Gasification Characteristics And Kinetics Of Lignite In A Fluidized Bed Gasifier

Fluidized bed has good gas-solid contact,heat and mass transfer efficiency and other characteristics.Fluidized bed technology is widely used in energy,chemical industry,environment engineering and other industrial processes.Lignite gasification technology has become an important way of efficient utilization of lignite.In this dissertation,gasification characteristics and kinetics of Xiaolongtan lignite are studied in a fluidized bed.Gasification characteristics of Xiaolongtan lignite are carried out by using air and steam as gasifying agent in a fluidized bed gasifier.Effects of particle size,bed temperature,air to coal ratio,and steam to coal ratio on the gasification behavior are explored.When bed temperature is increased,the carbon conversion,gas yield rate,and calorific value are increased;H₂ and CO concentration are increased,CO₂ concentration are decreased.When particle size is increased,the carbon conversion,gas yield rate,and calorific value are decreased;H₂,CO,and CO₂ concentration are decreased.When steam to coal ratio is increased,the carbon conversion and calorific value are decreased slightly,but gas yield rate remains unchanged;H₂ and CO₂ concentration are increased,CO concentration is decreased.When air to coal ratio is increased,the carbon conversion,gas yield rate,and calorific value are increased first and then gradually decreased;H₂ and CO concentration are increased first and then gradually decreased.The kinetic study is performed in an isothermal fluidized bed gasifier for the same particle size,steam to coal ratio and air to coal ratio at ambient pressure.It is found that the reactivity of lignite gasification is increased along with reaction temperature.Three kinetic models are applied to describe the varying conversion rate,volumetric model,grain model,and modified volumetric model.Based on which the activation energy is calculated using isoconversional method,while the accuracy of the method is verified with catalytic activity index.Results show that for conversion rates of 0.3,0.5,and 0.8,the corresponding activation energy lies in 104.75¹31.36kJ/mol,and the results calculated by three models are 93.95kJ/mol,83.37 k J/mol,and 124.83kJ/mol,proving modified volumetric model to be the most appropriate kinetic model.