The Chinese Journal of Process Engineering

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Chin. J. Process Eng.. 2020, 20(7): 0.

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Research progress on wet plume control technology in coal-fired power plants

Yan YAN Bo YU Hao WANG2, Xiaokang NIE1, Huaqiang CHU1*

Chin. J. Process Eng.. 2020, 20(7): 745-756. DOI: 10.12034/j.issn.1009-606X.219292

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The wet desulfurization method plays a major role in the desulfurization system of coal-fired power plants in China, among which limestone-gypsum wet desulfurization is the most widely used. The flue gas after wet desulfurization is usually wet saturated flue gas. If the ambient temperature and humidity of the flue gas are low, it will produce a “wet plume” phenomenon at the chimney. Wet plumes generally appear white or gray, which contains a large amount of water vapor and pollutants. The emergence of wet plumes will be harmful to the environment and human health. Therefore, enterprises adopting plume elimination technology to carry out emission transformation will reduce the emission of pollutants in the flue gas, make the flue gas diffuse better. To better understand the phenomenon of wet plume and help the enterprises to be transformed to choose the technical route that suits them, this work first introduces the wet desulfurization process and the causes of the wet plume formation, followed by the relevant policies issued in some parts of China. The research status of wet plume characteristics (including the length, lift height and elimination characteristics of the wet plume) was summarized. There are many control technologies for wet plume. The mainstream technology can be divided into flue gas condensation technology, flue gas reheating technology and flue gas condensation and reheating technology. The article then applies the temperature and humidity diagram to explain the principle of each control technology, according to the classification of control technology. The applications under the category are reviewed. At the end of the work, the possibility of combined use of control technology is proposed. Under the premise of energy-saving and economical permission, enterprises should try more technical routes to broaden the road for the management of wet plumes.

Simulation of gas-solid flow characteristics in feedstock injection zone for risers with double-layer nozzles

Mengqian FU Xiuying YAO Yiping FAN Chunxi LU

Chin. J. Process Eng.. 2020, 20(7): 757-769. DOI: 10.12034/j.issn.1009-606X.219296

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A new structure of injection zone with double-layer nozzles has been proposed in order to improve the product distribution of FCC process. Two supplementary nozzles are added below the primary nozzles. However, the research on gas?solid flow characteristics in this novel injection zone is rarely reported. In this study, the numerical investigation of the mixing and flow of catalyst/particles and oil/gas in the novel injection zone was carried out using the combination of two-fluid model with the energy minimization multi-scale (EMMS)-based drag model. The particle?wall specularity coefficient was first determined by comparing with experimental data. Four combination types of double-layers nozzles with a distance of 0.5 m between primary and supplementary nozzles were investigated, i.e. down?down, down?up, up?down and up?up types with different feeding directions. The hydrodynamic behaviors of gas and solid in the feedstock injection zone with these four nozzle combinations were investigated and further compared with the results with the single-layer nozzles. The results showed that the introduction of the supplementary nozzles had a great influence on the gas?solid flow in the feedstock injection zone, especially in the injection region with the primary upward feeding nozzles. The jet from supplementary nozzles can accelerate gas and solid phase to reach the uniform and stable state at the region above the primary nozzles. But an uneven distribution of solids volume fraction occurred at the zone above secondary nozzles. When the main nozzles were downward, the injection zone with single-layer nozzles showed the smaller mean residence time and heterogeneity. When the main nozzles were upward, the double-layers nozzles with the up?up structure showed the smallest mean residence time and heterogeneity. These results indicated that the feeding using double-layer nozzles can achieve the strong mixing within a shorter contact time and inhibit the over-cracking of desired products, thus increasing the yield of desired products.

