Table of Content

22 April 2019, Volume 19 Issue 2

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Reviews

Research progress of low-temperature SCR denitration catalysts

Ruliang NING Xiaolong LIU Tingyu ZHU

Chin. J. Process Eng.. 2019, 19(2):  223-234.  DOI: 10.12034/j.issn.1009-606X.218233

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Nitrogen oxide NOx (NO, NO2, and N2O) is one of the major pollutants in the air pollution, it can cause environmental problems such as photochemical smog, acid rain, and ozone layer destruction, which has posed threat to people's living environment and quality of life, and attracted great attention from the world. Countries made stricter emission standards for burning emissions from both fixed and mobile sources. The major denitrification technologies include selective catalytic reduction (SCR), selective non-catalytic reduction (SNCR), oxidative denitrification, and activated carbon adsorption and denitrification at present. The SNCR has higher conditions in industrial applications, the main factors affecting successful operation are temperature, ammonia?nitrogen ratio, distribution of ammonia gas in the flue gas and residence time, so there were certain limitations in industrial application of SNCR. Compared with other denitrification technologies, SCR denitration technology is more widely used in industrial application, in which denitration is mostly arranged after dust removal and desulfurization, at this time, the temperature is mostly between 100?250℃. The performance of SCR denitrification in low-temperature must be improved, which is one of the most promising flue gas DeNOx technology. In this paper, the recent works on low-temperature SCR catalysts were reviewed on manganese-based catalysts, vanadium-based catalysts and carbon-based catalysts. Single-component Mn-based catalysts, supported Mn-based catalysts and composite Mn-based catalysts were reviewed, the effects of preparation of V-based catalysts on the de-dumping and denitrification mechanisms were described. The effect of transition metal doping on C-based catalysts was reviewed. The influence of H2O and SO2 resistance on low-temperature NH3-SCR catalytic activity and reaction mechanism were also discussed. Finally, the virtues advantages and defects of low temperature SCR catalysts were summarized, and the future development direction was also given out.

Research status of hydrocyclone and its application prospect in wastewater treatment of coal chemical industry

Yuanwei SUI Guangru JIA Gaojie XU Qiang DONG Pengge NING Hongbin CAO

Chin. J. Process Eng.. 2019, 19(2):  235-245.  DOI: 10.12034/j.issn.1009-606X.218248

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The hydrocyclone is a kind of effective device for two-phase fluids separation using centrifugal force field. Although the hydrocyclone has a simple structure and small size, its separation efficiency is very high and it can be easily installed. Therefore, it is widely used in chemical, petroleum and underground mining industries. First, this work mainly introduces the working principle, theoretical research and application status of the hydrocyclone. The research development of hydrocyclone is discussed from the aspects of numerical simulation, structural parameters, operating parameters and physical parameters, as well as the progress of its application technology. And based on the characteristics: high emulsification, high dispersion and high viscosity of coal chemical wastewater water, the application prospect of hydrocyclone in coal chemical wastewater pretreatment is discussed. The combination of simulation and experiment of hydrocyclone has become the main research direction. The fluid condition of two-phase flow in hydrocyclone is deeply discussed, which provides theoretical basis for the improvement of the hydrocyclone structure, which is conducive to the rapid development of hydrocyclone and people's in depth understanding of it, and expands the application scope of hydrocyclone. We found that the research on structure improvement and operation parameters optimization of hydrocyclone are quite limited and the key to effective oil?water separation is the properties of the fluids. Therefore, it is very important to pretreat oily wastewater in the beginning. Demulsifier or flocculant, ultrasonic or microwave can be used to improve the physical properties of oily wastewater. For oily wastewater treatment, the detailed researches on the effects of oily wastewater?s physical properties and the application of numerical simulation will guide us to improve the separation efficiency of hydrocyclone in the future. It is certain that the hydrocyclone will have good economic benefits and wide application prospects in the deoiling and decoking process of coal-chemical wastewater.

Flow & Transfer

Numerical simulation and range analysis of off-design performance for a radial-inflow turbine

Zhenkang ZHANG Fanyun ZENG Zhiqi WANG Xiaoxia XIA Ni HE Yanhua HU Jianping ZHANG

Chin. J. Process Eng.. 2019, 19(2):  246-253.  DOI: 10.12034/j.issn.1009-606X.218179

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The radial-inflow turbine is a key component determining the performance of organic Rankine cycle (ORC) systems. Its isentropic efficiency and power output are mainly influenced by the working fluid and operation conditions. Although R245fa is a suitable working fluid for ORC systems, there is limited research concerning full structure numerical simulation and off-design analysis for the radial-inflow turbine using R245fa. In this work, a radial-inflow turbine using R245fa was designed by one dimensional design method and a three dimensional model including volute, stator and rotor was established. According to the developed model, a numerical simulation was carried out using CFD (computational fluid dynamics) method. The effects of inlet temperature, rotor speed and expansion ratio on turbine power and isentropic efficiency were analyzed. Additionally, the range analysis about main factors which influenced the radial-inflow turbine performance was conducted. The results showed that turbine power and isentropic efficiency changed slightly when rotor speed ranged from 80% to 100% of designed value. However, turbine performance decreased rapidly if rotor speed was larger than the designed value. Turbine power and isentropic efficiency increased with the increment of turbine inlet temperature. With the increase of pressure ratio (ratio of inlet pressure to outlet pressure), turbine power increases linearly and there was an optimal pressure ratio for the radial turbine to achieve the highest isentropic efficiency. Under nominal condition, the optimal pressure ratio was 3.23 which was slightly lower than the designed value. Besides, there was a little variation for isentropic efficiency when pressure ratio was larger than that of optimal value. Based on the range analysis, sensitivity of different factors influencing the turbine performance was evaluated. For the turbine output power, the sequence of the factors were listed as: outlet pressure, inlet pressure, rotor speed and inlet temperature. It meaned that turbine power was seriously influenced by outlet pressure and inlet pressure. As for the isentropic efficiency, the rotor speed had the largest impact, followed by the turbine outlet pressure, and the inlet pressure contributed the least.

