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Cooling towers on power stations - why?

Hi All


I was working on a power station in Oman last month and it was gas fired with condensing steam turbines - no evaporation.  This week I'm working on a coal fired one in Poland, which has cooling towers and evaporation.  Is it something to do with the gas or just that they have no water in Oman?


Thanks


Stephen
  • I honestly don't know the answer to your question, but it reminded me of something my late father said (he was very well educated, and a bottomless trove of knowledge with a great eye for a wind-up). When I was very young I lived not too far from the Chapelcross power station. The cooling towers, billowing steam all day long, were a source of mystery to the five-year-old me, and when I asked the great man what they were, I was reliably informed they were a cloud factory...
  • Cooling Towers are there to condense as much of the steam as possible to water for recycling in the power station, typically 70-75%.  The steam you see is the 25% that gets away.


    Sorry if that spoils anything for you Howard.....!
  • A quick web search took me to everything the non-specialist would want to know about different types of Cooling Towers and some . They also have additional uses as nesting sites for birds of prey,  adornments to the natural environment  and for navigation.  Back in the last century long before Sat Navs , I was able to navigate around large swathes of the UK using Cooling Towers as signposts, with the odd HV transmission line or substation thrown in.


    Perhaps it’s a sign of old age that I’m nostalgic for the CEGB.  The high-skill high-value jobs and wonderful training that it provided right across the country are something many have reason to be grateful for.   

    https://www.shropshirestar.com/news/local-hubs/telford/ironbridge/2017/11/30/ironbridge-power-station-demolition-would-be-sacrilege/

    https://www.bbc.co.uk/news/uk-england-nottinghamshire-34861835

    https://www.bbc.co.uk/news/uk-england-essex-32518047

    http://www.cegbmidreg.co.uk/


  • Not sure I understand what is meant by " gas fired with condensing steam turbines". Does this mean a gas boiler heating water to make steam which drives a turbine? This would need something to condense the steam and transfer the heat to something else (air, river, sea). Could it not have been gas turbines?
  • There is a power station in Slough which primarily feeds the industrial estate, the super heated steam from the turbines is fed out through, I believe, a sealed piped system supplying the neighbourhood housing estates with subsidized central heating . Similar to a non-vented pressurized CH boiler.


    Legh
  • The original question was making a comparison between a gas-powered power station and a coal-powered power station, the former apparently not having cooling towers whereas the latter had.


    Could it be that the gas-powered station is using some sort of combined-cycle system and it does have cooling towers but that they don't look like the conventional, waisted concrete structures that dominated coal-powered power station sites and BBC climate change reporting?


    As a non-power engineer my thinking would be that a) gas-powered stations are typically of lower output than coal-powered, and b) combined-cycle gives higher efficiency so there isn't as much low-grade heat to dump anyway. These two factors would lead to a smaller and different design for extracting the waste heat.


    The Musandam Independent Power Project in Oman,  for instance, is rated at (only) 120 MW - " The facility uses 15 Wärtsilä 34DF dual-fuel gas-powered engines with the ability to switch to light fuel oil. The engines are designed to operate in high-temperature environments; temperatures in the region often top 120F. The plant also uses minimal water for cooling, an important consideration in the arid region. "
    5d1dcafcf63a678a0ccaebadb4abc8a6-huge-2l-image-musandam.jpg

    (credit: Wärtsilä)
  • Hi Guys - I get the picture now.  Power stations in deserts that run on gas are highly efficient and have no water supply, so condense.  Coal stations are near the coal supply and use local water eg Nottingham and Derby.  Nuclear power stations use the sea for cooling.  Greenpeace use the photos of the cooling towers because they look dramatic, but are unfortunately misleading, so counterproductive.


    Have I got that right?


    Stephen

  • Have I got that right?




    Well, yes and no. Power stations using local water are also made to be as efficient as possible so efficiency of the power station is probably a red herring here. It is the supply of water for cooling that is the issue. I think that the major difference is going to be the machinery installed. The Oman power station mentioned by James uses diesel engines (i.e. internal combustion engines running on the diesel cycle - not necessarily engines burning diesel fuel) while the coal burning power stations all operate with steam turbines (on the basis that you can't burn lumps of coal in a diesel cylinder...). The efficiency of diesel engines is slightly better than steam turbines, but when the steam turbine power station provides local heating it can have the edge.

    The big difference between these is the cooling water for a diesel engine should be entering the engine cooling system at around 60-65 degrees Celsius, while for a steam turbine condenser you are aiming to get about a 90% vacuum and want the cooling water to be entering at 30 degrees Celsius or less. As we in Britain switch from coal to gas you will likely see a switch from steam turbines to dual fuel diesel engines and a similar switch away from cooling towers.

    Alasdair

    (Please note the above figures are quoted from memory so if anyone wishes to challenge or correct them, please feel free)

  • Stephen,


    Seems like a fair summary to me, but then I'm not a power engineer.


    Back in my student days I visited Ratcliffe-on-Soar, one of those Trent valley power stations that I think you have in mind. It had four 500 MW steam turbines and four 17.5 MW gas turbines for 'peak clipping'. It had eight cooling towers which dominated the site, despite the flue stack being taller, (but a lot smaller in diameter). Such a power station has more than sixteen times the output than somewhere like Musandam but perhaps a thermal efficiency of 40% against 60%. That would imply that R-o-S has to dump 3,000 MW of waste heat (up the flue and via the cooling towers) and Musandam only 80 MW, which given the absence of a nearby cold river and the high ambient air temperatures might be no mean feat. [Note, these are my estimates, If anyone knows better feel free to comment.]
  • This is the power plant I was working at in Oman.  It was built by the Chinese and I'm told it used gas powered steam turbines

    https://www.power-technology.com/projects/ibri-independent-power-project/


    Stephen