Experimental Study On Preparation Of Ultra-low Ash Coal By Oil Agglomeration Method

Most of China's coal is burned directly,and there is less deep processing of coal.However,the general coal washing process adopts shallow trough dense medium coal washing,which is only the preliminary processing of coal.There is little research on the preparation of ultra-low ash from deep processing of coal.Ultra-low ash coal plays an important role in some fine equipment and aerospace equipment.Ultra-low ash coal water slurry has a broader prospect for the technology of replacing oil with coal.Narinhe mining area is an important coal production and supply base in our country.Its ash content is generally 6%to 21%,and its sulfur content is 1.5%on average.It is suitable for the research on preparation of ultra-low ash coal.Traditional deashing methods mainly include physical method and chemical method.Chemical method is limited in application due to investment and environment.Among the physical methods,oil agglomeration deashing is considered to be the most effective method for fine particle deashing.Therefore,the process and mechanism of preparing ultra-low ash coal slurry by oil agglomeration method are studied in detail with Nalinhe coal as raw material.Through maceral analysis,elemental analysis,industrial analysis,infrared spectrum analysis and coal-water contact angle detection of coal and rock,it is determined that Nalinhe coal belongs to a young type of coal,and its surface contains a large number of hydrophilic oxygen-containing functional groups,which are difficult to agglomerate,agglomerate or flocculate.However,the addition of alcohol in the experiment is beneficial to the coalification of Nalinhe coal.Through a large number of experiments,the optimal conditions are determined as follows:grinding particle size of 250 mesh?58?m?,blending time of 50%and 20min gasoline,blending intensity of 2000 r·min^-1,0.8%sodium lignosulfonate,3%dodecanol and 15%Ferric chloride.Under these conditions,the ash content can be reduced from 13.27%to 2.51%of pellet product by one-time agglomeration with oil agglomeration method,and the removal rate can reach 81.08%.The mechanism of coalescing and deashing of Nalinhe coal oil is analyzed by infrared spectroscopy.The research shows that the rich hydrophilic and oxygen-containing functional groups are the main reason for the difficulty of coalescing of Nalinhe coal.In addition,dodecanol and coal act as physical adsorption,and the contact angle with water increases after the action of coal alcohol,thus enhancing the hydrophobicity of coal.The addition of sodium lignosulfonate into oil agglomeration forms a synergistic effect due to its dispersing effect and its interaction with the coal surface.Among them,the addition of salt ferric chloride has the best effect.The main reason is that ferric ions have a neutralization effect with the functional groups on the coal surface.The change of infrared spectrum of pellet products indicates that a large amount of surface functional groups shift in the agglomeration process to generate physical adsorption capacity,which results in strong hydrophobicity of coal and thus reduces ash content in the agglomeration process.Through the analysis of the function of neutral oil in oil agglomeration system,neutral oil not only wraps coal particles as bridging fluid,but also influences the agglomeration yield and filling rate in the process of oil agglomeration,in addition,by predicting the thermodynamics of coal-water contact with alcohol in the process of oil agglomeration,the measured data of interfacial tension,surface tension and contact angle are taken into account.After calculation,the oil agglomeration can proceed spontaneously,which indicates that the free energy of the oil agglomeration increases and the oil agglomeration proceeds smoothly.