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A co-reaction of methane with methanol over zeolite catalysts has emerged as a new approach to the long-standing challenge of methane transformation. However, the effect of catalyst acid properties on the co-reaction has been rarely studied. In this study, a series of HZSM-5 zeolites with comparable diffusion abilities and various acidities were synthesized directly through steaming with 100% water vapor at 693 K. The co-reaction of methane and methanol was subsequently evaluated. Bronsted acidity at 0.262 mmol/g was detected to reach the maximum methane conversion of 5.42% at 673 K, which was also the odd point in the relationship between acid concentration and C4 hydrogen transfer index. Moreover, the influence of methanol feed was investigated over parent and steamed ZSM-5 catalyst, with results showing that excessive acid sites or methanol molecules reduce methane conversion. It is proposed that acid sites adsorbed with methanol molecules construct the methane activation sites. Hence, a proper design of zeolite acidity should be achieved to obtain higher methane conversion in the co-reaction process.

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...

This work investigated the particle flow behaviors in the orifice downcomer of the multistage fluidized bed based on a simplified experimental device, in which the flow behavior can be observed conveniently and directly. Three flow patterns were observed, which were the stable moving bed, the bubbling moving bed, and the slugging bed. Furthermore, significant differences were found in the pressure pulsation signals of different flow patterns, thus a flow pattern identification method using pressure pulsation spectrum was proposed and the corresponding flow pattern maps were established for the orifice downcomer with different diameters. Finally, the difference between the stable moving bed and the bubbling moving bed was further studied. Results showed that the solid flow rate in the sable moving bed state was related to the superficial gas velocity in the downcomer, while it was only related to the cavity appearing near the orifice in the bubbling moving bed state.

This work first investigated the detection of slags, slag pool liquid level, and slag accumulation height in laboratory scale based on acoustic emission (AE) detection, and further tried the feasibility of this method in an industrial scale coal gasifier. Results show that the energy and variance of acoustic signals can realize the accurate detection of large slag (criterion: E > 1.5E0, S > 1.2S0), and the average relative error is only 0.28%. The acoustic energy in the frequency range of 20–40 kHz is defined as the characteristic energy, which can realize the accurate detection of slag accumulation height and slag pool liquid level, and the average relative error is only 3.94%. Furthermore, AE detection also realize accurate detection of large slag in an industrial scale gasifier and the acoustic signals at slag screen can be used to realize the early warning of the slag collapse (5 h earlier).

In this study, a non-invasive and environment-friendly acoustic emission (AE) technique, coupled with multiple analysis methods, was proposed to monitor the critical variation of separation efficiency of a cyclone separator by means of the gas-solid hydrodynamics. Acoustic energy analysis was used to reflect the characteristics of particle motion and particle-wall interaction. Shannon entropy analysis was adopted to reflect chaos and complexity of gas-solid two-phase motion. Multi-scale analysis (Hurst analysis and wavelet analysis) was used to obtain multi-scale characteristics inside the cyclone separator. To be specific, micro-scale collision behaviors of particle-particle and particle-wall, meso-scale interaction behavior between particle clusters and gas phase, and macro-scale interaction behavior (overall flow behavior). Furthermore, by comparison with the results of separation efficiency and pressure drop, the above-mentioned three methods based on AE technique can effectively reflect the critical variation of separation efficiency for cyclone separator.

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...

Gas phase fluidized bed processes have been widely applied to polyethylene production. In these processes, the flow, mass transfer, and reaction rate on the microscale and macroscale are strongly coupled because of the multiphase and multiscale nature of the fluidization system. Understanding mesoscale phenomena is therefore essential to the quantitative translation of the knowledge obtained from the microscale to the macroscale. This paper reviews the development of ethylene polymerization gas phase processes while focussing on studies regarding mesoscale phenomena. These include experimental characterizations, mathematical modelling and control strategies. Trends and future developments in this field are also discussed.

