Critical Value of CO of Forecasting Coal Spontaneous Combustion

Dec.2003Journal of China University of Mining TechnologyVol. 13 No.Critical Value of co of ForecastingCoal Spontaneous CombustionHEQi-ling(何启林)2, DAI Guang- -long(戴广龙), WANG De-ming(王德明)1(1. College of Mineral and Energy Resource, CUMT, Xuzhou, Jiangsu 221008, China;2. Department of Resources Exploration and Management Enginering, Anhui University ofScience and Technology, Huainan, Anhui 232001, China)Abstract CO has been used widely in the production process of colliery as an index gas to predict spontaneouscombustion of coal. But in some collieries there are co gas in the upper corner of the face all the times, sometimeco gas even exceeds the regulated critical index. This phenomenon is much more obvious in the fully-mechanizedlongwall face and fully-mechanized longwall and top- coal caving face. Although many measures of fire-proof andfire-extinguishing have been adopted, the flowing amount of co gas can be only decreasd, but can not beeliminated completely. Using the different kinds of coal, the experiment of coal oxidation was made at the lowtemperature. The experiment indicates that some kinds of coal can produce CO under the condition of normaletime the Co consistency is very high, and the intension of Co can be decreased withoxidation time prolonging. Selecting rational critical value of Co is the ke to predicting spontaneous combustion ofcoal correctly and reliably. The problem of selecting retional critical value of CO was studied. Finally, the amountof co gas released by different kinds of coal was obtained under normal temperature condition.Key words: coal spontaneous combustion; index gas: critical valueCLC number: TD75 Document code: a Article ID: 1006-1266(2003)02-0121-05of graham, the ratio of alkene to alkane1 Introductionhydrocarbon, ratio of chain to alkane and ratio ofSpontaneous combustion of coal is one of the single alkane hydrocarbon to all alkane hydrocarbonprimary disasters in coal mine safety-production, amount are usually used as index. In China manyestimating the temperature of coal or the extent of collieries adopt the single index-co to predict thespontaneous combustion is an important measure to spontaneous combustion of coal. In Some collieries itpredict spontaneous combustion and ignition of coal has been discovered that CO exists in the up cornersaccording to analyzing the results of index gas at of face all the times. This phenomenon is muchearly stage. Many kinds of predicting index of coal more obvious in fully-mechanized longwall face orspontaneous combustion, which are divided into the fullylongwall and top-coal caving face.sIngle index and moreindex, have been proposed. Although many measures of fire-proof and fireIn these indexes, for the single one the extinguishing have been adopted, the flowingconcentration or absolute formed amount of certain amount of Co gas can be only decreased, but cankind of gas (such as CO, the high-sulfur-coal can not be eliminated completely. This phenomenonlso use SO2) is used as index, or the formed confuses many engineers on the spot, so in thisamount of a kind of gas is used as index (for paper the authors made attempt to give explanationsexample C2H,). For the more indexes the coefficient中国煤化工CNMHGRecelved date: 2003-05-30Foundation item: Science of fire Natural Science Foundation of China (2001CB40960102)Biography: HE Qi-lin(1963-), male, from Wuwei county of Anhui Province, associate prof., doctorial student of safety science andhnology specialty, engaged in the research on colliery safety.122Journal of China University of Mining TechnologyVol. 13 No. 22 Oxidation Experiment of Coal UnderCondition of Static and NormalTemperature2. 1 Device of oxidation experimentIn order to compare the static breathing abilitycoal in oxygen with the amount of all kinds of gasreleasing, in the ventilation and safety laboratory ofAnhui University of Science and Technology theexperiment device of breathing under normaltemperature was made Fig. 1). It consists ofvitreous absorbing vessel, vitreous valves topper,Fig. 1 A set of static breathing experimentpiston triplet: 2. vitreous absorbing vesselpiston triplet, advection tube, down mouth bottle3. coal sample; 4. vitreous cotton interlaydirect valve, connection tube etc.5. glass stick: 6. advection tul2. 