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One question regarding low pressure Condenser

Sunday, August 13, 2017   By: P I [1983] 3 Stars
At present, low pressure condensers are in use to enhance power generation in steam turbine based power plants and its often found that steam compressors are attached to them to suck out extra steam out of the Condenser to keep the pressure level inside stable.
What I want to know that what is more effective in terms of commercial aspect for such plants. A single condenser or multiple condensers with intercoolers. A single Condenser means huge power consumption and that may offset the power gain by the lowering of pressure at the Condenser. Multiple condensers fitted with intercoolers may decrease the power consumption drastically but can increase the cost dramatically and they are more complex to set and maintain.
As for example, if the pressure level at the Condenser is set at 2.536 kPa saturated steam pressure at 20°C, then it would take around 1.3 MW of power to make just 1 kg/sec steam flow In comparison, three compressors in series fitted with intercoolers can suck out around 2 kg/sec steam flow from 1.29 kPa pressure. But that means three times the cost and more complex system.
Those who have some real life experience in such matter kindly tell me which one is better in terms of real use.

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Monday, August 14, 2017   By: Murphy [21] 4 Stars
This question seems to have been answered over 2 centuries ago, but needs to be addressed from time to time. The basis of your question is rooted in economics for yesterdays local economies seem vastly different from todays global economy. But no matter what the local economy still drives the decision to install main condenser with auxiliary machinery such as steam powered air ejectors with after-condensers, inter-condenser and gland exhaust condensers versus using a after condenser with steam powered ejectors and even then electric motor powered are now installed. Even now who wouldve thought some 50 years ago that air cooled condensers would be a substitute for a large surface condenser.

Without a doubt condensers are very important sense the inventor, Mr. Watts, developed the Newcomen engine who finally installed a jet like condenser to improve his steam engine efficiency. In the two centuries since then reciprocating steam engines became equipped with main condensers and auxiliary condenser machinery to improve the functions of the main condenser efficiency. Those included air ejectors, after condenser, inter-condenser and gland exhaust condenser. The arrangements would be determined by the need to decrease the cost of operating the plant.

Might be worth noting that the primary function of an efficient condenser is the production of condensate from low-pressure steam and maintaining a production of condensate with efficient heat transfer. The secondary function of the condenser is the collection of condensate to conserve water. Sometimes a third function is specified such as an old term that is called vacuum dragging where the power of the vacuum in the main condenser is utilized in the facility or plant.

Global financing and a companys internal rate of return to finance the additional capital for auxiliary machinery versus fuel cost with lifecycle cost is showing in recent times that minimizing capital equipment and machinery is cost-effective versus the modest savings from installing and operating such capital equipment and machinery. This seems to be a trend. Also whats troubling is the life expectancy that is used in the feasibility study of a plant that would use such capital.

Im hoping that others will answer your question more directly but I think it would be hard to expect hard numbers. Good luck Murphy.

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Tuesday, August 15, 2017   By: P I [1983] 3 Stars
Can you tell me about the most efficient in terms of power consumption Cold below ambient level Condenser working at present?

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Wednesday, August 16, 2017   By: Murphy [21] 4 Stars
I cant, but high efficiencies tend to be driven by colder environments which are passed on to the low pressure condenser that pull greater vacuums as a result and of course lower hot well temperatures.

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Wednesday, August 16, 2017   By: Jim Watts [764] 5 Stars
Your question does not arise in the real world because the reason for using multi stage ejectors is because the maximum pressure ratio between suction obtainable on a single stage is 5 to 1.
This means two in series are required for most applications and three for for very low condenser pressure.
These devices are removing air and gases from the condenser and are not steam compressors.
A typical installation has a high capacity single stage ejector called a quick start or hogging ejector to raise vacuum quiickly and a two stage running ejector. The steam is condensed against condensate so no heat is lost.
Liquid ring vacuum pumps are often used instead of steam ejectors or in combination where depending on economics.

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Thursday, August 17, 2017   By: P I [1983] 3 Stars
I want to know whats the power consumption of the process. What I can understand is that by intercooling we can reduce power consumption. What I want to is to vent steam from that low pressure to atmospheric level with minimum power consumption. I specifically how much stages would be most economic in terms of power consumption.

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Thursday, August 17, 2017   By: Jim Watts [764] 5 Stars
There is no intercooler.
The condenser you are refering to is the first stage condenser the second stage ejector takes suction from.
Your interpretation of the process in a condensing turbine is extremely far from reality.

The most efficient way to get steam out of a condenser is as water or alternatively not to put it in there in the first place.
Such turbines are called back pressure turbines and are used at the very high process efficiencies you are dreaming of.

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Friday, August 18, 2017   By: P I [1983] 3 Stars
You have misunderstood what I want to mean. I have never mentioned anything about condensing steam turbine. What I have asked is for the best way to keep the pressure and temperature inside a Condenser lower with minimal energy cost for venting a part of the steam and non-condensables into atmosphere to keep the pressure inside at the desired level.

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Saturday, August 19, 2017   By: Jim Watts [764] 5 Stars
What percentage of the steam do you want to vent.
Ie How much is a part.

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Saturday, August 19, 2017   By: P I [1983] 3 Stars
Consider the container like an enclosed container with pumping system to pump the leftover water out. The pressure inside is 0.9 barA saturation temperature of water at 5°C. The external temperature is around 30°C and we have to vent steam from inside to atmospheric level @ 1 kg/sec.
I just want to know how can I do the job with the least amount of energy spent on compressors.

