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Table of Content
25 February 2024, Volume 75 Issue 2
    Reviews and monographs
    Progress in preparation and CO2 adsorption properties of solid waste-based sulfur-doped porous carbon materials
    Baofeng WANG, Shugao WANG, Fangqin CHENG
    2024, 75(2):  395-411.  doi:10.11949/0438-1157.20230900
    Abstract ( 230 )   HTML ( 33)   PDF (3196KB) ( 444 )  
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    Carbon-containing solid wastes have a wide range of sources as well as large output, which seriously restricts the sustainable development of the environment. Therefore, the resource utilization of carbon-containing solid waste is of great significance. The preparation of porous carbon from carbon-containing solid wastes is one of the most important ways to utilize them cleanly and efficiently. Sulfur atom doping of porous carbon can not only improve the hydrophilicity of the material surface, but also changes the chemical heterogeneity, and then generates active sites favorable for CO2 capture, strengthens the adsorption performance of CO2 molecules by the material, thus increases the adsorption capacity of CO2. This paper briefly describes the preparation method of solid waste-based sulfur-doped porous carbon materials, summarizes the latest research progress of sulfur-doped porous carbon materials for CO2 adsorption, and looks forward to the future development trend of sulfur-doped porous carbon materials and their industrialized application in the field of CO2 adsorption.

    Research progress of two-dimensional MXene materials in solar cells and metal-ion batteries
    Yu CAO, Guohui ZHANG, Ang GAO, Xinyu DU, Jing ZHOU, Yongmao CAI, Xuan YU, Xiaoming YU
    2024, 75(2):  412-428.  doi:10.11949/0438-1157.20231082
    Abstract ( 168 )   HTML ( 24)   PDF (6831KB) ( 167 )  
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    MXene is a new two-dimensional material with the characteristics of high conductivity, rich surface functional groups, adjustable layer spacing and energy band structure, and thus has important research value in new energy devices. This review discusses the progress of MXene applications in solar cells and metal-ion batteries. In solar cells, based on the high electrical conductivity, high transparency, and flexible tunability of the work function of MXene, the progress in its application in electrodes and carrier transport layers is discussed, along with a summary of strategies for adjusting the work function of MXene. In metal-ion batteries, based on Mxene's unique two-dimensional layered structure, excellent mechanical properties, and good electrical conductivity, the enhancement of electrochemical performance through MXene as an anode material as well as its composite with carbon nanomaterials, metal oxides, and silicon is discussed. The application of MXene in cathode materials, current collectors, and separators is also introduced. Finally, the future development of MXene is envisioned.

    Thermodynamics
    Prediction of self-diffusion coefficients of ionic liquids using back-propagation neural networks
    Yongjun XIAO, Zhaochong SHI, Ren WAN, Fan SONG, Changjun PENG, Honglai LIU
    2024, 75(2):  429-438.  doi:10.11949/0438-1157.20230955
    Abstract ( 106 )   HTML ( 11)   PDF (1511KB) ( 88 )  
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    Using the charge density distribution fragment area (Sσ ) and hole volume (VCOSMO) obtained by the fragment activity coefficient conductor-like shielding model (COSMO-SAC) as structural descriptors, we developed a quantitative structure-property relationship (QSPR) model, namely the BP-ANN model, to predict cation and anion self-diffusion coefficients of ionic liquids. The range of applicability and predictive capability of the BP-ANN model were also examined and compared with another QSPR model established by linear regression (Model I). The results revealed that the BP-ANN model can be applied to a broader range of ionic liquid species compared with Model I. The BP-ANN model achieves a high coefficient of determination (R2) value exceeding 0.99 in the training, validation, and testing dataset for cations, and surpassing 0.98 for anions across all sub-datasets. For the total dataset, the BP-ANN model yields low average absolute relative deviations (AARD) of 2.8% for cations and 3.7% for anions between calculated and experimental values, while the corresponding values for Model I are 14.54% and 14.57%, respectively. Therefore, the prediction performance of the BP-ANN model is significantly better than that of the model based on linear regression.

    Study on the critical properties calculation models of CO2-based binary mixture working fluid
    Rui SUN, Hua TIAN, Zirui WU, Xiaocun SUN, Gequn SHU
    2024, 75(2):  439-449.  doi:10.11949/0438-1157.20231295
    Abstract ( 112 )   HTML ( 10)   PDF (1744KB) ( 60 )  
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    Carbon dioxide (CO2) mixed working fluid is a power cycle working fluid with application potential. Critical parameters are the key basic thermophysical properties of CO2 mixed working fluid, and its accurate calculation and prediction are of great significance. Four types of calculation models were used to calculate the critical temperature and critical pressure of three types of binary mixture working fluids, namely CO2+HFC, CO2+HFO and CO2+HC, and compared with the published experimental measured data and REFPROP database. The applicability of calculation models to each type of CO2-based binary mixture is analyzed and discussed. The results show that Li method has a simple form, and the calculation formula of mixture's critical temperature is only related to the critical temperature and critical volume of the pure substances, which can be used to quickly calculate critical temperature of CO2+HFC and CO2+HFO. For the CO2+HC, the RK method showed the lowest deviations when predicting the critical pressure. Due to the completeness on experimental data points and sets of critical properties, the correlation can be directly obtained through RK method for application.

    Study on adaptability of molecular dynamics in predicting density and viscosity of natural gas
    Fan WU, Xudong PENG, Jinbo JIANG, Xiangkai MENG, Yangyang LIANG
    2024, 75(2):  450-462.  doi:10.11949/0438-1157.20231028
    Abstract ( 85 )   HTML ( 12)   PDF (4673KB) ( 63 )  
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    Natural gas is a kind of relatively clean and low-carbon energy, the proportion of primary energy consumption in China continues to increase, and its accurate physical property prediction plays an important role in the process of natural gas gathering, transportation and utilization. By collecting the measured data of natural gas properties at different temperature and pressure in literature, we compared and analyzed the prediction accuracy of molecular dynamics simulations and commonly used empirical models to calculate the density and viscosity of natural gas, and clarified the best physical property prediction models suitable for natural gas with different compositions. The results show that molecular dynamics simulation has strong applicability in predicting the viscosity of natural gas, especially at high temperature and pressure, when the temperature is 444.4 K, the average absolute error is less than 5%. For natural gas density, it is more suitable to use the relatively mature empirical model, while several force field models using molecular dynamics simulation methods are not accurate in predicting it. In addition, the accuracy of the prediction model of natural gas density and viscosity is not only affected by the temperature and pressure range, but also by the composition of natural gas.

