Table of Content

22 August 2019, Volume 19 Issue 4

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Contents

Cover and Contents

Chin. J. Process Eng.. 2019, 19(4):  0. 

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Frontier Forum

Coupling of coarse-grained discrete particle method and particle-in-cell method for simulation of gas-solid flow

Fei-guo CHEN Wei GE

Chin. J. Process Eng.. 2019, 19(4):  651-660.  DOI: 10.12034/j.issn.1009-606X.218338

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Eularian?Lagrangian (EL) methods for the simulation of gas–solid flow are advantageous over Eularian–Eularian (EE) methods in terms of their more rigorous treatment of the particle motion and particle–particle interactions. But conventional EL methods are limited in the number of handled particles. Coarse-grained discrete particle method (CG-DPM) and multiphase particle-in-cell (MP-PIC) are two main methods in this category to increase the simulation scales by treating particle swarms as single computational particles. They are found to be more suitable for dense and dilute particle suspensions, respectively and hence coupled in this study to establish a more general, accurate and efficient EL method. The optimum coupling parameters are determined by comparing the flow patterns from different methods and quantitative analysis on their particle fraction distributions.

Flow & Transfer

Experimental test on heat exchanger performance of air conditioning with microchannel evaporator

Jinli LU Yajin LIU Yafang HAN Bangjie CHI Fuping QIAN

Chin. J. Process Eng.. 2019, 19(4):  661-667.  DOI: 10.12034/j.issn.1009-606X.218313

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With the advantages of high level of integration, high heat exchange efficiency, and low pressure drop penalty in refrigerant side, the refrigerant charge can be reduced effectively in microchannel evaporator, and the size and weight of heat exchanger also can be reduced, therefore the system energy efficiency can be improved effectively. In this work, an experimental system was designed and set up to research the performance of microchannel evaporators. The inlet and outlet temperature distribution of microchannel flat tube were measured. And the variations of inlet and outlet temperature difference, pressure drop, input power, cooling capacity, coefficient of performance with environmental chamber were also analyzed. In addition, the experimental results were compared with conventional finned-tube evaporators under the conditions of ambient chamber temperature in the range from 18 to 23℃. The experiment results indicated that microchannel evaporator had better distribution behavior of refrigerant and can improve the temperature uniformity of air-condition vent. The pressure drops of microchannel evaporator and finned-tube evaporator increased with the increasing of environmental chamber temperature. As the reason that refrigerant charge of microchannel evaporator was lower than finned-tube evaporator and the refrigerant flow path was also shorter than finned-tube evaporator, the maximum pressure drop between two evaporators was 111 kPa under the same temperature. The average pressure drop penalty of microchannel evaporator was reduced by 33.9% compared to the finned-tube evaporator. The compressor power consumption can be reduced by using microchannel evaporator. The system input power of microchannel evaporator was lower than that of finned-tube evaporator and the maximum value was 4.12%. Compared with finned-tube evaporator, the cooling capacity of microchannel evaporator increased by 2.95% and the system coefficient of performance improved by 6.69% under the same temperature of environmental chamber from 18 to 23℃. Based on the above researches, these experimental results can provide data support for application of microchannel evaporator.

Mixing efficiency of a concrete ribbon mixer and DEM simulation

Zechu LIAO Wei GAO Lei LIU Shengqiang JIANG Yuanqiang TAN

Chin. J. Process Eng.. 2019, 19(4):  668-675.  DOI: 10.12034/j.issn.1009-606X.218307

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The ribbon concrete mixer with double barrels is commonly used to improve the uniformity of the fresh concrete in construction industry. In order to investigate the mixing efficiency of this kind of ribbon concrete mixer, a discrete element method was used to simulate the mixing process of fresh concrete. Firstly, a discrete element model of the fresh concrete was established by using the Hertz?Mindlin with JKR contact method. The experiment processes, i.e. slump test, L box test and rheometer test were simulated by using this discrete element model and its parameters, and the simulation results were compared with the experimental ones to verify these model parameters. Afterwards, the mixing efficiencies under different initial loadings were investigated and the mixing efficiency under top?bottom loading was highest. Under each initial loading, the mixing efficiency of the fresh concrete in mixer's left region and front region was almost the same as that in their opposite regions respectively, while the mixing efficiency in the upper region was much higher than that in the lower one. Besides, a mixing blind area was found near the outlet in the bottom of the mixer, and the method of discarding the initial concrete discharge was proposed to improve the uniformity of fresh concrete. In addition, the effects of rotational speed on the mixing efficiency were investigated, and it was found that the mixing efficiency with a larger rotational speed tended to be higher. However, their mixing efficiencies were almost the same at the same rotation number of impeller. This numerical model and results provided an effective approach to solve the concrete mixing problems in industry and some scientific references for improving the mixing efficiency of a double ribbon concrete mixer.

Model construction and influence factor analysis of gas-liquid mass transfer in a fine-bubble oxidation ditch

Fengxia LIU Yongqiang LI Xiaofei XU Xin DONG Zhijun LIU

Chin. J. Process Eng.. 2019, 19(4):  676-684.  DOI: 10.12034/j.issn.1009-606X.218305

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The gas–liquid flow model and dissolved oxygen transport model in a fine-bubble oxidation ditch were established based on ANSYS Fluent software. Reliability of the model was verified under different operating conditions. The deviation between volumetric mass transfer coefficient obtained by simulation and experiment was less than 7%. Then, the effect of bubble diameter, aeration flow rate and transverse flow intensity on oxygen mass transfer were investigated by the verified model. The results indicated that as the bubble diameter increased from 1.5 mm to 3 mm, the volumetric mass transfer coefficient decreased from 15.80 h?1 to 5.83 h?1 and as the aeration flow rate increased from 0.5 m3/h to 2 m3/h, the volumetric mass transfer coefficient increased from 4.21 h?1 to 14.15 h?1. The volumetric mass transfer coefficient could be considerably improved by decreasing the bubble size and increasing the aeration flow rate. The distribution of dissolved oxygen and effect of oxygen mass transfer in the oxidation ditch would be affected by transverse flow intensity. Compared with operational condition with aerating only, the volumetric mass transfer coefficient increased by 27.7% and 42.4% respectively when single and double impellers were introduced in combination with aerating. The transverse flow could enhance the gas holdup in bubble plume and thus improve the effect of oxygen mass transfer.

