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Table of Content
25 August 2023, Volume 74 Issue 8
    Reviews and monographs
    Research progress and influencing factors of the heat transfer enhancement of spray cooling
    Tianhua CHEN, Zhaoxuan LIU, Qun HAN, Chengbin ZHANG, Wenming LI
    2023, 74(8):  3149-3170.  doi:10.11949/0438-1157.20230151
    Abstract ( 593 )   HTML ( 65)   PDF (10246KB) ( 325 )  
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    Spray cooling is one of effective and efficient cooling method, which is widely applied to the thermal management of high-power density electronics. In recent years, spray cooling has attracted great attention, and its heat transfer capacity has been significantly improved. Particularly, the development of new micro/nano surfaces has dramatically boosted the heat transfer of spray cooling, enriching the enhanced mechanisms of spray cooling. Herein, this review comprehensively summarizes the recent achievements of spray cooling and discusses the enhanced mechanisms. Furthermore, the effects of heat transfer surfaces, working fluids and parameters of nozzles, etc, on spray cooling have been systematically discussed. Finally, this paper further explores the mechanism of spray cooling to suppress the Leidenfrost effect, and looks forward to the future research direction of spray cooling.

    Progress and prospect of medium and high temperature thermochemical energy storage of calcium-based materials
    Yuyuan ZHENG, Zhiwei GE, Xiangyu HAN, Liang WANG, Haisheng CHEN
    2023, 74(8):  3171-3192.  doi:10.11949/0438-1157.20230338
    Abstract ( 393 )   HTML ( 64)   PDF (11443KB) ( 245 )  
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    Thermochemical energy storage has become an emerging research hotspot for efficient heat storage due to its high energy density and materials suitable for long-term storage and long-distance transportation. Calcium-based materials, which are low-cost, non-toxic, and non-polluting, have shown promising applications in this regard. This paper summarizes the current systems and categorization of the thermochemical thermal storage. It encompasses material modification, reactor design, and system integration applications for medium and high temperature calcium-based thermochemical storage. Then, the recent challenges and opportunities in calcium-based thermochemical energy storage technology are presented. Finally, this paper offers an outlook and provides suggestions for future research and development directions.

    Enhanced anaerobic removal of halogenated organic pollutants by iron-based conductive materials: research progress and future perspectives
    Longyi LYU, Wenbo JI, Muda HAN, Weiguang LI, Wenfang GAO, Xiaoyang LIU, Li SUN, Pengfei WANG, Zhijun REN, Guangming ZHANG
    2023, 74(8):  3193-3202.  doi:10.11949/0438-1157.20230441
    Abstract ( 209 )   HTML ( 13)   PDF (1115KB) ( 269 )  
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    With the development of industry and agriculture, more and more halogenated pollutants are being discharged into the environment. Given the characteristics of high toxicity and strong stability of halogenated pollutants, how to efficiently remove halogenated pollutants from the environment has become the focus of attention of scholars at home and abroad. Anaerobic biological treatment, due to its green and efficient characteristics, has been commonly used in recent years to remove halogenated pollutants from the environment. Among them, extracellular electron transfer by microorganisms is an important factor affecting dechlorination efficiency. Iron-based conductive materials have a large specific surface area, high conductivity, and the ability to increase the microbial activity of dehalogenation related bacteria, which can enhance the extracellular electron transfer process, thereby accelerating anaerobic dehalogenation efficiency and increasing methane production. This paper reviews the current research status of enhanced anaerobic dehalogenation with iron-based conductive materials, and focuses on the mechanism of electron transfer promoted by iron-based conductive materials. The existing problems in the current research on iron-based conductive materials are discussed, and the research direction of iron-based materials to promote anaerobic dehalogenation is prospected.

    Research progress of pervaporation technology for N-methylpyrrolidone recovery in lithium battery production
    Jiayi ZHANG, Jiali HE, Jiangpeng XIE, Jian WANG, Yu ZHAO, Dongqiang ZHANG
    2023, 74(8):  3203-3215.  doi:10.11949/0438-1157.20230541
    Abstract ( 291 )   HTML ( 17)   PDF (1784KB) ( 165 )  
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    N-methylpyrrolidone (NMP) is an essential solvent for the production of lithium batteries, and its demand is increasing year by year. However, in the late stage of lithium battery production NMP is produced as exhaust gas, and an effective method is to absorb it with water to form a solution. The recycling of NMP solution generated from lithium battery production process can reduce the cost of lithium battery production and promote the green and sustainable development of lithium industry. Compared with traditional processes such as distillation, the use of pervaporation technology to recycle NMP waste solution has the advantages of low energy consumption, high efficiency and environmental protection. This paper summarizes the advantages and mechanisms of permeation vaporization membrane separation technology, systematically summarizes the pervaporation membrane materials and separation processes used to recycle NMP waste liquid, and points out the corresponding advantages, disadvantages and applicable occasions by comparing the application scope and separation effects of different membrane materials and processes, so as to provide a reasonable reference for the effective utilization of NMP. The challenges of pervaporation technology for NMP recovery are discussed and the prospect of development is given.

    Thermodynamics
    Evaluation of vapor-liquid equilibrium models for mixtures containing HFOs
    Erqi WANG, Shuzhou PENG, Zhen YANG, Yuanyuan DUAN
    2023, 74(8):  3216-3225.  doi:10.11949/0438-1157.20230386
    Abstract ( 142 )   HTML ( 16)   PDF (1109KB) ( 150 )  
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    As the new environmentally friendly working fluid, HFOs have low global warming potential but are limited by their thermal performance and flammability. Mixtures containing HFOs can achieve complementary advantages and have good application prospects. Vapor-liquid equilibrium is the most basic thermodynamic property for the mixtures. To calculate the property of vapor-liquid equilibrium, the commonly-used PR equation of state, three mixing rules of vdW, HV and WS, and two activity coefficient models of NRTL and Wilson are selected to establish four theoretical models of PR-vdW, PR-HV-NRTL, PR-WS-NRTL and PR-WS-Wilson. Four sets of theoretical models were used to compare and evaluate the calculation performance of the vapor-liquid phase equilibrium of binary systems such as HFC+HFO, HC+HFO, and CO2+HFO, and further analyzed the calculation effect and the ability to predict the phase equilibrium of the ternary system. The results indicate that the PR-vdW model has stable and good calculation performance for most mixtures. The PR-WS-NRTL and PR-WS-Wilson models have excellent calculation performance but cannot perform stalely enough for predicting the critical properties locus and the ternary vapor-liquid equilibrium. The PR-HV-NRTL model has good performance for predicting the ternary equilibrium.

    Study on molecular level composition correlation of viscosity of residual oil and its components
    Shuang LIU, Linzhou ZHANG, Zhiming XU, Suoqi ZHAO
    2023, 74(8):  3226-3241.  doi:10.11949/0438-1157.20230431
    Abstract ( 144 )   HTML ( 14)   PDF (3476KB) ( 68 )  
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    The processing and transportation of residual oil are restricted by its high viscosity and poor fluidity, so the source of high viscosity of residual oil is the key to explore. Therefore, different residual oils were separated into four components of SARA (saturates, aromatics, resins, and asphaltenes) and the correlation between viscosity and molecular composition was studied. The results show that from the perspective of component content, the grey correlation order of the influence of residual oil viscosity is asphaltene > saturate > resin > aromatic. The viscosity of saturated fraction is much smaller than the viscosity of residual oil, indicating that saturated fraction is the main diluent of the residual oil system. From the perspective of component molecular level, it is found that the viscosity contribution of saturated components mainly come from the contribution of cycloalkanes, and the more rings there are, the greater the influences on the viscosity of saturated components are. The viscosity contribution of aromatics mainly comes from the distribution of N1O1 and N1 compounds. In addition to the metal elements Ni and Fe, the viscosity of resins is greatly affected by O1 compounds.