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Tuesday, August 22, 2017   By: Jim Watts [764] 5 Stars
I cannot bring myself to give further credibilty to the idea that steam is sucked out of a condenser using a steam compressor.
My biggest problem in answering was trying to think of a more ridiculous idea but I cannot.

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Tuesday, August 22, 2017   By: cmolanes@itba.edu.ar [50] 4 Stars
Hullo Jim!

I agree with you, there are several inconsistencies in the posting. Even the saturation temperatures and pressures are incompatible, since for 0.9 bar abs, saturation temperature, by heart I write the figure, should be around 90 C, and for 5C sat temp., pressures must be lower than 0,04 bar abs.

Regards

Claudio Molanes

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Wednesday, August 23, 2017   By: P I [1983] 3 Stars
I first want to apologise for the wrong information. Its 0.9 kPa, not 0.9 barA. Whatsoever, I have expected that it can be rectified by others. And I am not suggesting to set a single steam compressor and compressing the amount of steam and venting that into atmosphere. What I am suggesting is using a multi-stage system fitted with intercoolers.
A similar system has been used in OC-OTEC experiment http://www.otecnews.org/portal/otec-articles/ocean-thermal-energy-conversion-otec-by-l-a-vega-ph-d/#small-land-based and as per my calculations, the system can vent around 480 gm/sec from around the same level of pressure inside the Condenser. The power consumption is around 80 kW for the purpose.
What I have understood by reading the description that such systems can also be used in thermal power plants to keep pressure low inside the Condenser. And I just want to know whats the most efficient system available at present in this regards.

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Wednesday, August 23, 2017   By: Muphy [21] 4 Stars
Not sure if I can add to your discussion now. But precision of language may be needed since I ignored it earlier for I guessed you meant ejectors, steam powered, to pull a vacuum on a power generation surface condenser.

I can now say a thermo compressor is inefficient as an application for a surface condenser.
Attached are 2 bulletins from Schutte and koerting at s-k.com


steam_compressors.pdf

steam_jet_ejectors.pdf

Click on picture for full size view or to view PDF!

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Wednesday, August 23, 2017   By: P I [1983] 3 Stars
I know that. Thermocompressors were never in my mind from the very beginning. I have always meant mechanical compressors.

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Wednesday, August 23, 2017   By: Murphy [21] 4 Stars
Well then a mechanical compressor is reciprocating or what exactly to you mean?

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Thursday, August 24, 2017   By: P I [1983] 3 Stars
Not a single set of mechanical compressor, but rather a series of them fitted with intercoolers.

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Wednesday, August 23, 2017   By: Murphy [21] 4 Stars
Not sure if I can add to your discussion now. But precision of language may be needed since I ignored it earlier for I guessed you meant ejectors, steam powered, to pull a vacuum on a power generation surface condenser.

I can now say a thermo compressor is inefficient as an application for a surface condenser.
Attached are 2 bulletins from Schutte and koerting at s-k.com

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Thursday, August 24, 2017   By: Jim Watts [764] 5 Stars
The process in your reference is quite different to a thermal power plant condensing turbine.
The flash steam must be used somewhere and in this case the condenser heat balance is insufficient leaving steam which must be condensed at a higher temperature by compressing it.
The cost of compression is mass dependant so the compression is done in small stages with mass removed at each stage reducing the overall cost. The process also is desalinating water to justify its cost.

In the case of conventional power, all condensing is carried out before compression begins so only noncondensibles are involved. If cooling is limited the steam into the condenser is reduced.

The idea of expanding steam into a condensing turbine condenser and then compressing it out again is obviiously not a practical one in conventional power generation, multi stages with intercoolers or not..

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Friday, August 25, 2017   By: P I [1983] 3 Stars
You are right in your explanation but wrong in your assumption that I want to discuss condensing turbine here. What I want is to find out the best way to vent steam into atmospheric level with minimal power consumption. You are correct when you say that the cost of compression is mass dependant so the compression is done in small stages with mass removed at each stage reducing the overall cost. But what I want to know whats the most energy efficient system available for such purpose what would be the energy consumption for the system to vent steam into atmospheric level from 0.9 kPa to atmospheric level.

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Friday, August 25, 2017   By: Jim Watts [764] 5 Stars
Please reread all the comments in this thread until you understand that you have answered your own question and no one else has a better one from the practical world or the experiment would have used it.
If you think of repeating the question again try to ask about vacuum pumps not steam compressors as we use boilers for that.

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Friday, August 25, 2017   By: P I [1983] 3 Stars
What you are calling as vacuum pumps, is in fact steam compressors as they compress very low pressure steam to ambient level. Whatever we may call it, practically its the same. My question was what is the best in terms of power consumption system available at present for such process that I have described. I havent got any answer in this regards yet.
Kindly note that its not a theoretical discussion, but rather practical one.

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Friday, August 25, 2017   By: Jim Watts [764] 5 Stars
There is a pdf on this forum uploaded by me on tuesday 29 january 2013 wich goes in depth on this topic including costs and equipment used.

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Saturday, August 26, 2017   By: P I [1983] 3 Stars
Kindly reupload if its still intact in your hard disc.

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Sunday, August 27, 2017   By: Jim Watts [764] 5 Stars
Im working from my phone at present.

Just type Vacuum pump into the empty bar at the top of the page and press the find button to the right of it.
The eighth reference will be the thread st vacuum pump and contains your info

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