新型气液逆流接触洗涤器流动-传质模型

通过冷模实验对一种新型气液逆流式洗涤器流动传质特性进行了考察。实验结果表明,在不同的操作条件下,洗涤器内气液两相流动会呈现出不同的流型。其中,洗涤器在泡沫流状态下的高效传质段体积和解吸率的数值均较大。将实验结果与理论分析相结合,依据其气液接触表面更新极快、形成高度湍动泡沫流的特点,提出了一种基于该洗涤器结构和操作特性、可以预测洗涤器传质效果的“两段式”流动-传质模型。模型将洗涤器内气液作用区分为两个区段：旋转射流段和高效传质段。利用该模型分析了解吸率与液气比L/G和旋流比ω的变化关系;结果表明,在不同操作条件下,该模型的计算结果与实验数据吻合较好,可供工程设计参考。     

Predictive Model of Hydrogen Sulfide Absorption by Chelate Solution in a Venturi Scrubber

In the present study, a simple model was used to predict the removal efficiency of a venturi scrubber for H₂S absorption into a ferric chelate solution. From momentum and mass balances in the scrubber, a set of first‐order, nonlinear ordinary differential equations relating predominantly the liquid velocity with the H₂S concentration in the liquid along the axial direction in the scrubber were formulated. These relationships were numerically solved to give performance profiles. The validity of the model was examined by comparing the results of the model with experimental data from the working laboratory scale. The results predicted from the model are in good agreement with the experimental data obtained in different sizes of the venturi scrubber and operating variables.     

喷淋洗涤条件下水汽饱和度分布特性

为在脱硫喷淋塔中借助蒸汽相变原理促进PM_2.5凝结长大,需要在塔内建立适宜的过饱和水汽环境。基于此,建立喷淋洗涤条件下气液两相热质传递模型,系统研究了操作参数对塔内饱和度分布特性的影响规律。结果显示,通过降低喷淋液温度、增加塔进口烟气含湿量,以及在喷淋区上方添加蒸汽均能够在塔内建立过饱和水汽环境;采用较大的液气比、较小的喷淋液滴直径有利于水汽饱和度的提高。获得了改变操作参数在脱硫喷淋塔内建立过饱和水汽环境的措施,对实际的脱硫除尘工艺的设计和运行具有指导意义。     

水力喷射空气旋流分离器脱氨

空气吹脱被广泛用于从废水中脱氨,但其过程效率有待提高。为了提高过程效率,提出了一种新型气-液吹脱设备——水力喷射空气旋流分离器（WSA）,并以废水中氨的吹脱进行了实验。与传统的吹脱设备相比,WSA表现出较好的气-液传质性能,使氨的吹脱效率大大提高。在氨的吹脱过程中,液相温度和空气流量是影响吹脱过程中氨体积传质系数的主要因素。空气流量对于体积传质系数存在一个临界值,超过此值时,体积传质系数随空气流量增加而迅速增大。液相中存在的固体颗粒物对于吹脱过程的传质几乎没有影响。在该设备中没有填料,不存在堵塞问题,因而可以进行较长时间的分离操作。     

On the efficiency of a venturi scrubber

The performance of a venturi scrubber with a 1-in. by 3-in. throat was determined using monodispersed uranine-methylene blue aerosols in the size range 0.8 to 3.0μm at throat velocities ranging from 109.6 ft/sec to 245 ft/sec. Separate measurements on the water separator showed that substantial aerosol removal took place in this unit, and the efficiency of the scrubber itself was calculated from these measurements plus overall efficiency measurements on the combination scrubber and separator. These results were compared with values obtained from a theoretical model and agreement was generally satisfactory, although the theoretical efficiencies were lower than the experimental efficiencies at the highest air velocities, and viceversa. This discrepancy may be due to a number of factors which are discussed.     

Optimization of Gas Scrubbing in the Calcination of Struvite

During the calcination of magnesium ammonium phosphate hexahydrate (struvite) in the process of recycling to obtain phosphoric acid, ammonia is released in addition to water and carbon dioxide. With a gas scrubber, e.g., in the form of a bubble column reactor, ammonia can be recovered as a usable valuable material. With water as an inexpensive and effective absorbent, almost complete absorption (92 %) of the ammonia from the exhaust air can be achieved.     

