Page 15 - Modeling of Chemical Kinetics and Reactor Design

processes interact with chemical processes. The proposed model must
represent the flow behavior of an actual reactor, which is realistic
enough to give useful information for its design and analysis. The text
reviews different reactor flow models.

SAFETY IN CHEMICAL REACTION

Equipment failures or operator errors often cause increases in
process pressures beyond safe levels. A high increase in pressure may
exceed the set pressure in pipelines and process vessels, resulting in
equipment rupture and causing major releases of toxic or flammable
chemicals. A proper control system or installation of relief systems can
prevent excessive pressures from developing. The relief system con-
sists of the relief device and the associated downstream process
equipment (e.g., knock-out drum, scrubber, absorbers, and flares) that
handles the discharged fluids. Many chemical reactions (e.g., poly-
merization, sulphonation, nitration) in the chemical process industry
result in runaway reactions or two-phase flow. This occurs when an
exothermic reaction occurs within a reactor. If cooling no longer exists
due to a loss of cooling water supply or failure of a control system
(e.g., a valve), then the reactor temperature will rise. As the temperature
rises, the reaction rate increases, leading to an increase in heat genera-
tion. This mechanism results in a runaway reaction. The pressure
within the reactor increases due to increased vapor pressure of the
liquid components and gaseous decomposition products as a result of
the high temperature. Runaway reactions can occur within minutes for
large commercial reactors and have resulted in severe damage to a
complete plant and loss of lives. This text examines runaway reactions
and two-phase flow relief.

SCALE-UP

The chemical engineer is concerned with the industrial application
of processes. This involves the chemical and microbiological con-
version of material with the transport of mass, heat and momentum.
These processes are scale-dependent (i.e., they may behave differently
in small and large-scale systems) and include heterogeneous chemical
reactions and most unit operations. The heterogeneous chemical reactions
(liquid-liquid, liquid-gas, liquid-solid, gas-solid, solid-solid) generate
or consume a considerable amount of heat. However, the course of

xv