Search

Due to the serious economic losses and deaths caused by COVID-19, the modeling and control of such a pandemic has become a hot research topic. This paper finds an analogy between a polymerization reaction and COVID-19 transmission dynamics, which will provide a novel perspective to optimal control measures. Susceptible individuals, exposed people, infected cases, recovered population, and the dead can be assumed to be specific molecules in the polymerization system. In this paper, a hypothetical polymerization reactor is constructed to describe the transmission of an epidemic, and its kinetic parameters are regressed by the least-squares method. The intensity of social distancing u is considered to the mixing degree of the reaction system, and contact tracing and isolation ρ can be regarded as an external circulation in the main reactor to reduce the concentration of active species. Through these analogies, this model can predict the peak infection, deaths, and end time of the epidemic under different control measures to support the decision-making process. Without any measures (u = 1.0 and ρ = 0), more than 90% of the population would be infected. It takes several years to complete herd immunity by nonpharmacological intervention when the proportion of deaths is limited to less than 5%. However, vaccination can reduce the time to tens to hundreds of days, which is related to the maximum number of vaccines per day.

In the gas–solid fluidized bed with condensed liquid spray applied to ethylene polymerization, the collision characteristics of condensed droplets and polyethylene particles play an important role ...

We present a design strategy of in-line mixers for 3D printing and an evaluation protocol that comprehensively characterizes the performance of hydrodynamics, reagent mixing, heat exchange, and rea...

The work and heat exchange network synthesis problem refers to the problem of determining a network of heat exchangers and pressure equipment that minimize the total annual cost or exergy consumpti...

The jet bubbling column is a new type of gas–liquid two-phase reactor with excellent mixing ability. The evolution and interaction characteristics of liquid flow and bubbles in a jet bubbling colum...

Organic rankine cycle (ORC) has been regarded as the most promising measure for converting low-grade waste heat into electricity during the past decades. To take better advantage of ORC, the parame...

Ultrahigh-molecular-weight polyethylene (UHMWPE) with a low polydispersity exhibits excellently physical and mechanical properties. In this work, a polyhedral oligomeric silsesquioxane (POSS)-modif...

The dispersion trajectory and dynamics of particles injected from the sidewall were investigated in a pseudo-two-dimensional fluidized bed based on digital image analysis, and the effect of the inj...

Heat exchanger networks (HENs) discharge a large amount of low-grade heat to the cold utilities, resulting in excessive energy consumption. Organic Rankine cycle (ORC) which converts low-grade heat...

Work and heat are the two major forms of energy consumption in the process industry. They are respectively consumed in the work exchange and heat exchange networks. Due to the tight interactions be...

We present a miniaturized microbubble generator via three-dimensional (3D) printing for potential use in gas–liquid chemical reactions. We design it based on venturi channel structures to enable co...

Hydrogen reuse and purification reuse are two main methods to conserve hydrogen resources in refineries. They are achieved by hydrogen allocation networks and purification units such as pressure sw...

It is common to characterize fluidized bed dynamics using spectral analysis and nonlinear methods such as correlation entropy (Kolmogorov entropy). In this paper, an alternative method, the Hilbert...

At low liquid jet velocity (uj), bubble vortices do not appear and the bubble size distribution (BSD) shows a bimodal distribution. The number density function of large bubbles and small bubbles in...

Naphtha is an important feedstock in producing both fuels and chemicals. To optimize the product distribution of the naphtha conversion processes, it is necessary to obtain the molecular compositio...

This work proposes a simulation-based multi-objective optimization model for the operation of the product separation process in a methanol to propylene (MTP) plant, striving to enhance the system energy utilization eciency. The formation of byproducts including an oxygenated hydrocarbon, dimethyl ether (DME), makes the product rening process highly energy-intensive, not only because that the various hydrocarbon byproducts require a long train of distillation columns but also owing to the fact that DME forms azeotrope with product propylene. Furthermore, the formation of oxygenated DME byproduct varies with the catalyst activity, which makes the system more complex. The contribution of this paper is twofold. First, it proposes a novel way of DME removal with responsive consumption of extractant methanol according to the DME concentration during one production period. In this way, the energy consumption of the condenser and reboiler of the methanol recovery unit can be expected to decrease by 61.5% and 37.6...

This work investigates the electrostatic distribution in the riser of a multizone circulation fluidized bed for polypropylene by various electrostatic measurements. Results show all measured electr...

