A research study submitted in partial fulfillment of the requirements for the degree of Doctor of Engineering

Research Studies Project Report (M. Eng.) - Asian Institute of Technology, 2000

Fiber fractionation can be used to enhance or modify pulp and paper properties. The fractionation capacity of laboratory pressure screen, and factors affecting the fractionation result was examined in this study. The fractionation capacity of pressure screens can be examined by evaluating the effects of pressure screen design and operating variables on screen performance. This study was undertaken to determine the characteristics the fractionation capacity of laboratory pressure screen of Valmet TP 031. Fiber and pulp evaluations were used for further characterize the separation efficiency or selectivity of maximum or minimum of slots width of screen basket, concentration of infeed pulp, rejection ratio and rotor speed combination. Sampling and evaluation of the following analyses were conducted on feed, accept and reject samples: stock concentration; Bauer McNett classification, freeness, length-weighted fiber length (LWL), coarseness and length distribution using a Kajaani FS 200 fiber analyzer. The separation efficiencies of fibers and fines were interesting of this investigation. Maximum of long fibers in reject stream, and fines in accept stream were studied respectively in this investigation. For all screens, the fractions differed significantly in fiber and pulp parameters; accept fractions were shorter in fiber length, less coarse and of much lower freeness than corresponding reject fractions. Inter-relationships between capacity, separation and thickening were also examined. Generally, efficient separation and, by association, high thickening, were characterized by low capacity.