Performance Indicators for Benchmarking Solar Thermochemical Fuel Processes and Reactors

Concentrated solar energy offers a source for renewable high-temperature process heat that can be used to efficiently drive endothermic chemical processes, converting the entire spectrum of solar radiation into chemical energy. In particular, solar-driven thermochemical processes for the production of fuels include reforming of methane and other hydrocarbons, gasification of biomass, coal, and other carbonaceous feedstock, and metal oxide redox cycles for splitting H2O and CO2. A notable issue in the development of these processes and their associated solar reactors is the lack of consistent reporting methods for experimental demonstrations and modelling studies, which complicates the benchmarking of the corresponding technologies. In this work we formulate dimensionless performance indicators based on mass and energy balances of such reacting systems, namely: energy efficiency, conversion extent, selectivity, and yield. Examples are outlined for the generic processes mention above. We then provide guidelines for reporting on such processes and reactors and suggest performance benchmarking on four key criteria: energy efficiency, conversion extent, product selectivity, and performance stability.

Reversible Molten Catalytic Methane Cracking Applied to Commercial Solar-Thermal Receivers

When driven by sunlight, molten catalytic methane cracking can produce clean hydrogen fuel from natural gas without greenhouse emissions. To design solar methane crackers, a canonical plug flow reactor model was developed that spanned industrially relevant temperatures and pressures (1150–1350 Kelvin and 2–200 atmospheres). This model was then validated against published methane cracking data and used to screen power tower and beam-down reactor designs based on “Solar Two,” a renewables technology demonstrator from the 1990s. Overall, catalytic molten methane cracking is likely feasible in commercial beam-down solar reactors, but not power towers. The best beam-down reactor design was 9% efficient in the capture of sunlight as fungible hydrogen fuel, which approaches photovoltaic efficiencies. Conversely, the best discovered tower methane cracker was only 1.7% efficient. Thus, a beam-down reactor is likely tractable for solar methane cracking, whereas power tower configurations appear infeasible. However, the best simulated commercial reactors were heat transfer limited, not reaction limited. Efficiencies could be higher if heat bottlenecks are removed from solar methane cracker designs. This work sets benchmark conditions and performance for future solar reactor improvement via design innovation and multiphysics simulation.

Methodologies for the Design of Solar Receiver/Reactors for Thermochemical Hydrogen Production

Thermochemical hydrogen production is of great interest due to the potential for significantly reducing the dependence on fossil fuels as energy carriers. In a solar plant, the solar receiver is the unit in which solar energy is absorbed by a fluid and/or solid particles and converted into thermal energy. When the solar energy is used to drive a reaction, the receiver is also a reactor. The wide variety of thermochemical processes, and therefore of operating conditions, along with the technical requirements of coupling the receiver with the concentrating system have led to the development of numerous reactor configurations. The scope of this work is to identify general guidelines for the design of solar reactors/receivers. To do so, an overview is initially presented of solar receiver/reactor designs proposed in the literature for different applications. The main challenges of modeling these systems are then outlined. Finally, selected examples are discussed in greater detail to highlight the methodology through which the design of solar reactors can be optimized. It is found that the parameters most commonly employed to describe the performance of such a reactor are (i) energy conversion efficiency, (ii) energy losses associated with process irreversibilities, and (iii) thermo-mechanical stresses. The general choice of reactor design depends mainly on the type of reaction. The optimization procedure can then be carried out by acting on (i) the receiver shape and dimensions, (ii) the mode of reactant feed, and (iii) the particle morphology, in the case of solid reactants.

Micro-structured packed bed reactors for solar photocatalysis: impacts of packing size and material on light harnessing

The impact of the structuring material on the flow profile and light harnessing in solar reactors was quantified and discussed.

Concentrating and Nonconcentrating Slurry and Fixed-Bed Solar Reactors for the Degradation of Herbicide Isoproturon

This research demonstrates scale-up studies with the development of concentrating and nonconcentrating solar reactors employing suspended and supported TiO2 for the degradation of herbicide isoproturon (IPU) with total working volume of 6 L. Novel cement beads were used as support material for fixing the catalyst particles. In the case of nonconcentrating slurry reactor, 85% degradation of IPU was achieved after 3 h of treatment with four number of catalyst recycling, whereas nonconcentrating fixed-bed reactor using TiO2 immobilized cement beads took relatively more time (10 h) for the degradation of IPU (65%) due to mass transfer limitations, but it overcame the implication of catalyst filtration post-treatment. The immobilized catalyst was successfully recycled for ten times boosting its commercial applications. High photon flux with concentrating parabolic trough collector (PTC) using fixed catalysis approach with same immobilized catalyst substantially reduced the treatment time to 4 h for achieving 91% degradation of IPU. Working and execution of pilot-scale reactors are very fruitful to extend these results for a technology development with the present leads.