U.S. patent application number 12/514318 was filed with the patent office on 2010-03-04 for glass melting oven.
This patent application is currently assigned to GDF SUEZ. Invention is credited to Thierry Ferlin, Neil Fricker, Stephane Maurel, Richard Stanley Pont, John Ward.
Application Number | 20100050691 12/514318 |
Document ID | / |
Family ID | 38198269 |
Filed Date | 2010-03-04 |
United States Patent
Application |
20100050691 |
Kind Code |
A1 |
Ward; John ; et al. |
March 4, 2010 |
GLASS MELTING OVEN
Abstract
A combustion method for melting glass in which two fuels of the
same nature or different natures are fed into a fusion furnace at
two locations remote from each other for distributing the fuel to
reduce NOx emissions. The combustion air is supplied at only one of
the locations. In a method for operating a glass melting furnace,
the fuel injection is distributed to reduce NOx emissions. The
furnace includes a melting vessel for receiving the glass to be
melted and containing a bath of molten glass, walls defining the
furnace, a hot combustion air inlet, a hot smoke outlet, at least
one burner for injecting a first fuel, and at least one injector
for injecting a second fuel. The injector has an adjustable flow
complementary relative to the flow to the burner so that up to 100%
of the totality of the first and second fuels used may be
injected.
Inventors: |
Ward; John; (Cardiff,
GB) ; Fricker; Neil; (Solihull, GB) ; Pont;
Richard Stanley; (Edinburgh, GB) ; Ferlin;
Thierry; (Tinqueux, FR) ; Maurel; Stephane;
(Paris, FR) |
Correspondence
Address: |
LEYDIG VOIT & MAYER, LTD
700 THIRTEENTH ST. NW, SUITE 300
WASHINGTON
DC
20005-3960
US
|
Assignee: |
GDF SUEZ
Paris
FR
|
Family ID: |
38198269 |
Appl. No.: |
12/514318 |
Filed: |
December 14, 2007 |
PCT Filed: |
December 14, 2007 |
PCT NO: |
PCT/FR2007/052518 |
371 Date: |
August 10, 2009 |
Current U.S.
Class: |
65/29.13 ;
65/157 |
Current CPC
Class: |
Y02P 40/58 20151101;
F23C 5/08 20130101; Y02P 40/50 20151101; F23C 6/047 20130101; Y02P
40/57 20151101; C03B 5/235 20130101 |
Class at
Publication: |
65/29.13 ;
65/157 |
International
Class: |
C03B 18/20 20060101
C03B018/20; C03B 37/014 20060101 C03B037/014 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 15, 2006 |
FR |
0655571 |
Claims
1. A combustion process for melting glass comprising: supplying two
fuels, of the same nature or of different natures, to a melting
chamber at two spaced apart locations, thereby distributing the
fuel in the melting chambers and limiting NOx emissions, and
supplying combustion air at only one of the two locations.
2. A process of limiting production of NOx by a glass melting
furnace which has a melting tank for receiving glass to be melted
and a holding bath of melted glass, with, above the glass, chamber
walls, at least one intake for supplying hot combustion air, at
least one outlet for outputting hot waste gases, and at least one
burner and at least one injector for respectively injecting a first
fuel and a second fuel into the chamber, the process including:
injecting the first fuel and the second fuel into the furnace
through the burner and injector, the injector being arranged on a
different wall from a wall on which the burner is positioned,
adjusting the burner and the injector in a complementary manner so
that the total of the first and second fuels used by the injector
and the burner corresponds to a predetermined total flow rate,
regardless of whether the first and second fuels are of the same
nature or of different natures.
3. A glass melting furnace comprising: a melting tank for receiving
glass to be melted and for accommodating a melted glass bath; above
the glass, a front wall, a rear wall, side walls, and a roof
constituting a melting chamber; at least one intake for receiving
hot combustion air; at least one outlet for outputting hot waste
gases; at least one burner for introducing a first fuel into the
chamber, and at least one injector for injecting a second fuel into
the chamber, wherein the injector is located on a different wall of
the melting chamber from the burner and is spaced from the burner
in a zone situated between the roof and a horizontal plane situated
at a level at least as high as a horizontal plane passing through a
lower edge of the hot air intake, and the injector is adjustable in
flow rate in a complementary manner with respect to the burner so
that up to 100% of the total of the first and second fuels is used
by the injector and the burner, regardless of whether the first and
second fuels are of the same nature or of different natures.
4. The furnace according to claim 3, including a plurality of
injectors, wherein at least some of the injector are arranged on at
least one axis of symmetry of the roof of the furnace.
5. The furnace according to claim 3, including a plurality of
injectors, wherein at least some of the injectors are arranged on
at least one of the side walls of the melting chamber.
6. The furnace according to claim 3, including a plurality of
injectors, wherein at least some of the injectors are arranged on
the rear wall of the melting chamber.
7. The furnace according to claim 3, including a plurality of
injectors, wherein the injectors are oriented at least
approximately in a direction opposite from flames of the burner of
the furnace.
