Patent Application
20200148572
The present invention relates to a combustion method applied to a method of melting raw materials, for example glass, in an end-fired furnace and more specifically relates to a method aiming at reducing the formation of nitrogen oxides (NOx) in the flames used during the melting of the raw materials.
The invention further relates to an end-fired melting furnace implementing such a method aiming at reducing the emission of NOx.
Several types of melting furnaces for producing different types of glass or other materials are known, including end-fired furnaces. In these furnaces, the flame, which is sometimes called a “horseshoe flame”, and the flow of combustion products define a U-shape.
It should be noted that end-fired furnaces are sometimes referred to by the skilled person as “end-port furnaces” or “U-flame furnaces”. Hereinafter, the terms “end-fired”, “end-port” and “U-flame” may be equivalently used to describe one and the same type of furnace.
The following terms may be used in the present description. The following definitions are only given by way of example:
End-fired furnaces are typically operated with regenerative heat exchangers using alternately two ports located alongside each other on one wall (the back wall) of the furnace. During first periods of time (typically between 10 and 30 minutes) fuel and an oxidiser such as air are supplied to only a first one of the two ports, while combustion products are exhausted via the exhaust port. During alternate second period of time (also typically between 10 and 30 minutes) fuel and an oxidiser such as air are supplied to the other of the two ports, while the combustion products are exhausted via the exhaust port associated with the first burner. The ports act alternately as inlet ports or as exhaust ports.
Each port has associated with it one or more burners. The burners feed the fuel in through or near (usually under) the port serving as an inlet for the oxidiser. The burners in or near the exhaust port are idle. Fuel supply to the two sets of burners alternates in synchronisation with the oxidiser flow.
A regenerator is connected upstream from the supply opening of an inlet port in the supply path of the oxidiser. The exhaust side regenerator is heated by the outgoing exhaust gases. After the furnace firing direction is reversed, the hot regenerator heats the incoming oxidiser. This process of heat recovery into the incoming oxidiser increases the thermal efficiency of the melting furnace and ensures the achievement of the high temperatures needed to melt the raw materials (circa 1500° C., 2700° F.).
When the oxidiser is air, as is usually the case on industrial glass melting furnaces, Nitrogen Oxides (NOx), a regulated air pollutant, usually arise during the combustion of the fuel and oxidiser mixture. The nitrogen in the air combines with the oxygen in the air at the high temperatures found in glass melting furnace flames to form ‘thermal NOx’. In the case of regenerative glass melting furnaces, concentrations of NOx in the exhaust gases are typically in the range of 750 to 2500 mg/Nm3 at 8% O2, the standard condition for comparing NOx emissions.
It is important to try to reduce the nitrogen oxide fraction in the exhaust gas to meet the limit of 500 mg/Nm3@8% O2 set by current or imminent emissions regulations in many parts of the world. This requires ‘as found’ NOx emissions to be reduced by between 30% and 80%.
The option commonly deployed to reduce the NOx emissions from glass melting furnaces (or other types of furnaces) is post-treatment of the exhaust gas. However, such exhaust gas purification devices are costly and constitute additional equipment which requires additional space and high operating and maintenance cost. Typically, a selective catalytic reduction (SCR) plant to achieve up to 90% NOx reduction on a large end-fired glass melting furnace has a capital cost of one million Euros and annual operating costs of about €100,000. It requires the replacement of about ⅓ of the catalyst each year. It also requires the use of ammonia (NH3 or urea) as a reducing agent, a fluid that is itself a regulated pollutant. A lower capital alternative is selective non-catalytic reduction (SNCR) carried out inside the exhaust regenerator. SNCR uses ammonia or urea to react with the NOx and decompose the NOx. It must be carried out at a very particular temperature between 870° C. and 1090° C. Above this temperature the ammonia reacts to produce more NOx, while below it the ammonia leaves the regenerator unreacted to add to the emissions from the plant. On a reversing regenerative glass melting furnace, the right conditions for effective SNCR exist only for a small portion of the regenerative cycle at any given location in the regenerator. This renders SNCR quite ineffective.