Thermal stability is a crucial issue for fluidized-bed ethylene-polymerization reactors, especially when the particle-aggregation probability increases as a result of the high reaction temperature or operation under condensed mode. To determine the mean particle size, a population-balance model (PBM) considering particle growth and particle aggregation was implemented in the present study. Then, an integrated model including the two-phase model (TPM), the PBM, and an evaporation model was proposed to describe polymerization of ethylene in liquid-containing fluidized-bed reactors. The results demonstrate that the particle-growth rate and catalyst particle size dominate the particle size of the final product. Thermal stability of fluidized-bed reactors is mainly affected by the catalyst activation energy, the superficial-gas velocity, and the condensed-liquid flow rate.

Interplant heat integration (IPHI) using intermediate fluid circles provides an additional opportunity for energy saving and emission reduction, beyond traditional intraplant heat integration. However, the number of intermediate fluid circles as well as their heat capacity and temperatures are all variables. It is difficult to find promising solutions, since such conditions generally lead to nonlinearity. To deal with this problem, a transshipment type model, which holistically optimizes the parameters and interconnectivity patterns of intermediate fluid circles and keeps the constraints linear, is developed. New formulations are developed to identify exact distributions of intermediate fluid circles (namely heat transfer available intervals) among all temperature intervals, with unknown temperatures. Additionally, mixed-integer linear constraints are developed to describe interconnectivity patterns of intermediate fluid circles so as to calculate piping and pumping cost. The performances of different int...

Due to the superior performance in thermal conductivity and mechanical strength, the foam SiC-supported ZSM-5 catalyst is favorable in fixed bed methanol-to-propylene (MTP) reactions, where the temperature distribution and pressure drop are strictly controlled. However, its performance and service life in multiple reaction–regeneration cycles has not been proved yet. Both the activity and selectivity of the catalyst will be tested in six reaction–regeneration cycles in a fixed bed reactor. In addition, the properties of the catalyst during the fourth cycle were characterized by various techniques (scanning electron microscopy, Brunauer–Emmett–Teller, 27Al nuclear magnetic resonance). The results show that, as the reaction progresses, the catalyst continuously deposits carbon, and the local high temperature of carbon burning during regeneration leads to the removal of aluminum from the zeolite framework. Therefore, the catalyst life in one single process increases first and then decreases. At the same time...

Energy and resources saving is of significance to sustainable development. In the past decades, heat integrated water allocation networks (HIWANs) have been applied to generate effective strategies for water and energy management in chemical process industries, where large amounts of water and energy are consumed. In this paper, a graphical approach for the synthesis of heat exchanger networks (HENs) in HIWANs has been proposed to reveal the new insights into T–H/H–F diagrams and fully exploit the HEN structure possibilities. Current conceptual design methods for HENs in HIWANs by the original separate systems (T–H diagram) and the matching composite curve (H–F diagram) only generate two special kinds of HEN structures: series and parallel structures. A transformation method is proposed to generate HENs with different structures based on these two tools. Both simplex series or parallel structures and hybrid structures can be obtained via the transformation procedures. Two examples are illustrated to demon...

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 ...

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 fe...

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 ...

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 %, whic...

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 nozzl...

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 th...

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 pr...

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.

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.

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.

A general optimization model is proposed for the simultaneous optimization of integrated water allocation and heat exchanger networks (WAHEN). An improved superstructure and mathematical model for the WAHEN problem is presented. Complementary formulations are applied to model the discrete decisions, and a mathematical model with equilibrium constraints (MPEC) is formulated. Both the MINLP model and the MPEC model are developed and solved for the problem. The effectiveness of the proposed model is illustrated with two case studies. A comparison between the results obtained by the proposed model and those obtained from the model in the literature is carried out. Case studies show that the proposed simultaneous methodology performs well and is efficient.

The macromixing and flow characteristics of a low-density polyethylene autoclave reactor stirred with 32 impellers were investigated by experiments and computational fluid dynamics simulations. The simulation results were validated using the experimental data. The mixing curves show an excellent agreement with the experimental results. The flow field, distribution of velocity, and mass flux obtained from the simulations were further analyzed, and the results show that the reactor can be divided into two reaction zones. In each reaction zone, two axial flows form a big circulation loop. The downward flows near the reactor wall decrease along the flow direction, while the upward flows near the shaft increase. In each big circulation loop there are many small radial circulation loops that are similar to those encountered in continuous stirred-tank reactors. Finally, a more accurate macromixing model was proposed, which is helpful to reveal the multizone phenomenon and flow characteristics in reactors.