The present invention relates to a method for separation (isolation) of a 3-10 mm fraction of glass cullet of a quality of glass raw material and substantially homogenous (uniform) as to the glass color.

A glass cullet constitutes a valuable raw material for glass-making industry, provided that it meets respective quality requirements related to the level of impurities. Isolation of glass cullet from municipal wastes, and purification of the cullet from organic material residues involves considerable technical difficulties, in particular in the case of fine-grain fraction of glass cullet. These difficulties increase when separating cullet of a uniform color, being the most desirable material for the glass-works.

International publication WO 98/25860 discloses a method for thermal treatment of glass cullet in order to obtain raw material for glass-making industry, in which method through a bed of glass cullet hot gasses are passed of such temperature so as to cause pyrolysis of impurities. Usually, the hot gases are combustion gases of a temperature 400-500°C.

International publication WO 99/31022 discloses a method for the preparation of raw material for glass-making industry, wherein mixed glass cullet (non-sorted as to the color) is provided, a decolorizing agent is added that decolorizes at least one kind of glass in the cullet, and an colorizing agent which enhances another color, and the glass cullet is melted to obtain a glass product.

International publication WO 2005/016835 teaches a system for sorting a mixed stream of glass cullet into streams comprising glass of the same color, where the system comprises at least one source of light for emitting light of predetermined frequency towards the cullet, and at least one camera to detect the light transmitted through the cullet.

International publication WO 2006/055238 discloses a method for creating a batch of mixed glass cullet, comprising recovering first mixed cullet and second mixed cullet from a glass-making plant, and respectively combining first and second glass cullet according to the weight ratio and percent contents so as to obtain a formulation to produce glass of a desired color. It is the aim of the invention to provide a method for isolation of glass cullet of a glass raw material quality and substantially uniform as to the glass color, in a form of 3-10 mm fraction.

A method for isolation of 3-10 mm fraction of glass cullet of a glass raw material quality and substantially uniform as to the glass color, according to the invention, is characterized in that a material of granularity of 0-10 mm comprising glass cullet and substantially free of plastics, is subjected to a vibration drying at a temperature of 250-350°C with separation of fine-grained impurities by suction, and the dried and preliminary purified material comprising glass cullet is subjected to a mechanical abrasive treatment in a de-labeling machine, by moving the glass cullet-comprising material with the use of rotational paddles arranged on a common shaft, and then the sub-grain fraction of a size below 3 mm is screened off, said sub-grain fraction constituting entirely wastes, and the oversized particles constituting purified glass cullet are directed to color sorting, where during screening of the glass cullet-comprising material and during transferring the purified glass cullet to color sorting a suction of paper particles is performed, and the purified glass cullet is subjected to two-step color sorting with the use of an optoelectronic sorter, where in the first step of sorting from the purified glass cullet a main glass cullet stream is isolated that comprises mainly glass cullet of a first color with impurities of stones and ceramics and glass cullet of a second and third colors, and a secondary glass cullet stream comprising mainly glass cullet of the second and third color, as well as a waste stream comprising mainly stones and ceramics, and next the main stream of glass cullet is introduced into the second step of sorting to separate the remaining impurities of stones, ceramics and glass of the second and third colors, to obtain a 3-10 mm fraction of glass cullet of glass of the first color of a glass raw material quality and substantially uniform as to the glass color. Preferably, the glass of the first color is colorless glass, the glass of the second color is brown glass and the glass of the third color is green glass. During the first step of color sorting and/or during the second step of color sorting and/or during transferring the main glass cullet stream from the first step of color sorting to the second step of color sorting, especially a suction of paper particles is performed. Optionally, the secondary glass cullet stream, comprising mainly glass cullet of the second and third color, is introduced into a third step of sorting to separate the remaining impurities of ceramics and stones, to isolate furthermore glass cullet of the second and third colors of a glass raw material quality. Preferably, the second and third steps of sorting are carried out in parallel in a single optoelectronic sorter, said sorter having a first and second segment, where the second step is carried out in the first segment and the third step is carried out in the second segment. In particular, the main glass cullet stream discharged from the first step of color sorting, said stream comprising mainly glass cullet of the first color with impurities of stones and ceramics and glass cullet of the second and third colors, is a stream of colorless glass cullet containing at most 0.018% by weight of impurities of stones and ceramics, and at most 6% by weight of brown glass and/or 6% by weight of green glass. Preferably, the obtained 3-10 mm fraction of glass cullet of the first color of a glass raw material quality and substantially uniform as to the glass color, is the colorless glass cullet containing at most 0.002% by weight of impurities of stones and ceramics, and at most 3% by weight of brown glass and/or 1% by weight of green glass. According to the method, the colorless glass cullet of a glass raw material quality and substantially uniform as to the color, is obtained by processing of at least 6 t/h of material of a granularity of 0-10 mm comprising glass cullet. Preferably, the vibration drying is performed at a temperature of 280-320°C, in particular at a temperature of approximately 300°C.

