| Cemented backfill mining technology in coal mine has significant effect in controlling surface subsidence,improving coal resource recovery rate,promoting solid waste resource utilization such as coal gangue and fly ash,and has broad application prospects.Long distance pipeline transportation is the key link of cemented backfill mining technology.But unreasonable slurry mix proportion,inappropriate transportation flow,mismatched pumping pressure and slurry properties will increase the risk of slurry segregation during pipeline transportation,which may induce sedimentary pipe plugging accidents and then affect the backfill mining efficiency.Since cemented backfill slurry for the coal mine contains coarse aggregate gangue,segregation is prone to occur and then cause blockage in the transportation pipeline.This technology bottleneck restricts the popularization and application of backfill mining technology in coal mines.Consequently,it is significant to monitor the segregation state of slurry in the pipeline and effectively control the transportation flow for preventing pipe plugging accidents and ensuring the smooth operation of backfill mining.In view of the above problems,using the method of device research and development,indoor test,numerical simulation,and theoretical analysis,a resistivity monitoring method for the segregation state of gangue-cemented backfill slurry is proposed and the corresponding device is developed.The resistivity response law to the segregation state of slurry in the pipeline under static and dynamic conditions is studied by this method and device,and a feedback flow control system based on resistivity is constructed.The main research contents and results are as follows:(1)The binary structure model of gangue-cemented backfill slurry is constructed,and the influence law of coarse aggregate content on resistivity of slurry is analyzed.The mechanism of coarse aggregate content determining the tortuosity of ion transport path and ion flow area in slurry is revealed,which is used as the physical basis for monitoring the segregation state of gangue-cemented backfill slurry by resistivity method.The resistivity monitoring device and method of slurry segregation state are developed.The resistivity response characteristics of slurry during segregation are analyzed.It is found that in the monitoring area,when the increasing effect of segregation on resistivity is stronger than the decreasing effect of ion dissolution on resistivity,the resistivity shows an increasing trend,and the decrease of slurry segregation degree shows the decrease of resistivity difference at different heights of slurry in resistivity response characteristics.The segregation index and its change rate are used to quantify the segregation degree and segregation rate of slurry.Combined with the coarse aggregate settlement rate model,the evolution mechanism of segregation rate is analyzed.The feasibility of resistivity method is verified by establishing the corresponding relationship between coarse aggregate distribution and resistivity on resistivity profile and analyzing the internal relationship between slurry bleeding rate and resistivity.(2)A monitoring method of slurry segregation state in pipeline based on horizontal and diametrical resistivity is proposed.The temporal and spatial evolution laws of horizontal and diametrical resistivity of slurry under different segregation states are researched,and the difference characteristics are quantified by segregation index.It is found that segregation increases the decline rate of resistivity between measuring electrodes in the area where coarse aggregate is reduced.The corresponding relationship between horizontal and diametrical resistivity and coarse aggregate distribution is analyzed.It is concluded that the diametrical resistivity monitoring mode can’t identify the difference of static stability between high mass concentration slurry,and the horizontal monitoring mode is more suitable for slurry segregation state monitoring in the pipeline.(3)A backfill loop pipe-dynamic resistivity test system is independently built to realize the resistivity monitoring of slurry segregation state during pipeline transportation.The pumpability of slurry with different mass concentration,the variation law of straight pipe pressure and elbow pressure difference as well as the difference characteristics of resistivity at different flow rates are studied.It is concluded that at low flow rate,the horizontal resistivity stratification characteristics of slurry in the pipeline are obvious,and the segregation degree of slurry and the resistivity difference between layers gradually decrease with the increase of slurry flow rate.Meanwhile,the resistivity fluctuation degree is quantified by using the resistivity standard deviation of different layers,and the variation mechanism of resistivity fluctuation characteristics is clarified.(4)The mathematical model of the exponential function relationship between slurry resistivity and coarse aggregate volume fraction is established.In view of the influence of slurry rheological properties and flow velocity,the Euler two-fluid model is used to simulate the segregation state of slurry in pipeline.The three-layer flow regime of coarse aggregate segregation including coarse aggregate reduction zone,stable flow zone,and coarse aggregate increase zone was obtained,and the effects of slurry rheological properties and flow velocity on the three-layer flow regime were investigated.The results show that: increasing the yield stress,plastic viscosity,and flow rate of slurry can enhance the ability of suspending coarse aggregate and reduce the segregation degree of slurry.The segregation makes the slurry velocity in the pipeline asymmetrically distributed in the vertical direction,and the position of the maximum velocity shifts above the horizontal center line of the pipeline.With the increase of slurry yield stress,the velocity distribution in the vertical direction changes from asymmetric horizontal “arch” distribution to “plunger” distribution,and the velocity distribution characteristics of Bingham fluid gradually became prominent.Slurry segregation changes the value and range of the interaction force between coarse aggregates.The granular pressure presents different distribution forms,and the maximum granular pressure is located at the bottom of the pipeline.Finally,the response characteristics of resistivity in the pipeline under different flow velocities are obtained,and the quantitative relationship between resistivity and flow velocity is established,which is used as the basis for the development of resistivity feedback flow control system.(5)The scheme of feedback flow control system based on resistivity is proposed.The mathematical model of the control system is established,and the steady and dynamic state performance of the system are analyzed.PID correction is implemented for the control system,and the accuracy and rapidity of the corrected system are significantly improved.The on-line self-tuning of PID parameters is realized by fuzzy control technology.The simulation results show that compared with the conventional PID control,the regulation time and maximum overshoot of the feedback flow control system based on resistivity controlled by fuzzy adaptive PID control are reduced by 0.013 s and 22.1% respectively,and the transient performance of the system is significantly improved.Finally,the fuzzy adaptive PID algorithm is adopted as the core control strategy of the feedback flow control system based on resistivity. |
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