Influence Of The Addition Of CMC On The Yield Stress Of NBKP Fiber Suspension And Its Application In Pulp Transporting And Mixing

Papermaking is a major industry to manufacture products vital to education,communication,and packaging.Most operations in this industry deal with the flow of different mass concentrations of pulp suspensions.Therefore,the flow properties(rheology)of pulp suspensions are of great importance for the optimal functionality of most unit operations in the industry.Yield stress is one of the most important rheological properties in designing process equipment At present,there are few domestic studies on the rheological properties of pulp fiber suspensions,especially the yield stress,and there is no study on the effect of papermaking chemicals on the yield stress of pulp suspension.Based on the discussion of pulp fluid dynamics and the rheological properties of additive CMC,this paper proposes the idea of adding CMC to the pulp suspension to improve the rheological properties,especially the yield stress of the pulp.The experimental results show that the appropriate CMC addition,and the effect of CMC on the pulp energy consumption and transport fluidization was studied.The influence of CMC on the screening of pulp was studied by screening simulation experiment.The main results of this study are as follows:(1)Using the shear stress gradient method to measure the yield stress of the bleached softwood pulp suspension with 0.5% ~ 4.0% concentration,the yield stress increases nonlinearly with the increase of the pulp concentration,and the CMC is satisfied Index equation t_y=aC_m~b ,where a is about 2.5 to 3.8,b is about 2.6 to 2.9.(2)The addition of CMC in the bleached softwood pulp suspension reduced the yield stress yt of the pulp.In the experimental design,the pulp concentrations were 0.5%,1.0%,1.5%,2.0%,2.5%,3.0%,3.5% % and CMC additions(relative to absolute dry mass)were 0%,0.5%,1.0%,1.5% and 2.0%,respectively.When the addition of CMC was 1.5%,the effect was most significant and with the increase of pulp concentration,CMC's influence is more and more obvious.The addition of 1.5% CMC to the pulp suspension with a 4% concentration could reduce the yield stress by about 16.19%.(3)Adding CMC can reduce the yield stress of the pulp suspension,which can significantly reduce its agitating energy consumption.When the pulp suspension concentration is 4% and the CMC addition amount is 1.5%,the yield stress is reduced by 16.19%,and the corresponding stirring power of about 500 rpm is reduced by 40.58%.(4)The effect of the CMC on the initial fluidization of the pulp can be quantitatively described by the amount of energy consumed per unit volume ~?F of pulp.The influence of the CMC on the ~?F is consistent with the yield stress.Adding 1.5% CMC in the pulp,the energy consumption per unit volume of pulp reduced the most,with the greater the pulp concentration,the effect is more significant.The addition of 1.5% CMC to the caustic pulp suspension with a 4% concentration of pulp resulted in a reduction in energy consumed per unit volume of pulp by about 29.76%.(5)Pulp screening simulation experiments showed that the addition of CMC had no obvious effect on the screening efficiency of the low concentration pulp.For the high concentration of pulp,the screening efficiency was obviously decreased after adding CMC,and the rotation speed was 300 r / min,500 r / min and 700 r / min,the accept rate of the pulp adding CMC was corresponding increased by 9.26%,15.45% and 9.08% compared with that pulp without adding CMC.(6)During the screening process of high concentration pulp,the addition of CMC effectively promoted the separation of fiber and impurities in pulp.When the pulp concentration was 4%,the addition of CMC could reduce the fiber rate in the slurry,and the rotor speed was 300 r / min,500 r / min and 700 r / min,the fiber rate in rejects decreased by 18.34%,19.93% and 10.58%,respectively.By adding chemicals to the pulp to change the rheological properties and characteristic parameters of the pulp fiber suspension,it can provide a reference for the study of yield stress of t pulp fibre suspension,and a new thinking for the process optimization and energy saving and emission reduction in the paper industry.