    Prediction of vapor-liquid equilibrium data of uranium hexafluoride and fluoride and simulation of distillation process
    Tong YANG, Huan WANG, Chun DENG
    2024, 75(2):  463-474.  doi:10.11949/0438-1157.20230960
    Abstract ( 94 )   HTML ( 4)   PDF (2003KB) ( 81 )  
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    The purification of uranium hexafluoride by distillation technology is an important part of the uranium conversion process. The simulation of the distillation process can provide key support for process design and operation optimization. However, due to the lack of vapor-liquid equilibrium and physical properties data for uranium hexafluoride and fluoride, modelling and simulating the purification process of uranium hexafluoride became challenging. To address this issue, we utilized COSMOtherm and Turbomole software to predict vapor-liquid equilibrium data for UF6-TiF4 binary systems. We indirectly verified the accuracy of the COSMO-RS model by predicting known experimental data on vapor-liquid equilibrium for WF6-UF6 binary system. Additionally, Aspen Plus software's property constant estimation system was employed to estimate missing physical properties such as infinitely dilute aqueous Gibbs generating energy. The UF6 saturated vapor pressure experimental data and simulated values in the literature were compared, and the relative error was within 1.76%. Based on experimental data and predicted vapor-liquid phase equilibrium data in the literature, Aspen Plus software was used to regress the binary interaction parameters of the NRTL model. For separating uranium hexafluoride from fluoride, two purification schemes were designed: one involving direct separation sequence and another involving indirect separation sequence. Sensitivity analysis was conducted to optimize key parameters including plate number, feed position, and reflux ratio to minimize total annual cost (TAC) while maintaining desired purity levels in UF6 product output streams. The results indicated that TAC was lower for the indirect separation sequence purification scheme.

    Evaluation and predictive study of the mixing rules for vapor-liquid equilibrium of R1234yf mixtures
    Lin WANG, Rongding JIANG, Chunxiao ZHANG, Xiuzhen LI, Yingying TAN
    2024, 75(2):  475-483.  doi:10.11949/0438-1157.20231129
    Abstract ( 65 )   HTML ( 6)   PDF (880KB) ( 38 )  
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    The mixed refrigerant containing R1234yf has the characteristics of excellent system performance and environmental friendliness, and has received widespread attention in the current iteration of refrigerants. The vapor-liquid equilibrium is the most basic thermodynamic property for the mixtures, and its theoretical calculation is of vital importance. To enhance the accuracy of vapor-liquid equilibrium data for the R1234yf mixtures, the Peng-Robinson (PR) equation of state coupling with three mixing rules (vdW, WS, and MHV1), and the NRTL activity coefficient model are selected to evaluate the experimental properties of vapor-liquid equilibrium for 16 R1234yf binary systems. The results show that the calculation performance of WS mixing rules and MHV1 mixing rules is better than that of vdW mixing rules. The vdW mixing rule provides superior computational performance for the majority of mixtures. Finally, a predictive model is proposed to forecast the vapor-liquid equilibrium properties of R1234yf-based mixtures. The predicted AARD of pressure is 0.49% and the AAD of mole fraction of gas phase is 0.0031. These predictive deviations satisfy engineering applications.

    Fluid dynamics and transport phenomena
    Analysis of multi-scale fractal characteristics of severe slugging based on Hurst exponent
    Nailiang LI, Changsong LIU, Xueping DU, Yifan ZHANG, Dongtai HAN
    2024, 75(2):  484-492.  doi:10.11949/0438-1157.20231089
    Abstract ( 52 )   HTML ( 4)   PDF (1886KB) ( 40 )  
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    Based on the multi-scale method and Hurst analysis, the multi-scale structure and nonlinear characteristics of severe slugging flow were studied in the present work. Experimental investigation on severe slugging were performed in pipeline-riser system using air and water and the signal of pressure difference was recorded. Based on db4 wavelet, the signal of pressure difference was decomposed and reconstructed at 1—8 scales. The dynamics characteristics of gas-liquid two-phase flow at each individual scale were extracted. It was found that the transient process of gas blowout and liquid fallback in severe slug flow was mainly reflected in the detail signals at d5—d8 scales. The result of Hurst exponent analysis on the decomposed signals of pressure difference fluctuation shows that severe slug flow has significant bi-fractal characteristics, which are constrained by two dynamic factors, i.e. positive persistence and anti-persistence. However, the approximate component and the detail component exhibit completely opposite fractal structures. The approximate component has positive persistence, while the detail component has anti persistence. The detail component at scale d1 describes the interaction between micro-scale bubbles. The meso-scale interaction between liquid phase and gas bubbles was reflected by the detail components at the d2—d5 scales. The macro-scale interaction between gas-liquid phase and the pipe wall was described by the detail components at the d6—d8 scales. The energy of the pressure difference fluctuation signal is mainly distributed at the macro-scale.

