The Chinese Journal of Process Engineering

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Chin. J. Process Eng.. 2020, 20(5): 0.

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Mechanisms and suppression methods for attrition and carbon deposition of oxygen carriers in chemical looping combustion

Ying HU Xuefeng YIN He CHANG Xueyan FENG Zejia WANG Xuehui HAO Zhijuan GUO

Chin. J. Process Eng.. 2020, 20(5): 493-502. DOI: 10.12034/j.issn.1009-606X.219188

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The formation of carbon deposition causes the oxygen carrier (OC) to not fully contact with the fuel, and the attrition causes the loss of oxygen carriers, which seriously disturb the normal operation of chemical looping combustion (CLC). Cyclic combustion efficiency of oxygen carriers is closely related to the cost of CLC technology, and it is an important part of its near commercialization. The basic concepts, devices, reaction conditions, fuel composition and reaction process of CLC were introduced in this work. Two major problems in current CLC research were analyzed and summarized. The main contents included that: (1) prolonging the cycle life cycle of oxygen carriers providing combustion oxygen demand, (2) under the optimum reaction conditions, the mechanism of carbon deposition and the measures to solve the oxygen loss caused by carbon deposition were analyzed. Firstly, the oxygen carrier?s selection, preparation methods and characteristics briefly were introduced. Different oxygen carriers had their own advantages and disadvantages, it should select suitable oxygen carriers for different fuels. The attrition analysis of oxygen carriers point was carried out. Analysts believed that with industrial significance a way to select qualified oxygen carriers materials based on attrition resistance. Secondly, the reaction mechanism of polycyclic aromatic hydrocarbons (PAHs) and the precursor of carbon black deposit were analyzed in detail by analyzing the detailed reaction in the whole process of CLC. It was concluded that the carbon deposit was mainly caused by the reaction of hydrocarbons pyrolyzed by fuel with oxygen carriers and Boudouard reaction. The corresponding solutions for different types of carbon deposit were proposed. Among them, the combination of steam injection and carbon dioxide reflux injection was promising. On this basis, the potential research needs in this field were also discussed. To improve the cycle period of oxygen carriers and restrain carbon deposition, future research should focus on the characterization and reactivity of carbon deposition on the surface of oxygen carriers, the cyclic growth model of oxygen carriers under optimal combustion conditions and the reaction mechanism of particles, as well as the exploration of new technologies for coupling removal of carbon deposition.

Research progress of aluminum removal technology for cathode materials of spent lithium-ion batteries

Hejie ZHANG Xing CHEN Xing ZOU Wenke LIU Shili ZHENG Yi Zhang Ping LI

Chin. J. Process Eng.. 2020, 20(5): 503-509. DOI: 10.12034/j.issn.1009-606X.219260

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In recent years, lithium-ion batteries (LIBs) have been widely used in portable electronic devices and electric vehicles, because of their lightweight, small volume, low self-discharge, high voltage, high specific energy, no memory effect and long storage life. It is estimated that by 2020, the number and weight of spent LIBs will exceed 25 billion and 500000 tons, respectively, and the recycling and reuse of spent LIBs are receiving more and more attention. The spent LIBs are generally physically disassembled, crushed, sieved, magnetically selected, washed, and thermally pretreated, to obtain LiNixCoyMnOz positive electrode powders containing a small number of impurities such as Al, Cu, Fe, etc. As one of the main impurities in the LiNixCoyMnOz positive electrode powders, aluminum has attracted extensive attention from many scholars. At present, the neutralization method is mainly adopted to remove aluminum, and the Al(OH)3 is removed by adding an alkaline substance such as CaO to the acidic leachate. However, a large amount of slag, difficulty infiltration, and heavy loss of valuable metals such as Ni and Co make it unfavorable for the clean production. Various methods have been developed to solve these problems such as pretreatment, neutralization, solvent extraction methods, etc. In this work, the existing methods of removing aluminum from the LiNixCoyMnOz positive electrode powders were reviewed in detail. The principles, advantages and disadvantages of these methods were briefly introduced, and the development direction of the technology of removing aluminum was prospected.

