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Steam Power Cycle Design - please help!

  1. Oct 21, 2008 #1
    I am trying to come up with a design for a steam power cycle with a 40% thermal efficiency under the conditions that all turbines have isentropic efficiencies of 85% and all pumps have isentropic efficiencies of 60%.

    I have tried superheat, reheat, playing around with pressures/temperatures and having no luck. I also need to give a rough estimate on how much it would cost to build such a machine and I can't find anywhere that gives the cost of a steam turbine...

    Is there anyone who might be able to give me some advice on this subject? Perhaps something that I haven't thought of yet? I'm just looking for some ideas...

    Thank you for your help!
     
  2. jcsd
  3. Oct 23, 2008 #2
    40% efficiency is very high for a steam cycle. What temperature is your condenser cooling water? Can you lower that?

    Cost of a steam turbine - that depends of course on the size. Whats your system capacity supposed to be?
     
  4. Oct 23, 2008 #3
    Its difficult but possible. I have done it before but had the aid of a computer program to help me with the calculations. You just need to keep second law in mind. For example, transfer heat at the highest temperatures possible, reject as little heat as possible. Also, dont be suprised if you need to use many feed water heaters/reheaters. Just remember that adding FWH and the like obeys the laws of diminishing returns.
     
  5. Oct 23, 2008 #4
    I know - trust me - it is tough! What I have done so far is a superheat and reheat cycle. My maximum T is 950 degrees F and it works between the pressures of 1 psia and 2500 psia, with a reheat pressure of 400 psia. This gave me a cycle efficiency of 38% and this is the closest I've been. I've run it with numerous different numbers and couldn't get above that.

    I also have tried a superheat, reheat, and one open feedwater heater. Works between pressures of 1 psia and 2500 psia with regeneration pressure of 200 psia and reheats at 400 psia. The max temp on that was 950 degrees F. That was even worse, I got 30% cycle efficiency. I tried lowering the regeneration pressure to 40 psia and only got 33% cycle efficiency.

    I am having a tough time finding prices for the components also. It doesn't need to be exact, but a good estimation. I've found many websites that have turbines for sale, for example, but most of them say call for price and most of them are in Asia...

    Also, does anyone have any suggestions on how to determine the amount of piping I need? I know that the thermal resistance, Rth = deltaT/(Q/area)...works for heat exchangers, but what about the piping?

    I greatly appreciate everyone's help!
     
  6. Oct 23, 2008 #5
    Do you have to price all of the components? If this is an academic exercise, call the various vendors and tell them you're doing this for school - you don't need quoted prices but just ballpark estimates. And remember, you can't just ask "How much is a turbine?" - You need to be prepared to identify the power rating, and at least a few details. Otherwise, its like asking "how much does a house cost?" - the only answer is "somewhere between 10,000 and 100,000,000..."

    Big vendors might include Siemens, ABB, GE, Toshiba for the turbine & generator, TEI, Joseph Oats, or Foster Wheeler for the feedwater heaters and condenser, Ingersoll Rand/Flowserve for the pumps... Look on the internet for sales offices near you and call them. I think if you explain what you're up to they may be more helpful than you think. As long as you are prepared when you make the call. Don't forget, any time they spend talking to you is time away from their "real" customers.

    You could also try to find someone who works for a big A/E firm (Bechtel, Fluor, ...) Those guys build these plants for a living & if you can find the right person they could give you some thumbrules.

    Finally don't forget that the component cost is only one piece - there's the construction cost to put it together, the structure that supports all the equipment, the interest on the loan to borrow the money...
     
  7. Oct 23, 2008 #6
    The way the costing was described to me was like this: "How much does a new truck cost?" Which is more believable: $40,000 or $1? I just need my teacher to believe my cost estimates. This whole costing estimate part of the project is just a little over my head...a bit overwhelming if you will.

    Also, do you have any suggestions on how to determine how much piping I need?

    Thank you gmax137, I appreciate your help very much.
     
  8. Oct 26, 2008 #7
    I'm not to experienced in the pricing of such things but I do know that most of it is proprietary. The best advice I could give is just to call up such companies that supply the kind of piping your require or just do some RFQ online. A lot of times if you can get through to sales and just tell them your a student researching stuff for a project they will email you PDFs of pricing information.

    As for the length of pipiing, I don't know thats a good question. I suppose it ultimately depends on the layout of your plant and the amount of components you have. I would estimate maybe 300ft per component maybe. :confused:
     
  9. Oct 26, 2008 #8
    Call it $10 a pound. I'm serious, that would probably get you pretty close for steel piping, feedwater heaters, etc. Everything except things like turbines & pumps.
     
  10. Nov 10, 2008 #9
    what computer program did you use in your calculations and how did u get it or download it?
     
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