The Chinese Journal of Process Engineering

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The Chinese Journal of Process Engineering. 2026, 26(8): 0.

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Research progress on multi-objective comprehensive evaluation of sludge treatment and resource recycling process

Xinran REN Mingxue YANG Tian'ao CUI Zhongqiang WANG Longyi LÜ Xiaoyang LIU Jie ZHANG Wenfang GAO

The Chinese Journal of Process Engineering. 2026, 26(8): 813-829. DOI: 10.12034/j.issn.1009-606X.225284

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Under the background of industrialization, sludge treatment and recycling have become a crucial focus under the carbon peaking and carbon neutrality goals. This review systematically examines evaluation methodologies for sludge treatment technologies, with particular emphasis on environmental impact, techno-economic performance, and carbon footprint analysis. Environmental impact assessment based on life cycle assessment reveals that electricity and fuel consumption significantly contribute to global warming potential, acidification potential, and toxicity potential. Improving energy utilization efficiency demonstrates marked potential in reducing these environmental burdens. Technical economic assessment indicates that processes incorporating energy recovery—particularly biogas power generation and thermal energy recovery—substantially enhance economic viability through additional revenue streams. Carbon footprint analysis further establishes that energy and material recovery strategies offer greater emission reduction potential compared to merely reducing direct electricity consumption. For instance, anaerobic digestion with combined heat and power can achieve significantly lower net carbon emissions than conventional treatment pathways. Beyond these core aspects, comprehensive energy analysis and risk assessment are increasingly recognized as vital components in technology evaluation. Integrating these perspectives, this review proposes a holistic "6A" evaluation framework encompassing environmental impact, technical economic assessment, carbon footprint analysis, risk assessment, energy assessment, and material flow analyzation. This multi-criteria approach provides comprehensive support for decision-making in sludge management, facilitating the development of sustainable sludge treatment practices that align with environmental protection objectives and climate goals. The framework offers valuable guidance for policy formulation and technology optimization in sludge treatment sector.

Numerical simulation on erosion and pressure drop characteristics of combined elbows in ventilation and dust removal based on CFD-DPM

Mingyue LI Xinyu LIU Xinru YIN Liang AI Qi LIN Jinli LU Huaiyu ZHONG Fuping QIAN

The Chinese Journal of Process Engineering. 2026, 26(8): 830-837. DOI: 10.12034/j.issn.1009-606X.225239

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Long-term scouring by dust-laden airflow in industrial dust removal pipelines causes inner wall wear, leakage, and excessively high pressure drop that increases fan energy consumption. Since existing studies lack quantitative analysis on multi-parameter interactions of Z-type elbows, this study aims to provide a theoretical basis for their wear-resistant and energy-saving design. For Z-type combined elbows in ventilation and dust removal systems, this work adopted a bidirectional coupling method of computational fluid dynamics (CFD) and discrete phase model (DPM) combined with response surface methodology (RSM), established a gas-solid two-phase flow model, used a turbulent model to simulate the gas flow field and Oka erosion model to calculate wall erosion rate (validated with good simulation-experiment consistency). Five parameters (bend-radius-to-diameter ratio, inlet velocity, particle mass flow rate, particle size, and connection-length-to-pipe-diameter ratio) were systematically analyzed for their effects on pipeline erosion and pressure drop. A multi-objective optimization yielded the optimal parameter combination. The results showed that the minimum erosion occurred at a bend-radius-to-diameter ratio of 2~3, while low erosion was observed when the connection-length-to-pipe-diameter ratio was 2~3. Inlet velocity significantly increased both erosion and pressure drop, with the pressure drop tripling at 32 m/s. Erosion and pressure drop increased with particle mass flow rate. Erosion peaked at a particle size of 150 μm, whereas particle size did not influence pressure drop. The first elbow exhibited higher average wear with a wide distribution of erosion, while the second elbow experienced concentrated wear. The optimal combination (connection length ratio of 2.7, bend-radius-to-diameter ratio of 3.6, inlet velocity of 20 m/s, particle mass flow rate of 6×10-5 kg/s, particle size of 208 μm) realized coordinated optimization of low erosion and pressure drop. Findings provide quantitative references for pipeline design/protection and are practically valuable for reducing maintenance costs and system energy consumption.

