电阻层析成像技术在气液(固)多相流动体系中的应用进展

Electrical resistance tomography (ERT) has been widely used in monitoring and measuring gas?liquid?(solid) multiphase flow systems as a fast, non-invasive, radiation-free, simple equipment compared to conventional methods and other tomographic modes. For the gas?liquid?(solid) multiphase flow system, the principle of ERT test was introduced, and the characteristics of ERT and other measurement technologies were analyzed in this work. The three important characteristics and process parameters (flow pattern identification, phase holdup, bubble size and distribution) of ERT were reviewed in detail. Problems to be solved in the application process of ERT technology in the gas?liquid systems were discussed (the standardization of flow pattern identification, the accuracy of identification process parameters, the equalization of time resolution and spatial resolution, etc.). Based on the development trend of ERT technology in the field of multi-phase flow parameter detection and its subsequent research directions, a model based on electrode array optimization, image reconstruction algorithm or 3D/4D field establishment was proposed, which combined the dynamic information and fluid dynamics numerical simulation of industrial process parameters. And ERT's rich flow field information can effectively verify the accuracy of mathematical simulation, real-time monitor and predict industrial processes, and effectively prevent or inhibit the uncertainty of chemical production process. At the same time, it was proposed to use the cross-knowledge between different disciplines to broaden the application fields of ERT, such as fluid mechanics in microscale equipment, biomedical testing diffusion properties of serum in dry tablets, online monitoring and analysis in the field of food processing, etc. As a visualization tool of fluid flow, ERT 2D and 3D real-time visualized flow information deepened the understanding of the complex characteristics of multi-phase flow, realized the purpose of optimizing operating conditions, improving efficiency, reducing costs and overall monitoring of production process, and promoted the application of ERT in chemical industry, petroleum, medicine, environmental monitoring, food processing, mineral flotation, material transportation and other fields.     

CoO AS ADDITIVE IN POSITIVE ELECTRODE OF NICKEL-METAL HYDRIDE BATTERY

A series of positive electrodes for Ni/MH battery were fabricated by addition of CoO.The morphology and microstructure of the electrodes were examined by SEM and EDS, and electrochemical behavior was investigated in three-compartment appliances at room temperature.The electrochemical performance of the positive electrodes with CoO was improved. Under the same charge-discharge cycle, the electrodes with CoO showed higher specific capacity, lower charge mean voltage and higher discharge mean voltage. But further increasing the content of CoO in the electrodes contributed negative effect on the overall performance. Addition of 8% (mass) CoO was suggested to be a suitable content for the positive electrode.     

ELECTROSTATIC PSEUDO LIQUID MEMBRANE SEPARATION TECHNOLOGY

Electrostatic pseudo liquid membrane(ESPLIM)separation process,developed recently in this laboratory,is a novel chemical separation technology.ESPLIM is an interdisciplinary technology evolved from thecombination of solvent extraction,liquid membrane and electrostatic techniques.It can be used to separate,purify and concentrate specific solutes from aqueous solutions.Therefore,it is suitable for the recovery ofvaluable metals from aqueous solutions in the field of hydrometallurgy(including nuclear fuel cycles)and forthe processes of waste water treatment.This paper discusses the basic principles of this new technology.Taking the extraction of Co~(2+)by D2EHPA as an example,effects on metal extraction of electrical fieldstrength,extractant concentration and the flow ratio of feed to stripping solution have been studied.Exper-iments show that the once through extraction efficiency of Co~(2+)can reach 99% while Co~(2+)can be concen-trated up to 40—50g/L in the stripping solution.     

一种新的利用LNG冷能的回收油田伴生气凝液的工艺

A novel process to recovery natural gas liquids from oil field associated gas with liquefied natural gas (LNG)cryogenic energy utilization is proposed.Compared to the current electric refrigeration process,the proposed process uses the cryogenic energy of LNG and saves 62.6%of electricity.The proposed process recovers ethane, liquid petroleum gas(propane and butane)and heavier hydrocarbons,with total recovery rate of natural gas liquids up to 96.8%.In this paper,exergy analysis and the energy utilization diagram method(EUD)are used to assess the new process and identify the key operation units with large exergy loss.The results show that exergy efficiency of the new process is 44.3%.Compared to the electric refrigeration process,exergy efficiency of the new process is improved by 16%.The proposed process has been applied and implemented in a conceptual design scheme of the cryogenic energy utilization for a 300 million tons/yr LNG receiving terminal in a northern Chinese harbor.     

