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Table of Content
05 May 2020, Volume 71 Issue 5
    Reviews and monographs
    State of the art of flow field plates of proton exchange membrane fuel cells
    Qiang ZHAO, Hang GUO, Fang YE, Chongfang MA
    2020, 71(5):  1943-1963.  doi:10.11949/0438-1157.20191302
    Abstract ( 327 )   HTML ( 56)   PDF (967KB) ( 268 )  
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    The flow field plate is one of the core components of a proton exchange membrane fuel cell, and its structure directly affects the utilization efficiency of the reaction gas and the drainage and heat dissipation performance of the fuel cell. The design and research progress of flow field plates for proton exchange membrane fuel cells in the past decade have been reviewed. The design and optimization of flow channel sizes, flow channel cross sections, inlet distributors and flow channel arrangements improve fuel cell thermal and water managements, and electricity performance based on parallel, serpentine, interdigital and spot flow field. Various forms of combined flow field can combine the advantages of different flow fields. Multi-level fractal bionic flow field can optimize the reactants, current density and pressure distribution. Three-dimensional refined flow fields can reduce concentration polarization by improving the gas supply.

    Recent progress in microbial production of succinic acid
    Yao ZHANG, Xiaoman QIU, Chengpeng CHEN, Zhuoran YU, Housheng HONG
    2020, 71(5):  1964-1975.  doi:10.11949/0438-1157.20191430
    Abstract ( 181 )   HTML ( 33)   PDF (712KB) ( 125 )  
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    Succinic acid is considered to be a promising bio-based platform compound due to its potential value in the chemical industry for its C4 molecular structure. This article comprehensively analyzed the domestic and foreign scholars research status of succinic acid in three aspects which were production strains and strain transformation, biological process optimization and separation process of succinic acid. It emphatically introduced the main production strains and their modification strategies, such as Escherichia coli, Actinobacillus succinogenes and Yarrowia lipolytica. It included the biological process optimization programs such as low biomass utilization, two stages and low pH fermentation strategy and CO2 supply and pH regulation during fermentation. And it also included the separation process of succinic acid such as calcium salt method, electrodialysis method and direct separation method. At the same time, it pointed out that the emphasis of the future research will be to comprehensively consider the economic and energy consumption issues, integrate the whole process of strain fermentation and separation, increase the yield of succinic acid, reduce the cost of fermentation and separation and then to further expand the market of bio-based succinic acid.

    Fluid dynamics and transport phenomena
    Pore network simulation of transport properties in grooved gas diffusion layer of PEMFC
    Fangju LI, Wei WU, Shuangfeng WANG
    2020, 71(5):  1976-1985.  doi:10.11949/0438-1157.20191438
    Abstract ( 74 )   HTML ( 10)   PDF (1549KB) ( 45 )  
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    Three-dimensional pore network model was performed to investigate water and oxygen transport in gas diffusion layer (GDL) with groove. The capillary pressure at breakthrough, the capillary pressure curve, the oxygen effective diffusivity and the relative permeability as a function of liquid saturation were calculated. Moreover, the mechanism of groove was explored from the perspective of pore level. The results indicate that groove changes the capillary pressure distribution of the gas diffusion layer, provides a direct transport path for liquid water and optimizes the gas-liquid distribution in GDL, thereby improving the oxygen effective diffusivity. The position of groove has a significant influence on oxygen diffusion, the influence on liquid transport depends on whether a liquid transport path through GDL is formed. Additionally, the oxygen and water transport enhances with the groove deepen, especially the optimal transmission performance is obtained when the groove penetrates the gas diffusion layer. With increase of the width of groove, while liquid relative permeability improves, oxygen effective diffusivity increases first and then decreases at low water saturation. Based on various factors, the groove parameters are given when the oxygen and liquid water transmission performance is optimal.

    Numerical model of dust particle deposition process on surface of fin-and-tube heat exchanger under wet conditions
    Feilong ZHAN, Guoliang DING, Dawei ZHUANG, Hao ZHANG, Tao WU, Xiangyang YE
    2020, 71(5):  1986-1994.  doi:10.11949/0438-1157.20191435
    Abstract ( 87 )   HTML ( 14)   PDF (1216KB) ( 82 )  
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    The air conditioner uses a finned tube heat exchanger as the evaporator. Under the cooling condition, the dehumidification and dust deposition on the surface of the heat exchanger cause performance degradation. The purpose of this study is to develop a wet particle deposition model for predicting the particle-capturing by condensate water and the particle adhesion on wet particulate layer. The number of particles captured by condensate water is the number of incident particles whose trajectories intersect with the water surface. During the impact between subsequent incident particles and wet particulate layer, some incident particles may stick on the wet particulate layer while some deposited wet particles may remove from it, and the number of particles adhered on wet particulate layer equals to the number of stuck particles minus the number of removed particles. The validation results show that, the predicted shape of wet particulate layer agrees well with the experimental images, and the predicted mass of deposited particles agrees with 91% of the experimental data within a deviation of ±20% and the mean deviation is 11.8%.

    Mechanical design and hydraulics simulation of a new complex internal heat integrated distillation column
    Hong LIU, Yajing ZHAO, Yingdong LI, Pingli LI
    2020, 71(5):  1995-2003.  doi:10.11949/0438-1157.20191300
    Abstract ( 87 )   HTML ( 9)   PDF (1680KB) ( 78 )  
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    In this paper, based on the theory of HIDiC and the results of Aspen simulation, a new type of internal energy integration distillation structure was established, CFD simulation was conducted for the composite HIDiC with structures of sieve hole type, hydraulics properties under different parameters were explored, and the HIDiC structure was optimized. The results show that reducing the hole of the tray and the height of the exit weir can improve the effect of mass transfer and heat transfer. SolidWorks software was used to conduct static stress analysis on the dual effects of temperature and pressure. Through HIDiC theory, model construction, and mutual verification of hydraulic simulation, the theory of HIDiC heat transfer from plate to plate was perfectly combined with the actual model.

    Data-driven image reconstruction of electrical capacitance tomography based on convolutional neural network
    Xianliang SUN, Jian LI, Zhezhe HAN, Chuanlong XU
    2020, 71(5):  2004-2016.  doi:10.11949/0438-1157.20200021
    Abstract ( 84 )   HTML ( 5)   PDF (3807KB) ( 63 )  
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    A data-driven image reconstruction method based on convolutional neural networks is proposed for electrical capacitance tomography(ECT). According to the characteristics of the flow patterns of gas-solid two-phase flow, 60000 sets of particle distribution images are randomly generated by numerical simulation and the corresponding capacitance vectors are calculated by the finite element method, thereby creating a “capacitance vector - particle distribution” dataset. Then a convolutional neural network model is developed to learn and train the training dataset. The training result is verified and evaluated with the testing dataset. Further, static experiments and fluidized bed measurement experiments are performed on the ECT image reconstruction with the obtained convolutional neural network model. Simulation and experimental results show that the established convolutional neural network can well reconstruct ECT images and can be directly used for particle concentration distribution measurement in a fluidized bed.

    Effect of Cu content on phase change thermal storage properties of Al-Cu-Si alloy
    Yan SHI, Junwen ZHAO, Yanping YUAN, Guangze DAI, Jing HAN
    2020, 71(5):  2017-2023.  doi:10.11949/0438-1157.20191553
    Abstract ( 66 )   HTML ( 7)   PDF (580KB) ( 37 )  
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    With the advantages of low cost, high phase change latent heat, and high oxidation resistance, Al-Cu-Si alloy phase change materials (PCMs) are considered as one of the most promising solar energy storage materials. The content of Cu has an important effect on its heat storage performance, especially the volume latent heat. However, to the knowledge of the authors, no previous study has been reported. In this work, we studied the relationships between the Cu content and phase change temperature, mass latent heat, volume latent heat of Al-Cu-Si alloy, as well as the evolution of specific heat, thermal diffusivity, and thermal conductivity vs. the temperature, respectively, according to the differential scanning calorimetry and laser thermal conductivity analyzer. The results showed that for the Al-Cu-Si alloy with 35%—55%Cu, the phase change temperature of Al-Cu-Si alloy is 512.5—604.2℃, the mass latent heat is 354.4—458.1 J?g-1, and the volume latent heat is 1524.1—1763.8 J?cm-3. Meanwhile, both the mass latent heat and the volume latent heat showed a “bimodal” trend with the increase of Cu content. When the Cu content is 42%, the highest mass latent heat is 458.1 J?g-1, while the highest volume latent heat is 1763.8 J?cm-3, corresponding to 48%Cu content. Furthermore, with the increase of Cu content, the thermal conductivity of Al-Cu-Si alloy decreased in the range of 91.4 —137.5 W?m-1?K-1 at 500°C. Comperehensive research shows that Al-Cu-Si alloy has high application value on the field of solar thermal storage.

