BE1020903A3 - PROCESS FOR RECYCLING GLASS WASTE. - Google Patents

Description

Process for recycling glass waste Object of the invention

The present invention relates to a method of recycling glass waste.

The present invention also relates to a composition obtained by such a method of recycling glass waste and to a device for implementing said glass waste recycling process.

State of the art

Current glass recycling processes generally start with a first manual sorting step, in which about 7% by weight of the glass waste is discarded and discarded. This waste consists of waste of all kinds, mainly foreign to the packaging glass. This waste is evacuated to a landfill or is incinerated.

Then, this manually sorted glass is crushed coarsely and is then sorted (screened). The glass fragments resulting from grinding having dimensions of less than approximately 10 mm (fines) are then discarded, while the other fragments obtained are sorted by an optical detection device. Glass not separated by this optical sorting (screening) can then be used as purified cullet in glass manufacturing processes.

This optical sorting does not make it possible to economically and economically treat glass fragments smaller than 10 mm. Some recyclers work with significantly smaller fragment sizes (on the order of 7 mm). In this case, the efficiency of the optical sorting machines is improved, however to the detriment of the sorting quality. The choice of the type of recycling will depend on the final quality of the treated glass desired by the customer.

The fraction of the glass less than 10 mm is removed by screening at the outlet of the mill. In principle, this fraction of fines contains a higher rate of KSP (acronym meaning Keramiek, steen, porcelein, that is to say infusible materials, and in particular terracotta, ceramics and porcelain). Heat-resistant glass waste (such as pyrex (registered trademark)) and various glass-ceramics are also present in this scraped fraction.

In addition, these fines obtained from recycling are proportionally more rich in organic materials, including food residues contained in the packaging. This organic pollution concerns more the colorless glass where pots and jars are more frequent.

At this fraction eliminated by screening, is added the rejection from the actual optical sorting.

[0009] Optical sorting is mainly aimed at eliminating infusibles. However, the technology of ejection of the undesirable particles by compressed air jet does not allow a sufficiently fine discrimination and the rejection generated by this operation contains about 80% of recyclable glass which is found in the fines.

The use of these glass fines from recycling by glassmakers poses a large number of technical problems: • Very high reactivity to charging due to grain size, the presence of moisture and the presence of organic matter; • Presence of (organic) reducing material disturbing the control of the degree of redox of the melt; • Formation of foam on the surface of the bath which interferes with the thermal exchanges and • Possibly dangerous situation with the charging.

Despite these difficulties, the glassmakers who directly own the glass collected by the · municipalities will tend to bake the fines obtained from recycling, in greater or lesser quantity depending on the economic context in which the glass recycling takes place . Some develop initiatives to reduce the nuisances due to the presence of these fines.

According to a known method, the fines are conveyed against the current of an oven to dry the material. These fines once dried, sieving allows the elimination of a large part of the organic materials present on these fines.

According to another known method, washing is carried out, grinding and drying cullet fines, before introducing them into a glass manufacturing process.

Finally, it is also known to grind fines out of a purification line, these fines being washed beforehand without drying.

When glassmakers buy purified cullet by a third party recycler, they have no reason to accept the fines from the treatment since they are polluted and likely to cause the problems mentioned above.

This is for example the case for Belgian recyclers, these being structurally related to any glass group. Belgian recyclers are not alone in this case. The acceptance or refusal of fines is therefore essentially a question of commercial negotiation, made even more difficult in periods when the demand for cullet is not important.

For some recyclers active in Belgium, all scrap (about 18% of production) goes to landfill, to possibly serve as a cover layer. This 'valorisation' however requires a slight treatment. This is an elementary grinding to standardize the grain size, a suction of light fractions (paper and labels) and a déferrisation. Alternative outlets such as abrasives, paint fillers, etc. remain very marginal given the small volumes concerned.

In the current economic context of surplus cullet to be treated, glassmakers therefore refuse glass fines from independent recyclers. On the other hand, glassmakers regularly meet their quality requirements. These new stringent quality criteria could force recyclers to review the operational parameters of their facilities and consequently produce more fines and less cullet.

