Investigation of reactions occurring in waste combustion ash using thermal analysis coupled with gas analysis and characterization

Abstract

Waste-to-energy (WtE) ash was investigated for thermal reactions that generate gas components such as hydrogen and carbon dioxide. An evolved gas detection method coupled with thermal gravimetric analysis and differential scanning calorimetry provided insight into the possible reactions occurring in WtE ash at temperatures ranging from 90°C to 600°C in an inert environment. The combined analysis shows that H2 is produced from WtE ash at temperatures ~298°C and is detected until ~480°C. CO2 appears in the evolved gas starting at 290°C and continues to increase as the temperature is increased. The results reveal that the processes releasing H2 and the CO2 are independent of each other, and the CO2 generation depends on the constant input of energy. These results enable the identification of the possible processes occurring in WtE ash decomposition of Friedel’s salt at 280°C and dehydration of Ca(OH)2 at 410°C, both of which release H2O that reacts with the aluminium present to release H2. At temperatures higher than 480°C, an alumina layer is formed preventing further production of H2. X-ray diffraction analysis done on the WtE ash verifies the presence of chemical phases that support the proposed reactions. The outcome of this study enables identifying the possible reactions in WtE ash that can be causing the energy changes seen during disposal, storage and transportation of ash. These results can give direction for detailed understanding and development of the kinetics and the mechanisms of the reactions occurring in WtE ash which is important for optimization of reuse and disposal of ash.