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    28 June 2024, Volume 24 Issue 6
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    Contents
    Cover and Contents
    The Chinese Journal of Process Engineering. 2024, 24(6):  0. 
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    Review
    Main advances in preparation technology of zirconia hollow microspheres
    Baoqiang LI Huacheng JIN Fei DING Chun WANG Fangli YUAN
    The Chinese Journal of Process Engineering. 2024, 24(6):  627-635.  DOI: 10.12034/j.issn.1009-606X.223297
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    Zirconia hollow microspheres have attracted more attention because of their excellent performance, which combines the advantages of the properties of zirconia and hollow structural materials, such as low thermal conductivity, ablation resistance, and chemical corrosion resistance. Zirconia hollow microspheres is an important feedstock for preparing thermal barrier coatings. The thermal barrier coating prepared by zirconia hollow microspheres has the characteristic of excellent insulation and corrosion resistance. The performance of the coating is determined by the characteristics of the powder. The preparation of high quality zirconia hollow spherical powder has become a hot topic in the industry. In this work, the research status of the preparation technology of zirconia hollow spherical powder is analyzed, and the main preparation approaches are introduced, including templating, solvothermal, spray drying, and plasma sintering. In addition, the characteristic of these approaches is briefly summarized. Templating method contributes to obtaining hollow zirconia spheres with perfect morphology. However, some problems such as difficulty both in template synthesis and subsequent template removal, which can cause the material waste and damage to hollow particles. For solvothermal method, the reaction conditions are relatively harsh, and it also involves cumbersome process, such as separation, washing and drying process, which makes it difficult to batch preparation of hollow microspheres. The spray drying method is an effective approach for batch preparation of hollow microspheres. However, the hollow microspheres prepared by spray drying possesses have low strength and become easy to be damaged during application. Importantly, it is considered that the hollow microspheres prepared by spray drying combined with plasma sintering process have the advantages of high sphericity, good fluidity, and controllable particle size distribution, which are more conductive to preparation of coatings.
    Research progress on the mechanism and influencing factors of microorganisms to increase coalbed methane production
    Na ZHANG Xuefeng YIN Zichen WANG Hao LIU Minjie HUANG Hao WANG Dongxu LIANG Jianan HU
    The Chinese Journal of Process Engineering. 2024, 24(6):  636-646.  DOI: 10.12034/j.issn.1009-606X.223310
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    Microbially enhanced coalbed methane (MECBM) is an innovative technology for the extraction and utilisation of coalbed methane (CBM), which involves the microbial degradation and conversion of certain organic components of coal into methane gas. MECBM has great potential and environmental characteristics, and offers the prospect of establishing a new type of energy system, which will hopefully lead to the development of a sustainable energy source, and will effectively alleviate the challenges posed by energy shortages and greenhouse gas emissions. However, widespread application of MECBM technology faces the obstacles of historically low natural CBM production and sub-optimal quality. In order to understand the production potential of coal biogenic methane and the factors controlling the process, with a view to advancing the direction of its research towards continuous progress and effectively increasing coalbed methane production. This review summarises the mechanism and influencing factors of microbial CBM production, providing a theoretical basis for microbial CBM production. Firstly, the background and current research status of microbial production of CBM are reviewed. Subsequently, the basic theory and reaction process of coal biogenic methane production are summarised, showing that acidification of methoxy plays a decisive role in the process of coal biogenic methane production. Then, the environmental and biological factors affecting microbial enhancement of coalbed methane production are summarised, including the temperature of the coalbed, inoculum amount, nutrient addition, and pretreatment method. These factors have a significant impact on microbial CBM production, and optimising natural gas production conditions can not only increase CBM production but also significantly improve the methane concentration in CBM. In conclusion, microbial enhanced CBM technology has great potential and is expected to provide new solutions to the problems of energy shortage and greenhouse gas emissions by optimising production conditions and improving the viability and adaptability of microorganisms. Finally, this study outlines the current challenges and areas for further research in biogenic CBM development, providing a theoretical basis for increasing on-site production and enhancing CBM development.