Optimization of new type of gas-liquid countercurrent impinging scrubber nozzle

Sijia HAO Changzhuo MAN Jun XU Yiping FAN

Chin. J. Process Eng.. 2019, 19(2):  254-262.  DOI: 10.12034/j.issn.1009-606X.218217

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A new type of gas?liquid countercurrent impinging scrubber nozzle was put forward. By using the dissolved oxygen technique, the characteristics of the gas?liquid two-phase mass transfer with different structures of scrubber nozzles were investigated through cold model experiment. Combining the measured desorption rates with the observed flow patterns variation, the effects of five structural parameters including the nozzle outlet diameter, the tangential inlet angle, the conical swirl chamber cone angle, the tangential inlet diameter and the spout length on the mass transfer were analyzed. Thus the optimal structural dimensions were given. The features of the mass transfer of the optimal nozzle under different operating conditions including the gas velocity, the superficial liquid?gas volume flow rate ratio, and the axial-tangential volume flow rate ratio were investigated further. The nozzle with structure of horizontal angle of the tangential inlet, small outlet diameter (with high orifice speed), and small conical angle of the convergent section of the swirl chamber can gain high mass transfer efficiency. For industrial applications, large size scrubbers should provide as much tangential momentum as possible to cover the entire cross section and increase the gas?liquid contact area, such as choose the angle 0? and 90?, tangential inlet angle and conical swirl chamber cone angle respectively. The results showed that the desirable effect of mass transfer could be obtained then the axial?tangential volume flow rate ratio was 0.4~0.6, especially in a high gas velocity condition. Similarly, there was a better mass transfer area with the change of superficial liquid?gas volume flow rate ratio. In addition, high desorption rates can be achieved with a very small liquid?gas volume flow rate ratio under the condition of high gas velocity. It can also be concluded that this type of washing nozzle with higher operating elasticity can adapt to different conditions of liquid?gas volume flow ratio by adjusting the axial-tangential volume flow rate ratio.

Numerical simulation of coalescence of double bubbles using FTM

Jie LEI Yu WANG Ming MA Peisheng LI Ying ZHANG

Chin. J. Process Eng.. 2019, 19(2):  263-270.  DOI: 10.12034/j.issn.1009-606X.218221

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The front tracking method (FTM), which can track the maker points and capture the changes of the interface accurately was used to simulate the phenomenon of bubble coalescence. All governing equations were solved by using a second-order accurate project method, using centered-differences on a fixed, staggered grid and considering the effect of surface tension at the interface. The numerical simulations were compared with experimental and computational results from other literatures which modified the accuracy of calculation model. In this work, the rising process of coaxial bubbles and the process after fusion were analyzed in detail, and the existence of specific initial angle ?c and the relationship between ?c and Eotvos number (Eo) were analyzed. It was found that the rising velocity of both bubbles were higher than single bubble, and the coalesced bubble had the equal velocity with equivalent diameter single bubble in the rising process of coaxial double bubbles. The trailing bubble had higher velocity with the shorter distance of bubbles. In the range of Eo of leading bubble was 0.36~9, the time of rising stage was shorter and the time of contact stage was longer when the Eo of leading bubble increased. During contact stage, the thickness of liquid film between bubbles decreased because of the effect of pressure. Liquid film broke and coalescence of bubbles happened in the coalescence moment. The required time of coalescence increased as the distance of bubbles or Eo increased. However, the required time was stable as Eo was larger than 4.16. When the Morton number (Mo) was 0.57 and the range of Eo of leading bubble was 5.04~18.72, it was found that there was a specific initial angle ?c. The two bubbles repelled each other for 0?≤?≤?c but merge for ?c≤?≤90?, and ?c decreased with the increase of Eo.

Flow field analysis and structure optimization of honeycomb air filter

Shuting WEI Fuping QIAN Jialei CHENG Pengcheng XIAO Lianhua TANG Ronghe JIANG

Chin. J. Process Eng.. 2019, 19(2):  271-278.  DOI: 10.12034/j.issn.1009-606X.218226

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Air filter as the heart of the car filtering the dirty air entering the engine which plays a key role in protecting the engine. In this work, because the performance of the air filter has a direct impact on the engine's power performance and economy, a standard k?? turbulence model was used to simulate the internal flow field and resistance characteristics of macrohoneycomb air filters with different structures based on the theory of porous media, thus to optimized the structure and improved its performance. The model adopted the same filter element(pleat height h=5 mm), while the series of combinations of the inlet and outlet shapes of the housing were round and round (scheme 1), round and ellipse (scheme 2), ellipse and round (scheme 3), ellipse and ellipse (scheme 4), respectively. Then the optimized housing was combined with honeycomb filter element with pleat heights of 5, 10 and 15 mm. The results showed that the flow field distribution of scheme 2 was more uniform than that of schemes 1, 3 and 4, and the pressure drop increased approximately linearly with the increase of flow rate. When the flow rate was less than 60% of the rated flow, the values of pressure drop of these four schemes were approximately equal. However, the pressure drop of scheme 2 was smaller than that of schemes1, 3 and 4 when the flow rate was greater than 60% of the rated flow. Therefore, the housing of scheme 2 was more reasonable. For this structure, the difference in the pleat height of the filter element had a certain influence on the flow filed distribution of the air filter. Furthermore, the pressure drop decreased firstly and then increased in the range of pleat height studied. Therefore, there was an optimal pleat height to minimize the pressure drop of the honeycomb air filter, which provided theoretical guidance for the optimal design of air filter.

Effects of particle clusters on fluctuation coupling terms in dilute gas-particle turbulent flows

Heng FENG Qinghai LI Aihong MENG Yanguo ZHANG Bo KONG

Chin. J. Process Eng.. 2019, 19(2):  279-288.  DOI: 10.12034/j.issn.1009-606X.218230

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The effect of particle clusters on gas?solids fluctuation coupling terms in Reynolds stresses transport equations was investigated in this work. Based on its transport equation, covariance of solids phase volume fraction and gas phase fluctuating velocity, namely drift velocity was closured by an algebraic model, which was a function of both degree of segregation and mean slip velocity. Thereby two different kinetic-based Euler?Euler mesoscale methods were applied to simulate a dilute gas?particle flow in a triple periodic domain where solids phase averaged volume fraction was 1%. Stokes drag law was applied for inter-phase momentum transfer. Inter-particle collisions were approximated by Bhatnagar?Gross?Krook model. Mesh resolution in this study was as 1.75 times as particle diameter dp. The difference between these two approaches was the way to solve solids phase kinetic equation. The first approach was an Anisotropic Gaussian (AG) Quadrature based moment method of which particle phase velocity density function f was assumed to follow a multivariate anisotropic Gaussian. The second approach was a typical two-fluid model (TFM) of which assumed f to follow isotropic distribution. To validate these two methods, results were compared with results given by a Euler?Lagrange (E?L) method in the literature. It demonstrated that AG method was able to produce better comparable results than TFM. For instance, the flow field properties given by AG method were closer to results given by E?L method, including mean slip velocity, gas and solids phase turbulent kinetic energy. Results showed that the integral scale of particle clusters was smaller than that of gas-phase fluctuation velocities. And the integral scale of both particle clusters and gas-phase fluctuation velocities turned out to be anisotropic that vertical components were larger than lateral components. The falling of particle clusters was mainly suppressed by form drag (i.e. gas pressure between front and tail). In the end, the coefficients of both gas?solids fluctuation velocity covariance and drift velocity were identified.

