Gas Distributor Research Articles

SEDS: A Flexible Standard EEG Data Structure for Large-Scale EEG Applications

Coal beneficiation technology using gas-solid fluidized bed is a hot topic in recent decade, however its proper design and scale-up remain a great challenge due to the very complex gas-solid flow involved. To this end, an Eulerian-Lagrangian-Lagrangian (ELL) model (Zhang et al., Renewable Energy, 2019, 136:193-201) was used to intensify the coal beneficiation process, by systematically studying the effects of particle property, operating gas velocity, initial bed height, design of gas distributor and the size of fluidized bed. It was found that (i) coal beneficiation process can be improved significantly by using coarser beneficiated coal particles, adopting smaller initial bed height (or shallow fluidized bed) and/or operating at a properly selected gas velocity, all findings indicate that the process intensification can be realized via proper selection of operating conditions; (ii) the design of gas distributor was critical for process intensification and it should be designed properly to make the gas flow as uniform as possible; and (iii) there will be no scale-up effect, if ideally uniform gas flow at the inlet can be achieved. Present study demonstrates that computational fluid dynamics is a cost-effective tool for process intensification of gas-solid fluidized beds.

Microbubble-foam fractionation enabled long-term caffeic acid stability in the separation process: Self-assembly WSP as collector

Bioactive polyphenols are important anti-cancer phytochemicals in natural materials. It is essential to develop a cost-effective technology to enrich bioactive polyphenols from their leaching liquor and maintain their stability. In this study, a novel microbubble-foam fractionation technology was developed to effectively separate a bioactive polyphenol from its diluted solution. Caffeic acid (CA) was considered as a structure-representative bioactive polyphenol without foaming capacity. Whey soy protein (WSP), a natural surfactant prepared from a waste soymeal, was used as both a collector and a frother. Microbubbles were introduced for enhancing the interfacial adsorption of WSP. The nitrogen was sparged through the gas distributor to form normal bubbles in the liquid phase. With the coalescence between microbubbles and normal bubbles, CA was successfully embedded in WSP and adsorbed on the surface of final bubbles and finally concentrated in the foamate. The fluorescence and reductive capacity results indicated that CA was successfully embedded in WSP, and the WSP aggregation on the bubble interface maintained the antioxidant properties of CA in a concentrated solution. Besides, their interactions could be significantly influenced by pH. Then, in the concentrated solution, CA could be easily purified from WSP. The enrichment ratio and recovery percentage of CA reached 20.0 and 73.9% under the optimal operating conditions, respectively. The reuse of WSP and the pilot-scale microbubble foam fractionation demonstrated the feasibility of the technology using in the separation process of bioactive polyphenols.

Hydrodynamic behaviors of a spouted fluidized bed with a conical distributor and auxiliary inlets for the production of polysilicon with wide-size-distribution particles

In order to improve the fluidization quality of wide-size-distribution (WSD) particles in a spouted bed reactor for the production of polysilicon, a conical distributor with one central gas inlet and six auxiliary inlets was designed and applied in a cold-model reactor to form a spouted fluidized bed. The effects of the central and auxiliary gas velocities on the solid holdup were studied in the gas distributor region. The hydrodynamic behaviors inside the conical distributor were analyzed by pressure fluctuation in the time domain (standard deviation) and the frequency domain (power spectral density, PSD). The gas distribution was measured by the gas tracing method. It was found that the auxiliary gas feed significantly re-distributed the solid particles and effectively improved the fluidization quality; the dead zone phenomenon was well suppressed even at a low superficial gas velocity. Based on different flow behaviors, a regime map of fluidization was determined for fixed bed, bubbling bed, spouted bed, and spouted fluidized bed regimes. These results provided guidance for the reactor design because the gas and solid distributions would significantly affect the deposition efficiency of polysilicon.