一种新型共气化工艺的开发

As one of promising clean coal technologies used to reduce pollutant emission and CO2 discharge, cogasification has been extensively investigated. In this paper, a new co-gasification technology using coal and natural gas was developed. The distinct advantages of this technology are the excellent fuel flexibility and the availability to establish the gasifler by reconstructing the blast furnace or similar shaft furnace. Based on the concept of the new co-gasification technology, lab-scale experiments and modeling study were carried out. The obtained results indicate that gasification is undertaken at ideal thermodynamic environment where quasi-equilibrium could be reached without catalysts. The modeling results are in agreement with experimental data, demonstrating the validity of the model and that Aspen Plus is a useful tool for the analysis of the co-gasification process. Furthermore,the effect of major operation parameters, including oxygen flow rate and steam flow rate, on co-gasification process was investigated using the developed model.     

稀土萃取过程组分含量分布控制方法(英文)

Considering that the on-line measurement and automatic control of element component content (ECC) are dif-ficult to perform in rare earth cascade extraction process, the ECC distribution profile is dynamical y regulated at al stages to assess the effect of product purity control. Focusing on the theory of countercurrent extraction, the technology parameters and pre-setting flow-rates during the extract process are designed. Under varying process parameters, a novel step by step model is also proposed for each stage to analyze the impact on the distribution profile change. Combining the mass balance model and ECC changing trend at the monitoring stage, the ECC dis-tribution profile can be automatical y regulated by dynamical y compensating the related extract or scrubbing liquid flow-rate. To this end, the required product purity at the two outlets is achieved. Based on Wincc and Matlab dynamic simulators, a specific Pr/Nd cascade extraction process is used to illustrate and demonstrate the application of the present approach.     

Ultrasonically Assisted Extraction of Isoflavones from Stem of Pueraria lobata （Willd.） Ohwi and Its Mathematical Model

Ultrasonically assisted extraction of isoflavones from the stem of Pueraria lobata （Willd.） Ohwi has been carried out with an ultrasonic extracting apparatus （20kHz, electrical power input to the transducer in 0-650W）. The influence of the electrical power input and extraction time on the＇extraction yield is investigated in water, n-butanol, and 95% （by volume） and 50% （by volume） ethanol aqueous solution. The experimental results indicate that the yields of total isoflavones are higher in ultrasonically assisted extraction than those obtained from con-ventional extraction.Moreover,a mathematical model is proposed,by introducing the electrical power input to index the ultrsound intensity,to describe the behavior of ultrasonically assisted extraction.It is found that the model calcuations are in good agreement with the experimental data.     

Simulation of hydrocarbons pyrolysis in a fast-mixing reactor

Currently, thermal decomposition of hydrocarbons for the production of basic petrochemicals (ethylene, propyl-ene) is carried out in steam-cracking processes. Aside from the conventional method, under consideration are alternative ways purposed for process intensification. In the context of these activities, the method of high-temperature pyrolysis of hydrocarbons in a heat-carrier flow is studied, which differs from previous ones and is based on the ability of an ultra-short time of feedstock/heat-carrier mixing. This enables to study the pyrolysis process at high temperature (up to 1500 K) at the reactor inlet. A set of model experiments is conducted on the lab scale facility. Liquefied petroleum gas (LPG) and naphtha are used as a feedstock. The detailed data are obtain-ed on temperature and product distributions within a wide range of the residence time. A theoretical model based on the detailed kinetics of the process is developed, too. The effect of governing parameters on the pyrolysis process is analyzed by the results of the simulation and experiments. In particular, the optimal temperature is detected which corresponds to the maximum ethylene yield. Product yields in our experiments are compared with the similar ones in the conventional pyrolysis method. In both cases (LPG and naphtha), ethylene selectivity in the fast-mixing reactor is substantial y higher than in current technology.     

