Pressure Control of Liquid Filled Vessel

[dipbit]

I have a pressure vessel operating at about 250 kPag. Currently the pressure is being controlled by the water vapour that is flashed off. We are considering a process change whereby there will no longer be any vapour generated. If the vessel then operates as liquid filled, can the pressure be controlled by the discharge flow rate? Thanks.

 

[dcasto]

Well, indirectly yes. You will still control the pressure by measureing it and causeing a valve to open when the pressure is higher than set point. You will size the valve based on the expected flow rate out and the pressure difference between the set point and the outlet system pressure.

Trying to control pressure based on flow in versus flow out will not work.

 

[Xianglu]

You need vapour or gas surge volume to control the liquid pressure. Practically, you can have some N2 gas at the top of the vessel.

 

[dcasto]

You do not need vapor. A liquid full reflux drum on a total condensor is an example.

 

[dipbit]

So if I have a pressure transmitter on the vessel that sends its output to a control valve on the liquid discharge, I should be able to control pressure within that fully filled vessel?

 

[dcasto]

Yes you can.

 

[sv5676]

There are some other aspects of turning a pressure vessel handling liquid and vapor into a swole up piece of liquid filled pipe.

Is your energy source capable of overpressuring the vessel? If so, does your relief capacity measure up to relieving liquid as opposed to vapor?
Is your vessel capable of withstanding the higher velocity of pressure waves generated in water as opposed to steam?
Is your control source or exit valve capable of introducing conditions of hydraulic hammer?
Will a sudden and unyielding liquid presure wave cause problems at the seams of the vessel.

Yes, you can run the vessel liquid full but what are the consequences of changing the process going to do to the vessels integrity?

Also, the process of producing water vapor means you form bubbles on the surface of your vessel. If not this one then somewhere upstream. If you fill the vessel you are looking at liquid full, these bubbles might start collapsing at the vessel wall and cause surface cracking.

Some things to ponder........