Fluid flow and heat transfer characteristics of water-based graphene nanofluids in small rectangular channels

Dong LIU Yu SHU Anjie HU

Chin. J. Process Eng.. 2019, 19(2):  289-296.  DOI: 10.12034/j.issn.1009-606X.218300

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A small rectangular channel was designed and fabricated. The convective heat transfer properties of water-based graphene nanofluids in the channel were experimentally investigated by using it as the heat transfer medium under different experimental conditions [different mass concentrations, Reynolds numbers (Re) and heating powers], and some thermal properties of water-based graphene nanofluids were tested. The experimental results showed that the temperature along the wall of rectangular channel decreased with the increase of Re and increased with the increase of heating power under laminar flow (Re=500~1000). This change regulation was consistent with the heat transfer characteristics of conventional fluids, however, with the increase of mass concentration of nanofluids at same Re and heating power, the wall temperature decreased gradually because of the Brownian motion of graphene nanoparticles, the enhancement of scrambling by mixing of particles and the enhancement of thermal properties of nanofluids. The heat transfer intensity of water-based graphene nanofluid was higher than that of deionized water. When Re was 2000 and heating power was 210 W, the average Nusselt number (Nu) of water-based graphene nanofluids with 0.03wt% concentration was 9.3, which was 48.8% higher than that of the based water under the same conditions. Under the influence of inlet effect, the local convective heat transfer coefficient along the channel length decreased gradually, and the maximum local heat transfer coefficient of nanofluid increased by 39.1% compared with the deionized water. The flow heat transfer intensity of graphene nanofluids was obviously enhanced by the Brownian motion of graphene particles at certain Re (500~1400). In order to describe the heat transfer characteristics of water-based graphene nanofluids more clearly, a heat transfer relation was fitted by combining experimental data and theoretical models. Compared with the experimental results, the maximum relative error (MRE) was less than 25%, and the mean relative error was only 4.8%.

Effect of reactor structure on particle distribution in multi-stage gasifier

Meiyan FENG Fei LI

Chin. J. Process Eng.. 2019, 19(2):  297-308.  DOI: 10.12034/j.issn.1009-606X.218326

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The 3D full-loop multi-stage gasifier (upper fast fluidized bed with lower bubbling fluidized bed) was simulated with MP-PIC (Multi-Phase Particle In Cell) method successfully. To study the effect of reactor structure on the gas?solid flow in the multi-stage gasifier, the effects of diameter ratio of bubbling fluidized bed to fast fluidized bed and transition section heights on the flow characteristics of gasifier were systematically studied by simulations with MP-PIC method. The results showed that the circulating fluidization process of pulverized coal was successfully simulated by the current method. For basic case, coarse particles mainly resided in the lower bubbling bed, and fine particles mainly resided in the upper fast bed. However, fine particles can return to the bubbling bed from cyclone and stand pipe. Only the small particles with diameters less than 622 μm can enter the cyclone, where there were no particles with diameters larger than 1216 μm. The cyclone had a separation efficiency of 99.75% for small particles, which exhibits a good separation performance. Increasing the bed diameter ratio (ie, reducing the diameter of the fast bed) led to the increase of gas velocity in the fast fluidized bed. Under this condition the gasifier tended to reach steady state much faster. And more particles can be entrained into the fast fluidized bed. The entrained particle size range also increased. Compared to the basic condition, both increasing and decreasing the height of the transition section increased the particles concentration and solid flux in the fast fluidized bed. The efficiency of the cyclone was also higher than that of the basic condition. These implied that there existed an optimum value of the transition section height (between 0.6 and 1.0 m in this case). Increasing or decreasing this value will increase the solid flux in fast fluidized bed but will reduce the cyclone efficiency. These rules can be significant and helpful to the design and optimization of multi-stage gasifiers.

Reaction & Separation

Removal of iron-rich phases from coarse Al-Si alloy in the electromagnetic field

Yu BAO Shimin ZHAO Guoqiang Lü Yibo WANG Ting XIAO Wenhui MA

Chin. J. Process Eng.. 2019, 19(2):  309-316.  DOI: 10.12034/j.issn.1009-606X.218202

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Iron-rich phases mainly existing in the form of acicular-like in coarse Al?Si alloy has detrimental effects on the mechanical property of the alloy, which is urgently needed to be solved before used as materials for producing casting Al?Si alloys. Based on the traditional metal impurity removal theory, iron-rich phases in the coarse Al?Si alloy (Fe content 5wt%) can be removed by adding manganese during the electromagnetic directional solidification process, which mainly improves the structure and shape of iron-rich phases and reduces iron content to decrease the harmful influence of iron-rich phases on mechanical properties of Al?Si alloy. The effects of Mn addition on the removal rate of iron-rich phases from Al?Si alloy, influence of Mn on the improvement of morphology of iron-rich phases, and the separation mechanism were studied. The results showed that with the moderate increase of manganese addition, iron-rich phases in Al?Si alloy combined with Mn to form some complex intermetallic compounds with larger shape factors, decreasing the migrating resistance of iron-rich phases when conducting the electromagnetic directional solidification. The migrating velocity of iron-rich phases could be improved as the majority of iron-rich phases in the Al?Si alloy got regularized in shape and structure, therefore the separation efficiency of iron-rich phases was enhanced as well. Eventually, iron-rich phases could be enriched at the bottom of the alloy by the electromagnetic force as a result of larger magnetic susceptibility than that of Al melts. This new technology to remove iron-rich phases from coarse Al?Si alloy had the characteristics of high-efficiency, cost saving, environmental-friendly and energy conservation. It could hopefully become the substitute for preparing casting Al?Si alloy after the electro-thermal process, because not only iron-rich phases in Al?Si alloy were removed, but also primary silicon was accumulated at the bottom of the alloy. In other words, impacted by electromagnetic directional solidification and Mn addition, the purified alloy was divided into two parts: the upper Al?Si alloy with low iron and silicon contents, and the bottom impurity accumulating parts of Si and Fe. The residual iron content in Al?Si alloy was reduced to 0.39wt%, with the iron removal efficiency reaching 90%.

Process & Technology

Electrochemical behavior of Bi(III) in molten NaCl-KCl

Huan LIU Jiwen HE Zhongsheng HUA Liang XU Saijun XIAO Zhuo ZHAO

Chin. J. Process Eng.. 2019, 19(2):  317-322.  DOI: 10.12034/j.issn.1009-606X.218155

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Bismuth has a wide range of applications such as in metallurgy, chemical engineering, electronic industry, medical service, aeronautics, astronautics, and nuclear industry, etc., owing to its excellent properties including large density, low melting point, nontoxicity as well as the abnormal nature of expansion in cooling down and contraction in heating up. As one of the nonrenewable and scarce metal resources, the extraction and recycling of bismuth has received increasing attention in recent years. Molten salt electrolysis is one of the most widely used methods for metal extraction. Therefore, extraction of bismuth from BiCl3 directly by molten salt electrolysis was evaluated in the present work in order to develop an environmentally friendly technology for bismuth recovery. Firstly, the electrochemical behavior of Bi(III) ions in molten NaCl?KCl at 700℃ was investigated by cyclic voltammetry, square wavevoltammetry, and chronopotentiometry on a glassy carbon working electrode. The results indicated that the reduction of Bi(III) in the NaCl?KCl molten salt was a one-step process with three electrons exchanged Bi3++3e?=Bi, and the initial reduction potential of Bi(III) ions was detected at 0.05 V (vs. Ag/AgCl), approximately. Meanwhile, the reduction of Bi(III) ions in the melts was a quasi-reversible diffusion-controlled process, and the diffusion coefficient of Bi(III) in molten salt at 700℃ were determined to be 0.83×10–5 and 1.0×10–5 cm2/s, respectively, based on the results of cyclic voltammetry and chronopotentiometry using the Berzins-Delahay equation and the Sand equation. Then, potentiostatic electrolysis at –0.3 V (vs. Ag/AgCl) was carried out in molten NaCl?KCl?BiCl3 under 700℃ and spherical metal granules were obtained around cathode. The cathodic products were compact in microstructure and confirmed to be pure bismuth with no other impurities detected by XRD and SEM?EDS analyses. The present results confirmed that it was an effective method for extraction of bismuth by direct electrolysis of bismuth chloride in molten NaCl?KCl, which could be subsequently used to recycling of bismuth from bismuth-bearing materials.