Numerical analysis on dynamics and heat transfer progress of a granulated molten slag particle by gas

Yiming FAN Jingfu WANG

Chin. J. Process Eng.. 2019, 19(4):  685-692.  DOI: 10.12034/j.issn.1009-606X.218292

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In order to investigate the dynamics and heat transfer progress and characteristics of granulated molten blast furnace slag by blast air, a mathematical model was established and solved through the fourth order Runge?Kutta algorithm, the calculation program was compiled by FORTRAN. Considering that the efficiency of air cooling was low, a method of spray cooling was presented to improve the cooling rate. And the effects of varied particle size on movement and cooling were also researched. The variations of main thermal physical properties of slag and air with temperature were taken into account during the calculation progress that in order to enhance reliability of the study. And the temperature recovery method was used to deal with the solidification of molten slag. The results indicated that the motion trail of the slag particle was parabolic curve after granulation, and velocity of the slag particle was firstly increased and then decreased by the influence of quenching gas during the flight, the cooling rate of slag particle was mainly influenced by the convective heat transfer coefficient which varied with the relative velocity of blast air and slag particle. Meanwhile, the cooling rate of slag particle was significantly improved due to the addition of spray because of the evaporation of droplet and enhancement of convective heat transfer. The final temperature of the slag particle reduced with the decreasing particle size, which meaned that the smaller particle size can make better cooling effect. And the motion parameters of the particle which had smaller size was more susceptible to the blast air. Generally, the smaller size of slag particle, the better of blast air cooling, and the smaller the space needed for granulation.

CFD optimizations of spiral-wound heat exchangers

Xu ZHANG Mingkai LI Ping LU Fang BAI Chuan ZHOU Chao HUA

Chin. J. Process Eng.. 2019, 19(4):  693-703.  DOI: 10.12034/j.issn.1009-606X.218262

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As a new kind of efficient and compact heat exchange equipment, spiral-wound heat exchangers which has the characteristics of high heat transfer efficiency, high degree of intensification, less floor space and so on can realize heat transfer among multiple logistics. These advantages can decrease the overall investment. Although many scholars have studied the spiral-wound heat exchangers by numerical simulation, the effects of every operating parameter on the flowing and heat transferring in the shell domain still need to be studied deeply. In this work the shell fluid field of a simplified spiral-wound heat exchanger was simulated by finite volume method based on finite element method with the commercial software ANSYS CFX. By changing the helical leads of spiral tubes and shell inlet velocities, the flow characteristics and heat transfer performance of the shell fluids in spiral-wound heat exchangers were discovered. What is more, some beneficial reference basis was provided for the optimization designs of the spiral-wound heat exchangers. The results showed that the less the helical leads of spiral tubes in the spiral-wound heat exchangers, the higher vorticity and turbulence of the shell fluid domain, the less the temperature dead zone, the better the heat transfer performance between the shell fluid domain and tube fluid domain. Furthermore, reducing the helical leads of spiral tubes in the spiral-wound heat exchangers could make the pressure distribution in the shell fluid domain more balance, which reduced the damage caused by the pressure difference between different regions in the shell fluid domain. Increasing the inlet velocity of shell fluid field was beneficial to enhance heat transfer performance between the shell fluid domain and the tube fluid domain, the pressure drop between the inlet of the shell fluid domain and the outlet of the shell fluid domain increased.

Feature extraction and distribution of continuous phase in direct contact boiling heat transfer process

Wenzhen XIONG Jianxin XU Junwei HUANG

Chin. J. Process Eng.. 2019, 19(4):  704-713.  DOI: 10.12034/j.issn.1009-606X.218229

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Based on support vector machine (SVM) theory, a continuous phase feature extraction method for organic working fluid and heat conducting oil direct contact boiling heat transfer was constructed, and the two-phase flow pattern topological structure was obtained. Continuous phase feature extraction and homology group calculation were carried out for two-phase flow images of 9 sets orthogonal experimental conditions, the continuous phase quantizing the quantity index ?1 and the bubbles estimation number index ?0 were obtained, then the traditional digital image processing methods were compared and analyzed. The influence of morphological opening operation on SVM method was compared between in better and worse of the heat transfer efficiency. The number of bubble groups obtained from the traditional method and the quantitative evolution rule of the continuous phase hole obtained by the SVM method were compared. The results showed that SVM combined with Betty number method can not only accurately quantify the continuous phase of heat conduction oil, but also roughly represent the dispersed phase of bubbles. It was found that the number of continuous phase changes almost overlapped and relatively small fluctuation in L6 condition (thermal conductive oil height Z=0.5 m, initial temperature difference ?T=120℃, working medium flow rate U0=0.04 m/s, thermal conductive oil flow rate Uc=0.15 kg/s), but the number of continuous phases deviated from a larger degree in L4 condition (Z=0.5 m, ?T=80℃, U0=0.06 m/s, Uc=0.3 kg/s). The relationship between the evolution rule of Betty number and heat transfer efficiency was established. The evolution curves of continuous phase and bubble group number showed synchronization, and the time of mixing was the same. The local minimum of the median distance between the two numbers can be used as one of the performance indicators, the best heat transfer condition was selected through experiment. This method can be used to study a series of problems concerning the quantitative evolution of two phase flow topological structure.