The method of the invention enables to isolate from municipal wastes a quality raw material for glass-making industry, from a fine-grain fraction of below 10 mm, which usually constitutes wastes. The method enables effective removal of dust and fine particle impurities and effective sorting of the isolated glass cullet to obtain a fraction comprising glass of a uniform color. As a side product, a fraction comprising glass of other colors is obtained. Since the prevailing fraction in the glass cullet is colorless glass, and moreover this kind of glass is the most demanded one by the glass-works, then preferably the glass obtained of uniform color in the method of the invention is colorless glass, and the produced side fraction of glass cullet is a fraction comprising mixed brown and green glass.

The use in the method of the invention a mechanical abrasive treatment, following obligatory a vibration drying and suction of dust and fine particles, solves the problem related to the presence of impurities on a glass surface. It has been found that the total level of impurities remaining on the glass surface does not exceed 5%, and this makes it possible to recover effectively glass cullet of a lower limit of glass granularity of 3 mm, while maintaining the quality characteristics required by glass-making plants, including mainly the level of impurities in a form of stones and ceramics (identified by optoelectronic sorters by absence of transparency) at a level of 0.002% by weight. Fig. 1 shows a flow diagram of operations performed in the method of the invention.

Within this specification of the present invention and the patent claims, glass cullet of a glass raw material quality is the glass cullet comprising at most 0.002% by weight of ceramics and stones, substantially free of organic impurities.

Within this specification of the present invention and the patent claims, glass cullet substantially uniform as to the glass color is the glass cullet of first color, comprising at most 3% by weight of glass of second color and at most 1% by weight of glass of third color. Preferably, the glass cullet substantially uniform as to the glass color is the glass cullet of colorless glass comprising at most 3% by weight of brown glass and at most 1% by weight of green glass.

Within this specification of the present invention and the patent claims, material of a granularity of 0-10 mm comprising glass cullet, substantially free of plastics, is a sub- grain fraction being a side product from crushing wastes comprising glass and glass cullet, obtained as a result of screening of crushed wastes recovered from waste dumps, municipal wastes and wastes originated during recovering materials for recycling, as well as separated on sieves and non-purified production wastes from glass cullet treatment processes.

Till now, a material of a granularity of 0-10 mm comprising glass cullet has not been used for a glass recovery.

In the method of the invention, a material of a granularity of 0-10 mm comprising glass cullet and substantially free of plastics, is supplied. Glass cullet is typically the glass cullet of colorless, brown and green glass. The amount ratios of the individual kinds of glass in the glass cullet can vary, depending on the origin of the material, although usually 60-65% of the glass cullet constitutes colorless glass cullet. The material used of a granularity of 0-10 mm comprising glass cullet, is substantially free of plastics, in particular thermoplastic plastics. Plastics are mostly removed from the waste material by known methods, before screening off the 0-10 mm fraction of the material, e.g. by such methods as the ones disclosed in WO 2006/017285 and in the documents quoted therein. Presence of thermoplastic plastics may unfavorably affect sorting operations used in the method, due to a possibility of agglomeration of the components at higher temperatures.

