Change in Grain-Size Composition of Lignite under Cyclic Freezing-Thawing and Wetting-Drying

The paper presents the change in grain-size composition of lignite under cyclic freezing-thawing (FTC) and wetting-drying (WDC). The article shows that in the spring and autumn periods the lignites can be subjected to repeated freezing-thawing and wetting-drying, which determines the possibility of changing their grain-size composition and structure. Experimental studies in laboratory conditions on the influence of cyclic freezing-thawing (FTC) and wetting-drying (WDC) on the quality indicators of lignites have been carried out, their granulometric (fractional) composition has been studied. Freezing-thawing cycle conditions are as follows (FTC): minimum exposure temperature: -20°C;maximum: +5°C;relative humidity: 30%;number of processing cycles: 3. Wetting-drying cycles are as follows (WDC): drying temperatures are +20, +40, +60, +80°C, drying time 90 minutes, the coals are further subjected to rain (soaking) for a period of water saturation to humidity of 30% - 40% and dry again. The number of wetting-drying cycles is 3 times. The tests have revealed the destructive effects of FTC and WDC on the samples of lower metamorphic grade coal, and the cycles of wet-dry lead to the much higher yield of fine sizes (-6+0;-13+0 mm) than the cycles of freeze-thaw. Furthermore, it is found that the increase in the yield of fines depends on the heating temperature: coal disintegration proceeds more intensively at a higher temperature of drying.

Grain-size Characteristics of Sediment in Daniugou Peatland in Changbai Mountains,Northeast China:Implications for Atmospheric Dust Deposition

The grain-size distribution characteristics and grain-size parameters of sediment in two vertical sections of Daniugou peatland in the Changbai Mountains were systematically investigated.A comparative analysis of the sediment granularity using a discriminative function with Hongyuan peat,red clay,loess-paleosol,fluvial deposit as well as lacustrine deposit was also conducted.It turns out that the vertical section of Daniugou peat ash is primarily constituted by clay and silt particles,and the content of sand is relatively small.Grain-size frequency curves generally show a single-peak modality while a bimodal pattern is detected in the upper layer.The grain-size component and peak pattern of grain-size frequency curves also illustrate that peat ash materials were transported to the peatland by long-range aeolian dust during the deposition process,while there existed short-distance dust influence in peat deposition of the upper layer.Comparisons of grain-size parameters and the discriminative Y-value of Daniugou peat ash with those of typical aeolian sediments show close similarities,suggesting the possibility that atmospheric dust transport processes were involved in the accumulation of peat again.Moreover,the variations of grain-size distribution suggest the local environmental deterioration which is just the driving force of local dust elevation.Grain-size analysis of peatland sediment is demonstrated to be one effective method to extract information about regional and global environmental evolution,and more attention should be paid to current local ecological environment and to seeking a balance between economic development and environmental protection in Northeast China.

The Drift of Dust Grains Induced by Transient Magnetic Field

Our experiment shows that the dust grains, suspended on the edge of the sheath of a radio-frequency discharge, undergo a contraction when switching a vertical magnetic field on, and an expansion when switching the magnetic field off. We call this kind of magnetic field "transient magnetic field". A primary analysis is proposed for the phenomenon.

Surface Potential of Dust Grains at the Sheath Edge of Electronegative Dusty Plasmas

In this paper we investigate the dust surface potential at the sheath edge of electronegative dusty plasmas theoretically, using the standard fluid model for the sheath and treating electrons and negative ions as Boltzmann particles but positive ions and dust grains as cold fluids. The dust charging model is self-consistently coupled with the sheath formation criterion by the dust surface potential and the ion Mach number, moreover the dust density variation is taken into account. The numerical results reveal that the dust number density and negative ion number density as well as its temperature can significantly affect the dust surface potential at the sheath edge.

Cycloid motions of grains in a dust plasma

Hypocycloid and epicycloid motions of irregular grains （pine pollen） are observed for the first time in a dust plasma in a two-dimensional （2D） horizontal plane. These cycloid motions can be regarded as a combination of a primary circle and a secondary circle. An inverse Magnus force originating from the spin of the irregular grain gives rise to the primary circle. Radial confinement resulting from the electrostatic force and the ion drag force, together with inverse Magnus force, plays an important role in the formation of the secondary circle. In addition, the cyclotron radius is seen to change periodically during the cycloid motion. Force analysis and comparison experiments have shown that the cycloid motions are distinctive features of an irregular grain immersed in a plasma.

