Research on the separation mechanism of dry dense medium separation fluidized bed based on electrical capacitance tomography

Due to the contradiction between the distribution of coal and water resources in China,it is of great significance to develop dry separation technologies for coal processing.Dry dense medium fluidized bed provides an effective way to solve the problem of coal separation in arid regions due to its high separation efficiency and low investment. Dry dense medium separation fluidized bed belongs to the research field of bubbling fluidization.The bed contains bubbles,medium particles and coal particles.It is very important to capture precisely the movement behavior of bubble phase and separating minerals.It is crucial to reveal the gas solid phase interaction and the density segregation of coal particles.The above capture is also beneficial for understanding the separation mechanism. Electrical capacitance tomography(ECT),as a non embedded three dimensional imaging measurement method,can accurately capture the fluidization behavior without affecting the normal operation of the fluidized bed.The study firstly focused on the capture of bubble behavior by the ECT based on the difference of dielectric constant between air and dense medium.The mathematical models of bubble growth and velocity were established with high precision.The ECT was then used to explore the movement behavior of coal particles.The feasibility of tracing coal using the ECT was confirmed by the COMSOL simulation.The impacts,including operating conditions and coal properties,were further analyzed on the movement behavior. The research verified the reliability of the real time capture of coal particles in axial and radial directions.Through the capture of bubble phase and coal particles,the distribution of gas solid phases in the bed was analyzed for establishing separation density model. According to the theoretical separation density model,the error is less than 20% between the predicted value and the experimental data,providing a theoretical basis for the precise density regulation of dry separation process. The research realizes the non embedded imaging capture of bubbles in the dry dense medium separation fluidized bed,breaking the limitations of traditional methods,such as optical fiber probe and two dimensional imaging,solves the difficult problem of directly observing the separating process of coal and realizes the tracing of coal trajectory. It provides a theoretical basis for further understanding the gas solid two phase distribution in fluidized bed.