球柱形旋风除尘器分离性能数值模拟与实验

针对传统柱锥形旋风除尘器存在细颗粒分离效率低的问题,提出了一种新型球柱形旋风除尘器。采用数值模拟和实验研究手段,分析了柱段高度对球柱形旋风除尘器分离特性的影响。模拟结果表明:当球柱形旋风除尘器柱段高度不为零时,随着柱段高度的增加,静压力逐渐变小;球柱形旋风除尘器内流体的切向速度均呈"M"型分布;流体轴向速度随着半径的减小,其绝对值先增大后减小,在中心轴线处又开始增大;流体径向速度均关于中心轴线对称。实验结果表明,当球柱形旋风除尘器柱段高度为150 mm时,总分离效率最高,可达到92.01%。研究结果可为旋风除尘器中细小颗粒分离应用提供指导,对提高5μm以下颗粒分离效率具有重要意义。     

应用电声换能超声波雾化方法提高超细颗粒捕集效率

针对大气环境污染控制中超细颗粒难以捕集的问题,提出了一种高效、经济的新方法.其核心思想是将经电声换能超声波雾化得到的相对湿度过饱和雾气喷入含尘气体中,在“云”物理学、碰撞团聚等原理共同作用下,饱和水蒸汽在颗粒表面凝结,使超细颗粒的粒径增大,增加其捕集效率.为了证明这种方法的有效性,建立了小型电声换能超声波雾化捕尘实验台并在旋风除尘器中进行实验研究.实验结果表明,随着雾气浓度的增加,总除尘效率与超细颗粒的分级效率均有明显提高,并且旋风除尘器的压降(能耗)明显降低.     

基于ASMM模型对不同袋长袋式除尘器气固两相流的模拟

为了提高袋式除尘器内部流场的均匀性,延长滤袋的使用寿命以及降低能耗,以某环保公司下进风袋式除尘器为几何模型,采用简化的欧拉模型-代数滑移混合模型(algebraic slip mixture model,ASMM)模拟了3种袋长分别为6、8和10 m的袋式除尘器处理粒径为1、2.5、5、10和20μm颗粒时其内的气固两相流动。对比分析了不同袋长除尘器内速度云图、颗粒相体积份额以及压力损失等,结果表明:随着滤袋长度的增加,除尘器内部流场的均匀性提高;袋式除尘器对5种不同粒径颗粒都具有一定的去除能力,滤袋长度为8 m时受到的二次扬尘影响较小;滤料及粉尘层厚度为2 mm时,袋式除尘器的压力损失随着滤袋长度的增加而增加,颗粒粒径对除尘器压力损失的影响较小;通过对比袋长为8 m时除尘器模拟压降与实验结果,验证了模拟结果的可靠性。因此,除尘器的最优袋长为8 m,模拟结果为袋式除尘器的设计和优化提供了理论依据。     

新型电袋复合除尘器性能研究

为了提高布袋除尘器对细微粒子的捕集效率,同时降低压力损失,提出了一种新型的电袋复合除尘器,并利用这种新型的除尘器对2 500目的超细滑石粉进行了实验研究。通过普通布袋过滤、电袋复合过滤的对比实验研究,得到了电场强度、气布比、压损、清灰周期和除尘效率等参数的变化规律。实验结果表明,使用新型的复合除尘器过滤粉尘时,粉尘在进入袋室之前就被荷电,通过在滤料表面施加较强的静电场,使得被处理粉尘在滤料的表面有序堆积和排列,能有效地降低压力损失,提高过滤风速,除尘效率均达到97%以上。Vf=3.5 m/min,U=12.3 kV时,新型复合除尘器与普通布袋过滤相比压力损失降低了90 Pa;PM2.5的捕集效率提高了5.9%;清灰周期从10 min延长至36 min。     

锥度对旋风除尘器主要性能的影响

为了提高旋风除尘器的分离效率,研究了锥度对旋风除尘器主要性能的影响,建立了气体流场和颗粒动力场的理论模型,并应用SIMPLEC算法对不同锥度下旋风除尘器内部的总压、切速度、颗粒运动轨迹以及分离效率进行了数值模拟。数值结果表明:旋风除尘器内部的总压和切速度均基本呈轴对称分布,沿半径方向,总压呈非线性增大趋势,而切速度呈"驼峰"分布;通过减小锥度降低了总压和切速度,缩短了颗粒的停留时间,从而提高了分离效率,为旋风除尘器的结构优化设计、提高分离性能提供参考。     