    Analysis on thermal oxidation characteristics of VOCs based on molecular dynamics simulation
    Linzheng WANG, Yubing LU, Ruizhi ZHANG, Yonghao LUO
    2023, 74(8):  3242-3255.  doi:10.11949/0438-1157.20230426
    Abstract ( 165 )   HTML ( 15)   PDF (4844KB) ( 153 )  
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    Benzene, toluene and styrene were selected as model compounds of representative volatile organic compounds (VOCs), and molecular dynamics (MD) simulation was adopted to attain their conversion characteristics during pyrolysis and oxidation processes under different temperatures. The global kinetic parameters of pyrolysis and oxidation reactions of VOCs model compounds were derived based on first-order reaction assumption, and the kinetic parameters were further used in computational fluid dynamics (CFD) simulation of regenerative thermal oxidation (RTO) system for abatement of VOCs. MD simulation revealed that at the initial stage of the pyrolysis process of aromatic VOCs, mainly dehydrogenation, side-chain cleavage and ring-opening would occur, forming small hydrocarbon species and benzene, while for the oxidation of VOCs, CO and H2O would be directly released accompanied by some light hydrocarbons. There are significant differences in the pyrolysis and oxidation reaction rates of different VOCs. Kinetic analysis shows that the first-order reaction assumption is suitable for describing the reaction process in the initial stage of VOCs pyrolysis and oxidation. Furthermore, CFD simulations suggested that temperature was crucial to improve the conversion efficiency of RTO, but simply elevating the temperature would require extra energy input. It was found that when dealing with the same amount of VOCs, it would be advantageous to use high-concentrated VOCs with lower flow rate, which could also improve the efficiency of the abatement of VOCs while saving energy.

    Phase equilibria and calculation of aqueous ternary system KCl + CaCl2 + H2O at 298.2, 323.2, and 348.2 K
    Xudong YU, Qi LI, Niancu CHEN, Li DU, Siying REN, Ying ZENG
    2023, 74(8):  3256-3265.  doi:10.11949/0438-1157.20230470
    Abstract ( 137 )   HTML ( 7)   PDF (2044KB) ( 142 )  
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    The composition of equilibrium liquid of the ternary system KCl + CaCl2 + H2O were determined by isothermal dissolution method at 298.2, 323.2, and 348.2 K. The density and composition of the equilibirum liquid phase were measured experimentally. The equilibirum solid phase composition was determined by Schreinemakers wet residue method and X-ray diffraction method. It is found that at 298.2 K, the system is a simple ternary system without double salt formation, and the phase diagram consists of one ternary invariant point, two univariate curves and two crystalline phase regions. The ternary system belongs to complex type system with the formation of double salt chlorocalcite (KCl·CaCl2) at 323.2 and 348.2 K. And the phase diagrams consist of two invariant points, three univariate curves and three crystallization regions. By comparing the phase diagrams of the ternary system at 278.2, 298.2, 308.2, 323.2, and 348.2 K, it can be found that with the temperature increasing, the crystallization form of CaCl2 changes from CaCl2·6H2O (278.2, 298.2 K), CaCl2·4H2O (308.2 K) to CaCl2·2H2O (323.2, 348.2 K). The crystallization area of KCl is the largest at 323.2 K, and the size of the double salt chlorocalcite crystallization region increases with the temperature increasing. The thermodynamics calculations of KCl + CaCl2 + H2O at 298.2, 323.2, and 348.2 K were carried out by Pitzer-Simonson-Clegg model, and the calculation values agree well with the experimental values.

    Fluid dynamics and transport phenomena
    Study of reaction and flow characteristics in multi-nozzle pulverized coal gasifier with co-processing of wastewater
    Chen HAN, Youmin SITU, Bin ZHU, Jianliang XU, Xiaolei GUO, Haifeng LIU
    2023, 74(8):  3266-3278.  doi:10.11949/0438-1157.20230723
    Abstract ( 122 )   HTML ( 9)   PDF (2803KB) ( 138 )  
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    Entrained-flow coal gasification technology is the key technology of cleaning coal utilization. During the industrial gasification process, it is difficult to treat the waste brought by production. In this paper, an industrial OMB pulverized coal gasifier is taken as the research object. The multiphase flow and reaction process in the gasifier are studied by numerical simulation. The effects of injection of low-temperature wastewater on reaction and heat transfer processes in gasifier are studied. The comparison between the simulation results and the industrial data shows that the simulation methods in this paper are reliable. The results show that the injection of wastewater can effectively reduce the temperature of the top and upper cone of gasifier, and can also reduce the temperature of the whole refractory materials. The wastewater flow blocks the impact of the rising refracted flow in the furnace on the top, reducing the temperature of the top space. The ash deposition rate on the top wall of the gasifier first increases and then decreases as the wastewater increases, while other wall surfaces are less affected. The carbon conversion rate slightly decreases, while the effective gas yield increases. The input of wastewater leads to a significant impact in particle deposition rate on the top wall, while other parts of the wall are less affected. Co-processing of wastewater can increase the effective gas output of the gasifier and extend the service life of the top burner, which makes it a good way to utilize waste resources. Research has found that the recommended mass flow rate of wastewater is 12—14 t·h-1.

    Experimental study on flash and mixing evaporation of aqueous NaCl solution
    Yue YANG, Dan ZHANG, Jugan ZHENG, Maoping TU, Qingzhong YANG
    2023, 74(8):  3279-3291.  doi:10.11949/0438-1157.20230721
    Abstract ( 135 )   HTML ( 10)   PDF (5505KB) ( 144 )  
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    Flash and mixing evaporation (FME) was one of the effective methods to achieve complete desalination of saline wastewater. In this paper, an experimental system of flash and cross-flow mixing evaporation was built, and the motion and evaporation characteristics of droplets in FME were investigated by combining PIV and Malvern laser particle size analyzer. In the experiment, on the wind side, air temperature ranged from 104.7℃ to 145.3℃, air speed from 10 m∙s-1 to 17 m∙s-1. On liquid side, the initial mass fraction of aqueous NaCl solution ranged from 0 to 0.15, its temperature from 20.0℃ to 132.0℃, and spray pressure ranged from 0.5 MPa to 1.2 MPa. Flash evaporation in FME mainly affected the atomization and fragmentation zone, while mixing evaporation mainly affected the evaporation zone. The initial particle size of droplets tended to be uniform with the increase of spraying pressure or mass fraction. While with the increase of droplet temperature, it tended to be uniform first and then became worse. The momentum/energy exchange between air and liquid mainly occurred in the horizontal direction in the evaporation zone. The average velocity of droplet cross-section along the horizontal direction was defined as the characteristic velocity of FME. This characteristic velocity first increases sharply and then increases slowly as the mixing distance increases. While at the same mixing distance, the characteristic velocity increased with the increase of mixing air temperature, air speed or spraying pressure. The Sauter diameter of droplets decreased along the mixing direction. The results pointed out that increasing the mixing air temperature, mixing air velocity or spray pressure was an effective means to enhance the FME process. The average surface heat transfer coefficient of the droplet population was calculated based on the experimental results and the experimental correlation equation for this heat transfer coefficient was set up and its relative error between the calculated and experimental values fell mainly in ±20%.

