Are there standardized ways of dealing with precipitation in chemical engineering continuous flow processes? I have an application in which I need to cool a fluid via a heat exchanger and the fluid will precipitate some solid on cooling. The two specific issues I predict are:

  1. I need to select a type of heat exchanger that won't clog from the precipitate. Probably the best cases are something where the precipitate can just fall out by gravity or it is carried out by the fluid. What types of heat exchangers are good for this? Single pass shell-and-tube?

  2. I need an automated way to remove the precipitate from the fluid. What pieces of equipment are used for this?


My apologies for answering both 1) and 2) in the same answer, but...

This sounds a like a perfect application for a crystallization process.

Crystallizers use an external cooling loop, as opposed to the unit op being done inside of a heat exchanger. This often looks like a large vessel with a sloped bottom, and some sort of external cooling loop with tubes running inside of the tank. The tubes have a cold fluid flowing through that applies the cooling load, and can often act as the nucleation point for crystallization as well (be careful though, solids/crystal buildup could cause scaling/loss of heat transfer). After precipitation / crystallization, the solids will (usually) sink, and then get funneled into the bottom. From there they can be slurried/pumped to a solids/liquids separation unit, such as a classifier, gravity screen, mesh screen, filtration screen, etc all dependant on the physical properties of your material.

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Another option one could try is doing these two unit ops separately if possible. Often one can do a simple chemical adjustment to instigate the precipitation such as adjusting pH, ORP, adding a reagent etc. Separate with a settling tank and then as imilar method to the solid-liquid separation in the above diagram. Once separated, the fluid could then be sent to a traditional heat exchanger.


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