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Table of Content
05 July 2020, Volume 71 Issue 7
    Reviews and monographs
    Progress research on development of membrane technology and materials for health industry
    Yuanyuan CAI,Baitao GUO,Weihong XING,Congjie GAO
    2020, 71(7):  2921-2932.  doi:10.11949/0438-1157.20191557
    Abstract ( 263 )   HTML ( 26)   PDF (1239KB) ( 258 )  
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    The health industry has huge potential for development. Among them, the pharmaceutical, medical and healthcare industries occupy an important position, but it faces constraints such as low utilization of medical resources, serious pollution of production processes, dependence on imports of high-end products, and imperfect quality standard systems. Membrane technology is a novel high-efficient separation technique perfectly suitable for solving above-mentioned problems in pharmaceutical, medical and healthcare industries, which will play an important role in promoting development of health industry in China. To our knowledge, few literatures have reviewed on the research and development status of membrane technology and materials for health industry. In this review, we will focus on this subject, and discuss the specific conditions and related standards for membrane materials utilized in health industry, emphasizing on progress in microfiltration, ultrafiltration, reverse osmosis, nanofiltration, membrane bioreactor, pervaporation, gas separation, and membrane materials for application in artifical organs. Also, we will analyze the existing problems, and provide suggestions for promoting development of membrane technology and materials for health industry in China.

    Progress of magnetically responsive membranes
    Yajie WANG,Lei LI,Qian ZHANG,Qian LI,Wangliang LI
    2020, 71(7):  2933-2944.  doi:10.11949/0438-1157.20200169
    Abstract ( 165 )   HTML ( 19)   PDF (1533KB) ( 162 )  
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    With the development of intelligent materials and nanotechnology, new functional membrane materials with special stimulus-response have been one of the main directions of membrane separation technology. Magnetically responsive membrane is a kind of separation membrane prepared by mixing magnetic particles and polymers, which can respond to magnetic field stimulation. Magnetically responsive membrane has the advantages of low energy consumption and high efficiency of membrane separation technology and the magnetic and catalytic properties of magnetic particles. The response of magnetic particles to magnetic field not only affects the structure and separation performance of the membrane, but also benefits the wettability and anti-fouling of the membrane. In this paper, the preparation methods of magnetically responsive membrane including blending method, coating method, grafting method and in-situ growth method are discussed in detail. Then the advantages and disadvantages of different preparation methods and their future development are compared. And from four aspects of filtration, adsorption, degradation, exchange separation, the application field of magnetic response separation membrane is discussed. Finally, the development of magnetically responsive membrane is summarized and its development is prospected.

    Advances in biosynthesis of quercetin glycoside derivatives
    Yueyang FENG, Ying WANG, Mingdong YAO, Wenhai XIAO, Mingzhu DING
    2020, 71(7):  2945-2955.  doi:10.11949/0438-1157.20200070
    Abstract ( 100 )   HTML ( 21)   PDF (1937KB) ( 103 )  
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    Natural products of glycosides are the main forms of secondary metabolites in plants and have important biological activities. Glycosylation modification can change its water solubility and stability, and produce special biological activities and functions. Therefore, glycoside products are suitable for commercialization and have important medicinal and industrial values. Especially it is widely applied to anti-cancer drugs and daily chemical products, thus glycoside compounds have been concerned and studied. In recent years, the biosynthesis of glycoside products had made great progress. In this paper, the important glycoside compound quercetin is illustrated to introduce the biosynthesis of glycoside compounds, and the engineering strategy of high-yield glycoside compounds is described from the perspective of glycosyltransferase and precursor supply. It provides technological support for researchers to obtain the high-yield strains of plant glycosides by utilizing synthetic biology techniques.

    Recent advances in high value added reuse of waste polystyrene in environment and energy
    Changhui LIU,Wenbo HUANG,Yanlong GU,Zhonghao RAO
    2020, 71(7):  2956-2972.  doi:10.11949/0438-1157.20200051
    Abstract ( 139 )   HTML ( 17)   PDF (6505KB) ( 124 )  
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    Polystyrene is an important part of the plastic material family. It has a series of advantages such as light mass, heat insulation, waterproof, and cheap. Landfill and incineration are the two main ways to dispose the waste plastic, but they will inevitably cause environment damage and the waste of fossil resource. As the rapid advancement of chemistry and material science, high value added reuse waste PS has gained vast attention. In this paper we mainly focus on the recent advances in the application of waste PS in the fields of environment protection and energy issues. The main content of this paper can be divided into the following three parts in terms of high value added manner and the desired product: converting waste PS into functional materials via a physical or chemical approach; fabrication porous carbon materials or modular materials from waste PS; high temperature pyrolysis of waste PS into small organic molecules.

    Interaction of VOCs with different hydrophilic properties in biotrickling filters
    Yan JIANG, Zhe ZHANG
    2020, 71(7):  2973-2982.  doi:10.11949/0438-1157.20200026
    Abstract ( 74 )   HTML ( 7)   PDF (1204KB) ( 74 )  
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    Taking the hydrophilicity and hydrophobicity as the starting point, the research status and development trend of biotrickling filters (BTFs) for industrial waste gas containing multi-component volatile organic compounds (VOCs) are summarized. This paper focuses on antagonistic, synergistic, and mutual effects among multiple VOCs, which summarizes and analyzes the immanent cause leading to the interactions. Besides, the gas-liquid/solid two-phase mass transfer models and biodegradation kinetics models are used to elaborate the VOCs mass transfer and biotransformation processes and their mechanisms in BTFs. Furthermore, application prospect is prospected to satisfy to current market requirement through construction and strengthening of synergistic effect instead of antagonism. And the treatment systems of VOCs are constructed by strengthening theoretical cognition of co-metabolism and solubilization mechanisms, which would promote BTFs developments in two aspects of theory and application.

    Vapor-liquid equilibrium for citral + α-ionone + β-ionone systems using headspace gas chromatography method
    Pei ZHENG, Linlin WANG, Jiezhen LIANG, Xiaopeng CHEN, Zhangfa TONG, Xiaojie WEI, Rui TANG
    2020, 71(7):  2983-2992.  doi:10.11949/0438-1157.20191515
    Abstract ( 86 )   HTML ( 4)   PDF (1067KB) ( 72 )  
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    Isothermal vapor-liquid equilibrium (VLE) data for citral (1) +α-ionone (2), citral (1) +β-ionone (2) and α-ionone (1) +β-ionone (2) were measured at 333.15, 368.15 and 403.15 K using headspace gas chromatography method. Redlich-Kister area test method and van Ness point test method were used to check the thermodynamic consistency. Aspen plus V10.0 software and Britt-Luecke algorithm were used to return the NRTL and UNIQUAC activity coefficient model parameters. Furthermore,the excess Gibbs energy (GE) for all systems were calculated using the NRTL model. The results showed all experimental p-T-x-y data satisfied the requirements of thermodynamic consistency. The maximum absolute average deviation (AAD) of vapor compositions between calculated and experimental data for citral (1) +α-ionone (2), citral (1) +β-ionone (2) and α-ionone (1) +β-ionone (2) systems at the measured temperatures were 0.0044,0.0060 and 0.0032, respectively. The maximum GE for three systems were 0.4002, 0.2315 and–0.7143 kJ·mol-1, respectively.

    Measurement and correlation of liquid-liquid equilibrium data for o-cresol-m-xylene-ethylene glycol
    Li HE, Xiong ZOU, Haotian YE, Xiangqin LI, Hongguang DONG
    2020, 71(7):  2993-2999.  doi:10.11949/0438-1157.20200181
    Abstract ( 59 )   HTML ( 7)   PDF (908KB) ( 46 )  
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    Ethylene glycol can selectively extract phenols from oils containing aromatic hydrocarbon components. To provide fundamental data to help developing new processes for extracting and separating phenols from coking phenolic oil by ethylene glycol, a simplified design method was adopted due to the complicated components of coking phenolic oil, that was o-cresol and m-xylene chosen as typical substances of phenolic compounds and aromatics based on existing phase equilibrium data, respectively. The ternary liquid-liquid equilibrium data of the o-cresol-m-xylene-ethylene glycol system were measured at 303.15, 313.15 and 323.15 K under atmospheric pressure. The reliability of the liquid-liquid equilibrium data at different temperatures was verified by Othmer-Tobias, Hand as well as Bachman equations. All of squares of correlation coefficients were greater than 0.99, which indicates the reliability of the measured experimental data was good. The experimental data were correlated by both NRTL and UNIQUAC models. The binary interaction energy parameters at different temperatures were obtained by data regression. As a result, the phase equilibrium data were calculated and compared with the experimental data. The root-mean-square deviations (RMSD) were less than 1.8%, indicating that NRTL and UNIQUAC models can successfully describe the phase equilibrium behavior of the system.

