INFLUENCE OF AIR HUMIDITY ON THE SUPPRESSION OF FUGITIVE DUST BY USING A WATER-SPRAYING SYSTEM

One of the main origins of fugitive dust emission arises from bulk handling in quarries or mines, in particular, from bulk materials falling from a hopper or a conveyor belt. Water-spraying systems, using two-phase nozzles, are one of the methods to suppress such dust emission. In this work we tried to develop a mathematical model to correlate air humidity, water flux through the nozzle and the dust （in particular PM10） emission, in order to improve the application and efficiency of these systems. Sand from the Yellow River in China was dropped from a conveyor belt into a dust chamber at 1 kg·min^-1, wherefrom the emitted dust was sucked off and quantified via a cascade impactor. A two-phase nozzle was installed in the dust chamber with a water flux through the nozzle of 1.2 to 3 L·h^-1, whereas the relative air humidity changed between 55 and 73%. Dust emission was found to be linearly dependent on relative air humidity. Furthermore model equations were developed to describe the dependence of PM10 emission on water flux and relative air humidity.     

Chemical properties and origin of dust aerosols in Beijing during springtime

Ground observation of dust aerosols was conducted in Beijing in the spring of 2005 in order to investigate the element composition and origin of mineral dust. Mass concentrations of most mineral elements of particles increased during dust events. Mineral elements were predominant in the sums of total element loadings in both dusty and non-dusty days. Mg, Si, Fe, Al or Ti can be used as an indicator of dust outflow; Cl can be viewed as an evidence of dust particles mixing with anthropogenic emissions. Mineral and pollutant elements showed a bimodal mass particle-size distribution (MSD) in non-dusty days, and a trimodal distribution in dusty days, but their peak concentrations fell in different size stages. Zn and S were mainly enriched in fine particles, whereas Cl was enriched in medium particles, but most mineral elements and Cu were enriched in coarse particles. Mineral elements were dominated by crustal material in dusty even non-dusty days, but pollutant elements were from non-crustal material including local and remote sources. Back trajectory analysis indicated that dust particles in Beijing mainly originated from the Gobi and desert regions of Mongolian and northern China.     

Correlation analysis of three influencing factors and the dust production rate for a free-falling particle stream

The effects of three factors (i.e., drop height h, hopper outlet diameter d₀, and material temperature T) on the dust generation rate derived from a free falling particle stream were investigated via full factorial experiments. The correlation between the three factors and dust generation rate was also analysed. Results show that T and h affect the first fugitive dust rate largely, whereas the second fugitive dust rate is mainly dominated by h and d₀. Through analysing the first fugitive dust percentage data, it is found that h and T should be considered first for higher temperatures and lower flow rates, whereas h and d₀ can be considered under contrasting conditions, and h should be controlled in the remaining two sets of conditions. Relationships between the influencing factors and total and first fugitive dust rates were developed via multiple regression to quantify the dust emission rates for different contact surfaces (rigid or water).     

Source apportionment of atmospheric particulate carbon in Las Vegas,Nevada, USA

A study was conducted to quantify wintertime contributions of source types to carbonaceous PM_2.5 at four urban sites in the Las Vegas Valley, one of the most rapidly growing urban areas in the southwestern United States. Twenty-four hour average ambient samples were collected for mass, ions, elements, organic carbon (OC), elemental carbon (EC), and trace organic markers analysis. Additional measurements were made to determine diurnal patterns in light-absorbing black carbon (BC) as a marker for combustion sources. Carbonaceous PM sources of on-road gasoline vehicles, on-road diesel vehicles, and off-road diesel engines were characterized with their chemical profiles, as well as fuel-based emission factors, using an In-Plume Sampling System. The Effective Variance Chemical Mass Balance (EV-CMB) source apportionment model was applied to the ambient samples collected, using source profiles developed in this study as well as profiles from other relevant studies. Four main sources contributed to PM_2.5 carbon within the Las Vegas Valley: (1) paved road dust, (2) on-road gasoline vehicles, (3) residential wood combustion, and (4) on-road diesel vehicles. CMB estimated that on-road mixed fleet gasoline vehicles are the largest source for OC and EC at all the sites. The contribution of paved road dust to both OC and EC was 5–10% at the four sites. On-road diesel vehicles contribute 22% of the OC and 34% of the EC at a site near the city center, which is located immediately downwind of a major freeway. Residential wood combustion is a more important source than on-road diesel vehicles for two residential neighborhood sites. These results are consistent with our conceptual model, and the research methodology may be applied to studying other urban areas.     

