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    28 November 2022, Volume 22 Issue 11
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    Cover and Contents
    The Chinese Journal of Process Engineering. 2022, 22(11):  0. 
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    Research Paper
    Analysis method for outflow percentage of water model data of tundishes
    Yuqian LI Chao CHEN Guoguang CHENG Tianyang WANG Linbo LI Mengjiao GENG Jinping FAN
    The Chinese Journal of Process Engineering. 2022, 22(11):  1447-1457.  DOI: 10.12034/j.issn.1009-606X.221436
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    Mixing phenomena by means of tracer technology are vitally important to understand the flow in metallurgical reactors, for example, continuous casting tundish. The widely used analysis methods are RTD (Residence Time Distribution) curve or F curve, which is a time dependent integral of RTD E curve. For the two methods, in the normalization process, the outflow percentage of a single-strand tundish or the summation of the outflow percentages of each strand in the multi-strand tundish are all limited to 100%. Thus, the total amount of tracer outflow information is concealed, which may lead to the problem of inaccurate results. This study proposes an analysis method of the outflow percentage, and proposes the calculation method to convert the physical experiment results into the real-time outflow percentage curve. In addition, based on the outflow percentage curve, the time-weighted average variance and the residual tracer percentage can be calculated and used to evaluate the uniformity of each strand and dead volume, respectively. In this study, the water model experimental data of a single-strand tundish and a four-strand delta shape tundish, which is installed by double weir or U-shaped weir, under normal condition and one strand blockage conditions are all analyzed by the proposed outflow percentage method. The results show that the experimental results can be proofread by using the outflow percentage method to further verify the repeatability of the water model experiments. Meanwhile, the difference in the percentage of outflow at the end of the monitoring time and the proportion of the dead zone at twice of the theoretical residence time can be compared in double weir four-strand tundish and U-shaped weir four-strand tundish. It can also intuitively compare the uniformity of each strand of different multi-strand tundishes, and the distribution and uniformity of the tracer in other outlets after one of the strands is blocked.
    Numerical simulation of turbulence heat transfer enhancement and optimization of jet layer in circulating jet mixing tank
    Yanfang YU Lingmin KONG Huibo MENG Bowen SHI Dongzhou LIU Jianhua WU
    The Chinese Journal of Process Engineering. 2022, 22(11):  1458-1467.  DOI: 10.12034/j.issn.1009-606X.221345
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    Circulating jet mixing tank (CJT) as a process intensification can improve the turbulent mixing and reaction selectivity of flowing working medium. In order to further improve its industrial application value, the heat transfer capacity of the flow field inside the CJT was analyzed and the number of jet layers was optimized. Under the condition of constant wall temperature, the SST k-ω model was used to analyze the flow heat transfer performance of the flow field in the non-steady state calculation. The heat transfer uniformity of the wall and the heat transfer characteristics in the flow field was studied at Re= 3260~16 303 and the number of jet layers M=5~9. The variation coefficient Ch of convective heat transfer coefficient decreased and the uniformity of wall heat transfer increased by 2.8%~19.3% with the increasing Re for M=9. The field-synergy between flow field and temperature field increased with the increase of Re and the synergy angle at Re=16 303 is 75.5o, which is 0.5° less than that at Re=3260. The Ch decreased and the heat transfer uniformity increased by 2.7%~16.3% with the increasing M for Re=9782. The field-synergy between velocity vector and temperature gradient decreased with the increasing M. Compared with synergy at M=5, the global synergy decreased by 6.1% at M=9. When M=7, the field-synergy angles in the central mixing region and the jet mixing region were between 73° and 74°, and the heat transfer capacity between the two regions was well matched. The synergy of central mixing region was better than that of jet mixing region for M<7, and the situation was opposite when M>7. The influence of Re and M on the heat absorption and transfer performance of the CJT was studied. It was found that the change of Re had more influence on the heat absorption of the CJT with respect to M.