洗涤塔内相变脱除燃煤超细颗粒的试验研究

为研究洗涤塔内相变对燃煤超细颗粒的脱除,在洗涤塔液相进口上方注入蒸汽使烟气达到过饱和,由高效除雾器脱除凝并长大的含尘液滴。系统研究了蒸汽添加量、洗涤塔入口气液温差、液气体积比、烟气在相变区域的停留时间等操作参数对燃煤超细颗粒脱除效率的影响规律。结果表明:在塔内添加少量蒸汽,可显著促进燃煤超细颗粒的脱除,蒸汽添加质量浓度为0.03 kg/m3时,数量浓度脱除效率由10%增至60%以上;液气体积比的提高有利于燃煤超细颗粒的脱除,特别是当洗涤塔入口气液温差较大时。研究结果表明利用洗涤塔内相变脱除燃煤细颗粒是一种有应用前景的新方法。     

CFD simulation of chemical reaction between sulfur dioxide and water in a venturi scrubber

ABSTRACT

The use of fossil fuel, i.e., coal, was first initiated in 1880s for electricity generation. It was used extensively worldwide due to its cheap rate. Consequently, there is an adverse effect on the environment that results in a climate change. Many industries were working on cleaning flue gases emitted from coal power plants according to Environmental Protection Agency (EPA) standards by using different scrubbing technologies and venturi scrubber is one of them having ability to remove particulates and toxic gases simultaneously. Industries were using computational fluid dynamics (CFD) techniques to fully understand the gases behavior inside scrubbing technologies prior employed in the project. This research represents CFD simulation to study abatement process of sulfur dioxide through chemical reaction with water in a venturi scrubber. Parameters such as mass concentration of sulfurous acid formation, sulfur dioxide and water mass content distribution inside venturi scrubber were analyzed. The sulfur dioxide removal efficiency was also investigated. The results show that water mass content distribution was greatly influenced by sulfur dioxide mass flow rates. Desulfurization efficiency depreciates with an increase in sulfur dioxide mass flow rate, whereas efficiency increases with accession in liquid to gas ratio. Maximum sulfur dioxide removal was observed at lower sulfur dioxide concentration comparatively to higher concentration of sulfur dioxide.     

萃取车间化工废水的简易高效处理

采用空吹和吸附两步处理高浓度化工废水,研究了影响其效率的主要参数。结果表明,空吹法在一定的pH和温度下,能有效去除特殊化工行业废水中的有机物及氨氮,采用活性炭吸附并用可以使废水实现达标排放。     

SPRAY DRYING DYNAMIC MODELING WITH A MECHANISTIC MODEL

In this work we suggest the dynamic modeling of a spray dryer considered as a series of well-stirred dryers. That is, a series of dryers in which the output variables are equal to the state variables. The state equations were obtained from the heat and water mass balances in product and air. Additionally, heat and water mass balances in interface jointly with water equilibrium relation between product and air were considered. A pilot spray dryer was modeled assuming one, two, five and 20 well stirred steps. Low-fat milk with 10-20% of solids was dried at different inlet air temperatures (120-160°C), air flow rate of 0.19 kg dry air s^-1 and different feed rates (1.4 - 4.2 × 10^-4 kg dry solids s^-1). Stationary result showed that the model predicts the experimental air outlet temperature, at different inlet conditions with a maximum deviation of 6°C. The dynamic simulation reproduce the experimental one with moderate accuracy. Experimental dynamic showed that the pilot plant spray dryer has a well-stirred process behavior. The model represents a method for estimate outlet product moisture as function of the outlet air temperature. This has application for automatic control because there is not an easy way to measure on-line measure the outlet product moisture content.     

PVC dust removal from the air by a new dynamical scrubber

Removal of the poly vinyl chloride (PVC) dust particles by a new dynamical scrubber in a PVC manufacturing plant is presented in this work. The effects of inlet air flow rate (containing PVC particles) and water flow rate (the physical absorber of particles) on the PVC dust removal efficiency were investigated. The size of the PVC particles which have been treated in this study was ranging from 0.5 up to 20 μm. The experimental results showed approximately 100% removal efficiency for particles larger than 1 μm and 73% for 0.5 μm particles while employing low water flow rates. The results of these experimental tests indicate a good performance of the scrubber in a short residence time (about 2 s) which is also completely economic for removing fine particles.     

