Study On The Migration And Transformation Of Fluorine In Huainan Coal During Washing And Combustion

In the process of coal combustion,fluorine will migrate and transform to the outside world,which is harmful to the environment and human health,and coal washing is considered to be one of the most economical and effective means to reduce the harm of coal utilization.In order to study the migration and transformation of fluorine in coal during washing and combustion,In this paper,samples from coal preparation plant and coal-fired power plant were collected systematically,through screening,combustion test and leaching test,combined with element determination,step-by-step chemical extraction,X-ray diffraction,scanning electron microscope-energy spectrum and other test and analysis methods,the migration,distribution and morphological transformation of fluorine in coal during washing and combustion were studied,and the relationship between fluorine occurrence and leaching was revealed.The main results are as follows:(1)Fluorine in coal is mainly distributed in high density coal samples and has strong inorganic affinity.Selecting the heavy liquid with the density of 1.8g/cm~3 for washing and gangue discharge can remove nearly 76%fluorine from the raw coal.The industrial washing of coal preparation plant makes the fluorine in raw coal mainly enriched in gangue.The inorganic fluorine mainly in residual state is removed by washing.The migration of minerals is the factor of fluorine migration in the washing process.(2)the occurrence state of fluorine will affect the volatilization rate and rate of fluorine in the process of coal combustion.Organic bound fluorine can be released completely at shorter residence time and lower combustion temperature,the bound fluorine of iron and manganese oxides will be decomposed and released at higher temperature.Due to the different binding mode of fluorine and aluminosilicate minerals,the content of residual fluorine decreases rapidly at first and then slowly with the increase of combustion temperature.The inhibitory effect of calcium oxide on fluorine release is better than that of calcium carbonate and calcium acetate,and the inhibitory effect increases at first and then decreases with the increase of combustion temperature.(3)Fluorine is a volatile element.after combustion,fluorine in coal is mainly distributed in flue gas and captured by desulphurization gypsum,followed by fly ash,and a small part of fluoride with good thermal stability remains in slag.The leaching amount of fluorine in power plant coal and combustion products is between 0.12μg/m L～27.31μg/m L,which is lower than the limit of fluorine concentration in hazardous waste leaching solution.The leaching of fluorine is mainly related to the occurrence state and environment of fluorine.in the environment with weak acidity,the ion exchangeable fluorine in solid samples will affect the environment,while in the environment with strong acidity,ion exchangeable fluorine and carbonate bound fluorine are the main factors affecting fluorine pollution in the environment.