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Growth Techniques
Published in Alan Owens, Semiconductor Radiation Detectors, 2019
Distillation is most commonly used to purify volatile elemental precursors before compounding, for example, Cd, Hg and Te, used to produce HgCdTe. For these elements, the vapor pressures of the most common impurities (e.g., Zn, Mg, Cu …) are many orders of magnitude less at their melting points, allowing easy separation. The method is most effective if dynamically pumped; this has a number of advantages over conventional distillation, namely: the rate of evaporation increases with decrease in residual pressure,better separation of volatile constituents can be achieved at lower pressure,the possibility of interaction of distillate with ambient gas is reduced or eliminated andworking at a lower temperature reduces the possibility of metal/container interactions and reduces the running costs of the process.
Mixing and Separation Processes
Published in C. Anandharamakrishnan, S. Padma Ishwarya, Essentials and Applications of Food Engineering, 2019
C. Anandharamakrishnan, S. Padma Ishwarya
In fractional distillation, distillation occurs in a column (Figure 12.60). It contains multiple contact stages through which vapor and liquid move in a countercurrent manner. The name “fractional distillation” implies that at any position of the column, the distillate fraction has a different composition. Feed is introduced at a certain point of the column. The portion above the feed inlet is known as the rectification zone, whereas that below the feed inlet is known as the stripping zone (as shown in Figure 12.57). During the process, vapor moves in the upward direction and liquid moves in the downward direction. Heat exchange occurs between the vapor and the liquid, and thus, the less-volatile vapor component condenses into a liquid and high-volatile component vaporizes. Thus, the vapor is rich in the high-volatile component. The column is connected to a condenser to achieve a continuous heat exchange.
Heating Value and Combustion of Fuel
Published in Neil Petchers, Combined Heating, Cooling & Power Handbook: Technologies & Applications, 2020
Due to the methods used in their production, fuel oils fall into two broad classifications: distillates and residuals. Both distillate oils and residual oils are parts of the crude oil. As heat is applied to crude oil, the light, more volatile oil vaporizes and leaves the crude base. The vapors are then captured and condensed. The condensed liquid is the distillate. The distillates, therefore, consist of overhead or distilled fractions; the residuals are the bottoms remaining from the distillation, or blends of these bottoms with distillates. The American Society for Testing and Materials (ASTM) classifies the fuel oils by grade number.
Energy saving in a crude distillation unit with a divided wall column
Published in Chemical Engineering Communications, 2018
Compared to the product compositions computed by the product amounts, the prospective feed location in the prefractionator is near to the tray drawing kerosene, located at the middle of the main column. But in this case, the feed temperature has to be close to the feed tray temperature to avoid large phase change in the tray. The feed having large content of residue was overheated for easy transportation, and the feed tray was one stage above the bottom of the column in the conventional CDU. In the proposed CDU, the drawing temperatures of products were compared to the feed temperature to determine the feed location between the product drawing trays of AGO and residue. AGO is atmospheric gas oil, which derived its name from originally being used in the manufacturing of illuminating gas. It is used to produce distillate fuel oils and gasoline. The simulation result showed the proper predicted feed location. The flow rates of vapor and liquid of interlinking streams were also iteratively calculated to achieve minimum heating duty. The product specification was adjusted by controlling the temperature of product drawing tray with the rates of steam flow and bottom heat supply. The column pressure of the proposed CDU is the same as the conventional CDU. Table 2 lists the structural and operating conditions in both units.