The Chinese Journal of Process Engineering

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Chin. J. Process Eng.. 2020, 20(12): 0.

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Research progress on waste electric and electronic equipment mechanical–physical synergy and resource utilization

Wentao YANG Tianyi TAO Hao BAI Hongbin CAO Zhi SUN

Chin. J. Process Eng.. 2020, 20(12): 1363-1376. DOI: 10.12034/j.issn.1009-606X.219327

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With the rapid development of the information society and the digital economy, there is a huge amount of waste electrical and electronic equipment (WEEE) generated every year in the world. The composition of WEEE is complex, containing metal phase, organic matter, oxide materials, etc; the combinations are complicated, which are bonding, screw connection, solder fixing and snap connection. These complex components contain not only a variety of rare metals, but also various toxic heavy metals such as lead and cadmium, and various toxic organic substances such as various brominated flame retardants. If these WEEE cannot be effectively recycled, they will cause great harm to the environment. At the same time, the content of rare metals in WEEE is much higher than that in natural minerals. Therefore, rare metals recycling from WEEE can effectively alleviate the increasingly tense in resources. The traditional recycling method can recover various metal resources in electronic waste, but it has high energy consumption and serious pollution. While, the mechanical–physical recovery method has the advantages of simple operation, good economic benefit, small environmental pollution, and has been widely used in the recycling process of WEEE. The physical separation methods include gravity separation, magnetic separation, electrostatic separation, and eddy current separation. The mechanical–physical synergy has received extensive attention in recent years. This work summarized the research progress of mechanical waste utilization of WEEE in recent years, and systematically summarized the various processes of mechanical and physical recovery, including the previous disassembly and crushing process and the most important physical separation technology. The comparison of the advantages and disadvantages of the separation technology indicated that the morphological regulation of the crushed product will greatly improve the recovery efficiency of the mechanical–physical treatment.

Analysis of particle breaking in the shaft moving beds with discrete element method

Yewei HE Zhen LI Xinxin LI Zeyi JIANG Lin LIN

Chin. J. Process Eng.. 2020, 20(12): 1377-1385. DOI: 10.12034/j.issn.1009-606X.219365

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The breaking behavior of the burden in the vertically arranged cooler will cause the change in the voidage of the material layer, which will seriously affect the gas permeability of the material layer, and reduce the heat recovery efficiency of vertically arranged cooler. In order to investigate the break of particles in the coke dry quenching (CDQ) chamber, and sintering waste heat recovery vertical tank, the discrete element method was used to explore the falling movement of the burden material via considering the particle breakage in the shaft moving bed. The falling movement process of the particles with different shapes, sizes and bond strength in two vertically arranged cooler was simulated. The velocity and pressure distribution of burden were analyzed. The breaking of coke and sinter particles were compared. The results indicated that the device structure, burden height and particle strength were the main factors affecting particle breakage during the falling movement of the burden. During the falling process, the pressure of particle increased first, then decreased after entering the discharge zone, and the particle breakage was closely related to the pressure. When the coke fell into the corbel zone in the CDQ chamber, the average pressure of the material layer reduced and the breaking rate was slowed down due to the expansion of the device body diameter. Because the strength of the sintered ore was relatively small, the breaking phenomenon occurred when it entered the sintering vertical tank, and the expansion of the device body had little effect on the breaking. Owing to the influence of fixed furnace wall, particles were more likely to be broken near the device wall. Additionally, the square particles were broken along a diagonal from a certain apex. The rectangular particles were broken from one side to the other, and the irregular particles were broken inward from the missing side.

Modeling and numerical simulation of quasi-one dimensional gas phase flow in a supersonic nozzle

Lite ZHANG Qiuli YU Bowen WU Tiancheng LIU Zilong FENG

Chin. J. Process Eng.. 2020, 20(12): 1386-1396. DOI: 10.12034/j.issn.1009-606X.220026

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Mathematical modeling of the quasi-one dimensional gas phase flow in a nozzle, which accounted for wall friction and heat transfer, was established through theoretical analysis. Three flux vector splitting methods were used for the characteristic splitting of the aerodynamic equations. The variant form of them was discretized with a finite difference method. Specifically, the spatial and time derivatives were discretized with a fifth-order WENO scheme and a three-step third-order TVD Runge-Kutta method, respectively. The programming, calculations, validation and parameter study were performed based on the Fortran platform. The results showed that the numerical simulation agreed quite well with the experimental data if an appropriate friction correction factor was selected, which verified the availability of the established mathematical model and the adopted numerical methods and algorithms. It was found that as the half expansion angle of the nozzle was enlarged, both the gas velocity and the Mach number at the outlet increased, whereas the outlet static pressure decreased. The increase of the inlet total (or stagnation) temperature led to the significant increase of the outlet gas velocity and the decrease of the corresponding outlet Mach number due to the aggravation of wall friction and heat transfer. The increase of the inlet total (or stagnation) pressure cannot significantly increase the outlet gas velocity. The increase of the wall temperature led to the decrease of both the outlet gas velocity and the outlet Mach number.

