| Mine gas fire is an important disaster that affects the efficient and safe mining of coal mines.With the development of coal mine machinery automation technology,shearers are widely used in coal mine working faces.However,fire accidents caused by friction sparks in the process of coal mining are gradually increasing.Because the existing fire prevention and extinguishing technology is difficult to prevent and control the fire caused by the cutting spark in the coal face,this paper proposes and designs the technology and equipment to prevent and control the fire caused by the cutting spark of the shearer using the foam fire extinguishing theory.This paper mainly carries out theoretical and technical research on foam agent foaming technology through experiments and numerical simulation methods,determines the optimal parameters of foam agent foaming,factors affecting foam stability,reveals the rule of foam inhibiting sparks,and finally forms a complete set of foam system and technology to inhibit the cutting sparks of coal cutters.The main conclusions are as follows:(1)By setting up an experimental platform for measuring rock friction temperature and spark phenomenon,the laws of rock friction temperature rise and spark generation under different conditions are studied.Then,by comparing the influence of water mist and foam on rock friction temperature and spark suppression,the conditions for suppressing spark are obtained.By comparing the friction heating and spark occurrence of different rocks,it is found that the speed of friction heating of rocks is:yellow sandstone>granite>magnetite>quartz.The strength of friction affects the temperature rise of friction and the appearance of sparks.When the rotational speed of friction is greater,the pressure on the contact surface is greater,the speed of rock friction heating is faster,and the spark is more obvious.This is because the increase of friction speed and contact force can make the mechanical energy transform into heat energy faster,and also promote the strength of sparks generated by friction.The larger the water mist flow is,the better the effect of inhibiting temperature rise and sparks is.However,water mist can only inhibit the strength of sparks,and it is difficult to eliminate the appearance of sparks.Foam is not as good as water mist in cooling,but it has obvious effect in restraining friction sparks.(2)The quantitative addition of foam agent was carried out by using the characteristics of jet absorption.First,the rule of liquid absorption of jet under different working conditions is studied through experiments,and it is found that the liquid absorption of jet is mainly caused by the negative pressure of the suction chamber,and the negative pressure of liquid absorption is related to the inlet and outlet pressure.With the increase of the pressure difference,the negative pressure and liquid absorption of the jet ejector gradually increase.The critical pressure difference and the maximum pressure difference of the jet increase with the increase of the inlet pressure.When the inlet water pressure is constant,the pressure difference between the inlet and outlet is the main reason for determining the liquid absorption capacity of the jet ejector.By studying the mixing ratio under different conditions,it can be concluded that the mixing ratio is related to the pressure difference and valve opening.The determination of mixing ratio provides a basis for the quantitative addition of foam agent.Using ANSYS FLUENT to simulate the jet process,the limit value of liquid absorption is explained.The limit of liquid absorption of the jet ejector is mainly related to the"choking"phenomenon caused by the increase of inlet pressure and the reduction of negative pressure in the suction chamber caused by the increase of outlet pressure.(3)A coaxial gas-liquid mixing method is proposed for efficient foaming.The structure has uniform gas-liquid mixing,small pressure loss and can be used for efficient foaming.The optimum foaming parameters were determined by orthogonal experiments.The type of foaming agent is the most important parameter affecting the foaming ratio.Type A foaming agent and OS foaming agent have higher foaming ratio.The best parameters of foam preparation are water supply pressure of 0.8MPa,intake air flow rate of 28m~3/h and mixing ratio of 2%.(4)The influence of different factors on the stability of foam was obtained through the study of liquid film drainage of foam.The mass of liquid discharged from foam increases with time.With time,the discharge rate of foam increases first,then decreases and then stabilizes.The liquid discharging process of foam can be roughly divided into three stages:the forced liquid discharging stage of foam,the free liquid discharging stage of foam,and the dominant liquid discharging stage of foam coarsening.With the increase of the concentration of foam solution,the surface tension of the solution gradually decreases and the viscosity gradually increases.The smaller the surface tension,the greater the viscosity of foam liquid,the longer the liquid discharge time of foam,and the more stable the foam will be.(5)An airborne foam system integrated device for coal mining machine is designed and manufactured,which is suitable for preventing and controlling the cutting spark in the working face,and fills the gap in the field application of this technology.The structure of foam nozzle suitable for downhole foaming was optimized by studying the foaming performance of nozzles with different structures.Taking the 2506 working face of Zhangcun Coal Mine in Lu’an as the test site,the field application test of high efficiency control technology for cutting sparks and gas combustion of shearers was carried out.The integrated spark suppression system of the coal mining machine airborne foam equipment installed on the heading machine of the working face is established.Through the verification of the field test,the foam ejected by the foam system can completely cover the drum of the coal mining machine and meet the requirements of spark suppression. |
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