Process design


A process design is to a large extent a consequence of developments on catalyst, choice of reaction routes, selection of solvent system, fluid type etc. At this level of development the structure of the chemical system and the kinetics are determined. Much research is focused on these topics because even incremental improvements may have large economical consequences. The next major step is to find a suitable reactor and process in which to deploy the system on a larger scale.

The traditional way of doing design of new processes is by selecting reactor type and process configuration based on comparison to a similar known system. Design choices are often made on the basis of past experience or trial-and-error using laboratory tests and repeated simulations. These activities are necessary. However, it is not likely that the traditional way alone will lead to the best possible process configuration and design. Complementary tools and methods are needed to lead the design engineer onto the path of optimal design. Deviations from the optimal design will lead to unnecessary loss of product yield, unnecessary large volumes and loss of energy.

Within the conceptual process design activity some of the most important choices are made, which have large consequences on the profitability and environmental loads of the final process technology. According to Douglas (1988) the conceptual design of an integrated plant can be broken down into a hierarchy of decisions and organized into different levels of activities. Among the levels of activities are reactor-separator-recycle structures, heat integration, and separation train sequence design.

A method in focus here is a systematic procedure based on shortcut models. A path is a line of production on which basic operations or functions take place. Reactants pass through a series of functions or basic operations to form the desired products. The basic operations are represented by design functions on the volume path. The design functions are fluid mixing (dispersion), distribution of extra feed points, distribution of heat transfer area and coolant temperature, catalyst dilution distribution and more. The conceptual reactor design problem is solved as an optimal control problem.

Parameterization of the design functions and the state variables are applied. The realization is a staged process string of multifunctional units.


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Magne Hillestad

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