8. The furnace according to claim 3, including a plurality of
injectors, wherein the injectors are oriented at least
approximately in a direction transverse to flames of the burner of
the furnace.
9. The furnace according to claim 3, including a plurality of
injectors and a plurality of burners wherein the burners and the
injectors are made for first and second fuels of the same
nature.
10. The furnace according to claim 3, including a plurality of
injectors and a plurality of burners, wherein the burners and the
injectors are made for first and second fuels of different
natures.
11. The furnace according to claim 3, wherein the first and second
fuels are selected from the group consisting of natural gas, LPG,
fuel oil, coke-oven gas, blast furnace gas, reforming gas, biogas,
and hydrogen.
12. The furnace according to claim 3, consisting of at least one
injector including a device putting the second fuel injected into
rotation.
13. The furnace according to 3, comprising at least one injector
including a device impulsively adjusting injection of the second
fuel.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a combustion process for
melting glass, as well as mainly to a glass melting furnace for
implementation of this process, but the invention can also be
applied to other types of high temperature furnaces.
BACKGROUND
[0002] Most types of glass, and in particular plate glass and
container glass, are manufactured by melting of raw materials in
large melting furnaces producing a few tens to a few hundred metric
tons of glass per day and per unit. The fuel used in such furnaces
is generally natural gas or fuel oil, although other fuels can also
be used. Certain furnaces also use electricity to increase
production (electric boosting). High temperature furnaces
(typically 1,500.degree. C., but sometimes higher) are necessary
for the melting. Optimal furnace temperature conditions are
obtained by pre-heating the combustion air (typically up to
1,000.degree. C., but sometimes higher). The heat required for
pre-heating the combustion air is transmitted by the waste gases,
which is generally effected by using reversible regenerators. This
approach enables one to obtain a high degree of thermal efficiency
combined with high melting rates. Several types of melting furnaces
exist, including:
[0003] Cross-fired furnaces: in these furnaces, which have a
melting surface area generally greater than 70 m.sup.e and which
operate with a reversal of the direction of the flame approximately
every 20-30 min, the heat contained in the waste gases is recovered
in regenerators made up of stacks of refractory bricks. The cold
combustion air is pre-heated during its passage through the
regenerators (rising air), while the hot waste gases leaving the
furnace are used to re-heat other regenerators (descending waste
gases). These furnaces, with an output sometimes greater than 600
t/day and which are used for manufacturing plate glass and
container glass, are great energy consumers. The diagram of
cross-fired furnace operation is presented in FIG. 1.
[0004] End-fired furnaces: in these furnaces, the flame (sometimes
called a horseshoe flame) describes a loop. These furnaces operate
with recovery of the heat of the waste gases by stacks forming
regenerators which deliver it to the combustion air. The diagram of
the operation of this type of furnace is presented in FIG. 2.
[0005] The fuel is injected into the furnace into or near the air
stream leaving the regenerator. The burners are designed to produce
high temperature flames with good radiative qualities so as to
obtain an efficient heat transfer. A certain number of options
exist for producing the comburant/fuel mixture. The names of these
techniques show how the fuel is introduced. The most frequently
encountered configurations are the following: [0006] "Under port":
under the air stream, [0007] "Over port": above the air stream,
[0008] "Side port": beside the air stream, [0009] "Through port":
through the air stream.
[0010] The choice among these different injection methods is made
so as to obtain a suitable result for the configuration of the air
streams and of the type of melting furnace used, and as a function
of constraints connected with fuel supply (example: available gas
pressure for a furnace supplied with natural gas) or with the
nature of the fuel.
[0011] Although such combustion methods are very efficient in terms
of furnace operation, they induce adverse effects such as the
production of very high levels of nitrogen oxides (subsequently
called: NOx), one of the most regulated air pollutants. In the
majority of industrialized countries, limits (in terms of
concentration and flow rate) are imposed on large capacity glass
making furnaces in order to reduce NOx emissions. Furthermore,
regulation is becoming more drastic each year.
[0012] In high temperature furnaces as in glass melting furnaces,
the main avenue of NOx formation is the "thermal" avenue in which
the NOx are produced in zones of the furnace where flame
temperatures are greater than 1,600.degree. C. Beyond this
threshold, the formation of NOx increases exponentially with the
flame temperature. Unfortunately, the combustion techniques
generally used in melting furnaces for creating very radiative
flames such as those mentioned in the preceding induce high flame
temperatures (with maxima greater than 2,000.degree. C.) and have
the consequence of generating NOx emissions much higher than those
accepted in numerous countries of the world.
[0013] Furthermore, one of the consequences of conventional
combustion methods is that there is little heat released by
combustion in the major part of the volume of the furnace, since in
effect the combustion products surrounding the flame gradually cool
in giving up their heat to the glass bath.
