Assessment of gas and dust explosion in coal mines by means of fuzzy fault tree analysis

During the past decade, coal dust and gas explosions have been the most two serious types of disasters in China, threatening the lives of miners and causing significant losses in terms of national property. In this paper, an evaluation model of coal dust and gas explosions was constructed based on a fuzzy fault tree by taking the Xingli Coal Mine as a research site to identify the risk factors of coal dust and gas explosions.Furthermore, the hazards associated with such explosions were evaluated for this particular coal mine.After completing an on-site investigation, the fuzzy probabilities of basic events were obtained through expert scoring, and these expert opinions were then aggregated as trapezoidal fuzzy numbers to calculate the degrees of importance of all basic events. Finally, these degrees of importance were sorted. According to the resulting order, the basic events with higher probabilities were determined to identify key hazards in the daily safety management of this particular coal mine. Moreover, effective measures for preventing gas and coal dust explosions were derived. The fuzzy fault tree analysis method is of high significance in the analysis of accidental coal mine explosions and provides theoretical guidance for improving the efficiency of coal mine safety management in a scientific and feasible manner.

△P index with different gas compositions for instantaneous outburst prediction in coal mines

In this study we measured the △P(initial speed of gas emission) index with different gas concentrations of carbon dioxide(pure CO2,90% CO2+10% CH4,67% CO2+33% CH4,50% CO2+50% CH4,30% CO2+10% CH4 and pure CH4) of coal samples from the No.2 coal seam in the Yaojie Coal Mine,Gansu province,China.The effect of carbon dioxide concentration,gas composition,coal strength and particle size of coal samples on the △P index was investigated.The experimental results show that with gas of various compositions,the △P value of three samples were clearly different.The △P index of coal samples A,B and C(0.2～0.25 mm) were 4,6 and 7 with pure CH4 and 22,30 and 21 when pure CH4 was used.Carbon dioxide concentration affects the △P index markedly.The △P index increases with an increase in carbon dioxide concentration,especially for coal B.Hence,the △P index and K(another outburst index) values tested only with pure CH4 for prediction of the danger of outburst is not accurate.It is important to determine the initial speed of gas emission given the gas composition of the coal seam to be tested for exact outburst prediction.

Experiment study on the propagation laws of gas and coal dust explosion in coal mine

The experiment of gas and coal dust explosion propagation in a single lanewaywas carried out in a large experimental roadway that is nearly the same with actual environmentand geometry conditions.In the experiment,the time when the gas and coal dustexplosion flame reaches test points has a logarithmic function relation with the test pointdistances.The explosion flame propagation velocity rises rapidly in the foreside of the coaldust segment and comes down after that.The length of the flame area is about 2 timesthat of the original coal dust accumulation area.Shock wave pressure comes down to therock bottom in the coal dust segment,then reaches the maximum peak rapidly and comesdown.The theoretical basis of the research and assemble of across or explosion is suppliedby the experiment conclusion.Compared with gas explosion,the force and destructiondegree of gas and coal dust explosion is much larger.

Mechanism research of gas and coal dust explosion

Combined with the experimental results from the large tunnel of the ChongqingResearch Institute,the mechanism of gas and coal dust explosion was studied.Someconcepts about gas and coal dust explosion were introduced such as the form conditionand influential factors.Gas and coal dust explosion propagation was researched and thelifting process of coal dust was simulated.When an explosion occurred due to great mixtureof gas and air,the maximum explosion pressure appeared in the neighborhood of theexplosion source point.Before it propagated to the tunnel of the deposited coal dust,themaximum explosion pressure appeared to be in declining trend.Part of the energy waslost in the process of raising the deposited coal dust through a shock wave,so the maximumexplosion pressure was smallest on the foreside of the deposited coal dust sector.On the deposited coal dust sector,the explosion pressure rapidly increased and droppedoff after achieving the largest peak value.Because of coal dust participation in the explosion,the flame velocity rose rapidly on the deposited coal dust and achieved a basic stablevalue;coal dust was ignited to explode by initial laminar flame,and the laminar flametransformed into turbulent flame.The turbulence transformed the flame fold into a funnelshape and the shock wave interacted with the flame,so the combustion rate rose and thepressure wave was further enhanced.The regeneration mechanism between the flamecombustion rate and the aerodynamic flowing structure achieved the final critical state forforming the detonation.

