A unit operation is defined as a process which does not involve any chemical reaction. Unit operations only deal with physical changes of the materials involved in the process. They are equipments which cause the materials to undergo physical changes.
The physical changes are carried out for variety of purposes. Generally unit operations steps are carried out before subjecting the materials to chemical reactions so that chemical reactions happen smoothly.
The physical changes can imply phase changes such as; evaporation, condensation, crystallization etc. Thus Distillation is a unit operation step because condensation and evaporation happens inside the column. Evaporators, and crystallisers are also unit operations equipment.
Unit operation equipments are also responsible for mechanical operations which involves size reduction, physical separations, mixing, and grinding. The mass transfer, heat transfer process all may happen together. Chemical reaction doesn’t happen.
The unit operations are classified in the following manner:
- Fluid flow operations: Pumping, compression, and fluidisation.
- Mechanical operations: Size reduction, size enlargement, mixing, agitation, blending, filtration, classification-separation, etc.
- Mass transfer: Distillation, evaporation, crystallization, leaching, absorption, adsorption, extraction, etc.
Heat transfer: When materials are handled the heat transfer can take place by any fundamental mechanism; conduction, convection, or radiation. Usually two fundamental mechanisms occur simultaneously.
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