Effects of drying route on particle size and upconversion luminescence properties of NaY(WO₄)₂:Dy³⁺, Eu³⁺ phosphors

Zhongxiang SHI Jing WANG Yang LU Xin GUAN Jun SHI Lijing DAI Bingqian LIU

Chin. J. Process Eng.. 2019, 19(2):  323-328.  DOI: 10.12034/j.issn.1009-606X.218170

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Trivalent Dy3+ and trivalent Eu3+ ions co-doped NaY(WO4)2 upconversion phosphors were synthesized via traditional hydrothermal process. The effects of drying routes on the crystal structure, morphology, particle size and upconversion luminescence properties were investigated, and characterized by XRD, SEM, and photoluminescence spectrum (PL). The results showed that all the synthesized samples had the tetragonal scheelite structure with the space group I41/a, and the doping Dy3+ and Eu3+ ions did not evoke the changes of the host lattice parameters. In addition, the shape and size of products could be changed simply and effectively by different drying methods. The particle sizes of the phosphors drying by normal, spray, freeze and vacuum methods were 817.91, 486.04, 388.74 and 349.82 nm, respectively. It should be noted that the excellent dispersion of the particles were obtained by vacuum drying method. Under near infrared light excitation at 793 nm, the sample obtained by freeze drying had the better upconversion luminescence property than samples synthesized by normal drying, spray drying and vacuum drying. The possible reason for the above phenomenon were spread uniform, reunite decrease and surface defect layer decrease of powder particles during the freeze drying process. The NaY(WO4)2:Dy3+, Eu3+ phosphors exhibited yellow emission band at 576 nm corresponding to the 4F9/2→6H13/2 transition of Dy3+ ions, orange emitting lights (595 nm) were from the transition of 5D0→7F1 of Eu3+ ions, and red emitting lights at 616 and 655 nm, which were assigned to the energy level transition of 5D0→7F2 and 5D0→7F3 of Eu3+ ions, respectively. Moreover, the ideal red chromaticity was exhibited by the CIE color coordinates of NaY(WO4)2:Dy3+, Eu3+ phosphors. In view of this, the NaY(WO4)2:Dy3+, Eu3+ phosphors might have potential application in photoelectric device areas, such as light emitting diodes and color display systems.

Simulation of flue gas pollution control units of coal-fired power plant based on Aspen Plus

Jingxin YU Jing WANG Fengling YANG Yanhong HAO Fangqin CHENG

Chin. J. Process Eng.. 2019, 19(2):  329-337.  DOI: 10.12034/j.issn.1009-606X.218198

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The Aspen Plus software was used to simulate the flue gas pollution control units and the correctness of the model was verified using the actual operation data of one power plant. In the modeling process, in addition to the removal of conventional flue gas pollutants, the SO3 conversion and the change of dust concentration in the flue gas were taken into account. Furthermore, the effects of operating parameters on the pollutants removal efficiency were examined through influencing factors analysis. In this simulation model, the flue gas entered the SCR (Selective Catalytic Reduction) de-nitrification device firstly, followed by electrostatic precipitator, limestone-gypsum desulfurization, and finally went through the wet electrostatic precipitator process, achieving the ultra-low emission standards before discharges into the atmosphere. In the SCR denitration process, SO2 was oxidized to SO3 due to the catalyst. Ash had an adsorption effect on SO3 during the ESP (Eletrostatic Precipitator) process, and the desulfurization tower and the wet electrostatic precipitator process had a synergistic removal effect on SO3 and ash. To accurate the simulation results, all these details mentioned above were simulated in this study. The influencing factors analysis showed that when the molar ratio of ammonia to nitrogen was lower than 0.6 and the reaction temperature was lower than 400℃, the concentration of SO3 tended to rise. With the increase of the molar ratio of ammonia to nitrogen and temperature, part of SO3 would react with excess ammonia forming NH4HSO4 during the de-nitrification process, which could in turn caused blockage of the air pre-heater. Comprehensive analysis showed that the optimal ammonia?nitrogen molar ratio was in the range of 0.8~1.0. During the desulfurization process, the increase of the absorption liquid flux and the decrease of the inlet flue gas temperature were favorable for the removal of SO3. During the wet dust removal process, when the flow rate of the flue gas was in the range of 0.8~1.2 m/s, the removal of soot was facilitated.

Inhibition mechanism of citric acid on the floatability of muscovite

Yubin WANG Kan WEN Wangbo WANG

Chin. J. Process Eng.. 2019, 19(2):  338-344.  DOI: 10.12034/j.issn.1009-606X.218201

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Citric acid is usually used as an adjustment agent in mineral processing. In order to investigate the effect regularity of citric acid on the floatability of muscovite and the action mechanism of citric acid on muscovite under sodium oleate system, different muscovite samples were characterized by means of FT-IR, flotation solution chemistry, Zeta potential and XPS spectra etc. The results showed that the floatability of muscovite could be obviously inhibited by citric acid. The muscovite recovery rate only reached 0.40% when the concentrations of sodium oleate and citric acid were 9.20×10–4 and 4.76×10–5 mol/L respectively at pH value of 6. The reason for the inhibition of the floatability of the muscovite by citric acid was that citric acid generated C6H7O7– and C6H6O72– etc. in the solution. C6H7O7– and C6H6O72– etc. could adsorb on muscovite surface, then hinder oleate ions adsorbed on muscovite surface, and the collection performance of sodium oleate on muscovite could be weakened. Meanwhile C6H7O7– and C6H6O72– etc. which adsorbed on muscovite surface aroused muscovite surface Zeta potential negative direction increase, this means that the local positive region on the surface of muscovite will decrease, therefore the electrostatic adsorption action and the chemical adsorption of oleate ions on muscovite surface was weakened. Furthermore, these ions were generated by citric acid contained strong hydrophilic groups, and adsorbed on muscovite surface that caused muscovite surface with strong hydrophilicity, this means that the muscovite could be more difficult to float up, hence the floatability of muscovite decreased significantly under the above comprehensive effect. This work can provide a certain theoretical basis for the floatation separation of muscovite, and it can also provide some degree of reference for the selection of adjustment agents in the process of muscovite flotation.

