Study On Nozzle Atomization And Particle Agglomeration Characteristic In The Liquid-Containing Fluidized Bed

The natural gas resources in China are scarce,and the crude oil is generally heavy.For many years,it has been committed to using heavy oil directly as cracking raw material for the production of low-carbon olefins.With the improvement of petroleum processing technology and the rise of petroleum price,the increasing heavy oil supply in the future crude oil resources is inevitable.Processing and efficient utilization of the inferior crude oil have become the main problems.The fluidized coking process atomizes heavy oil in the form of steam through nozzle and injects it into the fluidized bed with hot coke.The liquid phase is introduced into the gas-solid fluidized bed in the form of discontinuous phase.Nozzle is the core of feeding technology for heavy raw liquids with high viscosity,and the atomization quality directly affects the contact sufficiency,reaction efficiency and stability between raw liquids and coke particles.The liquid-containing operation significantly affects the hydrodynamic behavior and fluidization stability of the bed materials in fluidized bed,but the specific liquid phase mechanism is still unclear.If bed material agglomeration occurs,the bed will collapse and production will be forced to stop.Therefore,to increase the cracking reaction rate and reduce the energy consumption,it is of great theoretical significance and industrial value to study how liquid phase affects the hydrodynamic behavior and agglomerate stability in the liquid-containing fluidized bed reactor.This paper focuses on the nozzle structure and atomization quality improvement,hydrodynamic behavior characterization,agglomeration identification and its fragmentation and thus the research work has been carried out from the following four aspects:Firstly,two types of nozzles commonly used in industry were selected,and the agglomeration size distribution in liquid-containing fluidized bed was measured using gravimetric analysis method to characterize the jet mixing of different nozzles.The nozzle upstream mixer was improved,and the liquid pulsation during the nozzle atomization process was eliminated.Then a gas shroud was used to push the atomized droplets to the outside of jet,and full mixing of the circumferential particles and droplets was achieved combining with the turbulent environment created through the solids entrainment attachment.The conical obstacle of a impact cone was used to disperse the atomized droplets in the central region,and the jet compression was inhibited combining with the gas space produced through the gas shroud.Secondly,the fluidization states of different agglomeration were made during the process of increasing liquid content,and the bubble morphology and its transition to channel flow were observed and analyzed in detail using photography method.Then the bed material agglomeration and channel flow were accurately indentified using the standard deviation of pressure signal.A method for characterizing the bubbles behavior in liquid-containing fluidized bed is established based on the algorithm principle using processing techniques such as power spectrum,wavelet analysis,coherence analysis and recursive analysis,revealing the variation of bubble growth,motion and number with liquid content.Thirdly,a water-sand system was used to simulate the hot bitumen-coke system at room temperature,and the contact between atomized droplets and particle surface during nozzle injection of multi-viscosity liquid was investigated based on a conductance method.Then the effect of liquid viscosity on the bed material agglomeration process was investigated in a fluidized bed operated at different mass ratios of the atomization gas to the liquid jets and gas velocities comparing with the results of blank experiment.This provides a new approach for on-line monitoring the bed agglomeration during liquid injection in different fluidization stages to guarantee perfect contact between the atomized liquid and the bed particles in liquid-containing fluidized bed.Finally,agglomeration process go through non-fragmentation,transition and complete fragmentation zone through controlling superficial gas velocity,and the agglomeration failure gradually changes from fragmentation to erosion stage.Then the bed material was recovered to determine whether agglomerate breakage or erosion occurred,and the effects of liquid content,gas velocity,liquid viscosity,initial agglomeration size,wettability as well as different liquid-solid systems on agglomerate stability were investigated.Moreover,the main factors of agglomeration failure were found.This provides an important theoretical basis for further research on agglomerate breakage and erosion behavior.