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    22 March 2021, Volume 21 Issue 3
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    Contents
    Cover and content
    Chin. J. Process Eng.. 2021, 21(3):  0. 
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    Flow & Transfer
    Effects of pole plate's concave?convex shapes on flow characteristics in water electrolyzer
    Jun LI Juan WANG Jia ZHANG Shuo ZOU Xingchen HE Jiayi WAN
    Chin. J. Process Eng.. 2021, 21(3):  251-258.  DOI: 10.12034/j.issn.1009-606X.220077
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    At present, spherical concave?convex combination structure is widely used in the plate of pressure-filtered water electrolyzer. The purpose is to enhance the disturbance degree of flow and make the distribution of electrolyte more uniform. In order to further improve the flow field distribution, five different concave?convex combination structures were combined with the electrolytic cell plate structure. The flow characteristics and flow field distribution characteristics in different concave?convex combination structures were analyzed and compared by numerical simulation method. The results showed that there were negative velocity distribution regions in the velocity component uz of the five structure channels, which was dominated by circulation flow, and the turbulent kinetic energy was also larger in this region, among which case C and case E structure were most obvious. The local vortices showed the vortices moved from the edge of the depression structure to the interior of the depression, and the details of the vortices flow were closely related to the the concave?convex structure. The distribution of the mean vorticity flux and the vorticity value showed that the concave?convex structure mainly affected the local vorticity intensity, but had little influence on the overall flow, and the local vorticity value in case B was the largest. The uniformity of the flow field distribution was related to the shape and size of the windward face of the concave?convex structure, among which case D teardrop structure had the best uniformity of flow field distribution and case C ellipsoid structure was the worst.
    Application of cutoff distance selection in molecular dynamics simulation of LJ argon system
    Chenyang SUN Chaofeng HOU Wei GE
    Chin. J. Process Eng.. 2021, 21(3):  259-264.  DOI: 10.12034/j.issn.1009-606X.220107
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    In Lennard-Jones (LJ) potential argon system investigated by molecular dynamics simulation, the different cutoff distances are frequently applied to calculate the interactive force between atoms, and some reports have given out the influence of the cutoff distances on the simulation systems. More and more calculations suggest to use 4.5? or even larger truncation distances (? is the diameter of argon atom) to obtain the more accurate thermodynamic properties of the systems. In this work, a simple method was proposed to solve the problem of superheating encountered in the calculation of melting point by direct heating, where an independent track and ensemble at each temperature point are run. And then, the effect of different cutoff distances on the phase diagrams of the melting and boiling points of argon system in the NPT ensemble was studied. The melting point was in good agreement with the experimental and theoretically calculated values when the cutoff distance of 2.5? was used. However, the deviation from the experimental melting point became more evident when the larger cutoff distances were employed. In order to find out the underlying mechanism behind the deviation, the radial distribution functions and velocity autocorrelation function at the melting points and different thermodynamic states of the liquid argon with different cutoff distances were analyzed. It was found that the same thermodynamic properties can be obtained at the corresponding thermodynamic state points under different truncation distances. The mapping between the different thermodynamic state points was understandable due to the different thermodynamic states at the same temperatures under the varied truncation distances, and was beneficial to significantly reduce the computational workload at the smaller cutoff distance. This work proposed an exploratory way for the selection of the cutoff distance in the simulation of liquid argon, where the truncation distance of 2.5? can meet the requirements of computational accuracy and performance in the simulations.
