Note: Descriptions are shown in the official language in which they were submitted.
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1 ¦ BACKGROUND OF THE INVENTION
I
2¦ It is known, in cyclone type melting furnaces, how to
3 ¦cause finely divided vitrifiable raw materials to ~low onto the
41 strongly inclined or vertical walls of revolution. In such con-
51 struction, the material is heated by jets of hot gases introduced
61 tangentially to the walls. The raw material must be finely
71 divided so that under the dynamic action of the gas jets, it is
81 distributed homogeneously and flows with a slow enough speed to
9¦ be able to melt during its travel. The drawback of these devices
10¦ is a segregation of the raw materials deposited on the wall caus-
11¦ ing heterogeneities during melting.
12¦ In Canadian Patent Application No. 233,203 filed
13¦ August 11,1975, entitled "Method and Apparatus for the Manufactur~
14¦ of Glass", a rapid glass refining process is described in which a
15¦ raw vitreous mass is brought to an elevated temperature while
16¦ maintaining the viscosity of the molten mass at less than 1000
17¦ poises. Then, an intense foaming of this molten mass is effected
18¦ throughout its entire thickness while ~eeping the viscosity at a
19 ¦ value less than 1000 poises. The rate of expansion of the mass
20 ¦is at least about 1.5. After the end of the foaming, a perfectly
21 ¦ refined glass is collected. The present invention relates to a
22 ¦prefusion process and devices that can advantageously be used in
23 ¦ association with the process described in said copending
24 ¦application.
25 I ~ SUMMARY OF THE INVENTION
I : ,,
26 ¦ The process according to the invention is characterized
27 ¦in that the vitrifiable material to be melted is in the form of
28 ¦an agglomerated mlxture divided into solid elements, each element
29 ¦ containing the totality of components in the proportions necessar~
30 ¦ for the formation of glass. These elements are preheated to a
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1 ¦temperature below that of fritting and then placed on the surface
2 ¦of a thin layer of molten material of the same nature and sub-
3 ¦jected to an intense heating by hot gaseous currents directed
4 ¦toward the molten surface. The molten mass is fed along a path
5 ¦to the entrance of a glass refining apparatus as disclosed in the
61 above-mentioned copending application. The movement of the molten
71 mass also continually renews the receiving layer on which the raw
8¦ material is deposited.
9¦ The apparatus for carrying out the process of the
10¦ present invention includes a hearth opposite and above which are
11¦ placed burners which direct the hot gases toward the hearth in a
12¦ direction preferably close to perpendicular. Means are provided
13¦ for depositing the mineral materials to be melted onto the hearth.
14¦ The material is deposited in a finely divided form such as gravel,
15 granules, balls, shot, small plates and the equivalent. Heat
16 exchange means preheats the material to a temperature below the
17 fritting point, before its arrival on the hearth. Finally, means
18 are provided for removing the melted material from the hearth and
19 directing it into the glass refining apparatus.
BRIEF DESCRIPTION OF THE DRAWINGS
..
21 Fig. 1 is a schematic view, in longitudinal section, of
22 the apparatus according to the invention for melting mineral
23 materials;
24 Fig. 2 represents, in longitudinal section, a modified
25 embodiment of~~he apparatus shown in Fig. 1 ~including structure
z-2~ 26 for the recovery of the/hot gases;
27 Fig. 3 represents, in vertical section, still another
28 embodiment comprising a drum-shaped hearth; and
29 Fig. 4 is a schematic overall view of an installation
2-2-~t ~ ~ 30 according to the invention with the heat recovery circuit.
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1 ¦ DETAILED DESCRIPTION OF THE PREFERRED EMBODI~ENTS
7~ 2 ¦ In the present example, the raw materials are agglo-
3 ¦ merated from a homogeneous mixture comprising all the constitu~n~-
2-2~ 4 ¦ of a c~mmon soda- lime glass so as to constitute small size solid I briquettes
Z~ 5 lelements such as gravel, granules, pellets, / and small plates.
6 IPreferably, the size of the elements will be on the order of 5 to
¦ 30 mm. Processes for making such elements are known in themselves .
8¦ Thus, granules can be obtained by extrusion with or without a
I Briquettes
Z~~ 91 binder. /- .can be made by standard devices such asbriquetting
1 10¦ machines.
