Overview
Water-steam cycle in waste incineration
Process control for high pressures and temperatures
The steam-water circuit operates according to the Clausius-Rankine process. Most waste incineration plants operate sub-critical and as combined heat and power plants (CHP), where the heat is used by either by private or industrial customers. De-aerated boiler feedwater is pre-heated by the feedwater heaters and fed to the economizer. The waterwall further increases the water temperature. The evaporator generates the main steam for the steam turbine. The exploited steam from the HP turbine is reheated for further usage in the LP turbine. There are differences in the general boiler design depending on the boiler maker. Most of the waste incinerators are sub-critical. Spray water is used to control the temperature in the gas path as well as the temperature in the steam pipes in order to control the steam temperature. The steam is supplied to the HP and LP steam turbine at different pressure and temperature levels. The steam leaving the turbine will go to the re-heater or to the lower pressure sections of the turbine. The exploited steam of the LP section leaves the turbine and enters the condenser. The low pressure of around 7 kPa in the condenser has a major influence on the cycle efficiency. External cooling loops absorb the remaining heat in the condenser: often this extracted heat is used for district heating, supplying both municipal and industrial customers.
Flow, level, temperature and pressure are the main properties being measured by instrumentation in the steam-water circuit of a waste incinerator. Pressures and temperatures are often high and can get to 150 bar or 440 °C in modern waste incinerators. Feedwater and condensate have low conductivity levels. The commonly used standard measuring technology in power generation uses differential pressure (dP) measurement. There are different international standards such as ISO 5167, ISO TR 15377, ASME MFC-3-M, ASME PTC6, BS 1042, DIN 19206, UNI 10023 defining the geometry and the accuracy of the primary element. This flow technology can be applied in virtually all kinds of flow applications, being suitable for high temperatures and pressures, and covering liquids, gases and steam. KROHNE offers complete dP-flowmeter solutions, including the primary element and the dP-transmitter system, with the required material specifications. The KROHNE OPTIBAR DP 7060 C transmitter is the perfect instrument for this duty, it is fully 3D-factory linearized over a wide dP, static pressure and temperature range and offers superb long term field performance in dP-flow applications.
The OPTISONIC 4400 series covers feedwater, condensate and other liquid applications up to 350 bar. OPTISONIC 8300 is designed for gases and steam up to 620 °C/ 200 bar. The OPTISONIC inline flowmeters measure wide flow ranges, virtually from zero flow upwards, have no wear, are maintenance free and don’t need winterization. They are available in redundant versions in the required materials and can easily be integrated in the pipe with only minor engineering effort. Furthermore, KROHNE as a pioneer in Radar level measurement offers TDR and FMCW level transmitters from 6 to 80GHz covering a wide range of applications up to very high temperatures and pressures.