T型微通道内吸收H_2S实验研究

在水力学直径为1.00 mm的方形T型微通道内,采用质量分数为40%的N-甲基二乙醇胺(MDEA)吸收含有体积分数为0.12%的H2S混合气体。实验发现,在微通道内可以获得很高的H2S脱除效率,在气液体积比为200∶1时,其脱除效率可以达到99.5%。在微通道内的H2S传质过程中,H2S传质的阻力主要集中在气侧,而且气侧体积传质系数随着气体和液体表观速率的增加而增加。提出了在过渡区的二相流型中,气侧体积传质系数的量纲一经验关联式,其计算值和实验值吻合得很好。通过比较发现,微通道比其他传统设备的气侧体积传质系数高出1—2个数量级。     

废水好氧生物处理工艺中氧的传质与强化的理论与实践

废水处理好氧生物工艺供氧过程的控制步骤是气液传质作用,即将气体分子氧转化为足够微生物用于氧化污染物的溶解氧（DO）,包含碳源BOD5的降解、氨氮的硝化和总氮的去除以及无机COD氧化的共同需求。文章指出DO的传质过程由总传质系数K_La决定,废水性质、生物量、污泥龄、微生物耗氧速率、微生物种群等因素都会影响K_La。DO的浓度梯度是气液固三相氧传质的主要推动力,气液传质受水温、水质、氧分压、气泡大小、液体紊流程度和液膜更新速度等的影响,通过提高氧气分压、增大气泡比表面积、强化气液混合以及无泡供氧等方式及其它们的结合,或者控制污泥流态化程度及其污泥龄,可以获得微生物摄氧能力的提高。本文指出在对水质特征、环境条件、微生物特性、反应器流体特性以及运行参数等优化的基础上,结合一些研究新的方向,如无泡供氧、纯氧/富氧曝气的气泡行为,流场分布、湍流构造、浓度梯度的流体行为,挡板内构件、流态化控制的反应器结构优化,以及充分考虑负荷的HRT和SRT的运行工艺条件,可以实现更加全面的节能目标。     

旋流气液两相强化吸收CO2的传质性能

为强化二氧化碳的吸收过程,采用一类旋流逆向气液多级接触的方式,以NaOH溶液为吸收剂,研究其与大跨度浓度CO₂(2.5%～15%)接触反应的传质性能。分别探讨了吸收剂浓度、吸收剂流量、烟气CO₂浓度、烟气流量及反应温度对气相总体积传质系数(K_ga)的定量影响。结果表明,在实验条件下,其K_ga可达(4.53×10^-5)～(9.22×10^-5)kmol·m^-3·s^-1·kPa^-1。与双级直流喷雾和单级旋流喷雾相比,旋流逆向气液多级接触能够有效强化大跨度浓度CO₂的吸收过程。K_ga随吸收剂浓度、流量和反应温度的增加而增加,随CO₂浓度增加呈现先增加后减小(CO₂浓度大于5%)的非线性关系,随气体流量增加先增加后趋于稳定。     

旋流吸收器气液吸收传质过程研究

根据旋流吸收器中分散液相不同的运动形态建立了伴有化学反应的气液吸收传质模型,且该模型的表达形式与Danckwerts的表面更新理论一致。从模型上看,液侧传质系数kL正比于扩散系数DA和表面更新率S的平方根,这一正比关系还得到了实验结果的部分验证。根据实验结果可以看出,与其他吸收器相比,作为一种结构简单的静态设备,旋流吸收器同样可以提供一个强化传热、传质的流体力学环境。     

浆料系统内上升气泡周围微细颗粒浓度分布和附着效率的理论研究

Quantitative prediction of distribution function and adhesion efficiency of particles around a rising bubble in slurry systems is presented in this work. By solving the convection-diffusion equation (Fokker-Planck equation), the influence of Brownian diffusivity of fine particles on concentration distribution and adhesion efficiency is demonstrated with the hydrodynamic force and van der Waals attractive potential between particles and bubble considered. It is found that two kinds of mechanism dominate the adhesion process of particles on bubble according to different Peclet number or size of particles and bubble, as well as other properties of the slurry systems. In addition, the viscosity ratio of bubble to the suspending fluid was found to have obvious influence on particle adhesion.     

搅拌反应器中氧气 - 正癸烷 - 水溶液体系的气液传质实验

用亚硫酸钠氧化法测定了机械搅拌高压釜中氧气-亚硫酸钠溶液体系、氧气-正癸烷-亚硫酸钠溶液体系和氧气-正癸烷-亚硫酸钠溶液+表面活性剂体系的气液体积传质系数(k La).研究了搅拌转速、搅拌桨高度、有机相与水相体积比和表面活性剂浓度对k La的影响,得到了经验关联式.k La随有机相体积分率和表面活性剂浓度的增大而降低,随搅拌转速、搅拌桨高度与液相高度比的增大而增大.     

