Drying and gas or vapor contact with solids – Apparatus – With means to treat gas or vapor
Patent
1985-08-16
1987-09-08
Schwartz, Larry I.
Drying and gas or vapor contact with solids
Apparatus
With means to treat gas or vapor
34111, 34116, 34123, 34 95, F26B 516
Patent
active
046914498
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method and apparatus for consolidating a moist web of fibre structure, involving the pressing and drying of a paper-pulp web or a paper web in the manufacture of paper, for example. The novel, fundamental principle on which the invention is based resides in heating a press felt comprising heat-resistant fibres, or alternately a roll made of heat resistant material and having a permeable surface, and pressing the heated felt or the heated roll against the moist fiber web, so that moisture is pressed into the felt or the permeable surface of the roll, and is subsequently removed therefrom. Distinct from traditional fibre web drying methods, for example drying methods employed in the manufacture of paper, thermal energy for drying the fibre web is transferred from a fibrillar and/or fibrous structure to the fibre web in a press nip.
In, for example, the initial installation of paper machines, the method according to the present invention enables the traditional press and drying sections of said machines to be combined into a cheaper unit requiring less space. In the case of existing paper machines, these can be made more effective by incorporating therein apparatus and means constructed in accordance with the invention. When practising the method according to the invention considerable savings in energy can be achieved, due to the higher pressing and drying efficiencies attained, i.e. a greater amount of water can be removed from the fibre web for a given energy input.
Although the invention is described in the following mainly with reference to the drying of paper webs, it will be understood that it can also be applied in conjunction with the pressing and/or drying of other types of fibre webs, for example paper pulp webs.
In the manufacture of paper, the pressing and drying of the paper sheets constitute two functions which are extremely important for reasons of economy and with respect to paper technology. The economic aspects will now be discussed in greater detail.
The extraction of water from a fibre web by pressing the same is far more economical than extracting water by drying. This applies both to the manufacture of pulp and to the manufacture of paper. Consequently, when manufacturing paper efforts are made to press as much water as possible from the paper, without jeopardising the quality thereof. Calculations have shown that removal of water from a paper web by pressing the web is seven times more rewarding than extraction of the water by drying the web.
Drying can be said to involve two cost categories, these being investment costs and operational costs. High investment costs are primarily caused by the fact that high-production machines require long dryer sections. These are expensive to construct and also contribute to high overall construction costs.
High operational costs are mainly due to the cost of the energy required to vapourise the water remaining in the fibre web downstream of the press section. The only way in which these energy costs can be reduced when practising methods known hitherto is to raise the dry solids content of the paper web entering the drying section. The method of increasing the dry solids content of the web upstream of the drying section available in this respect is to increase the efficiencies of the press section. This has resulted in press sections in which very high demands are placed on the components incorporated therein (press felts, rolls and frame). Naturally, these demands greatly increase equipment costs. It is not thought, however, that a dry solids content in excess of 45-50% can be achieved, despite the technically advanced press sections used. This is probably due, among other things, to the phenomenon known as re-wetting. Many explanations of the re-wetting phenomenon have been put forward. One explanation proposes that: when considering a wet paper sheet, the water present is found partly in the fibres and partly in the capillaries formed between the fibres. When the sheet is pressed, the press felt will compress th
REFERENCES:
patent: 3925906 (1975-12-01), Chance et al.
patent: 3981084 (1976-09-01), Sobota
patent: 4112586 (1978-09-01), Lehtinen
patent: 4324613 (1982-04-01), Wahren
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