    Simulation and analysis of mass transfer and absorption process intensification by villi movement
    Xiaolan HUA, Yanan ZHANG, Zhizhong DONG, Yong WANG, Xiao Dong CHEN, Jie XIAO
    2020, 71(5):  2024-2034.  doi:10.11949/0438-1157.20191101
    Abstract ( 75 )   HTML ( 6)   PDF (1749KB) ( 52 )  
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    The inner wall of the digestive organ has a multi-level and multi-scale structure and complex movement patterns. Understanding its role in the process of digestion and absorption is of great significance to human health. From a chemical engineer s unique perspective, this work developed a multi-physics computational fluid dynamics (CFD) model to describe nutrient transfer and absorption in the small intestine driven by villi movement. The moving mesh method was successfully implemented to realize the cyclic back-and-forth movement of villi. Furthermore, data analysis methods were developed to quantify mass transfer and absorption performance. Numerical simulation results show that the back and forth movement of villi along the axial direction can generate two characteristic vortexes. The formation of vortexes can effectively reduce mass transfer resistance in the radial direction. The top part of villi plays critical role in nutrient absorption. A shorter movement cycle offers a higher villi velocity, which results in a higher value of the maximum enhancement factor and hence a higher absorption amount. The case with taller villi demonstrates higher mass-transfer enhancement factor. At the same time, taller villi offer larger absorption area. These two positive factors together contribute to a much higher absorption amount as compared with the case with shorter villi. In this specific study, the case with 900 μm high villi and a movement cycle of 6 s, the mass transfer performance can be improved by over 500% as compared to the case without villi movement (i.e., a mass-transfer enhancement factor reaching 6).

    Study on influence of inclination of coils on melting process of waxy crude oil in a floating roof tank
    Min WANG, Qianqian SHAO, Xiaofan YANG, Jingfa LI
    2020, 71(5):  2035-2048.  doi:10.11949/0438-1157.20191431
    Abstract ( 53 )   HTML ( 2)   PDF (5456KB) ( 19 )  
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    Heating by coils are the most common used way for heating and melting waxy crude oil in a floating roof tank. And optimizing the layout of coils in the tank helps to improve the melting efficiency and reduce production cost. For this purpose, deep investigation on the temperature increase and melting processes of waxy crude oil by coil heating is necessary. This research establishes a physical and mathematical model describing the processes based on a comprehensive consideration of structure and rheological changes of the oil as well as the influence of turbulent flow during melting. Considering the irregularity of the oil domain and the regularity of other parts of the tank, immersed boundary method is employed to realize integrated calculation on structured grids over the whole computational domain. Results in literatures are used for model validation. Then the temperature increase and melting processes of waxy crude oil are simulated under three projects of coil layout. Taking an actual 1000 m3 floating roof oil tank as an example, the melting law of waxy crude oil in the tank is studied, and the influence of the inclination angle on the melting process is analyzed.

    Study on dynamic and static performance of external tubular molten salt receiver
    Mei XU, Huaiwu PENG, Dongsheng NIU, Xiao WANG, Bin XIAO, Zhi ZHOU, Yanglong DUAN, Junfeng ZHANG
    2020, 71(5):  2049-2060.  doi:10.11949/0438-1157.20191351
    Abstract ( 69 )   HTML ( 3)   PDF (3038KB) ( 26 )  
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    A 50 MW external tubular molten salt receiver model is developed for simulating the dynamic and static performance of the receiver in ideal conditions and actual meteorological conditions. The response curve is given to show that the maximum surface temperature, temperature gradient, and heat dissipation power of the receiver are basically proportional to the changes in direct normal irradiance (abbreviated as DNI); the efficiency grows with increase in direct normal irradiance, and the slope, however, decreases; wind speed mainly affects convection heat dissipation power; in the presence of direct normal irradiance step disturbance, the response time of the molten salt outlet temperature, the maximum surface temperature and the heat dissipation power of the receiver is longer than that of the receiver tube axial temperature gradient, and gradually the efficiency returns approximately to the level before a sudden change; flow step down have a greater impact on the receiver performance. Using the quantitative relationship between the characteristic parameters of the heat sink and the direct solar irradiance and molten salt flux can improve the molten salt flux adjustment strategy in operation.

    Pool boiling heat transfer characteristics of CeO2/deionized water nanofluids
    Zhongmin LANG, Gangqiang WU, Wenxiu HE, Xiaoxing HAN, Yanmeng GOU, Shuangying LI
    2020, 71(5):  2061-2068.  doi:10.11949/0438-1157.20191411
    Abstract ( 44 )   HTML ( 5)   PDF (1393KB) ( 22 )  
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    Pool boiling heat transfer characteristics of CeO2 nanofluids on the smooth surface were conducted at the atmospheric pressure. The pool boiling heat transfer performance of boiling heat transfer coefficient (HTC) as a function of heat flux and mass fraction of CeO2/water-based nanofluids have been measured and discussed. In addition, the thermal conductivities, static contact angle of different concentrations of CeO2 were determined. The surface deposition of different concentrations of CeO2 nanofluids after boiling was observed, and the contact angle of deionized water on the deposition surface was measured. From the pool boiling experimental results, it was indicated that CeO2 nanofluids enhanced the boiling HTC. The optimal mass fraction of nanofluids is 0.05%, and the boiling heat transfer coefficient is 36% higher than that of deionized water. The thermal conductivity and the static contact angle increase with the increase of the mass fraction of the nanofluids. In the experimental range, the thermal conductivity increases by 1% at the maximum, while the contact angle of the nanofluid increases from 50.5° to 92.9°. The surface deposition phenomenon increases with the mass fraction of nanofluids, and the contact angle of deionized water on the deposition surface changes greatly (51.4°~134.4°). The influence of the thermal conductivity of the nanofluid can be negligible. The contact angle and the particle deposition on the boiling surface have a greater effect on the enhanced heat transfer of the nanofluid.

    Effect of releasing dissolved gas from water though decompression on flow stability of water facility
    Yuhao LIU, Ying XU, Tao ZHANG, Qinghua FENG, Fengfeng QI
    2020, 71(5):  2069-2075.  doi:10.11949/0438-1157.20191455
    Abstract ( 64 )   HTML ( 5)   PDF (613KB) ( 37 )  
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    The effect of dissolved gas in water on the flow stability and measurement accuracy are analyzed for water flow, and a microbubble exhaust valve was installed for comparison experiments. The theoretical analysis and experimental tests show that the dissolved gas in water will separate and precipitate due to the pressure difference between the front and rear ends after undergoing the decompression process, and then form free tiny bubbles, which will affect the flow stability and measurement accuracy of the water-flow calibrated facility. When water flows through the microbubble exhaust valve, it can capture the tiny bubbles separated from the water, thus improving the flow stability and measurement accuracy of the water flow device. The microbubble exhaust valve can make the flow stability reach the level of 0.1%-0.2%, and put forward a new influence factor for the design of water flow standard device and the study of flow stability.

    Catalysis, kinetics and reactors
    Brönsted equation kinetic modeling for quantitative relationship between activity and acidity strength distribution in oligomerization and aromatization of ethylene over ZSM-5 catalyst
    Fang JIN,Peng ZHANG,Guiying WU,Di WU
    2020, 71(5):  2076-2087.  doi:10.11949/0438-1157.20191536
    Abstract ( 66 )   HTML ( 6)   PDF (1701KB) ( 45 )  
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    Ethylene catalyzed oligomerization and aromatization are the key processes for the high value of olefins and the synthesis of liquid fuels. The desorption activation energy of the probe molecule calculated in NH3-TPD was used as a parameter of the acid site intensity distribution of the catalyst, which correlate the information of the acid intensity distribution with the acid-catalyzed reaction activity. According to the linear free energy theory, the Br?nsted equation theory was further developed as the reaction kinetic model for establishing quantitative relationships between different acid strength sites and hydrogen transfer, oligomerization, and aromatization elementary steps corresponding to alkane,light olefins and aromatic products in the oligomerization and aromatization of ethylene on the ZSM-5 catalyst with the different Si/Al molar ratios. Both the elementary steps of hydrocarbon conversion and the basic probe molecule adsorption/desorption on acid sites follow the carbocation mechanism. Therefore, the desorption activation energy is related to the reaction activation energy based on the linear free energy by introducing γ as the kinetic parameter of reaction sensitivity to the acid strength of catalyst, which has a definite physical meaning in catalytic reaction kinetic modeling. The analysis of γ of different acid strength sites can conclude that acid sites with different strengths have different coefficients of action on ethylene oligomerization and aromatization. The acid site with ammonia desorption activation energy (DAE) of 90 kJ·mol-1 is the main active site for hydrogen transfer reaction, while the main active acid site for ethylene oligomerization is DAE 90 kJ·mol-1 and 124 kJ·mol-1.The acid site with DAE of 150 kJ·mol-1 is the main active site for the aromatization reaction.

