Distillation overall process

No attempt should be made to optimize pressure, reflux ratio, or feed condition of distillation in the early stages of design. The optimal values almost certainly will change later once heat integration with the overall process is considered. 

The scope for integrating conventional distillation columns into an overall process is often limited. Practical constraints often prevent integration of columns with the rest of the process. If the column cannot be integrated with the rest of the process, or if the potential for integration is limited by the heat flows in the background process, then attention must be turned back to the distillation operation itself and complex arrangements considered. 

LinnhoflF, B., Dunford, H., and Smith, R., Heat Integration of Distillation Columns into Overall Processes, Chem. Eng. Sci., 38 1175, 1983. 

It was noted earlier that dryers are quite difierent in character from both distillation and evaporation. However, heat is still taken in at a high temperature to be rejected in the dryer exhaust. The appropriate placement principle as applied to distillation columns and evaporators also applies to dryers. The plus/minus principle from Chap. 12 provides a general tool that can be used to understand the integration of dryers in the overall process context. If the designer has the freedom to manipulate drying temperature and gas flow rates, then these can be changed in accordance with the plus/minus principle in order to reduce overall utility costs. 

The Overall Process. Each distillation column should be examined in context with the rest of the process as well as by itself. For example, an opportunity for energy saving may be a reduction of process recycles via a purer overhead or bottoms stream. Lowering or raising column pressure to facihtate interchange with other parts of the process is another possible opportunity. 

Samanta A (2001) Modelling and Optimisation for Synthesis of Heat-Integrated Distillation Sequences in the Context of Overall Processes, PhD Thesis, UMIST, UK. 

Shortly after interruption of vacuum distillation from an oil-bath at 115°C to change a thermometer, the ester exploded violently and this was attributed to overheating [1]. A commercial sample of undetermined age exploded violently just after vacuum distillation had begun [2]. In an examination of thermal explosion behaviour, the title compound was used as a model compound in autoclave experiments at low, high or constant pressure. Three stages in the overall process were identified thermal runaway, initiation, and then explosion, and these are studied and discussed in detail. In the high pressure experiments, maximum rates of pressure rise approaching 1000 kbar/s were observed [3]. It is shock sensitive [4]. 

At PPG Industries in Lake Charles, Louisiana, numerous instrument loops provide critical safety, alarm, and shutdown functions. These protective instruments are located on reactors, oil heaters, incinerators, cracking furnaces, compressors, steam-heated vaporizers, kettles, distillation columns, boilers, turbines, and other critical equipment. Process analyzers and flammable vapor detectors also enhance the overall process safety environment. [8]... 

The washed alkylate is fed to a series of three distillation columns where benzene, ethylbenzene, and diethyl benzene-triethyl -benzene mixtures are removed as overhead products. The benzene is recycled to the benzene drying column before feeding again to the alkylator. The diethyl benzene mixture is recycled to the transalkylator. The bottoms from the last column is what we call "flux oil." This consists mainly of diphenylethanes. The amount of this material is good measure of the overall process yield. 

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