    Study on reaction mechanism of p-type dopant Cp2Mg in MOCVD gas phase
    Hong ZHANG, Liu TANG
    2020, 71(7):  3000-3008.  doi:10.11949/0438-1157.20191354
    Abstract ( 34 )   HTML ( 5)   PDF (3193KB) ( 40 )  
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    Using the density functional theory calculation of quantum chemistry, the reaction mechanism of p-type dopant Cp2Mg in the metal organic chemical vapor deposition (MOCVD) gas phase process was proposed and studied. The possibility of each reaction proceeding at various temperatures was determined, respectively. It was found that Cp2Mg mainly has two competing addition paths and hydrogenolysis paths. For adduct reaction path, complex Cp2Mg∶NH3 or Cp2Mg∶(NH3)2 will be formed in the temperature range of 293—573 K. For the hydrogenolysis pathway, the H radical in the gas phase was a “double-edged sword”. On the one hand, H radical exerted a positive auxiliary effect on Cp2Mg decomposition, significantly lowering the decomposition temperature of Cp2Mg. On the other hand, due to passivation, Mg-H gas phase complexes will be formed, which affects the p-type doping effect.

    Measurement and correlation of liquid-liquid equilibrium data for n-hexane- isopropanol azeotropic system
    Chong YANG, Xufeng LIN, Jinfeng ZHANG, Hong CHEN, Yepeng XIAO, Hui WANG, Lihua CHENG, Xinping OUYANG
    2020, 71(7):  3009-3017.  doi:10.11949/0438-1157.20191001
    Abstract ( 70 )   HTML ( 8)   PDF (1117KB) ( 93 )  
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    To provide basic data for the process design and process simulation calculation of solvent extraction and separation of n-hexane-isopropanol mixture, experimental liquid-liquid equilibrium (LLE) data for separation of isopropanol from n-hexane were measured at 30℃ under atmospheric pressure by using dimethyl sulfoxide, 1,4-butanediol, 1,2-propanediol, acetonitrile, furfural and N,N-dimethylformamide as extractants, respectively. The extraction properties of these selected solvents were assessed by the separation factor based on the experimental LLE data. It was found that separation factor were all higher than 1 with above solvents, corroborating that it is feasible to extract isopropanol from n-hexane using the selected extractants. The consistency and reliability of the experimental data were appraised using the Hand equation, and the correlation coefficients of fitting equations were all above 0.98. Furthermore, the non-random two liquids (NRTL) activity coefficient model in Aspen Plus software was utilized to correlate the experimental tie-line compositions, in which the binary interaction parameters between the components were acquired. Subsequently, the corresponding values of phase equilibrium were calculated and compared with the experimental data. As a result, the root mean square deviation (RMSD) between the calculated and experimental compositions was below 1.0%, indicating that the NRTL model can accurately describe the liquid-liquid phase equilibrium of the ternary system.

    Fluid dynamics and transport phenomena
    EMMS-based flow regime study of circulating fluidized beds
    Kaicheng CHEN, Yujie TIAN, Fei LI, Hao WU, Wei WANG
    2020, 71(7):  3018-3030.  doi:10.11949/0438-1157.20200062
    Abstract ( 69 )   HTML ( 7)   PDF (2983KB) ( 70 )  
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    The design, enlargement, and optimization of fluidized beds require a basic understanding of the watershed. However, the division of watersheds for gas-solid systems still has many controversies. In this paper, the state-of-the-art regime studies are summarized with the main disputes highlighted. Inconsistency is found on the demarcation of the fast fluidization. The steady-state EMMS (energy minimization multi-scale) drag model is thus integrated into two-fluid model (TFM) to simulate a circulating fluidized bed (CFB) with a variety of gas velocities and solids holdups. Particle refluxing and slugging are found in the simulation results, whereby bound the fast fluidization regime. A regime diagram is drawn, where the main features of the different regimes in CFBs are presented.

    Analysis of flow and heat transfer characteristics in external heat extractor of gas-solid fluidized bed
    Jiantao LI, Xiuying YAO, Lu LIU, Chunxi LU
    2020, 71(7):  3031-3041.  doi:10.11949/0438-1157.20191588
    Abstract ( 77 )   HTML ( 7)   PDF (1748KB) ( 83 )  
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    The external heat extractor is one of the key equipment to maintain the thermal balance of the catalytic cracking reaction system and keep the device running smoothly. It can process feed oils into products with higher value, such as gasoline, diesel, and olefins. The catalytic cracking reaction belongs to a parallel series reaction, and its desired products are the reaction intermediate. Meanwhile, a lot of heat is absorbed during reaction. The heat is mainly provided by coke-burning regeneration of the catalysts in regenerator. When processing heavy oils, the carbon amount on the catalysts will be increased, which can generate the extra heat during the catalysts coke-burning regeneration. A fluidized bed with external catalyst cooler can take the extra heat away to control the reaction temperature effectively and keep the heat balance between reaction and regeneration. The downflow external catalyst coolers have been widely used due to their high heat load and flexible adjustment. Both optimal design and effective control of downflow external coolers in industrial application require a deep understanding of gas-solid flow characteristics, heat transfer characteristics and their correlation. Therefore, a pilot scale cold mode experimental setup was built to investigate the effect of superficial gas velocity and solid mass flux on heat transfer, solid holdup and bubble frequency. The results showed that the instantaneous heat transfer coefficient presented the characteristics of low-frequency and high-amplitude as well as high-frequency and low-amplitude, and the former played a dominate role. The fluctuation periods of instantaneous heat transfer coefficient and instantaneous local solid holdup were both 25 s, which indicated that the heat transfer process between bed and heat transfer tube was directly related to the local solid holdup. Increasing superficial gas velocity can reduce local solid holdup, increase local bubble frequency, and enhance the heat transfer between bed and heat transfer surface. Moreover, local solid holdup and local bubble frequency were increased with solid mass flux. Heat transfer coefficient was decreased with solid mass flux at ug=0.1 m/s, while increased with solid mass flux at ug≥0.4 m/s. Influence of gas-solid flow characteristics on heat transfer characteristics was various under different flow patterns of fluidized beds. In bubbling bed flow pattern, local bubble frequency near the heat transfer tubes had a great influence on the heat transfer process, due to high local solid holdup impeded the renewal of particles on the heat exchange surface. In turbulent bed flow pattern, heat transfer coefficient was increased with local solid holdup and bubble frequency. Empirical correlations for predicting heat transfer coefficient at different flow patterns were built based on operation conditions and gas-solid flow characteristics. Their mean relative deviations between predicted value and experimental value were 6.9% and 1.3% respectively.

    Flow pattern and pressure drop on shell side of shell and plate heat exchanger under adiabatic state
    Pengfei WU, Ke WANG, Jue ZHAO
    2020, 71(7):  3042-3049.  doi:10.11949/0438-1157.20200109
    Abstract ( 50 )   HTML ( 3)   PDF (1980KB) ( 49 )  
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    The heat exchanger is one of the main equipment in the field of petroleum, chemical industry, nuclear energy and other industrial applications. The development of an efficient heat exchanger can effectively improve the energy utilization rate, which is an important way to solve the energy and environmental problems. Shell and plate heat exchanger is a new type of heat exchanger; it combines the advantages of shell and tube heat exchanger and plate heat exchanger. It has high heat transfer efficiency, high temperature and pressure resistance, compact structure and light weight, and makes up for the uneven stress distribution of plate heat exchanger. At present, there are few literature reports on the flow pattern and pressure drop characteristics of gas-water two-phase flow in the shell and plate heat exchanger. In this paper, the flow pattern and pressure drop of the vertical upward gas-liquid two-phase flow in the shell and plate heat exchanger are experimentally studied. The macro distribution characteristics of the vertical upward gas-water two-phase flow interface in the shell and plate heat exchanger are obtained by high-speed camera technology. The flow pattern is divided into bubbly flow, slug flow, film flow and churn flow according to the morphological characteristics of the phase interface; at the same time, the relationship between flow pattern and pressure drop is analyzed, and it is found that the amplitude of pressure drop fluctuation in bubble flow is the smallest, followed by the slug flow and the film flow, and the amplitude of pressure drop fluctuation in the agitated flow is the largest; based on Lockhart-Martinelli theory, the prediction model of two-phase flow pressure drop in the shell and plate heat exchanger is established by analyzing the relationship between two-phase multiplier and Martinelli parameter, it is found that the value of Chisholm parameter C is close to the value of Chisholm's original laminar-laminar flow in smooth tube.

