Abstract
In the loop reactor (LR) the system is composed of several reactor units that are organized in a loop and the feeding takes place at one of several ports with switching of the feed port in a periodic way. In its simplest operation a pulse is formed and rotates around it, producing high temperatures which enable combustion of dilute streams. A limiting model with infinite number of units was derived. Rotating pulses, that are steady in a coordinate moving with the switch velocity, emerge in both asymptotic and discrete models when the ratio of switching to front propagation velocities is around unity. But this behavior exists over a narrow domain of this ratio. Simulations were conducted with generic first order Arrhenius kinetics. Experimental observations of simple frozen rotating pulses are reviewed. Outside the narrow frozen rotating patterns domain the system may exhibit multi- or quasi-periodic operation separated by domains of inactive reaction. The bifurcation set incorporates many ’finger’-like domains of complex frequency-locked solutions that allow to significantly extend the operation domain with higher feed temperature or concentration. Control is necessary to attain stable simple rotating frozen patterns within the narrow domains of active operation. Various control approaches that were suggested, or experimentally applied for this purpose, are reviewed. Actual implementation of combustion in LR will involve several reactants of different ignition temperatures and varying concentration. Design and control should be aimed at producing locked fronts and avoid extinction of the slower reaction.
Highlights
Most of the processes in the chemical and petrochemical industries are catalytic, usually in packed beds in which the catalyst phase is solid and stationary
Several studies considered a loop reactor (LR) with the feed port jumping several units in every shift [3, 24, 25]. Such a strategy is claimed to allow better control, since it allows to increase the switching time, as we describe below, the main properties of the LR behavior are captured with a strategy using a one-unit shift
The aim of this article is to review the mathematical nature of dynamics and control of loop reactors, which may be of importance in designing such a system: We focus on a T -periodic solution with a one-unit switching strategy; this strategy admits an asymptotic solution. (N → ∞, the switching time σ →0, but a finite switching velocity)
Summary
Other solutions for attaining temperatures that exceed the adiabatic rise were suggested: In the reverse flow reactor (RFR [28]), that is based on operating under forced periodic flow conditions, the flow direction is alternated periodically (every 5-10 minutes): the temperature profile is symmetric and two fronts (on the left and right side) are trapped while their positions oscillate in time. The advantage of such reactors over simple once-through operation for attaining high temperatures has been demonstrated in many studies of adiabatic units (e.g., see [11, 19], for review). We conclude by pointing out open problems that we deem to be of importance in bringing this technology to maturity
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