GB2565261A

GB2565261A - A glass Briquette forming system

Info

Publication number: GB2565261A
Application number: GB1700091.0A
Authority: GB
Inventors: Gent Tim; Etches Simon
Original assignee: Individual
Current assignee: Individual
Priority date: 2017-01-05
Filing date: 2017-01-05
Publication date: 2019-02-13
Anticipated expiration: 2037-01-05
Also published as: GB201700091D0; GB2565261B

Abstract

A method of producing a glass briquette (20, fig 2) in which reclaimed glass fines are mixed with a binder material to create a mixture then compressed to conform in a chamber. The reclaimed glass comprises glass fines of a size of smaller than 10 mm e.g. smaller than 1 mm. The method is performed without melting the glass fines such that the resulting briquette contains the discrete glass fines held in the binder and may be used as a furnace ingredient for later glass product production. The moulding may be performed by tyres/rollers 11, 12 which may be counter-rotating and may have multiple pockets, e.g. in rows. The binder may be a lignosulfonate or sodium silicate binder, preferably from a spraying system 4. The glass briquette may contain other batch ingredients required in the production of glass. The briquette may be 1-10 wt % binder e.g. 2-5 wt. %. The relative breakability of glass and the size of the glass fines may aid in screening out contaminants.

Description

A Glass Briquette Forming System

The present invention relates to glass recycling, and in particular to the formation of briquettes from small particles of glass.

In an effort to drive recycling, it has become common for authorities to collect or accept mixed recyclable materials. Rather than requiring individuals or businesses to completely sort their waste into plastics, paper, glass etc at source, the mixed or co-mingled recyclables are taken to a Materials Recovery Facility (MRF) for separation and processing prior to being recycled.

Producing bottles and other glass products from recycled glass requires less energy input than working from raw materials, so is clearly desirable. However, problems can arise if contaminants such as paper labels, plastic or metal caps or lids and ceramic stones and porcelain (CSP) are present in the crushed glass product or cullet. These problems are typically more pronounced with glass obtained from a Materials Recovery Facility (MRF glass), where contaminants can often be present in unacceptable amounts in the crushed glass when it arrives. Impurities in the raw glass product can cause unwelcome chemical reactions during melting and thus make the product unsuitable for recycling. In some cases, the impurities can also cause damages to the furnaces used.

Various processing and cleaning methods for separating recoverable glass from MRF glass are known, but are generally inefficient. For example, screening the product is ineffective where there is little difference between the particle size of the glass cullet and the contaminants and/or where moisture is present causing the contaminants to stick to the glass. Separation by weight/density can be effective for lightweight contaminants, and ferrous metals can be removed using magnets, but contaminants such as CSP and non-ferrous metals which may have similar densities to glass and would not be removed.

These remaining contaminants, and many others, are less susceptible to breakage than glass, so one option would be to crush the glass cullet to a smaller particle size and then filter or screen the resulting material. This helps to ensure that there is a difference between the particle size of the glass and that of CSP or other contaminants prior to filtering/screening, such that the CSP or other contaminants can be separated from the glass more easily. Small particles (<5mm) of contaminants that remain in the cullet after this process will often melt in the heat of the furnace or pass through without causing significant problems. However, Larger (around 10-15mm) non-melt particles, of metal or CSP for example, have the potential to block the shear blade during processing of the molten glass. In extreme cases, this can lead to a blow back of molten glass from the furnace, representing a significant health and safety risk to operators. As such, even if the crushing operation fails to remove all of the remaining contaminants from the glass cullet, the removal or crushing of larger pieces is beneficial to the overall glass production process.

The key drawback of this approach is that glass particles or ‘fines’ of <10mm are generally not desirable, so much so that they are often sorted out of MRF glass at an early stage of processing. Among other things, there can be difficulties handling, storing and transporting the smaller particles, particularly finely ground or powdery material. The behaviour of glass fines during onward processing is also complicated. For example, there is a risk that the glass fines could be disturbed or agitated by jets of air used in a subsequent cleaning or sorting process or convection airflow within a furnace. The melt behaviour of glass fines and their reaction within a furnace is also unpredictable.