SEASONAL CHARACTERIZATION OF DUST DAYS, MASS CONCENTRATION AND DRY DEPOSITION OF ATMOSPHERIC AEROSOLS OVER QINGDAO, CHINA

1. Introduction Aerosols play an important role in affecting the atmos-pheric quality, cloud formation and precipitation, influenc-ing the energy balance of the earth-atmosphere system (Sokolik et al., 2001; Cao et al., 2003), although their concentration is very low. Recently, studies on atmospheric aerosols and their radiative forcing have been the inter-esting research area in global and/or regional environment and climate changes (Zhang et al., 2001; Menon et al., 2002). Among them, much…     

ANALYSIS OF PARTICULATE MASS CONCENTRATION, AEROSOL NUMBER CONCENTRATION AND VISIBILITY IN BEIJING

1.IntroductionAtmosphericaerosolsplayanimportantroleinatmos-phericvisibility,irradiationbalanceandclimate.Thenum-berconcentrationofsmallparticulatesisusuallyveryhigh,butitsmassconcentrationisrelativelylow.Buzoriusetal.(1999)andPetersetal.(1997)havereportedthatparticu-latehealtheffectsmaybemoresensitivetothenumberthantothemassconcentration.Thispaperstudiestheaverageddiurnalvariationsofparticulatemassconcentra-tion,numberconcentration,atmosphericvisibility,andtheaerosolsizedistribution,n(r),und…     

Filtration characteristics of a binary multi-layer granular bed filter based on CFD-DEM coupling simulation

The coupled CFD-DEM method with the JKR (Johnson-Kendall-Roberts) model for describing the contact adhesion of dust to filter particles (FPs) is used to simulate the distribution pattern of dust particle deposition in the granular bed filter (GBF) with multi-layer media. The minimum inlet flow velocity must meet the requirement that the contact probability between dust and FPs is in the high contact probability region. The air flow forms vortices on the leeward side of the FPs and changes abruptly at the intersection of different particle size FPs layers. Dust particles form large deposits at the intersection of the first and second layers and the different particle size filter layers. Dual element multilayer GBF can further optimize the bed structure by interlacing filter layers with different particle sizes. Compared with single particle size multi-layer GBF, the bed pressure drop is reduced by 40.24%–50.65% and the dust removal efficiency is increased by 21.93%–55.09%.     

燃料物性参数对瓦斯煤尘复合爆炸的耦合作用

为研究瓦斯煤尘复合爆炸影响因素的耦合规律,对煤粉质量浓度、甲烷体积分数、煤粉粒径、煤粉种类等4种影响因素进行了多因素与单因素实验分析。通过正交实验,将各因素对爆炸的影响进行了定量分析,结果表明,4个因素对最大爆炸压力p_max的影响由强到弱依次为:甲烷体积分数、煤粉质量浓度、煤粉种类、煤粉粒径;对最大爆炸压力上升速率(dp/dt)_max的影响程度由强到弱依次为:甲烷体积分数、煤粉质量浓度、煤粉粒径、煤粉种类。对于体积分数为9%、11%的甲烷,复合体系的p_max随煤粉的质量增加而减小。当煤粉质量浓度增加到100、200 g/m3时,在与体积分数为6%的甲烷耦合作用下,会产生更强的“激励”作用,且煤粉浓度较大时,挥发分低的煤种最佳瓦斯浓度会降低。甲烷体积分数存在临界值,该临界值会改变挥发分因素的影响方式:低于此临界值时,高挥发分煤尘体系的(dp/dt)_max更高,(dp/dt)_max来临时间更短;高于此临界值时,低挥发分体系具有更高的爆炸强度。粒径影响挥发分的作用,粒径越大,挥发分的影响差异越明显。当甲烷体积分数为11%时,挥发分高的煤尘更容易受粒径的影响,直径小的煤尘体系,爆炸系数K_st更小;而低挥发分煤粉在甲烷体积分数接近当量时受粒径影响更明显。     