In this work, experimental data from the novel high speed particle image velocimetry (HSPIV) measurements and pressure fluctuations complemented by numerical predictions from TFM simulations are processed using advanced signal processing protocols to identify and characterize coherent structures in a gas–solid fluidized bed with Geldart D particles. The time-frequency properties of the bed dynamics were studied using the wavelet coherent analysis (WCA) and the Hilbert Huang transform. The WCA of numerical pressure drop signals at different measurement positions showed the existence of spatial-temporal coherent structures. At close measurement positions phase locked coherent phenomenon due to bubble generation dominate most of the frequency and time scales due the proximity to the distributor. At a wider measurement spacing the fast traveling waves are attenuated due to gas bubble/void coalescence and acceleration and only pockets of highly coherent oscillations are visible mostly in the frequency range of 0.5–3 Hz at certain times. Multi-resolution of the particle fluctuations realized with the Hilbert–Huang transform. The structures were resolved into the micro, meso and macro scales of fluidization based on the energy and frequency distributions. The meso scale structures form the main contribution to the normal axial Reynolds stresses and bubble granular temperature and ultimately the mixing.

The flow and dispersion behaviors of the fine particle injection in a gas-solid fluidized bed were studied numerically based on the two-dimensional multi-fluid model. The injection path and flow pattern of the flotsam solids were investigated. A distinct pair of counter-rotating vortices of flotsam particles appeared in the middle and upper parts of the fluidized bed. Higher injection rate was preferred for faster flotsam dispersion. The effects of flotsam injection on bed hydrodynamics were investigated with regard to the velocity distribution and volume fraction of bulk materials and the bubble size. Consequently, the mixing properties of the flotsam particles and bulk solids were quantified by the fluid-free flotsam fraction profile and the standard deviation. The fluidized bed was mixed acceptably with modest local segregation for all the conditions simulated. Lower injection velocity made contributions to better mixing especially for the duration of injection.

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...

Chain entanglement was very important for adjusting the processability and mechanical property of nascent ultrahigh molecular weight polyethylene (UHMWPE). So far, it is still a mystery to unravel ...

CO2 capture is a promising way of offloading the impact of fossil fuels on global warming. Although various techniques have been proposed for CO2 capture, the main obstacle remains the economic per...

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...

Methane steam reforming is the main hydrogen production method in the industry. The product of methane steam reforming contains H2, CH4, CO and CO2 and is then purified by pressure swing adsorption (PSA) technology. In this study, a layered two-bed PSA process was designed theoretically to purify H2 from methane steam reforming off gas. The effects of adsorption pressure, adsorption time and purge-to-feed ratio (P/F ratio) on process performance were investigated to design a PSA process with more than 99.95% purity and 80% recovery. Since the feed composition of the PSA process changes with the upstream process, the effect of the feed composition on the process performance was discussed as well. The result showed that the increase of CH4 concentration, which was the weakest adsorbate, would have a negative impact on product purity.

•A new transshipment type model for inter-plant heat exchanger network is proposed.•New constraints are used to identify three inter-plant heat integration schemes.•A model with linear constraints is developed, allowing non-isothermal mixing.•Better results with lower total annual cost can be obtained by the proposed model.

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...

Acoustic and electrostatic signals were used to detect and analyze the flow regimes transition in vertical pneumatic conveying from the scope of particle motion. It was found that the minimum acoustic energy and electrostatic accumulation appeared close to the minimum transport velocity. Furthermore, analysis of particle velocity based on electrostatic signals demonstrated that negative particle velocities appeared in plug flow since particles fell down between plugs, thus collision between falling particles and plug dominated and the energy fraction of collision increased with the decreasing gas velocity in plug flow. Finally, based on combination of different detection methods, two new flow regimes transition diagrams were developed. The one based on AE energy and pressure drop indicated different relationships between particle-wall interaction and energy loss in different flow regimes, while another one based on the electrostatic accumulation demonstrated the transition zone between the minimum transport velocity and flow regime transition velocity.

The optimization of refinery hydrogen systems has become a significant issue with the tendency of heavier crude oils and stricter environmental regulations. The fluctuations in the concentration of hydrogen is a considerable problem that can affect the quality of refinery products and increase operating costs. The hydrogen deficit caused by concentration fluctuation is eliminated by excess supply of hydrogen utility in reality. More hydrogen utility consumption leads to lower product quality risk and higher operating cost. Therefore, it is necessary to strike a balance between risk and cost. To solve this problem, the Worst-Case Conditional Value-at-Risk (WCVaR) concept is applied to represent the minimum value of total pure hydrogen flowrate in hydrogen networks. The robustness of hydrogen supply is enhanced by maximizing of WCVaR associated with uncertainty distribution. Both adjustable and non-adjustable cases for hydrogen production are considered. The robustness of the obtained network structure is verified by Monte Carlo simulation. The results of this work indicate that optimizing WCVaR can improve the network robustness.

