Reducing nitrogen oxide emissions in oxyfuel furnaces

Abstract

Further limiting NOx emissions from oxygen-fuel combustion furnaces in plants for combustion processes. According to the present invention, a plant includes a furnace (12) for heating material. A burner (16) is configured to combust a carbon-based fuel with an oxidizing gas to provide a flame into the furnace. The oxidizing gas has at least 80 weight percent oxygen. The furnace has exhaust outlets (20, 22) providing communication between the furnace and a flue (26). The exhaust outlets are configured to remove exhaust gases produced during combustion of the carbon-based fuel from the furnace to the flue. A nozzle (30) positioned in the flue is configured to inject ammonia into the flue to reduce NOx emissions in the exhaust gas.

Description

[Technical Field]

[0001] The present invention relates to reducing nitrogen oxides (NOx) from oxyfuel furnaces. Such furnaces are used in industrial processes, including glass melting plants. [Background technology]

[0002] Nitrogen oxides (NOx) are problematic air pollutants. They are the gaseous forms of nitric oxide and nitrogen dioxide. These gases are responsible for the formation of smog and acid rain, as well as tropospheric ozone. NOx gases are produced when nitrogen reacts with oxygen during the combustion of fuels, such as hydrocarbon fuels, at high temperatures.

[0003] One of the primary sources of nitrogen in furnaces comes from air. Air contains approximately 78 volume percent nitrogen and 21 volume percent oxygen. This nitrogen reacts with oxygen in the furnace to form NOx gases. NOx emissions are regulated by federal agencies, including the U.S. Environmental Protection Agency, and state governments.

[0004] In air-fired furnaces, NOx emissions are controlled by electrostatic precipitators ("EP") and selective catalytic reduction ("SCR") systems. In NOx reduction systems, the EP is followed by the SCR, so the exhaust gas containing the NOx emissions passes through the EP and then through the SCR system.

[0005] SCR systems inject ammonia into exhaust gas in the presence of a catalyst, which reacts NOx with the ammonia to form water and nitrogen gas. In SCR systems, anhydrous ammonia, ammonia water, or urea is typically added before the exhaust gas reaches the catalyst between the EP and SCR. The flue contains exhaust gas, which in turn contains NOx gas. The catalyst typically contains several base metals, such as vanadium, molybdenum, or tungsten, zeolites, or other precious metals. One problem with metal catalysts, such as vanadium and tungsten, is that they are not durable at high temperatures. Metal catalysts can also convert SO2 to SO3, causing acid damage to the system. Zeolite catalysts are more stable at higher temperatures than metal catalysts and are less likely to further oxidize SO2. However, catalysts can deteriorate over time and require replacement.

[0006] Given these catalyst-related problems, methods and designs for reducing NOx in air-fired furnaces without a catalyst have been developed, known as selective non-catalytic reduction (SNCR). SNCR involves injecting ammonia into the exhaust gas stream from an air-fuel furnace, as disclosed in U.S. Patent No. 3,900,554 to Lyon. Such a technique would seem attractive, except that the process is effective only over a narrow exhaust gas temperature range. Below this critical range, no significant reaction occurs, and therefore NOx emissions are not improved. Within this temperature range, the reaction becomes dominant, resulting in a net reduction of NOx. At higher temperatures, the reaction between ammonia and excess oxygen becomes more pronounced, resulting in an increase in the amount of NOx in the exhaust gas stream. Therefore, this NOx reduction has been considered limited in its applicability to applications such as boilers, where a distinct, stable temperature zone for ammonia injection can be identified and utilized.

[0007] U.S. Patent No. 4,328,020 to Hughes discloses SNCR by injecting ammonia into the exhaust stream of an air-fuel furnace under certain conditions. Conditions suitable for ammonia reduction of NOx exist or can be created in the flue connecting the primary and secondary regenerator chambers for a significant portion of each heating cycle. Ammonia injection is discontinued whenever the temperature of the exhaust gas passing through the flue falls outside the range of 870°C to 1090°C (700°C to 1090°C with hydrogen). In another embodiment disclosed in the aforementioned patent, ammonia is injected sequentially into two or more zones of the regenerator as the temperature of each zone passes through an effective NOx reduction range. While this application method can remove most of the NOx from the exhaust gas, overall efficiency is reduced because the ammonia reduction technique is ineffective during a significant portion of each heating cycle when the exhaust gas temperature is inappropriate. Even under optimal conditions, the ammonia reduction reaction is not 100% efficient.