Numerical simulation of dispersion characteristics in a gas-liquid stirred tank with double-bend wide-skewed impellers

Liwei ZHANG Tianbao CHEN Guanqun XU Lanlan TAO Yongjun ZHOU

The Chinese Journal of Process Engineering. 2026, 26(8): 838-846. DOI: 10.12034/j.issn.1009-606X.225257

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Gas-liquid stirred tanks are widely used in chemical, pharmaceutical, and biochemical processes, where efficient dispersion of gas into liquid is essential for optimal mass transfer performance. Although various impeller designs have been developed, the gas dispersion characteristics of non-conventional impellers such as the double-bend wide-skewed (DBWS) impeller remain insufficiently explored. Based on a coupled computational fluid dynamics and population balance model (CFD-PBM), the gas holdup of DBWS was investigated under different rotational speeds and aeration rates. Additionally, the dispersion characteristics of DBWS impeller were compared with RT impeller under a specific operating condition. It was found that increasing rotational speed and aeration rate generally led to a higher gas holdup. However, excessively high aeration rates resulted in unstable gas dispersion, which negatively affected mass transfer reliability. Compared to the RT impeller, the DBWS impeller achieved a significantly higher stable gas holdup, despite requiring a longer time to reach steady state. A notable advantage of DBWS impeller was its ability to generate a larger proportion of fine bubbles in the 0~2 mm range, which promoted more efficient gas-liquid contact. In the DBWS impeller vessel, gas was primarily distributed between the two impellers and effectively contacted the liquid in both the mixing zone and near the vessel wall. Conversely, gas in the RT impeller vessel accumulated mainly near the shaft and impeller blades. In addition, the DBWS impeller produced slender and continuous vortex structures that effectively suppressed bubble coalescence. In contrast, the RT impeller formed intense and localized vortices near the blades, causing gas to accumulate behind the blades and form cavities, thereby reducing dispersion efficiency. Generally, these results demonstrated that DBWS impeller exhibited superior gas dispersion capability compared to the RT impeller, offering better gas distribution and higher gas holdup stability. These findings offer valuable insights for the practical engineering application of double-bend wide-skewed impellers.

Fault detection based on variational-attention-transformer-encoder for fluid catalytic cracking units

Xiaolong QIN Yiyang DAI

The Chinese Journal of Process Engineering. 2026, 26(8): 847-856. DOI: 10.12034/j.issn.1009-606X.225296

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Fluid catalytic cracking (FCC) is a pivotal secondary processing unit in the petroleum refining industry, primarily designed to convert heavy hydrocarbon fractions into high-value light products via catalytic reactions. The reliable operation of FCC units is paramount for global energy supply and economic efficiency, necessitating robust and timely process safety management. However, industrial FCC units operate under severe conditions characterized by high temperature, short reaction time and significant dynamic disturbances. This non-stationary characteristic presents a severe domain adaptation challenge for conventional data-driven monitoring schemes. The intrinsic coupling between the reaction-regeneration system and downstream fractionation units introduces substantial process variability and complexity. Furthermore, the stringent safety constraints of chemical facilities often result in a scarcity of labeled fault data, complicating the development of robust intelligent monitoring systems. To address these challenges, this work proposes a novel fault detection framework, VATE, tailored for FCC processes under non-stationary operating conditions. This study first utilizes a rigorous FCC process simulator to synthesize a comprehensive fault dataset, incorporating stochastic feedstock fluctuations to mimic real-world scenarios. In the proposed architecture, a variational mechanism is integrated into the attention module to achieve Variational Attention. The VATE framework leverages the probabilistic modeling capability of the variational mechanism to handle data uncertainty, while the attention mechanism focuses on relevant fault-indicative features. This structure enhances the model's ability to capture latent process features robust to fluctuations, thereby improving fault detection performance. A transformer encoder serves as the backbone for data reconstruction, using its intrinsic capability to model long-range temporal dependencies in the multivariate time-series data, while kernel density estimation (KDE) is employed to establish the statistical threshold strategy for anomaly detection. The VATE method was validated on a constructed catalytic cracking simulation dataset. When compared to the performance of principal component analysis (PCA), autoencoder (AE), variational autoencoder (VAE), long short-term memory autoencoder (LSTM-AE), long short-term memory variational autoencoder (LSTM-VAE), and dot-product attention transformer encoder (DATE), VATE achieved the best fault detection performance of 94.64% across eight fault types, providing valuable insights for future intelligent process monitoring of catalytic cracking processes.

