Tissue Pre-dewatering Unit for TAD Drying Efficiency
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Solution Overview
Problem
Conventional through-air drying methods for tissue production using TAD drums face inefficiencies due to low air permeability in moist fibrous webs, leading to impingement drying issues, increased energy consumption, and non-uniform moisture profiles, often requiring multiple dryers to achieve sufficient dryness.
Innovation Solution
A pre-dewatering method with a high specific volume flow of fluid (>100 m³/(m²·min) and differential pressure (>0.25 bar) is used to increase the dry content of the fibrous web, allowing through-air drying over the entire TAD drum area, with hot air or steam and a fine-pored felt structure to enhance capillary drainage and water evacuation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional TAD drying is used with low differential pressure (0.05 bar), then the fiber web can be processed gently, but the drying efficiency is low and energy consumption is high
Solution Approach 1:
The drying process is divided into two distinct stages: a pre-dewatering stage using high differential pressure (0.25-0.6 bar) to rapidly remove free water and increase web dryness to 30-40%, followed by a finishing drying stage using conventional low differential pressure (0.05 bar) to achieve final moisture content. This segmentation allows each stage to operate under optimal conditions, significantly improving overall drying efficiency and reducing energy consumption.
Solution Approach 2:
A pre-dewatering unit is installed upstream of the TAD drum to perform preliminary water removal from the fiber web before it enters the main drying drum. This preliminary action increases the initial dryness of the web, enabling flow-through drying to occur across the entire TAD drum surface area, thereby maximizing drying efficiency and eliminating the need for multiple TAD drums in series.
2Quantity of substance
If pre-dewatering presses or press belts are used to increase dry content, then the dryness level improves, but the fiber web quality deteriorates due to compression
Solution Approach 1:
The pre-dewatering unit utilizes pneumatic principles by applying a controlled differential pressure (0.25-0.6 bar) between the hood side and suction roller side to drive water evacuation from the fiber web. This pneumatic approach removes water through capillary action and pressure differential without the mechanical compression forces that would damage fiber structure, thus maintaining web quality while achieving the desired dryness increase to 30-40%.
3Ease of operation
If the fiber web is too moist before TAD drying, then the web remains soft and permeable, but hot air cannot penetrate and only impact drying occurs
Solution Approach 1:
The pre-dewatering unit performs a preliminary action by removing free water from the fiber web before it enters the TAD drum, increasing the dryness to 30-40%. This preliminary dewatering creates the necessary air permeability conditions for hot air to penetrate and flow through the entire web thickness, enabling efficient flow-through drying across the complete TAD drum surface area rather than limited impact drying.
Solution Approach 2:
The invention changes the moisture content parameter of the fiber web from conventional levels (25% dryness) to elevated levels (30-40% dryness) through the pre-dewatering unit. This parameter change fundamentally alters the web's physical properties, specifically its air permeability, enabling hot air penetration and flow-through drying mechanisms to operate effectively across the entire TAD drum surface.
4Quantity of substance
If two TAD drums are arranged in series to achieve sufficient dryness, then the final dryness level is adequate, but the device complexity and energy consumption increase
Solution Approach 1:
The drying system is segmented into a pre-dewatering unit handling the bulk water removal at high differential pressure, followed by a single TAD drum for finishing drying at low differential pressure. This segmentation allows one TAD drum to perform the work that would otherwise require two drums in series, simplifying the overall device configuration while achieving the same final dryness level and reducing energy consumption.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach increases the dry content of the fibrous web to over 30%, improving air permeability and enabling efficient through-air drying with a single TAD drum, reducing energy consumption and enhancing moisture profile uniformity across the machine direction.
Implementation Method 1
a pre-dewatering unit (20) consisting of a hood (17), a felt (5) and a suction roller (16) which is in running contact with the felt (5) in the region of the fiber web (9). The differential pressure in the pre-drainage unit (20) between the hood side and the suction roller side should be set to greater than 0.25 bar
Implementation Method 2
The differential pressure in the pre-drainage unit (20) between the hood side and the suction roller side should be set to greater than 0.25 bar, in particular greater than 0.45 bar, preferably greater than 0.55 bar
Implementation Method 3
It is then dried in the TAD dryer using large quantities of hot air. Air is heated by burners and, with the aid of blowers, forced through the fiber web over the TAD hood and into the TAD drum, causing the water in the fiber web to evaporate
Implementation Method 4
Air is heated by burners and, with the aid of blowers, forced through the fiber web over the TAD hood and into the TAD drum
Implementation Method 5
a very high specific volume flow of the fluid greater than 100 m³/(m²·min) through the fiber web (9), in particular greater than 200 m³/(m²·min), preferably greater than 250 m³/(m²·min)
Data Source
Figure 1
Figure 2
AI summary
The invention relates to a method for producing a fibrous material web (9), particularly for producing a tissue or hygienic paper web, in which a fibrous material suspension is dewatered in a twin wire former (18) to obtain a fibrous material web (9), and said fibrous material web (9) is dried with the aid of a TAD dryer (19). After the twin wire former (18) and before the TAD dryer (19), a pre-dewatering device (20) is provided which comprises a hood (17) and a suction roller (16), a hot fluid flow passing through the fibrous material web (9) that is embedded between one covering (3, 4, 5) on each side. The covering (5) between the suction roller (16) and the fibrous material web (9) is a felt (5), and the covering (3, 4) between the fibrous material web (9) and the hood (17) is a screen (3, 4). In said pre-dewatering device (20), a specific volumetric fluid flow greater than 100 m3/ (m2.min), particularly greater than 200 m3/ (m2.min), and preferably greater than 250m3/ (m2.min) is sucked through the fibrous material web (9).