Determination of the gas compositions for direct coal liquefaction by gas chromatography

Via multi-dimensional gas chromatography, configured with parallel dual-channel, double detectors, valves switching and back flushing, rapid analysis of the gas compositions consisting of C1-C5 hydrocarbons and permanent gases, such as CO2, H2S, H2, and CO, for direct coal liquefaction has been realized. With four packed chromatographic columns, which are Hayesep-Q pre-column, Hayesep-Q column, molecular sieve 5A column and one PLOT A1203 S capillary column, the gas compositions for direct coal liquefaction are analyzed qualitatively and quantitatively by the external standard method. The determination method has such advantages as excellent separation, simple operation, rapid analysis and accurate results.

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.

Three Stage Equilibrium Model for Coal Gasification in Entrained Flow Gasifiers Based on Aspen Plus

A three stage equilibrium model is developed for coal gasification in the Texaco type coal gasifiersbased on Aspen Plus to calculate the composition of product gas, carbon conversion, and gasification teml^erature. The model is divided into three stages including pyrolysis and combustion stage, char gas reaction stage, and gas p.hase reaction stage. Part of the water produced in thepyrolysis and combust!on stag.e is assumed to be involved inthe second stage to react with the unburned carbon. Carbon conversion is then estimated in the second stage by steam participation ratio expressed as a function of temperature. And the gas product compositions are calculated from gas phase reactions in the third stage. The simulation results are consistent with published experimental data.

Noble Gas Isotopic Compositions of Cobalt-rich Ferromanganese Crusts from the Western Pacific Ocean and Their Geological Implications

Noble gas isotopic compositions of various layers in three-layered （outer, porous and compact layers） cobalt-rich ferromanganese crusts and their basaltic and phosphorite substrates from the western Pacific Ocean were analyzed by using a high vacuum gas mass spectrum. The analytical results show that the noble gases in the Co-rich crusts have derived mainly from the ambient seawater, extraterrestrial grains such as interplanetary dust particles （IDPs） and wind-borne continental dust grains, and locally formation water in the submarine sediments, but different noble gases have different sources. He in the crusts derives predominantly from the extraterrestrial grains, with a negligible amount of radiogenic He from the eolian dust grains. Ar is sourced mainly from the dissolved air in the seawater and insignificantly from radiogenic Ar in the eolian continental dust grains or the formation water. Xe and Ne derive mainly from the seawater, with minor amounts of extraterrestrial Xe and Ne in the IDPs. Compared with the porous and outer layers, the compact layer has a relatively high 4He content and lower 3He/4He ratios, suggesting that marine phosphatization might have greatly modified the noble gas isotopic compositions of the crusts. Besides, the 3He/4He values of the basaltic substrates of the cobalt-rich crusts are very low and their R/R. ratios are mostly 〈0.1 R., which are similar to that of phosphorite substrates （0.087 R.）, but much lower than that of fresh submarine MORB （8.75±14 Ra） or seamount basalts （3-43 Ra）, implying that the basaltic substrates have suffered strong water/rock interaction and reacted with radiogenic ^4He and P-rich upwelling marine currents during phosphatization. The trace elements released in the basalt/seawater interaction might favor the growth of cobalt-rich crusts. The relatively low ^3He/^4He values in the seamount basalts may be used as an important exploration criterion for the cobalt-rich ferromanganese crusts.

Removal of sulfur in coke oven gas by mixing ZnO-based additive into coal

A new technology for recycling EAF dust and removal of sulfur from coking oven gas was investigated. The new technology does not need to set up special equipment to treat COG (coke oven gas), and it is only acquired by mixing the ZnO base additive into the coke coal. In the stage of pyrolysis of the coal volatile, ZnO of the additive combines with H 2S, CS 2, COS and C 2H 2SH of coal gas, forming ZnS in coal char. In the stage of coking of the coal char, Zn is gasified with S, then the gas Zn react with H 2S, CS 2, COS and C 2H 2SH, forming ZnS in coal gas and depositing as dust. After the collected ZnS dust was regenerated, it can be recycling as the additive again. The sulfur in coal gas can be completely removed if the mole ratio of the added Zn to the volatilized S is more than 1, and the sulfur in coke is also slightly decreased comparing with the coke without the additive. The EAF dust containing ZnO and Fe 2O 3 can be the base material of the desulfurizing additive.