[0014] Over time, the waste gases become less efficient in
transferring heat to the glass bath by radiation. The transfer of
heat by radiation from the flame to the glass bath can be increased
to a significant degree if a way is found to increase the
temperature of the combustion products still present in the melting
chamber.
[0015] Several techniques exist enabling reduction of regenerative
melting furnace NOx emissions. Among these can be distinguished
primary methods (in which reduction occurs during combustion),
secondary methods (in which reduction occurs by treatment of the
combustion products at the furnace outlet) and intermediate methods
in which the treatment occurs at the location of the outlet of the
melting chamber to the regenerators (the Pilkington 3R process or
re-burning).
[0016] The methods which can be used are the following:
[0017] Primary method--"Low-NOx" burners: There are several types
of "low NOx" burners on the market, that is to say burners which
enable reducing the NOx emissions even when used alone. However,
their performances do not always enable obtaining the necessary
reduction levels for compliance with European regulations or those
in force in other countries around the world. More particularly,
the following types of burners are encountered:
[0018] Double impulse burners--These burners produce a low gas
speed at the root of the flame so as to reduce the temperature of
the flame in the zone where the majority of the NOx is generated.
The burners also increase the luminosity of the flame, which
promotes a lowering of the temperature of the flame front by
increasing the radiative transfer of heat to the glass bath.
[0019] Injection of enveloping gas or "Shrouded Gas
Injection"--With this technique, gaseous fuel is injected at low
speed above the "underport" burners in order to block the comburant
flows and to delay mixing of the gas at high speed coming from the
"underport" burners with the air streams, thus reducing
temperatures at the root of the flame.
[0020] Ultra-low speed injection of the gas--Injections of fuel gas
at very low speeds (less than 30 m/s) are used with special burners
cooled by water circulation in order to minimize the local
temperature of the flame and to increase its luminosity. The
efficiency of this type of burner in terms of NOx reduction depends
greatly on the design of the furnace.
[0021] Primary method--Staging: This technique uses conventional
burners for injection of the fuel and reduction of the flow of
combustion air through the air stream in order to create conditions
of excess fuel and to introduce the rest of the comburant in
another location of the furnace in order to complete oxidation of
the fuel. This method, which can drastically reduce NOx emissions,
is nevertheless difficult to implement and expensive to use since
it requires pure oxygen or ducts for introducing air at
temperatures higher than 1,000.degree. C. in order to be thermally
efficient (staging of the comburant in cold air would induce a
reduction of energy efficiency). Examples of this staging technique
are:
[0022] Air staging: Diverting the hot combustion air coming from
the regenerators by using an ejector towards the combustion chamber
in the direction of the waste gases so as to produce complete
combustion. This method requires the use of heat-insulated ducts
and cold air for directing the ejector, hence a loss of thermal
efficiency. This technique has only been used on end-fired
furnaces, and mainly in Germany.
[0023] Oxygen-enriched air staging or OEAS (for Oxygen Enriched Air
Staging): The combustion air entering the air stream is introduced
with an insufficient flow for complete combustion in order to
create sub-stoichiometric conditions, and pure oxygen or oxygen
enriched air is injected at the rear of the furnace towards the
flow of waste gases so as to complete combustion in the
recirculation zone of the furnace. The OEAS injectors are generally
installed in underport position separately from the burners. This
technique has been applied successfully in end-fired furnaces and
in cross-fired furnaces, and mainly in the United States.
[0024] Among the various staging technologies, the patent WO
97/36134 discloses a device with line burners. This device makes it
possible to stage the fuel within the air stream. The fuel supplied
to the furnace is divided in two, and a portion is injected
upstream of the burner directly into the hot combustion air. This
methodology does not use an injection of fuel directly into the
combustion chamber as in the present invention. The technique uses
an injection of fuel but always coupled with an injection of
air.
[0025] Primary method--Rich operating conditions:
[0026] This technique reduces the NOx emissions by injecting
additional fuel into the combustion chamber so as to create a
"reducing atmosphere" in the combustion chamber. The reducing
atmosphere converts the NOx formed in the flame into nitrogen and
oxygen. In this technique, the NOx produced in the high temperature
flame front are reduced in a second step.
[0027] In effect, as shown, for example, by the document
JP-A-08208240, additional fuel introduced by injectors situated on
the wall supporting the burner, on the side wall or facing the
burner, is added to the original fuel supplying the burner or
burners. However, according to this method, while making possible
considerable NOx reductions in the combustion chamber, it is
necessary to provide additional combustion air after the exit from
the combustion chamber. Not only does this method require
additional consumption of fuel, but the additional fuel is not
burned in the combustion chamber and therefore does not participate
in the melting of the glass.
[0028] This process uses an over-consumption of fuel in order to
reduce the NOx, and its application can lead to an increase of the
temperatures in the regenerators and in time to degradation of the
regenerators.
[0029] Secondary method--Treatment of the waste gases: A major
portion of the NOx is treated at the outlet of the furnace by the
use of chemical reduction processes. Such processes require the use
of reducing agents such as ammonia or hydrocarbon-containing
combustion residues with or without the presence of catalysts.
