Mass Transfer of Ozone in a Novel In Situ Ozone Generator and Reactor

A porous tubular reactor that also served as an electrode for ozone generation was studied in this research to determine the effects of in situ ozone generation on mass transfer and reaction rates. Experimental data over a range of gas flow rates and ozone generation rates gave KLa values in the range 0.77–1.14?min?1. These values are more than double the values typically reported for bubble columns, and about 30% higher than that for packed beds. The specific power requirement for the laboratory-scale in situ reactor is an order of magnitude lower than that for bubble columns and stirred tank reactors that are used for ozone dissolution. A compartments-in-series fluid flow model was developed to describe the reactor system, and this model provides a good comparison to the experimental data for dissolved ozone and off-gas concentrations in the reactor. Sensitivity analyses indicate that the dissolved and off-gas ozone profiles are most sensitive to the gas–liquid partition coefficient and the overall mass transfer coefficient.     

高铝中钛高炉渣脱硫的动力学机制

 以现场高炉渣化学成分为基准,利用纯化学试剂制备试验渣样,研究了高铝中钛型高炉渣脱硫的动力学过程,确定了其脱硫的动力学参数。结果表明,当反应温度一定时,铁水中硫含量w(［S］)随脱硫反应时间的延长而降低。试验条件下,高铝中钛渣脱硫过程属于二级反应,其限制性环节是硫在熔渣中的扩散。熔渣中硫的传质系数βS随着温度的升高而增大,硫在熔渣中的扩散活化能ED为127.03kJ/mol。     

Physical modeling of gas/liquid mass transfer in a gas stirred ladle

The absorption of gas through the plume eye and of an injected gas in a steelmaking ladle process was investigated, using a physical model of CO₂ absorption into a NaOH solution. The results show that the inert gas escaping through the plume eye is ineffective in protecting the bath from the atmosphere, and placing an oil layer (simulated slag) decreases the absorption rate significantly. Increasing the flow rate of the inert gas not only exposes more of the liquid surface to the CO₂ atmosphere, but also increases the mass transfer coefficient at the surface. The overall mass transfer between an injected CO₂ gas and NaOH solution includes the mass transfer through the surface of the bath as well as the mass transfer in the bubble dispersion zone. The difference between the mass transfer in the bubble dispersion zone and the overall mass transfer was found to be significant for relatively low gas flow rates. The mass transfer coefficient of CO₂ in the bubble dispersion zone was estimated using available information regarding the bubble size and velocity. Mass transfer coefficient estimated for the constant bubble frequency regime shows a dependence on gas flow rate. However, if a constant characteristic size of bubbles is assumed as an alternative approach, the mass transfer coefficient is independent of the gas flow rate.     

CaO-SiO2-MgO-Al2O3-BaO渣系脱硫能力研究

为了探究温度、碱度（R）、MgO质量分数和BaO质量分数对高炉渣脱硫能力影响,以酒钢现场高炉渣实际成分为基准,选取分析纯化学试剂配制实验渣样,采用双层石墨坩埚法研究了含钡渣系的脱硫能力,并考察BaO对脱硫动力学条件的影响。研究结果表明,增大高炉渣碱度,提高渣中MgO质量分数均能使硫分配比增加,炉渣脱硫能力增强。渣中BaO质量分数由0增加到4%,硫分配比先逐渐升高后略有降低,BaO质量分数为35%左右时硫分配比达到最大值。BaO质量分数增加使得熔渣中硫的传质系数增大,脱硫速率明显提升。     

Mass Transfer of Ozone in Semibatch Stirred Reactor

The mass transfer of ozone from the gaseous phase into the aqueous phase plays an important role in determining the efficiency of ozonation. In this study, a mass-transfer model has been developed to simultaneously predict concentrations of the dissolved and outlet gaseous ozone in a semibatch reactor. A model in which the liquid phase is described as well mixed and the gas phase is described as a plug-flow system was used to estimate the mass transfer of ozone in both laboratory and pilot reactors. The self-decomposition of ozone was also incorporated into the model. The mass-transfer coefficient was found to increase with increasing gas flow rate, temperature, and ionic strength in the solution. Using a sensitivity analysis, the partition coefficient α was found to be the most sensitive factor that affects the concentration profile of dissolved ozone. However, the outlet gaseous concentration of ozone is quite insensitive to all physical parameters investigated in this study.     