    Universal calculation model of mass center equivalent rectangle for helical baffle heat exchangers
    Shuxing ZHENG, Zilong ZHU, Yaping CHEN, Jiafeng WU
    2020, 71(7):  3050-3059.  doi:10.11949/0438-1157.20200085
    Abstract ( 37 )   HTML ( 3)   PDF (2213KB) ( 30 )  
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    The existing approach of calculating cross-sectional area of the spiral channel of the helical baffle heat exchanger (HBHX) is according to the minimum cross section of the channel throttled by tube row, while the actual cross section of the spiral channel is composed of both the minimum cross section and the maximum cross section at inter tube space, and the spiral flow does not pass through the minimum cross section instantaneously. Thus the prediction has been in vain of the shell side Nusselt number and friction factor with universal correlations of the Reynolds number for helical baffle heat exchangers because of the incorrect value of Reynolds number. A novel model of mass center equivalent rectangle (MCER) is presented for more accurate calculation of the cross-sectional area of the helical flow channel of the HBHX. The verification of the MCER model is performed with satisfactory results for HBHXs by both the heat exchanger commercial design software HTRI and some experimental results in literatures. Under the same conditions, the error between the Nusselt number Nuo calculated by the MCER model and the result calculated using the heat exchanger design software HTRI is in the range of -10% to 5%, and the errors with the experimental results of the two groups of literature are within the range of ± 18% and -5%—15%, but the error of the friction factor formula results compared with the results of the above sources is relatively large, and needs to be further improved.

    Subcooled flow boiling resistance characteristics in narrow rectangular channel under natural circulation condition
    Kuan YANG, Changqi YAN, Xiaxin CAO
    2020, 71(7):  3060-3070.  doi:10.11949/0438-1157.20191379
    Abstract ( 32 )   HTML ( 3)   PDF (2744KB) ( 17 )  
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    Using deionized water as the experimental working medium, an experimental study of the frictional resistance characteristics of subcooled boiling in a narrow rectangular channel under single-sided heating visualization was carried out under low pressure and low flow rate natural circulation conditions. In the experiment study, the pressure drop data in the narrow rectangular test section was measured, high-speed camera was used as well to capture the two-phase flow images, calculation method that separates the two-phase frictional pressure drop in subcooled flow boiling was brought out. Based on the experimental data obtained, evaluation study of classical two-phase frictional pressure drop correlations from homogeneous flow and separated flow modes were carried out. The experimental results indicates that correlations that based on two-phase equivalent viscosity from homogeneous flow models significantly under estimate the friction pressure drop. Sun and Mishiba correlations and Tran correlations from separated flow models can predict the friction pressure drop pretty well with mean relative error under 15% error bands. Based on the experimental data obtained, empirically correlations for two-phase multiplier was obtained by considering the effect of liquid only Reynolds number, Martinelli parameter and Laplace number. The mean relative error of predicted result with the experimental data is within 10% error band.

    Numerical simulation of heterogeneous nucleation of water vapor on surface of fine particles based on molecular kinetics
    Tingfang YU, Ju GAO, Guilong XIONG, Shuiqing LI, Qiang YAO
    2020, 71(7):  3071-3079.  doi:10.11949/0438-1157.20191605
    Abstract ( 63 )   HTML ( 1)   PDF (1356KB) ( 65 )  
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    To investigate the heterogeneous nucleation characteristics of supersaturated water vapor on the surface of fine particles, and accurately predict the nucleation parameters, a molecular kinetic model of heterogeneous nucleation of supersaturated water vapor on the surface of coal-fired fine particles was established based on the theory of molecular kinetic heterogeneous nucleation. The promotion effects and relative importance of two diffusion condensation mechanisms of water and vapor molecules to accelerate embryo growth and the influences of supersaturation and macroscopic contact angle on nucleation rate are systemically analyzed. Furthermore, the critical supersaturation for fine particles under different temperature and macroscopic contact angles are also predicted. The results show that when the radius of embryo is less than critical embryo radius, the ratio of diffusion condensation rate of water molecules absorbed on particle surface to direct vapor deposition condensation rate is always above 100, it indicates that the surface diffusion mechanism of absorbed water molecules plays a dominated role in embryo growth. The nucleation rate is remarkable increased with the increase of supersaturation or the decrease of macroscopic contact angle. Additionally, the nucleation rate increases exponentially with the increase of supersaturation. Increase the vapor temperature or decrease macroscopic contact angle can lead to a lower critical supersaturation. For fine particles with a particle size of less than 0.1 μm, as the fine particle size increases, the critical supersaturation of heterogeneous nucleation decreases significantly.

    Thermal performance study of organic flash cycle based on internal heat exchanger
    Guidong HUANG, Songyuan ZHANG, Zhong GE, Zhiyong XIE, Huajiang XIANG, Yinlian YAN, Zhipeng YUAN
    2020, 71(7):  3080-3090.  doi:10.11949/0438-1157.20191294
    Abstract ( 48 )   HTML ( 2)   PDF (1710KB) ( 38 )  
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    In this study, an internal heat exchanger organic flash cycle (IHE-OFC) system model was built, using 100—200℃ geothermal water as the heat source, and R600a, R600, R601a, R601, R236ea, R227ea, R245fa, R123 as circulating working fluid. Thermodynamic analysis of the IHE-OFC system is conducted, and the system is optimized with net power output as the optimization objective. The results show that when the heat source temperature is less than or equal to 160℃, the net power output of the R601 IHE-OFC system is maximal. When the heat source temperature is higher than or equal to 190℃,the net power output of the R601 traditional OFC system is maximal. When the heat source temperature is 170℃, the net power output of the R601a IHE-OFC system is maximal. When the heat source temperature is 180℃,the net power output of the R601a traditional OFC system is maximal. Moreover, there is a characteristic temperature for each working fluid, which is the sum of the temperature corresponding to 0.85Pcri and pinch point temperature difference of heater. Due to the influence of the characteristic temperature of the working fluid, the optimal flash pressure, IHE temperature rise on the low temperature side, and the system efficiency initially increases and then remains constant with increasing heat source temperature.

    Lattice Boltzmann study on single solid particle promoting thin liquid film rupture
    Xuewen LIU, Jinjing LI, Xiaojun QUAN, Wei XIONG
    2020, 71(7):  3091-3097.  doi:10.11949/0438-1157.20200027
    Abstract ( 46 )   HTML ( 3)   PDF (1168KB) ( 41 )  
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    The isothermal lattice Boltzmann method two-phase flow model combined with the particle motion model was used to study the interaction between single particles and thin liquid film. The detailed process of liquid film rupture caused by a single spherical hydrophobic particle was visually shown through simulation. The whole process of the hydrophobic particles causing the rupture of the thin liquid film can be divided into two stages. Stage 1 is the stage in which the particle contacts the liquid film and moves to the inside of the liquid film under the action of the interfacial force until the particle just penetrates the liquid film. Stage 2 is the stage in which the upper and lower liquid surface are driven by the capillary force to move on the surface of the particle. It was found that hydrophobic particle with contact angle of 106.7° caused the shortest rupture time of liquid film. When the thickness of the liquid film is greater than the depth of the liquid immersed in the equilibrium of the particles at the vapor-liquid interface, the time of hydrophobic particle leading to the rupture of the liquid film will be greatly increased.

    Catalysis, kinetics and reactors
    Study on degradation kinetics of hemicellulose in wheat straw hydrothermal pretreatment
    Han ZHANG, Qian FU, Qiang LIAO, Ao XIA, Yun HUANG, Xianqing ZHU, Xun ZHU
    2020, 71(7):  3098-3105.  doi:10.11949/0438-1157.20200053
    Abstract ( 68 )   HTML ( 8)   PDF (1675KB) ( 69 )  
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    Hydrothermal pretreatment is one key process for efficient energy conversion of lignocellulose raw materials. However, the reaction path and reaction mechanism of hydrothermal pretreatment using wheat straw as raw materials are still insufficiently studied, limiting the optimization of the pretreatment process and the real-world application. In this paper, wheat straw was used as the research object, and the reaction kinetics of hydrothermal pretreatment of lignocellulose was experimentally studied. It was found that the degradation of hemicellulose to xylooligosaccharide, xylose, and furfural is the main degradation process in the hydrothermal pretreatment process. In addition, the concentration of xylooligosaccharide and xylose in the hydrolysate decreased with the increase of pretreatment temperature, while the concentration of furfural increased. The concentration of xylooligosaccharide and xylose in the hydrolysate first increased and then decreased with the incubation time, and the concentration of furfural tended to be stable with the incubation time. According to the experimental results, a new reaction path was proposed, and the kinetic rate constant and the activation energy of the reaction were obtained. The obtained kinetic model can well explain the changes in the concentration of the reactants, which was in a good agreement with the experimental data. This model can provide guidance for the design of wheat straw hydrolysis pretreatment system.

