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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]

Flow pattern of the fluidized bed is a key factor for heat transfer and the design of a new reactor. It is important to comprehend the fluidization conditions because the complex correlation between particle−particle and particle−environment in the reactor. In this study, we applied acoustic emission (AE) measurement in monitoring the particle fluidization pattern in a gas−solid bed fluidized with different sorts of particles classified by Geldart. With AE axial time average energy analysis, the flow structure of polyethylene particles was investigated both in the laboratory and plant apparatus. The results showed that the fluidization pattern in the bed is multicirculation, including the main-circulation zone, subcirculation zone, and the stagnant zone. Moreover, the influence of operating variables, such as particle size, superficial gas velocity, static bed height, and particle sorts had also been considered. It was found that the particle size, gas velocity, and particle sorts have significant impacts to the fluidization pattern. In contrast, the height of the stagnant zone did not show direct relation to the static bed height. AE measurement was proved to be reliable for understanding the dynamical features that affect the behavior of the fluidized bed. This can be useful guidance for an industrial process and help improve the process operation and the design of the new reactor. [ABSTRACT FROM AUTHOR]

The quantitative structure-property relationship (QSPR) of constrained geometry catalysts (CGCs) has been analyzed by combining density functional theory (DFT) and multivariate linear regression (MLR). QSPR models for determining the reaction energy barriers of ethylene and 1-octene and molecular descriptors were established and validated with a testing set. At the initiation stage, the quaternary QSPR models for ethylene and 1-octene feature R² values of 0.90 and 0.82, respectively, while the corresponding leave-one-out Q² values for ethylene and 1-octene are determined to be 0.82 and 0.69. Using the generated QSPR models, the electronic effect was proven to be more critical for determining the energy barriers of ethylene and 1-octene insertion processes. At the propagation stage, the quaternary QSPR models for ethylene and 1-octene feature R² values of 0.97 and 0.96, respectively, while the corresponding leave-one-out Q² values for ethylene and 1-octene are determined to be 0.93. Particularly, the impact of the steric effect on the energy barriers of ethylene and 1-octene insertion is more pronounced. Furthermore, the correlation between the corresponding energy barriers and experimental activities with three series of CGCs was discussed, which revealed that theoretical calculations are consistent with the experimental results. [ABSTRACT FROM AUTHOR]

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]

The validation of scaling rules with the consideration of cluster effect is investigated by two-fluid models. Glicksman's full and simplified scaling rules are used to build two 1:3 scaled-up risers. The cluster features within different particle classes or operation conditions are approached with the energy minimization multiscale drag model. The comparison of axial and radial solids concentration between three cases indicates that the simplified set scaled riser produces a poor fit throughout the length of the riser and that the full set scaled riser produces a good similarity only toward the top half of the riser. The analysis of cluster characteristics of three cases illustrates that the accurate repetition of the clusters is essential for the hydrodynamic similarity. The simplified set scaled riser presents lower cluster characteristic values along the riser, and the full set presents poor similarity of cluster characteristics in the riser's bottom region. [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]

The aim of this work was to investigate the application of an acoustic monitoring system for production scale circulating fluidized bed processes. The relationship between acoustic signals and the coke amount deposited on the catalysts was investigated on both lab scale and production scale reactors. By using Power spectrum density analysis, the relationship between the coke amount and the frequency shift of the characteristic peak of acoustic signals was found to be linear. In addition, a model to detect the coke amount on catalyst was established based on partial least-squares regression. Comparing the model results with experimental data, the amount of deposited coke is determined with a correlation coefficient 0.947 and a root mean squares error of cross validation 0.948%, which means that this model is accurate and capable of monitoring the coke amount on catalyst. Furthermore, the results of the preliminary industrial tests are considered to be promising. This work provides valuable insights into the online monitoring of coke amounts in circulating fluidized beds based on an AE technique. [ABSTRACT FROM AUTHOR]

This paper deals with the design of heat integrated water utilization networks. The nonisothermal mixing and freely splitting nature of hot and cold streams have made the problem far more complicated than the design of heat exchanger networks (HEN). By establishing an MILP model, promising heat exchange matches between hot and cold streams are obtained first without considering the detailed network design. Subsequently, a stage-wise HEN superstructure is introduced for the detailed network design. The proposed systematic approach can be applied for large scale problems. Examples from literature and a practical example in a PVC plant are used to illustrate the applicability of the approach. [ABSTRACT FROM AUTHOR]

