Method for studying water removal and air penetration during through air drying of tissue in laboratory scale

Abstract

Energy use, together with consumption of raw materials, machine clothing, and wet end chemicals, are some of the most critical aspects in successful tissue making today. This work was aimed at developing a laboratory-scale method of estimating dewatering mechanisms, vacuum efficiency, and energy use of Through Air Drying (TAD) of tissue. When compared to pilot data, the results of the new laboratory method for investigating dewatering during TAD were in the same magnitude, around 24 to 26% dryness after vacuum dewatering, and 27 to 29% dryness after TAD molding. Sheet properties, such as caliper and surface profile, were evaluated and compared to commercial tissue sheets. The results indicate that it will be possible to precisely measure accurate dryness development and penetrated air volume for tissue sheet forming and TAD molding at a laboratory scale. This can contribute to the efforts of implementing a circular forest-based bioeconomy by increasing the fundamental understanding of dewatering of tissue paper materials, which is facilitated by improvements in energy use. The new method developed in this work will make it easier to assess ideas that are difficult to bring to pilot scale or full scale before learning more of the dewatering capabilities. The authors are convinced that improved knowledge of tissue dewatering mechanisms, forming, and material transport during and after TAD dewatering can increase the efficiency of the industrial manufacturing processes.

Progression of vacuum level in successive vacuum suction boxes in a paper machine – Impact on dewatering efficiency and energy demand – A laboratory study

“…Both single and triple vacuum box dewatering results showed a similar shape of the curve as the theoretical appearance from Fig. 1 and from the literature (Attwood 1962;Neun 1994Neun , 1996Räisänen et al 1996;Baldwin 1997;Räisänen 2000;Ramaswamy 2003;Granevald et al 2004;Pujara et al 2008, Åslund andSjöstrand et al 2016Sjöstrand et al , 2017Sjöstrand et al , 2019Rahman et al 2018;Sjöstrand and Brolinson 2022;Sjöstrand et al 2023). Thus, the laboratory method was judged to be successful in simulating triple vacuum box dewatering, both when adding the correction for rewetting and when the measurements are used directly.…”

“…Figure 1 (A) shows the already described behavior of diminishing returns during vacuum dewatering, reported by numerous publications (Attwood 1962;Neun 1994Neun , 1996Räisänen et al 1996;Baldwin 1997;Räisänen 2000;Ramaswamy 2003;Granevald et al 2004;Pujara et al 2008, Åslund andSjöstrand et al 2016Sjöstrand et al , 2017Sjöstrand et al , 2019Rahman et al 2018;Sjöstrand and Brolinson 2022;Sjöstrand et al 2023). In this set of graphs, the blue dashed line represents the dryness development with vacuum dwell time and the red solid line is the energy expended by the vacuum pumps.…”

“…This is of course also true within each unit operation (Sjöstrand 2020). Vacuum dewatering diminishing returns have been shown in multiple previous publications (Attwood 1962;Neun 1994Neun , 1996Räisänen et al 1996;Baldwin 1997;Räisänen 2000;Ramaswamy 2003;Granevald et al 2004;Pujara et al 2008, Åslund andSjöstrand et al 2016Sjöstrand et al , 2017Sjöstrand et al , 2019Rahman et al 2018;Sjöstrand and Brolinson 2022;Sjöstrand et al 2023). One of the earliest arguments for progressively increasing vacuum levels based on the dewatering mechanism behind the diminishing returns in vacuum dewatering was discussed by Baldwin (1997).…”

“…The logged pressure drops were used to calculate the air volume that passed through the sheet using Eq. 1 (Granevald et al 2004;Sjöstrand et al 2016;Sjöstrand et al 2023),…”

“…In these manufacturing methods, understanding water removal and drying becomes increasingly more important when working towards a sustainable future where all products are required to have efficient and environmentally friendly manufacturing processes. This work focuses on vacuum dewatering of tissue, where there is potential for saving energy (Håkansson 2010;Lahtinen and Karvinen 2010;Holmberg et al 2013;Sjöstrand 2020;Sjöstrand et al 2023).…”