    Gas-liquid two-phase flow regimes and transformation mechanism in horizontal tube under fluctuating vibration
    Qichao LIU, Shibo ZHANG, Yunlong ZHOU, Yuqing LI, Cong CHEN, Yiwen RAN
    2024, 75(2):  493-504.  doi:10.11949/0438-1157.20231294
    Abstract ( 56 )   HTML ( 7)   PDF (1665KB) ( 32 )  
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    The accurate determination of gas-liquid two-phase flow patterns under fluctuating vibration is of great significance for the design of floating nuclear power plants. Experimental research was conducted on the characteristics of gas-liquid two-phase flow pattern in horizontal tube under fluctuating vibration. New flow patterns were defined and the distribution law of gas-liquid phase was obtained. The influence of pipe diameter, vibration frequency and amplitude on the transition boundary of the flow patterns was revealed. Finally, the transition relationships between bubbly flow and intermittent flow as well as that between intermittent or stratified flow and annular flow were established. The results show that there are four flow regimes, namely bubble flow, intermittent flow, stratified flow and annular flow. It is interesting that the intermittent flow has two types, which are bubble slug intermittent flow and slug plug intermittent flow. Besides, the distribution of gas-liquid two-phase shows a regular change with the change of vibration position. With the same gas superficial velocity, the boundary between bubble flow and intermittent flow moves upwards with the increase of pipe diameter, vibration frequency and amplitude, meanwhile the boundary between intermittent flow and stratified flow move downwards. Under the condition that the liquid phase conversion velocity is constant, increases in pipe diameter, vibration frequency, and amplitude will cause the intermittent flow/stratified flow-annular flow boundary to move to the right. Taking into account the influence of vibration, the transition boundary of intermittent flow to bubbly flow and annular flow were established suitable for low frequency and high amplitude fluctuating vibration. The mean absolute relative errors of prediction and experimental results are 7.62% and 12.68%, respectively.

    CFD numerical simulation of wet flue gas desulfurization:performance improvement based on gas-liquid mass transfer enhancement
    Wenjun LI, Zhongyang ZHAO, Zhen NI, Can ZHOU, Chenghang ZHENG, Xiang GAO
    2024, 75(2):  505-519.  doi:10.11949/0438-1157.20231100
    Abstract ( 94 )   HTML ( 17)   PDF (2181KB) ( 73 )  
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    In view of the desulfurization problem of flue gas containing high SO2 concentration resulting from burning high sulfur coal in flue gas desulfurization process of coal-fired power plants, the research on the high-efficient SO2 removal based onlimestone was carried out by computational fluid dynamics (CFD), and the enhancement method for SO2 removal by installing sieve plate and optimizing the spray system in the absorption tower simultaneously was proposed. A coupled model of SO2 multiform absorption including spray absorption and bubbling absorption was established at the scale of macro scale. Based on the model, the variation laws of pH and SO2 absorption rate during slurry droplets falling were obtained, and the gas-liquid flow, mass transfer and chemical reaction processes in the absorption tower are analyzed. The strengthening mechanism of sieve plate on the desulfurization efficiency is explored, and the optimization for the arrangement of sieve plate and spray system is carried out further. It was found that by optimizing the sieve plate components and the spray system in the tower, the SO2 removal efficiency of the desulfurization tower can be increased by 3%—8% under different working conditions.

    Experimental study of gas-liquid flow visualization in gradient porous transport layers based on hydrogen production by water electrolysis
    Zhipeng LIU, Changying ZHAO, Rui WU, Zhihao ZHANG
    2024, 75(2):  520-530.  doi:10.11949/0438-1157.20231165
    Abstract ( 113 )   HTML ( 21)   PDF (3473KB) ( 611 )  
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    During the process of electrolyzing water to produce hydrogen, the pores in the porous electrode will be blocked by bubbles, which will hinder gas diffusion and the flow of electrolyte in the porous electrode, resulting in an increase in the mass transfer resistance of the electrode. This in turn affects the rate and energy consumption of hydrogen production through electrolysis of water. Three regular shaped diffusion layers of nickel-iron alloy electrodes, LSL-PTL, MMM-PTL and SLS-PTL, were fabricated by 3D metal printing and visualized for water electrolysis experiments. In the experiments, the changes of gas-liquid two-phase flow in the gradient porous transport layer at different current densities were quantitatively recorded, including parameters such as bubble morphology, pore gas content and bubble detachment rate. The effects of the gradient of the diffusion layer on the gas-liquid mass transfer process were investigated, and the effects of different electrode gradient structures on the impedance and overpotential during electrolysis were analyzed. The experimental results show that compared with the two gradient structures of SLS-PTL and MMM-PTL, the gradient structure of LSL-PTL, i.e., gradually increasing the pore size from the catalytic layer, always maintains a lower volumetric gas content. It can accelerate the migration of gas bubbles in the diffusion layer, make the gas-liquid exchange more frequent, and effectively reduce the gas-liquid mass transfer resistance. Moreover, a lower mass transfer impedance and electrolytic overpotential can be obtained by using the diffusion layer with this gradient, and the relationship of electrolytic potentials of the three gradient electrodes at the same current density is ELSL<EMMM<ESLS. Therefore, a diffusion layer with LSL-PTL gradient in water electrolysis can improve the hydrogen production efficiency and reduce the energy loss. This study provides an intuitive basis for the active control of the gas-liquid mass transfer process in water electrolysis for hydrogen production and the structural design of the porous transport layer in the electrolytic cell, which will have a positive impact on the further development of electrolytic water hydrogen production technology.

    Research on power consumption characteristics of high viscosity fluid mixing in acoustic resonance mixer
    Xiaobin ZHAN, Huibin WANG, Yalong JIANG, Tielin SHI
    2024, 75(2):  531-542.  doi:10.11949/0438-1157.20231168
    Abstract ( 71 )   HTML ( 4)   PDF (2384KB) ( 46 )  
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    Acoustic resonance hybrid uses mechanical resonance to generate high-acceleration vibrations to promote fluid flow. Its power consumption characteristics play an important role in its design and application. In order to study the power consumption characteristics of the acoustic resonance mixer, a simulation model of the acoustic resonance mixing process was established based on CFD. The force and work power of the wall on the material during the acoustic resonance mixing process of high viscosity fluid were analyzed. The effects of changes in viscosity and vibration parameters on the mixing were explored. The influence of the power consumption characteristics of the acoustic resonance mixer is determined, and the prediction function of the mixing power of the acoustic resonance mixer is established. The research results show that during the mixing process, the instantaneous power of the wall surface working on the liquid phase shows a trend of first decreasing and then stabilizing fluctuations, while the effective power shows a trend of first increasing and then stabilizing fluctuations. This different change trend is caused by the change of the phase difference between the two. The research results show that during the mixing process, the instantaneous power of the wall surface working on the liquid phase shows a trend of first decreasing and then stabilizing fluctuations, while the effective power shows a trend of first increasing and then stabilizing fluctuations. This different changing trend is due to changes in the phase difference. Increasing the amplitude, frequency or low-frequency large amplitude under equal acceleration can increase the instantaneous power and effective power, and reduce the external energy absorbed by the liquid phase to enter the stable flow stage.

