Table of Content

28 September 2025, Volume 25 Issue 9

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Cover and Contents

The Chinese Journal of Process Engineering. 2025, 25(9):  0. 

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Research Paper

Numerical simulation and multi-objective optimization for high temperature composite SCR regenerator

Hanlin MAO Yonghua YOU Jiajun WU Zhengming YI

The Chinese Journal of Process Engineering. 2025, 25(9):  881-894.  DOI: 10.12034/j.issn.1009-606X.224394

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The molecular sieve catalyst of Ce-Cu-SSZ-13 has a good selective catalytic reduction (SCR) denitration performance at the temperature consistent with that of exhaust gas of industrial furnaces. It is proposed to be coated on the surface of honeycomb ceramics containing expansion and contraction channels to manufacture a high-temperature composite SCR regenerator, so that the integration of flue gas denitration and waste heat recovery equipment can be realized. To optimize the comprehensive performance of the new SCR regenerator, numerical simulation of SCR flue gas denitrification, coupled with regenerative heat transfer, is conducted with Fluent software, where regenerator length (L), expansion/contraction angle (θ), and flue gas flow rate (V) are adopted as design variables, and energy recovery ratio (ERR), denitrification efficiency (η), and flue gas pressure loss (?P) as objective functions. Based on the simulation results, an objective function regression model is established by using the response surface methodology (RSM). On this basis, the advanced non-dominated genetic algorithm (NSGA-II) is used to obtain the Pareto optimal solution set, from which the EWM (entropy weight method)-TOPSIS (Technique for Order Preference by Similarity to an Ideal Solution) method is employed to calculate the relative closeness between Pareto optimal solutions and negative ideal solutions, then the optimal solution is determined. Analysis of variance verifies the significance of the regression model, while response surface analysis reveals the synergistic effects of different design variables on the objective function. For the current new composite SCR regenerator, the optimal objective functions take the values of η=99.38%, ?P=52.57 Pa, and ERR=68.13%, while the corresponding design variables are V=4.03 m/s, θ=12.19°, and L=717.57 mm. At this time, the average temperature of flue gas outlet is about 150℃, and the mass concentration of NO is 4.3 mg/m3. Besides, after limiting the flue gas velocity to 5 and 6 m/s, it is found that a larger V results in a smaller optimal θ to prevent the pressure loss increase significantly.

Study on influence of structural design of shell and tube electric heater on temperature distribution

Chunhua JIA Wei WANG Xu DING Guanda WANG Liyan WEI Juan WANG

The Chinese Journal of Process Engineering. 2025, 25(9):  895-904.  DOI: 10.12034/j.issn.1009-606X.225006

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The development of heat conduction oil electric heaters has a profound impact on the realization of low-carbon and even zero-carbon emissions for industrial heat conduction oil electric heaters. This study introduces a novel shell and tube thermal oil electrical heating furnace, drawing inspiration from the design and manufacturing processes of traditional shell and tube heat exchangers. To evaluate the performance of this new furnace, a comprehensive numerical analysis is conducted using the RNG k-ε turbulence model, which is well-suited for capturing the anisotropic nature of turbulence in complex geometries. The simulation employs a second-order upwind scheme for the discretization of convection terms, ensuring accuracy in capturing the sharp gradients typically associated with high-temperature regions. Additionally, a semi-implicit pressure velocity coupling method is utilized to solve the fluid flow equations, facilitating a stable and convergent solution process.The study thoroughly examines the impact of various design parameters on the internal flow and temperature distribution within the heating furnace. The analysis reveals that a 25 mm spacing between triangular tubes outperforms both the 35 mm spacing between triangular tubes and the square tube arrangement, likely due to enhanced heat transfer and reduced flow resistance. Furthermore, the influence of support plate configurations, including their shape and spacing, is investigated. It is found that a 500 mm spacing between plum blossom-shaped support plates results in a more uniform temperature distribution across the furnace, which is crucial for efficient heat transfer and even heating. The findings suggest that the new shell and tube thermal oil electrical heating furnace is capable of meeting the heating demands of thermal oil, with the highest temperatures attained being in line with process and safety requirements. The structural design of the furnace shows promise for improving the efficiency and sustainability of industrial heating processes. The results are of great significance for guiding the green and zero carbon emission transformation and upgrading of existing heat transfer oil furnaces.

