PREDICTION OF PRESSURE DROP IN A VENTURI SCRUBBER: EFFECT OF LIQUID FILM AND RE-ENTRAINMENT

A mathematical model has been developed for prediction of pressure drop in a Venturi scrubber. This model includes the effect of the amount of liquid film and re-entrainment of liquid droplets from liquid film. The result of the present model is compared with experimental data of Viswanathan et al. (1985) as well as with the other models (Viswanathan et al., 1985; Boll, 1973). Results of this study indicate that at high liquid to gas ratios prediction of pressure drop can be improved by considering re-entrainment and liquid film effects. Also the effects of gas velocity and liquid to gas ratio were investigated on the rate of droplet re-entrainment and pressure drop.     

Mathematical Modelling of Non‐Isothermal Venturi Scrubbers

A mathematical model consisting of differential equations for energy, momentum and material exchange is developed for a non‐isothermal Venturi‐type scrubber. By this model, the effects of heat and mass transfer on droplets concentration distribution and removal efficiency of particulate in a non‐isothermal Venturi scrubber can be investigated. In order to approach a realistic model, the liquid film flow on the walls and droplet size distribution are considered. The model is validated by comparing the results of mathematical model by plant and experimental data reported in the literature. The Results section of this work reveals that the inlet humidity and temperature of the gas can affect the removal efficiency of the scrubber.     

Experimental and Theoretical Investigation of Droplet Dispersion in Venturi Scrubbers with Axial Liquid Injection

Droplet dispersion in a Venturi scrubber with axial liquid injection was investigated both experimentally and theoretically. The main objective of this study was to develop a mathematical model to predict droplet dispersion in a Venturi scrubber with axial liquid injection. The effects of the Peclet number and droplet size distribution on droplet dispersion were studied using the developed model. Sampling of the droplets was carried out, isokinetically, in 16 positions at the end of the throat section. The experimental data were used to find the parameters of the developed model, such as the Peclet number. From the results of this study, it was found that the Peclet number was not constant across the cross section of the scrubber channel. In order to achieve a better agreement between the results of the model and the experimental data, it was required to consider Peclet number variations across the Venturi channel. It was also revealed that the parameter representing the width of the Rosin‐Rammler distribution of droplet size could not be considered constant and it was influenced significantly by the operating parameters such as liquid flow rate and gas velocity.     

Experimental verification of the effect of liquid deposition on droplet size measured in a rectangular Venturi scrubber

It has been reported by previous studies [1], [2], [3], [4], [5], [6], [7] that droplet size in a Pease-Anthony Venturi scrubber depends on the jet atomization conditions, such as jet velocity and gas velocity. The assumption of this paper is that actual collector-droplet size in a confined tube such as the Venturi scrubber also depends significantly on preferential droplet deposition on the tube walls, which remove preferentially droplets of a certain size from the core, modifying the mean droplet size of the remaining droplets. To account for this effect, the present study is focused on the experimental measurement of the liquid deposition on the walls of a Pease-Anthony Venturi scrubber and the droplet size remaining in the core. The experiments were carried out varying jet penetration and the number of the injection orifices. A correlation, using dimensionless numbers, was proposed to quantify the influence of each experimental condition. The results showed that liquid deposition has a significant influence in actual collector-droplet size inside a Venturi scrubber.     

PREDICTION OF PRESSURE DROP IN A VENTURI SCRUBBER: EFFECT OF LIQUID FILM AND RE-ENTRAINMENT

A mathematical model has been developed for prediction of pressure drop in a Venturi scrubber. This model includes the effect of the amount of liquid film and re-entrainment of liquid droplets from liquid film. The result of the present model is compared with experimental data of Viswanathan et al. (1985) Viswanathan, S., Gnyp, W. A. and Pierre, St., C. 1985. Annular flow pressure drop model for pease-Anthony-type Venturi scrubbers. AIChE. J., 31(12): 1947–1958.  [Google Scholar] as well as with the other models (Viswanathan et al., 1985 Viswanathan, S., Gnyp, W. A. and Pierre, St., C. 1985. Annular flow pressure drop model for pease-Anthony-type Venturi scrubbers. AIChE. J., 31(12): 1947–1958.  [Google Scholar]; Boll, 1973 Boll, R. H. 1973. Particle collection and pressure drop in Venturi scrubbers. Ind. Eng. Chem. Fundam., 12: 40[Crossref], [Web of Science ®] , [Google Scholar]). Results of this study indicate that at high liquid to gas ratios prediction of pressure drop can be improved by considering re-entrainment and liquid film effects. Also the effects of gas velocity and liquid to gas ratio were investigated on the rate of droplet re-entrainment and pressure drop.     

