GB1598484A

GB1598484A - Method and system for treating a light fraction of refuse preferably household garbage

Info

Publication number: GB1598484A
Application number: GB1112/78A
Authority: GB
Original assignee: Svenska Flaktfabriken AB
Current assignee: Svenska Flaktfabriken AB
Priority date: 1977-01-17
Filing date: 1978-01-11
Publication date: 1981-09-23
Also published as: AU513766B2; FI780040A; DE2801106A1; FR2377238B1; DK20678A; AU3215378A; FR2377238A1; NO780150L; NL7800520A; CS214666B2; CH625432A5; BE862561A; IT7867074A0; JPS566345B2; IT1106968B; JPS5390662A

Abstract

The heavy components contained in domestic refuse are first separated out, the light fraction consisting of paper, tougher materials such as plastic film and particulate impurities remaining. This material mixture is comminuted in a shredder (1), the tougher materials, such as plastic films, being obtained in oversizes. The material treated in the shredder (1) is conveyed to a screen (2) having different hole sizes, where the oversizes are separated out. The system also comprises a drying device (3) and an air classifier (4). An intermediate fraction consisting essentially of paper flakes is removed from the screen device (2). The drying device (3) serves for drying the intermediate fraction and the air classifier (4) serves for separating the paper with a higher basis weight and that with a lower basis weight. <IMAGE>

Description

(54) METHOD AND SYSTEM FOR TREATING A LIGHT FRACTION OF REFUSE, PREFERABLY HOUSEHOLD GARBAGE (71) We, AKTIEBOLAGET SVENSKA FLAKTFABRIKEN, a Swedish Joint Stock Company, of Sickla Alle 1, Nacka, Sweden do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to a method of treating a light fraction of refuse, preferably a light fraction of household garbage, from which heavy components have been separated in known manner, which light fraction consists of paper, tougher material such as plastic foil, and particulate impurities, by shredding or disintegrating the material mixture in a shredder and separating and collecting the disintegrated material.

In the industrialised part of the world, trees are utilised at present to an extent which in the long run will result in an increasing shortage of raw material. This will create a demand of a more intensive utilisation of other sources of raw material.

One possibility is increasingly to make use of return paper as a raw material source. The collecting methods used at present, however, are insufficient and, therefore, projects are now going on to develop methods for recovering paper raw material in a mechanical way. Household garbage is treated for this purpose in several steps. At first the heavy components comprised in the garbage must be separated from the remainder. This is carried out by passing the material through mills, drums and wind sifters of known kind. After this primary treatment a light fraction remains, which substantially comprises paper and various impurities of textile, plastics, dust, sand type and the like These impurities can give rise to clogging in the screening departments of paper mills or to uneveness in the completed paper product and to breaks in the paper web.It is, therefore, important to eliminate these impurities in order to obtain a produce suitable for use in paper mills. The methods used up to now do not generally succeed in solving the aforesaid problems caused by impurities in the recovered paper fragments.

The paper included in the light fraction, moreover, consists of several different paper qualities. They are substantially composed of two types of paper fibres originating partly from so-called mechanical pulp and partly from chemical pulp. The proportions of these two types can vary. Chemical pulp and mechanical pulp have different properties, which make them suitable for use in different fields of application.

Mechanical pulp, for example, has low breaking strength and high bending rigidity, while for chemical pulp the situation is the reverse. Conventional methods of paper recovery, thus, have provided a product which consists of a mixture of paper fragments from chemical pulp and mechanical pulp. This mixture of different paper qualities has not been very attractive to the paper mills, and consequently the value of the paper recovered has been limited.

The invention has among its objects to seek to solve the aforesaid problems and to provide a method of treating a so-called light fraction separated from household garbage so that its main content, viz. paper, can be obtained in such a pure state as to permit its use in paper mill with a minimum of required complemtary equipment. A further object of the invention is to provide a method, by which the recovered paper is obtained as an end product in fractions consisting substantially of mechanical and chemical pulp fibres respectively so that its value and applicability as raw material in paper making is as high as possible.

According to a first aspect of the invention there is provided a method of treating a light fraction of refuse obtained by the previous removal of heavy components, the light fraction consisting mainly of paper, plastics and particulate impurities, comprising the steps of disintegrating the light fraction in a shredder where the tougher plastics is disintegrated to oversize and the paper to intermediate size, in the absence of added liquid in said shredder, and sieving the product obtained from the shredder to separate the paper from the plastics and from the particulate impurities.

