Resonance Response of Reverse Flow Reactors: A Numerical Simulation

Abstract

The effect of periodic time-varying inlet parameters on reverse flow reactor behavior is simulated using a onedimensional heterogeneous model with methane as the model reactant. When the flow-reversal cycle is an odd multiple of the inlet concentration variation cycle, a resonance response occurs. Such reactor behavior will occur with various values of superficial inlet velocity, mean inlet methane concentration, flow-reversal time and inert-to-catalyst ratios during this simulation work. A synchronization of the two cycles will cause a sharp increase in the variation of maximum temperature, which may impair reactor stability. Simulation results reveal that the resonance response is attributed to the breakdown of temporal and spatial symmetry in the temperature field of reactor. When a resonance response occurs, adjusting the flow-reversal time is a feasible method to maintain autothermal operation of the reactor. Different from commonly used control strategies both increasing and decreasing flow-reversal time can be used to avoid reactor extinction, and so does avoiding thermal runaway. Simulation work of introducing periodic variation of inlet gas velocity is performed, and a similar resonance response behavior is observed. INTRODUCTIONReverse flow reactors (RFRs), a type of forced unsteady state catalytic reactor, have proved to be one of the effective solutions for waste gas decontamination, such as SO 2 oxidation, 1−3 decontamination of a diluted VOC gas stream 4−7 and the selective reduction of NO x . 8−10 A RFR is a catalytic fixed bed reactor, in which the feed flow direction is reversed periodically. When exothermic reactions are conducted in the reactor, a temperature wave is generated that creeps along with the gas flow. The catalyst at either end acts as a heat regenerator, while the released heat is trapped in the reactor, which maintains the temperature plateau within the reactor and sustains the catalytic reaction even with weak exothermic effects. So, the catalyst packing at the two ends is normally substituted by inert materials for economic reasons.A determination of the steady states of such a system and the construction of a corresponding control strategies are of primary interest in chemical engineering because only steady state or pseudosteady state (PSS) operation has a realistic meaning. However, the RFR behaves in a rather sophisticated manner because of its inherent nonstationary character derived from forced unsteady operation. A number of efforts have been made to establish the dependence of reactor performance on many design and operating parameters, such as reactor length, gas flow rate, flow-reversal time, inlet concentration, wall effects and reaction kinetics. A number of mathematical models and simulation methods have been developed for the dynamic calculation of PSS and the sensitivity analysis over an extended range of parameters. Detailed reviews were provided by Matros 11 and Kolios. 12 A comprehensive survey on RFR performance and model simplification was given by Marín. 4,...

Reverse flow reactors as sustainable devices for performing exothermic reactions: Applications and engineering aspects

“…They found that hot gas extraction affected the temperature-control system leading to reaction extinction and, for this reason, the set a constant switching time when hot gas withdrawal was practised. Other works address this from a theoretical point of view based on model simulations [147][148][149][150].…”

Experimental Research on the Thermal Oxidation of Ventilation Air Methane in a Thermal Reverse Flow Reactor

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