    Study on low temperature selective catalytic reduction of NO by Ba and Co co-doped MnOx
    Tao LIU, Shuting ZHANG
    2020, 71(7):  3106-3113.  doi:10.11949/0438-1157.20191520
    Abstract ( 67 )   HTML ( 10)   PDF (3020KB) ( 87 )  
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    A series of Ba and Co doped MnOx doping catalysts were prepared by citric acid complex method. The effects of Ba and Co doping on the performance of MnOx low temperature NH3-SCR were studied. The test results showed that the addition of Ba inhibited the catalytic performance of MnOx. The Co addition promoted the catalytic performance of MnOx. When Ba and Co are co-doped, the performance of the catalyst increased obviously. 3BaMnCoOx showed the most excellent catalytic performance, and the catalytic activity was above 99% when the reaction temperature was higher than 180°C. It showed good water and sulfur resistance. The catalysts were characterized by XRD, SEM, NO-TPD, NH3-TPD, H2-TPR and NO adsorption in situ infrared spectroscopy. The results showed that MnCo2O4.5 solid solution was formed after Co doping, which guaranteed excellent redox performance. Ba doping provided a new NO adsorption site for the catalyst, which led to the formation of new active nitrate adsorption species. The NO adsorption performance of the catalyst was promoted. These characteristics make BaMnCoOx low-temperature denitration catalysts show excellent denitration performance.

    Separation engineering
    Effect of structured 5A molecular sieve adsorption bed structure and process parameters on N2/H2 adsorption performance
    Peng WANG, Jinglei LIU, Shengzhong ZHANG, Dequan FAN, Ying ZHANG, Hong XU
    2020, 71(7):  3114-3122.  doi:10.11949/0438-1157.20191349
    Abstract ( 57 )   HTML ( 3)   PDF (1153KB) ( 52 )  
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    The kinetic parameters were obtained by adsorption isotherm, and the CFD model was established to simulate the adsorption process of hydrogen/nitrogen in the structured 5A molecular sieve adsorption bed. The effects of structural parameters such as the adsorbent sheet spacing and thickness and process parameters such as adsorption pressure and volume flow rate on the adsorption performance to the mixed gas were discussed. The results show that reducing sheet spacing and thickness are beneficial to the mass transfer coefficient and bed saturation degree. Increasing the adsorption pressure can improve the bed saturation degree, but will reduce the mass transfer coefficient. The effect of the flow rate on mass transfer coefficient is not obvious, but when the flow rate is high, both the adsorption capacity and the bed saturation degree decrease. The structured 5A molecular sieve adsorbent has good adsoption performance.

    Extraction of berberine from Coptis chinensis assisted by ionic liquids and microwave: experiments and molecular modeling
    Yuhua WU,Xin DING,Xiaolu LI,Hongfeng GAO,Wei FENG,Hongcun BAI,Qingjie GUO
    2020, 71(7):  3123-3131.  doi:10.11949/0438-1157.20191365
    Abstract ( 46 )   HTML ( 4)   PDF (2003KB) ( 32 )  
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    The efficient extraction of berberine and other biologically active substances from Coptis chinensis is of great significance for the effective utilization of traditional Chinese medicine resources. However, the isoquinoline alkaloids in Coptis chinensis have relatively similar chemical structures and physicochemical properties, resulting in increased difficulty in efficient extraction. Ionic liquids as excellent reaction media exhibit good prospects in the extraction of natural active substances. At the same time, microwave as a new type of auxiliary method is beneficial to the extraction and analysis of pharmaceutical active components in natural plants. In this study, berberine, an effective component in medicinal plants, was extracted by ionic liquid and microwave co-assisted method to achieve the strengthened processes and high-efficient extraction. The effects of ionic liquid species, solid-liquid ratio, solution pH, microwave heating time, microwave temperature and microwave power on extraction yield were investigated in details. In addition, by using the molecular simulation calculations based on modern density functional theory, the effects of microwave and different ionic liquids on the extraction of berberine were studied. The physical nature of the interaction between ionic liquids and berberine was revealed at the molecular scale.

    Study on separation process of dicyclohexyl ether by catalytic hydrogenation from cyclohexanol distillation residue
    Erfu HUO, Yingchun LI, Shuai YANG, Ming FENG, Weiqin CHENG, Bonan WANG, Xinjun WEI
    2020, 71(7):  3132-3139.  doi:10.11949/0438-1157.20191212
    Abstract ( 37 )   HTML ( 6)   PDF (1073KB) ( 40 )  
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    In order to solve the key technical problems such as similar boiling points of cyclohexanol distillation residues and the difficulty of separation by conventional separation methods, the 3-cyclohexylcyclohexene, 1-cyclohexylcyclohexene and dicyclohexylidene were reduced to cyclohexylcyclohexane by catalytic hydrogenation and the boiling point difference between the two components was enlarged. High purity cyclohexylcyclohexane and dicyclohexyl ether were obtained by vacuum distillation. Using Pd/C as catalyst, the optimum conditions for catalytic hydrogenation of 3-cyclohexylcyclohexene, 1-cyclohexylcyclohexene and dicyclohexylidene to cyclohexylcyclohexane in residual solution were obtained. The reaction temperature was 120℃, the reaction time was 4 h, the reaction pressure was 4 MPa, the stirring speed was 550 r/min, the amount of Pd/C catalyst was 0.4% of the mass of the material, the selectivity was more than 99.5% and the conversion rate of the materials was 98.7%. After vacuum distillation, the purity of cyclohexylcyclohexane and dicyclohexyl ether is more than 99.5%.

    Process system engineering
    Mechanism modeling and real-time estimation application of thermal efficiency for delayed coking furnace
    Jian HUANG, Zhong ZHAO
    2020, 71(7):  3140-3150.  doi:10.11949/0438-1157.20191072
    Abstract ( 68 )   HTML ( 6)   PDF (1591KB) ( 62 )  
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    Coking heating furnace is the key plant in the delayed coking unit. Thermal efficiency is one of the most important key performance indications. In this work, the thermal efficiency dynamic model is established based on the first principles of heat transfer equations and heat balance conditions. A joint particle filtering method combined with Kalman filter and particle filter is proposed to correct the model prediction and the convergence of the proposed method has been analyzed. The application results confirmed the feasibility and effectiveness of the proposed method, and laid the foundation for the advanced control of the delayed coking unit.

    Research on refrigerant leakage identification for heat pump system based on PCA-SVM models
    Xianyi YU, Jianghong WU, Yunhui GAO
    2020, 71(7):  3151-3164.  doi:10.11949/0438-1157.20191139
    Abstract ( 33 )   HTML ( 3)   PDF (3336KB) ( 23 )  
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    To study the data mining theory method and experimental verification of the refrigerant leakage identification of the heat pump system, firstly establish an air source heat pump system refrigerant leakage test bench to test the experimental parameters of the heat pump system in normal working conditions, interference working conditions, and leakage working conditions. Then, principal component analysis (PCA) was used to process the experimental data, and support vector machine (SVM) was used to classify and identify the data. A leakage identification model based on PCA-SVM was established which verified in both two classification and multi classification model. The leakage rate and the influence of different fault conditions of the model was studied. RefliefF feature selection algorithm is used to screen the original feature parameters which simplify the feature parameters of the identification model. The results show that, for the air source heat pump water heater, the leakage identification model has a high identification of 100% in the leakage mode, and the slow leak diagnosis recognition performance of the weak in rapid leak, the same model in different fault diagnosis recognition performance is different, slight influence on the system s running fault diagnosis recognition performance is weaker than other malfunction. RefliefF feature selection method reduces the original 41 system characteristic parameters to 10 characteristic parameters. The identification accuracy of the leakage identification model after parameter screening and optimization is also maintained at a high level, the optimized leakage identification model is more conducive to practical application.

    Estimation of microbial metabolic state based on hybrid cybernetic model
    Yanru PAN, Fei LIU
    2020, 71(7):  3165-3171.  doi:10.11949/0438-1157.20191310
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    The components of microbial fermentation process are extremely complex. The physicochemical and biochemical reactions are mixed and overlapped. Many metabolic states cannot be measured directly. The hybrid cybernetic model combines the elementary mode analysis and the cybernetic model control. It not only involves both intracellular product information and metabolic behavior, but also introduces control variables to regulate the activity and synthesis of catalytic enzymes. Based on the kinetic equation of microbial metabolism, the real-time state monitoring of microbial metabolism could implement. In view of the fermentation process of poly-β-hydroxybutyrate, by means of the metabolic pathway analysis, the nonlinear dynamics of the existing hybrid cybernetic model is first linearized. Then the extended Kalman filter is used to estimate the metabolic state of fermentation process. Simulation results show that it has a good estimation effect on some important state variables in microbial metabolism.

