Comparison of design and operation strategies for temperature control during selective catalytic reduction of NOx

The problem of controlling temperature profile along a monolithic reactor in which an exothermic reaction (selective catalytic reduction of NOx by hydrocarbons) takes place is considered. Several solutions are proposed and compared. It is shown that a near optimum temperature profile can be achieved by two rather different approaches - one based on periodic switching of a hot reactant and a cold inert stream between two thermally coupled monoliths, and one based on pre mixing the reactant and coolant streams. An adaptive control scheme based on model-predictive control is proposed and shown to be efficient for the case of time-variable properties of the reactant stream.