Numerical simulation of seasonal wind pressure regulating for tempered glass

Gaowei YUE Hui LIU Hengbo WU Yanbing LI

Chin. J. Process Eng.. 2019, 19(2):  345-353.  DOI: 10.12034/j.issn.1009-606X.218208

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Wind temperature and wind pressure are important factors affecting tempering degree of glass. And the reasonable matching relationship should be sought between wind pressure and wind temperature due to seasonal variation, which satisfied the quality requirements of tempered glass and achieve the effect of energy conservation. In this work, the air-grid model of glass tempering was established to numerically simulate the change rules of glass temperature and stress during glass specimen process, and at the same time, the reasonable wind pressure was numerically calculated to match the wind temperatures in different season. The results showed that in the process of glass cooling, the glass surface cooling rate was fastest, and the internal cooling rate was slower. And the cooling rate of glass decreased gradually from outside to inside, and the influences of glass inner to surface weakened. But the curves of internal cooling rate and surface cooling rate reversed at about 15~17 s which meant that the internal cooling rate was larger, while the external cooling rate was smaller. The glass surface stress weakened by the internal temperature difference, in other words, the surface stress tended to be stable from 15 to 17 s in cooling process. At about 3 s, the tensile stress on the glass surface reached the maximum and was greater than the stress at all internal positions. When the stress was greater than the tensile strength of the glass at this time, the glass started to crack from the surface. Compared with the stress test results of the tempered glass, the numerical results were slightly smaller, but the relative error was not more than 5%. With the decrease of cooling air temperature, the wind pressure required for glass tempering was also decreasing. When the tempering degree of glass was close, the wind pressure decreased approximately linearly with the decrease of wind temperature.

Optimization of composition of dephosphorization residue based on response surface methodology

Shuangping YANG Zhengzhou JI Qishu WEI Jinkun PANG Chong WANG

Chin. J. Process Eng.. 2019, 19(2):  354-361.  DOI: 10.12034/j.issn.1009-606X.218223

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The lime-based slag system is generally applied to the treatment of pre-dephosphorization of molten iron, which mainly composed of CaO, FemOn, CaF2, etc. However, the CaF2 contained in the slag always results in the serious lining erosion and the environmental hazard caused by fluorine-containing dephosphorization by-product, which is not conducive to the comprehensive utilization of dephosphorization slag. The optimization design of dephosphorization slag system was carried out in the present study for the above problems. The effect of single factor (FeO, Na2CO3 and MnO content and basicity) on the dephosphorization of molten iron was investigated by Equilib modle in the FactSage calculation software. The main influencing factors such as FeO content, MnO content, Na2CO3 content, basicity and reaction temperature and the optimization design for the pre-melting dephosphorization slag composition were investigated by Box-Behnken modle in response surface methodology. A pre-mixing fluxing agent (Na2CO3 and MnO) was added to the CaO?SiO2?FeO slag system for dephosphorization pretreatment based on the single factor influence calculation. A multiple regression model to predict the dephosphorization rate of molten iron was established, the interaction of each factor and optimal composition of dephosphorization slag (CaO?SiO2?FeO?Na2CO3?MnO) were studied and optimized by variance analysis and response surface method, furthermore. The results showed that the calculated dephosphorization rate of molten iron was increased with the increasement of alkalinity, FeO content and flux content. The optimum dephosphorization conditions were 37.79% FeO, 6.24% Na2CO3, 9.89% MnO, with basicity of 4.50 and reaction temperature of 1387℃, the dephosphorization rate was 97.30% with relative error of 2.70%. The response surface methodology calculated result was in well accordance with experimental results of higher dephosphorization rate and can provide theoretical guidance for the industrial application of molten iron dephosphorization.

Effect of magnesium on eutectic carbides in GCr15 bearing steel

Lizhong CHANG Gang GAO Xiaofang SHI Fuzhou ZHENG Jiashun CHEN

Chin. J. Process Eng.. 2019, 19(2):  362-369.  DOI: 10.12034/j.issn.1009-606X.218227

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Eutectic carbides are very harmful to bearing steel, which is easy to cause stress concentration and lead to premature failure of bearing. Reducing the number of eutectic carbides and refining the size of carbide is one of the key factors to improve the fatigue life of bearing steel. Therefore, the effect of magnesium on the carbide was studied systematically by adding Ni?Mg alloy to GCr15 bearing steel. The magnesium content in steel was analyzed by ICP-OES method. The number, maximum size and average maximum size of the eutectic carbide in the 100 randomly selected field of view were counted by the optical microscope. The eutectic carbide was observed by SEM. The results showed that magnesium could be added to molten steel and the average yield of magnesium in steel was 9.20%. The number, maximum size and average maximum size of the eutectic carbide decreased first and then increased with the increase of magnesium content in the GCr15 steel. The refinement effect of magnesium on the eutectic carbide was best when the magnesium content in GCr15 bearing steel was 16?10?6(wt). The eutectic carbide precipitated in the large and lump shape in the steel without magnesium. When magnesium was added to the steel, carbides were still lumpy, but smaller in size. The main reason for the refinement of the eutectic carbide by trace magnesium was that the diffusion of magnesium atoms to the grain boundary or the phase boundary hindered the diffusion of C and Cr elements, so that the formation and growth of eutectic carbide was inhibited. At the same time, a large number of fine MgS?MnS could induce the precipitation of eutectic carbides, which led to the dispersion of carbides and make the carbide finer.

The effects of heat treatment temperature on performance and structure of phosphorus slag-coal gangue glass-ceramics

Wei CHEN Yanmei GUAN Kaiwei LIU Puhua HU Daosheng SUN

Chin. J. Process Eng.. 2019, 19(2):  370-376.  DOI: 10.12034/j.issn.1009-606X.218312

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Phosphorus slag is an industrial waste produced in the production of yellow phosphorus by the electric furnace method. For each 1 t of yellow phosphorus produced, it is necessary to discharge 8~10 t of phosphorus slag. Coal gangue is a solid waste produced in the coal industry. It is discharged from 10% to 15% of annual coal production. It has accumulated more than 4.5 billion tons of storage, which is the largest solid waste in China. Since a large amount of unexploited solid waste occupied industrial and agricultural land, safety problems and environmental pressures are presented. The disposal of solid waste is an urgent task. Therefore, the effective use of the solid waste resources and turning waste into treasure have important practical significance. In recent years, the glass-ceramics based on solid waste has been widely used in building decoration field. However, the technology has not been widely used due to high cost and defects in the preparation process. In this work, the feasibility of preparing glass-ceramics by the combination of phosphorus slag and coal gangue was studied. The effects of heat treatment temperature on the crystalline phase composition, microstructure and properties of the glass-ceramics were also discussed via differential scanning calorimetry (DSC), X-ray diffraction (XRD) and scanning electron microscopy (SEM). Powder base glass was obtained by melting phosphorus slag with coal gangue at 1250℃ for 2 h. The results indicated that the sintered glass-ceramics with pseudo wollastonite Ca3(Si3O9) as the main crystallization phase could be prepared after heat treatment at 850℃ for 2 h. The flexural strength, microscopic strength and bulk density of the sample were 74.4 MPa, 566.9 HV and 2.75 g/cm3, respectively. In addition, with the increase of heat treatment temperature, the main crystalline phase of the glass-ceramics changed from Ca3(Si3O9) to wollastonite (CaSiO3), the morphology of the crystal developed from spherical to the needle-like and short column, which were beneficial for improving the flexural strength. Both the microscopic strength and bulk density increased first and then decreased with the increase of heat treatment temperature.

