SYNMET – Solar Combined ZnO-Reduction and CH₄-Reforming

Funding source: external page BfE - Swiss Federal Office of Energy, Baugarten Foundation, external page Paul Scherrer Institute

Background – The conversion of solar energy into storable and transportable chemical fuels is investigated by means of thermochemical processes using high-temperature solar process heat. The SynMet-process, i.e. the solar combined reforming of CH₄ and reduction of ZnO is considered for co-producing Zn and synthesis gas (syngas). The advantage would be twofold: (1) the reforming of NG in the absence of catalysts may be made to produce high quality syngas with a H₂ to CO molar ratio of 2, which is especially suitable for methanol synthesis; (2) CO₂ emissions derived in the traditional carbothermic reduction and reforming processes are avoided. The technical feasibility of the SynMet-process was demonstrated using the 5 kW solar reactor.

Aims

Modelling of solar reactor using CFD and Monte Carlo ray-tracing simulations.
Establish optimal operating conditions for maximum exergy efficiency.

Fig. 1: Scheme of the solar process for the chemical storage and transport of solar energy. In the first, endothermic step, concentrated solar radiation is used for co-producing zinc and syngas by the combined ZnO-reduction and NG-reforming processes; syngas is further processed to methanol. In the second step, zinc is either used to split water and form H₂, or, alternatively, zinc is used in a Zn/air fuel cell or battery togenerate electrical work. In either case, the chemical product of the second step is ZnO which, in turn, is recycled to the first step.

Fig. 2: Scheme of the solar reactor configuration and photograph of the 5 kW reactor prototype for the SynMet-process. It consists of a gas-particle vortex flow confined to a solar cavity-receiver. ZnO particles, conveyed in a flow of CH₄, are continuously injected into the reactor's cavity via a tangential inlet port. The gas-particle stream forms a vortex flow that progresses towards the front along a helical path. With this arrangement, the chemical reactants are directly exposed to the high-flux solar irradiation, providing an efficient heat transfer directly to the reaction site. Energy absorbed by the reactants is used to drive the endothermic transformation at above 1250 K. The chemical products exiting the reactor are Zn(g) and syngas.

Fig. 3: Photograph of the vortex reactor.

Project-related Publications

SYNMET – Solar Combined ZnO-Reduction and CH4-Reforming

SYNMET – Solar Combined ZnO-Reduction and CH₄-Reforming