Although capable of achieving the NOx level reductions set by
regulations, these processes are very expensive to install and
operate, and in the case of processes based on hydrocarbons such as
the 3R process or system explained hereafter, a 5-15% increase of
the fuel consumption is observed. Examples of this technique are
given below:
[0030] 3R process (Reaction and Reduction in Regenerators; patented
process of the Pilkington company)--In this technique, the gas is
injected at the chamber roof so as to consume any excess air and to
produce reducing conditions in the regenerators situated at the
outlet of the furnace, resulting in the conversion of the NOx into
nitrogen and oxygen. Since an excess of gas must be used, it is
consumed in the lower part of the regenerators where the air is
infiltrated or injected. The additional heat generated is often
recovered by boilers. In order to minimize the quantity of gas
necessary for the 3R system, it is common to operate the furnace
with the lowest possible excess air. This technology enables
achieving the NOx reduction levels imposed by the current
regulations, and even to exceed them. Generally, 5-15% of the total
fuel consumption of the furnace is necessary for implementation of
the 3R process. The reducing atmosphere in the regenerators is
often the cause of problems with the refractory material composing
them.
[0031] Selective catalytic reduction or SCR (Selective Catalytic
Reduction)--This method uses a platinum catalyst for reacting the
NOx with ammonia or urea so as to reduce the NOx into N.sub.2 and
water. The process has to take place at a specific temperature and
requires precise control of the ammonia in order to avoid
accidental pollution-generating discharges. Since this reaction
occurs on the surface, large surface areas of catalyst are
necessary, involving relatively large installations. The chemical
process is relatively complex and demanding in terms of control and
maintenance. Very high NOx reduction levels are attained; however,
the contamination of the catalysts by the waste gases loaded with
particles coming from the glass melting furnace poses problems of
clogging and corrosion. After a certain length of time, the
catalysts have to be replaced at considerable cost.
SUMMARY OF THE INVENTION
[0032] The aim of the invention is thus to propose a process and
means making it possible to remedy all of the above
disadvantages.
[0033] More particularly, the invention must make it possible to
reduce the NOx emissions while increasing the temperatures of the
surrounding waste gases within the furnace (the NOx emissions
produced in these zones are very low). Moreover, the invention must
make it possible to maintain or even increase the transfer of heat
to the glass bath as well as the yield of the furnace.
[0034] The aim of the invention is attained with a combustion
process for melting glass according to which two fuels, of the same
nature or of different natures, are introduced into a melting
chamber at two locations a distance away from one another in order
to distribute the fuel in the melting chamber for the purpose of
limiting the NOx emissions, with combustion air being supplied at
only one of the two locations.
[0035] The aim of the invention is also attained with a glass
melting furnace which has a tank for receiving the glass to be
melted and holding the bath of melted glass, with, above the glass,
walls respectively forming a front wall, a rear wall, side walls
and a roof and constituting a melting chamber, also called a
combustion chamber, as well as at least one intake for hot
combustion air (the combustion air intake also being called an "air
stream"), for example, at the outlet of a regenerator, at least one
outlet for hot waste gases, and at least one burner for introducing
a first fuel into the melting chamber.
[0036] According to the invention, the melting furnace moreover has
at least one injector for injecting a second fuel into a zone of
the melting chamber which is a distance away from the burner and
between the roof and a horizontal plane situated at a level higher
than or equal to a horizontal plane passing through a lower edge of
the intake for hot combustion air, the injector being adjustable in
terms of flow in a complementary manner with respect to the burner
so that it is possible to inject up to 100% of the total of the
first and second fuels used by the injector and the burner,
regardless of whether the first and second fuels are of the same
nature or of different natures. Advantageously, said horizontal
plane delimiting the zone of injection of the second fuel is
situated between the roof and a horizontal plane whose distance
from the glass bath is greater than or equal to the minimum height
of the air stream in the melting chamber.
[0037] In no case is the second fuel injected directly into the hot
combustion air.
[0038] According to the language chosen for the preceding
paragraphs, in the whole of the present text, the term "burner"
exclusively designates a means for injecting and burning the first
fuel, while the term "injector" exclusively designates a means for
injecting and burning the second fuel.
[0039] Traditionally, and particularly when thinking of existing
furnaces which can be modified in order to implement the invention
in them, the burner could also be called a "burner," and the
injector then would have to be called an "auxiliary burner."
However, such language would weigh down the present text and would
be a source of errors.
[0040] Likewise, in the description of the furnace according to the
invention and in the description of other furnaces whose burners
are situated on a given wall or which have only one burner, the
front wall is that which bears the burner or burners, the rear wall
is the oppolocation wall, and the side walls are the other two
walls. And in the case of a furnace with a non-rectangular base,
the present definition applies in a similar manner to the
corresponding wall sections.