11¦ With reference to Fig. 1, the raw material to be melted
12¦ is placed in a hopper-heat exchange structure 1 which has an exit
131 at its lower end disposed over a distributor drum 2 by which the
14¦ basic elements of the raw material to be melted are guided through
15¦ a conduit 3 above the end of hearth 4, of melting furnace 10.
16¦ This hearth 4, which is constructed of refractory material, com-
17¦ prises an inclined part followed by a more steeply inclined over-
~-t-~ 18¦ flow part 4i. This hearth is made up of blocks of refractories /
191 sillimanite. Steel pipes 12 extend through hearth 4 perpendicu-
20¦ larly to the plane of symmetry of the installation. Cooling
21¦ fluids with variable delivery are fed through these pipes 12 to
22¦ regulate the temperature of the hearth. The arch 14 of the
231 furnace is covered with insulating bricks.
24 Burners 5 are dlsposed above the hearth. These burners
251 extend~th-rough the arch-14--~and-are directed preferably almost
26¦ perpendicularly to the hearth. Additional burners 6 extend
1 27¦ through the bottom of chimney 7 of the furnace and are directed
-28 so as to make their flame converge in the zone of arrival of the
29 raw materials introduced into furnace 10 by conduit 3. Burners
5 and 6 are of the so-called "intensive" type, i.e., ones in
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1 ¦which the rate of ejection of the gases is greater than the rate
2 ¦of combustion of the fuel mixture used and in which the flame is
¦caught ~tothe combustion chamber created in the arch.
4 ¦ Above the hearth 4, the chimney 7 collects the combustio
5 ¦fumes which go through a grill 1~ into a heat exchanger 15 in whic
6 ¦ the elements of the raw material to be melted travel by gravity in
71 a direction countercurrent to the flow of the fumes.
81 The gases thermally depleted in exchanger 15 and those
9¦ coming directly from chimney 7 through bypass 8 are sent into a
10¦ dust-removal cyclone 20. Circulation of these gases and their
11¦ evacuation are assured by a blower 22.
12¦ Exchanger 15 assures a preheating of the material to be
13¦ melted to a temperature between about 500C and 600C at the level
14¦ of distributor 2. The temperature of the combustion gases pene-
15¦ trating into exchanger 15 is on the order of 750C and is regulate
16 ¦ by dilution with cold air admitted through the orifice 18. Bypass
17¦ 8 is provided with an adjustable flap valve 8a making it possible
181 to control the delivery of combustion gases through this bypass.
19¦ Reference is now made to Fig. 2 which represents a
20¦ variant of the device of the invention. In this construction, the
21¦ hearth 30 and spout 30' are cooled by a cooling fluid, for
22¦ example, air, which is circulated through a circuit of pipes 31.
231 By regulating the air delivery, it is possible to control with
24 precision the temperature of the hearth. The raw materials brough t
251 ~from~hopper 45 fI-ow-onto the hearth~30 by means of distributor
26 drum 33 and conduit 34.
27 Burners 35 and 36 assure the melting of the raw material '
28 A burner 37 acts as the end of the hearth to prevent countercur-
29 rents and carrying of the material upstream. A conduit 38 assures
30 evacuation of the fumes into a heat recovery device 39 where they
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1 lare cooled during heating the air in pipe 40 which air serves to
2 ¦feed the burners and, optionally, the dryer of the installation
3 ¦described below with reference to Fig. 4. The fumes are then
4 ¦brought through a conduit 41 and a grill 42, into heat exchanger
32 where they heat the raw materials.
6 ¦ The air for cooling the hearth 30 which circulates in
7 Ipipes 31 is directed, by a conduit 43', to a point above the intakl ,
8 ¦conduit 34 of the material. This creates a dynamic counterpressurl ,
9 ¦at 43 which is directed downwardly to prevent rising of hot gases.
10 ¦Such gases, if they came to the height of distributor drum 33,
11 ¦could deteriorate it and cause premature meltings of the raw
12¦ materials and clogging. -
13 ¦ The upper part of exchanger 32 includes a conduit 44 for
14¦ evacuating the fumes which are then directed toward a scrubber
15¦ cyclone, not shown, before being released into the atmosphere by
16 ¦means of a centrifugal blower. This part of the installation is
17¦ identical with that described above with reference to Fig. 1.