Computational Fluid Dynamics Analysis of Particle Deposition Induced by a Showerhead Electrode in a Capacitively Coupled Plasma Reactor

Defect formation in the deposition of thin films for semiconductors is not yet sufficiently understood. In a showerhead-type capacitively coupled plasma (CCP) deposition reactor, the showerhead acts as both the gas distributor and the electrode. We used computational fluid dynamics to investigate ways to enhance cleanliness by analyzing the particle deposition induced by the showerhead electrode in a CCP reactor. We analyzed particle transport phenomena using a three-dimensional complex geometry, whereas SiH4/He discharges were simulated in a two-dimensional simplified geometry. The process volume was located between the RF-powered showerhead and the grounded heater. We demonstrated that the efficient transportation of particles with a radius exceeding 1 μm onto the heater is facilitated by acceleration inside the showerhead holes. Because the available space in which to flow inside the showerhead is constricted, high gas velocities within the showerhead holes can accelerate particles and lead to inertia-enhanced particle deposition. The effect of the electrode spacing on the deposition of particles generated in plasma discharges was also investigated. Smaller electrode spacing promoted the deposition of particles fed from the showerhead on the heater, whereas larger electrode spacing facilitated the deposition of particles generated in plasma discharges on the heater.

Ex-situ biogas upgrading in thermophilic up-flow reactors: The effect of different gas diffusers and gas retention times

Four different types of ceramic gas distributors (Al2O3 of 1.2 μm and SiC of 0.5, 7 and 14 μm) were evaluated to increase biomethane formation during ex-situ biogas upgrading process. Each type of gas diffuser was tested independently at three different gas retention times of 10, 5 and 2.5 h, at thermophilic conditions. CH4 production rate increased by increasing input gas flow rate for all type of distributors, whereas CH4 concentration declined. Reactors equipped with SiC gas distributors effectively improved biomethane content fulfilling natural gas standards. Microbial analysis showed high abundance of hydrogenotrophic methanogens and proliferated syntrophic bacteria, i.e. syntrophic acetate oxidizers and homoacetogens, confirming the effect of H2 to alternate anaerobic digestion microbiome and enhance hydrogenotrophic methanogenesis. A detailed anaerobic bioconversion model was adapted to simulate the operation of the R1-R4 reactors. The model was shown to be effective for the simulation of biogas upgrading process in up-flow reactors.

Review on the Effect of Gas Distributor on Flow Behavior and Reaction Performance of the Bubble/Slurry Reactors

Review on the Effect of Gas Distributor on Flow Behavior and Reaction Performance of the Bubble/Slurry Reactors

Investigation of a GL-EMMS gradual drag model by comparative simulations of bubble columns

The mesoscale model for gas–liquid flow based on the energy minimization multi-scale method, which is denoted by the GL-EMMS model, demonstrates its capability of predicting the regime transition in bubble columns. Since the dominant mechanisms and stability conditions are important for this mesoscale model, it is desirable to reveal more details through the computational fluid dynamics (CFD) work. This work proposes a gradual drag correlation based on the GL-EMMS model, and then incorporates it into the Euler–Euler (E–E) and Euler–Lagrange (E–L) frameworks respectively. Cases with different gas distributors are simulated via the opensource platform of OpenFOAM. A simplified meshing treatment of the inlet boundary is adopted and has proven effective to reducing the computing load. The E–E simulation predicts the total gas holdup and the radial distribution of liquid velocity well, but obvious deviation is observed in the radial distribution of gas holdup, especially at lower superficial gas velocities for the single-orifice aeration. Nonetheless, this shortage can be overcome saliently by the E–L method. These verified simulations enable further possible iterative investigation between the GL-EMMS model and the CFD work, and also inspire some meaningful simulating strategy for bubble columns.

