Study On Combustion Characteristics Of Upgraded Zhundong Lignite

With the decrease of high-quality coal resources,how to use lignite cleanly and efficiently has become an important research topic.Zhundong lignite has the characteristics of high water content,easy oxidation,and easy slag,which is not conducive to long-distance transportation and storage,and restricts its large-scale industrial application.The research of clean and efficient upgrading lignite technology is of great practical significance for the large-scale utilization of Zhundong lignite.The high-temperature flue gas upgrading lignite technology can not only effectively reduce the moisture content in the Zhundong lignite and change the combustion properties of the upgraded lignite,but also can effectively avoid the deflagration of lignite due to the high oxygen content in the high-temperature air drying technology.In this paper,the combustion kinetics and combustion characteristics of Zhundong lignite in fluid i zed bed are studied.The combustion characteristics and combustion kinetics of Zhundong lignite before and after upgrading were analyzed by thermogravimetric analysis method to evaluate the lignite upgrading scheme.Among them,the constant temperature thermogravimetric experiment can quantitatively analyze the pollutant generation in the combustion process of samples with different upgrading schemes,and study the combustion dynamics characteristics of Zhundong upgraded lignite.The results show that different upgrading temperatures have a great influence on the properties of Zhundong lignite after upgrading,and the parameters such as maximum weight loss temperature and flammability index show regular changes.With the increase of the upgrading temperature,the coal's pre-reactivity and flammability are enhanced,and the contents of carbon and nitrogen are significantly increased.The upgrading atmosphere has little effect on the ignition temperature of the upgraded lignite.Lignite has differe nt physical and chemical reactions under different upgrading atmospheres,which changes its combustion characteristics.The ANSYS FLUENT software was used to simulate the cold flow of bed materials with different particle sizes and densities in the fluidized bed.At the same time,the different coal feeds,different fluidized wind temperatures and different types of Zhundong lignite were in the fluidized bed.Numerical simulations of the combustio n characteristics were carried out to investigate the fluidization and combustio n characteristics in the fluidized bed.The results show that the bed material with a density of 2600kg/m~3 and a particle size of 0.75mm has better fluidization characterist ics,When the amount of coal is increased,the temperature inside the furnace rises continuously,the oxygen content decreases,and the nitrogen oxide content increases.When the fluidized air temperature is 673K,it is easy to cause flameout in the furnace.At 873K,the combustion condition in the furnace is good.Different upgraded lignite have different differences in the amount of heat released during the combustion process due to differences in elemental content,especially carbon content.Using a small laboratory fluidized bed,the combustion of quasi-east coal was experimentally studied under different coal supply conditions,and the semi-coke and bed materials under different conditions were analyzed.The temperature and polluta nt generation characteristics of actual combustion in fluidized bed were studied.The results show that with the increase of coal supply,the temperature in the furnace increases continuously,while the oxygen content decreases and the nitrogen oxides increase,which proves that the nitrogen oxides produced in the fluidized bed are mainly fuel-type nitrogen oxides.The color of the bed material in the hearth is changed from white to high temperature and broken to gray.The resulting semi-coke increases in carbon content as the amount of coal fed increases.Comparing the numerical simula t io n results,the experimental results are consistent with the simulation results,but some errors are caused by the model simplification without considering carbon black and semi-coke generation.