Dissolution and precipitation of air into various pulp suspensions and white waters

摘要

The main components in a pulp suspension are water, wood fibres, pigments and chemicals, but air is also dispersed and dissolved into the pulp suspension in various process stages. As air deteriorates paper quality and disturbs the functioning of process units such as pumping, screening and consistency transmitters, it decreases the profitability of paper processes. When aiming to remove air or otherwise reduce the disadvantages deriving from air, good knowledge on the behaviour of air in pulp suspension is required. The goal of the study was to gather information on gas dissolution and precipitation in paper machine waters and stocks. There were clear differences in the maximum amount of dissolvable gases, the solubility potential and in the release of dissolved gases between different circulation waters and headbox stocks. Some of these may even be explained by the differences in the adsorption amount gases. These differences should be taken into consideration when defining mechanical systems in particular, but also chemical degassing systems. In addition, when assessing the measurement results of different dissolved gas content measurement devices based on the expansion method, these differences in release of dissolved gases should to be evaluated.