EFFECT OF FINE SOLID PARTICLES ON GAS-LIQUID MASS TRANSFER RATE IN A SLURRY REACTOR

The influence of suspended fine particles of differing adsorbing capacity (activated carbon, avicell cellulose, SiO₂, and molecular sieves) on the liquid-film mass transfer coefficient κ_L, was examined experimentally in a stirred cell of well-defined gas-liquid interfacial area by chemical methods. The greatest effect on κ_L was observed with the activated carbon (about a threefold increase). An addition of glycerine in excess of 2.5 × 10^-3 k mol/m³, which was adsorbed on the particles preferentially, removed this increase in κ_L totally. Amongst other particles, only avicell cellulose showed measureable effects. The increase in κ_L values was inversely proportional to the temperature and the stirring speed, and the particle loading was found to be immaterial after a certain value. When the reaction rate increased (hence, when the thickness of dissolved gas-rich layer decreased) by gradual addition of a homogeneous catalyst (i.e. Co⁺⁺ for sulphite oxidation), the effect of particles on κ_L decreased and eventually it disappeared.     

INHIBITION OF MASS TRANSFER TO POROUS ADSORBENTS BY FINE PARTICLES AND ORGANICS

Activated carbon and ion-exchange resins are used industrially for the extraction of metal cyanides from slurries. This paper attempts to quantify the inhibition of mass transfer to these adsorbents owing to fouling by fine particles and organics usually present in leached pulps. In this study, resins and carbon were contacted with either solutions of organics, or dilute slurries of synthetic silica or alumina in batch stirred tanks. Silver cyanide was used as an adsorbate to detect changes in the mass transfer characteristics of the adsorbents, which were ashed to determine the loading of silica or alumina. The rate of intrusion of fine particles into the adsorbent matrix was relatively fast, and was dependent on the concentration of particles in the slurry. SEM mappings of Si and Al showed that the intruded particles were distributed fairly homogeneously throughout the adsorbent particles. It was found that the presence of fine inert particles and organics had no effect on the equilibrium loading of silver cyanide on either the resin or carbon. The reduction in the rate of adsorption appeared to be a kinetic influence, and could be attributed to two effects, viz.: (1) pore blocking, and therefore retarded diffusion into the resin bead or carbon granule, and (2) temporary blinding of the resin or carbon surface. By fitting a film transport-surface diffusion model to the profiles for the uptake of silver cyanide, it was found that a decrease in the intraparticle diffusivity was associated with pore blocking.     

多段内导流筒气升式反应器中气体分布器对气含率和气液传质特性的影响

在为微生物高密度培养而设计的１０Ｌ多段内导流筒气升式生物反应器中，研究了Ｎａ２ＳＯ３－空气体系单孔喷嘴和烧结金属管等不同气体分布器对气含率ε、体积氧传质系数ＫＬａ和流动特性的影响．结果表明，孔径为２０～２５μｍ的烧结金属管的整体性能最好，在最佳操作气速３．７～４．０ｃｍ／ｓ下，ε超过１９％，ＫＬａ可达０．２９ｓ－１．其ε和ＫＬａ随Ｕｇ有如变化规律：ε＝０．１９５２－１．５３５１０－２ｅ－１．３９１ＵｇＫＬａ＝０．２７＋２．９７１０－２Ｕｇ－７．２３１０－３Ｕ２ｇ（１．５＜Ｕｇ＜６ｃｍ／ｓ     

VOLUMETRIC MASS TRANSFER COEFFICENTS OF GAS LIQUID JET LOOP REACTORS BY OXIDATION OF HYDRAZINE

Oxidation of hydrazine in the presence of a homogeneous catalyst (CuTeSP) has been proved as a suitable reaction for the determination of volumetric mass transfer coefficients k_La of stirred tank reactors. This method is applied to a gas liquid jet loop reactor (JLR).At power inputs of N/V_R≤ 8 kW/m³ k_La values of about 0·1 and 0·4s^-1 were achieved. The evaluated values agree well with those determined by a stationary physical method.     