Setting network tariffs with heterogeneous firms: The case of natural gas distribution

The appropriate treatment of firm heterogeneity plays a crucial role in the application of benchmarking analyses for regulatory purposes. Within the realm of two-step approaches, this paper challenges the widespread adoption of single-variable clustering: heterogeneity has often multiple sources, which calls for more sophisticated clustering methodologies. In fact, reliable cluster-specific rankings provide firms’ management with more realistic objectives as well as freedom to identify the appropriate strategies to improve efficiency. In order to provide regulatory guidance on this issue, we use a unique dataset of detailed accounting data and unbundled network-related costs for a panel of Italian gas distributors and we test two alternative methods: a hybrid clustering procedure (HCP) and a latent class model (LCM). Our results show that HCP and LCM perform better than size segmentation in the identification of classes, thereby leading to more reliable production frontiers, but do not support a conclusive preference for one or the other method. While both methods are sensitive to outliers, LCMs seem to provide deeper insights on the drivers of firm inefficiency. However, they also present stationarity and convergence issues, which might favour the implementation of HCP methods. Furthermore, the degree of discretionary judgement in the modelling decisions (e.g., model specification and choice of the partition) is slightly higher with LCMs than with HCP. In this respect, the HCP, with its lower modelling and analytical complexity, may feature as a more appealing option, facilitating the interactions between regulator and firm managers.

A Review on Forecasting Models of Natural Gas

This work gives away a survey of different published papers related to forecasting techniques in natural gas demand and consumption. Demand forecasting plays an important role in the company's decision making and inventory management process. It is important for local natural gas distributors to accurately predict the natural gas needs of their customers. While classifying the recent natural gas demand forecasting techniques, we have taken into account their methodologies, approach, data size, performance, results and limitations. Aim of this survey paper is to present a classified study of liquefied petroleum gas and natural gas related assets forecasting algorithms. This study provides readers with an understanding of the recent research in the natural gas supply-demand forecasting techniques.

Foam fractionation for effective removal of Pseudomonas aeruginosa from water body: Strengthening foam drainage by artificially inducing foam evolution

Lack of microbial contamination is of great significance to drinking water safety and water reclamation. In this work, foam fractionation was employed to remove Pseudomonas aeruginosa (P. aeruginosa) from aqueous solution and dodecyl dimethyl betaine (BS12) was used as the collector. Since the attachment of strain cells on the bubble surface would impede the reflux of interstitial liquid in the plateau borders (PBs), a novel strategy in strengthening foam drainage was developed through artificially inducing foam evolution. Two gas distributors with different pore diameters had been mounted at the bottom of the column for regulating the radial distribution of bubble size in the foam phase. Experimental results indicated that gas diffuse and bubble coarsening could be significantly promoted by increasing the size difference among the adjacent bubbles. Bubble coalescence contributed to broadening the width of plateau borders, thereby avoiding the borders blockage by strain cells. During bubble coalescence, surfactant molecules would be partially shifted from the surface of small bubble towards that of large bubble due to the molecule density difference. The increase in surface excess of surfactant molecules on gas-liquid interface was conducive to improving foam stability. Under the suitable conditions of air flow rates of gas distributor with 0.125 mm of pore diameter 75 mL/min and gas distributor with 0.425 mm of pore diameter 125 mL/min, BS12 concentration 0.1 g/L, and P. aeruginosa concentration 2.0 × 104 CFU/mL, the removal percentage and enrichment ratio of P. aeruginosa were 99.6% and 10.6, respectively. This work is expected to provide some new light for strengthening foam drainage in the presence of solid particles and to facilitate the industrialization of foam fractionation in water treatment.

Secondary reactions suppression during fuel fast pyrolysis in an infrared heating apparatus for the fixed bed pyrolysis process with internals