    Intermittent process fault monitoring based on recurrent autoencoder
    Xuejin GAO, Tengfei LIU, Zidong XU, Huihui GAO, Yongchuan YU
    2020, 71(7):  3172-3179.  doi:10.11949/0438-1157.20191581
    Abstract ( 27 )   HTML ( 3)   PDF (1269KB) ( 12 )  
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    Aiming at the non-linear and dynamic characteristics of intermittent process data, a process fault monitoring method based on recurrent autoencoder (RAE) is proposed. To establish monitoring model, an autoencoder is constructed by using long short-term memory (LSTM) recurrent neural network. Compared with the traditional autoencoder, the proposed method can effectively extract the dynamic correlation information between time series samples. Firstly, a three-step expansion method combining batch expansion and variable expansion are used to expand the batch process data into two dimensions, and input sequences for modeling is obtained by sliding window sampling. Then, LSTM is used to reconstruct the input sequences to train an autoencoder model. Moreover, the Squared prediction error (SPE) statistics are constructed based on reconstruction error to achieve on-line monitoring. Finally, the proposed method is applied to penicillin fermentation process for simulation experiment and recombinant Escherichia coli fermentation process monitoring. The results show that the method can detect faults in time and has better monitoring performance.

    Simulation of rare earth extraction process based on separation coefficient correction
    Hui YANG, Wenhao DAI, Rongxiu LU, Jianyong ZHU
    2020, 71(7):  3180-3190.  doi:10.11949/.0438-1157.20191481
    Abstract ( 28 )   HTML ( 5)   PDF (1444KB) ( 39 )  
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    Because the process simulation model based on rare earth extraction mechanism does not consider the extraction efficiency of the extraction tank, it is difficult for the content of the components output by the model to meet the actual industrial conditions. Therefore, this paper combines the mechanism model with a data-driven method to establish the rare earth extraction process simulation which based on the correction of separation coefficient. Firstly, on the basis of the rare earth extraction process mechanism model with relative separation coefficient, the correction value of separation coefficient is introduced to expand the mechanism model of rare earth extraction. Secondly, the data-driven method and Fibonacci tree optimization algorithm(FTO) are used to optimize the correction value at all levels, and MATLAB GUI is used to develop the rare earth extraction process simulation system. Finally, according to the actual data of industrial field, the process of rare earth extraction is simulated and verified when the working condition is changed. The results show that the simulation of the process constructed in this paper conforms to the actual working conditions of the rare earth extraction process.

    Prediction of octane number of finished gasoline blend based on SHPSO-GA-BP
    Wei LI, Xiaoming WANG, Dongnian JIANG, Yajie LI, Chenglong LIANG
    2020, 71(7):  3191-3200.  doi:10.11949/0438-1157.20191453
    Abstract ( 37 )   HTML ( 2)   PDF (1404KB) ( 36 )  
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    In the production of finished gasoline,octane number as the key indicators of quality of finished product gasoline and foundation of formula model,it is import to accurate measuring its content. However, due to the existing measurement technology and the constraints of complex conditions, it is difficult to obtain the component data effectively. Considering the problems of genetic algorithm (GA), particle swarm optimization (PSO), and optimizing back propagation (BP) network, a serial hybrid particle swarm genetic algorithm (serial hybrid PSO-GA, SHPSO-GA) is proposed to optimize the BP network, and it is used to predict and model the octane number. In this method, the output of PSO algorithm is divided into two populations according to the fitness value, and the bad ones are discarded and the good ones are retained. Then the optimized population was further optimized by GA crossover and mutation, the optimal population was applied to BP network parameter optimization. Finally, based on the method and the industrial historical data, a prediction model of octane number of hydrogenated gasoline was established. The simulation results showed that, compared with the traditional BP, GA-BP, PSO-BP, PSO-GA-BP and other methods, SHPSO-GA-BP had better prediction performance due to the deeper integration of PSO and GA, it could be used for octane number prediction.

    Model predictive control of nonlinear system based on adaptive fuzzy neural network
    Hongbiao ZHOU, Yu ZHANG, Xiaoying BAI, Baolian LIU, Huanyu ZHAO
    2020, 71(7):  3201-3212.  doi:10.11949/0438-1157.20191531
    Abstract ( 31 )   HTML ( 4)   PDF (1449KB) ( 55 )  
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    Aiming at the control problem of nonlinear dynamic systems, a model predictive control (MPC) method based on adaptive fuzzy neural network (AFNN) was proposed. First, in the offline modeling phase, a rule automatic splitting technique is used to generate initial fuzzy rules, and an improved adaptive LM learning algorithm is adopted to optimize network parameters. Second, in the real-time control process, the network parameters of the AFNN are adjusted according to the error between the system output and the predicted output, so that providing an accurate prediction model for the MPC. Furthermore, the gradient descent optimization algorithm with adaptive learning rate is used to solve optimization problem and obtain the nonlinear control law online, which is applied to control the dynamic system. In addition, the convergence and stability analysis of the proposed AFNN-MPC are given to ensure its successful application in practical engineering. Finally, numerical simulation and two-CSTR process experiments are used to verify the effectiveness of AFNN-MPC algorithm. The results show that the proposed AFNN-MPC has superior control performance.

    Surface and interface engineering
    Study on adsorption and diffusion of MMAl on AlN(0001)-Al surface covered with NH2/H
    Wei SUN, Ran ZUO
    2020, 71(7):  3213-3219.  doi:10.11949/0438-1157.20200058
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    Using the density functional theory (DFT) of quantum chemistry, the adsorption and diffusion of the surface reaction precursor AlCH3 (MMAl) on the AlN (0001) -Al surface covered with NH2 and H during MOCVD growth of AlN were calculated and analyzed. By analyzing the surface adsorption energy, diffusion energy barrier, and Mulliken population, etc., the possible stable adsorption structure and diffusion path were determined.The study found that: on the AlN (0001) -Al surface covered with NH2 and H, with the change of the coverage of NH2 and H, MMA1 was stably adsorbed at the T4 and H3 positions with similar adsorption probability.As the proportion of NH2 increases and the proportion of H decreases, MMAl transfers charges to the surface of AlN after adsorption, at the same time its adsorption becomes relatively easy, and diffusion becomes gradually difficult.Compared with before adsorption, the Al-C bond length in MMAl after adsorption is shortened, the bond energy is enhanced, and the detachment of CH3 is not easy, resulting in a higher probability of introducing C impurities.It shows that MMA1 is not only one of the main reactive substances in growth, but also one of the main sources of introducing C impurities. If there is covering H on the AlN surface, the adsorbed MMA1 will cause the covered H atoms to tend to detach from the AlN surface, which is conducive to subsequent growth.

    Simulation and analysis of dynamic pressure effect of gas film on cylinder seal
    Shurong YU, Junhua DING, Shipeng WANG, Hong LIU, Xuexing DING, Baocai SUN
    2020, 71(7):  3220-3228.  doi:10.11949/0438-1157.20191501
    Abstract ( 33 )   HTML ( 1)   PDF (1775KB) ( 22 )  
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    For aeroengine cylinder seals, the floating ring is often broken due to insufficient dynamic pressure, which causes the floating ring to rub against. Based on this, the Fluent software is used to simulate the flow field of two kinds of models, namely, the existing cylindrical grooved gas film and the spiral grooved gas film, and carry out with test verification. The results show that for the grooveless gas film model, increasing the eccentricity, rotation speed and pressure difference will increase the dynamic pressure effect of the seal. The increase of eccentricity and pressure difference will increase the leakage of the model, but the change of rotation speed has little effect on the leakage of the model; for spiral groove gas film seal, the increase of eccentricity, rotation speed and pressure difference will increase the buoyancy of the gas film. With the increase of eccentricity and pressure difference, the leakage of the model increases. Based on the above two conclusions, it can be concluded that the speed is the secondary factor affecting the leakage; the spiral groove model has better dynamic pressure effect and less leakage compared with the grooveless model, so it can reduce the friction of floating ring. Therefore, this study has important reference significance for the development of better cylindrical seal structure.