布袋过滤除尘中气固两相流的格子Boltzmann模拟

使用格子Boltzmann方法对含尘气体通过布袋滤料纤维的流动进行了数值模拟,采用拉格朗日方法跟踪了颗粒相中每个粒子的位置和速度并进行单向耦合计算。分析了气流通过纤维捕集体过程中的压降的变化规律,结果与达西渗透定律吻合。与此同时,对粒径小于1μm的气溶胶粒子在布袋纤维捕集体上的沉积规律展开了讨论。结果表明,粒径小于0.01μm的粒子的捕集主要受粒子的布朗随机扩散效应的控制;粒径大于0.1μm的粒子则主要依靠纤维滤料的拦截作用而沉积在捕集体表面;而粒径在0.01～0.1μm范围的粒子则具有较低的捕集效率。模拟结果为研究袋式除尘的过滤机理提供了依据。     

旋风除尘器内部流场的数值研究

通过建立旋风除尘器模型，模拟了排气管插入深度对旋风除尘器的压降、气流的切向速度和轴向速度的影响。研究表明，增加排气管的插入深度会增大旋风除尘器的压力损失，但对其内部压力分布的影响却比较小；增加排气管的插入深度对气体切向速度和轴向速度的影响也比较小，在不同高度上，内外旋流交界处切向速度的最大值都有所增加，这会产生更大的离心力，除尘效率也会因此而提高。     

旋风-布袋复合除尘器优化和除尘效率的数值模拟

针对燃煤工业锅炉烟尘超低排放的要求,采用数值模拟方法,研究了旋风除尘器(A)和内部滤袋前无导流板(B)、有导流板(C)或开孔挡板(D)的几种旋风-布袋复合除尘器的流场。结果表明:除尘器C的流场较均匀,较高风速时压降低于除尘器B、D。进一步模拟了除尘器A、C的分级效率,发现对于粒径低于15μm的颗粒,除尘器A去除率低于60%,除尘器C去除率高于97.8%。且复合除尘器占地小,滤袋寿命长,具有广阔的应用前景。上述数值模拟结果可为复合除尘器的优化设计提供参考。     

燃煤电站湿法烟气脱硫的颗粒物脱除效果

伴随着我国燃煤电站污染物严峻形势湿法烟气脱硫协同捕集颗粒物越来越受到工程应用部门的重视。从基本理论出发,引入捕集体与颗粒碰撞、拦截与扩散的基本方程,推导并建立多液滴对多颗粒的捕集模型。研究结果表明:直径245μm的液滴,沉降速度小于气流速度,会被携带出脱硫塔;液滴对PM_(0.1)、PM_1、PM_5、PM_(10)。颗粒物的去除效率为U型曲线,910μm液滴对颗粒物的去除效率比4 666μm液滴高近百倍;同等质量浓度不同粒度分布,脱硫塔除尘性能仍然差异较大。     

基于颗粒能量耗散模型的多相网格质点法的旋风分离器模拟

提出一种配合网格质点法的能量耗散模型,考虑颗粒之间碰撞引起的能量耗散效应以描述颗粒的团聚行为。采用该模型模拟的旋风分离器颗粒流发现:较其他模型具有较高的预测精度,模拟结果与实验吻合较好,验证了耗散模型可行。旋风分离器的中心形成负压区域,而在靠近壁面处形成高压区域。气相场呈现以中心为轴同转向不同流向的双螺旋结构,大部分颗粒被夹带到壁面附近,聚集在一起,形成聚团并产生分离,模拟结果发现旋风分离器在模拟条件下的分离粒径为1×10~(-5)m。     

An efficient venturi scrubber system to remove submicron particles in exhaust gas

An efficient venturi scrubber system making use of heterogeneous nucleation and condensational growth of particles was designed and tested to remove fine particles from the exhaust of a local scrubber where residual SiH4 gas was abated and lots of fine SiO2 particles were generated. In front of the venturi scrubber, normal-temperature fine-water mist mixes with high-temperature exhaust gas to cool it to the saturation temperature, allowing submicron particles to grow into micron sizes. The grown particles are then scrubbed efficiently in the venturi scrubber. Test results show that the present venturi scrubber system is effective for removing submicron particles. For SiO2 particles greater than 0.1microm, the removal efficiency is greater than 80-90%, depending on particle concentration. The corresponding pressure drop is relatively low. For example, the pressure drop of the venturi scrubber is approximately 15.4 +/- 2.4 cm H2O when the liquid-to-gas ratio is 1.50 L/m3. A theoretical calculation has been conducted to simulate particle growth process and the removal efficiency of the venturi scrubber. The theoretical results agree with the experimental data reasonably well when SiO2 particle diameter is greater than 0.1 microm.     