    Multifractal analysis of concentration-time series in double-layer impinging stream mixer
    Jianwei ZHANG Jun TANG Xin DONG Ying FENG
    The Chinese Journal of Process Engineering. 2022, 22(11):  1468-1478.  DOI: 10.12034/j.issn.1009-606X.221440
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    The concentration field of a double-layer impinging stream mixer was measured by the planar laser-induced fluorescence (PLIF) technique. The multifractal characteristic of the concentration-time series was investigated by using the multifractal detrended fluctuation method (MF-DFA). The multifractal singular spectrum under different nozzle spacing and jet Reynolds number was analyzed to realize the quantitative characterization of flow field characteristics. The results showed that the singularity of the concentration-time series increased with the jet Reynolds number. With the increase of the nozzle spacing, the singularity of the concentration-time series became weakened, and the influence of nozzle spacing on the singularity of concentration-time series was more significant than that of Reynolds number. The stronger the singularity of concentration signal of the double-layer impinging stream mixer, the more intense the motion of fluid particles, and the stronger the mixing effect. The promoting effect of nozzle spacing on mixing effect was greater than jet Reynolds number. According to the variation of multifractal spectrum of concentration time series of double-layer stream mixer, the singular spectrum parameters of concentration time series were obtained. Based on the distribution of the multifractal spectrum parameters (Δα, αmin, α0) along the radial position in the multifractal singular spectrum, the flow field in the double-layer impinging stream mixer was divided into axial impingement zone, vortex zone, and radial impingement zone from the impact center downward. The singularity of concentration signal of double-layer impinging stream mixer was larger than the primary impact region and larger than the vortex region. The effect of secondary impact zone on mixing was stronger than that of primary impact area and stronger than that of vortex area. It can provide a theoretical basis for revealing the flow pattern of the impinging stream system and the complex and disordered flow mechanism of the impinging stream.
    Liquid-liquid two-phase flow patterns and mass transfer kinetics for vanadium extraction in microchannels
    Jing LUO Jiawei WEN Chunming LAN Xihua ZHANG Pengge NING
    The Chinese Journal of Process Engineering. 2022, 22(11):  1479-1489.  DOI: 10.12034/j.issn.1009-606X.221320
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    The liquid-liquid flow pattern and extraction mass transfer kinetics for V(V) were investigated in microchannels using primary amine N1923 extractant. 15vol% N1923 was used as the continuous phase and V(V) aqueous solution as the dispersed phase. The flow patterns of two immiscibility phases at different flow rates and the effects of residence time and microchannel diameter on mass transfer as a function of flow rate were studied. The study found that compared to 1:1, with the increase of the two-phase flow velocity, the slug flow length and the specific interface area remained unchanged, and two phase fluid by Raydrop microchannel flowed into the external capillary microchannel because of the expansion of microchannel changed the way of two-phase flow, made the same experimental conditions at the same time appeared a variety of flow pattern in the microchannel. At the same time the two-phase flow velocity was positively correlated with the total mass transfer coefficient, it showed that the influence of flow pattern on mass transfer can be ignored in this research system. In addition, the residence time was negatively correlated with the total mass transfer coefficient in the same channel, which indicated that significant mass transfer occurred at the entrance of the two-phase contact channel, and the mass transfer rate was the highest at this time. After the diameter of the external capillary microchannel was changed, the mass transfer effect of 254 μm tube diameter was 9 times that of 750 μm tube diameter at the same mixing rate, which indicated that the inner circulation strength and specific interface area of small tube diameter were more significant. Finally, the experimental results of the total volume mass transfer coefficient were correlated with the empirical formula of the total volume mass transfer coefficient, which provided a theoretical basis for the realization of green metallurgical technology of microchannel amplification.
