Trim cooler Design (flooded condensers)

[imatasb]

Dear colleagues,

I am currently working in a project which includes a decrease in the operating pressure of the stripper in the hydrobon unit (hydrotreatment of naphthas).

Due to this decrease the temperature on top of the column will decrease too and the area of the aereocondenser at the top of the column won't be enough to achieve the desired temperature.

For this reason I am designing a new trim cooler that will use cooling water to achieve the current temperature before the liquid/gas separator. To avoid revaporization downstream the trim cooler will have to cool down both the vapour and the liquid stream.

The inlet current is 7.300 kg/h with liquid phase stream being 6.000 kg/h.
I have simulated it with Aspen EDR and the resultant heat exchanger will have to operate 40% flooded in order to cool the liquid phase stream.

To achieve and control the level of flooding in the trim-cooler two ideas come to my mind: Level control and dam bafles.

This is the first time that I design a trim-cooler but I have checked out the designs of other trimcoolers installed on the refinery and I have NOT seen any level control instrumentation or dam baffles.

Can anyone familiar with the design of trim coolers comment please?

Thank you.

 

[georgeverghese]

So this trim cooler acts as a total condensor ? Usually total condensors are thermally designed with some subcooling of the liquid stream. There are many articles written by Henry Kister on the process design and control aspects of column overheads condensors. And there are a few options you'll have to sift through to see which one suits this process best. Also include an inerts bleed line from the top of this total condensor (for obvious reasons).

 

[imatasb]

Sorry, I forgot to mention that it won't act as a total condenser. It will condensate an additional amount of 300 kg/h of vapour (so 1000 kg/h will remain as vapor).

 

[georgeverghese]

You dont need level control in the layman's configuration. One way is to set up a TIC sensing temperature in the downstream accumulator / separator and have that modulate a TCV on this new water cooled HX liquid phase product ( or vapor side product) stream. This would back up the level in this new HX as required. It would be a replication of the current TIC scheme you have now at the air cooler. Can we see a PID of the current arrangement and controls ?

Obviously, you would have a continously downward sloping line from the existing air cooler exit to this new HX. And shellside baffles in this HX should be vertically oriented, if you have this HX lying horizontal. In most plants, there is no control on the water side - it runs with the water flow at design case flow at all times to minimise biofouling on the water-tubeside.

Since this is a partial condensor, you wont need to subcool or bleed any inerts to flare. What is the duty design margin you've allocated at this new unit to account for surges in vapor feed from the column?