PREPARATION OF A RAW MATERIAL COMPOSITION
20230391653 · 2023-12-07
Inventors
Cpc classification
International classification
Abstract
A method for preparing a raw material composition adapted to be fed into the melting chamber of a facility adapted to obtain cullet, glass wool and/or rock wool, textile glass yarns, flat glass and/or hollow glass, the method including grinding a mineral wool mixture adapted to enter into the raw material composition, such that the granular mixture obtained after grinding has a bulk density greater than or equal to 30 kg/m.sup.3.
Claims
1. A method for preparing a raw material composition adapted to be fed into a melting chamber of a facility adapted to provide cullet, glass wool and/or rock wool, textile glass yarns, flat glass and/or hollow glass, said method comprising grinding a mineral wool mixture adapted to enter into the raw material composition, such that a granular mixture obtained after grinding has a bulk density greater than or equal to 30 kg/m3 and less than or equal to 500 kg/m3.
2. The method according to claim 1, wherein a mass proportion of said granular mixture relative to a total mass of said raw material composition is greater than or equal to 5%.
3. The method according to claim 1, further comprising adding cullet to said granular mixture, a mass of cullet being greater than or equal to 1% of the total mass of the granular mixture.
4. The method according to claim 1, further comprising a prior step of determining a desired bulk density value of the ground granular mixture, as a function of dimensional characteristics of a feeder to be used, and/or a desired feed rate value.
5. The method according to claim 1, wherein said mineral wool mixture has a moisture content greater than 1% of the total mass of said mixture.
6. The method according to claim 1, wherein at least one grinder equipped with a screen whose mesh size is less than 20 mm is used during the grinding.
7. A raw material composition suitable for being fed into the melting chamber of an installation suitable for obtaining cullet, glass wool and/or rock wool, textile glass yarns, flat glass and/or hollow glass, comprising a granular mixture whose bulk density is greater than or equal to 30 kg/m3 and less than or equal to 500 kg/m3.
8. The raw material composition according to claim 7, comprising a mass of cullet of at least 1% of the total mass of the granular mixture.
9. A method for melting a raw material composition according to claim 7, for obtaining cullet, glass wool and/or rock wool, textile glass yarns and/or flat glass/hollow glass.
10. The method according to claim 9, wherein said raw material composition is fed by a screw feeder.
11. The method according to claim 9, wherein said raw material composition is fed at a feed rate greater than or equal to 5 tons per day.
12. The method according to claim 9, wherein said raw material composition is fed below a level of the glass melt.
13. The method according to claim 9, wherein said raw material composition is fed above a level of the glass melt.
14. A method of manufacturing cullet, glass wool and/or rock wool, textile glass yarns, flat glass and/or hollow glass, comprising a melting method according to claim 9.
15. Cullet, glass wool and/or rock wool, textile glass yarns, flat glass and/or hollow glass obtained through a manufacturing method according to claim 14.
16. The method according to claim 2, wherein the mass proportion of said granular mixture relative to the total mass of said raw material composition is greater than or equal to 90%.
17. The method according to claim 16, wherein the mass proportion of said granular mixture relative to the total mass of said raw material composition is greater than or equal to 99%.
18. The method according to claim 10, wherein said raw material composition is fed from a buffer silo containing said raw material composition.
19. The method according to claim 12, wherein said melting method employs a melting chamber equipped with submerged burners.
20. The method according to claim 13, wherein said melting method employs a melting chamber equipped with burners arranged above the level of the glass melt.
Description
[0095] It is further understood that the present invention is in no way limited by the particular embodiments described and/or depicted, and that other embodiments are perfectly possible.
[0096]
[0097] According to known methods, the molten mixture can alternatively be cooled and fragmented to obtain cullet, formed into fibers to obtain glass wool or rock wool, spun into glass textile yarns and/or poured onto a tin float to obtain flat glass, each of these industrial applications being designated by the expression “glass product (5)” throughout the description.
[0098] According to a particular embodiment of the invention, such a manufacturing method comprises melting a raw material composition (4) obtained at least in part from a granular mixture (2) whose bulk density is greater than or equal to 30 kg/m3.
[0099] According to an easily reproducible procedure for measuring the bulk density of the granular mixture (2), the latter is first poured into a container, for example a bucket, of known mass and volume. The container must be at least liters in size in order to have sufficient precision and to respect an aspect ratio that limits the settling of the mixture, by satisfying the formula:
L.sub.max≤2.sup.3√{square root over (V)} [Math. 1]
Wherein L.sub.max is the maximum extent of the container in a given direction, by analogy with the Feret diameter of a particle, and V is the volume of said container.
[0100] It is also important to ensure that the mixture is poured gently, without any movement of the bucket or mechanical compression of the mixture, in order to minimize the settling of the mixture. The filled bucket is then weighed to determine the mass of the poured mixture. The bulk density is the ratio of the measured mixture mass to the volume of the bucket.
[0101] It should be noted that such a method of characterizing bulk density is significantly more accurate and rigorous than any alternative method that simply estimates the size of a fiber agglomerate, also known as a “flake”. Indeed, any mineral wool mixture (1) can be seen as an agglomerate of mineral fibers, of expandable or compressible volume, which can itself be divided into a plurality of agglomerates of smaller and/or of lower density fibers. In the absence of additional information, the size of a mineral fiber agglomerate is therefore not usable as data to characterize a product and/or to compare two products.
[0102] In order to estimate more precisely the value of the glass feed rate as a function of the variations of various operational parameters of a furnace and of the bulk density of the loaded composition, the inventors carried out a test campaign of conveying two batches of glass wool waste having respectively bulk densities of 20 kg/m3 and 110 kg/m3.
