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High temperature pressing of fibrous materials


The manufacture of paper from pulp requires a large amount of energy and a major part of the energy consumption is connected with dewatering (i.e. the removal of water from the pulp) and consolidation. Laboratory experiments indicate that new high temperature pressing processes can reduce the energy consumed in dewatering and consolidation by 25% and in addition, reduce the capital costs for new paper machines. It will also make it possible to utilize a higher content of alternative rawmaterials such as recycled fibers and agrofibers (e.g. wheat straw).

A high temperature pressing operation is also used in the manufacture of Medium Density Fiberboard (MDF). Better design and operating procedures can reduce the energy consumed in MDF pressing by 20%.

Several similarities exist between high temperature pressing of the wet fibre web in a paper machine and pressing of MDF. In both cases a deformable and porous fibrous material is pressed at high temperatures and the main mechanisms are heat and mass transfer, water phase changes, densification and stress relaxation. Chemical reactions such as cross-linking are utilized in MDF pressing and may as well be important in applications of high temperature pressing in paper manufacture.

A better understanding of the physical and chemical phenomena involved in high temperature pressing will on the one hand make possible the development of procedures that permit energy savings and avoid raw material losses in the manufacture of MDF and - on the other hand - help to develop new unit operations in the papermaking process that will save energy and promote the use of a wider range of raw materials.

The proposed research aims to provide the necessary scientific and technical knowledge required for the understanding of new high temperature pressing processes and for the proper design of such processes. This goal will be achieved by a combination of theoretical analysis, experiments on laboratory equipment and extensive experiments on pilot-scale plant. A theoretical model of high temperature pressing of fibrous material will be developed using the results of a previous JOULE project in which four of the partners in this proposal participated. The model will be validated with the help of specially designed experiments on pilot plant.

The project will aim to demonstrate that:

a) a suitably designed high temperature pressing process for papermaking can:
- increase the solids content of the fibre web after pressing by 17%.
- reduce the energy consumed in dewatering and consolidation by 20%.
- increase the strength properties by 20%.

b) better design and operating procedures for MDF pressing can give energy savings of 20%.

The final report will include recommendations regarding the commercial design of a high temperature pressing process for papermaking, including machine layout, choice of construction materials, raw materials and energy supply.
The consortium consists of five research organisations, a manufacturer of papermaking machinery and a manufacturer of press felts.

This proposal is covered by the JOULE Area 2.2.1A1.1 (R.U.E. in industry/Advanced unit operations/Process intensification).

Funding Scheme

CSC - Cost-sharing contracts


Drottning Kristinas Vaeg 61

Participants (6)

Albany Nordiskafilt AB
301 80 Halmstad
Institut National Polytechnique de Grenoble
461 Rue De La Papeterie
38402 Saint-martin-d'hères
Lunds Universitet

221 00 Lund
53,Drottning Kristinas Väg 53
100 44 Stockholm
Rua Dos Bragos
4099 Porto
Valmet - Karlstad AB
6,Axel Johnsons Väg
651 15 Karlstad