On sulphur behaviour in steelmaking with sponge iron in an electric arc furnace

The sulphur behaviour in steelmaking by melting of charges containing from 38.7 to 95.4 wt.% sponge iron in the metallic input in a 70 t UHP electric arc furnace is investigated. The effect of both slag composition and temperature on the sulphide capacity of the slag and on the sulphur distribution ratio between slag and metal is studied. The kinetics of desulphurization are also treated. Regression analysis shows that the logarithm of sulphide capacity varies linearly with total lime equivalent, theoretical optical basicity and logarithm of slag basicity. Equations relating the sulphide capacity to these parameters as well as to the temperature are given. Based on these equations, functional relationships for the calculation of sulphur distribution between slag and metal are derived. Metallurgical reactions for metal desulphurization by slag and equilibrium relationships are given from which the slag-metal sulphur partition ratio can be calculated. In all cases, the results of the calculations are in line with the experimental data. The rate of desulphurization is expressed by an equation based on the boundary layer diffusion theory. Under the conditions of the present investigation, the activation energy of desulphurization is found to be 39 kJ/mol and the mass transfer coefficient of sulphur at 1600°C is equal to 0.014 cm/s.     

Design Model for Selective Catalytic Reduction Process: Solution of Convective Diffusion and NOx Reaction

A simple model for the design of selective catalytic reduction (SCR) process is presented. The two-dimensional mass transfer equation shown in Bai and Chwu (1997) is simplified and the analytic solution is obtained. The analytic solution is verified by the solution of the numerical two-dimensional model as well as published experimental data. Then it is applied for the design of the SCR reactor. Effects of operating temperature, inlet molar ratio of NH3∕NO, channel pitch, and gas flow rate on the SCR reactor volume are evaluated based on a designed NO removal efficiency. The NH3 slip problem of a given inlet ratio of NH3∕NO also is discussed. It is shown that the injection ratio of NH3∕NO must be slightly higher than the desired NO removal efficiency so that the reactor volume can be reduced and the problem of NH3 slip is not a major concern.     

Dynamic Mathematical Modeling of an Isothermal Three-Phase Reactor: Model Development and Validation

A catalytic reactor model (CatReac) that describes the transport and series reactions of compounds in a three-phase fixed-bed catalytic reactor is developed for the purpose of describing the volatile assembly reactor system within the potable water processor on-board the International Space Station. CatReac includes these mechanisms: advective flow, axial dispersion, gas-to-liquid and liquid-to-solid mass transport, intraparticle mass transport with pore and surface diffusion, and series reactions of multiple compounds. A dimensional analysis of CatReac revealed the following seven dimensionless groups may be used to determine the controlling transport and/or reaction mechanisms: (1) the Peclet number is the ratio of the advective to the dispersive transport; (2) the Stanton number is the ratio of the external mass transfer rate to the advective rate; (3) the Damk?hler number compares the reaction rate to the advective transport rate; (4) the surface diffusion ratio equals the rate of transport by surface diffusion divided by the rate of transport by advection; (5) the pore diffusion modulus is the ratio of the rate of transport by pore diffusion to the rate of transport by advection; (6) the ratio of the gas to liquid advective rates; and, (7) the Biot numbers for surface and pore diffusion compare the external mass transfer rate to the intraparticle mass transfer rate. These dimensionless numbers are used to evaluate the impacts of the different mechanisms on the overall performance of the reactor. The numerical solution using orthogonal collocation was validated for a wide range of controlling mechanisms by comparing model simulations with several analytical solutions: (1) Gas-to-Liquid mass transfer controlling the overall mass transfer-reaction mechanisms, for a wide range of Pe number values; (2) Liquid-phase dispersion controlling the overall process; (3) Liquid-to-solid mass transfer resistance controlling the overall mass transfer-reaction process; (4) Reactions in series with two possibilities (4a): No intraparticle mass transfer resistance, and (4b): Significant intraparticle mass transfer resistance; (5) Langmuir isotherm (5a): single compound, no mass transfer resistance, and (5b): multicomponent competitive adsorption without mass transfer resistance; (6) Unsteady state operation: Plug flow with mass transfer and no reaction. These validations systematically examine all the mechanisms that are included in the general model and examine the model limitations based on the controlling mechanisms.     

