Analytical models for high-temperature corrosion of silica refractories in glass-melting furnaces

Abstract

Corrosion of refractory silica brick used to line the crown of many glass-melting furnaces is a serious problem in furnaces using oxygen-fuel rather than air-fuel mixtures. To better understand and to quantify this process analytical models are utilized to evaluate the importance of four potential rate-limiting processes: a) gas-phase transport of NaOH to the crown surface; b) diffusion of sodium-containing reactants through a liquid product layer that forms on the brick face; c) gas-phase diffusion of NaOH into refractory pores; and d) chemical-kinetic limitations at the silica grain surface. Predictions are compared with reported corrosion rates and product compositions previously determined by post-mortem analysis of refractory samples. It is concluded that corrosion occurs largely by reaction and removal of material from the exposed brick face, rather than by transport of reactants into the porous bricks. The observed presence of corrosion products deep within the brick pores is shown to be consistent with capillary suction of high-viscosity liquid products from the hot face into the interior. The results further suggest that mechanisms (b) and (c) do not substantially limit the rate of corrosion, but that mechanisms (a) and (d) may both be important. Comparison of measurements with equilibrium predictions of corrosion-product composition indicate that the corrosion reactions are likely to be close to equilibrium at the conditions and lifetimes typical of full-scale furnaces, but that significant departures from equilibrium may occur in short-duration tests. Although computed corrosion rates based on mass transport through a gas boundary layer are somewhat greater than those observed, the results are very sensitive to the gas-phase concentration of NaOH and to the refractory temperature, both of which contain significant uncertainties