Paper making and fiber liberation – Processes and products – Reclamation – salvage or reuse of materials
Reexamination Certificate
1997-05-23
2001-02-20
Nguyen, Dean T. (Department: 1731)
Paper making and fiber liberation
Processes and products
Reclamation, salvage or reuse of materials
C162SDIG008, C210S710000, C210S928000
Reexamination Certificate
active
06190504
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method in a paper machine for arranging its water circulation and an arrangement for the water circulation in the paper machine.
BACKGROUND OF THE INVENTION
Paper and board grades are produced in a paper machine by draining water out of a mixture of water and wood fibers prepared in a stock preparation plant and by using constantly moving fabrics in the different principal parts of the paper machine, which parts are typically called the wire part, the press section, and the dryer section. The fabrics in a paper machine are usually permeable members which form a closed loop, i.e., are endless, and which are made of a plastic and/or a metal material and/or which are felts consisting of natural and/or synthetic fibers. The fabric loops are rotated constantly by means of drive rolls or some other comparable equipment. During the draining of water from the mixture, the fabrics are contaminated by materials which come from the paper web and from the different process waters. In order that the fabrics and the elements in the paper machine, such as rolls, doctors, forming ribs, suction boxes, etc., may operate satisfactorily, they must be washed constantly or at least periodically by means of water jets, and the resultant wash water must be removed. The wash water from the fabrics is contaminated, but it can, however, be used as circulation water in the paper machine.
In present-day paper mills, an abundance of fresh water is needed for cooling and, after that, among other things, for the above washing requirements in the wire part and in the press section and for dilution in the stock preparation plant. After the wire part and the press section, these waters are passed mainly to mix with the fibrous circulation waters. Any excess amount of circulation water is disposed of as waste water. The net amount of fresh water that is needed for the washing jets in a paper machine is of an order of about 10 cubic meters per ton of paper produced. Thus, from a paper mill, an abundance of warm waste water is obtained, which must be cleaned, for example biologically, and, if necessary, cooled before the cleaning.
As known in the prior art, the wash jet waters in a paper machine are collected by means of various basins and troughs and passed into the circulation water system. Besides fresh water, circulation water of the paper machine is also employed as the jet water in the wire part and the press section. The circulation water is usually cleaned by means of filters having screens whose measure is about 150&mgr; (corresponding to about 100 mesh). Such a screen measure, however, permits the passage of fine particles and dissolved material. A clear filtrate obtained from such a filtering device still contains finer particles and dissolved material. These impurities may cause blocking of jet nozzles and their structures and contamination of these devices and other equipment out of the disturbing materials in the water system in a paper machine, which results in negative effects in the quality and production of paper. The use of such water as an additional substitute for fresh water would risk damage to the efficient operation of the equipment and the production of paper. Therefore, for more demanding washing of the fabrics and parts of a paper machine, fresh water is used, which is often chemically cleaned prior to actual use in the paper machine.
Fresh water is generally cold, and it must be heated to a considerable extent, often to the operating temperature that is required in the papermaking process. The temperature of new, fresh cold water must be raised, for example, from about 7° C. to about 50° C., and usually it is treated chemically in order to remove humus materials and provide a proper color, in compliance with the quality requirements of the paper machine, and its use involves high processing costs. The high cost of cleaning of fresh water and waste water arises from the fact that an abundance of fresh water must be introduced into the process constantly. Fresh water which is used in the jets in a paper machine and which has been treated chemically also increases the concentrations of inorganic materials in the system.
OBJECTS AND SUMMARY OF THE INVENTION
It is an important object of the present invention to lower the consumption of fresh water in a paper machine.
More specifically, it is an object of the present invention to improve the papermaking process from the point of view of decreasing the burden on the environment (in the form of less water products) and the requirement of fresh water (in the form of lowering the amount of fresh water needed). In particular, the object is optimal cleaning of the various contaminated waters present in a paper machine by interconnecting different cleaning devices in a novel manner and by using cleaned waters and the concentrates coming from the cleaning devices in an optimal manner in consideration of their degree of purity and their washing potential.
Another object of the present invention is to provide novel overall solutions of technology, which solutions, at the same time as they reduce the burden on the environment in the form of lower consumption of fresh water and lower quantities of waste water, also provide economies of energy and reduce the consumption of chemicals in the different parts in a paper mill.
In order to achieve these objects and others, in accordance with the invention, in view of full or partial closing of the water circulations in a paper machine, the wash waters from the fabrics and from other devices in the paper machine as well as the waters drained from the paper web to be produced are recovered selectively based on the place of origin of the waters, and at least a part of the recovered different waters are cleaned, and the cleaned waters are recirculated to applications of reuse suitable in view of their washing potential in the papermaking process.
It has been estimated that the cleaning and evaporation of process waters optimally in a plant integrated in accordance with the present invention considerably lowers the burden to the environment, in the form of a reduction in waste water and a lower requirement of fresh water, and is more advantageous compared with the unlimited and abundant use of fresh water with the resulting high requirement of cleaning in most present-day paper mills.
The trough waters from the wash jets in a paper machine are, on the average, cleaner than the waters of the short cycle in a paper machine. In the prior art, all of these wash waters are mixed with fibrous circulation waters after their use, but in a preferred embodiment of the present invention the semi-clean fabric conditioning water coming from the formers and presses is cleaned and used in a novel manner. The waters that clean the wires and felts have not been contaminated to the level of contamination of wire water, so that these waters still have a washing potential etc., potential of use, which are utilized in the present invention. In the present invention, this washing potential still possessed by the relatively clean waters is utilized. Moreover, in the present invention, the waters that are collected selectively in accordance with the place of origin can also be cleaned more readily.
In respect of the waste waters, in the present invention a so-called sorting based on the place of origin is applied. For example, water from conditioning of fabrics in a paper machine can be collected and taken for useful use. In this manner, the use of chemically pure fresh water can be reduced. It is an advantage of the invention that chemically purified fresh water is not needed in equally large quantities as in prior art systems for jet water in a paper machine. For example, the jet waters can be cleaned by means of cleaning systems of their own so that a paper machine is obtained which requires a smaller amount of fresh water.
In one preferred embodiment of the invention, the water flows recovered by means of selective collecting of wash waters can be cleaned within the limits tha
Gartz Rainer
Kaijaluoto Sakari
Karlsson Markku
Suonpera Antti
Nguyen Dean T.
Steinberg & Raskin, P.C.
Valmet Corporation
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