Influence Of Drag-reducing Additive On Yield Stress Of Waste Pulp Fiber Suspension And Its Application In Paper Industry

As the important basic raw material industry,the eternal theme of paper industry is energy conservation,emission reduction,cost reduction and efficiency improvement.As the raw material with the highest resource utilization rate,waste paper pulp currently accounts for more than 62%of China's paper industry.The research on the rheological properties of pulp(especially the yield stress)has important influence on the energy consumption of pulp fiber suspensions in various sections of transportation and process(such as beating,screening,mixing,conveying,forming,etc.).In this paper,the main factors of the yield stress of waste pulp fiber suspension are discussed,including fiber type and morphology,slurry concentration change and measurement method.Two kinds of drag-reducing additive(CMC and APAM)used in papermaking were added to analyze and compare their effects on the rheological properties of the pulp.Through the application of yield stress in papermaking industry,the influence of the addition of drag-reducing additive on the energy loss in pipeline transportation,slurry mixing and stirring is analyzed.After research,the main conclusions obtained in this paper are as follows:(1)By measuring the yield stress of 1.5%~4.0%pulp concentrate ONP pulp and OCC pulp fiber suspension,the relationship?_y=aC_m~b is verified.The yield stress increases nonlinearly with the increase of slurry mass concentration.Both methods of measuring the yield stress prove that the yield stress of ONP fiber suspension is greater than that of OCC fiber suspension,and the difference of yield stress increases gradually between 2.7~17.2 Pa.(2)For the same mass concentration of slurry,the yield stress measured by shear stress gradient method is higher than that by rheological curve regression method.For the same kind of slurry,the yield stress of the American OCC fiber suspension is much larger than that of the domestic OCC,mainly because the yield stress increases as the fiber length and aspect ratio increase.(3)The CMC solution was continuously added to the OCC with a pulp concentration of0.5%to 4.0%(based on the mass of the dry pulp),and the yield stress value firstly decreased and then increased.When the pulp concentration was 3.5%and the CMC addition amount was 0.5%,the yield stress reduced from 122.651 Pa to 109.882 Pa,and the reduction effect was the most pronounced at 10.4%.(4)Similarly,the APAM solution was continuously added to the OCC(based on the mass of the dry pulp),and the yield stress value was slowly decreased first and then increased.When the pulp concentration was 3.5%and the APAM addition amount was 0.4%,the yield stress reduced from 135.223 Pa to 120.805Pa,and the reduction effect was the most pronounced at 10.7%.When APAM was added to the same slurry-concentrated OCC,the solution with high molecular weight(10 million)had better effect on the reduction of yield stress of the slurry than the solution with low molecular weight(3 million).(5)For the addition of drag-reducing additive solutions in the waste pulp fiber suspension,adding less APAM solution can achieve better effect of reducing the yield stress than CMC solution.(6)In the process of slurry transportation in pipelines,when 0.4%APAM solution is added,loss of pressure head in the pipeline can be reduced by 10.7%,the critical flow velocity of the slurry required for drag reduction can be reduced by 6.54%,and the energy dissipation factor can be reduced by 20.2%.The stirring power of rotor can be reduced by about 10%during pulp mixing.Through adding the drag-reducing additive to the slurry to reduce the yield stress of the waste pulp,it can provide guiding significance for industrial energy saving,emission reduction,process improvement and application of various sections of papermaking.