Comparison of reverse flow and counter-current reactors in the case of selective catalytic reduction of NOx
Abstract The paper is focused on the comparison between a reverse flow reactor (RFR) and a counter-current reactor (CCR) in terms of the performances that may be achieved in these kinds of reactors when selective catalytic reduction (SCR) of NO x with ammonia is carried out. In order to investigate the performances of both reactor configurations, a mathematical model based on heat and mass balances for gas and solid phase was used. The possibility of achieving auto-thermal operation, even when a gas with a low temperature is going to be fed to the reactor was investigated. The temperature profiles, the reactants conversion, as well as the response to disturbances in the feeding flow have been used as criteria for comparison. Numerical simulations have shown that the CCR model is able to provide the same results as the RFR model in terms of temperature profiles when certain values of heat transfer coefficient, switching time, flow conditions and reactor geometry are taken into consideration. As a consequence of such similar thermal behaviour, the CCR model could be applied as a limiting case of RFR operation when the fast switching of the flow direction conditions is taken into account. Nevertheless, this analogy provides a simple basis for short-cut calculations since the steady-state profile of a CCR can be computed much easier than the periodic steady-state of a RFR.
Reverse flow reactors as sustainable devices for performing exothermic reactions: Applications and engineering aspects
Abstract Reverse flow reactors are fixed-bed reactors combining in a single intensified device chemical reaction and regenerative heat transfer (energy is stored in a bed as sensible heat). To accomplish this goal, reverse flow reactors are operated in a forced unsteady state created by periodically changing the flow direction. The most important applications of reverse flow reactor are reviewed: oxidation of hydrocarbons and sulphur dioxide, and selective catalytic reduction of nitrogen oxides. These applications involve exothermic reactions. However, recent developments have also made possible it possible the use of reverse flow reactors with endothermic reactions, such methane steam reforming. The modelling of reverse flow reactors is addressed based on the models available for fixed-bed reactors. Practical considerations regarding reverse flow reactors are considered: the selection of the type of bed, the issues of the use of lab-scale devices at dynamic conditions, the assessment of autothermal operation and heat extraction and the integrated adsorption concept. The latter is an innovative concept based on the periodical adsorption in the bed of some of the reactants, products or other feed compounds. This mass regeneration can be combined with the heat regeneration capabilities of reverse flow reactors to increase the degree of process intensification.
THE DYNAMICS OF REVERSE FLOW CHROMATOGRAPHIC REACTORS WITH SIDE STREAM FEED
A combination of analytical and numerical techniques is used to study the dynamics of a chromatographic reactor with flow reversal and side stream feed. We show that effective operation of such a reactor depends upon the existence of sharp slowly moving fronts and that it can be much more efficient than an equivalent continuous flow reactor. The numerical difficulties associated with the sharp fronts can either be overcome by integrating the equilibrium equations or by using a hierarchical adaptive j;rid on the full equations. The flow in the reactor is assumed to be uniform, but our methods can readily b; extended to deal with more complicated cases.