THE SPLIT OF THE LIQUID PHASE IN DROPS AND FILM IN AN EJECTOR-VENTURI SCRUBBER

Liquid distribution along an ejector-Venturi scrubber was determined experimentally in an industrial-scale pilot plant. The effects of geometry as well as flow rates were studied. The results showed that a significant fraction of the liquid travels as a film. Therefore, it should be taken into consideration in mass transfer studies, where usually it is neglected. The data were used to test a model, that allows for interchange of liquid between drops and film flowing on the Venturi walls. There was good agreement between experiment and predictions.     

THE SPLIT OF THE LIQUID PHASE IN DROPS AND FILM IN AN EJECTOR-VENTURI SCRUBBER

Liquid distribution along an ejector-Venturi scrubber was determined experimentally in an industrial-scale pilot plant. The effects of geometry as well as flow rates were studied. The results showed that a significant fraction of the liquid travels as a film. Therefore, it should be taken into consideration in mass transfer studies, where usually it is neglected. The data were used to test a model, that allows for interchange of liquid between drops and film flowing on the Venturi walls. There was good agreement between experiment and predictions.     

The Use of Surface Renewal and Eddy Diffusivity Theories in the Ozonation of a THM Precursor: 1,3-Cyclohexanedione

Kinetic equations derived from surface renewal and eddy diffusivity theories for fast and instantaneous kinetic regimes of absorption have been applied to the results of the ozonation of 1,3-cyclohexanedione (CYC) in water. This has allowed the determination of the rate constant of the direct reaction of ozone with CYC and the liquid phase volumetric mass transfer coefficient of the system. The results obtained are close to those reported in the preceding paper (SOTELO et al., 1991) when using the film theory. However, the ozone partial pressure necessary to reach the instantaneous kinetic regime is higher for the case of the theories applied in this work.     

Investigations on hydrodynamics and mass transfer in gas–liquid stirred reactor using computational fluid dynamics

In this work, the hydrodynamics and mass transfer in a gas–liquid dual turbine stirred tank reactor are investigated using multiphase computational fluid dynamics coupled with population balance method (CFD–PBM). A steady state method of multiple frame of reference (MFR) approach is used to model the impeller and tank regions. The population balance for bubbles is considered using both homogeneous and inhomogeneous polydispersed flow (MUSIG) equations to account for bubble size distribution due to breakup and coalescence of bubbles. The gas–liquid mass transfer is implemented simultaneously along with the hydrodynamic simulation and the mass transfer coefficient is obtained theoretically using the equation based on the various approaches like penetration theory, slip velocity, eddy cell model and rigid based model. The CFD model predictions of local hydrodynamic parameters such as gas holdup, Sauter mean bubble diameter and interfacial area as well as averaged quantities of hydrodynamic and mass transfer parameters for different mass transfer theoretical models are compared with the reported experimental data of [Alves et al., 2002a] and [Alves et al., 2002b] . The predicted hydrodynamic and mass transfer parameters are in reasonable agreement with the experimental data.     

文氏栅洗涤器除尘脱硫实验研究

采用双碱法脱硫技术 ,在自行设计的多通道文丘里洗涤器 (简称文氏栅洗涤器 )进行模拟燃煤烟气的除尘脱硫试验。其试验过程是 :先在三种不同喉部参数 (分别称为 1# ,2 # ,3 # )的文氏栅洗涤器进行除尘试验 ,经过优选后 ,在 2 #文氏栅洗涤器上进行脱硫试验。试验结果表明经过优选的 2 #文氏栅洗涤器有着较高的除尘脱硫效率。当文氏栅洗涤器的运行参数为 :pH =12、液气比为 0 .75L/m3、 [Na+ ]=0 .3mol/L、 [SO2 ]=12 0 0× 10 -6,文氏栅洗涤器的除尘效率大于 96 % ,脱硫效率大于 80 %。经过完善后可用作中小型燃煤锅炉烟气的除尘脱硫     