    Study on adaptability of scaling law to residence time distribution in bubbling fluidized beds with continuous operation
    Nan TU, Xiaoqun LIU, Chiyu WANG, Jiabin FANG
    2024, 75(2):  543-552.  doi:10.11949/0438-1157.20231195
    Abstract ( 62 )   HTML ( 6)   PDF (2065KB) ( 259 )  
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    Particles residence time distribution (RTD) in bubbling fluidized beds is important for its performances, and the evaluation of particles RTD in large-scale bubbling fluidized beds is a critical issue. In this study, a diffusion criteria number was introduced based on the scaling law proposed by Glicksman. Then the fluidized bed similarity scaling law that exhibits RTD similarity was obtained, and the transformation relations for the similarity of particles RTD was clarified. The flow behaviors and particles RTD of the scaled-down and original fluidized beds were numerically simulated. The results show that within the specific range of geometric similarity constants (1 < k < 200), the computational time for the scaled-down model could be reduced from 22.8 days to 1.4 days. Moreover, the particles RTD exhibits similarity to that of the original bed, with a maximum error not exceeding 9.24%. Following the similarity transformation, the particles RTD of the scaled-down model demonstrates a favorable ability to predict the particles RTD of the original bed, with a maximum error for key characteristic values of 17.8%. Furthermore, variations in particle flow rate, fluidization velocity, and static bed height do not influence the accuracy of scaled-down model in predicting the particles RTD of the original bed. The maximum error of its key characteristic values does not exceed 10.32%. This confirms the applicability of the similarity scaling law under varying operating conditions. All the results demonstrate the effective of presented similarity scaling law for the rapid and accurate prediction of particles RTD in large-scale fluidized beds.

    Model development for simulating bubble breakup in gas-liquid bubbly flows with the Eulerian-Lagrangian approach
    Dong HAN, Ningning GAO, Xinde TANG, Shenggao GONG, Liangshu XIA
    2024, 75(2):  553-565.  doi:10.11949/0438-1157.20231145
    Abstract ( 108 )   HTML ( 10)   PDF (2118KB) ( 84 )  
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    The Eulerian-Lagrangian method has been widely used to simulate the flow pattern, bubble size (or gas holdup) and its distribution in gas-liquid reactors. However, this method reported in literature is mainly based on the critical Weber number viewpoint to describe the bubble breaking behavior, and the size of the broken sub-bubbles is determined by random numbers. The existing experimental and theoretical studies have shown that the viewpoint of critical Weber number cannot reflect the influence of physical parameters (e.g. gas density) such as gas density and gas redistribution within the bubble on bubble breakup behavior. In view of above shortcomings, this paper proposes a new bubble breakup model suitable for the Eulerian-Lagrangian framework that considers the contribution of gas redistribution mechanism, and develops a solver based on this new model on the basis of open-source software OpenFOAM. The model predictions are in good agreement with the measured time-averaged axial liquid velocity and bubble size distributions. Particularly, the proposed model considering gas redistribution mechanism successfully predicts the bimodal distribution characteristic of bubble size distribution observed in the experiments.

    Experimental investigation of droplet formation in coaxial microchannels with different geometries of inner channel
    Shirong SONG, Hongchen LIU, Xiaotian MI, Chao XU, Mei YANG, Chaoqun YAO
    2024, 75(2):  566-574.  doi:10.11949/0438-1157.20231245
    Abstract ( 67 )   HTML ( 4)   PDF (989KB) ( 58 )  
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    The droplet generation process of the water-silicone oil system in the coaxial microchannel was studied. Under different continuous capillary number Cac and dispersed phase Weber number Wed, two different flow patterns, dripping flow and jet flow, were observed. Experiments examined the effects of two-phase flow, viscosity, and inner tube structure on droplet size and droplet generation frequency. The results showed that droplet size increased with the increase of dispersed phase flow rate and decrease of flow rate and viscosity of continuous phase. Additionally, with the increase of Wed, jetting occurrence was found to be easier in relatively larger capillary, which in turn generated larger droplets. The generation frequency of droplet increased fast firstly then slow down to a plateau with the increasing of Cac and Wed. When the hydraulic diameters of inner channel were almost same, the deviation in the generation frequency of droplet obtained from different geometries of inner channel was small at fixed Cac. And the generation frequency of droplet increased with the decrease in the hydraulic diameters of inner channel. Based on the obtained results, an empirical correlation was proposed to predict the droplet size with good prediction performance.

    Catalysis, kinetics and reactors
    Carbon supported Cs- and Cu-based catalysts for gas-phase dehydrochlorination of 1,1,2-trichloroethane
    Xingyu GAI, Yuxue YUE, Chunhua YANG, Zilong ZHANG, Tianzi CAI, Haifeng ZHANG, Bolin WANG, Xiaonian LI
    2024, 75(2):  575-583.  doi:10.11949/0438-1157.20231104
    Abstract ( 83 )   HTML ( 10)   PDF (2593KB) ( 58 )  
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    Cs/AC and Cu/AC catalysts were prepared by impregnation method and evaluated in the gas-phase dehydrochlorination reaction of 1,1,2-trichloroethane. Highly dispersed Cs species and crystalline Cu species are generated on the carbon surface during the impregnation process. Superior catalytic performance is triggered for the Cs/AC catalyst, with an 86.7% stable conversion under reaction conditions of 573 K and a gas hourly space velocity of 1000 h-1. Experimental and theoretical calculations show that the adsorption and activation 1,1,2-trichloroethane is facilitated over the CsCl species, thereby enhancing the catalytic performance. This work provides a promising strategy to explore highly efficient and economic catalysts for the synthesis of 1,1-dichloroethylene.