    Influence of interface between dense and dilute phases on microscopic drag force in gas-solid suspensions at low Reynolds numbers and its modeling
    Teng MA Xiao CHEN Qiang ZHOU
    The Chinese Journal of Process Engineering. 2022, 22(11):  1490-1503.  DOI: 10.12034/j.issn.1009-606X.222019
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    Gas-solid two-phase flow is widely encountered in energy and chemical industries and the interphase drag force is believed to be the dominant factor affecting the flow. Although the homogenous microscopic drag models, e.g. the BVK drag law (AIChE Journal, 2007, 53(2): 489-501), could accurately predict the drag force for homogenous regions, i.e. the dilute or dense phases, they failed to predict the drag at the interface of dense and dilute phases where the surface of particle clusters was located. To study the influence of the interface on the drag force, the particle-resolved direct numerical simulation (PR-DNS) was performed on the process of fluid flowing through different particle clusters at low Reynolds numbers. The results showed that at the interface of dense and dilute phases, the predictions of the BVK drag model were significantly different from the PR-DNS results. Meanwhile Chen et al.'s model (Int. J. Multiphase Flow, 2020, 128:103266), which considered the influence of the interface, cannot accurately predict the drag force where the solid holdup of the dilute phase was not zero. Therefore, this work proposed a method of decomposing the mesh near the interface to predict the drag force. To validate the proposed model, PR-DNSs of flow past various particle clusters, were performed and the predictions of several drag force models were calculated. It was found that the new model not only had a similar predictability with Chen et al.'s model when the dilute phase solid holdup approaches 0, but also had better Pearson correlation coefficients and fitness than the Chen et al.'s model when the solid holdup of the dilute phase was not zero. In conclusion, the proposed drag model could accurately account for the influence of the interface on drag force with different dilute and dense solid volume fractions, and it recovered the BVK law when the local gradient of volume fraction approached zero.
    Preparation of CNT supported MnFe2O4 nanomaterial based on high-gravity technology and its application for the adsorption of Pb(II)
    Yusong GAO Guisheng QI Wenchao YAN Da GUO Youzhi LIU
    The Chinese Journal of Process Engineering. 2022, 22(11):  1504-1511.  DOI: 10.12034/j.issn.1009-606X.221431
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    In order to overcome the agglomeration problem of MnFe2O4 nanoparticles in practical applications, the high-gravity technology combining with the in?situ support of multiwalled carbon nanotubes (CNT) is proposed to prepare the CNT supported MnFe2O4 nano-material (MnFe2O4/CNT). The typical heavy metal pollution Pb(II) is selected as the research object to study the adsorption performance of MnFe2O4/CNT. First, the effects of different MnFe2O4 loads on the adsorption capacity toward Pb(II) are investigated, and the optimal MnFe2O4 load is determined to be 83.3wt%. The obtained MnFe2O4/CNT in the optimal MnFe2O4 load is charactered by XRD, SEM, N2 adsorption-desorption specific surface analyzer and VSM, and which exhibits an excellent magnetic property with a high saturation magnetization of 35.85 emu/g. Thus, the obtained MnFe2O4/CNT can be applied for the magnetic separation of pollutants in water. The results of adsorption experiments show that under the conditions of initial Pb(II) 300 mg/L and solution pH=6, the adsorption of Pb(II) on MnFe2O4/CNT in solution reached equilibrium after 180 min, and the adsorption equilibrium capacity is 80.7 mg/g, which is much higher than pure CNT (28.4 mg/g). The kinetic study demonstrates that the adsorption behavior of Pb(II) on MnFe2O4/CNT is most consistent with the Elvoch kinetic model,which suggests there exists a chemical adsorption in the adsorption mechanisms. Freundlich isotherm model describes well the adsorption process of Pb(II) on MnFe2O4/CNT, which represents a multilayer adsorption process on heterogeneous surfaces. In addition, the maximum adsorption capacity of MnFe2O4/CNT obtained from adsorption isotherm experiment is 106.2 mg/g, which displays excellent adsorption performance for Pb(II) and has a great potential in heavy metals removal in solution. According to the X-ray photoelectron spectroscopy analysis, it can be concluded that the adsorption mechanisms involve the complexation between Pb(II) and the hydroxyl groups on the surface of MnFe2O4.
