3D modelling of a solar thermochemical reactor for MW scaling-up studies

Abstract

A lab-scale solar reactor, equipped with a porous CeO 2 structure with dual-scale porosity for CO 2 and H 2 O splitting, has been simulated and validated using available experimental results. The validated model was then used to scale-up the geometry to the MW scale and to investigate the benefits in the studied reactor. The larger reactors displayed partially better performance, but their potential was limited by the restricted thickness of the porous structure during scaling-up. This restriction accelerated the temperature uniformity in the CeO 2 volume, followed by saturation and a steady-state effect with reduced O 2 production. The validated model can be used for further reactor optimization, which should be addressed in combination with a dedicated plant design study for continuous carbon-neutral fuel production.

Performance Assessment of a Heat Recovery System for Monolithic Receiver-Reactors

“…The reactor is modeled using a simplified one-dimensional (1D) representation. The obvious benefit of a simplified 1D model is the reduced computational demand compared to geometrically accurate three-dimensional representations of the reactor geometry [18] and even more to simulations with locally resolved RPC structure [19,20]. The simplified model approach allows simulations for a larger number of design and operational parameter combinations.…”

Quantifying the Impact of Intraparticle Convection within Fixed Beds Formed by Catalytic Particles with Low Macro-Porosities

“…In recent years, computational fluid dynamics (CFD) models have been instrumental in the advancement of fixed bed chemical reactors, which are utilized both as investigative and as optimization tools. ,− In particle-resolved CFD (PR-CFD) models, realistic particle arrangements are generated primarily through the discrete element method (DEM), ,, and the individual particles are resolved and meshed. Particle sizes and shapes within the packed bed can either be mono- − or poly-dispersed − in nature, with modern DEM-based beds implementing multiple particle shapes, such as spherical, cylindrical, or Raschig rings. ,,,,− PR-CFD models yield key information regarding the interconnected nature of the physicochemical phenomena during operation of the fixed bed system. ,, Specifically, their ability to consider the impact of the geometrical bed structure to predict the interparticle heat and mass transfer yields highly valuable insights for reactor engineering. − Fixed bed reactors include different levels of “porosity” (Figure ). The particles (gray spheres in Figure a) are immobile, having interconnected gaps between them, referred to as “interparticle network”, where reagents can flow through.…”

“…Each of these pore-scales offers distinct advantages to the porous medium. Specifically, macro-pores allow convective flow to traverse the medium, increasing the effective heat and mass transfer compared to what would be possible solely through intraparticle diffusion. , On the contrary, there is no convection through the micro-pores, and the role of this pore-scale is to maximize the effective surface area and thus the reactivity of the porous medium. , In fact, catalytic porous media with dual-scale porosities have been introduced at different applications to reinforce heat and mass transfer through intraparticle convection. ,− These can be broken down into porous media with large macro-porosities, above 0.5, and with low macro-porosities, below 0.5. For the latter, Yang et al examined the intraparticle flow phenomena within a porous particle containing 10 nm meso-pores and 0.1 mm macro-pores .…”

“…In most PR-CFD studies, the catalytic particles are treated as solid for the purpose of intraparticle flow, with the external particle surface being modeled as an impermeable wall. ,,,, By enforcing the no-slip boundary condition on their surface, viscous flow, and thus intraparticle convection, does not penetrate the intraparticle structure, where only species diffusion is assumed to exist. However, catalytic porous media with multi-scale porosities are routinely used for various applications, reinforcing the need for advanced CFD models, able to reproduce the complex intraparticle structure and its impact on all aspects of physicochemical phenomena, including intraparticle convection. ,− …”

Modeling of Ceria Reduction in a Solar Thermochemical Reactor via DEM Method

“…In the studied power range (0.8 kW to 3.8 kW), the temperature of the CFD model has an error range between -0.3% to 7.15% compared with experiment results. Kyrimis et al [46] numerical studied the scale-up solar thermochemical reactor geometry. The results showed that the scale-up geometry has a benefit for the solar-to-fuel efficiency at the beginning of the reduction but limited due to the thickness of CeO2 RPC.…”