Tsai (EP 0882488 and U.S. Pat. No. 5,893,940) introduces additional fuel and oxidiser into the exhaust gases in an attempt to stabilise their temperature entering the regenerative heat exchanger and thus to extend the portion of the furnace cycle for which SNCR is effective. The method works although is very difficult to control the temperature within the required range. Thus the effectiveness of Tsai's approach is limited and in addition it adds to the cost of the ammonia by increasing the fuel consumption and. CO2 emissions of the furnace by several percentage points.
A more successful approach to cleaning up the exhaust gas after it leaves the melting chamber has been the addition of excess fuel either to the exhaust or within the melting chamber so that there is insufficient oxidiser available for complete combustion. In this circumstance, carbon monoxide (CO) and Hydrogen (H) is formed in the exhaust (reducing atmosphere), and these reduce NOx to nitrogen (N2) and carbon dioxide (CO2) and water (H2O) in the exhaust port and within the regenerators. Air must be introduced at the downstream end of the regenerator (sometimes called “over fired air”) to burn the excess CO (another regulated pollutant) and to try to recover part of the heat lost in the additional fuel.
This method, called “reburning fuel technology”, was originally proposed by Quirk (EP0599548—the so-called 3R process) who used the non-firing burners in or near the exhaust ports to introduce the excess fuel. However, although it has the potential to achieve the required 80% reduction in NOx at a very low capital cost, this is at the price of an increase of between 5% and 15% in fuel consumption and CO2 emissions. The 3R approach also imposes chemical and thermal stress on the regenerators leading to a reduction in regenerator life. For these reasons, this approach has almost been abandoned by the glass industry.
In an attempt to improve this “reburning fuel technology”, Ichiraku (JP08208240) proposed a method of reducing NOx using after-burning in the regenerator. In this method excess fuel is injected into the furnace through injectors in the crown or in the exhaust port or, in the case of an End-fired furnace, near the front wall. NOx formed by the conventional burners enters the regenerators in a highly reducing atmosphere which results in decomposition of the NOx into nitrogen and carbon dioxide. A certain time is required for this “After-burning” reaction which is usually complete part way through the regenerator. At this point air may be injected to burn the excess fuel at a relatively low temperature. Some of the heat generated is recovered by the regenerator and some leaves in the higher temperature gases from the regenerator. The technique is similar to the Quirk 3R process except that in 3R the excess gas is injected in the exhaust port neck. It suffers from similar drawbacks and it has not seen widespread application.
In summary, while all the exhaust gas clean up approaches discussed above are capable of achieving the required NOx reductions of up to 80%, they only achieve this at the price of high capital cost, or high running costs, or in some cases both. In addition, the Quirk and Ichiraku approaches lead to a large (circa 10%) increase in CO2 emissions.
An alternative approach is to reduce or avoid the formation of NOx in the melting chamber. Burner tuning, including the reduction of excess oxidiser (removing the available oxygen for the NOx forming reaction) and lengthening the flame (reducing peak flame temperature and hence the rate of NOx formation) is possible, but will typically yield not more than 10% to 20% reduction before high levels of CO appear in the exhaust. This or an associated loss of furnace output prevents their further use.
Moreau (U.S. Pat. No. 6,047,565) proposes to create a “blanket” of inert gas between the oxidiser entering through the inlet port and the fuel entering through the burner, thus delaying combustion of the main fuel producing lower temperatures in the main flame and thus reducing NOx formation. The method applies only to underport firing arrangements where the fuel is introduced through one or more burners situated below the oxidiser ports and the stream of oxidiser flowing through them. Moreau proposes various methods of producing this “blanket”. Usually the “Blanket” is formed in or below the combustion inlet port by introducing at low velocity a small (typically 5% and always less than 30%) quantity of the fuel between the main fuel jet and the oxidiser. The method can produce excessively long flames which do not complete combustion in the furnace and may result in undesirable reducing conditions at the glass surface. U.S. Pat. No. 6,047,565 proposes methods to overcome these undesired effects by injection of high pressure jets of oxygen or air between the main fuel jets and the surface of the molten glass. This is quite a complex arrangement to manage. The total oxidiser supplied through the oxidiser port and the supplementary oxygen lances is held close to or below the amount needed for complete combustion. This fuel rich operation also contributes to reducing the NOx but the inventor gives no indication of the method's effectiveness in reducing NOx.
