Table of Content

28 September 2023, Volume 23 Issue 9

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Contents

Cover and Contents

The Chinese Journal of Process Engineering. 2023, 23(9):  0. 

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Review

Research progress of lithium polysulfide capture in lithium-sulfur batteries

Tingting HU Haijian LIU Yunyi CHEN Lingli LIU Chun'ai DAI Yongsheng HAN

The Chinese Journal of Process Engineering. 2023, 23(9):  1231-1243.  DOI: 10.12034/j.issn.1009-606X.222413

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Lithium-sulfur battery has an ultra-high theoretical specific capacity (1675 mAh/g) and theoretical specific energy (2600 Wh/kg), which is far higher than commercial secondary batteries. In addition, the sulfur element is rich in the earth, and its price is cheap, the extraction process is environmentally friendly. Therefore, a lithium-sulfur battery is considered as an ideal energy storage unit for the future energy storage system. However, the lithium polysulfide intermediates generated in the charging and discharging process are easily soluble in the electrolyte, resulting in a loss of active materials and an increase in the electrolyte viscosity. In addition, the dissolved lithium polysulfide is inclined to migrate between positive and negative electrodes, and reacts with the lithium negative electrode, causing irreversible loss of active substance sulfur, greatly reducing the battery life and safety. This phenomenon is called the shuttle effect, which hinders the commercialization process of lithium-sulfur batteries. In recent years, researchers have attempted to solve this problem through physical adsorption, chemical action, and external field constraint, and achieved impressive progress. This work summarizes the research progress of capturing lithium polysulfide, and compares the characteristics of each approach and its impact on the electrochemical performance of lithium-sulfur batteries. Whether it is the physical constraint of the porous structure of carbon materials, the chemical interaction between the carrier materials and lithium polysulfide, or the adsorption of electric and magnetic fields on lithium polysulfide, lithium polysulfide is fixed on the positive side and to inhibit its dissolution and diffusion to the negative electrode. Capturing lithium polysulfide by external magnetic field, internal magnetic field induced by magnetic particles, and internal electric field generated by spontaneous polarization of ferroelectric materials is also highlighted. Finally, the challenges in capturing lithium polysulfide and the possible solution are prospected.

Research Paper

Numerical study on CO₂ bubble rise process coupled with mass transfer

Donghao PEI Lexiang ZENG Mengdie GAO Jincheng RUAN Jun CAO

The Chinese Journal of Process Engineering. 2023, 23(9):  1244-1255.  DOI: 10.12034/j.issn.1009-606X.222385

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Gas-liquid two-phase flow and mass transfer phenomena widely exist in nature and daily life. Studying the mass transfer process of bubbles in water is of great significance for understanding the mass transfer mechanism and exploring the enhancement of the mass transfer process. The volume of fluid (VOF) method was used to simulate the rising process of CO2 bubble in still water, and the mass transfer process was considered by a user defined function program. The instantaneous velocity, mass transfer coefficient, CO2 dissolved amount, and mass transfer wake changes of bubbles with different initial diameters during the rising process were studied. In the process of bubble rising, the transverse velocity changed periodically and the oscillation amplitude decreased with the increase of bubble initial diameter, while the longitudinal velocity increased with the increase of the bubble initial diameter. Between 3.5 mm and 6 mm, with the increase of the bubble diameter, the CO2 dissolved amount increased, and the wake stream showed three states: symmetrical state, transitional state, and periodic shedding. The critical Re number of 3.5~6 mm bubble wake transition increased with the increase of bubble initial diameter, the frequency of wake periodic shedding was 17~22 Hz, and the departure frequency decreased with the increase of bubble initial diameter. The bubble wake was consistent with the mass transfer wake. With the increase of the bubble initial diameter, the influence range of the bubble mass transfer wake increased.