Materials Engineering

Optimization of activated carbon preparation from sawdust and plastics using response surface method

Peiyong MA Tian WANG Jinzhou WU Xianjun XING Xianwen ZHANG

Chin. J. Process Eng.. 2019, 19(2):  377-386.  DOI: 10.12034/j.issn.1009-606X.218186

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Activated carbon was prepared from the mix of sycamore tree sawdust and polypropylene plastics by activation of K2CO3. Based on the central composite design (CCD) of response surface method (RSM), the preparation process was optimized, for the purpose of the highest methylene blue adsorption with higher iodine number. The optimum conditions were plastic content of 19wt%, K2CO3/sawdust mass ratio of 1.73, activation temperature of 958℃, and activation time of 91 min. The adsorption capacities of iodine and methylene blue were 1320.97 and 471.95 mg/g, with the predictive errors of 1.64% and 8.56%, respectively, which proves the high credibility of second-order model. The analysis of variance showed that the salt/sawdust ratio, activation temperature, and activation time were significant factors influencing the iodine adsorption capacity of activated carbon, which had a promoting effect, while plastic percentage had an inhibitory effect on the iodine adsorption capacity of activated carbon. The activation temperature and activation time had significant effects on the adsorption capacity of methylene blue on activated carbon, and had a promoting effect on the percentege of plastic. The salt/sowdust was a non-significant factor and had an inhibitory effect. The specific surface area, total pore volume and average pore size of the optimum sample were 1916.10 m2/g, 1.12 cm3/g, and 2.63 nm. Among them, the mesopore volume was 0.75 cm3/g, and the mesoporosity reached 70.10%. Compared with the activated carbon prepared by single factor optimization experiments, the specific surface area was increased by 454.11 m2/g. FT-IR analysis showed that the functional groups of the activated carbon prepared by the two optimization experiments did not change basically, and the increase of the activated carbon methylene blue adsorption was mainly due to the increase in specific surface area. The results suggested that the activated carbon optimized by response surface method has good absorptive property of macromolecules.

Preparation mechanism of modified porous steel slag-based rubber composite materials

Hao ZHANG Yuandi XU Yuan FANG

Chin. J. Process Eng.. 2019, 19(2):  387-392.  DOI: 10.12034/j.issn.1009-606X.218196

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Modified porous steel slag was obtained by treating steel slag with phosphoric acid and silane coupling agent KH550，and with it partially replaces carbon black and rubber to prepare modified porous steel slag-based rubber composite materials. Composition structure of substances in preparation stage of porous steel slag and modified porous steel slag were characterized and analyzed by fourier transform infrared spectrometer (FT-IR). Mineral composition of substances in different preparation stages were characterized and analyzed by X-ray diffractometer (XRD). Pore structure of porous steel slag was characterized and analyzed by brunauer-emmett-teller surface areas analyzer (BET) so as to preparation mechanism of composite materials was revealed from the micro level. Tensile strength, tear strength and Shore A hardness of composite materials were tested by referring to relative national standards GB/T 528-2009, GB/T 529-2008 and GB/T 531.1-2008. The results indicated that the suitable amount of phosphoric acid can effectively remove most of the f-CaO in the steel slag without damaging the steel slag structure, thus forming porous steel slag with good surface area and pore volume. The silane coupling agent KH550 was adsorbed on the surface of porous steel slag and chemically acted with the hydroxyl group, the surface composition of porous steel slag was changed to improve the surface inorganic properties of modified porous steel slag. The modified porous steel slag and rubber were combined by physical way in composite materials, and the rubber had a good effect on the modified porous steel slag. In the process of vulcanization, the inner rubber was transformed from a linear macromolecule to a three-dimensional network, and the hydration reaction of Ca2SiO4 in the modified porous steel slag formed Ca(OH)2.

Phase evolution and corrosion resistance of MgxTiAlFeNiCr (x=0.6~2.0) high-entropy alloys

Tingzhi SI Qinghua LIU Wenxiang XU Xiaoli DING

Chin. J. Process Eng.. 2019, 19(2):  393-399.  DOI: 10.12034/j.issn.1009-606X.218204

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The novel low density MgxTiAlFeNiCr (x=0.6~2.0) high-entropy alloys were prepared by mechanical alloying, the relation of Mg content, thermodynamic parameter and phase structure was researched. The results showed that the prepared high-entropy alloy powders were approximately spherical particles with a diameter about 3 μm. The measurements of X-ray diffraction (XRD) and analyses of energy-dispersive X-ray spectrometry (EDS) revealed that Mg had a high solid solubility in BCC (body center cubic) lattice. The results of thermodynamic calculation showed that the alloys (x=0.6~1.4) had a single BCC1 phase when 8.68%≤δ≤9.77% (δ was atomic radii mismatches), 14.78 J/(mol?K)≤ΔSmix≤14.82 J/(mol?K) (ΔSmix was mixing entropy) and –14.13 kJ/mol≤ΔHmix≤–6.76 kJ/mol (ΔHmix was mixing enthalpy). However, the alloys (x=1.6~1.8) consisted of BCC1 and BCC2 phases when 10.0%≤δ≤10.1%, 14.65 J/(mol?K)≤ΔSmix≤14.74 J/(mol?K) and –5.40 kJ/mol≤ΔHmix≤–4.19 kJ/mol. When x≥2.0, Mg content exceeded the solid solubility of Mg in BCC1 and BCC2 lattices. As a result, Mg2.0TiAlFeNiCr alloy contained the main phases BCC1 and BCC2 and the minor phases Mg and intermetallic compound. The lattice constant (a) of BCC1 and BCC2 were determined respectively to be 0.289 and 0.291 nm by the XRD measurement and high resolution transmission electron microscope (HRTEM) analysis. For BCC1 phase, Fe acted as a solvent element whereas Mg, Ti, Al, Ni and Cr behaved like solute elements. For BCC2, however, Cr acted as a solvent element whereas Mg, Ti, Al, Fe and Ni behaved like solute elements. Compared with BCC1, high Mg content was achieved in BCC2 phase. Moreover, BCC1 and BCC2 displayed a semicoherent interface. The MgxTiAlFeNiCr (x=0.6~2.0) high-entropy alloys exhibited a good corrosion resistance in 3.5wt% NaCl solution. But the corrosion resistance decreased with the increasing of Mg in the alloys.