    Simulation of pores-scale reaction?diffusion coupling for the design of catalyst structure
    Gelin WEI Chengxiang LI Wei GE Jinbing LI
    Chin. J. Process Eng.. 2021, 21(3):  265-276.  DOI: 10.12034/j.issn.1009-606X.220111
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    Most catalysts have complicated pore structures, and the coupling of reaction and diffusion processes in the pores determines the overall performance of catalysts. Understanding the reaction-diffusion coupling in the pores is important for better design of catalysts to improve their performance. In this work, the coupling of reaction and diffusion of reactants and products in catalyst pore structures was simulated by using the hard-sphere/pseudo-particle modeling (HS-PPM) approach which is combined with a simplified lumped reaction model for the C4 olefin cracking process. A controllable approach was proposed to construct more realistic model for the pore structure in catalyst materials, with which the effect of porosity, pore diameter and pore volume ratio could be studied independently and quantitatively. In addition to the effectiveness factor ?, a quantitative parameter JC was proposed to characterize the coupling of reaction and diffusion processes. The results showed that JC tended to be zero, which indicated that the overall diffusion process was significantly limited due to the competition between reactant diffusion and product diffusion in the complex pores. The reactant molecules were mainly diffused into the catalyst through the larger pores, and the larger product molecules were also mainly diffuse out of the catalyst through the larger pores. The competition between these two processes made it difficult for the reactants to diffuse into the pore, and the products to diffuse out of the pore, which led to the decrease of the overall performance of the catalyst albeit the potentially high reaction rate allowed by the intrinsic kinetics. The simulation approach used in this study could be helpful for the design of pore-scale structure of catalyst materials.
    Numerical simulation of flow field characteristics of gas?liquid mixed impinging stream reactor
    Dong GUO Haifeng LIANG
    Chin. J. Process Eng.. 2021, 21(3):  277-285.  DOI: 10.12034/j.issn.1009-606X.220114
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    Impinging stream reactors have been widely applied in industry with the advantages of efficient mass transfer and strong interaction between phases. Based on the traditional impinging stream reactor, a novel two-way accelerating tube coaxial opposing impinging stream reactor was constructed. The flow field mixing characteristics simulation was carried out in the reactor with air as the continuous phase and liquid water as the discrete phase. The high-speed gas?liquid mixed flow process at different gas flow rates was analyzed. Moreover, the changes of velocity, pressure distribution, particle diameter and stagnation time in the internal flow field were explored. The results showed that the flow field distribution was symmetrical above the impact surface, and the pressure and velocity at the stagnation point fluctuated most violently. With the increase of initial gas phase velocity, the flow field velocity rose slowly, then decreased slowly, and finally decreased sharply, and the pressure in the flow field decreased slowly, then increased slowly, after increased sharply and gradually coincided in the form of the double peaks of M-type. In addition, the pressure value at stagnation point increased non-linearly. When the initial gas velocity uout=30 m/s and uin=15 m/s, the velocity and pressure gradient of impact region were the largest, the turbulent kinetic energy was the strongest. Furthermore, the average diameter of the droplets in the new reactor was smaller and the residence time was longer, which were obviously superior to traditional reactor.
    Reaction & Separation
    Study on phase equilibrium of NaCl–NaBr–CH3OH ternary system at 273 K and 323 K and its application
    Yao WU Yun LI Hongfei GUO Xiuwu LIU Xueqing CHEN Jilin CAO
    Chin. J. Process Eng.. 2021, 21(3):  286-297.  DOI: 10.12034/j.issn.1009-606X.220084
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    In order to separate sodium chloride and sodium bromide from the solid solution Na(Cl,Br) crystallized from bittern, the isothermal solubility data of NaCl–NaBr–CH3OH ternary system at 273 and 323 K was measured by isothermal solution equilibrium method, and the solid phase points were determined according to the measured liquid phase points and wet slag phase points, from which the phase diagrams at two temperatures were obtained. The results showed that the phase diagram characteristics of the ternary system were similar at 273 and 323 K. There was only one invariant point and two univariant curves, and there were three solid-phase crystallization regions: NaCl pure salt crystallization region, the co-crystallization zone of NaCl and Na(Cl,Br) solid solution and Na(Cl,Br) solid solution crystallization region. This was different from the phase diagram of NaCl–NaBr–H2O system, which only had the crystallization region of solid solution. The liquid composition of the invariant point at 273 K was 0.2904wt% NaCl, 14.66wt% NaBr and the liquid composition of the invariant point at 323 K was 0.2529wt% NaCl, 13.45wt% NaBr. The mass fraction of NaBr at the boundary of the solid solution crystallization region at 273 and 323 K was 28.93% and 34.28%, respectively. The solubility of NaBr in anhydrous methanol was much higher than that of NaCl, which indicated that NaBr had a strong salting-out effect on NaCl, and the solubility of these two solutes in methanol at 273 K was higher than that at 323 K, which was opposite to that in aqueous solution. According to the phase diagrams of NaCl–NaBr–CH3OH system at 273 and 323 K and NaCl–NaBr–H2O system at 298 K, the process for the separation of sodium chloride and sodium bromide was designed. Not only the pure salt of NaCl was obtained, but also solid solution with extremely high NaBr content was obtained. And the mass fraction of NaBr in the separated solid solution was 98.06% and 98.15%, respectively.
