Jani Lehmonen: Foam-laid forming technology for fiber webs

Abstract:

The forest industry is in the midst of a structural change. The goal is to renew the paper and board industry to produce higher value-added products for future markets. The launch of new wood fiber-based products also requires novel production technologies to achieve the goals of renewal.

Current fiber web production technologies are based on water as a flowing medium and a carrier phase of raw materials. In these water-laid processes, a huge amount of water is used and recirculated, and reducing the total amount of water is challenging. Processes are also typically energy intensive. A foam-based process makes it possible to reduce the amount of water as it replaces about two-thirds of the flowing medium with air. In addition, it allows the broad utilization of raw materials in terms of length and density since foam as a flowing medium is more viscous than water, thus leading to a homogeneous distribution of materials, even though the nature and properties of the used raw materials vary considerably. From this perspective, the focus of this dissertation was to investigate the role of flowing medium in the production of wood-fiber containing sheets using an academic approach and applying novel research environments.

The studies were performed on the laboratory, semi-pilot and pilot scale. The fundamental research was done on the laboratory scale, where water- and foam-formed sheets were produced using a dynamic vacuum-assisted sheet former simulating the dynamic initial dewatering phase of the forming section. The water-laid semi-pilot-scale process, formerly used for the water process, was modified to foam. The potential of foam-laid technology was investigated by examining the effects of essential process and product parameters. Despite the fact that foams are much more viscous than water, the results showed that the dewatering times were approximately the same in water and foam processes at higher vacuum levels, while at the lowest vacuum level the dewatering time for foam was about 50% higher.

From the perspective of dewatering, process efficiency and the functionality of water vs. foam processes and sheets, an increase in the solids content of the foam-formed sheets after the forming section was observed on the laboratory, semi, and pilot scales when a foam density level of ∼ 400 kg/m3 was applied. In addition, the effect of a wet pressing load on the sheet density decreased as a function of the foam density, especially at the highest wet pressing loads. The sheets formed by water and foam were identical in density at the highest wet pressing load and a foam density level of 400 kg/m3. It must be highlighted that a production machine converted to use foam technology can still be run in water mode. This aspect opens up new possibilities for conventional smaller-scale production capacity machines, which in principle are more suitable for converting into foam operating machines.

Opponent: Professor Mark Martinez, University of British Columbia, Canada

Supervisor: Professor Jouni Paltakari, Aalto University, School of Chemical Engineering, Department of Bioproducts and Biosystems

Link to electronic thesis: Foam-laid forming technology for fiber webs