The Chinese Journal of Process Engineering

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The Chinese Journal of Process Engineering. 2021, 21(6): 0.

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Progress on biomethane production via biogas cleaning and upgrading

Gama YANG Tingzhen MU Maohua YANG Delu MIAO Xuhao ZHAO Bin TANG Jianmin XING

The Chinese Journal of Process Engineering. 2021, 21(6): 617-628. DOI: 10.12034/j.issn.1009-606X.220154

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Biomethane is a kind of renewable fuel produced after the biogas is purified by desulfurization, decarbonization and dehydration. Its composition and calorific value are almost same as natural gas which means biomethane is a promising renewable energy to be used as vehicle fuel or injected to the natural gas grid. To enable the efficient use of biomethane in these applications the biogas must be cleaned and upgraded. Removal of H2S and CO2 are necessary processes for the commercial utilization of biogas and a number of techniques for transformation of biogas to biomethane have been developed. In this review, the main desulfurization and decarbonization technologies for the production of biomethane were systematically reviewed with their upgrading efficiency, methane (CH4) loss, energy requirement, environmental effect, development and industrialization. The technologies for the removal of H2S discussed in this work including absorption (physical and chemical), adsorption and biodesulfurization. And the technologies for the removal of CO2 including absorption (physical and chemical), pressure swing adsorption (PSA), membrane separation, cryogenic separation and the emerging biological methanation processes were discussed. Process flow and mechanism of each technology, as well as commercialization examples were introduced in detail with emphasizing their critical points and analyzing their advantages and deficiencies. Particularly, the review emphasized that biodesulfurization and biological methanation possess significant advantages over conventional physical/chemical technologies for biogas upgrading. Main advantages were that biotechnologies operated at normal temperatures and pressures, without the use of toxic complex chemicals, especially the biological removal of H2S in biogas had undergone a rapid development over the past 20 years and was nowadays commercially available and implemented in full scale facilities. The current challenges and future perspectives of biogas desulfurization and decarbonization processes were also discussed. Finally, the aim of the review was to provide process references for the research and industrial development of biomethane.

Research status of mineral admixtures on properties and mechanism of magnesium phosphate cement

Yue MA Xintao ZHOU Jing HUANG Zhongqiu LUO Yizhong FU Weihong MU Luxing WANG Zhoujun SHAO

The Chinese Journal of Process Engineering. 2021, 21(6): 629-638. DOI: 10.12034/j.issn.1009-606X.220157

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Magnesium phosphate cement (MPC), a new kind of inorganic cementing material, has some special performances such as rapid setting, fast hardening, and low drying shrinkage, etc. It has been widely used in the fields of repair and rehabilitation of civil structures, dental and bone restoration, stabilization of toxic matter or radioactive waste and treatment of wastewater. However, MPC faces some challenges, including high cost, potentially high energy consumption and high heat releasing, etc. For the sustainable development of MPC, it is urgent to address the above problems. In MPC system, the addition of mineral admixtures can not only decrease the preparation cost, but also greatly improve the setting behavior, mechanical properties, water resistance, etc. Based on various research documents on MPC and mineral admixtures, the influence of mineral admixtures such as fly ash, slag, metakaolin and silica fume on the fluidity, setting time, mechanical properties and durability of MPC were discussed. Then, the modification mechanism of MPC with mineral admixtures was also summarized. Finally, the advantages and disadvantages of MPC modified by mineral admixtures were pointed out, and the research direction of MPC modification was prospected according to the actual application requirements.

Techniques of recycling gallium from e-waste

Yifan YANG Guoqin LENG Boli CHEN Zhaohui HUANG Zhi SUN Tianyi TAO

The Chinese Journal of Process Engineering. 2021, 21(6): 639-648. DOI: 10.12034/j.issn.1009-606X.220167