Finally, note the existence of glass waste comprising significant amounts of organic material that can not be removed by washing, or by simple mechanical methods. This is for example the case of sized glass fibers, or even composites with fiberglass reinforcements.

In addition, in the composition of the glass, a calcium intake is necessary (addition of +/- 10% by weight of CaO). It is present in the atomic structure of glass in the form of oxide CaO.

For economic reasons, calcium as raw material is incorporated into the melting bed in the form of carbonates CaCO 3 (or CaMg (CO 3) 2 / limestone and / or dolomite, or other residual material from another production, such as marble sludge, for example).

Calcium can also be incorporated into the glass as lime (CaO), a form closer to its chemical structure in the glass. A calcium intake in this form is however not practiced industrially given the price of lime.

In a glass furnace, the limestone undergoes decarbonation. Between 500 and 800 ° C, carbonates react with release of CO2

In a glass furnace, these reactions occur in an area close to charging.

The conventional method of vitrification with limestone charging must support the energy cost of the reaction and the emission of greenhouse gas (CO2) concomitant from the combustion and the decarbonation reaction.

Goals of the invention

The present invention aims to provide a method for the recycling of waste comprising glass in the glass recycling channels which does not have the disadvantages of the prior art or which reduces the disadvantages of the state of the art. technical, in particular a method that reduces the amount of glass waste landfilled. The present invention also aims to provide a method that simplifies the steps of sorting and recovering recycled glass.

Summary of 11 invention

The present invention discloses a method of recycling glass waste comprising the following steps: grinding the glass waste to be recycled; mixing ground glass waste with calcium carbonate; a heat treatment of the mixture obtained in the preceding step at a temperature permitting the decarbonation of the calcium carbonate and its conversion to calcium oxide (CaO).

According to preferred embodiments of the invention, the process comprises at least one or any suitable combination of the following characteristics: the crushed glass waste has a particle size of less than 0.5 mm; the waste ratio of glass / calcium carbonate is between 10 and 1, preferably between 5 and 2; - the glass waste is dried before being crushed; the drying is obtained by circulation of the gases resulting from the heat treatment; the heat treatment reaches a minimum temperature of 550 ° C., preferably 825 ° C. the heat treatment is carried out at a temperature below the softening temperature of the glass, preferably below 1000 ° C., advantageously below 900 ° C .; - Glass waste is glass fines from a process of sorting glass waste.

The present invention also discloses a composition suitable for the manufacture of glass obtained by the process according to the invention comprising: 10 to 50% by weight of CaO or Ca (OH) 2; 50 to 90% by weight of soda-lime glass; a concentration by weight of organic matter of less than 0.1%.

[0029] Preferably, the composition according to the invention has a particle size of between 1 and 10 mm, preferably between 2 and 5 mm.

Advantageously, the composition of the invention comprises infusible residues having a particle size less than 0.5 mm.

[0031] The present invention also discloses the use of the composition of the invention in a glassmaking process.

Finally, the invention discloses a device for implementing the method of the invention comprising: an oven whose gas evacuation pipe comprises a drying zone suitable for drying glass waste; a grinding system downstream of the drying zone for grinding glass waste with a grain size of less than 0.5 mm; means making it possible, in use, to mix the crushed glass waste with limestone; means for transporting the waste mixture of glass / limestone to said furnace.

Advantageously, the oven of the device of the invention is a lime kiln rotary type or fluidized bed.

Brief description of the figures

[0034] Figure 1 schematically shows the method according to the invention.

Detailed description of the invention

The present invention relates to a method of recycling and recovery of. glass waste to reduce the amount of waste ultimate dispose of landfill. Glass waste to recycle in! the present invention generally comprise large amounts of organic residues, which pose the problems mentioned above.

The recyclable glass waste by the present invention will be, for example, insulation or reinforcement fibers, glass fibers sized by organic coatings, fiberglass reinforcing composites, glass fines, or any other waste comprising significant amounts of glass, either in the form of glass contaminated with organic residues, or organic matrices comprising glass fillers.

By the terms "fines" or "glass fines" is meant the waste fraction spread during a recyclable glass sorting process, either because of the too small dimensions of said fraction to be sorted by automatic optical devices, ie waste separated during optical sorting itself .; These fines are usually composed of 80% soda-lime glasses, the rest being composed of various infusible materials (porcelain, ceramic, terracotta, ...) and / or organic residues.