Thermodynamic behaviors of SiCl2 in silicon deposition by gas phase zinc reduction of silicon tetrachloride☆

The modified Siemens process, which is the major process of producing polycrystal ine silicon through current technologies, is a high temperature, slow, semi-batch process and the product is expensive primarily due to the large energy consumption. Therefore, the zinc reduction process, which can produce solar-grade silicon in a cost effective manner, should be redeveloped for these conditions. The SiCl2 generation ratio, which stands for the degree of the side reactions, can be decomposed to SiCl4 and ZnCl2 in gas phase zinc atmosphere in the exit where the temperature is very low. Therefore, the lower SiCl2 generation ratio is profitable with lower power consumption. Based on the thermodynamic data for the related pure substances, the relations of the SiCl2 generation ratio and pressure, temperature and the feed molar ratio nZn=nSiCl4 ? ? are investigated and the graphs thereof are plotted. And the diagrams of KpΘ–T at standard atmosphere pressure have been plotted to account for the influence of temperature on the SiCl2 generation ratio. Furthermore, the diagram of KpΘ–T at dif-ferent pressures have also been plotted to give an interpretation of the influence of pressure on the SiCl2 gener-ation ratio. The results show that SiCl2 generation ratio increases with increasing temperature, and the higher pressure and excess gas phase zinc can restrict SiCl2 generation ratio. Finally, suitable operational conditions in the practical process of polycrystalline silicon manufacture by gas phase zinc reduction of SiCl4 have been established with 1200 K, 0.2 MPa and the feed molar ratio nZn=nSiCl4 ? ? of 4 at the entrance. Under these conditions, SiCl2 generation ratio is very low, which indicates that the side reactions can be restricted and the energy consumption is reasonable.     

CFD simulations of quenching process for partial oxidation of methane:Comparison of jet-in-cross-flow and impinging flow configurations

A new quenching process using the cold pyrolysis gas has been proposed for the partial oxidation (POX) of methane to recover the heat.The mixing of hot product gas and cold pyrolysis gas in milliseconds is critical to this new approach.Two most widely-used rapid mixing configurations,i.e.the jet-in-cross-flow (JICF) and impinging flow configurations,are compared in terms of mixing and quenching performances using computational fluid dynamics (CFD) coupled with detailed reaction mechanism Leeds 1.5.The mixedness,residence time distribution,temperature decreasing rate and loss ratio of acetylene during the quenching are systematically studied.The results show that the impinging flow has a more uniform mixing and narrower residence time distribution than the JICF.However,the temperature decreasing rate of the mainstream is faster in the JICF than in the impinging flow.The loss ratio of acetylene in the quenching process is 2.89％ for the JICF and 1.45％ for the impinging flow,showing that the impinging flow configuration is better and feasible for the quenching of POX of methane.     

Experimental investigation of two-phase electrolysis processes: comparison with or without gravity

During two-phase electrolysis, bubble production occurs at one or two electrodes. This yields a large change for the electrolyser electrical and hydrodynamic properties. Under normal Earth gravity, the bubble production at the electrodes induces a macro-convection in the electrolyser. This leads to a modified local current density distribution at the electrodes. When gravity is avoided, bubbles are no longer subject to buoyancy forces and to the induced natural flow friction forces. Electrolysis was performed using a potentiostat, and gas bubble evolution was observed with cameras. Quantitative evolution laws for the electrochemical cell voltage, bubble diameter and population during two-phase electrolysis are established in function of the current density and gravity variation.     

Studies of the discharge mechanisms in electrochemical arc machining

The electrochemical arc machining (ECAM) process combines features of ECM and EDM by application of a pulsed voltage between a cathode-tool and anode-workpiece in a liquid electrolyte. The new process offers rates of metal removal as much as five and fifty times greater than ECM and EDM, respectively. The study reported in this paper explores some of the fundamental processes which occur during ECAM. Experimental apparatus was constructed to enable single pulse discharges to be studied. Results are presented for 200μs pulses between 2 mm diameter silver steel electrodes in NaNO₃ and NaCl electrolytes over a gap range of 10 to 90μm. Four stages of electrical phenomena were distinguished within a pulse: (a) high frequency voltage and current oscillations, (b) high rate electrochemical action, (c) low rate electrochemical action, and (d) electrodischarge action. The relative durations of the electrochemical and discharge phases, respectively, increase and decrease with increasing gap width, and vary with electrolyte type and concentration. High speed photography with an image-converter camera was used to record the occurrence of both spark and arc discharge in an electrolyte.     

