粒径对中密度纤维板粉尘爆炸特性影响实验研究

为探究粒径对中密度纤维板粉尘爆炸及相关特性的影响,采用20 L爆炸球、粉尘云最低着火温度装置、锥形量热仪和哈特曼管装置,对不同粒径粉尘的爆炸下限、最大爆炸压力、最低着火温度、热释放速率和火焰传播规律进行研究。结果表明,随着粉尘粒径减小,爆炸下限和粉尘云最低着火温度降低,最大爆炸压力逐渐增大;粉尘燃烧过程分为升温、着火、过渡、加剧和熄灭5个阶段,并出现2个峰值,热释放速率变化时间和吸热时间随着粒径减小而增加,热释放速率峰值增大;火焰在管道内的传播随着粒径减小先增强后减弱,管道外“火球”形状更大,火焰消散后火星数量变少,火焰尾端更加细长。     

浓度对垂直独头管道玉米淀粉火焰传播的影响

选择真空干燥后的食品级玉米淀粉，利用激光粒度分析仪和扫描电镜分析颗粒的形状和几何尺寸。利用高速摄像机技术，在1.2 m长的垂直独头管道内对玉米淀粉粉尘云的爆炸火焰传播行为进行实验研究，考察有、无障碍物的条件下粉尘云浓度对火焰传播的影响。结果表明：火焰整体上呈先增加再降低的发展趋势。粉尘云浓度和障碍物均对玉米淀粉粉尘云火焰传播形态及火焰速度具有显著影响。随粉尘云浓度增加，粉尘燃烧不充分，导致出现最大火焰速度和火焰亮度均逐渐降低，火焰轮廓不清晰,火焰分段等现象。障碍物的湍流效应会加速粉尘燃烧，增加粉尘火焰传播速度，提高火焰亮度和轮廓清晰度，但粉尘云浓度增加会降低障碍物对火焰传播的加速效应，促使最大火焰速度呈先增加再降低的趋势。     

Measurements of the explosibility of peat dust

Results from dust explosion tests carried out with peat dust samples are reported. The maximum explosion pressure and the K_St value have been measured, and especially their dependences on the moisture content and mean particle size have been investigated. It is concluded that the maximum explosion pressure and the K_St value of homogeneous dry (moisture content <35% W/W) and fine (mean particle size <200 μ)_peat dust can be estimated with a reasonable accuracy from the moisture content and the mean particle size. For moist (moisture content >35% W/W) and/or coarse (mean particle size >200 μm) peat dust, it is often possible only to predict whether the dust is explosible or not. For heterogeneous peat mixtures composed of dusts with very different moisture contents and/or mean particle sizes, it is not possible in a reliable way to estimate the maximum explosion pressure or the K_St value based on the mean moisture content and the mean particle size of the mixture. It is not always even possible to predict whether the mixture is explosible or not.     

稻壳粉尘着火敏感性试验研究

摘 要：为探究稻壳粉着火敏感性,利用激光粒度分析仪和SEM对其粒度进行分析及形貌表征,利用Godbert-Greenwald炉、固体自燃点、粉尘层最低着火温度测试仪对自燃点温度、最低着火温度进行试验研究。结果表明：稻壳粉颗粒越大粒度分布越集中;粉尘云最低着火温度随粒度的减小呈降低趋势;标准试验模式下,粒度D50=52.9 μm的稻壳粉自燃点为225.1 ℃;粒度一定时,粉尘层最低着火温度随模具高度的增大而降低,当高度达到20 mm最低着火温度达到最低,且不再随模具高度的升高继续降低。本试验结果可为工业过程安全提供数据和理论支撑。     

Heating of indoor dust causes reduction in its ability to stimulate release of IL-8 and TNFalpha in vitro compared to non-heated dust

Dust is a major contaminant of the indoor air environment and may affect human health. Indoor dust accumulates on surfaces including heaters and light fixtures, and will be heated when these devices are used. Heat treatment of the dust may change its biologic properties and in this study we simulated the heat treatment with a dust-heating model (50-250 degrees C). The residual and the non-heated dust from seven samples were tested in cultures of fresh peripheral blood mononuclear cells and in A549 cell culture using the release of TNFalpha and IL-8, respectively, as effect indicators. The endotoxin-content and the particle size distribution of the residual and the non-heated dust suspensions were determined for some of the samples. We found that the residual dust had less ability to induce the release of TNFalpha and IL-8. The cytokine decline pattern was similar for all the dust tested and could partly be explained by the reduction in endotoxin content or possibly by inhibitory decomposition products. No correlation was found between the measured particle size distribution and the decreased cytokine levels. The results in this study suggest that the residual dust promotes reduced cytokine response and thereby a possibly lower inflammation reaction in the airways if suspended and inhaled compared with the non-heated dust. PRACTICAL IMPLICATIONS: Accumulation of indoor dust on electric heaters and light fixtures may produce a bad odor when switched on in the cold season and some people claim respiratory distress during such events. To investigate to what extent the residuals of heated indoor dust represent a health hazard, we measured the effect in cell cultures before and after heat treatment of the dust. The in vitro results imply that the residual dust will cause a lower proinflammatory response in the airways if suspended and inhaled compared with non-heated dust. This is partly explained by heat destruction of inflammatory components in the dust.     

