PREPARATION OF RAW MATERIALS FOR GLASS FURNACE

Abstract

A device and to a process for the preparation and charging of starting materials for a glass furnace includes a system for carrying out a mixing of starting material powder and of liquid water producing a moistened mass of starting material powder, to a system for carrying out a mixing of cullet with the moistened mass of starting material powder producing a mixture of starting material and of cullet, known as SM/C mixture, a starting material preheater in which the SM/C mixture circulates and is heated and dried in order to produce a mass to be charged, then a system for charging the glass furnace with the mass to be charged.

Claims

1. A device for the preparation and charging of starting materials for a glass furnace, comprising: a means for carrying out a mixing of starting material powder and of liquid water, producing a moistened mass of starting material powder, said means comprising a tank provided with a stirring means, with an inlet for the starting material powder, with a feed of liquid water and/or of steam and with an outlet for the moistened mass of starting material powder, a system for carrying out a mixing of cullet with the moistened mass of starting material powder which has exited from the tank, in order to produce a mixture of starting material and of cullet, known as SM/C mixture, a starting material preheater in which the SM/C mixture circulates and is heated and dried in order to produce a mass to be charged, and a system for charging the glass furnace with the mass to be charged.

2. The device as claimed in claim 1, wherein the system for producing the SM/C mixture comprises a forwardly progressing belt on which the moistened mass of starting material powder and the cullet are deposited separately.

3. The device as claimed in claim 1, wherein the SM/C mixture flows at least partially vertically in the preheater.

4. The device as claimed in claim 1, further comprising a pipe adapted to convey combustion flue gases generated by the glass furnace to the preheater, so as to provide the latter with the thermal energy for heating and drying the SM/C mixture.

5. The device as claimed in claim 1, wherein the combustion flue gases and the SM/C mixture circulate in separate pipes in the preheater.

6. The device as claimed in claim 1, wherein the device is configured in order for the SM/C mixture to circulate continuously in the preheater and in order for the mass to be charged to be charged continuously to the furnace.

7. The device as claimed in claim 1, wherein the device is configured in order for the means for carrying out the mixing of starting material powder to operate noncontinuously.

8. The device as claimed in claim 7, wherein a regulating system is capable of detecting free space in the preheater and, according to the free space detected, of controlling the preparation of a mixture of starting material powder, the preparation of SM/C mixture and the introduction of SM/C mixture into the preheater.

9. A glass furnace equipped with the device of claim 1.

10. A process for the melting of glass in a furnace, comprising: carrying out, in a tank, a mixing of starting material powder and of liquid water, producing a moistened mass of starting material powder, said tank being provided with a stirring means, with an inlet for the starting material powder, with a feed of liquid water and/or of steam and with an outlet for the moistened mass of starting material powder, then mixing cullet with the moistened mass of starting material powder which has exited from the tank, in order to produce a mixture of starting material and of cullet, known as SM/C mixture, then heating and drying said SM/C mixture in a preheater, producing a mass to be charged, then charging to the furnace said mass to be charged.

11. The process as claimed in claim 10, wherein, in order to produce a mixture of starting material powder and of liquid water, liquid water is added to the starting material powder so that a sum of the mass of the liquid water contributed by the starting material powder and of the liquid water added to the starting material powder represents from 0.5% to 10% of the moistened mass of starting material powder.

12. The process as claimed in claim 10, wherein the SM/C mixture comprises from 0.2% to 9% by total mass of water, sum of the complexed water and of the liquid water.

13. The process as claimed in claim 10, wherein, at the inlet of the preheater, the SM/C mixture comprises from 0% to 9% by mass of liquid water.

14. The process as claimed in claim 10, wherein the mixing of starting material powder and of liquid water producing a moistened mass of starting material powder is carried out in a tank equipped with a stirring means, the moistened mass of starting material powder being brought therein to at least 36° C.

15. The process as claimed in claim 10, wherein the SM/C mixture enters the preheater while having a temperature of between 36° C. and 90° C.

16. The process as claimed in claim 10, wherein cullet is mixed with the moistened mass of starting material powder in order to produce the SM/C mixture containing from 1% to 60% by mass of cullet.

17. The process as claimed in claim 10, wherein the starting material powder comprises silica and a flux for silica.

18. The process as claimed in claim 10, wherein the starting material powder comprises a compound capable of dissolving at least partially in the liquid water of the moistened mass of starting material powder and of then precipitating in the hydrate form.

19. The process as claimed in claim 10, wherein a particle size of the starting material powder has a D50 of between 50 and 500 μm.

20. The process as claimed in claim 10, wherein at least 90% of the mass of cullet consists of particles with a size of between 1 mm and 10 cm.

21. The process as claimed in claim 10, wherein the SM/C mixture is heated to a temperature of between 100° C. and 500° C. in the preheater.

22. The process as claimed in claim 10, wherein the mass to be charged comprises less than 0.1% by total mass of water, sum of the mass of liquid water and of water in complexed form.

23. The process as claimed in claim 10, wherein the SM/C mixture circulates continuously in the preheater and wherein the mass to be charged is charged continuously to the furnace.

24. The process as claimed in claim 10, wherein a mixing of starting material powder and of liquid water which produces the moistened mass of starting material powder is carried out noncontinuously.

