REVERSE-FLOW REACTOR

A reverse-flow reactor is a fixed-bed adiabatic reactor in which the locations of inlet and the outlet are periodically switched (see figure 1). This way the middle part of the reactor can operate at a very high temperature (typically 500 °C), while the outlet temperature is only the inlet temperature plus the adiabatic temperature rise (typically 40 °C). Hence, a reverse-flow reactor operates in the temporal regime and combines the functions of heat exchange and reaction in a single vessel. The periodic operation causes an effective counter-current heat exchange, without the need to install heat exchangers at the front and the back of the reactor. This way investment cost is strongly reduced compared to a conventional set-up of a reactor with a heat exchanger to recover the heat from the outlet and use it to heat the feed stream. The first implementation was in 1982 [1]. By 2012 thousands of these reverse flow reactors were in commercial scale operation [3]. Reverse flow reactors are used in dilute gas systems with a limited adiabatic temperature rise [2]. They are used in SO₂ oxidation, NO_x reduction, N₂O decomposition and VOC oxidation [1]. Either a heterogeneous catalyst is employed or inert ceramic materials. For VOC oxidation Bunimovich shows the cost advantages when using a catalytic system [4]. For a VOC oxidation of a gaseous effluent of an ethylene oxide plant Mc Namara describes a system with ceramic balls [5].