Comparison of the Performance of a Reverse Flow Reactor and Networks of Non-stationary Catalytic Reactors for Catalytic Combustion of Methane in Lean Mixtures

Although the operation under unsteady state is generally avoided and continuous operation is preferred in the chemical industry, this mode of operation can often lead to a better performance. Because of this, forced unsteady state reactors are object of increasing interest. In particular, the systems based on the periodic reversal of the feed flow direction, called reverse flow reactors (RFR), and the reactor networks of two (RN2) or three reactors (RN3) in series where the feed position is periodically changed from a reactor to the following one in the sequence seem to be particularly promising (1, 2). The simple operation procedure of the RFR leads to important advantages in some catalytic processes. So, reverse flow operation is particularly advantageous in the case of the catalytic combustion of lean air-hydrocarbons mixtures, mainly due to its high thermal efficiency. This technology has been implemented industrially for the abatement of VOCs, and the research on this field is still very active. One of the main drawbacks of this technology is the by-pass of relatively large amounts of unconverted hydrocarbons when the flow direction is reversed (2). Unsteady reactor network consists of a series of fixed bed reactors connected in a closed sequence with periodical variations of the feed position. Contrary to the RFR, the flow direction is maintained in this device. This fact has two important advantages: ensure uniform catalyst utilization and avoid the presence of unconverted gas by-pass. The scope of the present work was to compare, for similar operation conditions, the performance of a RFR and RN of two and three reactors. Different CH4/air mixtures of 0.1-1 % were selected as feed for the combustors. It should be taken into account that studies with these kind of reactors working with methane concentrations close to 1 % are very scarce, in spite of their practical interest (these concentrations are very common in real emissions, such as coke ovens or coal mine ventilation systems).