Effect of Calcium Hydroxide on the Pyrolysis Behavior of Sewage Sludge: Reaction Characteristics and Kinetics

摘要

The effect of calcium hydroxide (Ca(OH)(2)), a promising additive to control the pollutants released during sludge pyrolysis, on the pyrolysis behavior and kinetics of sewage sludge was investigated in detail in this study. The obtained thermograms of Ca(OH)(2)-blended sludge showed that the addition of Ca(OH)(2) influenced the thermogravimetric characteristics of sludge, especially in the temperature range of 340-700 degrees C where the decomposition of Ca(OH)(2) happens. An increasing addition of Ca(OH)(2) improved the pyrolysis conversion of sludge at temperatures of more than 600 degrees C, which was verified by the increase of the process heat flow. Importantly, the transformation of elements in sludge was promoted, resulting in a lesser content of impurities, which existed mostly in the thermally stable forms, in the remaining char. Kinetic analysis revealed that the pyrolysis behavior of sludge was influenced by the addition of Ca(OH)(2) and reaction temperature. At low temperatures, Ca(OH)(2) acted as the source of nuclei required for the establishment of reaction interface and then induced the secondary cracking of the pyrolytic compounds in the sludge matrix when the reaction came to high temperatures. A retrofitted kinetic model, overcoming the drawback faced by most Arrhenius-derived models that the integral of temperature-induced item was resolved by approximation, is developed and exhibits superiority in describing the reaction characteristics of sludge pyrolysis.