Performance of the steam ejector used for low pressure gas well drainage gas recovery

Zhiyi XIONG Yang LIU Yuan LI Hongtao HUANG Tao LI

Chin. J. Process Eng.. 2020, 20(7): 770-778. DOI: 10.12034/j.issn.1009-606X.219309

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At present, traditional drainage gas recovery technology is not suitable for low-pressure gas wells. In this work, a new type of ejector drainage gas recovery technology was proposed to solve this problem. High-pressure gas was used as a driving fluid to prevent secondary contamination. The problem of low efficiency was solved by forming a composite process with the foam scrubbing, and the ejector was the core of the technology. The aim of this study was to investigate the ejector flow characteristics for gas flow field by Computational Fluid Dynamics (CFD), the entrainment ratio was selected as the performance index, and the influence of ejector structure size and operation condition was obtained. The results showed that the ejection process both of pumping action and shear acceleration action existed in ejection process, and the shear acceleration action only made the ejection fluid to run up to sonic speed. The mass flow rate of ejection fluid was controlled by area and speed together, if the flow area was steady, and the gas speed could not increase in any condition, so that the flow state was in chocking phenomenon. In the chocking condition, the performance of ejector was determined by pumping action. Furthermore, the chocking condition retarded with the increasing of diffused segment conical degree and area ration of the ejector nozzle. In addition, the shear acceleration action played the major role if the flow was not in chocking condition. Operation parameters had an impact on shock wave intensity and ejector flow state, the increasing of operation pressure and the decreasing of outlet pressure would enhance entrainment ratio and cause the chocking condition occur.

Hydrodynamic study on a gas-liquid bubble column with high viscosity SEBS solution

Shanglei NING Fangfang TAO Haibo JIN Guangxiang HE Suohe YANG Xiaoyan GUO

Chin. J. Process Eng.. 2020, 20(7): 779-787. DOI: 10.12034/j.issn.1009-606X.219280

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For development and design of SBS hydrogenation reactor, the hydrodynamic behavior of high viscosity solution in gas?liquid bubble column using SEBS-1650 hexane solution as liquid phase was studied by differential pressure method and gas disengagement method. The effects of viscosity on gas holdup of solution with low surface tension, gas holdup of large and small bubbles, rise velocity of large and small bubbles and specific surface area were investigated. With the increase of viscosity, gas holdup decreased significantly, and flow pattern directly transited turbulent regime. From the curve of gas disengagement method, three types of bubbles were identified in bubble column: large bubbles, small bubbles and fine small bubbles. The gas holdup of small bubbles and fine small bubbles gradually decreased with the increase of viscosity. Viscosity has a slight influence on the rise velocity of large and small bubbles, and the specific surface area decreased significantly with the increase of viscosity. Based on the experimental results, the formulas for calculating gas holdup of large and small bubbles and average gas holdup were listed. These results provided some necessary and reliable basic data for designing and developing a SBS hydrogenation reactor.

Comparison of discrete method and QMOM in CFD-PBM simulation of gas-liquid bubble column

Xuejing QU Min AN Xiaoping GUAN Ning YANG Guogang SUN

Chin. J. Process Eng.. 2020, 20(7): 788-797. DOI: 10.12034/j.issn.1009-606X.219291

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In bubbly flow systems, bubbles may break or coalesce due to bubble?bubble or bubble?fluid interactions in presence of turbulence. In general, the population balance equations (PBEs) need to be solved to model the bubble size distribution (BSD). Two methods for solving the PBEs, i.e., the classes method and the quadrature method of moments (QMOM), were compared in this work. In the classes method, BSD was represented through a finite number of bubble classes, and coalescence rates and breakup rates were transformed into birth and death rates for each class. QMOM solved the equations of lower-order moments of BSD, instead of tracking the representative bubble size. A three-dimensional simulation of two-phase flow (air?water) was performed for a cylindrical gas?liquid bubble column reactor operated at high superficial gas velocities, and the computational fluid dynamics (CFD) were coupled with PBEs. An Euler-Euler two fluid model approach with an RNG k?? model of turbulence model was used. The predictions of the classes method (20 bins), QMOM with four moments and QMOM with six moments were compared with the experimental data in literature. The results showed that both the classes method and QMOM can reasonably predict the time-averaged gas volume fraction, liquid velocity profiles, mean diameter and bubble size distribution. Nevertheless, compared with the classes method, QMOM can save 2~3 times of computational resources. And for the QMOM four moments suffices were used to accurately describe the evolution of the gas phase. In fact, the results found by using the QMOM with four moments and the QMOM with six moments were very similar. In addition, the continuous bubble size distribution was reconstructed by using the low-order moments of QMOM. The predicted BSD was similar to that of the classes method, demonstrating that QMOM was a more efficient method than classes method when the PBM was coupled with CFD simulations for bubbly flow systems.

