A. D. Little introduced the Unit Operations of Chemical Engineering concept in 1905.
The field of chemical engineering is the combination of two-part unit operations and unit processes.
The difference between unit operation and the unit process lies in their effects on materials. Unit operations involve only physical changes in the materials handled in the system. In contrast, the unit process involves physical and chemical changes in materials handled by the system.
Unit Operations are the most important part of Chemical Engineering. Let’s understand this concept in detail.
What is Unit Operation?
The operations carried out in the chemical industries involving physical changes in the considered system are regarded as unit operations.
A physical change results in any property of matter and requires some driving force.
Features of Unit Operations
They are physical in nature.
They are common to all types of diverse industries.
Each operation has common techniques based on the same scientific principles regardless of the material being handled.
They are independent of the industries in which they are carried out.
Practical methods of carrying out unit operations are different in different industries.
So, the concentration of solutions by evaporation is a unit operation that can be carried out in diverse industries. This operation is similar to the handling of sugar, salt, or fruit juices. However, there are some differences in the most suitable arrangement.
Unit operations are used to prepare the reactants. They separate and purify the products. They recycle the uncovered reactants. They also control the energy transfer in and out of the chemical reactor.
A physical change in any property of matter occurs by the action of some driving force. The normal driving force in heat flow is the temperature difference.
Unit Operations of Chemical Engineering
Fluid Flow Operations
It focuses on the principles that determine the flow of any fluid. These principles also govern transportation from one point to another.
A fluid is a substance or component capable of flowing if allowed to do so. Gas, liquid, and vapor have this capability, so they are called fluids.
The driving force for the fluid flow operation is Pressure Difference.
Mechanical Operations
Mechanical Operation means mechanical power is used to perform these operations.
For example, Size reduction, Screening, and Mixing are mechanical operations.
Classification of Mechanical Operations
- Size Reduction
Cutting, Crushing, Grinding
- Classification
Screening, Froth Flotation, Magnetic Separation, Jigging, Tabling, Electrostatic Separation, Wet Classification
- Solid-Fluid Separations
Filtration, Sedimentation, Centrifugal Separation
- Gas-Solid Separations
Dust Collection, Bag Filtration, Electrostatic Precipitation
- Solid Handling
Storage, Feeding, Conveying
- Size Enlargement
Pelletization, Agglomeration, Granulation, Extrusion
Mechanical Separation
Many unit operations of chemical engineering are directed toward separating a substance into its parts.
These separation techniques apply to heterogeneous mixtures and are grouped into five headings as
Separation of Solids from Solids
Solids are separated in the dry state by Screening, Electrostatic Separation, and Magnetic Separation.
Separation of Solids from Solids in Liquids
Various methods used to separate solids from solids in liquids include Jigging, Flotation, Classification, and Tabling.
Separation of Solids from Liquids
Solids are separated from liquids by Filtration and Sedimentation.
Separation of Solids or Liquid drops from Gases
Solids are separated from gases by Gravity Settling, Centrifugal Separation/Settling Filtration and Electrostatic Precipitation.
Separation of Liquids from Liquids.
Immiscible liquids are separated by a technique called Decantation using either a Gravity Decanter or a Centrifugal Decanter.
Mixing and Agitation
Mixing is a process. At least two separate materials are taken, which are present in the same or different phases. They are forced to be randomly distributed through one another by some mechanical means.
If materials present for mixing are in the same phase is called Homogeneous mixing.
If materials are in different phases is called Heterogeneous mixing.
Mixing and Agitation are not the same but different from each other.
Agitation means the induced motion of material in a circulatory pattern inside a tank or vessel. Mixing occurs simultaneously. It is the random distribution into and through one another of two or more initially separate phases.
Heat Transfer Unit Operations of Chemical Engineering
Heat transfer is the process of moving heat or thermal energy. The transfer occurs within a body or between two bodies. This happens because of temperature differences.
The temperature difference is the driving force of the heat transfer.
Heat transfer can occur through three modes of heat transfer Conduction, Convection, and Radiation.
Classification
- Phase Change Operations
Evaporation, Condensation
- No-Phase Change Operations
Heating, Cooling
Operations in which Heat and Mass Transfer are both associated
Distillation, Crystallization, Sublimation, Evaporation, Drying, Condensation
Mass Transfer Unit Operations of Chemical Engineering
Mass transfer is concerned with the transfer of mass from one phase to another different phase.
It depends on the molecules diffusing or vaporizing from one phase to another. It is based on differences in vapor pressure, solubility, or diffusivity.
Concentration difference is the driving force for mass transfer.
Classification
- Liquid – Gas (Vapour)
Distillation, Gas Absorption, Stripping, Humidification, Dehumidification
- Liquid – Solid
Crystallization, Leaching (Solid Extraction)
Adsorption
- Liquid – Liquid
Extraction
- Solid – Gas (Vapour)
Adsorption, Drying, Sublimation
FAQs
What are unit operations of chemical engineering?
Unit operations involve physical changes in a chemical system. These include separating and purifying products, preparing reactants, and recycling uncovered reactants. They also entail controlling energy transfer in and out of a chemical reactor.
What are the features of unit operations of chemical engineering?
Unit operations are physical in nature. They are common to all types of industries. Unit operations are independent of the industries in which they are carried out. They have common techniques based on the same scientific principles. Practical methods of carrying out unit operations are different in different industries.
What are the different types of mechanical operations?
Mechanical operations in chemical engineering include size reduction, screening, mixing, solid-fluid separations, gas-solid separations, and solid handling.
What are the different types of mechanical separation?
Mechanical separation techniques in chemical engineering include the separation of solids from solids. They also involve the separation of solids from solids in liquids. These techniques encompass the separation of solids from liquids. Additionally, they include the separation of solids or liquid drops from gases and the separation of immiscible liquids.
What is the difference between mixing and agitation?
Mixing refers to the random distribution of two or more initially separate phases into and through one another. Agitation means the induced motion of material in a circulatory pattern inside a tank or vessel.
What is heat transfer?
Heat transfer is the transfer of thermal energy from one place to another due to a temperature difference. It can occur through three modes: conduction, convection, and radiation.
What are the different types of heat transfer unit operations of chemical engineering?
Heat transfer operations in chemical engineering can be classified into two types. The first type is phase change operations such as evaporation and condensation. The second type is no-phase change operations, including heating and cooling. Some operations involve both heat and mass transfer, such as distillation, crystallization, sublimation, evaporation, drying, and condensation.
What is mass transfer operation?
Mass transfer is the movement of molecules or atoms from one place to another due to a concentration gradient. It is often associated with chemical reactions or changes in the phase of a substance.
References
“Unit Operations of Chemical Engineering”, McCabe W L, Smith J C, Harriott P, Mc Graw Hill Publication, 7th edition 2005.
“Process Heat Transfer”, D. Q. Kern, McGraw Hill.
“Chemical Engineers Handbook”, Perry R.H. & Chilton C.H., 7th ed. McGraw hill.
“Mass Transfer Operations” by R. E. Treybal, Mc-Graw Hill International, 3rd edition
Read Also:
Laws of Heat Transfer: Key Concepts and Application
Newtonian and Non-Newtonian Fluids
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