“Vybuchovy trojuhelnik”: A software tool for evaluation of explosibility of coal mine atmosphere

Rescue operations during mine fires or methane explosions are highly dangerous for rescue workers. The knowledge of the composition of the coal mine atmosphere and the calculations of its explosibility may help to increase the safety of the rescuers. In the Czech Republic, a system called “Mine Gas Laboratory” (DPL) has been used for these purposes. The DPL allows measurement of the composition of the mine atmosphere and transmits the data necessary for evaluation to the surface. Up to now the explosibility evaluation of the coal mine atmosphere has depended either on the rescuers’ experience or on software code calculation. The code called “Vybuchovy trojuhelnik” (explosion triangle) is a graphical computing system intended for fast assessment of explosibility of fuel–air mixture. This article introduces the code and describes two simple methods of explosibility evaluation. The first method is “explosion triangle analysis”—a graphical method based on empirical graphs transformed into equations. The second method uses thermodynamic calculation based on chemical balance dynamics and Gibbs and Helmholtz energy. According to the requirements of the Czech Bureau of Mining (CBU) and Central Mine Rescue Service (HBZS), the code solves the problems of explosion triangle for both standard and non-standard coal mine atmosphere compositions. Unfortunately, the atmosphere composition must be introduced manually due to the unknown format of the data transmitted from the old DPL model. On 1 September 2005, a project started to develop a new system for on-line monitoring and atmosphere explosibility evaluation. The system should be able to measure CO₂, O₂, CH₄, H₂ and CO concentrations as well as the wind speed, temperature and humidity. The “Vybuchovy trojuhelnik” code will be used as a basis for explosibility evaluation, and an on-line connection with the new model of DPL will be established.     

中国GBZ2.1与德国MAK工作场所化学有害因素职业接触限值比较研究

系统比较中国现行职业接触限值标准GBZ2.1-2007与德国职业接触限值MAK在定义、制定原则和具体数值方面的差异,为中国GBZ2.1的修订提供建议和依据。将 GBZ2.1中规定的OELs与德国MAK于2015年公布的化学有害因素 OELs ,按不同类型建立比较分析数据库,并进行比较分析,分析结果表明:中德2国在职业接触限值的制定原则,化学有害因素的来源、数量与标识等方面有显著差异。 因此,我国应加强对化学性有害因素孕期毒性接触限值的研究和应用。中德在选择化学性有害因素制定OELs时各有侧重,我国在重金属方面制定的OELs,如:钴、钼、铍、铊等,是德国MAK以及美国ACGIH中所未有的,而德国则不再为致癌物质制定OELs。中、德均制定有OELs的化学性有害因素在数值上差异较大,中国有部分OELs同时高于德国MAK和美国ACGIH。我国的职业接触限值更新频率较慢,应缩短OELs更新周期,在对现行的GBZ2.1进行制修订时,可将发达国家OELs作为1项参考。德国风险分级评估方法对致癌物质的管理和评估值得进一步探讨及研究。     

低压下聚乙烯绝缘层导线火蔓延熔融滴落实验分析

低压导线火蔓延的研究对于飞机和航天器的防火安全具有重要意义。针对镍铬合金线芯、聚乙烯(PE)绝缘层导线火蔓延过程中的熔融滴落现象,在低压舱内开展了不同气压、不同氧气浓度的大量实验研究,获得了导线熔融滴落频率、质量和火蔓延速度,以及不同氧浓度熔融滴落的上下限。结果表明:(1)在熔融滴落过程中,由于滴落会产生向上的动量,从而使火焰在滴落后发生突然的"跳动"现象,火焰高度先增加后降低;(2)滴落上限和滴落下限随着氧浓度的增加而降低,并且可以划分为3个不同的区域:火蔓延仅存区;滴落和火蔓延共存区;无滴落无火蔓延区。滴落上限和滴落下限下降曲线在50%氧浓度、5kPa压力发生会合,此后只有火蔓延而不存在滴落现象。(3)当压力降低时,由于线芯温度增加,线芯传导热量增加,导致绝缘层熔融速率加快,从而使得滴落频率增加,同时液滴的表面张力随着压力的降低而增加,使得低压下液滴的质量变大。     

