Study On Upgrading Process Of Lignite Based On The Horizontal Moving Bed Technology

For the lignite upgrading technology based on the principle of horizontal movingbed which proposed by Tsinghua University the mechanism and model research hadbeen carried out by experimental measurements and theoretical analysis, and the finalgoal of the research is to provide theories and guidelines for the lignite upgradingtechnology.First, single coarse lignite particle drying and hydrolysis mechanism was studied.The drying kinetics of single coarse lignite particles in hot air were investigatedexperimentally, and a coupled heat and mass transfer mathematical model for the dryingof single particles was developed assuming local thermodynamic equilibrium. Thenumerical results agree well with the experimental data verifying that the mathematicalmodel can evaluate the drying performance of porous lignite particles, and a lumpeddrying model for single coarse lignite particle was established by simulation resultsfrom the coupled heat and mass transfer mathematical model. The lumped drying modelfor single particle is available for air and flue gas, and it is simple and can be easilycoupled for drying of packed lignite particles. The mathematical model of the pyrolysisof single coarse lignite particles was established using a parallel reaction kinetics modelcoupled with a heat transfer model.Then, the drying process of packed lignite particles (packed bed and moving bed)was studied. A multi-scale model was used in a numerical investigation of ligniteparticle drying in a fixed bed. The multi-scale model simultaneously analyzed amacroscopic thin bed layer and a microscopic thin particle layer. The macroscopic heatand mass transfer between the drying gas and the lignite particle surfaces was calculatedin conjunction with the microscopic intra-particle heat and mass transfer using transientboundary conditions. Meanwhile, a lumped drying model of fixed bed was establishedbased on the lumped drying model of single coarse lignite particle. Compared withexperimental results of drying of fixed bed it can be found that the both drying model offixed bed are available for drying process simulation of packed lignite particles. Forproposed horizontal drying technology, the influence of operating parameters wasstudied using lumped drying model, and suitable parameters and optimationrecommendations were determined. Finally, the spontaneous combustion propensity and water vapour readsorptioncharacteristics were studied, and the range of water content of the lignite upgradingproduct was determine to ensure secure and long-term stacking. For the spontaneouscombustion UN basket method and oxidation kinetics testing method were used toresearch the influence of water content on spontaneous combustion of the ligniteupgrading product. The bituminous coal was selected as benchmark, so the watercontent of upgraded lignite product can be calculated to avoid the spontaneouscombustion. For the water vapour readsorption characteristics, considering the effect ofinitial water content the equilibrium water content model was developed. The goal ofthe above research is to provide theoretical guidelines for the target control of theupgrading process and storage conditions.