U.S. patent application number 10/556666 was filed with the patent office on 2007-01-25 for burner control method involving the injection of an additional gas and associated combustion system.
Invention is credited to Son-Ha Giang, Luc Jarry, Gerard Le Gouefflec, Dominique Robillard.
Application Number | 20070018011 10/556666 |
Document ID | / |
Family ID | 33306321 |
Filed Date | 2007-01-25 |
United States Patent
Application |
20070018011 |
Kind Code |
A1 |
Giang; Son-Ha ; et
al. |
January 25, 2007 |
Burner control method involving the injection of an additional gas
and associated combustion system
Abstract
Methods and apparatus for controlling the operation of a burner
used for heating liquid glass feeders of a glass furnace. A burner
is supplied with a fuel and oxygen. An additional gas is injected
so that the sum of the oxygen flow, the fuel flow and the
additional gas flow is greater than a minimum cooling flow for the
burner.
Inventors: |
Giang; Son-Ha; (Sucy en
Brie, FR) ; Jarry; Luc; (Meudon, FR) ; Le
Gouefflec; Gerard; (Velizy, FR) ; Robillard;
Dominique; (Versailles, FR) |
Correspondence
Address: |
AIR LIQUIDE
2700 POST OAK BOULEVARD, SUITE 1800
HOUSTON
TX
77056
US
|
Family ID: |
33306321 |
Appl. No.: |
10/556666 |
Filed: |
May 7, 2004 |
PCT Filed: |
May 7, 2004 |
PCT NO: |
PCT/FR04/01124 |
371 Date: |
November 10, 2005 |
Current U.S.
Class: |
239/13 ; 239/399;
65/134.4 |
Current CPC
Class: |
F23N 2237/26 20200101;
C03B 7/065 20130101; F23L 2900/07007 20130101; Y02T 50/677
20130101; F23L 2900/07006 20130101; Y02P 40/55 20151101; Y02P 40/57
20151101; C03B 5/173 20130101; F23D 14/32 20130101; F23N 5/184
20130101; Y02T 50/60 20130101; F23L 2900/07003 20130101; F23D 14/78
20130101; F23N 3/002 20130101; Y02E 20/344 20130101; F23N 2005/181
20130101; Y02E 20/34 20130101; Y02P 40/50 20151101 |
Class at
Publication: |
239/013 ;
239/399; 065/134.4 |
International
Class: |
B05B 17/04 20060101
B05B017/04; B05B 7/10 20060101 B05B007/10; C03B 5/16 20060101
C03B005/16 |
Foreign Application Data
Date |
Code |
Application Number |
May 13, 2003 |
FR |
0305735 |
Claims
1-16. (canceled)
17. A method which may be used for controlling a burner for heating
liquid glass feeders of a glass furnace, said method comprising: a)
feeding at least one burner with a combustible gas and oxygen; and
b) injecting an additional gas as a complement to said oxygen such
that the sum of the flow rates for said combustible gas, said
oxygen, and said additional gas is greater than or equal to a
minimum flow rate for cooling the burner.
18. The method of claim 17, wherein said additional gas comprises
at least one member selected from the group consisting of: a) air;
b) carbon dioxide; c) argon; d) helium; and e) nitrogen.
19. The method of claim 17, further comprising mixing said
additional gas and said oxygen prior to introducing said
combustible gas.
20. The method of claim 17, wherein said minimum flow rate is set
according to the flow rate of said combustible gas.
21. The method of claim 17, wherein the sum of the flow rates for
said additional gas and said oxygen is greater than or equal to
said minimum flow rate.
22. The method of claim 17, wherein said flow rate for said
additional gas is controlled by a pressure regulator located on a
line which delivers oxygen to said burner.
23. The method of claim 17, wherein said burner comprises: a) a
first duct for the passage of said oxygen; b) a second duct for the
passage of said combustible gas, wherein: 1) said second duct is
coaxially located substantially inside of said first duct; and 2)
said second duct's end portion is located back from said first
duct's end portion.