    Adsorption properties and kinetics of modified bentonite for Cd(II) in waste water
    Xiumin YANG Wen WANG Qiongdan XIE
    The Chinese Journal of Process Engineering. 2022, 22(11):  1512-1520.  DOI: 10.12034/j.issn.1009-606X.221424
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    Bentonite is an excellent environmental material. In order to study the adsorption characteristics of bentonite for Cd(II), hydrochloric acid, sodium hydroxide and sodium dodecyl sulfonate were used as modifiers to prepare modified bentonite. The effects of pH value, initial concentration and reaction time on the adsorption of Cd(II) by modified bentonite were investigated by isothermal adsorption experiments, and the adsorption kinetics mechanism of Cd(II) by modified bentonite was also discussed. XRD analysis showed that the layer spacing of modified bentonite increased and the diffraction peak intensity decreased. The removal rate of Cd(II) by HCl-B increased with the increasing of pH value of the solution, and the removal rate of NaOH-B reached the maximum at pH=6, while B and SDS-B at pH=7. The removal rate of Cd(II) by bentonite and modified bentonite decreased with the increasing of initial concentration, and the adsorption capacity of the adsorbent increased with increasing of the equilibrim concentration of Cd(II). The equilibrium adsorption capacity of the bentonite and modified bentonite for different concentrations of Cd(II) was corresponding with the Langmuir isotherm equation, and indicating that the adsorption of Cd(II) on bentonite and modified bentonite was a monolayer adsorption process. The adsorption reaction of bentonite and modified bentonite basically reached equilibrium within 240 min. The pseudo-second-order kinetic model can better describe the adsorption mechanism, and the chemisorption was main adsorption process, and the process of liquid film diffusion and intra-particle diffusion was rate-determining step for this adsorption prosess. This study can provide reference for the treatment of Cd-containing wastewater and remediation of Cd-contaminated soil by modified bentonite.
    Volatilization characteristics of lead, zinc, potassium and chlorine in blast furnace dust by vacuum reduction
    Yaoning WANG Hongzhou MA Ziyu WANG Bixia WANG Ruimeng SHI
    The Chinese Journal of Process Engineering. 2022, 22(11):  1521-1527.  DOI: 10.12034/j.issn.1009-606X.221347
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    In the iron smelting process, a large amount of blast furnace (BF) dust enriched with lead, zinc, chlorine, potassium and other elements will be produced. The existence of these elements has a negative impact on the recycling of iron in the BF dust. Therefore, the separation of these elements is the primary condition for realizing the efficient recycling of the BF dust. In this work, TG-DSC comprehensive thermal analysis was carried out for BF dust, and the water-soluble characteristics of lead, zinc, chlorine, potassium and their volatilization characteristics in the vacuum reduction process as well as the phase of iron in the reduction slag were studied. The results showed that the smoke had obvious endothermic peaks at 744 and 963℃, which indicated that there was a strong reaction at this temperature. According to the water-soluble characteristics of lead, zinc, chlorine and potassium in the smoke, it was qualitatively judged that the main forms of the four elements in the smoke were ZnCl2, KCl, ZnO, ZnFe2O4 and PbO. The vacuum reduction can effectively extract lead, zinc, potassium, chlorine and other elements from the blast furnace dust. Under the furnace pressure of 10 Pa and the temperature of 1100℃ for 30 min, the volatilization rates of lead, zinc, potassium and chlorine in the dust were 99.90%, 99.76%, 98.31%, and 99.70% respectively. The existing forms of chlorine in smoke were mainly ZnCl2 and KCl. Chlorine volatilized mainly in the form of ZnCl2 at 400~600℃ and KCl above 600℃. In addition to the volatilization of zinc in smoke by ZnCl2, zinc in smoke was volatilized by the reduction of ZnO and ZnO?Fe2O3 to metal zinc at high temperature stage. The volatilization of potassium was mainly KCl, and the volatilization of lead was caused by the reduction of PbO by carbon in smoke to metal lead vapor. The iron in the blast furnace dust was mainly Fe2O3. Fe2O3 was reduced to Fe3O4, FeO and Fe by vacuum reduction at 895℃ for 30 min, and Fe2O3 was basically transformed into Fe with good crystallinity at 1075℃ for 30 min.