Reaction & Separation

Removal of Cr(VI) from water by granular activated carbon supported nanoscale zero-valent iron

Jian LIU Li HUANG Gang PENG Zhengji YI

Chin. J. Process Eng.. 2019, 19(4):  714-720.  DOI: 10.12034/j.issn.1009-606X.218294

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The removal rate of Cr(VI) from water by using granular activated carbon (GAC) supported nanoscale zero-valent iron (nZVI) composites (GAC-nZVI) was studied through batch experiments. The GAC-nZVI composites were synthesized from Fe2+ aqueous solution by traditional liquid-phase reduction technique with NaBH4 as a reducing agent. The composites were characterized by SEM. The effects of pH value, reaction temperature, GAC-nZVI composites addition and initial Cr(VI) concentration on the removal rate of Cr(VI) were studied. The removal processes were analyzed by a pseudo first-order kinetic model. The results showed that granular activated carbon supports could effectively prevent nanoscale zero-valent iron particles from aggregating together. Synthesized GAC-nZVI composites was efficient in removing Cr(VI) from water, 99.4% of Cr(VI) was removed from water containing 50 mg/L Cr(VI) within 5 min using 3.0 g/L GAC-nZVI composites at pH 2.0 and 40℃. The total Cr concentration in treated water was below 1 mg/L at pH 2.0?4.0, suggesting that little Cr(III) was residue. When pH was 1.0, the removal rate of Cr(VI) reached 98.8% within 2 min, but the total Cr concentration in water after reaction was 32.506 mg/L. The removal rate of Cr(VI) decreased with the increase of pH value and initial Cr(VI) concentration, and increased with the increase of reaction temperature and GAC-nZVI composites addition. Pseudo first-order kinetic model was suitable for describing the removal process of Cr(VI), and the fitting correlation coefficients R2 were all over 0.98 (except R2=0.9367 with GAC, R2=0.9277 when pH=3.0). The reaction rate constant (k) of GAC-nZVI composites was 0.19797 min?1, it was 86 times of original granular activated carbon (0.0023 min?1) at the same experimental conditions. The reaction rate constant increased with decreasing the initial pH value or increasing the reaction temperature and GAC-nZVI composites addition.

Impurity removal from leaching solution of laterite nickel ore and preparation of nickel hydroxide

Chaoqun NIE Xubin WANG Bo LI Yonggang WEI Hua WANG

Chin. J. Process Eng.. 2019, 19(4):  721-727.  DOI: 10.12034/j.issn.1009-606X.218309

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With sulphuric acid leaching solution of low-grade silicon?magnesium nickel laterite ore as raw material, iron was removed by jarosite precipitation, magnesium was removed using sodium fluoride, nickel was precipitated and neutralized from the leaching solution. The effects of different factors on the removal rates of iron and magnesium, and the loss rate and extraction rate of nickel were investigated. The results demonstrated that after oxidative pretreatment of the leaching solution by adding 4 mL/L hydrogen peroxide solution, the removal rate of iron reached 92.1%, the loss rate of nickel was 6.7%, and the main phase in the residue was jarosite [Na2Fe6(SO4)4(OH)12] with Na2SO4 as sodium source for iron removal, solution pH controlled within 1.6?2.2 and reaction time of 1.5 h. After iron removal, magnesium ions in the filtrate were removed using sodium fluoride. Under the best conditions of stirring speed 300 r/min, solution pH 5.5?6.0 and addition of sodium fluoride 25 g/L, the removal rate of magnesium reached 90.9%, and the loss rate of nickel was 6.8%. After the removal of impurities, nickel in the purified solution was extracted by neutralization and hydrolysis with NaOH as precipitating agent. At room temperature, addition of 8 g/L NaOH, extraction rate of neutralized and precipitated nickel was 95.1%. Nickel hydroxide products with purity of 99.5%, with an overall recovery rate of nickel of 82.70%. The removal of impurity elements in the leachate and the extraction of valuable metal nickel are realized, which provides technical support for the efficient utilization of the silico?magnesium type laterite nickel ore.

Extraction of hydroxycobalamin with the method of macroporous resin adsorption

Jun YANG Ziqiang WANG Yunshan WANG Wanzhong ZHANG Zhiguo SU

Chin. J. Process Eng.. 2019, 19(4):  728-734.  DOI: 10.12034/j.issn.1009-606X.218311

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Propionibacterium freudenreichii is regarded as a GRAS (generally recognized as safe) strain, and has been successfully applied to industrial anaerobic production of deoxyadenosylcobalamin, known as the natural structure of vitamin B12. Generally, due to the unstable of deoxyadenosylcobalamin, it needs to be converted to cyanocobalamin by cyanidation during the subsequent extraction and purification steps. Hydroxycobalamin is another form of vitamin B12 and widely used in the treatment of neurological diseases and cyanide poisoning. For the industrial production of hydroxycobalamin, cyanocobalamin is usually used as the raw material and then deacylated to form hydroxycobalamin. According to this principle, the production of hydroxycobalamin involves multiple chemical reactions, including cyanidation and deacylation, along with the high cost, environmental pollution, and hazardous conditions to the operators. To avoid these disadvantages, the photolysis production of hydroxycobalamin directly from deoxyadenosylcobalamin was proposed. In this work, the adsorption and extraction of hydroxycobalamin in the deoxyadenosylcobalamin photolysis solution were studied. The adsorption properties of 8 kinds of different macroporous resins on hydroxycobalamin were compared, and the effects of pH and ethanol concentration on hydroxycobalamin adsorption and desorption were discussed. The loading and elution velocity were optimized to improve the hydroxycobalamin yield. The results showed that LX-50B macroporous resin had the best adsorption performance for hydroxycobalamin in the static adsorption process. The adsorption capacity of LX-50B macroporous resin reached 203.87 mg/g at pH 6.0. For hydroxycobalamin eluent, 60% ethanol solution with pH 2.0 was the best choice. The optimal loading velocity and elution velocity were 2 and 0.5 BV(bed volume)/h, respectively. Under the above conditions, the concentration of hydroxycobalamin in the elution was 1863.32 mg/L, improved by 35 times compared with the original photolysis solution, while the purity of hydroxycobalamin increased from 0.38% to 15.73%, with an acceptable extraction yield of 92.46%, which achieved to a good extraction and preliminary purification result.