INFLUENCE OF ASIAN DUSTS ON THE PHYSICOCHEMICAL PROPERTIES OF ATMOSPHERIC AEROSOLS IN TAIWAN DISTRICT USING THE PENGHU ISLANDS AS AN EXAMPLE

1. Introduction In the early months of each year, Asian dusts transport frequently from Northwest China and Mongolia to the Pa-cific-Rim countries (Kagawa et al., 2001; Uno et al., 2002). It causes significant environmental effects such as ambient air quality deterioration, atmospheric visibility impairment, radiation energy reduction, mineral deposition, and acid rain neutralization (Terada et al., 2002; Zhang & An, 1999). During Asian dust periods, significant increases of atmos-pheric …     

Aerosol observation in Fengtai area, Beijing

Measurements of aerosol number concentration and particulate matter with diameter less than 10μm (PM10) mass concentrations of urban background aerosols were performed in Fengtai area, Beijing in 2006. Black carbon (BC) was collected simultaneously from the ground and analyzed to determine the particulate matter components. To satisfy the interest in continuous monitoring of temporal and spatial distribution of aerosols, the relationship between extinction coefficient (visibility) measured by lidar remote sensing and the aerosol number concentration measured from the ground was derived by using statistical method. Vertical particle number concentration profile within the planetary boundary layer could be inversed through the lidar data as well as the statistical relation.     

Dust distribution of solid and adhesive mixed dust in a granular bed filter

Granular bed filters can effectively filter adhesive dust in high-temperature flue gas. In this study, polyvinyl chloride (PVC) powder was used as adhesive dust, and the mixture of PVC and ash powder was used to simulate solid and adhesive mixed dust. The effects of gas temperature, velocity, and inlet adhesive dust mass content on dust distribution in granular bed (GBF) were discussed. Results show that the mixed dust mainly accumulates on the upper part of the granular bed, and the mass of the collected dust decreases exponentially from the upper layer to the bottom layer in the GBF. The adhesive dust content collected in each layer differs from that of the incoming dust, and their deviation varies approximately linearly along with the depth of the bed. The total dust distribution and adhesive dust content deviation are influenced by gas temperature and inlet adhesive dust content but independent of gas velocity. The correlations of dust distribution of solid and adhesive mixed dust are presented based on the experimental results.     

POWER LAW DISTRIBUTION AND SELF-ORGANIZED CRITICALITY OF DISPERSED PARTICLES

Research on particulate characteristics has been an important frontier in physics and chemistry during the past decades. It has however been mostly focused on granular materials with short-range interactions. In this work, it was found that the power law of particle size distribution applied to the long-range interacting system of floating dust in air, from which we deduced that self-organized criticality might hold for floating dust just as granular materials with short-range interactions. This feature may reveal underlying kinetic mechanisms, important in dispersed particle systems. In industry, power law of size distribution of dispersed particles can be used to investigate the change of dust size, and the power law parameter could be taken as an important index for dust separation.     

密闭空间油页岩粉尘爆炸特性研究

为探究油页岩粉尘的爆炸特性,以龙口（Longkou, LK）、茂名（Maoming, MM）、桦甸（Huadian, HD）和抚顺（Fushun, FS）4种油页岩粉尘为研究对象,采用20 L球形爆炸装置,对这4种油页岩粉尘样品开展系统的爆炸实验,探讨油页岩粉尘的粉尘云质量浓度、粒径、挥发分、灰分、氧含量等对其爆炸特性的影响。结果表明:挥发分含量越高,油页岩粉尘的最大爆炸压力p_max、最大压力上升速率(dp/dt)_max越高,爆炸下限越低;挥发分和灰分对油页岩粉尘云爆炸分别有显著的促进和抑制作用。在37.52～106.43 μm粒径范围内,这4种油页岩粉尘样品的p_max和(dp/dt)_max均随其粉尘粒径的增大而降低,且到达最大爆炸压力的时间逐步缩短,说明小粒径油页岩粉尘较高的脱挥发速率能提高爆炸的反应程度。当粉尘质量浓度在400～2 500 g/m3范围内时,p_max和(dp/dt)_max均随粉尘云质量浓度的升高呈现先升高后降低的变化趋势,高于最佳粉尘云质量浓度（1 000 g/m3）时略有下降,但维持在较高水平,表明超过最佳质量浓度的粉尘云引燃后仍有较强的破坏力;LK样品的p_max和(dp/dt)_max均最高,分别为0.61 MPa和29.32 MPa/s,与挥发分含量相当的褐煤在同一水平,其爆炸下限为200 g/m3,在4种样品中最低,高于挥发分含量相当的褐煤;在N₂惰化条件下,LK样品的p_max和(dp/dt)_max均随环境氧含量的降低而降低,当氧含量降至15%时,系统不再发生爆炸,极限氧含量为16%。     