    Biochemical engineering and technology
    Study on catalytic synthesis of boldenone by recombinant E. coli expressing 17β-hydroxysteroid dehydrogenase
    Yuling WU, Minglong SHAO, Wulin ZHOU, Huifang GAO, Xian ZHANG, Meijuan XU, Taowei YANG, Zhiming RAO
    2020, 71(7):  3229-3237.  doi:10.11949/0438-1157.20200011
    Abstract ( 26 )   HTML ( 3)   PDF (2606KB) ( 16 )  
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    Boldenone, as an important anabolic androgenic steroid, has the function of improving muscle mass and endurance. The traditional synthesis method of boldenone is to synthesize from 1,4-androstenedione (ADD) by chemical method, but the process is complex and the pollution is serious. 17β-hydroxysteroid dehydrogenase (17β-HSD) can catalyze the redox reaction of C-17 site of steroids, and realize the conversion of ADD and boldenone. In this study, six different 17β-HSD genes were screened and heterologously expressed in E. coli. Using different recombinant strains to transform ADD to boldenone, the results showed that E. coli BL21/pET28a-HSDPy had the highest conversion rate of ADD, so BL21/pET28a-HSDPy was selected for further study. The enzymatic properties of the recombinant strain were identified and the whole cell transformation conditions were optimized. The results showed that under the condition of 36 g·L-1 biomass and 5.40 g·L-1 substrate concentration, 3.66 g·L-1 boldenone was obtained after two batches of feeding, which was 4.1 times higher than before optimization. Moreover, no by-products were detected during biotransformation. This study provides the possibility for the biosynthesis of boldenone.

    Energy and environmental engineering
    Kinetic study on MSW components with particle swarm method
    Ruiqu DENG, Linzheng WANG, Ruizhi ZHANG, Yonghao LUO
    2020, 71(7):  3238-3246.  doi:10.11949/0438-1157.20200034
    Abstract ( 43 )   HTML ( 4)   PDF (1864KB) ( 40 )  
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    Cardboard, rubber, pine wood and nylon were selected as representatives of household wastes, and their pyrolysis characteristics were investigated through thermal gravimetric analysis under different heating rates (15, 40 and 200℃/min). Based on the characteristics of the weightlessness curve of each household garbage component, a finite parallel response model was established, and the corresponding dynamic parameters were calculated by particle swarm algorithm, and cross-validation was performed. The results indicated that the kinetic parameters obtained through PSO could not only accurately reproduce the complex peak distribution of the weight-loss curves, but also effectively predict the alteration of weight-loss characteristics under different heating rates.

    Analysis of PEMFC water management status based on DC internal resistance and AC impedance characteristics
    Ru WANG, Yongchao SHEN, Dong WEI, Qian GUO
    2020, 71(7):  3247-3257.  doi:10.11949/0438-1157.20191126
    Abstract ( 18 )   HTML ( 1)   PDF (2679KB) ( 10 )  
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    Based on the Randles equivalent circuit, this paper studies the coupling relationship between operating temperature and humidity of proton exchange membrane fuel cell (PEMFC), establishes the direct current (DC) internal resistance and alternating current (AC) impedance characteristics of the stack, and studies the electrochemical impedance spectrum and U-I output characteristics under different operating conditions. The AC impedance method and the U-I characteristic method are combined to obtain the correspondence between the AC impedance and the DC internal resistance under different water management states, and the influence of the water management state on the output performance of the stack is analyzed. The simulation and experimental results show that the different water management states have consistent variation rules and corresponding quantitative relationships in the AC impedance spectrum and the U-I characteristic curve. The phenomenon of membrane dryness, flooding, etc. in the output performance of the stack is in the DC internal resistance. And the change of the AC impedance map has clear performance characteristics. By studying the impact of water management states on both, it is possible to optimize the operating conditions and optimize the output performance of the stack.

    Research on effect of ultrafine ash particles on acid dew point and acid condensation for coal-fired boilers
    Wei WEI, Xiucai LI, Fengzhong SUN
    2020, 71(7):  3258-3265.  doi:10.11949/0438-1157.20200022
    Abstract ( 43 )   HTML ( 5)   PDF (1387KB) ( 33 )  
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    Accurate prediction of acid dew point(ADP) and acid condensation is the key to deeply reduce the flue gas temperature and to ensure the safe and efficient operation of the heat exchange equipment in coal-fired power plants. The ash particles in the flue gas have great influence on the occurrence of ADP and acid condensation droplets. The iterative calculation method of ADP and acid condensation considering the effect of fly ash particle radius on local condensation mass transfer were proposed for the first time in this paper. When the fine ash particles radiuses are smaller than the critical radius (rash<r0), with the reduction of fine ash particle radius, the condensation rate around fine ash particles, especially acid condensation rate, is markedly increased at ADP. And the acid condensation is easier to occur with the smaller ash particle radius. However, when the supercooling degree exceeds 30℃, the effect of ultrafine ash particles on the acid condensation of heating surface can be ignored. The amount of acid solution condensed around fine fly ash particles, which can not be caught on the heating surface, is small, and the reduction effect of the fly ash particles on the acid vapor of flue gas can be negligible. The theoretical calculation method in this paper provides a theoretical basis for the analysis of acid-ash fouling layer on the field experiments, and useful guiding significance for the safe and efficient operation of the heat exchange equipment in the coal-fired boiler.

    Control optimization of R744 duo-temperature supermarket refrigeration system with multi-ejector
    Wei CHEN, Meihong YU, Hongxia ZHAO
    2020, 71(7):  3266-3277.  doi:10.11949/0438-1157.20191076
    Abstract ( 31 )   HTML ( 3)   PDF (1489KB) ( 15 )  
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    In order to make the duo-temperature R744 supermarket refrigeration system operate at maximum efficiency in any ambient temperature, a multi-ejector circuit (including gas-gas ejector and gas-liquid ejector) is added to the R744 parallel compression refrigeration system to ensure that the system can still operate at higher efficiency in high ambient temperature, and automatically switch between parallel compression refrigeration mode and boost refrigeration with multi-ejector mode with the change of ambient temperature. The thermodynamic model of the system is established. The calculation results show that when the ambient temperature is lower than 17.32℃, the parallel compression refrigeration system mode is adopted; when the ambient temperature is higher than 17.32℃, the transcritical boost refrigeration system with multi-ejector mode is adopted. When the ambient temperature changes from 21.1℃ to 36℃, the COP of the multi-ejector refrigeration system is 15.91%—32.61% higher than that of the parallel refrigeration system.

    LB simulation of anode mass transfer characteristics in cotton thread-based microfluidic fuel cell
    Aiping MU, Dingding YE, Rong CHEN, Xun ZHU, Qiang LIAO
    2020, 71(7):  3278-3287.  doi:10.11949/0438-1157.20200019
    Abstract ( 30 )   HTML ( 3)   PDF (1873KB) ( 14 )  
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    Cotton threads are employed as flow channels in thread-based microfluidic fuel cells, which eliminates external pumps and benefits for miniaturization, showing a promising power source for portable microfluidic devices. However, the cell performance is limited by the fuel transfer at the anode. To better understand the fuel transfer characteristics coupled with electrochemical reaction at the anode, lattice Boltzmann (LB) method was used for the cotton thread-based microfluidic fuel cell. A three-dimensional numerical model of the cotton thread flow channel was developed and the distributions of velocity and concentration of fuel were calculated. The effects of inlet fuel concentration and flow rate on performance and mass transfer characteristics of anode were also discussed. The results show that LB results agree well with experimental results of the anode polarization curve. The velocity of fuel inside the cotton thread is lower than that in the gaps among threads. The fuel concentration decreases along the flow direction under different anodic over potentials and larger decrement is found at higher anodic over potentials. An increasing average current density is obtained with an increase in the inlet fuel concentration, leading to a better anode performance. Moreover, with an increase in the inlet fuel flow rate, a greater difference in the fuel concentration is observed between the location where the cotton thread contacts with reaction interface and other regions. When the inlet flow is low, the difference in concentration is small and the concentration in the rear part of the flow channel is low.

    Morphology of phosphorus and metal extraction behavior in sewage sludge during hydrothermal carbonization treatment
    Junhua FANG,Qi TANG,Yang LI,Yaoyao LI,Qiuying LYU,Zhun FAN,Jian ZHOU,Jin XU
    2020, 71(7):  3288-3295.  doi:10.11949/0438-1157.20200042
    Abstract ( 31 )   HTML ( 1)   PDF (1471KB) ( 26 )  
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    Hydrothermal carbonization (HTC) treatment of sewage sludge was conducted at different temperatures. The conventional fractionation of phosphorus in hydrochar was investigated by Hedley fractional extraction method, and to achieve a comprehensive understanding of the morphology of phosphorus-containing substances with consideration of Ca, Fe, Al. The results showed that phosphorus was mainly concentrated in the hydrochar. organophosphorus (Po) almost transformed into inorganic phosphorus (Pi), and NaOH-extractable P (NaOH-P) converted to HCl-extractable P (HCl-P) and residue state (Res-P) in the process of HTC. Ca and Fe in the sludge and hydrochar were dominantly extracted by HCl whereas Al was transformed from NaOH-soluble to HCl-soluble. Moreover, the HTC process promoted the transformation of phosphorus form aluminum phosphate (Al-P) and iron phosphate (Fe-P) to calcium phosphate (Ca-P) and magnesium phosphate (Mg-P). Finally, a theoretical simulation of P-containing minerals suggested the existence of Al2PO43+ and AlHPO4+ complex in the hydrochar. Hydroxyapatite was the main existing form of Ca-P. Part of the phosphate may be fixed by iron oxides or hydroxides. This work provides a theoretical basis for the subsequent recycling of hydrochar.