Simulation of heat transfer enhancement and flow resistance characteristics of twisted slice tubes with openings

Juan WANG Xingchen HE Jun LI Jiayi WAN Shuo ZOU Haohan XU

Chin. J. Process Eng.. 2020, 20(5): 510-520. DOI: 10.12034/j.issn.1009-606X.219242

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In the industrial application of ethylene pyrolysis tubular heating furnace, the fluid transferred from horizontal to rotary flow by adding twisted slices internals, which increased the tangential velocity and strengthened the flushing effect on the tube wall, so as to achieve the purpose of enhancing heat transfer. Based on the second generation of twisted slices, the structure was improved, and RNG k?ε turbulence model was used to simulate the flow details inside the furnace tube. The longitudinal vorticity structure, resistance coefficient, Nusselt number Nu, comprehensive heat transfer coefficient PEC and the coupling coordination between velocity vector field and temperature gradient field in different twisted slice structures were compared and analyzed. The results showed that the structure with "slit" openings along the wall can reduce the loss of flow resistance while increased the strength of fluid swirl. The resistance coefficient of twisted slices with opening structure of 7 mm length, 2 mm width and 2 mm interval was 93.75% of the first generation and 8.67% more than the second generation, but the comprehensive heat transfer coefficient was 1.56% higher than that of the second generation and 1.29 times of the smooth tube. It can be considered that the optimized structure improved the stability of longitudinal vortex structure as well as strengthened the coupling between flow and heat transfer. Besides, along the central opening of the slices, the resistance coefficient at the twisted slices increased, resulting in larger local losses.

Numerical simulation of deposition characteristics for high moisture viscous particles on the surface of polytetrafluoroethylene microporous membrane filtration materials

Zhiyi XUE Fuping QIAN Jingjing ZHU Wei DONG Yunlong HAN Jinli LU

Chin. J. Process Eng.. 2020, 20(5): 521-530. DOI: 10.12034/j.issn.1009-606X.219256

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Based on the scanning electron microscopy (SEM) image of polytetrafluoroethylene (PTFE) microporous membrane filtration material, the micro-structure model of PTFE filtration material was established, and the coupling method of computational fluid dynamics and discrete element method (CFD?DEM) was used to simulate the deposition of the viscous particles on the surface of microporous membrane. In addition, the force of the particles in the calculation domain was calculated by introducing the liquid bridge force model and without considering the effect of Van der Waals force. Then the deposition characteristics of 3~6 ?m particles on the surface of microporous membrane at different surface energies were analyzed, the simulation results were compared with the empirical formula of adhesion efficiency. The results showed that the relative errors between adhesion efficiency and empirical value, the force of particles and liquid bridge force model were less than 6%, which indicated that the CFD?DEM coupling method can be used to simulate particle deposition under different environmental relative humidity conditions. Filtration velocity, particle size and viscosity were important factors affecting the deposition morphology. When the filtration velocity, particle size and viscosity increased, the particles were more likely to form a stable dendritic structure on the surface of the filter material, which made the adhesion efficiency and dust-containing pressure drop increased. The environmental relative humidity affected the volume of liquid bridge between two objects, and the contact force affects the deposition of particles. With the increase of the surface energy and liquid bridge volume, contact force and liquid bridge force increased correspondingly. The environmental relative humidity had a great influence on the deposition of particles, according to the principle of force balance.

Flow field simulation and structure optimization of hot air circulation tunnel oven

Zhiqi WANG Yujie ZOU Baixi LIU Zhenkang ZHANG

Chin. J. Process Eng.. 2020, 20(5): 531-539. DOI: 10.12034/j.issn.1009-606X.219277

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Sterilizing tunnel oven is the key equipment to realize aseptic production in the pharmaceutical industry. The uniformity of air flow is the key index of sterilizing effect, which is influenced mainly by the structure of sterilizing oven. Therefore, the rational design of oven internal structure is an important way to achieve uniform airflow. However, there are few researches on the uniformity of air flow in the sterilizing oven. A hot air circulation tunnel oven was taken as the research object, the CFD numerical simulation method was used to study the internal temperature and flow field of the oven, and six optimized structures were proposed according to the internal flow condition of the tunnel oven, and the airflow distribution characteristics of different optimized structures were compared and analyzed. The results showed that the local temperature difference at the outlet of the oven was less than 1 K, the temperature distribution was relatively uniform. The air velocity distribution was the main factor affecting the drying quality, while the high-speed airflow cannot spread evenly because of the small space of the fan cover. The flow distribution of outlet was extremely uneven under the original structure, and there was a local high-speed region at the corner of the outlet surface. The maximum speed was 3.48 m/s, the average speed was 0.94 m/s, and the relative root mean square of airflow velocity was 0.73. Compared with the original structure, the maximum outlet velocities of the six optimized structures were significantly reduced. The percentages of the optimum velocity range increased in different degrees and the airflow uniformity was improved. While the elbow structure with three baffles had the lowest relative root mean square value of the outlet, the maximum speed decreased by 51.4%, the percentage of the optimum speed area increased to 75.17%, and the rectification effect was the most obvious. At the same time, after setting three baffles in the elbow, setting baffles in the fan cover had little effect on improving airflow uniformity, which provided a reference for improving airflow uniformity of the hot air circulation tunnel oven.