Air Pollution Due to Opencast Coal Mining and the Characteristics of Air-Borne Dust--An Indian Scenario

Opencast coal mining creates more air pollution problem in respect of dust and the fines contain coal particles, benzene soluble matters etc. To maintain the energy demand, opencast mining has been growing at a phenemenon rate in India. There is no well defined method for assessing the impacts on air quality due to mining projects. An investigation was conducted to evaluate the impacts on air quality and the characteristics of the air-borne dust due to opencast coal mining in Indian context. The study area has been described and the sources of air pollution were identified. Methodology adopted for the selection of air monitoring stations and air pollution monitoring to evaluate the impacts on air environment due to coal mining activities have been discussed. Impacts on air quality have been assessed on the basis upwind and down wind concentrations of air pollutants. SPM and RPM concentrations were found to be very high in work zone as well as surrounding locations. The SPM was subjected to particle size analysis using different techniques. It was observed that the particulates were more respirable in nature and the median diameter was around 20 w . Variation of weight percentages for different size ranges has been discussed as a function of mining activity. Benzene soluble matters and anions in SPM were found to be high in comparison to other areas. Settleable dust and its compositions were also analysed. The methodology adopted for the study may be utilised to assess the actual contribution of air pollutants due to other coal projects.     

惰性粉体对铝粉尘层着火影响实验研究

通过构建铝粉尘层底板加热条件下着火燃烧的数值模型,探究铝粉尘层着火燃烧规律,同时结合碳酸钙惰性原理,开展碳酸钙粉体惰化条件下铝粉尘层最低着火温度实验。研究表明,铝粉尘着火燃烧具有加热温度高、燃烧温度大的特征,碳酸钙可以有效提高铝粉尘的点火温度,碳酸钙粉体粒度越小、浓度越大,对铝粉尘层的惰化效果越显著。     

HDPE粉尘云最小点火能试验研究

为研究高密度聚乙烯(HDPE)粉尘云燃爆的敏感性参数,采用粉尘云最小点火能(MIE)试验装置对HDPE粉尘进行试验研究.首先研究3个单一因素(粉尘粒径、粉尘云质量浓度和喷粉压力)对MIE的影响,然后对一定条件下不同质量浓度的HDPE粉尘云在哈特曼管中燃烧的火焰传播行为进行分析,最后采用正交试验法分析了多因素对MIE的影...     

Use of (dP/dt)max from closed-bomb tests for predicting violence of accidental dust explosions in industrial plants

The rate of combustion of a given dust cloud depends not only on the chemical composition and particle size distribution of the dust, but also to a marked extent on the dust concentration, the extent to which particle agglomerates are broken up, and not least on the cloud turbulence. The three latter factors are entirely dependent on the way in which the dust cloud is generated in the actual industrial plant, and therefore the combustion rate per unit volume of cloud may in practice vary considerably for a given dust, depending on the industrial situation.Existing test methods for assessing the combustion rate to be expected from a given dust do not account for this. On the contrary, they all seem to work with largely arbitrary cloud generation processes. The present paper proposes some possible lines of development that may be followed to make the test methods more realistic.     

Lead and cadmium composition in indoor dust

Pb and Cd levels in different size fractions of indoor dust have been analyzed by differential pulse anodic stripping voltammetry (DPASV) after digestion with HNO₃ and HF using a microwave oven. The relationship between Pb and Cd levels with dust size have been investigated and the metal levels in different sources of indoor dust are compared. In addition, the Pb and Cd composition in different size fractions of dust have been investigated by a sequential extraction method. Dusts are dominated by particulate matter < 500 μm. Pb levels in office dust in the particulate fraction > 75 μm are clearly shown to be higher than that in domestic dust. Generally, for domestic premises, Pb and Cd levels increase with a decrease in the particle size and with an increase in house age, while for office dust, the Pb level increases with an increase of particle size. For domestic houses, most of the metals are bound to carbonate and FeMn oxides in fine dust. For office dust, the situation is more complicated, with a clear increase in Pb in the organic and residue fractions in coarse dust.