    Advances in wet particle size-grading technologies and precise grading of aluminum hydroxide
    Jianqing Pi Mingli WANG Ruyi YANG Haidong ZHANG Xiaona REN Qingshan HUANG Ping LI
    The Chinese Journal of Process Engineering. 2024, 24(6):  647-659.  DOI: 10.12034/j.issn.1009-606X.223331
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    With the booming development of the electrolytic aluminum industry, both modern large-scale prebaked aluminum reduction cells and dry purification technology require sandy alumina as the production raw material. However, domestic alumina enterprises mainly produce intermediate or "quasi-sand" alumina, and the particle size changes periodically. The product quality differs significantly from the world's advanced level, mainly due to differences in raw materials and substandard aluminum hydroxide particle screening technologies in the prior art. Therefore, it is urgent to develop a high-precision and high-efficiency wet particle classification device for aluminum hydroxide to produce high-quality sandy alumina with large and narrow particle size distribution (+80 μm≥90%, -45 μm<8%). The commonly employed and large-scale application of wet particle size-grading technologies in domestic and foreign countries are first reviewed. The performance of hydraulic classification, wet screening, and some new coupling classification technologies are analyzed. Then, a new particle grading method of fluidization followed by screening for precise grading of aluminum hydroxide particles is proposed by combining hydraulic classification and sieve screening. Finally, a small-scale grading device (3.3 m3/h) capable of achieving large-scale continuous production is developed and passed the verification of on-site production siding in the production enterprise. This new type of precise particle classification technology is not only expected to realize energy conservation and emission reduction, transformation and upgrading, reduction of production costs, and significant economic benefits in the alumina industry but also promote the rapid development of mineral processing and fine powder industries, having some important and practical application and promotion values.
    Research Paper
    Evaporation characteristics of multiple droplets of isobutane alkylated effluent during refrigeration
    Xu HAN Rui ZHANG Xianghai MENG Tao ZHENG Haiyan LIU Mengxi LIU Chunming XU Zhichang LIU
    The Chinese Journal of Process Engineering. 2024, 24(6):  660-669.  DOI: 10.12034/j.issn.1009-606X.224001
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    Isobutane alkylation catalyzed by composite ionic liquid is a new technology for the production of high quality and clean gasoline blending components. Maintaining the appropriate temperature during the alkylation reaction is crucial, and effluent cooling emerges as a pivotal measure in this regard. Currently, heat exchangers are used to cool the effluent, but there are shortcomings such as large heat exchange area requirements, high equipment cost and limited cooling effect. The presence of excess isobutane makes it possible to cool the effluent with flash spray. In order to develop a new refrigeration process for alkylated effluents, the evaporation characteristics of isobutane droplets under reduced pressure were studied. Since isobutane is a gas at room temperature and pressure, it is difficult to exist as a liquid. Therefore, a special experimental device was set up to study the evaporation process of isobutane droplets in this work. Single isobutane droplet or multiple droplets were suspended at the top of thermocouples to measure the temperature variation of each droplet, while a high-speed camera recorded the evaporation process. The effects of final pressure, ambient temperature, and droplet spacing on droplet evaporation characteristics were analyzed. The results showed that isobutane droplets underwent intense evaporation and stable evaporation phases, and the evaporation behavior of multi-droplet was similar to that of single droplet. During the stable evaporation phase, all droplets followed the classical d 2 law, and the evaporation rate of the edge and center droplets was below the single droplet. With the increase of the final pressure and the decrease of the ambient temperature, the difference between the evaporation rate of the center droplet and the single droplet gradually increased. The temperature field and vapor concentration field during droplet evaporation had a limited range of variation. When the distance between the two droplets increased to 5.48d0, the evaporation rate of the droplet gradually approached that of the single droplet.
