| Hemihydrate phosphogypsum(HPG)is an industrial solid waste during phosphate rock processing.The paste filling material prepared with modified HPG as cementitious material has prominent advantages of quick-setting,early-strength,green and low cost.However,in practice,it was found that the fluidity of the HPG-based(HPGB)paste has an obvious time effect,which was manifested as the gradual deterioration of the fluidity of the paste with the prolongation of delivery time or pump shutdown time.As a result,there is a huge risk that the HPGB paste blocks the transport pipeline under transport or pump shutdown conditions.In order to solve the undesirable problems of easy pipeline blockage,difficult blockage prediction and unclear anti-blocking measures,considering the two working conditions of transport and pump shutdown,experimental research and theoretical analysis are carried out from four aspects:time effect of rheological behavior and its influencing factors,time effect of pipeline resistance and drag reduction measures.The main work is as follows:(1)Shearing and resting rheological experiments were carried out respectively to study the time dependence of rheological parameters of HPGB paste under transport and pump shutdown conditions.The time-varying model of rheological parameters of HPGB paste under two working conditions-LinExp model was proposed,and the influence of initial consistency,initial setting time and settlementation rate on the time dependence of rheological parameters was quantified by regression analysis.(2)The three interval thixotropic experiments were carried out.On the one hand,the anti-thixotropy phenomenon of HPGB paste was found and its influencing factors were analyzed.On the other hand,the structural resting recovery model of HPGB paste-S-E model was established to realize the accurate description of the structural resting recovery law and the prediction of the static yield stress of HPGB paste with the maximum failure structure at different resting times.In addition,the influencing factors of different structural resting recovery stages were determined.(3)Firstly,the hydration of HPGB paste was studied,and then the microstructural parameters such as particle spacing and paste porosity were obtained by using FBRM and ESEM techniques.Further,based on the correlation law of hydration,interparticle interaction and rheological parameters,the timevarying mechanisms of rheological parameters of HPGB paste under transport and pump shutdown conditions were revealed.(4)By coupling LinExp model,S-E model,stress attenuation function and state parameter evolution function of pipeline segment with the traditional pipeline resistance model,the time-varying model of pipeline transportation resistance under transport condition and the time-varying model of start-up resistance under pump shutdown condition were derived,and the validity of the two models was verified by engineering cases.(5)The COMSOL software was used to realize the numerical simulation of the pipeline resistance characteristics of the HPGB paste under the long-distance transportation condition.The evolution law of the velocity distribution and the pressure distribution of the HPGB paste with the transport time was studied,and the influence of the paste setting speed on them was analyzed.In addition,the transport time range prone to pipeline blockage was determine.(6)Based on the time-varying model of flow resistance in pipeline of HPGB paste under two working conditions,the problem that it was difficult to determine key parameters such as the farthest pumping distance and the longest pump shutdown time in the design of long-distance pipeline transportation of HPGB paste of a phosphate mine was solved,and an economic and efficient measure to reduce the flow resistance in pipeline of HPGB paste was proposed. |
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