Air Bar Arrangement for Tissue Drying on Air-Permeable Belt
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Solution Overview
Problem
Conventional paper and tissue web drying methods face limitations in achieving high drying rates due to the mechanical constraints of cast iron drums, which block mass transfer on one side, and air flotation systems that are not suitable for supporting tissue webs at high speeds, leading to web instability and breaks.
Innovation Solution
An air flotation dryer system with specially arranged air bars and impingement nozzles that alternately force the web onto and lift it from an air-permeable belt, allowing high-velocity hot air to dry the web efficiently while maintaining stability and reducing energy consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional cast iron dryer cans are used for drying, then heat conduction to the web is achieved, but mass transfer is blocked on the drum surface side
Solution Approach 1:
The patent replaces the mechanical contact drying system (cast iron drums) with a pneumatic system (air bars). Instead of using a solid drum surface that blocks mass transfer, the invention uses jets of hot air to provide both heat and mass transfer to both sides of the web simultaneously, eliminating the blockage problem while maintaining effective drying.
Solution Approach 2:
The invention transitions from surface contact drying (two-dimensional contact with drum surface) to volumetric air drying (three-dimensional hot air flow around and through the web). This allows hot air to access both sides of the web simultaneously, providing mass transfer on both surfaces without the limitation of drum contact.
2Productivity
If air bar arrangements operate at high air velocities (above 4000 fpm) to achieve sufficient drying rates, then heat and mass transfer is improved, but web handling becomes unstable causing billowing and lateral bunching
Solution Approach 1:
The patent applies different air velocities to different locations of the web. The air bars are positioned and configured to provide higher velocities at the edges and lower velocities in the center, or vice versa depending on web tension requirements. This localized control of air flow characteristics maintains web stability while achieving sufficient drying rates across the entire web surface.
Solution Approach 2:
The invention uses adjustable and controllable air bar systems that can dynamically adapt air velocity and distribution based on web conditions. The air bars can be independently controlled to provide varying air flows across different sections of the web, allowing the system to maintain stability during transitions and prevent billowing while achieving high drying rates when needed.
3Productivity
If air velocities are increased to 10,000 fpm or higher for economical production rates, then drying efficiency is improved, but web breaks occur due to excessive web movement
Solution Approach 1:
The patent changes the physical parameters of the air delivery system, including air bar geometry, slot size and orientation, and air pressure distribution. These parameter changes allow the system to deliver high-velocity air (10,000+ fpm) in a controlled manner that provides sufficient drying force without causing excessive web movement or breaks. The air bars are designed to distribute air in a pattern that maintains web tension and stability.
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
The system achieves faster drying rates, reduces web breaks, and lowers energy and capital costs, while maintaining web flatness and stability, enabling higher machine efficiency and self-threading capabilities.
Implementation Method 1
a type of impingement dryer which supports the web using flotation nozzles or 'air bars'
Implementation Method 2
remove water by evaporation following initial dewatering steps
Implementation Method 3
Heat and mass transfer may be brought to both sides of the web by a type of impingement dryer
Implementation Method 4
The air bar array is typically inside a dryer housing which can be maintained at a slightly sub-atmospheric pressure by an exhaust blower that draws off the moisture or other volatiles emanating from the web
Data Source
AI summary
Apparatus and methods particularly suited for drying tissue grade paper. In certain embodiments, a wet web, such as a web exiting a tissue manufacturing machine, is transferred to an air floatation dryer with specially arranged air bars and impingement nozzles described herein where the wet web is dried while still at least partly supported by an air-permeable belt. In certain embodiments, the specially arranged air floatation dryer comprises one or more air floatation dryer units through which the wet web is conveyed by way of a supporting endless loop or belt of air-permeable construction. The air bars and opposing impingement nozzles are so arranged as to force the web into contact with the belt and then subsequently lift the web from the belt surface in a repetitive and alternating fashion as the web and belt travel through the dryer.