Nakamura (JPH5180410) reduces the formation of NOx by injecting part of the fuel through two injectors located on the same wall as the combustion air inlet port at a location adjacent to the port and directed in the same direction as the air and flame. Fuel from the two injectors is mixed with re-circulated waste gases which are low in oxygen and therefore burns slowly at a lower temperature resulting in lower NOx formation. In practical terms it is difficult to fit injectors at this location. Due to the proximity of the incoming oxidiser stream, there is insufficient distance available for the injector fuel to mix with the combustion products before encountering and mixing with the combustion air thus reducing the effectiveness of the Nakamura injection method.
Demarest (U.S. Pat. No. 4,599,100) discloses a method for operating a cross-fired melting furnace using excess air firing. In this document, additional fuel is introduced through an additional burner to consume the excess air. The injection of additional fuel in this document is such that the reduction of excess air is on top of the flame so that the area between the flame and the glass remains oxidising and the exhaust from the furnace still contains some excess air. As the total amount of excess air is typically 20% the amount of additional fuel must be small. In order to achieve significant NOx reduction the total excess air must be reduced to very close to stoichiometric which is unlikely using the described technique. Demarest does not specify the amount of NOx reduction obtainable using this method.
Ward (WO 2008/074961 A2) discloses a combustion method fur melting glass in which two fuels of the same nature or of different natures are fed into a melting chamber through a burner and an auxiliary injector at two locations remote from each other for distributing the burner fuel and the auxiliary fuel in the melting chamber in order to reduce the NOx emissions, the oxidiser being supplied only at the location of the burner. The method takes advantage of the stream of recirculating combustion products that occupy a substantial fraction of the space above the incoming oxidiser and its burner flames. The design of the ports and the burners is such that these flames lie close to the surface of the molten glass, with the rest of the furnace filled with recirculating exhaust gases into which Ward injects part of the fuel. According to Ward, a portion (from 10% to 100%) of the fuel supplied through the burners is removed and introduced into the recirculating combustion products in such a way and at such a location so as to completely mix with and partially burn in the oxygen poor combustion products before they encounter and completely burn in the incoming oxidiser above the inlet port, a process labelled Auxiliary Injection.
Also, it should be noted that the teachings of Ward are generic and not adapted to the specificities of end-fired melting furnaces.
In addition, the use of the recirculating combustion products of Ward can be improved.
The present invention proposes and claims new auxiliary injection configurations to prevent the creation of NOx and furthermore to improve on Ward's (WO 2008/074961 A2) combustion process in ways that are specific to end-fired furnace configurations designed for melting various materials.
The technical problem to be solved is to provide a combustion method for an end-fired melting furnace which remedies the above-mentioned problems or drawbacks and in particular diminishes the creation of NOx while maintaining the output and quality of molten material from the end-fired melting furnace.
In particular, the invention aims at reducing the nitrogen oxide fraction of the exhaust gas at low cost and without introducing cumbersome additional equipment while maintaining or improving the melting process.
The invention is defined in the appended claims.
