Hydrogen production by cracking of methane in a solar reactor

 

Solar thermal decarbonization of methane has been proposed as a midterm step towards a renewable energy scenario in which hydrogen plays a key role Thermo-chemical conversion of solar energy can be also regarded as an efficient long-term storage option for solar energy. The feasibility of solar thermal cracking technology of methane has been demonstrated by several research groups, in particular, by A. Steinfeld and co-workers  [1-3]. However, further research is needed in order to increase thermo-chemical efficiency and to enable scale-up of the proposed processes.

In a previous master thesis project [4], theoretical predictive models for multiphase reactive flow in a reactor for solar thermal cracking of natural gas has been formulated. The solar reactor proposed by Maag et al. [5] was taken as reference for the theoretical modeling. This reactor is characterized by a flow of methane mixed with argon laden with carbon particles and exposed to concentrated solar radiative energy. The carbon particles are necessary since they act as radiant absorbers and provide surface needed to enhance the cracking reaction of methane. As the reaction progresses, hydrogen is produced together with solid carbon. The solid carbon produced is deposited on the particle surface, resulting in particle growth.

In [4] a model applicable in the case of laminar flow has been applied to simulate one of a set of conditions studied experimentally in the literature. Turbulent flow is expected at scale-up of the process to larger throughput. A model applicable in the case of turbulent flow has been formulated but has not been applied yet. The proposed approach employs a model equation for the joint velocity-composition probability density function (PDF) that is solved by a hybrid Finite-Volume/Monte Carlo algorithm. In the proposed PDF approach, mean quantities, such as mean hydrogen concentration, are obtained as averages over multiple samples of the flow, represented in a Monte Carlo simulation. This approach provides the mean chemical source terms in exact form, in the evolution equation for the gas mass density function and thus, the effect of the non-linear reaction rates is taken into account without approximation.

Objective

The objective of this proposed Master Thesis project is to continue the investigation on modeling of the solar reactor in two ways:

- starting from the existing implementation in ANSYS Fluent, continue the study of the laminar flow reactor. Extend the study to a number of cases studied experimentally and evaluate the quality of the model predictions by comparison with experiments. On the basis of the results make recommendations for reactor design.

- implement the proposed PDF model in the TU-Delft in-house code PDFD and in numerical studies investigate the influence of turbulent fluctuations on the conversion to hydrogen in various conditions. On the basis of the results make recommendations for scale up of the solar reactor.

Depending on the interests and experience of the student executing the project emphasis can be on one or more of the following aspects: reactor design, CFD validation, theoretical modeling, numerical simulation.

Supervisor: Prof. dr. D.J.E.M. Roekaerts

Project suitable for MSc Thesis AP, SET, SPET, SFM

References

[1] D. Hirsch and A. Steinfeld (2004). Solar hydrogen production by thermal decomposition of natural gas using a vortex-flow reactor. International Journal of Hydrogen Energy, 29(1):47 – 55

[2] G. Maag, (2006). Monte Carlo radiative heat transfer analysis of a CH4  flow laden with carbon particles. Master Thesis, ETH Zürich

[3] A. Steinfeld (2005). Solar thermochemical production of hydrogen. A review. Solar Energy, 78(5):603 – 615

[4] A. Rubino (2013). Theoretical modeling of laminar and turbulent dispersed multiphase flow in a solar reactor for hydrogen production by cracking of methane, MSc Thesis, TU Delft

[5] G. Maag, G. Zanganeh and A. Steinfeld, (2009). Solar thermal cracking of methane in a particle flow reactor for the co-production of hydrogen and carbon. International Journal of Hydrogen Energy , 34(18):7676 – 7685.

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