Development and optimisation of different overall concepts for the thermal decomposition of methane using a porous Fluid-Wall-Flow Reactor and a Molten-Metal Capillary Reactor
Final Report Abstract
The convective introduction of heat via preheated gases or liquids to drive the high temperature endothermic methane pyrolysis for the CO2-free manufacture of hydrogen has the potential to alleviate the problems arising with carbon deposition that have been encountered with alternative recuperative or regenerative heating strategies. The use of multiple side-jets of heated nitrogen in a ‘hot-shot’ reactor proved able to prevent the diffusion of methane back into the surrounding heating chamber, but no suitable heat shielding technique could be developed to preclude the uncontrolled conductive flow of heat through the inner reactor wall, which resulted in the formation of unwanted carbon deposits. The generation of a protective wall film of a molten metal heat transfer medium in a gas-liquid slug flow to avoid carbon deposition in a capillary pyrolysis reactor was primarily impeded by unfavourable wetting properties of the quartz glass reactor material. Under the prevailing reducing conditions the oxides which seem otherwise to enhance the affinity between the metal and the wall are reduced. It also proved unfeasible to compel wall film formation hydrodynamically at high throughputs. Nevertheless, previous issues with molten metal handling and delivery together with the introduction of gaseous reactants and products were successfully resolved and experimentally implemented using the low-temperature molten metal system GalnSn. In view of the difficulties encountered with the slug flow reactor, a falling film concept was devised which circumvents all the shortcomings of the molten metal slug flow reactor and the bubble column configurations proposed elsewhere. A plug flow characteristic guarantees extended and uniform residence times, while the counter-current flow of gas and liquid ensures high conversions due to the separation of the reaction products (carbon and hydrogen) and can simultaneously accomplish the heat recovery task. Simulations were carried out with a model of this falling-film reactor to demonstrate its efficacy. Either molten salts or metals may be utilised in this concept to mitigate the wettability issue, which is once again crucial to forestall carbon deposition on the reactor wall. Initial experiments to exploit rotation to promote complete wetting of the reactor wall were also conducted.
Publications
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(2016) Convective heat supply reactor concepts for the high-temperature pyrolysis of methane, AIChE 2016, American Institute of Chemical Engineers Annual Meeting 13.-18.11.2016, San Francisco, USA
A. A. Munera Parra, D. W. Agar
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(2016) Molten metal capillary and falling film reactors for the high-temperature pyrolysis of methane, WHEC 2016 – 21st World Hydrogen Energy Conference 13.-16.06.2016, Zaragoza, Spain
A. A. Munera Parra, D. W. Agar
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(2017) Molten metal capillary reactor for the hightemperature pyrolysis of methane, International Journal of Hydrogen Energy, 42(9):13641-13648
A. A. Munera Parra, D. W. Agar
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(2018) Reactor design, modelling and optimisation for the high temperature methane pyrolysis and reverse water-gas shift reaction, Ph.D. Dissertation
A. A. Munera Parra