Comparison of chemical wet scrubbers and biofiltration for control of volatile organic compounds using GC/MS techniques and kinetic analysis

Increasing public concerns and EPA air regulations in non‐attainment zones necessitate the remediation of volatile organic compounds (VOCs) generated in the poultry‐rendering industry. Wet scrubbers using chlorine dioxide (ClO₂) have low overall removal efficiencies due to lack of reactivity with aldehydes. Contrary to wet scrubbers, a biofilter system successfully treated the aldehyde fraction, based on GC/MS analysis of inlet and outlet streams. Total VOC removal efficiencies ranged from 40 to 100% for the biofilter, kinetic analysis indicated that the overall removal capacity approached 25 g m⁻³ h⁻¹, and aldehyde removal efficiency was significantly higher compared with chemical wet scrubbers. Process temperatures monitored in critical unit operations upstream from the biofilter varied significantly during operation, rising as much as 30 °C within a few minutes. However, the outlet air temperature of a high intensity scrubber remained relatively constant at 40 °C, although the inlet air temperature fluctuated from 50 to 65 °C during monitoring. These data suggest a hybrid process combining a wet scrubber and biofilter in series could be used to improve overall VOC removal efficiencies and process stability. Copyright © 2005 Society of Chemical Industry     

SPRAY DRYING DYNAMIC MODELING WITH A MECHANISTIC MODEL

ABSTRACT

In this work we suggest the dynamic modeling of a spray dryer considered as a series of well-stirred dryers. That is, a series of dryers in which the output variables are equal to the state variables. The state equations were obtained from the heat and water mass balances in product and air. Additionally, heat and water mass balances in interface jointly with water equilibrium relation between product and air were considered. A pilot spray dryer was modeled assuming one, two, five and 20 well stirred steps. Low-fat milk with 10–20% of solids was dried at different inlet air temperatures (120–160°C), air flow rate of 0.19 kg dry air s^?1 and different feed rates (1.4 ? 4.2 × 10^?4 kg dry solids s^?1). Stationary result showed that the model predicts the experimental air outlet temperature, at different inlet conditions with a maximum deviation of 6°C. The dynamic simulation reproduce the experimental one with moderate accuracy. Experimental dynamic showed that the pilot plant spray dryer has a well-stirred process behavior. The model represents a method for estimate outlet product moisture as function of the outlet air temperature. This has application for automatic control because there is not an easy way to measure on-line measure the outlet product moisture content.     

Simulation and Optimization of Semicontinuous Industrial Tunnel Dryers for Fruits

Semicontinuous industrial tunnel dryers were simulated and optimized for concurrent and countercurrent configurations. Mass and energy balances for the solid and gas phase were used to describe the operation of the dryer and a semi-empirical model for the mass transfer rate; the drying rate equation parameters were fitted using experimental data for Italy grapes. The simulation programs coded in Fortran 90 calculate the moisture and temperature profiles for grapes and humidity and temperature for air throughout the tunnel, cycle time, recirculation ratio, thermal load, and fresh air flow rate. The optimization minimizes the energy input considering the degradation of ascorbic acid in the fruit as the main constraint.     

Mathematical modeling and numerical simulation of ammonia removal from wastewaters using membrane contactors

This study investigates simulation of ammonia transport through membrane contactors. The system studied involves feed solution of NH₃, a dilute solution of sulfuric acid as solvent and a membrane contactor. The model considers coupling between equations of motion and convection-diffusion. Finite element method was applied for numerical calculations. The effect of different parameters on the removal of ammonia was investigated. The simulation results revealed that increasing feed velocity decreases ammonia removal in the contactor. The modeling findings also showed that the developed model is capable to evaluate the effective parameters which involve in the ammonia removal by means of contactors.     

Numerical Spray Model of the Fluidized Bed Coating Process

In this study, a new model for the batch top-spray fluidized bed coating process is presented. The model is based on the one-dimensional (axial) discretization of the bed volume into different control volumes, in which the dynamic heat and mass balances for air, water vapor, droplets, core particles, and coating material were established. The coupling of the droplet phase's mass and heat transfer terms with the gas and solid phases was established by means of a droplet submodel in which droplet trajectories were individually simulated.