As a result of the various problems outlined above, it is quite common for MRF glass, particularly the smaller particles or fines, to be sent for use as an aggregate material in the building industry rather than being fully recycled into new glass products as would be preferable.

It is therefore an aim of the invention to overcome or mitigate the abovementioned problems and allow or simplify the recycling of MRF glass.

According to a first aspect of the invention there is provided a method of forming a glass briquette as defined in the appended claim 1. Further optional features of the method are recited in the associated dependent claims.

The method comprising the steps of mixing reclaimed glass, comprising glass fines of a size of smaller than 10mm, with a binder material to create a mixture, and subsequently compressing said mixture in a chamber to form a briquette having the shape of the interior of the chamber. The use of a binder material and the application of pressure helps to ensure that robust briquettes are forms from the reclaimed glass fines.

The reclaimed glass may comprise MRF glass, mixed glass or any other postconsumer glass, ie glass that has had at least one prior use.

Smaller glass fines, for example 5mm, 2mm, 1 mm may also be reclaimed and used in the method of the invention.

The chamber may be formed from a pair of opposing cavities, for example using a press comprising a pair of counter-rotating rollers with one of said pair of opposing cavities is provided as a pocket on the outer circumference of each roller.

Each roller may comprise a plurality of pockets, for example a plurality of rows of pockets provided across a width of the roller. For example, between 1 and 5 rows may be provided, and the total number of pockets may be as many as 268, 420 or more.

The binder material may be sprayed onto the reclaimed glass and/or may comprise a lignosulfonate (a sulfonate of lignin) or sodium silicate (often referred to as liquid glass).

The mixing step may comprise mixing in a ploughshare mixer.

The method may further comprise the step of crushing reclaimed glass to provide glass fines of a size of smaller than 10mm, 5mm, 2mm or 1 mm; said crushing step being performed prior to the mixing step. The initial crushing step may be of assistance in separating contaminants from the reclaimed glass, allowing higher quality glass products to be produced and/or avoiding potential health and safety issues.

The method may further comprise the step of separating any loose material from the briquette formed in compressing step, for example by moving the briquette formed in the compressing step, and any remaining loose material, across a screen. Any separated loose material separated at this stage could be returned to the mixing step of the compressing step for re-use. A time delay may be introduced between the compressing step and the separating step. For example, the briquette may pass along a conveyor between these two steps. The delay provides some time for the briquette to cure, improving its properties.

The mixture may comprise less than 10% by weight of binder material to avoid introducing unnecessary impurities into the glass in the briquette. The mixture may comprise from 2-5% by weight of binder material, for example 4% by weight of binder material.

All of the previously described steps may be performed at ambient temperature.

The method may further comprise the step of transferring the briquette to an oven for drying.

The invention also provides a glass briquette as defined in the appended claim 18. Further optional features are recited in the associated dependent claims.

The glass briquette comprises a compressed mixture of reclaimed glass and from 1-10% by weight of a binder material. The reclaimed glass comprises glass fines of a size of smaller than 10mm.

The mixture may comprise from 2-5% by weight of a binder material, for example 4% by weight of a binder material to avoid introducing unnecessary impurities.

The reclaimed glass may comprise glass fines of a size of smaller than 2mm or 1 mm. The binder material may comprise a lignosulfonate (a sulfonate of lignin) or sodium silicate (often referred to as liquid glass).

The glass briquette may be formed using a method as previously described.

Wherever practicable, any of the essential or preferable features defined in relation to any one aspect of the invention may be applied to any further aspect. Accordingly, the invention may comprise various alternative configurations of the features defined above.

Practicable embodiments of the invention are described in further detail below by way of example only with reference to the accompanying drawings, of which:

Figure 1 shows a schematic view of an example briquette forming plant according to the present invention

Figure 2 illustrates the form of a briquette formed with the system of Figure 1; and

Figures 3A to 3C show standard projections of the views of the briquette illustrated in Figure 2.

The briquette forming plant of Figure 1 comprises a hopper 1, for receiving raw material, which feeds out onto a weighing/dosing conveyor 2. The raw material comprises crushed glass with a small grain/particle size of less than 10mm, which would typically be considered glass fines not suitable for processing. In one particular example the raw material comprises MRF glass that has been crushed to a grain/particle size of less than 2mm and screened to remove larger pieces of harder or more resilient contaminants that survived the crushing operation. A weighing/dosing conveyor 2 transfers the material from the hopper 1 into a ploughshare mixer 3, where it is mixed with a binder material such as sodium silicate or a lignosulfonate (sulfonated lignin) which is sprayed into the mixer 3 from a spraying system 4.

