Study On The Process Of Aspen Bleached Extruder Chemi-Mechanical Pulping

As a new method of high yield pulping, BECMP (Bleached Extruder Chemi-Mechanical Pulping) has such characteristics, good pulp quality, low consumption of energy and pollution, short sequence, and the relevant equipment has already been commercialized in China.Based on the BECMP production line, this article analyzed the material quality and discussed the characteristics of chemical composition and fiber configuration of the materials takeing from each working procedure. For better understanding of the new pulping method, the properties of the BECMP pulp were assessed synthetically.The results showed that the fiber maturity of BECMP raw materials was lower, and the chips acceptability could not meet the industry requirement in the range of this study. The extract contents of BECMP raw materials were higher, and the average length and the length-width ratio of fibers were shorter and lower.During BECMP pulping process, the pulping yield decreased gradually and the final yeild was 79.89%. The extract of 1%NaOH and alcohol-benzene, acid-insoluble lignin and holocellulose were all dissolved partially. The dissolved rates were 23.70%,75.28%,5.50% and 22.84% respectively. The second stage of extruded pulping and bleaching all have obvious effect on the chemical composition of cellulose. The processes that had an obvious relation to chemical composition were impregnated reaction, the second stage of extruded pulping and bleached reaction.In this article, the changes of fiber configuration during the whole process of BECMP were recorded as viewed from both microcosmic and macrocosmic aspects. The results implied that the fibers were gradually defibered mainly by mechanical grinding and extruding. The chemical process could also lead to defibering fiber bundles in small size through reducing the fiber stiffness. Shortening of the fibres causing by the twin screw extruder were less, compared with other pulping methods. Comparations among the scanning electron microscopy (SEM) observation of feedstock from different stage showed that the screwing process could result in changes of fiber configuration, such as fiber curvature, folding, bursting and fibrillation.The properties of the pulp were analyzed in this thesis. The properties of the pulp are capable of reaching the industrial requirements, and simultaneously, its tensile strength is better than that of the APMP pulp.