Comparative study on the mechanism and efficacy of polyacrylamide and polyethylene oxide in enhancing limonite dewatering

Jiandong HE Kun WANG Pengpeng ZHANG Zhifang GAO Fanfei MIN Mingyang LI

The Chinese Journal of Process Engineering. 2026, 26(8): 857-864. DOI: 10.12034/j.issn.1009-606X.225244

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This study systematically examines the effects of polyacrylamide (PAM) and polyethylene oxide (PEO) as filter aids on the dewatering performance of limonite ore, and explores their underlying mechanisms of action through comprehensive experimental analysis. The solid-liquid separation behavior was evaluated using bench-scale sedimentation tests, vacuum-assisted dewatering experiments, and pilot-scale plate-and-frame filter press filtration. The samples were comprehensively characterized by Zeta potential analysis, Fourier-transform infrared (FTIR) spectroscopy, laser-diffraction particle-size distribution measurements, and high-resolution scanning electron microscopy (SEM). The results showed that PAM and PEO could reduce the moisture content of filter cake. Under optimal dosage (PAM 20 g/t, PEO 10 g/t) and acidic conditions (pH=2), the filter cake moisture contents decreased to 17.42% and 16.55%, respectively. In addition, under simulated industrial conditions with a filter press pressure of 0.8 MPa, the moisture contents further decreased to 16.85% (PAM) and 15.88% (PEO), which were 0.57 and 1.54 percentage points lower than that of the raw ore, demonstrating a remarkable improvement in dewatering efficiency. Mechanistic analysis revealed that PAM promoted particle flocculation primarily through electrostatic repulsion and adsorption bridging, whereas PEO improved the filtration performance by forming surface complexes and enhancing particle hydrophobicity. These findings indicated that PEO outperformed PAM in limonite dewatering. PEO can not only achieve lower moisture content at lower dosage, but also obtain higher dehydration efficiency and more stable filtration performance. This study provides theoretical basis and technical support for efficient dehydration of limonite. By improving the dehydration efficiency, the research helps to significantly reduce energy consumption and operational costs, while improving the overall production efficiency. The findings lay a foundation for future scientific research and large-scale industrial application of limonite dewatering, and also provide a new way to optimize the beneficiation process.

Research on enrichment of low-concentration methane by pressure swing adsorption using Na-ZSM-5

Xu YANG Xiaomin LI Xuan TANG Yang ZHOU Jinping LI Jiangfeng YANG

The Chinese Journal of Process Engineering. 2026, 26(8): 865-873. DOI: 10.12034/j.issn.1009-606X.225298

