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Steve Beck

Energy obtained from a Steam Power

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The term "steam power plant" usually refers today to an electric generating plant driven by a steam turbine supplied by a boiler.

DrD

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The answers you get to this question may not be what you're looking for. "Extraction" has a definite meaning in the context of steam turbines. In a Rankine cycle with regenerative heating, steam is bled off the turbine at various stages and directed to feedwater heaters, which raise the temperature of the compressed liquid upward toward the inlet of the boiler, as with an economizer. This actually decreases the power output of the steam turbine, but it increases the efficiency of the overall process. This is often illustrated in textbooks, showing that the regenerative Rankine cycle is more rectangular (closer to Carnot in shape) and generates less entropy for the same work output; thus, the increase in efficiency. You must distinguish between extracting steam (i.e., a mass flow rate) and extracting power (i.e., an energy flow rate). I suspect you mean to ask, "is is possible to get more power out of a steam turbine? (with the same input)" While the answer to this question is technically, "yes," that doesn't mean it is practical to do so or that anyone has figured out how. I have been asked many times why we don't just build more efficient machines or just increase the efficiency to 100% so that there will be no waste heat? Many smart and resourceful people have been trying to do just that for a very long time. The big bad oil companies don't have a secret carburetor that would get 500 miles per gallon locked away in a safe in Switzerland so that they can gouge motorists at the pump. Humanity has accomplished many remarkable things, which is good reason to keep on trying to do better. Before we can do better, we must understand what has already been done--then try to improve upon it. This has always been the challenge for the next generation. The expression "standing on the shoulders of giants" is applicable in this case. You need to read Ken Cotton's book, "Evaluating and Improving the Performance of Steam Turbines." It's expensive, but well worth it. Ken Cotton was very influential in the development of the modern steam turbine and one such giant.

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You misunderstand the principle. Whether some working fluid is hot or cold compared to what humans consider normal atmospheric conditions isn't what determines whether or not a device is efficient. When I taught thermodynamics at university, I would always give a test question regarding a cup of coffee cooling to room temperature or a can of beer warming to room temperature. Both generate entropy (dS>0). I work out this example in my book, Thermodynamics. There are several reasons we build power plants using steam instead of air as the working fluid. The latent heat is a very important part of this. Water and ammonia have two of the largest latent heats of any substance known. This is why ammonia was used in refrigeration for decades, even into the 1990s and beyond at some skating rinks and commercial facilities. Another reason is the HUGE difference in specific volume (V=1/density). For a flowing device, dW=VdP. The work required to pump liquid water up to 200 or more atmospheres is nothing compared to what it would cost to pump gaseous air up to that same pressure because of the difference in V. Expansion works in our favor too. The specific volume of steam at atmospheric temperature is significantly larger than air (compare molecular weights of 18 vs 29 and the ideal gas constant R/MW). With a large V, we get more power out of expanding steam than air.

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