Research On Understanding Fractionation And Low Consistency Refining Of Old Corrugated Container Pulp

The proportion of waste paper pulp in papermaking pulp has been increasing year by year due to the strengthening of forest resource protection and fibre recycling awareness.However,due to the problems of unstable sources of waste paper,increased using and recycling times,and different storage periods,the fiber length distribution of waste pulp is very uneven.At present,there is still no systematic experimental research on the performance of waste pulp pulping.Therefore,optimizing the waste pulp production process is an urgent problem to be solved.Fractionation and refining are the two key stages of waste paper pulping,and the flow of waste pulp fiber suspension in the fractionation and refining system is a complex process.Its efficient treatment is related to pulp flow,pressure,pulp consistency,cylinder structure,rotor type,refining plate and so on.Mastering their influence on fractionation and refining efficiency is the goal of this article.Therefore,the research of understanding waste pulp fractionation and refining is of great practical significance,both from the basic theoretical research level and the guidance of practical application research.Based on the technical problems existing in the actual waste pulp pulping production line,this paper analyzed the research progress of equipment,process control and mechanism of pulp fractionation and refining.Firstly,the impact factors of pulp fractionation and refining performance were reviewed,and the preparation method of microfibrillated cellulose?MFC?and its application in papermaking industry were discribed;Secondly,pilot trials investigated the effects of cylinder type,the size of the slots,volumetric reject ratio,R_v,and aperture velocity,V_s,on the fractionation performance of American old corrugated container?AOCC?pulp;In addition,trials were performed on AOCC pulp fiber properties,pulp suspension characteristics,refining energy consumption,and properties of produced handsheets under different refining plate geometries and refining intensity;Then,on the basis of summarizing the previous research experience of preparing MFC,AOCC pulp wasused as raw material,without any chemical addition and chemical pretreatment,using pilot-scale refining equipment to prepare MFC at different refining energy consumpation;Finally,compared with the actual production of waste pulp pulping,combining the fractionation of AOCC pulp,low consistency refining and the addition of MFC under the energy consumption evaluation model,and analyzed the mechanism of adding MFC to enhance the properties of produced handsheets,and finally a new and more optimized and more reasonable process design of waste paper pulping technology was proposed.Main conclusions of this research are identified as followed:?1?For the AOCC pulp fibre suspension,under the same volumetric reject ratio,R_v,and aperture velocity,V_s,the fibre passage ratio,P,of holed and slotted cylinders were different.When fractionation at R_v of 0.15 and V_s in 0.5?1.0 m/s,the passage ratio,P,of 0.20 mm,0.15mm slot cylinder and 0.81 mm hole cylinder were 0.90,0.60 and 0.35,respectively.That is,the passage ratio,P,of 0.81 mm hole cylinder was 61.11%and 41.67%smaller than 0.20 mm and0.15 mm slot cylinder.It showed that comparing with 0.15 mm and 0.20 mm slot cylinder,the0.81 mm hole screen cylinder was more conductive to the fractionation of long fibres,and achieved the best fractionation performance for AOCC pulp.?2?During fractionation with both hole and slot cylinders,the fibre passage ratio,P,decreased with the decrease of aperture velocity,V_s,volumetric reject ratio,R_v,and contour height,h;Moreover,under the interaction of V_s and R_v,V_s had the most significant impact on the fibre passage ratio of AOCC pulp;the lower fiber passage ratio,P?better fractionation performance?could be achieved by a combination of a lower volumetric reject ratio,R_v,and aperture velocity,V_s.?3?The freeness of the long fiber fraction?rejects?and short fiber fraction?accepts?was more significantly affected by the aperture velocity,V_s.Among them,the freeness of the short fiber fraction,F_a,increased with the increase of the aperture velocity,V_s,and volumetric reject ratio,R_v,while the freeness of the long fiber fraction,F_r,showed decreasing trends with the increasing aperture velocity,V_s,and volumetric reject ratio,R_v.?4?Within a certain range of refining energy consumption,during low consistency refining with both interim 2.01 km/rev BEL and wide 0.99 km/rev BEL plates,with increasing the SRE,the fibre length,curl index,kink index,and freeness values of the AOCC pulp decreased,while fines content and tensile strength of the produced handsheets increased.Under the same SRE,refining with 2.01 km/rev BEL plate generally resulted in higher fibre length,curl index,freeness,and tensile strength of AOCC pulp than the refining with 0.99 km/rev BEL plate.When using2.01 km/rev BEL plate to LC refining AOCC pulp,fibre length and tensile strength of the produced handsheets increased by 4.08%and 4.95%;Moreover,to achieve the given tensile strength,less refining energy was required for the interim 2.01 km/rev BEL plate?saving about20.02%?.?5?Under low consistency refining conditions,the AOCC pulp paper tensile index increased nonlinearly with the increase of total specific refining energy,the tensile index,Tindex,and sum SRE,Es,satisfied the functional relationshipT_{ind ex}=aE_s ²+bE_s+c.Due to the complexity and change of the AOCC pulp refining process,in the actual industrial production process,regression equationT_index=-2.8611?10^-4E_s²+0.1865E_s+40.6662could be used directly in predicting the tensile strength of AOCC pulp.The model could provide a theoretical reference for the relevant technical papermakers of waste paper pulping to adjust the refining parameters.?6?Within the range of 0?150 kWh/t specific energy consumption of refining,for the AOCC pulp without fractionation and directly low consistency refining,the tensile strength,ring crush strength,tear strength,and burst strength could be increased by about 13.11%,9.63%,18.45%and 21.07%,respectively for firstly fractionation and then long-fiber refining.?7?By using a combination of coarse and fine refining plates to low consistency refining of the waste pulp fiber suspension,MFC could be prepared in batches purely mechanically.First using a coarser plates to fully dissolve AOCC pulp fibers and partially fine-fibrillate?2.01 km/rev BEL plate was used in this study?,and then using a narrower refining plate?12.90 km/rev BEL plate was used in this study?to make individual fibers stripped and lysed to form fine filaments.?8?A modified process to produce high performance of paper strength and energy savings in AOCC papermaking process was proposed.The optimization procedure made it possible to produce higher tensile,burst and ring crush strength of produced handsheets under the same refining energy from AOCC pulp.Compared with the hansheet of primary unscreened AOCC,the hansheet of screened OCC-MFC-blend?at 1340 SRE?at the same refining energy had on average 28%higher tensile strength.When making handsheets with a tensile index of 50 Nm/g,the sum SRE for direct low consistency refining of AOCC pulp was 87.71 kWh/t,and the total SRE for the novel process was only 18.00 kWh/t,which would yield refining energy savings of80%.This research theoretically and experimentally solved some technical problems in the actual waste paper pulp production process.The proposed novel process for waste paper pulping could effectively reduce the consumption of resources and improve economic benefits,and at the same time,could provide a theoretical basis for the high-efficient,energy-saving and consumption-reducing process of waste paper pulping and papermaking.It is a perfect new process technology that can be transformed into productivity,and has certain engineering application value.