Freezing Temps in a Heat Exchanger

[ms323]

Greetings, all.

I have a hydrocarbon stream which contains no more than 2% Water, (often much less, but there is always SOME water).

For a variety of reasons, it is desired to cool this stream to around 20 degrees F.

However, this will (obviously) cause freezing of water, and very likely the subsequent plating of ice on the heat exchanging surfaces.

The water is not needed in the stream. In fact, the argument could be made that it is be beneficial to remove this water from the hydrocarbon stream (although it is not necessary).

So, my thinking is that there should be a way to intentionally freeze the water out, that would allow for the removal of water from my hydrocarbons, but also would faciliate effective cooling on the stream without having to deal with the hassle of plated exchanger internals.

Any thoughts?

 

[ornerynorsk]

Running the process flow through a centrifugal seperator prior to chilling would be more efficient than trying to freeze out and recover the water. What kind of hydrocarbon and what kind of flowrates? What is the entry temp into the chiller? Is this downstream from a distillation process?
Just a few thoughts.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[ms323]

ornerynorsk - thanks for the quick response!

Agreed that a centrifugal separator is a far more efficient way of removing water... however, removing the water is not 'necessary' for the process. Unless, removing water (prior to freezing) is the only way to effectively chill the stream, and that is a completely different discussion (that I may need to have later, depending on the outcome of this thread) on water removal techniques.

The thing that must be accomplished is to chill this stream to 20 degF. Removal of water would just be icing on the cake.

I would like to avoid specifics, if at all possible, but the hydrocarbon is used as a raw feedstock brought in from OSBL via pipeline and stored onsite before use (so, possibly downstream of distillation process, although not directly), and chiller entry temp would be ambient.

 

[moltenmetal]

You have two choices:

1) Remove the water, and hence have a hydrocarbon-saturated water disposal problem on your hands, or

2) Leave the water in there, monitor differential pressure across the exchanger and outlet temperature, and deal with the outages resulting from freeze-up either with down-time or with parallel exchangers. You'll need equipment to warm up the utility side when you're down, because blocked tubes will take forever to clear with warm process fluid.

By the way, in the 2nd case you'll have to deal with whatever water you thaw out of the fouled exchanger too, but probably a smaller quantity of it. But you NKOW that the water you leave in there will become somebody else's problem downstream- it's not just going to pass through the rest of whatever you're doing without any harm, unless the very next thing you do after chilling this stream is heat it back up again. So water removal would seem to be part of your future either way.

As to the water removal, you don't need to do such a good job of it, so your choices are many.