煤矿运输复合降尘剂的制备与降尘性能研究

为了降低煤炭资源运输过程中粉尘的污染程度,以烷基糖苷、3-氯-2-羟丙基三甲基氯化铵和助剂A为主要原料,制备了一种适合煤矿运输用的新型复合降尘剂JCS-1,以除尘效率为评价指标对其制备条件进行了优化,并考察了不同质量分数复合降尘剂JCS-1的表面活性、润湿性能和降尘性能。实验结果表明:在反应温度为85℃、反应时间为5 h、助剂A的质量分数为5%的条件下制备的复合降尘剂JCS-1的除尘效率最高;随着复合降尘剂JCS-1质量分数的不断增大,溶液表面张力和其在煤薄片表面的接触角均呈现出逐渐降低的趋势,而除尘效率则呈现出先增大后减小的趋势;当复合降尘剂JCS-1的质量分数为0.05%时,除尘效率可以达到最大(96.6%),降尘效果较好,能够满足煤矿运输过程中降尘作业的需求。

采煤面顺逆风情况粉尘逸散数值模拟分析及防治

为了更深入了解采煤面粉尘污染规律并进行有效防尘,依据流体力学理论,运用Fluent软件对工作面采煤机顺逆风2种情况下截割-移架的产尘逸散规律进行数值模拟研究。结果显示:工作面平均风速顺风较逆风大。由于移架相对位置差异和工作面煤壁变截面位置不同,顺逆风割煤时粉尘分布存在较大差异。顺风割煤时,粉尘带位于采煤机下风侧50 m范围内人行道周围区域;逆风割煤时,产尘集中在滚筒附近及其下风侧0~45 m,浓度最高达2000 mg/m^(3)。从底板至顶板高度来看,顺风割煤时对底板和顶板附近的污染更为严重,但对呼吸带高度污染范围较小。根据模拟结果,提出了以导流板、采煤机喷雾杆(块)相结合的综采面粉尘防治措施,以达到高效抑尘的目的。

Self-reduction Mechanism of Coal Composite Stainless Steel Dust Hot Briquette

To efficiently recycle valuable metals such as chromium and nickel in stainless steel dust, self-reduction ex- periments were carried out to study the reduction mechanism of metal oxides in coal composite stainless steel dust hot briquette, which is defined as a CCSB here. Self-reduction of CCSB is proceeded by volatile matter and fixed carbon contained within CCSB. Experiments were performed to study the effects of temperature and carbon to oxygen （C/OCoal） ratio on self reduction of CCSB. At 1400 and 1450℃, volatile matter in coal used for experiment could take the place of about 40℃ of fixed carbon in coal. Under the present experimental conditions, reduction product of chromium appears as FeCr2O2, Cr2O3, Cr7C3 , and [Cr] in turn during reduction. To evaluate the formation of met al nuggets in self reduction process of CCSB, metal nuggets containing chromium and nickel were observed in outside of reduction products under various conditions, and thermodynamic equilibrium calculation was carried out for possi hie products and formation of molten metal by fixed carbon. SEM and EDS analyses were made for metal nugget and slag in reduced product. The results reveal that it is reasonable to achieve the metal nuggets at 1450℃, 0.8 of C/OCoal ratio and 20 min of reduction time. The nugget formation can indicate one innovative process for comprehensive utilization of stainless steel dust.