2 Gas analysis equipment7. connection tube: 8. water bottleFor gas analysis gas chromatography apparatusExperiments requested a original coal sampleSP-2308 and hydrogen flames detector were used. that have never been exposed in the air. ThereforeIn the process of analyzing hydrocarbon gas, such samples were taken from the depths of 2 m in theas CH,, C2H4, C2H6, C3Ha, the steel cylinder (Lcoal1 bed of the new miining face. The picke5 m, =31 mm) filled with GDX-502 was used samples were filled in the sample-taking machinewith high pure hydrogen(99. 999%); in the process and pressed solidly then the machine was coveredof analyzing gas such as CO, CO2 and CH4, up completely. On the ground the cover should bestainless steel cylinder (L=0. 7 m, p= 3 mm) sealed completely using vinegar, and winded up,filled with TDX-01 was used with the converting finally the samples were sent to analyze infurnace (L=0. 2 m) using nickel as catalyst. The laboratory. The coal samples were crushedarrying gas was high pure N2(99. 999%), and the laboratory and then sieved, the samples about ofburning gas was high pure H2(99. 999%), the 1 mm in diameter were selected for experiment.combustion-supporting gas was the compressed air.2) ExperimentGas samples flowed into detector through convertingThe coal samples were taken from 12furnace after separated in chromatogram column. coal in 6 collieries. They belong to the EnergyTwo kinds of gas were analyzed respectively. The Incorporated Company of Shanghai and Mineralinstrumentation accuracy: carbon hydrogen Group of Huainan and Mineral Group of Huainancompound was0.01×10°; CO kind was0.1×106Xingji. The geological condition and primary2. 3 Experiment processcomponents of coal seam are shown as Table 11) Preparation of experimental coal samplesTable 1 The existing conditions and primary components of experimental coal samplesSource of7th bed 8th bed 7th bed 8th bed 13-1 bed 11-2 bed 13-1 bed 11-2 bed 13-1 bed 11-2 bed 13-1 bed 11-2 bedThickness/m2.8-5.323-3.82.2-4.61.8—2.34.6-7.83.2-6.82.6-4.63.7-7.22.8-5.73.3-6.62.64,83.3-5.7Depth of coal/m670690Ash content/%9.910.819.419.3Water content/%YH中国煤化工12.62.8Gas content/(m2 t-1) 2.32.30.520.460.550.580.710.6CNMHG30.610.3The coal samples were oxidized 15 d at 22 C. The gas samples were bled from the oxidationHE Qi-ling et al.Critical Value of CO of Forecasting Coal23equipment every day one time for analyzing. The consistency of CO samples in the first 6 days and theaccumulative releasing amount m(10-3mm/kgincremental value Aq. (10 mm/kg. d)are shownd) of co gas which were calculated according to the in Table 2.Table 2 Calculation of Co gas which release on static and normal temperature conditionTime/dqm△q1qmqem9m138613861953292816201301231533153371856540883704313225451520247002424338146703449502852195098456782339233928695303217346925237122433928153315332112535253529864513362376322637962083984188I9831983243745427983612I193115198329818321381382693555313143832423589216378719821662166264848230894413295348118611m18971897243253527963643001233190189336817821482696548303533347421636621882. 4 Analysis of the experiment resultsrelationship between Aq and t as follows1) Each coal sample that was tested can releasego(1)CO on the condition of normal temperature. Andthe release first of Co gas decreases with oxidation where: Ag is the increment of CO gas, mm/time prolonging. Because the releasing amount Ag(kg·d); go is constant value,mm3/kg·d,qof CO from 12 coal samples with oxidation time varies with different coal samples and their valueshave the same changing trend(Fig. 2)are obtained by regression measure and are shown in3.5Table 3; t is the time that coal have been exposed inthe air, d; B is the exponential coefficient, whichvaries with different coal beds(Table 4)258,10,121.52)The difference of Co formed by differentcoal seams is large. For example. The range ofamount of co gas formed by the coal samplesoxidized is from 0. 242-3. 153 mm. Thereforeduring normally mining process Co gas formed fromFig. 2 The increment of CO gas Aqsome working faces can't be detected in the return(6 coal samples)airflow, but can be detected in others airflow all theThrough analyzing the data of Table 2 and times, especially in the up corner of faceFig. 2, there is a minus approximate exponentialTable 3 B regression value and qo of tested coal samples11465166215958545459281.6192.1951.8920.9681.8151.4941.7691.9931.8651.9971.8941.9213 Determin Reasonable Critical Value of advanmeasurability andCO Index gH中国煤化工onship between theCNMHG3. 