Study On Flow Pattern Transition And Separation Density In The Gas-Solid Separation Fluidized Bed

As the main fossil energy in the world,coal has always occupied an important position in the world energy structure.China is the world’s largest coal producer and consumer,and the pattern of coal as the main energy will not change for a long time.With the proposal of double carbon policies“carbon peak”and“carbon neutralization”in China,a broad platform and opportunities are provided for the promotion of dry coal separation technology.Gas-solid separation fluidized bed is an efficient and clean coal separation technology,which has a good separation effect for coal particles.The bed layer state has a dominant influence on the separation effect,so the flow pattern transition process of gas-solid separation fluidized bed needs to be identified accurately.In addition,there is a lack of systematic research on the complex motion behavior of the feeding particles in the gas-solid separation fluidized bed.In this dissertation,by air distribution process intensification of the gas-solid separartion fluidized bed,the stability of the bed is improved,coal separation effect is also improved.Flow pattern transition process of fluidized bed is studied,the separation density prediction model for feeding particle in the gas-solid separation fluidized bed is proposed.On the basis of gas-solid separation fluidized bed,microporous sponge is introduced to strengthen the air distribution process.The effect of the air distribution process intensification and the regulatory mechanism of bed stability in the gas-solid separation fluidized bed are studied.The air distribution process intensification increases the pressure drop of the air distributor,promotes the uniform distribution of air volume,and strengthens the effective contact between particles and air flow.The pressure drop ratio after the air distribution process intensification in the the gas-solid separation fluidized bed is 2.03.The stability of bed pressure fluctuation is improved by the air distribution process intensification,and bed pressure fluctuation index is less than 0.1.The air distribution process intensification makes bed layer reach a higher expansion rate and weakens the violent bubble movement.The air distribution process intensification improves the stability of bed density,and the minimum standard deviation of bed density fluctuation index can reach 0.03.According to the two-phase theory,a bed density prediction model which is suitable for the gas-solid separation fluidized bed is proposed.Homogeneous fluidization is of significance for the gas-solid separation fluidized bed.With the increase of gas velocity,the fluidized bed experienced three flow pattern stages:fixed bed,critical fluidization state and bubbling fluidized bed.According to the relationship between medium wave and voidage wave,the criterion equation from non-bubbling fluidization to bubbling fluidization in the gas-solid separation fluidized bed is derived by theoretical calculation.The calculation results show that for Geldart A particles with Reynolds number less than 2,when the prediction error is 30%,the confidence degree is 84%.For Geldart B particles with Reynolds number between 2and 500,this discriminant is not applicable.In order to further improve the accuracy of flow pattern discrimination of fluidized bed,machine learning algorithm is adopted.Among them,the three-layer neural network algorithm(ANN3)has the highest recognition rate of bed flow pattern,and the prediction accuracy has reached 95.8%.Compared with the theoretical calculation method,the machine learning method has convenient operation and high prediction accuracy.It has broad application prospects in the classification of fluidized bed,and lays a solid foundation for the flow pattern identification of fluidized bed industrialization.The particle sphericity coefficientΦis introduced to characterize the morphology of irregular coal particles,the drag coefficient for the feeding particles is modified to verify the suitability of the non-spherical particle drag model for gas-solid fluidized bed separation.After optimizing and correcting,theρS.sus prediction model of single non-spherical feeding particle in the gas-solid separation fluidized bed is obtained.when the prediction accuracy of theρS.sus prediction model is 90%,the confidence degree is 85.72%.ThisρS.sus of single non-spherical feeding particle prediction model points out the control direction for improving the separation effect,provides a theoretical basis for the industrialization of gas-solid fluidized bed,and promotes the process of dry fluidized separation.Based on the relationship between the separation density of the single-component particle group and the voidage of gas-solid separation fluidized bed,theρG.drag prediction model of the single-component feeding particle group in the the gas-solid separation fluidized bed is established with the voidage correction.When the prediction error of theρG.drag prediction model is 10%,the confidence degree is90.00%.Based on the particle separation model and theρG.drag prediction model,a separation density prediction model for the single-component feeding particle group in the gas-solid separation fluidized bed is proposed.The separation density prediction model has important guiding significance for the the gas-solid separation fluidized bed.The effect of the air distribution process intensification on the separation efficiency of gas-solid separationfluidized bed is discussed.When-13+6 mm coal is separated,the clean coal ash content of the gas-solid separation fluidized bed after the air distribution process intensification is 10.56%,and the clean coal yield is 72.32%.More clean coal products with lower ash content can be ontained after the air distribution process intensification in the gas-solid separation fluidized bed.The separation characteristics of narrow-size coal in the gas-solid separation fluidized bed are systematically studied.The feeding particles are divided into narrow particles with a particle size change range of 1-2 mm.The separation effect is evaluated from all aspects and angles with evaluation indexes such as ash segregation degree(Sash),possible error(E)and total misplaced material content(M).The results show that when then feeding particle size decreases,the Sash decreases,the E increases from0.125 g/cm~3 to 0.270 g/cm~3,and the M increases from 5.48%to 19.36%.Especially when the particle size is less than 5mm,the values of the Sash,E and M all change greatly,and the separation effect becomes worse.In addition,it can be seen from XRF and FT-IR analysis that it has a certain removal effect on harmful elements during separation process.In the process of coal separation,with the increase of middling coal content,the E value is increasing.In order to reduce the particle loss rate,and to ensure the effective separation of particles,the residence time of intermediate density products in the fluidized bed should be reduced.In order to obtain the separation density prediction model of the feeding coal particles in the gas-solid separation fluidized bed,the separation density prediction model for the single-component feeding particle group is modified by empirical coefficient.The separation density prediction model of the feeding coal particles lays a theoretical foundation for the efficient separation of the gas-solid separation fluidized bed,and also provides a possibility for the large-scale promotion and industrial application of the gas-solid separation fluidized bed.There are 121 figures,13 tables and 283 references in this dissertation.