Diffusion and mixing behaviors of nozzle jet in the gas-solid riser

Zihan YAN Jun XU Yiping FAN Chunxi LU

Chin. J. Process Eng.. 2020, 20(7): 798-806. DOI: 10.12034/j.issn.1009-606X.219320

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The gas tracer technology was employed in this research to investigate the jet diffusion and its mixing with particles in the gas?solid riser. Studies were finished in a large scale cold model riser. In order to investigate the influence of different types of jets, both upward and downward injections were used during experiments. By introducing the jet characteristic concentration, the radial distributions of jet after injecting into the riser were obtained. Results showed that the distribution of jet concentration was more uniform for the case of downward injection. By detecting the tracer gas at various axial and radial points, the local residence time distributions of feed jet were obtained. On this basis, the dimensionless variance was calculated and comparison between upward and downward injections was made. It showed that the values of variance and their fluctuations were large at most axial cross sections when the jet was upward, indicating some serious local backing-mixing of feed jet. If the direction of injection changed to downward, the calculated value of variance was large under the feed nozzles, while the value of variance was small and its radial distribution was uniform at the locations above nozzles. This result meant that the jet-solid mixing flow can change into the likely plug flow from a likely full mixed flow easily and quickly under the influence of downward injection. Based on experimental results, the residence time variance was fitted with operating conditions and axial height. Empirical formulas for the cases of both upward and downward injections were obtained. Finally, comparing fitted results with the variance value in the riser full mixing zone, the influence height of jet in the riser was calculated. Results showed that the influence height of feed jet can be shortened by 50% if the downward injection was chosen.

Studies on reaction kinetics and phase changes during the synthesis of ionic liquids using an in-situ low-field MRI spectrometer

Yadi LIU Niklas HEDIN Lina JIA Guoying ZHAO Yi NIE

Chin. J. Process Eng.. 2020, 20(7): 807-821. DOI: 10.12034/j.issn.1009-606X.220067

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Ionic liquids (ILs) have a wide range of applications due to their many beneficial properties. However, the production cost of ILs is still high, which is limiting further industrialization. Hence, in-depth studies of the reaction kinetics and phase changes are essential to optimize the synthesis processes for ILs and the key equipment involved. An in-situ low-field magnetic resonance imaging (MRI) device was used to monitor the reaction kinetics and phase changes that occurred during the synthesis of ILs in real time. Quantitative analysis of the ILs components in the reaction system was performed using an established two-component analysis model via 1H low-field nuclear magnetic resonance (LF-NMR) relaxometry data. This analysis allowed investigating the effects of haloalkanes chain length, halogen species, stirring speed, and temperature on the reaction kinetics of the synthesis of imidazole-based ILs. Through the detected spatiotemporal T2 distributions of the phases state during the solvent-free synthesis of the 1-buty-3-methylimidazole ([C4mim]Br) IL by reacting 1-bromobutane (BuBr) with 1-methylimidazole (MIM). This study provided a set of fast, convenient, and non-destructive technical means for the detection of different aspects of the synthesis of ILs, including detection of the residual amount of ILs in organic solvents. Meanwhile, further exploration of using low-field MRI to study the combined mass transfer and reaction kinetics in ILs systems as the studied ones could be expected.

