Analysis of Catalytically Enhanced Solar Absorption Chemical Reactors: Part II—Predicted Characteristics of a 100 kW_chemical Reactor

The CAtalytically Enhanced Solar Absorption Receiver (CAESAR) is a 100 kW_chemecal test reactor currently in operation. This type of high-temperature chemical reactor volumetrically absorbs concentrated solar energy throughout a catalytic porous absorber matrix volume, promoting heterogeneous reactions with fluid-phase reactant species flowing through the absorber. A numerical model of these reactors has been developed to provide guidance in the catalytic matrix design for CAESAR. In the CAESAR reactor, methane is reformed using carbon dioxide and a rhodium catalyst. In addition, the model is being used to evaluate both the reactor performance and test data. This paper presents the thermal and chemical characteristics of the reactor for varying incident solar flux, fluid mass flow, convective heat-transfer coefficient, solar and infrared extinction coefficients, and catalyst loading. Predicted CAESAR performance is based on a prototype absorber and anticipated operating conditions. Model results suggest the mass flux must be proportioned to the incident solar flux radial distribution to prevent unacceptably high local temperatures and to provide a reactor having more uniform exit conditions. Either the catalytic loading or geometric thickness of the absorber should be increased for conversion to approach equilibrium levels. Also, the optical density of the matrix (particularly at the sunlit side of the reactor) should be decreased to distribute solar energy more uniformly in depth and decrease matrix temperatures at the front of the absorber.