Amyloid-β (Aβ) peptides exhibit many distinct structural morphology at the early aggregate stage, some of which are biological relevant to the pathogenesis of Alzheimer’s disease (AD). Atomic-resolution structures of the early Aβ aggregates and their conformational changes in amyloid aggregation remain elusive. Here, we perform all-atom molecular modeling and dynamics simulations to obtain two stable triangular-like Aβ structures with the lowest packing energy, one corresponding to the Tycko’s model (Paravastu, A.; Leapman, R.; Yau, W.; Tycko, R.Proc. Nat. Acad. Soc. U.S.A.2008, 105, 18349−18354) (referred to C-WT model) and the other corresponding to computational model (N-WT model). Both models have the same 3-fold symmetry but distinct β-sheet organizations in which three Aβ hexamers pack together via either C-terminal β-strand residues or N-terminal β-strand residues forming distinct hydrophobic cross section. Structural and energetic comparisons of two 3-fold Aβ oligomers, coupled with structural changes upon the mutations occurring at the interacting interfaces, reveal that although hydrophobic interactions are still dominant forces, electrostatic interactions are more favorable in the N-WT model due to the formation of more and stable intersheet salt bridges, while solvation energy is more favorable in the C-WT model due to more exposed hydrophilic residues to solvent. Both models display many common features similar to other amyloid oligomers and therefore are likely to be biologically relevant. [ABSTRACT FROM AUTHOR]

• Agitation results in a constant bed voidage with periodically fluctuation. • Axial gas mixing can be described by the "open" vessel dispersion model. • Gas flow is divided into two regions by the inner diameter of the helical ribbon. • Flow regimes are classified with an empirical correlation of Re and Fr number. The gas–solid vertical single helical ribbon agitated reactor is widely used in the polypropylene industry. The gas flow and mass transfer determine the heat transfer capacity and product quality. In this work, the pressure drop was measured below and above minimum fluidization velocity (u mf). Then, the axial and radial dispersion coefficients (D L and D R) were estimated below u mf by measuring the step residence time distribution and the stationary radial tracer profiles, respectively. Pressure analysis show the agitation significantly reduces the bed pressure drop, changing the fixed bed below u mf and bubbling bed above u mf to an agitated bed with a periodic voidage. The D L was proportional to the gas velocity, with little influences of the stirring speed. The radial tracer profiles show the bed is divided by the inner diameter of the helical ribbon into the peripheral ascending region and the central descending region, without gas exchange between them. Furthermore. the tracer profiles in the descending region are classified into two types. For type I, the D R , calculated by the plug flow model with radial dispersion, is proportional to the gas velocity, with little effects of stirring speed. Type II shows uniform profiles due to the deflection of the gas flow toward the low pressure area at the inner diameter of helical ribbon. The causes of the two types are explained by the relative size of particle circulation and gas flux. These two flow regimes are quantitatively clarified with an empirical correlation of Re and Fr as flow regime transition boundary, namely dispersed plug flow and perfect mixing flow. With lower Re and higher Fr , it changes from dispersed plug flow to perfect mixing flow. [ABSTRACT FROM AUTHOR]

Through gasification and methanol synthesis, biomass can produce methanol and then produce light olefins through the methanol-to-hydrocarbon (MTH) process. To make this new biomass based production route profitable, the efficiency of the MTH process is important. Catalyst deactivation is the main reason for the decline of conversion and selectivity. NMR was applied to detect the relaxation and diffusion of liquid molecules in a series of coked ZSM-5, investigating the effect of coke on molecular transport properties. n-Heptane was chosen as a probe molecule in describing pore network connectivity, whereas methanol was used for relaxation measurements. Though there were only minor differences of pore connectivity among the samples, the longitudinal relaxation time showed an almost linear relationship with coke contents, suggesting that the interaction between reactants and catalyst surface influences the catalyst performance within low coke contents. PFG-NMR and NMR relaxation, as fast and straightforward measurements, could simulate catalyst behaviors during the reaction process. [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]