    Separation engineering
    Research on spray coupled cooling to enhance the removal of fine particles by cyclone separator
    Mingqing TAO, Minghao MU, Teng CHENG, Bo WANG
    2024, 75(2):  584-592.  doi:10.11949/0438-1157.20231175
    Abstract ( 51 )   HTML ( 8)   PDF (935KB) ( 33 )  
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    By coupling the spray in front of the condensing heat exchanger, atomization agglomeration and heterogeneous vapor condensation were combined to improve the removal effect of fine particles in the cyclone separator, which is used for the deep treatment of nearlysaturated wet flue gas after the wet dust collector. The particle removal characteristics were investigated through laboratory tests and flue gas bypass tests in a metal smelter. The laboratory results show that spray coupled cooling can significantly enhance the removal of particles by cyclone separators under typical conditions, and had better enhancement effect than spray or cooling alone. By increasing the spray volume and heat exchanger temperature drop, the removal efficiency of fine particles first increased and then tended to be stable, and the optimal removal effect was achieved when the temperature drops by 6℃ and the atomization volume was 0.046 L/m3. The higher the flue gas temperature was, the closer the humidity was to saturation, and the higher the fine particle removal efficiency was. The industrial flue gas bypass tests prove that the system was suitable for nearlysaturated wet flue gas after wet dust removal, and had strong adaptability to fluctuating conditions. When the particle concentration at the inlet flue gas did not exceed 2000 mg/m3, the particle concentration at the outlet can be kept below 20 mg/m3, and the average removal efficiency was above 99.2%.

    Process system engineering
    Prediction of NO x emissions for municipal solid waste incineration processes using attention modular neural network
    Xi MENG, Yan WANG, Zijian SUN, Junfei QIAO
    2024, 75(2):  593-603.  doi:10.11949/0438-1157.20231081
    Abstract ( 107 )   HTML ( 4)   PDF (2210KB) ( 167 )  
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    Real-time and accurate measurement of NO x emissions is indispensable to achieve closed-loop control of the denitrification process during municipal solid waste incineration (MSWI). To this end, this paper proposes a NO x emission prediction method for the MSWI process based on attention modular neural network (AMNN). First, it simulates the“divide and conquer”characteristics of the brain network in processing complex tasks, and uses the fuzzy C-means (FCM) clustering algorithm to divide the task to be predicted into multiple subtasks, thereby reducing the complexity of the prediction task. Second, to handle the sub-tasks efficiently, a self-organizing fuzzy neural network (SOFNN) is designed to construct the sub-models, in which a growing and pruning algorithm and an improved second-order learning algorithm work together to ensure both the learning efficiency and accuracy. Then, the attention mechanism is utilized to integrate the sub-models during the testing or application stages, which can further improve the generalization performance of this AMNN-based prediction model. Finally, the proposed prediction method is verified by Mackey-Glass time series and the real data from a MSWI plant in Beijing.

    Surface and interface engineering
    Study on critical chocked characteristics of supercritical carbon dioxide spiral groove dry gas seal under thermal-fluid coupling lubrication
    Zhi ZHU, Hengjie XU, Wei CHEN, Wenyuan MAO, Qiangguo DENG, Xuejian SUN
    2024, 75(2):  604-615.  doi:10.11949/0438-1157.20231101
    Abstract ( 51 )   HTML ( 5)   PDF (1930KB) ( 168 )  
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    Under the premise of stable operation of the seal, promoting the formation of blocked flow at the seal end face outlet to increase the air film opening force and reduce end face leakage is an effective way to optimize dry gas sealing performance. Taking supercritical carbon dioxide (CO2) spiral groove dry gas seal as the object, the finite difference method was used to solve the pressure and temperature governing equations on the basis of the effects of real gas, centrifugal inertia, turbulence and chocked flow. The critical chocked characteristics (e.g. critical chocked inlet pressure po_cir, critical chocked speed N_cir, critical chocked film thickness h0_cir and chocked critical instability film thickness hsc) under thermal-fluid coupling lubrication were qualitatively studied. The results show that there is a chocked interval at the outlet of supercritical CO2 dry gas seal in isothermal and adiabatic model. The intervals corresponding to the inlet pressure, film thickness and rotational speed are po>po_cir,h0_cir<h0<hsc and N<N_cir, respectively. The increase of the rotating speed can continuously enhance the critical chocked inlet pressure and the critical chocked film thickness. The increase of the film thickness will lead to the decrease of the critical chocked pressure and the increase of the critical chocked speed. The high-pressure inlet will make the chocked zero stiffness corresponding to the film thickness (chocked critical instability film thickness hsc) down. Compared with the isothermal flow hypothesis, the influence of gas film thermal effect on the critical chocked characteristic parameters of supercritical CO2 dry gas seal is significant, and the influence rules are different.