The invention provides a method of melting raw materials by an end-fired melting furnace which has:
in the direction of the flow of said re-circulating combustion products,
without additional oxidiser,
into said re-circulating combustion products, the auxiliary fuel injector being located at a point where said second fraction X2 of auxiliary fuel will mix with the re-circulating combustion products, before reaching incoming oxidiser introduced by a port,
the velocities of the jets introducing the fraction X1 of fuel and the fraction X2 of auxiliary fuel being adapted so that the sum of their corresponding jet momenta is comprised between −30% or +30% of a value corresponding to the jet momentum of the fuel when X2 equals zero (and X1 equals 1), and
the energy provided by the quantity of the sum of the first fraction of fuel X1 and the second fraction of fuel X2 being adapted to produce a given required energy for melting said materials without over-fuelling the furnace.
Over fuelling refers to an introduction of fuel which is in excess of the amount of fuel which can be burned by available oxidiser. Over fuelling may occur in solutions of the prior art in which fuel is added into the melting chamber such as in Ichiraku.
Thus, the second fraction of auxiliary fuel X2 is introduced in the recirculating combustion products in a manner which enhances the flow of recirculating combustion products, ensuring an effective dilution of the auxiliary fuel to reduce NOx formation.
This results from the position and direction of the jet of auxiliary fuel which introduces the fraction X2 of auxiliary fuel, and from the velocity of the auxiliary injection. It should be noted that this feature is not disclosed in document Ward which is silent on how the auxiliary fuel is introduced. As a matter of fact, in document Ward, the quantity of fuel introduced by a burner may be reduced so as to introduce another quantity of fuel through an auxiliary fuel injector. However, reducing the quantity of fuel introduced by a burner reduces the mass flow (for example expressed in Kg/s) of the recirculating combustion products. The inventors of the present invention have discovered that by changing the direction and the velocity of the injection of the auxiliary fuel, and the velocity of the injection of the burners, it is possible to maintain the mass flow of the recirculating combustion products and thus to obtain a better NOx reduction effect.
The skilled person knows how to determine the required energy for melting materials efficiently for a given furnace and application. The sum of the momenta of the two fluids can be deduced from this energy (at plus or minus 30%). Furthermore, the fractions X1 and X2 may be chosen so as to obtain a desired level of NOx reduction.
Contrary to those known solutions of the prior art which require modifications of the excess (to stoichiometric) oxygen levels leaving the melting chamber, the invention may operate within the existing (corresponding to X2 being equal to zero) stoichiometric levels for a furnace and a specific melting application (with X2 being equal to zero).
It should be noted that the expression “X2+X1 being equal to 1” is equivalent to the expression: the quantity (for example the mass) of fuel per unit time (or the corresponding energy per unit time) introduced in the melting chamber will be divided, or substantially divided, between the fuel introduced through the burner(s) and the auxiliary fuel.
Also, the value corresponding to the jet momentum of the fuel when X2 equals zero corresponds to the value when the fuel is only injected using the burner(s) to operate the furnace and to melt the same materials. Thus, this value corresponds to the normal functioning of the furnace for this application in which the auxiliary fuel injector is not used.
According to a particular embodiment, the auxiliary fuel injector has an orientation which will reinforce the mass flow of the recirculating combustion products.
According to a particular embodiment, the at least one auxiliary fuel injector is arranged so that the direction of the jet of auxiliary fuel forms a first acute angle θ with a horizontal plane and a second acute angle α with a vertical plane parallel to the side walls.
According to a particular embodiment, at least one port is associated with a plurality of individual burners.
According to a particular embodiment, the first fuel and the second auxiliary fuel are different or identical fuels.
In this particular embodiment, when using identical fuels, a fraction of a fuel is routed to the burners and the remainder is routed to the at least one auxiliary fuel injector. When using different fuels, two fuels are used corresponding to a quantity of energy which will be divided between the burners and the at least one auxiliary fuel injector.
According to a particular embodiment, at least one burner and said at least one auxiliary fuel injector each operate with a fuel selected from the group consisting of natural gas, LPG, fuel oil, coke-oven gas, blast furnace gas, reforming gas, biofuel and hydrogen.
According to a particular embodiment, the at least one auxiliary fuel injector is located downstream and within a distance from the back wall which is less than half the length of the furnace.