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.

Accurate prediction of the onset of turbulent fluidization still remains elusive owing to the dependence of the transition velocity on several factors including measurement methods and interpretation of results. In this work, numerical simulations using the two fluid model (TFM) are performed in an attempt to predict the regime change reported by Gopalan et al. (2016) in a small scale pseudo-2D gas–solid fluidized bed containing Geldart D particles. Various time and frequency domain analyses were applied on predicted absolute and differential pressure time series data to reveal the bed dynamics. Numerical predictions of the transition velocity, Uc are in reasonably good agreement with experimental results from the small scale challenge problem. The literature correlations completely fail to predict the transition velocity for the system considered in this work. This work thus provides a different approach for validating the CFD model against experimental measurements.

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...

Fluidized beds with the liquid spray have been widely applied due to efficient heat transfer ability. In this work, the liquid-containing particles and the liquid dispersion pathway are visualized by a unique reversible thermochromic material (RTM) tracking method. The effects of evaporative liquid considering different nozzle modes on bubble density, particle motion and heat transfer are investigated combining PIV and DIA. The results indicate that the liquid injection decreases particle fluctuation and promotes bubble generation. A stable liquid-containing zone is observed under the top spray mode, whereas liquid disperses rapidly under the side-wall spray mode. A multi-zone heat transfer model (MHTM) is then developed based on the bubble growth and inter-layer exchange models. Experimental and calculated temperature profiles indicate that the side-wall spray mode leads to larger temperature differences. The methods proposed can be applied for the analysis of the complex multiphase system and optimization of the nozzle configuration. This work is supported by the National Natural Science Foundation of China for Young (No. 21808198), the Major Research Project of National Natural Science Foundation of China (91834303), the Natural Science Foundation of Zhejiang Province for Young (No. LQ18B060001), the National Science Fund for Distinguished Young (No. 21525627).

Inter-plant hydrogen network with reuse/recycle optimization is important for saving hydrogen resource. Thus, it's necessary to optimize the inter-plant hydrogen network. In this paper, a novel two-step method that combines the pinch insight with mathematical programming is developed to optimize the inter-plant hydrogen network with purification reuse/recycle. A new transhipment model for targeting inter-plant hydrogen network is built to target the hydrogen utility consumption for each refinery. After the hydrogen consumption is determined, individual plant hydrogen networks are designed separately. The mathematical model is linear to guarantee global optimal solution. Furthermore, the model can also optimize the number of inter-plant connections of the hydrogen network. Case study indicates the effectiveness of model.

Molecular reconstruction is popular in current oil refinery modeling. It aims to understand the refining process from the molecular level, to predict product properties accurately, to optimize the processes, and to increase the value of each molecule. Molecular reconstruction technique determines the detailed molecular composition of petroleum fractions through obtainable bulk properties and chemical details. In this paper, the existing molecular reconstruction models involving models with a set of predefined deterministic molecules, stochastic reconstruction method, structure-oriented lumping method, molecular type-homologous series matrix method, reconstruction by entropy maximization method, stochastic reconstruction-entropy maximization method and state space representation method are reviewed and compared. The credibility of the simulated composition and the drawbacks of molecular reconstruction technique are also discussed.

In many industrial processes, electrostatic charges are inevitable and affect the hydrodynamic behavior and heat transfer ability of chemical equipment. A comprehensive study of the electrostatic effect on bubble behavior, particle fluctuation velocity and heat transfer coefficient in the fluidized bed with a central jet has been evaluated in this paper by Eulerian-Eulerian two-fluid model coupled with electrostatic model and energy model. The simulated voidage profiles at different positions, bubble detachment time and initial bubble diameter are compared with experimental results from the literature without charge. The bubble behaviors including bubble frequency and bubble numbers, combined with particle fluctuation parameters are analyzed in both charged and uncharged system. The electrostatic effect on two kinds of heat transfer coefficients is quantitatively compared, namely bubble to emulsion phase heat transfers based on the gas throughflow velocity and gas-solid local heat transfer coefficient. Simulation results show that electrostatic charges decrease bubble numbers and granular temperature, whereas the averaged heat transfer coefficients are enhanced. Overall, the electrostatic effect on the hydrodynamic and heat transfer characteristics can be revealed. This work was supported by the Project of National Natural Science Foundation of China (No. 91434205), the National Science Fund for Distinguished Young Scholar (No. 21525627), the Science Fund for Creative Research Groups of National Nature Science Foundation of China (No. 61621002).

