A new method for controlling the ignition state of a regenerative combustor using a heat storage device Pablo Marín, Fernando V. Díez, Salvador Ordóñez ⇑ Department of Chemical and Environmental Engineering, University of Oviedo, Facultad de Química, Julián Clavería 8, Oviedo 33006, Spain highlights  Dynamic modelling using heterogeneous one-dimensional models.  Design and simulation of regenerative thermal oxidizer and heat storage system.  Feedback control determines the heat extracted/introduced in the oxidizer.  Demonstration for a real coal mine ventilation air emission. article info Article history: Received 30 July 2013 Received in revised form 16 November 2013 Accepted 28 November 2013 Keywords: Ventilation air methane Methane complete combustion Unsteady state reactor Reverse flow reactor Sensible heat storage Feedback reactor control abstract Regenerative oxidizers are very useful for combustion of methane–air lean mixtures (<1 vol.% and as low as 0.15%), as those generated in coal mines (ventilation air methane, VAM). However, the performance of the oxidizer is unstable, leading to overheating or extinction, when methane concentration varies. We propose a new procedure for overcoming this problem, using the heat storage concept. Thus, this issue is addressed by proposing the use of an external sensible heat storage system, added to the regenerative oxidizer, capable of storing the excess of heat released in the oxidizer during rich concentration periods, and using it to heat the feed as needed during lean concentration periods. The performance of the heat storage system has been studied by simulating the behaviour of a regenerative thermal oxidizer designed to operate at 0.25 vol.% nominal feed methane concentration. It was found that the regenerative oxidizer, provided with the heat storage system together with a feedback controller that regulates the heat extracted/introduced in the oxidizers can operate satisfactory, dealing with the variations in methane concentration found in ventilations of coal mines. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction The environmental concern about methane emissions has risen in the last years, because this gas is the second contributor to glo- bal warming, after carbon dioxide. The most important sources of methane emissions are coal mines, natural gas extraction and pro- cessing facilities, landfills, etc. Among the different technologies for controlling methane in air emissions, oxidation to carbon dioxide is the most effective: methane global warming potential is 20 times higher than that of carbon dioxide, so there is a clear environmen- tal advantage in oxidizing methane to carbon dioxide before releasing it to the atmosphere [1–3]. The most appropriate combustion technology depends on the concentration of methane in the emission. Gas turbines allow direct production of electricity from the combustion reaction, but require a high concentration of methane [4]. For lower concen- trations, autothermal oxidation of methane (e.g., without the need of additional fuel) is feasible, but it requires heat exchange between the inlet and outlet streams. This heat exchange can be done using recuperative or regenerative devices [5,6]. Recuperative heat exchange is based on indirect heat exchangers, whereas in regenerative heat exchange, the heat of the outlet stream is first stored in a solid bed, which is later used to pre-heat the inlet stream. Due to the direct gas-to-solid heat transfer, the thermal efficiency of regenerative heat transfer is higher. For this reason, regenerative oxidizers are usually the most appropriate devices to carry out methane combustion at low concentration [7–9]. Regenerative oxidizers operate under forced unsteady-state conditions, created by periodically reversing the feed flow direc- tion. Therefore, the heat released by the exothermic reaction is trapped inside the reactor bed between two consecutive flow reversals, being used to preheat the cold feed up to the reaction temperature. Further explanations about this technology and its applications have been exhaustively reported in recent reviews and articles cited therein [9–11]. There are two types of regenerative oxidizers, depending on the type of methane oxidation reaction: regenerative thermal oxidizers 0306-2619/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.apenergy.2013.11.070 ⇑ Corresponding author. Tel.: +34 985 103 437; fax: +34 985 103 434. E-mail address: sordonez@uniovi.es (S. Ordóñez). Applied Energy 116 (2014) 322–332 Contents lists available at ScienceDirect Applied Energy journal homepage: www.elsevier.com/locate/apenergy