Dissolution behavior of main minerals in hydrothermal leaching process of LF refining spent slag

Huanyu HE Weiwei HOU Hongling LIU Yang LI

Chin. J. Process Eng.. 2019, 19(4):  735-741.  DOI: 10.12034/j.issn.1009-606X.218325

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Ladle furnace (LF) refining spent slag is a by-product of molten steel refining process. The reutilization of LF refining slag is rare because of the high content of sulfur in the slag. However, the hydrothermal leaching method can effectively reduce the sulfur content in refining slag and the leached slag has high recycling value. As a composite mineral consisting of a variety of single mineral phases, many components of the refined slag dissolve into the solution during the hydrothermal leaching process, forming a multi-component complex leaching system. It is of great significance to study the dissolution behavior of LF refining slag in hydrothermal leaching process for the recycling of waste residue resources. In order to investigate the dissolution behavior of refining slag, the leaching behavior of LF refining slag and its two main mineral phases (12CaO?7Al2O3 and 2CaO?SiO2) by hydrothermal leaching treatment were studied and the difference between them was compared. The results showed that the pH value of leaching solution was higher than 12 during the leaching process. With the increase of leaching time, both the concentration of Ca and the conductivity of solution increased subsequently, but the concentration of Al decreased sharply. Furthermore, the concentration of Si with a low concentration of less than 0.1 mg/L remained constant. With the increase of time, in the leaching processing of 12CaO?7Al2O3, the pH value of leaching solution was stable with around 11.3, the concentration of Al improved, and the concentration of Ca decreased slightly. Whereas for 2CaO?SiO2, the leaching solution with low concentration of Si (lower than 0.6 mg/L) mainly contained Ca2+. Overall, the pH value and the concentrations of Al and Si of the leaching solution of the slag were close to those of single mineral phase. The dissolution behavior of LF refining slag in hydrothermal leaching process can be studied by the dissolution behavior of single mineral phase. However, the concentration of Al and Si were lower than that of single mineral phase, indicating that the dissolution of 12CaO?7Al2O3 and 2CaO?SiO2 in slag were restricted by the dissolution of CaO and other components.

Process & Technology

Temperature field simulation of thick galvanized sheet in radiant tube furnace

Xican ZENG Fangqin DAI Yue GUO Luwei PAN Jiangjun KE Jiamou WU Yuansheng LEI Yuncheng LI

Chin. J. Process Eng.. 2019, 19(4):  742-749.  DOI: 10.12034/j.issn.1009-606X.218324

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Based on the energy balance, the energy equations of the furnace gas, furnace wall, radiant tube surface and strip surface were established by the ternary method for radiation tube furnace (RTF) of process section of the continuous hot-dip galvanizing line, and the energy exchange between the model sections was shielded to achieve the effect of accelerating calculation and the dynamic adjustment need was satisfied. According to the internal heat conduction equation of thick strip steel, the internal temperature field of the strip and the temperature field in the furnace were obtained by the finite-difference method, which was consistent with the on-site detection value. The correctness of the model was verified. Under the assumption of pursuing the highest production efficiency, offline simulation results of an optimized process parameters were achieved. As a result, when the thickness of the incoming strip was 2 mm, the matching running speed reached the speed limit value of the conveyor of 200 m/s. The first heating section opened the maximum fuel flow rate of 255~260 L/min. The second section increased the product temperature while reducing the cross-section temperature difference and improved fuel utilization by reducing the flow rate. 2 mm strip steel corresponding minimum temperature difference was 0.18℃, fuel flow reduced to 174 L/min, corresponding minimum unit energy consumption was 1049 L/t. The maximum temperature difference of 5 mm strip was 0.60℃, the second section fuel flow was 230 L/min, corresponding maximum unit energy consumption was 1071 L/t. Reasonable determination of process parameters was conducive to heating the strip and improving the overall production efficiency.

Numerical simulation on thermal process of recycling jet cooling in heat treatment of strip steel in protective hydrogen atmosphere

Ping'an CHEN Fangqin DAI Yue GUO Luwei PAN Jiangjun KE Jiamou WU Yuansheng LEI Yuncheng LI

Chin. J. Process Eng.. 2019, 19(4):  750-758.  DOI: 10.12034/j.issn.1009-606X.218285

