Extended Press Nip Layout for High-Dry Fibrous Web Pressing
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Solution Overview
Problem
Existing press arrangements for fibrous webs, particularly packaging paper webs, face challenges in reducing energy costs and CO2 footprint while avoiding web crushing due to high linear loads, which increase energy consumption and investment costs.
Innovation Solution
A press arrangement with two presses, including a first press for pre-solidification and a second extended press with a quotient of average pressure and peak pressure less than 0.5, operated at a linear load of at least 500 kN/m, utilizing a geometric design with a long press zone length and high peak pressure to achieve efficient dewatering without crushing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the linear load in the press arrangement is increased to achieve greater dry content, then the energy consumption increases and the risk of web crushing increases, but the dry content of the fibrous web improves
Solution Approach 1:
The press arrangement is divided into multiple presses (at least two presses arranged one behind the other) with different press nip configurations. The first press handles initial dewatering while the second press with extended press nip achieves final dewatering at high linear load, segmenting the dewatering process to optimize energy efficiency and prevent web crushing
Solution Approach 2:
The first press performs preliminary dewatering and solidification of the fibrous web before it enters the second press. This preliminary action prepares the web structure to withstand the high linear load in the second press without crushing, enabling efficient energy use in the final dewatering stage
2Quantity of substance
If the linear load in the press arrangement is increased to achieve greater dry content, then the investment costs rise due to more massive machine frame, but the dry content of the fibrous web improves
Solution Approach 1:
The press arrangement segments the dewatering function across multiple presses, allowing each press to be optimized for its specific function. This avoids the need for a single massively oversized press frame, reducing overall investment costs while achieving the required dry content
Solution Approach 2:
The first press performs preliminary solidification to prepare the web for the second press, enabling the second press to operate at high linear load without requiring excessive frame mass. This preliminary preparation reduces the overall investment required compared to using a single high-capacity press
3Device complexity
If a conventional roll press with linear press nip is used, then the structure is simple, but the dewatering efficiency is reduced due to sudden pressure application
Solution Approach 1:
The extended press nip uses curved or elongated contact surfaces between press elements, creating a gradually increasing pressure distribution along the press zone. This curved geometry allows continuous pressure buildup from low to high values, improving dewatering efficiency while preventing web crushing
Solution Approach 2:
The press nip transitions from a conventional linear contact to an extended press nip that increases in length in the machine direction. This dimensional extension creates a gradual pressure gradient, improving dewatering efficiency without requiring complex additional components
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 solution reduces energy consumption and investment costs while achieving high dry content in the fibrous web, suitable for packaging paper production, especially with recycled fibers.
Implementation Method 1
the fibrous web is dewatered or demoistened by way of mechanical pressure
Implementation Method 2
The press nip is planiform and not essentially linear as in conventional roll presses. As a result, the pressure to be exerted on the fibrous web to be dewatered does not start suddenly in the press nip in the direction of travel but can be continuously brought from a low value to a high value
Implementation Method 3
An especially efficient type of mechanical dewatering can be achieved via a so-called extended press nip
Implementation Method 4
a first press with a first press nip and a following second press with a second press nip which is an extended press nip
Data Source
AI summary
A press arrangement for pressing a web of fibrous material includes at least two presses which are arranged one behind the other in a direction of travel of the web of fibrous material, the at least two presses including a first press and a second press following the first press, the first press including a first press nip, the second press including a second press nip which is an extended press nip, the second press being configured for being operated at a linear load of at least 500 kN/m, the second press being configured such that a quotient of an average pressure and a peak pressure in the second press nip is less than 0.5, the second press being configured for applying the peak pressure of at least 12 MPa onto the web of fibrous material.