Toluene vapor capture by activated carbon particles in a dual gas-solid cyclone system

Capturing of odorous compounds such as toluene vapor by a particulate-activated carbon adsorbent was investigated in a gas-solid cyclone, which is one type of mobile beds. The test cyclone was early modified with the post cyclone (PoC) and a spiral flow guide to the vortex finder. The proposed process may contribute to the reduction of gases and dust from industrial exhausts, especially when dealing with a low concentration of odorous elements and a large volume ofdust flow. In this device, the toluene capturing efficiency at a 400 ppm concentration rose up to 77.4% when using activated carbon (AC) particles with a median size of 27.03 microm. A maximum 96% of AC particles could be collected for reuse depending on the size and flow rate. The AC regenerated via thermal treatment showed an adsorption potential up to 66.7% throughout repeated tests.     

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.     

粉尘对电除尘器气流分布影响仿真研究

为了更加精确地研究电除尘器入口气流分布特征, 论文采用欧拉-拉格朗日多相流模型，对电除尘器内部气流分布进行了数值仿真。由于在进入除尘器的气流中引入了粉尘粒子，不仅可获得粉尘及粉尘颗粒粒径大小对气流分布均匀性的影响，而且这种模拟更加接近除尘器的气流实际情况。提出的模拟方法为电除尘器的气流分析提供了一条新的途径。     

Chemical Composition and Source Apportionment of PM25 Particles in the Sihwa Area,Korea

ABSTRACT

To investigate the chemical characteristics of fine particles in the Sihwa area, Korea, atmospheric aerosol samples were collected using a dichotomous PM₁₀ sampler and two URG PM_2.5 cyclone samplers during five intensive sampling periods between February 1998 and February 1999. The Inductively Coupled Plasma (ICP)-Atomic Emission Spectrometry (AES)/ICP-Mass Spectrometry (MS), ion chromatograph (IC), and thermal manganese dioxide oxidation (TMO) methods were used to analyze the trace elements, ionic species, and carbonaceous species, respectively. Backward trajectory analysis, factor analysis, and a chemical mass balance (CMB) model were used to estimate quantitatively source contributions to PM_{2 5} particles collected in the Sihwa area.

The results of PM_2.5 source apportionment using the CMB7 receptor model showed that (NH₄)₂SO₄ was, on average, the major contributor to PM_2.5 particles, followed by nontraffic organic carbon (OC) emission, NH₄NO₃, agricultural waste burning, motor vehicle emission, road dust, waste incineration, marine aerosol, and others. Here, the nontraffic OC sources include primary anthropogenic OC emitted from the industrial complex zone, secondary OC, and organic species from distant sources. The source impact of waste incineration emission became significant when the dominant wind directions were from southwest and west sectors during the sampling periods. It was found that PM_2.5 particles in the Sihwa area were influenced mainly by both anthropogenic local sources and long-range transport and transformation of air pollutants.     

Effect of Dust Concentration Upon the Gas-Flow Capacity of a Cyclonic Collector

The flow rate through an industrial gas-cleaning cyclone at a fixed pressure drop is greater when the incoming gas is dusty than when it is clean. This observation by Briggs for a single cyclone tube was extended to multiple tubes, and ike results compared to observations by Soo and Trezek that the fraction factor for turbulent flow in a pipe is less for dusty gas than for clean. Empirical considerations indicated tJtat both of these observations should be connected with a rather large reduction in gas viscosity due to the dust. This predicted viscosity decrease was later observed. A physical theory accounting for viscosity reduction by a dust cloud is proposed. This effect also offers a means for increasing the heat, transfer coefficient in gas heat exchangers.     

Penetration of Evaporative Emissions into a Home from an M85-Fueled Vehicle Parked in an Attached Garage

ABSTRACT

The use of both oxygenated fuels in carbon monoxide (CO) nonattainment areas and reformulated gasoline in ozone nonattainment areas has been mandated by the 1990 Clean Air Act Amendments. Methanol has been proposed as an alternative fuel for CO nonattainment areas. Its use will potentially increase indoor methanol inhalation exposure resulting from the evaporation of metha-nol vapor from methanol-fueled vehicles parked in residential garages. Indoor air concentrations of metha-nol, benzene, and toluene were measured in a residential home with an attached garage. The effects of vehicle emission control devices (charcoal canister hose connection); home heating, ventilation, and air conditioning (HVAC) fans; ambient air, garage, and fuel tank temperatures; and wind speed were examined.

