新型离心式脱硫塔气液两相流数值模拟

利用FLUENT软件和SIMPLE算法对新型旋流脱硫塔的气液两相流场进行了数值模拟。计算中气相采用了RSM湍流模型,颗粒相采用了Lagrange坐标系下的随机轨道模型。分析结果表明,气相流场具有强旋流特性;喷射液滴的直径、喷淋量和烟气流速影响其在塔内的分布:喷射液滴粒径越大、喷射量越小、烟气流速越大,入口段降温越少;塔体上方截面平均浓度随液滴粒径的增加而降低,随液气比的增加而增加,随烟气流速的增加会先增加至最高值然后降低。喷淋液滴在其他运行参数不变时,平均粒径范围为0.5～1 mm,会对进口烟气起到较好的净化与降温的作用,并使塔体上方喷淋液滴在截面z=4.15 m处浓度分布均匀且覆盖率高;在保证液滴粒径较小时,通过降低烟气流速或增加喷淋量可提高液滴喷淋覆盖率,使得烟气与喷淋充分接触。计算得到的气相流场分布与实测值吻合较好,证明了数学模型的合理性,为进一步优化分离器结构提供了可靠依据。     

Dust Collection Efficiency Analysis in a Two-Dimensional Circulating Granular Bed Filter

Abstract

Dust collection efficiency data were analyzed to determine better operating conditions for a two-dimensional circulating granular bed filter (CGBF). The dust collection efficiency in the granular bed was affected by the following operating parameters: the louver angle, the solids mass flow rate, and the particle size of the bed material. Experimental results showed that higher dust collection efficiency occurs when the solids mass flow rates were 20.34 ± 0.24, 21.50 ± 0.11, and 30.51 ± 0.57 g/sec at louver angles of 45°, 30°, and 20°, respectively. Optimal dust collection efficiency peaked with a louver angle of 30°. Average particle sizes of bed material by sieve diameters (μm) of 795 μm had higher dust collection efficiency than the average collector particle size of 1500 μm. Dust collection efficiency is influenced by bed material attrition phenomenon, causing dust collection efficiency to decrease rapidly. The dust collection efficiency analysis not only found the system free of design defects but also assisted in the operation of the two-dimensional CGBF system.     

微波协同霍加拉特剂催化氧化苯的影响因素

为了探索一种高效、快速处理典型挥发性有机物的方法,对微波协同作用下霍加拉特剂催化氧化苯的性能进行了研究,主要考查了微波作用模式、微波功率、苯初始浓度、气体流量、催化剂用量和气体湿度对处理苯效果的影响,并对影响规律进行总结。实验结果表明,微波功率70 W,苯初始浓度1 917 mg/m3,气体流量1.0 L/min,催化剂床层高度3.86 cm时,苯转化率可达99.2%。微波辐照条件下霍加拉特剂能够有效实现苯的催化氧化,并且比传统加热具有更高的能量利用率。     

Experimental analysis of particle concentration heterogeneity in a ventilated scale chamber

The mixing processes of the aerosol particles from an outdoor environment in a ventilated scale chamber were experimentally studied. The particles were classified into five groups by size: 0.3–0.5 μm, 0.5–1.0 μm, 1.0–3.0 μm, 3.0–5.0 μm and 5.0–10.0 μm. The developing process for the concentration of each particle group was measured in different kinds of flow fields.The results show that the flow field configuration can effectively influence the dispersion time rate of the particles at certain positions. The increase in particle diameter can decrease the dispersion time rate. When the gas flow velocity is high, the particle dispersion time rate is independent of particle size; but when the gas flow velocity is low, particle size can significantly affect the particle dispersion time rate because the turbulent diffusion becomes important in the air and particle transport. The uniformity of the particle concentration for certain positions in steady state tends to be controlled by the inflow velocity, flow field configuration and the particle diameters.     

