Evaporation from aqueous glycerin solution for concentration

Various industrial processes, such as biodiesel production, generate aqueous glycerin solutions that must be concentrated for further processing. Solutions with a low concentration in the range of 25% by weight of glycerin are typically concentrated to a final concentration of approximately 85% by weight of glycerin.

Various processes are available for concentration. In the past, final evaporation was always carried out in multi-stage evaporation plants (usually 2 or 3 stages). However, depending on the quantity ratio, it may also make sense to first concentrate the product in a pre-concentration stage using mechanical vapor recompression or thermal vapor compression and then carry out the final evaporation in a multi-stage plant.

As a rule, plants with falling film evaporators are used for this purpose, as they offer the optimum balance between investment costs and operating costs for the application in question.

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Frequently Asked Questions

Why are glycerin concentration plants not designed solely as plants with mechanical or thermal vapor compression?

Since the water-glycerin mixture does not have a high boiling point increase at lower concentrations, evaporation with mechanical or thermal vapor compression is useful and is selected depending on the total cost of the plant. However, since higher concentration results in higher boiling point increases, it is generally no longer economical to work with mechanical or thermal vapor compression only, as the operating and investment costs for the vapor compressors are too high.

Why is a design with falling film evaporators chosen?

Typically, glycerine solutions produced in industry do not tend to crystallize into individual substances during evaporation. It is therefore possible to choose the falling film evaporator process, as this is usually less expensive in terms of investment costs than a forced circulation system.