    Biochemical engineering and technology
    Study on the mimic enzymatic performance of amino acid modified MOF-808 for nerve agents decontamination
    Keqing LIU, Yan CUI, Qiong YU, Likun CHEN, Yongchao ZHENG, Zhiwei QIAO, He ZHENG
    2024, 75(2):  616-625.  doi:10.11949/0438-1157.20231210
    Abstract ( 101 )   HTML ( 6)   PDF (1771KB) ( 65 )  
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    A series of MOF-808-AA catalysts grafted with different amino acids were prepared by post-synthesis modification method. The effects of pore structure and pore microenvironment on the catalytic performance of nerve agent simulant were studied, and the mimic enzyme properties of MOF-808 and MOF-808-AA were further explored. The results showed that amino acid modification caused changes in the pore structure and pore microenvironment of MOF-808, thereby affecting the catalytic performance of the catalyst against the mimic agent. Among them, the hydrogen bond and hydrophobic interaction provided by the amino acid side chain improve the affinity of MOF-808-AA to the simulant. After amino acid grafting, the number of active metal sites in the original structure of MOF-808 decreased, resulting in the decrease in the degradation rate. The acidity and alkalinity of the amino acid side chain groups could lead to differences of the pore microenvironment. When the side chain is a basic group such as amino, the catalytic efficiency of the simulant decontamination is significantly improved. However, when the side chain is a carboxyl group, the catalytic efficiency is significantly reduced.

    Energy and environmental engineering
    Pyrolysis and coking behavior of typical liquid hydrocarbon fuels in hot pipe
    Haowen LI, Hao LAN, Youdan ZHENG, Yonghui SUN, Zixin YANG, Qianshi SONG, Xiaohan WANG
    2024, 75(2):  626-636.  doi:10.11949/0438-1157.20231190
    Abstract ( 59 )   HTML ( 4)   PDF (4145KB) ( 56 )  
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    The fuel molecular structure is an important factor affecting the pyrolysis coking process in the active cooling channel. Stripping the effect of turbulent diffusion on pyrolysis coking, the pyrolysis coking patterns of typical aviation kerosene components such as n-heptane (nC7H16), iso-heptane (iC7H16), methylcyclohexane (MCH), n-dodecane (nC12H26), and toluene (A1CH3) were compared in a pre-oxidized STS304 (Φ3.0 mm×0.5 mm×1.0 m, outer diameter × wall thickness × length) flow reactor tube at 600—800℃, 1.0 MPa, and under a laminar near-chemical kinetic state. The normalized molar fraction distributions of pyrolysis gas-liquid products of the five typical fuels were quantitatively obtained, and the unsteady-state coking characteristics and along-range coking distribution patterns of the fuels were compared by weighing method. The results show that the conversion of chain alkanes is higher at the lower temperature of 650℃, the conversion of MCH as well as A1CH3 is lower due to the stabilized cyclic structure, and the conversion of A1CH3 increases abruptly above 775℃. The hydrogen (H2), methane (CH4) content of iC7H16 and MCH is significantly higher due to the presence of branched methyl groups. Straight-chain alkanes have higher contents of ethylene (C2H4) and ethane (C2H6) through β-scission. Propylene (C3H6) is a by-product of C—C bond breakage. The content of C3H6 is higher at lower temperatures, while the content of C2H4 and C3H6 tends to decrease due to the secondary reaction of coking at high temperatures. The main products in the liquid phase included benzene, A1CH3, naphthalene and other diphenyl aromatic hydrocarbons. The content of polycyclic aromatic hydrocarbons (PAHs) increased at high temperatures, and tetraphenyl aromatic hydrocarbons such as perylene, phenanthrene, and anthracene were detected by GC-MS, but they accounted for a very low molar fraction of the bulk phase. The coking rates of MCH and nC12H26 were low at lower temperatures, and the coking rates of MCH and A1CH3 increased significantly at higher temperatures. Branched and long straight-chain alkanes favor high-temperature coking inhibition. Straight-chain alkane coking peaks at the beginning of the thermostatic zone, with coking by addition of unsaturated light hydrocarbons. MCH and A1CH3 coking peaks are closer downstream, with coking by deposition of aromatic polymerization. Straight-chain alkanes have the highest content of cracked C2H4 and C3H6, which is conducive to providing high heat sink. The cleavage of nC12H26 firstly produces 1-olefins such as 1-dodecene, 1-undecene, 1-decene, 1-octene, 1-hexene, 1-pentene etc., and the deep cleavage of these 1-olefins produces C2H4 and C3H6etc. Since the depth of pyrolysis of long carbon-chain nC12H26 is lower than that of the short-chain nC7H16, it exhibits the heat sink that is even lower at high temperatures. Branched-chain alkanes are more stable than straight-chain alkanes and have a weaker tendency to form carbon deposition, but the presence of methyl group makes the product alkylated to a higher degree. The coking rates of the five typical hydrocarbon fuels were closely related to the temperature, showing a three-stage unsteady-state growth pattern, with differences in the location of the peak coking along the process. The coking rate of straight-chain alkanes was larger at low temperatures, and the contribution of MCH and A1CH3 coking was significantly higher at high temperatures.

    Research on membrane electrode assembly consistency of high-power proton exchange membrane fuel cell stack
    Hong CHEN, Kun JIANG, Tingjiang TANG, Yiyuan HUANG, Bin CHI, Shijun LIAO
    2024, 75(2):  637-646.  doi:10.11949/0438-1157.20230745
    Abstract ( 88 )   HTML ( 7)   PDF (4024KB) ( 139 )  
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    With the continuous increase of the application fields and scale of fuel cells, there is a growing demand for high-power fuel cell stacks. The voltage consistency of high-power fuel cell stacks is an important indicator to measure or affect the performance of the stack. In this paper, the single-cell voltage consistency of a 65 kW high-power stack produced by a certain company was studied, the influence of various operating conditions on stack consistency was investigated, and the possible reasons causing consistency problems were deeply analyzed and discussed. It is showed that the stack exhibited good consistency under rated power and its given operating conditions. The output power of the stack, stack operating temperature and temperature range, reactant gas stoichiometry, gas humidity, and other factors all have impact on the voltage consistency of the stack. Among them, the output power, air stoichiometry, and gas humidity dramatically influenced on cell consistency most significantly, and an increase in output power, a decrease in air stoichiometry and air humidity will greatly reduce the stack consistency. On the basis of the research results, suggestions on operating conditions for maintaining the consistency of high-power fuel cell stacks were put forward in this paper. This work is of great significance for improving the design and optimizing the operating conditions of high-power stacks, and promoting the development of fuel cell technology and industry in China.

