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A liquid-containing gas-solid fluidized bed reactor (FBR) is the core equipment for the ethylene polymerization process operated in the condensed mode. However, the thermal stability characteristics of the liquid-containing gas-solid FBR is far from understood. In this work, a novel model based on the combination of a two-phase model and a liquid evaporation model is developed to describe the thermal stability of a liquid-containing FBR. The effects of catalyst activation energy and condensed agent content on the thermal stability and multiplicity of the ethylene polymerization in a liquid-containing FBR is studied through the homotopy continuation method. With the increase of activation energy and increase of condensed agent content, the stable branch is reduced and the steady state multiplicity appears. Furthermore, the dynamic behaviors of the liquid-containing FBR at the Hopf bifurcation points of the low-temperature branch are characterized. It is shown that a negative perturbation of the catalyst feed rate leads to the state variables oscillating and evolving into a stable state, while a positive perturbation of the catalyst feed rate leads to running away of the state variables. Results from this work provides a guidance to the industrial operation of liquid-containing FBRs and the design of the corresponding control systems. [ABSTRACT FROM AUTHOR]

An induction heating fluidized bed with liquid injection was designed to mimic the exothermic process of particles in industrial olefin polymerization fluidized beds. The effects of liquid injection flow rate on agglomeration behaviors were investigated through the characterization of agglomerate size and mass. Agglomeration mechanisms were proposed based on the experimental data of bed pressure drop, axial temperature distribution, and microscale visualization. Results have revealed that, with the increase of liquid injection flow rate, the agglomeration mechanism was controlled by the solid bridge force, the liquid bridge force, and the cooperative action of them, respectively. Wet agglomerates caused by the liquid bridge force induced local dead zones and provided a good environment for the occurrence of a hot spot and growth of solid bridge, and thus the formation of solid agglomerates. Besides, elevating the liquid injection position and increasing the induction heating power can widen the operation range of the liquid injection flow rate for fluidized bed reactors. [ABSTRACT FROM AUTHOR]

Particles and bubbles are important discrete elements in gas-solid fluidized beds. The interactions between them affect the evolution of agglomerates. Based on the analyses of microscopic physical processes, mathematical models of particle coalescence and agglomerate breakage caused by bubble expansion were developed. Coupling with the constant-number Monte Carlo method, the evolution of particle size distribution was simulated. Modeling results matched well with cold-mode experiment results, which demonstrated that the approach is a promising way to predict agglomeration behavior in the fluidized beds. Also, the coalescence efficiency β0 and breakage efficiency βb extracted from Monte Carlo results can provide rate constants for the kernels in population balance modeling. Further investigations of the effects of process parameters show that decreasing bed temperature or increasing superficial gas velocity reduces the coalescence efficiency and increases the breakage efficiency, which are beneficial to prevent agglomeration. [ABSTRACT FROM AUTHOR]

Numerical simulations using the Gidaspow and Syamlal-O'Brien drag models have been performed based on the National Energy Technology Laboratory small scale challenge problem for three test cases. Validation tools including statistical moments, spectral analysis, and the autocorrelation function are used to analyze the pressure drop fluctuations. The analyses using these tools reveal a regime change from bubbling/slugging to turbulent flow with increasing superficial gas velocity. 1D discrete wavelet analysis is utilized in the study of the distribution of energy between the macro-, meso-, and microscales and also in the characterization of turbulence quantified in terms of the flatness factor. 1D fast Fourier transform energy spectra are constructed from the predicted and measured particle velocity data and compared. Predicted and measured granular temperatures are found to be in reasonable agreement with literature values. [ABSTRACT FROM AUTHOR]

A novel induction heating apparatus is designed to mimic the exothermic process in an olefin polymerization gas-solid fluidized bed. Wax/graphite composites with core-shell structure are used as tracer particles to capture the agglomerates formed in the cold mode experiments. Pressure fluctuation sensors and image analysis methodology are used to characterize the detailed information on agglomerates such as mass, size, and compositions. Experimental results reveal that when the mass fraction of tracer particles is above 10%, agglomerates are formed in the fluidized bed. Compared with coarse particles, small particles lead to agglomeration much easier, and coalescence of small-small particles or small-coarse particles is the main mechanism by which agglomeration occurs. Analyzing the collision process of small particles and coarse particles, we conclude that collisions among small particles or collisions between small and coarse particles are more frequent and efficient than that of coarse particles. [ABSTRACT FROM AUTHOR]

The performance of gas-solid fluidized bed reactors (FBRs) strongly depends on the behavior of gas bubbles. Mechanical agitation is widely used in industrial FBRs to enhance gas-solid mixing; however, its influence on bubble behaviors has been poorly studied, especially in experimental study. Pressure fluctuations in a 300 mm inner diameter plexiglas column fluidized bed of Geldart D particles with an arch agitator were measured under various gas velocities and agitation speeds. The bubble sizes were evaluated by incoherent analysis of pressure fluctuations. The effects of mechanical agitation on axial bubble growth, bubble sizes, regime transition velocity and fines elutriation were comprehensively investigated. Results show that mechanical agitation promotes bubble growth at 1.7 Umf but reduces the bubble sizes with increasing gas velocities. The axial maximum bubble size with increasing gas velocity occurs at 1.2 m/s without agitation and 1.0 m/s with agitation speeds of 14 and 21 rpm. Interestingly, mechanical agitation leads to a small increase in minimum fluidizing velocity and a slight decrease in critical turbulent velocity. Furthermore, the entrainment rate is reduced with mechanical agitation, due to the decreasing bed height and small fines ejection at the bed surface. The arch agitator helps to reduce the channel flow, enhance the gas-solid contact efficiency and improve the fluidization quality. [ABSTRACT FROM AUTHOR]