To probe the primary reaction characteristics in coal pyrolysis, the suppression of secondary reactions was systematically examined and optimized by pyrolyzing a kind of compressed thin-layer coal sample in an infrared (IR) heating device with the high heating rate. The effect of pyrolysis temperature, thin-layer thickness, and reactor structure on product distribution and component was comprehensively examined. In the tested experimental temperature range from 600 to 1000 °C, by reducing the thin-layer thickness to 1.5 mm, the yields of fuel gas and tar increased synchronously, and the volume yields of H2 and CO were improved obviously. By comparing with the pyrolysis of a single thin-layer coal sample and the samples of one piece of coal and one piece of char together, one can see that there were serious interactions between char and volatile, leading to the decrease of tar yield and the increase of its fractions with the high boiling temperature. On this basis, by removing the gas distributor in the adopted pyrolyzer, the tar yield was raised further, reaching the 1.56 times of G–K assay. And its components became much light due to the less pitch generation. Moreover, the tested gas components, such as H2, CO, CH4, and CO2, were greatly promoted. Finally, the results demonstrated the availability of thin-layer coal pyrolysis method and the optimized reactor restructure in the suppression of secondary reactions.

CFD Modelling of a Hydrogen/Air PEM Fuel Cell with a Serpentine Gas Distributor

Hydrogen-fueled fuel cells are considered one of the key strategies to tackle the achievement of fully-sustainable mobility. The transportation sector is paying significant attention to the development and industrialization of proton exchange membrane fuel cells (PEMFC) to be introduced alongside batteries, reaching the goal of complete de-carbonization. In this paper a multi-phase, multi-component, and non-isothermal 3D-CFD model is presented to simulate the fluid, heat, and charge transport processes developing inside a hydrogen/air PEMFC with a serpentine-type gas distributor. Model results are compared against experimental data in terms of polarization and power density curves, including an improved formulation of exchange current density at the cathode catalyst layer, improving the simulation results’ accuracy in the activation-dominated region. Then, 3D-CFD fields of reactants’ delivery to the active electrochemical surface, reaction rates, temperature distributions, and liquid water formation are analyzed, and critical aspects of the current design are commented, i.e., the inhomogeneous use of the active surface for reactions, limiting the produced current and inducing gradients in thermal and reaction rate distribution. The study shows how a complete multi-dimensional framework for physical and chemical processes of PEMFC can be used to understand limiting processes and to guide future development.

Investigation of Bubble Behavior in Gas‐Solid Fluidized Beds with Different Gas Distributors

AbstractThe behavior of gas bubbles in a gas‐solid fluidized bed was investigated by computational fluid dynamics simulation. A two‐phase flow model incorporating the kinetic theory of granular flow was used to study the effect of gas distributor design on the size distribution and the rise velocity of gas bubbles in the bed column. The experiments were conducted on four gas distributors with different orifice sizes and pitches. The geometry of the gas distributor had a significant influence on the bubble behavior in the gas‐solid fluidized bed. The effects of static bed height and superficial gas velocity were also considered. Bubble diameter and bubble rise velocity increased with gas velocity. However, at low bed height, the deviation in bubble size was indistinct because at higher gas velocity the rising tendency of the bubble formed just above the gas distributor increased and the probability of bubble coalescence decreased.

Improvement of nisin production by using the integration strategy of co-cultivation fermentation, foam fractionation and pervaporation

In this work, an integrated strategy of fermentation and separation was developed to improve nisin production. During fermentation, the acidification of fermentation liquid would hinder the synthesis and maturation of nisin inside strain cells. First, Saccharomyces cerevisiae (S. cerevisiae) was co-cultivated with Lactococcus lactis subsp. lactis (L. lactis) to overcome above obstacle. Experimental results indicated that lactose could be used as the substrate carbon source of co-cultivation fermentation. When inoculation ratio of L. lactis and S. cerevisiae was 102:1, nisin titer and ethanol concentration in the fermentation liquid were 3436.3 ± 171.8 IU/mL and 5.9 ± 0.2 mg/mL, respectively. Subsequently, glucose (500 g/L) was supplied into the culture at 24 h for further increasing nisin yield through the quorum sensing of microorganisms. Foam fractionation was used to recover nisin from fermentation liquid. Under the conditions of volumetric air flow rate 40 mL/min, pore diameter of gas distributor 180 μm and initial coupling time of fermentation and foam fractionation after sugar supplementation 9 h, enrichment ratio and recovery percentage of nisin reached 5.8 ± 0.2 and 63.1 ± 2.8%, respectively. Through integrating pervaporation after sugar supplementation for 9 h, permeate concentration and recovery percentage of bioethanol were 367.2 ± 16.5 mg/mL and 76.2 ± 3.4%, respectively. The total nisin titer was 4593.2 ± 206.6 IU/mL.