    Separation engineering
    PSA simulation and adsorption separation of CH4-N2 by self-supporting pellets Silicalite-1
    Hua SHANG, Honghao BAI, Jiaqi LIU, Jiangfeng YANG, Jinping LI
    2020, 71(5):  2088-2098.  doi:10.11949/0438-1157.20191357
    Abstract ( 71 )   HTML ( 4)   PDF (1410KB) ( 69 )  
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    Pure-silica zeolite Silicalite-1 powder was pressed at 6 MPa pressure to form self-supporting pellets. By characterization of powder X-ray diffraction and 77 K nitrogen adsorption-desorption, there was no change in crystalline and specific surface area after pelletization. Single component adsorption equilibrium isotherm of CH4 and N2 on the self-supporting pellets Silicalite-1 at 273/298/313 K were measured by static gravimetric method. Selectivity of CH4/N2 mixtures on the adsorbent were calculated from Ideal Adsorbed Solution Theory (IAST). Separation effects of CH4/N2 mixtures on the adsorbent were investigated by dynamic mixtures breakthrough experiments, which show it is more suitable for enrichment and nitrogen removal from low concentration coal-bed methane. Separation and enrichment of methane from low concentration coal-bed methane by pressure swing adsorption (PSA) on the particle-shaped Silicalite-1 were predicted using total mass-transfer model by numerical simulation based on abovementioned data. The simulation results show that once the 20% / 80% CH4 / N2 mixture is concentrated, the CH4 concentration can be increased to 37%—41%, and the recovery rate can be 60%—92%; 30%/70% CH4/N2 mixture is once concentration, CH4 concentration can be increased to 50%—53%, and the recovery rate is 58%—92%.

    Investigation on separation of CO2 from biogas by hydrate method in impinging stream reactor
    Shuqi FANG, Xinyue ZHANG, Siqi LI, Donghao BAI, Jing BAI
    2020, 71(5):  2099-2108.  doi:10.11949/0438-1157.20191432
    Abstract ( 53 )   HTML ( 5)   PDF (919KB) ( 37 )  
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    The characteristics of CO2 separation in biogas by hydrate method in impinging flow reactor were investigated experimentally. Two different systems, pure water and sodium dodecyl sulfate (SDS), were selected to investigate the effects of pressure, temperature and impact intensity during hydrate formation process. The experimental results showed that the increase of pressure in pure water system or SDS system was conducive to the rapid formation of hydrate, but not conducive to the CO2 capture. By changing the impact intensity of the impinging stream reactor, it was found that the CO2 separation factor (S.F.) reached the maximum in both systems when the impact intensity was 0.128, the maximum value of S.F were 138.9 and 64.5, respectively.The experimental results showed that the additive SDS could promote the formation of hydrate, and the optimal concentration was 600 mg/L when the gas consumption,CO2 recovery S.Fr.(CO2) and CH4 recoveryS.Fr.(CH4) reached the maximum. However, the promotion effect of SDS on CH4 hydrate formation process was greater than that of CO2 hydrate, which was not conducive to the CO2 separation from biogas, but the separation factor of CO2 would be reduced.

    Preparation of amino modified styrene-divinylbenzene resin and its adsorption of rhenium
    Yu ZHANG, Rong HUA, Xiaokang KOU, Fuping LIU, Jie KONG, Feng ZHANG, Feifan HE, Yu FENG
    2020, 71(5):  2109-2117.  doi:10.11949/0438-1157.20191459
    Abstract ( 50 )   HTML ( 2)   PDF (2946KB) ( 38 )  
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    The ion exchange method is widely used in the hydrometallurgical industry because it is suitable for the separation and enrichment of low-concentration substances. The synthesis and application of new high-efficiency adsorption materials have become the development trend in this field. In view of the current situation that the associated scarce rhenium minerals in uranium mine need to recover synchronously, the preparation of amino modified styrene-divinylbenzene resin (LSC-Re) was used to recover rhenium in this work. The effect of aqueous acidity, initial concentration, adsorption time and adsorption temperature on the adsorption performance were systematically investigated by static and dynamic adsorption desorption experiments. The results show that 6 h is sufficient up to equilibrium for the LSC-Re anion exchange resin at room temperature, and the acidity has little effect on the adsorption. The LSC-Re anion exchange resin exhibited higher affinity toward Re (Ⅳ) than U(Ⅵ) at pH 1.5, the maximum value of separation factor βRe(Ⅳ)/U(Ⅵ) is 41.68. The saturated adsorption capacity of resins could reach 129.3 mg·g-1 at present conditions. The adsorption mechanism is in accordance with Langmuir adsorption isotherm model and quasi-second-order kinetic model, and the adsorption process is a spontaneous endothermic from the perspective of thermodynamics and kinetics. The dynamic saturated adsorption capacity could reach 76.17 g·L-1 and the saturation ratio could reach 2.35 by controlling the solution flow rate to 0.5 ml·min-1 in the dynamic adsorption experiment. The 8 resin bed volumes can be desorbed completely by 1 mol·L-1 NH3·H2O, the enrichment factor is close to 70 times, which means that the LSC-Re anion exchange resin has good industrial application prospects in recovery Re (Ⅳ).

    Process system engineering
    Improved equation oriented inside-out method of complex crude distillation column simulation
    Guangjie LIU, Xiaoyan SUN, Rongshan BI, Jianping WANG, Shuguang XIANG
    2020, 71(5):  2118-2127.  doi:10.11949/0438-1157.20191403
    Abstract ( 59 )   HTML ( 2)   PDF (922KB) ( 52 )  
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    Based on inside-out method, adopting the equation oriented idea, main tower and strippers were regarded as a whole for modeling. Algorithm improvement according to the characteristics of complex crude distillation tower was also conducted. Due to the simplified K model of traditional inside-out method is insensitive to the variation of component, when dealt with the system involving petroleum fraction ,it is prone to cause more iterations even abnormal temperature update in partial stages. Thus, the weighting factors for simplified K model by vapor sum rate equation were employed. Moreover, the product flow of strippers were viewed as design variables, taking example by the sum rate method to update the rate of flow, which enabled the algorithm easier to convergent. In order to verify the effective of the improved model, an atmospheric tower have been simulated when used different methods. The results show that the improved algorithm is suitable for simulation calculation of complex refinery towers.

    Research on semi-supervised heterogeneous adaptive co-training soft-sensor model
    Dong LI, Daoping HUANG, Yiqi LIU
    2020, 71(5):  2128-2138.  doi:10.11949/0438-1157.20191378
    Abstract ( 40 )   HTML ( 5)   PDF (1709KB) ( 39 )  
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    Soft-sensing technology is widely applied to the prediction of important and difficult to measure variables online in industrial processes. However, due to the complexity of industrial processes, non-linearity and high costs to acquire data, the ratio of input and output variables data required for modeling is seriously unbalanced. Therefore, depending on the existing co-training model, this paper combines the co-training algorithm with the back propagation neural network (BP) algorithm to propose a co-training BP model for nonlinear problems. However, due to the time variability and uncertainty of the application process, as well as the negative influences of external environment, and so on, the data exhibit mutation, delay and high volatility, even the prediction performance of the model deteriorated. Thus, this paper proposed a semi-supervised heterogeneous adaptive co-training RPLS-RBP model. On the one hand, the model used odd-even grouping to equalize two parts of the labeled data. On the other hand, RPLS and RBP are used simultaneously for modeling and the prediction on labeled data. To demonstrate the prediction performance of the model, the proposed model is verified by a simulation benchmark platform (Benchmark Simulation Model-1) and a real sewage treatment plant (UCI database). The results show that the proposed model achieved better prediction performance.

    Control strategy and simulation research of water-cooled PEMFC thermal management system
    Hongbo ZHAO, Jie LIU, Biao MA, Qiang GUO, Xiaohui LIU, Fengwen PAN
    2020, 71(5):  2139-2150.  doi:10.11949/0438-1157.20191257
    Abstract ( 95 )   HTML ( 6)   PDF (2101KB) ( 82 )  
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    In order to solve the problems of large temperature fluctuation, long regulation time and slow response speed in the current fuel cell thermal management system, this paper proposes two thermal management control strategies: flow following current and power mode and neural network auto disturbance rejection method. The results show that the flow following current and power control strategy can effectively reduce the coupling effect of water pump and radiator fan, and significantly reduce the overshoot and regulation time of the temperature and the temperature difference of the cooling water at the inlet and outlet of the stack. In addition, although the neural network auto-disturbance control strategy has a poor control effect at the maximum power condition, the overall control effect is better than the flow following current control strategy.

    New fault detection and diagnosis strategy for nonlinear industrial process based on KECA
    Mingyue DENG, Jianchang LIU, Peng XU, Shubin TAN, Liangliang SHANG
    2020, 71(5):  2151-2163.  doi:10.11949/0438-1157.20191518
    Abstract ( 40 )   HTML ( 4)   PDF (1897KB) ( 43 )  
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    A new method for non-linear process fault detection and diagnosis based on kernel entropy component analysis (KECA) is proposed. Firstly, the score vectors and nonlinear feature space are obtained using KECA. Since KECA can reveal the underlying cluster structure in the data in the form of the angular structure, an angle-based monitoring index referred to as vector of angle (VoA) is designed. This index measures the structural difference between the transformed data by the angle variance of each score vector, and realizes fault detection according to the change. Then, in order to effectively identify faults after detection, KECA similarity factor is constructed to measure the similarity of feature space to identify fault patterns. Finally, the feasibility and validity of the proposed method are demonstrated by the nonlinear numerical case and Tennessee Eastman (TE) process.