多相机械搅拌气升式环流反应器中的气液传质

由空气水玻璃珠（ρ＝２６３０ｋｇ／ｍ３,ｄｐ＝２５μｍ）构成三相体系,在内置机械搅拌桨的内循环反应器中进行实验。实验条件：表观气速Ｕｇ０．５～１９．０ｃｍ／ｓ,固含量εｓ１％、２％、４％（质量分数）,搅拌桨速度为０～１２００ｒ／ｍｉｎ。结果表明总体积传质系数ＫＬａ随气体表观气速和搅拌速度增加而增加。总能量耗散速率同时受通气能量耗散速率与搅拌机械能量耗散速率的影响。搅拌转速一定时,搅拌机械能量耗散速率随表观气速的增加而下降。从能量角度考虑,表观气速和搅拌速度的选择应有一个良好的匹配。存在固体颗粒时,传质系数ＫＬａ与传质界面面积ａ均得到改进。对于２５μｍ玻璃珠体系,ＫＬａ值随固含率变化,其最大值的产生在２％固含率左右,固含率继续增加,则ＫＬａ降低。最后对ＫＬａ固含率及能量耗散速率作了关联。     

INFLUENCE OF INITIAL LIQUID DISTRIBUTION ON MASS TRANSFER IN PACKED BEDS

1 INTRODUCTIONA major problem in the design of packed columns is dimensioning the liquid distributor.Thenumber of outlets is an important factor,because it governs the quality of the liquiddistribution at the inlet cross-section and thus the extent to which the packing is Wetted.Thehigher the degree of wetting and thus the greater the area of phase contact,the more efficientthe mass and heat transfer within the bed of packing.     

UNSTEADY, TWO-DIMENSIONAL HEAT AND MASS TRANSFER IN A PACKED BED OF FINE PARTICLES WITH AN ENDOTHERMIC PROCESS

The basic differential equations controlling the temperature and concentration field in a single packed bed of fine particles were derived and solved for the general case in which unsteady, two-dimensional heat and mass transfer lakes place with an endothermic process.

The time-change of particle- and fluid-temperature and concentration of water vapor (humidity) were calculated by a numerical method which assumed that the rate of the endothermic process can be expressed by a first-order rate equation and that the fluid flowing through the bed is of the piston flow type.

The experiments were conducted for the drying of silica-gel and the two-stage dehydration reaction of natural gypsum to demonstrate the applicability of the present theoretical analysis.

It has been found that the calculated results show satisfactory agreement with the measured data within the range of the experimental conditions employed.     

THE EFFECTS OF THE SOLUBILITY LAW ON MASS TRANSFER IN ANNULAR LIQUID JETS

Underpressurized, annular liquid jets have been studied under steady and transient conditions in order to assess the effects of Henry's and Sievert's solubility laws on mass transfer. It is shown that, in general, Henry's solubility law predicts a higher, steady state mass absorption rate than Sievert's law. The rate at which the under-pressurized, annular liquid jet tends towards an equilibrium, non-pressurized configuration is higher for Henry's than for Sievert's solubility law. Both this rate and the steady state mass absorption rate increase as the Weber number, the ratio of the solubility at the inner interface to that at the outer one, the product of the gas constant times the temperature and the solubility of the gases surrounding the jet, the ratio of the product of the pressure of the gases surrounding the annular jet times the annular jet's mean radius at the nozzle exit to the liquid surface tension, and the nozzle exit angle are increased, and as the Froude and mass Peclet numbers, the annular jet's thickness-to-mean radius ratio at the nozzle exit and the initial pressure of the gases enclosed by the annular jet are decreased.     