Collection of Aerosol Particles by Electrostatic Droplet Spray Scrubbers

Theoretical calculations and experimental measurements show that the collection of small aerosol particles (0.05 to 5 micron diameter range) by water droplets in spray scrubbers can be substantially increased by electrostatically charging the droplets and particles to opposite polarity. Measurements with a 140 acfm two chamber spray scrubber (7 seconds gas residence time) showed an increase in the overall particle collection efficiency from 68.8% tit uncharged conditions to 93.6% at charged conditions, with a dioctyl phthalate aerosol (1.05 μm particle mass mean diameter and 2.59 geometric standard deviation). The collection efficiency for 0.3 μm particles increased from 35 to 87% when charged. During 1973–1974 a 1000 acfm pilot plant electrostatic scrubber was constructed inside a 40 ft trailer for evaluation on controlling particu-late emissions from pulp mill operations (funded by Northwest Pulp and Paper Association). Field tests performed on the particle emissions exhausting from SO₂ absorption towers treating the gases from a magnesium based sulfite recovery boiler have shown particle collection efficiencies ranging from about 60 to 99% by weight, depending on the electrostatic scrubber operating conditions. Energy requirements for the University of Washington electrostatic scrubber are about 0.5 hp/1000 acfm (350 Watts/1000 acfm) including gas pressure drop, water pressure drop, and electrostatic charging of the water spray droplets and the particles.     

Product Guide/1982

Abstract

An efficient venturi scrubber system making use of heterogeneous nucleation and condensational growth of particles was designed and tested to remove fine particles from the exhaust of a local scrubber where residual SiH₄ gas was abated and lots of fine SiO₂ particles were generated. In front of the venturi scrubber, normal-temperature fine-water mist mixes with high-temperature exhaust gas to cool it to the saturation temperature, allowing submicron particles to grow into micron sizes. The grown particles are then scrubbed efficiently in the venturi scrubber. Test results show that the present venturi scrubber system is effective for removing submicron particles. For SiO₂ particles greater than 0.1 μm, the removal efficiency is greater than 80–90%, depending on particle concentration. The corresponding pressure drop is relatively low. For example, the pressure drop of the venturi scrubber is ～15.4 ± 2.4 cm H₂O when the liquid-to-gas ratio is 1.50 L/m³. A theoretical calculation has been conducted to simulate particle growth process and the removal efficiency of the venturi scrubber. The theoretical results agree with the experimental data reasonably well when SiO₂ particle diameter is greater than 0.1 μm.     

离心脉冲静电除尘器内颗粒浓度场测试分析

在离心脉冲静电除尘器研究的基础上 ,进行了离心脉冲静电除尘器内的浓度场的测试分析 ,并得出了在一定入口风速、工作电压、入口粉尘浓度下其颗粒浓度场分布规律及实测回归方程。     

A Cyclone for Size-Selective Sampling of Ambient Air

A cyclone with a 47 mm after-filter has been developed for ambient air size-selective monitoring. It has been extensively evaluated with laboratory-generated aerosol. Variation of the pressure drop and 50% cut point with flow rate show that the cyclone operates in a single flow regime with a vortex in the outlet flow. The particle size cutoff curve is comparable in sharpness to a cascade impactor and is the same for solid or liquid particles. At 21.7 L/min, D ₅₀ is 2.5μm and at 15.4 L/min, D ₅₀ is 3.5 μm. Collection efficiency data for flow rates from 8 to 27 L/min fit a universal curve when plotted vs. the normalized particle diameter, (D-D ₅₀)/D ₅₀ Reentrainment of previously deposited particles is less than 1 % of the loading per day. In field tests the cyclone has proved to be a very satisfactory size-selective sampler.     

Fine Particle Control Using Sulfur Oxide Scrubbers

Compliance with sulfur oxides standards will in many cases result in the installation of scrubbing devices. If these devices operate on an effluent gas stream containing particulate as well as sulfur oxides, simultaneous removal would be expected. Since effective simultaneous removal of particulate matter and sulfur oxides is economically desirable, it is of considerable import to characterize scrubber designs being considered as sulfur oxide absorbers as particulate control devices; especially, for fine particulate control.

