Javier Fernandez

University College London, UK

Title: Catalytic combustion in reverse flow reactor with integrated adsorption

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Biography

Javier Fernández obtained his bachelor degree in Chemical Engineering in 2007 and his masters degree in Environmental and Processes Engineering in 2010 from the University of Oviedo, Spain, while he worked in research activities for different companies such as Saint-Gobain, Biogas Fuel Cell and XSTRATA. In 2011 he started his PhD in Chemical Engineering, working in the LOWCARB ERC Project. He received the Cum Laude award in 2014 and then he moved to the Warwick Manufacturing Group, where he worked as a research fellow. He also worked in a spin-out company (Stoli Catalysts Ltd) for a year. In 2017, he was appointed as Assistant Professor in Chemical Engineering and finally as lecturer in Chemical Engineering in 2020 at University College London.

Abstract

1.   Short Description of what will be discussed during the presentation

High flow rate methane-containing emissions (0.1-0.6 %) are released during coal mine operation (ventilation gases). In the last years, the concern about these emissions has increased; since methane is an important greenhouse effect gas (its global warming potential is 23 times higher than the one for CO₂). Hence, its contribution to the environmental impact in the coal mining has been determined taking into account the carbon and ecological footprints.

Considering the emission flow rates and methane concentration, catalytic combustion could be an interesting alternative for the treatment of these emissions. Therefore, the use of a regenerative system integrated in the reactor (reverse flow reactor, RFR), which is based on the use of regenerative beds for heating the feed and in the change of flow direction, leads to a high energetic efficiency and to autothermal operation (the heat from the reaction is used to heat the feed stream, without needing external energy).

The RFR operation has been experimentally studied by using a pilot scale reactor (0.05 m diameter and 0.4 m bed length). Taking into account that the ventilation air has no sulphur compounds, the most suitable catalyst for methane combustion is palladium. Therefore, a monolithic catalyst (Pd/Cordierite) has been chosen, because this kind of beds has key advantages, such as a lower pressure drop, but also some drawbacks, as a reduction in the reactor stability.

Firstly, the intrinsic kinetics for the methane combustion has been determined, first-order dependence on methane concentration providing the best fitting to the experimental data. Then, considering that several coal mines present high CO₂ concentrations (up to 2.5 %), its possible effect on the kinetics has been analyzed, determining that this effect is negligible. On the other hand, mine ventilation systems present high moisture contents (water molar fraction between 0.02 and 0.05), water being considered a strong inhibitor in catalytic combustion. This behavior has been modeled considering a Langmuir-Hinshelwood approach.

Concerning to the operation with the reverse flow reactor for the catalytic combustion of the coal mining ventilation air, firstly the influence on the reactor performance of the switching time (50 – 600 s), the initial methane concentration (1000 – 6000 ppm) and the flow rate (15 – 30 NL/min) was studied, concluding that switching time and initial methane concentration are key the parameters in order to avoid the extinction of the reactor.

The moisture inhibition effect has been also considered in the operation of the reverse flow reactor. Therefore, it was observed that it has an important influence on the reactor stability, given that an increase in the methane initial concentration was needed in order to keep reactor stability at a given switching time in presence of H₂O. In order to overcome this problem, a new approach is taken in this PhD, consisting of adding an adsorbent bed at both ends of the catalytic zone. An appropriate selection of the adsorbent (g-Al₂O₃) leads to a totally compensation of the effect of the moisture in the reactor performance.

The information from the experiments allows the validation of a dynamic one-dimensional heterogeneous model for the RFR, which was solved using a MATLAB code. Using the experimentally validated model, and considering a typical coal shaft of the Asturian basin (Candín) with a flow rate of 45 m³/s and a methane concentration of 3000 ppm, the influence of the humidity, concentration and flow rate variations in the performance of a full-scale reverse flow reactor was analyzed. 

2.   What will the audience take away from your presentation? (Try to list 3-5 specific items)

1.          Explain how the audience will be able to use what they learn? This presentation could boost collaborations as people would like to study the feasibility of this innovative reverse flow reactor. They will learn how temperature could be controlled with this approach, so this could be a breakthrough in reaction engineering.
2.          How will this help the audience in their job? This presentation will show a possible new technology for combustion and exothermic reactions. This temperature control is a new approach which could mean new research lines for other exothermic reactions.
3.         Is this research that other faculty could use to expand their research or teaching? Possible academics and industries could be interested in testing their catalysts with this approach. Strong collaborations could be developed and discussed.
4.         Does this provide a practical solution to a problem that could simplify or make a designer’s job more efficient? This can have an impact on thermal or catalytic combustion or high temperature processes.
5.          Will it improve the accuracy of a design, or provide new information to assist in a design problem?  It will provide a much wider variety and possibilities for desired products in catalytic reactions.