Selective catalytic reduction of NO in a reverse-ﬂow reactor: Modelling and experimental validation Emilio Muñoz, Pablo Marín, Fernando V. Díez, Salvador Ordóñez ⇑ Department of Chemical and Environmental Engineering, University of Oviedo, Facultad de Química, Julián Clavería 8, 33006 Oviedo, Spain highlights  Reverse-ﬂow reactors easily overcome feed concentration disturbances.  Central feeding improves ammonia adsorption in reverse-ﬂow reactors.  Dynamic heterogeneous model validated with bench-scale experiments.  Optimum reverse-ﬂow reactor design improves efﬁciency and reduces reactor size. article info Article history: Received 30 July 2014 Received in revised form 29 September 2014 Accepted 26 October 2014 Available online 13 November 2014 Keywords: Forced unsteady state reactor Periodically operated reactor Chromatographic reactor NO x abatement Dynamic reactor modelling abstract The abatement of nitrogen oxides produced in combustion processes and in the chemical industry requires efﬁcient and reliable technologies capable of fulﬁlling strict environmental regulations. Selective catalytic reduction (SCR) with ammonia in ﬁxed-bed (monolithic) reactors has stood out among other techniques in the last decades. In this work, the use of reverse-ﬂow reactors, operated under the forced un-steady state generated by the periodic reversal of the ﬂow direction, is studied for improving the SCR performance. This reactor can take advantage of ammonia adsorption in the catalyst to enhance concen- tration proﬁles in the reactor, increasing reaction rate, efﬁciency and reducing the emission of un-reacted ammonia. The process has been studied experimentally in a bench-scale device using a commercial monolithic catalyst. The optimum operating conditions, best ammonia feed conﬁguration (side or central) and capacity of the reactor to deal with feed concentration disturbances is analysed. The exper- iments have also been used for validating a mathematical model of the reactor based on mass conserva- tion equations, and the model has been used to design a full-size reverse-ﬂow reactor able of operating at industrial conditions. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Nitric oxides (NO x ) are released to the atmosphere in large amounts, mainly as result of transportation and industrial pro- cesses obtaining the energy from combustion reactions, and are an important environmental hazard, as they participate in the greenhouse effect, acid rain, and in lakes and rivers eutrophication, and, more markedly in the formation of troposphere ozone (photo- chemical smog) [1,2]. Because of these reasons, NO x emissions are very tightly regu- lated in industrialized countries, and their abatement has become of great industrial importance in combustion-based systems (power plants ﬁred with fossil and non-fossil fuels, waste inciner- ators, cement kilns, etc.) and is being actively studied [3–7]. NO x emissions can be reduced by decreasing NO x formation (primary strategies, e.g. by modifying the process design or operat- ing conditions), or by separating or eliminating NO x from efﬂuents (secondary strategies). Among the secondary ones, NO x selective reduction, either non-catalytic (SNCR) or catalytic (SCR), are the most used (i.e. are considered by the EU as Best Available Techniques for NO x abatement from large stationary sources) [2,8]. NO x selective reduction is based on the reaction of NO x with a reducing agent, most commonly ammonia, yielding molecular nitrogen and water. The main reactions in ammonia SCR are: 4NH 3 þ 4NO þ O 2 ! 4N 2 þ 6H 2 O ð1Þ 2NH 3 þ NO þ NO 2 ! 2N 2 þ 3H 2 O ð2Þ 8NH 3 þ 6NO 2 ! 7N 2 þ 12H 2 O ð3Þ http://dx.doi.org/10.1016/j.apenergy.2014.10.081 0306-2619/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +34 985 103 437; fax: +34 985 103 434. E-mail address: sordonez@uniovi.es (S. Ordóñez). Applied Energy 138 (2015) 183–192 Contents lists available at ScienceDirect Applied Energy journal homepage: www.elsevier.com/locate/apenergy