[0041] Furthermore, any indication of the number of burners or
injectors in a melting furnace according to the invention is given
purely as an example and in no way presumes a particular embodiment
of such a furnace. In effect, the principle of the present
invention is just as valid when a melting furnace according to the
invention has a single burner and a single injector as when it has
several, and not necessarily an equal number of burners and
injectors.
[0042] According to the present invention, the burners present on a
traditional furnace are kept. They are supplemented by one or more
injectors, making it possible to introduce into the melting
chamber, in one or more zones a distance away from the burners,
either another fuel or a fraction of the same fuel as that
introduced by the burners. This injection is sometimes called
auxiliary--as opposed to an additional injection, for example, in
afterburning--because its purpose is not to increase the fuel
quantity or flow rate but rather to better distribute or spread the
quantity of fuel necessary for the quantity and type of glass to be
melted and thus to obtain a better heat transfer towards the glass
to be melted, while at the same time reducing the NOx
emissions.
[0043] This arrangement of the invention, which is furthermore just
as valid when the first and the second fuels are of the same nature
as when they are of different natures, is moreover the basis for
the so-called "complementary" method of adjusting the flow rate of
the injectors indicated above.
[0044] In effect, the flow rate of the second fuel is varied as a
function of the flow rate of the first fuel so that when the burner
does not introduce all of the fuel necessary for melting the glass,
the rest is introduced by one (or more) injector(s) arranged a
distance away from the burner and if necessary a distance away from
one another, in regions or zones of the furnace where the second
fuel will mix initially with the re-circulated combustion products,
that is to say coming from the burner or burners and therefore
having a low oxygen content, before igniting in contact with the
hot combustion air not consumed by the flame of the burner or
burners.
[0045] Let us expressly note on this subject that in the melting
furnaces according to the present invention, there is no secondary
air intake for combustion of the second fuel, since there is no
afterburning.
[0046] Generally, in order to obtain a reduction of the NOx
emission, the burner operates in an excess of air, that is to say
that the burner introduces less first fuel than the flow rate of
combustion air would permit. This lowers the temperature of the
flame of the burner with respect to temperatures that the flame
would have under stoichiometric conditions, and thus reduces the
NOx emission.
[0047] In the case of our invention, when the first fuel is burned,
the combustion products fill the combustion chamber and are
therefore present at the location or at all the locations where an
injector is placed for introducing the second fuel. During the
introduction of the second fuel, it is first diluted by the
products of combustion of the first fuel and then ignites with the
arrival of the combustion air not consumed by the combustion of the
first fuel.
[0048] With regard to the "distant" arrangement of the injectors,
the distance of the zones (for arrangement of the injectors) away
from the burner or burners depends, for example, on the geometric
data of the furnace and therefore on the time that it takes for the
waste gases to arrive at the injector: the injector must be
sufficiently far from the burner to allow the waste gases to arrive
at the injector and to mix with the second fuel before the
non-consumed combustion air from combustion of the first fuel
arrives and ignites the second fuel.
[0049] The arrangement of one or more injectors with respect to the
burner(s) of a glass melting furnace according to the present
invention leads to a gradual combustion of the fuel introduced in
these regions or zones, producing an increase of the temperature of
the waste gases in these fuel rich zones, as well as to an increase
of heat transfer to the glass bath.
[0050] The aim of the invention is also attained with a process for
operating a glass melting furnace which has a melting tank for
receiving the glass to be melted and holding the bath of melted
glass, with, above the glass, walls forming a melting chamber, at
least one intake for hot combustion air, at least one outlet for
hot waste gases as well as at least one burner and at least one
injector for respectively injecting a first fuel and a second fuel
into the chamber.
[0051] According to this process, a first fuel and a second fuel,
of the same nature or not, are injected into the furnace by the
burner(s) and injector(s), the injector(s) being arranged on a
different wall or on different walls from that on which the
burner(s) is (are) positioned and being a distance away from the
burner or burners, and the burner(s) and the injector(s) are
adjusted in a complementary manner so that the total of the first
and second fuels used by injector(s) (4) and burner(s) (1)
corresponds for the most part to the total flow used normally on
the furnace, regardless of whether the first and second fuels are
of the same nature or of different natures.
[0052] The fraction of the fuel which is introduced as second fuel,
or the quantity of a second fuel different from the first, is
determined for each furnace, and can range up to the entire
quantity of fuel.
[0053] With this technique, according to which a first fuel is
introduced into the melting furnace with an excess of air with
respect to the stoichiometric flow of combustion air, since the
fuel fraction introduced by the injectors no longer supplies the
burner, the portion of fuel burned with a high temperature flame
front is reduced, thus generating less NOx emission by the thermal
avenue.
[0054] The combustion air not used by the burner remains available
for combustion of the second fuel introduced by the injector.
[0055] It is also likely that the fuel introduced in the zones of
the furnace with high temperatures, but with a reduced oxygen
content, will crack in order to produce soot, thus increasing the
heat transfer from these zones to the glass bath.
