Flash tank Design

[zamu2010]

Hi Folks,
I have to design a flash tank for the discharge stream of a Reactor. The reactor is operating at 4. 78 bar a amd the flast tank is supposed to be operated at 0.8 bar a. My concerns are;
-Do I need to create vaccum in the flast tank? Why and how?
-Would it more logical to flast the stream in 2 steps. First at 2 bar a and then 0.8 bar a. Any recomendation?

Thanks in advance for your comments on the issue.
Best Regards
ZAMU

 

[Latexman]

0.8 bara is below atmospheric pressure, so yes, a vacuum must be created. How? One way is to pull the vapor fraction flashed from the flash tank through a condenser. The non-condensable gases that exit the condenser go into a vacuum pump and exit to atmosphere. You may have to have a treatment system somewhere in the process to emit the gases safely to atmosphere. The gases must be compatible with the vacuum pump (and it's internals/fluids for reliable, long-term operations.

Good luck,
Latexman

 

[zamu2010]

Hi Lateman,
Thanks for our reply.
I presume a liquid ring pump will work in this case.
Just a bit concerned if it would be possible to maintain that vaccum the whole time... (never dealt with flash tanks before)
What about if the flashing is done in 2 steaps. Any energy saving constrants???
Best Regards
Zahid

 

[rmw]

Your condenser will determine the vacuum. The liquid ring will just remove non condensables.

rmw

 

[zamu2010]

Thanks for your reply rmw.
I am afriad i did got yout point.
Does the flash tank should have a condenser to creat vaccum?
We are flashing the stream (from 5 bar a to 0.8 bar a) to recover some low pressure steam to be used for other consumers.
The intension is not to use condensor to recover heat.
Does it make sense??
Thanks for your reply....

 

[whammett]

Listen to RMW. And liquid ring compressors would not be the way to go. They are relatively expensive, hard to work with, and mainly just used in vapor recovery service.

The easiest way to do it would to have a venturi tube or nozzle directly after an air injection site(utility air should work fine, especially for the pressures you are describing), leading to the condenser. It will create higher pressures at the nozzle "pulling" the pressure from the condenser reciever. The steam collasing into condensate will also help to create a vacuum. This should set you on the right track.

Cheers.


Will Chevron Corp.

 

[zamu2010]

Hi Whammett,
Thank you very much for your reply.
The flash stream is low pressure steam and I wanna use it for some other consumers. Not really interested in condensing it.
What's about a steam ejector?
thanks in advance for your reply..

 

[bimr]

Here is a link to assist you in designing a flash tank.

http://www.shipcopumps.com/literature/download.asp?d=Misc&f=MLIT_SKFT_FlashTanks.pdf

Flash tanks are typically operated at 5 psig.

http://www.armstronginternational.com/files/common/allproductscatalog/flashrecovery.pdf