文丘里卷吸型气液分配器液体分配性能的结构参数研究

为了改善滴流床用的内卷吸型气液分配器的液体分散差的现象,提出了一种文丘里卷吸型气液分配器,并对其结构参数进行了参数化研究,定量认识卷吸型分配器的结构参数对其气液分配性能的影响。在冷态实验装置上进行了文丘里卷吸型气液分配器性能实验,建立了耦合群体平衡模型的欧拉-欧拉两相流模型,数值模拟了文丘里卷吸型气液分配器气液两相分配流动过程。冷模实验结合数值模拟,系统性考察了各结构参数对卷吸型气液分配器的液体分布均匀性、喷淋半径以及压降的影响。结果表明,采用具备缩-扩结构的文丘里管作为降液管能够有效提升卷吸型分配器的分布均匀度和喷淋半径,并显著降低压降。通过正交试验,获得了主要结构参数与分配性能的相关性,给出了结构参数与性能指标的经验关联式。降液管的扩张段是改善液体分配性能的关键结构,其扩张角为30°时液体分配性能最好。     

Settling velocity of droplets in turbulent flows

Two parameters of particle or droplet dynamics which are of importance in describing their behaviour in turbulent pipe flows are their settling velocity and eddy diffusivity. It is usually assumed that the settling velocity in turbulent flow is equal to that in still fluid and on the basis of this assumption the eddy diffusivity is usually determined experimentally from the distribution of droplets or particles in horizontal turbulent flow. Since the settling velocity has a strong influence on the resultant value of the eddy diffusivity, the influence of turbulence on settling velocity is investigated in this work. A simple stochastic model of settling in turbulent flow is developed and it is shown that a considerable retardation of still fluid settling velocity is possible for a wide range of conditions.     

气液向下并流填料塔的持液量

用φ15mm的陶瓷拉西环和塑料鲍尔环填料,在内径153mm的有机玻璃塔内,采用空气-水体系,测量了气液向下并流流动时的持液量数据。以Bemer等人提出的颈缩管模型为基础,推导了向下并流填料塔内的持液量计算式,较好地关联了本实验和Dodds等人的结果。并检验Larkins,Charpentier,佐藤等人提出的持液量关联式。     

On the efficiency of a centrifugal fan wet scrubber

An inertial theoretical model is proposed to predict the capture of aerosol particles by accelerating liquid droplets in a centrifugal fan scrubber. The results are in good agreement with literature experimental data for micron and large submicron size particles. The theory tends to underestimate the scrubber performance for submicron size particles of less than 0.3 μm in diameter. The discrepancy may be due to the lack of a reliable expression predicting the diffusion deposition of aerosol particles on an isolated liquid droplet. The effects of variables such as fan speed, sizes of liquid droplets and particles, gas and liquid flow rates predicted by the theory are discussed and agree with literature observation.     

An atomization model for splash plate nozzles

A model for the atomization and spray formation by splash plate nozzles is presented. This model is based on the liquid sheet formation theory due to an oblique impingement of a liquid jet on a solid surface. The continuous liquid sheet formed by the jet impingement is replaced with a set of dispersed droplets. The initial droplet sizes and velocities are determined based on theoretically predicted liquid sheet thickness and velocity. A Lagrangian spray code is used to model the spray dynamics and droplet size distribution further downstream of the nozzle. Results of this model are confirmed by the experimental data on the droplet size distribution across the spray. © 2009 American Institute of Chemical Engineers AIChE J, 2010     

文丘里洗涤器压力损失的计算

在进行文丘里洗涤器设计或结构优化时，准确地预测其压力损失数值大小非常重要，多年来一直受到众多研究者的关注。本文对国内外用于计算文丘里洗涤器压力损失的研究成果，即经验关联式、解析解法与数值解法进行了简单地介绍，并将由不同的计算方法得到的预测值与本文作者实测的数据进行分析比较，以期为设计者在进行文丘里洗涤器设计或优化操作时选用合适的计算方法提供理论参考。     