According to a particular embodiment, the method comprises adjusting or altering the jet momentum of the introduced fraction X2 of auxiliary fuel so as to reinforce the mass flow of re-circulating combustion products. For example, this may be done by the use of a pressurised jet of fuel, air or inert gas, or steam concentric with the Auxiliary fuel jet.
According to a particular embodiment, the method comprises adjusting or turning off some of the burners so as to reinforce the mass flow of re-circulating combustion products.
According to a particular embodiment, the method comprises operating alternately said first and second ports as inlet port for introducing oxidiser and as exhaust port.
According to a particular embodiment the velocity of the jet introducing the second fraction X2 of auxiliary is comprised between 100 m/s and 250 m/s.
The invention further provides an end-fired melting furnace comprising:
without additional oxidiser,
into said recirculating combustion products, the auxiliary fuel injector being located at a point where said second fraction X2 of auxiliary fuel will mix with the recirculating combustion products, before reaching incoming oxidiser introduced by a port,
the velocities of the jets introducing the fraction X1 of fuel and the fraction X2 of auxiliary fuel being adapted so that the sum of their corresponding jet momenta is comprised between −30% or ±30% of a value corresponding to the jet momentum of the fuel when X2 equals zero, and
the energy provided by the quantity of the sum of the first fraction of fuel X1 and the second fraction of fuel X2 being adapted to produce a given required energy for melting said materials without over-fuelling the furnace.
The above defined end-fired melting furnace may be able to perform all the embodiments of the method as defined above.
According to a particular embodiment, the at least one auxiliary fuel injector has an orientation which will reinforce the mass flow of the recirculating combustion products.
According to a particular embodiment, the at least one auxiliary fuel injector is arranged so that the direction of the jet of the auxiliary fuel forms a first acute angle θ with a horizontal plane and a second acute angle α with a vertical plane parallel to the side walls.
According to a particular embodiment, at least one port is associated with a plurality of individual burners.
According to a particular embodiment, the first fuel and the second auxiliary fuel are different or identical fuels.
According to a particular embodiment, said at least one burner and said at least one auxiliary fuel injector each operate with a fuel selected from the group consisting of natural gas, LPG, fuel oil, coke-oven gas, blast furnace gas, reforming gas, biofuel and hydrogen.
According to a particular embodiment, the at least one auxiliary fuel injector is located downstream and within a distance from the back wall which is less than half the length of the furnace.
According to a particular embodiment, the end-fired melting furnace comprises a device for adjusting or altering the jet momentum of the introduced fraction X2 of auxiliary fuel so as to reinforce the mass flow of re-circulating combustion products.
According to a particular embodiment, the end-fired melting furnace comprises a device for adjusting or turning off some of the burners so as to reinforce the mass flow of re-circulating combustion products.
According to a particular embodiment, said first and second ports are configured to operate alternately as inlet port for introducing oxidiser and as exhaust port.
According to a particular embodiment, the velocity of the jet introducing the second fraction X2 of auxiliary is comprised between 100 m/s and 250 m/s.
Other characteristics and advantages of the invention appear from the following description of particular embodiments, given as examples and with reference to the accompanying drawings.
The present invention will be described in connection with preferred embodiments which are given by way of examples. In the following examples, glass is the material to be melted by the furnace. However, the invention is also directed to the melting of other types of materials. Also, in the following examples, the end-fired melting furnace is a reversing melting furnace. However, the invention also applies to other types of end-fired melting furnaces, and notably to non-reversing end-fired melting furnaces. The features of the different embodiments may be combined unless otherwise stated.
A typical arrangement of an embodiment of the invention is illustrated in
As shown in
A melting chamber 8 is located above the melting tank 7 and comprises a first side wall 1, a second side wall 2, a back wall 3 located at the upstream area of the melting tank 7, a front wall 4 located at the downstream area of the melting tank 7, and a roof 6.
