Analysis Of Bubble Characteristics And Agglomeration In The Spray Gas-solid Fluidized Bed

With the advancement of science and technology,the research of gas-solid two-phase flow has been rapidly developed.Spray gas-solid fluidized bed is an important type of reactor developed on the basis of gas-solid fluidized bed,which is widely used in chemical processes such as catalytic cracking,coal gasification,olefin polymerization,drying and granulation.Due to the complexity of bubbles,agglomerates and other effects of atomized gas-solid fluidized bed,the flow process in the reactor is complicated.This hinders the understanding of the flow characteristics of the gas-solid two-phase flow,which limits the optimization of the industrial equipment structure and inprovement of the production efficiency.In this paper,the spray gas-solid fluidized bed experimental bench was set up to conduct different experimental conditions.Combining digital image processing techniques,power spectrum analysis and other methods,the bubble size and bubble position in the fluidized bed were studied.At the same time,time domain analysis and recursive analysis was adopted to analyze and identify different agglomeration states,in order to deeply study the influence mechanism of agglomerates on the chaotic characteristics of the system.Firstly,high-speed camera was used to collect the bubble images in the flow process.Through the image processing technology,the bubble area under different viscosity liquids was analyzed.The bubble area increased with the viscosity of the injected liquid,but after the high viscosity solution was sprayed,the air bubbles in the bed were drastically reduced,and the gas basically passed through the bed in the form of a channel flow.That is,low-viscosity liquids have little effect on fluidization,and high-viscosity liquids cause fluidization instability.At the same time,the bubble area of the fluidized bed under different liquid-solid ratios was analyzed.It was found that there was a linear correlation between the bubble area and the liquid content change.Secondly,under different experimental conditions,bubble images and pressure signals in the fluidized bed were collected at the same time.The Fourier transform of the pressure signal was performed first,followed by a coherent analysis to calculate the standard deviation of the incoherent power spectral density,and then the average bubble diameter in the fluidized bed could be estimated.At the same time,the image method was used to extract the bubble area in the image,and then the equivalent diameter of the bubble was calculated.Compared with the bubble diameter obtained by the pressure analysis method,the results obtained by these two methods were basically consistent.Therefore,the bubble behavior could be effectivelycharacterized by pressure measurement technology,and then the bubble characteristics could be analyzed to reflect the flow state in the fluidized bed.Finally,in the fluidized bed,ethylene glycol solution with different viscosity was sprayed to artificially make particle agglomerates to simulate agglomeration during the industrial production of polyethylene.The pressure signal in the flow process was analyzed in the time domain.At the same time,the gas-solid flow pattern was collected by a high-speed camera to visualize the agglomerates,focusing on the effect of liquid viscosity on particle agglomerates.Recursive analysis of the differential pressure signals revealed that the recursive graphs under different conditions emerged different structural features along the diagonally developed texture features,which could realize the sub-region identification in different agglomeration stages.At the same time,the change trend of the recursive feature quantity with increasing liquid viscosity was analyzed.The findings were consistent with the results of the recursive graph analysis,which proved that the recursive analysis of the pressure signal could clearly reflect the fluidized bed agglomeration state.