Study On Generation And Migration Of CO From Coal Oxidation Under Ambient Temperature In Active Goafs Of Fully Mechanized Longwall Panels In Shendong Mine District And Its Application

Shendong mining district is one of13mining districts with one hundredmillion tons of coal production each every year in our country. Its mines are allthe national first-class modern high production and efficiency mines, and itsannual coal output is200million tons. Its main coal type is the lowmetamorphic grade of long-flame coal and non-caking coal, and its workingseams are easy to spontaneous combustion and the spontaneous combustioncoal seam. CO accumulation and CO continuous overrun (exceeding themaximum allowable concentration24ppm ruled by the coalmine safetyregulations) often occur in the return corner of fully mechanized face due tostrong mining, large goafs and the coal seam prone to oxidation etc, interferingwith the forecasting of coal spontaneous combustion and bringing thebewilderment in working out the measures of preventing and putting out a fireand the measures of managing and controlling CO concentration in the returncorner of fully mechanized face, which seriously affects the mine safety production. CO production mechanism, accumulation and migration law in themining goaf has always been the key scientific problems of mine disasterprevention and control, so the paper took Shendong mining district as theresearch object, studying the CO production mechanism during coal oxidationunder ambient temperature, CO accumulation and CO migration law in the goaf,the safe concentration and the warning concentration of spontaneouscombustion on CO in the return corner of fully mechanized face, and COcontrolling measures and managing standards; providing the basis for workingout the management standards of mine fire prevention and control technology inaccordance with the actual condition at site to solve the problem about therelationship between CO overrunning with spontaneous combustion which hasbeen preoccupying the key coal production bases in northwest and north Chinafor a long time. The main conclusions are as follows:（1）CO concentration in the return corner of fully mechanized face inproduction period overruns seriously compared with in the maintenance period,10～20ppm higher; the CO concentration overrunning is the most serious in theleaving top coal caving method, but nearly doesn’t overrun in a mining overallheight face. CO in the return corner of fully mechanized face comes mainlyfrom coal oxidation of mined-out area, rubber-tyred vehicle tail gas and thecrushing coal during the winning machine cutting coal, among, the coaloxidation of mined-out area is the main source and generates CO concentrationreaching up to80～150ppm, taking up about76%, and the tail gas of rubber-tyred vehicle gets to10～20ppm, taking up18%, and the crushing coalduring the wining machines cutting coal comes to10ppm, taking up6%.（2）The original CO content in the mining coal seam of Shengdong minearea was measured by scene sampling and laboratory analysis. It turned out thatthe original CO content in the mining coal seam is very little, with the contentof0.38～0.52×10-6cm3/g, meanwhile, the air volume in the fully mechanizedface is large with the volume of1000～3000m3/min, so the original CO contentin the mining coal seam doesn’t result in the CO continuous overrunning in thereturn corner of fully mechanized face.（3）Researched and developed the coal experimental oxidation apparatusunder ambient temperature and took the enclosed oxidation test under ambienttemperature on5typical coal samples (1.3kg) by scene sampling. The resultsshow that the coal of Shengdong mining district could produce CO andconsume a certain amount of O2below20℃, and the concentration of COincreases gradually when temperature keeps stable, after a certain period of time,up to a certain of value and then stabilizes, the most concentration of CO willarrive at154～425ppm, while the stabilization time is380～980min as usual.With the process of oxidation going on, the generation rate of CO lowersgradually, down to a certain degree, the accumulative concentration of CO nomore rises and keeps on a certain level. In general, the average generation rateof CO in all kinds of coal samples is0.56～1.64cm3/（min·m3）, and theconsumption rate of O2is proportional to generation rate of CO, the coal samples have the different consumption rate of O2with range0.36～1.301/(min-m3).(4) The generation rate of CO is found with the similar process between desorption and oxidation according to many times’experimental studies on CO desorption with inert gas and coal oxidation under ambient temperature. Research shows that the generation rate of CO declines sharply in the first hour, after a period of time, the decreasing trend of CO generation rate slows down and tends towards stability. Meanwhile, it is found that coal oxidation under ambient temperature is the main reason to produce CO, and the reciprocal of CO generation rate become the linear relation with logarithm of time, the relationship is RCO=a/Int-b,by this formula, the relation between CO generation rate and the oxidation time can be studied quantitatively.(5) The coal oxidation experiments under ambient temperature shows that CO generation rate is affected mainly by the oxidation products from coal oxygen inhibition reaction, except for the influence from the oxygen concentration and the active site in the coal surface. When these oxidation products are removed, the process of oxidation resumes, resulting in CO generation rate increasing. It demonstrates that CO could regenerate by goaf coal under frequentative air infiltration, and CO will arrive at the return concern of fully mechanized face with the air infiltration, which results in the continuous overrunning of CO in the return concern.(6) The production mechanism of CO under ambient temperature was achieved by establishing the functional relationship between the consumptionrate of oxygen and oxygen concentration. Ambient temperature oxidationmechanism of coal is divided into five stages:“chemical control”,“transitionstate”,“diffusion control”,“inhibitory control”, and “similar burn-off reaction”.Research results could provide the theoretical basis for managing CO overrun inthe return concern of fully mechanized face.（7）The dangerous zones producing CO are identified by the fieldobservation of CO and O2in the goaf of the fully mechanized face, combinedwith the oxidation experiment results under ambient temperature. COconcentration achieves the maximum about60～100m from the working face,ranging71～230ppm in general, and keeps stable about120m from theworking face within50ppm.（8）Gas distribution characteristics in the working face of U-shapedventilation was researched and analyzed by establishing CFD model of3D gasmigration at the different propulsion positions of working face, on the basis, thedistribution characteristics of CO produced by coal oxidation in the goaf ofworking face of U-shaped ventilation was simulated and analyzed, and COmigration law in the goaf was achieved.（9）Based on a large number of experiments and the field observations,the prediction model was established on CO concentration on behalf of safetyand warning spontaneous combustion in the return concern of fully mechanizedworking face in Shendong minging area. The model could calculate CO concentration on behalf of safety and warning spontaneous combustion, fitting well with the values measured in the scene. The CO safe concentration during normal mining in the return concern of fully mechanized working face in Shendong minging area is determined to be85ppm, and CO concentration warning spontaneous combustion is350ppm.(10) Based on the mining technology conditions and coal spontaneous combustion characteristics in Shendong mining district; based on a large number of field observations, laboratory studies and the theoretical analysis and calculation; combined with the existing fire prevention and control technology and equipments, the "fire prevention and control regulations in Shendong mining district" was compiled. The regulations provide the scientific basis for the fire prevention and control in Shendong mining district, which has the reference significance on the technology management of fire prevention and control to Shenhua group and the other coalmines with the similar conditions.