| 内容提要: |
Due to the growing population, and rapid economic growth, thegeneration of municipal solid waste (MSW) is rapidly increasing. Waste-to-energy (WtE), as an environmentally preferred method now play an increasing role in waste management as it has the advantage of energy recovery and ~90% volume reduction of waste for final landfill disposal. WtE operating and maintenance costs however, increase due to superheater corrosion induced by large amounts of alkali chloride (KCl), H2O vapour, and SO2 released from MSW during combustion. Understanding the corrosion mechanism, reaction rates, and
identification of important reaction pathways enable the mitigation of the corrosion problem. Thus a novel kinetic model was developed to study the corrosion behaviour of pure Fe-metaland reaction pathways using chemkinPro and Gaussian 09. It relies on a detailed chemical kineticmodel for the high-temperature gas-phase interaction between potassium chloride, the O/H radicals,chlorine/sulphur species and the Fe-metal.The rate coefficients for the surface reactions were estimated based on density functional theory and
conventional transition state theorycomputations using several Fe clusters that represented the Fe metal surface. The model was validated by the experimental results obtained from well-controlled simulated corrosion experiments conducted in an electrically heated furnace at 500°C and each test lasted for 50hours.The exposure conditions consisted of 0-600mg KCl, 0-2000ppm SO2, 0-30vol.%
H2O, 8vol.% O2 and N2 as the carrier gas.Comparison of the kinetic model and the experimental data showed therewas a good agreement. The results showed that increasing KCl concentration accelerated the corrosion of Fe with a parabolic rate law. The concentration of SO2 >500ppm enhanced the rate of
iron mass loss while 250-500ppm concentration reduced corrosion of Fe and 0-250ppm SO2 had less effect on corrosionrate. Increasing moisture concentration increased the corrosion rate of Fetube metal. At constant SO2 and O2
concentrations, maximum reaction kinetics in the sulphation of KCl occurred when H2O vapour concentration approaches 10 vol.%. Moisture concentration of10vol.% was the criticalpoint at which concentration abovethe corrosion rate was accelerated. The reaction series that replenished the Cl radicals and KSO3Cl promoted the high corrosion rates while reaction path that forms sulphate suppresses it. The effect of steam parameters on SO2 and KCl induced corrosion rate were presented and discussed. |