Reaction Mechanism for Sulfur Species during Pulverized Coal Combustion

Abstract

Low-NOx combustion technologies are widely applied in pulverized coal-fired boilers. But it promotes the formation of high concentration of H2S, which is one of the main reasons for high-temperature corrosion. To limit the H2S formation, it is urgently necessary to reveal the evolution behavior of the sulfur species. In this work, the reaction mechanism for sulfur species was investigated using a tube-heating furnace for low-sulfur bituminous coal combustion. In the primary stage of combustion, the O2 concentration decreased sharply. Meanwhile, the sulfur species of SO2, H2S, COS and CS2, and significant amount of reductive gases CO and H2, were generated. After the sulfur release finished, the distribution of the sulfur species in the downstream region depended on only the gas-phase reactions. With the reduction of CO and H2, part of SO2 was converted to H2S and COS. There also exited some shift relationships among SO2, H2S, COS, and CS2 in the presence of abundant of CO2 and H2O. On the basis of the experimental results and the principles of Gibbs free energy and chemical equilibrium constant, a new gas-phase reaction mechanism for sulfur species, consisting of 9 reactions, was established. Furthermore, the kinetic parameters were also determined by a strict mathematical optimization process, and the predication errors for sulfur species were within 20%. The new built mechanism was expected to provide great assistance for the control of H2S formation and the prevention of the high-temperature corrosion.