| Underground coal gasification (UCG) is a comprehensive energyproduction technology, which can gasify unrecoverable and uneconomical coalresource into gas (CH4and CO, etc.), and send them to the ground forproduction and living. As the change of energy structure in China, gasificationof coal underground has obvious advantages in environment benefit, utilizationof resources, economic efficiency of enterprises and the safety of constructorscompared with former modes of coal exploitation and utilization. After30years’development, China’s underground gasification has gradually transformed fromlaboratory research to industrial production and application currently. However,compared to the coal gasification on the ground, the control of variables and thesurveillance of combustion states of underground furnace are difficult to achieveeffective control during the process of underground coal gasification.Based on the comprehensive detection technology of gasification face,which is a sub-project of national863significant program, radioactive radonmeasurement was applied to monitor the combustion states of coal gasification underground at coal gasification test area. Moreover, multi-fractal theory wasused to analyze the distribution characteristics of radon concentration over time.The results show that the distribution of radon concentration has obviousmulti-fractal characteristics and multi-fractal parameters are inversely associatedwith gasification temperature.At shallow ground, the concentration of radon varies without factors(pressure, temperature, humidity) as well as the type of the medium. Therefore,the multi-fractal characteristics of radon concentration at different mediums anddepths were researched at Ulanqab test area naturally and a best sampling depthwas carried out at soil area and basalt area respectively. The results indicate thatthe distributions of radon concentrations perform obvious multi-fractalcharacteristic with different mediums and the multi-fractal spectrum width (α)of soil area is nearly the same with that of basalt area. Based on the spectrumwidth (α) and symmetry (α) of the curve,30cm~40cm underground is thebest symmetry depth for the two mediums. For soil area,40cm underground isthe best symmetry depth for radon concentration and radon distribute stabilitythere. For basalt area,30cm underground is the best symmetry and stable depthfor radon. As a result, the ideal depth of radon adsorption device should be30cm~40cm underground for field survey at soil and basalt area that30cm is forbasalt area and40cm is for soil area. When we failed to reach the ideal burydepth at some field work because of restrictions, the concentrations of radonmeasured at different depths should be revised to a certain same level on the basis of reasonable sampling depth, then compared and analyzed.The multi-fractal characteristic of radon concentration in low radioactivearea and gasification area of Ulanqab was researched, which provides a newmethod for the surveillance of combustion states of gasification area. Based onthe reasonable sampling depth, correcting the radon concentrations of differentmediums and depths to a same level can direct the field work scientifically. |
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