Investigation of pulp dewatering – relating freeness to filtration properties
For Sweden the forest sector is of great importance and contributes significantly to the Swedish export. One of the most important products is pulp, which can be used for production of packing material, printing paper and tissue paper. Pulp is also produced in several other countries (e.g. Finland, Canada and Brazil) and the world production is around 180 million tons during 2010. There are several different methods used for pulp production, both mechanical and chemical methods can be used. Among the chemical methods the kraft process is the most common. One important product based on pulp is paper. Paper is formed by dewatering a mix of pulp and additives, to achieve a proper formation the starting pulp needs to be severely diluted, consistency as low as 0.1 % is required to form a paper of a good and even quality. The formation of the paper takes place on a wire section, where large amounts of water are removed by filtration. Further dewatering is then performed in the pressing section and finally the paper is dried. In the industry the dewatering properties of the pulp are measured using simple equipment measuring the freeness of the pulp, normally no filtration properties are measured. The goal for this study has been to investigate pulp dewatering behaviour and relate freeness measurements to measured filtration properties. The fibres used in this study are produced in a kraft process based on softwood material To investigate how the filtration properties change with the dewatering rate, the pulp was treated in a PFI-mill to change the structure on the pulp and thus the dewatering rate. The dewaterbility was measured using two industrial methods Canadian standard freeness (CSF) and Schopper-Riegler (SR). The filtration resistance of the pulp was also measured at 1 bar filtration pressure. A model for CSF from the literature was used to compare a theoretical relation between freeness values and specific filtration resistance and the relation found from the filtration experiments in this study. The range of the freeness value of the processed pulp was from 695 ml to 125 ml for CSF, which corresponds to a specific filtration resistance of 9×10 9 m/kg to 7.7×10 12 m/kg at 1 bar filtration pressure. The model for CSF indicated lower filtration resistances than the ones measured in the experiments. An important explanation for this is the difference in filtration pressure and with the following difference in compression of the filter cake. Table of
Quality Developments in Pulp Fibers using Conventional Papermaking Laboratory Beaters and an Industrial Pilot Refiner
The research focused on the examination of quality developments of bleached kraft softwood pulp in the papermaking process. The pulp was mechanically treated using conventional papermaking laboratory beaters and an industrial pilot refiner. The conventional laboratory devices studied were a PFI mill and a Valley beater, while a Voith LR 40 industrial pilot refiner was used to represent a mill refiner. The results showed that the pulp fibers developed in different directions depending on the testing devices. The pulp samples treated using the laboratory equipment were found to contain a higher ratio of long fibers, a higher coarseness and a greater internal change of fiber structure, while the pulp samples refined using the industrial pilot refiner consisted of a shorter fiber, a lower level of internal structural changes in the fiber walls and a higher content of fines. The paper made from the pulp manipulated using the laboratory equipment had a superior strength, while the paper made from the pulp treated using the industrial pilot refiner had a poorer strength and a lower density, but had a higher light scattering value. The results of this study indicated that laboratory pulp cannot be used directly to examine fiber actions under industrial operations. Further research should study pulp characteristics and their effects on the papermaking process with regard to the correlation between laboratory work and industrial
Evolution of carbide precipitates in Hastelloy N joints during welding and post weld heat treatment
Abstract The effects of welding and post weld heat treatment (PWHT) on the morphology, composition and lattice parameter of the precipitates in the welding joints of Hastelloy N alloy have been investigated. Joint samples were prepared using a gas tungsten arc welding process with ERNiMo-2 fillers, and then solid-solution treated at 1100 °C for 20 min. After welding, eutectic M6C carbides can be observed in the heat affected zones (HAZ) and weld zones (WZ). These eutectic M6C carbides become spheroidized during the following PWHT. The concentration of Si decreases during the transformation from the primary ones to eutectic ones, and then increases during the spheroidizing process. The total concentration of Si + Cr in M6C carbides remains stable during welding and PWHT. At the same time, the heat leads to the outward diffusion of Mo from the M6C carbides, which results in a decrease of the lattice parameter.