    Techno-economic analysis of oil and coal to ethylene glycol processes
    Qing YANG, Simin XU, Dawei ZHANG, Qingchun YANG
    2020, 71(5):  2164-2172.  doi:10.11949/0438-1157.20191195
    Abstract ( 101 )   HTML ( 4)   PDF (2543KB) ( 91 )  
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    The traditional oil to ethylene glycol (OtEG) route is heavily dependent on petroleum resources and has high production costs, and China has abundant coal resources, which makes coal to ethylene glycol (CtEG) technology increasingly valued. Based on the simulation results, a detailed technical and economic analysis of the OtEG and CtEG routes was performed. The results show that the unit energy consumption of CtEG process is 2.62 t-ce standard coal higher than OtEG process. CtEG process has a better cost advantage, saving production cost by 802 CNY?t-1, but its total capital investment is about 2.58 times that of the OtEG process. Appropriate expansion of plant scale significantly increases the economic benefits of the OtEG and CtEG processes, especially the total investment of CtEG process. After investigating the effect of raw material price fluctuations on the economic performance on these two routes, it is found that when the oil price is lower than 40 USD?bbl-1 and the coal price is higher than 500 CNY?t-1, the production cost ratio of CtEG and OtEG will be higher than 1.0. When the oil price is higher than 60 USD?bbl-1 even if the coal price is as high 850 CNY?t-1, the production cost ratio will also be less than 1.0. In addition, the CO2 emissions and water consumption of the CtEG process are about 5 t?t-1and 20 t?t-1 higher than those of the OtEG process. Therefore, while vigorously developing the CtEG industry, it is urgent to solve problems such as high energy consumption and high emissions.

    Fractional step reduction method for sensitive variable selection of refining processes
    Ling LI, Yalin WANG, Bei SUN
    2020, 71(5):  2173-2181.  doi:10.11949/0438-1157.20191499
    Abstract ( 33 )   HTML ( 0)   PDF (1552KB) ( 20 )  
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    Variable selection has always been a hotspot in product quality prediction of modern industrial production. Due to the fast calculation speed and do not easily cause overfitting, filter methods have been widely used.However, because the correlation of variables is easily ignored and no information of working condition reflected in the filter methods,it is no longer suitable for solving the disaster problems of high-dimensional data. To cope with these problems, a fractional step reduction method for sensitive variable selection is proposed in the paper. First, two concepts of sensitive variables (SV) and key sensitive variables (KSV) are first identified. Then, a sensitivity index (SI) is developed to select the sensitive variables preliminarily. After that, a weighted cosine Mahalanobis-Taguchi system (WCMTS) is proposed to precisely select the key sensitive variables. Finally, the proposed method is applied to an industry hydrocracking process. Practical industrial application results show that the method can not only improve the prediction accuracy of the model, but also effectively reduce the complexity of the model.

    Multi-objective optimization of co-processing of bio-oil and vacuum gas oil in FCC
    Le WU, Jing WANG, Yuqi WANG, Lan ZHENG
    2020, 71(5):  2182-2189.  doi:10.11949/0438-1157.20191483
    Abstract ( 53 )   HTML ( 3)   PDF (543KB) ( 49 )  
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    As a potential energy source that can partially replace fossil fuels, biofuels have the advantages of green, renewable, and sulfur-free, but their production costs are generally higher. The co-processing of bio-oil and vacuum gas oil in a fluid catalytic cracker (FCC) can effectively reduce the investment cost of a bio-refinery and the production cost of bio-fuels by utilizing the existing equipment in a refinery. To obtain the optimal biomass raw material and bio-oil production technology, Eco-indicator 99 was used to quantify the environmental impacts of the co-processing process, and a multi-objective optimization model was proposed to simultaneously reduce the economic costs and the environmental impacts. The results showed that catalytic pyrolysis was superior to fast pyrolysis in both reducing economic costs and environmental impacts; the different optimal biomasses were obtained under different objectives; biomass cost accounted for the largest proportion of costs and environmental impacts. Therefore, when optimizing the co-processing process, the environmental impact of the process should be considered. Reducing the biomass consumption is the most effective way to reduce both the costs and environmental impacts of the co-processing process.

    Surface and interface engineering
    Study of thermal-fluid-solid coupling on dynamic characteristics of oil-gas miscible backflow pumping seal
    Shicong LI, Caifu QIAN, Shuangxi LI, Lian CHEN
    2020, 71(5):  2190-2201.  doi:10.11949/0438-1157.20191026
    Abstract ( 53 )   HTML ( 4)   PDF (2247KB) ( 46 )  
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    The dynamic characteristics of oil-gas two-phase dynamic pressure seal were studied. The oil-gas two-phase Reynolds equation was established based on the Reynolds equation for compressible fluid, and the physical properties of oil-gas two-phase fluid. The effect of deformation on fluid film was considered, thus the thermal-fluid-solid coupling method was adopted and solved by finite element method. The effects of operating parameters (oil-gas ratio, rotational speed and pressure difference) on the dynamic performance of oil-gas miscible backflow pumping seal were analyzed. The results show that the viscosity of oil-gas miscible fluid is larger, which makes the seal have greater dimensionless stiffness, dimensionless damping and better dynamic characteristics. The deformation of seal ring reduces the dimensionless stiffness and increases the dimensionless damping, and the maximum influence is 16.9% and 31.2%. High speed increases the dimensionless stiffness and dimensionless damping, which is beneficial to the dynamic characteristics of the seal. While large pressure difference increases the dimensionless stiffness and decreases the dimensionless damping, which is not conducive to the dynamic characteristics. Therefore, the oil-gas miscible backflow pumping seal is suitable for oil-gas lubrication with high speed and low pressure difference.

    Performance analysis on diffuser self-pumping hydrodynamic and hydrostatic mechanical seal
    Cheng GE, Jianjun SUN, Xuchen SU, Chenbo MA, Qiuping YU
    2020, 71(5):  2202-2214.  doi:10.11949/0438-1157.20191586
    Abstract ( 36 )   HTML ( 3)   PDF (3765KB) ( 28 )  
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    The opening force of the seal end face is an important index to ensure the non-contact operation of the non-contact mechanical seal. To overcome the shortcoming that the opening force of the seal face decreases with the increase of the rotating speed, a kind of diffuser self-pumping hydrodynamic and hydrostatic mechanical seal was designed based on the working principle of the diffuser of the centrifugal pump or compressor. The three-dimensional flow fields of the seal face was analyzed by Fluent, the sealing performance of the self-pumping mechanical seal was compared with ordinary self-pumping mechanical seal, and the influence of structural and operational parameters on the performance of self-pumping mechanical seal was discussed. Results show that the opening force of the face of self-pumping mechanical seal with the diffuser is more than 50% higher than that of the ordinary self-pumping mechanical seal with the same spiral groove parameters, and the opening force increases with the speed. With the increase of the width of diffuser ring, the opening force and the leakage rate increase significantly. Reducing the depth of diffuser ring can effectively improve the opening force. Even the structure size of the expansion ring is changed, the effect of the width ratio of groove to diffuser ring, groove number and helix angle on the diffuser self-pumping mechanical seal sealing performance is not affected. Consequently, through the matching of structural parameters, the better sealing performance can be obtained under certain operating conditions.

    Effects of the real-gas characteristics of carbon dioxide with impurities on the dry gas seal performance
    Wei CHEN, Pengyun SONG, Hengjie XU, Xuejian SUN
    2020, 71(5):  2215-2229.  doi:10.11949/0438-1157.20191556
    Abstract ( 44 )   HTML ( 1)   PDF (2152KB) ( 21 )  
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    Based on the EOS-CG model and GERG-2008 model, the density of the mixed carbon dioxide gas containing impurities is calculated, and the viscosity of the mixed gas is calculated based on the CO2-Pedersen model. The relationship between density, viscosity and pressure of pure carbon dioxide and mixed gas are obtained by fitting the calculated data of these models to describe the real gas behavior and the law of viscosity changing with pressure of pure carbon dioxide and mixed gas. The steady-state Reynolds equation is solved by using the finite difference method, and the opening force, leakage rate and film stiffness of the dry gas seal lubricated by pure carbon dioxide or carbon dioxide with impurities are obtained, and the influence of impurities on the performance (opening force, leakage rate, film stiffness) is also analyzed. The variables considered include the average linear velocity of the end face, film thickness, inlet temperature, and inlet pressure. The results show that when inlet pressure is 15.26 MPa, and inlet temperature is 363.15 K, and linear velocity of the end face is 74.030 m/s, and film thickness is 3.05 μm, both the opening force and leakage rate of the dry gas seal lubricated by carbon dioxide with impurities are lower than those of pure carbon dioxide dry gas seal. The more impurities content, the more obvious the difference. The effect of impurities on the opening force, leakage rate, and film stiffness of the carbon dioxide dry gas seal increases with the increasing of the averaged linear velocity of the end face. The effect on the leakage rate and film stiffness decreases with the increasing of the film thickness. The effect on the opening force, leakage rate, and film stiffness decreases with the increasing inlet temperature. The influence on the opening force of carbon dioxide dry gas seal decreases firstly, then increases, and finally decreases with the increasing of the inlet pressure, and the influence on the leakage rate of carbon dioxide dry gas seal increases firstly and then decreases with the increasing of the inlet pressure, and the influence on the film stiffness decreases firstly and then increases with the increasing of the inlet pressure.