24. The method of claim 17, wherein said burner comprises: a) a
first duct for the passage of said oxygen; b) a second duct for the
passage of said combustible gas, wherein said second duct is
coaxially located substantially inside of said first duct; c) an
end-fitting located at said first duct's end portion; d) a nozzle
located at said second duct's end portion; and e) a combustible gas
swirling means, located at said second duct's end portion, to cause
said combustible gas to move in a swirling manner.
25. The method of claim 24, wherein: a) said swirling means
comprises an object of elongated shape which is centered
aerodynamically within said nozzle; and b) said nozzle has an
inside diameter which is greater than the diameter of said object
of elongated shape.
26. The method of claim 25, wherein: a) said object of elongated
shape comprises at least one helical rod; and b) said helical rod
is located over a portion of said object's length.
27. The method of claim 24, wherein said burner comprises an
oxidizer swirling means located on said end-fitting.
28. An apparatus which may be used as a combustion system, said
apparatus comprising: a) an oxyfuel burner; b) a means for feeding
said burner with fuel; c) a means for feeding said burner with an
oxidizer; d) an oxygen feed means; e) an additional gas feed means,
wherein said oxidizer feed means cooperates with said oxygen feed
means and said additional gas feed means; f) a means for measuring
a flow rate, wherein said flow rate comprises at least one member
selected form the group consisting of: 1) said oxygen's flow rate;
and 2) said fuel's flow rate; and g) a means for controlling said
additional gas's flow rate.
29. The apparatus of claim 28, wherein said means for controlling
said additional gas's flow rate is slaved to said means for
measuring a flow rate.
30. The apparatus of claim 28, wherein said means for controlling
said additional gas's flow rate is a pressure regulator.
31. The apparatus of claim 28, wherein said means for controlling
said additional gas's flow rate is a servovalve.
32. A method which may be used for heating a liquid glass feeder of
a glass furnace, said method comprising, heating at least one
liquid glass feeder with a combustion system, wherein: a) said
liquid gas feeder is connected to a glass furnace; and b) said
combustion system comprises: 1) an oxyfuel burner; 2) a means for
feeding said burner with fuel; 3) a means for feeding said burner
with an oxidizer; 4) an oxygen feed means; 5) an additional gas
feed means, wherein said oxidizer feed means cooperates with said
oxygen feed means and said additional gas feed means; 6) a means
for measuring a flow rate, wherein said flow rate comprises at
least one member selected form the group consisting of: i) said
oxygen's flow rate; and ii) said fuel's flow rate; and 7) a means
for controlling said additional gas's flow rate.
33. A method which may be used for controlling a burner for heating
liquid glass feeders of a glass furnace, said method comprising: a)
feeding at least one burner with a combustible gas and oxygen,
wherein said burner comprises: 1) a first duct for the passage of
said oxygen; 2) a second duct for the passage of said combustible
gas, wherein said second duct is coaxially located substantially
inside of said first duct; 3) an end-fitting located at said first
duct's end portion; 4) a nozzle located at said second duct's end
portion; and 5) a combustible gas swirling means, located at said
second duct's end portion, to cause said combustible gas to move in
a swirling manner; b) injecting an additional gas as a complement
to said oxygen such that the sum of the flow rates for said
combustible gas, said oxygen, and said additional gas is greater
than or equal to a minimum flow rate for cooling the burner,
wherein said additional gas is mixed with said oxygen prior to
introducing said combustible gas; and c) controlling said flow rate
for said additional gas by a pressure regulator located on a line
which delivers oxygen to said burner.
Description
[0001] The present invention relates to a method of controlling the
operation of a burner for heating the liquid glass feeders coming
from a glass furnace.
[0002] In a continuous glass manufacturing line, the glass is
melted in relatively large capacity furnaces that deliver molten
glass as output. In certain industries, such as glass furnaces for
hollowware, the molten glass must be conveyed right to the
glass-forming machines. To transport this molten glass, "feeders"
or "forehearths" lined with refractory materials are used. As the
glass is being conveyed in this way, it is cooled and also
conditioned so that, on leaving the feeders, its temperature is
perfectly stable and homogenous to within .+-.1.degree. C. To
achieve this, the temperature of the glass leaving the feeders must
therefore be constant but also perfectly uniform transversely, that
is to say over the width of each feeder.