[0008] Given the limitations of SNCR systems, other methods of reducing NOx have been developed. One such method is the use of oxyfuel combustion gas rather than air. These furnaces use pure or nearly pure oxygen rather than air. Almost all of the nitrogen is removed from the atmosphere inside the furnace. In the absence of nitrogen, NOx emissions are dramatically reduced, so SCR is not required to meet current NOx emission standards.

[0009] However, oxyfuel furnaces are not hermetically sealed. Inevitably, some air containing nitrogen enters the furnace. Additionally, the carbon-based fuel burned in the furnace may also contain some nitrogen. Therefore, even with oxyfuel furnaces, some NOx is produced, although the levels produced are low enough to be acceptable emissions under previous standards.

[0010] For this reason, although some nitrogen is inevitably present in oxyfuel furnaces, SCR and SNCR NOx reduction systems have not been used in oxyfuel furnaces because there is no reason to believe that SCR or SNCR should be able to reduce NOx without causing significant ammonia slip. Ammonia slip is the release of unreacted ammonia into the atmosphere. Because there is a limit to the amount of ammonia that can be released, SCR and SNCR NOx reduction systems have not been used in oxyfuel furnaces. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] U.S. Patent No. 3,900,554 [Patent Document 2] U.S. Patent No. 4,328,020 [Patent Document 3] U.S. Patent No. 4,372,770 Summary of the Invention [Problem to be solved by the invention]

[0012] However, given the environmental impact of NOx, there is a need to further limit NOx emissions from oxyfuel furnaces. [Means for solving the problem]

[0013] The present invention generally relates to a plant having an oxyfuel furnace and an in-flue NOx reduction system having a nozzle configured to inject ammonia into the flue. Additionally, the present invention relates to injecting ammonia into the exhaust gas of an oxyfuel furnace (also known as an oxyfuel furnace) to reduce NOx emissions. Injection occurs in the flue at some point after the exhaust gas leaves the furnace.

[0014] The plant for the combustion process includes an oxyfuel furnace. The furnace is configured to heat a material. The material is heated by a burner. The burner forms a flame that exits the furnace, the burner being configured to supply an oxidizing gas and a carbon-based fuel to the furnace. The oxidizing gas has at least 80 weight percent oxygen. Inside the furnace, the carbon-based fuel burns in the presence of the oxidizing gas to create the flame. The furnace has an atmospheric nitrogen content of less than 5 volume percent. The combustion also produces exhaust gases. An exhaust outlet allows communication between the furnace and the flue. The exhaust outlet is configured to remove exhaust gases generated during the combustion process from the furnace to the flue. The exhaust gases contain NOx. A NOx reduction control device is present in the flue. The NOx reduction control device includes an injection nozzle positioned in the flue and configured to inject ammonia into the exhaust gas. The ammonia can be selected from the group consisting of aqueous ammonia, anhydrous ammonia, urea, and combinations thereof. Injecting ammonia into the exhaust gas allows the NOx to react with the ammonia, thereby reducing the amount of NOx emitted from the flue.

[0015] A method for reducing NOx production in an oxyfuel furnace includes burning a carbon-based fuel in an oxidizing gas. The oxidizing gas has at least 80 weight percent oxygen. Burning the carbon-based fuel in the oxidizing gas produces an exhaust gas containing NOx. The exhaust gas is discharged through an exhaust outlet into a flue. In the flue, the exhaust gas reacts with ammonia, which may be aqueous ammonia, anhydrous ammonia, urea, or a combination thereof. The reaction reduces the amount of NOx in the exhaust gas to form a NOx-depleted exhaust gas. This reaction occurs without the use of a catalyst. The NOx-depleted exhaust gas is discharged through the flue. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a schematic diagram of a top-down view of a plant having an oxyfuel combustion furnace. [Figure 2] 1 is a cross-sectional view of a plant having an oxyfuel combustion furnace. [Figure 3A] FIG. 1 shows the inner sidewall of the flue and downcomer. [Figure 3B] FIG. 1 shows the inner sidewall of the flue and downcomer. [Figure 4A] FIG. 1 shows the outer sidewall of the flue and downcomer. [Figure 4B] FIG. 1 shows the outer sidewall of the flue and downcomer. [Figure 5] 1 is a table showing the flow rates of ammonia water injected into the exhaust gas and flue in each example. [Figure 6] 1 is a schematic diagram of a plant having an oxyfuel combustion furnace, two upstream exhaust outlets, two downstream exhaust outlets, two upstream downcomers, two downstream downcomers, two flues, a connector flue, and a chimney. DETAILED DESCRIPTION OF THE INVENTION