Local and long-range transport influences on PM2.5 at a cities-cluster in northern China,during summer 2008

Hourly PM2.5 concentrations were observed simultaneously at a cities-cluster comprising 10 cities/towns in Hebei province in China from July 1 to 31, 2008. Among the 10 cities/towns, Baoding showed the high- est average concentration level （161.57μg/m3） and Yanjiao exhibited the lowest （99.35 μg/m3 ）. These observed data were also studied using the joint potential source contribution function with 24-h and 72-h backward trajectories, to identify more clearly the local and countrywide-scale long-range transport sources. For the local sources, three important influential areas were found, whereas five important influential areas were defined for long-range transport sources. Spatial characteristics of PM2.5 were determined by multivariate statistical analyses. Soil dust, coal combustion, and vehicle emissions might be the potential contributors in these areas. The results of a hierarchical cluster analysis for back trajectory endpoints and PM2.s concentrations datasets show that the spatial characteristics of PM2.5 in the cities-cluster were influenced not only by local sources, but also by long-range transport sources. Different cities in the cities-cluster obtained different weighted contributions from local or long-range transport sources. Cangzhou, Shijiazhuang, and Baoding are near the source areas in the south of Hebei province, whereas Zhuozhou, Yangfang, Yanjiao, Xianghe, and Langfang are close to the sources areas near Beijing and Tianjin.     

风洞中灰尘在不同特性玻璃表面上粘附形貌和粘附程度的实验研究

为探究室外环境中玻璃上灰尘的形貌特征和粘附程度,本研究选择三种生活中常见的玻璃安装的角度以及三种不同特性的玻璃,利用风洞实验可控环境条件和实验参数的特性,通过工业相机拍摄得到灰尘在玻璃上的粘附形态．本方法解决了过去玻璃积灰实验周期长、难定量、误差大的问题,并利用改进的区域自适应阈值图像识别算法,分别得到不同角度下玻璃上灰尘的总数、灰尘粒径大小、不同粒径灰尘的占比、灰尘平均长轴长度等．结果表明：相同时间内,同种角度下没有涂层的玻璃比有涂层的玻璃更易吸附灰尘,且没有涂层玻璃上面积较大的灰尘更不容易脱落．同种玻璃,放置角度越大,灰尘数量越多．同种玻璃上颗粒物面积大于15 μm2灰尘颗粒数量占灰尘总数的41.9 %左右．所有实验组玻璃上的灰尘平均长轴长度均在11~18 μm之间,灰尘的长宽比均分布在1.34 上下．此项研究可为定量研究玻璃积灰奠定基础,并为工业领域中玻璃防尘、除灰技术等提供技术参考．     

比色测温技术在瞬态爆炸温度场测量中的应用研究

为了研究瞬态爆炸温度场分布规律,基于高速相机、黑体辐射理论、图像传感器的拜尔阵列和自编python代码,构建了依据比色测温原理的高速二维温度测试系统,并对添加不同含量TiH₂的乳化炸药、TiH₂粉尘以及C₂H₂气体的爆炸温度场进行了测量。实验结果表明:TiH₂的加入可以显著提高炸药的爆炸温度和火球持续时间,当乳化炸药中的TiH₂质量分数为6%时,爆炸平均温度最大值为3048 K,相比纯乳化炸药提高了41.5%;此外,TiH₂粉尘云火焰平均温度呈现先增大,再稳定,最后减小的趋势,浓度为500 g/m3的粉尘云火焰平均温度高于浓度为833 g/m3的平均温度,其最高平均温度分别为2231 和 2192 K;10%C₂H₂/90%空气预混气体（即体积分数为10%的C₂H₂和90%空气组成）的早期火焰温度均匀,内部略低于边缘温度,随着火焰膨胀,火焰边缘温度逐渐升高,火焰平均温度开始降低。与传统爆炸测温手段相比,比色测温方法可以准确测量某区域的瞬态爆炸温度,获得温度分布云图,为研究瞬态爆轰温度规律及影响因素提供了一种新的技术手段。     