Preparation of W18O49/PET-ITO flexible electrochromic film and its performance

Jiangbo SUN Jie ZHANG Di WANG Jiangyin LU Yanbin CUI

Chin. J. Process Eng.. 2019, 19(2):  400-406.  DOI: 10.12034/j.issn.1009-606X.218218

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Due to the limited energy resource on earth, energy saving is critical for the sustainable development. Therefore, ways to reduce energy consumption and energy-saving materials are highly desirable. The optical properties (coloring/bleaching) of electrochromic (EC) materials can be changed by a reversible electrochemical process. EC materials are suited to energy saving because the amount of light and heat entering building or automobile can be controlled by changing the transmittance of light. EC materials have shown widespread applications, such as smart windows for energy-saving buildings, low-power displays, self-dimming rear mirrors, electrochromic e-skins, etc. So far, many inorganic and organic materials have been used as EC materials, such as transition metal oxides, Prussian blue, viologens, conducting polymers, and so on. Among these materials, tungsten oxide has attracted considerable attention due to its multiple oxidation states. In this work, W18O49 nanowire was prepared by solvothermal method and sprayed on a PET?ITO (35 Ω square) flexible transparent conductive substrate to obtain W18O49/PET?ITO flexible EC film. The microstructures and valence states of W18O49 nanowire were characterized by XRD, SEM, high-resolution transmission electron microscopy and XPS. The optical modulation range, response time and cycle stability of W18O49/PET?ITO flexible EC film were characterized and analyzed by electrochemical workstation and UV?visible spectrophotometer. The experimental results indicated that the optical modulation range (ΔT) of W18O49/PET?ITO flexible EC film was 23% when the EC film was scanned at the wavelength of 633 nm. The time for colored and bleached switching of W18O49/PET?ITO flexible EC film were 12.8 and 10.6 s when the optical transmittance change of EC film was 90%. Moreover, the W18O49/PET?ITO flexible EC film had excellent cycle stability. The optical transmittance changes of W18O49/PET?ITO flexible EC film was still high (80.9%) when the film was continuous switched between colored and bleached state for 3000 s.

Effect of ρ-Al₂O₃ addition on the properties of in situ reaction-bonded porous SiC membrane support

Zhiyong LUO Kaiqi LIU Wei HAN Wenqing AO Yunfa CHEN

Chin. J. Process Eng.. 2019, 19(2):  407-412.  DOI: 10.12034/j.issn.1009-606X.218225

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The silicon carbide ceramic membrane support bonded by mullite (3Al2O3?2SiO2) which formed by in situ reaction has good thermal shock resistance, however, few studies have been made for in situ reaction by adding ρ-Al2O3. In this paper, the porous SiC membrane support using black silicon carbide as aggregate, and by adding different content of ρ-Al2O3, was prepared by the reaction of Al2O3 and SiO2 which produced by the oxidation of the SiC particles surface under pressureless sintering at 1430℃ for 3 h in a muffle furnace. The effects of ρ-Al2O3 addition on the phase composition and properties of silicon carbide support were studied. The results showed that the mullite content in the bonding phase increased with the addition amount of ρ-Al2O3 powder increased, and the cristobalite content decreased relatively but could not be completely eliminated. The interconnected pores of support were produced mainly by SiC coarse particles (150?180 μm) packing. The surface of SiC was oxidized to amorphous SiO2 that further crystallized to form cristobalite during sintering at higher temperatures in air. Meanwhile, pre-added ρ-Al2O3 eventually converted into highly activated α-Al2O3 after a series of crystal transformation with increasing temperature. The mullite was formed by in situ reaction between the obtained cristobalite and α-Al2O3 at higher temperature. SiC particles were strongly bonded by mullite and oxidation-derived SiO2 to obtain porous SiC membrane support. The open porosity of the samples decreased from 37.4% to 34.8% with the amount of ρ-Al2O3 powder increasing from 3wt% to 15wt%, and the air permeability of the samples dropped from 1127.8 m3?cm/(m2?h?kPa) to 210.4 m3?cm/(m2?h?kPa) with median pore diameter reduced, accordingly. However, the bending strength increased at the first stage and then decreased with the increase of ρ-Al2O3 powder addition. The support with the flexural strength of 25.1 MPa and air permeability of 372.7 m3?cm/(m2?h?kPa) were developed by adding 9wt% ρ-Al2O3. The porous SiC membrane support could meet the needs of high temperature gas filtration under normal pressure.

Preparation and properties of naphthalenesulfonic acid type polysulfone proton exchange membrane

Zongwen QIAO Long MENG Tao CHEN

Chin. J. Process Eng.. 2019, 19(2):  413-418.  DOI: 10.12034/j.issn.1009-606X.218235

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With 1,4-bischloromethyoxyl butane as chloromethylated reagent, the chloromethylated polysulfone (CPS) was obtained by introducing chloromethyl group onto main chain of bisphenol type A polysulfones (PS) according to Fridel?Crafts alkylation reaction. Subsequently with 2-naphthol-6,8-disulfonic acid dipotassium (HNS) as nucleophilic reagent, the naphthalenesulfonic acid type side chain sulfonated polysulfones (PS-NS) were prepared by nucleophilic substitution reaction. Their chemical structures were characterized by FT-IR and 1H-NMR. The relationship between nucleophilic substitution reaction and factors was explored and the appropriate reaction conditions were found. The corresponding proton exchange membranes (PEMs) were fabricated by solution casting method and the basic properties of PEMs including water uptaking and proton conductivity were explored. The results showed that the nucleophilic substitution reaction was SN1 reaction. The appropriate reaction solvent was dimethyl sulfoxide (DMSO) which had strong polarity, the appropriate reaction temperature was 100℃ and the appropriate reaction time was 40 h. The bonding amount of sulfonate acid group reached up to 1.51 mmol/g at the appropriate reaction conditions. The corresponding PEMs indicated excellent water uptaking and proton conductivity due to the side chains structure enhancing the degree of micro-phase by locating the sulfonic acid groups far away from the hydrophobic polysulfone main chains. The water uptaking and proton conductivity of PEMs increased with the bonding amount of sulfonic acid group increasing. The water uptaking and proton conductivity of PEMs reached up to 21.3% and 0.049 S/cm at room temperature, respectively. The properties of PEMs could meet the demand of actual application of proton exchange membrane fuel cells, and these properties were very close to the commercialized Nafion117 series proton exchange membranes.