[0017] As used herein, spatial or directional terms such as "left," "right," "inside," "outside," "top," and "bottom" refer to the present invention as shown in the drawings. However, it should be understood that the present invention may contemplate various alternative orientations, and therefore, such terms should not be considered limiting. Furthermore, herein, all numbers expressing dimensions, physical properties, processing parameters, quantities of ingredients, reaction conditions, and the like used in the specification and claims are to be understood as being modified in all instances by the term "about." Accordingly, unless indicated to the contrary, the numerical values ​​set forth in the following specification and claims can vary depending on the desired properties sought to be obtained by the present invention. At the very least, and without intending to limit the application of the doctrine of equivalents to the scope of the claims, each numerical value should be construed in at least light of the number of reported significant digits and by applying ordinary rounding techniques. Furthermore, any range disclosed herein should be understood to encompass the beginning and ending values ​​of that range, and any and all subranges subsumed therein. For example, a specified range of "1 to 10" should be considered to include any and all subranges between (and including) a minimum value of 1 and a maximum value of 10, i.e., any subrange beginning with a minimum value of 1 or greater and ending with a maximum value of 10 or less, e.g., 1 to 3.3, 4.7 to 7.5, 5.5 to 10, etc. Additionally, all documents referenced herein, including but not limited to issued patents and patent applications, should be considered "incorporated by reference" in their entirety. Unless otherwise specified, any references to amounts are by "volume percent."

[0018] The discussion of the present invention herein may describe certain features as "specifically" or "preferably" within certain limitations (e.g., "preferably," "more preferably," or "even more preferably" within certain limitations). It is to be understood that the present invention is not limited to these specific or preferred limitations, but encompasses the entire scope of the present disclosure.

[0019] The discussion of this invention will refer to components as being "upstream" or "downstream." These terms are used in relation to the flow of exhaust gases.

[0020] The present invention relates to a plant for an industrial process. The industrial process may be any industrial process in which an oxyfuel furnace can be used. For example, the industrial process may be the manufacture of glass.

[0021] The plant includes a furnace. The furnace may be a large-capacity furnace. For example, the furnace may be a glass production furnace. The furnace may include a first end or opening through which raw materials can be delivered to the furnace. Once in the furnace, the raw materials are melted to form a molten material. The molten material can flow through a second end or discharge end.

[0022] The furnace has a combustion chamber and a melting tank. The melting tank is in communication with a feeder. The melting tank is where the raw material is melted. The feeder holds unmelted raw material and delivers unmelted raw material to the melting tank. Located within the furnace above the melting tank is the combustion chamber. The combustion chamber has one or more burners that provide oxidizing gas and carbon-based fuel for combustion, thereby providing heat to melt the material in the melting tank.

[0023] In one example, the frit may be glass frit. The frit is introduced into the furnace at a first end or opening to the furnace by an input device or feeder. Inside the furnace, the frit is melted to form molten glass. The molten glass flows from the discharge into the fining zone.

[0024] Burners are positioned in openings in the side walls of the furnace. Furnaces typically have at least two side walls (a first side wall and a second side wall), with the first side wall facing the second side wall. The side walls have openings configured to receive the burners. The burners are configured to supply oxyfuel combustion gas, fuel, and / or a mixture of oxyfuel combustion gas and fuel to the furnace, where the fuel burns to form a flame. The flame from the burners provides the energy needed to melt the raw materials. The burners can extend through the walls of the furnace or through the furnace ceiling. The furnace may have burners on one side wall or on the first and second side walls. The furnace may have at least 4, at least 6, at least 8, at least 10, or at least 12 burners, and / or up to 30 burners, up to 24 burners, up to 20 burners, or up to 16 burners. The burners on the first sidewall may be staggered (rather than in line) with the burners on the second sidewall.