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The effective enrichment and utilization of low-concentration methane are of strategic importance for mitigating greenhouse gas emissions and improving the recovery efficiency of coal-associated resources. CH4, although a cleaner fuel relative to conventional fossil fuels, has a high global warming potential, and substantial quantities of coal mine methane in China remain underexploited despite its large proven reserves. Current regulatory requirements prohibit the discharge of drainage gas with methane concentrations above 8%, highlighting the necessity of developing technically viable enrichment processes. Among available gas separation technologies, pressure swing adsorption (PSA) has emerged as a promising method for CH4/N2 separation due to its low energy demand, operational simplicity, and strong adaptability to varying gas compositions. Existing studies have primarily focused on the purification of medium and high concentration methane mixtures, whereas systematic investigations targeting the enrichment of dilute methane streams are still limited. In this work, a four-tower, five-step PSA system (pressurization, adsorption, equalization depressurization, vacuum desorption, and equalization pressurization) was constructed to evaluate the separation performance for an 8vol% CH4/92vol% N2 feed mixture. Na-ZSM-5 molecular sieve was employed as the adsorbent owing to its representative adsorption characteristics for methane-nitrogen systems. The effects of adsorption time and feed flow rate were quantitatively examined with respect to product purity, recovery, and productivity. Experimental results demonstrated that, under optimal conditions (single-cycle throughput of 1.8×10-3 m3/kg, adsorption time of 540 s, and feed flow rate of 4 L/min), the CH4 purity in the product gas increased to 14.6% with a recovery of 83.0%, while a productivity of 0.82 m3/(h?tadsorbent) was obtained at a low energy consumption of 0.82 kWh/Nm3. These findings provide fundamental insights into the enrichment behavior of dilute methane mixtures under cyclic adsorption conditions and offer an empirical basis for the optimization and engineering application of PSA-based low-concentration methane utilization processes.

Effects of distillation temperature and time on the separation of tin from ferrophosphorus by vacuum distillation

Wenbo GUO Xiaohua YU Changli CAI Jiawei GENG

The Chinese Journal of Process Engineering. 2026, 26(8): 874-887. DOI: 10.12034/j.issn.1009-606X.225331

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This study investigates the effects of distillation temperature and time on the tin removal rate from ferrophosphorus during vacuum distillation, based on vacuum distillation separation theory.Theoretical analysis demonstrates that the majority of tin could be effectively separated from ferrophosphorus materials by controlling appropriate distillation temperature and vacuum pressure. Taking tin-rich ferrophosphorus materials as the experimental raw materials and a vacuum induction melting furnace as the separation equipment, the vacuum distillation experiments were carried out at a vacuum of 10 Pa to explore the effects of temperature and time on tin separation performance. The experimental results showed that the tin removal rate increased rapidly with the rise of temperature and reached the maximum value above 1873 K, and higher temperatures barely contributed to extra tin removal. At 1823 K, appropriately extending the distillation time was conducive to enhancing the tin removal rate, while extending the distillation time at 1873 K exerted little promoting effect on tin removal. Through process optimization, the optimal distillation process parameters were determined as follows: a vacuum pressure of 10 Pa, distillation temperature of 1873 K, and distillation time of 60 min. Under this condition, the tin removal rate reached 99.6%, and the Sn mass fraction in condensate reached approximately 90.5wt%. The theoretically calculated optimal distillation temperature was 1820 K, which deviated from the experimental optimal value. Such discrepancy was mainly attributed to the reduced activity coefficients caused by impurity elements in the actual system, which endowed the molten system with non-ideal solution characteristics.

Leaching characteristics of heavy metals in cement concrete under carbonation

Yulong XUAN Yihao SONG Minglei GUO Zhong LÜ

The Chinese Journal of Process Engineering. 2026, 26(8): 888-897. DOI: 10.12034/j.issn.1009-606X.225148

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During the co-disposal of heavy metal-containing waste in cement kilns, the kiln environment contributes significantly to the solidification of heavy metal ions. Nevertheless, partial heavy metals can permeate cement matrices via clinker phases, posing a potential leaching risk of heavy metal ions during the service life of cement products. Carbonation can reduce the alkalinity of concrete materials, alter their phases and microstructures, and enhance the leaching risk of heavy metal ions. The clinker prepared from urban sludge co-disposal in a commercial cement plant contains manganese and chromium, whose contents approach or exceed regulatory thresholds. Accordingly, the carbonation resistance of cement concrete containing high heavy metal residues in cementitious systems is explored, and the effects of carbonation on the leaching characteristics of heavy metal ions in concrete are analyzed in this study. Furthermore, the environmental hazards induced by heavy metal leaching are systematically evaluated. The results indicate that the relatively high-content heavy metals exert a slight influence on the carbonation resistance of cement concrete, and the law of development of its carbonation depth over time is similar to that of ordinary concrete. Heavy metals such as Mn can be effectively solidified in cement concrete with low leaching susceptibility; by contrast, the solidification efficiencies of Cr and Cr6+ are relatively inferior. Carbonation increases the leaching amounts of Cr and Cr6+ in concrete. Although the Cr content in cement clinker complies with the production limit requirements, the long-term cumulative leaching amount of Cr6+ in cement products under carbonation may exceed the limits set by surface water quality standards.