The disconnection of the charcoal canister hose, which simulates a spent evaporative emission control device, resulted in elevated benzene, toluene, and metha-nol concentrations in the garage and attached home. Higher fuel tank temperatures resulted in higher benzene and toluene concentrations in the garage, but not methanol. The concentrations for all compounds in the garage and concentrations of benzene and toluene in the adjacent room were lower when the HVAC fan was on than when it was off, while the concentrations of all three compounds in the rest of the house were higher, although these differences were not statistically significant. Thus, the portion of the population that parks cars in garages attached to homes will experience increased methanol exposures if methanol is used as an automotive fuel.     

Adsorption Behavior of Toluene on Modified 1X Molecular Sieves

In this paper, the toluene adsorption/desorption properties of modified 13X molecular sieves (M-13X) are discussed. M-13X molecular sieves were prepared by acidic and steam treatments of 13X molecular sieves. The structural parameters of M-13X were evaluated and compared with those of other molecular sieves (HY, HZSM-5, Cs7NaMOR, and a commercial 13X). The results show that the specific surface area, average pore diameter, and pore volume of M-13X were 414.17 m²/g, 2.98 nm, and 0.31 mL/g, respectively. The pore size distribution of M-13X was 1.8–3.0 nm. Because of its larger Si/Al ratio (Si/Al = 6.77), the hydrophobicity of M-13X is much higher than that of 13X (Si/Al = 1.28), indicating that it is particularly well suited to toluene control applications. The saturation adsorption capacity of M-13X was 0.045 g/g for simulated toluene at a temperature of 293 K and a relative humidity of 50%. The optimal regeneration temperature of M-13X was 473 K for 120 min with a hot air flow rate of 140 L/min.

Implications: The modified 13X molecular sieves (M-13X) are adsorbents with a high adsorption capacity and great hydrophobicity, suitable for the treatment of VOCs. The purpose of the present investigation is to provide a practical guide for their design.     

活性碳纤维吸附甲苯废气吸附等温方程的研究

研究了固定床吸附器中粘胶基活性碳纤维（viscose rayon-based ACFs）吸附甲苯废气的特性，通过实验测定活性碳纤维吸附不同浓度甲苯废气的穿透曲线，作出等温吸附曲线。根据实验数据拟合出几个吸附平衡方程，并与实验结果进行比较。实验结果可为工业设备设计提供参考。     

活性碳纤维吸附甲苯废气吸附等温方程的研究

研究了固定床吸附器中粘胶基活性碳纤维(viscose rayon-based ACFs)吸附甲苯废气的特性,通过实验测定活性碳纤维吸附不同浓度甲苯废气的穿透曲线,作出等温吸附曲线,根据实验数据拟合出几个吸附平衡方程,并与实验结果进行比较.实验结果可为工业设备设计提供参考.     

湿式旋流脱硫除尘一体化装置在燃煤锅炉烟气净化上的应用

某中药厂4 t/h燃煤锅炉烟气采用湿式旋流脱硫除尘一体化装置取得了良好的效果,经实际运行测定除尘率达95%,脱硫率达77%,排出的烟气均能达到排放标准.该净化装置具有旋风水膜除尘器和湿式旋流板洗涤器的双重功能,通过介绍该一体化装置的机理、设计参数和技术经济分析,为燃煤锅炉烟气的脱硫除尘提供参考.     

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.     