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As an important rare element, gallium has a wide range of applications in many fields such as industry, medicine, military, etc. However, due to the low concentration of gallium in the earth's crust and its wide distribution, it exists in the form of chalcopyrite. It is generally recovered from the by-products of gallium-containing waste in traditional industries such as sphalerite, aluminum ore, fly ash, etc. Gallium-containing electronic waste can be divided into two types of waste electronic products and gallium-containing waste generated in the production process. To solve the problem of shortage of gallium resources, researchers currently recover gallium from gallium-containing electronic waste. Due to the associated heavy metals, flammable organic substances, and other harmful substances, it has the dual attributes of environment and resources extensive attention. Gallium mainly exists in the form of compounds in e-waste such as GaN, GaAs, CIGS, IGZO, and has the characteristics of many associated elements and stable physical and chemical properties. Generally, the fire or wet method is used to recover gallium from GaN waste; gallium of GaAs waste is mostly obtained by wet method; gallium is extracted from IGZO (GZO) display screen by acid leaching and then purified. This article systematically sorts out the current status of gallium-containing electronic waste recycling and treatment, summarizes the applications of hydrometallurgy, pyrometallurgy, and biometallurgy in recycling different types of gallium-containing electronic waste. The difference in the use of material recovery technology and the separation and purification methods points out the current technical problems and the future development direction of recycling gallium-containing electronic waste.

A correlation model of drag coefficient for bubbles/droplets in a wide Reynolds number range

Shenggao GONG Ningning GAO Lelin ZENG Anwu LI Xiaoyu LIU Qing TANG Laibing LI

The Chinese Journal of Process Engineering. 2021, 21(6): 649-657. DOI: 10.12034/j.issn.1009-606X.220166

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It is of great significance to predict the drag coefficient CD and the rising velocity of fluid particles (i.e. bubbles or droplets) accurately because they are helpful to estimate the phase holdup distribution, liquid phase velocity distribution, fluid particle residual time and mass transfer rate in the reactor. However, most of the correlations in the literature to estimate CD are piecewise, only valid in the low Reynolds number (Re) range and difficult to be extended to different experimental systems. In the view of these shortcomings, based on the experimental and theoretical results, this work proposed a new mathematical correlation model which can describe CD evolution observed by experiments in a wide Re range, and complied a program to solve the multi-dimensional unconstrained linear optimization problem to determine the model parameters. The new fluid particle CD correlation showed a good prediction ability and reasonably predicted the fluid particle CD value measured by different researchers under different experimental systems (e.g. air?water, air?glycerol, air?glycerol?water, n-butanol?water, n-octanol?water, toluene?water etc.) and different operating conditions (e.g. bubble: 0.1<Re<104, 10?11<Mo<7; droplet: 5<Re<2000, 10?11 <Mo<10?6). In addition, the rising velocities of fluid particles were predicted by combining the new fluid particle CD correlation and single fluid particle motion equation. The predicted terminal velocity and rising velocity of fluid particles also were consistent with the results of different experimental systems. The above predictions presented that the new CD correlation model was universal, reasonable and reliable to some extent.

Numerical simulation on fluid flow past a circular heterogeneous porous particle

Chunyu WANG Chenggong LI Mao YE

The Chinese Journal of Process Engineering. 2021, 21(6): 658-670. DOI: 10.12034/j.issn.1009-606X.220213

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The two-phase flow of porous particles widely exists in industrial processes. However, the internal structure of most porous particles is heterogeneous, which has been homogenized in previous studies and may affect the interaction between the particle and the fluid. Therefore, the volume-average macroscopic control equation based on the intrinsic phase average velocity was used to describe the fluid flow inside and outside the porous particles. Then, an improved lattice Boltzmann method (LBM) was used to solve the macroscopic control equation. Two-dimensional fluid flow around and through a heterogeneous porous particle was simulated numerically. By introducing difficult-to-permeable regions to adjust the internal porosity of porous particle, the effect of heterogeneity on the force of particle and evolution of flow field was simulated. The results showed that the heterogeneous structure could induce the lift force of the particle and realize the longitudinal mass transfer inside the particle compared to the homogeneous porous particle. Moreover, both the lift force and the mass transfer strength increased with the increase of the hard-to-penetrate area and Da number due to the asymmetric interaction between the particle and the fluid, but showed a peak value with Da number increasing to sufficiently large, mainly because of the effect of the internal structure diminished as the great quantity of fluids through the particle. On account of the lift force and mass transfer in the longitudinal, the presence of the hard-to-penetrate area also generated the wake vortex behind the particle to no longer be symmetrically distributed at a lower Re number, and to fall off at the Re number around 38, which enhanced the intensity of the disturbance of the flow field. In general, the existence of heterogeneous structure inside particle has an important influence on the force of the particle-fluid system and the evolution of the flow field, which is worth considering in future research.