First and second ports 21, 22 are provided in the back wall 3 of the melting chamber 8 in first and second horizontally spaced locations. The first and second ports 21, 22 are associated with first and second burners 11, 12 for injecting a first fuel into the melting chamber 8. The first and second ports 21, 22 are alternately operable as an inlet port for introducing oxidiser (for example air) in the chamber and as an exhaust port for combustion products. The first port 21 is an inlet port when the second port 22 is an exhaust port and the first port 21 is an exhaust port when the second port 22 is an inlet port. In the example of
As schematically shown in
A proportion of the combustion products recirculate towards the second port 22 and flow around the furnace, above the flame, in a substantially horizontal loop schematically represented by arrows 104. Such recirculation of combustion products has been known to exist in reversing regenerative furnaces since the 1950s (e.g. M W Thring & M P Newby, ‘Combustion length of enclosed Turbulent Jet Flames’, Symposium (International) on Combustion, 1952, or in document Craya mentioned hereinafter).
Similarly during alternate periods, an almost symmetrical flame is created when the first port 21 is operated as an inlet port and a first fuel is injected through the first burner 11. Coincidentally, combustion products flow to the second port 22 and a recirculation of combustion products occurs above the flame in the counter clockwise direction (dewed from above the furnace
The first and second ports 21, 22 and the associated first and second burners 11, 12 are thus alternately and repeatedly used to emit respectively an oxidiser (air or oxygen) and a first fuel. The changeover between the first and second ports 21, 22 and correspondingly the first and second burners 11, 12 occurs cyclically, with a cycle time being e.g. between 10 and 30 minutes, more specifically between 20 and 30 minutes. A first fraction X1 of fuel is injected into the melting chamber 8 via the alternately operated first and second burners 11, 12.
In order to reduce the formation of NOx in the end-fired melting furnace 10, the furnace is further equipped with a first auxiliary fuel injector 13 and with a second auxiliary fuel injector 14.
The first auxiliary fuel injector 13 is located on the first side wall 1 and the first auxiliary fuel injector 13 is associated with the first burner 11. More precisely, in a period of time in which the first port 21 introduces oxidiser and the first burner 11 injects fuel, the first auxiliary fuel injector 13 is controlled to inject a second fraction X2 of auxiliary fuel (with X1+X2=1). The first auxiliary fuel injector 13 is located downstream from the first burner 11 within a distance from the back wall 3 equal to half the length of the furnace.
The length of the furnace is the distance between the back wall 3 and the front wall 4.
The second auxiliary fuel injector 14 is located on the second side wall 2 and the second auxiliary fuel injector 14 is associated with the second burner 12. More precisely, in another period of time (corresponding to
In an alternative, the two auxiliary fuel injectors may be positioned in the roof.
In the example of
in the direction of the flow of said re-circulating combustion products,
without additional oxidiser,
into said recirculating combustion products, the second auxiliary fuel injector 14 being located at a point where said second fraction X2 of auxiliary fuel will mix with the recirculating combustion products 104, before reaching incoming oxidiser introduced by the second port 22,
the velocities of the jets introducing the fraction X1 of fuel and the fraction X2 of auxiliary fuel being adapted so that the sum of their corresponding jet momenta is comprised between −30% or +30% of a value corresponding to the jet momentum of the fuel when X2 equals zero (and X1 equals 1), and
the energy provided by the quantity of the sum of the first fraction of fuel X1 and the second fraction of fuel X2 being adapted to produce a given required energy for melting the glass without over-fuelling the furnace.
The fractions X1 and X2 (i.e. the proportion of the fuel entering the furnace which is auxiliary fuel and which is first fuel) are chosen so as to reduce the formation of NOx. The fractions X1 and X2, and their corresponding energies, are chosen so that the entire energy entering the furnace is at the level required for melting the glass (which corresponds to 1, the sum of X1 and X2). Thus, the total quantity of energy required for melting, which may correspond to 100%, is split between the first fraction X1 and the second fraction X2 so as to maintain this 100%.
