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How is this Bio-mass power plant plausible?

  1. May 27, 2009 #1
    How is this Bio-mass [basicaly just a steam power plant] power plant plausible?

    It says it is going to supply 29 MW of electricity by burning biomass to heat some fluid (I suppose an ammonia-water mixture, but I really do not know) and turn a turbine (Something like a Rankine cycle I guess). It also says that is will use two boilers capable of consuming 150 tons a day while getting 5200 btu/lb.

    29MW*1 day=2.51*10^12 J.

    Now, if they turned 100% of that heat energy into mechanical and then electric energy without loss, it would only come out to 3.43*10^12 J/day.

    They are claiming they will get this thing to 73% efficency. The problem is, even a carnot engine would need to operate with a temperture difference of around 850 C to achieve this, and since they have no chance of making a system that can match a carnot engine, I would imagine they would really need something like a 1400 C difference.

    Isnt that above the creep value of anything they could make the turbines out of?

    What am I doing wrong?
  2. jcsd
  3. May 27, 2009 #2


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    I agree with your calculation, it seems a little suspicious.
  4. May 27, 2009 #3
    All the documentation I have seen is really only in the conceptual phase, but the company that submitted it to us to make a bid on it (They want approximate costs of construction so they can start trying to sell it) has already looked like they put a fair amount of work into it (made some isometric drawings and whatnot), which makes me hesitant to think they missed something so basic.

    Anyways, I am just an intern, so I wanted to get someone elses input before I asked my boss about this, no reaosn to look like a complete fool on my first week!
  5. May 27, 2009 #4


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    :smile: well... I hope someone else responds to check this because I also think it's rather surprising that they would have missed something basic like that. Unless they are trying to pull a fast one on your company. And if they are, imagine how much your superiors would love you if you call them on it and save the company from entering into an impossible project ;-) (although I guess it'd be the kind of thing you'd want to bring up discreetly first)
  6. May 27, 2009 #5
    Coal-fired power plants (500 - 1000 MW) are roughly 33 - 35% efficient; about 10,000 btu per kilowatt-hour. Gas-fired power plants may be as good as 8,000 btu per kilowatt-hour (40 - 42% efficient).
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