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A one-dimensional unsteady heat transfer model was established for the cyclic spray cooling heat transfer of strip steel protective atmosphere. The temperature field of strip steel was calculated by finite difference numerical calculation method. The comprehensive heat transfer coefficient required of the strip steel at different thicknesses, different initial temperatures and operating speeds were determined. The effects of structural parameters of the spray box and the parameters of the circulating cooling medium on strip steel outlet temperature were studied. The results showed that there was a maximum operating velocity for strip steel with different thicknesses on the premise of meeting the performance requirements and safety. For strip steel with thickness of more than 3 mm, the influence of the section temperature difference on the strip steel properties could not be ignored. The temperature of strip steel outlet increased with the increase of the ratio (H/D) of distance between strip and orifice (H) to orifice diameter (D), but increase rate gradually decreased as ?/D increased. There was an optimal range of the ratio (?n/D) of the orifice spacing (?n) to the orifice diameter (D) which was related to H. Therefore, when actually designing the spray box structure, it is necessary to consider not only the optimal value of D, but also the H. As the temperature of the cooling medium increased by 10℃, strip steel outlet temperature increased by about 3℃. When the volume percentage of hydrogen in the cooling medium and the flow rate of the cooling medium increased, the temperature of strip steel outlet decreased, however, the decrease rate gradually decreased as the volume percentage of hydrogen in the cooling medium and its flow rate increased. The industrial application results showed that the calculated value of the outlet temperature of strip steel was in good agreement with the measured value, and the error was about 3.4% which meant that the model met the application requirements.

Reduction and dilution of melting copper slag by blowing waste cooking oil

Guangping DAI Yu SHI Shiwei ZHOU Bo LI Yonggang WEI

Chin. J. Process Eng.. 2019, 19(4):  759-766.  DOI: 10.12034/j.issn.1009-606X.219114

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Waste cooking oil is a kind of biomass energy that has not been used very well. In this work, waste cooking oil was used as reducing agent to reduce the copper slag by pyrolysis at different temperatures. The pyrolysis experiments at high temperature (1373?1573 K) showed that the pyrolysis products were mainly small molecule reductive substance such as C, H2, CO and CH4. At 1373, 1473 and 1573 K, the conversion rates of carbon deposits were 78.36%, 79.83% and 80.07%, respectively, so after pyrolysis the carbon element in waste cooking oil mainly existed in the form of carbon deposits. Thermodynamic analysis showed that these pyrolysis products had good reduction activity to magnetic (Fe3O4) at high temperature, it was feasible to use waste cooking oil instead of traditional fossil reductant to realize the reduction of magnetic in copper slag. Using N2 as the carrier gas was not only conducive to the waste cooking oil blowing into copper slag at high temperatures, but also agitates the slag through the momentum transfer, increasing the chance of the tiny copper droplets aggregating and growing. Under the optimum conditions of melting temperature 1573 K, flow rate of waste cooking oil 2.055 mL/min, flow rate of carrier gas 3 L/min, blowing time 4 min and settling time 50 min, the content of Fe3O4 in copper slag decreased from 33.40wt% to 1.60wt%, the content of Cu in copper slag decreased from 4.49wt% to 0.49wt%, the Fe3O4 phase was transformed into 2FeO?SiO2 phase. According to the Einstein?Roscoe equation, the decrease of Fe3O4 in slag was favorable to the decrease of viscosity, thus improving the settling conditions of copper droplets. However, increasing the blowing time of waste cooking oil to deeply reduction of Fe3O4 would increase the impurity content in the deposited metal and prolonging the settling time, because of the mechanical entrainment and chemical dissolution of copper slag to the copper, it could not bring a better settlement effect. The final recovery rate of copper in experiment was 89.09%.

Preparation and properties of porous hydroxyapatite for orbital implants

Zhenling SHI Mei YANG Quan JIN Dan MAO Nan XU Ranbo YU

Chin. J. Process Eng.. 2019, 19(4):  767-774.  DOI: 10.12034/j.issn.1009-606X.218306

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The bio-eye porous hydroxyapatite (HAP) orbital implants are attracting considerable attention for the requirement of anophthalmus reconstruction. It is crucial to have the highly interconnected porous structure including appropriate macropores and micropores for improving the penetration and ingrowth of vascular orbital tissues. However, the mechanical strength of HAP to maintain the natural lid shape and prevent damage over time will decrease with the porosity increasing. Addressing this challenge, HAP with good mechanical performance for orbital implants were designed and prepared through a simple process. Hydroxyapatite powders with different particle sizes were synthesized by homogeneous precipitation method using commercially available calcium salt and phosphate salt as raw materials. The effects of addition method of reactants and pH value of system on morphology and composition of HAP powders were investigated. HAP powders were characterized by SEM, TEM, XRD, Raman spectrum and FT-IR. Uniform porous hydroxyapatite bulks were sintered at 1000℃ and fabricated using urea as pore generator and silica sol as binder. Detailed studies were performed to evaluate its structure, porosities, and mechanical properties, emphasizing the effect of different particles size of HAP and feeding content of urea. The results showed that the HAP microspheres with a diameter of 39?154 ?m and rod-shaped HAP powders with a diameter of 10?15 nm and a length of 24?36 nm were prepared. The as-prepared samples were hexagonal hydroxyapatite and had good crystallinity, due to the abundant phosphate and hydroxyl groups on the surface of powders, good biocompatibility can be expected. Nano-sized powders was helpful to the formation of porous bulks and the porosity was controlled by adjusting the amount of urea. The apparent porosity up to 69% and compressive strength reached 8 MPa when the mass ratio of HAP to urea was 1.5:1.