According to a second aspect of the invention there is provided apparatus for carrying out the method defined in the immediately preceding paragraph comprising a shredder for disintegrating the light fraction, in which shredder the tougher plastics is given form of oversize and the paper is given the form of intermediate size; sieve means downstream of the shredder for sieving the product obtained from the shredder to separate the paper from the plastics and from the particulate impurities, a drier for drying the paper fraction; and a wind sifter for dividing the paper fraction into a lighter paper fraction and a heavier paper fraction so that the lighter paper fraction consists substantially of paper fibres originating from mechanical pulp and the heavier paper fraction consists substantially of paper fibres originating from chemical pulp.

Thus using the invention it is possible to obtain paper in the form of flakes of uniform size and of high purity. It will be understood that, using the invention, materials of great toughness, such as plastics foil, on passaage through a shredder, are disintegrated less than the paper and therefore can be obtained as oversizes downstream of the shredder. It is, thus, possible to separate these oversizes on a subsequent sieve. Furthermore a certain division of the paper flakes into chemical pulp fibres and mechanical pulp fibres can be obtained because flakes of a lower density consist for the most part of mechanical pulp fibres, while flakes with a higher density substantially consist of chemical pulp fibres. An end product comprising separated chemical and mechanical pulp fibre types of uniform high quality can thus be obtained using the invention.

A refuse treating apparatus embodying the invention is hereinafter described, by way of example, with reference to the accompanying drawing, which shows a schematic layout of the apparatus.

Refering to the drawing, the apparatus includes a shredder 1 to which a light fraction of refuse is supplied. The light fraction has been separated from heavier elements, by a known technique, of household refuse and consists substantially of paper, plastics and particulate impurities.

The treatment in the shredder 1 results in the exposing and releasing of impurities in the form of particles from the material, at the same time as the material is reduced in size. The properties of the shredder 1, furthermore, are such that tough materials, such as plastics foil, are only affected to a low degree by the treatment and, there fore, are obtained in the form of oversizes downstream of or after the shredder. The material treated in the shredder 1 is trans ported to a sieve 2 located downstream of the shredder. At the sieve 2, the material consists of several fractions comprising substantially fine particles, paper flakes and oversizes of the tougher material. By screening the material from the shredder 1 through different hole sizes of the sieve 2 different fractions can be separated as desired.An intermediate fraction is obtained, from which impurities in the form of fine particles and oversize material, respectively, consisting substantially of plastics, have been screened off. The material thus purified and consisting of paper is passed through a dryer 3. The heated and dried material includes a mixture of chemical pulp fibres and mechanical pulp fibres. By passing this mixture through a wind sifter 4 material is separated in such a manner, that paper with a high density drops out as a heavy fraction, while paper with a lower density provides a light fraction, which is collected in a cyclone 5 located downstream of the wind sifter 4. During the separation process, further, particulate impurities adherent to the paper are released from the paper.By passing the material treated in the wind sifter 4 and cyclone 5 through a sieve equipment 6 and 7, respectively, with fine holes, the released particulate impurities can be separated. The resulting end product, thus, is a light fraction consisting substantially of paper of mechanical pulp fibres, and a fraction consisting substantially of paper of chemical pulp fibres.

In the system described above the separation takes place in the wind sifter.

Several such wind sifters, of course, can be arranged in series when an increase in the degree of purity of one fibre fraction is desired.

The invention has been described with reference to the treatment of a light fraction recovered from household refuse. It will be understood that other refuse, however, such as refuse from offices and industry can be treated using a method embodying the invention.

It will be understood that the term "oversize" used herein means a size greater than that of the paper, and the term "intermediate" means a size between that of the plastics and that of the particulate impurities.

\NEAT WE CLAIM IS: 1. A method of treating a light fraction of refuse obtained by the previous removal of heavy components, the light fraction consisting mainly of paper, plastics and particulate impurities, comprising the steps of disintegrating the light fraction in a