Exergy analysis of synthesis of methanol from methane based on closed loop carbon dioxide reforming process

Ling SUN Lin ZHU Yangdong HE

Chin. J. Process Eng.. 2020, 20(7): 822-831. DOI: 10.12034/j.issn.1009-606X.219290

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The process of carbon dioxide reforming to methanol is of great significance for the efficient use of carbon sources and environmental protection, used as a way to replace the traditional high energy consumption and high emission steam reforming process. With aid of Aspen Plus, the process of methane to methanol in closed loop carbon dioxide reforming was simulated. The results showed that the exergy loss of this process mainly concentrated on the chemical process, accounting for 76.47% of the total exergy loss. The combustion reaction and reforming reactions accounted for 41.62% and 27.69%, respectively, while the methanol synthesis reaction and the water gas shift reaction accounted for 3.55% and 3.61%, respectively. Compared with the traditional steam reforming methanol process in the case of a certain amount of raw material methane input, the carbon dioxide reforming methanol system reduced in exergy loss of 21.44%, in water vapor consumption of 77.02%, in overall system carbon dioxide emissions of 25.89%, and increased in methanol production of 12.03%. In addition, in order to further improve the efficiency of the carbon dioxide reforming methanol process, the impacts of temperature and pressure in the reforming process were analyzed, showing that the exergy efficiency and methanol yield of the system increased first with the increase of reforming reaction temperature, then stabilized, and the reached maximum at 980℃. And the lower reforming reaction pressure was, the more beneficial improved methanol production.

Influence of surface hydrophobicity of epoxy resin coatings on microalgae adhesion property

Guoqiang DAI Jing TANG Wen LIU Shujun TAN Bin LIU Wenqing WANG Tianzhong LIU, Ge SU

Chin. J. Process Eng.. 2020, 20(7): 832-842. DOI: 10.12034/j.issn.1009-606X.220033

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Formation of bio?lm on solid surfaces is a common feature of microalgae, which is tightly associated with the properties of microalgae and substratum material. Increasing interests on microalgae biofilm attached cultivation or antifouling require to determine the effect of material surface physico-chemical characteristics on algal adhesion. However, reference researches are usually inconclusive and do not work well. This work is to evaluate the influence of hydrophobicity/hydrophilicity of substratum on microalgae adhesion. First, this work reported a novel method for surface hydrophobic modification of bisphenol-A Epoxy (EP) resin by adding hydrophilic diethanolamine (DEA) or hydrophobic polymethylhydrosiloxane (PMHS). The results showed that the water contact angles of the modified EP resin coatings were regulated in the range from 36.80? to 98.34?. With the increase of DEA, the water contact angle linearly declined. While, with the increase of PMHS, the water contact angle linearly increased. However, little difference between the two kinds of modified EP materials was observed through the characteristics of morphology, surface texture and roughness. Then, the static adhesion of microalgae C. vulgaris and S. dimorphus was investigated. The results showed that both C. vulgaris and S. dimorphus could adhere on all the coating surfaces with different wettabilities, but preferred to adhere more and faster on the hydrophilic ones. The linear relationships of two microalgae between their maximum adhering capacities and the water contact angles of the modified EP coatings were existed respectively. Hydrophobic surface had less adhered algal cells. The adhesion amount of S. dimorphus was larger than that of C. vulgaris.

Research on vertical flame spread characteristics over flame retardant rigid polyurethane polymer

Xinjie HUANG Chunjie WANG Jinda GAO Cheng CHEN Gang TANG Changlong WANG

Chin. J. Process Eng.. 2020, 20(7): 843-851. DOI: 10.12034/j.issn.1009-606X.219257