Once mixed, the glass and binder material passes into a briquetting press 5 where pressure is applied to form briquettes from the mixture. A further, intermediate, conveyor 6 then transfers the briquettes to a screen 7, across which the briquettes pass before they reach a final conveyor 8 which transfers the briquettes to an oven for drying or simply to a storage or transport container. A power drive and control cabinet 9, for driving and controlling the process, is also illustrated.

The briquetting press 5 takes comprises a gravity feeder 10 and a pair of counterrotating tyres/rollers 11,12, each of which is provided with a plurality of cavities or pockets around their circumference. In one example, each tyre 11,12 has a diameter of 800mm and a width of 180mm, and is provided with five rows of eighty-four pockets. The pockets on the tyres 11,12 align with each other as the tyres 11,12 rotate to produce four hundred and twenty individual chambers for forming individual briquettes for every complete rotation of the tyres 11,12. An offload gap 13 is provided between the tyres 10,11.

The mixture from the ploughshare mixer 3 passes into the gravity feeder 10 of the press 5 and is drawn between the tyres 11,12 and compressed into the chambers to form a number of briquettes. As the pockets of the tyres move apart again the briquettes are deposited onto the intermediate conveyor 6, together with any mixture or loose glass fines that passed through the press 5 without being compressed.

The intermediate conveyor 6 provides time for the briquettes to cure and stabilise once formed. The screen 7 then separates out any loose mixture and glass fines from the briquettes so that only whole briquettes are transferred to the final conveyor 8 while the uncompressed mixture and loose glass fines pass through the screen 7 and are collected below 14.

Various aspects of the illustrated briquette forming plant can be adjusted if required using the control cabinet 9. For example, the speed of rotation of the tyres 11,12 in the press 5 may be altered, as can the applied pressure and off-load gap 13. The volume of binder applied by the sprayer 4 could also be modified, and the speed of the various conveyors 2,6,8 could be adjusted either to adjust the overall production rate or simply to increase or decrease the curing time on the intermediate conveyor 6.

Figure 2 shows the form of an example briquette 20 formed according to the present invention. The briquette 20 has curved upper and lower surfaces 22,24 which correspond to the shape of the opposing pockets provided on the tyres 11,12. The upper and lower surfaces 22,24 are separated by an edge section 26 which is formed as a result of the off-load gap 13 between the tyres 11,12.

The curved upper and lower surfaces 22,24 and the edge section 26 are more clearly shown in the side view of Figure 3A. The plan view of Figure 3B shows that the length 28 and width 30 of the example briquette 20 are 36mm and 27.8mm respectively. The depth 32, as shown in the end view of Figure 3C is 15.5mm. This represents a briquette volume of 8cm3.

The briquetting process of the invention was tested using a raw product of crushed glass mixed with various amounts of sodium silicate binder. The crushed glass used in the tests had a grain size of <2mm, a bulk density of 1.38g cm’3 and a moisture content of 0.47%.

All tests were conducted with 100% raw product in the mixture, ie with zero recycled fines, at ambient temperature throughout the forming process.

The press comprised a gravity feeder and a pair of counter-rotating tyres/rollers, and was similar to the press 5 described with reference to Figure 1. However, in the experiments the tyres were 600mm in diameter and 145mm wide. Two hundred and sixty-eight pockets were provided per tyre, each measuring 36x26x14.5mm giving a pocket volume of 7cm3. The off-load gap, ie the adjustment gap between the tyres in the press to prevent damage to the tyres, was consistently set at 1 mm.

The adjustment pressure for the press was uniformly 10 kilonewtons per linear centimetre (kN Icnr1) lower than the listed operating pressure. Although some pressure adjustment is achievable by varying the off-load gap, separate pressure adjustment means were provided.

In tests 1 to 10 a flap of the gravity feeder was opened 20%. In test 11 the flap of the gravity feeder was opened 35% to provide a difference in throughput/flowrate. Test 12 was a production test of 300kg of briquettes, and the gravity feeder was opened 35%.