Fluidization of fine fluorite particles, classified as Geldart A/C particles, was studied at ambient/high temperatures by experiments. Results showed that fine fluorite particles could not be fully fluidized at ambient temperatures, due to the agglomeration phenomenon. What's worse, due to the great increase of van der Waals forces with the increasing temperature, the fluidization quality was further depressed and they were totally defluidized at 723 K unless the loose gases were used during the heating process. In order to improve the fluidization quality, an enhancement method of adding cohesive calcium sulfate particles was established. The best improvements at ambient/high temperatures both appeared when the addition fraction was 20 wt %. Moreover, theoretical analysis showed that the effect mechanism of a calcium sulfate particle was the "coordination" theory. According to the "coordination" theory, the optimum addition fraction of calcium sulfate particles was calculated as 16.5 wt %-22.4 wt %, which agreed well with the experimental results. [ABSTRACT FROM AUTHOR]

In industrial fluidized beds with liquid spray, dynamic and steady-state characteristics of the liquid spray zones are of significant importance for operation optimization and products control. In this study, a conductivity probe array, two thermocouple arrays, and a pressure sensing system are applied to an externally heated gas-solid fluidized bed with a side-wall liquid spray. Nonstationary and nonlinear characteristics are exhibited in the Hilbert spectra of the conductivity probe signals, and the fluctuation energy distribution shifts to higher frequencies with the liquid spray velocity, related to the liquid-induced higher-frequency bubble motion. The variation coefficient analysis of temperature data is a reliable approach to characterizing the liquid spray zone boundary. The liquid spray zone is enlarged and extends downward along the wall with the liquid spray velocity and shrinks with the gas velocity. Moreover, the liquid spray zone is enlarged and extends downward along the wall with the nozzle installation height. [ABSTRACT FROM AUTHOR]

The hydrogen supply in many refineries is becoming a critical issue because of a trend of heavier crude oils and increasingly rigorous environmental legislation. One of the significant problems is that the concentration fluctuation of hydrogen affects product quality of refineries and causes economic losses. In this article, we investigate the disturbance resistance ability of the hydrogen network with multiple impurities. The previously defined mixing potential of a single impurity is extended to the multiple impurity case. Then, the disturbance resistance ability is optimized under minimum hydrogen utility consumption by the mathematical programming method. Later, such disturbance resistance ability of the obtained network structure is verified by Monte Carlo simulation. Several literature examples are investigated to illustrate the effectiveness of the method. Monte Carlo simulation results show that the disturbance resistance ability of the hydrogen network obtained by the proposed method is better than the literature performance in five cases, while one case stays the same. [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]

The conventional methods for recovering effluent gas in polyethylene processes include compression condensing, membrane separation, cryogenic separation systems and pressure swing adsorption. Since the effluent gas content varies with the process, there is no single recovery technic can meet all effluent gas content conditions. Therefore, a systematic strategy is needed to guide the selection of recovery technologies. This article introduces a method to select the best recovery system for certain compositions of effluent gas. After searching the feasible content region for the recovery systems according to the specified concentration of recycle stream and outlet streams, it shows PSA system has the largest feasible region while compression condensation system has the smallest one. In comparison of economic and exergetic performance, the cryogenic separation system shows its outstanding peculiarity to recover the effluent gas. The obtained result is effective in guiding the design of recovery system. [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]

Granules polymers electrostatic behavior in a fluidized bed can be complicated by the differences in catalyst residue and surface properties among them. Electrically charged particles cling together in large aggregates and adhere to the wall of the apparatus. Polymer particles with the same chemical composition but different sizes would have their own special contributions to the generation of static charges. It is improtant to understand polymer particles role on electrostatic charge generation and dissipation. Experiments are carried out in a gas−solid fluidized bed with nitrogen as the fluidization gas to determine the relationship between the electrostatic charge level and the size of the polyethylene granule. By measuring the electrostatic potentials at different bed axial heights, it is found that the electric field inside the bed is significantly influenced by the size, weight fractions, and catalyst residue of added granular polyethylene. Consequently, an impact factor of granules (Fb) is proposed to study the influence of particle size and the weight percent of the residual catalyst to the electrostatic potentials. And it is found that the greater the degree of fineness of the granules, the more percentage of the residual catalyst in the particles, which results in the stronger affect on the electrostatic behavior in the fluidized bed. [ABSTRACT FROM AUTHOR]