One of de most important environmental problems nowadays is the abatement
of NOx emissions. NOx are involved in photochemical reactions that produce smog and
acid rain, and (together with CO2, CH4 and H2O), take part in the greenhouse effect.
One of the most efficient ways to reduce NOx emissions is Selective Catalytic
Reduction (SCR). In SCR NOx are reduced to N2 and H2O by reaction with ammonia or
urea. Ammonia is most commonly used and is the reactant considered in this study.
Conventionally, this reaction is performed in steady fixed bed reactors, but there are
other reactor types that can be used, including those operating in dynamic conditions,
such as Reverse Flow Reactors (RFR). RFR consist of a fixed bed catalytic reactor in
which the direction of the inlet flow is reversed periodically. Among other advantages,
the periodic change in the inlet flow allows autothermal operation even for weakly
exothermal reactions. This study is devoted to the modeling a monolithic RFR used for
NH3-SCR. An unsteady one-dimensional heterogeneous model has been developed for
simulating the reactor behaviour. The model is formed by differential equations
corresponding to conservation equations, applied separately to the gas and solid phases,
and algebraic equations used for estimating the physical and transport properties. The
model considers internal and external mass and heat transfer resistances, and axial
dispersion. Experimental validation of the model allows its use for the optimization of
the most important variables that affect the process.
Keywords: Reverse flow reactor (RFR), selective catalytic reduction (SCR),
dynamic modeling, NOx abatement, pilot scale reactor, autothermal operation,
transient respond method, non-stationary reactors, structured catalysts, greenhouse
gases abatement.