[0025] The furnace is an oxygen-fuel combustion furnace. In an oxygen-fuel combustion furnace, the contribution of convection to heat supply is limited. Therefore, the burner must be placed on the side wall at a certain distance from the surface of the molten material to allow for adequate energy distribution to melt the glass frit. For example, the burner may be at least 0.25 m or at least 0.40 m from the surface of the molten material, but less than 1.0 m or less than 0.8 m.

[0026] The oxy-fuel combustion gas has at least 80 volume percent, at least 85 volume percent, at least 90 volume percent, at least 92 volume percent, at least 94 volume percent, or at least 95 volume percent oxygen. The oxy-fuel combustion gas is delivered to the burner through connection with an oxygen source containing oxy-fuel combustion gas.

[0027] The furnace is an oxy-fuel or oxy-fuel furnace. The furnace has an atmosphere above the molten material. The atmosphere in the furnace has little or no nitrogen. For example, the atmosphere in the furnace has less than 20 volume percent, less than 15 volume percent, less than 10 volume percent, less than 5 volume percent, less than 3 volume percent, less than 2 volume percent, less than 1 volume percent, or 0 volume percent nitrogen. The concentration of nitrogen may be higher or uncontrolled. Nitrogen may enter the furnace, for example, through leaks between the wall bricks of the furnace.

[0028] The carbon-based fuel may be any hydrocarbon that is commonly burned in industrial furnaces. Examples of carbon-based fuels include natural gas, fuel oil, coke, coal, or diesel oil.

[0029] There is a ratio of oxidizing gas to carbon-based fuel that is at least 1 part oxidizing gas to 1 part carbon-based fuel, at least 1.5 parts oxidizing gas to 1 part carbon-based fuel, 2 parts oxidizing gas to 1 part carbon-based fuel, 2.5 parts oxidizing gas to 1 part carbon-based fuel, or 3.0 parts oxidizing gas to 1 part carbon-based fuel, and / or at most 8 parts oxidizing gas to 1 part carbon-based fuel, at most 7 parts oxidizing gas to 1 part carbon-based fuel, at most 6 parts oxidizing gas to 1 part carbon-based fuel, or at most 5 parts oxidizing gas to 1 part carbon-based fuel.

[0030] The combustion process produces exhaust gases in the combustion chamber. The exhaust gases include NOx gases. NOx gases are formed by the reaction of oxygen with nitrogen gas. The high heat present in the furnace causes the reaction. The reaction may also occur in the downcomer, flue, or elsewhere, as long as the gas temperature is high enough to cause the oxygen gas to react with the nitrogen gas. While nitrogen gas may not be intentionally pumped into the melting chamber, furnace, or flue, it may find its way into the melting chamber, furnace, or flue because these components are not hermetically sealed or because nitrogen gas is released from the materials being melted.

[0031] The furnace has an exhaust outlet. The exhaust outlet may be in a sidewall of the furnace or in the roof or ceiling of the furnace. The exhaust outlet may be positioned above the burner in the sidewall or ceiling. The exhaust outlet allows communication between the furnace and the flue. The exhaust outlet is configured to remove exhaust gases generated during the combustion process from the furnace. The furnace may have one, two, three, four, or more exhaust outlets. In embodiments with two or more exhaust outlets, at least one exhaust outlet may be positioned downstream of the furnace and at least one second exhaust outlet may be positioned upstream of the furnace.

[0032] Optionally, a downcomer may connect the exhaust outlet to the flue. The downcomer is a duct through which exhaust gases pass downward from the exhaust outlet to the flue. The flue will therefore be positioned below the exhaust outlet. Of course, a downcomer is not required, and the flue may be positioned in the same horizontal plane as the exhaust outlet or above the exhaust outlet.

[0033] The flue includes a first or left side wall, a second or right side wall, a first or upstream end wall, and a second or downstream end wall. The flue is in communication with a chimney. For example, the flue may connect to a chimney or a connector flue at or near the downstream end wall of the flue, and the connector flue may provide communication between the flue and the chimney.

