Claims
- 1. In a papermaking installation: means for making a web of paper; web drying means which has an external surface that is adapted to be contacted by the web and, also, means through which a heat transfer liquid can be circulated to elevate the temperature of said surface; steam supply means; a heat exchanger means; means for circulating steam from said supply means and the heat transfer liquid in heat transfer relationship through said heat exchanger means to heat the heat transfer liquid; and means for thereafter circulating said heat transfer liquid to and through the web drying means.
- 2. A papermaking installation in accord with claim 1, in which the drying means through which the heat transfer liquid is circulated comprises a series of rotary, equitemp dryers.
- 3. A papermaking installation in accord with claim 1, which has means for condensing blow-through steam from the heat exchanger means and for returning the condensate to the steam supply means.
PAPERMAKING INSTALLATIONS AND METHODS (I)
This application is a continuation-in-part of application No. 622,617 filed Oct. 15, 1975.
The present invention relates to papermaking and, more particularly, to novel, improved methods and apparatus for supplying heat to the dryer section appended to a papermaking machine.
The term "paper" is used herein in the same generic sense as it is in the papermaking industry. Products embraced by this term include but are not limited to: newsprint; uncoated, ground wood paper; coated printing and converting papers; uncoated book paper; writing and related papers; bleached bristols; unbleached kraft packaging and industrial converting papers; other packaging and industrial converting papers; special industrial papers; tissue paper; unbleached kraft and industrial converting paperboard; bleached packaging and industrial converting paperboard; semichemical paperboard; combination furnish paperboard; wet machine board; and construction paper and board.
Large quantities of steam are consumed in making paper, especially in the making and preparation of the pulp which is converted into a web, dried, and calendared to complete the manufacturing process. In a sulphite pulp mill alone, for example, steam may be employed in presteaming and digesting the wood chips from which the pulp is made, in the preparation of the liquor in which the chips are digested, in recovering chemicals from the digestion process, and in generating electricity for operating process machinery, for example.
Modern steam generators are highly efficient pieces of equipment; and I have now discovered that advantage can be taken of this and the large capacities in which such equipment is or can be made available in drying the product made in typical mills.
Specifically, in the conventional paper mill steam is employed to heat the 100 or more rotary dryers in the dryer section. Parent application No. 622,617 discloses that substantial reductions in the cost of drying the paper can be made and a better product produced by substituting liquid heated, equitemp dryers for those of conventional character.
It is of course necessary in an installation as just described to provide a way of heating the heat transfer liquid.
I have now discovered that steam generated in the mill can be used to advantage for this purpose. In particular the economics of heating the heat transfer liquid in this manner are often favorable because of the above-noted efficiency of available steam generators, because heat exchangers in which the energy can be efficiently transferred from the steam to the heat transfer liquid are also available, and because the scheme in question eliminates the necessity of providing a separately fired unit for heating the heat transfer liquid.
A variety of heat exchange liquids which can be employed in the manner and for the purpose just described are available. Among these are Therminol heat transfer fluids, proprietary products of Monsanto Chemical Company, which may be used at temperatures as high as 800.degree. F. Other suitable heat transfer liquids are marketed by the Dow Chemical Company under the name Dowtherm and by Chemische Werke Huls AG under the name Marlotherm.
The heat exchanger in which the transfer of heat is made can be of the conventional shell and tube type. Steam can be diverted from the mill steam line through the heat exchanger and the condensate returned to the main condensate return line.
It will be apparent to the reader from the foregoing that one important and primary object of the invention is to lower the cost of making paper.
A related and also important object of the invention resides in reducing the cost of operating the dryer section of a papermaking machine.
An also related and important object of the invention resides in the provision of novel, improved dryer sections in which a high boiling point liquid is used to heat the dryers and in which the heat transfer liquid is indirectly heated by steam.
US Referenced Citations (2)
| Number |
Name |
Date |
Kind |
|
2811787 |
Clements |
Nov 1957 |
|
|
3236292 |
Smith, Jr. |
Feb 1966 |
|
Continuation in Parts (1)
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Number |
Date |
Country |
| Parent |
622617 |
Oct 1975 |
|
Patent Grant
3988200
