Best practice for evaporation processes

Evaporation is an important industrial process, used for concentrating solutions in a range of sectors including manufacturing and even the food and pharmaceutical sectors.

By Arnold Kleijn, product development manager, HRS Heat Exchangers

Evaporation is a process where a material moves from its liquid state to a vapour (or gas). The most common example of evaporation seen in everyday life is the transfer of water from the earth’s surface to the atmosphere as part of the water cycle. When liquids evaporate, and materials which they contain in solution or suspension are left behind; this becomes a useful process to concentrate solutions or to separate materials.

Evaporation is different from dehydration or drying because the product is a concentrated liquid, rather than a dry solid. However, evaporation and drying processes can be combined: an evaporation process first removes the bulk of the water, and a final dryer eliminates the last bit, to obtain the final dried product. As evaporation plants are usually more energy efficient than dryers, it makes sense to combine the two technologies. Evaporation is different from distillation: a distillation process separates two or more liquids that have different boiling points (and which normally contain no solids). In contrast, evaporation eliminates water from a solution that contains dissolved and/or suspended solids, thus obtaining a more concentrated solution.

In general terms, the rate of evaporation depends on the temperature (the warmer it is, the faster the rate of evaporation), but the boiling point of a material varies with pressure (water boils at a lower temperature as pressure reduces), and so industrial processes often use a reduction in pressure to speed up the evaporation process.

Evaporation is used for different purposes in multiple industries and sectors. In the food industry, some products are concentrated to increase shelf life, reduce volume or weight, or reduce storage and transport costs. In contrast, in the pharmaceutical sector, evaporation is often used to create concentrated solutions which can then be dried to create powdered products. In each sector, although the basic principles of evaporation remain the same – the removal of water (or another solvent) from a solution by converting that water or solvent into its vapour phase.

Different techniques (using different temperature and pressure conditions) can be applied in different situations. The type of evaporation which is most suitable for a particular purpose depends on a large number of factors, including the nature of the solvent and the solution, the required end products, and the energy available for the process.

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