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cdotter
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Why is this done? Wikipedia says that condensing the steam makes the cycle 'more efficient.' How is it more efficient? Why can't the de-energized steam be transferred to the boiler without condensing it?
turbo said:The work done by the boiler (heat of vaporization) can be extracted elsewhere to take advantage of it. That's why steam-based industrial processes are so common. These extraction processes (such as turbines) may be made much more efficient by adding post-process condensers to the line, before returning the condensate to the boiler's feedwater system.
When the steam exits a turbine, it should still be a vapor, so that the end-stages of the turbine blades don't get eroded by contact with fast-moving liquid. This is enhanced by adding a condensation stage to the turbine discharge, so that the steam can remain in the vapor stage longer.cdotter said:Maybe I'm completely misunderstanding something.
When the 'steam' exits a turbine, is it still in the vapor phase, or is it a liquid?
gmax137 said:0. The steam exiting the turbine is steam (vapor) at very low pressure (like, below atmospheric pressure)
1. condensing the steam creates a vacuum on the downstream side of the turbine.
2. condensing the steam allows you to use a pump (rather than, say, a fan) to push it back into the boiler
3. (most important but hardest to understand) a thermal plant works by catching some of the energy as heat 'moves' from a hot place to a colder place. If you didn't condense the steam you wouldn't have a 'colder' place. Look up 'Carnot cycle' on Google/wiki
4. oddly enough, it does increase the efficiency (in the thermodynamic sense of the word, see 'Carnot cycle' above) to send some (but just some) of the steam back to the boiler (actually it is used to heat the liquid water before it goes into the boiler). Lookup 'Rankine cycle' and 'feedwater heater'
Although it appears as though a vacuum pulls the steam, there is no 'tension' in the steam.Lsos said:Condensing the steam also creates a vacuum, which "pulls" the steam through the turbine.
It takes much less work/energy to pump a given mass of liquid than would be to blow an amount of steam/vapor. The pumping also pressurizes and adds momentum to the liquid.cdotter said:Oops, I should have made my original post more clear.
I understand that passing steam through a turbine removes some of its energy. I wanted to know why thermal plants have a separate condenser after the turbine (eg, item #8 in this diagram http://en.wikipedia.org/wiki/File:PowerStation2.svg )
But you say it's simply to make the steam condensate easier to transfer back to the boiler?
Which would be incredibly expensive for a boiler/T-G set. That feedwater has to be demineralized, heated, treated with additives to inhibit corrosion and the production of precipitates, etc. Condensate is very valuable, and its loss would quickly make many steam systems uneconomical.gmax137 said:If you don't re-use the fluid (like say, in a jet engine) you can just blow the turbine exhaust to atmosphere.
Astronuc said:Although it appears as though a vacuum pulls the steam, there is no 'tension' in the steam.
cdotter said:Oops, I should have made my original post more clear.
I understand that passing steam through a turbine removes some of its energy. I wanted to know why thermal plants have a separate condenser after the turbine (eg, item #8 in this diagram http://en.wikipedia.org/wiki/File:PowerStation2.svg )
But you say it's simply to make the steam condensate easier to transfer back to the boiler?
Steam is condensed in a thermal power cycle because it is more efficient to use liquid water as a working fluid than steam. Condensing the steam back into liquid form allows for easier transport, storage, and use in the power generation process.
Steam is condensed in a thermal power cycle by using a condenser, which is a heat exchanger that cools the steam and turns it back into liquid form. This is typically done by circulating cool water through the condenser, which absorbs the heat from the steam and allows it to condense.
The energy released during steam condensation in a thermal power cycle is used to generate electricity. As the steam condenses, it releases heat energy which is used to turn a turbine and generate electricity. This process is known as a Rankine cycle.
Steam is condensed at low pressure in a thermal power cycle to increase the efficiency of the power generation process. By condensing the steam at low pressure, the temperature difference between the steam and the cooling water is increased, allowing for more efficient heat transfer and thus more electricity generation.
Condensing steam in a thermal power cycle has several environmental benefits. It reduces the amount of water used in the power generation process, as the condensed water is recycled back into the system. It also reduces the amount of greenhouse gases emitted, as the use of steam turbines produces less emissions compared to other forms of power generation. Additionally, condensing steam allows for more efficient use of fuel, reducing overall energy consumption and environmental impact.