[0034] The plant may have two or more flues. In such a plant, the furnace has a first sidewall and a second sidewall opposite each other. The first sidewall may have a first exhaust outlet, and the second sidewall may have a second exhaust outlet. The first exhaust outlet is in communication with a first flue, and the second exhaust outlet is in communication with a second flue. The first exhaust outlet may be in communication with the first flue by an optional first downcomer connecting the first exhaust outlet to the flue, the first flue being positioned below the first exhaust outlet. Similarly, the second exhaust outlet may be in communication with a second flue by an optional second downcomer connecting the second exhaust outlet to the second flue, the second flue being positioned below the second exhaust outlet. Typically, such a plant will have a first upstream exhaust outlet and a first downstream outlet in fluid communication with the first flue to enable fluid communication between the first flue and the furnace, so that exhaust gases can flow from the furnace into the first flue. Similarly, the plant will have a second upstream exhaust outlet and a second downstream exhaust outlet in fluid communication with the second flue to enable fluid communication between the second flue and the furnace, so that exhaust gases can flow from the furnace into the second flue.

[0035] Within the flue is a NOx abatement control device that includes one or more nozzles configured to inject ammonia into the flue and into the exhaust gases, which may be aqueous ammonia, anhydrous ammonia, urea, or a combination thereof.

[0036] The nozzle or nozzles are attached to a mount (not shown), which is configured to be inserted into the flue. For example, if the flue is constructed of brick, the mount can be configured to be inserted where the brick has been removed.

[0037] The nozzles can be located in various locations within the flue. They may be located in the sidewall, the end wall, or a combination thereof. In the sidewall, the nozzle may be located where the most upstream downcomer joins the flue, between the most upstream and most downstream downcomer, where the most downstream downcomer joins the flue, or at a location between the most downstream downcomer and the downstream end wall or connector flue.

[0038] The nozzle may be positioned in the flue at a location where the exhaust gases are at a reaction temperature where the ammonia reacts with the NOx, the reaction temperature being between 850°C and 1200°C, or between 875°C and 1150°C, between 900°C and 1100°C, or between 950°C and 1050°C.

[0039] The flue is in communication with the exhaust outlet. The flue may be directly connected to the exhaust outlet or may be in communication with the exhaust outlet. The flue may be in approximately the same horizontal plane as the exhaust outlet, above the exhaust outlet, or below the exhaust outlet. The flue may be connected to the exhaust outlet by a downcomer.

[0040] The flue has an upstream end wall and a downstream end wall, where the flue may connect to a chimney or to a connector flue that allows communication to the chimney and / or a second flue.

[0041] The upstream end wall of the flue is located at the upstream end of the flue. Typically, this will be where the most upstream downcomer connects to the flue, or alternatively, where the upstream exhaust outlet connects to the flue.

[0042] The downstream end wall of the flue is at a point downstream of the most downstream downcomer where the flue connects to other components of the plant. This will usually be the point where the flue connects to a connector flue that allows communication between the first flue and the second flue, or between the flue and the chimney.

[0043] Nozzles for the NOx abatement device may be located on the upstream end wall, the downstream end wall, or a combination thereof.

[0044] Additionally or alternatively, the nozzle for the NOx reduction device is positioned on the sidewall, roof, or floor of the flue. The nozzle may be located on any of the sidewall, roof, or floor. A sidewall is a wall that is vertical (relative to the floor of the flue). Typically, each flue has two sidewalls: a first sidewall and a second sidewall, a floor, or a roof. The nozzle can be located on the first sidewall, the second sidewall, the roof, the floor, or a combination thereof. For example, the nozzle may be located on the sidewall at a location downstream of the most downstream downcomer or downstream exhaust outlet, or on the sidewall between the most downstream end wall and the most downstream downcomer or downstream exhaust outlet, or on the sidewall between the most downstream downcomer or exhaust outlet and the most upstream downcomer or exhaust outlet. The nozzle is preferably positioned between the most downstream downcomer or downstream exhaust outlet and the most downstream end wall, more preferably closer to the most downstream downcomer or downstream exhaust outlet than the most downstream end wall, or at the junction where the most downstream downcomer connects to the flue.

[0045] Nozzles for the NOx reduction device may be located on the upstream end wall, the downstream end wall, the first side wall, the second side wall, the flue floor, the flue roof, or a combination thereof. The nozzles may be positioned only on the upstream end wall, only on the downstream end wall, only on the first side wall, only on the second side wall, only on the flue roof, or only on the flue floor.