    Corrosion inhibition of ionic liquids on the surface of Q235 steel in methanol/sulfuric acid medium
    Tianyu ZHENG, Lu WANG, Jinyan LIU, Jia WANG
    2020, 71(5):  2230-2239.  doi:10.11949/0438-1157.20191372
    Abstract ( 34 )   HTML ( 4)   PDF (2909KB) ( 14 )  
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    The corrosion behavior of Q235 steel in methanol medium in the presence of sulfuric acid and the inhibition properties of 1-butyl-3-methylimidazolium chloride ([Bmim]Cl) for Q235 steel in methanol/sulfuric acid aqueous solutions were studied in the paper. The corrosion inhibition characteristics of [Bmim]Cl for Q235 steel were evaluated by static mass loss method, polarization curve method, electrochemical impedance spectroscopy (EIS) and scanning electron microscope (SEM). The corrosion inhibition mechanism of [Bmim]Cl was analyzed by quantum chemical calculation and molecular dynamics simulation. The corrosion rates of carbon steel increased with the increase of sulfuric acid in methanol. The results of experiments showed that the corrosion inhibition efficiency increased gradually with the increase of the concentration of [Bmim]Cl in methanol solution containing 59.51 ml 0.05 mol·L-1 H2SO4 aqueous solutions. When the concentration was 0.6 mol·L-1, the corrosion inhibition efficiency can reach the optimal, that is 90.63%. And [Bmim]Cl was a mixed inhibitor, which mainly controlled by the anodic reaction. Frontier orbitals analysis and Fukui function showed that the adsorption sites of ionic liquids on the surface of carbon steel were distributed on the imidazole ring and chemisorbed with Fe. The molecular dynamics simulation results showed that the inhibitor molecules were adsorbed parallel to the metal surface by cationic [Bmim]+, and the anion Cl- diffuses in solution to achieve the inhibition effect. The theoretical calculation results are consistent with the experimental results, that is, [Bmim] Cl has a good corrosion inhibition effect on Q235 steel in a methanol / sulfuric acid aqueous solution, laying a foundation for the research and application of new ionic liquid corrosion inhibitors.

    Biochemical engineering and technology
    Process and kinetics studies of catalytic cyclodehydration of galactaric acid to 2,5-furandicarboxylic acid
    Haifeng XU, Liping ZHENG, Hongying WANG, Xilei LYU, Xujie CHEN, Ling XU, Yanchen LI, Yuxi JIANG, Xiuyang LYU
    2020, 71(5):  2240-2247.  doi:10.11949/0438-1157.20191239
    Abstract ( 58 )   HTML ( 6)   PDF (1397KB) ( 29 )  
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    2,5-Furandicarboxylic acid (2,5-FDCA) is one of the biomass-based platform compounds, which has an extensive application prospects in the field of polymers. In order to solve the problems of low yield and lack of kinetic data in the process for preparing 2,5-FDCA from galactaric acid cyclodehydration, the effects of different catalysts and solvents were investigated, and the optimized conditions were obtained: with 15%(mass) sulfuric acid as catalyst and sulfone as solvent, the yield of 2,5-FDCA was 49.1% at 130℃ and 16 h reaction time. The kinetics of galactaric acid cyclodehydration at different concentrations of sulfuric acid and different temperatures were determined. According to the first-order reaction kinetics, the degradation activation energy of galactaric acid was 54.4 kJ/mol, the generation activation energy of 2,5-FDCA was 57.8 kJ/mol, the activation energy of other side reactions was 50.7 kJ/mol, and the degradation activation energy of 2,5-FDCA was 130.6 kJ/mol, at 15%(mass) sulfuric acid. The research work has promoted the industrialization of 2,5-FDCA in hexedioic acid route.

    Biosynthesis of ZnO nanoparticles and their application in lipase immobilization
    Chunhua YIN, Siyu PENG, Leizhen MA, Haiyang ZHANG, Hai YAN
    2020, 71(5):  2248-2255.  doi:10.11949/0438-1157.20191375
    Abstract ( 54 )   HTML ( 9)   PDF (900KB) ( 25 )  
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    Zinc oxide nanoparticles (ZnO-NPs) were synthesized by a strain of L. plantarum and used as carriers for the immobilization of Candida sp. lipase. Firstly, a strain of L. plantarum with high tolerance to zinc sulfate was screened and used to synthesize ZnO-NPs. The synthesized particles were characterized by SEM, TEM and XRD and UV-vis spectroscopy tests. The ZnO-NPs are found to be almost spherical in shape, with a radius of 9—35 nm. XRD analysis indicated the biosynthesized particles had a hexagonal wurtzite structure and the corresponding X-ray diffraction peaks were consistent with the standard ZnO-NPs. UV-vis spectroscopy revealed that the biosynthesized ZnO-NPs displayed a clear absorption peak at 359 nm. These obtained results proved that ZnO-NPs were successfully synthesized. Furthermore, the biosynthesized ZnO-NPs, native ZnO and traditional ZnO-NPs were used as carriers for the immobilization of Candida sp. lipase, respectively. The results showed that the biosynthesized ZnO-NPs were the most suitable for the lipase immobilization, and the recovered activity was 114.2% and 20.5% higher than that of the native ZnO and traditional ZnO-NPs, respectively. The pH and thermal stabilities of the lipase immobilized on the biosynthesized ZnO-NPs showed a considerable increase in stability compared to the free lipase. Moreover, the immobilized lipase showed good reusability.

    Energy and environmental engineering
    Efficient adsorption of DBT from model oil by the nitrified thiophenic sulfides via complexation thereof
    Ruiyang SUN, Yingzhou LU, Hong MENG, Chunxi LI
    2020, 71(5):  2256-2264.  doi:10.11949/0438-1157.20191262
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    Adsorption is an effective method for deep desulfurizaton of diesel, and the key is the research of high-efficiency adsorbents. In this paper, four activated carbon supported adsorbents (NBT/C, NDBT/C, NDBTO2/C and NDMDBT/C) were prepared by nitrifying the corresponding carbon loaded benzothiophene (BT), dibenzothiophene (DBT), dibenzothiophone (DBTO2) and 4,6-dimethyldibenzothiophene(DMDBT) with mixed acids of H2SO4 and HNO3, their composition and structure were characterized, and their adsorptive desulfurization performance were studied. The results show that there exists a strong interaction between NDBTO2 and DBT, forming a charge transfer complex. The adsorption isotherms of NDBTO2/C follow the Langmuir equation, with its saturated adsorbance being 87.4, 10.6 and 8.3 mg S·g–1, respectively for BT, DBT and DMDBT in model oils, and 37.2 mg S·g–1 for DBT in real diesel. The used adsorbents can be regenerated easily by toluene/methanol washing, and 95% adsorptivity can be remained after four recycles. This study provides useful inspiration for the comprehensive utilization of thiophene sulfide mixtures obtained during oxidative desulfurization or adsorption desulfurization.

    Exploration of nitrogen transformation pathway in Feammox
    Yuexi WU, Wei ZENG, Hong LIU, Jianmin LI, Yongzhen PENG
    2020, 71(5):  2265-2272.  doi:10.11949/0438-1157.20191529
    Abstract ( 48 )   HTML ( 2)   PDF (941KB) ( 31 )  
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    Ferroammonium oxidation (anaerobic ammonium oxidation coupled to Fe (Ⅲ) reduction, Feammox) refers to a new type of sewage biological denitrification process under the condition of anaerobic, ammonia-nitrogen oxidation coupled with ferric iron reduction. To explore nitrogen conversion pathways and their contribution to nitrogen removal in Feammox, the activated sludge was used as seed sludge to acclimate. After 120 d of operation, the maximum conversion efficiency of NH4+-N reached 53.8% and the maximum conversion amount was 26.9 mg/L, in which Feammox accounted for about 57.7% and Anammox about 42.3%. In typical cycle operation, nitrogen conversion was 14.74 mg/L within 0—7 h, in which Anammox dominated. During 7—24 h the nitrogen conversion was 12.16 mg/L, mainly by Feammox. The nitrate removal through NDFO during the whole operation was about 5 mg/L. Based on the correlation analysis, NH4+-N concentration was significantly positively related to Fe(Ⅲ) and NO2--N (PFe<0.05,PNO2<0.01), while NO3--N was negatively related to Fe(Ⅲ) (P < 0.5). Synergy of Feammox, Anammox and NDFO achieved the autotrophic nitrogen removal from wastewater.