低浓度瓦斯燃料电池发电技术研究

为了解决我国矿井风排瓦斯因浓度低、不易利用而直接排放,污染空气这一难题,提出了低浓度、超低浓度瓦斯燃料电池中发生氧化还原反应产生电能的瓦斯利用新技术。该技术是将低浓度瓦斯与氧气分别从燃料电池的不同电极充入池内,发生得失电子的化学反应,将化学能转化为电能,可以将这部分电能加以储存利用。分析表明:瓦斯在燃料电池中氧化产生的电能比其经过其他形式产生的电能高50%。此外,瓦斯燃料电池发电利用技术还具有不受瓦斯浓度、湿度、杂质等因素制约的优点,有效地克服了低浓度瓦斯在内燃机中燃爆发电等技术的弊端。     

熔体静电纺丝中电极结构对电场和纤维的影响

采用Ansys数值模拟方法,建立了电场分析的有限元模型,研究了电极结构不同时的电场分布及其对纤维直径的影响,以及电压大小对纤维直径的影响。并进行了实验对照分析,发现电极结构包括圆板电极和圆环电极影响熔体静电纺丝的电场分布,但场强最大都出现在喷嘴处,并随接收距离的增大成不同趋势减小,但中空电极能集聚电场,稳定场强,获得更细的纤维。     

Polarization curves for an alkaline water electrolysis at a small pin vertical electrode to produce hydrogen

During two‐phase electrolysis for hydrogen production, according with alkaline–water electrolysis process, there are bubbles which are created at electrodes which imply a great hydrodynamic acceleration in the normal earth gravity field and then a quite important electrical properties and electrochemical processes disturbance, for both transport and reaction. This disturbance can lead to the modification of the local current density and to anode effects for example. In this work, a model experimental set‐up is studied. The vertical pine electrode of small electro active surface area is surrounded with a large surface counter electrode. The hydrogen production is performed at the working electrode and effort is focused here upon the global electrochemical cell electrical performances. The polarization curves intensity vs. applied voltage are experimentally measured and presented for different factors such as: the electro active species concentration, nature and counter electrode diameter factors. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

Two phase visualization by electrical impedance tomography with prior information

Numerical and experimental work was conducted to develop a visualization technique for the phase distribution in a two-phase flow field with known internal structures by electrical impedance tomography technique, which reconstructs the resistivity distribution with the electrical responses that are determined by corresponding excitations. The finite element method is employed to solve the electrical field induced by the currents through electrodes placed along the boundary and a modified Newton-Raphson iterative method is used to determine the search step minimizing the error between the calculated and the measured voltages at the electrodes. The locations and resisitivities of the known structures are considered as prior information. To mitigate the ill-posedness of inverse problem and to incorporate prior information, the modified Tikhonov regularization technique is employed. Also, with an apparatus developed for impedance imaging this study attempts to reconstruct the images of the simulated bubble distributions and the reconstructed images imply the potential possibility of the electrical impedance tomography for the two-phase flow visualization.     

Experimental studies and model validation for the optimization of electrodes configuration in a molten salt electrorefiner

Molten salt electrorefining is a high-temperature electrochemical process for treating the spent metallic fuel from fast reactors and is aimed at the separation of U and Pu from fission products. Potential and current distribution analysis was carried out by experimental studies as well as modelling using COMSOL Multiphysics for various electrode configurations. A 2D/2D axisymmetric geometry model was used to evaluate the potential and current distributions. The effect of the following parameters was evaluated: (1) configuration having two pairs of electrodes in parallel/staggered arrangement; (2) centre-to-centre distance between the electrodes; (3) solid cathode with and without insulation at the bottom; (4) Cd cathode and (5) cathode surface area. The resistance of the electrorefiner was calculated using COMSOL model for various electrode configurations and compared with that obtained experimentally. There was very good agreement between the experimental values and the simulation results. The computed cell resistance was also validated with published data. A sensitivity analysis was also performed to determine the parameter that more significantly influences the cell resistance. The two parameters that were varied were the electrolyte conductivity and the cell voltage. It is observed that of the two parameters the cell resistance is most sensitive to the electrolyte conductivity and there is no change in cell resistance with cell voltage.     