An engineering model of solids diffusivity in hydraulic conveying

An engineering model of solids diffusivity in a turbulent pipeline slurry flow is developed. While the model assumes that the liquid eddy diffusivity is uniform across a pipe the non-uniform distribution of solids diffusivity is obtained by analyzing the dependence of the turbulence kinetic energy transferred from liquid to particles on solids concentration. The turbulence kinetic energy transferred to particles is determined as the turbulence kinetic energy calculated for slurry minus the energy spent on the liquid-solids viscous friction due to turbulence induced liquid-solids velocity difference. The two empirical coefficients of the equation of the solids diffusivity have been identified from the measured solids concentration profiles. The numerical study has shown that the model accurately predicts the slurry concentration distribution in the wide range of flow parameters. The predictive capability of the developed model is much better that that of the conventional model of the solids diffusivity.     

Droplet vaporization modeling of rapeseed and sunflower methyl esters

For numerical simulations of the combustion of liquid fuels, a thoroughly validated and verified quantitative model for droplet evaporation is necessary. In this work a simple single droplet infinite conductivity model is simulated for low pressure (0.1 MPa) and various temperatures (550–1050 K) using a chosen property rule (see Eq. (7)) and five convection correlations (C1, C2, C3, C4, and C5, see (Table 1) to obtain the temporal evolution of droplet diameter squared, droplet surface temperature and average evaporation rates of vegetable oil derived biofuels – rapeseed methyl ester (RME) and sunflower methyl ester (SME) – under near-quiescent conditions. The predictions are compared with the experimental and analytical results of Morin et al. [1]. The model uses an effective Reynolds number to conflate the effects of forced and natural convection. It is observed that the predicted temporal history of droplet diameter for RME droplet matches more closely with correlation C1 for T_amb ? 748 K and correlation C2 for T_amb ? 803 K at various ambient temperatures (i.e., from low to high evaporation rate). The correct droplet lifetime is predicted best by C1 for all temperatures. For average evaporation rates for SME, C1 best fits the experimental data. For the average evaporation rate of RME, the present model with C1 gives a better prediction than the theoretical, and corrected theoretical results of Morin et al. [1], and is observed to match closely with their experimental results. The present results using C2 are also found close to the experimental results for RME and SME. It is observed that the oxidation of RME/SME is similar to n-decane – a pure component fuel.     

转盘离心粒化中丝状成粒特性

针对转盘离心粒化工艺,以水为工质开展可视化实验。采用高速摄影仪对液膜波动、液丝断裂等粒化过程进行了捕捉,并利用MATLAB自编程序对获得的图像进行了处理。分析了离心粒化过程中液丝形成过程以及液丝断裂形成液滴的过程。研究了运行工况对液丝、液滴形成机制的影响。讨论了液丝形成对液滴形成的影响并获得了Weber数、Reynolds数对粒化效果的影响程度。结果表明,表面不稳定波是形成液丝的主要因素,且液丝在Rayleigh不稳定性的作用下断裂形成液滴。升高转速或者减小流量有利于获得均匀的小液滴。Weber数对液丝、液滴形成具有显著影响;Reynolds数仅对液丝数目有显著影响。     

Modeling the mixing of a gas-liquid spray jet injected in a gas-solid fluidized bed: The effect of the draft tube

In several important industrial processes such as fluid coking, fluid catalytic cracking and gas-phase polymerization, a gas-liquid spray jet is injected into a fluidized bed. Recent findings [Chan et al., 2004. US Patent, US 2004065590] have shown that for the fluid coking operation, locating a cylindrical draft tube near the exit of the injector can enhance the contacting efficiency of the droplets and the particles.The main objective of this paper was to model the liquid-solids mixing in the draft tube. A two-dimensional model that characterizes the radial mixing by means of an eddy diffusivity coefficient is presented. The model predictions are validated by experimentally measuring the liquid-solids mixing by a technique based on temperature measurements in the spray region. The simulation results for a commercial fluid coking nozzle confirm the potential benefits of the mixing chamber. Moreover, the model allows ascertaining the effect of some important parameters such as nozzle size, gas and liquid properties, and the air-to-liquid mass ratio to the nozzle.