Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – With classifying – separating or screening of pulp
Reexamination Certificate
1997-10-22
2001-01-16
Nguyen, Dean T. (Department: 1731)
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
With classifying, separating or screening of pulp
C162S189000, C162S190000, C162SDIG009, C210S800000, C210S806000, C210S928000
Reexamination Certificate
active
06174410
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a process and installation for recovering raw materials from a stream of residual or collected material which includes a plurality of different materials and which results from the manufacture of paper in a paper mill, from a material processing installation and/or a paper machine. In particular, to a process for recovering raw materials from a stream of residual or collected material via a screening operation and for separating an ash fraction containing black particles.
The manufacture of paper mill is a paper mill is usually effected in a manner such that a paper raw material suitable for the paper manufacture concerned is produced from fresh or waster paper fibers or from a mixture of said fibers in a material processing installation of the paper mill, which material processing installation is disposed upstream of the paper machine. Depending on the quality of the final product, this paper raw material consists of a mixture of fibers of very different qualities. Residual or collected material arises in the process water stream, both in the material processing installation during the material processing stage, and in the paper machine. Amongst other constituents, this residual or collected material contains coarse contaminants such as plastics and metal parts, fibrous material, black particles such as soot and printing ink residues, and contains fillers comprising a large proportion of kaolin, pigments, calcium carbonate and titanium dioxide. The process water stream which contains the residual or collected material snad which is discharged by the paper mill, and which is hereinafter termed the stream of residual or collected material, has hitherto usually been fed to a water treatment stage. The filtrate thereby obtained was then recycled to the paper mill, whilst the sludge removed from the water treatment stage had to be disposed of. The present invention is exclusively concerned with the stream of residual or collected material discharged from the paper mill.
In the process which is known from German Patent DE 40 34 054 C1, the entire residual or collected material is fed as a waste water stream to a residual waste water clarification installation and is subjected to a sedimentation operation, optionally with the assistance of flocculants. A thin sludge is then taken off from the sludge collecting compartment of the clarification installation. Residual waster water is admixed with the thin sludge in order to obtain an accurately determined consistency. The coarse contaminants contained in the stream of residual or collected material are subsequently removed by screening. The screened throughput stream is fed to a centrifuging installation having a plurality of hydrocyclones for separating black particles. The material stream which is discharged from the hydrocyclones is then fed to a screening stage in which fractions comprising fibers and agglomerates, as well as pigments and fillers, are produced. The pigments and fillers are separated from each other in a subsequent process stage. Finally, the fibers, pigments and fillers are recycled to the material processing stage of the paper mill.
Thus known process has various significant disadvantages. The clarification installation and the centrifuging installation with is hydrocyclones are very expensive and cost-intensive. Moreover, the energy requirement for operating the clarification installation, and particularly for operating the centrifuging installation, is very high, since there is a comparatively high pressure drop in the hydrocyclones during operation. Furthermore, the accurate adjustment of the thin sludge stream fed to the hydrocyclones is firstly expensive and secondly essential, since if the thin sludge concentration departs from the optimum consistency the hydrocyclones can no longer be operated or can only be operated at low efficiency. This known installation is explicitly designed for use in the wood pulp processing industry, since the fibers obtained from the waste water sludge are essentially pulp fibers. This known installation is not designed for use in an industry which also processes waste paper, where the fibre fraction obtained from the residual or collected material contains very many short and broken fibers, which makes the use of this fibre fraction very difficult and makes it impossible for most paper mills.
SUMMARY OF THE INVENTION
With the present invention, it has firstly been recognized for the first time that the black particles in part only adhere to the fibers and to the coarse contaminants with forces of adhesion which are very weak. During the separation of the fibre fraction, the black particles can in part be separated very easily from the coarse contaminant and from the fibers, due to the turbulence effects which occur, and by means of the screening operation. It is therefore not necessary to separate the black particles as a whole in an expensive manner beforehand. Separation of the black particles when the fibers are screened even results in part in a higher degree of whiteness than that achieved by centrifuging. The costly plant engineering of the prior art for the preliminary separation of the black particles is not necessary with the present invention.
It has also been recognized according to the invention that the fibre fraction can be utilized without difficulty in a particularly economic manner, even if it contains large proportions of short and broken fibers, if the fibre fraction is classified via corresponding screens, depending on the desired fibre size, into different classes of fibre, for example into long fibers, short fibers and/or broken fibers. This gives rise to the possibility, even in the waste fibre processing industry, of recycling the recovered fibers to the production operation in a manner which is quite specific, depending on the demands imposed on the product to be produced. The grades or classes of fibers which cannot be used by the paper mill concerned can be supplied, i.e. sold, to other paper mills for the manufacture of grades of paper where the final product is subject to different requirements, or to other branches of industry.
A significant process simplification is achieved if the stream of residual or collected material discharged from the material processing installation and/or from the paper machines is fed directly or immediately to the installation—i.e. without the interposition of a clarification or water treatment installation—and in particular without pre-adjustment of the consistency. Moreover, only relatively simple plant engineering is required.
Furthermore, the process provides the possibility of first separating, by a screening operation, a coarse contaminant fraction which contains plastics and/or metals, for example, from the stream of residual or collected material before the classification of the fibre fraction. The fibre fraction is subsequently classified into the desired classes of fibre. Finally, separation of the ash fraction can also be effected via a screening operation. Due to the use of the screening technique, at least for separating or classifying the coarse contaminants ans the classes of fibre, it is possible, if the corresponding screens are arranged in cascade, to effect separation or classification and thus to effect the recovery of very different classes of fibre, substantially under the action of the force of gravity. The requisite energy consumption for producing the various grades of fibre is thus restricted to a minimum.
Moreover, the thorough treatment of the stream of residual or collected material results in a filtrate of sufficiently high quality so that a further water treatment stage is unnecessary. The filtrate, the quality of which can be adjusted corresponding to the requirements, can be recycled directly to the material processing installation, and/or to the paper machine, and/or to the stream of residual or collected material upstream of and/or in the installation, or to the waste water.
REFERENCES:
patent: 3833468 (1974-09-01), Boniface
paten
Braun Wolfgang
Trutschler Dieter
Valdivia Juan
Julia Innotec GmbH
Nguyen Dean T.
Nixon & Peabody LLP
Safran David S.
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