    Numerical simulation of transport characteristics in biocathodes catalyzing carbon dioxide to methane
    Xun SONG, Qian FU, Jun LI, Liang ZHANG, Qiang LIAO, Xun ZHU
    2020, 71(5):  2273-2282.  doi:10.11949/0438-1157.20191600
    Abstract ( 44 )   HTML ( 3)   PDF (1785KB) ( 27 )  
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    The carbon-fixing methanogenic microbial electrosynthesis system uses a biofilm attached to the surface of its electrode as a catalyst, which can convert CO2 into methane while treating wastewater, which has great application prospects. As one of the core components, the biocathode determines the performance of the system. Herein, we derived a Nernst-Monod equation applicable to biocathodes, and constructed a mathematical model of the electron and mass transfer within the biocathode. The effects of different biocathode potentials, biofilm conductivity, and biofilm porosity on transport characteristics of the biofilm are studied. The results showed that the current density within the biofilm increased, and the substrate concentration within the biofilm decreased towards the direction of electrode with the decreasing cathode potential when the potential > -0.5 V (vs SHE). On the other hand, the capability of biofilm consuming electrons was almost saturated when the cathode potential < -0.5 V(vs SHE). A low conductivity of the biofilm (<10-3 S/m) could cause an obvious potential difference within the biofilm, reducing the substrate utilization rate and biocathode performance. When the biofilm porosity is controlled at 0.4, the microbial cathode can reach the optimal current density.

    Experimental study on the hydrogen production with RED reactor powered by concentration gradient energy
    Shiming XU, Zhiqiang LIU, Xi WU, Youwen ZHANG, Junyong HU, Debing WU, Qiang LENG, Dongxu JIN, Ping WANG
    2020, 71(5):  2283-2291.  doi:10.11949/0438-1157.20191468
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    The hydrogen production technology by low-grade heat (LGH) is that the LGH is first converted to the concentration gradient energy (CGE) of solutions, and then it is converted to hydrogen energy by reverse electrodialysis (RED) reactor. In order to verify the hydrogen production with RED reactor powered by CGE, and to explore the influence of key operating parameters on the energy conversion process, an experimental system of hydrogen production with RED reactor powered by CGE was developed. The RED reactor in the system consisted of 40 membrane pairs and NaCl and NaOH aqueous solutions were used as the working solutions and the electrode rinse solution respectively. By changing the inlet concentration of diluted or concentrated solution, the flow velocity of solution and the output current, the effects of those parameters on the hydrogen production rate, hydrogen production and energy conversion efficiencies were investigated experimentally. The results showed that the variations of inlet concentrations and the flow velocity would significantly affect the output current of RED reactor. Under the short circuit condition of the external circuit, the larger the output current, the higher the hydrogen production rate and hydrogen production efficiency of the reactor, but the lower the energy conversion efficiency.

    Preparation of C/ZnO composite based on camellia oleifera shell and its application in lead carbon battery
    Qiuqun LIANG, Zheng LIU, Huiting AI, Xinxin LIU, Shufen ZHANG
    2020, 71(5):  2292-2304.  doi:10.11949/0438-1157.20191007
    Abstract ( 55 )   HTML ( 11)   PDF (2950KB) ( 29 )  
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    Lead carbon battery is a new type of lead-acid battery, to a certain extent, lead carbon batteries can inhibit the irreversible sulfation phenomenon of the negative electrode under the high-rate partial charge state (HRPSoC). However, due to the addition of carbon, lead carbon batteries may have problems such as hydrogen evolution, and how to further inhibit irreversible sulfation of the negative electrode is still a problem faced by lead carbon batteries. In this paper, the sol-gel method was used to prepare the C/ZnO composites of camellia oleifera shell, XRD, SEM, BET, EDS, electrochemical measurement and other methods were used to characterize and analyse the composite materials. The results show that ZnO is successfully coated on the surface of the carbon materials, and the optimal mass ratio of Zn(Ac)2∶camellia oleifera shell carbon material is 1∶5.69, at this mass ratio, the structure of the camellia oleifera shell is well preserved, and the specific surface area is 152.04 m2/g, the specific capacitance of the negative electrode material with C/ZnO composite is 5.25 F/g, the electrode resistance is 0.22498 Ω. The simulated lead carbon batteries were assembled and the first charge-discharge curves and cycle lifes of the batteries were tested, the camellia oleifera shell C/ZnO composite material with a mass ratio of 1∶5.69 has better electrochemical performance than the physical grinding compared material, and its first discharge capacity is 177.6 mA·h/g, the capacity retention rate after 250 cycles is 64.3%. This shows that the addition of camellia oleifera C / ZnO composite material to the anode material can effectively inhibit the irreversible sulfate and hydrogen evolution of the anode of lead-carbon batteries.

    Nitrification characteristics and application research of high-efficiency embedded filler
    Shaolun WANG, Hong YANG
    2020, 71(5):  2305-2311.  doi:10.11949/0438-1157.20190953
    Abstract ( 42 )   HTML ( 2)   PDF (923KB) ( 25 )  
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    In order to investigate nitrification characteristics of high-efficiency embedded filler under municipal sewage, polyvinyl alcohol (PVA) was used to immobilize nitrifying bacteria. After the recovery culture in the laboratory, the experimental study on the adaptability of the embedded filler to the hydraulic retention time (HRT) and temperature and the application of the embedded filler in municipal sewage. The results showed that the efficiency of filler reached 93.20 mg·(L·h)-1 eventually after recovery culture. Under normal temperature conditions, HRT has little effect on the nitrification efficiency of embedded filler; temperature has a significant effect on nitrification efficiency. When the water temperature was 12℃, the ammonia oxidation rate of the filler was up to 30.70 mg·(L·h)-1. Under the conditions of low temperature and normal temperature of municipal sewage, when the HRT is 3 h and 1 h respectively, the influent ammonia was completely removed, indicating that the embedded filler is completely feasible for municipal sewage nitrification. Scanning electron microscope (SEM) observations showed that the filler had good porosity inside and the network structure was obvious. Quantitative real-time PCR results showed the number of bacteria has greatly increased, indicating that the filler provided a good microenvironment for microorganisms.

    Effect of cellulose composition on amino acids pyrolysis
    Meng GONG, Yang FANG, Wei CHEN, Yingquan CHEN, Qiang LU, Haiping YANG, Hanping CHEN
    2020, 71(5):  2312-2319.  doi:10.11949/0438-1157.20191391
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    The study aims to uncover the influence of cellulose components on the N-contained components pyrolysis during biomass pyrolysis process. The separation characteristics and distribution rules of pyrolysis from the main N-contained components (phenylalanine and glutamic acid), glucose unit of cellulose and mixture were analyzed by rapid pyrolysis-gas chromatography/mass spectrometry and density functional theory calculation to reveal the effect of glucose on amino acids pyrolysis. The result showed that glucose and phenylalanine mainly polymerized, and it supplied hydrogen, which promoted the deamination of phenylalanine / phenylethylamine to styrene. Glucose and glutamic acid mainly polymerized which promoted the decarboxylation and dehydration of glutamic acid to form 2-pyrrolidone. The calculation results show that the hydroxyl group at C1 of glucose provided hydrogen for the amino group connected with phenylethylamine C2, which can reduce the reaction energy barrier of phenylethylamine deamination. Combining the chain glucosyl group with glutamic acid amino group can reduce the reaction energy barrier of decarboxylation and promote the production of 2-pyrrolidone.

    Investigation on thermochemical conversion characteristics and regularity of co-hydrothermal carbonization solid fuel from sewage sludge and lignite
    Yanpei SONG, Xiuzheng ZHUANG, Hao ZHAN, Bin XU, Xiuli YIN, Chuangzhi WU
    2020, 71(5):  2320-2332.  doi:10.11949/0438-1157.20191419
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    The sludge and lignite are pretreated by co-hydrothermal carbonization to prepare high-quality solid fuel, which provides a feasible solution for the effective treatment of sludge and low-rank coal. This study mainly investigated the thermochemical conversion characteristics and regularity of solid phase products (hydrochars) prepared by Co-HTC of sewage sludge (SS) and lignite (LC) at different temperatures (120, 180, 240 and 300℃). Experiments included combustion, pyrolysis and char CO2-gasification processes, and the synergistic effects in these processes were also analyzed. The results show that Co-HTC pretreatment has some significant effects on the thermal behavior of SS and LC. On the one hand, compared with the calculated value, the hydrochars after co-hydrothermal carbonization have higher yield, fuel rate, coalification degree, calorific value, etc., and they have lower ash content. On the other hand, all hydrochars have a certain synergistic effects in combustion, pyrolysis and char CO2-gasification (promoting combustion and pyrolysis behavior, reducing gasification activity), and when the hydrothermal temperature is around 240℃, these synergistic effects are most obvious. Given that the synergistic effects of the pyrolysis and gasification processes are lower than the combustion process, co-hydrothermal carbonization products are considered to be more suitable for combustion. These findings indicate that the combination of the upgrading of Co-HTC with subsequent thermochemical processes has positive implications for the generation of energy and the utilization of organic wastes.