Analysis of liquid-solid separation characteristics of a new two-stage swirling cyclone

Jing ZHANG Shaozhe WANG Wenhao HOU Guangtian LIU Yaxia LI Bin GONG

The Chinese Journal of Process Engineering. 2025, 25(9):  905-913.  DOI: 10.12034/j.issn.1009-606X.225030

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A two-stage cyclone combining multiple helical tubes and a cylinder was designed to improve the separation efficiency. The liquid-solid two-phase flow characteristic and separation performance were investigated inside the cyclone by experiment and numerical simulation. The enhanced separation mechanism was revealed which the spiral tube group in parallel connection method was used as the cyclone inlets. The results showed that the first stage swirling flow was formed inside the spiral tube, and the fluid was subjected to centrifugal force based on the Dean eddy current principle. The denser solid particles moved towards the outside of the spiral tube, and the solid phase was concentrated on the outside and bottom of the spiral tube. Multiple spiral tubes were evenly arranged in the circumferential direction, and all of the spiral tube outlets were tangentially installed to the inner wall of the cyclone. The jet flow superposition was generated and the second stage swirling flow was strengthened. Three factors and five levels of the first stage swirl parameters were selected for orthogonal test, and the conclusion was obtained that the spiral tube number N had the most significant impact on the liquid-solid separation in the second stage swirling region. Under the same flow rate of a single tube, the solid bottom flow distribution rate decreased as the number of helical tubes increased. In the second stage swirling region below the spiral tube outlets, the swirling velocity and axial velocity were relatively lower for N≤3, and there were a large number of particles in the central region. In the secondary swirl region with N>4, the shear layer between adjacent jets was superimposed, and the fluid vortex near the outlet of the spiral tube was significantly increased, resulting in enhanced disturbance of axial flow to the central fluid. The appropriate number of spiral tubes effectively enhanced the swirling intensity near the inner wall, with relatively less disturbance to the central fluid. The distribution of particles in the near wall swirl zone increased, which was beneficial for the liquid-solid separation process in the two-stage swirling cyclone.

Simulation study on effects of near-wall region on transient heat transfer characteristics of fixed beds

Haitao ZHAO Zhichao GUO Jun SHEN Nan ZHANG

The Chinese Journal of Process Engineering. 2025, 25(9):  914-922.  DOI: 10.12034/j.issn.1009-606X.225001

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The distribution of particle packing in fixed beds, influenced by wall effects, has been extensively researched, however, the impact of this distribution on heat transfer characteristics has been less studied. This study aims to investigate the specific effects of wall effects on heat transfer properties by utilizing discrete element method simulation to analyze the radial voidage distribution, particle coordination number, and the contact conditions between particles and the wall within the fixed bed. These data are then applied to Eulerian simulations to investigate their impact on the bed's heat transfer performance. The discrete element method simulation results reveal that wall effects significantly influence the radial voidage distribution and particle coordination number within the fixed bed. Notably, only about 10% of the particles in the layer adjacent to the wall are in direct contact with it, a finding that is crucial for understanding the heat transfer mechanism. The Eulerian simulation study indicates that wall effects have a significant impact on the rate of temperature rise within a range of one particle diameter from the wall. However, under the current parameter settings, the radial voidage distribution and particle coordination number have a relatively minor impact on the bed's temperature increase rate. By accounting for the thermal resistance in the near-wall region or by adjusting the model to reflect the particle-wall contact ratio, a more accurate prediction of the bed's temperature increase can be made, thereby improving the understanding of the heat transfer process in fixed beds subject to wall effects. Compared to the thermal resistance model, incorporating the contact ratio between the wall and adjacent particles not only maintains calculation accuracy but also improves computational efficiency. This approach is crucial for the heat transfer simulation of industrial-scale fixed beds and can provide important guidance and assistance for the design and optimization of industrial-scale reactors.

Study on the dissolution behavior of lime in CaO-Al₂O₃-SiO₂(-MgO) slag based on SHTT

Yunjin XIA Jianhui SONG Xinyu LI Jie LI Dingdong FAN

The Chinese Journal of Process Engineering. 2025, 25(9):  923-932.  DOI: 10.12034/j.issn.1009-606X.225029