    Study on influence of pit defects on cavitation flow characteristics of throat of thick orifice plates
    Linjing YUE, Yihan LIAO, Yuan XUE, Xuejie LI, Yuxing LI, Cuiwei LIU
    2023, 74(8):  3292-3308.  doi:10.11949/0438-1157.20230465
    Abstract ( 110 )   HTML ( 15)   PDF (8107KB) ( 63 )  
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    Various valves, orifice plates and other throttling parts in the pipeline system will experience hydraulic cavitation as the pressure difference increases before and after the system works, which will seriously affect the working performance and safety of the system. The critical pressure ratio of cavitation of a thick orifice plate and the influence of pits on the critical pressure ratio of cavitation of an orifice plate were explored through numerical simulation. Furthermore, the cavitation flow characteristics under the coupling of pits and cavitation were further studied, and the mechanism of cavitation collapse under the action of pits was elucidated. The results show that cavitation occurs only when the ratio of orifice outlet pressure to inlet pressure is less than 0.5. The pit has the effect of promoting the primary-development-collapse evolution behaviour of cavitation bubbles, and a single small pit has almost no effect on the critical pressure ratio of cavitation, but the pit tends to increase the critical pressure ratio of cavitation. When the pressure ratio is near the critical pressure ratio of cavitation, the pressure peaks at each point appear on the pit side of the pit-free orifice plate and the pit side of the pit defective orifice plate, accompanied by periodic cavitation. In the safety design of liquid pipelines and valves, the risk of cavitation under the cavitation critical pressure ratio and the hazard of pipeline wall thinning caused by cavitation and ablation of pit defects should be considered.

    Analysis on mechanism of heat transfer deterioration of supercritical carbon dioxide in vertical upward tube
    Rui HONG, Baoqiang YUAN, Wenjing DU
    2023, 74(8):  3309-3319.  doi:10.11949/0438-1157.20230472
    Abstract ( 149 )   HTML ( 5)   PDF (2215KB) ( 366 )  
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    The phenomenon of heat transfer deterioration occurs during the heat transfer process of supercritical carbon dioxide (SCO2) flow, and there is still significant controversy in the field about the mechanism. Based on the four different types of heat transfer deterioration mechanisms proposed, numerical simulation research is conducted to analyze the flow and heat transfer process of a vertical upward tube with an inner diameter of 5 mm under different operating conditions, and to explore the heat transfer deterioration mechanism from a microscopic perspective. The research results indicate that the heat transfer deterioration of SCO2 is mainly caused by the buoyancy effect caused by density changes. When the influence of gravity is ignored, the heat transfer deterioration disappears. The buoyancy effect reduces the generation of turbulent kinetic energy (laminarization) by changing the turbulent flow structure of the internal flow field, and the weakening of turbulent thermal diffusion reduces the heat transfer efficiency, leading to the deterioration of heat transfer. The research results have certain guiding significance for the theoretical research and prediction correlation of heat transfer deterioration in supercritical carbon dioxide.

    Measurable range of nanoparticle concentration using optical fiber backward dynamic light scattering
    Xianheng YI, Wu ZHOU, Xiaoshu CAI, Tianyi CAI
    2023, 74(8):  3320-3328.  doi:10.11949/0438-1157.20230576
    Abstract ( 102 )   HTML ( 3)   PDF (1256KB) ( 55 )  
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    The commonly used dynamic light scattering (DLS) method requires sufficient sample dilution when measuring high-concentration nanoparticles to avoid multiple scattering effects to obtain accurate results. In this paper, a set of optical fiber backward DLS measurement device based on the principle of single-mode optical fiber backward dynamic light scattering was developed. By simultaneously emitting laser and receiving scattered light through a single-mode optical fiber, multiple scattering can be suppressed without diluting the sample, achieving direct measurement of the particle size of high-concentration nanoparticles. The device uses the heterodyne mode, with the back-reflected light on the fiber end face serving as the reference light signal, and the volume concentration of particles below 14% can meet the requirements of this mode. To determine the applicable concentration range of the device, theoretical and experimental research was carried out. First, the relationship between the scattering mean free path of particles of different sizes and the volume concentration was theoretically analyzed, and the upper limit of the theoretical measurement concentration was calculated based on the scattering area characteristics of the device. Secondly, the device was used to measure the particle size of nanoparticles with different particle sizes and various volume concentrations. Theoretical and experimental results show that with the increase of particle size, the upper limit of measured concentration decreases, and the trend of both is consistent. However, when the particle size is larger than 300 nm, the deviation between experimental results and theoretical analysis results gradually increases, and the experimental concentration is slightly lower than the theoretical concentration by 1%—2%(volume).

    Research on topology optimization of microchannel based on field synergy and entransy dissipation
    Wenzhu LIU, Heming YUN, Baoxue WANG, Mingzhe HU, Chonglong ZHONG
    2023, 74(8):  3329-3341.  doi:10.11949/0438-1157.20230632
    Abstract ( 145 )   HTML ( 7)   PDF (5125KB) ( 191 )  
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    Based on the bi-objective topology optimization method, five microchannel structures with different aspect ratios of the design domains were optimally designed, and the optimal design variable field, temperature field and pressure field under each working condition were obtained. On this basis, the effects of different Reynolds numbers on the microchannels were investigated, and the theoretical analysis and comparison of microchannels with different structures were carried out by combining the field synergy principle and entransy dissipation theory to provide a theoretical basis for optimizing the microchannel structures. The findings demonstrated that when the Reynolds number rose in the laminar flow region, the complexity of the topological flow channels also rose. The average temperature decreased, the Nu rose, the inlet and outlet pressure drop gradually increased, the PEC gradually decreased, the field synergy number increased, the pressure drop synergy angle gradually increased, the entransy dissipation increased, and the flow heat transfer characteristics of each heat dissipation channel tended to be optimized. The investigation of microchannels with various topologies structures revealed that the microchannels with a design domain aspect ratio of 25/64 had the best synergy effects of velocity-pressure gradient and velocity-temperature gradient, the best heat transfer effect, and the best flow characteristics.

    Catalysis, kinetics and reactors
    Design of cobalt-nitrogen-carbon/activated carbon rich in zero valent cobalt active site and application of catalytic oxidation of formaldehyde
    Kaixuan LI, Wei TAN, Manyu ZHANG, Zhihao XU, Xuyu WANG, Hongbing JI
    2023, 74(8):  3342-3352.  doi:10.11949/0438-1157.20230402
    Abstract ( 130 )   HTML ( 18)   PDF (6527KB) ( 248 )  
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    Low-cost, high-efficiency volatile organic compound (VOC) oxidation catalysts are crucial for environmental protection. Cobalt-nitrogen-carbon (CoNC) materials are able to activate oxygen species effectively, thanks to the highly dispersed Co coordinated with nitrogen to form CoN x . This property makes CoNC a promising candidate in the fields of photocatalytic and electrocatalytic oxidation. Despite this, the application of CoNC catalysts in the catalytic oxidation of formaldehyde has not been extensively studied. In this study, a series of cobalt-nitrogen-carbon/activated carbon (CoNC/AC) catalysts were synthesized by controlling the pyrolysis temperature to tailor the chemical composition and active site distribution on the CoNC/AC surface. The CoNC/AC catalyst obtained at 700℃ showed a 95% conversion rate of 70 mg·m-3 HCHO at 25℃, and stability tests over 3300 h demonstrated that the HCHO conversion rate remained steady at around 90%. Compared to noble metals, the transition metal CoNC/AC catalyst possesses superior HCHO removal capability and cost-effectiveness. Furthermore, the HCHO removal mechanism on the CoNC/AC catalyst was elucidated through correlation analysis and in situ infrared spectroscopy. The results indicated that the HCHO molecule can react with O2 adsorbed on the zero-valent Co site to generate CO2 and H2O (CH2O→HCHO2→CHO2→CO2) at ambient temperature.

