In
chemical engineeringChemical engineering is the branch of engineering that deals with physical science , and life sciences with mathematics and economics, to the process of converting raw materials or chemicals into more useful or valuable forms...
and related fields, a
unit operation is a basic step in a
processIn engineering a process is a set of interrelated tasks that, together, transform inputs into outputs. These tasks may be carried out by people, nature, or machines using resources; so an engineering process must be considered in the context of the agents carrying out the tasks, and the resource...
.Unit operation involves bringing a physical change such as separation, crystallization, evaporation, filtration etc.. For example in milk processing,
homogenizationHomogenization or homogenisation is any of several processes used to make a chemical mixture the same throughout.-Definition:Homogenization is intensive blending of mutually related substances or groups of mutually related substances to form a constant of different insoluble phases to obtain a...
,
pasteurizationPasteurization is a process of heating a food, usually liquid, to a specific temperature for a definite length of time, and then cooling it immediately. This process slows microbial growth in food...
, chilling, and packaging are each unit operations which are connected to create the overall process. A process may have many unit operations to obtain the desired product.
Historically, the different chemical industries were regarded as different industrial processes and with different principles.
Arthur Dehon LittleArthur Dehon Little was an American chemist and chemical engineer. He founded the consulting company Arthur D. Little and was instrumental in developing chemical engineering at the Massachusetts Institute of Technology...
propounded the concept of "unit operations" to explain industrial chemistry processes in 1916. In 1923,
William H.WalkerWilliam Hultz Walker April 7, 1869 – July 9, 1934 was born in Pittsburgh, Pa., and graduated in 1890 at Penn State College and took his Ph.D. at Göttingen . In 1894 he accepted the chair of industrial chemistry at the Massachusetts Institute of Technology, where from 1908 he was also director of...
,
Warren K. LewisWarren Kendall Lewis was an MIT professor who has been called the father of modern chemical engineering. He co-authored an early major textbook on the subject which essentially introduced the concept of unit operations...
and William H. McAdams wrote the book
The Principles of Chemical Engineering and explained the variety of chemical industries have processes which follow the same physical laws. They summed-up these similar processes into unit operations. Each unit operation follows the same physical laws and may be used in all chemical industries. The unit operations form the fundamental principles of chemical engineering.
Chemical engineering unit operations consist of five classes:
- Fluid flow processes, including fluids transportation, filtration
Filtration is commonly the mechanical or physical operation which is used for the separation of solids from fluids by interposing a medium through which only the fluid can pass...
, solids fluidization
- Heat transfer
Heat transfer is a discipline of thermal engineering that concerns the exchange of thermal energy from one physical system to another. Heat transfer is classified into various mechanisms, such as heat conduction, convection, thermal radiation, and phase-change transfer...
processes, including evaporationEvaporation is a type of vaporization of a liquid that occurs only on the surface of a liquid. The other type of vaporization is boiling, which, instead, occurs on the entire mass of the liquid....
, condensationCondensation is the change of the physical state of matter from gaseous phase into liquid phase, and is the reverse of vaporization. When the transition happens from the gaseous phase into the solid phase directly, the change is called deposition....
- Mass transfer
Mass transfer is the net movement of mass from one location, usually meaning a stream, phase, fraction or component, to another. Mass transfer occurs in many processes, such as absorption, evaporation, adsorption, drying, precipitation, membrane filtration, and distillation. Mass transfer is used...
processes, including gas absorption, distillationDistillation is a method of separating mixtures based on differences in volatilities of components in a boiling liquid mixture. Distillation is a unit operation, or a physical separation process, and not a chemical reaction....
, extractionThe related terms natural resource extraction both refer to the practice of locating, acquiring and selling natural resources....
, adsorptionAdsorption is the adhesion of atoms, ions, biomolecules or molecules of gas, liquid, or dissolved solids to a surface. This process creates a film of the adsorbate on the surface of the adsorbent. It differs from absorption, in which a fluid permeates or is dissolved by a liquid or solid...
, dryingDrying is a mass transfer process consisting of the removal of water or another solvent by evaporation from a solid, semi-solid or liquid. This process is often used as a final production step before selling or packaging products. To be considered "dried", the final product must be solid, in the...
- Thermodynamic processes, including gas liquefaction, refrigeration
Refrigeration is a process in which work is done to move heat from one location to another. This work is traditionally done by mechanical work, but can also be done by magnetism, laser or other means...
- Mechanical processes, including solids transportation, crushing and pulverization
A crusher is a machine designed to reduce large rocks into smaller rocks, gravel, or rock dust. Crushers may be used to reduce the size, or change the form, of waste materials so they can be more easily disposed of or recycled, or to reduce the size of a solid mix of raw materials , so that pieces...
, screening and sieving
Chemical engineering unit operations also fall in the following categories:
- Combination (mixing
In industrial process engineering, mixing is a unit operation that involves manipulating a heterogeneous physical system, with the intent to make it more homogeneous...
)
- Separation (distillation
Distillation is a method of separating mixtures based on differences in volatilities of components in a boiling liquid mixture. Distillation is a unit operation, or a physical separation process, and not a chemical reaction....
)
- Reaction (chemical reaction
A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, typically following the input of some type of energy, such as heat, light or electricity...
)
Chemical engineering unit operations and chemical engineering unit processing form the main principles of all kinds of chemical industries and are the foundation of designs of chemical plants, factories, and equipment used.
See also
- Distillation Design
Distillation Design is a book which provides complete coverage of the design of industrial distillation columns for the petroleum refining, chemical and petrochemical plants, natural gas processing, pharmaceutical, food and alcohol distilling industries...
- Separation process
In chemistry and chemical engineering, a separation process, or simply a separation, is any mass transfer process used to convert a mixture of substances into two or more distinct product mixtures, at least one of which is enriched in one or more of the mixture's constituents. In some cases, a...
- Transport phenomena
Transport Phenomena is the first textbook that is about transport phenomena. It is specifically designed for chemical engineering students...
- Unit Operations of Chemical Engineering
Unit Operations of Chemical Engineering, first published in 1956, is one of the oldest chemical engineering textbooks still in widespread use. The current Seventh Edition, published in 2004, continues its successful tradition of being used as a textbook in university undergraduate chemical...
- Process simulation
Process simulation is used for the design, development, analysis, and optimization of technical processes and is mainly applied to chemical plants and chemical processes, but also to power stations, and similar technical facilities.- Main principle :...