低压下近熄灭极限区域纸火蔓延实验研究

对低压下的近熄灭极限区域水平纸火蔓延进行了实验研究。通过降低环境压力和氧气浓度,确定了水平纸火蔓延的着火极限,并得出了在极限氧气浓度条件下的火蔓延速度变化规律。在相同氧气浓度下(43%)进行了不同压力的水平纸火蔓延实验。结果表明,火蔓延速度在近熄灭极限区域内非线性增加,通过比较分析前人火蔓延速度实验结果,确定了火蔓延近熄灭极限区域和线性增长区域的分界压力值。此外,得出了压力分界处的火焰变化特征,并根据火焰图像与理论分析,得出了不同区域内的火蔓延传热机制。     

中国水排污许可证制度的定位及改革建议

从点源控制的基本目标出发,按照命令控制型政策的特点和要求,对排污许可证制度重新进行了定位;采用环境政策分析的一般方法,借鉴美国和中国台湾地区的相关经验,分析了我国排污许可证制度存在的问题.研究指出,排污许可证制度是点源排放控制的最基本、最核心的手段,同时也是其他政策手段的“载体”;我国现有的水污染排放许可证制度尚不符合命令控制型政策的要求;存在相关政策间缺乏协调、政府和企业环境管理能力不足、缺乏专业人才等问题,因此,无法保障点源的连续达标排放.需要尽快改革我国的水污染物排放许可证制度,尽快出台实施该制度的专门条例、建立排污许可证制度的分级管理体制、制订实施技术规范、进行基于排污许可证制度的政策整合、培养管理相关人才及建立排污许可证制度的评估、更新和完善机制.      

Determination of explosion limits – Criterion for ignition under non-atmospheric conditions

Many industrial processes are run at non-atmospheric conditions (elevated temperatures and pressures, other oxidizers than air). To judge whether and if yes to what extent explosive gas(vapor)/air mixtures will occur or may be generated during malfunction it is necessary to know the safety characteristic data at the respective conditions. Safety characteristic data like explosion limits, are depending on pressure, temperature and the oxidizer. Most of the determination methods are standardized for ambient conditions. In order to obtain determination methods for non-atmospheric conditions, particularly for higher initial pressures, reliable ignition criteria were investigated. Ignition tests at the explosion limits were carried out for mixtures of methane, propane, n-butane, n-hexane, hydrogen, ammonia and acetone in air at initial pressures up to 20 bar. The tests have been evaluated according to different ignition criteria: visual flame propagation, temperature and pressure rising. It could be shown that flame propagation and occasionally self-sustained combustion for several seconds occurred together with remarkable temperature rise, although the pressure rise was below 3%. The results showed that the combination of a pressure rise criterion of 2% and a temperature rise criterion of 100 K seems to be a suitable ignition criterion for the determination of explosion limits and limiting oxidizer concentration at higher initial pressures and elevated temperatures. The tests were carried out within the framework of a R&D project founded by the German Ministry of Economics and Technology.     

Application of CFD on the sensitivity analyses of some parameters of the modified Hartmann tube