    Photo-assisted regeneration of titanium dioxide/layered double hydroxide for removal of organic dyes in water
    Jingyu HU, Rong YAO, Yuhang PAN, Chao ZHU, Shuang SONG, Yi SHEN
    2020, 71(7):  3296-3303.  doi:10.11949/0438-1157.20191579
    Abstract ( 35 )   HTML ( 3)   PDF (1590KB) ( 34 )  
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    Removal of organic dyes in water by adsorption-photocatalysis technology is one of the efficient and energy-saving methods. However, in the process of photocatalytic degradation of pollutants by carbon-based sorbents, gradual oxidation of carbon-based adsorbents occurs due to active oxygen attack. In this study, titanium dioxide/layered double hydroxide (TiO2/LDH) non-carbon-based composites are synthesized using the urea hydrolysis hydrothermal method. They not only have high adsorption capacity for organic dyes in water, but also are capable to regenerate themselves by light irradiation. Their adsorption capacity for methyl orange is 527.5 mg/g, which regenerate percentage is up to 88.6% after 4 cycles. In addition, their adsorption capacity for methylene blue is 208.3 mg/g, which regenerate percentage is up to 94.7% after 4 cycles. During the adsorption-photocatalytic regeneration process, the LDH substrate itself has strong oxidation resistance and high adsorption capacity. Moreover, LDH improves light absorption efficiency of the loading agent TiO2. It provides a feasible strategy for the removal of organic pollutants in water and optimization of adsorption-photocatalytic composite materials.

    Advanced nitrogen removal of autotrophic denitrification by integrated iron substrate biofilm reactor
    Zhifeng HU,Shihai DENG,Chao ZHANG,Desheng LI,Shuai PENG
    2020, 71(7):  3304-3312.  doi:10.11949/0438-1157.20191482
    Abstract ( 32 )   HTML ( 1)   PDF (2402KB) ( 36 )  
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    Taking wastewater treatment plant as the research object, the iron matrix biological carrier and biofilm were used to achieve efficient autotrophic denitrification. The effect of HRT on autotrophic denitrification was studied. The mechanism of denitrification was revealed through the analysis of the dynamics and microbial community structure. The results showed when HRT was 8 h, for the tail water of primary A and primary B, the average removal rate of total nitrogen (TN) were 95.41% and 92.55%, and TN loads were 0.48 kg TN/(m3·d) and 0.58 kg TN/(m3·d), which reached the standard of “The Environmental Quality Standard of Surface Water”. The saturation constants of NH4+-N in nitrification process were 1.17 mg/L and 0.72 mg/L and the saturation constants of NO3--N in denitrification process were 0.87 mg/L and 0.67 mg/L, respectively. In the system, the dominant microorganisms were Maritimimonas, Rhodobacter and Sphaerotilus. They are autotrophic denitrification bacteria, which confirmed that the iron matrix biological carrier can provide electron for autotrophic denitrification bacteria, achieving autotrophic denitrification.

    Effect of calcium phosphate monobasic on ash fusion and sintering characteristics of cornstalk
    Youjian ZHU, Xianxian ZHANG, Yiming CHEN, Xuehong WU, Haiping YANG, Hanping CHEN
    2020, 71(7):  3313-3321.  doi:10.11949/0438-1157.20191566
    Abstract ( 37 )   HTML ( 2)   PDF (2811KB) ( 24 )  
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    Agricultural straw usually contains high alkali metals, which can easily cause high temperature melting and sintering of the boiler during the combustion process and affect the normal operation of the boiler. In this work, the effect of a phosphate additive, Ca(H2PO4)·H2O (calcium phosphate monobasic, CPM), on ash sintering characteristic of a typical agricultural biomass cornstalks was investigated by using standard ash fusion measurement and ash sintering test at 700—1000℃. Meanwhile, the reaction behavior and the possible reaction products from the calcination of calcium phosphate monobasic and potassium salts at elevated temperature were investigated. The results showed that, during the heat treatment at elevated temperatures, temperature and mixing ratios of CPM and potassium salts had significant influence on reaction products. Meanwhile, when the mixture of CPM is excessive, in addition to the two reactions, there is high temperature decomposition reaction of CPM and secondary reaction between the reaction products. The reaction of CPM and potassium salts started at 300℃, with mainly Ca2P2O7, Ca(PO3)2, KCa(PO3)3 at 300—600℃ and mainly K2CaP2O7 at 700—900℃. Thermal decomposition of CPM and secondary reactions between the resultant products occurred when the P/K molar ratio was larger than 1, in addition to the reaction between CPM and K salts. In addition, it was found that K2CO3 has a higher reactivity with CPM compared to KCl. The addition of CPM in cornstalk significantly increased the ash fusion temperature and reduced the sintering degree by forming high melting phosphates mainly Ca9MgK(PO4)7 and CaKPO4. These results can provide theoretical guidance for the application of phosphorus-based additives in alleviating ash fusion and sintering issues during agricultural biomass combustion.

    Analysis on removal effect of micro-contamination of PhACs by composite modified bio-sand filter
    Yufeng XU, Ming GUO, Rang WANG, Wei XIAO, Yuanhui LIU, Simin LI
    2020, 71(7):  3322-3332.  doi:10.11949/0438-1157.20191259
    Abstract ( 19 )   HTML ( 1)   PDF (2808KB) ( 14 )  
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    Aiming at the surface characteristics and properties of quartz sand (OQS), surface morphology reconstruction and surface coating modification were performed. According to the coating modification difference, hydrophilic modified sand (IMS), hydrophobic modified sand (OMS), cationic modified sand (CMS) and amino modified sand (AMS) were prepared. The laboratory simulated secondary treatment effluent was taken as the research object, and the biological sand filtration process centering on 6 kinds of quartz sand [4 kinds of composite modified sand, surface reconstituted sand (control 1), and original sand (control 2)] was investigated. The reduction effect of carbon, nitrogen, phosphorus and sudden pharmacologically active substances (PhACs), the microbial population structure of each group of bio-sand filters was analyzed, and ecological risk assessment was performed. The results show that the removal rate of conventional pollutants by various processes is between 24.22%—90.35%, and the removal effect of CM-BSF on conventional pollutants is the best; 6 types of biological sand filtration processes remove 12 types in 5 categories of PhACs. The rate is between 7.9%—50.3%, and the removal effect of CM-BSF by modified sand filtration process is better. High-throughput testing shows that the microbial species in each group are highly similar, but the abundance is different. Generally speaking, it has PhACs degradation ability. The abundance of the functional bacteria in the composite modified quartz sand-covered biological samples is relatively high. According to the analysis of the ecological risk assessment method, the ecological risk of effluent from the CM-BSF process is the lowest.

    New measurement methods for wax appearance temperature of petroleum fluids using NIRS and RI techniques
    Si LI, Kaifeng FAN, Qiyu HUANG
    2020, 71(7):  3333-3344.  doi:10.11949/0438-1157.20191524
    Abstract ( 22 )   HTML ( 1)   PDF (2267KB) ( 20 )  
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    Wax appearance temperature (WAT) is an important parameter of petroleum fluids. Obtaining accurate wax appearance temperature is a prerequisite for ensuring the safe transportation of waxy crude oil pipelines. New measurement methods were proposed in this study, including temperature scanning method using near infrared spectroscopy (NIRS) and refractive index (RI) method. Furthermore, wavelength scanning method using NIRS was improved in its testing and data analysis process. In addition, these methods were compared with two commonly used ones, polarizing microscopy (PM) and differential scanning calorimetry (DSC). The results showed that reliable WAT results could be obtained by NIRS and RI methods with high sensitivity and stability. The measurement results were less susceptible to the simple testing and analysis process, especially suitable for volatile samples. Moreover, the stirring in the testing process of NIRS methods effectively reduced the influence of supercooling degree, while it was still different from the flowing condition in real pipelines.