气相异辛醇影响溴化锂溶液传质特性研究

通过溴化锂溶液传质性能测试装置,研究了气相异辛醇添加量对溴化锂溶液表面张力的影响,以及在降膜吸收的过程中气相异辛醇的添加量和溶液的流量对传质系数的影响。结果表明：气相异辛醇的添加对溴化锂溶液的表面张力和传质系数均有明显影响,表面张力随异辛醇添加量的增加而减小,传质系数的变化规律与其相反。气相异辛醇分子在溶液表面的吸附作用降低了溶液表面张力梯度,从而引起的Marangoni效应,是对流传质强化比增大的重要原因。     

气升式反应器内流动与传质研究进展

综述近几年来气升式反应器内流动与传质研究成果.介绍气升式反应器结构上的改进以及操作条件等对气升式反应器内流动与传质的影响;揭示传质过程中各动力学模型;总结气升式反应器在生物、环境领域方面的应用研究进展.研究内容为功能性气升式反应器的设计和放大提供理论依据.指出今后的研究方向与重点是要探索各操作条件对气升式反应器性能的影响规律,同时必须结合其它领域研究成果、采用CFD模拟技术、实验流动测量技术等来开发高效新型气升式反应器.      

移动电磁场对铁水预处理脱硫速度的影响

 为探讨移动电磁场对冶金反应速度的影响作用,本研究对电磁搅拌下的铁水预处理脱硫进行了实验研究。将CaO-10 mass%CaF2脱硫剂加至铁水的自由表面或用载气带入铁水内部,并采用不同的搅拌方式和强度进行了电磁搅拌下的实验,得到了铁水中硫浓度随时间的变化曲线。研究发现电磁搅拌通过改变渣金界面状态及边界层厚度从而提高铁水脱硫速度,并得到了不同搅拌强度和不同搅拌方式的容量传质系数。最后提出一种环保和易操作的电磁搅拌下铁水预处理脱硫工艺。     

Perturbation Solutions for Thermal Process of Honeycomb Regenerator

 A parameter perturbation for the unsteady state heat transfer characteristics of honeycomb regenerator is presented. It is limited to the cases where the storage matrix has a small wall thickness so that no temperature variation in the matrix perpendicular to the flow direction is considered. Starting from a two phase transient thermal model for the gas and storage matrix, an approximate solution for regenerator heat transfer process is derived using the multiple scale method for the limiting case where the longitudinal heat conduction of solid matrix is far less than the convective heat transfer between the gas and the solid. The regenerator temperature profiles are expressed as Taylor series of the coefficient of solid heat conduction item in the model. The analytical validity is shown by comparing the perturbation solution with the experiment and the numerical solution. The results show that it is possible for the perturbation to improve the effectiveness and economics of thermal research on regenerators.     