Mechanisms of carbon isotopic fractionation in the process of natural gas generation: Geochemical evidence from thermal simulation experiment

Low maturity coal samples were taken from the Ordos Basin to conduct gold tube thermal simulation experiment in a closed system,and the characteristics of the products were analyzed to find out the fractionation mechanism of carbon isotopes and the causes of abnormal carbon isotopic compositions of natural gas.At the heating rates of 2℃/h(slow)and 20℃/h(rapid),the low maturity coal samples of the Ordos Basin had the maximum yields of alkane gas of 302.74 mL/g and 230.16 mL/g,theδ13C1 ranges of-34.8‰to-23.6‰and-35.5‰to-24.0‰;δ13C2 ranges of-28.0‰to-9.0‰and-28.9‰to-8.3‰;andδ13C3 ranges of-25.8‰to-14.7‰and-26.4‰to-13.2‰,respectively.Alkane gas in the thermal simulation products of rapid temperature rise process showed obvious partial reversal of carbon isotope series at 550℃,and at other temperatures showed positive carbon isotope series.In the two heating processes,theδ13C1 turned lighter first and then heavier,and the non-monotonic variation of theδ13C1 values is because the early CH4 is from different parent materials resulted from heterogeneity of organic matter or the carbon isotope fractionation formed by activation energy difference of early enriched 12CH4 and late enriched 13CH4.The reversal of carbon isotope values of heavy hydrocarbon gas can occur not only in high to over mature shale gas(oil-type gas),but also in coal-derived gas.Through thermal simulation experiment of toluene,it is confirmed that the carbon isotope value of heavy hydrocarbon gas can be reversed and inversed at high to over mature stage.The isotope fractionation effect caused by demethylation and methyl linkage of aromatic hydrocarbons may be an important reason for carbon isotope inversion and reversal of alkane gas at the high to over mature stage.

散货港口输煤系统多维度粉尘治理技术研究与应用

散货港口输煤系统粉尘治理是环保改造的难题。对此提出了散货港口输煤系统多维度粉尘治理方案,重点研究了高压喷雾抑尘技术、输送带清洁和物料回收技术以及复合式缓冲床技术,并在唐山港曹妃甸港区煤码头进行了现场试验。试验结果表明,此方案解决了装船机溜筒物料起尘和扬尘、回程输送带物料撒漏及运行扬尘、落料点漏料撒料和异物穿透输送带的问题,实现了散货港口输煤系统全区域、全作业过程,多维度、主动式的粉尘综合防治,取得了较高的社会效益和经济效益。

碳氢-生物表面活性剂在电解质加载下的降尘及防爆性能研究

为了了解碳氢-生物表面活性剂在电解质加载下的降尘和防爆性能,开展碳氢-生物表面活性剂在电解质加载下的三元复配体系对煤尘降尘防爆特性的一体化研究,并探明润湿及团聚特性对降尘防爆特性的影响。其中,表征降尘性能采用表面张力及煤尘沉降时间等润湿性能指标;防爆特性采用最小点火能(MIE)、最低引燃温度(MIT)参数进行表征;团聚特性以稳定性指数(TSI)作为评价指标。研究结果表明:二元表面活性剂之间复配之后的润湿团聚效果不存在种类决定性优劣,对于粒径小于50μm的普通烟煤,溶液表面张力降低不会促进煤尘沉降速度的提升;此外,从实验数值和数据变化看,鼠李糖脂相较槐糖脂展现了更好的团聚润湿表现与数值稳定性,0.1~0.2 wt%NaCl的加入较同浓度NaHCO3对二元材料作用下的煤尘有更好的抑爆效果;最佳复配组合为SDBS-鼠李糖脂-NaCl,新型三元复配材料进一步降低36.57%~44.94%煤尘沉降时间,TSI值提升了2.65%~27.34%,展现了更好的团聚特性。爆炸极限参数方面,三元复配材料使得煤尘的最低引燃温度提升0.51%~1.19%,最小点火能提高了13.63%~88.89%。该材料在降尘防爆一体化方面效能显著,可为井下降尘防爆提供一种高效的选择,对煤矿安全多种防护材料的研发具有一定的指导意义。

电袋复合除尘技术研发现状及展望

介绍了中国火力发电厂除尘设备历史,分析静电除尘的除尘效果受飞灰性质影响大,无法达到较高的排放标准;布袋除尘的除尘效率高,但布袋阻力大,相对易损坏,消耗大,运维费用高,电袋复合除尘器结合了静电除尘和袋式除尘的优点,在提高除尘效率的同时,可降低运行成本。为此,论述了电袋复合除尘器的发展进程、技术优势、型式、工艺流程、不同流派、运用实例,最后指出电袋复合除尘技术的发展方向。