    Material science and engineering, nanotechnology
    Permeation properties and regeneration of a ZSM-5 zeolite membrane for bio-oil dehydration
    Shanhong MA, Feng YE, Yanhong WANG, Xuemei LANG, Shuanshi FAN, Gang LI
    2020, 71(7):  3345-3353.  doi:10.11949/0438-1157.20200143
    Abstract ( 52 )   HTML ( 8)   PDF (1617KB) ( 63 )  
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    A ZSM-5 zeolite membrane was hydrothermally synthesized using a template-free method for bio-oil pervaporation dehydration. The ZSM-5 zeolite membrane showed both excellent chemical stability and selectivity in the highly acidic and multi-component bio-oil system. However, the membrane encountered serious membrane fouling in bio-oil during pervaporation, which resulted in a significant loss in the permeation flux. The membrane regeneration test showed that the permeation flux increased with increasing the regeneration temperature, and the value could be recovered to 88% of the original flux of the fresh ZMS-5 membrane after the membrane was regenerated at 220℃. The membrane regeneration mechanism showed that the intracrystalline pores of the ZSM-5 zeolite membrane were easily fouled in the bio-oil system, which was responsible for the rapid decrease of the permeation flux; while the intercrystalline pores with a relatively larger pore size were difficult to be completely blocked, thus the intercrystalline pores functioned as the main channels for water permeation through the fouled ZSM-5 zeolite membrane. The above results indicate that the bio-oil pervaporation, dehydration performance of a ZSM-5 zeolite membrane can be effectively improved by properly adjusting the number and size of intercrystalline pores of ZSM-5 zeolite membranes.

    Preparation and thermal storage performance of novel composite sorbent with activated alumina matrix
    Hua LIU, Jiajie PENG, Kai YU, Yi NI, Fang WANG, Quanwen PAN, Tianshu GE, Ruzhu WANG
    2020, 71(7):  3354-3361.  doi:10.11949/0438-1157.20191537
    Abstract ( 48 )   HTML ( 5)   PDF (1738KB) ( 50 )  
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    A new type of composite adsorbent based on activated alumina(AA) and CaCl2 as a hygroscopic salt was developed. It can be used in thermochemical adsorption heat storage systems with water as the adsorbent, and its internal structure, adsorption performance and heat storage performance were studied. Samples with different salt contents were fabricated to store low-temperature thermal heat by impregnation methods. Morphologies records, sorption kinetics and thermal energy storage performance of AA/CaCl2 composite sorbent were investigated. The maximum salt content of the solution leakage phenomenon was determined. Sorption kinetics and equilibrium sorption capacity under conditions of 30℃ and multi relative humidity were studied by utilizing constant temperature and humidity chamber. Influence of salt content and relative humidity on the sorption performance of AA/CaCl2 composite sorbent was studied. Results showed sorption capacity of AA/CaCl2 composite sorbent increased with increasing salt content and relative humidity. The specific surface area and pore volume were measured by automatic specific surface area and porosity analyzer. Energy storage density was measured by simultaneous thermal analyzer. The sample with highest salt content had the best energy storage performance with 0.51 kW·h/kg mass energy storage density and 610.2 kW·h/m3 volumetric energy storage density. As a consequence, AA/CaCl2 composite sorbent is promising sorbent in field of chemisorption thermal energy storage.

    Experimental study on melting performance of paraffin and paraffin/expanded graphite
    Zhenghao LIU, Xiaosong ZHANG, Changling WANG, Muxing ZHANG
    2020, 71(7):  3362-3371.  doi:10.11949/0438-1157.20191527
    Abstract ( 38 )   HTML ( 3)   PDF (1367KB) ( 22 )  
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    To improve the melting performance of paraffin (PA) during the phase change energy storage process, a small amount of expanded graphite (EG) was added to the PA to prepare four kinds of paraffin/expanded graphite composite phase change materials (PA-EG). The PA-EG with suitable proportion was screened out by thermophysics analysis, with melting process of PA-EG and PA in the horizontal shell and tube latent heat thermal energy storage unit being experimentally studied. Based on the changes in the temperature field of the phase change material and the weighted melting fractions calculated, the melting performance between PA and PA-EG was compared. Also, the effect of the heating temperature on the melting performance was explored. The results indicated that the thermal conductivity of PA-EG3 was 7 times higher than that of PA, while the phase transition temperature and latent heat remained relatively identical. The natural convection effect of PA-EG3 during melting was weaker than that of PA. However, higher thermal conductivity resulted from added EG could significantly improve the melting of middle and lower parts in the latent heat thermal energy storage unit, making its overall melting rate higher than that of pure PA. When the heating temperature was 80℃, the melting process of PA-EG3 is 78.16% shorter than that of PA. In addition, reduced heating temperature can significantly increase the complete melting time of PA and PA-EG3, with smaller increment for PA-EG3 under the same condition.

    Process safety
    Failure analysis of weak connection structure of vaulted oil tank under fire condition
    Yu LI, Chunming XU, Shuai HAN, Hongye LI
    2020, 71(7):  3372-3378.  doi:10.11949/0438-1157.20200030
    Abstract ( 38 )   HTML ( 4)   PDF (1154KB) ( 91 )  
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    The vaulted oil tank fails to explode after being roasted by external flames, which may cause serious casualties and huge economic losses. To warn the failure and explosion of vaulted oil tank under fire condition, through the high temperature material mechanical performance experiment platform, the weak connection structure of the vaulted oil tank is tested for destruction. The breaking force and stress values of weak connection structure failure under different fire temperature conditions are obtained. The results show that when the temperature is higher than 300℃, the values of pulling force and failure stress change significantly, of which 450℃ is the peak temperature. Furthermore, the failure pressure of 1 m3 vaulted oil tank under different temperature conditions was tested by establishing failure test platform for small-sized vaulted oil tank. The comparison between the calculated and experimental results shows the accuracy of the failure pressure of 1 m3 vaulted oil tank. On this basis, the failure pressure calculation model of vaulted oil tank was constructed, and the failure pressure of vaulted oil tank with different volume under different fire temperature was deduced. The results can be used as the criterion for the failure of vaulted oil tank to provide data support for the explosion warning for vaulted oil tank.

    Effect ofinitial fuel temperature on burning characteristics of transformer oil
    Jinlong ZHAO, Jie YUAN, Fengshi TIAN, Hong HUANG, Rui YANG
    2020, 71(7):  3379-3386.  doi:10.11949/0438-1157.20200122
    Abstract ( 33 )   HTML ( 4)   PDF (1842KB) ( 15 )  
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    To study the influence of the initial fuel temperature of the transformer oil on the combustion characteristics, an oil pool fire combustion test platform was set up, and pool fire experiments with different initial fuel temperatures and different oil pool diameters were conducted. The whole burning process, burning rate and boiling layer thickness were measured and discussed with the variation of initial fuel temperature. The results show that the whole burning process can be divided into three stages: (1) initial development stage; (2) steady burning stage; (3) extinguishment. The burning rate shows an increasing trend with the increase of initial fuel temperature at the initial development stage. This is because the heat used to increase the fuel temperature will decrease with the increase of initial temperature. At the steady burning stage, although the burning rate will increase with the initial fuel temperature increasing, the increasing rate is slow and can be nearly neglected. In the experiments, the burning rate is increasing obviously with the increase of burning size. In addition, the boiling layer thickness is around 2.17 mm, independent of the initial fuel temperature at the steady burning, except the tests with a diameter of 20 cm. Therefore, it is necessary to improve the fire extinguishing efficiency to respond the initial fire development and build some barriers to avoid the leakage fuel spread.

    Study on fire extinguishing efficiency of the mixtures of C6F12O and (C2F5)3N
    Tianshui LIANG,Dezhi LIU,Yongjin WANG,Wei ZHONG,Jun ZHAO
    2020, 71(7):  3387-3392.  doi:10.11949/0438-1157.20191526
    Abstract ( 44 )   HTML ( 4)   PDF (1039KB) ( 41 )  
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    C6F12O is one of halon alternatives for fire extinguishing. However, researchers found that C6F12O has a combustion enhancement phenomenon at its low concentrations. The defect may bring some harms in the process of firefighting, and may limit its application in some scenario. To suppress the combustion enhancement effect of C6F12O, this article adopts the method of mixed gas and introduces perfluorotriethylamine (C2F5)3N as a cooperative fire extinguishing agent with C6F12O. Firstly, the cupburner experiment was used to obtain the flame height and flame width at different concentrations of C6F12O, and the minimum extinguishing concentration (MEC) of C6F12O was obtained as well. The flame height and flame width were used as the criterion for the combustion enhancement phenomenon. The results show that the most obvious enhancement is observed at the concentration of around 3.00% (volume fraction, the same below); and the MEC of C6F12O is about 5.80%. Secondly, the experiment on the effect of (C2F5)3N in suppressing the combustion enhancement was conducted. In this test, the volume fraction of C6F12O was maintained at 3.00%; then (C2F5)3N was added and gradually increased. The MEC of the mixture, the flame height and the flame pulsation frequency were obtained. The results show that (C2F5)3N has the ability to inhibit the combustion enhancement, that the MEC of (C2F5)3N is about 4.86%.In the mixed fire extinguishing gas of perfluorohexanone and perfluorotriethylamine, after the volume fraction of perfluorotriethylamine exceeds 10.00%, perfluorohexanone and perfluorotriethylamine have a better synergistic fire extinguishing effect.