Rheological Characteristics And Combustion Mechanism Of An Indonesian Lignite Washery Tailing In Fluidized Bed

The amount of lignite coal washery tailings grows rapidly these years,as the proportion of coal washing improves according to the government.Fluidized bed technology is preferred for its advantage of fuel wide adaptability and low pollutant emission.However combustion mechanism of lignite washery tailings in fluidized bed are not clear,which hinders the promotion to further increasing the combustion efficiency and reducing emissions.Funded by SHENHUA GUOHUA electric power research institute(Beijing)LTD,a lot of research were studied for a special fuel,i.e.,an Indonesian lignite washery tailing(LWT).(1)Kinetic analysis of the combustion and pyrolysis of LWT were studied.(2)The wall slip and true rheological properties of LWT were studied.(3)Experimental studies and simulation of the drying and devolatilization processes of LWT particle in fluidized bed(FB)were studied.(4)The combustion adjustment of LWT in a pilot fluidized bed was studied.(5)A 75 t/h circulating fluidized bed system for the disposal of LWT was designed.(1)In Chapter 3,the combustion and pyrolysis characteristics of LWT were investigated using TG-FTIR at different heating rates of 5,15,25,35,and 45 ? min-1.In Chapter 4,kinetic analysis of combustion and pyrolysis of LWT were studied.Two methods were compared to evaluate the activation energy E of LWT,i.e.,iso-conversional method and model-based method.Furthermore,a complementary method of iso-conversional and model-based was also used to determine the kinetic mechanism of LWT.The results provide useful information for the following research,i.e.,the combustion and pyrolysis mechanism research of LWT.(2)In Chapter 5,the rheological properties of LWT were studied using Q-?P method.The rheological properties were modified based on the modified Mooney method to get the true rheological properties.Results provide useful information for pipeline transportation of LWT.(3)In Chapter 6,the combustion and agglomeration characteristics of LWT in a lab-scale fluidized bed were studied.The effect of bed temperature,residence time,and initial water content on the combustion and agglomeration characteristics of LWT were analyzed.The agglomeration mechanism of LWT was obtained based on the EDS analysis.A model which can predict the intensity of LWT agglomeration was proposed.In Chapter 7,this study gives a detailed review of the proposed combustion models for common solid fuels,i.e.,coal,biomass,and solid waste.The existing combustion models for single solid fuels were listed in this review,providing a reference for the following study of the combustion model of a single LWT particle.Based on experimental analysis,the drying and devolatilization processes and their crossing period were studied thoroughly in Chapter 7.The drying and devolatilization model of LWT was thus proposed.A model was proposed for the drying and devolatilization of LWT particle in FB.The shrinkage was considered in this model.The predictions based on this model is proved to be in good agreement with the experimental results.(4)In Chapter 8,the combustion and emission characteristics of LWT were studied in both a bubbling fluidized bed(BFB)and a circulating fluidized bed(CFB).The effects of excess air ratio,feeding rate,secondary air ratio and secondary air location on the flue gas emissions were analyzed.Based on the combustion adjustment and the optimization of operating conditions,the combustion and pollutant emission characteristics of LWT were improved.The results show that it is feasible to directly fire LWT slurry in a CFB.The temperature of the dense-phase bed firing the LWT slurry can reach 800 ?.Both SO2 and NO emissions of bituminous coal are below the limits for both EU and Chinese regulations.All of the analyses will provide useful information for the design and operation of a commercial FB system using LWT as feedstock.(5)In Chapter 9,a 75 t/h circulating fluidized bed system of combustion of LWT was designed on base on above research.Based on the boiler thermodynamic calculation,boiler design parameters and structure were obtained.The variable load calculation analysis was also conducted.The system can fulfill the effective disposal of LWT.