    Study of the sintering mechanism of Fe2O3 nanoparticles based on molecular dynamics simulation
    Rubin ZENG, Zhongjie SHEN, Qinfeng LIANG, Jianliang XU, Zhenghua DAI, Haifeng LIU
    2023, 74(8):  3353-3365.  doi:10.11949/0438-1157.20230499
    Abstract ( 212 )   HTML ( 22)   PDF (7855KB) ( 114 )  
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    Iron oxide is an important raw material in the fields of chemical industry, metallurgy and energy, and its sinterability at high temperature is crucial to product performance. In this study, the sintering mechanism of Fe2O3 nanoparticles was investigated by molecular dynamics simulation (MDS) at different temperatures, particle sizes and vacancy defect concentrations. The results showed that when the particle size of Fe2O3 nanoparticles increased from 3 nm to 5 nm, the post-sintering shrinkage decreased from 25.0% to 10.8%, and the relative neck width decreased from 96.6% to 49.5%. When the temperature was increased from 900 K to 1300 K, the atomic diffusion coefficient for the sintering process increased from 1.758 × 10-3 nm2/ps to 4.303 × 10-3 nm2/ps, which was increased to 2.45 times. Atomic migration at high temperature (1300 K) transformed some of the particle structures from HCP and BCC structures to amorphous structures with 66.7% of amorphous atoms. The diffusion activation energy of the sintering process of nanoparticles containing 10.0% initial vacancy defect concentration was reduced by about 63.5% compared with that of perfect crystals (0 vacancy concentration), and the atom mobility and sintering densification were enhanced. The above results are of great significance for the optimization of the high-temperature heat treatment process of iron oxide particles.

    Sn doped In2O3 catalyst for selective hydrogenation of CO2 to methanol
    Feifei YANG, Shixi ZHAO, Wei ZHOU, Zhonghai NI
    2023, 74(8):  3366-3374.  doi:10.11949/0438-1157.20230442
    Abstract ( 191 )   HTML ( 28)   PDF (5671KB) ( 192 )  
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    Selective hydrogenation of CO2 to methanol is one of the most important ways of resource utilization of CO2, so it is very necessary to develop efficient methanol synthesis catalysts. In this study, the Sn promoter has been incorporated into In2O3 to modify its reducibility and the surface oxygen vacancy, in order to optimize the catalytic performance of In2O3 catalyst for CO2 hydrogenation to methanol. Several characterizations including XRD, TEM, H2-TPR, H2-D2-TPSR, Raman, XPS, and CO2-TPD were conducted to reveal the effect of Sn promoter on the structure and chemistry of the catalysts. The activity tests were performed in a high pressure fixed-bed reactor to study the catalytic performance. The results showed that the Sn atoms were highly dispersed in In2O3 and tended to accumulate on the surface through forming Sn—O—In structure, which promotes the formation of surface oxygen vacancy, and can inhibit the excessive reduction of In2O3. As a result, the Sn promoted In2O3 catalysts exhibited higher methanol selectivity and productivity. The Sn-In2O3 catalyst with a Sn/In molar ratio of 0.5% possessed the optimized catalytic performance, which showed a CO2 conversion of 6.2% and methanol selectivity of 70.4% at the reaction conditions of 300℃ and 3 MPa with GHSV of 15000 ml·g-1·h-1. With further increment of Sn content, the CO2 conversion would slightly decrease, while the methanol selectivity would increase to 80.8%, significantly higher than that of 55.4% on the pure In2O3 catalyst.

    Separation engineering
    Study on lithium resource separation from underground brine with high concentration of sodium by aluminum-based lithium adsorbent
    Bingchun SHENG, Jianguo YU, Sen LIN
    2023, 74(8):  3375-3385.  doi:10.11949/0438-1157.20230375
    Abstract ( 127 )   HTML ( 9)   PDF (2333KB) ( 231 )  
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    Aluminum-based lithium adsorbent is the only adsorbent which has achieved industrial application of lithium recovery from salt lakes due to its moderate desorption conditions without dissolution loss. However, its application feasibility in high-sodium underground brine remains to be investigated. The effects of the flow rate of brine, desorption temperature and the initial concentration of ions in eluent on adsorption and desorption processes in the fixed bed were systematically investigated with granular H-LDHs adsorbents homemade in the laboratory. The results showed that the breakthrough time decreased by 79% while the breakthrough adsorption capacity only decreased by 17.8% when the flow rate rose from 1 BV/h (1 BV/h = 0.170 L/h) to 4 BV/h in high Na+ brine. Increasing desorption temperature could significantly enhance the Li+ desorption amount, however, the Li+ desorption amount was suppressed with the increasing concentration of Na+ in eluent. In addition, a stage-by-stage cyclic desorption technology was designed and applied on the real underground brine somewhere in Sichuan, which could effectively achieve the enrichment of Li+ in the eluent during the desorption process.

    Analysis of key parameters affecting product purity of natural gas ethane recovery process via ZIF-8 nanofluid
    Ruihang ZHANG, Pan CAO, Feng YANG, Kun LI, Peng XIAO, Chun DENG, Bei LIU, Changyu SUN, Guangjin CHEN
    2023, 74(8):  3386-3393.  doi:10.11949/0438-1157.20230562
    Abstract ( 127 )   HTML ( 7)   PDF (1259KB) ( 171 )  
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    Porous nanofluid absorption-adsorption coupling separation is an emerging gas separation technology based on ZIF-8/water-glycol nanofluid, which can recover ethane in natural gas with high efficiency and low consumption by using the traditional absorption-desorption process. The equilibrium stage method is used to model the new process, and improving the ethane product purity is an important goal of process simulation. The simulation results indicate that the theoretical stage number of the absorption-adsorption column and the flash pressure are key parameters affecting the product purity. As the theoretical stage number of the absorption-adsorption column increases, the product purity first rises and then tends to remain constant. It can be seen from the y-x diagram that the reason why the product purity is difficult to increase continuouslyis that the operating line approaches the phase equilibrium line, which reduces the efficiency of each theoretical stage. The flash pressure affects the product purity by the flash boilup ratio. When the flash pressure decreases, the flash boilup ratio of the absorption-adsorption column increases, and the ethane content of the slurry phase from the reboiler (flash tank) increases, resulting in an increase in the ethane product purity.

    Optimal design and performance analysis of downhole micro gas-liquid hydrocyclone
    Lei XING, Chunyu MIAO, Minghu JIANG, Lixin ZHAO, Xinya LI
    2023, 74(8):  3394-3406.  doi:10.11949/0438-1157.20230358
    Abstract ( 119 )   HTML ( 5)   PDF (3877KB) ( 55 )  
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    In view of the adverse influence of the produced fluid gas-containing in the single-well injection-production system, an innovative downhole micro gas-liquid hydrocyclone is proposed based on the principle of cyclone separation. Based on Plackett-Burman (PB) design, steepest climbing design and response surface methodology combined with computational fluid dynamics, the significant structural parameters of the downhole micro gas-liquid hydrocyclone are analyzed and optimized, and the quadratic polynomial mathematical relationship between structural parameters and separation efficiency is constructed. The effects of inlet flow rate, overflow split ratio and volume fraction of gas on the performance of downhole micro gas-liquid hydrocyclone are analyzed systematically. The experimental process of gas-liquid hydrocyclone separation performance is constructed to experimentally verify the accuracy of numerical simulation results and the high efficiency of the optimization structure. The experimental results show that the optimized structure of downhole micro gas-liquid hydrocyclone can improve the de-watering efficiency from 84.10% to 87.22%. The optimal overflow split ratio of the micro-gas-liquid cyclone separator is 6%, the optimal inlet flow rate is 13.77 L/h, the most suitable gas phase volume fraction is 5.5%, and the average gas-liquid separation efficiency under the optimal working condition is 99.66%. The mathematical relationship between volume fraction of gas, overflow split ratio and separation efficiency is constructed to guide the optimal operation parameter regulation of the hydrocyclone under the conditions of different gas content, and the corresponding optimal split ratio under different gas volume fraction is obtained quantitatively.

