Chemical engineering distillation/evaporation

Biochemical engineering is a subspecialty of chemical engineering. Chemical engineering began in 1901 when George E. Davis, its British pioneer, mathematically described all the physical operations commonly used in chemical plants (distillation, evaporation, filtration, gas absorption, and heat transfer) in his landmark book, A Handbook of Chemical Engineering. 

Simultaneous heat and mass transfer also occurs in drying processes, chemical reaction steps, evaporation, crystallisation, and distillation. In all of these operations transfer rates are usually fixed empirically. The process can be evaluated using either the heat- or mass-transfer equations. However, if the process mechanism is to be fully understood, both the heat and mass transfer must be described. Where that has been done, improvements in the engineering of the process usually result (see Process energy conservation). 

In the majority of chemical processes heat is either given out or absorbed, and fluids must often be either heated or cooled in a wide range of plant, such as furnaces, evaporators, distillation units, dryers, and reaction vessels where one of the major problems is that of transferring heat at the desired rate. In addition, it may be necessary to prevent the loss of heat from a hot vessel or pipe system. The control of the flow of heat at the desired rate forms one of the most important areas of chemical engineering. Provided that a temperature difference exists between two parts of a system, heat transfer will take place in one or more of three different ways. 

Figure 13.30. Molecular distillation and related kinds of equipment, (a) Principle of the operation of the falling film still (Chemical Engineers Handbook, McGraw-Hill, New York, 1973). (b) Thin-layer evaporator with rigid wiper blades (Luwa Co., Switzerland), (c) The Liprotherm rotating thin film evaporator, for performance intermediate to those of film evaporators and molecular stills (Sibtec Co., Stockholm), (d) Centrifugal molecular still [Hickman, Ind. Eng. Chem. 39, 686 (1947)].

Fooler The Elements of Chemical Kinetics and Reactor Calculations A Self-Paced Approach Himmelblau Basic Principles and Calculations in Chemical Engineering, 5th edition Holland Fundamentals and Modeling of Separation Processes Absorption, Distillation, Evaporation, and Extraction... 

Warren Kendall Lewis (1882-1978) studied chemical engineering at the Massachussetts Institute of Technology (MIT) and gained his chemistry PhD in 1908 at the University of Breslau. Between 1910 and 1948 he was a professor at MIT. His research topics were filtration, distillation and absorption. In his paper The evaporation of a liquid into a gas , Mech. Engineering 44 (1922) 445-448, he considered simultaneous heat and mass transfer during evaporation and showed how heat and mass transfer influence each other. 

However in many heat and mass transfer processes in fluids, condensing or boiling at a solid surface play a decisive role. In thermal power plants water at high pressure is vaporized in the boiler and the steam produced is expanded in a turbine, and then liquified again in a condenser. In compression or absorption plants and heat pumps, boilers and condensers are important pieces of equipment in the plant. In the separation of mixtures, the different composition of vapours in equilibrium with their liquids is used. Boiling and condensing are, therefore, characteristic for many separation processes in chemical engineering. As examples of these types of processes, the evaporation, condensation, distillation, rectification and absorption of a fluid should all be mentioned. 

Perfectly isothermal systems are rare in chemical engineering practice and many processes, such as distillation, gas absorption, stripping, condensation, and evaporation, involve the simultaneous transfer of mass and energy across fluid-fluid interfaces. Representative temperature profiles in some nonisothermal processes are shown in Figure 11.1. The temperature profile also has a large influence in chemically reacting systems. For nonisothermal systems it is important to consider simultaneous heat transfer even though we are primarily interested in the mass transfer process. 

An economical method of organizing much of the subject matter of chemical engineering is based on two facts (1) although the number of individual processes is great, each one can be broken down into a series of steps, called operations, each of which in turn appears in process after process (2) the individual operations have common techniques and are based on the same scientific principles. For example, in most processes solids and fluids must be moved heat or other forms of energy must be transferred from one substance to another and tasks like drying, size reduction, distillation, and evaporation must be performed. The unit-operation concept is this by studying systematically these operations themselves—operations that clearly cross industry and process lines—the treatment of all processes is unified and simplified. 

The use of the FF x diagram for the analysis of chemical engineering unit operations such as distillation, evaporation and refrigeration processes, is now quite common, and the procedures are well described in textbooks, e.g. Coulson and Richardson (1991), McCabe, Smith and Harriott (1985). These charts are less frequently applied to crystallization processes, however, because not many H x diagrams are available. 

Throughout the chemical engineering literature, many kinds of equipment, so-called unit operations, are described, including distillation columns, absorbers, strippers, evaporators, decanters, heat exchangers, filters, and centrifuges. Just to mention a few. The members of this large collection, many of which are listed in Tables 4.1 and 4.2, in connection with process simulators, all involve one or more of these basic operations ... 

Sections 10.4 and 10.5 cover some of the classical unit operations of chemical engineering. Section 10.4 covers basic fluid dynamics and the fluid-handling operations common to brine and cell gases. Section 10.5 turns to the transport operations of heat transfer, absorption, adsorption, ion exchange, distillation, and evaporation. 

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