A drop test was performed, from around 1 m, on briquettes from each of tests 1 to 11. The briquettes were then dried in a variety of different ways, and crush tests were performed on briquettes from tests 6 to 9. The results of the tests are summarised below. TEST 1 - 50 kg of raw product + 8% (by weight) of sodium silicate TEST 2 - 50 kg of raw product + 6% of sodium silicate TEST 3 - 50 kg of raw product + 4% of sodium silicate

In each of the first three tests the briquettes obtained were well shaped, particularly in the middle rows, but rather fragile at the drop test. Ten briquettes were dried in an oven at 100°C for one hour, resulting in very hard briquettes. TEST 4 - 50 kg of raw product + 2% of sodium silicate

Compared to tests 1 to 3 the briquettes produced were more fragile, at the press outlet, with a dry appearance. Ten briquettes were again dried in an oven at 100°C for one hour, but the briquettes remained less hard and crumbled more readily than in the previous tests. TEST 5 - 50 kg of raw product + 8% of sodium silicate

The results were generally in line with test 1, producing well shaped and good quality briquettes. Despite the higher operating pressure of the press, the briquettes weren't noticeably harder than the briquettes from test 1. Drying ten briquettes in an oven at 100°C for one hour again produced very hard briquettes. TEST 6 - 50 kg of raw product + 4% of sodium silicate

As expected, well shaped and good quality briquettes were produced as in test 3, which was performed using the same variable values. In test 6, the briquettes were placed in an oven at 100°C and crush tests were then performed, typically on two briquettes, at the furnace outlet after different time periods. The results were as follows: • 10 min - 56 kg, 63 kg • 20 min - 100 kg, 98 kg • 30 min - 92 kg, 95 kg • 40 min - 95 kg, 98 kg • 50 min (1 briquette) - 102 kg TEST 7 - 50 kg of raw product + 4% of sodium silicate

Test 7 was performed using the same product and binder amounts as test 6, but with the press at a lower operating pressure. This produced briquettes that were well shaped, but more fragile at the press outlet. As in test 6, the briquettes were then placed in an oven at 100°C and crush tests were performed on pairs of briquettes at the furnace outlet after different time periods, with the following results: • 10 min - No result • 20 min - No result • 30 min - 102 kg, 100 kg • 40 min - 94 kg, 97 kg • 50 min - 106 kg, 102 kg TEST 8 - 50 kg of raw product + 6% of sodium silicate

This test was performed at the same operating pressure as test 7, but with the amount of binder material increased. The briquettes obtained were again well shaped, but crumbled more easily. The crush test results after periods in 100°C oven were: • 10 min - 58 kg, 56 kg • 20 min - 70 kg, 73 kg • 30 min - 87 kg, 78 kg • 40 min - 53 kg, 55 kg TEST 9 - 50 kg of raw product + 8% of sodium silicate

Test 9 replicated the conditions and variable values used in test 1, and once again good quality briquettes were obtained. Crush tests were performed on cold briquettes both after heating as before and on unheated briquettes as follows: • After 10 min at 100°C in the oven - 66 kg, 65 kg, 68 kg • After 20 min at 100°C in the oven -101 kg, 94 kg, 120 kg • After 15 hours at ambient temperature (10°C) - 20 kg, 21 kg, 23 kg, 21 kg TEST 10 - 50 kg of raw product + 8% of sodium silicate

The test conditions again matched those of test 1. 20 kg of briquettes were put in the oven at 100°C for 20 minutes and then crush tests were performed on both warm and cold briquettes for comparison: • Warm briquettes - 62 kg, 64 kg, 63 kg, 71 kg • Cold briquettes -106 kg, 94 kg, 100 kg, 96 kg TEST 11 - 50 kg of raw product + 8% of sodium silicate

The test conditions for test 11 matched those for test 1, with the exception that the rotational speed of the press was doubled to 10 rpm. Well shaped and good quality briquettes were still obtained, although a relatively larger percentage (around 10% of the total material) passed through the press as fines without being formed into briquettes.