[0103] Two types of tests were implemented: [0104] “cold” tests, in which a screw feeder is fed for a given period of time with glass wool waste which is then collected at the exit of the feeder and weighed, in order to deduce the mass flow rate of the feeder. [0105] so-called “hot” tests, for which the same batch charger is arranged at the entrance of a working melting furnace. A known mass of waste is fed and the time taken to feed the total quantity is recorded in order to calculate the feed rate.
[0106] For both tests, the endless feed screw has a diameter and a pitch of 30 cm. The filling rate is 100%, with the screw loading hopper being filled to ensure constant feeding.
[0107] In parallel to these two industrial tests, theoretical feed rate values are calculated under the same operational conditions and based on the following formula, which gives an approximation of the feed rate Q carried by the screw (in kg/s):
Q=r*d*V*π*R.sup.2*H,
where r is the filling rate of the screw, d is the density of the mixture fed (in kg/s), V is the rotational speed of the endless screw (in s.sup.−1, 10 rpm under standard feeding conditions), R is the radius of the screw (in m) and H is the value of the screw pitch (in m).
[0108] Table 1 [Table 1] below shows the results obtained for four glass wool samples with different bulk densities. These four samples are fed into the furnace via the endless screw at different screw rotation speeds.
TABLE-US-00001 TABLE 1 Variation of the feed rate as a function of different operational parameters of a furnace and the bulk density of the composition being fed in Bulk Screw Feed rate in kg/h Ratio Sample density speed in Cold Hot Hot/Theory number in kg/m3 rpm Theory tests tests in % 1 20 10 232 216 150 65 2 110 2 248 254 147 59 3 110 3 372 360 283 76 4 110 4 495 492 383 77
[0109] Comparing the theoretical feed rate values and the results obtained with the cold tests, a negligible difference is observed. The screw transport theory (theoretical values) can therefore give a relatively accurate estimate of the cold results.
[0110] On the other hand, when comparing the theoretical values of feed rate and the results obtained with the tests carried out in hot conditions, a significant reduction in feed rate is surprisingly observed, of between 20% and 40% of the theoretical value. Several hypotheses could possibly justify such a difference in values, observed empirically, including the pressure exerted by the glass melt on the mixture to be loaded, and/or the rise of combustion gases from the furnace, these gases then occupying part of the space available in the screw.
[0111] Accounting for such a discrepancy has a direct application in industrial reality. For example, it is commonly accepted that for reasons of melting furnace profitability, the minimum feed rate of raw materials into the furnace should be 5 tons per day, or 208 kg/h. If a person skilled in the art sticks to the theory or to the results obtained in cold tests, i.e. in tests that are significantly easier to carry out than hot tests, they will come to the conclusion that under standard loading conditions, the use of glass wool waste with a bulk density of kg/m3 is sufficient to obtain a loading rate of 232 kg/h, i.e. a satisfactory rate.
[0112] And yet, this is not the case. The hot tests carried out on sample number 1 (see Table 1) show that the feed rate actually obtained is 150 kg/m3, i.e. a flow rate well below the set criterion.
[0113] For equivalent operational conditions, and taking into account a maximum deviation of 40%, the bulk density necessary to obtain a feed rate of 208.8 kg/m3, i.e. a value almost equal to the minimum threshold set, is in fact kg/m3.
[0114] Obtaining this threshold value of bulk density is not obvious, since it is the result of a series of complex (hot) tests carried out by the inventors.
[0115] In order to increase the bulk density of the granular mixture, the inventors used a standard industrial manufacturing grinder, and carried out a test campaign during which three batches of glass wool waste were ground up before the bulk density of the granular mixtures obtained was measured for each of these batches. The objective of this campaign was in particular to evaluate the influence of the various parameters of the grinder and the wetting rate on the bulk density of the ground mineral wool mixture.
[0116] A first batch consisted of standard glass wool panels only.
[0117] A second batch corresponds to this first batch to which 8.8 kg of moistened glass wool waste was added.
[0118] A third batch corresponds to this second batch to which 6.4 kg of moistened glass wool waste was added.
[0119] On the basis of these three batches, five (5) tests were implemented. Tests 1 to 3 being carried out with the first batch, varying the settings of the grinder. Test number 4 was implemented with the second batch, and test number 5 was implemented with the third batch.
[0120] Table 2 [Table 2] below presents the results obtained for each of these tests. In the absence of further clarification, all parameters not specified in this table are the same between each of these tests.
TABLE-US-00002 TABLE 2 Variation of the bulk density of ground glass wool waste as a function of the operational parameters of the grinding machine and the wetting rate of the ground mixture. Test Mesh size Speed Capacity Bulk density number in mm in rpm in kg/h in kg/m3 1 10 150 288 110 2 15 150 414 64 3 15 210 454 68 4 10 210 554 142 2 10 210 776 223
[0121] Comparing the results of tests 1 and 2, it is observed that reducing the mesh size of the grinder screen from 15 mm to 10 mm increases the bulk density of the granular mixture obtained by 72%, as well as the capacity of the grinder by 9.6%.
[0122] Comparing the results of tests 2 and 3, it can be seen that increasing the rotation speed of the drum from 150 to 210 rotations per minute (rpm) increases the bulk density of the resulting granular mixture by 6.5%.
[0123] Comparing the results of tests 1 and 4, it can be seen that the addition of moistened waste material to the ground glass wool mixture increases the bulk density of the resulting granular mixture and the capacity of the grinder. This is confirmed by the comparison of tests 4 and 5, where it is observed that increasing the proportion of wet waste further increases the bulk density of the ground mixture and the capacity of the grinder.