In my power plant we face problem in the vacuum in the summer time.

I know the steam ejector is respansable about maintane the back pressure in the cool condser [mods note condenser, I think] & the vacuum area.

the qustion is How I can adjust the steam ejector and get back in the service?

 

vacuum in condenser is not only maintained by steam jet ejector, but cooling water entering into condenser has significant.

also, does your plant cooling water inlet is maintained as per design conditions, check for terminal temperature difference across condenser.

also, what is type of steam turbine in your plant, extraction cum condensing or fully condensing? what load it maintains base load or part load?

 

GT man is correct; as steam condenses the volume is greatly reduced and this by itself is responsible for most of the vacuum created in the condenser. (I find this concept of condensing steam creating a vacuum very confusing to most people. Think about it as the opposite of what happens when water is converted to steam. As water is boiled and converted to steam, it's volume increases greatly and it's this volume increase that creates the pressure in the system. Once most of that pressure has been removed from the steam in the steam turbine, the final act of steam returning to water creates a "negative" pressure, or, a vacuum.)

Steam is used as the "motive" medium for the <b>air</b> ejectors, which are used to "raise" (initiate) vacuum when starting the steam turbine, but then to remove air and non-condensable gases from the condenser when the steam turbine is operating.

"Air and non-condensable gases?" you say; "How do they get into the condenser? It's a closed-loop system!"

Packing leaks; air (and other gases) entrained in solution in the feedwater; leaking joints; porous castings are the major sources of air in the condenser.

The (steam) air ejectors cannot maintain vacuum during normal operation; they just don't have the volume capability to be able to do so. When there is little or no steam condensing during starting, they are capable of initiating or maintaining vacuum but once more steam moves through the turbine the air ejectors only really contribute to vacuum by removing air and non-condensable gases.

Air decreases the efficiency of the condenser, greatly, and it must be removed and not allowed to accumulate. That is the primary function of any <b>air</b> ejector, be it a steam-driven air ejector, or an electric motor-driven air ejector pump.

But, again, the primary contributor to vacuum is cooling water (sometimes called circulating water) temperature, along with tube cleanliness. In hot climes, if circulating water temperature is not maintained then the ability to condense steam is reduced.

Steam air ejectors also have condensers, and they also rely on the temperature of the water running through them to operate efficiently. Some sites use hotwell condensate as the cooling medium for air ejector condensers.

Look at plots of condenser cooling water (circulating water) temperature over the year, during cooler ambients and hotter ambients. Also look at condensate temperature if that's what's being used in the air ejector condensers. If the cooling water temperature in the main condenser is high, then the condensate temperature will also likely be higher and that will have an effect on air ejector efficiency.

It's all relative. But, as GT man says, (steam) <b>air</b> ejectors (which are typically used to raise or initiate vacuum in a condenser during starting) are primarily only there during normal operation to remove air and non-condensable gases. The temperature of the water entering the condenser tube nests has the greatest effect on vacuum, presuming there are no air leaks in the condenser, packing, piping joints, etc., and that the air ejectors are working at or near design efficiency to remove any "naturally-occurring" air and non-condensable gases.

When a steam turbine is running one can shut off the air ejector for a short period of time and condenser vacuum will not decrease greatly until the air and non-condensable gases start to accumulate. (This is not for the faint of heart.)

 

why the condenser has been maintained in negative pressure?

 

I have not seen a more thorough, comprehensive description of a steam turbine condensing system (with all the little nuances). Very, very good!

 

View the replies by GTman and CSA--

In the summer, your cooling water temps are much higher, so they have less ability to cool the exhaust steam, increasing condenser backpressure. The steam jet air ejector only removes the non-condensable gases from the main condenser, thus helping to MAINTAIN vacuum--not create it.

if you are experiencing this lower vacuum as a function of ambient temps (a small change is normal-maybe as much as 1" backpressure increase).

If this is a year-'round problem, you may have issue with condenser tube fouling. what is the chemistry of your cooling water? - saline, brackish, etc.? When was the last time the water boxes were inspected/cleaned?