    Process & Technology
    Effect of high-pressure water jet on monomer dissociation degree in Bayan Obo Mine
    Yibo GAO Chunhua BAI Jianying WANG Xu WU Xiao LEI
    Chin. J. Process Eng.. 2021, 21(3):  298-304.  DOI: 10.12034/j.issn.1009-606X.220014
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    The dissociation of mineral monomers is one of the key factors that can be efficiently sorted. The crushing method has a great influence on the dissociation degree of mineral monomers. The Bayan Obo rare earth mine contains more than a dozen rare earth minerals, with the close symbiosis of minerals and complex embedded types. Among them, the rare earth is mainly concentrated in bastnaesite and monazite ore. The analysis shows that minerals form contiguous, network veins, dissolution and ring embedment due to mutual enveloping, interpenetrating and alternation. To improve the dissociation degree of mineral monomers, the water jet mineral dissociation device was independently developed to explore the influence of water jet velocity on the dissociation degree of rare earth monomers in Bayan Obo Mine. Under the same particle size distribution, the experimental results of high-pressure water jet pulverization and conventional ball milling (iron medium) were compared, and the effects of the two pulverization methods on the dissociation state of rare earth minerals and the particle interface were analyzed. The analysis by laser confocal microscope and the automatic quantitative analysis system of mineral characteristics (AMICS) showed that the dissociation degree of the high-pressure water jet crushing Bayan Obo rare earth mineral monomer was better than that of ball milling, and it had the characteristics of high dissociation degree and relatively uniform particle size, the natural interface of mineral particles keep better, the surface was smoother, the rare earth minerals were concentrated in the particles below 0.038 mm, which was beneficial to the flotation separation of rare earth, and had certain guiding significance for the ore crushing of the Bayan Obo mine.
    Biochemical Engineering
    Optimization of preparation of sulforaphane proliposome in broccoli seeds by response surface method
    Huanpu XU Zhaoyang PEI Shijie SUN Yingxue WU Lulu XU Jing HAN Hui XU
    Chin. J. Process Eng.. 2021, 21(3):  305-313.  DOI: 10.12034/j.issn.1009-606X.220055
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    Sulforaphane is made into proliposomes to improve the stability of liposomes, while improving the water solubility and bioavailability of sulforaphane. Taking the encapsulation efficiency and particle size as indicators, the carrier materials, the type and amount of surfactants and the effects of lipid-drug ratios were investigated respectively. The optimal formulation of proliposome was optimized by response surface method. The stability of liposomes and proliposomes was investigated through room temperature stability experiments. The results showed that the optimal prescription was that the mass ratio of lipid phase to sulforaphane was 6.5:1, the mass ratio of NaCl to sulforaphane was 105:1, and the mass ratio of poloxamer-188 to sulforaphane was 1.5:1. The maximum average encapsulation rate was 77.43%, and the average particle size was 160.5 nm. Stability experiment results showed that when the drug retention rate was used as an indicator, liposomes and proliposomes had good stability within 60 days and a high retention rate of sulforaphane. When the encapsulation rate was used as an indicator, the liposome suspension produced precipitated, the encapsulation rate decreased, and the encapsulation rate of the proliposome did not decrease significantly within 60 days. This indicated that the proliposome can solve the oxidative deterioration of sulforaphane and the decrease of the encapsulation rate of the liposome due to precipitation, flocculation and other reasons. The proliposome has high encapsulation efficiency and simple preparation. It not only improves the stability of sulforaphane, but also improves the water solubility of sulforaphane and has broad application prospects.