Effect of polyaniline particles on corrosion resistance of waterborne epoxy resin coatings

You FENG Jingkun ZHANG Yang XUE Haosheng WANG Donghai ZHANG Yunfa CHEN

Chin. J. Process Eng.. 2019, 19(2):  419-426.  DOI: 10.12034/j.issn.1009-606X.218237

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Conductive polyaniline (PANI) particles were synthesized by chemical oxidation polymerization using hydrochloric acid as dopant, ammonium persulfate as oxidant and imidazole ionic liquid as stabilizer. Polyaniline waterborne epoxy anticorrosive coating was prepared by dispersing as-prepared polyaniline into waterborne epoxy resin (ER). And the effects of polyaniline particles on the corrosion resistance and mechanical properties of the coating were studied. Electrochemical impedance spectroscopy (EIS) results of the coating showed that the addition of polyaniline significantly improved the barrier properties of the aqueous epoxy coating. The impedance (|Z|f=0.01Hz) of all PANI/ER coatings were higher than pure ER coating. ER coating had the best barrier performance when adding 5.0wt% PANI, the |Z|f=0.01Hz value during 0~168 h immersion was stable at around 8.0?108 Ω?cm2 and after immersion for 168 h was 7.5?108 Ω?cm2, which was much higher than ER and other PANI/ER systems. The neutral salt spray test showed that the addition of polyaniline imparted the coating of the ability to passivate corrosion, significantly improving the corrosion resistance of the coating. The higher the PANI amount, the better the corrosion resistance. The bending and impact tests showed that the mechanical properties of the coating increased first and then decreased with the increase of polyaniline content. When the addition amount of polyaniline did not exceed 5.0wt%, the mechanical properties of the coating were excellent and the adhesion and toughness were both very good. When the PANI addition amount increased to 7.0wt%, the brittleness of the ER coating was remarkably strong, and the mechanical properties were degraded. The optimum addition amount of polyaniline in the aqueous epoxy system was 5.0wt%. Under this condition, the mechanical properties of the coating were good and the comprehensive anticorrosion performance was optimal.

Preparation and properties of copper slag-based oxalate cement

Hao WANG Zhongqiu LUO Xintao ZHOU Naqiu LI Jianhui ZHANG Sen HE

Chin. J. Process Eng.. 2019, 19(2):  427-433.  DOI: 10.12034/j.issn.1009-606X.218241

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Mixing according to a certain ratio, the copper slag and the oxalic acid were used as raw materials to prepare the copper slag-based oxalate cement by an acid-base reaction. The influence of the mass ratios of copper slag to oxalic acid (CS/OA) and water to cement (W/C), the retarder type and its content on the mechanical properties and setting time of copper slag-based oxalate cement ware discussed. The morphology and phase composition of the copper slag based oxalate cement were analyzed by SEM and XRD. The results showed that with the increase of mass ratios of CS/OA and W/C, the compressive strength increased first and then decreased, and the setting time decreased with the increasing of CS/OA and increased with the increasing of W/C. The borax and the sodium tripolyphosphate had a very negative influence on the compressive strength of the material, which lead to a significant decrease in the mechanical properties of the material as the amounts of the borax and the sodium tripolyphosphate increased. The proper amount of the boric acid can improve the compressive strength of the material and had a good retarding effect, therefore, the boric acid was preferred as a retarder. The material properties were optimum when CS/OA was 4, the W/C was 0.16?0.17, and the boric acid content was 2.5wt%. Its compressive strength reached 38.5 MPa after curing 28 d and the setting time was 24 min. The main hydration product of the copper slag based oxalate cement was a column type FeC2O4?2H2O, which has a dense structure and good crystallization. The addition of the borax and the sodium tripolyphosphate could cause stomata and gap in the copper slag based oxalate cement structure, while the boric acid could promote the hydration reaction to optimize crystallization of the hydrated product without compromising the compactness of the material structure.

Environment & Energy

Application of phosphorus-doped sunflower disk-based activated carbon in anode materials of lithium ion batteries

Xianjun XING Jianhua LIU Wenquan WANG Zeyu CHEN Yixuan FU

Chin. J. Process Eng.. 2019, 19(2):  434-439.  DOI: 10.12034/j.issn.1009-606X.218220

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Lithium ion batteries (LIBs) have progressively attracted researchers in recent years because of their environmental friendliness and adequate resources. In order to take full advantages of the active carbon in nature, the cheapest and most efficient negative electrode material for lithium ion battery is in great need. Because sunflower was fully-infected compositae, the sunflower disk had a more stable nanostructure than other biochars. Moreover, the sunflower dish is not only rich in nitrogen and oxygen element, but also widely distributed in the world. In this work, P-doped activation carbon composites were prepared to achieve excellent electrochemical performance in rechargeable LIBs. Phosphorus-injected biomass activated carbon was prepared with simple hydrothermal and calcine methods. The characteristics of activated carbon were then tested with field emission scanning electron microscope (FE-SEM), transmission electron microscope (TEM), X-ray diffractometer (XRD), Raman spectrometer, Brunauer Emmett Teller (BET), etc. When these products were applied in lithium ion battery anode materials, the electrodes achieved high energy density and Coulombic efficiency, and cycling stability simultaneously. When the battery cycling at the current density of 500 mA/g, the elementary charge capacity reached to 1052 mAh/g, with the Coulombic efficiency of 48.9%. After 200 cycles, the capacity still maintained 1000 mAh/g or more. However, activated carbon capacity of the contrast sample without phosphoric acid activation can only be maintained at 300 mAh/g, which was similar to ordinary carbon materials. Hence, the preparation method of the P-doped biomass resulting in activated carbon was simpleness, and the raw material was low cost and environmentally friendly. Most importantly, the electrode potential of the material was low, and the discharge platform remained stable, which was of great research value in the lithium ion battery in a commercial application.

Experimental study on desulfurization and denitration of sintering flue gas by activated carbon mixed with steel slag

Xiaobai YANG Yunlong HAN Yinggen LI Hao ZHANG Fuping QIAN Yongmei HU

Chin. J. Process Eng.. 2019, 19(2):  440-446.  DOI: 10.12034/j.issn.1009-606X.218257

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Absorbent, i.e. activated carbon mixed with steel slag was prepared by mixing method for desulfurization and denitration of sintering flue gas. The samples of absorbent were characterized by XRF, BET, SEM and FT-IR. Experiments of desulfurization and denitration of simulated sintering flue gas were carried out in a programmable electrically heated fixed-bed reactor. The effects of reaction temperature, SO2 concentration, concentration ratio of [NH3]/[NO] and O2 content were considered. The results showed that the maximum desulfurization and denitration rates were 79% and 34%, respectively, under the conditions of contents of SO2 0.06vol%, NO 0.04vol%, O2 15vol% and at 120℃ of reaction temperature. When NH3 was introduced into the reactor with concentration ratio of [NH3]/[NO]=1, the desulfurization and denitration rates increased. When NH3 existed, activated carbon mixed with steel slag kept high desulfurization efficiency. The steel slag had a certain catalytic reduction effect. The denitration rate decreased with the increase of reaction temperature. The increase of O2 content can promote the absorption of NO and SO2 by activated carbon mixed with steel slag. Combined with characterization analysis, it was found that the specific surface area of the absorbent reduced by the mixing with steel slag. But activated carbon mixed with steel slag contained a certain amount of Fe2O3 which has a certain catalytic reduction effect and can increase the denitration efficiency. At the same time, the addition of steel slag can also utilize rationally solid waste so as to achieve the purpose of "treatment of pollutants with solid waste".