Glass manufacturing – Processes – Fining or homogenizing molten glass
Reexamination Certificate
1997-12-04
2001-12-25
Vincent, Sean (Department: 1731)
Glass manufacturing
Processes
Fining or homogenizing molten glass
C065S136300, C432S019000, C432S020000, C431S008000, C431S126000
Reexamination Certificate
active
06332340
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a burner for gas fuels, in particular natural gas.
2. Description of the Related Art
In most industrial furnaces, for example glassmaking furnaces, the transfer of heat to the charge by radiation plays a dominant role. However, this radiative heat transfer depends, on the one hand, on the emissive power of the combustion products and, on the other hand, on their spatial distribution.
In the glassmaking industry, it has been observed that the manufacture of certain glasses in a furnace, for example technical glasses for liquid-crystal displays (LCDs), which are about 1 mm thick, demands quite particular properties of the flame heating the furnace.
Among these properties, it has been observed that, on the one hand, it is preferable to have a flame which preferably comprises substantially no reducing species, such as soot particles and, on the other hand, to have a flame whose emission range is in the wavelength band between about 2 &mgr;m and about 5 &mgr;m, that is to say flames which are blue in colour.
Blue flames fulfil these two conditions. They do not produce soot. Their emission is for the most part due, on the one hand, to the emission from water vapour whose favoured emission range is between 2.2 &mgr;m and 2.8 &mgr;m and, on the other hand, to the emission from carbon dioxide whose emission range is between 2.8 &mgr;m and 3 &mgr;m, as well as between 4 &mgr;m and 5 &mgr;m.
Finally, it has been observed that the heat transfer from a flame may be connected with its momentum. Thus, the higher the momentum of a flame is, the further the heat transfer from this flame is shifted longitudinally downstream.
For manufacturing the aforementioned technical glasses, it has also been observed that a flame having limited (or low) momentum is needed, that is to say a flame which is non-hard, and preferably soft, so as not to overheat the refractory walls of the furnace which face the burner.
FR-A-1,441,671, in the name of the Applicant Company, discloses a variable-flame burner for hydrocarbon gases, in particular natural gas. This known burner has a plurality of tubes which are arranged concentrically so that they respectively form a central duct, an intermediate annular duct and a peripheral annular duct. The central duct and the peripheral duct are fed with an oxidant, and the intermediate annular duct is fed with a fuel, or vice versa.
Even though it was possible to adjust the flame of this burner in order to obtain a blue flame, this flame is only obtained with flames having a high momentum, that is to say hard flames.
SUMMARY OF THE INVENTION
The object of the present invention is to improve the burner of the aforementioned type so that it can produce a “blue” flame with low momentum.
To this end, the invention relates to a burner for gas fuels, in particular natural gas, having three coaxial ducts for feeding gas into a combustion zone, namely a central duct for feeding oxidant, an intermediate annular duct for feeding fuel, and a peripheral annular duct for feeding oxidant, the total oxidant flow rate Q
o
TOT
being determined by the equation:
Q
o
TOT
=(
R
0
+&Dgr;R
)
Q
c
where Q
c
represents the nominal fuel consumption of the burner,
R
0
is the stoichiometric ratio between the fuel and the oxidant, and
R is a stoichiometric excess,
characterised in that, with a view to obtaining a blue flame having low momentum, the dimensions of the three ducts satisfy the following equations:
25 (
R
0
Q
c
)
½
≦D
1
≦62 (
R
0
Q
c
)
½
, (i)
113 (
Q
c
)
½
≦(
D
3
2
−D
2
e
)
½
≦291 (
Q
c
)
½
, (ii)
211 (
Q
o
TOT
)
½
≦(
D
6
2
−D
4
2
)
½
≦479 (
Q
o
TOT
)
½
, (iii)
1≦
D
2
−D
1
/D
1
≦20 (iv)
1≦
D
5
−D
4
≦5 (v)
in which equations:
D
1
is the diameter of the central duct,
D
2
is the internal diameter of the intermediate annular duct,
D
3
is the external diameter of the intermediate annular duct,
D
4
is the internal diameter of the peripheral annular duct,
D
5
is the external diameter of the peripheral annular duct, and
in that the central duct has a flared wall end making an angle of between 20° and 45°, preferably 40°, with the axis of the burner.
The invention may include one or more of the following characteristics:
the intermediate annular duct has an internal wall end inclined in the direction of the axis of the burner and making an angle of between 5° and 30°, preferably 25°, with this axis,
the peripheral annular duct has an internal wall end inclined in the direction of the axis of the burner and making an angle of between 5° and 30°, preferably 25°, with this axis,
the outlet end of the central duct is set back with respect to the outlet end of the peripheral annular duct by a distance h of between 0 and 1.5D
1
, preferably equal to D
1
.
The invention also relates to a process for the manufacture of technical glass, such as glass for liquid-crystal display screens, in which the glass bath is heated with at least one of the flames, characterized in that at least one of the flames is a non-hard flame which is blue in colour, that is to say has an emission spectrum essentially lying between 2 &mgr;m and 5 &mgr;m, and includes substantially no reducing species and in particular soot.
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Bodelin Pierre
Nakano Kazuyoshi
Oguro Takashi
Recourt Patrick
Takaha Toshi
Burns Doane Swecker & Mathis L.L.P.
L'Air Liquide, Societe Anonyme pour l'Etude et l'
Vincent Sean
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