    Effects of two-compartment gas interflow on the performance of photosynthetic microbe fuel cell
    Xintong ZHU Huan HE Runyun ZHU Zhiang XU Fengxia HAN Hongping PU
    Chin. J. Process Eng.. 2021, 21(3):  314-322.  DOI: 10.12034/j.issn.1009-606X.220088
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    Microbial carbon capture cell (MCC) was assembled with a photo biocathode where growing Scenedesmus obliquus to produce oxygen as an electron acceptor after the operation of photo-microbe fuel cell (PMFC) and an added CO2 photo-MFC (AC-PMFC). The voltage generation, dissolved oxygen and pH were measured over each day in the different systems. It was demonstrated that cell voltage produced by MFC was in line with the oxygen concentration in all systems with algae cathode. The pH of the electrolyte can also affect voltage generation. The highest voltage and power density of MCC were obtained in the three types of MFC with 492 mV and 102.3 mW/m2, respectively. Its maximum power density was higher than that of PMFC and AC-PMFC. The three systems received different concentrations of carbon dioxide for photosynthesis. The AC-PMFC achieved the lowest voltage and power density due to the excessive concentration of CO2, which could inhibit the biological activity and photosynthesis of microalgae. The scanning electron microscope (SEM) was measured to observe the morphology characteristics of algae on the cathode surface of MCC after long-term operation. A layer of in situ oxygen film with high concentration could be generated on the surface of algae biofilm and electrode plate. The electrochemical analysed demonstrated that the biofilm could not directly receive the electrons from the plate and had no biocatalytic activity. This biofilm could increase the rate of oxygen reduction, which can effectively reduce the resistance of the battery surface. Polymerase chain reaction (PCR) and 16S rRNA gene detection technology indicated that the Chao1 index in MFC was 170, while the PMFC was 152 and the MCC was 145. The oversaturated oxygen in the cathode could be transported to the anode by pipeline and affect the microbial community in the anode. This study could provide a basis for further understanding of algae-based microbial carbon-trapping cells to improve MCC performance.
    Materials Engineering
    Properties and application of coal-based high purity graphite in polysilicon preparation
    Qili WANG Fengtao ZHANG Xiaofeng GAO Jianwen HU
    Chin. J. Process Eng.. 2021, 21(3):  323-331.  DOI: 10.12034/j.issn.1009-606X.220030
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    High-purity graphite was prepared from coal coke particles and high-temperature coal pitch, and its micro-structure characteristics and physical properties were measured and analyzed. High-purity graphite was used in the reduction furnace of the polysilicon preparation, which played the role of clamping the silicon rods, conducting electricity and transferring heat. Measures to improve production reliability and reuse rate of the graphite assembly in the reduction furnace were discussed. The results showed that the structure of the high-purity graphite samples was relatively smooth in general, and exhibited good similarity overall structure at different scales. The prepared high-purity graphite materials had outstanding physical properties: the bulk density of 1.84~1.88 g/cm3, the shore hardness of 55.2~62.4 Hs, the flexural strength of 33.9~45.6 MPa, the compressive strength of 66.3~78.8 MPa, the thermal expansion coefficient of 3.76×10–6/℃~4.08×10–6/℃, the electrical resistivity of 8.92~11.98 μΩ?m, and the ash content of 133~202 mg/kg, respectively. All the parameters of the samples were excellent. From the analysis of elemental composition, carbon element is the absolute main body, its weight content was between 88.71wt%~90.57wt%, and its atomic content was between 92.09at%~93.25at%. In addition to the matrix carbon, other elements are mainly O, S, Si, and Al. The weight content of O was between 7.15wt% and 9.79wt%, and the atom content was between 5.61at% and 7.57at%. Except for C and O, the content of other elements was lower, and the atomic content was lower than 1at%. In addition, the phenomenon of “bright spot” and “collapse of the silicon rod” in reduction furnace applications due to heterogeneous conductivity and heat concentration in the silicon cores was analyzed. By optimizing the structure of the graphite assembly, the reuse rate of the graphite cap was increased from 5.85% to 7.28%, the reuse rate of the graphite seat was increased from 7.95% to 9.01%, and the collapse rate of silicon rods was reduced from 14.22% to 4.43%. Consequently, the safe production in the reduction furnace was more effectively improved, the reject rate and the production cost of silicon rods were reduced, which demonstrated good application prospects of the coal-based high purity graphite in the field of the preparation of polysilicon.