The experimental results, particularly from tests 3 and 6, show that the proposed method is quite capable of producing briquettes from glass fines with a particle/grain size of under 2mm. Indeed, briquettes could similarly be formed from smaller grain sizes of 1 mm or below. Once formed into briquettes, the glass can be handled, stored, transported and used far more easily.

It is envisaged that the resulting briquettes would generally be processed into products such as glass fibre or glass blocks where a lower purity is required. However, with appropriate sorting and decontamination it would be possible to use the same process to produce higher quality products such as bottles and other containers.

Although developed primarily to address problems associated with contaminated MRF glass, there is no reason why the method of the present invention could not be used with glass fines from other sources that would otherwise be deemed too difficult to process in a recycling operation, or simply to improve the appearance and/or simplify the handling of the glass cullet. There may be no need to crush the glass as an initial step, for example where the source material consists of clean glass fines that has been separated from larger pieces. Indeed, it would be quite possible for any glass fines 14 collected at the screening stage 7 in Figure 1 to be fed back into the hopper 1 to minimise waste.

Various types of glass that would otherwise be discarded or lost to the cycle of glass production can therefore be reclaimed due to the present invention.

Claims

CLAIMS:

1. A method of producing a glass briquette comprising the steps: a) mixing reclaimed glass with a binder material to create a mixture; and subsequently b) compressing said mixture in a chamber to form a briquette having the shape of the interior of the chamber; wherein the reclaimed glass comprises glass fines of a size of smaller than 10mm.

2. A method according to claim 1, wherein the chamber of step b) is formed from a pair of opposing cavities.

3. A method according to claim 2, wherein step b) is performed using a press comprising a pair of counter-rotating rollers, and wherein one of said pair of opposing cavities is provided as a pocket on the outer circumference of each roller.

4. A method according to claim 3, wherein each roller comprises a plurality of pockets.

5. A method according to claim 4, wherein each roller comprises a plurality of rows of pockets provided across a width of the roller.

6. A method according to any preceding claim, wherein the binder material is sprayed onto the reclaimed glass in step a).

7. A method according to any preceding claim, wherein the binder material comprises a lignosulfonate.

8. A method according to any preceding claim, wherein the binder material comprises sodium silicate.

9. A method according to any preceding claim, wherein the mixing of step a) comprises mixing in a ploughshare mixer.

10. A method according to any preceding claim, further comprising the step c) crushing reclaimed glass to provide glass fines of a size of smaller than 10mm; wherein step c) is performed prior to step a).

11. A method according to any preceding claim, further comprising the step d) separating any loose material from the briquette formed in step b).

12. A method according to claim 11, wherein a time delay is introduced between step b) and step d).

13. A method according to any preceding claim, wherein the mixture comprises less than 10% by weight of binder material.

14. A method according to any preceding claim, wherein the mixture comprises from 2-5% by weight of binder material.

15. A method according to any preceding claim, wherein the mixture comprises 4% by weight of binder material.

16. A method according to any preceding claim, wherein all steps are performed at ambient temperature.

17. A method according to any preceding claim, further comprising the step e) transferring the briquette formed in step b) to an oven for drying.

18. A glass briquette comprising a compressed mixture of reclaimed glass and from 1-10% by weight of a binder material, wherein the reclaimed glass comprises glass fines of a size of smaller than 10mm.

19. A glass briquette according to claim 18, wherein the mixture comprises from 2-5% by weight of a binder material.

20. A glass briquette according to claim 18, wherein the mixture comprises 4% by weight of a binder material.

21. A glass briquette according to any of claims 18 to 20, wherein the reclaimed glass comprises glass fines of a size of smaller than 2mm.

22. A glass briquette according to any of claims 18 to 20, wherein the reclaimed glass comprises glass fines of a size of smaller than 1 mm.

23. A glass briquette according to any of claims 18 to 22, wherein the binder material comprises a lignosulfonate.

24. A glass briquette according to any of claims 18 to 22, wherein the binder material comprises sodium silicate.

25. A glass briquette according to any of claims 18 to 24, formed using a method according to any of claims 1 to 23.

26. A method of producing a glass briquette substantially as hereinbefore described with reference to the accompanying drawings.

27. A glass briquette substantially as hereinbefore described with reference to the accompanying drawings.