Preparation of functionalized sodium alginate hydrogel composite membrane and analysis of its Pb²⁺ adsorption behavior

Ziqi BIAN Yu GUO Hongmei WU Yali GONG Shan ZHANG Changsheng DING

The Chinese Journal of Process Engineering. 2026, 26(8): 898-910. DOI: 10.12034/j.issn.1009-606X.225291

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A novel sodium alginate hydrogel composite membrane (U-MCM-41@ASA) was successfully prepared using 3-aminopropyltrimethoxysilane functionalized sodium alginate (ASA) with 3-urea-propyltrimethoxysilane functionalized MCM-41 molecular sieve (U-MCM-41) for the highly efficient adsorption of Pb2+. The incorporation of functionalized MCM-41 into the sodium alginate hydrogel network significantly increased the amount of active adsorption sites and enhanced the adsorption performance of the composite membrane. A variety of characterization techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), energy dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS), were used to systematically analyze the microstructure, surface morphology, functional groups, surface chemical states, and thermal stability of the U-MCM-41@ASA composite membrane. The results indicated that U-MCM-41 was uniformly dispersed within the sodium alginate matrix, and the surface was rich in active groups such as amino groups, providing abundant adsorption sites for Pb2+. The removal of Pb2+ from aqueous solution by the U-MCM-41@ASA composite membrane was primarily achieved through coordination and chelation between the organic functional groups on the membrane surface and Pb2+, as well as electrostatic adsorption and ion exchange. Adsorption kinetics and thermodynamics analyses revealed that the adsorption process conformed to the pseudo-second-order kinetic model and the Langmuir isotherm model, and it was a spontaneous, endothermic, entropy-increasing behavior. Under the adsorption conditions of 15 mg composite membrane dosage, solution pH of 5.5, adsorption temperature of 45℃, initial Pb2+ concentration of 200 mg/L, and adsorption time of 240 min, the maximum adsorption capacity of the U-MCM-41@ASA composite membrane for Pb2+ reached 266.67 mg/g. Furthermore, the composite membrane exhibited excellent regeneration capability, with only a 10% decrease in adsorption capacity after five consecutive adsorption-desorption cycles. The U-MCM-41@ASA composite membrane not only possesses favorable adsorption performance and remarkable regeneration ability, but also offers advantages such as simple preparation and environmental friendliness, demonstrating potential application prospects in the treatment of lead-containing wastewater.

Determination and correlation of liquid-liquid equilibrium data for the n-butanol-n-butyl acetate-ionic liquid system

Jiahui LIU Yangyang WANG Hua XIN Zhigang ZHANG Wenjun WANG Qinqin ZHANG

The Chinese Journal of Process Engineering. 2026, 26(8): 911-920. DOI: 10.12034/j.issn.1009-606X.225187

