Overview of Mechanical Pulps

Abstract

Mechanical pulps have higher yields than chemical pulps. With refiner pulps (RMP, TMP. CTMP) in particular, the choice of wood species and process parameters (temperature, pressure, and chemicals) means that a wide range of pulp properties can be covered and, thus, custom-tailored pulps produced.During the past five years. development in refining technology has focused on the reduction of specific energy consumption (SEC) in the production of low freeness TMP for communication papers. The RTS process reduces SEC by virtue of the increasing refining intensity afforded by operating the primary refiner at high speeds. Pulp strength properties are maintained by pre-heating the chips to elevated temperatures for 10-18 seconds immediately prior to refining and again in a similar manner immediately prior to impregnation. The RTS process has been installed at two mills. The Thermopulp process reduces energy consumption at the secondary refiner by heating the chips at 160-165°C for 5-10 seconds between the first two refining stages. This process has been installed in seven newsprint mills.BCTMP is defined here as high yield (greater than 85%) pulp produced by impregnating chips with a mild application of chemicals, refining the chips to produce pulp and bleaching the pulp to approximately 80% ISO for softwood grades and 85% ISO for hardwood grades. The growth of hardwood BCTMP grades is primarily due to its application in printing and writing grades, especially in Europe and Asia.