Mathematical modeling of mechanical dewatering in the press section - Paper Technology International 2023 - Paper Technology International 2023 - Flipbook - Page 83

Mathematical modeling of mechanical dewatering in the press section - Paper Technology International 2023

PAPERTECHNOLOGYINTERNATIONAL
Mathematical modeling of mechanical dewatering in the press section - Paper Technology International 2023
Timo Frick, Simulation Expert, Voith Paper
Dr. Siegfried Graser, Simulation Expert, Voith Paper
Dr. Bettina Grashof, Senior R&D Manager Simulation, Voith Paper
Dr. Natalie Osti, Simulation Expert, Voith Paper
INTRODUCTION:
Sustainability has recently been a focal point of attention in the industry. This development has been highly accelerated by the
soaring prices for fossil energy following the current global market situation. Sustainability comprises decarbonization of energy sources
as well as lower energy and resource consumption. An improved mechanical drainage significantly reduces thermal energy consumption
in the subsequent dryer section and hence increases the energy efficiency of the papermaking process. Furthermore, mechanical draining
significantly defines the properties and quality of the paper. However, the physical processes inside the press nip are still poorly understood
and can be only measured with high efforts. Sophisticated mathematical modelling and high-performance simulations offer process
insights, which are difficult to achieve by measurements, and can be used to improve and redesign the process and components involved.
The drying process of the paper web is the reason that
the pulp and paper industry is one of the most energy intensive
industrial sectors. Within an integrated pulp and paper mill the
energy requirements of the dryer section is one of the largest energy
consumers [1] and is responsible for about 20% of the total energy
consumption in the papermaking process [2]. By increasing the dry
content of the paper web before it enters the drying section, high
energy savings can be achieved (see Figure 1).
To reach this goal, the mechanical dewatering in the press
section plays an integral role and needs to be optimized. In the
press section the dry content of the paper web is increased by
the application of mechanical pressure leading to a removal of
free water from its pores. The mechanical dewatering in the press
section not only allows for a reduction of steam consumption
crucially in the dryer section, but also increases the strength of the
web crucial to avoid web breaks. However, despite the economic
and environmental importance of press dewatering, the processes
taking place inside the press nip are not yet fully understood. These
include the interaction between the two-phase flow of water and air,
as well as the mechanical compression and expansion of the porous
materials of the press fabric and the paper web.
Figure 1: Comparison of the press section with the forming and
drying sections concerning overall water removed and energy
used [3].
Modeling and simulation of the process steps involved in the
dewatering of the paper web offers insights into the mechanisms of
water removal and sheet formation, which are not available solely
from measurements and experiments. Additionally,
virtual parameter studies allow for the identification
of important influencing factors that are the basis for
a suitable choice of test cases. In this work we will
show that our simulations give new impulses that can
directly be used to improve processes and redesign
components. We will start by introducing our modeling
approach and then present results of our simulations
which are used to support and speed-up the
development of new products in the press section. We
will also point to challenges of the method especially
in the identification of effective material parameters to
describe the wet paper web and fabrics.
Figure 2: Voith’s Tandem NipcoFlex press which
combines two inline shoe presses is a press
concept with a wide application window.
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