EQUILIBRIUM POTENTIAL OF DUST GRAINS IN COMETARY PLASMA ENVIRONMENTS

The equilibrium potential of fluffy dust grains in plasma are calculated for comet P/Halley and comet P/G-Z. It is found that the dust equilibrium potential linearly correlates with the logarithm of electron density. We propose this relationship can also be applied to comet Hale-Bopp.

抓斗式散粮卸料过程逸尘机理探究

为探究抓斗卸料过程中的逸尘机理,解决当前港口物料转运过程中存在粉尘外逸严重的难题,搭建抓斗卸料逸出气流在线测试实验平台。采用试验与数值计算相结合的方式,以典型主粮散体颗粒为卸料对象,基于气固两相流理论,探究卸料高度和卸料质量流量对料斗内逸出气流速度的影响映射耦合关系,结合粉尘颗粒逸出过程的运动特性和规律推导出粉尘逸出的临界粒径。结果表明:逸出气流速度峰值与卸料高度成正相关,同一卸料高度下,逸出气流峰值与质量流量成幂函数关系;基于粉体颗粒受力,推导出粉尘颗粒逸出的临界粒径计算公式,并验证公式的计算误差在11%以内;大豆、玉米和小麦卸料时,粉尘颗粒逸出的临界粒径范围分别为160.9~292.5,182.6~359.6,95.1~196.1μm。研究为抓斗式散粮卸料过程中的粉尘控制和抑尘装置设计提供理论支撑。

某泊位改建工程设计要点分析

某泊位改建工程是在现有泊位的基础上,新增带式输送机接卸进口散粮和中转装船,新增油管装卸植物油。文中对该泊位改建工程的设计要点进行了分析,设计方案充分考虑了对现有码头作业模式的影响和适应性,最大程度提升码头的利用率。在场地受限、功能众多的情况下,通过科学、合理的布置,针对地形特点满足各项功能的需求,并使各环节能力相匹配,为以后类似工程码头的改造设计提供经验借鉴。

Features of Sand-dust Deposits in Harbin City,China

From the sedimentologic view,this paper analyses the grain-size distribution and the chemical composition of the deposits from sand-dust storm,occurring in Harbin on March 20,2002.The result indicates that there exist plentiful coarse matters in the sand-dust deposits in Harbin,and the sand-dust composition presents obvious three peak distribu-tion characteristics,indicating that the sand-dust in Harbin is composed of multi-origin components.The grain-size composition consists of silt(4-8Ф),accounting for 71.18% of the total,sand(>4Ф),21.70%,and clay(<8Ф),only 7.13%.The average grain size(Mz) is 5.14Ф.The chemical elements of the deposits are mainly SiO2 and Al2O3 and Fe2O3,totally occupying 77.8%.The enrichment factors(EF) of Mg,K,Si,Fe,Mn,P,Ti,Co,Ni and V elements are all about 1,which mainly come from lithosphere source,while parts of Cu,Pb,Zn,Cr and Se elements are from pollution sources out of lithosphere source,and As,Cd and Sb elements are mainly from pollution sources.Based on the com-prehensive analysis of grain-size,chemical composition,enrichment factor(EF),discriminant function(DF) and matter source index(PI),this paper points out that the grain-size distribution and element composition of the sand-dust deposits in Harbin are evidently different from the loess and sand-dust in Lanzhou,and that matter source of the sand-dust in Harbin is different from the loess in Northwest China and the sand-dust in Lanzhou.The sand-dust deposits in Harbin are an admixture of coarse grains transmitted in short distance and fine grains transported in long distance.The plentiful coarse grains of the sand-dust deposits in Harbin origin from sand of local spot,and are the near-source deposits transported by low altitude airflow.