It should be noted that the total amount of fuel supplied to a melting furnace remains just the amount required to melt the raw materials (for example glass), with combustion completed within the melting chamber under conditions of a small amount of excess oxidiser, as for a conventional combustion system.
The above mentioned recirculation of combustion products extends in a substantially horizontal loop above the flame over a length (measured from an inlet port) which is preferably known so as to find the optimum location for the auxiliary fuel injectors.
x=4.5×h (1)
in which:
x is the distance from the inlet port wall to the point where there is no longer recirculation in the furnace,
h is the height between the glass surface and the furnace roof.
In the case of an end-fired melting furnace, the maximum melting chamber length has evolved over the decades so that the recirculation zone generally reaches the front wall. This avoids a stagnant ‘dead’ pocket forming over the molten glass near the front wall.
Also, the injection parameters of the auxiliary fuel have to be determined in a manner such that the mass flow of combustion products recirculated is maintained. The strength of the recirculation can be calculated for example using the following equations derived by Craya (Craya A and Curtet R, ‘On the spreading of a confined jet’, Comptes-rendus de l'Academie des Sciences, Paris, 241, 1955) and others:
in which:
qr is the mass of combustion products recirculating per unit time,
Q is the total mass of fuel and oxidiser entering the furnace per unit time,
G0 is the sum of the jet momenta of incoming fuel jets X1 and X2 (their respective mass flow rates multiplied by their respective velocities),
Ga is the momentum of the incoming oxidiser (its mass flow rate multiplied by its velocity).
Ginf is the momentum of the outgoing hot exhaust gases (their mass flow rate multiplied by their mean velocity when they fill the furnace chamber), and
m is a dimensionless number (Craya Curtet number) that relates to the relative jet momenta of the incoming fuel and oxidiser flows, and the outgoing combustion products.
As far as the mass flow rate of recirculating combustion products is concerned, typical values for natural gas as fuel and for air as oxidiser together with typical air and gas velocities, when applied to equation (2), suggest that the mass of exhaust gases recirculating in a horizontal loop below the roof and above the flame typically lies in the range from a quarter to 3 quarters of the incoming mass flow of fuel and oxidiser. This confirms that there is sufficient recirculation to support the Auxiliary Injection of up to 100% of the total fuel flow entering the furnace (about 1/20th of the total mass flow entering the furnace) without affecting the furnace flow pattern and furnace operation.
However, as fuel is removed from the burners to supply the Auxiliary fuel injectors (for example because as the second quantity X2 is introduced, the first quantity X1 has to be reduced by the same amount), equation (2) indicates that the recirculation rate will eventually fall to values that are too low to carry the auxiliary fuel and maintain the furnace flow patterns, if the injectors are not in the above defined direction and if they do not inject with the above mentioned velocity.
In the example of
It should be noted that on
The angle θ of
The end-fired melting furnace 10 is represented on
In the example of
The angle α is chosen so as to ensure mixing with the recirculating combustion products. Analogous angles may be defined for auxiliary fuel injectors located in the roof.
As shown on
It should be noted that for the first auxiliary fuel injector, another second angle α′ may be defined when auxiliary fuel is emitted. The orientation of the second angle α′ is also shown on the figure.
The embodiment of
It should be noted that in the above examples, the auxiliary fuel jets emitted by the auxiliary fuel injectors have substantially the same direction as the recirculating combustion products 104. The auxiliary fuel injectors also make it possible to introduce either a fraction of the fuel injected by the burners or a quantity of a different fuel (while maintaining the total energy constant).
It should also be noted that the auxiliary injection of fuel made through the first and second auxiliary is not an additional fuel injection causing after-burning and no additional oxidiser is introduced together with the fuel injected via the first and second auxiliary fuel injectors 13, 14. In embodiments of the invention, the total fuel quantity is not creased (or the total energy if different fuels are used), but there is only a modification of the distribution of the quantity of fuel necessary for the quantity and type of glass to be melted. Due to the auxiliary injection of fuel through the first and second auxiliary fuel injectors 13, 14, one can obtain a better heat transfer towards the glass to be melted and at the same time, NOx formation is reduced.