Testing and optimization of gas-liquid filtration performance of folded filter

Jing CHEN Zhongli JI Zhen LIU

Chin. J. Process Eng.. 2019, 19(4):  775-782.  DOI: 10.12034/j.issn.1009-606X.218301

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Clean environment is required in many industrial processes, such as pharmaceutical production, large rotating machinery crankcase ventilation and petroleum refining, because liquid droplets can corrode and clog the equipment. As an important branch of filtration, the purpose of gas?liquid filtration is to effectively remove liquid droplets from gas. In this work, according to the ISO-8573-2 standard, a gas?liquid filtration performance testing system of folded filter was established. The effect of oil mist loading rate and filter apparent velocity on the gas?liquid filtration performance of cylinder folded filter element were studied. The effects of the coating binder on the filter surface pressure drop and filtration efficiency were analyzed. The results showed that the tensile strength of the filter material increased, and the pore size of the material decreased significantly after coating binder. Filtration pressure drop of folded filter had the same trend as that of winding filter because of the same filtration mechanism. With the increase of the oil mist loading rate, the number of liquid transport channels in the filter layers increased, and channel pressure drop rose because more oil droplets were transported per unit time through filter,. The initial pressure drop grew up with the increase of filter apparent velocity. The binder mainly coalesced in the area where the filter glass fiber was dense and low permeability, because of uneven glass fibre. Coating binder had less influence on the pressure drop of the folding filter. With the increase of filter apparent velocity, the filtration efficiency increased, because entrainment was inhibited. In the case of high concentration and low filter apparent velocity, due to binder coalesced on filter material inhibits entrainment, the filtration efficiency increased obviously. The binder peeled off as filter apparent velocity increased, and the filtration efficiency of filter coated with binder decreased significantly.

Effects of modified bauxite on the pyrolysis and gasification of rice straw

Jinde WANG Haipeng PEI Baosheng JIN Xin DAI Yiqing SUN

Chin. J. Process Eng.. 2019, 19(4):  783-791.  DOI: 10.12034/j.issn.1009-606X.218317

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The effects of modifiers of bauxite and its concentration and reaction temperature on the pyrolysis of rice straw were investigated in the fixed bed reactor. According to the results, the optimum modifiers and concentration and reaction temperature were selected for the rice straw gasification experiment, which was conducted in the bubbling fluidized bed reactor. The influences of modified bauxite on the gasification characteristics and the tar yield of rice straw were studied in a bubbling fluidized bed reactor. The results showed that the effects of bauxite modified by different modifiers on the gasification characteristics of rice straw were different, and the four kinds of modifiers catalytic ability were CaCl2<Fe(NO3)3<CuCl2≈Ni(NO3)2. The effective coating of bauxite multiplied with the concentration increasing of CuCl2 modifier, and the amount of pyrolysis gas rose correspondingly. The low heat value of rice straw pyrolysis gas increased from 2.93 MJ/Nm3 to 3.89 MJ/Nm3. Furthermore, the increase of reaction temperature improved the components of pyrolysis gas. Compared with 650℃, the gas production of CO, H2 and CH4 increased by 40.6%, 110.8% and 70.0% at 800℃, and the low heat value of rice straw pyrolysis gas increased from 1.74 MJ/Nm3 to 4.09 MJ/Nm3. The modified bauxite improved the gas components of rice straw and reduced tar component and tar production rate. The content of tar decreased from 27.01 g/m3 to 20.09 g/m3 and tar production rate decreased from 29.06 g/kg to 23.10 g/kg. Meanwhile, the low calorific value of rice straw gasification gas increased from 3.74 MJ/Nm3 to 4.28 MJ/Nm3, and the gasification efficiency increased by 22.3%.

Reaction mechanism of alanine pyrolysis

Liang LIU Yijie CAI Hong TIAN Hui XIA Ya CAO

Chin. J. Process Eng.. 2019, 19(4):  792-800.  DOI: 10.12034/j.issn.1009-606X.218296

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Alanine was selected as a nitrogen-containing model to research the conversion mechanism of nitrogen-containing gas, the quantum chemical simulation calculation was carried out by using density functional theory (DFT) methods at B3LYP/6-31+G(d, p) level. Three initial reaction paths and one secondary reaction path were designed. Geometric optimization and frequency calculation were used in reactants, transition states, intermediates, and products in each reaction path. The standard kinetic parameters in each reaction pathway were calculated and the formation and evolution mechanism of main pyrolysis products were analyzed. The thermogravimetric and Fourier transformer technology (TG?FT-IR) technique was used to identify the released gas during the nitrogen-containing gas pyrolysis process, to verify the simulation results. The experimental and simulation results showed that the initial reaction was that two alanine molecules dehydrated by a condensation reaction to form a propylene?propylene dipeptide, and then the propylene?propylene dipeptide formed diketopiperazine (DKP) by condensation reaction. This path had the smallest enthalpy change value and the minimum activation energy required for its reaction as the main reaction, and the secondary reaction path of path 1 was the cleavage of DKP. During the pyrolysis of alanine, there were mainly three kinds of nitrogen-containing products HCN, NH3 and HNCO. The nitrogen-containing gas products detected in the experiment were consistent with the products obtained by the simulated route. The alanine pyrolysis interval range was 250~330℃. At 290℃, the yield of NH3 was higher than that of HCN, and the yield of HNCO was the lowest. At 400~450℃, the amount of HCN was increased. Nitrogen-containing products were mainly NH3 and HCN. The above analysis was consistent with previous experimental results and analysis.