    Numerical study on heat transfer and resistance characteristics of heat transfer element of rotary heat exchanger
    Yi SUN Fuping QIAN Lingtao YU Yue WU Naijin HUANG Hao WU
    The Chinese Journal of Process Engineering. 2024, 24(6):  670-680.  DOI: 10.12034/j.issn.1009-606X.223248
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    In this work, the rotary heat exchanger for waste heat recovery of SCR (Selective Catalytic Reduction) low temperature denitration system in cement kiln is taken as the research background, and a typical heat transfer element in the rotary heat exchanger is selected as the base plate type. The structural improvement methods with different proportions of corrugated height and different corrugated inclination angle are proposed and a series of new-style heat transfer elements are obtained. The flow resistance and heat transfer characteristics of different heat transfer elements are compared and analyzed by three-dimensional numerical simulation method, and the area mass factor j/f is introduced to represent the comprehensive heat transfer performance of the heat transfer elements. The results show that under the same heat transfer condition, the flow disturbance at the boundary layer of the heat transfer element with the corrugated height proportion of 3:1 is gentler than heat transfer elements that of other corrugate height proportion. Therefore, its Nusselt number value is the smallest, the value of the friction coefficient is the smallest, but the area mass factor is the largest. This also proves that the heat transfer element after the adjustment of the corrugated height proportion has improved the comprehensive heat transfer performance compared with the original CU heat transfer element. Under the premise of a heat transfer element with the corrugated height proportion of 3:1, the inclination angle of corrugate is changed in the range of 30°~60°. It is found that, the greater the inclination degree of the heat transfer element, the stronger the flow mixing, the larger the value of the corresponding Nusselt number is, and the larger the value of the friction coefficient is, while the increase of the friction coefficient with the increase of the degree of corrugate inclination is greater than that of the Nusselt number. When the inclination angle of the corrugate is 30°, the comprehensive heat transfer characteristics of the heat transfer element are optimal. The results show that the structure improvement can improve the comprehensive heat transfer performance of flow heat transfer element.
    Application research based on optimization of key parameters in heavy gas dispersion model
    Jiamei YIN Haiyan LIU Zechun LIU Wei WU Juanxia HE
    The Chinese Journal of Process Engineering. 2024, 24(6):  681-691.  DOI: 10.12034/j.issn.1009-606X.223272
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    Leakage accidents from storage tanks with dangerous chemicals may cause catastrophic consequences. For the purpose of improving the predicted accuracy of heavy gas dispersion during release incidents, the dispersion coefficients were improved in SLAB to obtain the SLAB-D model. Then SLAB-MD model was developed by integrating the optimization algorithms of dispersion coefficients based on the SLAB-M. The Jack Rabbit II (Trials 1, 7, and 9) liquid chlorine leakage experiments were employed as the dataset to evaluate and validate models' performance. The outcomes revealed that the four models' performances were ranked as SLAB-MD>SLAB-D>SLAB-M>SLAB, and the statistical performance measurements (SPMs) of the SLAB-MD model were close to the ideal values, among which the mean relative bias (MRB), geometric mean (MG), mean relative square error (MRSE), geometric variance (VG), and factor of 2 (FAC2) were 0.27, 1.34, 0.18, 1.24, and 0.93, respectively, which proved that SLAB-MD was excellent in accurately predicting the dispersion of heavy gas leaks. Finally, the model was used to analyze three typical heavy gas leakage and dispersion accidents at domestic and international, which obtained key information such as heavy gas concentration distribution and three-dimensional concentration surface. Additionally, the range of potential casualties was predicted based on the protective action criteria values (PACs). The potential impact zones at the downwind distance, including fatalities, serious injuries, and minor injuries, were 0.15, 1.75, and 7.6 km2, 0.22, 1.98, and 7.03 km2, and 0.12×10-3, 0.29×10-3, and 0.88×10-3 km2 in the context of liquid chlorine continuous release, liquid chlorine instantaneous leakage, and vinyl chloride continuous discharge, respectively. At sensitive points, the longest escape time was 28 min for liquid chlorine continuous leakage accident, and aftereffect time was 40 min for vinyl chloride continuous release accident. In summary, these predictions provide critical information and effective technical guidance that can be used for emergency response planning and management involving hazardous chemical material spills.