    Process system engineering
    Multi-step predictive soft sensor modeling based on STA-BiLSTM-LightGBM combined model
    Linqi YAN, Zhenlei WANG
    2023, 74(8):  3407-3418.  doi:10.11949/0438-1157.20230458
    Abstract ( 149 )   HTML ( 6)   PDF (4176KB) ( 130 )  
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    In complex industrial production processes, it is necessary to establish a multi-step forecasting model for key variables in order to improve product quality, but traditional soft sensor modeling methods are difficult to focus on the complex characteristics of industrial data, resulting in inaccurate forecasting. This paper proposes a multi-step predictive soft sensor model, which is the combination of the bi-directional long short-term memory network based on spatial-temporal attention mechanism and light gradient boosting machine (STA-BiLSTM-LightGBM). Firstly, the STA-BiLSTM is trained, meanwhile the spatial-temporal attention mechanism assigns weights to the input features according to the temporal and spatial dimensions, and the BiLSTM captures the temporal features of the data. Secondly, the implicit state of the last time step of BiLSTM is used to extend the original input data, and then LightGBM is trained. By training LightGBM with a weak learner, the optimal model can be obtained through iterative training. The predicted outputs of STA-BiLSTM and LightGBM can then be weighted to obtain the predicted results using the error reciprocal method. Finally, the simulation results demonstrate that the combined model is superior to both BiLSTM and LightGBM, and it maintains high prediction accuracy even as prediction steps increases.

    Early warning method of aluminum reduction cell leakage accident based on KPCA and SVM
    Gang YIN, Yihui LI, Fei HE, Wenqi CAO, Min WANG, Feiya YAN, Yu XIANG, Jian LU, Bin LUO, Runting LU
    2023, 74(8):  3419-3428.  doi:10.11949/0438-1157.20230508
    Abstract ( 110 )   HTML ( 6)   PDF (2082KB) ( 70 )  
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    The slot leakage accident will cause enormous economic losses and casualties during the production process of aluminum reduction cell. Therefore, the accurate early warning of aluminum reduction cell leakage accident is significant for enterprises. As for the issue that the operation data of aluminum reduction cell is multidimensional, nonlinear, and the sample size of failure is smaller than that of normal operation, a data-driven model for early warning model of slot leakage accident is proposed. The support vector machine (SVM) algorithm with good robustness and high efficiency was adopted to avoid over-fitting due to small fault sample size. Then, cross-validation and sparrow search optimization algorithms (SSA) were used to optimize the parameters of SVM. The F1 score and AUC value of the optimized model were increased by 0.166 and 0.163 respectively. To better mine the characteristic information in the running data of aluminum electrolysis, the kernel principal component analysis (KPCA) method was used to reduce the data dimension. Eight principal components were selected when the cumulative variance contribution was 80%. The running time of the model was thereby decreased by about one minute. The F1 score and AUC value of optimized model were also increased by 0.046 and 0.038, respectively. Thirteen characteristic parameters were selected from many production parameters of aluminum electrolysis as input of model. Then, the missing data in the collected data were interpolated by K nearest neighbor (KNN) algorithm. When setting the classification labels, three characteristic parameters of temperature, Fe content, and Si content of the electrolysis process with obvious changes were selected as auxiliary classification conditions and combined with the actual situation. Thus, the fault feature range and the size of fault samples were expanded, indirectly solving the problem of small fault sample size to a certain extent. The experimental results showed that the F1 score and AUC value of the early warning of aluminum reduction cell leakage accident model reached 0.995 and 0.998, respectively. The feasibility and effectiveness of machine learning application in the field of early warning of aluminum reduction cell leakage accident are verified. It demonstrates that the KPCA-SSA-SVM model performed better than other classification models, which is more favorable for early warning of aluminum reduction cell leakage accident with small fault sample data. The results have important practical significance in prolonging the remaining life of aluminum reduction cell, improving the safety in the production process, and promoting the intelligent production of aluminum electrolytic enterprises.

    Operation optimization of ethylene cracking furnace based on improved deep reinforcement learning algorithm
    Chengying ZHU, Zhenlei WANG
    2023, 74(8):  3429-3437.  doi:10.11949/0438-1157.20230451
    Abstract ( 156 )   HTML ( 11)   PDF (1626KB) ( 265 )  
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    The ethylene cracker is the core of ethylene production, and the study of its production optimization is of great significance in improving the production level and economic efficiency of ethylene plants. The cracking process in the cracking furnace has high-dimensional, multi-modal and nonlinear characteristics, and it is difficult for traditional optimization methods to achieve operation optimization according to changes in working conditions. Therefore, we propose an improved deep reinforcement learning-based optimization method for ethylene cracker operation. Firstly, the operation strategy of the cracker within one cycle is considered as a sequential decision sequence, and then the process of ethylene cracker production operation optimization is modeled by combining the actual production process and artificial neural network. Secondly, the multi-Critics network mechanism is introduced to estimate the state-action value, which effectively reduces the slow training and conservation strategy of twin delayed deep deterministic policy gradient (TD3) algorithm. Finally, the algorithm is applied to solve the ethylene cracker production operation optimization problem to obtain an effective optimization strategy, which verifies the effectiveness of the proposed algorithm. The experiment results show that the proposed operation optimization strategy significantly improves the yields of the main product of the cracker.

    Surface and interface engineering
    Preparation and drag reduction effect of silicon-based liquid-like anti-crude-oil-adhesion coatings
    Dian LIN, Guomei JIANG, Xiubin XU, Bo ZHAO, Dongmei LIU, Xu WU
    2023, 74(8):  3438-3445.  doi:10.11949/0438-1157.20230633
    Abstract ( 122 )   HTML ( 6)   PDF (1582KB) ( 109 )  
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    The strong hydrogen bonding of nitrogen and oxygen heteroring structures in crude oil makes crude oil easy to adhere to different kinds of materials including Teflon, resulting in fouling and blockage challenges of oil wells, pipelines, containers and equipments in the process of crude oil exploitation, transportation, storage and processing. At present, there is still little research on anti-adhesion materials targeting crude oil, and there is still a lack of research conclusion on whether anti-adhesion materials have drag reduction effects on crude oil fluids such as crude oil transportation. In this paper, based on the development of silicon-based liquid-like anti-adhesion coatings, the coating's antifouling and self-cleaning function and their long-term stability were systematically studied. The drag reducing effect of the anti-adhesion functional coating on crude oil was studied, and the drag reducing effect of the coating under different crude oil fluidity, viscosity and other conditions was theoretically calculated. The results indicated that the coating exhibited outstanding anti-adhesion and drag reduction effects on crude oils of different viscosities. Compared with the conditions without coating, the drag reduction effect of the coating on higher viscosity crude oils is relatively more significant. It provides theoretical, material and technical bases for the scientific design and controllable preparation of drag reduction coating materials for the application such as crude oil transportation.

    Synthesis of pistachio shell-based carbon dots and their corrosion inhibition behavior on Q235 carbon steel
    Jiaqi CHEN, Wanyu ZHAO, Ruichong YAO, Daolin HOU, Sheying DONG
    2023, 74(8):  3446-3456.  doi:10.11949/0438-1157.20230555
    Abstract ( 98 )   HTML ( 6)   PDF (4982KB) ( 76 )  
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    To achieve the sustainable utilization of waste shells and develop eco-friendly carbon dots (CDs) corrosion inhibitors, the pistachio shell carbon dot (pvs-CDs) and pistachio shell-tartaric acid carbon dot (pt-CDs) were synthesized. The as-prepared CDs were characterized by using Fourier infrared spectroscopy, X-ray electron spectroscopy, transmission electron microscopy and fluorescence spectroscopy. The corrosion inhibition properties of synthesized CDs were evaluated by the electrochemical method. The results show that the corrosion inhibition efficiency of the prepared carbon dots on Q235 carbon steel in 1 mol·L-1 hydrochloric acid is above 90.0%, and the corrosion inhibition performance of pt-CDs is more excellent. Electrochemical impedance spectroscopy showed that the corrosion inhibition efficiency of pt-CDs on carbon steel after soaking for 6 h could reach 94.5%, which was mainly due to the formation of a protective film on the surface of carbon steel, which significantly increased the activation energy of corrosion reaction of carbon steel. The superior corrosion inhibition performance of pt-CDs can be attributed to the formation of a protective film on the surface of carbon steel, which is facilitated by the strong adsorption ability of pt-CDs. The established film effectively increases the activation energy of the carbon steel corrosion reaction, leading to superior corrosion inhibition properties. Fluorescence spectroscopy and differential UV-Vis spectra analyses were performed to investigate the interaction between pt-CDs and Fe3+, which can significantly enhance the adsorption of pt-CDs onto the carbon steel surface. This study will provide an idea to explore the research of biomass CDs-based corrosion inhibitors.