1 Co as index gas to predict coal spontaneouscoal. And the coal samples have good repeatabilityIn pyrogenAs index gas, Co has the following124Journal of China University of Mining& TechnologVol 13 No. 23.2 Setecting rational critical index value of Co where L,, l2 are width of radiator and oxidationll of up and down airway of strip, m v is speed of the mining, m/dthe face is always oxidized in the air, the releasingThe leakage amount Qr (m/d)formula of theamount of co gas can be regarded as 0 when goaf in the "U" ventilation system under thediscussing the releasing amount of co gas. With condition of having leakage near the face and nohe unceasing refreshing of the coal wall, the leakage at the other isoxidation time is very short, so the releasingQi=aQ2(4)amount of CO is less then the total amount released where a is regression coefficient measured on theby the whole face, and it can be neglected. The spot Q is the ventilation amount of face, m/dmain part of Co in the return airway is the result ofTherefore, the average concentration C of COthe left coal oxidation in the goaf. The absolute in the up corner of the goaf under the normalreleasing amount of Co in the whole face can be production condition can be calculated by thecalculated from the following formulafollowing formulaQ-J。×10a4。(-1,(2)Q×100%(5)where: Q is the total amount of cO released by theleft coal in goaf, t(m); P is the extraction rate,To use CO as the index gas the key problem%:G is day production, t/d; T is the oxidation determining the rational predicting critical value. Iftime of left coal in the goaf, dthe critical value is too low, the sensor willFor the leakage wind rate of the left coal of the misinform; if it's too high, the sensor will fail togoafs choky strip at the face of the"U"ventilation report. In order to improve the accuracy of thesystem is small, we can approximately think that critical value of Co gas predicting, for the COthe gas doesnt exchange with the gases in oxidation concentration of the goafs up corner of 12 collieriesstrip. Therefore, T only includes the oxidation time the calculated results were compared with thespends in radiator and oxidation strip of coal goaf. measured values(Table 4)T can be calculated by the following formulal1+l2(3)able 4 Comparison of the measured values with the calculaed results of the concentration of COCollieryZhangnji-1 Xinji-2KongzhuangXuzhuangCO measured/10-6Co Calculated/10121.685.682.735.8Error K/%1.101.12The calculated values are smaller than that of4 Conclusionsthe measured one, therefore, the critical value ofCO index gas should be revised using the following1)Coal is oxidized and releases co gas rapidlyformulaas soon as It is exposThe relationshi(6)between the released amount o of co gas and timehere:k is the coefficient of correction It was t can be considered as a minus exponentialinfluenced largely by coal kinds, existing conditions appro中国煤化工 nount of co gasof coal and technology of mining, and it can be decreaCNMHGprolonging. Theobtained by measurement.HconsistwillI 1D 1cacased byoxIdized coavaries with different kinds of coal. If the releasingamount Co of coal is big, there is co gas in the upQi-lingCritical Value of CO of Forecasting Coalcornerof the face all the times. Therefore, it is geological condition of coal mines, we must take theimportant to determine the rational critical value Ceri coal samples and test the released intension of coof co gas predicting the spontaneous combustion laboratory when using the Co gas as index gas, andsituation of the left coal in theprecisely and use the relative formulas in this paper to calculatetaking measures to prevent coal spontaneous the predicting critical value of co gas. Then2) The absolute amount of co gas released coefficient of K must be modified to predict thefrom the coal in goaf under the condition of normal spontaneous combustion of the left coal in goafoxidation condition depends upon the factors of the preferably.coal seam, the coal output, the extraction rate and4) Because of the complexity and variation ofso on For the same kind of coal the consistency of the colliery and some factors have influence upon theco gas in the large output goaf of fully-mechanized consistency of index gas, such as the ventilationlongwall face and fully-mechanized longwall and amount, gas flowing amount, taking samplestop-coal caving face is larger than the cannoned and analysis, we can adopt the more index gases ormechanized faceseveral combined index gases to improve the3)Because of the difference of coal seam and predicting accuracyReferences[1]邵辉.浅谈煤炭自燃指标的优选与使用].煤炭科学技术,1996(9):23-26.[2]张国枢.无煤柱阶段连续开采综放工作面煤炭自燃综合治理[J].煤炭科学技术,2001(11):32-36.[3]李宗翔,海国治,秦书玉采空区风流移动规律的数值模拟与可视显示[].煤炭学报,2001,26(1):76-80中国煤化工CNMHG