Occurrence state and separation method of heavy metal element arsenic in coal fly ash

Fuli LIU Shuhua MA Kun REN Xiaohui WANG

Chin. J. Process Eng.. 2020, 20(5): 540-547. DOI: 10.12034/j.issn.1009-606X.219275

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The migration, transformation and accumulation in the environment of heavy metal elements in coal fly ash are the barriers to the comprehensive utilization of coal fly ash. To clarify the occurrence state of heavy metal elements in coal fly ash and to explore an efficient removal method, it is the key to solve the large-scale utilization of coal fly ash. The improved BCR continuous extraction method found that the water soluble and acid exchangeable states of heavy metal element arsenic in fly ash accounted for a high proportion, which proved that heavy metal arsenic easily migrated in the environment and affected the surrounding environment. Based on the occurrence characteristics of heavy metal arsenic in coal fly ash, a new method for removing heavy metal element arsenic by sulfuric acid was established. The effects of sulfuric acid concentration, reaction temperature and reaction time on the removal rate of heavy metal arsenic were investigated. The results showed that the removal rate of arsenic increased with the increase of the concentration of sulfuric acid solution, decreased with the increase of reaction temperature, and increased with the increase of reaction time. Considering the removal rate of heavy metal arsenic, the loss rate of constant elements in coal fly ash and the degree of damage of spherical particles, the optimum conditions for removing heavy metal arsenic from coal fly ash by one-step method of sulfuric acid determination were as follows: the sulfuric acid concentration of 2.0 mol/L, the reaction temperature of 20℃, and the reaction time of 60 min. At this time, the removal rate of heavy metal arsenic reached 75.21%.

Increase of magnesium during electroslag remelting process and its effect on inclusions

Gang GAO Xiaofang SHI Xiongming ZHU Kaihua CHANG Lizhong CHANG

Chin. J. Process Eng.. 2020, 20(5): 548-556. DOI: 10.12034/j.issn.1009-606X.219276

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The experiment of electroslag remelting (ESR) was carried out under argon atmosphere by designing magnesium-containing slag system and adding strong deoxidizer to the slag pool continuously, and the possibility of increasing magnesium to electroslag ingot during ESR process was studied in detail. Magnesium content in electroslag ingot was analyzed by inductively coupled plasma atomic emission spectrometry (ICP-AES) and the effect of different magnesium content on the size, type and morphology of inclusions in electroslag ingots were analyzed in detail by ASPEX scanning electron microscopy. The research results showed that when the slag contains more than 20wt% MgO, even if the metal consumable electrode did not contain Mg, the MgO in slag pool still transferred Mg to the molten steel due to the strong reduction condition of deoxidizer. Under laboratory conditions, the Mg content in the slag ingot reached 0.0034wt%, 0.0039wt% and 0.0043wt% respectively when 55wt% CaF2–15wt% Al2O3–10wt% CaO–20wt% MgO slag, 65wt% CaF2–10wt% Al2O3–25wt% MgO slag and 51wt% CaF2–8wt% Al2O3–8wt% CaO–23wt% MgO–10wt% MgF2 slag were used for electroslag remelting. With the increase of Mg content in ESR ingots, the composition of inclusions in the electroslag ingot gradually changed from Al–Ca, Al–Mn–S, Al–Mg–Mn–S to Mg-containing inclusions, and the maximum content of Mg in inclusions was 98wt%. The number of inclusions decreased greatly, and the diameter of inclusions was smaller with the increase of Mg in the electroslag ingot. Especially, the maximum diameter of inclusions in electroslag ingots treated with Mg was less than 10 μm, and most of them were less than 5 μm. Compared with the electroslag ingot containing 0.0003wt% Mg, when the Mg content in the electroslag ingot increased to 0.0034wt%, the number of inclusions decreased from 357 to 31 pcs. The maximum diameter of inclusions decreased from 11.0 to 8.5 μm, and the average diameter decreased from 3.7 to 3.2 μm.