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Based on the frequent occurrence of fire accidents on insulation materials rigid polyurethane (RPUF), which can cause great economic loss and casualties, RPUF was prepared by one-step water-blown method and hope to reduce the fire hazards in reality. A small and medium-scale insulation flame spread experimental platform was built, which was used to reveal the flame spread characteristics over RPUF and flame retardant RPUF. The flame structure, flame spread speed, flame temperature and mass loss rate etc. characteristics were analyzed. The results showed that the surface of all the samples was charred during flame spread. The non-flame retardant RPUF showed the largest combustion intensity, while the flame retardant expanded graphite (EG), aluminum hypophosphite (AHP) and aluminum diethylhypophosphite (ADP) resisted the flame spread in some degree, respectively, which was shown in the reduced flame spread speed, mass loss rate, and flame temperature parameters etc. It was also found that RPUF/AHP5 flame spread could sustain a period, while after 20 s the extinguishment was formed. It was because that, the flame retardant RPUF/AHP5 released non-combustion gas when heated, and AHP decomposed into the phosphorus-containing compound, which promoted the formation of charcoal in the polyurethane molecular chain. At the same time, flame retardant RPUF/ADP5 samples distinguished during flame spread, however, the distinguish degree was lower than that of flame retardant RPUF/AHP5. Meanwhile, the surface temperature had two peaks during the flame spread over RPUF/EG5, which were attributed to the instability of the char layer. When the temperature was higher than 400℃, the char layer was oxidized immediately and the heat penetrated the char layer, and unburned material continued to pyrolysis, therefore, the second temperature peak was formed.

Physical properties test of a composite porous wick based on foam metal

Dongdong WANG Pengjie LIU Huaqiang CHU Jinxin WANG Houyang LU

Chin. J. Process Eng.. 2020, 20(7): 852-859. DOI: 10.12034/j.issn.1009-606X.219310

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In order to improve the heat and mass transfer performance of porous wicks, a composite porous wick was prepared by using copper or nickel foam as the skeleton and filling with the dendritic copper or nickel powders in this work. The foam metal can provide reliable porous framework and good heat transfer performance. And the dendritic metal powders can regulate the pore structure and pore size distribution inside the foam metal. The physical properties of the composite porous wick, including the porosity, capillary pumping capacity, effective thermal conductivity and evaporating rate, were studied experimentally. The prepared composite porous wicks had high porosity and low effective thermal conductivity in the range of 4.1?9.8 W/(m?K). According to the filling amount of metal powders and the microstructure of samples, the foam nickel and dendritic nickel powder were the most suitable combination for loose sintering of composite porous wick. Porosity had little effect on capillary pumping capacity of the composite porous wicks, but the porous structure and pore size distribution of porous wicks can cause the obvious effect. Due to the use of metal foam as skeleton, partial evaporation can be formed locally on the surface of composite porous wicks, and heat transfer equilibrium can be achieved by surface evaporation at low heat load of 30 W. Increase the heat load to 50 W or 70 W, local temperature on composite porous wick was over 100℃, and heat transfer entered the meniscus evaporation inside composite porous wick. Based on capillary pumping characteristics, effective thermal conductivities and evaporating rates in these porous samples, the composite porous wick with nickel foam as the skeleton and the mass ratio of dendritic nickel powder to the pore former of 5:5 had the best performance. The simple preparing method for the composite porous wick was proposed, and it was expected to be used for further practical application in loop heat pipe.

Modified zeolite-coupled activated carbon enhanced coagulation treatment of micro-pollution source water

Yaqian MA Yanli KONG Lei DING Zhonglin CHEN Jimin SHEN

Chin. J. Process Eng.. 2020, 20(7): 860-869. DOI: 10.12034/j.issn.1009-606X.219287