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...

This work explores the ability of the two-fluid-model (TFM) to model the dynamical and turbulent features of a pseudo 2D gas-solid fluidized bed operated under slugging conditions. 2D and 3D numerical simulations are performed to investigate the effect of the bed thickness on predicted quantities. Hi fidelity raw pressure drop and particle velocity data from the NETL small scale challenge problem is processed and used to validate the CFD model. Our work shows that the differences between 2D and 3D simulations in predicting the fluidized bed dynamics using pressure fluctuation data is minimal. However the effect of the bed thickness on turbulent properties namely the normal Reynolds stresses, turbulent kinetic energy, granular temperatures is significant. Taking into account the bed thickness does not necessarily improve the model predictions of all the dynamic and turbulent features. Furthermore mean profiles alone are not sufficient to validate TFM models as is quite common in the open literature. Mixing in the slugging bed is predominantly due to coherent meso-scale structures (voids and slugs) rather than individual particles as revealed from computed granular temperatures.

Vortex and electrostatic charges in the gas-solid fluidized bed have a significant influence on its transport abilities and hydrodynamics. In this work, the electrostatic model coupled with energy model has been applied to reveal the electrostatic effect on hydrodynamics, vorticity and local heat transfer coefficients based on the kinetic theory of granular flow. The results indicate that particle vortices change the gas and solid phase interaction around the bubble and enhance the local heat transfer coefficients. Gas interchange decreases by 6.5% compared to Davidson model at the jet velocity of 10 m·s−1 and 13% of 5 m·s−1. After adding electrostatic charges, bubble diameter decreases with the increasing specific charges. Furthermore, vorticity at the initial stage of bubble formation is larger and the particle vortex diffuses to a large extent. The simulation results can be applied to modify and estimate the overall heat transfer coefficient of the fluidized bed reactor and provide the basis for studying the effect of electrostatic effect on heat transfer.

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...

A Polyhedral oligomeric silsesquioxane (POSS) modified Ziegler-Natta catalyst is reported to synthesize the weakly entangled ultra-high molecular weight polyethylene at a high temperature and with a high activity. Incorporation of POSS can form numbers of aggregates with a mean size of 48 nm adsorbing on the surface of SiO 2 . The structure of nanoaggregates is evidenced by the experiments and theoretical calculations where one POSS can coordinate with multiple MgCl 2 molecules serving as an electric donor to the further immobilized TiCl 4 . The catalyst is thus featured by two distinct active regions positioned in the POSS/MgCl 2 nanoaggregates and δ -MgCl 2 , respectively. The former regions present extremely low activity on ethylene polymerization, which function as horizontal separators for isolating the active TiCl 4 sites and the growing chains. This catalyst exhibits an exceptional activity ( i.e. 1.3 × 10 6 gPE mol Ti −1 h −1 bar −1 ) for the synthesis of weakly entangled polyethylene at 60 °C.

Combining cryogenic flash units with membrane units is attractive for gas separation processes such as effluent gas recovery and CO2 capture. However, systematic design methodology for such hybrid systems have not been reported yet. The hybrid system is a complicated system that not only includes separation units, but also includes pressure manipulation units and heat exchangers. A two-step decomposition strategy is proposed to deal with the design of such complicated system. The separation sequence is first determined with energy consumption consideration in the first step. Subsequently, the remaining energy recovery units, the heat exchanger network and turbines are simultaneously synthesized with the separation flowsheet optimization. When applying the proposed strategy to recover the effluent gas from polyolefin plant, we find a novel flowsheet that avoid intensive capital and operating cost by tightly integration of process units.