    Fabrication and characterization of form-stable solar salt/steel slag composite phase change material for thermal energy storage
    Yan WANG Yun HUANG Hua YAO Xianggui XU Qiao HUANG Junlei WANG Pusheng MA Junsheng WANG
    Chin. J. Process Eng.. 2021, 21(3):  332-340.  DOI: 10.12034/j.issn.1009-606X.220096
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    Renewable energy has been actively developed due to the global energy shortage and environmental pollution. The technology of thermal energy storage (TES) is the key to deal with the instability of new energy. Because of its advantages of high heat storage density and wide operating temperature range, molten salts have attracted extensive attention in the medium and high temperature ranges. A form-stable solar salt/steel slag composite phase change material (PCM) was developed in this work for solving the problems of leakage, poor heat transfer performance and high cost of molten salts. The optimum mass ratio of steel slag and molten salt (solar salt) was obtained as 5:5. The microstructure, thermal property and chemical compatibility of the composites were characterized subsequently by scanning electron microscope (SEM), thermogravimetric–differential scanning calorimeter (TG–DSC), laser flash analysis (LFA) and X-ray diffraction (XRD), respectively. The results showed that there was no leakage as the composite material keeps good shape and compact microstructure. The composite material showed good chemical compatibility between molten salt and steel slag. The latent heat was 64.0 kJ/kg, the thermal energy storage density was 945 kJ/kg (100~500℃) and the thermal conductivity was up to 2.23 W/(m?K). Thus, the developed solar salt/steel slag composite PCM is not only of interest to the large-scale application of thermal energy storage, but also provide an excellent option for waste recycling in steel industry.
    DEM modeling of mechanical behavior of partially sintered ceramics
    Zengxu ZHANG Yongchang WANG Yin YU Xiaoxing LIU
    Chin. J. Process Eng.. 2021, 21(3):  341-352.  DOI: 10.12034/j.issn.1009-606X.220116
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    In this work, the mechanical behavior of partially sintered ceramics under both tensile and compressive loadings was investigated by performing 3D discrete element method (DEM) simulations. The simulation results indicated that the failure of samples under tensile loading was dictated by the nucleation of crack, whereas for compressive loading it was linked to the coalescence of cracks. By monitoring the time sequence of bond breakage and its failure mode, it was found that for tensile loading the dominate failure mode of bond was tensile fracture, whereas for compressive loading it was shear fracture. The fracture strength of sample was closely related to the critical tensile (?c,t) and shear (?c,s) fracture strengths of bond. As to the partially sintered alumina ceramics considered in this work, it was found that the predicted tensile and compressive fracture strengths can both be in quantitative agreement with experimental data. The simulation results indicated that the influence of the distribution of bond strength on the compressive fracture strength of sample was minor. While for tensile fracture strength, it depended on the type of distribution: for Gaussian distribution, the strength of sample only weakly depends on the distribution width, whereas for uniform distribution, the strength of sample decreases notably with the increase of distribution width.
