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Preventing Crystallization On Coils?

Preventing Crystallization On Coils?

Preventing Crystallization On Coils?

(OP)
We have a batch solution around 75*C that is charged to a process vessel to be cooled. The tank has a jacket and coils. We circulate tempered water though these and slowly over several hours lower the jacket temperature to cool the batch down. As we cool the solution down, our product precipates out of solution.

We cool the batch slowly because it helps make large fluffy crystals that are easier to separate out down stream. We have to regulate the agitator speed to around 40 RPM to prevent damanging the crystals.

Over time product builds up and coats our coils. Over several months, the 3" pipe may develope 2 to 3" of build up. As this happens, heat transfer obviously drops off, and our 4 hour cooling times turn into 8 hour or more.

Once this extra time becomes the bottle neck of the process, we fill the tank up with water, dissolve the product, and send it to waste water. Needless to say, a substantial amount of product and money is lost by this practice.

With the constraints of slow agitation, and with out adding anti-scaling dispersences to the product, are there any reasonable ways to prevent buildup on coils?

RE: Preventing Crystallization On Coils?

The crystals don't remelt when the next hot batch is charged?

RE: Preventing Crystallization On Coils?

myrdale.
What we would do would be to re-disolve the crystals and feed them in again upstream in the process so they were not lost.   This requires creative solvent choice and sometimes heat.   Have you tried increasing the rpm back to full speed for a few minutes right before you begin discharging to fluidize the solids?   Maybe you could use N2 injected into the bottom of the tank for rapid fluidization to get the settled material off.

Regards
StoneCold

RE: Preventing Crystallization On Coils?

At the start of each batch heat the coils to dissolve any accumulated crystals and then proceed with cooling.

RE: Preventing Crystallization On Coils?

(OP)
ash9144, the crystals do not seem to do such. This last week, after we had washed the system out, after our third batch I was able to glimps into the vessel and we had a thin coating on the visible coils.

We already warm the jacket and coils up to around 70*C when the batch is transfered over. I need to find a chart for BP vs concentration of methanol and water, but I suspect we can not get much warmer before we start flashing methanol off.

Turning the agitation up for a period is definately a good idea StoneCold. I have proposed using the mother liquor from the batch to dissolve then recrystallize this material. However because of our ISO QMS they seem to think it is easier just to let the product go to waste *sigh*.

Thankyou all.

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