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n-Butyl acetate (NBA), a key organic chemical intermediate, is widely applied in coatings, paints, inks, printing, electronics, and leather processing. The primary method for NBA production is the esterification of n-butanol. During this process, a mixture of n-butanol and NBA is produced, and it is necessary to separate them. However, the azeotrope formed between NBA and n-butanol at atmospheric pressure makes conventional distillation ineffective. In this work, three ionic liquids (ILs), 1-ethyl-3-methylimidazolium acetate ([EMIM][AC]), 1-ethyl-3-methylimidazolium dimethyl phosphate ([EMIM][DMP]), and 1-ethyl-3-methylimidazolium diethyl phosphate ([EMIM][DEP]) were screened as extractants using the COSMOthermX software based on COSMO-RS theory, with selectivity as the main indicator, combined with the viscosity of ILs. Liquid-liquid equilibrium (LLE) data for the ternary systems (n-butanol+NBA+ILs) were measured at 303.15 K and atmospheric pressure. The reliability of the LLE data was verified via Othmer-Tobias, Bachman, and Hand equations. The extraction performance of the three ILs was evaluated by selectivity and distribution coefficient, and the non-random two-fluid (NRTL) model was used to correlate the LLE data. Finally, the separation mechanism of the three ILs was explored by means of σ-profile and σ-potential analysis. The results indicated that the linear correlation coefficients (R2) of the Othmer-Tobias, Bachman, and Hand equations for the ternary LLE data all exceed 0.95, demonstrating high reliability of the data obtained in this work. The distribution coefficients (D) and selectivity (S) of the three ILs were all greater than 1, confirming their suitability for separating the n-butanol and NBA mixture. The separation performance followed the order of [EMIM][AC]>[EMIM][DMP]>[EMIM][DEP]. All three ILs were deemed suitable for separating the n-butanol and NBA mixture. The root mean square deviation (RMSD) between the results calculated by the NRTL model and the experimental data was less than 3%, indicating that the NRTL model was highly applicable for describing the LLE behavior of the n-butanol-NBA-IL ternary system studied in this work. There was a stronger hydrogen bond interaction between ILs and n-butanol, so ILs could separate n-butanol from its mixtures with NBA. The order of the interaction strength between the three ILs and n-butanol was [EMIM][AC]>[EMIM][DMP]>[EMIM][DEP].

Effect of preheating treatment on performance of the magnesium aluminum silicate-coated FeSiAl magnetic powder cores

Li WANG Qi SUN Ruchang SHENG Liming ZHAO Aiqin MAO Cuihong ZHENG

The Chinese Journal of Process Engineering. 2026, 26(8): 921-928. DOI: 10.12034/j.issn.1009-606X.225181

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Magnesium aluminum silicate gel was employed as a coating agent for gas-atomized spherical FeSiAl alloy magnetic powder in this work. The coated magnetic powders were pre-heated to explore the effects of preheating process parameters on the surface microstructure of FeSiAl magnetic powder and the performance of the prepared composite magnetic powder cores. The results showed that magnesium aluminum silicate could uniformly coat on the surface of FeSiAl magnetic powder particles. After preheating the coated magnetic powder, the interlayer hydroxyl groups (-OH) in the magnesium aluminum silicate coating were removed.The proportion of Fe0 and Fe2+ on the magnetic powder surface decreased, while elemental Al and Si were oxidized, accompanied by an increase in the content of Al3+ and Si4+. During preheating treatment, recrystallization occurred within the magnetic powder, resulting in an increase in grain size. The elimination of lattice distortion reduced the unit cell parameters, which significantly decreased the coercivity (Hc) of the magnetic powder. Meanwhile, the release of internal stress increased the saturation magnetization. In addition, slight agglomeration of magnetic powder particles appeared after preheating treatment, which reduced the density (ρ) and substantially lowered the effective permeability (μe) of the prepared composite magnetic powder cores. The eddy current loss (Pe) of the magnetic powder was almost unaffected before and after the preheating treatment of magnetic powder, while the hysteresis loss (Ph) was greatly reduced, resulting in a remarkable decrease in core loss (Pcv). When the magnesium aluminum silicate coating content was 1.0wt%, compared with the un-preheated coated magnetic powder, the μe of the composite magnetic powder decreased from 86.0 to 50.2. Under the conditions of 100 mT magnetic induction intensity and 50 kHz frequency, the Pcv decreased from 181.5 kW/m3 to 103.0 kW/m3. With the consistent preparation conditions of composite magnetic powder cores, the μe decreased with the increase of magnesium aluminum silicate coating content, whereas Pcv remained nearly unchanged across all samples.

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