level positioning in a seperator

[oyebaba]

l am working on a three phase separator and having determined the critical velocity and other parameters,l will like to know how the various levels are determined during the design of a three phase separator and the effect of inappropriate level control positioning .

 

[gr2vessels]

oyebaba,
first drain the vessel before flooding it, size the demister to remove the airborne droplets and contaminants without choking the flow, use an inlet distributor for the initial gas and liquid separation. The levels are determined by the inlet flow and therefore by the size of your vessels. I believe that you already know all this. If you don't do all the above, your gas flow will carry over to much droplets and the demister will be flooded and the pressure drop will force the droplets to be dispersed downstream of the demister. If your vessel is not tall enough, to allow separation height, you won't achieve the desired separation. The design of these vessels is described in great detail, including the free downloads on the internet. As you said, the critical velocities allows you to size the vessel, the rest is your mechanical engineers job to make it happen.
All this is good, however, every fabricator of these separators, knock-out vessels, drums have their own guaranteed software to design and produce guaranteed process vessels. Do you really think you'll out-perform their experience and design a better separator (minus guarantees) than them?
Anyway, good luck to you.
cheers,
gr2vessels

 

[dcasto]

The levels are based on residence time or surge time needed to smooth out the process.

Residence time is "How long does it take to allow the the gas to break out of solution and/or how long does it take to allow the water and oil to break any emulsion". So if it takes 5 minutes and the oil is coming in at 100 bbls/hr, then 5/60*100= 5 bbls of level.

Surge time is "If the down stream can only handle 100 bbl/hr and the oil comes in at a peak rate of 130 bbls/hr for 10 minutes, then you need to store (130-100) = 30 bbls/hr over 10 minutes therefore 30 /60 *10 = 5 bbls of level." Of course the oil would slowdown to 7o bbls/hr for a while.