Cleaning is the process of removing unwanted substances, such as dirt, infectious agents, and other impurities, from an object or environment. Cleaning is often performed for aesthetic , hygienic , functional , safety , or environmental protection purposes. Cleaning occurs in many different contexts, and uses many different methods. Several occupations are devoted to cleaning.
15-428: Cleaning occurs in various commercial, domestic, personal, and environmental contexts, which differ in scale and requirements. Cleaning is broadly achieved through mechanical action and/or chemical processes (usually solvation ); many methods rely on a combination of mechanical and chemical action. Methods include: Some items and materials require specialized cleaning techniques, due to their shape, size, location, or
30-447: A chemical reaction of some sort. In an " engineering " sense, a chemical process is a method intended to be used in manufacturing or on an industrial scale (see Industrial process ) to change the composition of chemical(s) or material(s), usually using technology similar or related to that used in chemical plants or the chemical industry . Neither of these definitions are exact in the sense that one can always tell definitively what
45-409: A unit operation is a basic step in a process . Unit operations involve a physical change or chemical transformation such as separation, crystallization, evaporation, filtration, polymerization, isomerization, and other reactions. For example, in milk processing, the following unit operations are involved: homogenization , pasteurization , and packaging . These unit operations are connected to create
60-429: A plate column is analyzed by writing down the mass balances for each plate, wherein the known vapor-liquid equilibrium and efficiency, drip out and drip in comprise the total mass flows, with a sub-flow for each component. Combining a stack of these gives the system of equations for the whole column. There is a range of solutions, because a higher reflux ratio enables fewer plates, and vice versa. The engineer must then find
75-447: A stream of flowing or moving material; see Chemical plant . For a given amount of a feed (input) material or product (output) material, an expected amount of material can be determined at key steps in the process from empirical data and material balance calculations. These amounts can be scaled up or down to suit the desired capacity or operation of a particular chemical plant built for such a process. More than one chemical plant may use
90-414: Is a chemical process and what is not; they are practical definitions. There is also significant overlap in these two definition variations. Because of the inexactness of the definition, chemists and other scientists use the term "chemical process" only in a general sense or in the engineering sense. However, in the "process (engineering)" sense, the term "chemical process" is used extensively. The rest of
105-462: Is a physical transport process, while a mixed chemical/physical process requires modeling both the physical transport, such as diffusion, and the chemical reaction. This is usually necessary for designing catalytic reactions , and is considered a separate discipline, termed chemical reaction engineering . Chemical engineering unit operations and chemical engineering unit processing form the main principles of all kinds of chemical industries and are
120-436: Is the basic processing in chemical engineering . Together with unit operations it forms the main principle of the varied chemical industries. Each genre of unit processing follows the same chemical law much as each genre of unit operations follows the same physical law. Chemical engineering unit processing consists of the following important processes: Unit operation In chemical engineering and related fields,
135-585: The article will cover the engineering type of chemical processes. Although this type of chemical process may sometimes involve only one step, often multiple steps, referred to as unit operations , are involved. In a plant , each of the unit operations commonly occur in individual vessels or sections of the plant called units . Often, one or more chemical reactions are involved, but other ways of changing chemical (or material) composition may be used, such as mixing or separation processes . The process steps may be sequential in time or sequential in space along
150-425: The book The Principles of Chemical Engineering and explained that 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 relevant chemical industries. For instance, the same engineering is required to design a mixer for either napalm or porridge, even if
165-451: The foundation of designs of chemical plants, factories, and equipment used. In general, unit operations are designed by writing down the balances for the transported quantity for each elementary component (which may be infinitesimal) in the form of equations, and solving the equations for the design parameters, then selecting an optimal solution out of the several possible and then designing the physical equipment. For instance, distillation in
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#1732852348596180-405: The material properties of the object and contaminants. Several occupations involve cleaning, either in their entirety or among other duties. Chemical process In a scientific sense, a chemical process is a method or means of somehow changing one or more chemicals or chemical compounds . Such a chemical process can occur by itself or be caused by an outside force, and involves
195-462: The overall process. A process may require many unit operations to obtain the desired product from the starting materials, or feedstocks. Historically, the different chemical industries were regarded as different industrial processes and with different principles. 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
210-838: The same chemical process, each plant perhaps at differently scaled capacities. Chemical processes like distillation and crystallization go back to alchemy in Alexandria , Egypt . Such chemical processes can be illustrated generally as block flow diagrams or in more detail as process flow diagrams . Block flow diagrams show the units as blocks and the streams flowing between them as connecting lines with arrowheads to show direction of flow. In addition to chemical plants for producing chemicals, chemical processes with similar technology and equipment are also used in oil refining and other refineries , natural gas processing , polymer and pharmaceutical manufacturing, food processing , and water and wastewater treatment . Unit processing
225-487: The use, market or manufacturers are very different. The unit operations form the fundamental principles of chemical engineering. Chemical engineering unit operations consist of five classes: Chemical engineering unit operations also fall in the following categories which involve elements from more than one class: Furthermore, there are some unit operations which combine even these categories, such as reactive distillation and stirred tank reactors . A "pure" unit operation
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