Characteristics of particle concentration gradient force in riser

Yafei ZHAO Yiping FAN Han Lü Yang ZHAO

Chin. J. Process Eng.. 2020, 20(5): 557-568. DOI: 10.12034/j.issn.1009-606X.219245

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The particles in the riser are exerted by the Kutta-Joukowski transverse force and the concentration gradient force simultaneously in the radial direction. Thereby a great number of particles gather near the wall, as a result, a stable core-annulus structure occurs. Based on the experimental data, the radial distribution characteristics of the particle concentration gradient were analyzed. In addition, according to the proposed the relationship of the Kutta-Joukowski transverse force to the concentration gradient force, the s of the concentration gradient force, Fρ=K(dρ/dr)A, and that of the concentration gradient force coefficient K=[?ρg(νg?νp)(?v/?r)r]/[dρ/dr+(d2ρ/dr2)r] were presented. The concentration gradient force on the particles in riser was dependent on the concentration gradient force coefficient. Radial profiles of the concentration gradient force coefficient (K) in the riser was given and the influences of operating parameters were investigated. The results showed that the value of the concentration gradient force coefficient was 0 at riser center while the radial distribution assumed the N-profile. The concentration gradient force coefficient increased with the increasing of the superficial gas velocity. The value of the coefficient in the fully developed zone of the riser was significantly higher than that in the acceleration zone as well as the outlet constraint zone. Based on the analysis results, the empirical correlation of K in riser was established.

Adsorption and reaction of both C and Cl₂ on TiO₂(100) surface based on the first principles calculation

Fan YANG Liangying WEN Yan ZHAO Jian XU Shengfu ZHANG Zhongqing YANG

Chin. J. Process Eng.. 2020, 20(5): 569-575. DOI: 10.12034/j.issn.1009-606X.219262

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Based on the first principles ab initio method of density functional theory, the rutile TiO2(100) surface adsorption models were established. The mechanism of adding C to promote the chlorination process of TiO2 is revealed through the calculation and analysis of adsorption energy, charge density, state density. The simulated results indicated that the adsorption process of Cl2 on TiO2(100) surface was physical adsorption. The adsorption process of both C and Cl2 on TiO2(100) surface was chemical adsorption. The addition of C atom promoted the dissociation of Cl2, and the formation of C?Cl bond or Ti(5c)?Cl bond. Moreover, the stability of the system containing C?O(2c) bond was higher than that of the system containing C?O(3c) bond. The C atom can bond with O(2c) or O(3c), and weaken the strength of Ti(5c)?O(2c) bond. Thus, the dissociated Cl atom tended to bond with Ti(5c) on the surface of TiO2(100) or with C atom. It was found that the number of Ti(5c)-Cl bonds in the system had certain influence on the stability of the system. When one of the dissociated Cl atoms in the system was free, the other Cl atom bonded with C atom, and the adsorption energy of the system was the highest for ?5.25 eV, its stability was lowest. When the two dissociated Cl atoms form Ti(5c)?Cl bond and C?Cl bond with Ti(5c) respectively. The adsorption energy of the system was the second for ?6.75 eV. When two Cl atoms and surface Ti(5c) form Ti(5c)?Cl bond, the adsorption energy of the system was the lowest for ?7.78 eV and the structure was the most stable. At this point, the bond between C and O(2c) was the strongest in this structural system, and more electrons were transferred around the Cl atoms. It indicated that the addition of C can form the C?O(2c) double bond, promote the dissociation of Cl2, and adsorption reaction on the surface of TiO2 (100) which played an important role in improving the chlorination process of TiO2.

