Unit Operation and Unit Process
Unit Operation
Operation that involve only physical changes to material but no chemical changes.
The operations carried out in the chemical process industry involving physical changes in the materials handled in the system under consideration are regarded as unit operations.
Arthur Dehon Little developed the concept of unit operations to explain industrial chemistry processes in 1916. In 1923, William H. Walker, Warren K. Lewis and William H. McAdams wrote the book The Principles of Chemical Engineering and explained that the variety of chemical industries have processes which follow the same physical laws.
The concept of unit processes was introduced in 1923 by P.H. Goggin.
Features Of Unit Operations
(i) They are physical in nature. physical change results in a change in property of matter and it requires some sort of driving force.
(ii) They are common to all types of diverse industries (with no change in concept, merely change in conditions).
(iii) Individual operations have common techniques and are based on the same scientific principles irrespective of/regardless of the materials being processed.
(iv) Practical methods of carrying them out/conducting them may be more or less different in different industries.
(v) They are independent of industries in which they are carried out.
The operations involving physical changes are termed as unit operations to indicate that each single operation, such as distillation, is used in a wide range of industries and normally under varying operating conditions (temperature, pressure).
Classification Of Unit Operation
(i ) Mechanical operations
Involve physical actions such as crushing, grinding, mixing, and sieving, where there is no change in chemical composition.
Example :
- Size reduction-crushing and grinding.
- Mixing-solid-solid and liquid-liquid, etc.
- Classification-screening, froth flotation, magnetic separation, jigging, tabling and electrostatic separation (classification – it comprises of techniques of classifying a solid mixture into fractions, which differ from each other in some property) and wet classification.
- Solid-fluid separations – filtration, sedimentation and centrifugal separation.
- Gas-solid separations – dust collection, bag filtration, electrostatic precipitation.
- Solid handling – storage, feeding and conveying.
- Size enlargement – palletization, agglomeration, granulation and extrusion.
(ii) Fluid flow operations :
Fluid flow operations involve the movement of fluids through pipes, valves, pumps, and other equipment.
Example : Fluid transportation, filtration and solids fluidization. Pumping, compression, and fluidization.
(iii) Heat transfer :
Heat transfer operations involve the transfer of heat from one medium to another to achieve heating or cooling.
Example : evaporator and heat exchanger
(iv) Mass transfer :
Mass transfer operations involve the movement of components from one phase to another, often separating different components of a mixture.
Examples include distillation, absorption, adsorption, extraction, leaching, and membrane separation processes.
Other Example Of Unit Operation
Steam distillation : Live steam is passed in the still to recover the solvent. Vapors of solvent and water are passed in a shell-tube type condenser and cooler. Then the cooled distillate are taken in a
separator where solvent and water separate out and are diverted to respective storage.
Heating : Heating operation can be done either directly or indirectly. In direct heating, steam is passed in the material directly to heat the material. In indirect heating, heating media (e.g. steam, hot oil,
hot flue gases etc.) are passed in jacket / coil of the vessel.
Cooling : It can be done directly or indirectly. In direct cooling, ice or cooled water is added to the material directly. In indirect cooling, cooling media (raw water, chilled brine, cold oil etc.) are passed
in jacket / coil of the vessel.
Drowning : It means transferring reaction mass from the reaction vessel to a tank which is containing water or other medium (e.g. dilute acid, dilute alkali etc.)
Filtration : This operation is for separating solids and liquids. The conventional items used for this operation are press, nautch, centrifuge. The filtration can be done either under vacuum or pressure or at atmospheric pressure.
Pulverisation : This operation is done to reduce size of the material. Usually crushers, pulverises, ST mill are used.
Blending : This operation is done in a blender to mix thoroughly two or more dried products.
Washing : This operation is done in presses, nautches or centrifuge to remove soluble impurities and acid/alkali from the product.
Packing : is filling up of finished product in the containers.
Storing of liquid raw materials : Bulk liquid raw materials which are received in tanker loads are emptied out in storage provided for this purpose.
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Unit Process
Unit process Occur chemically change no physical change.
Chemical process is combination of unit processes and unit operation.
A process may require many unit operations to be obtain the desired product from the starting materials or feedstocks.
Unit process involves principle chemical conversion leading to synthesis of various useful product and provide basic information regarding the temperature and pressure, chemical conversion and yield of product, nature of reaction whether exothermic and endothermic, type of catalyst used.
Example of Unit process
Alkylation
Hydrogenation
Sulphonation
Dehydration
Nitration
Oxidation
Reduction
Biochemical process
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Difference Between Unit operation And Unit process
| No. | Unit Operation | Unit Process |
|---|---|---|
| 01. | Unit operation is reversible. | Unit process is irreversible. |
| 02. | Unit operation involve physical changes. | Unit process involve chemical changes. |
| 03. | Unit operation is just primary activity. | Unit operation is secondary activity. |
| 04. | Unit operations involve a physical change or chemical transformation such as separation, crystallization, isomerization, distillation, filtration, evaporation. | Unit operations involve a chemical change such as hydrogenation, oxidation, chlorination, nitration, reduction and other reaction. |
Conclusion Of Unit Operation And Unit Process
- Both unit operations and unit processes are essential in chemical engineering and industrial processes.
- Unit operations deal with physical transformations and manipulations of materials without altering their chemical composition.
- Unit processes involve chemical changes in substances, resulting in the conversion of raw materials into desired products.
- Understanding the distinction between unit operations and unit processes is crucial for designing, optimizing, and controlling various industrial processes efficiently.
- Industrial processes involve a combination of unit operations and unit processes to achieve the desired transformations and produce the desired products.