Study on suppression effect of apex cone on secondary flow in cyclone

Dong LI Honggang YANG Yi WANG Xiaofan CAI Ruming CAI

Chin. J. Process Eng.. 2020, 20(12): 1397-1405. DOI: 10.12034/j.issn.1009-606X.220020

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The secondary flow effect existing in the hopper of the cyclone caused the captured particles to re-enter the airflow, which decreased the separation efficiency of the cyclone. In order to effectively suppress the secondary flow effect in the hopper, the two-phase flow numerical simulation study of the cyclone with different geometric dimensions and installation positions of the apex cone was carried out by means of built-in apex cone. The results showed that the built-in apex cone reduced the tangential, axial velocity and turbulence intensity of the flow field in the hopper, and had a significant suppression effect on the re-entrainment caused by the secondary flow in the hopper of the cyclone. The simulation results recommend that the optimal angle of the apex cone was 80?, and the best installation position was that the vertical distance between the bottom surface and the cone section was 0.375B≤Bs≤0.5B. When the inlet velocity was 12 m/s, compared with the original structure, the overall separation efficiency was improved by 11.50%, and the pressure drop increased by 8.29%.

Local momentum exchange coefficient in distribution channel of centrifugal radial fixed bed

Hongsheng WEI Ruojin WANG Dewu WANG Tianhang WU Yan LIU Shaofeng ZHANG

Chin. J. Process Eng.. 2020, 20(12): 1406-1415. DOI: 10.12034/j.issn.1009-606X.220007

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For the characteristic of gas variable mass flow in distribution/collection channels of centrifugal radial fixed bed, the pressure distribution was measured and analyzed in these two channels under both Π-type and Z-type operation modes in a set of cold experimental apparatus. The pressure had an increasing trend along the gas flow direction in the distribution channel, while it had opposite trend in the collection channel. According to the uneven index of pressure distribution in particle bed and the axial distribution of gas radial velocity obtained by Ergun equation, it was found that the centrifugal Π-type was slightly better than the centrifugal Z-type. With the gas radial velocity distribution in particle bed, the flow and momentum balances were applied in the elemental body of the channels to obtain the gas velocity in distribution/collection channels and the local momentum exchange coefficient. Compared to the collection channel, the sensitivity of local momentum exchange coefficient to pressure change was relatively small in the distribution channel. In the distribution channel, the overall momentum coefficient almost unchanged with the operating mode, gas flow rate, and axial position. While the local momentum exchange coefficient was only a function of the flow rate ratio u/u0 (or axial position), which first decreased and then remained unvaried with the flow rate ratio. According to the experimental results, the equation of the local momentum exchange coefficient were obtained by the regression method within 11% error. It was anticipated to provide reference for the calculation of local pressure in the gas channels and the designation of the structural optimization.

Numerical simulation of heat transfer enhancement in honeycomb regenerators with expansion and contraction square channels

Zhongda WU Yonghua YOU Sheng WANG Zhuang ZHANG Sikai ZHOU Fangqin DAI Zhengming YI

Chin. J. Process Eng.. 2020, 20(12): 1416-1423. DOI: 10.12034/j.issn.1009-606X.220009

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In this work, expansion and contraction square channels were presented for honeycomb regenerators to recover more waste heat from flue gas. A 3D numerical model of unsteady heat transfer was built with ANSYS Fluent for the new type of regenerators and user-defined functions (UDFs) were compiled to express the changes of fluid type, inlet velocity and temperature, etc. due to the switch between the flue gas and air blows. The current numerical model was validated by comparing its predicted results to experimental data in the literature. With the present model, the effects of expansion and contraction angle (θ), pitch (S) and regenerator length (L) on the performances of heat transfer and flow resistance were investigated for the novel regenerators. Temperature contours were presented to discuss the physical mechanism for the performance enhancement of regenerators with the expansion and contraction square channels. Numerical results confirmed that the expansion and contraction channels can improve the performance of honeycomb regenerators effectively, and regenerator effectiveness was improved by about 5 percentage under the premise of a limited increment of pressure loss. Besides, it was found that the longer the new regenerator, the better heat transfer performance it had. For the regenerators with a constant L, when the θ (or S) was fixed, the heat transfer performance can become better with the increment of S (or θ). However, the overall performance of the regenerator with a big θ can be undesirable because of its large flow resistance. The current numerical study on the heat transfer enhancement of honeycomb regenerators via the secondary development of CFD software presented a new way for the optimal design and performance improvement of regenerative heat exchangers.