Gas Supply Reliability Analysis of a Natural Gas Pipeline System Considering the Effects of Demand Side Management

Abstract At present, China has a developing natural gas market, and ensuring the security of gas supply is an issue of high concern. Gas supply reliability, the natural gas pipeline system's ability to satisfy the market demand, is determined by both supply side and demand side and is usually adopted by the researches to measure the security of gas supply. In the previous study, the demand side is usually simplified by using load duration curve (LDC) to describe the demand, which neglects the effect of demand side management. The simplification leads to the inaccurate and unreasonable assessment of the gas supply reliability, especially in high-demand situation. To overcome this deficiency and achieve a more reasonable result of gas supply reliability, this paper extends the previous study on demand side by proposing a novel method of management on natural gas demand side, and the effects of demand side management on gas supply reliability is analyzed. The management includes natural gas prediction models for different types of users, the user classification rule, and the demand adjustment model based on user classification. First, an autoregressive integrated moving average (ARIMA) model and a support vector machine (SVM) model are applied to predict the natural gas demand for different types of users, such as urban gas distributor (including residential customer, commercial customer, small industrial customer), power plant, large industrial customer, and compressed natural gas (CNG) station. Then, the user classification rule is built based on users' attribute and impact of supplied gas's interruption or reduction. Natural gas users are classified into four levels. (1) demand fully satisfied, (2) demand slightly reduced, (3) demand reduced, and (4) demand interrupted. The user classification rule also provides the demand reduction range of different users. Moreover, the optimization model of demand adjustment is built, and the objective of the model is to maximize the amount of gas supplied to each user based on the classification rule. The constraints of the model are determined by the classification rule, including the demand reduction range of different users. Finally, the improved method of gas supply reliability assessment is developed and is applied to the case study of our previous study derived from a realistic natural gas pipeline system operated by PetroChina to analyze the effects of demand side management on natural gas pipeline system's gas supply reliability.

CFD-PBM simulation of hydrodynamics of microbubble column with shear-thinning fluid

Abstract A numerical simulation was performed to study the hydrodynamics of micro-bubble swarm in bubble column with polyacrylamide (PAM) aqueous solution by using computational fluid dynamics coupled with population balance models (CFD-PBM). By considering rheological characteristics of fluid, this approach was able to accurately predict the features of bubble swarm, and validated by comparing with the experimental results. The gas holdup, turbulent kinetic energy and liquid velocity of bubble column have been elucidated by considering the influences of superficial gas velocity and gas distributor size respectively. The results show that with the rise of the superficial gas velocity, the gas holdup and its peak width increase significantly. Especially, the curve peak corresponding to high gas velocity tends to drift obviously toward the right side. Except for the occurrence of a smooth holdup peak at the column center under the condition of the moderate distributor size, the gas holdups for the small and large distributor sizes become flat in the radial direction respectively. The distribution of turbulent kinetic energy presents an increasingly asymmetrical feature in the radial direction and also its variation amplitude enhances obviously with the rise of gas velocity. The increase in gas distributor size can enhance markedly turbulent kinetic energy as well as its overall influenced width. At the low and moderate superficial gas velocity, the curves of the liquid velocity in radial direction present the Gaussian distributions, whereas the perfect distribution always is broken in the symmetry for high gas velocity. Both liquid velocities around the bubble column center and the ones near both column walls go up consistently with the gas distributor size, especially near the walls at the large distributor size condition.