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Lime is one of the slag making materials in the steelmaking process. Its rapid and sufficient dissolution can accelerate the dephosphorization and desulfurization reaction rates. The dissolution process of lime in CaO-Al2O3-SiO2(-MgO) slag system at 1550℃ was studied using the single hot thermocouple technique (SHTT). The results showed that when lime dissolved in CaO-Al2O3-SiO2 slag without MgO, its apparent radius ratio gradually decreased with increasing dissolution time, and the dissolution rate remained relatively stable throughout the entire dissolution process, with the shortest dissolution time among all systems. When lime dissolved in CaO-Al2O3-SiO2 slag containing MgO, the dissolution time increased gradually with increasing MgO content. According to the change in dissolution rate, the dissolution process could be divided into three stages. In the first and third stages, the lime dissolved quickly. However, in the second stage, the formation of MgAl2O4 solid phase product layer hindered the dissolution of lime. The analysis of lime dissolution kinetics showed that in CaO-Al2O3-SiO2 slag without MgO, the dissolution was controlled by boundary layer diffusion as the limiting step. In contrast, in CaO-Al2O3-SiO2 slag with MgO, the dissolution limiting step varied with both dissolution time and MgO content. Specifically, for Slag 2 (3wt% MgO) and Slag 3 (6wt% MgO), the dissolution limiting step was controlled by interfacial chemical reactions in the early stage, but shifted to boundary layer diffusion control in the middle and late stages. For Slag 4 (9wt% MgO), the limiting step was interfacial chemical reaction only in the initial part of the first stage, with product layer diffusion becoming the controlling factor thereafter.

Synergistic oxygen-enriched alkaline leaching of vanadium mud and slag for enhanced extraction

Chang CHEN Zhenquan ZHANG Baohua WANG Hao DU Jian QI Shaona WANG Haonan LI Minghua WANG Biao LIU

The Chinese Journal of Process Engineering. 2025, 25(9):  933-942.  DOI: 10.12034/j.issn.1009-606X.224369

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Vanadium mud is a kind of solid waste produced in the process of vanadium leach solution decontamination, which has a high recovery value. In this study, to address the problem that vanadium mud is difficult to be utilized in large quantities, vanadium is extracted from vanadium mud by alkaline leaching of vanadium mud. The effects of reaction temperature, reaction time and NaOH concentration on vanadium extraction were investigated. The best conditions were found to be: 90℃, 2 hours, 20wt% NaOH, liquid to solid ratio of 2∶1. Under these conditions, the leaching rate of vanadium reached 99.23%, and the V2O5 content in tailings was only 0.48wt%. On the basis of alkaline leaching of vanadium from vanadium mud, the extracting vanadium from vanadium mud and vanadium slag by alkaline leaching was studied based on the existing process of extracting vanadium from vanadium slag by oxygen-enriched alkaline leaching. Under the optimized conditions, the vanadium content in the mixed slag was 0.68wt%, the leaching rate of vanadium from vanadium mud was 92.40%, and the vanadium extraction effect from the vanadium slag was improved by about 6 percentage points. The optimal conditions for the oxygen-enriched alkaline synergistic leaching process were a temperature of 150℃ and an oxygen pressure of 0.5 MPa.The leaching slurry was diluted to NaOH concentration of 25wt%, with adding the initial vanadium slag quality of 10wt% of the vanadium mud, leaching temperature of 90℃, leaching time of 1 h. Finally, the mechanism behind collaborative vanadium extraction was investigated during the extraction process. It was clear that the addition of vanadium mud can change the silicon phase to promote the efficient extraction of vanadium from vanadium slag. The method can realize the efficient synergistic extraction of vanadium from svanadium mud and vanadium slag.

CuAlCl₄ complex-melting crystallization for separation of para-xylene from xylene mixture

Han LIU Mengfan YIN Jiaxin CUI Tao ZHENG Xianghai MENG Rui ZHANG Haiyan LIU Zhichang LIU Chunming XU

The Chinese Journal of Process Engineering. 2025, 25(9):  943-952.  DOI: 10.12034/j.issn.1009-606X.225015

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Para-xylene (PX) is a fundamental chemical raw material that is utilized in the production of polyester fibers, dyes, and pesticides. It often existed in mixtures with meta-xylene (MX) and ortho-xylene (OX). Separating PX from xylene mixtures is essential for its chemical application. Due to their highly similar physicochemical properties, the separation and purification of xylene isomers have always been a significant challenge. Among the separation processes, melt crystallization is an effective technology to obtain high-purity PX based on the difference in the melting points of each xylene isomer. It is more efficient and environmentally friendly than other methods. However, the presence of eutectic points necessitates the separation of mixed xylene isomers at significantly low temperatures. The complex-melting crystallization method combines complexation with crystallization processes, which improves the melting points of the isomers to be separated. In this research, the bimetallic halide CuAlCl4 was used as a complexing agent, forming complexes with the three xylene isomers. The complex system had higher melting points and eutectic temperatures than pure xylene system, and the temperature required for crystallization operation was closer to normal temperature. A xylene mixture with a PX content of 74.60% was used as feedstock, and the operating conditions of the complex-melting crystallization process were optimized. In the first crystallization stage, crystallization time was 1.0 h, final crystallization temperature was 5℃, cooling rate was 0.15℃/min, sweating temperature was 36℃, and sweating rate was 1.0℃/min. In the second crystallization stage, final crystallization temperature was 15℃, sweating temperature was 38℃. Through the implementation of two-stage melting crystallization, the purity of PX was successfully increased from 74.60% to over 99.50%, and the yield of PX reached 43.12%. Compared with the pure mixed xylene isomers system, the operating temperature was increased by 20℃ at a similar yield. The results demonstrated that CuAlCl4 was able to separate PX from xylene mixtures and significantly decrease the refrigeration energy consumption during the crystallization process.