In the paper, a novel dual circulating fluidized bed (DCFB) reactor is introduced, which can be widely applied in catalytic cracking, chemical looping combustion, coal/biomass combustion and gasification, and gas adsorption, etc. The study mainly investigates the effects of specific operating parameters on pressure balance and solid circulation rate, including total solids inventory, riser gas velocity, bubbling fluidized bed gas velocity and pot-seal gas velocity. It is found that changes of those parameters lead to variations in pressure balance and riser axial voidage in DCFB system, and further affect solid concentration and solid circulation rate in the system. To be more specific, total solids inventory, riser gas velocity and bubbling fluidized bed gas velocity have a major impact on solid concentration and solid circulation rate, while pot-seal gas velocity only exerts a minor impact. Besides, the changing of overall pressure drop across the bubbling fluidized bed is consistent with variations in pressure drops in the other parts of the system, with the former equaling △Pr + △Pc + △Pp-t + △Pud1 + △Pud2. In this way pressure balance in the system is maintained. Eventually the paper reaches the conclusion that relevant operating parameters can be adjusted to control pressure distribution and solid circulation rate in different parts of the system and further to ensure the safe and stable operation of DCFB reactors.

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...

Sustainability is essential for process industries, as energy and resources are getting scarcer and scarcer. For the past decade, heat integrated water allocation networks (HIWANs) have drawn more and more attention, owing to the efficient utilization of water and energy. In this article, a systematic procedure for the synthesis of heat exchanger networks (HENs) in HIWANs has been proposed. A graphical tool, named heat transfer blocks diagram, is developed to improve the conceptual understanding for the implications of HEN structures in HIWANs. The minimum hot/cold utility consumption can be obtained by analyzing heat surpluses and heat deficits between cold stream and hot stream heat transfer blocks, while heat transfer matching blocks are introduced to deal with the heat exchange matches. Not only simplex series or parallel structures but also hybrid structures can be obtained via this graphical tool. Besides, a heuristic of step by step maximizing the heat load of heat exchangers is presented to guide ...

Water and energy management issues in process industries are generally related to the synthesis of heat integrated water networks (HIWN), because water and energy are inextricably intertwined in process water networks. The aim of this study is to present a novel mathematical programming model for HIWN synthesis problems and develop an efficient solution strategy. This research is an extension of our previous work, where the targeting of heat integrated water-using networks (HIWUN) has been addressed. In this model, wastewater treatment units and multiple contaminants are embedded, and the total annual cost (TAC) is optimized rather than targeting a simplified TAC. What is more, a three-step solution strategy is proposed to guarantee obtaining promising solutions. The freshwater consumption, the relaxed TAC (rTAC), and the TAC are optimized successively. Good initial points for the rigorous HIWN model in the last step can be generated by the minimizing the rTAC. Four examples including two large-scale exam...

The conversion of carboxylic acid through ketonization process reduces O-atoms and increases C C bonds, which can provide attractive routes for upgrading biomass feedstocks into biofuels. The key factors influencing the surface ketonization activity over CeO2-based oxides catalysts remain matters of active discourse. Here, a series of Ce1-xFexO2-δ catalysts were investigated for vapor-phase ketonization of acetic and propionic acid. The catalysts were characterized in detail using various physico-chemical techniques both before and after reaction to gain understanding of the ketonization process. The turnover frequency (TOF) based on the basic sites changed with the Fe content. The Ce0.8Fe0.2O2-δ sample showed the prominent ketonization activity with the highest TOF value. On one hand, for samples with a lower Fe addition (x O bonds of Ce-O-Fe species thereby promote the ketonization activity. On the other hand, the higher Fe addition (x > 0.3) caused the damage of the Ce-O-Fe structure, thus reducing ketonization activity. Notably, the investigation of the reaction temperature regime of Ce0.8Fe0.2O2-δ sample directly proved the existence of surface redox cycle during the ketonization process.