Material of a granularity of 0-10 mm comprising glass cullet is moist or wet and this assists adherence of grains included therein of diverse size and content. The inventors have found that this property unfavorably affects the processes of mechanical sorting used in the method of the invention, and the process of drying of the material is obligatory required. Therefore, it is contemplated in the method that the material of a granularity of 0-10 mm comprising glass cullet is fed by means of a hopper 1 into a conveyor device that conveys the material to a drying device 2. The conveyor device may by a conveyor of any type, such as for example belt conveyor.

The drying is performed in a drying device 2, through which the material of a granularity of 0-10 mm comprising glass cullet is passed on a vibration supporting member. The drying temperature amounts to 250-350°C, preferably 280-320°C, and more preferably approximately 300°C. The dwelling time for the material inside the drying device 2 is about 1 minute.

It has been unexpectedly found that drying combined with vibrating of the material causes the effective separation of fine-grained impurities, such as clays, sands, fibers and other organic impurities. The purification of the material is enhanced by suction of impurities that are discharged by venting systems into an external filter 3 where they are collected.

The drying device 2 is preferably a gas dryer equipped with a vibrating supporting member such as a vibrating gutter or a vibrating plate. The vibrating gutter or plate is provided with perforations by which a gaseous mixture flows from below, such as air, combustion gases and/or a mixture of air and combustion gases. Exhaust gases along with evaporated water and at least a part of dust impurities are discharged from above the layer of the material being dried.

The gaseous mixture flowing through perforations is a hot gaseous mixture, but it can also be a cold gaseous mixture, if thermal energy is supplied by other means (e.g. IR radiators). It is also contemplated a solution of the inventive method wherein to the drying device 2 hot gaseous mixture is supplied and at the exit from the drying device 2 cold gaseous mixture is supplied so as to cool the dried material down.

The drying process may be also performed in a drying device 2 of another type, provided that drying is effected with vibrating of the material to be dried so as drying is accompanied by suction of dust, sand, fibers and other fine-grained impurities, since during the process of drying and vibrating of the material, an effective separation of impurities from the glass cullet occurs. As a result, unexpectedly, considerable purification of the glass cullet-comprising material is obtained. The dried and preliminary purified material comprising glass cullet is transferred to a further process which is a mechanical abrasive treatment. Therefore, it is contemplated in the method of the invention to supply the material to a conveyor device that conveys the material to another device. The conveyor device may by a conveyor of any type, such as for example a belt conveyor.

The purpose of mechanical abrasive treatment is to remove impurities strongly adhered to the glass surface, such as sand, clays and organic impurities, in particular to remove portions of labels that had been glued to glass packagings subjected to commercial turnover. The process of mechanical abrasive treatment is preferably carried out in a de-labeling machine 4. For example, the de-labeling machine 4 is a form of an inclined gutter with a rotary shaft positioned along the gutter axis, on which shaft paddles (blades) are transversely arranged. The planes of the paddles are inclined by an angle different than 90° to the gutter axis, being in conformity with the material movement direction. The material fed at the lower end of the gutter, as a result of rotation of paddles arranged on the shaft, is conveyed along the rising gutter. From the upper end of the gutter the material comprising purified glass cullet and non-vitreous particles separated from the glass surface is discharged. The dwelling time of the dried and preliminary purified glass cullet-comprising material in the de-labeling machine 4 amounts to approximately 5 minutes.

It has been unexpectedly found that the use of the process of glass fragments abrading in the case of glass cullet of a granularity of 3-10 mm is considerably more effective than in the case of glass fragments abrading in the glass cullet of a granularity higher than 10 mm. For example, for the glass cullet of a granularity higher than 10 mm, as a result of 5 minutes long abrasive processing in a de-labeling machine 4, the extent of impurities still adhered to the glass surface is even as high as 20% of the glass surface. To the contrary, for the glass cullet of a granularity of 3-10 mm, the extent of impurities that are still adhered to the glass surface does not exceed 5% of the surface.