    Kinetics and intensified leaching of valuable elements in KOH solution in alunite concentrate from copper tailings
    Ling LIU Siqiang JIN Binxin DONG
    The Chinese Journal of Process Engineering. 2022, 22(11):  1528-1537.  DOI: 10.12034/j.issn.1009-606X.221362
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    Alunite concentrate can be obtained from Zijinshan copper tailings by flotation process, which contains a large amount of potassium alunite accompanied by kaoline and quartz. It is a potential source for the recovery of aluminum, potassium and gallium. Therefore, alunite flotation concentrate extracted from copper tailings is considered for the recovery of aluminum, potassium and gallium in this work. Compared with the traditional process, direct leaching of alunite concentrate in KOH solution has the advantages of avoiding the thermal decomposition process with high energy consumption and reducing the interference of impurity ions. The direct leaching behavior of alunite concentrate in KOH solution is researched. The variation of element leaching ratio with time under different KOH concentration (4~8 mol/L) and leaching temperature (60~90℃) is investigated emphatically. The control step of the direct leaching of alunite concentrate in KOH solution is investigated on the research of kinetic analysis. Based on the above studies, mechanical activation is introduced to promote efficient leaching of valuable elements from the concentrate. The results show that only the alunite phase decomposes during the alkaline leaching under experimental conditions. The increase of KOH concentration and leaching temperature is beneficial to the rapid leaching of elements. According to the kinetic theory of the shrinkage core model of liquid-solid reaction, it is found that the leaching reaction is controlled by chemical reaction step. The apparent activation energy of the reaction is 79.5 kJ/mol, and the order of chemical reaction of KOH is 2.31. According to the laser particle scanning analyzer, XRD and FTIR analysis, it is found that the mechanical activation reduces the particle size, increases the specific surface area and improves the degree of amorphous of the alunite ore. The reactivity of the concentrate is thus enhanced, and the leaching experiment shows that the leaching ratio of aluminum, potassium and gallium are increased for the ore after mechanical activation.
    Oxidative decomposition behavior of chromite in aqueous sodium hydroxide solution saturated with sodium chromate
    Shuang LI Hongling ZHANG Honghui LIU Zengli GAO Xichuan CHENG Minghua WANG Zaihua CAI Hongbin XU
    The Chinese Journal of Process Engineering. 2022, 22(11):  1538-1546.  DOI: 10.12034/j.issn.1009-606X.221433
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    In order to investigate the effects of recycling NaOH as reaction medium on the oxidative decomposition process of chromite ore, aqueous NaOH solution saturated with Na2CrO4 at 90℃, instead of single aqueous NaOH solution, was chosen as the reaction medium and the effects of alkali concentration, oxygen partial pressure, particle size of chromite ore powder, reaction temperature and reaction time on the chromite decomposition process were systematically investigated. The results showed that, the extraction rate of chromium could reach as high as 95.24% after 240 min at 250℃ with NaOH mass concentration of 50wt%, oxygen pressure of 3.2 MPa and partial size less than 48 μm. As far as the separation efficiency of chromium from alkali and impurities was also considered, about 96.36% of the chromium extracted from the chromite ore was found in the mixed solids of chromite ore processing residue (COPR) and sodium chromate crystal, while 84.92% of aluminum and 95.04% of silicon extracted from chromite ore was found in the leaching liquor of chromite ore under the better process conditions. At the same time, 89.41% of the unreacted NaOH, was found in the leaching liquor of chromite ore. Compared with the original method with single NaOH as the reaction medium, the new reaction mode in this work enabled the main element of chromium from the chromite ore, the impurities of aluminum and silicon from the chromite ore, and the unreacted NaOH to distribute respectively into the leaching liquor of COPR and crystal mixture, and the leaching liquor of chromite ore, therefore achieving a high separation efficiency. It solved the problems of separation of chromium from alkali and impurities in the leaching liquor of chromite ore and leaching liquor of COPR and crystal mixture in the oxidative decomposition process of chromite ore.