The model calculation method combines a Monte Carlo technique for the simulation of the particle exchange with the first-order Euler's method for solving the heat and mass balances, enabling the prediction of both the dynamic coating mass distribution and the one-dimensional (axial) thermodynamic behavior of the fluidized bed during batch operation. The simulation results were validated using experimental two-dimensional spatial air temperature and air humidity distributions, which were measured in a fluidized bed pilot reactor using a scanning probe.

Sensitivity analysis was carried out to study the effect of controllable process variables, such as fluidization air and atomization air properties, as well as the properties of the spraying liquid upon the simulated dynamic temperature and humidity distributions. Also, the effects of relevant process variables on growth rate uniformity and process yield were studied. Based on these sensitivity studies it was concluded that nozzle parameters, such as air pressure and positioning with respect to the bed, are as important as the fluidization air properties (humidity, temperature, and flow rate) for the coating growth rate uniformity and process yield.     

大颗粒尿素造粒尾气冷却洗涤器技术应用进展

化肥厂尿素车间造粒工段不可避免地会产生含尿素粉尘的气体,尤其是在大颗粒尿素的造粒过程中会产生温度及尿素粉尘浓度都较高的气体,生产中需要将这些粉尘捕集回收利用,以增加经济效益和避免环境污染。本文指出,根据尿素水溶性好的特点,国内外一般都采用湿法捕集技术,其核心装置就是尿素尾气冷却洗涤器。通过该系统对尿素造粒产生的尾气进行冷却洗涤处理后排放大气,同时回收尿素粉尘。文中简述了尿素尾气冷却洗涤装置发展经历的不同阶段,包括最初的散堆填料塔、塔盘和喷头组合、规整填料和MD塔盘复合结构、气液并流式冷却洗涤器和隔壁塔型气液混流式冷却洗涤器。指出气液并流式冷却洗涤器与传统的逆流吸收塔相比,操作不会产生液泛,气速范围大,处理能力高,排放更加环保化,同等条件下投资降低40%,系统压力降降低50%以上,风机功率降低,节省了操作费用,近些年来已被国内多数厂家采用。     

Numerical Spray Model of the Fluidized Bed Coating Process

In this study, a new model for the batch top-spray fluidized bed coating process is presented. The model is based on the one-dimensional (axial) discretization of the bed volume into different control volumes, in which the dynamic heat and mass balances for air, water vapor, droplets, core particles, and coating material were established. The coupling of the droplet phase's mass and heat transfer terms with the gas and solid phases was established by means of a droplet submodel in which droplet trajectories were individually simulated.

The model calculation method combines a Monte Carlo technique for the simulation of the particle exchange with the first-order Euler's method for solving the heat and mass balances, enabling the prediction of both the dynamic coating mass distribution and the one-dimensional (axial) thermodynamic behavior of the fluidized bed during batch operation. The simulation results were validated using experimental two-dimensional spatial air temperature and air humidity distributions, which were measured in a fluidized bed pilot reactor using a scanning probe.

Sensitivity analysis was carried out to study the effect of controllable process variables, such as fluidization air and atomization air properties, as well as the properties of the spraying liquid upon the simulated dynamic temperature and humidity distributions. Also, the effects of relevant process variables on growth rate uniformity and process yield were studied. Based on these sensitivity studies it was concluded that nozzle parameters, such as air pressure and positioning with respect to the bed, are as important as the fluidization air properties (humidity, temperature, and flow rate) for the coating growth rate uniformity and process yield.     

卧式错流填料层洗涤器的开发

介绍一种新的磷肥厂除氟除氨洗涤器－卧式错流填料层洗涤器。该洗涤器气液呈错流接触。传质效果好,压力降低,采用卧式结构和可卸式聚丙烯丝填料,便于安装,清洗和维护。     

轻油裂解法生产氰化钠尾气净化新工艺

介绍了一种氰化钠尾气的净化工艺,将轻油裂解法生产液体氰化钠中富含氢气的尾气净化处理．在脱氰塔内用氢氧化钠溶液吸收尾气中的氰化氢,脱氨塔内用水吸收尾气中的氨气,通过脱氰、脱氰工艺将净化后的含氢气体输送到合成氨车间作为生产液氨的原料。