Numerical analysis of hydraulic performance of tilted shaft agitator based on fluid-structure interaction

Yibin LI Kaiyi LIANG Zhenggui LI

Chin. J. Process Eng.. 2020, 20(12): 1424-1431. DOI: 10.12034/j.issn.1009-606X.220015

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In order to reveal the shear-dispersion performance of gas?liquid two-phase agitator, a double-layer agitator with six flat blade disk turbine on the upper layer and propeller blade on the lower layer was proposed and models of tilted shaft agitators with different angles (0°~30°) were established. Calculation and analysis of the hydraulic performance in a stirred tank were carried out by Reynolds average Navier-Stokes equation, RNG k?? turbulence model and VOF multiphase flow model. Unidirectional fluid-structure interaction was used to analyze the stress magnitude and distribution characteristics of tilted shaft agitator, and the material failure was checked based on the ANSYS Workbench platform. It was concluded that the inclined shaft improved the axial flow in the agitator, and the gas phase diffusion ability in the axial direction was enhanced; when the inclination angle was between 0°~30°, the time for the agitator to reach 95% gas content was significantly shorter than that at 0°, and the time required for 25° and 30° tilting shaft stirrers were shortened by 12.50% and 22.71%. At the same rotating speed, the shaft power increased with the increase of shaft tilt angle. The higher the rotation speed, the shorter the time for the agitator to reach the ideal gas content. The variation law of the mixing time with the shaft tilt angle under different rotation speeds was basically consistent. As the inclination angle increased, the equivalent stress and shaft power of the agitator increased. When the inclination angle was 30°, the stress at the dangerous section of the flat disk turbine agitator exceeded the range of safety stress, which was prone to fracture failure. When the inclination angle was 30°, the stress at the dangerous section of the straight blade disc turbine was higher than the allowable torsional stress of the blade by 8.7% which was beyond the safe stress range, and the blade was prone to fracture failure.

Numerical simulation of collision removal of inclusions in swirling flow tundish

Jinlin LU Dongsheng ZHANG Zhiguo LUO Zongshu ZOU

Chin. J. Process Eng.. 2020, 20(12): 1432-1438. DOI: 10.12034/j.issn.1009-606X.220021

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The SFT (swirling flow tundish) is a tundish with swirl chamber placed in the flow injection zone. The gravitational potential energy is converted into swirling kinetic energy as the liquid steel flows into the tundish from the bottom of the SC (swirling chamber) through a nozzle along the tangent direction. The swirling molten steel promotes the inclusions to gather towards the center of the swirling chamber, promoting the inclusions to collide and polymerize. In this work, the PBM model in ANSYS Fluent was used to simulate the growth of inclusions in SFT, the DPM model was used to simulate the removal rate and trajectory of different particle size inclusions. Simulation results showed that the average diameter of inclusions in the tundish without swirling chamber increased from 3.93 μm to 4.25 μm and the inclusion removal rate was 40.07% considering the collision polymerization between inclusions. Under the same operating conditions, the average diameter of inclusions in swirling flow tundish increased from 3.93 μm to 4.35 μm, and the removal rate of inclusions increased from 30.09% to 43.20%. The removal capacity of SFT was better than that of NSCT (non-swirling chamber tundish).

Design and experiment research of the liquid accumulator in compact phase-change energy storage refrigeration system

Junfei YUAN Lin WANG Zhanwei WANG Yonggang JIAO

Chin. J. Process Eng.. 2020, 20(12): 1439-1447. DOI: 10.12034/j.issn.1009-606X.219345

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Compact phase-change energy storage refrigeration system, which cools the short-time high-power electronic appliances directly, is an important thermal management system. The effective control of the temperature and pressure in the working process is the main problem to be solved during the application of the system cooling a high power heat source. In this work, theoretical analysis, design and calculation of the liquid accumulator for the energy storage refrigeration system of 10 kW heat source with NH3 as the refrigerating working medium was studied theoretically, and the experimental platform for the experimental research was also built up. The results showed that the liquid accumulator, as the constant pressure equipment of the system, played a role of replenishing and storing the working medium of the storage system during the system start-up and operation. The pressure fluctuation in the accumulator was related to heat addition, evaporation temperature, volume of reservoir and initial system pressure. The temperature fluctuation of the heat source during operation was only 1.2℃, as the volumetric ratio of accumulator to system of 1.48. The coupled working characteristics of the condensing reservoir and the accumulator can restrain the temperature and pressure fluctuation of the system, when the heat source was disturbed.