The present invention is suitable for all types of silica-based glass, in particular so-called soda-lime glasses. composition comprising predominantly silica, mixed with other oxides, in particular magnesium and calcium oxides.

The waste to be treated may vary in composition significantly, the composition of the melting bed in the subsequent process being adapted according to the composition of the product of the invention.

In the process of the invention, the fines separated during traditional sorting processes are first finely ground, so as to allow a rapid dissolution ("digestion") of infusible impurities in the molten glass.

By way of example, Table 1 gives the duration of the "digestion" by a bath of molten glass of a given particle in an oven at 1350 ° C.

Table 1

(*) ZAC 1711 is a refractory material resulting from the degradation of the furnace

It appears that for particle sizes less than about 500 .mu.m. the digestion time of the particles is compatible with an industrial glass processing process.

Preferably, said glass fines are dried before grinding, which improves the efficiency thereof.

The powder of glass fines produced by grinding then poses two main problems: on the one hand, the presence of organic residues induces a gassing during the melting process, which produces a "foaming" of the molten glass and, on the other hand, the combustion of these residues induces a variability of the oxidation-reduction conditions in the melting bed.

In a second step, the powder obtained is freed of these organic residues by pyrolysis at high temperature. Advantageously, this firing step is carried out in the presence of calcium carbonate at a temperature permitting decarbonation thereof, ie at a temperature above about 550 ° C. Indeed, from 550 ° C., the thermodynamic equilibrium between the partial pressure of atmospheric CO2 and the calcium carbonate displaces the CaCO 3 <-> CaO + CO 2 reaction to the right. Preferably, for reasons of reaction kinetics, the decarbonation is carried out at a temperature greater than 825 ° C., preferably greater than 912 ° C. It is interesting to note that the presence of silica makes it possible, by a catalytic effect, to accelerate the kinetics of decarbonation.

The source of calcium carbonate will be any source suitable for the glass industry. This may be in particular raw natural sources such as dolomite or other limestone rocks.

At the end of this heat treatment, we obtain a mixture of quicklime (CaO) and soda-lime glass optionally comprising inclusions of infusible material. These inclusions, however, have a particle size allowing them to be rapidly dissolved, when the mixture obtained is used in a traditional glass manufacturing process.

The mixture obtained comprising quicklime will then be used directly in a conventional glassmaking process, or later, for example after transport to a remote glass production line. In the latter case, the mixture may include, when introduced into the glass process, large amounts of slaked lime (Ca (OH) 2), the slaked lime from the absorption of moisture by quicklime.

The stability of the glass process is essential, the quicklime will preferably be extinguished in a controlled manner when the storage and transport will not allow sufficient control of the stability of the quicklime.

Advantageously, the mixture of slaked lime and soda-lime glass of the invention may be mixed with crushed glass fines to a particle size less than 0.5 mm but not heat treated, quicklime for predigestion of organic residues.

Advantageously, the proportion of soda-lime glass in the mixture obtained will be between 10 and 90% by weight, preferably between 50 and 90% by weight.

Preferably, the. final composition of the mixture will comprise at least 10% by weight of quicklime or extinguished, preferably between 10 and 50% by weight of quicklime or extinct.

In addition to the composition aspect of the mixture, the pyrolysis heat treatment also induces a coalescence of the glass particles and an aggregation with the quicklime, producing fragments of dimensions adapted to the glass manufacturing process, in particular at the level of of the charging. These dimensions may be modulated according to the needs of the glass manufacturing process by parameters such as processing time, temperature, composition, and / or rotation speed in the case of a process based on the use , of a rotary kiln.

Preferably the particle size of the product obtained will have sufficient dimensions to reduce the dispersion of fine particles in the glass furnace. Advantageously, these dimensions will be greater than 1 mm, more preferably still greater than 2 mm.

The energy consumption required for the process of the present invention is saved at the glass furnace, as is the emission of CO 2. The overall energy balance is therefore neutral except for the rise in temperature during charging.