[0003] It is essential to control the heat transfer method at the
surface of the glass over the entire length of the feeder in order
to reduce the output temperature gradient. To do this, it is common
practice to equip the feeders with a heating device, which heats by
combustion of an air/combustible gas mixture above the free surface
of the stream of molten glass. This combustion is obtained using
air/fuel burners. While the molten glass is flowing, in order for
the temperature of the molten glass to be both lowered and
homogenized, series of burners are distributed over the entire path
of the molten glass. Owing to the number of burners and the
difficulty of detecting and controlling the volumes of flue gases
that they create, the combustion may be carried out by burners
whose oxidizer is cold air; now, these burners have a generally
mediocre efficiency and offer little flexibility as regards
obtaining a good transverse thermal profile.
[0004] To solve these problems, the combustion of an
air/combustible gas mixture has been replaced with combustion of an
oxygen/combustible gas mixture using oxyfuel burners. This
modification has increased the glass production capacity, and also
the combustion efficiency and radiative transfer. Such burners have
been described, for example, in Documents U.S. Pat. No. 6,431,467
B1 and U.S. Pat. No. 5,500,030. These burners have in particular
the advantage of providing a large operating range, that is to say
the possibility of varying the power--and therefore the fuel and
oxidizer flow rates--much more widely than in the case of air/fuel
burners. Furthermore, the length of the flame of these burners is
constant over their entire operating range. This property allows
them to heat the edge of the feeders, at the point where the glass
cools upon contact with the refractories. They also limit the
thermal gradient, and therefore the difference in viscosity,
between the core of the feeder and the edges; thus preferential
flow of the glass at the center of the feeder is limited. Moreover,
the heating power for a section of feeder by oxyfuel combustion or
with oxygen-enriched air is greater than that which can be achieved
in air/fuel combustion. The wide power range within which the
oxyfuel burners operate allows dynamic regulation which rapidly
compensates for the variations in the process and stabilize the
glass temperature. The feeders may be equipped over their entire
length with several heating zones; in this case, the oxyfuel
burners provide great operating flexibility thanks to greater
precision in the temperature regulation. If the entire length of
the feeder is fitted with oxyfuel burners, this operating
flexibility is even greater. Furthermore, the gas consumption is
reduced. Oxyfuel burners also allow the volume of flue gases to be
reduced, which may in certain cases lead to a reduction in the
fly-off and volatilization of certain components conveyed in the
feeders, such as pigments.
[0005] However, this oxyfuel combustion may have certain drawbacks.
Firstly, the flame geometry of the feeder burners is particularly
important as it is necessary to ensure that the glass stream
heating profile is particularly stable and uniform. However, the
thermal behavior of the materials that make up the self-cooled
oxyfuel burners is generally difficult since the ambient
temperature therein is generally high, whereas the gas and oxygen
flow rates in each burner are low (low unit power). Thus, to ensure
a stable flame profile, there is not as much operating flexibility
for these burners as the oxyfuel would allow. In addition, the
low-speed flow of the burners may be the source of burner failures
requiring maintenance. This is because the burners are cooled by
convection with the flow of both the oxidizer and the fuel that
they use. In the case of combustion with oxygen, the flow volume is
about 70% less than that of combustion with air. The cooling is
therefore less effective for the same power. The combustion flame
with oxygen is also hotter and more radiating. In addition, at low
power, the heating of the burner end-fitting may cause premature
cracking and therefore as a consequence rapid fouling and premature
wear of the burner. Finally, the feeders must always be at an
overpressure, and this pressure is maintained by the volume of the
burner flue gases. In aerocombustion, this volume is stabilized--a
set of flue gas discharge dampers allows the pressure to be
adjusted, which it is necessary to monitor and regulate. In
oxycombustion, the volume of flue gases is much lower, and in
addition, varies greatly with the power, thereby making it
difficult to control the pressure in the feeders. A pressure-stable
method independent of the instantaneous power conditions is
therefore sought.
[0006] It is an object of the present invention to propose a method
of heating glass feeders using oxyfuel burners that does not have
the above drawbacks.