    Biochemical engineering and technology
    Preparation of magnetic agarose microspheres based on a two-fluid nozzle and their protein adsorption properties
    Yan GAO, Peng WU, Chao SHANG, Zejun HU, Xiaodong CHEN
    2023, 74(8):  3457-3471.  doi:10.11949/0438-1157.20230211
    Abstract ( 139 )   HTML ( 9)   PDF (4529KB) ( 257 )  
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    Aiming at the problems of the existing magnetic agarose microspheres (MAM) preparation technology, such as long process flow, poor repeatability, and difficulty in achieving large-scale and continuous production, a new preparation method of magnetic agarose microspheres based on two-fluid nozzle atomization technology was proposed. The variation of droplet size under different atomization conditions was investigated. Moreover, under the optimized spray conditions, MAM with high sphericity, small particle size and fast magnetic response were successfully prepared. The microspheres after sieving were prepared as DEAE anion exchanger (DEAE-MAM), and bovine serum albumin (BSA) was used as a model protein to explore the protein adsorption performance of DEAE-MAM with different particle sizes. The results show that the spray conditions affected the droplet size and thus the particle size by changing the gas-liquid ratio under the premise that the water phase properties were consistent. The DEAE-MAM with the smallest particle size (d32 = 36 μm) had the largest ion exchange capacity (192.5 μmol/ml) and the highest saturated adsorption capacity (150.0 mg/ml).

    Immobilization of carbonic anhydrase on modified polyethylene membrane and silica
    Lingding MENG, Ruqing CHONG, Feixue SUN, Zihui MENG, Wenfang LIU
    2023, 74(8):  3472-3484.  doi:10.11949/0438-1157.20230348
    Abstract ( 124 )   HTML ( 15)   PDF (3517KB) ( 117 )  
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    The activity of carbonic anhydrase (CA) immobilized by different methods was investigated using modified polyethylene (PE) membrane and silica (SiO2) as carriers, and then modified with polydopamine/polyethyleneimine (PDA/PEI) PE- and SiO2-immobilized CA were used as research objects. The optimum reaction conditions and stability were investigated. The results show that under the same reaction conditions, the activity recovery of PDA/PEI-SiO2 immobilized CA was the highest, which was 58.8%, and the activity recovery of PDA/PEI-PE immobilized CA was 17.1%. Their retentive activities were 84.8% and 90.2%, respectively, after 10 use recycles. The optimum reaction conditions of immobilized enzymes were 35℃ and pH 8.5, which were the same as those of free enzymes. The stability of the two immobilized enzymes at higher temperature (55—65℃) and higher acid concentration (>0.010 mol/L) was better than that of free enzyme. Mg2+ could significantly promote the activity of free enzyme and immobilized enzyme, while K+ and Mg2+ had no obvious effect. PDA/PEI-SiO2 and PDA/PEI-PE immobilized CA retained 95.2%和92.4% activity after stored at 4℃ for 10 d. When used in the CO2 hydration reaction, the amount of CaCO3 produced was 120% and 70% of free CA. The immobilized CA has great potential in the industrial application of CO2 capture.

    Energy and environmental engineering
    Study on waste heat boiler ash deposition characteristics in sensible heat recovery process of converter gas
    Wenxiang NI, Jing ZHAO, Bo LI, Xiaolin WEI, Dongyin WU, Di LIU, Qiang WANG
    2023, 74(8):  3485-3493.  doi:10.11949/0438-1157.20230726
    Abstract ( 116 )   HTML ( 7)   PDF (1992KB) ( 167 )  
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    The fully dry sensible heat recovery process of converter gas is an alternative to the existing OG and LT processes, and can further recover sensible heat resources of converter gas. However, the dust accumulation of waste heat boiler caused by the heavy dust of converter gas is seriously affecting the long-term stable operation of the system. In this paper, based on the ash accumulation of a 100 t converter boiler during actual operation, the particle size distribution of ash particles was analyzed by using molecular sieve and DLPI, and then the main components and proportion of ash particles with different particle sizes were analyzed in detail by XRD, XRF and SEM-EDS characterization methods. Finally, the bonding characteristics of ash particles were studied through experiments. The results show that the particle size of boiler ash deposition in the dry process is mainly distributed between 0.3—3 μm and 70—100 μm, and the main components are iron oxides of different valence states. The bonding experiment shows that the smaller the particle size of ash particles, the greater the adhesion strength after sintering, the adhesion strength will increase significantly with the extension of sintering time, and the thermal shock will reduce the adhesion strength of ash particles.

    Performance comparison of different working pairs on a liquid desiccant dehumidification system with vacuum regeneration
    Xiaosong CHENG, Yonggao YIN, Chunwen CHE
    2023, 74(8):  3494-3501.  doi:10.11949/0438-1157.20230646
    Abstract ( 86 )   HTML ( 0)   PDF (2012KB) ( 55 )  
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    An experimental and simulation study on a liquid desiccant dehumidification system with vacuum regeneration is carried out in this paper. The experiment compares the system performance of LiCl solution and mixed solution of CaBr2∶CaCl2=1∶1. It is found that the outlet moisture content and COP of the two solutions are relatively close. When the driving temperature is 62℃, the system COP is about 0.65. The simulation results show that the dehumidification performances of the two solutions are very close under the same heat and mass transfer coefficient, and the COP of the mixed solution is slightly higher than that of the LiCl solution. At the driving temperature of 84℃, the outlet humidity of the mixed solution is about 6.0 g/kg, and the system COP is about 0.81. The higher the inlet humidity, the higher the system COP will be. Due to the lower specific heat capacity of the mixed solution, the heat consumption of the mixed solution in the regenerator is slightly lower, resulting in a slightly higher COP than that of the LiCl solution. In summary, the mixed solution of CaBr2-CaCl2=1∶1 can be a good substitute for LiCl solution in the liquid desiccant dehumidification system, which can achieve low cost and high performance.

    Working fluid screening and thermodynamic optimization of hazardous waste incineration coupled organic Rankine cycle system
    Manzheng ZHANG, Meng XIAO, Peiwei YAN, Zheng MIAO, Jinliang XU, Xianbing JI
    2023, 74(8):  3502-3512.  doi:10.11949/0438-1157.20230371
    Abstract ( 93 )   HTML ( 2)   PDF (2242KB) ( 122 )  
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    In addition to meeting the heat demand and loss of the own system, most of the heat generated by the incineration of hazardous waste can be used as a heat source for the low-temperature power generation system. The saturated steam generated from the waste heat boiler is used as a latent heat type heat source to drive the organic Rankine cycle system. The screening of working fluid is performed based on the thermodynamic and thermo-economic analysis. The basic process of the hazardous waste incineration system was further optimized. The regenerative ORC was analyzed and compared with the basic ORC. The results show that Benzene can provide the optimal performance and is suggested as the ORC working fluid. The optimization of the hazardous waste system increases the ORC capacity by 24.5%. Compared with the basic ORC, the net output work, thermal efficiency, and exergy efficiency of the regenerative ORC system are increased by 19.98%, 35.57%, and 19.99%, respectively.

