Study On Foam-water Mist Integrated Dust Control Technology And Its Application In Fully Mechanized Excavation Face Of Coal Mines

The fully mechanized excavation face is one of the largest dust producing points in the underground.80% of the dust in the excavation face is produced by broking coal and rock during the tunneling process,which is the main dust source of the fully mechanized excavation face.The change of the structure parameters and operation parameters of the roadheader,the cutting coal and rock properties and cutting position will lead to different dust production amount.At present,the commonly used dust control technology in coal mines is water spraying.It can capture dust efficiently when the dust production is small,but in the case of large dust production,the water mist can not contact with dust fully,resulting in its efficiency is general.The foam technology can control high concentrate dust efficiently by using the accumulation and encapsulation of foam,but the waste of foam and high cost are serious when dust production is small.The effective combination of water spraying and foam technology is proposed.Besides,the deficiencies of existing foam technology are solved in the paper.In this paper,the research method,which combines theoretical analysis,laboratory experiment,numerical simulation and field test,is put forward and the novel technology was studied systematically.The main results are as follows:The method of adding foaming agent using two-stage jet cavitation device is put forward.The principle of jet cavitation is that when the jet pump reaches cavitation state,its liquid absorption is not affected by the fluctuation of outlet pressure in a certain range of outlet pressure.At the same time,the two-stage jet device can reduce the pressure loss and increase the critical outlet pressure in the process of liquid absorption.Compared with the single-stage jet cavitation pump and the two-stage jet cavitation pump,the two-stage jet cavitation pump can be used to reduce the pressure loss and increase the critical outlet pressure.The critical pressure ratio of single stage pump is independent of water quantity,and the critical pressure ratio of two stage pump will increase with the increase of water quantity.From another point of view,it is shown that with the increase of water quantity,the efficiency of two-stage cavitation jet adding device is higher.When the outlet pressure fluctuates,the stability of the device is stronger.With the increase of the outlet pressure,the inlet pressure of the two-stage jet device increases slowly in the working area,and when the outlet pressure exceeds the critical exit pressure,the pressure ratio of the device is opposite to the inlet pressure,and the critical pressure ratio of the device decreases gradually with the increase of the steady liquid absorption,showing a quadratic relationship.The circular vertical net foaming method is put forward,the vertical design is adopted to avoid the uneven distribution of the foam caused by gravity,and the contact area between the foaming fluid and the air flow can be increased by using spiral nozzle injection foaming fluid and the uniform gas supply.For the new foaming apparatus,when the amount of liquid supply remained constant,the production of foam increased firstly in a straight line and then tended to balance with the increase of gas supply.When the quantity of gas supply is constant,the change of foam quantity with the amount of liquid supply can be divided into three different trends.When the new device is in the optimal liquid supply and gas supply,the optimum proportion of the foaming agent is 0.4%.The outlet pressure of the foaming device is mainly determined by the gas pressure.The relationship between outlet pressure and gas pressure is nearly linear.When the outlet pressure is below the critical value,the foam flow will not be affected by the pressure fluctuation;when the pressure exceeds the critical value,the increase of outlet pressure will cause the foam to burst seriously,and the amount of foam will decrease in a straight line.The critical outlet pressure varies with the amount of liquid and air supply,and the greater the amount of gas and water,the greater the critical outlet pressure.The characteristics of dust production of roadheader are analyzed,and it is concluded that the escape passage of dust in the working process of roadheader is concentrated in the annular rock breaking area around the cutting head,and the target of dust suppression medium is determined.Combined with the position of dust producing circle,the small angle flat fan foam is chosen as the optimal jet flow pattern,and the foam injection parameters of a single nozzle are determined.The structure of small angle flat fan foam nozzle is designed.The unique design of compression angle and uniform angle of the nozzle can guarantee the diffusion angle of foam injection and the uniformity of injection at the same time.By using Fluent simulation and field experiment,finally,the compression angle and the uniform angle of the foam nozzle are determined to be 6° and 25°,respectively.The air atomization function is added on the basis of the original foam nozzle.The nozzle is evenly arranged around the nozzle with 10 inlet channels with the diameter of 1.5mm symmetrical up and down.The original foam inlet is changed into gas inlet,and the nozzle shape is flat sector shape,which can ensure that a flat fan fog flow with a large diffusion angle can be produced after the water mist is ejected and the effective package of cutting head is realized.The performance experiment of the new air atomizing nozzle shows that,the active change of any one phase of gas-liquid phase causes the change of mixing pressure at the nozzle,and the change of mixing pressure will lead to the change of the flow rate of the other phase.Along the axial direction of the nozzle,as the distance from the nozzle increases,the particle size of the droplets increases.The diameter of droplets increases along the radial direction with the increase of the distance from the axis of the nozzle.At the same time,due to the influence of gravity,the droplet size presents an asymmetric distribution,the lower half of the droplet size is larger than the upper half area at the same distance from the axis of the nozzle,and the farther the injection distance is,the stronger the inhomogeneity is.The droplet size decreases with the increase of pressure and increases with the increase of water pressure.A foam-water spray integrated dust control device is designed,which can be used in the field of fully mechanized excavation face.The design of function switch box realizes the one-key switch of foam and water mist technology,which solves the application of this technology in the field.An integrated dust control system of foam and water spray in fully mechanized mechanized face has been established.The efficiencies of water spraying and foam functions of this technology are higher than those of traditional water mist and foam technology.The dust control efficiencies of the integrated technology are not different from that of foam function.However,the amount of foaming agent is only 60% of foam technology,which greatly reduces the cost,ensures the health of workers and produces remarkable economic benefits.