    Analysis and control of abnormal wear of reciprocating compressor in natural gas underground storage cavern
    Sijia ZHENG Xueyuan LI Hua CHENG Siluo LEI Jingdong CHEN Feng WANG Jiawen CHEN Xinghong HUANG Lin ZHONG
    The Chinese Journal of Process Engineering. 2022, 22(11):  1547-1557.  DOI: 10.12034/j.issn.1009-606X.222121
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    During China's 14th five-year plan period, the national natural gas pipeline network has been interconnected, and the gas quality became more complex. A certain amount of dust particles widely spread in the natural gas pipeline, and led to abnormal wear of the reciprocating compressor's cylinder in the underground storage cavern. Based on the SIEM (Shear Impact Energy Model), combined with field measurement and moving-grid method of computational fluid dynamics, the wear characteristics of the compression cylinder are well demonstrated. The results show that the lubricating oil is mixed with dust particles to form grinding paste. With the increase of particle mass concentration from 0.01% to 3.00%, the viscosity of grinding paste increases from 4.51×105 mPa?s to 1.27×106 mPa?s, and the density increases from 890 kg/m3 to 980 kg/m3. The abnormal wear often occurs at 12 o'clock and 6 o'clock of the compression cylinder. When the piston is in the midpoint of the stroke, the wall shear rate as well as the wear rate are the highest. When the piston is in the two end points of the stroke, the wall shear rate as well as the wear rate are the slightest. For every 1000 hours of operation without repairing the cylinder, the particle mass concentration should be controlled below 0.60%. For every 5000 hours and 10 000 hours of operation without replacing the cylinder, and the particle mass concentration should be controlled below 1.30% and 0.40% respectively. When the particle mass concentration is 0.01%, the wear rate decreases with the decrease of lubricating oil viscosity. When the particle mass concentrations are 0.51% and 1.00%, the lubricating oil viscosities are 2.59×105, 2.21×105 and 1.97×105 mPa?s, the calculated wear rate increases sharply with decrease of lubricating oil viscosity.
    Experimental study on removel of dust by wet filtration under synergistic effect of surfactant
    Houcheng DING Yuandi XU Quanlong DENG Mengyuan GE Yakai LIU Yuanyuan XU
    The Chinese Journal of Process Engineering. 2022, 22(11):  1558-1564.  DOI: 10.12034/j.issn.1009-606X.221410
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    In this study, anthracite powder was selected as the object to study the related properties of surfactants and the wettability of anthracite powder. On this basis, a wet fiber grating dust removal system was designed and built to study the effects of different wind speeds, water pressures, fiber grating mesh numbers and the types of compound surfactants on dust removal efficiency. The experimental results show that the surfactant can effectively reduce the surface tension of water, making the coal powder more easily wetted. When the dust removal system has not added surfactant, the single filtration efficiency of dry fiber grid to dust is low. After adding the spray device, the dust removal efficiency increases first and then tends to be stable with the increase of spray pressure, and the overall efficiency is significantly higher than that under the condition of single fiber grid dust removal. However, too high speed and too small droplet size are easier to pass through the fiber grating and reduce the water volume on the fiber grating, which is not conducive to the formation of water film between fibers, thus affecting the improvement of dust removal efficiency. The number of fiber grids is positively correlated with the dust removal efficiency, and when the wind speed is greater than 0.7 m/s, due to the formation of more water film on the fiber network, there will be certain resistance to the wind speed. At this time, the wind speed has no obvious effect on the change of dust removal efficiency. After adding surfactants, the dedusting efficiency of the system is significantly improved. By comparing the dedusting efficiency of several complex solutions, it is found that LAB-35+X-100 surfactant complex solution have the highest dedusting efficiency, which can reach 97.03%. Moreover, the growth rate of dedusting efficiency is relatively stable with the change of water pressure. It can be seen that this complex solution had good dust removal effect. In terms of economy, the CMC of X-100 and LAB-35 solutions are 0.07wt% and 0.5wt%, which are easy to reach saturation and simple to be configured. Therefore, they can be considered to be used in industrial dust removal in the future.