    Development of novel working fluid and study on electrochemical characteristics of reverse electrodialysis heat engine
    Yali HU, Junyong HU, Suxia MA, Yukun SUN, Xueyi TAN, Jiaxin HUANG, Fengyuan YANG
    2023, 74(8):  3513-3521.  doi:10.11949/0438-1157.20230595
    Abstract ( 91 )   HTML ( 1)   PDF (1762KB) ( 102 )  
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    Reverse electrodialysis (RED) heat engine can convert low grade heat into electricity. As the core component of the heat engine, the performance of the RED stack directly affects the overall performance. In order to enhance the energy conversion efficiency of the heat engine, this paper develops a ternary working fluid composed of lithium chloride, ammonium chloride, and water suitable for RED heat engine, and compares the electrical conductivity and electrochemical properties of the inlet and outlet solutions of the RED stack with conventional sodium chloride aqueous solution. Firstly, the electrical conductivity of lithium chloride and ammonium chloride with different ratios as the working fluid of the RED stack was tested, and the optimal ratio of the two salts was screened out by comprehensive evaluation based on the electrochemical performance indicators of the stack, such as internal resistance and maximum power density. The optimal molality ratio was found to be 2∶8. The lithium chloride and ammonium chloride salt solution with this optimal ratio were then applied to the RED stack. The influence of different concentrations of concentrated and dilute solutions on the electrical conductivity of the inlet and outlet solutions of the RED stack and the internal resistance of the stack were studied by experimental comparison with conventional NaCl aqueous solution. The results show that appropriately increasing the concentration of concentrated and dilute feed solutions is beneficial to reducing the internal resistance of the RED stack, thereby improving the stack performance.

    Oxalic acid and UV enhanced arsenic leaching from coal in flue gas desulfurization by coal slurry
    Jintong LI, Shun QIU, Wenshou SUN
    2023, 74(8):  3522-3532.  doi:10.11949/0438-1157.20230513
    Abstract ( 75 )   HTML ( 3)   PDF (2387KB) ( 94 )  
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    Currently, coal is still the main energy source in our country. During coal combustion, arsenic will be discharged into the atmosphere with flue gas. Arsenic is highly toxic and harmful to the environment and human health. Therefore, it is of great practical significance to study the arsenic removal technology from coal. Using N2, O2 and SO2 to simulate flue gas, the effects of main factors on arsenic leaching from coal, As(Ⅲ) oxidation and SO2 removal were studied in a 1 L photoreactor. The process mechanism was analyzed, and the rate control step of the leaching process was determined. The results showed that both ultraviolet(UV) irradiation and oxalic acid could effectively increase the extraction ratio of arsenic. At 180 min, under pH 2.5 and dark conditions, adding 1.0 mmol/L oxalic acid could increase the arsenic extraction ratio by 32.9%. Under UV irradiation, the arsenic extraction ratio could be further increased by 21.3%, and the ratio of As(Ⅲ) in the leaching solution to the total arsenic was less than 13%, and the SO2 removal efficiency could also be improved. Low pH was beneficial for arsenic leaching from coal, but unfavorable for SO2 removal. Both arsenic extraction ratio and SO2 removal efficiency increased significantly with the increase of temperature. The apparent activation energy for process of arsenic leaching from coal was calculated to be 4.9 kJ/mol, indicating that the arsenic leaching process was controlled by the diffusion process in the reacted solid layer. The free radical quenching experiments showed that sulfate radical and hydroxyl radical were the main free radicals in the oxalic acid-enhanced coal arsenic leaching system under UV irradiation. ATR-FTIR and XPS characterization results further confirmed the measured results of the leaching solution.

    Optimal power point optimization method for aluminum-air batteries under load tracking condition
    Guoze CHEN, Dong WEI, Qian GUO, Zhiping XIANG
    2023, 74(8):  3533-3542.  doi:10.11949/0438-1157.20230485
    Abstract ( 70 )   HTML ( 2)   PDF (2472KB) ( 51 )  
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    Based on the second-order equivalent circuit of aluminum-air battery stack, the models of internal resistance and electrical output characteristics was established, and the effects and variation rules of operating conditions on activation internal resistance, ohmic internal resistance, concentration internal resistance and total internal resistance of stack was studied. On the premise that the output of the stack meets the demand of any load, taking the minimum total internal resistance as the optimization objective, and based on the concept of “optimal power point”, an optimization method of operating conditions based on particle swarm optimization were proposed. The optimal working temperature, electrolyte concentration and output voltage are obtained, and the output performance of the stack is optimized. Through simulation research and experimental research, the validity and reliability of the model and method are verified. The results show that under the condition of load tracking, the total internal resistance of the stack is the lowest at the optimal power point, and the effect and variation law of operating conditions on the output performance of stack are consistent in AC impedance characteristics and U-I output characteristics. The optimization method can improve the output performance of the stack and reduce the energy loss in the stack.

    Effects of environmental factors on calcium carbonate precipitation induced by Klebsiella aerogenes
    Chongda DUAN, Xiaowei YAO, Jiahua ZHU, Jing SUN, Nan HU, Guangyue LI
    2023, 74(8):  3543-3553.  doi:10.11949/0438-1157.20230318
    Abstract ( 118 )   HTML ( 8)   PDF (8785KB) ( 59 )  
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    As the core product of microbially induced calcium carbonate precipitation (MICP) reaction, the precipitation characteristics of calcium carbonate have an important influence on the engineering properties of MICP-treated materials. The effects of calcium acetate (CA) concentration, bacterial solution (BS) concentration, and pH of initial solution on the precipitation characteristics of calcium carbonate induced by Klebsiellaaerogenes were investigated by full factor experiments, X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM). When the concentration of calcium acetate was 0.5 mol/L, the concentration of bacterial solution was ODnature, and the initial solution pH was 10, the amount of calcium carbonate precipitation was the largest. When the CA was 0.25—0.5 mol/L, calcite and vaterite coexisted; when the CA was 1.0 mol/L, calcium carbonate crystals had the polymorph of vaterite. When the CA was 0.25 mol/L, the BS concentration and pH of initial solution had a major impact on the polymorphs of calcium carbonate. The crystal size of calcium carbonate ranged from 7.6 μm to 15.1 μm; the calcite crystals had rhombohedral and lamellar shapes, and vaterite crystals had spherical and fusiform shapes. The average elastic modulus of vaterite is 15.9 GPa, and calcite is 22.7 GPa. The three main environmental factors can regulate the precipitation amount, polymorph, and morphology of calcium carbonate crystals induced by Klebsiellaaerogenes while the pH of initial solution plays a prominent role in regulating the particle size of calcium carbonate. This provides theoretical support for regulating the MICP process and establishing the relationship between the microscopic properties of calcium carbonate crystals and the engineering properties of the processed materials.

    Research on F3EACl modification layer for improving performance of perovskite solar cells
    Yu FU, Xingchong LIU, Hanyu WANG, Haimin LI, Yafei NI, Wenjing ZOU, Yue LEI, Yongshan PENG
    2023, 74(8):  3554-3563.  doi:10.11949/0438-1157.20230347
    Abstract ( 126 )   HTML ( 9)   PDF (4272KB) ( 283 )  
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    In general, traps and grain boundaries (GBs) on the perovskite surface are very detrimental to the performance and long-term stability of perovskite solar cells (PSCs). In this study, a trifluoroethylamine hydrochloride (F3EACl) containing F atoms was used as a modified layer deposited between the perovskite (PVSK) layer and the hole transport layer (HTL) to passivate the perovskite defects and GBs on the surface. Through the study of the crystallinity, morphology, photophysical properties, and photovoltaic performance of F3EACl modified perovskite films, it was found that the N—H … F hydrogen bonding between F3EACl and perovskite, as well as the interaction between F3EA+ and I- in perovskite, can passivate defects on the perovskite surface, thereby improving the performance and stability of the device. In addition, the F3EACl modified layer can also adjust the energy level distribution between the perovskite layer and the HTL, thereby improving the hole extraction efficiency. The results showed that the power conversion efficiency (PCE) of PSCs modified by F3EACl increased from 19.15% to 22.45%. This indicates that F3EACl is a better material to passivate perovskite traps to improve the performance and stability of PSCs.