18¦ The raw materials are introduced into exchanger 32 from
19 la filling hopper 45 whose lower section is cut at a bevel to bal-
20¦ ance the losses of load in exchanger 32 and to avoid a greater
21 Idelivery of hot gasses on one side of the exchanger in relation
22 ¦to the other. This characteristic facilitates the flow of product
231 and the homogeneity of their temperature at the level of the
24 distribution drum.
25 ¦ In the embodiment shown in Fig. 3, the melting hearth is
26¦ defined by the peripheral walls of two hollow drums 50 and 51. -
2r¦ These walls are constructed of refractory materials such as, for
28¦ example, concrete of refractory cement and corundum. They are
29¦ monolithic or an assembly of molded pieces. These drums are
S0 driven in rotation in the direction of arrows F by a motor not
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¦shown. Cold air pipes 52 and 53, extending concentrically to
2 ¦shafts 54 and 55 of the drums, make it possible to direct an air
3 ¦current f against the inside walls of the periphery of the drums
4 ¦to keep them at the desired temperature which is on the order of
5 ¦9oooC. The outside surfaces of the drums define between them a
~ 6 ¦space 62, of some centimeters, sufficient to a~commodate
; 7 ¦the molten layer. The raw material to be melted is delivered to
8 ¦the drums by conduits 56 and 57 and slides to the point 62a above
9 ¦the space 62. ~
10 ¦ A housing 58 surrounds the drums in spaced relation
11¦ thereto. The housing carries burners 59 directed approximately
12¦ along the radii of the drums to apply jets of hot gases on their
13¦ periphery. Additional burners can be provided between the drums
14¦ and the housing, at each end of the drums, to direct the charge
15¦ of melting material toward the median part of the drums. These
16¦ additional burners are aligned with the burner 59 which overlies
17 ¦the space 62. Thus, cloggings due to an incomplete melting of the
18¦ raw material are avoided; and the molten material flows at 60 into
19¦ the refining furnace, not shown. Because of its nature, the melt-
20 ¦ing technique according to the process of the invention should
21¦ preferably employ a compact mixture, which is, for example, in the
22¦ form of pellets or small plates and which lends itself to preheat-
231 ing of the charge in a column through which hot fumes pass.
24 Reference is now made to Fig. 4 which schematically
25¦ represents an installation according to the invention. The raw
26 materials stored in hoppe~ 63 are weighed, mixed in mixer 64, com-
27 pacted in a compacting installation 65 and finally dried in a
28 dryer 66. As described above, these raw materials are introduced
29 into a preheating heat exchanger 67 from which they are brought
30 into a melting unit 68 comprised of a hearth 68' cooled by
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circulation of a cooling fluid 69. The mixture of raw materials,
preheated in the heat exchanger 67 to temperatures on the order of -
500C to 600C, is brought into unit 68 at its melting temperature.
The temperature of the hearth is about 900C so that the under
layer of the molten material is fixed at its contact, it means it
is practically immobilized. The upper surface of this material,
for example glass paste at 1300C, flows by gravity to the
refining furnace 70 of the type described in the above-mentioned
copending application. The glass exits from the furnace through
a drawing off orifice 71.
The circuit of the fumes from the burners will now be
described. The fumes are evacuated from the melting unit 68 via a
conduit 72 at a temperature on the order of 1350C. They are
then delivered to a heat recovery device 73 (identical with heat
recovery device 39 of Fig. 2) where they are used to heat the
air being supplied to the burners 74. This combustion air is col-
lected by hood 75 disposed above the furnace 70. Consequently,
this air is charged with sulfur dioxide emitted by the refining
reactions, which makes it possible to oppose the premature
decomposition of the sulfates at the level of the premelting. The
air is directed into the heat recovery device 73 and then to the
burners 74. A bypass 76 allows a part of the hot air coming from
the heat recovery device to be shunted directly to the dryer 66.
The fumes coming out from heat recovery device 73 at
about 700C are directed by a conduit 77 through the column of
materials in the heat exchanger 67 where they are used to bring
the temperature of the materials to values on the order of 500C
to 600C. These fumes, after passing through the heat exchanger -~
are on the order of 300C and are thereafter aspirated through
a conduit 77, by a blower 79, to direct them to a scrubber
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1¦ cyclone 78j From the cyclone, they are finally delivered to the
21 dryer 66 before their evacuation through chimney 80.
31 Of course, many other materials can be melted or
: 4 elaborated by modifying for instance, the slope of the hearth
or the working temperatures without departing from the scope of
: 6 the invention.
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