15.2. Steady-State and Dynamic Effects of Recycle

A typical chemical process includes a chemical reactor to create products from reactants. Generally, the larger the reactor the greater the conversion of reactants to products; the main limit is imposed by equilibrium considerations. Rather than having a chemical reactor that is large enough to approach equilibrium conversion, it is usually more economical to have a smaller reactor, with a separator and a recycle stream to improve the overall conversion of reactants to products. If secondary reactions occur, or inert components can “build up,” it is common to include a purge stream. Recycle systems are a source of challenging control problems, including the so-called “snowball” effect (sensitivity ...

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