    Numerical simulation of oxygen-enriched combustion in secondary air of rotary kiln
    Quanliang LI Shuxia MEI Junlin XIE Jun CHEN Gang LIU Xinfu YANG Haibo ZHANG Gang LIU
    The Chinese Journal of Process Engineering. 2022, 22(11):  1565-1573.  DOI: 10.12034/j.issn.1009-606X.221393
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    To explore the influence of secondary air oxygen enrichment on flame shape, temperature distribution, radiation, NOx concentration and other parameters of rotary kiln, the feasibility of secondary air oxygen enrichment was studied. The numerical simulation of oxygen enriched combustion in secondary air were carried out for a rotary kiln under actual working conditions by using ANSYS Fluent 15.0 software. For the gas phase, the RNG k-ε model was used to simulate the turbulent flow. For the particle phase (pulverized coal), the discrete phase model and discrete random walk model were used to calculate the trajectory of the particle phase. For the pulverized coal combustion process, the species transport model combined with the Finite-Rate/Eddy-Dissipation model was used, and radiation was expressed with the P-1 radiation model. The pollutant model was used to calculate the generation of NOx in the rotary kiln, considering the generation of thermal NOx and fuel NOx in the rotary kiln, and NOx reduction by reburning. The results showed that after the secondary air was enriched with oxygen, the gas flow fields near the burner did not change significantly, the covering shape of the high temperature area did not change obviously, and it was still in the shape of "mallet". At the front end of the rotary kiln, the combustion speed of pulverized coal volatile and char was accelerated, the overall temperature increased, the maximum temperature was increased from 2386 K to 2427 K, and the radiation received by the wall surafce was also increased. However, the generation of NOx had also increased significantly. According to the calculation, the mass concentration of NOx at the outlet increased from 247 mg/m3 to 367 mg/m3. Considering the cost of oxygen production and NOx emission, the overall effect of oxygen enriched combustion in secondary air was not ideal.
    Study on inactivation of Microcystis aeruginosa by dielectric barrier discharge low-temperature plasma
    Sichuan PU Lanting SHI Jia HE Na BIAN Zhao LIU
    The Chinese Journal of Process Engineering. 2022, 22(11):  1574-1583.  DOI: 10.12034/j.issn.1009-606X.221304
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    Dielectric barrier discharge (DBD) low temperature plasma was used to inactivate Microcystis aeruginosa. The effects of DBD low temperature plasma discharge conditions on Microcystis aeruginosa inactivation were investigated,such as discharge parameters, field structure parameters and solution liquid phase system factors, etc. Several analytical methods [e.g., acetone extraction spectrophotometry, conductivity measurement, scanning electron microscopy (SEM) and high performance liquid chromatography (HPLC)] were used to test the inactivation effect of Microcystis aeruginosa. The experimental results show that the discharge conditions have a great influence on the inactivation rate. Under the optimum conditions (discharge voltage 160 V, discharge current 0.63 A, dielectric spacing 4 mm, initial OD value of solution 0.2, pH value is weakly alkaline), discharge time 5 min, the inactivation rate of Microcystis aeruginosa can reach more than 90%. After discharge treatment, the color of Microcystis aeruginosa solution changed from bright green→light green→light yellow→colorless. The Chl-a content of Microcystis aeruginosa decreased significantly. The photosynthetic ability was inhibited, and the growth of Microcystis aeruginosa was blocked. SEM results showed that the algal cells were full and complete before discharge treatment. After discharge treatment, the cell structure of Microcystis aeruginosa was seriously damaged. The cell membrane was broken, and the cell content was leaked, which only left a small amount of cell debris. After discharge treatment, the electrolyte exudation rate of Microcystis aeruginosa increased. The cell membrane structure was seriously damaged, resulting in the increase of permeability and the leakage of cell contents. In the process of Microcystis aeruginosa inactivation, the content of microcystins first increased and then decreased with the discharge time. Under the optimum discharge conditions, after 5 min discharge treatment, not only the microcystins released by the rupture of Microcystis aeruginosa were completely degraded, whose removal rate was 100%, but also the microcystins in the original water were degraded. The above experimental results indicate that DBD low temperature plasma technology is a better method to remove Microcystis aeruginosa. This method can not only inhibit the proliferation of Microcystis aeruginosa, which has remarkable inactivation effect, but also will not cause secondary pollution of water body. So this method has good application value.