    The CO2 adsorption performance under flue gas for TEPA-impregnated composited oxidized activated carbon
    Yanxia WANG, Xiude HU, Jian HAO, Qingjie GUO
    2020, 71(5):  2333-2343.  doi:10.11949/0438-1157.20191178
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    Commercial coal-based activated carbon was used as raw material, roasted with low concentration of oxygen, oxidized and modified with H2O2, and impregnated with tetraethylenepentamine (TEPA) to obtain an amine-loaded composite oxidized activated carbon, which was used to simulate flue gas [(15%(vol) CO2 + 85%(vol) N2) +10%(vol) H2O] adsorption of CO2. After low concentration oxygen modification, activated carbon showed highest specific surface area of 1421.82 m2/g and highest pore volume of 0.83 cm3/g. The content of oxygen-containing groups on the activated carbon surface and mesoporous volume increased through composited oxidation, resulting higher CO2 adsorption performance on TEPA-impregnated composited oxidized activated carbon. Compared different adsorbents, the sample COAC-4-40TEPA prepared through 4 h oxidation, H2O2 oxidation and 40% TEPA impregnation, showed highest CO2 adsorption capacity of 2.45 mmol/g, which is 2.02 times of AC-40TEPA. Moreover, the CO2 adsorption capacity could maintain 92.24% after ten adsorption cycles. The deactivation model analysis showed that initial adsorption rate of COAC-4-40TEPA was 1.64 times of AC-40TEPA, and the deactivation rate was lower.

    Mechanisms of anti-agglomeration and anti-clogging by using zero-valent iron entrapmented in calcium alginate beads
    Wenhui ZHU, Xiahui WANG, Xintong YANG, Xingrun WANG, Jun HE, Guoxin HUANG, Guohua JI
    2020, 71(5):  2344-2351.  doi:10.11949/0438-1157.20191366
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    Zero-valent iron micron-particles have been successfully entrapped in calcium alginate beads (CAZ) by using sodium alginate (SA), calcium chloride, micro zero-valent iron (MZVI). Through static beaker experiment and dynamic PRB model experiment, the performance of CA in Cr(Ⅵ) removal was discussed, and the mechanisms of CA avoiding agglomeration and blocking were analyzed by scanning electron microscopy. The results show that the application of CA gel particles can significantly improve the Cr (Ⅵ) removal performance of MZVI. Compared with MZVI, the removal rate and reaction rate of Cr(Ⅵ) by CAZ are 7.1 times and 23.0 times, respectively. The increased treatment capacity of Cr(Ⅵ) contaminated groundwater was mainly attributed to higher utilization rate caused by CAZ reactor more than by MZVI, and the increased MZVI reaction rate was the main reason for lower Cr(Ⅵ) effluent concentration in CAZ reactor than that in MZVI reactor. Analysis results by scanning electron microscopy showed that rich skeleton framework and pore structures were formed by crosslinking reaction of SA and calcium chloride. For this pore structure which played a skeleton supporting role, the defects of agglomeration and reduced specific surface in Fe0 caused by gravity were overcame. In prior period, significantly decreased effluent volume in dynamic PRB test could be attributed to the release of MZVI particles which were fixed on CA surface, together with precipitates which broke through CA surface. In later period, most MZVI particles were fixed in CA while the complex-precipitation of (FexCr1-x)(OH)3 was trapped inside the pore structure, which could efficiently alleviate the blocking problems caused by long and continuous operation of Fe0-PRB system.

    The efficiency and mechanism of U(Ⅵ) removal from acidic wastewater by sewage sludge-derived biochar
    Guanhai MO, Shuibo XIE, Taotao ZENG, Yingjiu LIU, Pingli CAI
    2020, 71(5):  2352-2362.  doi:10.11949/0438-1157.20191505
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    Sewage sludge-derived biochar (SSB) was prepared by slow pyrolysis of sewage sludge (SS), and the effect factors, including initial pH, dosage, coexisting ions, contact time and temperature, on the U(Ⅵ) adsorption by SSB were investigated. The adsorption kinetics and isotherm were also studied. The mechanism of U(Ⅵ) adsorption removal was analyzed by elemental analysis, scanning electron microscopy (SEM), Fourier infrared spectroscopy (FTIR), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The results showed that the suitable conditions for U(Ⅵ) removal were pH of 3, dosage of 1 g/L and adsorption time of 240 min under 30°C. Under these conditions, a maximum adsorption capacity of 34.51 mg/g was obtained. The adsorption kinetics of U(Ⅵ) was accurately described by a pseudo-second-order model. Langmuir adsorption isotherm model can describe the adsorption behavior of U(Ⅵ) well. The adsorption mechanisms mainly include electrostatic interaction, n-π interaction of Si—O—Si, coordination complexation of hydroxyl (—OH) and carboxyl (—COOH) groups. Based on 5 adsorption-desorption cycles, the efficiencies of both U(Ⅵ) removal and SSB regeneration were above 80%. This study indicated that sewage sludge-derived biochar has the potential for acidic U(Ⅵ)-containing wastewater treatment.

    Treatment of high-strength domestic wastewater by two-stage MBfR processes
    You WANG, Xingyan WANG, Liangchang ZHANG, Weidang AI, Shuangsheng GUO
    2020, 71(5):  2363-2372.  doi:10.11949/0438-1157.20191340
    Abstract ( 40 )   HTML ( 2)   PDF (1175KB) ( 21 )  
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    A two-stage MBfR system with anaerobic and aerobic process was established to treat domestic wastewater (including sanitary wastewater and urine wastewater) and meet the plant nutrient solution recycling requirements for controlled ecological life support system (CELSS). The effects of hydraulic retention time (HRT) and urine concentration on organic removal and nitrogen conversion efficiency were studied. When HRT ≥1 d, TOC removal ratio is not affected by HRT with removal rate above 90% and the effluent concentration below 15 mg/L. When HRT =1 d, the nitrification capability of the system was optimal, volumetric removal rate was 0.418 kg N/(m3·d). When HRT ≥2 d, the nitrogen conversion efficiency was more stable. The developed system could treat the 1 /5 concentration urine wastewater at the highest level. At this time, TOC removal ratio was 94.3%, with the effluent concentration below 20 mg/L. The nitrification efficiency of the system was 90.6%, and volumetric removal rate was 0.409 kg N/(m3·d). The developed two-stage MBfR system could effectively achieve the organic removal and nitrogen conversion of the domestic wastewater in CELSS. The research results can provide reference for the design and operation of domestic wastewater microbial treatment system in CELSS.

    Thermo-economic modelling and optimization of a zeotropic organic Rankine cycle with composition adjustment
    Chaonan CHEN, Xianglong LUO, Zhi YANG, Renlong HUANG, Pei LU, Jianyong CHEN, Ying CHEN
    2020, 71(5):  2373-2381.  doi:10.11949/0438-1157.20191081
    Abstract ( 46 )   HTML ( 0)   PDF (1161KB) ( 21 )  
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    As one of the most promising low-grade thermal power generation technologies, the organic Rankine cycle (ORC) has received increasing attention in recent years. Compared to the conventional high-grade fossil energy to power conversion technologies, ORC is much more sensible to the environmental temperature variation due to the low temperature nature of heat sources. This study proposes a novel zeotropic ORC in which the mixture composition can be tuned in response to the environmental temperature using liquid - separation condensation. A thermodynamic optimization model is formulated to optimize the mixture composition according to the environmental temperature. A superstructure of liquid-separation condensation based composition tuning system is constructed. The tuning process of the novel system is modelled and incorporated into the zeotropic ORC. Case study is elaborated to validate the thermo-economic effectiveness of the novel ORC. The results show that the thermo-economic effectiveness of the proposed ORC can be improved by up to 38.90%/15.35% for constant/sliding pressure regulation compare to the conventional ORC in terms of 100℃ heat source. Furthermore, the comparison of five zeotropic mixtures indicates that the performance improvement is significantly sensible to the mixtures.

    Aqueous products prepared by hydrothermal and hydrothermal oxidation processes of cotton stalk
    Mengyuan SUN, Shouyu ZHANG, Caiwei WANG, Nan HU, Xiaobing SONG, Hongyu LIU, Xiaofeng LI
    2020, 71(5):  2382-2388.  doi:10.11949/0438-1157.20191090
    Abstract ( 51 )   HTML ( 3)   PDF (472KB) ( 29 )  
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    The characteristics of biomass could be changed by hydrothermal and hydrothermal oxidation process, so that the quality of pyrolytic products and pyrolytic efficiency are improved. In this study, the hydrothermal aqueous product (HTAP) and hydrothermal oxidation aqueous product (HOAP) were prepared by the processing of cotton stalk without or with oxidant at 180—280℃ in an autoclave reactor. The organic compounds, refraction indexes and pH values of HTAP/HOAP were investigated using gas chromatography-mass spectrometry, Baume densitometer and pH acidometer, respectively. The results show that the content of the acids in HOAP reached the maximum at 200℃, which is lower than that in HTAP (at 230℃). The content of the phenols in HOAP at 200—230℃ are significantly higher than that in HTAP. The formation of the ketones is inhibited under hydrothermal oxidation. The refraction indexes of HOAP at 180—280℃ show an obvious downtrend with the increase in temperature and are higher than that of HTAP. The pH values of HOAP at 180—280℃ increase with the increasing temperature. Besides, the pH values of HOAP at 180—260℃ are lower than that of HTAP. The physical and chemical properties of HTAP and HOAP are basically the same as those of wood vinegar, which has the potential to be used in agriculture, forestry and other fields.