Biochemical Engineering

Direct production of curdlan oligosaccharides by coupled fermentation system of Agrobacterium sp.-Pichia pastoris

Feifei LI Shuxia JIN Li ZHU Xiaobei ZHAN Yue ZHAO Liping LIU Minjie GAO

Chin. J. Process Eng.. 2019, 19(4):  801-808.  DOI: 10.12034/j.issn.1009-606X.218319

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Curdlan oligosaccharides are widely used in biomedicine and food. Agrobacterium sp. ATCC 31749 can produce curdlan under nitrogen-deficient conditions, and endo-?-1,3-glucanase can hydrolyze curdlan to curdlan oligosaccharides. To improve the production efficiency of curdlan oligosaccharides, a coupled fermentation system of Agrobacterium sp.?Pichia pastoris is constructed, in which the Agrobacterium sp. metabolite curdlan can be directly used to produce curdlan oligosaccharides by endo-β-1,3-glucanase (secreted by Pichia pastoris). This microbial consortium omits the steps of extraction, purification, and drying of curdlan and endo-β-1,3-glucanase, and it has considerable potential for use in the industrial production of curdlan oligosaccharides. The commercially available β-1,3-glucanase is a complex enzyme (it contains a variety of exoglucanases and endoglucanases), and the specific endoglucanase is difficult to obtain. In is work, to avoid the effects of exo-β-1,3-glucanase, the endo-β-1,3-glucanase (BGN13.1) was expressed in Pichia pastoris GS115 by different promoters (AOX1, GAP and FLD), and they were all verified to be effective in hydrolyzing curdlan to curdlan oligosaccharides, the endo-β-1,3-glucanase enzyme activities reached 51.24, 49.64, and 46.99 U/mL, respectively. On this basis, the Pichia pastoris engineered by the GAP promoter was selected for co-culture with Agrobacterium sp. to avoid the methanol-induced process, and soybean sprout extract was the optimal source of nitrogen for both curdlan and endo-?-1,3-glucanase production. In the end, the coupled fermentation system was divided into two stages to produce the best culture effect: Agrobacterium sp. cell growth stage (pH=7.0), and curdlan oligosaccharides production stage (pH=5.6). Potassium phosphate buffer was added to the medium to keep the pH of the fermentation broth within a constant range. When the initial inoculation ratio of Agrobacterium sp. to Pichia pastoris was 1:2, and fermentation time in shaker flasks was 79 h, respectively, the maximum production of curdlan oligosaccharides (degree of polymerization between 17 and 22) reached 4.278 g/L.

Materials Engineering

Synthesis and tribological properties of lubricant oil with highly dispersed and stable nanodiamond

Chuan LI Kai WU Bo WU Weimin FENG Xianguo HU

Chin. J. Process Eng.. 2019, 19(4):  809-816.  DOI: 10.12034/j.issn.1009-606X.218327

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In mechanical systems, high-efficiency and environmentally friendly lubricant oil is demanded for extension of the equipment service life and energy saving demand highly efficient and environmentally friendly lubricating oil. Over last few decades, more attention have been paid to the addition of carbon nanoparticles, such as graphite, graphene and carbon nanotubes etc., in order to reduce the friction and wear in lubricating oil. At present, nanodiamond particles (NDPs) have been considered to be one of the most promising candidates for enhancing the friction reduction and anti-wear properties of lubricating oil effectively and economically due to its excellent properties of hardness, chemical stability, thermal stability and high thermal conductivity. Although NDPs as lubricant additives in lubricating oil have been reported, its dispersity in lubricating oil has not been well investigated. NDPs are easy to agglomerate in many media and have poor dispersive capacity in lubricating oil. In this work, in order to improve the dispersity of NDPs in anti-wear hydraulic oil (AHO), acidified and heat-treated NDPs (T-NDPs) were prepared and mixed with a variety of additives [oleylamine, polyisobutylene succinimide (T154) and high alkaline calcium sulfonate (T106)], then the mixture was added into AHO to prepare AHO containing T-NDPs. The materials and dispersity were characterized by FESEM, a Zeta potentiostat, FT-IR and static sedimentation experiment. The tribological property of AHO with T-NDPs and worn surfaces were investigated by the four-ball tribometer, 3D laser scanning microscopy and SEM/EDS. The results showed that the average diameter of NDPs decreased from 270.2 nm to 153.5 nm after acidified and heat-treatment. The average diameter of T-NDPs after adsorption additives was 101.5 nm. Additives could increase oil solubility of T-NDPs and imped their aggregation. Hence, AHO with T-NDPs possessed good dispersion stability. Particularly, the friction coefficient and wear scar diameter of AHO containing 0.04wt% of T-NDPs were reduced 13.2% and 17.8% compared with AHO without T-NDPs. We can analysed the friction reduction and anti-wear mechanism of T-NDPs as lubricant additives from two aspects, one is that the T-NDPs could support the load and act as roll bearing between the friction interfaces, and the other one is that the T-NDPs participated in the lubricating film formation between the friction surfaces.

Synthesis of magnesium oxysulfate whiskers from bittern and post-sequence separation process

Xue BAI Hongfei GUO Xueqing CHEN Bin ZHAO Jilin CAO

Chin. J. Process Eng.. 2019, 19(4):  817-825.  DOI: 10.12034/j.issn.1009-606X.218328

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Based on the comprehensive utilization of bittern resources, the synthesis of magnesium oxysulfate whiskers from bittern and the separation of potassium salt and sodium salt in the subsequent process were studied. Magnesium oxysulfate whiskers were synthesized by hydrothermal reaction of bittern with NaOH. The effects of raw material ratio, reaction temperature, concentration of liquid alkali and reaction time on liquid phase composition and product morphology were investigated. The products were characterized by XRD and SEM. The optimum conditions were determined as follows: the raw material molar ratio of Mg2+ to OH? was 1:1.5, the concentration of liquid alkali was 4 mol/L, the reaction temperature was 200℃ and the reaction time was 7 h. The Mg2+ in the mother liquid was completely converted into magnesium hydroxide crystals with the theoretical molar ratio of Mg2+ to OH? of 1:2. According to the phase diagrams of Na+, K+//Cl?, SO42??H2O system at 0 and 25℃ and NaCl?KCl?H2O ternary system at 25 and 100℃, NaCl, Na2SO4?10H2O and KCl were separated from the remaining mother liquor by evaporation concentration crystallization and freezing crystallization.

