Chemical Engineering Science, Vol.81, 285-297, 2012
Computational modeling of a multiple tube solar reactor with specularly reflective cavity walls. Part 2: Steam gasification of carbon
A three-dimensional, steady state computational model coupling radiative transfer with fluid flow, heat transfer, mass transfer, and chemical reaction kinetics is developed to describe a solar receiver consisting of an array of five tubes enclosed within a specularly reflective cylindrical cavity with a windowed aperture. Radiation heat transfer is incorporated via a combination of ray tracing, Monte Carlo, and finite volume techniques. Steam gasification of entrained 42 nm acetylene black particles is considered and particle transport is described by an aerosol population balance featuring convection, Brownian motion, and thermophoretic diffusion. Maximum temperatures of 1813 K, 1343 K and 1546 K are predicted for the center, front and back tubes respectively, with corresponding reaction conversion of 40%, 2.5% and 9.2% for a solar power input of 6 kW and a carbon feed rate of 0.5 g/min. Temperature of the fluid/particle mixture tracks closely with that of the surrounding tube walls owing to radiative absorption by the particulate phase. Estimated solar-to-chemical receiver efficiency is limited by comparatively low temperatures achieved in outlying tubes and ranges between 1% and 4% with up to 9 kW solar power. Experimentally measured carbon conversion is compared with predictions from the theoretical model utilizing various sets of kinetic parameters available in the literature for steam gasification of petcoke, graphite, activated carbon and low ash coal char. (C) 2012 Elsevier Ltd. All rights reserved.