A hybrid biological process of indoor air treatment for toluene removal

Bioprocesses, such as biofiltration, are commonly used to treat industrial effluents containing volatile organic compounds (VOCs) at low concentrations. Nevertheless, the use of biofiltration for indoor air pollution (IAP) treatment requires adjustments depending on specific indoor environments. Therefore, this study focuses on the convenience of a hybrid biological process for IAP treatment. A biofiltration reactor using a green waste compost was combined with an adsorption column filled with activated carbon (AC). This system treated a toluene-micropolluted effluent (concentration between 17 and 52 µg/m³), exhibiting concentration peaks close to 733 µg/m³ for a few hours per day. High removal efficiency was obtained despite changes in toluene inlet load (from 4.2 × 10^?3 to 0.20 g/m³/hr), which proves the hybrid system’s effectiveness. In fact, during unexpected concentration changes, the efficiency of the biofilter is greatly decreased, but the adsorption column maintains the high efficiency of the entire process (removal efficiency [RE] close to 100%). Moreover, the adsorption column after biofiltration is able to deal with the problem of the emission of particles and/or microorganisms from the biofilter.

ImplicationsIndoor air pollution is nowadays recognized as a major environmental and health issue. This original study investigates the performance of a hybrid biological process combining a biofilter and an adsorption column for removal of indoor VOCs, specifically toluene.     

Letters to The Editor

Abstract

Since 1990, basic knowledge of the “chemical climate” of fine particles, has greatly improved from Junge’s compilation from the 1960s. A worldwide baseline distribution of fine particle concentrations on a synoptic scale of approximately 1000 km can be estimated at least qualitatively from measurements. A geographical distribution of fine particle characteristics is deduced from a synthesis of a variety of disparate data collected at ground level on all continents, especially in the northern hemisphere. On the average, the regional mass concentrations range from 1 to 80 μg/m³, with the highest concentrations in regions of high population density and industrialization. Fine particles by mass on a continental and hemispheric spatial scale are generally dominated by non-sea salt sulfate (0.2 to ～20 μg/m³, or ～25%) and organic carbon (0.2->10 μg/m³, or ～25%), with lesser contributions of ammonium, nitrate, elemental carbon, and elements found in sea salt or soil dust. The crustal and trace metal elements contribute a varied amount to fine particle mass depending on location, with a larger contribution in marine conditions or during certain events such as dust storms or volcanic disturbances. The average distribution of mass concentration and major components depends on the proximity to areal aggregations of sources, most of which are continental in origin, with contributions from sea salt emissions in the marine environment. The highest concentrations generally are within or near very large population and industrial centers, especially in Asia, including parts of China and India, as well as North America and Europe. Natural sources of blowing dust, sea salt, and wildfires contribute to large, intermittent spatial-scale particle loadings beyond these ranges. A sampling of 10 megacities illustrates a range of characteristic particle composition, dependent on local and regional sources. Long-range transport of pollution from spatially aggregated sources over hundreds of kilometers creates persistent regional- and continental-scale gradients of mass concentration, sulfate, and carbon species especially in the northern hemisphere. Data are sparse in the southern hemisphere, especially beyond 45° S, but are generally very low in mass concentrations.     

Index

Abstract

Activated carbon (AC) adsorption has long been considered to be a readily available technology for providing protection against exposure to acutely toxic gases. However, ACs without chemical impregnation have proven to be much less efficient than impregnated ACs in terms of gas removal. The impregnated ACs in current use are usually modified with metalloid impregnation agents (ASC-carbons; copper, chromium, or silver) to simultaneously enhance the chemical and physical properties of the ACs in removing specific poisonous gases. These metalloid agents, however, can cause acute poisoning to both humans and the environment, thereby necessitating the search for organic impregnation agents that present a much lower risk. The aim of the study reported here was to assess AC or ASC-carbon impregnated with triethylenediamine (TEDA) in terms of its adsorption capability for simulated hydrogen sulfide (H₂S) and sulfur dioxide (SO₂) gases. The investigation was undergone in a properly designed laboratory-scale and industrial fume hood evaluation. Using the system reported here, we obtained a significant adsorption: the removal capability for H₂S and SO₂ was 375 and 229 mg/g-C, respectively. BET measurements, element analysis, scanning electron microscopy, and energy dispersive spectrometry identified the removal mechanism for TEDA-impregnated AC to be both chemical and physical adsorption. Chemical adsorption and oxidation were the primary means by which TEDA-im pregnated ASC-carbons removed the simulated gases.     