Electric fields have great potential to control meso-scale structures, typically bubbles and agglomerates in gas-solid fluidized beds. However, previous research only considered the effects of polarization forces and ignored the electrostatic effects. This work, by means of cold model experiments, for the first time investigates the effects of DC electric fields on meso-scale structures in a 3-D fluidized bed with electrostatic effects. Results show that particles will also experience the Coulomb force under the effects of electrostatics besides of polarization forces, and the effects of these two electric field forces are different. The Coulomb forces make particles migrate at lower field strengths, then increases the bubble size and breaks up agglomerates. While at higher field strengths, the polarization forces result in formation of agglomerates and reduction of bubble size. Therefore, the effects mechanism of electric fields is the competition effects between the Coulomb force and the polarization forces. The critical transition field strength, at which the predominant position of Coulomb and polarization forces on bubbles and agglomerates changes, is significant in the control of meso-scale structures by DC electric fields.

Fluidized beds reactors with liquid bridge and solid bridge coupling actions have been widely used in industry and thus studies of particle agglomerations under such fluidization conditions are of great significance. This work proposed an experimental apparatus combining electro-magnetic induction heating system with fluidized bed to simulate the real conditions for particle reaction heat release and heat transfer in industrial polymerization fluidized bed reactors. The effects of liquid content on agglomeration behavior of wax/graphite composite particles under different fluidization gas temperatures, gas velocities and heating powers have been studied. Through a force balance analysis of particles with liquid bridge and solid bridge coupling actions, relative solid bridge force was taken as a key parameter to demonstrate the effects of solid bridge force and other forces on agglomerations. Results showed that as the relative solid bridge force varied in different ranges, the agglomeration mass presented three different variation trends with liquid increases, namely monotonic increasing, non-monotonic changing and monotonic decreasing, due to different dominating agglomerating mechanisms (liquid evaporation and liquid bridge) during fluidization. According to the results of this study, the proposed criterion based on relative solid bridge force can be used to guide the regulation and control of particle agglomerations in fluidization with liquid bridge and solid bridge coupling actions.

In the refinery, purifiers are widely used in the recovery of hydrogen components of the emissions from hydrogen consumption units. Hydrogen network containing purification units have been optimized and integrated by lots of researchers. However, purifier models such as PSA, membrane separation have nonlinear characteristics. Even if minimizing hydrogen utility, mathematical programming models adopted by most of the researchers belong to the non-convex and nonlinear models, not guaranteeing global optimal solution. On the basis of previous studies, this paper proposes a mixed integer linear programming model to obtain a minimum hydrogen utility consumption. This method can get the inlet flowrate simultaneously. Case studies indicate that this method is effective for both hydrogen and water networks.

Bubble and particle motion behaviors are investigated experimentally in a gas solid fluidized bed with liquid spray on the side wall. The particles used in the experiment are classified as Geldart B particles. The results reveal that when the fluid drag force is less than the liquid bridge force between particles, liquid distribute all over the bed. Bubble size increases as the increase of inter-particle force, then decreases owing to the increase of particle weight with increasing liquid flow rate. When the fluid drag force is greater than the liquid bridge force, liquid mainly distribute in the upper part of the bed. And it is difficult for the wet particles to form agglomerates. Bubble size decreases with increasing liquid flow rate due to the increasing of minimum fluidization velocity. Besides, the acoustic emission (AE) measurements illustrate that the liquid adhesion and evaporation on particles could enhance the particles motion intensity. Consequently, the bubble and particle behaviors change due to the variation in fluidized gas velocity and liquid flow rate should be seriously considered when attempting to successfully design and operate the side wall liquid spray gas solid fluidized bed.

Heat integrated water allocation networks (HIWAN) is a system where water and energy are highly interconnected. Well arranged nexus between water allocation networks and heat exchanger networks would reduce the water and energy consumption significantly. The aim of this study is to develop a novel mathematical programming model for targeting minimum simplified total annual cost of HIWAN. A new transshipment type of heat exchanger networks (HEN) representation is proposed, with features of stream splitting, stream by-pass, non-isothermal mixing, and isothermal mixing. Constraints are added to follow up on the flowrate consistency when stream splitting or mixing happens. Furthermore, a new formulation is presented to count heat exchanger units. The proposed model is formulated as a mixed-integer linear programming (MILP) problem. It is much easier to get feasible solutions than mixed-integer non-linear programming (MINLP) problems, especially for large-scale problems. Three examples including an industrial example and a large-scale case are solved by the proposed model. It is shown that the proposed model is suitable for the synthesis of HIWAN, and more importantly, the obtained results are better than literature records.