| Coal is the most important basic energy in China.In accordance with the requirements of the national"the 14th Five-Year Plan"to"enhance overall energy production capacity"and"accelerate the transition to a model of green development",playing the role of coal as a guarantee and accelerating green transformation has gradually become the main theme of the development of the coal industry.The coal preparation process plays a significant role in energy conservation and emission reduction,and is an important measure for China’s clean and efficient utilization of coal,achieving high carbon energy and low carbon emissions.Among them,fluidized bed dry coal preparation technology provides an effective solution for the clean and efficient utilization of coal in arid and water deficient areas in China.The existing research on the binary dense medium system of gas-solid separation fluidized bed mostly focuses on the gradation of wide particle size magnetite powder,and the theoretical model of the binary dense medium gas-solid separation fluidized bed is often based on the description of the characteristic parameters of single particle composition,which lacks universality for the binary dense medium system with large differences in physical properties,This seriously affects the further prediction of the bed characteristics of gas-solid separation fluidized beds and the development of gas-solid separation fluidized bed equipment.This paper systematically studied the fluidization characteristics of a binary dense medium system in a gas-solid separation fluidized bed.Based on the characteristic parameters of binary dense medium,a semi empirical model was constructed for the incipient fluidization velocity and average bed density of the gas-solid separation fluidized bed.The two-phase characteristics and elutriation phenomenon in the binary dense medium gas-solid separation fluidized bed were studied,providing a theoretical basis for the industrial design and promotion of gas-solid separation fluidized bed.Through the derivation and analysis of the physical model of pressure drop in a fixed bed,the variation regularity of incipient fluidization velocity of binary dense medium under different Geldart particle classification combinations was studied,and the unstable fluidization mechanism of the bed under the influence of the content of fine fractions was revealed;A incipient fluidization velocity prediction model was constructed based on the effective characteristic parameters of the binary dense medium and the introduction of modified parameters related to the mass ratio of the binary dense medium.Based on the literature and experimental data,the calculated correlation of incipient fluidization velocity is corrected and calibrated,and an empirical model of incipient fluidization velocity with high prediction accuracy is obtained.Based on the gas-solid two-phase theory and the law of mass conservation,the average density model of the bed for the binary dense medium system in the gas-solid separation fluidized bed is derived and established;The spatial density distribution characteristics of binary medium in the bed were studied,and the radial density distribution regularity of the bed under the influence of the sidewall effect was explored;Based on the experimental data,the prediction model of the average density of the bed was empirically correlated with the particle size difference of the binary medium,and the correlation formula for calculating the average density of the bed suitable for the Geldart B-A/C binary medium system was constructed.The error of the predicted value was controlled within±12%,with good accuracy and reliability.Based on the bed expansion test and collapse test,the variation regularity of the bed overall expansion rate and the emulsion phase expansion rate under different operating conditions were studied,and the influence mechanism of the content of fine fractions on the bed emulsion phase expansion was explained;Based on image processing technology,the bubble distribution characteristics in the bed and the variation regularity of bubble size in the axial position of the bed of the Geldart B-C binary medium system were studied,the applicability of different bubble growth rate models to the Geldart B-C binary medium gas-solid separation fluidized bed was analyzed,and the bubble size variation phenomenon in the bed under the influence of splitting behavior was explained.Based on the elutriation rate constant,the elutriation behavior of binary dense medium in gas-solid separation fluidized bed under different operating conditions(coarse particle size,fine particle mass fraction and superficial gas velocity)was studied,and the elutriation rate constant of fine particles was corrected and calibrated by combining with the experimental data.The empirical model of fine particles elutriation rate constant for the binary mixture of Gelart B-A/C in gas-solid separation fluidized bed was constructed,with the prediction error within±20%.The separation characteristics of the feed particles in the gas-solid separation fluidized bed of the Geldart B-C binary dense medium system composed of magnetite powder and coal powder were studied.The effects of the mass fraction of the fine fraction components,the superficial gas velocity and the particle size of the feed particles on the fluidization dry separation process were investigated,and the mismatch phenomenon in the fluidization dry separation process was explored.The results show that the gas-solid separation fluidized bed of Geldart B-C binary medium system can achieve efficient separation of particles larger than 3 mm,and the possible deviation is less than 0.125 g/cm~3.Based on the average density model of the bed and the correlation of the variation of the bed separation density caused by the drag force of the air flow,a prediction model of the bed separation density for the gas-solid separation fluidized bed of the Geldart B-C binary medium system was constructed.The prediction error is within±6%,which has good accuracy and reliability.This dissertation consists of 92 figures,12 tables and 236 references. |