The aim of this work is to determine the influence of operating parameters such as the dispersion pressure, the ignition delay and height on the dust flammability. A Computational Fluid Dynamics (CFD) simulation, based on an Euler–Lagrange approach, was developed with Ansys Fluent™ and validated experimentally. Such analysis will facilitate the choice of the most conservative conditions for a flammability test. This paper is focused on a case study performed on wheat starch with the modified Hartmann tube. The dispersion process of the powder was studied with granulometric analyses performed in situ and high speed videos. Tests were performed with injections at gas pressure ranging from 3 to 6 bars and the evolution of the particle size distribution (PSD) was recorded at different ignition heights (5, 10 and 15 cm over the dispersion nozzle). The observations highlighted the presence of agglomeration/deagglomeration processes and dust segregation. Besides, a CFD simulation analysis was aimed at evaluating the impact of a set of parameters on the PSD and the local turbulence, which are closely linked to some flammability parameters. For this computational analysis, the CFD simulation was coupled with a collision treatment based on a Discrete Element Method (DEM) in order to consider the cohesive behavior of the combustible dust. Thus the results suggest performing the injection of the gases at approximately 5 bars for the flammability tests of wheat starch in order to obtain the finest PSD at a given ignition height. It is also shown that the finest PSD are obtained at 5 cm over the dispersion nozzle. However, the local instabilities and turbulence levels are so high during the first stages of the dispersion that the flame growth can be disturbed for short ignition delays. Moreover, the stabilization of the bulk of the dust cloud requires longer periods of time when the ignition sources are located at 15 cm. As a result, the recommended height to perform a flammability test is 10 cm in this case. Finally, this study proposes some tools that might improve the procedure of dust flammability testing.     

Determination of 2,4- and 2,6-dinitrotoluene biodegradation limits

This study was carried out to explore the lowest achievable dinitrotoluene (DNT) isomer concentrations that would support sustained growth of DNT degrading microorganisms under an aerobic condition. Studies were conducted using suspended (chemostat) and attached growth (column) systems. The biodegradation limits for 2,4-dinitrotoluene chemostat and column system were 0.054 ± 0.005 and 0.057 ± 0.008 μM, respectively, and for 2,6-dinitrotoluene, the limits for chemostat and column system were 0.039 ± 0.005 and 0.026 ± 0.013 μM, respectively. The biodegradation limits determined in this study are much lower than the regulatory requirements, inferring that bacterial ability to metabolize DNT does not preclude applications of bioremediation (including natural attenuation) for DNT contaminated media.     

Stochastic bycatch, informational asymmetry, and discarding

The existing literature (i) examines bycatch and discard behavior in a static framework and (ii) treats bycatch as a deterministic process uniform across vessels. Using a dynamic representative agent model in a two-stock resource, this paper explores strategic interactions between a social planner and two groups of harvesters, one of which imposes a stochastic “technological externality” (bycatch) on the other. In addition to limitations on entry and the number of trips taken in each industry, three bycatch control instruments are compared to the unconstrained case: taxes, trip limits, and value-based quotas. Implementation and enforcement costs aside, taxes dominate both types of quota, and value limits outperform trip limits by eliminating one type of discarding. In simulations, relative performance depends upon variance in the bycatch process, differences in the ex vessel prices of stocks, relative efficiency of the harvester types, and fixed costs on the trip and industry margins.     

THE INFLUENCE OF CLIMATE VARIATION ON THE ESTIMATION OF LOW FLOWS USED TO PROTECT WATER QUALITY: A NATIONWIDE ASSESSMENT1

ABSTRACT: Historical flow records are used to estimate the regulatory low flows that serve a key function in setting discharge permit limits through the National Pollutant Discharge Elimination System, which provides a nationwide mechanism for protecting water quality. Use of historical records creates an implicit connection between water quality protection and climate variability. The longer the record, the more likely the low flow estimate will be based on a broad set of climate conditions, and thus provides adequate water quality protection in the future. Unfortunately, a long record often is not available at a specific location. This analysis examines the connection between climate variability and the variability of biologically based and hydrologically based low flow estimates at 176 sites from the Hydro‐Climatic Data Network, a collection of stream gages identified by the USGS as relatively free of anthropogenic influences. Results show that a record of 10 to 20 years is necessary for satisfactory estimates of regulatory low flows. Although it is possible to estimate a biologically based low flow from a record of less than 10 years, these estimates are highly uncertain and incorporate a bias that undermines water quality protection.