Numerical And Experimental Study On Slime Water Treated By Decanter Centrifuge And Flow Characteristics Of Coal Slime

Slime water is a solid-liquid mixture left in the process of coal washing in coal preparation plant.It is mainly composed of micro fine coal particles,gangue,clay and water.The water content of coal slime water is generally as high as 70~90%.After dewatering,slime water will form a high viscous material,coal slime,whose calorific value is usually between 2000~4000kcal/kg with utility value.With the development of combustion technology of low calorific value fuel and application of circulating fluidized bed boiler,more and more power plants use coal slime mixed with coal for combustion.More and more attention has been paid to the utilization of coal slime in CFB boilers.This technology not only saves coal resources,protects the environment,but also can reduce the emission of pollutants from power plants.Therefore,the power generation technology of coal slime water combustion has important economic and social benefits.In view of problems in the traditional slime water power generation process,environmental pollution caused by the open loop process,low efficiency dewatering equipment problem,this dissertation introduces decanter centrifuge into slime water power generation technology,and puts forward a new kind of slime water power generation technology.On the basis,for optimizing two key links of the new process for slime water power generation(dewatering process of slime water in decanter centrifuge and transporting process of slime water in pipeline),this dissertation systematically carried out numerical simulation on coal slime water treated by decanter centrifuge and experimental study on flow characteristics of coal slime.It studied the influence factors of decanter centrifuge on the dewatering process and efficiency,analyzed the fluid characteristics of coal slime and its pipe resistance characteristics for the efficient transportation of coal slime.The main work of this dissertation is as follows:(1)with decanter centrifuge introduced into slime water power generation technology,this dissertation puts forward a new kind of slime water power generation process.The new process consists three steps: dewatering of coal slime water produced from coal preparation plant,pipe transportation of coal slime between coal preparation plant and power plant,and power generation of coal slime combustion in CFB boilers.(2)Established the mathematical model of solid-liquid separation for treatment of slime water by decanter centrifuge.Through numerical simulation,studied the velocity field,pressure field and the turbulence distribution,as well as the effects of structural and running parameters on the separation efficiency.It obtained the relationship between the flow field and separation performance,the effects of structural parameters on the separation performance of slime water,such as the ratio of length to diameter of the drum,half cone angle and inlet angle and pitch.The effects of running parameters,such as the differential rotational speed and feed flow,on the separation performance of slime water were also obtained.(3)A bench for dewatering treatment of slime water was built,and the experiment of dewatering of coal slime water was carried out.The results show that the solid-liquid separation rate increases first and then decreases with the increase of the differential speed,and there is the best difference speed(40~45rpm);and the solid-liquid separation rate increases first and then decreases with the increase of feed flow rate,and the optimum feed flow rate is about 15m3/h.Furthermore,the numerical simulation and experimental results of coal slime treatment by decanter centrifuge are compared,and the reliability of the numerical simulation results is verified.(4)Laboratory experiments were conducted to study the non-Newtonian characteristics of coal slime and the resistance characteristics of pipe transportation.The results show that slime presents Bingham plastic fluid characteristics when water content is low;when the water content is 37.5%,Bingham pseudo-plastic fluid is presented;the slime is pseudo-plastic fluid when water content is 40%;the higher the water content of slime is,the smaller the transport resistance is,and the transfer resistance of slime water at about 30% will produce sudden change.The increase or decrease is 1%,and the pump pressure will increase by nearly 40%.The results of this dissertation can guide the efficient dewatering of coal slime water and the efficient pipe transportation of the slime,thus improving the efficiency of coal slime combustion power generation technology.At the same time,the theory of the non-Newtonian fluid flow characteristics and the pipe resistance characteristics of coal slime has been perfected,which has important theoretical and practical value.