The raw material thus obtained is advantageously suitable for the production of glass for the following reasons: absence of organic materials; • infused crushed; • suitable particle size; • the composition is dried and / or • incorporation of calcium in the form of CaO.

FIG. 1.shows in a synthetic way a theoretical flow sheet of the installation 1 repeating the various steps described above. In this installation 1, the glass fines (or other waste), resulting from the rejection of a traditional glass sorting process are conveyed via a hopper (10) to a drying zone (2). This drying zone (2) is advantageously supplied with hot and dry air from a heat recuperator (4) recovering heat (and dry gases) from an oven (7).

The dried fines are then conveyed by any suitable means to a grinding device (3) for reducing fines to a powder of particle size less than 0.5mm.

This glass powder is then mixed with limestone from a second hopper (11) in a mixing and feeding device (5). This feed device (5) feeds a hopper (6) which drives the glass / limestone mixture to an oven (7) heated by a burner (8). Preferably, this furnace (7) is a lime kiln of rotary type or fluidized bed.

At the outlet of the furnace (7), particles (9) of composition according to the invention are recovered to be subsequently valorized in a conventional glass manufacturing process. <

The product resulting from the process of the invention is advantageously a raw material composed of lime and cullet, intended for the glass industry. The method of the invention also makes it possible advantageously to incorporate in the melting bed the glass fines obtained by the rejection of the cullet purification process, and in particular makes it possible to recycle the rejects of the optical sorting described above.

This incorporation into the melting bed is without the difficulties and disorders caused by the charging of untreated fines, as it is sometimes practiced when the glassmakers are forced for economic reasons.

This new raw material responds advantageously and unexpectedly to all constraints specific to the charging of virgin raw materials and recycled cullet in a glass furnace, that is to say: - elimination of organic ; - Elimination of moisture; - suitable particle size; - infusible reduced by grinding into particles sufficiently fine to be digested during vitrification; - elimination of the cost of landfill (the value of fines is zero or negative); - compensated energy cost (heat of decarbonation).

Since it is the energy necessary for decarbonation which is used alternatively to remove organic matter and the moisture contained in the glass fines, a saving of the process is particularly favorable.

Claims (13)

1. A method for recycling glass waste comprising the following steps: grinding the glass waste to be recycled; mixing the crushed glass waste with calcium carbonate; a heat treatment of the mixture obtained in the preceding step at a temperature permitting the decarbonation of the calcium carbonate and its conversion to calcium oxide (CaO). 2. The method of claim 1 wherein the crushed glass waste has a particle size less than 0.5mm. 3. The process according to claims 1 or 2 wherein the waste ratio of glasses / calcium carbonate is between 10 and 1. 4. The process according to any one of the preceding claims wherein the glass scraps are dried before being crushed. 5. The method of claim 4 wherein the drying is obtained by circulating the gases from the heat treatment. 6. The process according to any preceding claim wherein the heat treatment reaches a minimum temperature of 550 ° C, preferably 825 ° C. 7. Process according to any one of the preceding claims, in which the glass waste is glass fines resulting from a process for sorting glass waste. 8. A composition suitable for the manufacture of glass obtained by the process according to any one of the preceding claims comprising: 10 to 50% by weight of CaO or Ca (OH) 2; 50 to 90% by weight of soda-lime glass; a concentration by weight of organic matter of less than 0.1%. 9. The composition of claim 8, characterized in that it has a particle size of between 1 and 10mm, preferably between 2 and 5mm. 10. The composition according to one of claims 8 or 9 characterized in that it comprises residues -infusibles having a particle size less than 0.5mm. 11. The use of the composition of any one of claims 8 to 10 in a glassmaking process. 12. A device (1) for carrying out the method according to any one of claims 1 to 7 comprising: --a furnace (7) whose gas evacuation pipe (4) comprises a drying zone ( 2) suitable for drying glass waste; - A grinding system (3) downstream of the drying zone (2) for grinding glass waste to a particle size less than 0.5 mm; - means (5) allowing, in use to mix the crushed glass waste with limestone; - Transport means (6) of the waste mixture of glass / limestone to said lime kiln. 13. A device according to claim 12 wherein the furnace (7) is a lime kiln rotary type or fluidized bed.