    Mechanism study of oxytetracycline hydrochloride degradation through activating sulfite by Fe2+/Mn2+
    Yanping JIA, Dongxu YIN, Jingyi XU, Haifeng ZHANG, Lanhe ZHANG
    2024, 75(2):  647-658.  doi:10.11949/0438-1157.20231088
    Abstract ( 77 )   HTML ( 6)   PDF (2092KB) ( 110 )  
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    Oxytetracycline hydrochloride is often used in the treatment of livestock and poultry diseases, however, it cannot be completely metabolized. The residual oxytetracycline hydrochloride entering water poses a threat to the health of water environment. Bivalent iron and bivalent manganese, as common transition metals, can usually activate sulfides to degrade organic pollutants. Its reaction conditions are mild and the operation is simple. However, the redox potential of single divalent iron and single divalent manganese is low, and the performance of activating sulfide is poor. In this experiment, Fe2+/Mn2+ coactivating Na2SO3 was used to degrade oxytetracycline hydrochloride in water. The effects of reagent dosage, pH, dissolved oxygen, chloride ion, carbonate ions and humic acid on the degradation of oxytetracycline hydrochloride in the Fe2+/Mn2+/Na2SO3 system were investigated. The oxidizing active substances in the Fe2+/Mn2+/Na2SO3 system were analyzed using pyrophosphate test, free radical quenching test and EPR experiment. The changes of functional groups and degradation intermediates of oxytetracycline hydrochloride were identified by UV-Vis spectroscopy, Fourier transform infrared spectroscopy and gas chromatography-mass spectrometry, and the degradation pathway of oxytetracycline hydrochloride was inferred. The results showed that when the concentration ratio of Fe2+/Mn2+/Na2SO3 was 1∶4∶20 (the concentrations were 0.1, 0.4 and 2 mmol/L, respectively),the reaction time was 45 min and the pH was 9.0, removal efficiency and mineralization rate of oxytetracycline hydrochloride were the highest, and up to 94% and 49%, respectively. When dissolved oxygen decreased from 9 mg/L to 1.89 mg/L, removal efficiency of oxytetracycline hydrochloride decreased from 94% to 17%. Chlorine ions, humic acids and carbonate ions all had inhibitory effects on the degradation of oxytetracycline hydrochloride. Mn (Ⅲ) and SO4- were main active oxidants for the degradation of oxytetracycline hydrochloride, and the degradation underwent the processes of electron transfer, ring opening and acylation.

    Numerical study on combustion zone behaviors of a slagging gasifier
    Xueyun WANG, Xiaobing YU, Wanwang PENG, Yansong SHEN
    2024, 75(2):  659-674.  doi:10.11949/0438-1157.20230681
    Abstract ( 68 )   HTML ( 6)   PDF (4157KB) ( 50 )  
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    The combustion zone is an important region in a slagging gasifier, as it determines the working state of a coal gasifier. This study applies the Eulerian-Eulerian model to study the gas-coal behaviors in this region in an industrial-scale coal gasifier. The model considers the flow, heat transfer and chemical reactions for both gas and coal phases. The model is also used to explore the formation process of the combustion zone and the distribution of velocity, temperature, and species in and around it. It is found that the combustion zone is of a plume-like shape, extending to the centre of the gasifier and then towards the top obliquely; the gas velocity is about 2.5 m/s in the central regions of the gasifier, without forming a high-speed collision zone; the high-temperature zone appears near the surface of the combustion zone, especially that facing the nozzle and near the centre of the gasifier, where the temperature can reach as high as 2000℃. Besides, it is found that oxygen is mainly distributed at about 0.5 m in front of the nozzle, while the distribution of carbon monoxide and water vapor overlap in space to a large extent; carbon dioxide is mainly generated near the outer surface of the combustion region while a higher concentration of hydrogen appears above the combustion region. Along the direction of the nozzle axis, the gas temperature first increases to a peak and then gradually decreases. With increasing gasification agent flow rate, the position where the maximum value of combustion temperature appears gradually moves to the centre of the gasifier, showing an obvious linear change pattern.

    Purification mechanism of hydrogen cyanide by corona discharge and dielectric barrier discharge
    Xin ZHANG, Yu XUE, Yixing MA, Xueqian WANG, Langlang WANG, Nifei XIE, Yi CHEN, Xiaoxia ZHOU
    2024, 75(2):  675-684.  doi:10.11949/0438-1157.20231039
    Abstract ( 51 )   HTML ( 5)   PDF (2501KB) ( 45 )  
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    Two low-temperature plasma generation methods, corona discharge and dielectric barrier discharge(DBD), are used to purify hydrogen cyanide (HCN), and the reaction mechanisms of the two are discussed. The results show that the purification efficiency of HCN is 76% when the specific input energy (SIE) is 8.3 kJ/L in corona discharge, and 94% when SIE is 11.9 kJ/L in dielectric barrier discharge. By using density functional theory (DFT) to introduce external electric field, Gaussian software is used to calculate and analyze the differences between the two different discharge modes in the HCN purification process. After the introduction of external electric field, the molecular structure and system energy of HCN molecules have changed. In corona discharge, OCN, the intermediate product of HCN conversion, is mainly converted into CO2 and N2, while in dielectric barrier discharge HCN is more easily combined with OH in the system to form H2O and —CN, and —CN will be polymerized into C3N4 under the action of high electron and particle density in DBD.

