Investigation of a Direct Catalytic Absorption Reactor for Hazardous Waste Destruction

Direct Catalytic Absorption Reactors (DCARs) use a porous solid matrix to volumetrically absorb solar energy. This energy is used to promote heterogeneous chemistry on the catalytic surface of the absorber with fluid-phase reactant species. Experimental efforts at Sandia National Laboratories (SNL) are using a DCAR to destroy hazardous chemical waste. A numerical model, previously developed to analyze solar volumetric air-heating receivers and methane-reforming reactors, is extended in this work to include the destruction of a chlorinated hydrocarbon chemical waste, 1,1,1-trichloroethane (TCA). The model includes solar and infrared radiation, heterogeneous chemistry, conduction in the solid absorber, and convection between the fluid and solid absorber. The predicted thermal and chemical conditions for typical operating conditions at the SNL solar furnace suggest that TCA can be destroyed in a DCAR. The temperature predictions agree well with currently available thermocouple data for heating carbon dioxide gas in the DCAR. Feasibility and scoping calculations show trichloroethane destruction efficiencies up to 99.9997 percent at a trichloroethane flow rate of 1.7 kg/hr may be obtainable with typical SNL solar furnace fluxes. Greater destruction efficiencies and greater destruction rates should be possible with higher solar fluxes. Improvements in reactor performance can be achieved by tailoring the absorber to alter the radial mass flux distribution in the absorber with the radial solar flux distribution.