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

Abstract

Producing tissue paper is an energy-demanding process; a significant amount of energy is expended when removing water by vacuum, mechanical pressing, and thermal drying. Because the water is most energy-demanding to remove in drying, making the preceding step of vacuum dewatering more efficient would benefit the whole process. This article focuses on developing a laboratory-scale method for verifying the nature of diminishing returns of water removal and investigating efficiency strategies of the vacuum dewatering. The theoretical concept of successive vacuum suction boxes with progressing vacuum levels was tested at the laboratory scale in order to show quantifiable results of the previously solely theoretical concept. The results confirmed that vacuum dewatering can be improved by adding progressively higher vacuum levels and that such a practice can benefit both outgoing dryness levels and expended vacuum pump energy. To truly examine the power of progression of vacuum levels, rewetting can be included in the calculations, by using an approximate value collected from pilot or full-scale measurements. For any new fiber mix, pulp type, vacuum level setup, basis weight, etc. the vacuum levels, rewetting, and dwell times need to be tuned to that specific case.

Enhancing Through Air Drying process efficiency: Investigating laboratory-to-pilot scale correspondence and impact of process variables on tissue paper manufacturing

“…The air volumes are directly connected to the pump energy in the vacuum section and thus connected to energy consumption of the process (Sjöstrand 2023). The dewatering behavior for the forming fabric was expected and in line with previous observations of vacuum dewatering and penetrated air volume (Attwood 1962;Neun 1994Neun , 1996Räisänen et al 1996;Ramaswamy 2003;Pujara et al 2008;Sjöstrand et al 2016Sjöstrand et al , 2017Rahman et al 2018;Sjöstrand and Brolinson 2022;Sjöstrand et al 2023;Sjöstrand 2023). According to the laboratory results of solids content development for TAD fabrics (Fig.…”

“…Only one parameter was varied at once, and the bold variations in Table 3, were the default settings. Unbeaten, Beaten TAD fabric design 1, 2, 3, 4, 5 Bold variations were set at the standard parameters and kept constant when the others were varied All variations from Table 3 were subjected to vacuum dewatering and TAD molding in laboratory scale according to the new method developed in a previous article by Sjöstrand et al (2023). All testing were carried out in room temperature of approximately 20 °C and without controlled humidity.…”

“…1) differs from a conventional dry creped tissue (DCT) machine, where the press is replaced by one or two TAD cylinders, and a structured molding TAD fabric receives the sheet by transfer with vacuum boxes. Water is removed before and during TAD molding (Sjöstrand et al 2023) and also by hot air blown through the perforated TAD cylinders. The tissue sheet's structure and bulk are primarily attributed to the structured TAD fabric.…”

“…There is a noticeable speed difference between the forming section and TAD section, which significantly influences sheet properties compared to DCT by providing an effect related to creping. Although the lack of wet pressing in the TAD method makes it less energy efficient than DCT, TAD yields higher performing products compared to DCT (Tysén 2018;Sjöstrand et al 2023).…”

“…Previously, a laboratory method for measuring the initial vacuum dewatering on the forming fabric, as well as the dewatering during TAD molding was developed (Sjöstrand et al 2023). The developed method were used in this work to investigate the influence of different TAD fabric designs, sheet basis weights, pulp beating level, and fiber mixtures, on the dewatering and energy efficiency during vacuum dewatering and TAD molding.…”