Displacement Dewatering Paper Web Using Compressed Gas
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Solution Overview
Problem
The papermaking industry faces limitations in efficiently removing water from nascent paper webs before the dryer section, leading to high energy demands and reduced paper bulk and absorbency, due to the limitations of mechanical pressing and suction methods.
Innovation Solution
A method and apparatus that combine mechanical pressure with compressed air to remove water from the paper web, using a web sandwich structure with carrier fabrics that inhibit water rewet, allowing for independent control of mechanical and air pressure to achieve higher solids content and bulk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If mechanical pressing is used to remove water from the web, then water is removed by hydraulic pressure gradients, but the web thickness is reduced and the web rebounds with rewet upon exiting the press section
Solution Approach 1:
The dewatering process is segmented into two independent stages: mechanical pressing followed by air displacement. This segmentation allows each method to operate at its optimal capability without the limitations of the other, particularly preventing rewet by maintaining positive air pressure during the transition phase
Solution Approach 2:
The invention transitions from purely hydraulic pressure (mechanical pressing) to pneumatic pressure (compressed air) for the second stage of dewatering. This pneumatic approach removes water without the rebound effect that plagues mechanical pressing, as air can penetrate and displace water from the web structure without causing fiber compression and subsequent rewet
2Quantity of substance
If suction/vacuum is used to remove additional water from the web, then water removal is increased by air pressure differential, but the pressure differential is limited by atmospheric pressure
Solution Approach 1:
Instead of using suction/vacuum (negative pressure) to remove water, the invention inverts the approach by using positive compressed air pressure to displace water from the web. This inversion overcomes the fundamental limit of atmospheric pressure that constrains vacuum-based systems, as compressed air can generate much higher pressure differentials in the positive direction
Solution Approach 2:
The invention replaces the hydraulic/suction-based first stage with a pneumatic second stage that uses compressed air. This pneumatic approach enables water removal with pressure differentials far exceeding what is possible with vacuum systems limited by atmospheric pressure
3Use of energy by stationary object
If higher solids content is achieved before the dryer section, then energy demand for evaporation is reduced, but water removal efficiency is limited by press section constraints
Solution Approach 1:
The invention establishes continuous useful action in water removal by adding a second dewatering stage that operates continuously after the press section. This continuous air displacement process maintains high water removal efficiency while achieving the high solids content needed to reduce downstream energy demand
Solution Approach 2:
The invention uses pneumatic power (compressed air) to drive the second stage of water removal, providing a highly efficient means of extracting water that does not suffer from the limitations of mechanical pressing. This enables achievement of high solids content with maintained productivity
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 solids content and bulk of the paper web, reducing energy consumption in the drying process and enhancing water absorbency, while allowing for the production of multiple paper grades with adjusted mechanical and air pressure settings.
Implementation Method 1
Compressed air is passed through the nascent paper web to remove water from the web
Implementation Method 2
A limitation of use of mechanical pressure in dewatering the web is that the thickness of the web, after exiting the press section, is typically reduced as a result of such pressing
Data Source
AI summary
Apparatus, methods, and fabrics for dewatering a nascent paper web, carried in a web sandwich, in a dewatering section of a papermaking machine. Water is driven from the web by a combination of mechanical pressure and compressed air, both typically applied in a nip. The mechanical pressure and air pressure can be applied in the same nip, or in separate nips, where the mechanical pressure is applied upstream, in the papermaking machine, from the air pressure application. The mechanical pressure can be lower than pressures used in conventional press sections of known papermaking machines. Air pressure is that pressure which can be contained in a seal section between the web sandwich and the structure supplying the air. Fabrics supporting the nascent paper web through the air dewatering station have limited lateral air flow under compressed air conditions, whereby air flows generally perpendicularly through the web being dewatered.