Mechanism Investigation on the Sulfation of Condensed Sodium Chloride at 523–1023 K

Abstract

Sulfation of alkali chlorides has significant effects on relieving deposition and corrosion in the heat exchanging surfaces during combustion of fuels abundant in alkali and chloride. This paper studies the effects of sulfation temperature and reactants concentration on the sulfation of condensed sodium chloride in a fixed bed reactor. Results showed that only Na₂SO₄ was found in the products. The sulfation ratio for variation of temperature in 523–1023 K was divided into two stages, first almost no change below 773 K and exponential increase with temperature further increasing. It indicated a different sulfation mechanism existed between low and high temperatures, which was further validated by the kinetic analysis of the sulfation and results of the effects of reactant concentrations. The difference on the sulfation mechanism was mainly due to the formation of a eutectic of NaCl–Na₂SO₄ mixture at high temperatures, which was further confirmed by the results of scanning electron microscopy. The sulfation reaction rate of condensed NaCl at 823–1023 K is described by the expression ${\text{d}}X/{\text{d}}t = 0.218\exp^{ - 10,320/T} (1 - X)^{2/3} \left( {C_{{{\text{O}}_{2} }} } \right)^{0.58} \left( {C_{{{\text{SO}}_{2} }} } \right)^{0.85} \left( {{\text{H}}_{2} {\text{O}}} \right)^{1.87}$.