DDGS粉尘燃爆特性试验研究及热反应分析

为研究饲料加工行业酒精糟及其干燥物(DDGS)粉尘的着火爆炸特性,采用热板炉、G-G炉、哈特曼管和20 L球爆炸装置对实际工段收集的DDGS粉尘进行试验分析;同时,采用热重-红外联用技术进一步分析DDGS受热分解反应过程以及该过程可能产生的可燃气体。研究结果表明:DDGS粉尘的粉尘层着火温度为280℃,粉尘云最低着火温度为460℃;最小点火能为30~100 mJ,粉尘云爆炸下限质量浓度为140 g/m 3,最大爆炸压力为0.68 MPa,爆炸强度属于St1级;DDGS受热分解过程中会产生小分子可燃气体,增加DDGS粉尘爆炸危险性。研究结果可为预防DDGS粉尘爆炸提供数据参考,并为今后进一步研究其热解过程的反应途径提供思路。

蒙古西北部Tolbo湖沉积物粒度敏感组分记录的全新世风沙活动

作为全球主要的粉尘源区之一,亚洲中部干旱区全新世环境变化备受关注,但目前仍缺乏连续的风成沉积记录。本文利用蒙古西北部Tolbo湖岩芯(TB19-A,332 cm)沉积物,在AMS 14 C定年和粒度分析基础上,采用对数正态分布函数拟合及粒级-标准偏差相结合的方法分离出沉积物中风成组分以重建区域风沙活动历史。结果显示,Tolbo湖沉积物中值粒径为15~84μm和大于84μm的组分分别是区域尘暴和局地风沙活动的良好指标。蒙古西北部地区末次冰消期晚期(13.7511.6 cal ka BP),Tolbo湖流域内有较强的局地风沙活动,可能与YD寒冷事件有关。全新世以来,流域内局地风沙活动与蒙古西北部区域尘暴活动的变化具有一致性,具体表现为:早中全新世风沙活动总体较弱,其中9.78.6 cal ka BP和76 cal ka BP为区域尘暴较强时段;5 cal ka BP之后局地风沙活动与区域尘暴强度显著增加,直至0.7 cal ka BP两者均维持在较高水平;0.3 cal ka BP以来区域尘暴活动再次增强。蒙古西北部与中国北方公海、博斯腾湖记录的尘暴历史具有一致的变化趋势,反映了与西伯利亚高压相联系的大气环流对于干旱区大范围风沙活动的影响。晚全新世风沙活动的增强可能还与冬季太阳辐射的增加有关,最近300年来强烈的区域尘暴活动除了自然因素外,可能还叠加了人类活动的影响。

散粮发放计量抑尘系统研发与应用

在散粮发放环节,针对粉尘污染问题及装车量不易准确把握,致使车辆往返过磅及补卸问题,研究在线精准计量和散粮发放抑尘技术,开发兼具计量和抑尘双功能的新型技术产品,可远程控制实现无人值守作业。有助于提升散粮发放作业效率、减少人工劳动强度并有效降低粉尘污染,精准、环保、高效。

粮食储备库粉尘物性特征参数研究

对采集到的小麦、稻谷、玉米3大粮种进出库过程粉尘从物理性质、成分、元素和表面形貌特征等进行多维度分析。结果表明:3个粮种的总粉尘质量浓度均高于400 mg/m^(3),粉尘粒径近似呈正态分布,并且真实密度约是堆积密度的3.6倍。粉尘中灰分占比在40%左右,有机物含量中淀粉含量最高。粮食粉尘中元素种类复杂,非金属元素种类少但占比大;金属元素种类达30余种,并含有Hg、Cr等重金属元素。稻谷粉尘呈现大量的细长纤维形貌,玉米粉尘淀粉颗粒较多,小麦粉尘成分多样。数据可为粮食储备库防尘、防爆、个体防护等提供理论支撑。

高大粮食平房仓火灾致灾机理与预防技术探究

粮食仓库是国家贮存粮食的重要场所,做好防火工作十分重要。我国是世界粮食生产、消费和储备大国,因此,粮食的储备安全对于国家的稳定发展具有重要战略意义。在我国,每年新收获的粮食通常会收储于粮仓中,保证国家粮食储备安全的任务依然任重道远。深入探究粮仓易发生的两种类型的火灾机理以及对火灾预防的关键技术的研究对于保证粮食的储备安全具有重要意义。

卸粮坑卸粮粉尘外溢原因及解决办法研究

由于卸粮坑除尘效果不明显,卸粮坑卸粮作业容易产生粉尘外溢的情况。本文基于卸粮坑卸粮时粉尘外溢的情况,设计开发一种专用吸尘罩,可快速处理不同卸粮点的粉尘,有效控制粉尘外溢,改善卸粮工作环境。