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. and sieving the product obtained from the shredder to separate the paper from the plastics and from the particulate impurities. According to a second aspect of the invention there is provided apparatus for carrying out the method defined in the immediately preceding paragraph comprising a shredder for disintegrating the light fraction, in which shredder the tougher plastics is given form of oversize and the paper is given the form of intermediate size; sieve means downstream of the shredder for sieving the product obtained from the shredder to separate the paper from the plastics and from the particulate impurities, a drier for drying the paper fraction; and a wind sifter for dividing the paper fraction into a lighter paper fraction and a heavier paper fraction so that the lighter paper fraction consists substantially of paper fibres originating from mechanical pulp and the heavier paper fraction consists substantially of paper fibres originating from chemical pulp. Thus using the invention it is possible to obtain paper in the form of flakes of uniform size and of high purity. It will be understood that, using the invention, materials of great toughness, such as plastics foil, on passaage through a shredder, are disintegrated less than the paper and therefore can be obtained as oversizes downstream of the shredder. It is, thus, possible to separate these oversizes on a subsequent sieve. Furthermore a certain division of the paper flakes into chemical pulp fibres and mechanical pulp fibres can be obtained because flakes of a lower density consist for the most part of mechanical pulp fibres, while flakes with a higher density substantially consist of chemical pulp fibres. An end product comprising separated chemical and mechanical pulp fibre types of uniform high quality can thus be obtained using the invention. A refuse treating apparatus embodying the invention is hereinafter described, by way of example, with reference to the accompanying drawing, which shows a schematic layout of the apparatus. Refering to the drawing, the apparatus includes a shredder 1 to which a light fraction of refuse is supplied. The light fraction has been separated from heavier elements, by a known technique, of household refuse and consists substantially of paper, plastics and particulate impurities. The treatment in the shredder 1 results in the exposing and releasing of impurities in the form of particles from the material, at the same time as the material is reduced in size. The properties of the shredder 1, furthermore, are such that tough materials, such as plastics foil, are only affected to a low degree by the treatment and, there fore, are obtained in the form of oversizes downstream of or after the shredder. The material treated in the shredder 1 is trans ported to a sieve 2 located downstream of the shredder. At the sieve 2, the material consists of several fractions comprising substantially fine particles, paper flakes and oversizes of the tougher material. By screening the material from the shredder

1 through different hole sizes of the sieve

2 different fractions can be separated as desired.An intermediate fraction is obtained, from which impurities in the form of fine particles and oversize material, respectively, consisting substantially of plastics, have been screened off. The material thus purified and consisting of paper is passed through a dryer 3. The heated and dried material includes a mixture of chemical pulp fibres and mechanical pulp fibres. By passing this mixture through a wind sifter 4 material is separated in such a manner, that paper with a high density drops out as a heavy fraction, while paper with a lower density provides a light fraction, which is collected in a cyclone 5 located downstream of the wind sifter 4. During the separation process, further, particulate impurities adherent to the paper are released from the paper.By passing the material treated in the wind sifter 4 and cyclone 5 through a sieve equipment 6 and 7, respectively, with fine holes, the released particulate impurities can be separated. The resulting end product, thus, is a light fraction consisting substantially of paper of mechanical pulp fibres, and a fraction consisting substantially of paper of chemical pulp fibres.

In the system described above the separation takes place in the wind sifter.

shredder where the tougher plastics is disintegrated to oversize and the paper to intermediate size, in the absence of added liquid in said shredder, and sieving the product obtained from the shredder to separate the paper from the plastics and from the particulate impurities.

2 A method, according to Claim 1, in which the sieving step has two stages, the first stage separating the particulate impurities from the remainder of the product and the second stage separating the paper from the plastics.

3. A method according to Claim 1 or Claim 2, comprising subjecting the paper fraction obtained from the sieving step to the action of a wind sifter in such manner that a lighter paper fraction consisting substantially of paper fibres originating from mechanical pulp is separated from a heavier paper fraction consisting substantially of paper fibres originating from chemical pulp.

4. A method, according to Claim 3, in which the lighter and heavier paper fractions obtained from the wind sifter are subjected to a purifying action for the removal of any entrained particulate impurities.

5. A method of treating a light fraction of refuse substantially as hereinbefore described with reference to the accompanying drawings.

6. Apparatus, for carrying out the method according to Claim 1, comprising a shredder for disintegrating the light fraction, in which shredder the tougher plastics is given the form of oversize and the paper is given the form of intermediate size; sieve means downstream of the shredder for sieving the product obtained from the shredder to separate the paper from the plastics and from the particulate impurities; a drier or drying the paper fraction; and a wind sifter for dividing the paper fraction into a lighter fraction and a heavier fraction so that the lighter paper fraction consists substantially of paper fibres originating from mechanical pulp and the heavier paper fraction consists substantially of paper fibres originating from chemical pulp.

7. Apparatus according to Claim 6, further comprising sieves located downstream of the wind sifter for treating the lighter and heavier paper fractions, respectively so as to separate any entrained particulate impurities therefrom.

8. Apparatus for treating a light fraction of refuse substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawing.

9. Paper whenever separated by the method according to any one of Claims 1 to 5 or in the apparatus according to any one of Claims 6 to 8.