Issues with a large approach temperature? OH Condenser

Question

Issues with a large approach temperature? OH Condenser

vladrath (Chemical)

(OP)

24 Jun 20 17:42

I'm a little stuck. I have been looking into this and find all the issues associated with a small approach temperature on an exchanger.

Conditions: I have a BEU heat exchanger acting as an overhead condenser. I have an organic vapor entering the shell at 430°F and distillate leaving the exchganger at 350°F. The exchanger is cooled with water on the tube side entering at 85°F and leaveing at 87°F.

I've already identified that we do not have sufficient cooling water flow at the exchanger. So I'm working on fixing that (Control valve issues).

What I am really wondering about is whether cooling water is the right cooling medium for this condenser. It seems to me that we have a large approach temperature. Perhaps we are plating out solids from our water supply and in addition to low CW flow we might have fouled up the exchanger?

In my past experience we've used oil as the condenser cooling fluid for hotter services.

The reason that this is important to me is that we're losing vapor to the enivornmental device (buring product instead of capturing it).

Compositepro (Chemical) · Answer 1 · 2020-06-24 18:21:37

How can you think you do not have enough cooling water flow if it is only rising 2F and the distillate is at 350F. The exchanger is fouled or you are leaking non-condensibles into your process. What is the process pressure?

georgeverghese (Chemical) · Answer 2 · 2020-06-25 05:17:48

Your tubes must be nearly all bunged up with scale, which may explain why you perceive low flow. Nothing to do with control valves, you've got high dp on the tubes with all this scale. At 350degF on the shell side, you've got to have good quality low TDS water to avoid scaling. Else try anti scalant injection into CWS to dissolve out this scale.

EdStainless (Materials) · Answer 3 · 2020-06-25 14:28:52

The tubes are fouled.
Most scale inhibitors will break down if you boil the water, and you should be doing that easily.
A small clean oil loop would make sense.
What is your goal for outlet temp?
What would the coolant temp rise be using water? oil?
What is MOC?

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P.E. Metallurgy, consulting work welcomed

georgeverghese (Chemical) · Answer 4 · 2020-06-27 00:25:25

In this service with high shellside htc (condensing service) and low tubeside htc, the tube id surface temp will be close to shellside T, and hence there is no way of getting this to work with a higher surface area HX.
Another solution would be to use a fin fan aerial cooler.

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Issues with a large approach temperature? OH Condenser