Process for dissolving used paper

Abstract

Process for dissolving used paper including adjusting a content of solid particles of used paper to a range between about 15 and 35%, kneading the used paper with a specific work of at least about 10 kWh / t, diluting the kneaded used paper to a content of solid particles below about 6%, separating non-fibrous contaminants with wet screening, adjusting a solid material content to less than about 3%, and separating heavy particles with at least one hydrocyclone.

Description

[0001] The present application claims priority under 35 U.S.C. .sctn. 119 of German Patent Application No. 100 00 181.5, filed on Jan. 5, 2000, the disclosure of which is expressly incorporated by reference herein in its entirety.[0002] 1. Field of the Invention[0003] The present invention is directed to a process for dissolving used paper.[0004] 2. Discussion of Background Information[0005] It is known that processes of the above-mentioned type are performed in such a way that the used paper is supplied to a pulper in the state in which it was delivered to the paper factory. Here, this pulper serves to mix in water and to dissolve the paper webs. If necessary, a station for removing bale wires or bale edges can be provided before the pulper. As a rule, all components of the used paper bale, possibly without these wires or edges, are dropped into the pulper and are mechanically processed with more or less intensity. Besides the high energy consumption in the pulper, another undesire...

AI Technical Summary

Benefits of technology

[0011] The dissolving effect can be increased by heating the used paper. However, this temperature must be adjusted to impurities still present in the used paper in order to prevent undesired grinding of soft, non-fibrous impurities. In such raw materials, plastic coatings are often present on the paper webs that are relatively thin and easily torn, even if not as easily as paper webs that have been swollen by water. It is precisely these impurities that can be removed in a particularly effective and economical fashion in the subsequent mid-consistency sorting. In special cases, a thin stock sorting can occur instead of the mid-consistency sorting, which leads to greater success, but also to a higher expenditure. The impurities that are very small and have not yet been removed, in particular, small, heavy particles, can be removed in the subsequent hydrocyclone treatment, for which purpose highly effective cleaners are particularly well-suited.

[0032] In accordance with a further feature of the present invention, the amount of water added may be adjusted in accordance with a power consumption for kneading, thereby regulating the power consumption.

[0033] According to yet another feature of the present invention, the amount of water added can be adjusted to a power consumption for kneading and to an amount of used paper, thereby regulating the specific work of the kneading.

Problems solved by technology

Besides the high energy consumption in the pulper, another undesired result of the known process can be a breaking down of non-fibrous attendant materials to the extent that it becomes difficult to remove these particles.

The large amount of such foreign materials arriving in the suspension necessitates a high sorting and cleaning expenditure.

While this process is good and effective, it is also expensive.

In this process, a type of used paper occurs as well, which exists as air-dry pieces or scraps of paper and already has a certain degree of purity; however, it is not free of impurities, in particular adhering plastic films, for example, of beverage cartons.

In such raw materials, plastic coatings are often present on the paper webs that are relatively thin and easily torn, even if not as easily as paper webs that have been swollen by water.

In special cases, a thin stock sorting can occur instead of the mid-consistency sorting, which leads to greater success, but also to a higher expenditure.

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