Effect of winglet pair geometry parameters on fluid flow characteristic in helical channels with semicircular cross section

Yaxia LI Xiaohang SHI Jing ZHANG Li ZHANG Bin GONG Jianhua WU

The Chinese Journal of Process Engineering. 2021, 21(6): 671-679. DOI: 10.12034/j.issn.1009-606X.220224

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Experimental and numerical methods have been employed to study the influence of winglet pair geometry parameters on fluid flow and vortices characteristics in helical channels with semicircular cross section. The curvature ratios of helical channels are within the range of δ=0.05~0.125. Simulated data of three dimensional velocities have good agreements with those obtained by Laser Doppler velocimeter when δ=0.067. The results showed that the longitudinal vortices induced by the wing pair developed spirally along the main flow and strengthened the vortices produced by centrifugal force to a certain extent. The larger the Reynolds number was, the closer of the vortices were to the centerline of the cross section. There may be additional vortices in the range of 7.09~13.04 times of wing height behind the winglet pair when δ≥0.1. The value of La/b was used to indicate the occurrence position of the additional vortices. La/b value increased with the increasing of Reynolds number and the aspect ratio of the winglet, but it decreased with the increasing of curvature ratio and attack angle. As curvature ratio and the aspect ratio of the wing increasing, the strength of the combined longitudinal vortices would be enhanced and the affecting range of combined vortices in the helical channel became larger at the same time. The maximum strength of the combined longitudinal vortices was 6.48 times that of the smooth helical duct in the studied range. The longest affecting range of combined vortices reached the length of about 20 times the wing height in the helical channel. The aspect ratio of the wing and dimensionless thickness had significant impacts on flow resistance.

Research on mathematical modeling of particle classification process based on vertical mill separator

Penghao GENG Yanxin CHEN Yanfei YAO Bo ZHAO Ding HAN

The Chinese Journal of Process Engineering. 2021, 21(6): 680-686. DOI: 10.12034/j.issn.1009-606X.220161

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In this work, the experiment was carried out through the pilot test platform for vertical mill, and the change rule of the classification performance of the classifier under different system air volumes and classifier speeds were compared and analyzed. The cumulative distribution function of the normal distribution was used to correlate the operating parameters of the classifier with the collection probability of particles of different particle sizes. The test data of the system air volume and the speed change condition of the powder separator were used to fit the mean and variance in the model. A mathematical model can be established to quantitatively analyze the relationship between the system air volume, the speed of the separator and the particle classification efficiency. The fitted standard deviation of the verified regression was RMSE=0.0046, the deviation between the predicted value and the true value was small, and the coefficient of determination R-square=0.9863, which was close to 1, the model had higher credibility. Under the conditions of known system air volume and separator speed, the model prediction curve of the classification efficiency of the separator basically coincided with the test curve, and the model prediction effect was good.

Effect of slag nails on heat transfer of water-cooled gasifier

Ying XIA Haoyong KAN Hui FAN Ping LI

The Chinese Journal of Process Engineering. 2021, 21(6): 687-694. DOI: 10.12034/j.issn.1009-606X.220220

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The water-cooled wall of the gasifier plays an important role in maintaining the safe and stable operation of the gasifier under high temperature and pressure. The ANSYS software was used to simulate the temperature distribution on the inner wall surface of the water-cooled wall. The effects of three conditions including slag nails, no slag nails, and replacement of slag nails by gills of equal area on the heat transfer process were investigated. The influence of the arrangement of nails on the temperature of water-cooled wall was researched. The results showed that the slag nails can effectively improve the heat transfer efficiency and take away the excess heat in the gasifier in time. The slag nails with a small angle and a triangular arrangement had better heat transfer efficiency and more uniform temperature distribution. This simulation calculation was significant for the design of heat transfer structure and long-term safe operation of water-cooled wall gasifier.

Comparison and study on the flocculation effect of peppermint water-extraction solution by different folded-plate flocculators

Ying FENG Qingjin ZHANG Jianwei ZHANG Tianyang ZHANG

The Chinese Journal of Process Engineering. 2021, 21(6): 695-703. DOI: 10.12034/j.issn.1009-606X.220186