Dust collection efficiency analysis in a two-dimensional circulating granular bed filter

Dust collection efficiency data were analyzed to determine better operating conditions for a two-dimensional circulating granular bed filter (CGBF). The dust collection efficiency in the granular bed was affected by the following operating parameters: the louver angle, the solids mass flow rate, and the particle size of the bed material. Experimental results showed that higher dust collection efficiency occurs when the solids mass flow rates were 20.34 +/- 0.24, 21.50 +/- 0.11, and 30.51 +/- 0.57 g/sec at louver angles of 45 degrees, 30 degrees, and 20 degrees, respectively. Optimal dust collection efficiency peaked with a louver angle of 30 degrees. Average particle sizes of bed material by sieve diameters (microm) of 795 microm had higher dust collection efficiency than the average collector particle size of 1500 microm. Dust collection efficiency is influenced by bed material attrition phenomenon, causing dust collection efficiency to decrease rapidly. The dust collection efficiency analysis not only found the system free of design defects but also assisted in the operation of the two-dimensional CGBF system.     

Liquid Entrainment from a Mobile Bed Scrubber

Liquid entrainment rate and drop size distribution were measured in the exhaust gas stream from a mobile bed scrubber. The pilot plant scrubber was 46 cm (18 in.) square and was packed with 3.8 cm (1.5 In.) diameter hollow polyethylene spheres to a static depth of 25 cm (10 in.). Entrainment flow rate depends on both gas and liquid rates. At a liquid/gas ratio of 6.7 l/m³ (50 gal/Mcf) and a superficial gas velocity of 2.6 m/sec (8.5 ft/sec) the entrainment flow rate was 0.0064 l/m³ (0.05 gal/Mcf) and at 3.75 m/sec (12.3 ft/sec) it was 0.031 l/m³ (0.23 gal/Mcf). The mass median drop diameter was about 400 nm at a liquid/gas ratio of 6.7 l/m³. The drop size distribution appears to be bimodal. Dye impregnated paper and cascade impactor techniques were used to measure drop size.     

并流旋转床气体出口压降数值分析

气体出口是旋转床的重要组成部分,对旋转床流场与气相压降有着重要的影响。研究并流旋转床结构、构建气体出口物理模型,利用RNG k-ε湍流模型,探索不同气体出口结构对并流旋转床流场的影响。模拟结果表明:具有4个切向气体出口的DCRPB3615型旋转床有利于旋转床内速度分布均匀、降低湍动能,减小气相压降。模拟与实验对比表明,DCRPB3615压降比单一径向出口的CRPB3615型旋转床降低10%左右。     

Air Pollution Acronyms

Abstract

Computational fluid dynamic (CFD) analysis of the thermal flow in the combustion chamber of a solid waste incinerator provides crucial insight into the incinerator’s performance. However, the interrelation of the gas flow with the burning waste has not been adequately treated in many CFD models. A strategy for a combined simulation of the waste combustion and the gas flow in the furnace is introduced here. When coupled with CFD, a model of the waste combustion in the bed provides the inlet conditions for the gas flow field and receives the radiative heat flux onto the bed from the furnace wall and gaseous species. An unsteady one-dimensional bed model was used for the test simulation, in which the moving bed was treated as a packed bed of homogeneous fuel particles. The simulation results show the physical processes of the waste combustion and its interaction with the gas flow for various operational parameters.     