Influence mechanism of surface properties of coal and kaolinite on coagulation process

Xixi WANG Yuan HUANG Yue SUN Mengyun SHI Anran NIU Zhe LIN

Chin. J. Process Eng.. 2020, 20(12): 1448-1454. DOI: 10.12034/j.issn.1009-606X.219369

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Coal slime water contains a large amount of clay minerals such as kaolinite, which brings great difficulties for flocculation and sedimentation. In order to clarify the influence mechanism of these mineral properties on the coagulation process, the interaction between the particles of coal or kaolinite were calculated by the extended DLVO theory, and the coagulation process of 20 g/L coal and kaolinite suspension with a CaCl2 dosage of 4.5 mmol/L was monitored by a focused beam reflectometer at the stirring speeds of 60, 100 and 150 r/min. The results showed that the electrostatic interaction played a dominant role in the range of 2?200 nm for particle surface distance. The kaolinite particles had larger electronegativity, so it was more difficult to approach to and collide to each other during the coagulation process. The higher rotation speed increased the momentum of particles and was beneficial to increase the collision frequency and shorten the time required to complete the coagulation. Under the experimental conditions, the coagulation times of coal and kaolinite were shortened from 74 and 123 s to 47 and 89 s, respectively. The hydrophobic force played a leading role in the range of particle spacing less than 2 nm, which determined the adhesion efficiency of the particles. With strong hydrophobic surface, coal particles were easier to adhere to each other after collision, and can resist higher fluid shearing action. As the result, coal particles can agglomerate to form large agglomerates of 100 μm from its initial size of 19.32 μm, while kaolinite was difficult to obtain agglomerates larger than 30 μm due to their hydrophilicity.

Cross-flow ultrafiltration refolding of ribonuclease A

Xiangjuan WANG Xiunan LI Chao CHEN Zhiguo SU Guanghui MA Dawei ZHAO Rong YU

Chin. J. Process Eng.. 2020, 20(12): 1455-1462. DOI: 10.12034/j.issn.1009-606X.220038

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Performance of cross-flow ultrafiltration refolding strategy based on hollow fiber membrane for ribonuclease A was investigated. To improve the refolding efficiency, effects of operating conditions of ultrafiltration refolding on the activity yield and mass recovery were studied. Parameters of RNase A concentration (A), transmembrane pressure (B), circulation velocity (C) were chosen as the three test factors, with three level for each factor an L9(34) orthogonal array was implemented. Results of the orthogonal test showed that these three factors had a significant influence on the activity yield of the ultrafiltration refolding of ribonuclease A, whether based on variance analysis or range analysis. However, results of ANOVA (Analysis of Variance) showed that the three factors had no significant effect on mass recovery rate of ultrafiltration of ribonuclease A. Therefore, the optimal conditions for ultrafiltration of ribonuclease A were A1B1C2, that was, the concentration of refolding was 0.3 mg/mL, the transmembrane pressure was 34.0 kPa and the circulation velocity was 935 cm/min. Verification test was performed under the optimal conditions with the active yield of 92.31% and the mass recovery rate of 77.56%, respectively. Furthermore, the reliability of ultrafiltration refolding was confirmed by characterization of refolding products with circular dichroism, reversed-phase high performance liquid chromatography and high-performance gel filtration chromatography.

Influence of spraying power on mechanical and resistance to aluminum–silicon melt corrosion properties of YSZ coating

Wen HUANG Zhaolu XUE Xia LIU Zhenhang NI Chaojun WU Shihong ZHANG

Chin. J. Process Eng.. 2020, 20(12): 1463-1471. DOI: 10.12034/j.issn.1009-606X.220005