Description

EXAMPLES

Influence of the Water Content

[0051] Measurements of the cohesion of moistened starting material powder as a function of the water content show that the cohesion increases with the water content. Graded pellets of moistened mixtures of starting materials were prepared which contain the following mixture of powders (% given on a dry basis), none of these components of which was a hydrate: [0052] 60.3% by mass of sand [0053] 4.5% by mass of limestone [0054] 18.3% by mass of sodium carbonate [0055] 1.1% by mass of feldspar [0056] 14.9% by mass of dolomite [0057] 0.9% by mass of sodium sulfate,
to which mixture liquid water was added in different proportions (2%, 4%, 6% of water of the sum of the mass of liquid water and of powder). These pellets were subsequently dried at 150° C. overnight in the air. Finally, they were crushed with a uniaxial compression measurement apparatus. The maximum force at the moment of breaking, that is to say immediately before crushing, was measured. The pellets with 6% by mass of water initially introduced are stronger than those with 4% of water, which are themselves stronger than those with 2% by mass of water. Observation of the aggregates with a scanning electron microscope shows that these increase in size with the water content of the moistened starting material powder. When the water content increases, the grains are connected together better by bridges, the aggregates formed are larger and more compact. Generally, aggregates with a size of greater than 2 cm are not observed. An aggregate size is the distance between its two most distant points.

Influence of the Particle Size of the Cullet

[0058] A mixture of starting material powder and of liquid water is prepared in a jar in order to produce a moistened mass of starting material powder in a proportion of 3.6% of added water with respect to the moistened mass of starting material (mixture of sand, sodium carbonate, limestone, feldspar, sodium sulfate, coke). In order to do this, the mixture of dry powders is prepared beforehand and heated in a drying oven to 60° C., then the water is added and then the mixture is stirred in a 3D dynamic mixer for 5 minutes. This mixture finally has a temperature of at least 36° C. Stirring is halted, cullet is then added and the jar is stirred by hand for 1 minute. The amount of cullet was 40% by mass of that of the SM/C mixture. The contents of the jar are subsequently transferred into a cylinder-shaped mold in which they are gently pushed down manually so that their surface becomes flat. The mold is placed in a drying oven at 120° C. for 20 hours. The block formed is removed from the mold and then its uniaxial compressive strength is evaluated. The block and its compression test simulate the strength of an aggregate formed in the process according to the invention. The results giving the maximum forces achieved before failure of the block as a function of the particle size of the cullet are collated in the table below.

TABLE-US-00001 Example Cullet size Mean maximum force (N) 1 <1 mm 420 2 4-8 mm 100 3 8-16 mm 96

[0059] The “Cullet size” column gives the size range of the cullet particles per 100% of its mass. It is seen that the blocks of examples 2 and 3 fracture under a weaker force than for example 1, which is favorable to the unblocking of the materials flowing in the preheater since the large blocks possibly being formed in the latter will break up more easily.

[0060] FIG. 1 diagrammatically represents a device according to the invention. The different compounds 1, 2, and the like, participating in the composition of the pulverulent starting material 3 (sand, sodium carbonate, and the like) are deposited in successive layers one after the other on a forwardly progressing belt 4. This powdered starting material is subsequently poured into the tank of a kneader 5 provided with a paddle stirrer 6 and into which liquid water and steam (condensing to give liquid water in the tank) are introduced. In this kneader, the moistened mass of starting material powder is generally heated to at least 36° C. The kneading operation is carried out noncontinuously (“batchwise”), that is to say with a given amount of material, the outlet door 8 being closed and opening periodically to deliver moistened mass of starting material powder 9 to a forwardly progressing belt 10. Cullet 11 is subsequently deposited at a fixed point 12 on this moistened mass in forward progression in order to constitute the SM/C mixture 13. This SM/C mixture feeds the inlet 15 of a preheater of starting materials 14. In this preheater, the SM/C mixture descends vertically into parallelepipedal steel compartments. Hot combustion gases 17, the temperature of which is approximately 800° C., originating from the glass furnace 16 are conveyed by a pipe and introduced at 18 into a bottom part of the preheater. These gases circulate by winding in the preheater around the parallelepipedal compartments in order to heat the SM/C mixture which they contain. Overall, these gases circulate countercurrentwise to the SM/C mixture. These gases subsequently exit at 19 in a top part of the preheater. The heating of the SM/C mixture produces steam. This is free water of the SM/C mixture and, if appropriate, water originating from the dehydration of a hydrate, such as sodium carbonate hydrate, present in the SM/C mixture. This steam can be removed during the descent of the SM/C mixture by virtue of orifices in the parallelepipedal compartments, in which case this steam mixes with the combustion gases circulating around the parallelepipedal compartments. The dry and hot SM/C mixture exits at the bottom of the preheater and then constitutes the mass to be charged 20. The latter is subsequently charged at 21 to the furnace 16 containing a glass bath 22. A forwardly progressing belt 24 conveys this mass to be charged 20 to a recess 21 for introduction of vitrifiable starting materials. The descent of the SM/C mixture is continuous in the preheater 14 and the feeding of the furnace with mass to be charged is also continuous. The feeding at 15 of the preheater with SM/C mixture can be periodical (semicontinuous) according to the descent of the material in the preheater. According to the free space in the preheater, a regulating system triggers the opening of the outlet 8 of the tank 5, the preparation of SM/C mixture on the belt 10 and the introduction of SM/C mixture into the preheater. Protection 23 surrounds the SM/C mixture between the preheater and the furnace in order to limit its loss of heat.