A New Method for the Rapid Determination of Volatile Organic Compound Breakthrough Times for a Sorbent at Concentrations Relevant to Indoor Air Quality

Abstract

The use of sorbents has been proposed to remove volatile organic compounds (VOCs) present in ambient air at concentrations in the parts-per-billion (ppb) range, which is typical of indoor air quality applications. Sorbent materials, such as granular activated carbon and molecular sieves, are used to remove VOCs from gas streams in industrial applications, where VOC concentrations are typically in the parts-per-million range. A method for evaluating the VOC removal performance of sorbent materials using toluene concentrations in the ppb range is described. Breakthrough times for toluene at concentrations from 2 to 7500 ppb are presented for a hydrophobic molecular sieve at 25% relative humidity. By increasing the ratio of challenge gas flow rate to the mass of the sorbent bed and decreasing both the mass of sorbent in the bed and the sorbent particle size, this method reduces the required experimental times by a factor of up to several hundred compared with the proposed American Society of Heating, Refrigerating, and Air-Conditioning Engineers method, ASHRAE 145P, making sorbent performance evaluation for ppb-range VOC removal more convenient. The method can be applied to screen sorbent materials for application in the removal of VOCs from indoor air.     

Determination of the Sodium Carbonate-Sulfur Dioxide Reaction Rate Coefficient at 450°F

Abstract

Gas-phase dispersion in granular biofilter materials with a wide range of particle sizes was investigated using atmospheric air and nitrogen as tracer gases. Two types of materials were used: (1) light extended clay aggregates (LECA), consisting of highly porous particles, and (2) gravel, consisting of solid particles. LECA is a commercial material that is used for insulation, as a soil conditioner, and as a carrier material in biofilters for air cleaning. These two materials were selected to have approximately the same particle shape. Column gas transport experiments were conducted for both materials using different mean particle diameters, different particle size ranges, and different gas flow velocities. Measured breakthrough curves were modeled using the advection-dispersion equation modified for mass transfer between mobile and immobile gas phases. The results showed that gas dispersivity increased with increasing mean particle diameter for LECA but was independent of mean particle diameter for gravel. Gas dispersivity also increased with increasing particle size range for both media. Dispersivities in LECA were generally higher than for gravel. The mobile gas content in both materials increased with increasing gas flow velocity but it did not show any strong dependency on mean particle diameter or particle size range. The relative fraction of mobile gas compared with total porosity was highest for gravel and lowest for LECA likely because of its high internal porosity.     

HCI Sorption by Dry NaHCO3 for Incinerator Emissions Control

The sorption of hydrochloric acid (HCI) by thermally decomposed sodium bicarbonate (NaHCO₃) was investigated using a fixed-bed reactor containing sorbent particles dispersed in a bed of spherical glass beads. The gas flow rate (68° F and 760 mm Hg) was 0.039 cfm (1.1 liter/min) and the bed had a cross-sectional area of 0.0055 sq. ft. (5.1 sq. cm). The influence of particle diameter (10, 45 and 163 μm), temperature (225, 275, 375, 455, and 550° F), superficial gas velocity (11 and 21 fpm at reactor conditions, 375° F), and Inlet HCI gas concentration (415 ppm and 760 ppm in N₂, 275 and 455° F) were studied. Results showed that HCI sorption increased strongly with increasing temperature but was only weakly dependent on particle diameter, superficial gas velocity, and HCI gas concentration.     

Combined simulation of combustion and gas flow in a grate-type incinerator

Computational fluid dynamic (CFD) analysis of the thermal flow in the combustion chamber of a solid waste incinerator provides crucial insight into the incinerator's performance. However, the interrelation of the gas flow with the burning waste has not been adequately treated in many CFD models. A strategy for a combined simulation of the waste combustion and the gas flow in the furnace is introduced here. When coupled with CFD, a model of the waste combustion in the bed provides the inlet conditions for the gas flow field and receives the radiative heat flux onto the bed from the furnace wall and gaseous species. An unsteady one-dimensional bed model was used for the test simulation, in which the moving bed was treated as a packed bed of homogeneous fuel particles. The simulation results show the physical processes of the waste combustion and its interaction with the gas flow for various operational parameters.     

