| Coal has been an important energy resource for over 100 years and will continue to be in this century. However, traditional schemes for coal utilization have been criticized for low efficiency and high pollution characteristics. Some clean coal technologies have been identified as being viable to address these problems. The fundamental understanding of the physical and chemical processes involved in these advanced coal conversion technologies is necessary. To gain this understanding, extensive experimental and modeling efforts were made to characterize these processes for several carbonaceous materials.; Coal char particles burn with reductions in diameter and apparent density due to the oxygen concentration gradients established inside particles burning at high temperatures. No model based on fundamental principles has been developed that accurately predicates the observed reductions. In this study, a mode of particle burning model was developed that allows for variations in particle size and apparent density during conversion that depend on the instantaneous state of the char particle. It was demonstrated that this model can predict the burning mode of char particles undergoing oxidation in environments similar to those in real furnaces.; In advanced coal conversion technologies, the char conversion process occurs at elevated pressures. To assure that high-pressure effects are fully characterized in our model, oxidation data were obtained at high pressures and used to validate the model. It was demonstrated that the model accurately describes the dual effects of pressure on chemical kinetics and mass transport rates. The different type structures of char particles that are formed during devolatilization were also characterized. Models for the conversion of cenospherical, mixed and dense char particles were developed and used in a robust model for char oxidation.; Most advanced coal conversion technologies employ gasification process. In order to provide a framework for developing models of gasifiers, a carbon-carbon dioxide reaction mechanism was developed and validated. With the mechanism, coal conversion in advanced gasifiers can be predicted. |