[0007] It is an object of the present invention to propose a method
of heating glass feeders using oxyfuel burners that is flexible and
can be easily modified.
[0008] For this purpose, the subject of the invention is a method
for controlling the operation of a burner for heating the liquid
glass feeders coming from a glass furnace, the said burner being
fed with a combustible gas and with oxygen, in which an additional
gas is injected as a complement to the oxygen so that the sum of
the additional gas, oxygen and combustible gas flow rates is
greater than or equal to the minimum flow rate D.sub.MIN for
cooling the burner.
[0009] The invention also relates to a combustion system
comprising: [0010] an oxyfuel burner; [0011] a means for feeding
the burner with fuel; [0012] a means for feeding the burner with
oxidizer, cooperating with an oxygen feed means and an additional
gas feed means; [0013] a means for measuring the flow rate of at
least the oxygen or the fuel; and [0014] a means for controlling
the additional gas flow rate.
[0015] Finally, the invention relates to the use of the above
system for heating the liquid glass feeders coming from a glass
furnace.
[0016] Other features and advantages of the invention will become
apparent on reading the following description. Embodiments of the
invention and methods of implementing it are given by way of
non-limiting examples illustrated by FIG. 1, which shows the range
of power levels obtained with the method and the system of the
invention and with the method of the prior art.
[0017] The invention therefore firstly relates to a method for
controlling the operation of a burner for heating the liquid glass
feeders coming from a glass furnace, the said burner being fed with
a combustible gas and with oxygen, in which an additional gas is
injected as a complement to the oxygen so that the sum of the
additional gas, oxygen and combustible gas flow rates is greater
than or equal to the minimum flow rate D.sub.MIN for cooling the
burner.
[0018] The invention therefore allows the operation of an oxyfuel
burner to be controlled. The term "oxyfuel burner" is understood to
mean a burner implementing oxycombustion obtained by mixing a fuel
with oxygen. The term "oxygen" is understood to mean an
oxygen-containing gas comprising more than 90% by volume of oxygen.
The oxygen produced by a VSA (vacuum swing adsorption) process is
particularly suitable. According to the essential feature of the
invention, an additional gas is injected into the burner as a
complement to the oxygen. In general, the additional gas is mixed
with oxygen before it is brought into contact with the fuel, for
example in a premixing chamber. The amount of additional gas
injected as a complement to the oxygen and to the fuel allows the
operation of the burner to be controlled according to the following
rule: the sum of the additional gas, oxygen and combustible gas
flow rates must be greater than the minimum flow rate D.sub.MIN for
cooling the burner. The value of D.sub.MIN may be set for each type
of burner according to the flow rate of the fuel introduced into
the burner. More precisely, the value of D.sub.MIN may be set in
the following manner: D.sub.MIN must be sufficient to cool the
burner. This flow rate value needed for cooling is specific to the
burner used; it can be determined by a person skilled in the art
according to the withstand temperature of the said burner. This
burner withstand temperature is itself determined beforehand by
tests. In practice, the additional gas flow rate may be controlled
by a pressure regulator inserted into the line for delivering
oxygen to the burner and regulated so as to deliver a stream of
oxygen and additional gas at defined pressure. This pressure is set
so as to correspond to the minimum gas flow rate needed to cool the
burner. Thus, if the oxygen flow rate varies following a variation
in fuel flow rate, and so as to maintain a fixed combustible
gas/oxygen stoichiometric ratio, the additional gas flow rate also
varies in order to compensate or not compensate for the variation
in oxygen flow rate in the burner.
[0019] According to a first further improved version of the method,
it is possible to vary the additional gas flow rate according to
the oxygen and combustible gas flow rates by permanently measuring
the latter two flow rates and by adjusting the additional gas flow
rate so that the sum of the oxygen, additional gas and fuel flow
rates is greater than D.sub.MIN.