Oxidation processes of MoSi₂ and (Mo,W)Si₂ coatings in wide temperature range

Shaobao MAO Ying YANG Haiqing LI Shihong ZHANG

Chin. J. Process Eng.. 2019, 19(4):  826-835.  DOI: 10.12034/j.issn.1009-606X.218310

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MoSi2 and (Mo,W)Si2 coatings were prepared on Mo and Mo?W substrates respectively by means of pack cementation, and the effects and mechanisms of W element doping on the oxidation resistances of MoSi2 coating were investigated systematically. XRD, SEM and EDS were used to determine the phase structure, morphology and composition of the coatings. The results showed that W element was dissolved in MoSi2 coating in the form of (Mo,W)Si2 solid solution, and the microstructure of (Mo,W)Si2 coating was denser compared with that of MoSi2 coating as a result of W element doping. After static oxidation at 1600℃, the antioxidant life of (Mo,W)Si2 coating reached 70 h, while MoSi2 coating was failed after 25 h oxidation due to severe weight loss. Moreover, (Mo,W)Si2 coating exhibited excellent high-temperature protection performance after oxidation at 1200℃ for 1000 h. At the initial stage of the oxidation, the oxidation rate of (Mo,W)Si2 coating was higher than that of MoSi2 coating owing to W element doping, which led to lower formation velocity of dense oxide layer on the surface of (Mo,W)Si2 coating. After the dense SiO2 covering the surface completely, the oxidation rate of (Mo,W)Si2 coating decreased dramatically. The diffusion reaction between the Si element and the substrate was hindered by the addition of W element, the consumption rate of Si element in the coating was reduced remarkably, and the high-temperature oxidation resistance of (Mo,W)Si2 coating was enhanced significantly. After static oxidation at 500℃, comparing with MoSi2 coating, (Mo,W)Si2 coating exhibited a typical “Pest” phenomenon after oxidation for 50 h, and the coating failed in the form of disintegration. The addition of W element reduced the diffusion rate of Si element in the coating, therefore, a dense oxide layer could not be formed on the coating surface at low-temperature, which caused the rapid oxidation of the coating.

Environment & Energy

Effect of oxygen/coal ratio of two-stage entrained flow bed on gasification characteristics of dry coal powder

Lijun WANG Lingfeng XU Xiaocheng DU

Chin. J. Process Eng.. 2019, 19(4):  836-844.  DOI: 10.12034/j.issn.1009-606X.218303

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Based on the Eulerian?Lagrangian method, a 3D computational fluid dynamics (CFD) model of a two-stage dry coal powder entrained flow gasifier was established and the coal gasification process in the entrained flow bed was simulated and analyzed using the homogeneous and heterogeneous multistep chemical reaction kinetics to define the coal gasification reaction, the k?? model was used to describe the gas phase turbulent flow, and stochastic tracking method (STM) was used to indicate motion track of char particles. At the oxygen/coal mass ratio of 0.9, 1.0 and 1.1, respectively, different reaction mechanisms were simulated to determine the optimal reaction mechanism according to the published experimental conditions. Further, the effect of coal/oxygen ratios in the upper and lower stages on the coal gasification characteristics were studied at the oxygen/coal ratio of 1.0. The results showed that the reaction mechanism adopted a complete combustion reaction of coke and volatiles and neglected the participation of CO in the gas phase combustion reaction (Case E), the simulation results was in good agreement with the experimental data with an error of less than 2%. In the case of total oxygen/coal ratio of 1.0, the reaction mechanism of Case E was selected to examine the effect of coal/oxidant between the various stages on the overall performance of the gasifier. When the primary feed (A?A) coal and oxidant reached and exceed 50wt% of the total feed, the overall performances of the gasifier such as syngas composition, carbon conversion and active ingredients were optimized. The carbon conversion rate reached 99.6% when 70wt% coal and 60wt% oxygen were injected at the first nozzle (A?A level), and the maximum synthesis gas yield was 78.24mol% when the first nozzle injected 50wt% coal and 50wt% oxygen.

High gravity intensified dry denitrification process for ammonia production

Hui HE Guisheng QI Youzhi LIU Qi ZHENG Huiyun REN

Chin. J. Process Eng.. 2019, 19(4):  845-852.  DOI: 10.12034/j.issn.1009-606X.218289

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At present, liquefied ammonia is mostly used as reducing agent in selective catalytic reduction (SCR) denitrification. But there are some safety problems such as high pressure storage and easy leakage of liquefied ammonia. The use of ammonia as reducing agent can effectively avoid such problems and the cost is low. In this work, the technology of ammonia stripping from ammonia water by high gravity was applied to SCR denitrification process (needs ammonia gas 5vol%~10vol%). Taking air?ammonia water as experimental system and rotating packed bed as ammonia blowing equipment. The effects of inlet temperature, high gravity factor and volume ratio of gas to liquid on blowing rate and ammonia production rate with two packings of stainless steel were investigated. The results showed that when the treatment gas was 4~10 m3/h, the blowing rate of the two packings was accelerated with inlet temperature, high gravity factor and volume ratio of gas to liquid increased. The inlet temperature and high gravity factor performed a positive effect on ammonia production rate while the volume ratio of gas to liquid showed a negative effect. The ammonia production rate was more than 10%. The high gravity ammonia water blowing technology could be used in SCR denitrification technology. When the treatment gas was 50?700 m3/h, the high concentration of ammonia nitrogen wastewater (1wt%) was stripped off, the ammonia production rate was at most 3.0%. Although it did not meet the SCR denitration requirements, but could combine the blown ammonia nitrogen wastewater with the ammonia stripping process to save ammonia consumption.