    Bed characterization and flow heat transfer simulation of fixed bed reactor with low tube to particle diameter ratios
    Weinan MO Youyong SU Dongdong ZHU
    The Chinese Journal of Process Engineering. 2024, 24(6):  692-704.  DOI: 10.12034/j.issn.1009-606X.223294
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    Tubular fixed beds are widely used in high-temperature catalytic cracking processes. Investigating the structural characteristics of fixed beds with low tube to particle diameter ratios and the flow heat transfer laws at high temperatures can provide valuable insights for optimizing the fixed bed high-temperature catalytic cracking process. To address the issues of inaccurate particle description in the discrete element method and difficulty in mesh delineation in the particle resolution method, a new contact point method is proposed. This method does not alter the particle and bed size and shape parameters, adapts to various particle shapes, and significantly reduces the difficulty of model contact processing. Three cylindrical particle beds with different ratios of the inner diameter of the reaction tube to the equivalent diameter of spheres of equal specific surface area of the cylindrical particles (tube-diameter ratio D/dp) and one spherical particle bed are generated to investigate the effects of tube size ratio and particle shape on bed structure and flow heat transfer characteristics. The results show that the overall void ratio of the bed layer decreases with increasing tube to particle diameter ratio, the particle stacking is distributed in circles, and the radial distribution curves of radial void ratio and axial mean velocity are highly consistent. Additionally, the pressure drop is generally consistent with Eisfeld modified equation. Furthermore, the bed flow field distribution is highly correlated with the bed structure, and the size of the flow channel voids directly affects the generation of channel flow phenomena, which further impacts its temperature field distribution and heat transfer performance. The sphere particle bed exhibits a more uniform temperature field distribution, but its heat transfer performance is not as good as that of the cylind particle bed.
    Study on effect of common liquid hopper of parallel hydrocyclones on pressure drop
    Xiulin LIU Jianyi CHEN Hongbin ZHANG Shenrou GAO
    The Chinese Journal of Process Engineering. 2024, 24(6):  705-715.  DOI: 10.12034/j.issn.1009-606X.224078
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    To reduce the pressure drop of the parallel hydrocyclones, a new type of common liquid hopper for the circumferential type was designed. The pressure drop and separation efficiency of four conventional parallel hydrocyclones with and without the common liquid hopper were measured experimentally. The flow field inside the parallel hydrocyclones was numerically simulated using Fluent software, and the influence of common liquid hopper on the air core, tangential velocity, and swirl stability were analyzed. The results showed that the pressure drop of the parallel hydrocyclones group with common liquid hopper was lower than that of the conventional group, while the separation efficiency remained unchanged. The average pressure drop reduced by 1.9%, and the maximum pressure drop reduced by 3.36% when the inlet velocity reached 5.0 m/s. Compared with conventional parallel connection, a common liquid hopper could form a bottom flow liquid seal, causing the disappearance of air core in the parallel hydrocyclones group, resulting in a reduction in turbulent energy dissipation. And at high flow velocity, the area of quasi forced vortices expanded, making the gradient of tangential velocity change smoother and the maximum tangential velocity remained unchanged. So these phenomena helped to reduce energy consumption. A parallel vortex flow system could be formed inside a common liquid hopper. In this system, each flow vortex was constrained by other vortices. The oscillation amplitude of the vortex core in the system was smaller than that of a single vortex, so its stability was stronger. This self stability of the vortex flow system in the common liquid hopper also enhanced the stability of the swirling flow in each hydrocyclone, which helped to reduce pressure drop. Therefore, the common liquid hopper could reduce the pressure drop of parallel hydrocyclones while maintaining separation efficiency, providing guidance for the design and application of circumferential parallel hydrocyclones.