Numerical investigation of effects of bath flow on melting behavior of scrap

Xiaobin ZHOU Yu TENG Wanxing WANG Qiang YUE Zhenghai ZHU

The Chinese Journal of Process Engineering. 2023, 23(9):  1256-1267.  DOI: 10.12034/j.issn.1009-606X.222403

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Nowadays, more and more scrap is required to be added in the bath of the converter accompanied by the increasing requirements on the environment and increasing volume of available scrap in China. Consequently, the melting rate of the scrap would be significant if a large amount of scrap is added into the bath for the steelmaking process. The carbon content, temperature, and flow of the bath are the main factors that influence the scrap melting process in a bath of hot metal. The current study mainly focused on the effects of bath flow on the melting behavior based on a scrap melting process performed in the experiment in which the scrap melting behavior in a bath was investigated. Specifically, the effects of nature convection and driven convection on the meting process were investigated by applying a mathematical model. The results found that nature convection was formed in the vicinity of the melting interface when a scrap bar was immersed in the melting bath of hot metal. As a result, the heat transfer between bath and scrap can be enhanced by the flow at the melting interface. Also, the hot metal with high carbon content was driven to the melting interface. In turn, the melting rate was accelerated. The intensity of nature convection decreased when the initial temperature of the scrap was increased. The melting rate was remarkably increased when the driven convection was introduced to the bath. Compared to the initial temperature of 25℃ with a melting rate of 107 mm3/s, the melting rate was only 50 mm3/s when the initial temperature of scrap was 1000℃ at 5 s. In addition, when the melting was performed at 15 s, the rest volume of the scrap with the nature convection was 1054 mm3, which was 2.3 times for driven convection with the driven flow velocity of 0.15 m/s. Also, the melting rate of the scrap with the driven flow velocity of 0.15 m/s was about 1.8 times that of the nature convection at 10 s.

Study on wave dynamics and energy transfer mechanism in gas wave oscillation tube

Zhaofeng HUANG Yihui ZHOU Dapeng HU Zhijun LIU Jiangtao GUO Feng GAO

The Chinese Journal of Process Engineering. 2023, 23(9):  1268-1279.  DOI: 10.12034/j.issn.1009-606X.222434

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With the characteristics of higher refrigeration efficiency, smaller equipment size and applicability in extreme operation condition, gas wave refrigeration technology has been widely used in petrochemical, national defense and other fields. Gas wave refrigerator is based on gas wave motion, which has been studied to some extent. Large eddy simulation is employed to obtain the instantaneous spatial form and numerical distribution of shock wave, expansion wave, and other non-stationary motion in oscillation tube. A three-dimensional large eddy simulation model for the oscillation tube of a double open gas wave refrigerator is established. The characteristics of the dynamic shock wave, expansion wave in the oscillation tube are obtained. For violent oscillation, energy loss is caused during the contact of each nozzle and the oscillation tube especially at the high pressure inlet. The influence mechanism for the energy loss of the operation and structural parameters on the energy transfer efficiency is discussed. The numerical results show that there are strong eddies which lead to turbulent kinetic energy dissipation during the contact process. The energy loss is quantitatively evaluated by the instantaneous turbulent kinetic energy loss ratio. The major instantaneous turbulent kinetic energy loss ratio exists at the vortex core, and increases first and then decreases with the increasing of the absolute pressure ratio and reaches the maximum value of 9.0%, when absolute pressure ratio is 3.61. The instantaneous turbulent kinetic energy loss ratio decreases from 10.7% to 6.0% at the vortex center with the increase of rotational speed from 1100 r/min to 2000 r/min. The instantaneous turbulent kinetic energy loss ratio at the vortex center of the far and the near wall both decrease with the increase of the tube width. The instantaneous turbulent kinetic energy loss ratio at the vortex center of the near wall is larger than that of the far wall, and the difference between the two walls reaches a maximum of 3.2%. The energy transfer efficiency of the gas wave refrigerator could be improved by decreasing absolute pressure ratio, increasing rotational speed and the width of oscillation tube, which also has guiding significance for industrial large flow gas wave refrigerator design.

Emission characteristics of NOx and CO during the combustion of distiller's grains derived from different liquor-making materials

Weiqiang LI Huawei JIANG Hongshuai GUO Miao YUAN Xiangli ZUO Cuiping WANG Yanhui LI

The Chinese Journal of Process Engineering. 2023, 23(9):  1280-1289.  DOI: 10.12034/j.issn.1009-606X.222367

