Experimental Study And Numrical Simulation On A New Type Of Jet Flotation Column

In recent years,the content of high-ash fine particles in raw coal is getting higher and higher,and the proportion of hard-flotation and extremely hard-flotation slime is increasing.Based on the above understanding,it is of great significance to separate this part of hard-flotation coal slime.Flotation column is a kind of flotation equipment with the characteristics of simple structure,energy-saving and widespread application,and it has a good separating performance on fine particles.Based on our long-term research of the flotation column,thus,in this study,we designed a new type of jet flotation column and experimental system.This system can realize the recycling of middlings and improve the yield of clean coal,furthermore,it can change cyclic multiplication rate to achieve the best separating effect by adjusting the circulation amount and the input amount.Using a gas bubble generator with chamber as aerator,it would make a preliminary judgment of its performance by gas holdup test experiment,coal slime separation experiment and numerical simulation.ANSYS FLUENT,a computational fluid dynamics software,was performed to simulate the velocity distribution,turbulence intensity,and the volume fraction of gas-liquid two phases under different operating factors of the flotation column.The results showed that the gas phase moved down and liquid phase moved up,and the turbulence intensity near the outlet of the downcomer and the bottom of the flotation column was larger,which was favorable to the combination of bubbles and minerals.While the foam layer of the flotation column had a lower velocity,and a stable foam layer could be formed.The turbulence intensity of the flotation column was approximately 2%to 10%,and it is beneficial to separating.We tested its gas holdup by pressure difference under different circulation rates,air intake volume,feed volume,and dosage of secondary octanol,and the influence of various factors on the gas holdup was analyzed.The experimental results showed that the gas holdup increased with the increasing of the circulation amount,however,when the air intake amount was small,the gas holdup rate increased firstly and then decreased with the increasing of the circulation amount;the gas holdup increased first with the increasing of the air intake after reaching a certain value,due to the increase of the air intake volume,large bubbles were more,the cavitation phenomenon was weakened,and the gas holdup no longer raised;the gas holdup increased with the increasing of the dosage of secondary octanol;and the gas holdup increased firstly and then decreased with the increasing of feeding amount.The experimental results is similar to the numerical simulation results,and the maximum difference is about10%,because the simulation haven't consider the breakage and merger of bubbles,so the experimental results can be considered to have a higher reliability.An flotation experiment of releasing steeply was conducted on the coal slime of the Yangluhe Coal Preparation Plant using a mechanically agitated flotation machine.The method of one-factor test was used to find the optimum values of the flotation column's operating factors at the separation of the coal slime of Yangluhe Coal Preparation Plant,and then separated the coal slime under the optimum values of various operating factors by two different processes.Compared the results of flotation column and flotation machine,the experimental results showed that the optimum value of operating factors were the airintake volume is 1.1m~3/h,the circulation volume is 0.714m~3/h,the dosage of secondary octanol is 100g/t and the feeding amount is 0.7m~3/h when the new jet flotation column separating the coal slime of Yangluhe Coal Preparation Plant.From the comparison of the experimental results of flotation machine and flotation column,it could be seen that when the clean coal ash content was the same,the yield of clean coal of new jet flotation column was nearly the same with the that of the experiment of releasing steeply.Therefore,the flotation column has a good performance and can separate fine-grained high-ash coal slime effectively.