Structure of operating domains of loop reactors

Abstract

A loop reactor (LR), composed as an N‐unit loop with step‐wise shifted inlet and outlet ports, is one of suggested technological solutions for low‐concentration volatile organic compounds (VOC) combustion. Such a scheme ensures a sufficiently high temperature with autothermal behavior and nearly uniform catalytic utilization. The main drawback of the LR is a very narrow window of switching velocities that sustain a stable “frozen” solution that exists if the switching and the pulse velocity are synchronized. In the present work we show the existence of many “finger”‐like domains of complex frequency‐locked solutions that allow to significantly extend the operation domain, rendering the LR scheme more attractive for practical implementation. A brief comparison with the other heat recuperation technologies (reverse flow and circular loop reactors) is presented. © 2008 American Institute of Chemical Engineers AIChE J, 2008

What is the leanest stream to sustain a nonadiabatic loop reactor: Analysis and methane combustion experiments

“…The operation domain determined for ethylene or for methane oxidation in an uncontrolled system is shown in Figure . The domain of operation becomes narrower with decreasing feed concentration (or ΔT a ) and forms a U‐ or V‐shaped domain in the ( ΔT a ,ν sw ) plane . The boundaries of the operating domain have been approximated: e.g., the lower‐switching boundary is approximated by the front propagation velocity ( ν fr ) which, in an adiabatic reactor, can be determined by system (1), (2) with T m as a parameter, the upper‐switching boundary of a quasi‐frozen patterns corresponds to v sw = v th .…”

“…The domain of operation becomes narrower with decreasing feed concentration (or DT a ) and forms a U-or Vshaped domain in the (DT a ,m sw ) plane. [3][4][5][6][7][23][24][25][26][27][28] The boundaries of the operating domain have been approximated: e.g., the lower-switching boundary is approximated by the front propagation velocity (m fr ) which, in an adiabatic reactor, can be determined by system (1), (2) with T m as a parameter, the upper-switching boundary of a quasi-frozen patterns corresponds to v sw 5 v th . The great advantage of operating a LR, when compared to a once-through reactor, is demonstrated in comparing the smallest concentration required to sustain the system (DT lim ) with that at the lower boundary (m sw 5 0) of the operation domain: Methane combustion in a once-through reactor (i.e., m sw 5 0) requires DT a > 1100 K, as opposed to (DT lim )$50 K in a LR with eLem sw /u$1.…”

Control of Traveling Solutions in a Loop-Reactor

“…Rotating pulses in a loop reactor may emerge provided that the switching velocity ( V sw = ∆/σ i.e., unit length/switching time) and the pulse velocity V f r are matched in a certain way, V sw ∼ = V f r (see [18]) and the pattern is "frozen" in moving coordinates. The "frozen" pulse solutions exist only in a narrow domain of switch velocities (see [14]) and are very sensitive to fluctuations in operating conditions and uncertainties in the model parameters resulting to reaction extinction. To overcome this instability we consider the problem of stabilization of a rotating pulse by automatically tuning the parameter V sw to the value that corresponds to the stable moving the pulse solution.…”

On the MPC of the Methanol Synthesis in a Simulated Moving Bed

“…The concept of rotating port feeding in a loop-shape system made of N units (the loop reactor) was investigated by Sheintuch and Nekhamkina (2005): they developed simplified (asymptotic) models to determine the influence of the external forcing (switching) rate on the performance of such device (Nekhamkina and Sheintuch, 2008a). The autothermal operation in a loop reactor for the catalytic abatement of lean VOC-air mixtures was investigated experimentally by Madai and Sheintuch (2008), and theoretically by Nekhamkina and Sheintuch (2008b): they evidenced that the switching velocity has to be chosen in a very narrow range in order to guarantee full VOC conversion, but, beside these values, there are many complex frequency-locked solutions that allow to significantly extend the operation domain, thus making this reactor configuration more attractive for practical implementation. The possibility of carrying out the process of low-pressure methanol synthesis in the loop reactor was investigated theoretically by Sheinman and Sheintuch (2009): they presented simplified (asymptotic) models, and analyzed the dynamic features of this process.…”