Research On Characteristics Of Coal Particles Migration In Drill As Negative Pressure Drilling And Drilling Equipment Development

Gas pre-drainage drilling was an effective measure of gasmanagement,but it was a difficult thing drilling in soft coal,the application of traditional hydraulic drilling was easy to collapse the borehole and suspend the drilling,designrequirement and gas extraction could not be achieved.The application of pressured wind drilling also has problem whether the pressure was high or low,when the pressure was high,there was more pulverized,gas ejection in serious area,gasoverrun,induction of outburst,environmental pollution and healthydamage of miner;when the pressure was low,the drill got stuck and borehole got blocked was common,theaccident broken and seized the drill occurred usually,also design requirement could not be realized.Drilling of soft coal was the key issue of gas prevention and the prerequisite of the realization of gas prevention.The paper focused on the characteristic of the soft mine,investigated the process that drilling in soft mine,the coal mine,thefacilities,the driving force and so on,put forward that using the indicated negative pressure system as the driving force and in a manner of blow-out pulverized from interior of drill to drilling,the fundamental purpose was to resolve the problem thatgas ejection,drill got stuck,gasoverrun and pulverized in engineering,theoreticalresearchedthe law and characteristics that the pulverizedmigrated in the interior of drill provided the theoretical foundation for blow-out pulverized.The paperused the negative pressure gas conveying theory,gas-solid two-phase flow theory,CFD numerical simulation and field test as the method to make the study of basic parameters about the process of drilling as wind velocity,pressure loss,aperture,transmission capacity,and conveying distance.The study found that the size of drill diameter had a significant impact on the delivery performanceof the particle;Found out the relationship between the transmission capacity and the flow parameters that included transport pressure,solid velocity,gas velocity,slip velocity,solidgasratio and porosity,and inferred the formula.Therelationshipbetween transmission capacity,conveyed distance andangle of drilling was investigated out.Found out the factors that influencedthe characteristics of dense phase pneumatic conveying resistance based on the analysis on the flow theory,probed the mechanism of dense phase pneumatic conveyingsimultaneously.Fitout high precision resistance characteristics formula ofhorizontal and vertical pipe andthe formula that considered the drill rotational resistance.The negative pressure drilling system,special drill and special drill pipe and pulverized collecting box has been developed.It could make pulverizedand gas migrated in closed system when used the new drilling system to drill,realized the drilling had no pulverized andno gas.The operation process and specification has been made according to the geological conditions of coalseam and drilling parameters of test coal mine.The equipment,developed by the application of research findings,achieved great consequent through fieldapplication,resolved the problem drilling in soft coal effectively,implemented the purpose of the research,and provided new method and apparatus for drilling in soft mine.