[0020] According to a second, simplified, particular version of the
invention, all that is required is to ensure that the sum of the
additional gas and oxygen flow rates is greater than or equal to
the minimum flow rate D.sub.MIN for cooling the burner. A fortiori,
the sum of the additional gas, oxygen and combustible gas flow
rates is also greater than the minimum flow rate D.sub.MIN for
cooling the burner. This particular method of implementation is
simpler since it is now a question merely of slaving the additional
gas flow rate to the measurement of the oxygen flow rate, for
example by means of a simple pressure regulator, without taking
into account the value of the combustible gas flow rate.
[0021] According to the invention, the additional gas may be an
oxidizer gas different from oxygen, or a gas that is inert with
respect to fuel. It is preferably at least one of the following
gases: air, carbon dioxide, argon, helium, nitrogen or a mixture of
these gases. Air is generally best suited owing to its low cost and
its composition. An additional gas composed of a quantity of oxygen
of around 21% by volume and of at least one other gas different
from oxygen is beneficial as, on the one hand, it is favorable to
combustion and, on the other, the quantity of oxygen that it
introduces may be deducted from the main oxygen injected for
burning the fuel.
[0022] During a variation in the power of the burner, the fuel and
oxygen flow rates increase or decrease proportionally so as to
maintain a constant predefined stoichiometric ratio. Depending on
the value of the oxygen flow rate used, the additional gas is added
as a complement to the oxygen so that the total flow rate of oxygen
and additional gas is greater than or equal to D.sub.MIN.
Consequently, the burner does not suffer any low-power
deterioration since, despite the injection of oxygen and fuel at
low flow rates, the additional gas provides the gas volume needed
to cool the burner. This additional gas also prevents the burner
end-fitting becoming fouled by glass deposits and prevents it from
being damaged. Furthermore, the additional gas creates a volume of
flue gases that allows the operator to obtain and control the
overpressure within the feeders. At high power, the additional gas
flow rate may optionally be reduced to zero in order to allow
operation only with oxygen. In this case, the sum of the oxygen and
the combustible gas flow rates is greater than D.sub.MIN.
[0023] According to a first preferred version of the method, this
uses a burner of the type described in U.S. Pat. No. 5,500,030.
More particularly, this type of burner comprises: [0024] a first
duct for passage of the oxygen; [0025] a second duct, coaxial with
the first duct and placed inside the said first duct, for passage
of the fuel.
[0026] It is preferable for the end of the second duct to be placed
set back from the end of the first duct. More preferably, burners
of this type are used in which the ratio of the inside diameter of
the first duct to the inside diameter of the second duct is between
2/1 and 8/1.
[0027] According to a second preferred version of the method, this
uses a burner of the type described in U.S. Pat. No. 6,431,467 B1.
More particularly, this type of burner comprises: [0028] a first
duct for passage of the oxygen; [0029] a second duct, coaxial with
the first duct and placed inside the said first duct, for passage
of the fuel; [0030] an end-fitting placed at the end of the first
duct; [0031] a nozzle placed at the end of the second duct; [0032]
a means for making the fuel swirl, placed on the nozzle at the end
of the second duct. According to this second version, the means for
making the fuel swirl comprises an object of elongate shape
centered aerodynamically inside the nozzle of the second duct, the
inside diameter of the said nozzle being greater than the diameter
of the object of elongate shape of the means for making the fuel
swirl. The object of elongate shape of the means for making the
fuel swirl may consist of at least one helical rod over a portion
of its length. This burner may also include a means for making the
oxidizer swirl, placed on the end-fitting at the end of the first
duct; this means for making the oxidizer swirl may consist of a
helical spring. This type of burner is particularly suitable for
implementing the method of the invention because it produces a
flame of constant length independently of the power variations.
[0033] The invention also relates to a system comprising: [0034] an
oxyfuel burner; [0035] a means for feeding the burner with fuel;
[0036] a means for feeding the burner with oxidizer, cooperating
with an oxygen feed means and an additional gas feed means; [0037]
a means for measuring the flow rate of at least the oxygen or the
fuel; and [0038] a means for controlling the additional gas flow
rate.