MP-PIC simulation of the effects of spent catalyst distribution and horizontal baffle in an industrial FCC regenerator. Part I: Effects on hydrodynamics

Improving distribution uniformity of spent catalyst and adding horizontal baffles are two effective measures to improve the regeneration performance of a fluid catalytic cracking (FCC) unit. In this study, an industrial coaxial compact FCC regenerator is simulated using a Eulerian- Lagrangian multi-phase particle in cell (MP-PIC) method. By using the energy-minimization multi-scale (EMMS) drag model based on turbulent flow regime, the MP-PIC simulation predicts the typical solids fraction profile which is in good agreement with industrial data. The Crosser grid (a typical horizontal baffle) is successfully constructed with the help of “virtual baffles” in simulation. The simulation results show that, after adding Crosser grid (a new horizontal fluidized bed baffle by our group), the bed height increases slightly, the lateral mal-distribution index of solids decreases and the descending flux of spent catalysts decreases significantly. The distribution uniformity of spent catalyst distribution along the bed cross section is more uniform when spent catalyst particles are distributed more uniformly. The presence of gas cushion beneath the Crosser grid allows it to act as a pseudo gas distributor, eliminating gas channeling and decreasing zones of low fluidization quality. The rising bubbles are absorbed by the gas cushion and new small bubbles are generated above the Crosser grid, thereby strengthening the gas–solid contact. The guiding vanes of Crosser grid accelerate the lateral movement of particles. The Crosser grid also proves its stronger suppression on the axial back-mixing of solids.

Development of a Simple Correlation between the Mal Distribution Factor and Geometrical Parameters of the Two-Direction Vapor Horn Gas Distributor

Development of a Simple Correlation between the Mal Distribution Factor and Geometrical Parameters of the Two-Direction Vapor Horn Gas Distributor

Foam fractionation for the separation of SDBS from its aqueous solution: Process optimization and property test

Foam fractionation is an adsorption bubble separation technique allowing recovery and immediate reuse of surfactants. This work was aimed at investigating the variations in recovery efficiency and physicochemical property of sodium dodecyl benzene sulfonate (SDBS) through multiple foam fractionation operation. First, a suitable SDBS concentration of 0.05 g/L was determined for preparing feeding solution. Subsequently, effects of volumetric air flow rate, height ratio of liquid phase and foam phase, and pore diameter of gas distributor on recovery efficiency of SDBS were investigated, respectively. Response surface methodology (RSM) was used to optimize the operating conditions of foam fractionation for separating SDBS. Under the conditions of volumetric air flow rate 80 mL/min, height ratio of liquid phase and foam phase 1:2, and pore diameter of gas distributor 0.180 mm, enrichment ratio and recovery percentage of SDBS were 134.83 ± 6.74 and 63.43 ± 3.17%, respectively. In repetitive separation experiments, the maximum separation number of recovered SDBS by foam fractionation was 3. Experimental results of surface activity and foam properties of recovered SDBS solution suggested that the interfacial adsorption and desorption processes had induced the structural transition and irreversible aggregation of SDBS molecules after multiple foam fractionation operation.

CFD-PBM investigation of the hydrodynamics in a slurry bubble column reactor with a circular gas distributor and heat exchanger tube

In this work, the effects of a circular gas distributor with the opening downward and a circular heat exchanger tube on the hydrodynamics of a pilot-scale slurry bubble column reactor were investigated by employing the CFD-PBM modeling. The simulations indicated that the circular structure of heat exchanger tube leads to a significant gas phase dispersion, inducing a stronger circulation flow of slurry. Different from the traditional perforated plates, the gas holdup profile with the circular gas distributor shows a bimodal structure in the radial direction. Moreover, the circular heat exchanger tube intensifies the bimodal distribution, resulting in a higher gas holdup in the reactor. Increasing the superficial gas velocity was beneficial in improving the whole time-averaged gas holdup. While the increase of the initial loading height of slurry has insignificant effect on the momentum transfer. In addition, proper axial height of the gas distributor is beneficial to enhance gas holdup.