Relationship between pressure fluctuations and generation of organic pollutants with different particle size distributions in a fluidized bed incinerator

The hydrodynamic behaviors of fluidization perhaps significantly influence the uniformity of fluidization in fluidized bed incinerator. Good uniformity of fluidization expressed the air across uniformly through the bed and the particles being distributed well in the fluid stream. The aggregates, flocs and channels of particles do not happen during fluidization. The Good uniformity will maintain high heat and mass distribution to improve reaction efficiency. These parameters include the height of static bed, gas velocity, mixing and distribution of bed particle, which have rarely been studied in previous investigations. Consequently, this study examines how the hydrodynamic parameters affect the generation of organic pollutants (BTEXs and PAHs) during incineration. The statistical and power spectral analysis of the measured pressure fluctuation during incineration are used to elucidate the relationship between behaviors of fluidization and generation of pollutants during incineration. Experimental results show the organic concentration does not increase with uniformity of fluidization decreasing. The reason may be the explosion of the gas and the consequent thermal shock destroy the coalescent bubbles to form small bubbles again and enhance the efficiency of transfer of oxygen to increase combustion efficiency. Additionally, the mean amplitude and fluidized index of pressure fluctuation similarly vary with the concentration of organic pollutants. These two indices can be used to assess the efficiency of combustion. The four particle size distributions could be divided into two groups by statistical analysis. The Gaussian and narrow distributions belong to one group and the binary and flat the other. The organic concentration of the Gaussian and narrow distributions are lower than that of the other distributions. Consequently, the bed materials should maintain narrow or Gaussian distributions to maintain a good combustion efficiency during incineration.     

A design of a vermiculite column adsorber for the removal of lead from water

Mini-column techniques were employed to determine the mass transfer coefficient for lead adsorption onto vermiculite. Variation of the mass transfer coefficient with flow rate, particle size of sorbent, and influent lead concentration were studied. Multiple linear regression (MLR) analysis showed that the mass transfer coefficient varied as the 0.43 power of the liquid flow rate and inversely as the 0.272 power of particle diameter of the vermiculite, but was independent of the influent concentration of lead. Different parameters of a fixed bed column design for the removal of lead by vermiculite were determined using the data from the batch sorption study. The performance of the liquid bed column in removing lead was in close agreement with predicted performance using the batch isotherm data.     

湿污泥在流化床中干燥特性

在鼓泡流化床干燥器内,床料采用0～1 mm的石英砂,以热空气作为干燥介质,对城市污水污泥的流态化干燥特性进行实验研究。通过控制送风温度、流化风量、加料量、污泥粒径等参数,研究在不同工况条件下床温以及干污泥含水率的变化情况。结果表明,随着送风温度的升高,床温升高,干污泥含水率下降,最终趋向于一个稳定值8%。床温随流化风量的增加先是减小而后升高,干污泥的含水率随流化风量的增加先是降低而后增大。当加料量从11 kg/h增加到13kg/h时,干污泥的含水率基本没有变化,当加料量超过13 kg/h时,干污泥的含水率从8.1%开始呈递增趋势。随污泥粒径的增大,床温升高,干污泥含水率也随之升高。     

A new method for the rapid determination of volatile organic compound breakthrough times for a sorbent at concentrations relevant to indoor air quality

The use of sorbents has been proposed to remove volatile organic compounds (VOCs) present in ambient air at concentrations in the parts-per-billion (ppb) range, which is typical of indoor air quality applications. Sorbent materials, such as granular activated carbon and molecular sieves, are used to remove VOCs from gas streams in industrial applications, where VOC concentrations are typically in the parts-per-million range. A method for evaluating the VOC removal performance of sorbent materials using toluene concentrations in the ppb range is described. Breakthrough times for toluene at concentrations from 2 to 7500 ppb are presented for a hydrophobic molecular sieve at 25%) relative humidity. By increasing the ratio of challenge gas flow rate to the mass of the sorbent bed and decreasing both the mass of sorbent in the bed and the sorbent particle size, this method reduces the required experimental times by a factor of up to several hundred compared with the proposed American Society of Heating, Refrigerating, and Air-Conditioning Engineers method, ASHRAE 145P, making sorbent performance evaluation for ppb-range VOC removal more convenient. The method can be applied to screen sorbent materials for application in the removal of VOCs from indoor air.     

