Heat and Mass Integration

Trends include further heat and mass integration, pollution prevention, and consideration of impacts throughout the production supply chain (life-cycle assessment). 

Summarizing, the output of the reactor is an integral over time and over the entire reaction space with all interconnections between different zones of the reactor. Mixing and heat- and mass-transfer conditions are usually different in various zones and the pattern of these differences as well as proportions between size of zones vary with scale. Obviously, the histories of concentrations and temperatures in the zones differ. Whether the integral outputs of laboratory and full-scale reactors differ from each other, depends on the sensitivity of the process to mixing and heat- and mass-transfer conditions. If the sensitivity is low only minor... 

Ideal reactors can be classified in various ways, but for our purposes the most convenient method uses the mathematical description of the reactor, as listed in Table 14.1. Each of the reactor types in Table 14.1 can be expressed in terms of integral equations, differential equations, or difference equations. Not all real reactors can fit neatly into the classification in Table 14.1, however. The accuracy and precision of the mathematical description rest not only on the character of the mixing and the heat and mass transfer coefficients in the reactor, but also on the validity and analysis of the experimental data used to model the chemical reactions involved. 

The integral reactor is useful for modeling the operations of larger packed bed units with all their heat and mass transfer effects, particularly for systems where the feed and product consist of a variety of materials. 

This integration by quadratures works well for a number of transfer problems in burning or dissolution, for example, the burning of a sphere where the burnt ash builds up an insulating layer on the outside. With the various resistances to heat and mass transfer in series and the assumption that the... 

Selectivity may be determined in the integral or differential mode. Integral selectivity depends on the overall extent of the reaction (degree of conversion) and on the type of reactor used even if heat and mass transfer effects are eliminated. It may be called reactor selectivity for the formation of product P, from the set of reactants B when it is calculated as the mole fraction of P, in the products (exluding unconverted feed) at the exit of the reactor ... 

Determination of the efficiency of the integrated processes, and how to optimize it through careful thermal management of the heat and mass flows. 

The steady-state heat and mass balance equations of the different models were numerically integrated using a fourth-order Runge-Kutta-Gill method for the one-dimensional models, while the Crank-Nicholson finite differences method was used to solve the two-dimensional models. 

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