    Preparation of molecularly imprinted-TiO2 and its properties of photoelectrocatalytic degradation of solubilized PHE
    Xin YANG, Xiao PENG, Kairu XUE, Mengwei SU, Yan WU
    2023, 74(8):  3564-3571.  doi:10.11949/0438-1157.20230304
    Abstract ( 99 )   HTML ( 2)   PDF (1302KB) ( 43 )  
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    Three types of molecularly imprinted-TiO2 (MIP-TiO2) were prepared by sol-gel method using phenanthrene (PHE), the Triton X-100 (TX-100) and their mixture as templates, respectively, and n-butyl titanate as the functional monomer. The corresponding thin film electrodes were prepared for treating simulated soil washing effluent within solubilized PHE by photoelectrocatalytic method. The properties of the MIP-TiO2 and their thin film electrodes were characterized by XRD, nitrogen adsorption-desorption and SEM. The results showed that MIP-(TX-100) TiO2 present outstanding property of removal solubilized PHE. With TX-100 as imprinted molecules, the crystallization of MIP-(TX-100) TiO2 appears rutile phase, its specific surface area reached 63.533 m2/g, and the agglomeration of nanoparticles was also improved. The adsorption process of MIP-(TX-100) electrode towards solubilized PHE (30 mg/L) by TX-100 (5 g/L) followed the secondary kinetic model, which suggested that the process was mainly controlled by chemisorption. It is speculated that TiO2 produces a large number of imprinted holes due to the molecular imprinting process. After the imprinted holes are enriched in TX-100 during the photocatalytic process, PHE breaks the micelle barrier, thereby improving the degradation efficiency of PHE.

    Material science and engineering, nanotechnology
    Preparation and properties of silicone/phenolic hybrid aerogel
    Wenjie XU, Xianfeng JIA, Jitong WANG, Wenming QIAO, Licheng LING, Renping WANG, Zijian YU, Yinxu ZHANG
    2023, 74(8):  3572-3583.  doi:10.11949/0438-1157.20230500
    Abstract ( 183 )   HTML ( 13)   PDF (6778KB) ( 235 )  
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    The inherent brittleness of phenolic aerogels limits its application in the fields of adsorption and heat insulation. In this study, silicone solution was prepared by using 3-aminopropyltriethoxysilane and terephthalaldehyde, which is mixed with the solution of thermoplastic phenolic resin and hexamethylene tetramine, solving the compatibility problem between the two systems through chemical bonding, and sol-gel reaction and ambient pressure drying were carried out to obtain the silicone/phenolic hybrid aerogel. Due to both the introduction of flexible silicone molecular chains and the effect of smaller gel particle size, the brittleness of phenolic aerogel is overcome. The results indicate that obtained hybrid aerogel possesses nanoscale gel network structure, and has a low density of 0.187 g/cm3 and a low room-temperature thermal conductivity of 0.035 W/(m·K). Besides, the hybrid aerogel can better dissipate the stress instead of experiencing brittle fractures under compressive stress. The modulus of the hybrid aerogel is as low as 13.92 MPa, 46% lower than that of phenolic aerogel. This hybrid aerogel prepared with a facile and efficient method is of promising application prospects.

    Preparation and microwave absorption properties of carbon nanofibers embedded with ultra-small CeO2 nanoparticles
    Xingzhi HU, Haoyan ZHANG, Jingkun ZHUANG, Yuqing FAN, Kaiyin ZHANG, Jun XIANG
    2023, 74(8):  3584-3596.  doi:10.11949/0438-1157.20230607
    Abstract ( 116 )   HTML ( 23)   PDF (5970KB) ( 194 )  
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    Ultra-small CeO2 nanoparticles uniformly embedded in carbon nanofibers (CeO2@CNFs) composites were prepared by electrospinning and subsequent heat treatment. The effect and regulation mechanism of CeO2 content on the electromagnetic characteristics and microwave absorption properties of CeO2@CNFs were investigated in detail. It is found that with the increase of CeO2 content, the dielectric loss and electromagnetic attenuation ability of the composites decreases while the impedance matching is effectively improved, and the microwave absorption ability first increases and then weakens. The CeO2@CNFs-2 sample with a CeO2 content of about 24.6%(mass) exhibits the best microwave absorption performance due to its better balance between electromagnetic attenuation and impedance matching. When the filler loading is only 10%(mass) in paraffin wax matrix and the absorber thickness is 3.0 mm, the minimum reflection loss (RL) of CeO2@CNFs-2 reaches -45.4 dB at 10.7 GHz, and the effective absorption bandwidth (RL <-10 dB) is 5.6 GHz (9.1—14.6 GHz), covering approximately 75% of X-band and 45% of Ku-band. Notably, the microwave absorption intensity of CeO2@CNFs-2 is 3.1 times that of pure CNFs, indicating that the synergistic effect of both CNFs and CeO2 can effectively boost the microwave absorption performance of the composite.

    Process safety
    Study on the inhibition effect and mechanism of waste incineration fly ash on gas explosion pressure and flame propagation
    Ke YANG, Yue JIA, Hong JI, Zhixiang XING, Juncheng JIANG
    2023, 74(8):  3597-3607.  doi:10.11949/0438-1157.20230740
    Abstract ( 101 )   HTML ( 15)   PDF (5072KB) ( 114 )  
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    The effects of different mass of waste incineration fly ash ( FA ) powder on methane explosion pressure, flame propagation velocity and flame propagation morphology were studied by self-built visual methane explosion experimental platform under the conditions of methane gas concentration of 8% (oxygen-enriched), 9.5% (equivalent) and 12% (oxygen-poor). The composition, particle size, surface microstructure and thermal stability of FA were analyzed by XRD, particle size analysis, scanning electron microscopy and thermogravimetric analysis. Combined with physical characterization, the explosion suppression mechanism of FA was analyzed. The results show that FA has a good explosion suppression effect on different concentrations of methane explosion. In this experiment, the best spraying amount of FA for 8%, 9.5%, and 12% methane inhibition was 360 mg, 360 mg, and 400 mg, respectively. The addition of FA powder hinders the development and propagation of methane explosion flame, disrupts the flame shape, and the flame intensity is obviously weakened. The FA has smaller particle size, porous microstructure, larger specific surface area and porosity, and higher heat absorption, with a total mass loss change of 37.07%. FA powder has dual explosion suppression properties of physics and chemistry.

    The microscopic mechanism on MPP inhibiting explosion of Al-Mg alloy powder
    Zhenbao LI, Chao LI, Hu WANG, Shaorui WANG, Quan LI
    2023, 74(8):  3608-3614.  doi:10.11949/0438-1157.20230598
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    There is a certain explosion risk in the polishing process of Al-Mg alloy. To reduce the damage of explosion accident on Al-Mg alloy powder, melamine polyphosphate (MPP) was selected to study the suppression mechanism of Al-Mg alloy powder explosion. The effect of MPP on the dust explosion characteristics of aluminum-magnesium alloy was analyzed by using 20 L explosion ball and thermal analysis experiment. Combined with the chemical composition analysis and the functional group change of the explosion products, the mechanism on MPP inhibiting the explosion of Al-Mg alloy powder was analyzed. The results show that the addition of 70% (mass) MPP in Al-Mg alloy dust can achieve complete explosion suppression. It was endothermic during MPP decomposition and inert gases (NH3, H2O, and CO2) were generated for reducing oxygen concentration. In this process, the polyphosphate transformed to phosphoric acid, which can reacts with the active group. The effect of MPP on inhibiting the oxidation of Al to form AlO groups is obviously better than that on inhibiting the oxidation reaction of Mg. The results can provide theoretical basis for industrial prevention on explosion accident of Al-Mg alloy powder.