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As a part of the excellent culture of the Chinese nation, traditional Chinese medicine have been favored by more and more people in recent years due to its high safety and low side effects. At present, most of the researches on impurity removal of traditional Chinese medicine by flocculation were based on the flocculation operating conditions, such as flocculation temperature, pH value of the traditional Chinese medicine solution and different flocculants. In order to optimize the structure of the folded-plate flocculator and enhance the flocculation effect of the Chinese medicine liquid. Vortex distribution and vorticity in the flow field of the same wave folded-plate flocculator and the opposite wave folded-plate flocculator were simulated and analyzed by FLUENT. Taking the peppermint water-extraction solution as the research object, using chitosan as a flocculant, flocculating the peppermint water-extraction solution by different folded-plate flocculators, let clear layer height, sedimentation velocity, total flavonoid retention rate, flocculation rate, absorbance and fractal dimension of flocs index, the influence of different inlet flow rates on flocculation for the effect of flocculant by different folded-plate flocculators were discussed. Results showed that the vortex positions of the same wave folded-plate flocculator were respectively unilateral vortex, and the vortex position of the opposite wave folded-plate was distributed on the two sides of the folded plate, under the same inlet flow rate, the vorticity generated by the same wave folded-plate flocculator was smaller than that of the opposite wave folded-plate flocculator. The flocculation effect of the same wave and the opposite wave folded-plate flocculator on the mint water extract showed a trend of first increasing and then decreasing, the optimal flocculation inlet flow rate of the same wave folded-plate flocculator was 0.068 m/s, the total flavonoid retention rate of the peppermint water-extraction solution was 91.2% , the flocculation rate was 85.3%, the optimal flocculation inlet flow rate of the opposite wave folded-plate flocculator was 0.051 m/s, the total flavonoid retention rate of the peppermint water-extraction solution was 91.8%, the flocculation rate was 85.4%.

Study on the comprehensive recovery of zinc from tailings of a lead-zinc ores from Yunnan province

Bo YANG Xiong TONG Xiao WANG Yonggang XIE Xian XIE

The Chinese Journal of Process Engineering. 2021, 21(6): 704-712. DOI: 10.12034/j.issn.1009-606X.220177

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Tailings of Pb–Zn ores from Yunnan province of China are of high sulfur content and contains the Pb 0.84% and the Zn 3.67% respectively, it is economic to comprehensive recovery these valuable minerals from the tailings. The results from processing mineralogy of these tailings, the Pb-containing minerals existed mainly as galena and cerusite and the Zn-containing minerals as sphalerite and smithsonite. The laboratory-scale flotation experiment indicated that the valuable minerals were effectively recovered by the differential flotation of sulfide minerals, followed by the desliming and flotation of smithsonite. It is also found that the recovery and grade of Zn concentrate are significantly improved by using the amine collector with the different chain lengths during the roughing and scavenging flotation stage of zinc oxide minerals. Besides, these problems such as a large amount of foam and the difficulty in defoaming existed in the flotation of smithsonite were avoided by using the different chain lengths amine collector. The recovery rate and grade of zinc sulfide concentrates were 23.46% and 13.04%, and the recovery rate and grade of zinc oxide concentrates were 27.86% and 51.69% respectively. The total recovery rate of Zn concentrates was 64.73%. The “Sulphide Ore Priority Flotation-Floating Sulfur Tailings Desliming-Zinc Oxide Flotation” process successfully realized the efficient recovery of lead and zinc minerals in the tailings. In addition, organic amine salts with different carbon chain lengths are used as collectors in the roughing and sweeping stages of zinc oxide, which successfully solves the problems of defoaming difficulties and low concentrate grades that are common in the zinc oxide flotation process. It realizes the efficient recovery of valuable minerals in the tailings, and provides an important basis for the reutilization of this tailings.

Kerf-loss silicon encapsulated with Zn/N co-doped carbon as anode material for lithium ion batteries

Qiqi ZHOU Xuzhong GONG Zhi WANG Junhao LIU

The Chinese Journal of Process Engineering. 2021, 21(6): 713-723. DOI: 10.12034/j.issn.1009-606X.220143

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Because there is still a long way to go before kerf-loss silicon can be reused for solar-grade feedstock, which requires that the purity of silicon reaches at least 6 N, it is meaningful and feasible to apply the kerf-loss silicon to the raw material for anode material used in lithium-ion batteries. In this work, the kerf-loss silicon encapsulated with Zn/N co-doped carbon mesoporous core-shell structure had been rationally designed and constructed. PDDA acts as a "glue" to bond phenolic resin and Si. It was believed that the introduction of PDDA can solve the problem that the heterogeneous nucleation of phenolic resin can not be realized on the surface of kerf-loss silicon, which may be caused by the larger scale and irregular morphology of kerf-loss silicon. The co-doping of Zn and N improved the conductivity of the wSi@NC/Zn-2 electrode and inhibited the occurrence of side-reaction. At the same time, the carbon shell could alleviate the huge volume expansion and accelerate the transportation of Li-ion. Thanks to the co-doping of Zn and N and the porous carbon shell, the obtained wSi@NC/Zn-2 electrode delivered a reversible capacity of 1392 mAh/g after 300 cycles at a current density of 0.2 A/g. When tested at a heavier current at 0.5 A/g, the wSi@NC/Zn-2 electrode still exhibited a reversible specific capacity of 1082 mAh/g. At the same time, the wSi@NC/Zn-2 electrode also showed a pretty good rate of performance. When tested at 0.5, 1, 2, 3, 4, 5 and 0.5 A/g, reversible capacities of ~1704, 1345, 1157, 1038, 884, 752 and 1638 mAh/g were obtained. Once the current density returned back to the initial value, namely 0.5 A/g, the reversible capacity could reach 96% of initial discharge capacity, showing good capacity recovery capability.