[0056] The potential injection points can be situated on the side
and rear walls of the furnace and on the wall forming the roof. In
certain cases, the center of the roof which, in the case of the
traditional rectangular shapes of glass melting furnaces, is a
transverse line of symmetry or a longitudinal line of symmetry of
the roof with respect to a reference direction given by the
direction of the burner flame, can be particularly advantageous for
injection of the second fuel, because by choosing this location it
is possible to reduce by two the number of injectors necessary for
execution of the invention.
[0057] The selection of the injection points, of the direction of
the jets coming out of the injector and of the speed of these jets
is essential for the success of this combustion technique. The most
suitable positions as well as the geometry of the injectors have to
be identified for each melting furnace.
[0058] The speed and the direction of introduction of the second
fuel have an influence on the result obtained by implementation of
the various arrangements of the invention. However, these two
characteristics are determined during design of the device. An
error in determination of the position of the injectors or of their
geometry can not only compromise the efficiency of the combustion
technique but can also lead to a lowering of the furnace yield as
well as to an increase of the temperature of the refractory
regenerators. In extreme cases, premature shutdown of the furnace
can occur.
[0059] The most favorable locations for the injectors and the
directions and speeds of fuel injection, but also clear indications
as to the injector geometries which risk being counterproductive,
are advantageously determined using models obtained by computations
and tests. Such models are based on a combination of physical and
mathematical modeling techniques and take into consideration the
technical constraints imposed by the construction of each furnace.
The adoption of the most favorable auxiliary combustion
configuration suggested by the modeling results in NOx emissions
much lower than those generated by combustion methods different
from those of the invention, and without this being done at the
cost of lowering the furnace yield. The auxiliary fuel ratio is
adjusted to obtain a compromise between furnace efficiency and
level of NOx emissions. By predicting the temperature within the
chamber, the model makes it possible to adjust the auxiliary fuel
ratio to avoid any hot spot as well as any cold spot on the
internal surfaces of the furnace. Particular care should be taken
to avoid: [0060] condensation of alkaline materials on the roof or
walls of the furnace (wear and tear of the refractory materials),
[0061] condensation of hydrocarbons on the internal walls of the
furnace, [0062] as well as modification of the nature of the glass
by addition of carbon to its composition.
[0063] This is made possible by the modeling which enables one to
choose a sensible location.
[0064] Such models make it possible, for a cross-fired furnace, for
example, to determine the injection position situated in the roof
and in the center for a burner as being one of the most favorable
for intended reduction of the NOx emissions, with an injected
secondary fuel ratio that can vary as a function of the emission
level limits that need to be achieved for this burner. A great
advantage of symmetrical injection in the roof with respect to
lateral injection is the use of the same injectors for the flame on
the left and the flame on the right.
[0065] The number of burners to be equipped with an injector can
vary as a function of the overall level of NOx reduction to be
achieved for the furnace.
[0066] With regard to end-fired furnaces which have two ports at
one end of the melting and refining chamber, and two sealed
regenerators, each connecting respectively with a port, the
auxiliary injections in the roof, like the injections on the walls,
should preferably occur in a zone situated between the roof and a
horizontal plane whose distance from the glass bath is greater than
or equal to the minimum height of the air stream.
[0067] The injections should occur, symmetrically or not, on both
sides of the furnace. Locating the injection point(s) optimally is
done by use of a model, since end-fired furnaces can differ from
one another, mainly because of the width/length ratio of the
furnace.
[0068] Consequently, it is proposed to implement the auxiliary
combustion technique developed here while adding to it the
combustion technique already present on the furnace. This is done
by adjusting the fuel flows between the injectors and the burner so
as to produce a balance between NOx reduction, the nature of the
glass, and suitable thermal efficiency for each installation under
consideration.
[0069] An embodiment of a melting furnace according to the
invention enabling one to obtain NOx reduction while maintaining or
even increasing the heat transfers is described further on.
[0070] The approach of the invention also makes possible a gradual
implementation of this novel combustion technique, thus reducing or
eliminating the risks of production loss due to damage to the
furnace. Finally, this approach allows the operator at any time to
go back to his initial combustion configuration.
[0071] Although developed for use on regenerative glass melting
furnaces, the auxiliary combustion technique of the invention can
also be used on other types of glass melting furnace (for example,
Unit-Melter furnaces or recuperator furnaces), as well as on
furnaces other than glass melting furnaces.
[0072] Although it is anticipated that the fuel injected by
auxiliary routes is natural gas for furnaces supplied with natural
gas or fuel oil, the use of various fuels such as biogas, hydrogen,
LPG and fuel oil is not excluded.
