There is a very reliable relationship between the temperature and pressure of pure saturated steam; reliable values of which can be found in steam tables.

The vacuum pumps are to remove noncondensable gasses so that the above relationship will be the dominant one.

Yes, condensing stream (and the absence of noncondensable gasses or leaks) is essentially what is creating the vacuum.

Dear sir,

can u give a clear explanation how condensing the steam leads to vacuum creation...

It's all in a set of Steam Tables.

If you have a certain mass of saturated steam filling a container that maintains constant volume and you remove all the steam without anything replacing it, you can understand that you would have a high vacuum in the container, correct?

If you just remove half the steam from the volume, then can you see that internal pressure would be reduced below the pressure before any steam had been removed?

When the steam is condensed to liquid water it then occupies far, far less space and the condensate pump works to make sure the liquid does not build up, so in essence condensed steam removes material from the area above the condensate in the condenser.

The volume is relatively fixed, and if you use the assumption of mass of steam from the turbine being about equal to the mass of condensate pumped, then you might more easily understand how vacuum is maintained by condensing steam.

I hope that in your case, the water vapour is coming from a generator and condensed in the condenser with cooling water. At a constant steam flow and constant steam temperature in and cooling water in temperature and flow, pressure is decided by heat transfer equilibrium. Let us say the cooling water temperature increased, while all the parameters are constant. Now the LMTD in condenser resulting less heat transfer. To maintain the heat transfer equilibrium, the pressure will automatically increases(Latent heat will be less at higher pressure). Similar phenomenon occurs in the case of cooling water flow decrease.

Coming to your question whether steam creates vacuum in condenser, the initial vacuum is created by the vacuum pump and later it is maintained by the heatflow equilibrium.

Anybody have a different opinon, I welcome the comments

The lower the condenser pressure the more efficient will be the turbine. Imagine it as the condenser "sucking" the expanded steam out of the back end of the turbine, thereby obtaining more shaft work from it.

The saturation pressure of H₂O at a cooling water temperature of 40degC is about 74mBara, which is the lowest achievable condenser pressure at that temperature; in practice the pressure will be higher than this so that the condenser can remove the heat. The figure at 30degC is 42mBara [Reference: Mayhew & Rogers, "Thermodynamic and Transport Properties of Fluids", 1976].

If a stronger vacuum is needed than what is currently being obtained then there are only two possibilities:

1. stop the leak of non-condensibles such as air into the condenser, or
2. lower the cooling water temperature.

Something has changed since the installation was commissioned.

Recommendations:

1. concentrate on fixing the leaks in the condenser steam-side
2. make sure the condenser cooling water circuit isn't fouled and clean it if it is
3. make sure the condenser is correctly sized for the job. Is someone "pushing" the turbine beyond its design operating point, for example, and the condenser isn't up to it?
4. make sure the cooling tower equipment is correctly sized for the condenser and whatever else has been added to it since it was installed. Are the flows through the condenser too low? If so, find out why, and sort it out.
5. concentrate on the cooling tower water loop chemical treatment to make sure that everything is as it should be and there is no tendency for crud formation in the circuit, particularly the heat exchange surfaces in the condenser
6. focus on the cooling tower blowdown equipment and make-up water, and make sure everything is as it should be.

Then re-post with the findings.

Dear Mr. SriRam Sandip,

You have raised issue which relates to Design Aspect and when ever the Design Parameters are deviated, we cannot achieve the result. I am assuming that there is NO EXTERNAL AIR LEAKAGE and based on that I furnish the reply as follows.

1. The condenser is basically a HEAT EXCHANGER - involving the philosophy HEAT LOST BY STEAM = HEAT GAINED BY CIRCULATING WATER, represented by the Equation W x L = Q x (Tout-Tin) where W = QUANTITY OF STEAM FLOW/Hr. and L = LATENT HEAT of Steam to the condenser, Q = quantity of water circulated/Hr. and Tout = Outlet Temp. of Water, Tin = Temp. of Inlet water.

Heat is removed from the steam to the condenser, and this heat is absorbed by the circulating water, asper the above Equation. CONDENSING ALSO WILL CREATE VACCUUM.

Again, the heat absorption by water depends upon, the rate of circulation of water and the inlet temperature of the water. If the inlet water temp. is higher than the required/design value, the temp.gradient for Heat Transfer is disturbed and the LOG MEAN TEMPERATURE is affected and due to less condensation of steam, the vaccuum will drop, and vise versa.

2. Regarding the Ejector - Yes, the Ejector will remove the NON-CONDENSIBLE GASES ONLY and water cannot condense it. If external air-leakge is found, then the ejector has to do extra work, but it cannot. Hence vaccuum will fall.

DHAYANANDHAN.S

Dear dhayanandhan sir,

firstly thank you very much for giving reply to my thread. I came to understand almost 75% through your feedback. According to you" condensing the steam leads to vacuum creation". Can u give me a clear explanation about this....how does condensing steam leads to vacuum.

#7↑.

Dear Mr. SriRam Sandeep,

I can answer your question.

But,Please Note that CR4 FORUM is a forum to exchange ideas, share experience, and seek advise for a problem from the learned CR4 MEMBERS.

If you take the Standard Text Books on THERMODYNAMICS, you will find good explanations how steam is formed, vaccum is created. Please attempt to read by yourself about the fundamentals.

Now coming to your questin - HOW CONDENSING OF STEAM RESULTS IN CREATING VACCUUM, is as follows.

When the steam is condensing, it is transferring its latent heat to the cooling medium instantly - the volume of steam is reduced to 1/1600 th of its Volume. i.e., suppose 1 Kg. of steam at Zero Pressure absolute occupies 1600 M^3.

On condensing the volume condensate is 1 M^3 only and hence 1600-1 = 1599 M^3 is VANISHED by CONDENSATION, and thus vaccuum is created.

Non-condensible gases to be removed by Ejectors.

any doubt pl. put mail through CR4 LINK as personal mails etc. is not allowed as per CR4 FORUM RULES.

DHAYANANDHAN.S