Crystallizer

Crystallizer is a process vessel equipped with cooling coils, where the hot oil is being progressively cooled down according to various recipes.Various suppliers propose different designs and all claim that “their one is the best”. The “perfect” crystalliser has to compromise:

• correct geometry
• agitation to avoid “dead zones” during processing
• efficient cooling surface

Due to increasing viscosity and growing solid fat content in the slurry during cooling, as well as high sensibility of the crystalisation, the progress in crystalliser design has been achieved much trough field experience. Without doubts, the company who had the biggest experience in this design was Fractionnement Tirtiaux S.A.. As this development took place over two generations of engineers and R&D scientists, one need solid experience and good engineering knowledge to understand importance of various details.

As example here some aspect when we see crystallizer as “heat exchanger” that transfers the heat from processed oil to cooling water. So it follows thermodynamic equation:

However we must see the cooling surface is actually the triple layer of materials of various conductivity.

The equation for the flat surface heat transfer: 

Then we must keep in mind that thermal conductivities of “our layers” are very different:

1 mm SOLID OIL = 70 mm STEEL

Means : thick solid oil deposit can stop heat transfer !!

1 mm SCALE = 21 mm STEEL

Means : water quality ( so deposit ) affects cooling surface !!

The information that is often communicated to the potential customer is the “cooling surface per ton of oil” ( Am / ton ). It is very misleading and does not represent the “quality of crystallizer”.

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