[0073] Thus, the present invention relates equally to the following
characteristics considered alone or in any technically possible
combination: [0074] the injector or each injector is arranged in a
zone situated between the roof and a horizontal plane whose
distance from the glass bath is greater than or equal to the
minimum height of the air stream; [0075] the injector or each
injector can be adjusted in terms of flow rate so that it is
possible to inject up to 100% of the total of the fuel used by the
injector(s) and the burner(s); [0076] at least some of the
injectors are arranged on the roof of the furnace; [0077] at least
some of the injectors are arranged on the side walls of the
furnace; [0078] at least some of the injectors are arranged on the
rear wall of the furnace; [0079] at least some of the injectors are
arranged on the wall of the furnace on which the burner is
situated; [0080] the injectors are oriented at least approximately
in a direction oppolocation from the main direction of the flames
of the furnace burners; [0081] the injectors are oriented at least
approximately in the same direction as the flames of the furnace
burners; [0082] the injectors are oriented at least approximately
in a direction perpendicular to the flames of the furnace burners;
[0083] the injectors are oriented at least approximately in a
direction transverse to the flames of the furnace burners; [0084]
the first fuel and the second fuel are of the same nature; [0085]
the first fuel and the second fuel are of different natures.
[0086] The injectors can be equipped with a system of rotation
(swirler) making it possible to control the shape of the flame
independently of the flow rate of secondary fuel so that it is
possible to inject up to 100% of the total of the fuel used by the
injector(s) and the burner(s) without affecting the glass bath.
[0087] The injectors can be equipped with a device making it
possible to adjust the impulse of the fuel (double impulse)
independently of the flow rate of secondary fuel so that it is
possible to inject up to 100% of the total of the fuel used by the
injector(s) and the burner(s) without affecting the glass bath.
[0088] The injectors can have a non-circular shape or can have
multi-jets in order to adjust the shape of the flame without
affecting the glass bath.
[0089] In a modified melting furnace according to the invention,
reduction of the nitrogen oxides contained in the combustion
products is obtained by using the combination of the burners
already present on the furnace along with auxiliary injections of
fuel in the zones of re-circulation of the waste gases of said
furnace. The injections are made according to one or more jets
situated in optimal locations on the furnace which are defined by
using a methodology based on digital simulation, which can be
coupled or not with the representation of the flows by a mock-up of
the furnace. The plane of the injections can be parallel,
perpendicular or transverse to the surface of the glass bath. The
invention can be applied in the domain of reduction of the nitrogen
oxides by primary method in glass melting furnaces.
[0090] The invention makes it possible: [0091] to reduce the NOx
emissions, [0092] to reduce or eliminate the post-treatment costs,
[0093] to improve the yield of the furnace, and [0094] to reduce
the NOx emissions while improving the yield of the furnace.
[0095] Furthermore, the invention [0096] can be applied regardless
of the fuel supplying the burner, [0097] can be applied with a fuel
supplying the injectors which is of a different nature from that
supplying the burners of the furnace, if necessary the type of
injector being adapted to the chosen fuel, [0098] can be applied
with a fuel supplying the injectors which is of the same nature as
that supplying the burners of the furnace, with it then being
possible for the type of injector to correspond to that of the
burners with regard to their adaptation to the fuel, [0099] is
implemented directly in the combustion chamber, also called the
melting chamber, [0100] makes it possible to distribute the fuel
between the main burners already equipping the furnace and
injectors in such a way as to bring about reduction of the NOx
emissions combined with a suitable yield for each particular
furnace, [0101] can be used with under-port burners, side-port
burners, through-port burners or with any other type of burner
originally equipping the furnace, [0102] can use the injection, by
the injectors, of a fraction of the fuel injected by the burners
but [0103] can just as well use all of the fuel by the
injectors.
[0104] The auxiliary injection [0105] is not implemented directly
in the air stream, [0106] can be done from the roof, [0107] can be
done from the walls situated to the front or rear of the furnace,
[0108] can be done from the side walls, [0109] uses positions as
well as angles and speeds of injections which are determined by a
parametric study using modelings of the furnace that is intended to
be transformed, [0110] can be done with the same fuel or with a
different fuel from that injected by the burners, [0111] can be
done with natural gas, [0112] can be done with LPG, [0113] can be
done with fuel oil, [0114] can be done with coke-oven gas, [0115]
can be done with blast furnace gas, [0116] can be done with
reforming gas, [0117] can be done with biogas, [0118] can be done
with hydrogen, [0119] can be done with any other fuel.
BRIEF DESCRIPTION OF DRAWING FIGURES
[0120] Other characteristics and advantages of the present
invention will emerge from the description hereafter of an
embodiment of a furnace according to the invention. This
description is given with reference to the drawings in which:
[0121] FIGS. 1 and 2 represent two types of melting furnaces used
before the invention;
[0122] FIG. 3 represents a cross-fired melting furnace according to
the invention in the form of a horizontal section indicating the
zone of the auxiliary injections;
[0123] FIG. 4 represents, in a diagram, the NOx levels as a
function of the distribution of power between the burners and the
associated injectors;
[0124] FIG. 5 represents a diagrammatic view of a furnace according
to the invention in the form of a vertical section indicating an
auxiliary injection zone example;
[0125] FIG. 6 represents, in a diagram, a comparison of the levels
of NOx and CO obtained in a furnace with and without use of the
invention;
[0126] FIG. 7 represents, in a diagram, temperature levels obtained
in a furnace with and without use of the invention; and
[0127] FIG. 8 represents, in a diagram, a comparison of heat
transfers obtained with and without use of the invention.
