrasonic flowmeters are available.