The objective of this project is to develop a press section engineering tool for paper machines, based on a flexible model and a parameters' data base. This tool should promote the pressing and drying field for energy efficiency and process intensification.
The main output from the project was the construction and validation of a model to simulate wet and hot pressing. Practical applications of the software were identified, in particular ways to optimise the operation of the press section of a paper machine. These aspects may be water removal, or paper quality, or both water removal and paper quality combined. In addition, the software could be applied to optimise the design of the press, the felt, and the press covering. All of these factors can be significant in influencing the efficiency of operation of the paper machine.
The project is split in six phases :
- CTP will be in charge of the numerical integration of the model. - STPI, using its wet press simulator, will carry out fundamental studies on the compression behaviour of wet fibre webs and felts (flow resistance, viscoelastic behaviour, effect of temperature), and determine the time-dependent mechanical response to a compressive force, of press felts and press roll covers.
- In order to understand pressing, permeability aspects of the web and fabrics, as a function of moisture content, pressure, structure of the porous medium and temperature, are essential.
EFPG will study the microscopic aspects of the phenomena, both theoretically and experimentally. TNO will carry out a macroscopic validation of the elaborated models. They will also investigate and assess the mechanism of steam generation and steam flow in the web.
- The rewetting phenomenon occurs at the exit from the press, as the paper web starts to expand. It is caused by the negative pressure generated in the paper web, capillary forces drawing water from the felt surface, and film splitting. KTH in its laboratory press (especially designed to approach dynamic rewetting) will conduct an extensive experimental program, at normal and elevated temperatures. PIRA and KTH will define the physical laws describing the rewetting phenomena. This aspect is essential in order to design efficient felt structures and optimal press geometries for best energy efficiency.
- LTH will measure, in a static press rig, the heat transfer coefficients in the different materials of the press section, and the contact coefficient between these materials.
- The global validation of the model in realistic environments will be performed on the machines of STFI. Tests on extended press nips, with possibilities of warming the press rolls up to temperatures used for impulse drying, are planned .
Process limitations which cannot be modelled very simply, such as crushing, sheet delamination, sheet adhesion on rolls or felts, will also be studied. PIRA on its press drying and impulse drying experimental rigs, will concentrate on validation at high temperature and in relation with quality limitations. They will also, in cooperation with LTH, evaluate the potential energy savings which can be expected with the new pressing and drying technologies.
Funding SchemeCSC - Cost-sharing contracts
221 00 Lund
2600 JA Delft
KT22 7RU Leatherhead
100 44 Stockholm