SOLAR REFORMING OF METHANE IN A DIRECT ABSORPTION CATALYTIC REACTOR ON A PARABOLIC DISH .2. MODELING AND ANALYSIS

The CAtalytically Enhanced Solar Absorption Receiver (CAESAR) test was conducted to determine the thermal, chemical, and mechanical performa nce of a commercial-scale, dish-mounted, direct catalytic absorption r eceiver (DCAR) reactor over a range of steady state and transient (clo ud) operating conditions. The focus of the test was to demonstrate ''p roof-of-concept'' and determine global performance such as reactor eff iciencies and overall methane conversion. A numerical model was previo usly developed to provide guidance in the design of the absorber. The one-dimensional, planar, and steady-state model incorporates the follo wing energy transfer mechanisms: solar and infrared radiation, heterog eneous chemical reaction, conduction in the solid phase, and convectio n between the fluid and solid phases. Improvements to the model and im proved property values are presented here. In particular, the solar ra diative transfer model is improved by using a three-flux technique to more accurately represent the typically conical incident flux. A spati ally varying catalyst loading is incorporated, convective and radiativ e properties for each layer in the multilayer absorber are determined, and more realistic boundary conditions are applied. Considering that this test was not intended to provide data for code validation, model predictions are shown to generally bound the test axial thermocouple d ata when test uncertainties are included. Global predictions are made using a technique in which the incident solar flux distribution is sub divided into flux contour bands. Reactor predictions for anticipated o perating conditions suggested that a further in optical density (i.e., extinction coefficient) at the front of the absorber inner disk may i mprove absorber conditions. Code-validation experiments are needed to improve the confidence in the simulation of large-scale reactor operat ion.