More specifically, of the fuel injected into the melting chamber 8 through the first and second burners 11 and 12 and the auxiliary fuel injected by auxiliary fuel injectors 13 and 14, the proportion of the fuel jet emitted by the first and second auxiliary fuel injectors 13 and 14 is preferably from 10% to 100% and most preferably about 20% to 50% of the total fuel entering the furnace, the amount being chosen to achieve the desired NOx reduction on a given furnace. It should be noted that the proportion may relate to the corresponding energies, especially if the fuel introduced by the burners and the auxiliary fuel introduced by the auxiliary fuel injectors are different.
The fuel injected through the first and second burners 11, 12 and the first and second auxiliary fuel injectors 13, 14 may be selected from the group consisting of natural gas, LPG, fuel oil, coke-oven gas, blast furnace gas, reforming gas, biofuel and hydrogen.
Also, the fuel jets introduced through the first and second auxiliary fuel injectors 13, 14 are substantially in the same direction as the direction of the existing flame 103 and more specifically in the direction of the flow of recirculating combustion products 104 in the first branch of the U-shaped path, but the auxiliary fuel injection is made so as to be mixed in a co-flowing manner with the flow of re-circulated combustion products 108 just above the flame and before mixing with the remaining combustion air (oxidizer).
More specifically, an auxiliary fuel jet may be introduced with a velocity optimized so that said fuel is injected in the re-circulation loop from a certain distance from the exhaust port, as measured around the loop. The velocity and position of the auxiliary fuel jet can be determined by the person skilled in the art in such a way that the auxiliary fuel follows a path long enough to be completely burned inside the furnace.
The injection speed (in m/s) of the auxiliary fuel through an auxiliary fuel injector 13 or 14 may be typically 100 to 250 m/s.
According to another variant embodiment, the first and second auxiliary fuel injectors 13, 14 each include a device to adjust or alter the jet momentum of the introduced second fraction X2 of auxiliary fuel.
According to another variant embodiment, when the quantity of fuel flowing through them is reduced to supply the auxiliary fuel injectors, the burners are adjusted, or some of their number turned off so as to maintain their momentum and hence to maintain the mass flow of combustion products in the recirculation loop, especially when introducing high proportions of auxiliary fuel (more than 30%).
According to another variant embodiment, the first and second auxiliary fuel injectors 13, 14 are located and directed so as to maintain or enhance the mass flow of combustion products in the recirculation loop especially when introducing high proportions of auxiliary fuel (more than 50%).
The invention also relates to a method of melting raw materials by an end-fired melting furnace 10 which has:
in the direction of the flow of said re-circulating combustion products 104,
without additional oxidiser,
into said re-circulating combustion products, the auxiliary fuel injector being located at a point where said second fraction X2 of auxiliary fuel will mix with the re-circulating combustion products, before reaching incoming oxidiser introduced by a port,
the velocities of the jets introducing the fraction X1 of fuel and the fraction X2 of auxiliary fuel being adapted so that the sum of their corresponding jet momenta is comprised between −30% or +30% of a value corresponding to the jet momentum of the fuel when X2 equals zero, and
the energy provided by the quantity of the sum of the first fraction of fuel X1 and the second fraction of fuel X2 being adapted to produce a given required energy for melting said materials without over-fuelling the furnace.
| Number | Date | Country | Kind |
|---|---|---|---|
| 17305979.1 | Jul 2017 | FR | national |
This application claims priority as a continuation of International Patent Application No. PCT/EP2018/069819 filed on Jul. 20, 2018, which claims priority to French Patent Application No. 17305979.1 filed on Jul. 21, 2017. Both of these applications are hereby incorporated by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2018/069819 | Jul 2018 | US |
| Child | 16745616 | US |