Geometric effects of organic monomers on catalytic activity of conjugated microporous polymers

Chen WANG Huiling MAO Hu CHENG Xuan DU Xiaobing LIAN Jinliang ZHUANG

Chin. J. Process Eng.. 2020, 20(5): 576-582. DOI: 10.12034/j.issn.1009-606X.219264

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Conjugated microporous polymers (CMPs) exhibit extended p-conjugated frameworks, and are typically built from aromatic organic building blocks. CMPs decorated with functional groups are of particular interest in catalysis because these functional groups can serve as potential catalytic sites. Despite great efforts have been devoted to the synthesis of functionalized CMPs, there is still much room for the development of functionalized CMPs with stable and accessible catalytic sites. Two TEMPO (2,2,6,6-tetramethylpiperidinyloxy) decorated conjugated microporous polymers (CMPs), named CMP-3-TEMPO and CMP-4-TEMPO by Sonogashira-Hagihara coupling reaction were synthesized in this work. A TEMPO radical appended 2,5-dibromo-N-(2,2,6,6-tetramethylpiperidinyloxy)benzamide serving as a build block and reacted with 1,3,5-triethynylbenzene (trigonal planar, D3h symmetry) and tetrakis(4-ethynylphenyl)methane (tetrahedron geometry, Td symmetry), to form CMP-3-TEMPO and CMP-4-TEMPO, respectively. The as-synthesized CMP-3-TEMPO and CMP-4-TEMPO were characterized by SEM, PXRD, FT-IR, and EPR spectroscopy. Moreover, the catalytic activity of CMP-3-TEMPO and CMP-4-TEMPO toward the selective oxidation of 5-hydroxymethylfurfural (5-HMF) to 2,5-diformylfuran (2,5-DEF) were investigated. Importantly, the results indicated that the geometry of organic monomers played a key factor for the morphology and catalytic activity of CMPs. CMP-3-TEMPO consisted of micro-chunks and micro-rods, while CMP-4-TEMPO exhibited microspheres with uniform sites in the range of 2~3 ?m. Catalytic performances indicated that both TEMPO-CMPs enabled the selective oxidation of alcohols to their corresponding aldehydes with high efficiency. However, the stability and reusability of CMP-4-TEMPO was much better than CMP-3-TEMPO, which can be attributed to specific geometry of the corresponding organic monomers. It is anticipated that our findings could provide useful information for the design and synthesis of functionalized CMPs.

Optimization of hydrothermal process conditions of nanometer fluorescent powder YPO4:2%Sm³⁺ and fluorescence property

Jinxiu WU Hengjun JIA Huiling JIA Mei LI Zhaogang LIU Jing GUO

Chin. J. Process Eng.. 2020, 20(5): 583-590. DOI: 10.12034/j.issn.1009-606X.219267

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In order to study the optimal hydrothermal process conditions of nano-phosphor YPO4:2%Sm3+, using the fluorescence intensity as an indicator, the hydrothermal process conditions (reaction temperature, reaction time, the ratio of anion to cation in the solution and pH value) of the nano-phosphor YPO4:2%Sm3+ were optimized by L9(34) orthogonal experiment. Then, the composition, structure, morphology and luminescent property of the sample were characterized and analyzed by X-ray diffractometry (XRD), scanning electron microscopy (SEM and EDS), infrared spectrometer (FT-IR), ultraviolet spectrometer (UV) and fluorescence spectrophotometer (FL). The experimental results showed that the primary and secondary factors affecting the hydrothermal process conditions of nano-phosphor YPO4:2%Sm3+ were reaction temperature>pH value>reaction time>the ratio of anion to cation. The optimal hydrothermal process conditions of nano-phosphor YPO4:2%Sm3+ were reaction temperature of 200℃, pH=3, reaction time of 12 h, the ratio of anion to cation of 3:1. The optimum nano-phosphors was a single tetragonal crystal with the morphology of nanospheres, the maximum fluorescence intensity, and fluorescence life time of 0.1719 ms, band gap of 5.14 eV, color coordinate of X=0.5563, Y=0.4339.

