Study On The Interaction Mechanism Between Foam And Mine Dust And High-Efficiency Dust Suppression Technology

Coal dust not only causes explosion accidents but also causes workers pneumoconiosis,which has become a major threat to human health and safety.With the continuous improvement of coal mining intensity in China,there is an urgent need for further improvement of mine dust control technology.Foam dust suppression technology has the advantages of good wettability,large coverage area,low water consumption,and good dust suppression effect.In recent years,it has achieved good results in some dust suppression practices.However,in the heading face with large wind volume,small section,and low water pressure,the current foam dust suppression system is not effective enough,and sometimes it is difficult to work normally.On the one hand,the current dust suppression foam tends to break up once interact with the dust,so it is not able to continuously suppress the hydrophobic dust.On the other hand,the pressure loss in the current foaming system is too large.It leads to a series of problems,such as the weak ability of the jet to resist wind flow,insufficient foaming capacity and a large amount of foam loss.To solve the above problems,the performance improvement of both the foaming agent and the device is necessary.The author studied the interaction mechanism between foam and coal dust and the advanced foam preparation technology.The research methods including theoretical analysis,experimental demonstration,numerical simulation analysis,and on-the-spot industrialization experiment were conducted.The main results and conclusions are as follows.After the ingredient change of the foaming agent,the foam can stay stable during the capture of the hydrophobic dust,and dust suppression efficiency is improved.The liquid film drainage process under the interaction of dust particles was studied using the Sheludko cell.The relationship between the dust surface wettability and the stability of dust suppression foam is determined.It is confirmed that the very hydrophobic dust(forward contact angle greater than 90 degrees)can cause instant rupture of foam films.Based on the air-liquid interface curvature around the particles,the Laplace pressure distribution in the liquid film around the particles was analyzed theoretically,and the intrinsic dynamic mechanism of the liquid film drainage process was reinterpreted.The stability of foam after capturing very hydrophobic dust is greatly improved by adding a trace amount of octanol to the existing foaming agent.It is the first time that a jet pump simultaneously works as a flowmeter andadding device in the dust suppression practices.The pressure loss is reduced from60% to 20% while ensuring the accurate and stable addition of the foaming agent.The influence of the jet pump structure on the critical point of cavitation is studied.The effects of turbulence and local low pressure in the jet pump on the development of cavitation are obtained by experiments and numerical simulation.Due to the new structure of the cavitating jet pump,local low-pressure zone and local strong turbulence zone coincided,which promotes the occurrence of cavitation phenomena.An experience curve is proposed to guide the design of new jet pumps.When the liquid adding ratio is less than 1.4 wt%,the critical pressure ratio of the proposed jet pump is as high as 0.8.Also,the experiment proves that the cavitating jet pump can work as a flowmeter and has reliable measurement accuracy.It not only saves equipment cost and volume but also ensures the intrinsic safety of the dust suppression foam system.A new vertical foam generator is proposed,and effective foaming with low-pressure loss is realized.In the vertical foam generator,the gas and liquid flow in a bottom-up direction,which is different from the traditional horizontal direction.It transforms the negative effect of gravity on the gas-liquid mixing into the promotion effect.When the gas-liquid flow ratio is lower than the critical value,at least 84.5% of the air is dispersed in the liquid phase for foaming,which is 27.4% higher than that of the horizontal spiral mesh foam generator under the same conditions.The internal flow cross-section area of vertical foam generator is large and the resistance of disturbance structure is small,which makes the foaming capacity of the new foam generator higher than that of the original foam generator and the pressure loss greatly reduced,not more than 0.08 MPa.The proposed foam generator not only lays the foundation for efficient dust suppression but also improves its compatibility in the dust suppression system.The effect of flow passage structure on the characteristics of foam jets is studied.Through numerical simulation analysis of the flow field inside the nozzle,it is found that the local turbulence caused by the structural defects of the nozzle is the main reason leading to the loss of foam and the runaway of the jet shape.When the foam is ejected from the jet at high speed,the surrounding air will be entrained by the foam jet and form strong turbulence on the jet surface.The turbulence on the jet boundary is also one of the reasons for the breakup and deformation of the jet.Using 3D printing technology,we designed and manufactured a new foam nozzle based on foamflow characteristics.The proposed foam nozzle completely avoids the abrupt change of the cross-sectional area and the obstruction of the foam flow,so the proposed foam nozzle has better performance than the existing ones in aspects of jet continuity,jet stability,jet evenness,and foam loss rate.A single foam nozzle can cover the area of0.4×1.6 m and the foam jet can remain stable at the wind velocity of 7m/s.The proposed nozzle lays the foundation for efficient dust suppression.A new foam dust suppression technology with low energy loss is developed,and a simulated dust suppression effectiveness test system was built in the laboratory.To some extent,the simulated dust suppression effectiveness test system can predict the situation that a dust suppression technology may encounter in the field,and can quantitatively test the performance of the dust suppression technology under extreme conditions.The proposed foam dust suppression system can achieve high-efficiency dust suppression in a high wind tunnel(560-570 m3/min)with low water pressure supplied(0.87MPa).The industrial experiment of the proposed foam dust suppression technology was carried out in the 120702 track roadway heading face of the Da Wan coal mine in Guizhou province.The heading face has the typical characteristics of large dust production,small section,large air volume,and low water pressure.The dust removal efficiency of the total dust reaches 86.8% in the tunneling face,and the time-averaged concentration of the respirable dust is reduced to 3.9-5.7mg/m3.Because the water entry pressure requirement of the proposed system is reduced significantly,the foam dust suppression technology can be used in a wider range of dust pollution sites.Dust suppression efficiency is greatly improved after the addition of octanol in the foaming agent.The present dissertation has 86 figures,32 tables and 137 references.