    Performance of alkaline bentonite?calcium alginate immobilized particles for micro?polluted wastewater treatment as microbial carriers
    Xiaoyu LIU Yifei ZHANG Licong DENG
    The Chinese Journal of Process Engineering. 2022, 22(11):  1584-1592.  DOI: 10.12034/j.issn.1009-606X.221418
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    In recent years, the water quality of micro-polluted landscape water shows the deterioration trend of ammonia nitrogen and chemical oxygen demand (COD) exceeding the standard. The use of adsorption materials is one of the effective ways to solve this situation, but such materials often do not have long-term stable in-situ treatment performance. To solve this problem, the alkalized bentonite-calcium alginate immobilized particles were prepared by using calcium alginate with good biocompatibility as a fixative. And the removal effect of NH3-N and COD in simulated micro-polluted water was investigated by using immobilized particles as microbial carriers. A series of alkalized bentonite-calcium alginate immobilized particles were synthesized by sol-gel method using calcium alginate to fix alkaline bentonite, which was treated with different concentrations of NaOH solution. The prepared alkaline bentonite and immobilized particles were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), Zeta test and BET specific surface area test. Meanwhile, the treatment performance of immobilized particles on micro-polluted wastewater as microbial carriers was analyzed. The results showed that the bentonite treated with 0.5 mol/L NaOH solution increased surface lamellar structure, and had the lowest Zeta potential of -27.4 mV, which meant that the surface electronegativity was enhanced. 0.5B-CA immobilized particles had the maximum BET specific surface area of 12.1 m2/g, which was 28% higher than that of 0B-CA immobilized particles, providing more sites for microbial attachment. 0.5B-CA immobilized particles as microbial carriers had the best removal effect on NH3-N and COD. In the 10 cycles of treatment, the concentration of NH3-N and COD in all treated wastewater were reduced to below 1 and 20 mg/L, respectively, reaching the national surface water environment class III water standard. The combination of adsorption of bentonite as adsorption matrix and microbial removal makes the material as microbial carrier show excellent removal performance and long-term stable removal ability of NH3-N and COD, which provides the possibility for its application in practical scenes.
    Preparation of pyrroline-5-carboxylate and piperidine-6-carboxylate by enzyme catalysis
    Chen SHEN Aimin HUANG Zhenghua GU Yu XIN Liang ZHANG
    The Chinese Journal of Process Engineering. 2022, 22(11):  1593-1600.  DOI: 10.12034/j.issn.1009-606X.221397
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    1-Pyrroline-5-carboxylate (P5C) and 1-piperidine-6-carboxylate (P6C) are cyclic imine compounds closely related to metabolic reactions and disease diagnosis and treatment. They are respectively involved in the metabolism of L-proline and L-lysine and play an essential role in maintaining the balance of cell oxidation, regulating the concentration of NADP(H)/NADP, and inducing cell apoptosis. Therefore, it is necessary to develop a green, efficient and sustainable preparation method. Biocatalysis is widely used in various industries such as medicine, chemicals, energy, and materials for its advantages of environment friendliness, economy, mildness, and specificity. In this work, an effective enzymatic method for the preparation of P5C and P6C is established and optimized based on the catalytic ability of the sarcosine oxidase (SOX) against the -C-N- bond. TrSOX is derived from Thermomicrobium roseum, which possesses excellent stability and tolerance. The target compounds are separated and identified by thin-layer chromatography (TLC), liquid chromatography-mass spectrometry (LC-MS), and 1H-NMR, and the concentration determination method was created. The single-factor experiment is conducted to analyze the influence of reaction temperature, pH, and substrate concentration on the product yield, and it is discovered that the optimum reaction temperature, pH and substrate concentration was respective 80℃, 9.5, and 100 mmol/L. Furthermore, reliable models were obtained through response surface design by taking the product yield as the response value. It is found that the best reaction conditions of P5C are 79.33℃, pH=8.54, substrate concentration 112.82 mmol/L, and that of P6C are 80.19℃, pH=8.31, and substrate concentration 83.58 mmol/L. After a 30 min reaction under the above conditions, the yield of P5C and P6C is 340.15±9.12 and 450.87±8.54 mg/L, respectively, which is 1.35% and 1.47% different from the theoretical value. Finally, after 48 h of reaction, the conversion rate of L-proline and L-homoproline reached 81.94% and 99.99% respectively. This study provides a new preparation method for P5C and P6C with a high conversion rate and mild reaction conditions. Taken together, the research results laid a theoretical foundation for the enzymatic preparation of P5C and P6C, provided a reference model for industrial applications, and offered a new method for synthesizing pyrroline and piperidine compounds.