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Hot-dip Al–Si alloy coating is an effective corrosion resistant coating for modern steel. However, the molten Al–Si alloy corrosion has become one of the problems to be urgently solved for sink rollers and their spare parts in the hot-dip Al–Si alloy production line. In this work, yttria partially stabilized zirconia (YSZ)/NiCrAlY protective coating was fabricated by air plasma spraying. The influence of spraying power on the microstructure and mechanical properties of the YSZ coating, and its corrosion behavior in Al–Si melt at 700℃ was also investigated. The results showed that YSZ coating presented a typical layered structure with lath-shaped and interlayer columnar grains. The interlayer columnar grains tended to grow up with the increase of spraying power from 37 kW to 46 kW. YSZ coating was mainly composed of t-ZrO2 phase and small amount of m-ZrO2 phase, and spraying power had no obvious influence on the phase compositions. The YSZ coating with 40 kW spraying power had relatively high microhardness and adherence strength values (642.4 HV0.3 and 62 MPa). Additionally, no reaction layer was formed at the interface between YSZ coating and Al–Si melt at 700℃ for 240 h, and the Si and Al elements in the molten Al–Si alloy also did not infiltrate into the YSZ coating, suggesting that YSZ/NiCrAlY protective coating could effectively prevent Al–Si alloy melt on the surface of coating.

Preparation of nano Co/rGO magnetic materials and the adsorption properties to Cu²⁺ ions

Jingjing ZHANG Jian LI Qinggui XIAO Hui ZHANG Xuan DU Tianyan XUE Tao QI

Chin. J. Process Eng.. 2020, 20(12): 1472-1482. DOI: 10.12034/j.issn.1009-606X.220006

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Flaky graphene oxide (GO) prepared by the improved Hummer method was used as a carrier and template to load cobalt ions. Then, nano-metal Co/graphene magnetic composite adsorption material (Co/rGO) was prepared using in situ reduction method and was applied to adsorb and remove Cu2+ to provide the guidance for the synthesis and application of remover with efficient and reusable copper ion. The experimental results showed that Co/rGO composite materials had super paramagnetism, and could be easily separated by magnets as well as be oscillating dispersed without magnetic field. Co/rGO composite materials had stable adsorption and desorption properties for Cu2+. The maximum adsorption capacity for Cu2+ could reach 117.5 mg/g under experimental conditions and the adsorption balance could be achieved within 5 min, which was far superior to its raw material GO with the adsorption capacity of 27.6 mg/g in 60 min. In this work, the key factors including the amount of NaOH addition, the type of complexant, and the type of solvent on the morphology and distribution characteristics of Co particles on rGO carrier were systematically investigated. The adsorption effects for Cu2+ of composite materials under different synthesis conditions were compared. The properties of Co/rGO composite materials prepared in preferred conditions were characterized by FT-IR, XRD and SEM. The results showed that the adsorption process of Cu2+ by nano-Co/rGO magnetic materials was more consistent with Freundlich model and belonged to multilayer adsorption. The adsorption enthalpy ΔH was 17.81 kJ/mol, and the equilibrium constant of adsorption reaction Kθ was 3.65 at room temperature. When the initial concentration of Cu2+ was 39.22 mg/L, the desorption rate exceeded 93%, and initial value of adsorption capacity remained at 94% after five adsorption/desorption cycles. The residual concentration of Cu2+ in the solution after each adsorption always met the requirements of cobalt electrolyte for the removal of impurity copper ions (5 mg/L) or GB 8978-1996 level 3 (2 mg/L) of comprehensive sewage discharge, which was expected to play a role in related fields.

Fault diagnosis for chemical processes based on deep residual network

Lusheng ZHONG Xiangming XIA

Chin. J. Process Eng.. 2020, 20(12): 1483-1490. DOI: 10.12034/j.issn.1009-606X.219374

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A fault diagnosis method for chemical processes based on deep residual network (DRN) was proposed, which could automatically extract fault features from a large number of chemical processes operation data. The model adopted the shortcut connections to alleviate the training difficulty in the traditional deep neural network, and adopted the batch normalization (BN) method, which could effectively alleviate the problem of vanishing/exploding gradients. The Tennessee Eastman (TE) process was used as the experimental object to evaluate the diagnostic performance of the proposed method. The proposed method and the previous TE process fault diagnosis method based on traditional deep learning model were compared. Furthermore, the effects of the number of layers, BN technology and residual structure on fault diagnosis rate were studied. Finally, the output of some layers was visualized by the t-distributed stochastic neighbor embedding (t-SNE) method. The results showed that the model achieved an average fault diagnosis rate of 94% and an average false positive rate of 0.30% for 21 working conditions, showing more excellent diagnostic performance. The two-dimensional scatter plot of the output layer showed clear clustering, which indicated that the proposed DRN model can accurately diagnose the faults.

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