    Effect of LF refining slag addition on wear resistance of Fe-Cr based ceramic composites
    Guochun DONG, Hao WU, Haoran LIN, Sufen TAO, Long CHEN
    The Chinese Journal of Process Engineering. 2024, 24(6):  716-725.  DOI: 10.12034/j.issn.1009-606X.223267
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    LF refining slag contains iron oxide, calcium oxide, silicon dioxide, aluminum oxide, magnesium oxide, iron and so on. However, it is always piled up as solid waste, which not only pollutes the environment but also results in the waste of alloying elements. Some of the alloying oxide can be reduced by Al during thermite reaction, which can reduce waste of alloying elements in LF slag. Calcium oxide can react with aluminum oxide formed by thermite reaction, which can reduce melting point of aluminum oxide and make it easy to float. In addition, mixture of LF refining slag and CaF2 can be added as coolant, which will solve the problems of evaporation of reaction raw materials and low density of Fe-Cr based ceramic composites caused by high heat release of combustion synthesis reaction system, to absorb reaction heat and reduce the temperature of reaction system to reduce the evaporation of raw materials. However, the wear-resistant layer could not connect with the steel plate as too many LF refining slag were added. In this work, in order to explore the appropriate amount of LF refining slag, 2, 4, 6, 8, 10 g LF refining slag and 2.39, 2.50, 2.60, 2.71, 2.81 g CaF2 were designed to study the welding area of steel plate and wear-resistant layer, the density, hardness, and wear resistance of samples fabricated by combustion synthesis. The results showed that the density of wear-resistant layer was the best as added 8 g LF refining slag; abrasion loss per unit area of wear-resistant layer was the least as added 8 g LF refining slag; the hardness of the wear layer was the highest as added 10 g LF refining slag; the welding area of wear-resistant layer and steel plate was the largest as added 10 g LF refining slag. Both density and hardness had positive effect on the wear resistance of the composite, which would be increased with increase of each of them as difference of the other property was not large. In summary, in order to obtain high wear resistance while ensuring the uniformity of other properties of Fe-Cr based ceramic composites, the optimal addition amount of LF refining slag is 8 g.
    Study on optimization parameters for ceramic ball of magnetite-quartz mixed system by response surface methodology
    Jiaqi TONG Jingkun TIAN Yihan WANG Xin YAO Zheyang LI Feng XIE Caibin WU Guisheng ZENG Jindong XU
    The Chinese Journal of Process Engineering. 2024, 24(6):  726-733.  DOI: 10.12034/j.issn.1009-606X.223298
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    Seeking to replace steel balls as fine grinding media to improve the grinding effect is the pursuit of mineral processing plant. In this work, the grinding test of magnetite-quartz system ore with ceramic ball as grinding media were conducted, the response surface method was used to study the effect of ceramic ball size, filling rate and grinding concentration on the average particle size of the grinding product, and the significance of their interaction was analyzed. The results showed that the filling rate had the greatest influence on the average particle size of grinding products, followed by the grinding concentration, and the ball size was the smallest. The interaction between ball size and grinding concentration was the most significant, followed by the interaction with filling rate, while the interaction between filling rate and grinding concentration was not significant. The optimal test conditions predicted by the model were the ball size was 25.96 mm, the filling rate was 34.04%, and the grinding concentration was 70.86%, and the predicted value of the average particle size of the ground product under these conditions was 54.46 μm, which is similar to the experimental average value of 54.41 μm, indicating that the prediction model was reasonable and effective. Comparison of ceramic ball and steel ball test research showed that fine grinding with ceramic ball as grinding media, grinding effect can be significantly improved, and the -0.075 mm particle size yield increased, which was related to the ceramic ball in the mill falling motion was better than the steel ball, ceramic ball crushing rate of fine particle size was higher than the steel ball, which was conducive to improving the effect of grinding. Ceramic ball milling was a new generation of fine grinding technology development direction.
