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Another clean coal power idea

Discussion in 'The Pub' at netrider.net.au started by robsalvv, Nov 17, 2008.

  1. http://www.theaustralian.news.com.au/story/0,25197,24654074-11949,00.html


    Any of these CO2 capture ideas decreases the efficiency of coal powered stations because they need to produce the extra electricity to power the capturing process... BUT it's the necessry cost to capture CO2 if it is indeed the demon it's meant to be.

    You'd think a coal burning environment that's rich in oxygen would burn more efficiently producing less combustion byproducts...

    Any comments?

     
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  2. this is assuming they have very clean coal to start with?? Black coal that is?

    I know the problem we face in Victoria is we have 'brown' coal, the dirty s*** laced with other base elements (sulfur been the dominate nasty) that pollute the atmosphere in far worse ways. But from this capture idea I'm assuming (that dreaded A word) that all emissions would be captured and stored?
     
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  3. 'far more concentrated CO2'..... wtf?

    surely burning in O2 simply means there is more likelihood of complete combustion ie C+O2 --> CO2 rather than incomplete combustion resulting in CO plus all the other nasties
     
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  4. Interesting point Browny.

    The idea is only to capture the carbon, in the form of CO2. I guess the rest of the gases would go through scrubbers and then out to the environment. One of the other benefits I see from an oxygen rich environment is little to no NOx, which is smog pollutant and no CO.


    Victoria has a CO2 sequestration trial in the Otways and I understand Hazelwood power station is being sized up for a trial CO2 capture project. It's still early days.

    I guess clean coal is a bit of an oxymoron. You can capture most of the the CO2, which is good supposedly from the GHG point of view... but you'll have to burn more coal to do it... which means consuming more fossil fuels...
     
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  5. They are talking about Callide A. It's a very old plant and not very big. It really is just a test to get an idea about what will happen and the problems around it.

    Yes NOx will be low
    Yes it is black coal. It quite high in mineral content and quite abbrasive.
     
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  6. If I read it right it's not only the NOx they're talking about, but the sheer volume of waste gas. After all, the vast majority of the nitrogen doesn't burn at those temperatures, it just goes through as nitrogen gas, expanded because it's at a higher temperature. That means to extract the CO2 at the end you have to extract it from a large volume of gas which is mostly N2 (normal atmospheric nitrogen).

    Of course, I'm not sure of the energy savings if you have to extract pure O2 from air at the beginning of the process... but presumably if they consider it worth pursuing there must be some net gain with doing it that way rather than after combustion.
     
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  7. To answer this question is largely why they are doing it. there has been a debate in the industry for a long time time as to whether it will be more efficient or not to burn pure oxygen.

    I think the carbon capture part of this project is something they've tacked on in the last 12 months.
     
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  8. For me it opens up more questions than anything else…
    As you have mentioned Rob what is the efficiency drop for scrubbing.
    My follow up questions are
    How much is the energy expenditure to separate the oxygen and nitrogen?
    What is done with the nitrogen? Is it used, discarded, stored???
    Does this mean cheap NOS For All? :LOL:
     
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  9. Scrubbing isn't the inefficient bit.

    Cooling and compressing the adsorbed/absorbed/somehow seperated CO2 gas into liquid form for transport, is where the big biccies are... and they're big biccies in terms of power consumption.

    Taking N2 out of the combustion gases at the front end will mean that the flue gas will be concentrated so presumably driving up the gas recovery efficiency by some margin. Not sure whether this will reduce the size of plant and equipment needed to cool and compress.

    As for where to get it, well, Air Liquide are a gas supply company and they readily distill and fractionate air into it's various components. We have a plant just down the road here, but the size of the plant to feed the hungry boilers at a major power station would be collosal! The other commercial O2 production method is electrolysis of dilute sulphuric acid... but is much less popular.

    You could also electrolyse water or get it as a byproduct of quite a number of different chemical reactions...

    In the fractionating case, the nitrogen could be sold as a viable commercial product for welding (TIG/MIG) and other commercial consumable gas applications like in petrochemical plants.


    Not sure NOS would be a by product/side line business... but I'd like to see how the ZZR goes with a shot of the stuff. Just let me get my vid cam first OK :grin:
     
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  10. To give you an idea of quantities, a typical brown coal fired boiler of 500MW capacity will burn around 600 tonnes of coal an hour. Typical content is around 2-4 percent ash, and similar figures for sulphur, and 60% moisture content..

    SO2 emissions typically run around 30 milligrams a second out of flue gas. Flue gas emissions are around the 900 cubic metres/sec flow rate. Combustion air flow to give an excess O2 of around 1.5% is around 550 kg/sec.

    I am not sure how viable running a pure oxygen combustion environment would be on a brown coal boiler. Given the massive requirements of the stuff it'd be hideously expensive I'd guess.

    ie. what does a bottle of oxy cost for your welding set?

    I shall talk to the ginger beers who are involved in the ETS side of things about this.
     
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  11. paging jd :p
     
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  12. Old idea. Oxyfiring was proposed at least as far back as 2000 (probably well before) as a way to remove the energy intensive CO2 separation stage.

    The problem with this approach is that oxygen is expensive. A typical cryogenic air separation unit (ASU) uses ~300 kWh/tonne of oxygen produced. Then, you need excess oxygen because you don't want to emit tonnes of carbon monoxide (CO), and of course you need to vaporise the water in the coal. This becomes a lot of energy when you're trying to combust 600 tonnes/hour of coal, although I'm too lazy to do the sums to work out exactly how much.

    From memory, I think the operating costs comes out slightly more expensive on a dollars per kWh basis than post combustion capture.

    The other reason that the generators may be steering clear of this is that ASUs are very expensive, as they use cryogenic temperatures (~ minus 190 deg C) which means exotic materials. Handling oxygen in large quantities also introduces a whole new set of hazards that they wouldn't want to deal with - they'd all become major hazard facilities. Pure oxygen introduces a whole new way to light your plant on fire, because steel can burn in a pure oxygen environment.
     
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  13. Good point. Imagine a fuel leak with a high concentration of oxygen behind it. It'd be like a huge flare shooting out of the plant.
     
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  14. and the greenies complain about the wind turbines killing birds...
     
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  15. given the atrocious level of maintenance I've witnessed at power plants around Australia, the thought of firing on Oxygen is really quite scary.

    I'd like to know what they are physically doing at Callide A, because it was really, really run down.
     
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