鞍钢烧结烟气脱硫灰综合利用研究

采用化学分析、XRD和SEM等检测手段研究了鞍钢烧结烟气脱硫灰的化学成分,分析了烧结烟气脱硫灰再利用的影响因素,提出了鞍钢烧结烟气脱硫灰的综合利用思路。     

Inactivation of Cryptosporidium Oocysts in a Pilot-Scale Ozone Bubble-Diffuser Contactor. I: Model Development

A mathematical model was developed to simulate the performance of a pilot-scale ozone bubble-diffuser column. The reactor hydrodynamics was represented with the axial dispersion reactor model. An analytical solution was developed for the liquid and gas phase ozone mass balances in which dissolved ozone decomposes by first-order kinetics. Numerical approximations were provided for the mass balances for viable microorganisms and the more general case of dissolved ozone decomposition through a second-order reaction with fast ozone demand in natural organic matter. Model components required to predict the liquid and gas phase ozone concentration and viable microorganism number density profiles throughout the bubble-diffuser column included input parameters (liquid and gas flow rates, influent gas and dissolved ozone concentrations, temperature, and countercurrent or cocurrent operation mode), empirical correlations (dispersion number, volumetric mass transfer coefficient, Henry’s law constant), and batch or semibatch kinetic information (ozone decomposition rate constants and fast-ozone demand, and microorganism inactivation lag phase and rate constant). A sample model run for the case of first-order ozone decomposition revealed that the analytical and numerical solutions were practically identical.     

Separation of Th~(4 ) and RE~(3 ) with Hollow Fiber Extraction

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折流式移动流化床COREX煤气预还原粉铁矿的数值模拟

建立了折流式移动流化床内粉铁矿预还原的二维气固反应流CFD模型.模型的数值求解采用PHOENICS和FLUENT的联合求解.与之前的实验结果相比,在冷态条件下单床层平均压降和气固相流动行为的数值模拟结果与其基本一致,得出所提出的数学模型是可靠的.在此模型基础上,对采用COREX输出煤气对铁矿粉预还原的工艺过程进行热态模拟.在模拟的工况条件下,还原气温度的整体降幅700 K,气相CO和H_2还原势的利用率分别达到38%和26%,矿粉的还原分数达到75%,即反应器内有良好的气固换热而且对COREX煤气还原势的利用率较高,实现了对还原气热能和还原势的梯度利用.      

烧结烟气脱硫技术的研究与发展

从中国烧结烟气SO2排放的严峻形势出发,论述了烧结烟气的特点及SO2的控制方法,介绍了石灰 石膏法、氨 硫酸铵法、密相塔法、循环流化床法、MEROS法和活性炭法等几种典型烧结烟气脱硫技术的工艺原理,分析了中国烧结烟气脱硫技术的发展,通过研究提出了选择性脱硫方法与实施方案,并论述了烧结烟气脱硫技术的选定原则与发展方向。     

Mass Transfer Effects on Kinetics of Dibromoethane Reduction by Zero-Valent Iron in Packed-Bed Reactors

Mass transfer effects on the kinetics of 1,2-dibromoethane (EDB) reduction by zero-valent iron (ZVI) in batch reactors, a laboratory scale packed-bed reactor, and a pilot scale packed-bed reactor are described. EDB was debrominated by ZVI to ethylene and bromide. EDB sorption to the cast iron surface was nonlinear and was described by a Langmuir equation. Laboratory scale column studies showed a nonlinear dependence of EDB removal on flow rate and initial EDB concentration. A nonequilibrium model of EDB sorption and reaction dependent on mass transfer was constructed using the laboratory scale data. The model was verified using data from a larger pilot scale packed-bed reactor that was used to remove EDB from contaminated groundwater. The data showed two distinct removal processes, an initial rapid phase dominated by mass transfer followed by a slower phase where surface reactions dominated. The model successfully predicted the transition from mass transfer controlled to surface reaction controlled conditions in the pilot scale data.     

RH-KTB精炼中钢液溶氧过程动力学的水模拟研究

用顶吹CO2－NaOH溶液体系模拟了RH－KTB顶吹氧溶氧过程。通过对碱液吸收CO2反应动力学的研究,考察了操作参数对RH－KTB顶吹氧脱碳过程中溶氧反应的影响。结果表明：提高气相中氧分压、增加提升氩气流量或采用低枪位喷吹都有利于加速溶氧脱碳。实验中还发现：顶吹氧气流量对容积传质系数影响很小,对熔池内的钢液流动状态影响不大。