Reduction of dioxin emission by a multi-layer reactor with bead-shaped activated carbon in simulated gas stream and real flue gas of a sinter plant

A laboratory-scale multi-layer system was developed for the adsorption of PCDD/Fs from gas streams at various operating conditions, including gas flow rate, operating temperature and water vapor content. Excellent PCDD/F removal efficiency (>99.99%) was achieved with the multi-layer design with bead-shaped activated carbons (BACs). The PCDD/F removal efficiency achieved with the first layer adsorption bed decreased as the gas flow rate was increased due to the decrease of the gas retention time. The PCDD/F concentrations measured at the outlet of the third layer adsorption bed were all lower than 0.1 ng I-TEQ Nm⁻³. The PCDD/Fs desorbed from BAC were mainly lowly chlorinated congeners and the PCDD/F outlet concentrations increased as the operating temperature was increased. In addition, the results of pilot-scale experiment (real flue gases of an iron ore sintering plant) indicated that as the gas flow rate was controlled at 15 slpm, the removal efficiencies of PCDD/F congeners achieved with the multi-layer reactor with BAC were better than that in higher gas flow rate condition (20 slpm). Overall, the lab-scale and pilot-scale experiments indicated that PCDD/F removal achieved by multi-layer reactor with BAC strongly depended on the flow rate of the gas stream to be treated.     

Biosorption of copper, cobalt and nickel by marine green alga Ulva reticulata in a packed column

Biosorption of copper, cobalt and nickel by marine green alga Ulva reticulata were investigated in a packed bed up-flow column. The experiments were conducted to study the effect of important design parameters such as bed height and flow rate. At a bed height of 25 cm, the metal-uptake capacity of U. reticulata for copper, cobalt and nickel was found to be 56.3+/-0.24, 46.1+/-0.07 and 46.5+/-0.08 mgg(-1), respectively. The Bed Depth Service Time (BDST) model was used to analyze the experimental data. The computed sorption capacity per unit bed volume (N0) was 2580, 2245 and 1911 mgl(-1) for copper, cobalt and nickel, respectively. The rate constant (K(a)) was recorded as 0.063, 0.081 and 0.275 lmg(-1)h(-1) for copper, cobalt and nickel, respectively. In flow rate experiments, the results confirmed that the metal uptake capacity and the metal removal efficiency of U. reticulata decreased with increasing flow rate. The Thomas model was used to fit the column biosorption data at different flow rates and model constants were evaluated. The column regeneration studies were carried out for three sorption-desorption cycles. The elutant used for the regeneration of the biosorbent was 0.1 M CaCl2 at pH 3 adjusted using HCl. For all the metal ions, a decreased breakthrough time and an increased exhaustion time were observed as the regeneration cycles progressed, which also resulted in a broadened mass transfer zone. The pH variations during both sorption and desorption process have been reported.     

Modeling of Solid Particle Flow and Heat Transfer in Rotary Kiln Calciners

Abstract

Contaminated solid wastes exist in many industrial sites, gas plants, and oil refineries. One method of decontaminating the soil is to subject it to high temperatures in a rotary calciner in an anaerobic environment. Preliminary results from a computational model are presented in this paper for the flow and heat transfer from granular solid particles under treatment in a rotary kiln calciner. A fluidization model using kinetic theory of granular flow has been employed to solve the particle flow and heat transfer problem. While a two-dimensional model is used to predict the rotation induced flow of the solid particles, a pseudo three-dimensional model for heat transfer is developed where the axial bulk temperature gradient is obtained from a one-dimensional energy balance model. The model predictions indicate interesting features of the flow and temperature fields in the bed material. Future tasks include the development of a devolatilization model to study the decontamination of waste soil in the rotary calciner.