Reversed-flow reactor technology overview

im1

Phase 1: Forward direction of the flow

im2

Phase 2: Reverse direction of the flow

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Temperature profile dynamics in an RFR: lines show boundary positions for heat wave oscillation

As its name indicates, a Reversed – Flow Reactor (RFR) operates with periodical reversals of gas flow through beds of catalyst and, when necessary, ceramic packing. Figures in the sidebar illustrate the simplest configuration of the RFR. More complex schemes are often used for practical purposes.

Cold incoming gas flow enters the reactor through one of the valves V1 or V2. During the first half-cycle (Phase 1), the valves V1 and V4 are opened while the valves V2 and V3 are closed. This sends the gas flow in the direction shown by arrows. While passing through solid material, the gas accepts heat from the hotter solid material. Thus, gas temperature rises while the solid material is cooled. Dramatic difference in heat capacity of solid and fluid phases allows for preheating large volumes of gas using a relatively small bed.

Once the gas flow is sufficiently heated, catalytic reaction begins and, in the case of exothermic reaction, heat is released. After leaving the reaction zone, hot gas flow passes through outlet portion of the bed. Heat is transferred from the gas to colder catalyst. Cooled gas flow then leaves the reactor through the valve V4.

After the inlet portion has been sufficiently cooled, the flow is reversed and Phase 2 begins. The gas flow now enters catalyst bed from the side preheated during the previous phase, through the valve V2. After reaction zone, it gives up heat energy to previously cooled portion of the bed and leaves the reactor through the valve V3. The valves V1 and V4 are closed.

Periodical reversals of the gas flow help maintain the catalyst temperature at design conditions as long as enough heat is released by the reaction. The resultant temperature profile (shown on the left) has a characteristic shape: the temperature is at maximum in the central portion of the bed, decreasing towards the inlet and outlet. The ‘heat wave’ moves periodically through the bed in the direction of gas flow, oscillating between two symmetrical end positions.

In-depth discussion of theoretical fundamentals, laboratory and pilot tests, and design and operation of commercial plants using reversed-flow reactor technology can be found in numerous publications by Matros Technologies' team.

 

 

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