The stable carbon isotope composition of PM2.5 and PM10 in Mexico City Metropolitan Area air

The sources and distribution of carbon in ambient suspended particles (PM_2.5 and PM₁₀) of Mexico City Metropolitan Area (MCMA) air were traced using stable carbon isotopes (¹³C/¹²C). Tested potential sources included rural and agricultural soils, gasoline and diesel, liquefied-petroleum gas, volcanic ash, and street dust. The complete combustion of LP gas, diesel and gasoline yielded the lightest δ¹³C values (?27 to ?29‰ vs. PDB), while street dust (PM₁₀) represented the isotopically heaviest endmember (?17‰). The δ¹³C values of rural soils from four geographically separated sites were similar (?20.7 ± 1.5‰). δ¹³C values of particles and soot from diesel and gasoline vehicle emissions and agricultural soils varied between ?23 and ?26‰. Ambient PM samples collected in November of 2000, and March and December of 2001 at three representative receptor sites of industrial, commercial and residential activities had a δ¹³C value centered around ?25.1‰ in both fractions, resulting from common carbon sources. The predominant carbon sources to MCMA atmospheric particles were hydrocarbon combustion (diesel and/or gasoline) and particles of geological origin. The significantly depleted δ¹³C values from the industrial site reflect the input of diesel combustion by mobile and point source emissions. Based on stable carbon isotope mass balance, the carbon contribution of geological sources at the commercial and residential sites was approximately 73% for the PM₁₀ fraction and 54% for PM_2.5. Although not measured in this study, biomass-burning emissions from nearby forests are an important carbon source characterized by isotopically lighter values (?29‰), and can become a significant contributor (67%) of particulate carbon to MCMA air under the prevalence of southwesterly winds. Alternative sources of these ¹³C-depleted particles, such as cooking fires and municipal waste incineration, need to be assessed. Results show that stable carbon isotope measurements are useful for distinguishing between some carbon sources in suspended particles to MCMA air, and that wind direction has an impact on the distribution of carbon sources in this basin.     

氧化锰矿渣改性制备SCR脱硝催化剂

以锰酸钾生产过程中产生的氧化锰矿渣为原料,制备了一系列Mn基SCR脱硝催化剂。研究了活性炭、二氧化钛、以及含锰量的变化对催化剂的脱硝活性的影响。结果表明,直接由矿渣制备的催化剂和添加活性炭、二氧化钛制备的催化剂,其最大脱硝率分别为40%和78%。XPS表征发现催化剂中的锰元素存在多种氧化价态,活性炭的加入在一定程度上改变了不同价态之间的相对含量;在矿渣中加入硫酸锰后,发现总锰含量达到10%时,催化剂的最大脱硝率从78%降低至57%,XRD测试发现硫酸锰的加入导致S2O27-物种的生成,可能是引起催化剂活性下降的原因之一;而加入醋酸锰至总锰含量达到10%时,增大了催化剂的活性温度窗口,当总锰含量达到20%时,在空速10 000 h-1条件下,催化剂的最大脱硝率达到86.7%。     

Mineralogical and chemical characterization of suspended atmospheric particles over the east Mediterranean based on synoptic-scale circulation patterns