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Distiller's grains are the residues produced after the fermentation of corn, wheat, or sorghum, in the brewing process of different kinds of liquors. They have higher heat values after drying and thus can be burned to achieve harmless disposal, minimization, and resource utilization. However, there are differences in the composition between different distiller's grains, and the nitrogen contents are generally high, so NOx would be produced during their combustion. They also have high moisture and volatile matter, so incomplete combustion products such as CO are easy to generate. To reveal the differences in NOx and CO emissions during the combustion among distiller's grains derived from different liquor-making materials, and to solve the problems of unclear emission laws, a one-dimensional tube furnace was used to investigate the NOx and CO emissions during the combustion of distiller's grains derived from corn, wheat, or sorghum at different temperatures and moisture contents. The results showed that with the increase of temperature, the combustion reactions were accelerated, the peaks of NOx emissions appeared earlier, the peak values and average values of NOx emission concentrations both increased, NOx emission masses and nitrogen conversion rates showed a trend of increasing first and then decreasing, and reached the maximum value at 700℃. NOx emission masses of sorghum-based distiller's grains (SDGS), wheat-based distiller's grains (WDGS), and corn-based distiller's grains (CDGS) reached 1.32, 1.64, and 1.89 mg, respectively, and nitrogen conversion rates of these three kinds of distillers grains reached 12.4%, 15.6%, and 21.1%, respectively. For three kinds of distiller's grains, with the increase in temperature, the peak values and average values of CO emission concentrations both increased first and then decreased, they reached the maximum values at 600℃. CO emission masses of SDGS and CDGS reached the maximum at 600℃, at 20.27 and 19.80 mg, respectively, but for WDGS, the maximum value of 20.20 mg appeared at 500℃. At 700℃, with increasing moisture content, combustion reactions were delayed, peak values and average values of NOx or CO emission concentrations both increased, and CO emission masses also increased.

Design of temperature control system for evaporator based on cascade fuzzy self-adaptive PID method

Jun SUN Dian ZHANG Qingshan HUANG Liang TIAN Tianqi CHANG Qi LIU

The Chinese Journal of Process Engineering. 2023, 23(9):  1290-1299.  DOI: 10.12034/j.issn.1009-606X.222320

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It has been widely accepted that applying the traditional control method is difficult to achieve precise temperature control of the evaporator because the evaporator temperature has nonlinear, time-varying characteristics with a significant lag. Based on the evaporator production process analysis, an evaporator temperature control method based on the cascade fuzzy adaptive proportional-integral-differential (PID) is proposed here, which combines the fuzzy control theory with the cascade PID control theory to set up a Continuous Function Charts (CFC) configuration of fuzzy adaptive PID control for the main loop and the secondary loop. A real-time self-adapting amendment of PID parameters in the main loop and the secondary loop during the evaporator temperature control can be realized using this control strategy. The experimental results with the SMPT-1000 simulation equipment and Siemens PCS7 process control system show that after the real-time self-adapting amendment of PID parameters, the computed new proportional parameter can successfully accelerate the response speed of the system, the calculated new integral parameter can efficiently reduce the deviation of the system, and the deduced new differential parameter can wisely play an essential role in the anticipatory control. The corresponding experimental results demonstrated that the adjustment time of temperature response could be shortened by one-half, and the maximum deviation could be reduced by more than four-fifths. Additionally, the adjustment time of the temperature rise load could be shrunk by more than three-fifths, and the maximum deviation could be decreased by more than four-fifths. Moreover, the recovery time for the superheated steam perturbation could be narrowed by more than one-half, and the deviation of minimum and maximum temperature could be condensed by more than one-tenth. It is noteworthy that compared with the traditional cascade PID control method, the cascade fuzzy self-adaptive PID control strategy proposed here has the notable advantages of short regulation time, slight overshoot, and good robustness, which can overcome the shortcomings of the traditional cascade PID control method and provide an effective way and mathematical models to solve the problem of accurate temperature control in the evaporator. Therefore, the control strategy developed here has a particular significance in ensuring the smooth operation of the evaporator.

Analysis of influence mechanism of zinc volatilization rate based on neural network prediction

Zhi ZAN Chenmu ZHANG Jijun WU Yao SHI Langming LIU Weiping LIU Caibei ZHUANG

The Chinese Journal of Process Engineering. 2023, 23(9):  1300-1312.  DOI: 10.12034/j.issn.1009-606X.222390