受限空间煤尘爆炸残留气体特征分析

采用20 L球形爆炸装置进行煤尘爆炸实验,研究了不同条件下煤尘爆炸后气体体积分数变化及生成规律。结果表明:爆炸残留气体成分及体积分数与煤尘浓度、粒径、点火能量以及煤尘变质程度关系密切。随煤尘浓度升高,爆炸后残留气体体积分数φ(CH4),φ(CO),φ(H2)及φ(CO)/φ(CO2)呈上升趋势,φ(CO2)呈先上升后下降趋势。一定范围内随煤尘粒径减小,φ(CH4)增大,φ(CO)及φ(CO)/φ(CO2)呈减小趋势,当粒径小于25μm时,φ(CH4)急剧减小。随点火能量增大,φ(CH4)及φ(CO)增大,φ(CO)/φ(CO2)整体变化量不大,当点火能量大于10 k J时,φ(O2)明显减小。随煤尘变质程度增加,φ(CO)/φ(CO2)先增大后减小,φ(CH4)整体呈降低趋势,烟煤煤尘爆炸消耗的O2量较褐煤、无烟煤少。

高性能陶瓷内衬复合煤粉喷枪的研制

采用燃烧合成方法制备了Al2O3陶瓷内衬复合煤粉喷枪,但单一的Al2O3陶瓷内衬层韧性差,抗热震性能低,造成喷枪的寿命短。通过在(CrO3+Al)燃烧体系中添加ZrO2组元,采用SHS重力分离技术,制备出了高强度、高韧性的陶瓷内衬复合弯管煤粉喷枪,陶瓷内衬层为具有共晶结构的Al2O3-ZrO2复相陶瓷。在共晶结构中,ZrO2纤维直径可达到纳米/微米尺度,从而使陶瓷基体得以强化;同时棒状共晶结构的生长取向分布,又使陶瓷因棒晶桥接与拔出得以韧化,改善了喷枪陶瓷内衬的高温强度和耐磨性,有效地提高了煤粉喷枪的使用寿命。

煤尘化学组成及结构参数对煤尘润湿性的影响规律

通过煤质化学组成和结构参数对煤尘润湿性的影响规律,进而采用多元逐步回归确定主要影响因素.结果表明:1煤质化学组成是导致煤体润湿能力存在较大差异的内在因素,固定碳含量和氧含量对煤尘润湿性的影响显著,颗粒平均孔直径和比孔容与煤尘润湿性的相关性较低;2煤尘润湿性最佳线性回归方程为y=31.471+0.825[固定碳含量]-0.631[氧含量],复相关系数R=0.871.

散堆煤体复合型抑尘剂性能表征及应用研究

复合型抑尘剂是解决散堆煤体煤粉扬尘问题的重要途径.在实验室对喷洒抑尘剂后煤粉的固结时间、固结层厚度及抗压强度、抗风蚀性、耐雨淋性和耐温抗冻性等抑尘性能进行测评;为保证使用过程不对接触的作业人员、设备造成不良影响,对抑尘剂的腐蚀性和毒理性进行测评;在现场应用试验中,通过喷洒、未喷洒煤堆的大气总悬浮颗粒物浓度值对比分析及现场固结效果评估其抑尘效果.结果表明:喷洒抑尘剂后固结时间为5h;完全固结后固结层厚度为23mm;抗压强度为249kPa;在风速30m/s的风洞中吹蚀5min,固结层不破裂;在雨淋时间10min内,表层煤粉平均含水量为0.06g/cm^2;抑尘剂能适应-15~40℃的温度变化;抑尘剂毒理性、腐蚀性均符合现行抑尘行业标准要求,使用过程不会对接触的人员和设备造成不良影响;喷洒抑尘剂对煤堆附近大气TSP的平均削减率达67.7%;喷洒、未喷洒抑尘剂煤质检测报告表明喷洒抑尘剂不影响煤炭品质.使用抑尘剂可节约50%的煤扬尘经济损失.