| Description |
The coal combustion process simulated employing high-fidelity models in both gas and particle phase using an Euleraian formulation of One-Dimensional Model (ODT). The coal submodels including vaporization, devolatilization and char oxidation and gasification are described and implemented within the ODT framework. Two coal devolatilization models: a two-rate model based on the Kobayashi-Sarofim and the Chemical Percolation Devolatilization (CPD) are described and implemented. In the gas phase, new formulation of an infinitely fast chemistry (flame-sheet) is developed and implemented. The main aim of this dissertation is to apply ODT model to simulate a large/pilot scale coal combustor. To achieve this aim, the models are first challenged in much simpler cases. An experiment conducted on single particle combustion in laminar flow is simulated to challenge the gas phase and coal submodels. The effects of the thermochemical models from the turbulence models are isolated. Ignition delay reported by experiment is applied as a metric to measure the accuracy of simulation predictions. The predicted ignition delays indicate that simpler Kobayashi-Sarofim and flame-sheet models roughly capture general trends present in the experimental data, but fail to provide quantitative agreement. On the other hand, the CPD model paired with detailed gas-phase chemistry provides reasonable agreement with the experimental observations over all reported conditions. Oxy-coal combustion is among the promising technologies to reduce greenhouse gas emissions for stationary power generation. An oxy-coal combustor located at the University of Utah is simulated using the ODT model. Predictions of flame stand-off distance are compared with experimental results. The impacts of models complexity and parameters as well as system parameters on the flame stand-off prediction and flame stability are studied. The influence of gas models, detailed kinetic vs flame-sheet, and devolatilization models, CPD vs Kobayashi-Sarofim models on the prediction of flame stand-off distance are investigated. Furthermore, the impacts of mixing rate and radiative temperature on the flame stability and flame stand-off are studied. Increase in the mixing rate shrinks the flame stand-off Probability Distribution Function (PDF) and moves the mode of PDF to shorter distances, however, the minimum flame stand-off distance is relatively insensitive to mixing rate. Impact of radiative temperature on flame stand-off distance is significant where an increase in radiative temperature shifts the whole flame stand-off PDF to shorter distances and also decreases the width of PDF. Using flame-sheet calculation in the gas phase, decreases the flame stand-off PDF width and moves the mode of PDF to shorter distances. Nevertheless, the minimum flame stand-off distance is insensitive to use flamesheet model. It is shown that the devolatilization model dictates the minimum flame standoff distance. |