Study on the Ag-based catalysts for the catalytic degradation of MEA and collaborative production of NH₃

Shuaili JIN Jiancheng WANG Xiaolong LIU Tingyu ZHU

The Chinese Journal of Process Engineering. 2025, 25(9):  953-962.  DOI: 10.12034/j.issn.1009-606X.225003

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In the context of carbon peaking and carbon neutrality goals, ethanolamine (MEA) has found widespread application in CO2 removal due to its excellent CO2 capture performance. However, during storage and usage, MEA inevitably undergoes leakage and emission, which cand easily lead to its escape from the liquid phase to the gas phase, posing risks to the environment and human health. To mitigate the adverse effects of MEA on the external environment, it is necessary to achieve the green and resourceful degradation of MEA. In this work,different types of TiO2, including anatase TiO2, P25 TiO2, and rutile TiO2, were employed as supports to prepare three Ag/Ti catalysts (Ag/TiO2-A, Ag/TiO2-P, Ag/TiO2-R) via an impregnation method. These catalysts were then used to investigate the catalytic degradation of MEA coupled with the simultaneous production of ammonia. The study found that compared with the other two catalysts, Ag/TiO2-R catalyst exhibited the highest MEA removal efficiency and NH3 yield. Through characterization and analysis using X-ray photoelectron spectroscopy (XPS), oxygen temperature-programmed desorption (O2-TPD), and hydrogen temperature-programmed reduction (H2-TPR), it was determined that the rutile TiO2 support not only facilitates activation on Ag/TiO2-R catalyst, enhancing its degradation efficiency, but also enabled the loaded Ag to exist in an oxidized state on the catalyst. This phenomenon was attributed to the presence of more lattice defects on Ag/TiO2-R, which enhanced the anchoring effect of the catalyst, promoting the loaded silver to exist in an oxidized state. The presence of oxidized silver facilitated the cleavage of C-N bonds during MEA degradation, thus improving the NH3 yield. Therefore, the Ag/TiO2-R catalyst prepared with rutile TiO2 support exhibited the optimal catalytic performance, it achieved complete degradation of MEA at 270℃, and when the reaction temperature reached 300℃, the yields of the products NH3 and CO2 were 80% and 97%, respectively.

Preparation and evaluation of self-healing materials for oil-water dual-response cementing cement sheath

Zhiping ZHU Chunmei ZHANG Kun LI Shuai LIU Xiaowei CHENG Kaiyuan MEI Xinyu LI

The Chinese Journal of Process Engineering. 2025, 25(9):  963-974.  DOI: 10.12034/j.issn.1009-606X.225007

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Aiming at the problem that the micro-fractures of the cement sheath destroy the integrity of the cement sheath, this work successfully prepared an oil-water dual-response self-healing material using sodium silicate as a self-healing agent, diatomite as a carrier, and ethyl cellulose as a surface coating material, and evaluated its self-healing effect. The results showed that the optimum calcination temperature of diatomite was 600℃. At this time, the specific surface area and pore volume of diatomite were the largest, and the pore distribution was uniform, which was most conducive to the adsorption of sodium silicate. Ethyl cellulose did not react with sodium silicate and diatomite. The 2wt% ethyl cellulose solution had the best coating effect on sodium silicate, and could form a smooth and dense film on the surface of diatomite adsorbed with sodium silicate. The optimum content of coated self-healing material in cement was 4wt%. After 14 days of self-healing, the micro-cracks of cement paste were completely closed, and the permeability of cement paste decreased to 0.31 mD, which was 69.31% lower than that of blank cement paste. After 14 days of self-healing, the compressive strength of cement paste with 4wt% coated self-healing material reached 26.6±1.3 MPa, and the recovery rate of compressive strength was 85.3%, which was 2.1 times that of blank cement paste. It was found by data fitting that the compressive strength recovery rate of cement paste increased first and then decreased with the increase of self-healing material content, and the self-healing effect was the best when the content was 4.5wt%. The results of XRD and TG analysis showed that when cracks occurred in the cement paste, the ethyl cellulose film on the surface of the self-healing material dissolved in oil, and then the self-healing agent sodium silicate consumed calcium hydroxide and water in the cement paste to form hydrated calcium silicate, and then filled the cracks to achieve self-healing.