Global modelling of heat release during initiation and propagation of detonation and deflagration waves in methane-air-particle systems

In the present paper the direct initiation of a self supporting detonation and propagation of a low-speed combustion in methane-air-coal particles mixtures are solved. For particles, a heterogeneous regime of combustion is used, for methane one overall chemical reaction is taken into account: CH + 2O = CO + 2HO. The heat release rate is assumed to be defined as a delay time based on the well-known thermal theory of Frank-Kamenetsky (1967). The proposed model allows one to investigate the influence inert particles or coal dust on the explosion limits of methane-air mixtures. It is shown that the addition of a limited quantity of particles leads to detonation stability. In low speed combustion problems this method allows one to get a good correlation between theoretical and experimental velocities of steady flame propagation in carbon-hydrogen gaseous mixtures. Coal dust influence on gasdynamics of a methane-air mixture combustion is investigated in an unsteady problem by using of the global modelling. It is shown that limited coal dust concentration increases the flame wave intensity in lean methane-air mixtures in contrast to inert particles. In stoichiometric gas mixtures, sand and coal dusts decrease a flame velocity. Far from the ignition point flame, the velocity is largely defined by the dust mass concentration and not by the size of particles. Received 5 July 1997 / Accepted 13 July 1998     

Reconstruction of road defects and road roughness classification using vehicle responses with artificial neural networks simulation

The road damage assessment methodology in this paper utilizes an artificial neural network that reconstructs road surface profiles from measured vehicle accelerations. The paper numerically demonstrates the capabilities of such a methodology in the presence of noise, changing vehicle mass, changing vehicle speeds and road defects. In order to avoid crowding out understanding of the methodology, a simple linear pitch-plane model is employed. Initially, road profiles from known roughness classes were applied to a physical model to calculate vehicle responses. The calculated responses and road profiles were used to train an artificial neural network. In this way, the network renders corresponding road profiles on the availability of fresh data on model responses. The results show that the road profiles and associated defects can be reconstructed to within a 20% error at a minimum correlation value of 94%.     

Variation of granule mass fraction with coordination number in wet granulation process

In granulation, fine particles combine to form a coarse granule in the form of a particle matrix partially or fully saturated with a binder liquid. The final product of granulation possesses a wide variety of granule size distributions with surface mean diameters which differ with operating conditions. The final granule size depends on the operating conditions, e.g. operating gas velocity, inlet air temperature, initial feed particle size, and viscosity of the binder. The objective of this paper is to find out the uniformity in the relation between the granule mass fraction in the final granule size distribution and the number of feed particles present in the granules. The total number of granules obtained depends on the experimental conditions but the granule mass fraction and the number of feed particles forming a single granule are independent of operating variables, feed material and method of granulation. The paper purports further to compare the uniform nature of mass fraction of the granules in final granule size distribution and the primary particles required to form that particular granule size irrespective of experimental conditions of granulation.     

不同粒径PMMA粉尘云火焰温度特性研究

为揭示粒径分布对聚甲基丙烯酸甲酯（polymethyl methacrylate，PMMA）粉尘云火焰温度的影响，本文分别采用热电偶和高速比色测温法测量了开敞空间不同粒径PMMA粉尘云的火焰温度特性。结果表明:相比30 μm粉尘粒子，100 nm粉尘粒子热解/挥发速率较快，燃烧更加充分，粉尘云火焰的最高温度可达1 551℃，而30 μm粉尘云火焰最高温度仅为1 108℃；在微米尺度，随着PMMA粉尘粒径的增大，火焰最高温度和高温火焰区面积先增大后减小；20 μm粉尘粒子由于其分散性较好，裂解气化特征时间尺度与燃烧反应特征时间尺度较接近，燃烧反应充分，火焰最高温度和高温火焰区面积均最大。