电场强化铜矿排土场氧气传质

在排土场微生物浸出过程中,通过电场作用下的气泡受力分析和强化传质实验,首次提出了利用电场强化氧气向溶浸液中传质过程的方法,结果表明：电场能够强化氧气向溶浸液中的传质过程,而且效果和电场的强弱以及浸矿溶浸液的性质有关;实验中所加电场强度和溶浸液浓度越高,电场强化传质的效果越明显。传质速率的大小和传质系数、气泡大小、气泡在水中的运动、气液比以及气相氧气的质量浓度等因素有关。在强度为80 V·mm^-1的电场作用下,和没有电场的情况相比,总传质系数提高28. 2%。     

不同中空纤维膜组件对甲烷和氧气无泡曝气过程的影响

为探索无泡膜曝气用于甲烷高效、安全生物转化的可能性,测试了3种中空纤维膜组件对甲烷和氧气传质速率的影响.所测膜组件分别为致密硅胶中空纤维膜(A)、疏水性微孔聚丙烯中空纤维膜(B)及亲水性微孔聚醚砜中空纤维膜(C).结果表明,膜组件A和B可以同时强化甲烷和氧气的气液传质过程,对甲烷进行无泡曝气,两者的体积甲烷传质系数(KLa)相近,分别为3.19和3.78h·1,约为传统鼓泡曝气的3倍.对空气进行无泡曝气时,膜组件B的KLa值(溶氧)为61.1h·1,是A的2.6倍,是传统鼓泡曝气的24.8倍.     

吸收过程的界面非平衡传质机理

针对气体吸收过程,以分子热力学为基础,结合普遍化的化学势推动力通量方程,导出了传质存在时两相界面处的浓度关系,并针对不同情况进行了求解.提出了一个反映液相侧动力学状况的无因次数群Biot数Yo,Yo数越大界面处两相越偏离平衡.界面浓度是与Yo和液相主体浓度密切相关的.对于气相阻力可以忽略的吸收过程,两相传质速率的大小主要取决于液相的溶质界面浓度和液膜厚度.采用激光显微全息干涉技术对甲醇,乙醇,正丙醇静止吸收CO2时的界面浓度进行了测定,试验结果表明了本研究模型的正确性.     

有机分散相强化气体吸收的研究

分析了有机分散相强化气体吸收机理,阐述了分散相强化气液传质的意义.以水吸收二氧化碳为研究体系,实验考察了加入辛醇、辛烷对吸收过程影响,运用因次分析法分析有机分散相分散程度对吸收效果的影响,进而确定强化气体吸收的最小搅拌速度,并用插值函数微商法确定体积传质系数KLa.研究结果表明:有机分散相的加入能够显著提高气体吸收速率;适宜的搅拌速度有利于液液体系分散,促进传质;降低界面张力和增加气含率也有利于传质.     

Ammonia synthesis enhanced by magnesium chloride absorption

Conversion to ammonia with Haber–Bosch catalysts can be increased above 95% by selective absorption of ammonia by MgCl₂. The maximum conversion depends on reaction and absorption equilibria. At very short times, the measured conversion rate is the same with and without absorption by the MgCl₂ salt; the overall rate constants are comparable to those in the literature. At larger times, conversion to ammonia can be over seven times greater with MgCl₂ than without. However, the overall rate constants can be over 10 times slower because they are controlled by ammonia diffusion in the solid salt. An approximate, pseudosteady state theory consistent with these results provides a strategy for improving the overall rate while keeping the conversion over 90%. For example, the absorption rates might be increased using smaller particles of absorbent on a porous inert absorbent support. The results provide part of the basis for designing small scale ammonia plants. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1364–1371, 2015     

微通道内单乙醇胺水溶液吸收CO2/N2混合气的传质特性

采用高速摄像仪对400 μm×400 μm T形微通道内单乙醇胺（MEA）水溶液吸收混合气中CO₂过程的气液两相流及传质特性进行了实验研究,微通道内的压力降采用压力传感器进行测量。考察了弹状流型下气液两相流量及MEA浓度对压力降、比表面积和传质性能的影响。结果表明,当MEA浓度不变,气液两相流量增大时,压力降、比表面积、传质系数、体积传质系数和增强因子均增大,并逐渐趋于恒定。当气液流量不变,MEA浓度增大时,压力降、传质系数、体积传质系数和增强因子增大,但比表面积减小。实验条件下,压力降范围为2.00~5.23 kPa,化学吸收过程的传质系数范围为7.74×10^-4~2.97×10^-3 m·s^-1。对于伴有快速化学反应的传质过程,以Sherwood数、Reynolds数、Schmidt数及增强因子为变量建立了体积传质系数的预测关联式,平均偏差为5.09%,具有良好的预测性能。     