Effect of surface modification of activated carbon on its specific capacitance and mechanism of energy storage

Dapeng WANG Baoan FAN Fen GUO Ya HU

The Chinese Journal of Process Engineering. 2021, 21(6): 724-733. DOI: 10.12034/j.issn.1009-606X.220124

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The surface of activated carbon was modified by melted sodium sulfide and its specific capacitance was evaluated by the cyclic voltammetry experimental data. The reason for specific capacitance changed with this treatment and the mechanism of energy storage were investigated by FT-IR, BET, EIS, and electrophoresis experiments. The results showed that the specific capacitance of activated carbon in 10% sodium sulfate electrolyte solution was elevated from 44.6 F/g to 80.8 F/g after treated with sodium sulfide at 1000℃ for 1 h. The increment of specific capacitance mainly came from double-layer capacitance and secondarily from redox pseudocapacitance (the ratio of pseudocapacitance to total capacitance was only 5.6%). After adding 37 mmol/L ferric chlorides in the electrolyte solution, the specific capacitance was further elevated to 103 F/g, in which the proportion of pseudocapacitance capacitance to total capacitance amounted to 12.6%. However, the capacitance value was unstable and decreased gradually during subsequent cycles, which may be caused by the electronegativity of the activated carbon surface. It had been verified by the electrophoresis experiment that the surface of activated carbon after heat treatment by sodium sulfide was positively charged. The law of same charge mutual repulsion lead to unstable adsorption of Fe3+ on the surface of activated carbon. However, if 30 mmol/L K3[Fe(CN)6] was added in the electrolyte solution, the specific capacitance was promoted to 126 F/g and kept stable, even slightly and slowly increased during subsequent cycles. The cyclic voltammetry curve showed that the specific capacitance at this time still mainly came from the double-layer and the EIS experiment confirms that the charge exchange resistance was dramatically reduced when the [Fe(CN)6]3– anion appeared in the electrolyte solution. According to the shape of the CV curve and the results of EIS, FT-IR and BET, it can be concluded that the energy-storage mechanism of activated carbon changed from physical double-layer to physical and chemical double-layer together with redox pseudocapacitance after treated by sodium sulfide.

Modeling and analysis of liquid real-time continuous leakage in horizontal liquid ammonia tank

Juanxia HE Dongmei ZHOU Lei LIU Qiyong ZHOU Liwen HUANG Jianting YAO

The Chinese Journal of Process Engineering. 2021, 21(6): 731-740. DOI: 10.12034/j.issn.1009-606X.220171

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Based on Van der Waals equation and theory of fluid mechanics, the liquid real-time continuous leakage model of horizontal liquid ammonia tank was established considering the changes of tank pressure and liquid surface area. Mathematical modeling of a horizontal liquid ammonia tank in a refrigeration company was performed by this model, and the calculation results were compared with PHAST simulation results. The results showed that the decreasing range of liquid level height h grew slowly and then increased quickly, the decreasing range of liquid leakage mass flow rate Qm and liquid leakage rate v and the increasing range of liquid leakage mass m decrease slowly. At the beginning of leakage, Qm and v were the maximum values, at the end of leakage, m was the maximum values. When the diameters of leakage hole were 5, 30 and 100 mm, leakage time t were 29884.027, 837.289, 77.550 s, Qm(max) were 0.552, 19.913 and 221.160 kg/s, v (max) was 46.733 m/s, m(max) were 10255.649, 10339.923 and 10572.760 kg, respectively. The deviation between the calculation results of the model and the PHAST simulation results was less than 24%. From the analysis of parameter variation and risk emergency, the model had the certain applicability for the theoretical calculation of liquid leakage in horizontal liquid ammonia tank.

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