平房仓散粮入仓作业线粉尘抑制效果对比分析

本文针对平房仓散粮入仓作业产生粉尘飞散,造成安全隐患和污染严重的问题,采用局部可密封设计,对卸粮、输送、清理、除尘等环节的移动式设备进行改造。结果表明,散粮入仓粉尘抑制改造设计可有效降低粉尘外溢,抑制粉尘飞扬,改善作业环境。

浅谈汽车卸粮坑粉尘综合防治措施

本文主要从汽车卸粮坑粉尘控制原理、直接粉尘防治措施、辅助粉尘防治措施等多方面综合对比,分析了汽车卸粮坑各种粉尘防治措施的原理、优缺点及改进建议,为完善汽车卸粮坑除尘设计、改善作业环境提供一定的思路。

管道相连泄爆容器中粉尘爆炸的实验研究

采用管道相连容器进行了工业规模的粉尘爆炸实验,目的是研究粮食粉尘在管道相连的加工和输送工业设备中发生粉尘爆炸时火焰和爆炸压力的传播过程及粉尘的Kst值对爆炸的影响。实验装置为一个气力输送系统,由两个不同体积的容器通过管道连接构成。采用粮食工业上具有代表性的两类粉尘进行了粉尘爆炸测试,爆炸从一个容器中通过管道传播到另一个容器中并引发了随后的二次爆炸,测试了不同位置的火焰和压力信号。实验结果表明:即使在起爆容器采取了泄爆措施,管道中没有粉尘喷入的情况下,粉尘爆炸火焰也可沿管道传播达30m并引发二次爆炸;随着粉尘爆炸指数的增大,初始爆炸的猛烈程度增强,火焰传播速度加快,二次爆炸的猛烈程度也随之增强。

两种方法描记谷物粉尘所致豚鼠哮喘模型呼吸曲线的对比观察

为了研究动物哮喘模型的阳性判定标准,本文观察分析了对同一批哮喘模型用两种不同方法描记的激发前后呼吸曲线。结果发现呼吸频率和潮气量不能非常准确地反映哮喘发作。肺总阻力(R_L)和动态肺顺应性(Cdyn)则可以直接反映哮喘反应,但测定装置和方法复杂。用简易方法描记的规律性叹气频率与R_L 呈非常显著地正相关(r=0.81,P<0.01),而与Cdyn则呈非常显著地负相关(r=-0.73,P<0.01)。因此,叹气频率能间接地反映支气管哮喘发作。

塔克拉玛干沙漠土壤粒度分布特征及其对粉尘释放的影响

塔克拉玛干沙漠是中国西北的重要粉尘源区,研究区域粒度分布特征及粉尘释放量有助于评估区域大气环境质量及其气候效应。基于此,按照空间分布特征及下垫面类型(农田、沙丘、荒漠)环塔克拉玛干沙漠采集地表土壤样品138个,利用Mastersizer2000激光粒度仪分析土壤粒度组成,利用DPM模型计算粉尘释放通量,以期揭示塔克拉玛干沙漠地表土壤微团粒粒度分布特征及其对粉尘释放通量的影响,研究结果表明:1)138个样品中流动沙丘和沙垄的粉砂和黏粒含量累计之和最少,约占10%~18%左右,属于砂质土和砂壤质土。农田(绿洲、林带区)样品多为草甸土,粉砂和黏粒累计含量约占50%~80%,戈壁(荒漠区)样品中粉砂和黏粒的含量差异较大,砂质土和砂壤土的粉砂和黏粒的含量累计之和约占20%~30%。2)地表土壤微团粒中粒径较小的是细砂和粉细砂,可用3个对数正态分布群体表示,即:粉细砂群体、细砂群体、粗砂群体,中值粒径依次为90、225、500μm,标准偏差分别为1.02、1.53、1.08,各占比例约为30%、49%、21%。3)塔克拉玛干沙漠粉细砂和细砂的粉尘释放量最大,中砂粗砂次之,极粗砂最少,其最大差值的数量级为10^-2μg/(m^2·s)。研究结果可以较好地反映不同下垫面粉尘释放差异,对定量评估区域乃至全疆的粉尘释放量等具有重要意义。