Study on the stability and stabilizers of supercoiled plasmid DNA during ultrafiltration membrane separation processes

Mengxiao LI Kaixuan JIANG Jingyang ZHAO Songping ZHANG Zhiguo SU Zhengjun LI Yanju JIA

The Chinese Journal of Process Engineering. 2025, 25(9):  975-986.  DOI: 10.12034/j.issn.1009-606X.225048

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The stability of supercoiled plasmid DNA (sc DNA) is a core issue in the development of nucleic acid vaccines, directly determining the efficacy and safety of the vaccines. This study investigated the effects of ultrafiltration membrane packs with different molecular weight cut-offs on the concentration and purification of plasmid DNA, and the effects of different stabilizers on the stability of plasmid DNA during purification process and storage were evaluated. The results showed that as the molecular weight cut-off of the ultrafiltration membrane pack increased, the yield of sc DNA significantly decreased, the damage to the supercoiled structure was exacerbated, the melting temperature (Tm) dropped, and the degradation rate during storage accelerated. These findings suggested that larger pore sizes in the membrane packs may lead to increased physical or chemical damage to sc DNA, such as double-strand breaks or the formation of open circular structures. Adding trisodium citrate during ultrafiltration significantly enhanced the stability of sc DNA, reducing losses during the ultrafiltration purification and subsequent storage processes. Molecular dynamics simulations further revealed that trisodium citrate formed a protective layer around DNA molecules through hydrogen bonds, effectively reducing damage to sc DNA during purification and storage. Additionally, the addition of trisodium citrate significantly increased the yield of mRNA after in vitro transcription but had no significant effect on the content of by-products such as dsRNA. Therefore, using a membrane pack with a smaller molecular weight cut-off (e.g., 30 kDa) in combination with trisodium citrate as a stabilizer can significantly improve the purification efficiency and stability of sc DNA. This finding provides theoretical support for optimizing the purification and storage conditions of plasmid DNA and lays an important foundation for the development of more stable and efficient DNA and mRNA vaccines, which is crucial for advancing nucleic acid-based therapeutic strategies.

Catalytic cracking fault diagnosis method and application based on deep category-supervised stacked autoencoders

Zhiqiang GENG Haiying QI Qingxu NI Tao LI Bo MA Feng PAN Lei TAN Yongming HAN

The Chinese Journal of Process Engineering. 2025, 25(9):  987-994.  DOI: 10.12034/j.issn.1009-606X.225004

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The reaction-regeneration system in catalytic cracking unit is an important core equipment for the secondary treatment of crude oil. The increased operational complexity of catalytic cracking units, which is often operated under high pressure, leads to a significant increase in the probability of faults. Therefore, efficient and stable fault diagnosis and condition monitoring are of great significance to ensure the safe operation of catalytic cracking unit. The deep learning methods represented by stacked autoencoder (SAE) is an effective feature extraction method, which is widely used to extract features from collected data quickly and can preserve the original structure of the data thus it is particularly suitable for dealing with chemical fault data. However, it has limited ability as an unsupervised model to deal with classification problems and cannot fully utilize the category information. In order to improve the performance of fault diagnosis in catalytic cracking systems against data imbalance and small sample problems, this work proposes a fault diagnosis method based on deep category-supervised stacked autoencoders (DCSAE). The proposed model extracts deep features layer by layer by stacking multiple category-supervised self-encoders, and introduces category-supervised information to improve the recognition of different fault types by effectively learning useful features with high dimensional unbalanced data and few samples. Then, Bayesian classifiers are utilized for fault diagnosis. Finally, the proposed method is validated on a reaction-regeneration system dataset, and compared with the SAE, the multilayer perceptron (MLP), deep belief network (DBN), the t-distributed stochastic neighbor embedding (TSNE), and the principal component analysis (PCA), the proposed method achieves an accuracy of 96.0%. In addition, the proposed method performs well in dealing with fault data and achieves the highest diagnostic accuracy. In summary, the proposed method provides an innovative idea for the fault diagnosis of catalytic cracking unit, and also provides a valuable reference for the practice in related engineering fields.