THERMODYNAMIC EQUILIBRIUM CALCULATIONS OF DEPOSITS ON SUPERHEATER TUBES IN WASTE INCINERATORS

摘要

Thermodynamic equilibrium calculations were conducted to obtain flue-gas composition and molar amount of volatile condensate deposits on superheater tubes upon combustion of municipal solid waste. Effects of sodium, potassium, chlorine, and sulfur involved in municipal solid waste on deposit chemistry were examined. Possible influence of flue-gas temperature and metal temperature on corrosion were investigated as well. Calculated flue-gas composition agreed relatively well with the flue gas composition in real incinerators. Equilibrium calculation showed that vapor condensate deposits on the 550°C tube surface from 650 and 750~C flue gases consisted predominantly of sodium and potassium chlorides. Sulfate precipitation from hot gases was slight. The amount of molecular chloride precipitates was greater for flue gas of 750°C than of 650°C. For the same gas and metal temperature, 0.1-0.5wt.% chlorine in municipal solid waste did not affect the tube deposit chemistry drastically. It is suggested that high chlorine, low sulfur, moderate amount of sodium/potassium, and trace inclusion of heavy metals such as lead and zinc in waste are the principal factors in the fuel chemistry which cause severe corrosion attack of superheater tubes in waste incinerators.