[0039] This combustion system allows the variations in power of the
burner to be finely controlled without the drawbacks encountered in
this type of burner. Such a system allows the method of controlling
the operation of the oxyfuel burner, as described above, to be
implemented. In general, the means of controlling the additional
gas flow rate is slaved to the means of measuring the flow rate of
at least the oxygen or the fuel. This means of controlling the
additional gas flow rate may be a pressure regulator or a
servovalve, that is to say a valve slaved to a control value. When
the means of controlling the additional gas flow rate is a pressure
regulator, all that is required is to regulate it so as to deliver
the additional gas until the pressure generated by this additional
gas and the oxygen that is delivered is greater than the pressure
needed to obtain the minimum oxidizer flow rate D.sub.MIN. When the
means of controlling the additional gas flow rate is a servovalve,
it is possible to slave the opening of the additional gas feed
means to one of the following control values: the oxygen flow rate
or the fuel flow rate, taking into account the fixed oxygen/fuel
stoichiometric ratio. According to one particular method of
implementation, in which the additional gas is air, the servovalve
may take into account the supply of oxygen from the air in
calculating the oxygen/fuel stoichiometric ratio; this method of
implementation makes it possible to economize on consumption of
oxygen.
[0040] Finally, the invention relates to the use of the above
system for heating the liquid glass feeder channels coming from a
glass furnace.
[0041] The graph shown in FIG. 1 illustrates the power ranges
obtained with the method and the system of the invention and with
the method of the prior art. In the case of the system of the
invention (solid curve) and the oxyfuel burner of the prior art
(dotted curves of the . . . and .cndot.-.cndot.-.cndot.- type), the
curves give the power (in kW) that it is possible to transfer as a
function of the developed power (in kW). The developed power is the
power created by the stoichiometric combustion using an oxidizer
comprising only oxygen. The transferred power is the power that is
actually transferred to the glass. In the case of oxycombustion
using an oxidizer comprising only oxygen (oxyfuel burner of the
prior art), it may be seen that the transferred power corresponds
to the developed power. For combustion using an oxidizer comprising
oxygen and the additional gas, although the same power is developed
as with the burner of the prior art, it may be seen that the power
transferred by the burner implementing the invention may be lower,
on account of the power losses due to the volumes of flue gases in
a certain power range. It has been observed that the burner of the
prior art is limited to operation, in terms of transferred power
and developed power, within the 7 to 10 kW range since below 7 kW
the burner cannot operate without suffering deterioration by the
absence of a sufficient gas stream (deterioration in the range
defined by the dotted curve of the . . . type). Thanks to the
system of the invention, this same burner may have its operating
range broadened to 0.15 to 10 kW. It may also be emphasized that
the method and the device of the invention make it possible to
broaden the operating range of the burners of the prior art within
a power range that was not accessible in the prior art, even by
making them operate in the power range causing them to deteriorate,
and that corresponds to the dotted curve of the . . . type in FIG.
1; it may be seen that this "deteriorating" power range cannot drop
below 1 kW of transferred power, whereas the method of the
invention allows access to transferred power levels between 0.15
and 1 kW.
[0042] By implementing the method and the system of the invention,
it is possible to heat the molten glass feeders coming from a glass
furnace while maintaining the advantages of oxyfuel burners--namely
a broader operating range than for air/gas burners, again for high
power levels, optionally controlled flame length and reduction in
fuel consumption--while improving the low-power heating profile
without the burner deteriorating.
[0043] The invention also has the advantage that a stable pressure
can be maintained in the feeders because of a flue gas volume that
is higher than during low-power all-oxygen combustion.
[0044] Owing to the possibility of working with low-power burners,
the invention also makes it possible to work with a larger number
of burners operating at lower power levels--the heating may thus be
more uniform and the quality of the transfer to the glass is
improved.
[0045] In addition, although the complementary injection of
additional gas into the oxygen degrades the combustion efficiency,
it does allow, however, the power transferred to the glass to be
very finely regulated.
[0046] The combustion efficiency is a minimum when the burners
operate at low power. However, at these levels the fuel saving is
potentially lower. This method has little impact on the
economics.
[0047] Another advantage of the invention is that it allows the
power of the burner to be rapidly adjusted according to the nature
of the glass flowing through the feeders. This advantage is more
particularly important at the present time because of the continual
modifications made to glasses produced in order to follow the
fashion trends (colors, etc.).
* * * * *