Suspended atmospheric particles were collected in Israel in order to identify their nature and relationships with the major synoptic-scale circulation patterns. The particles were analyzed for their major and trace element concentrations and mineralogical composition. Samples were collected during three synoptic systems associated with desert dust storms: Red Sea trough, Sharav cyclone and cold depression, and during deep and shallow modes of Persian Gulf trough, which prevails in the summer months and is not associated with dust storms.All samples mostly contain particles smaller than 2 μm. The suspended desert dust is composed primarily of illite–smectite and calcite. Some indicative secondary minerals were found for each of the dust transporting synoptic systems (e.g., palygorskite for Red Sea trough). The bulk chemistry data support the mineralogical observations and reveal additional chemical signatures of each dust transporting system. For instance, Red Sea trough samples have significantly higher Ca/Al and Ca/Mg in the carbonate and Mg/Al in Al-silicate fraction than cold depression samples. Nevertheless, Sharav cyclone samples have intermediate values in spite of the fact that the source of the dust during these conditions is similar to cold depression (i.e., North Africa). Even though differences in the chemical and the mineralogical composition of desert dust do exist, this study reveals their overall chemical and mineralogical similarities.In contrast to the synoptic systems that carry desert dust, the inorganic fraction of the Persian Gulf trough samples contains significant amount (up to 50%) of non-mineral material that has a pronounced chemical signature in terms of major element concentrations (e.g., Al, Ca, Mg, Na, S) implying their anthropogenic nature, probably from countries around the Black Sea. This striking finding is indicative for atmospheric pollution in the Eastern Mediterranean region during the summer.     

Feasibility of granular bed filtration of an aerosol of ultrafine metallic particles including a pressure drop regeneration system

A process for filtering an aerosol of ultrafine metallic particles (UFP) has been designed and tested, based on the principle of a multistage granular bed. The filtration system comprised a succession of granular beds of varying thickness composed of glass beads of different diameters. This system allows the pressure drop to be regenerated during filtration (“on-line” mode) using a vibrating probe. Tests monitoring the pressure drop were conducted on a “10-L/min” low airflow rate device and on a “100-m³/hr” prototype. Granular bed unclogging is automated on the latter. The cyclic operation and filtration performances are similar to that of filter medium-based industrial dust collectors.

Implications:?Filtration of ultrafine metallic particles generated by different industrial processes such as arc welding, metal cutting, or spraying constitutes a difficult problem due to the high filter clogging properties of these particles and to the high temperatures generally encountered. Granular beds represent an advantageous means of filtering these aerosols with difficult properties.     

Size and Concentration Measurements of Particles Produced in Commercial Chromium Plating Processes

Abstract

Optical measurements of particle size and concentration were made at the chromium plating tank and exhaust system at a commercial hexavalent chromium plating facility. Particles were examined at three locations in the exhaust system: 1) directly at the hexavalent chromium plating bath surface, 2) at the exit of a cyclone separator located in the exhaust system approximately three to four meters downstream of the bath, and 3) in the exhaust stack, downstream of the induced draft fan and all abatement devices. Particle diameters at the bath surface ranged from 0.3 to 25 μm. Downstream of the cyclone exit and mesh pad filters, particle top sizes were approximately 5 and 0.7 mm, respectively. On a mass basis, the collection efficiency of all abatement devices was 99.997%. Assuming that droplets in the flow consist primarily of water and chromium, correcting the total particle mass flow against water content gives a chromium emission rate of 64,000 μg/hr, which compares favorably with a value of 77,000 μg/hr measured with EPA methods. This initial agreement, which should be validated through additional measurements over a broad range of flow conditions, raises the possibility of continuous monitoring for chromium metal emissions using particle size/mass as a surrogate.     

活性炭孔隙结构在其甲苯吸附中的作用

选用4种商用活性炭(AC),利用氮气绝热吸附、扫描电子显微镜(SEM)和傅立叶变换红外光谱(FTIR)测试了活性炭的物化性质。以甲苯为吸附质,在温度为298.15 K下进行了静态和动态吸附实验,研究了活性炭孔结构对其吸附性能、吸附行为、表面覆盖率和吸附能的影响。结果表明:活性炭的比表面积和孔容是其吸附性能主要影响因素,孔径在0.8～2.4 nm之间的孔容和甲苯吸附量之间存在较好的线性关系,且线性斜率随甲苯浓度增加而变大。甲苯吸附行为符合Langmuir吸附等温模型和准一阶动力学方程式。活性炭孔结构是甲苯吸附速率的主要制约因素。在甲苯快速吸附阶段,微孔为吸附速率主要制约因素,在甲苯颗粒内扩散阶段,微孔和表面孔为吸附速率的主要制约因素,在吸附末尾阶段,中孔和大孔为吸附速率的主要制约因素。4种活性积炭对甲苯的吸附能随其比表面变大而变大。