    Impact of different carbon conductive agents on performance of iron-air battery
    Yuhua YIN, Can FANG, Qingfeng YI, Guang LI
    2024, 75(2):  685-694.  doi:10.11949/0438-1157.20231212
    Abstract ( 51 )   HTML ( 4)   PDF (2316KB) ( 42 )  
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    Metal-air batteries (MABs) have the advantages of low cost, environmental friendliness, high specific power and specific energy, among which iron-air batteries (IAB) are more resource-rich and have high specific energy. Problems in IAB such as passivation, corrosion, self-discharge, hydrogen evolution reaction and volume change of iron electrodes restrict its development. Considering that acetylene black is commonly used as a conductive and supportive active material in the preparation of iron negative electrodes, to further investigate the impact of other carbon materials on the electrochemical performance of iron electrodes, we prepared different iron electrodes using acetylene black, graphite powder, and carbon nanotube. Corresponding iron-air batteries were assembled with the prepared iron electrodes and Pt/C air electrode. Charge/discharge curves at different current densities and discharge polarization curves were obtained on these batteries. The results indicate that the overall performance of the carbon nanotube modified iron negative electrode battery is excellent, exhibiting high cycle stability, high charge discharge voltage efficiency, and power density. This work provides reference value for the in-depth study of IAB by preparing stable and reliable iron electrodes.

    Influence of pollutants in seawater on performance of reverse electrodialysis stacks
    Lingjie WANG, Hailong GAO, Jipeng JIN, Zhihao WANG, Jianbo LI
    2024, 75(2):  695-705.  doi:10.11949/0438-1157.20231166
    Abstract ( 69 )   HTML ( 3)   PDF (2853KB) ( 53 )  
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    Salinity gradient energy, existing in electrolyte solutions with different concentration, can be harnessed for power production cleanly. The concentrated brine discharged from the seawater desalination device will cause a waste of salt difference energy. The reverse electrodialysis (RED) stack can effectively recover this salt difference energy and directly convert it into electrical energy. However, the performance of the RED stack using seawater and concentrated brine as the working solution is affected by insoluble substances in the working solution, which may cause performance decrease of the RED. Here, experiments were conducted on a RED stack to investigate the degradation phenomenon caused by the pollutants in concentrated brine and seawater. The experiments aimed to assess the impact on the performance of the RED stack, as well as the types of contaminants and elements in the RED stack. First, the performance of the RED stack was periodically tested to monitor changes in open-circuit voltage, maximum power density, energy conversion efficiency, internal resistance, and pressure drop. These measurements were recorded to analyze the causes of the performance degradation. Subsequently, scanning electron microscope and energy dispersive spectrometer were used to analyze the types of contaminants and elements present on the ion-exchange membranes and the spacers. Experimental results show that the open-circuit voltage, maximum power density, and energy conversion efficiency of the power reactor decrease rapidly, and there is a noticeable increase in internal resistance at the early stage of operation (0—20 d), and in the later stage of operation (20—45 d), the pressure drop increases on both the concentrated brine and seawater sides, with the concentrated brine side showing a particularly rapid growth rate. The decline in the performance of the RED stack is primarily attributed to the accumulation of pollutants on the ion exchange membrane and spacer pads. Additionally, due to their different charges, the anion exchange membrane and spacer pads exhibit different behaviors. The main reason for the decline in performance of the RED stack is the buildup of contaminants on the ion exchange membrane and spacer. The types of contaminants on the anion exchange membrane and cation exchange membrane differ because of their distinct charges. This study provides theoretical support for cleaning strategy of the RED stack.

    Material science and engineering, nanotechnology
    Investigation of the thermal storage mechanism of porous TiO2 enhanced phase change materials
    Changhui LIU, Tong XIAO, Qingyi LIU, Long GENG, Jiateng ZHAO
    2024, 75(2):  706-714.  doi:10.11949/0438-1157.20230728
    Abstract ( 70 )   HTML ( 10)   PDF (2386KB) ( 154 )  
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    The application of phase change materials in thermal energy storage technology is often limited by unstable shape and low thermal conductivity. In the present work, a novel phase change materials for in situ encapsulation of titanium dioxide were synthesized by a one-step method based on the hydrolysis reaction of tetrabutyl titanate. The encapsulation process of phase change materials does not require any curing agents or organic solvents and does not emit any pollutants. Moreover, the material exhibits excellent shape stability and leak resistance, and has a high latent heat (115 J/g). Further study revealed anomalous bimodal phase change behavior in the incompletely dried samples. Taking the drying time as a variable, it was found that the synergistic effect of the residual nonparaffinic liquid phase material and titanium dioxide in the sample promoted the growth of (110+111) crystal structure, which increased the average crystallite spacing of the paraffin waxes during the crystallization process, and further led to an imbalance of the (110+111) crystallite to 020 crystallite ratio during the crystallization process of encapsulated paraffin waxes. This further leads to an imbalance in the ratio of the (110+111) crystal face and the 020 crystal face during the crystallization process of the encapsulated paraffin wax, and eventually an abnormal bimodal phase transition phenomenon appears in the differential scanning calorimetry (DSC) curve.

    Numerical analysis of the effect of temperature and its fluctuations on the vulcanization process of rubber seals
    Zhaoxiang ZHANG, Maokun CAI, Zhiying REN, Xiaohong JIA, Fei GUO
    2024, 75(2):  715-726.  doi:10.11949/0438-1157.20231213
    Abstract ( 82 )   HTML ( 10)   PDF (2250KB) ( 56 )  
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    As a key process in the rubber sealing molding, vulcanization has a significant impact on the performance of rubber sealing products. However, the rubber industry often adopts empirical vulcanization molding methods, lacking understanding of the evolution of vulcanization, making it difficult to theoretically guide the actual production process of rubber seals. In response to this weak link that restricts the improvement of rubber sealing quality, the paper conducted numerical simulation research on the vulcanization molding process of rubber seals. A transient simulation model for thermal-chemical coupling of rubber products was established based on an integral reaction kinetics model and a heat transfer control equation with variable physical parameters. Real time prediction of the time-varying temperature field and vulcanization degree field during the rubber product forming process was achieved, and the correctness of the model and solution method was verified through experiments. Furthermore, the vulcanization process of typical structural seals was simulated and analyzed, and the influence of mold temperature, rubber preheating temperature and temperature fluctuation behavior on the rubber seal vulcanization molding process was discussed. Finally, suggestions and references were provided for the actual vulcanization production of rubber seals.