    Environment & Energy
    Response surface methodology for optimizing CO2 regeneration in MDEA/PG rich solutions
    Weifeng ZHANG Juan LI Qiuhua WANG
    Chin. J. Process Eng.. 2021, 21(3):  353-362.  DOI: 10.12034/j.issn.1009-606X.219366
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    Post-combustion CO2 capture (PCC) facilities are set up at the power plants to reduce substantial carbon dioxide emissions. However, the significant energy penalty and high capital cost remain the most critical challenge hindering the large-scale application of amine-based PCC technologies. Also, CO2 enriched by amine-based scrubbing requires storage processes. To overcome the shortage of CO2 desorption process, a chemical regeneration process was developed in which uses Ca(OH)2 to capture CO2 from rich solution and fix CO2 in the form of CaCO3. The Box-Behnken Design methodology was used to optimize desorption conditions, including CO2 loading, Ca(OH)2 dosage, reaction time and stirring rate. The performance stability of the MDEA/PG was verified in multiple regeneration-mineralization dynamic cycle experiments under the optimal conditions. We further confirm the coordinated mechanism of carbonation reaction between CO2 and Ca(OH)2 using X-ray diffraction (XRD) and transmission electron microscope (TEM). The desorption-mineralization experiment was performed in a flask with three necks respectively. Acid titration was used to measure the CO2 loading of the liquid sample. XRD and TEM were respectively used to determine the composition of solid products and observe the micromorphology of carbonated products after regeneration. The CO2 loading, Ca(OH)2 dosage and stirring rate were the three key factors influencing the uptake of desorption rate. The optimal desorption conditions were CO2 loading 0.8 mol/L, Ca(OH)2 dosage 1:1, reaction time 20 min, stirring rate 800 r/min, and under these conditions, their desorption rate was 83.68%. The results of multiple desorption-mineralization cycle dynamic experiments showed that the regenerated solution of MDEA/PG desorbed by calcium method has good reusability. The results of X-ray diffraction and transmission electron microscope after carbonation also confirmed that Ca(OH)2 can effectively mineralize CO2 and regenerate MDEA/PG. The chemical regeneration process can effectively reduce and reuse emitted CO2, thereby making CO2 a potential future resource.
    Study on NH3-SCR denitration performance of rare earth concentrate supported Fe2O3 mineral catalytic material
    Zhaolei MENG Baowei LI Jinyan FU Chao ZHU Wenfei WU
    Chin. J. Process Eng.. 2021, 21(3):  363-372.  DOI: 10.12034/j.issn.1009-606X.219383
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    In this work, a series of mineral catalytic materials were obtained by using Bayan Obo rare earth concentrate rich in Ce oxide as the catalyst material, impregnated with ferric nitrate solution and microwave roasted. XRD, SEM, EDS, XPS and other methods were used to characterize the mineral phase structure and surface morphology of the catalyst, and to determine its denitration activity. The results showed that the rare earth concentrate impregnated in 0.5 mol/L ferric nitrate solution (Catalyst 3) had the best structural characteristics, the surface was rough and porous, and obvious and deep cracks appeared, which was conducive to the diffusion of gas on the surface of the material. Most Fe2O3 was embedded in the rare earth concentrate in a highly dispersed or amorphous form. The content of Ce3+ and Fe2+ were increased after immersion in ferric nitrate solution and microwave roasting. Active components Ce coexisted in the form of Ce3+ and Ce4+, Fe coexisted in the form of Fe2+ and Fe3+. The conversion of adsorbed oxygen and lattice oxygen increased significantly, and there were more oxygen vacancies for oxygen transfer. The change in the valence of Fe ions and Ce ions indicated that Fe and Ce had a combined effect to generate a small amount of Fe and Ce composite oxides. With the increase of medium and strong acid sites on the surface of Catalyst 3, the ability of the surface to adsorb NH3 increased, and its denitration effect was the best. When the microwave roasting temperature was 350℃, the denitration rate can reach 80.6%.