Study On Hydrogen Production And Its Relevance With Other Indicator Gases During Coal Spontaneous Combustion

One of the key problems concerned in the coal mining and coal storage iscoal spontaneous combustion, it not only restrict the safety production of coaland the development of coal industry in our country, but also impact theeconomic development in China. Early prediction of coal spontaneouscombustion is significance to guide coal spontaneous combustion and coal minefire. Through long-term experimental study and field test, the coal producingcountries widely use “index gas” to predict coal spontaneous combustion. Coalspontaneous combustion is caused by the coal low-temperature oxidation，it hasimportant theoretical significance and application value to study the generatingrules and correlation of the index gas in the coal low temperature oxidationprocess.Although the quality percentage of hydrogen elements contained in thecoal is small, but percentage of atomic hydrogen has the same magnitude order with carbon atoms, C-H bond is not only the main bonding in the complexmolecular structure of coal, and C-H bond is highly vulnerable to oxygen attackand fracture in the coal low-temperature oxidation process. In recent years,some scholars from America, Australia etc country have put forward H2as the“index gas” to predict coal spontaneous combustion state. Reference the abroadresearch method to study on the rules of gas released small but perceptible (forexample: CO, CO2and hydrocarbon gas), this paper researches the release ruleof the H2in addition to the conventional oxidation products within the limitedspace of coal low temperature oxidation process, and the correlation between H2and other index gases.This paper selects three different metamorphic degree of coal as theresearch object: lignite from XiMeng, long flame coal from Shendong andcoking coal from ZaoZhuang. Perform the coal low temperature oxidationexperimental in limited space using constant temperature device system and airchromatography. Research the changes of H2produced by coal oxidation ofdifferent metamorphic grade with the oxidation temperature. In the experiments,this paper researches the effects of temperature process, coal quality, coalparticle size, volume of reactor to H2emissions. This paper also studied therelationship between H2and other gas products (mainly CO, CO2and CH4). Themain conclusions as follows:(1) H2which generated under the same temperature in the process of coallow-temperature oxidation shows linear trend with oxidation time. No matter temperature programmed condition or with constant temperature, H2released inthe condition of coal oxidation showes index regularity with coal temperature, itconform to the principle for the selection of forecasting coal spontaneouscombustion index gases.(2) In the process of low temperature oxidation of coal with differentmetamorphic grade, the concentration of H2present index trend with coalsample temperature, the index form is CbH2=AeT, the lower of coalmetamorphic grade, the bigger of b value, the more of the hydrogen content incoal, the higher of A value.The amount of H2released of coal low-temperatureoxidation process determins by the coal metamorphic degree.(3) Temperature process does not affect the trend which the amount of H2released along with temperature of coal low temperature oxidation.But contrastwith the condition of temperature programmed, the oxidation temperature thatcan detect H2is earlier under the condition of constant temperature; Thequantity of H2released increases with the decreasing of the particle size of coalsamples, after achieving the optimal particle size, with the further reducing ofcoal sample particle size, the emission of H2decreases. Coal sample qualityplays significantly role to promote the release of H2.(4) Using the method of temperature programmed, the ratio between H2and O2changes with oxidation temperature exponentially; The ratio between H2and CH4is parabolic shape opened to the bottom with oxidation temperature,the higher the degree of metamorphism, the lower temperature achieve the maximum; Within the limited space oxidation process, the ratio between H2andO2present exponential form with oxidation time.(5) using the multiple linear fitting model, to fit the mathematicalrelationship between H2and O2, CO, CO2and CH4under a constant temperature,it shows that the rest of the O2in the limited space blocks H2releasing, CO andCO2collaborativly promote H2releasing for two low metamorphic coal, CH4have played an important role on to the releasing of H2, in promoting beforeblock in the coal oxidation.