8 replies to this topic

[RDENG]

Hi!

 

I'm trying to understand the fundamentals of distillation condenser duty control and I'm looking for your assistance for it. Thanks in advance!

 

I'm thinking of very simple and common control merhod for column pressure control shown in attachment (total condenser, atmospheric column, vent released to atmosphere, no control in CW flow).  Question is: what is controlling condenser duty in this method?

 

Lets assume that we have this column operating at 50 % capacity, so also the condenser duty is at 50 % capacity and the pressure remains constant. When we increase duty to 100 % also the condenser duty must increase to 100 % to keep column pressure at the setpoint. Cooling water flow is not increased. Increased vapor load is not diverted to vent. So what changes and causes increased condensing duty? Reduced inert concentration in condenser?

 

Regards,

 

 

Attached Files

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[Pilesar]

If you have a total condenser, there is no duty control. The duty varies as the feed varies. As long as you have enough exchanger capacity and cooling utility flow, all the feed is condensed. The heat transfer coefficient is greatest on the exchanger surface where the vapor changes to liquid. Any extra surface area beyond what is necessary to condense the feed is available as reserve.

 

As an imperfect analogy, think of hot vapor bubbling into a pool of water... what controls the duty? As long as there is enough water, the vapor will cool to approach the temperature of the water. Your atmospheric condenser is similar except there is a thin piece of metal between the water and the hot vapor feed.

[Nikolay_]

Partial condenser is on your drawing. To set pressure in the column the control valve on vent line is needed.

[Nikolay_]

For total condenser find "Troubleshooting a Hot Vapor Bypass Control Instability"  Henry Z. Kister, Daryl W. Hanson. Hope it helps.

[breizh]

HI ,

You may find hints in the doc attached .

Good luck

Breizh 

[breizh]

Hi,

A more general paper about Distillation column control .

Good luck

Breizh 

[RDENG]

Thank you all for your replies! Let me just challenge a bit of your views for better understanding.

PILESAR: "As long as you have enough exchanger capacity and cooling utility flow, all the feed is condensed... ... Any extra surface area beyond what is necessary to condense the feed is available as reserve." Is it really that simple? Ain't it so that condenser is always full of vapor and condensing rate determines the inlet flow (condensing reduces pressure and sucks more inlet vapor). There must be some effect that adjusts condensing rate automaticly?

Nikolai T: you're rigth that valve in vent line is needed if we wan't to set the pressure different than atmospheric. In my understanding small vent is needed almost always to remove non-condensables.

Regards,

[breizh]

Hi,

Another good reference about Distillation control .

Enjoy the reading

Breizh 

[RDENG]

Thanks Breizh for the shared documents!

 

I found some discussion close to this in a very good topic ("vacuum condenser configuration"):

https://www.cheresou...-configuration/

 

In this topic Katmar mentions that condenser duties are self-adjusting, but the working principle is not mentioned in detail. Please help me understand this phenomenon.

 

BR, RDENG