概览
Binary cycle power plant in geothermal energy power plant
Process instrumentation in ORC plants
A binary cycle power plant is used where there are lower temperature levels from the geothermal source. The organic Rankine cycle is a closed cycle using an organic working fluid like iso-pentane or iso-butane with a lower boiling temperature than water. The loop is kept isolated from the brine through the heat exchanger design of the pre-heater and evaporator. The geothermal brine is directly used in the vaporisers/pre-heaters without further separation. The working fluid is first pre-heated and then evaporated in the evaporator – the resulting gas (approx. 20 bar, 150 °C) drives the turbine, generating electricity – then this gas (approx. 4 bar, 75 °C) is condensed back to liquid again in the condenser. The feed pump closes the loop and starts the cycle again. Furthermore, geothermal fluids contain entrained non condensable gases (NCGs) which need to be removed from the process for higher efficiencies. Steam ejectors or vacuum pumps are used to remove NCGs from the system.
Geothermal brine is hot and corrosive: it contains H2S, silica and other unwanted substances. Vacuum may occur in the lines, along with elevated temperatures. KROHNE has the best suitable measurement technology for every measuring point based on dedicated OPTIFLEX electromagnetic flow meters with special liners that offer low diffusion and vacuum resistance. Pentane, butane and other low boiling fluids are used as the ORC fluids in binary and hybrid plants. Flows and levels in the organic Rankine cycle need to be measured for efficient and safe process control. OPTIMASS Coriolis mass flow meters and OPTISONIC 3400 ultrasonic flowmeters are ideally suited for these Rankine cycle applications. These meters also supply additional process information about the fluid density for process diagnostics. Liquid levels can be measured by directly applying OPTIFLEX 2200 guided radar level meters or via bypass gauges type BM 26 which can incorporate a variety of different measurement sensor technologies.