Data on the fine particle collection efficiency of sulfur oxides scrubbers at two power generating stations is presented. At the first, a venturi and a turbulent contacting absorber (TCA) both with capacities of 30,000 cfm were tested. At the second, a venturi with 600,000 scfm capacity was tested. Fine particle collection efficiency was determined at three pressure drops for the TCA using a cascade impactor. Results for the TCA show high removal efficiencies. It collected more than 90% of submicron particles when the pressure drop was nearly 10 in. H₂0. The overall particulate removal in the TCA scrubber as determined by modified method 5 or by Brink impactor was greater than 99% when the pressure drop was greater than 6 in. H₂0. For both the venturi scrubber at the Shawnee Steam Plant and that at the Mystic Power Station, the collection efficiency decreased rapidly with decreasing particle size in the fine particle region.     

An Analysis of Visual Range in the Eastern United States Under Different Meteorological Regimes

ABSTRACT

The issue of fine particle (PM₂₅) exposures and their potential health effects is a focus of scientific research because of the recently promulgated National Ambient Air Quality Standard for PM_{2 5}. Before final implementation, the health and exposure basis for the standard will be reviewed by the U.S. Environmental Protection Agency within the next five years. As part of this process, it is necessary to understand total particle exposure issues and to determine the relative importance of the origin of PM_{2 5} exposure in various micro-environments. The results presented in this study examine emissions of fine particles from a previously uncharacterized indoor source: the residential vacuum cleaner. Eleven standard vacuum cleaners were tested for the emission rate of fine particles by their individual motors and for their efficiency in collecting laboratory-generated fine particles. An aerosol generator was used to introduce fine potassium chloride (KC1) particles into the vacuum cleaner inlet for the collection efficiency tests. Measurements of the motor emissions, which include carbon, and the KCl aerosol were made using a continuous HIAC/Royco 5130A light-scattering particle detector. All tests were conducted in a metal chamber specifically designed to completely contain the vacuum cleaner and operate it in a stationary position. For the tested vacuum cleaners, fine particle motor emissions ranged from 9.6 x 10⁴ to 3.34 x 10⁸ particles/min, which were estimated to be 0.028 to 176 mg/min for mass emissions, respectively. The vast majority of particles released were in the range of 0.3-0.5 mm in diameter. The lowest particle emission rate was obtained for a vacuum cleaner that had a high efficiency (HEPA) filter placed after the vacuum cleaner bag and the motor within a sealed exhaust system. This vacuum cleaner removed the KC1particles that escaped the vacuum cleaner bag and the particles emitted by the motor. Results obtained for the KC1 collection efficiency tests show >99% of the fine particles were captured by the two vacuum cleaners that used a HEPA filter. A series of tests conducted on two vacuum cleaners found that the motors also emitted ultra-fine particles above 0.01 mm in diameter at rates of greater than 10⁸ ultra-fine particles/CF of air. The model that had the best collection efficiency for fine particles also reduced the ultra-fine particle emissions by a factor of 1 x 10³.     

Engineering Design of Fine Particle Scrubbers

A concise, quantitative picture of the state of the art of particle scrubbing is presented in the form of performance prediction methods. A new relationship between the particle diameter collected at 50% efficiency and scrubber pressure drop for several of the most common scrubber types is a design tool of great utility. Scrubber capability for the collection of submicron particles by diffusion is described in a graph for several scrubber types.     

Removal of Ultrafine and Fine Particulate Matter from Air by a Granular Bed Filter

Abstract

The removal efficiency of granular filters packed with lava rock and sand was studied for collection of airborne particles 0.05–2.5 μm in diameter. The effects of filter depth, packing wetness, grain size, and flow rate on collection efficiency were investigated. Two packing grain sizes (0.3 and 0.15 cm) were tested for flow rates of 1.2, 2.4, and 3.6 L/min, corresponding to empty bed residence times (equal to the bulk volume of the packing divided by the airflow rate) in the granular media of 60, 30, and 20 sec, respectively. The results showed that at 1.2 L/min, dry packing with grains 0.15 cm in diameter removed more than 80% (by number) of the particles. Particle collection efficiency decreased with increasing flow rate. Diffusion was identified as the predominant collection mechanism for ultrafine particles, while the larger particles in the accumulation mode of 0.7–2.5 μm were removed primarily by gravitational settling. For all packing depths and airflow rates, particle removal efficiency was generally higher on dry packing than on wet packing for particles smaller than 0.25 μm. The results suggest that development of biological filters for fine particles is possible.