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In recent years, the water quality of drinking water sources in China is facing very serious situation, especially for micro-polluted water, and the existing water plant conventional treatment process cannot effectively ensure the removal of pollutants from the water plant, so it is necessary to use enhanced coagulation treatment technology, economically to improve the water quality, and to ensure the safety of drinking water is particularly important. The combination modified zeolite powder (MZ) coupling powder activated carbon (PAC) to enhance coagulation removing micro-pollution sources of ammonia nitrogen (NH3-N), oxygen consumption (CODMn), UV254 and turbidity were studied using static adsorption and six-link mixer beaker experiments. Experimental water was taken from micro-polluted water sources in a city of south China, and the water quality was more seriously polluted with higher concentrations of soluble organic matter. The results showed that MZ increased the surface area and average adsorption aperture, the surface of MZ was rougher while the crystal structure of the MZ had not changed and the removal ability of NH3-N enhanced. MZ-PAC adsorption had the synergetic action for NH3-N removing, there was slightly antagonism for CODMn removal. MZ-coupled PAC to enhance coagulation significantly improved the removal of NH3-N, CODMn, UV254, and turbidity, with the treated water NH3-N<0.5 mg/L, CODMn<3.0 mg/L and turbidity<1 NTU. The different cast-plus methods of MZ and PAC influenced the enhanced coagulation treatment effect, and the best way to add PAC and MZ was in the early stages of flocculation, which avoided the flocs of MZ packages, strengthened the PAC on organic matter removal, and further improved the removal of NH3-N by MZ. Otherwise, the turbidity of the water increased, especially in the late stage of flocculation. Coupling enhancing coagulation results in lower the absolute value of Zeta potential and repulsion between colloid. Floc size increasing and sticky phenomenon made the resistant ability stronger.

Data analysis and optimization of butane oxidation reactor

Mingyu CHEN Zheli WEI Jian LI Xiangdong ZHU Ruhui YANG Xing XIANG Erqiang WANG Xiaoxiang SUN

Chin. J. Process Eng.. 2020, 20(7): 870-876. DOI: 10.12034/j.issn.1009-606X.219321

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As an important reaction system, butane oxidation to produce maleic anhydride has already been industrialized with lots of advantages compared with other production processes. In this process, fixed-bed tubular reactor was used and recycling molten salt was selected as the cooling media to take out huge amount of reaction heat. Due to the complexity of the reactor internal structure and the reaction mechanism, it is difficult to develop a rigorous mathematical model to simulate and optimize this reactor. Black-box models, such as artificial neural network (ANN), could not provide detailed information about inherent mechanism of research process, and could be only used in the manner of interpolation within fixed range. The principle component analysis (PCA) is one of the most popular statistical methods for data mining and analysis. PCA can help to reduce the dimensionality of the variable space by representing it with a few orthogonal (uncorrelated) variables that capture most of its variability. So PCA retains those characteristics of the data set that contribute most to its variance, by keeping lower-order principal components (the ones that explain a large part of the variance present in the data) and ignoring higher-order ones (that do not explain much of the variance present in the data). In this work, lots of historical data of butane oxidation reactor was firstly selected from the DCS device, and then corrected to be as the basis of data mining analysis. The PCA technology was used to dig the relationship between these reactor parameters. The results showed that these outliers can be effectively detected as abnormal or normal data point and the former data would be removed from the data before next analysis. It was also found that there was a negative correlation between the conversion of butane and CO/CO2 ratio at reactor outlet. So, these conclusions from this PCA analysis could be used as useful guide for reactor operation and optimization. The principle component analysis (PCA) is one of the most popular statistical methods for data mining and analysis. PCA can help to reduce the dimensionality of the variable space by representing it with a few orthogonal (uncorrelated) variables that capture most of its variability. So PCA retains those characteristics of the data set that contribute most to its variance, by keeping lower-order principal components (the ones that explain a large part of the variance present in the data) and ignoring higher-order ones (that do not explain much of the variance present in the data). In this article, lots of historical data of butane-oxidation reactor was firstly selected from the DCS device, and then corrected to be as the basis of data mining analysis. The PCA technology was used to dig the relationship between these reactor parameters. The results showed that these outliers can be effectively detected as abnormal or normal data point and the former data would be removed from the data before next analysis. It was also found that there was a negative correlation between the conversion of butane and CO/CO2 ratio at reactor outlet. So, these conclusions from this PCA analysis could be used as useful guide for reactor operation and optimization.

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