I passed the Ratcliffe-on-Soar Power Station today and noticed the huge volume of steam coming from the cooling towers.
Silly question...
Why do they need to cool the water as the water is used to generate steam and if the water is already hot then why not pump it back round to be re-heated using less energy?
BTW when working out a funding package for a coal mining co a few years back I was surprised to find that coal sold to power stations was not sold on weight but by calorific value. The power station told the supplier how much energy was generated and paid based on that.
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Similar to how your gas bill works IIRC?
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>>coal sold to power stations was not sold on weight but by calorific value
Wet coal = wet logs
Heavier but less energy output.
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>>Why do they need to cool the water as the water is used to generate steam
They don't. They cool the steam to turn it back to water and then use it again.
High pressure water heated giving high pressure steam used to drive turbine therefore losing heat and pressure resulting in a lower pressure mess of water/vapour/steam which is then cooled to just water under low pressure & then repeat
Last edited by: No FM2R on Thu 31 Jan 19 at 02:53
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Yer, its not steam that drives turbines and stuff, its high pressure steam. (superheated high pressure steam), If your water is hot before being heated, insufficient expansion takes place within the boiler - a pressure vessel - to create high pressure steam. When you additionally heat the steam outside the boiler, superheat it, it gives it further thermal expansion properties.
Having said that, you can't put very cold water into a boiler, so the water evaporated from the steam is the perfect temperature, plus because its evaporated its very pure and won't fur up the boiler
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Did you just pick randomwords associated with power generation and jumble them up in a post....!:)
Unfortunately about 50% of the energy put into the water to make steam, and in turn drive the turbines to generate electricity, is wasted, as this is the energy required to turn it from water into steam - this energy needs to be removed, and is what is chucked up the cooling towers. There is a way out of this, but it requires a super critical steam system, which requires very high pressures (>220 bar) and temperatures, and some special alloys - and strange things start happening in supercritical fluids!
2 separate water systems in power generation:
Boiler water: this is turned into steam at high pressure (typically >100 bar), then superheated to >500°C (boils at somewhere over 300°C at this pressure). Superheat is required to extract as much energy as possible out of the steam when the pressure is let down through the turbines - if no superheat then it tends to just condense which is not that good for turbine blades, and doesn't produce much useful energy! To maximise the energy recovered in the turbines the exhaust is usually run under vacuum which makes the water condense at about 50-60°C. This condensed water is then recycled back into the boilers - made up with demineralised water which is usually produced in an ion exchange bed.
Cooling water: this is used to condense the boiler water, and carry away the waste heat. It in turn is cooled in the cooling towers - which generally use evaporative cooling (i.e. some of the water evaporates - this is the steam that comes out of the top of the towers). Evaporative cooling is good because it requires a relatively small footprint, and gets you close to the atmospheric wet bulb temperature - any other method (e.g closed circuit air cooling like your car radiator) would require massive foot print to get any where near the wet bulb temperature. Sadly all this waste heat is very low grade, being rejected at about 20-30°C, so is no use for anything else, e.g. district heating.
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Cooling Towers - zippy