MASS TRANSFER CHARACTERISTICS OF THE MEMBRANEOUS GAS DISTRIBUTOR

1 INTRODUCTIONIt is well known that the throughput of many gas-liquid reactors is limited by the rate atwhich a gaseous component can be transferred from the gas to the liquid.For example,it isthe oxygen transfer capacity of a fermentor that set the upper limit to the productivity ofmost aerobic fermentation.Therefore,studies have been in progress to increase the masstransfer rate between the gas bubble and the broth by acting on classical parameters of bubblesize and the turbulence of flow.However,the intensive turbulence of flow usually means     

HYDRODYNAMICS AND MASS TRANSFER CHARACTERISTICS OF A LIQUID/LIQUID STIRRED CELL

The hydrodynamics and mass transfer characteristics of a stirred cell for contacting immiscible phases are examined. When each phase is stirred with a rotating disk in laminar flow, such that the interface is stationary, the rate of diffusion in the absence of any interfacial resistance is obtained using a similarity solution. The hydrodynamics, specifically the radial velocity derivative at the interface, which is the most important component of the mass transfer solution, is obtained by combining the solutions for a finite disk and for the relationship between disk velocity and fluid core velocity. Excellent experimental agreement, within 5% of the theory, is observed.     

浓度对传质系数的影响及多元物系传质

在筛板塔中对甲醇-乙醇-水三元物系进行精馏传质过程实验,考虑浓度对传质系数的影响建立了一个数学模型,对各组分在塔中的浓度分布进行模拟计算,计算结果能正确反映各组分在塔中浓度分布的变化规律.实验与计算结果都表明在某些浓度范围内乙醇呈现出比较复杂的变化规律.     

气液环流反应器中基于大、小两类气泡的气相返混模型和气液传质特性

在矩形卧式多级串联环流反应器中，改变气速和液相表面张力，将气泡分为大气泡和小气泡两大类，进行研究。着重考察了两者对气相返混和气液界面传质的贡献，利用气相大、小气泡的分区模型，传质模型等进行了模拟计算，并提出了“有效气含率”这个新概念     

EFFECT OF MICROBIAL ADSORPTION AT THE GAS/LIQUID INTERFACE ON OXYGEN ENHANCEMENT FACTORS

The adsorption of micro-organisms at the gas/liquid interface causes both an increase in the oxygen respiration rate and a decrease in the oxygen diffusion coefficient near the interface. An increase in the oxygen consumption rate increases the oxygen mass transfer rate into the bacterial broth but a decreased oxygen diffusion coefficient reduces the mass transfer rate. These two factors must be taken into account when enhancement factors are calculated.     

EFFECTS OF MASS TRANSFER ON THE THINNING AND RUPTURE OF A PLANE PARALLEL LIQUID FILM

The effects of mass transfer and physical properties upon the thinning and rupture of adraining plane parallel film are investigated.An equation is derived in which the thinning rate is afunction of bulk properties.surface properties(surface tension,surface viscosities,and the variationof surface tension with surface concentration),intermolecular forces(London-van der Waals forcesand electrostatic double layer forces),adsorption and surface diffusion coefficients,bubble size andfilm thickness.An estimation for the critical thickness at which a film rupture is carried out and thecoalescence time is obtained by integration to the critical thickness,The coalescence time is predictedas a function of bulk and surface properties,London-van der forces,adsorption and surfacediffusion coefficients,and bubble size.     

EFFECT OF MICROBIAL ADSORPTION AT THE GAS/LIQUID INTERFACE ON OXYGEN ENHANCEMENT FACTORS

The adsorption of micro-organisms at the gas/liquid interface causes both an increase in the oxygen respiration rate and a decrease in the oxygen diffusion coefficient near the interface. An increase in the oxygen consumption rate increases the oxygen mass transfer rate into the bacterial broth but a decreased oxygen diffusion coefficient reduces the mass transfer rate. These two factors must be taken into account when enhancement factors are calculated.     