Gas-liquid mass transfer in two and three-phase upflows through a vertical tube

Oxygen absorption rates were measured to determine volumetric coefficients of gas-liquid mass transfer coefficients k_La in gas-liquid and gas-liquid-solid upward flows through a vertical tube. The liquid was deionized water or aqueous glycerol solution, and the solids were glass beads or polystyrene beads. The dependencies of k_La on gas velocity, liquid velocity, temperature, solid material, and solid concentration were examined. The experimental results were correlated with empirical equations. The mechanisms of the solid loading effect are discussed.     

A contribution to the measurement of oxygen mass transfer in a laboratory pressure reactor

A method was used to measure the liquid‐side volumetric coefficient of oxygen mass transfer (k_La) in closed, semi‐batch pressure reactors used in hydrometallurgical laboratories. In this method, the oxygen pressure was monitored as oxygen was continuously sparged into a pressure vessel containing a sodium sulfite solution. A material balance equation was derived for oxygen in the vessel and the experimental data were fitted to this equation. From the constant parameters of the equation, k_La was calculated. The solution in the vessel also contained an appropriate amount of cobalt catalyst so that oxygen was consumed rapidly by oxidation of sulfite to sulfate. Under these conditions, the oxygen concentration in the bulk liquid phase could be assumed to be equal to zero. Values of k_La determined by the method under various conditions were reproduced within 12% deviation from the average values. k_La was found to increase moderately with temperature in the range of 25 to 75 °C, with an activation energy of 33.09 ± 1.33 kJ mol⁻¹. The presence of hydrophobic or hydrophilic solids was found to have a deleterious effect on k_La. © 2000 Society of Chemical Industry     

Kinetics of oxygen absorption in aqueous sodium dithionite solutions

The absorption and reaction of oxygen in aqueous alkaline solutions of sodium dithionite has been experimentally investigated in a novel gas-liquid contactor. The novel gas-lift bubble column contactor was used to study the kinetics over wide ranges of reactant concentrations, temperature, and pH. The oxygen-sodium dithionite reaction was found to be first-order with respect to dithionite in the range of dithionite concentration < 0.1 M, and second-order in the range of dithionite concentration > 0.1 M. The reaction with respect to oxygen was found to be zero-order for all dithionite concentrations. These results and experimental investigations of the effect of solution alkalinity and temperature on the reaction rate are consistent with previous findings obtained in different gas-liquid contactors. The results thus confirm the feasibility of using the gas-lift bubble column for the kinetics of gas-liquid reactions.     

运动颗粒对传质过程影响的格子Boltzmann模拟

颗粒的主动运动对传质过程有重要影响.以表面恒浓度的二维球形颗粒为研究对象,采用耦合传质的格子Boltzmann方法(LBM)模拟了颗粒在自旋和振动两种情况下的相间传质过程.选择浸入运动边界法和非平衡态外推法处理运动颗粒边界,研究了颗粒自旋速度、颗粒振幅及振动频率对传质过程的影响.结果表明,中等雷诺数的自旋颗粒绕流中,随...     

磷石膏强化氨法CO2捕集机理与模型

基于化学活性颗粒强化气液吸收机理,建立了磷石膏悬浮液强化氨法烟气CO₂捕集模型。以液膜内量纲一传质距离λ^*为特征参数,增强因子E=1/λ^*+qβλ^*/2。用恒温反应器在不同搅拌转速及磷石膏颗粒固含量下实验测定CO₂吸收增强因子对模型进行检验,结果表明:随颗粒固含量由5%增加到30%(质量分数),增强因子由1.69增加到2.10;而随搅拌转速从150 r·min^-1增加到300 r·min^-1,增强因子仅由1.75略增到1.80,表明磷石膏颗粒固含量及溶解速率是影响增强因子的控制性因素。实验结果与模型预测值吻合良好, 偏差小于10%。     

活性炭/水浆料中CO2吸收过程的增强

针对分散相微粒增强难溶气体的吸收过程,提出了一个一维非稳态非均相传质的二区模型,并进行了理论求解。根据表面更新理论,得到了增强因子的数学表达式。利用恒温反应釜,对活性炭/水浆料中发生的CO2吸收过程进行了实验研究,测定了不同颗粒浓度及转速下的增强因子。实验结果与模型预测值吻合良好,表明本文模型具有很高的预测精度。