    Optimization of lentivirus production process in a fixed-bed bioreactor
    Siran TAO Jun CHENG Lei CAO Yan ZHOU Wensong TAN
    The Chinese Journal of Process Engineering. 2024, 24(6):  734-745.  DOI: 10.12034/j.issn.1009-606X.223245
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    The lentivirus vectors can stably integrate exogenous genes into the genomes of various cells, making it useful in gene therapy. Among various bioreactors, fixed-bed bioreactors are increasingly used to scale-up the cultivation of adherent cells for the manufacture of lentivirus through plasmid transient transfection. In the fixed-bed bioreactor the production of lentivirus vectors can be heavily affected by various operating parameters. This study aims to optimize the transfection conditions and cell culture parameters during the production of lentivirus, and then validate optimized process conditions in China's domestically-made fixed-bed reactor. The results showed that during the plasmid transfection, the transfection efficiency could be significantly improved in the optimized conditions where the mass ratio of PEI to DNA was 2:1, the DNA concentration during transfection was 2 μg/mL, and the transfection time was 6 hours, respectively. The mass ratio of PEI to DNA was the key factor to the success of transfection. When the ratio of PEI to DNA was below 2:1, the transfection efficiency noticeably reduced and exogenous gene could not be expressed in the HEK293T cells. However, DNA concentration during mixing and mixing time have little effect on transfection efficiency, which mainly affects the expression of exogenous genes in cells. When the HEK293T cells were cultured in shaking bottles based on PET nonwoven fabric, the cells were evenly distributed on the surface of the scaffold and quickly entered the exponential growth phase at a high inoculation density of 5.0×104 cells/cm2. The cell densities that are too high or too low during transfection are not conducive to lentivirus production, and a high lentivirus titer can be obtained when the cell density is 1.0×106 cells/cm2. After process optimization, the lentivirus yield reached 2.4×1010 TU in the fixed-bed bioreactor with an surface of 2.0 m2. The results of this study can provide data support for the development and establishment of the production of lentivirus vectors based on a fixed-bed bioreactor.
    Preparation and electrochemical properties of Li0.98Ca0.02Mn2O4
    Mingsi SHEN Haibo YUAN Doudou ZHANG Jing WANG Gaotian NIU Yangzhou MA Yaxin SUN
    The Chinese Journal of Process Engineering. 2024, 24(6):  746-752.  DOI: 10.12034/j.issn.1009-606X.223075
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    Many research focus on improving the electrochemical properties of LiMn2O4 by chemical doping method. In cubic spinel structure LiMn2O4, the diversity of doping elements and doping positions provides a wide space for improving performance. Doping at the 16d octahedral position occupied by Mn can effectively suppress the Jahn-Teller effect and maintain the stability of the structure. By comparison, using elements with large ion radius to dope at the 8a tetragonal position occupied by Li can enlarge the Li+ diffusion channel and enhance the kinetics diffusion coefficient. In this work, pure phase of Li0.98Ca0.02Mn2O4 was successfully synthesized using the hydrothermal method followed by annealing at 750℃ for 5 h. The crystal structures and the morphologies of the products were analyzed by powder X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). The electrochemical properties were characterized by galvanostatic charge/discharge experiments and electrochemical impedance spectroscope (EIS) tests. XRD analysis showed that the lattice constant increased by 0.12% in Ca-doped LiMn2O4 and the expansion of the crystal cell was beneficial to improving the diffusion of Li+. The small aggregates with porous channels formed by stacking nanoparticles were observed by FESEM. The results showed that Li0.98Ca0.02Mn2O4 exhibited the excellent rate capability with the larger discharge capacity at the relatively current rate range of 0.5 C~5 C. Especially, at 0.5 C, Li0.98Ca0.02Mn2O4 delivered the first discharge capacity of 126 mAh/g, which was 17.8% higher than that of undoped LiMn2O4 samples. The capacity retention of both samples was maintained at about 88.8% after 50 cycles. At 1 C, Li0.98Ca0.02Mn2O4 still holded its high discharge capacity of 117.5 mAh/g and capacity retention of 90% after 50 cycles, 80% after 150 cycles, and 60% after 1000 cycles. Undoped LiMn2O4 sample had low capacity of 57.0 mAh/g, but the capacity retention reacheed 67% after 1000 cycles, indicating good cycle stability. The calculated kinetics diffusion coefficient of Li0.98Ca0.02Mn2O4 was 2.5×10-11 cm2/s, which was about 1.6 times of undoped sample.