Moreover, the inventors have unexpectedly found that insufficient separation of sand grains preceding the mechanical abrasive treatment causes that the extent of impurities still adhered to the glass surface (mainly constituted by label residues) exceeds 5% of the surface, and this is an undesirable effect. On the other hand, the use of the drying process along with vibrations and suction of fine-grained impurities, as a process preceding the mechanical abrasive treatment in the de-labeling machine 4, makes it possible to achieve a high level of separation of impurities strongly adhered to the glass surface, i.e. at a level not exceeding 5% of the surface. Hence solely as a result of the use of this combination of the processes where a drying device 2, such as gas dryer with a vibrating gutter and a venting system for suction of sand and similar impurities to a filter 3, it is possible to carry out subsequently abrasion of labels with the use of the de-labeling machine 4 and cleaning of the glass surface. In the case of moist glass, there occurs re-adhesion of label residues to the glass surfaces of the cullet, and in the case of appearance of sand grains in the de-labeling machine, the abrasion process does not ensure conformity with normative requirements and precludes correct identification of glass by the optoelectronic sorters 6 and 7 used in subsequent steps of the method of the invention.

The material comprising purified glass cullet and non-vitreous particles separated from the glass surface, discharged after the mechanical abrasive treatment process in the de-labeling machine 4, is conveyed to at least one sieve to separate an oversized particle fraction constituting purified glass cullet (3-10 mm fraction). Sub-grain of a size smaller than 3 mm constitutes wastes and it is not useful for further sorting.

During screening of the material comprising purified glass cullet and non-vitreous particles separated from the glass surface, as in the course of conveying the purified glass cullet to further sorting, the suction of paper fragments is performed. For transportation of the material a conveyor device of any type is used, such as for example a belt conveyor.

The purified glass cullet-comprising typically a mixture of glass of a first color, glass of a second color, glass of a third color, as well as stones and ceramic particles (porcelain, faience, etc.) is transferred for color sorting. Sorting is performed with the use of optoelectronic sorter 6, 7, for example as the one disclosed in WO 2005/016835. In the method of the invention two-step color sorting is applied, where in the first step a three-way optoelectronic sorter 6 is used to separate purified glass cullet into three streams: a main glass cullet stream comprising mainly the glass cullet of the first color, a secondary glass cullet stream comprising mainly glass cullet of the second and third colors; and a waste stream comprising mainly stones and ceramics. After sorting, the main glass cullet stream comprising mainly glass cullet of the first color also comprises impurities in a form of glass of the second and third colors, and stone and ceramics impurities.

Typically, the purified glass cullet constitutes glass cullet comprising colorless glass, brown glass and green glass. Usually, 60-65% by weight of glass cullet constitutes colorless glass cuUet. This is also the most valuable raw material for glass-making plants. Preferably, in the method of the invention, it is the purpose of color sorting to obtain colorless glass cullet. As a result of previous drying with vibrations and mechanical abrasive treatment, color sorting of 3-10 mm glass cullet is very efficient. For example, already the first step of color sorting leads to obtaining colorless glass cullet comprising at most 0.018% by weight of impurities constituted by stones and ceramics, and comprising at most 6% by weight of brown glass and/or at most 6% by weight of green glass.

In order to obtain glass cullet of a glass raw material quality and substantially uniform as to the glass color (preferably such as colorless glass cullet comprising as impurities at most 0.002% by weight of ceramics and stones, and at most 3% by weight of brown glass and 1% by weight of green glass), the main glass cullet stream comprising mainly glass cullet of the first color is conveyed to the second step of color sorting. In the second step of color sorting a two-way optoelectronic sorter 7 is used, to separate the remaining impurities of stone and ceramics and glass of the second and third colors. On the exit from the sorter 7, a stream of glass cullet of the first color is obtained as well as a stream comprising impurities (stones and ceramics, as well as glass of the second and third colors, jointly). Preferably, the stream of glass cullet of the first color is a stream of colorless glass cullet comprising as impurities at most 0.002% by weight of ceramics and stones, and at most 3% by weight of brown glass and/or at most 1% by weight of green glass (3-10 mm fraction). Glass cullet of this level of impurities meets the requirements for the glass raw material with regard to the level of stone and ceramics impurities and as to the color uniformity.

