Designing a High-Efficiency Steam Power Cycle: Tips and Cost Considerations

In summary: I have tried 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.
  • #1
emilynb
8
0
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!
 
Engineering news on Phys.org
  • #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?
 
  • #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, don't 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.
 
  • #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!
 
  • #5
emilynb said:
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...

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...
 
  • #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.
 
  • #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 that's 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:
 
  • #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.
 
  • #9
what computer program did you use in your calculations and how did u get it or download it?
 

1. What is a steam power cycle design?

A steam power cycle design is a thermodynamic process that converts heat energy into mechanical work by using water as the working fluid. It is commonly used in power plants to generate electricity.

2. What are the components of a steam power cycle?

The main components of a steam power cycle are a boiler, turbine, condenser, and pump. The boiler heats the water to produce steam, which is then used to turn the turbine. The turbine drives a generator to produce electricity. The steam is then condensed back into liquid form in the condenser and the pump circulates the water back to the boiler to repeat the cycle.

3. How is the efficiency of a steam power cycle determined?

The efficiency of a steam power cycle is determined by the Carnot efficiency, which is the maximum possible efficiency for a heat engine operating between two given temperatures. The actual efficiency of a steam power cycle is lower due to various losses, such as heat loss and friction.

4. What factors affect the performance of a steam power cycle?

The performance of a steam power cycle is affected by several factors, including the temperature and pressure of the steam, the type and efficiency of the turbine, the type and efficiency of the boiler, and the type and efficiency of the condenser. Other factors such as the quality of the working fluid and the maintenance of the components also play a role.

5. How can the efficiency of a steam power cycle be improved?

The efficiency of a steam power cycle can be improved by using higher temperature and pressure steam, improving the design and efficiency of the turbine, using more efficient boilers and condensers, and implementing better maintenance practices. Additionally, incorporating technologies such as cogeneration, which uses the waste heat from the power generation process, can also increase efficiency.

Similar threads

  • Engineering and Comp Sci Homework Help
Replies
1
Views
751
  • Engineering and Comp Sci Homework Help
Replies
1
Views
576
  • Engineering and Comp Sci Homework Help
Replies
4
Views
973
  • Mechanical Engineering
Replies
9
Views
477
  • Engineering and Comp Sci Homework Help
Replies
1
Views
469
Replies
1
Views
2K
  • Engineering and Comp Sci Homework Help
Replies
9
Views
2K
  • Engineering and Comp Sci Homework Help
Replies
8
Views
3K
  • Introductory Physics Homework Help
Replies
1
Views
2K
Replies
4
Views
3K
Back
Top