Experimental Study On The Inhibition Of Spontaneous Combustion Of Coal By Pre-injection Inhibitor

The spontaneous combustion of coal in China is serious.The fire preventing and extinguishing technique of inhibitor as a simple and efficient method has been widely used in the spontaneous combustion of coal.The existing methods of spraying,atomizing and injecting inhibitors into the goaf have achieved certain fire prevention effects,but there are still deficiencies.In recent years,some scholars have proposed a method for preventing coal fired by pre-injection inhibitors.This method is a means of "precaution in advance" and is expected to fundamentally solve the problem of spontaneous combustion of coal.However,there are few studies on this method at present,and only stay at the surface layer.There is still no systematic experimental research on the pre-injection effect of the inhibitor,the effect of resisting the spontaneous combustion of coal and the influence of the inhibitor on the coal quality.On the basis of previous studies,the Nantun,Luning and Fangezhuang coals were used as experimental coal samples,and MgCl2,CaCl2 and NH4H2PO4 were selected as inhibitors,and the self-made pressurized pre-injection inhibitor experimental device was used.In the pre-injection experiment,a better pre-injection scheme was determined by orthogonal test,and a coal sample of the pre-injection inhibitor was obtained.Then,the temperature test and thermogravimetric analysis were carried out on the raw coal and the resistive coal samples.The concentration of CO and O2,Cco/T,TG and DTG curves of the coal before and after the pre-injection inhibitor were studied.The law of change,and the change of oxygen consumption rate,inhibition rate and characteristic temperature point as the evaluation index of the pre-injection inhibitor’s resistance effect,the comparative analysis of the resistance effect of the pre-injection inhibitor on oxidation and spontaneous combustion of coal.Secondly,industrial analysis of coal samples before and after resisting was carried out.The variation rules of ash,volatile matter,fixed carbon and calorific value were studied.The influence of pre-injection inhibitor on coal quality was analyzed.Finally,a pre-injection test of the inhibitor was carried out at No.93Below09 working face of Nan tun Coal Mine to examine the effect of the field application.Research indicates:(1)Under the same pre-injection conditions,the pre-injection effect of different coals is obviously different.Pre-injection effect:Luning coal>Nantun coal>Fangezhuang coal;for the same coal sample,the pre-injection effect of MgCl2,CaCl2,NH4H2PO4 is close,and when the concentration of the inhibitor solution is 25%,the injection pressure is 4Mpa.and the pressure is continued for 2d,a better pre-injection effect can be obtained.(2)The coal sample of the pre-injection inhibitor has a significantly lower CO concentration,CCO/T and oxygen consumption rate and higher O2 concentration than the original coal sample during the temperature programming process.Its inhibiting rate is between 15%and 30%,and it plays a significant role in the dynamic equilibrium of coal spontaneous combustion.The pre-injection of NH4H2PO4 still has a inhibiting effect on the spontaneous combustion of coal at higher temperatures,but the pre-injection of MgCl2 and CaCl2 plays a catalytic role in the stage of thermal decomposition of coal.(3)The pre-injection inhibitor has an effect on the coal quality,which is manifested in an increase in ash content,a decrease in volatile matter,fixed carbon and calorific value.Among the three inhibitors,NH4H2PO4 has the greatest influence on coal quality,but the effect is acceptable.(4)After pre-injection of the inhibitor on the site,the CO concentration area in the goaf is pushed back by about 30m.If the normal coal mining progress is 4.2 m/d,the oxidation process of the coal is pushed back by about 7d,which greatly reduces the risk of spontaneous combustion in goaf of the working face.The research results of this paper provide relevant basic data for pre-injection inhibitors to prevent and control the spontaneous combustion of coal,and provide theoretical and experimental basis for the development and application of this technology.