THE USE OF FRACTAL DIMENSION TO QUANTIFY THE EFFECT OF SURFACE ROUGHNESS ON FILM MASS TRANSFER ENHANCEMENT

Experimental results from previous work, contained in a companion paper by Van Vliet and Weber (1988), have shown qualitatively that the external film transfer coefficient for adsorption on particulate adsorbents is very dependent on the roughness of the mass transfer surface. Until recently a suitable method to quantify surface roughness was not available. Experimental data of film mass transfer coefficients of various activated carbons, carbonaceous adsorbents, and polymeric adsorbents are investigated. It is shown that film mass transfer is enhanced by the effect of surface roughness. The fractal dimensions of the adsorbent particle surfaces are determined and are shown to be linked to the degree of mass transfer enhancement. This suggests that the external mass and heat transfer enhancement properties of a rough surface are related to its fractal dimension.     

ON THE ROLE OF CONCENTRATION LEVEL OF NONDIFFUSING SPECIES IN GAS PHASE MASS TRANSFER AT HIGH TRANSFER RATES

Re-evaluation of high mass flux literature data from evaporation and absorption experiments suggest the validity of y_BM as a good correlation variable for predicting gas phase mass transfer at high transfer rates. This was done by testing Greiner and Winter's engineering model where y_BM explicitly emerges after manipulating their model equations. The manipulated model agrees well with the literature data within the range of 0.961 ≥y_BM ≥ a 0.549 and 7.3333 ≥ B ≥ -0.4757 which covers the mostly commonly chemical engineering conditions and geometries. Thus, the y_BM serves not only as a good correlation variable as has been commonly used under low to moderate mass transfer rales, but also applies to the controversial case of high mass transfer rates.     

THE STUDY ON THE MASS TRANSFER MECHANISM OF EUROPIUM ION THROUGH LIQUID SURFACTANT MEMBRANES

The transfer of trivalent europium ion in a liquid surfactant membrane system is investigated in order toclarify the characteristics of liquid membrane separation process and the availability of this technique forrecovering trivalent lanthanides and actinides.A layered structure model for the emulsion globule is sug-gested.The equations describing the relationship among the effective membrane thickness,the time andother factors are derived and verified experimentally.Results show that under certain conditions the decreas-ing concentration of europium ion in the external phase is proportional to the square root of the time,the acidity of the internal phase and the carrier concentration in the membrane phase.The membrane phase consists of kerosene(solvent),Span-80(surfactant)and di-(2-ethylhexyl) phosphoricacid(HDEHP,carrier).The internal phase is dilute nitric acid and the external phase is aqueous solu-tion containing Eu(NO_3)_3.The mass transfer rate of europium in this system is high and the recovery ofeuropium may be more than 99%.     

一种能同时提高固体吸附制冷吸附剂传热传质性能的方法

通过在沸石分子筛中添加膨胀石墨和发泡剂并固结成型进行处理,使吸附剂的导热系数和渗透性有了显著提高,并测定了几种吸附剂的导热系数,采用SEM观察了发泡前后的沸石分子筛的晶体结构和微观形貌的变化,分析了膨胀石墨所具有的特性是使其成为合适的添加剂的原因。通过TGA测试表明吸附剂的传质性能有提高。     

化学聚合法强化吸附剂热传导

采用化学聚合法强化吸附剂——沸石颗粒的热传导性能,利用苯胺单体在沸石颗粒表面氧化聚合,使少量的聚苯胺形成均匀连续的导热性能好的高分子材料网,在实验条件下可使该种吸附剂的有效导热系数提高到原来的4倍多。同时,将强化后的吸附剂挤压成型,进行强化吸附床层的传热研究,结果表明堆积密度为原来的1.5倍的成型块,其有效导热系数比原来提高30％,对比混合法的实验和数据分析表明,化学聚合法较物理混合法效果更明显,是一种适宜吸附剂热传导强化的新途径。