DETAILED DESCRIPTION
[0128] FIGS. 1 and 2 each very diagrammatically represent two types
of glass melting furnaces that are traditionally used, namely a
cross-fired regenerative furnace and an end-fired furnace. Both
types of furnaces have a rectangular base bound by four walls, of
which the two walls extending in the lengthwise direction of the
furnace are in this case called the side walls and of which the
other two walls are called the transverse walls. At the top, both
furnaces are bounded by a roof.
[0129] In a cross-fired regenerative furnace (FIG. 1), burners 1
are arranged in side walls 2 and operate alternately on one side
and then the other for approximately 20-30 min per side. Cold
combustion air A is pre-heated in two heat recuperators R, namely
in an alternating manner according to the rhythm of operation of
the burners, in that one of the two recuperators which is near the
burners in operation. The resulting waste gases F then re-heated in
that one of the two recuperators R which is remote from the burners
in operation.
[0130] In the end-fired glass melting furnace (FIG. 2), in which
the length of the furnace does not greatly exceed its width,
burners 1 are arranged in transverse wall 3. The range of the flame
of each of burners 1 is such that, under the influence of the
oppolocation transverse wall, the end of each of the flames
describes a loop. The cold combustion air is pre-heated in a part
of regenerator R with several chambers before being directed as hot
combustion air AC towards the burners. The resulting waste gases
are then directed towards the other regenerator in order to re-heat
it.
[0131] In both furnaces, the flames are directed approximately
parallel to the surface of glass bath B.
[0132] FIG. 4 represents, in a diagram indicating the NOx level
achieved as a function of the power distribution between burner 1
and injectors 4, the results obtained in a semi-industrial test
furnace (or a test cell). It should be noted more particularly that
the NOx emission level decreases with the increase of the portion
of fuel injected through the secondary injectors.
[0133] FIG. 5 once again represents the end-fired furnace of FIG.
2, but in this case with indication of zone IN in which, according
to the invention: the secondary fuel injections must occur in a
defined space above the flames, that is to say between roof V and
horizontal plane P whose distance from glass bath B is greater than
or equal to the minimum height of air stream VA, that is to say in
a zone of the melting chamber which is a distance away from the
burner and situated between the roof and horizontal plane P
situated at a level higher than or equal to a horizontal plane
passing through the lower edge of the hot combustion air inlet.
[0134] The auxiliary injections advantageously but not necessarily
take place symmetrically on both sides of the furnace.
[0135] According to an embodiment which is particularly economical
in terms of number of injectors 4, as diagrammatically represented
in FIG. 3, the injectors are arranged in a zone corresponding at
least approximately to a central zone with respect to the burners
that are arranged in the side walls of the furnace and that operate
in an alternating manner or simultaneously.
[0136] In this view, one also sees the introduction of cold
combustion air A, its passage through heat recuperators R in order
to be pre-heated before entering melting tank or chamber L, the
exit of the hot waste gases from the melting chamber, and their
passage through the heat recuperators before leaving the melting
furnace. And an example of an injector arrangement is seen more
particularly. Recall that the precise position of each of the
injectors is determined by a combination of computations according
to a model and tests with the specific furnace that is to be
equipped with such injectors.
[0137] Tests have been done with such a furnace with a unit power
of the under-port burners of 1.03 MW with an angle of injection to
the burner of 10.degree., an air factor of 1.1, a pre-heated air
temperature of 1,000.degree. C. and a furnace temperature of
1,500.degree. C. The results are represented in FIGS. 4, 6, 7 and
8.
[0138] FIG. 6 represents, in the form of a diagram, the levels of
CO and NOx with 8% oxygen for different distributions of power
between a burner and one or more allotted injectors, the injector
or injectors being arranged in the roof of the furnace.
[0139] FIG. 7 represents, in the form of a diagram, the temperature
levels of the roof for different methods of operation of the
furnace, namely in the case of a single burner and in the case of a
burner with an injector that injects between 30 and 100% of the
fuel. It is observed that the process does not bring about any
overheating of the roof.
[0140] FIG. 8 represents, in the form of a diagram, the heat flows
transmitted to the load without and with secondary injection. In
this example, the heat flow is highest in the case of secondary
injections of between 30 and 80% of the fuel.
[0141] FIG. 6 represents, in the form of a diagram, the levels of
NOx and CO of a furnace without and with auxiliary injection
ranging up to 100% of the fuel. It is observed that the levels of
NOx decrease when the auxiliary fuel portion increases. As for the
CO levels, they gradually increase with the auxiliary fuel portion
but in completely tolerable proportions.
[0142] A compromise therefore has to be reached between the NOx and
CO levels and the yield. In the example presented, this compromise
is reached with a fuel flow rate of between 50 and 70% of the total
flow rate.
* * * * *