    Material science and engineering, nanotechnology
    Application of manganese dioxide nanosheets modified separator for lithium-sulfur batteries
    Na PENG, Pengfei ZHAI, Jingtao WANG, Junxiao WANG, Yong LIU
    2020, 71(5):  2389-2400.  doi:10.11949/0438-1157.20191319
    Abstract ( 35 )   HTML ( 6)   PDF (3764KB) ( 39 )  
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    Lithium-sulfur batteries have a higher theoretical energy density and are considered to be one of the most promising next-generation high-energy-density energy storage devices. However, the commercialization of lithium-sulfur batteries is seriously hindered by capacity decay and poor cyclic life caused by polysulfide shuttle. Manganese dioxide nanosheets were prepared by redox method using graphene oxide nanosheets as template. TEM, XRD, FTIR, SEM, AFM were used to characterize the microstructure and morphology of the manganese dioxide nanosheets and the modified separator. The electrochemical properties of the manganese dioxide modified separator were tested by using constant current charge and discharge, cyclic voltammetry and electrochemical impedance method. The results show that the manganese dioxide nanosheets can cover the micropores on separator surface of polypropylene uniformly, thus effectively inhibiting the shuttle of polysulfide through physical barrier and catalysis, and improving the specific capacity and cycle stability of lithium-sulfur battery.

    Effect of pH control of KMnO4 solution on physicochemical properties and fouling behavior of PVDF membrane
    Xuehui ZHAO, Xiaole LI, Yang LIU, Yan HU, Qing XU, Hongwei ZHANG
    2020, 71(5):  2401-2412.  doi:10.11949/0438-1157.20191278
    Abstract ( 56 )   HTML ( 3)   PDF (2276KB) ( 38 )  
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    The morphological structure and physicochemical properties of membrane materials are critical to the safety and stability of membrane filtration systems. The polyvinylidene fluoride (PVDF) modified hollow fiber membrane was used to investigate the effect of KMnO4 on the surface morphology, hydrophobicity, mechanical strength, pure water flux and membrane fouling behavior at pH 5, 7 and 9, respectively. The results indicate that KMnO4 destroys the modified and separated layers on the surface of PVDF membrane under different pH conditions, which leads to the evolution of different morphological structure, chemical composition, hydrophobicity and antipollution. Under acidic conditions, due to the oxidation of potassium permanganate, the CC of the PVDF membrane material is destroyed, and the hydroxyl group (OH) is introduced, then the aldehyde and ketone compounds are further oxidized. However, in the alkaline condition, the dehydrofluorination reaction took place on the membrane surface, resulting in the formation of carbonyl (CO). Membrane fouling experiments indicate that the change of physicochemical properties of membrane separation interface seriously affected the membrane fouling behavior. With the decrease of pH of KMnO4 solution and the increase of contact time, the irreversible fouling of membrane surface became more and more serious. This study provides data references for the effect of pH changes on the morphology and properties of PVDF membrane materials in the pre-oxidation membrane filtration process.

    Systematic study on preparation and properties of boron film materials based on inner wall of Tokamak device
    Xiaorang TIAN, Xin ZHAO, Guanchao ZHAO, Zhikai GAO, Peide HAN
    2020, 71(5):  2413-2422.  doi:10.11949/0438-1157.20200025
    Abstract ( 31 )   HTML ( 0)   PDF (1465KB) ( 9 )  
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    Growing a boron film on the inner wall of a vacuum chamber is a critical wall treatment technology for a Tokamak device. In this paper, the spherical glow discharge vacuum chamber was built by ourselves. The boron film was successfully prepared on the wall of the vacuum chamber by plasma chemical vapor deposition with diborane as boron source. The results of SEM and adhesion test show that the boron film has compact structure, complete coverage and good adhesion, and the adhesion of the film is more than 240 N/m. The effects of the concentration of diborane, pressure, current density and temperature on the growth of boron films were systematically studied. The optimum preparation conditions of room temperature, 1%—2% ethoborane, 5—10 Pa pressure and 4.7—6.2 μA/cm2 current density are obtained. The suppression effect of boron film on impurities in the vacuum chamber was explored via a residual gas analyzer (RGA). The results show that the partial pressures of the residual gases H2O, CO2, CO and O2 after boronization are lower 200%, 400%, 200% and 10% than that before boronization, respectively. The suppression mechanism was deduced by analyzing the partial pressure of residual gases and the composition of boron film obtained by X-ray photoelectron spectroscopy (XPS).

    Research on preparation and thermodynamic properties of chloride molten salt materials
    Xiaolan WEI, Pei XIE, Xuechuan ZHANG, Weilong WANG, Jianfeng LU, Jing DING
    2020, 71(5):  2423-2431.  doi:10.11949/0438-1157.20191541
    Abstract ( 64 )   HTML ( 2)   PDF (1674KB) ( 48 )  
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    Six chloride molten salt materials, NaCl-CaCl2, NaCl-KCl-CaCl2, NaCl-CaCl2-MgCl2, KCl-CaCl2-MgCl2, NaCl-KCl-MgCl2 and NaCl-KCl-CaCl2-MgCl2, were prepared. Then the DSC method was used to determine the eutectic temperature and composition of those molten salts, and the other thermophysical properties were also measured, which were heat capacity, density and viscosity. Also, the mass loss of molten salt materials was investigated to determine the upper limit of working temperature. Correspondingly, energy storage density was calculated for each salt. The results shows that NaCl-KCl-CaCl2-MgCl2 has an eutectic temperature of 380.3℃ with good fluidity. The operating temperature range is 430—700℃, and the energy storage density is 625.1 J?cm-3. By comparison, NaCl-KCl-CaCl2-MgCl2 has the lowest eutectic temperature and the highest energy storage density, which is suitable to be used as heat transfer and heat storage material. The eutectic temperature of NaCl-KCl-CaCl2 is 503.8℃, and the working temperature range is 550—850℃. The energy storage density is 559.9 J?cm-3, that means NaCl-KCl-CaCl2 is suitable for high-temperature heat storage material.

    Preparation and properties of epoxy POSS modified epoxy resin
    Jing JIN, Qiufeng AN, Bowen YANG, Shuyuan SHI, Huapeng TIAN
    2020, 71(5):  2432-2439.  doi:10.11949/0438-1157.20191584
    Abstract ( 62 )   HTML ( 2)   PDF (2273KB) ( 38 )  
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    With phenyltriethoxysilane (PTES) and β-3,4-cyclohexyl epoxy silane preparation oxygen radicals (A186) as raw material, mixing methanol and ethanol as solvents, the reaction is carried out under acidic conditions to prepare compounds with Si—H bonds called epoxy oligosilsesquioxane(EP-POSS). The structures of the compounds were characterized by Fourier transform infrared (FT-IR), nuclear magnetic resonance (1H NMR), and nuclear magnetic resonance (29Si NMR). The epoxy resin was modified with the prepared EP-POSS, and the influence of the amount of EP-POSS on the adhesion, impact resistance, hydrophobicity and heat resistance of the resin coating was analyzed. The results showed that when the amount of EP-POSS is 5%, the adhesion of the epoxy resin coating reached grade 1, the impact resistance reached 50 cm, the contact angle to water is 90°, and the thermal stability is greatly improved.

    Process safety
    Study on flame behaviors induced by spill fire deflagration in adjacent space of hazardous chemical containers
    Kan WANG, Tingting SHI, Jinhui WANG, Xue ZHANG
    2020, 71(5):  2440-2454.  doi:10.11949/0438-1157.20191393
    Abstract ( 58 )   HTML ( 3)   PDF (2718KB) ( 21 )  
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    In this study, a model of a container explosion accident of hazardous chemicals was established, and the simulation study was made on the propagation law and temperature field distribution of the overflow fire formed by the accident in the restricted space of the adjacent container facade. According to data collected from on-site investigation, the spill flame characteristics and temperature field distributions of the three types of container openings with different sizes were analyzed in open space. A new air entrainment model where spill fire was triggered under different spacing conditions was then proposed, and the correction factor was introduced to correct the flame height. The results showed that the container opposite to the opening of the blasting container blocked the air entrainment in the vicinity, thus affecting the evolution of spill fire behaviors. With the increase of the spacing, for the smaller spacing conditions, the air entrainment mainly came from the side; the higher flame height was, the greater damage to the superimposed container and the opposite container. For the bigger spacing conditions, the larger air volume came from the front and side, while lower flame height could be observed, indicating that less damage would be imposed on the superimposed container and opposite container, with more thermal damage and destruction seen on the adjacent container.