What really goes on inside a coal power station?

The recent demolition of the Athlone power station cooling towers sparked some discussion around coal power. I was very surprised to learn that very few people actually understand the inner workings of a coal power plant, and even fewer really understand the relationship to carbon emissions. Perhaps those of us in the renewable energy industry take these things for granted? So this month I want to try to provide an uncomplicated description of what is actually going on inside one of these filthy giants.

I think the best place to start is with the generator. You are likely to be imagining that dirty diesel generator sitting next to the dam on your uncle’s farm, but this is only one form of an electric generator. A generator is a device which converts mechanical energy to electrical energy. In other words it converts movement into electricity. The process is relatively simple, but let’s leave the technicalities out for now. Think of it as the opposite of an electric motor, similar to the one in your lawnmower. You put electricity in your lawnmower and the resulting output is movement, or rotation, of the blades. A power generator works due to the very same principle, however the other way around – you put rotation in and electricity comes out.

So, all you need to produce electricity is the rotation of a shaft in a generator. This can be done in a variety of ways. The diesel generator at your uncle’s farm uses the combustion of fuel (diesel) inside an engine to provide rotation, much like an engine turns the wheels of your car. The flow of water in a river can do the same, i.e. hydro power. Or wind can turn the blades of a wind turbine, and so forth. There is another way of doing it though – with steam.

If you create steam and try to contain it, pressure will build up inside the container. This pressure can be harnessed to provide mechanical energy. Think of a steam train – coal is burned to create steam which provides the necessary energy to move the wheels. This is, in principle, exactly how coal power stations produce electricity. Coal is burned in a furnace to heat water which creates steam. This steam is then forced through turbine blades to rotate a shaft in the generator, which generates electricity. Electricity is produced in the very same way at a nuclear power station, however there they are using heat from nuclear reactions to produce steam. So you can see that the mechanism of electricity generation in many technologies is essentially the same. The main difference lies in the source of the required mechanical energy, or the fuel.

Coal is primarily made up of carbon, the element central to all life on earth. All living things, including the plants in your garden, are forms of carbon-based life. Plants absorb carbon dioxide from the air and use it to grow. The carbon then forms part of the plant until it dies and decomposes, at which point the carbon is released back into the environment ( keep a look out for an upcoming article on the “Carbon Cycle”). To make coal all we need is lots of dead carbon-based things and we need to compress them under very high pressures for a very long time. The carbon then becomes concentrated into a very effective fuel. The problem is that when it is burnt, all the carbon is released again in the form of carbon dioxide.

Now I can imagine you’re thinking that since the carbon was part of the system in the first place, it shouldn’t be a problem when it is released back into the system? The problem here is down to time. One lump of coal comprises carbon from hundreds of thousands of plants. Our coal reserves are a result of millions of years of accumulated organic material. If we burnt the coal as slowly as it was formed, there wouldn’t be any problem. The problem is that we releasing large amounts of carbon in a very short period of time by burning millions of plants in an instant. This in turn leads to the increase of carbon dioxide in our atmosphere, which of course, leads to global warming.

These are both very straightforward descriptions of electricity production, as well as global warming, hopefully providing a basic understanding of the fundamental principles.

The bottom line here is that not only is the combustion of coal bad for the environment, it is going to eventually run out. So, the more ways we can find to turn shafts in generators without burning coal, the better. May I ask that my fellow engineers/scientists humour my overly colloquial descriptions and analogies in this article. Anyone requiring more detailed information is welcome to contact me.

Gary Fahy (gary@90×2030.org.za)

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5 responses to “What really goes on inside a coal power station?

  1. I blog occasionally at news24 and my blog is called Miss Cellany.

    Re the above blog I have a question or two. Firstly both carbon and nuclear make use of steam which implies that water also has to be present. Where does the water come from? Secondly and I’m only assuming this is so as you don’t mention steam in the case of wind. Why does the world not make more use of wind or wave driven energy which are natural resources? Thirdly if as many scientists believe the universe never mind our world evolved and had no originator why do scientists actually believe that man can control climate change? I believe climate change has been happening since the beginning of time in cycles controlled by something/one greater than man – a force of some kind lets call it. Aren’t we actually kidding ourselves when we think that man is greater than whatever force led to the evolution of our planet? We may be able to limit the damage mankind specifically has caused but we are a long way from being able to control natural forces/energy to the point where life on this planet can continue to expand in size requiring ever more control mechanisms. Dis ease is a natural controller which man has attempted to overcome with varying success which has lead to dwindling resources because there is too much life requiring water and food. What man should be doing is controlling the numbers of lifeforms and specifically his own to limit the call for power and water which is essential to all life. Knowledge is said to be power by man but is it really? An interesting blog.

  2. Thanks for your comments Gail. I must disagree with you though, I believe that man can control climate change – as we are the ones who were responsble for it. Yes, the earth has natural cycles but the problem comes in when humans, through the burning of fossil fuels, radically accelerate these processes. Before the industrial revolution the concentration of CO2 in the atmosphere was 280ppm, today it sits at 380ppm. In the last 20 years alone CO2 concentrations have increased by 20ppm! Also I think it is more important to concentrate on the consumption habits of people rather that ultimate numbers.

  3. Gail,

    I must confess I am a little confused by your comments, since they are in response to an article about the operation of a coal power station. Nevertheless, it’s a Friday afternoon and I don’t feel like working, so let me respond.

    I assume you mean “coal” rather than “carbon” in your first statement. Yes, your assumption is correct. We would need water to create steam, since steam is water, just in a gaseous state. I assumed this would have been intuitive, however it appears not. The source of the water will vary depending on the location of the power station, but it would typically be either from the ocean or a river.

    With regards to your question why the world does not make more use of wind and wave energy? This is the message we here at Project 90×2030 are trying to get across. The answer to this is not simple and the subject of much debate. The quick response is simply a matter of cost. Coal power is typically cheaper.

    I must admit, your comments get more and more strange as I read on. We (man) are not “controlling” the climate. It’s a cause and effect relationship, whereby our actions can influence factors which affect the climate. Our climate is a result of a vast interconnected web of geological events, the movements of the earth around the sun, the constituents of our atmosphere, ocean currents, vegetation and the amount of ice on the earth’s surface to name a few. As far as I know, no scientist have ever claimed that man controls the climate. Although I have seen a few movies in which this is the case.

    Your comment about disease has left me baffled. Although I think you mean something like disease is the earth’s way to control population growth, and that we have found ways to cure disease which has led to diminished resources? Can the same then be said for any form of human advancement? We now have operating theatres where we can perform life saving surgeries on people that have, for example, been in a car accident or stabbed by a burglar. Is modern medicine therefore responsible for overpopulation and shortage of natural resources? Is it not perhaps more sensible to try encourage people to make more efficient use of what we have, and to supply energy and food in more sustainable and environmentally sensitive ways, instead of allowing disease (like HIV AIDS) to wipe out half our population so that there is more water and food? let’s not forget about the problem of supporting and educating children who have been orphaned by disease. Anyway, we are drifting off the topic here a bit….

    If possible, could you elaborate a little on your last comment? Are you suggesting knowledge is not power? I am intrigued.

  4. Pingback: Project 90 By 2030 | Babazeka blog

  5. Cooling towers may either use the evaporation of water to remove process heat and cool the working fluid to near the wet-bulb air temperature or, in the case of closed circuit dry cooling towers, rely solely on air to cool the working fluid to near the dry-bulb air temperature.

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