Mist cooling technology for thermoelectric power plants
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A novel mist-based cooling concept is analyzed with the objective of reducing water consumption in thermoelectric power plants. Additionally, this concept offers the potential to increase electricity generation capacity by lowering the steam condensation temperature. The mist-based cooling concept consists of two independent technologies. The first technology consists of replacing the cooling tower with a two stage heat exchanger consisting of air-cooled and water mist-cooled heat exchangers. The mist-cooled heat exchanger chills the cooling water to near wet bulb temperature ambients which enables lowering of condenser pressures and temperatures. The mist is a saturated air stream at wet bulb temperatures obtained by adding water droplets to ambient air. The air-water ratios and droplet sizes can be optimized to reach wet bulb temperatures with minimum water consumption. The enhanced control of evaporation through mist cooling will allow the mist to reach closer to wet bulb temperatures than cooling towers. The second technology consists of replacing the shell-and-tube condenser with a direct contact condenser, wherein the steam from the Rankine cycle condenses on water mist streams. The large area offered by mist droplets increases heat transfer rates significantly, resulting in compact and low maintenance condensers. Technical and techno-economic analyses are carried out to map the potential of mist cooling technology. The technical analyses show that mist cooling technology can reduce water consumption by up to 65 %, compared to present-day cooling towers of the same power output. Furthermore, by reducing the condenser pressure, the electricity generation capacity can be increased by 4 % while still consuming less water than existing cooling towers. First-order techno-economic analyses have also been conducted to quantify the economic benefits of mist cooling for thermoelectric power plants in Texas. These analyses reveal that mist cooling technology can greatly help 17 out of 18 coal-fired power plants in Texas. It is expected that this technology will significantly benefit other U.S. power plants located in water-stressed areas.