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The recovery and reuse of zinc and other valuable metals in leaching residues is a key segment in the green recycling of resources in the zinc hydrometallurgy industry. The typical process of zinc leaching residues treatment in rotary kilns is characterized by multivariate coupling, large delays, therefore, extensive energy consumption, unstable zinc volatilization rate and other problems arise, which is hard to be optimized rapidly and regulated immediately. The research object is about the recovery engineering of leaching slag in the large-scale rotary kiln of 300 000 tons/year in China. A particle swarm optimization BP neural network to predict the zinc volatilization rate had been established as a prioritization scheme in conjunction with a grey relational analysis of the main process parameters. Based on the single factor scenario analysis method, three model scenarios such as coke powder, kiln tail temperature, and mainly associated element of Fe content in the leaching slag had been set up, which were applied to analyze the trend and the impact mechanism of three aspects on zinc volatilisation rate. The results showed that the coke powder input intensity had the greatest influence on the zinc volatilisation rate and the correlation coefficient is 0.842. Meanwhile, the fit goodness of the PSO-BP (Particle Swarm Optimization Back Propagation) prediction model reached 0.987 and the prediction error is within ±0.6%, which achieved fast prediction of zinc volatilization rate and well solved the industrial process lag problem. The effect mechanism of coke powder input intensity, kiln tail temperature, and Fe content of the leaching residues on the volatility of zinc was illustrated in conjunction with the chemical reaction mechanism. Under the condition that the other influencing parameters were taken as the average of the sample data for the stable working conditions, the optimal simulation values for coke powder input intensity, kiln tail temperature, and Fe content of the leaching residues were 0.60 t/t, 680℃ and 23wt%. The theoretical guidance for the energy-efficient recovery of zinc from leaching residues and the optimal regulation of prevention and control of secondary pollution was demonstrated in the research.

Preparation of nano-calcium carbonate intensified by CO₂ micro bubble and transfer-reaction analysis

Liheng WANG Xiaoping GUAN Ning YANG Zuze MU

The Chinese Journal of Process Engineering. 2023, 23(9):  1313-1324.  DOI: 10.12034/j.issn.1009-606X.222450

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Carbonization is one of the common methods to prepare nano calcium carbonate. Controlling the particle size and particle size distribution of calcium carbonate is the key to the preparation of high-quality nano-calcium carbonate by carbonization. Different operating conditions have different effects on the reaction products. The particle size and size distribution of calcium carbonate can be effectively controlled by controlling different reaction conditions to improve the mass transfer and reaction conditions in the slurry. In batch-operated bubble column reactor, gas flow rate and bubble size are factors affecting mass transfer. This study investigates the influences of operation condition (gas flow rate, initial slurry condition), bubble type (ordinary bubble, micro bubble) on carbonation reaction rate and particle size distribution of calcium carbonate. Furthermore, the effects of bubble type on the stable region and abrupt change region in carbonation reaction process are analyzed. The experimental results show that when using ordinary bubble, the increase of CO2 flow rate accelerates the reaction process and reduces the particle size of calcium carbonate, but it does not affect the time of abrupt change region. With increasing the slurry concentration, the particle size first decreases and then increases in small-diameter column with ordinary bubble. However, when using micro bubble, the particle size of calcium carbonate is significantly reduced, and the time of abrupt change region decreases with the increase of gas flow rate. Moreover, the CO2 flow rate is no longer an influential factor on calcium carbonate particle size, which means that the gas-liquid mass transfer process is not the rate controlling step of carbonation reaction. This study provides some references for studying the application of micro bubbles in calcium carbonate crystallization.

Dissolution kinetics of the roasting clinker of nickel-chromium mixed oxidized ore using ammonium sulfate

Hanwen ZHANG Liang WANG Mingyu HAN Xiaoyi SHEN Yan LIU Yuchun ZHAI

The Chinese Journal of Process Engineering. 2023, 23(9):  1325-1332.  DOI: 10.12034/j.issn.1009-606X.222332

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Nickel is an indispensable resource in national defense, aerospace, energy, transportation, petrochemical and other fields, and is also one of the most important strategic non-ferrous metals in China. As nickel demand increases, nickel sulfide ore resources are rapidly decreasing and tending to be depleted. Nickel oxide ore offers new possibilities for future nickel smelting due to its abundant resources, low mining costs and other strengths. In order to better utilize chromium-bearing nickel oxide ores, it is necessary to conduct research on the extraction and separation of valuable components from such ores. The effects of liquid-solid ratio, reaction temperature, reaction time, and stirring rate on the dissolution rate of nickel, iron, and magnesium were investigated to determine the appropriate water dissolution process conditions. The kinetics of the dissolution of nickel, iron, and magnesium in the roasting material of nickel-chromium mixed oxide ore roasted with ammonium sulfate was investigated. The nickel-chromium mixed oxidized ore was roasted with ammonium sulfate under the conditions of ammonium ore ratio of 1.7:1, roasting temperature of 748 K, and roasting time of 2 h. The effects of various factors on the dissolution efficiency of nickel, iron, and magnesium in roasted materials were investigated. The suitable dissolution conditions were as follows: reaction temperature of 353 K, reaction time of 60 min, a liquid-solid mass ratio of 5:1, and stirring rate of 500 r/min. The dissolution efficiencies of nickel, iron, and magnesium reached 94.3%, 88.7%, and 84.9%, respectively. The dissolution of nickel, iron, and magnesium from roasted materials can be divided into two stages: 0~15 min and 15~40 min, which were both controlled by external diffusion with no solid product layer formation.

