Disperser Bleaching with Hydrogen Peroxide ― A tool for brightening Recycled Fibres

摘要

Given the increasing use of recycled fibres in a wide variety of paper applications, emphasis is continually being put on the production of cleaner and brighter deinked pulps. Due to the poorer quality of some currently available grades of waste paper, this objective is now more and more difficult to achieve. This has contributed to the development of more sophisticated technologies to meet the higher quality requirements. To reduce the size of remaining visible ink specks after deinking, a hot dispersion system is normally installed. While it gives the paper a more uniform appearance, the ink dispersion has a negative impact on the overall brightness. This brightness loss can be avoided by converting the dispersion system to serve the additional role of a hydrogen peroxide bleaching device. The high consistency and high temperature that are normally operated in the dispersion unit are ideally suited for hydrogen peroxide bleaching. The different parameters that could influence disperser bleaching with hydrogen peroxide have been studied and are described in this paper. Many mills are now installing post-flotation units to improve the overall cleanliness of the deinked fibre. The addition of chemicals to the disperser to improve the brightness has also been shown to have a beneficial effect on post-flotation deinking efficiency. Typical hydrogen peroxide disperser bleaching applications are outlined for a number of different waste paper furnishes including newspapers, magazines and office waste. Optimisation of a number of particular industrial applications are described. In all disperser bleaching cases reported, mill expectations of improved brightness and cleanliness are achieved with moderate additions of hydrogen peroxide.