Optionally, the secondary stream from the first step, comprising mainly glass cullet of the second and third color, is conveyed to a third step of color sorting. In this process, from the glass cullet comprising glass of the second and third colors, the residual impurities constituted by stones and ceramics are removed, to obtain additionally glass cullet of a glass raw material quality (but non-uniform as to its color).

In a particularly preferred embodiment of the method of the invention, the two-way optoelectronic sorter is equipped with a partition that divides the separation volume of the sorter into two segments, a segment intended for receiving the main stream of glass cullet from the sorter 6, and a segment intended for receiving the secondary stream of the glass cullet from the sorter 6. As a result of this arrangement of color sorting in the method of the invention, the second step and the third step of sorting are carried out in parallel, in one sorter 7.

Feeding individual streams from the sorter 6 into the respective segments of the sorter 7 is effected by gravity, i.e. the mutual arrangement of sorters is such that the respective streams of glass cullet discharged from the sorter 6 fall down directly to the respective segments of the sorter 7.

During the first step of color sorting and/or during the second step of color sorting and/or during the second step of color sorting and/or during conveying the main glass cullet stream from the first step of color sorting to the second step of color sorting, the suction of the remaining paper particles and other dust particles is carried out, into the cyclone 8.

Example

Material of a granularity of 0-10 mm comprising glass cullet (sub-grain fraction constituting a side product from crushing wastes comprising glass and glass cullet, obtained as a result of screening crushed wastes) in an amount of 6 t/h is fed through a hopper 1 to a gas dryer 2 of an internal temperature of approximately 300°C, onto a vibrating gutter on which the material is transferred with vibrations, staying inside of the dryer 2 for 1 minute. The vibrating gutter has perforations through which hot combustion gases are blown from below. Fine-grained organic impurities, sand and dusts are removed by suction and transferred to an external filter 3. The dried and preliminary purified material comprising glass cullet is transported on a belt conveyor to a de-labeling machine 4 of a type BET 10/40 (Binder & Co. AG). The material comprising purified glass cullet and non-vitreous particles separated from the glass surface, is discharged from the de-labeling machine 4 on a belt conveyor and fed to a sieve to separate the oversized particle fraction constituting the purified glass cullet (3-10 mm fraction) which is transported on a belt conveyor to an optoelectronic sorter 6. Over the belt conveyors (between the de-labeling machine and the sieve, and between the sieve and the sorter) there are arranged suction tips for suction of cellulosic fibers and dust released (suction through the cyclone) during mechanical abrasive treatment in the de-labeling machine 4.

Sub-grain particles of a size below 3 mm constitute wastes. In the first step of color sorting a three-way optoelectronic sorter 6 is used to separate the purified glass cullet into three streams:

(1.1) colorless glass with a presence of impurities of stones, ceramics and color glass (mainly brown and green);

(1.2) color glass with impurities of sand and ceramics;

(1.3) ceramics and sands that constitute wastes.

From the sorter 6 the stream 1.1 and the stream 1.2 are poured directly to the sorter 7 where two segments of different functions are defined:

(II.1) a segment to which white glass is directed, where all elements non being colorless glass are removed from the stream (elimination from the glass cullet of impurities constitutes by stones, ceramics and color glass);

(II.2) a segment to which color glass is directed, where stones and ceramics are removed.

The stream 1.1 after the first step of sorting comprises:

maximally 0.018% by weight of impurities constituted by stones and ceramics;

maximally 6% by weight of impurities constituted by green glass, in white glass;

maximally 6% by weight of impurities constituted by brown glass, in white glass.

The stream after sorting of the second step (discharged from the segment II.1 of the sorter) comprises:

maximally 0.002% by weight of impurities constituted by stones and ceramics;

maximally 1 % by weight of impurities constituted by green glass, in white glass;

maximally 3% by weight of impurities constituted by brown glass, in white glass.