Study of immobilized glycerol dehydrogenase on modified agarose microspheres

Min ZHANG Lin HAN Yueyue HU Jian LI Bing YAN

Chin. J. Process Eng.. 2020, 20(5): 591-598. DOI: 10.12034/j.issn.1009-606X.219263

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1,3-dihydroxyacetone (DHA) is one of the most valuable chemicals with a wide range of applications in cosmetics and pharmaceutical industry. Glycerol dehydrogenase (GlyDH) is able to selectively catalyze the transformation of glycerol to DHA, by which glycerol, the oversupply by-product of the biodiesel industry is highly valued. To make enzymatic production of DHA practically feasible, immobilizing GlyDH onto a suitable insoluble support is critical for facilitating biocatalyst recovery and improving stability of the enzyme. Agarose microspheres as carrier were prepared by membrane emulsification method. Then the agarose microspheres were activated with epichlorohydrin and reacted with polyethyleneimine (PEI) to introduce the amino group into the agarose microspheres. The morphology and structure of the microspheres were characterized by scanning electron microscope (SEM), energy dispersion spectrum (EDS), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR). GlyDH was covalently fixed with glutaraldehyde and then catalyzed the formation of 1,3-dihydroxyacetone. The results showed that the spherical degree of microspheres was enhanced due to the membrane emulsification process. The N content in grafted products was obviously effected by the relative molecular weight of PEI. The N content of PEI graft was the highest when the relative molecular mass of PEI was 10000. The effect of pH and temperature dependence, thermal stability and the reusability of GlyDH were systematically investigated. The optimum pH value of free enzyme and immobilized enzyme activity was 10.0. The storage efficiency of immobilized GlyDH was higher than that of free GlyDH after storage at 4℃ for 21 days. After 7 cycles, the activity of GlyDH was still partly remained.

Preparation and high-efficiency hydrogen evolution performance of iron-boron-based sponge catalytic electrode

Qiuyu XU Chenfeng WANG Lincai WANG Chenglong ZHANG Weiju HAO

Chin. J. Process Eng.. 2020, 20(5): 599-608. DOI: 10.12034/j.issn.1009-606X.219250

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Developing a high efficiency, stability and low cost catalytic electrode is of great practical significance to reduce the overpotential of hydrogen evolution. For this reason, NiB@Fe–B/PU catalytic electrode on non-conductive base material polyurethane sponge (PU) was prepared by a mild electroless plating method in this work. NiB@Fe–Co–B/PU, NiB@Fe–Mo–B/PU catalytic electrode were successfully prepared by doping a small amount of the third element, such as cobalt, molybdenum and other metal elements to improve its hydrogen evolution performance in neutral electrolyte solution. The results showed that the performance of NiB@Fe–B/PU catalytic electrode had significant improvement by doping of cobalt and molybdenum, and the performance of doping cobalt was better. The overpotential was only 161 mV(current density, j=50 mA/cm2) and the Tafel slope was 68.24 mV/dec for NiB@Fe–Co–B/PU catalytic electrode to hydrogen evolution reaction (HER) in 0.5 mol/L phosphate buffered saline (PBS). At the same time, the electrode showed good stability, which can work stably for more than 24 h under the overpotential of 61 mV.

Process integration and energy analysis of bischofite producing metal magnesium

Zhaoyuan WAN Huan ZHOU

Chin. J. Process Eng.. 2020, 20(5): 609-618. DOI: 10.12034/j.issn.1009-606X.219259

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Magnesium metal production from bischofite is a process of high energy consumption. It is necessary to explore the process of lowest energy consumption. In this work, with anhydrous magnesium chloride and magnesium oxide as intermediate products, electrolysis and thermal reduction as key methods, a comprehensive process network from bischofite to magnesium metal was constructed, which involved 24 species, 20 chemical processes and 25 process routes. Furthermore, one minimum energy consumption model was proposed to evaluate the thermal effect of multi–chemical process, or multi–process routes. Using the standard enthalpy of formation and temperature-depended isobaric molar heat capacity, the energy consumption and heat removal of all 25 process routes were calculated. The results showed that the optimum path based on thermal reduction method was converting bischofite to magnesium hydroxide by lime method, calcining to obtain magnesium oxide, and further reducing to magnesium metal by aluminum. The energy consumption was 360.15 kJ/mol, and the heat released was –315.46 kJ/mol. Compared with this, the better path of electrolysis was producing magnesium hydroxide by lime method, calcining to get magnesium oxide and further producing magnesium metal by electrolyze in molten electrolyte. The energy consumption of the process was 738.54 kJ/mol, and the heat released was –135.42 kJ/mol. Because of the high energy consumption of anhydrous magnesium chloride preparation, it was not in the optimal path.

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