Study on the safety of recombinant human rhinovirus 3C fusion protease

Yuying LIU Shuming WU Xulin JIANG Fei YIN Ercui SHEN Guifeng ZHANG Hongcai ZHANG Haijiang ZHANG Yongjiang LIU

The Chinese Journal of Process Engineering. 2023, 23(9):  1333-1339.  DOI: 10.12034/j.issn.1009-606X.222329

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In order to evaluate the safety of recombinant human rhinovirus 3C fusion protease (GST-3C), the toxicity of GST-3C was studied by single-dose toxicity test and immunotoxicity test. Single-dose toxicity test: a drug administration group was set up, and 10 male and 10 female ICR mice were prepared. GST-3C was injected into the tail vein by maximum dose method, and the maximum dose of single dose was 25.25 mg/kg. Another normal saline control group was set up. The symptoms, degree, nature, recovery, and death of ICR mice were observed, and the mice were dissected in time at the end of the observation period to observe the effects of GST-3C on the organs of mice. Immunotoxicity test: 50 mice were randomly divided into five groups (solvent control, cyclophosphamide positive control group, adjuvanted GST-3C low-dose group, adjuvanted GST-3C high-dose group, GST-3C control group without adjuvant). Spleen index, thymus, index and swelling degree were calculated by delayed hypersensitivity method to observe the effect of GST-3C on delayed hypersensitivity. 40 mice were randomly divided into four groups (solvent control, adjuvanted GST-3C low-dose group, adjuvanted GST-3C high-dose group, GST-3C control group without adjuvant). The effect of hemolytic plaque on humoral immune function of mice was evaluated by counting hemolytic plaque test. Single-dose toxicity test showed that compared with the normal saline control group, there was no significant difference in the body weight of the mice in the experimental group, and no abnormal performance was found in the organs of the animals in the administration group. Under the conditions of this experiment, the maximum tolerated dose (MTD) of a single intravenous injection of GST-3C in ICR mice was greater than 25.25 mg/kg. Immunotoxicity test showed that during the administration period, compared with the solvent control group, the body weight of the animals in each group administered with GST-3C did not decrease significantly, and no abnormal changes related to administration were observed beside the animal cage. The results of delayed hypersensitivity test and hemolytic plaque test showed that GST-3C had no inhibitory effect on the cellular immunity and humoral immunity of animals, which provides a basis for evaluating the safety of GST-3C.

Metabolic engineering of Escherichia coli to produce glutaric acid

Zhilan ZHANG Cong GAO Liang GUO Xiulai CHEN Wanqing WEI Jing WU Wei SONG Liming LIU

The Chinese Journal of Process Engineering. 2023, 23(9):  1340-1350.  DOI: 10.12034/j.issn.1009-606X.222453

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Glutaric acid is an important intermediate, which is widely used in chemical industry, agriculture, medicine and other fields. At present, there are some problems in the biosynthesis pathway of glutaric acid, such as long synthesis path, high consumption of cofactors and low yield. In order to develop an efficient method for the synthesis of glutaric acid, a new way to produce glutaric acid using glucose as substrate was constructed by combining enzyme engineering with metabolic engineering. Firstly, a novel catalytic pathway composed of lysine α-oxidase (LO), monoamine oxidase (MAO), α-ketoacid decarboxylase (KDC) and aldehyde dehydrogenase (ALDH) was designed by database mining. AB initio synthesis of glutaric acid was realized by introducing lysine producing strain E. coli CCTCC M2019435. In order to further improve the synthesis efficiency of this pathway, rational analysis and protein modification were carried out for the rate-limiting enzyme KpALDH of the pathway, and the catalytic efficiency of the enzyme was increased by 66.5 times. On this basis, the yield of glutaric acid was increased by 2.0 times through metabolic engineering to enhance the expression of rate-limiting enzyme KpALDH and block the by-product acetic acid metabolic branch. Finally, the glutaric acid fermentation conditions were optimized, the glutaric acid yield increased to 62.0 g/L at the end of fermentation, and the production intensity and yield reached 1.6 (g/L)/h and 0.3 g/g glucose, respectively.