Electrochemical analysis of a photoelectrochemical chloralkali reactor

In the present study, the electrochemical model for a newly designed photo electrochemical hydrogen production reactor is discussed. The reactor integrates the photochemical hydrogen production with an electrochemical chloralkali process. To neutralize the hydroxyl ions into the chloralkali process, the ideal minimum required potential is 2.18 V. However, there are losses in the solution, membranes and electrodes. These losses should be calculated to find the exact voltage requirement of the photoelectrochemical hydrogen production reactor. An electrochemical model is developed to calculate these losses in the reactor. Effect of brine concentration, electrolyte concentration, distance between the electrodes, current density and temperature are evaluated. The results show that a minimum voltage is required when the distance between the electrodes becomes a minimum at the highest possible temperature, lowest current density and at highest concentrations of brine and electrolyte. Furthermore, they indicate that brine and electrolyte concentrations do not have significant effect on required voltage.     

Electrochemical performance of polymer-derived SiOC and SiTiOC ceramic electrodes for artificial cardiac pacemaker applications

In an implantable electrode, such as a pacemaker electrode, fibrotic tissue formation due to a foreign body reaction is an important challenge affecting the efficiency to transmit the electrical signal of the device. The chemical inertness, biocompatibility, and electrical conductivity of polymer-derived ceramics (PDCs) are promising features in terms of overcoming this challenge. Here, the electrochemical behavior of polymer-derived silicon oxycarbide (SiOC) and titanium-doped SiOC (SiTiOC) ceramic electrodes for use as pacemaker electrodes is investigated by measuring impedance spectroscopy and cyclic voltammetry. In addition, typical stimulation electrodes such as iridium oxide, titanium nitride, platinum, and glassy carbon were prepared and loaded simultaneously into a custom-made electrochemical testing platform for comparison with SiOC and SiTiOC electrodes under identical conditions. The SiOC and SiTiOC electrodes shows a wide electrochemical stability window in the range of ?0.9 to 1.2 V with a double layer capacitance as the charge injection mechanism at the electrode/phosphate-buffered saline interface. Also, analyzing the voltage transient shows that the maximum charge injection of the SiTiOC electrode was about 28 μC/cm². The results of the electrochemical evaluation and comparison of SiOC and SiTiOC stimulating electrodes will be helpful to understand fundamental characteristics for the potential of this material as candidate for next-generation pacemaker electrodes.     

Variation of Cell Voltage with Reaction Time in Electrochemical Synthesis Process of Sodium Dichromate

To address the problems existing in the traditional production technique of sodium dichromate, a new green technology of producing sodium dichromate with an electrochemical synthesis method was studied. Using a self‐made electrosynthesis reactor of pure titanium and stainless steel, with a multiple‐unit metal oxides combination anode, a cathode of stainless steel, and a reinforcing combination cation exchange membrane with perfluorosulfonic and perfluorocarboxylic polymers, experiments were carried out on the direct electrochemical synthesis of sodium dichromate from sodium chromate. From the experimental results and electrochemical reaction principles, it was shown that the electrochemical synthesis reaction process of sodium dichromate may be quantitatively determined from the variation of the cell voltage measured macroscopically with reaction time. Cell voltages were experimentally measured at different initial sodium chromate concentrations in the anolyte, and the dependence of the cell voltage on reaction time was discussed. The mathematical model of the variation of cell voltage with reaction time and the change rate equation of cell voltage were established, and satisfactorily formulated the change law of cell voltage in the electrochemical synthesis process of sodium dichromate.