Automatic identification method of batch time node of fuel ethanol fermentation based on SSAE-FCM

Xiaojun TIAN Meng WANG Xiaochen LIU Haoyue ZHENG Hailong LIN Jinsong LIU Meng YANG Guangrui WEN

The Chinese Journal of Process Engineering. 2023, 23(9):  1351-1358.  DOI: 10.12034/j.issn.1009-606X.222382

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The control and optimization of the fermentation process are the key technologies in batch production of fuel ethanol, it has been attracting continuous attention in the control and optimization of a biological fermentation plant. Although many detection methods are proposed in the literature, the increasing demand for green renewable energy and the increasing reliability of biological fermentation plant also brings a new challenge to the control and optimization of the fermentation process. On the one hand, fuel ethanol has developed from laboratory scale to industrial scale production, but the traditional detection methods are also useful. On the other hand, the plant becomes extremely complex and intelligent which made the control optimization process more difficult. As a response, an automatic identification method for key time nodes of batch fermentation of fuel ethanol based on stacked sparse autoencoder (SSAE) and fuzzy C-means clustering (FCM) is proposed. Firstly, SSAE is employed to extract the high-level features of the original data (boolean data, process data, and energy consumption data) layer by layer from low to high levels. Then, the high-level features that reflect the essential attributes of the data are taken as the input data of FCM clustering operation, and an automatic identification model of batch time nodes in fuel ethanol fermentation based on FCM is established. Finally, the batch process data of fuel ethanol fermentation from SDIC Bioenergy Company is used as training samples to validate the SSAE-FCM. And the two indicators of recognition accuracy (RV) and recognition speed (RN) are employed to characterize the effect of the detection model. In contrast, the control of the fuel ethanol fermentation process based on kinetic models and multiparameter correlation analysis method are introduced to carry on optimization results under the same condition. By comparison, the results show that the method proposed in this work has better identification performance, which satisfies the requirements of batch process control of ethanol fermentation.

A novel approach of harvesting microalgae based on re-frying oil and the mechanism analysis

Hao WEN Wei QIN Hongwei YIN Yue WANG Meili WU Xu LIU Xiaomin KONG Haowen ZHANG Ziyang ZHANG Xichen ZHENG

The Chinese Journal of Process Engineering. 2023, 23(9):  1359-1370.  DOI: 10.12034/j.issn.1009-606X.222471

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With the development of modern energy, the use of clean and renewable new energy has gradually become the main idea to solve environmental and energy problems. Among the many new energy sources, biomass energy not only reduces greenhouse gas emissions, but also has good renewable properties. Microalgae is an ideal preparation of biomass raw materials which can grow fast and are rich in oil. However, their density are close to water making harvesting difficult. Harvesting difficulty is one of the main constraints on the development of the microalgae industry. In this study, a flotation method based on bead flotation is using a re-frying oil emulsion as flotation beads for harvesting Chlorella vulgaris. The re-frying oil will be fully emulsified with pure water in a certain proportion under the action of emulsifier. Combining with the response surface method, the significant factors affecting the harvesting efficiency were screened as pH, stirring rate, and proportion of protoalgae; the significant factors affecting the enrichment ratio were pH, flotation time, and proportion of protoalgae. The optimal harvesting efficiency and enrichment ratio were obtained as 92.79% and 2.07%, respectively. By taking Chlorella vulgaris as the research object, using XDLVO theory (extended Derjaguin-Laudau-Verwey-Overbeek), the mechanism of action between re-frying oil floating beads and Chlorella vulgaris was discussed. The mechanism of harvesting microalgae by re-frying is that microalgae and buoy beads form aggregates by electric neutralization and bridging due to of aluminum ion. The microalgae and the buoy beads first approach each other under the action of kinetic energy provided by stirring, and then by van der Waals force to adhere. The gravitational action reaches the critical value at 14.73 nm. The harvesting cost is only 4.38 ￥/t under the optimal harvesting conditions. This method reduces the harvesting cost and energy consumption which provides a method for the reuse of re-frying oil.