[0046] The plant may have two flues (a first flue and a second flue). In such a plant, nozzles for the NOx abatement device may be located in both flues or only one flue at any location described herein, where the other flue does not include only a nozzle for injecting ammonia. This allows ammonia to be injected only into the first flue or only into the second flue. In some cases, nozzles for the NOx abatement device may be located in the first flue and the second flue at any location described herein, with the nozzle of the second flue closed, so that ammonia is not injected into the second flue, and only the nozzle of the first flue open, so that ammonia is injected only into the first flue.

[0047] Each nozzle injects ammonia into the flue and / or exhaust gas at a rate. The ammonia may be aqueous ammonia or anhydrous ammonia. If aqueous ammonia, the ammonia may be of any concentration. The rate of ammonia injected from all nozzles is at least 0.01 gallons per minute (GPM), at least 0.03 GPM, at least 0.05 GPM, at least 0.07 GPM, at least 0.09 GPM, at least 0.11 GPM, at least 0.13 GPM, or at least 0.15 GPM. ), and / or the rate may be up to 0.4 GPM, up to 0.35 GPM, up to 0.32 GPM, up to 0.3 GPM, up to 0.28 GPM, up to 0.25 GPM, or up to 0.22 GPM. The rate of ammonia discussed herein refers to the amount of ammonia being injected. This excludes any water that may simply be injected, for example. So, for example, if you want to inject 0.07 GPM of ammonia and your solution contains 20 percent ammonia by volume, the ammonia solution will be injected at a rate of 0.35 GPM, since at this rate the ammonia will be injected at a rate of 0.07 GPM.

[0048] The ammonia injected into the flue and / or exhaust gases may be anhydrous ammonia, aqueous ammonia, urea, or a combination thereof.

[0049] Optionally, air may be injected into the flue. Ideally, the air should be injected where the exhaust gas temperature is at least 700°C, at least 750°C, or at least 760°C, and the exhaust gas temperature should be less than 1000°C, less than 950°C, less than 900°C, or less than 890°C. The air should be injected at a rate of at least 5 ml / min, at least 7 ml / min, or at least 10 ml / min, and / or at a rate of at most 700 ml / min, at most 600 ml / min, or at most 500 ml / min. Air may be injected into the flue anywhere within the flue, including the sidewall where the upstream downcomer joins the flue, the sidewall between the upstream and downstream downcomer pipes, the sidewall where the downstream downcomer joins the flue, the sidewall between the downstream downcomer pipe and the downstream end wall or connector flue, the downstream end wall, or the upstream end wall.

[0050] The plant does not have a flue gas heat recovery system or regenerator system. A regenerator system is a system that recovers heat from exhaust gases. This is done by periodically reversing the flow of the exhaust gases. The flue is made of a material, such as brick, that can absorb some of the heat contained in the exhaust gases. To operate an air-fuel furnace efficiently, the air must be preheated before combustion. This is done by a regenerator system that uses the heat trapped in the bricks to heat the air. An example of such a system is presented in U.S. Patent No. 4,372,770 to Krumwiede et al. The invention described and claimed herein does not require the use of a regenerator system.

[0051] Plants using the NOx reduction systems described herein also do not require electrostatic precipitators or catalysts to react NOx with ammonia.

[0052] The present invention also relates to a method for reducing NOx emissions from exhaust gases produced during an industrial process. The exhaust gases are produced by burning a carbon-based fuel in an oxidizing gas in a furnace. The furnace may be a large-volume furnace, such as a glass production furnace. Raw materials are fed into the furnace. Once in the furnace, the raw materials are melted to form a molten material. The raw materials are melted by burning the carbon-based fuel in the oxidizing gas.

[0053] The oxidizing gas has at least 80 volume percent, at least 85 volume percent, at least 90 volume percent, at least 92 volume percent, at least 94 volume percent, or at least 95 volume percent oxygen. The oxidizing gas is delivered to the furnace through a burner. For example, the burner is connected to an oxidizing gas source and a carbon-based fuel source, and the burner delivers the oxidizing gas and the carbon-based fuel to the furnace.

[0054] The oxidizing gas and carbon-based fuel are provided in a ratio of 1 part oxidizing gas to 1 part carbon-based fuel, at least 1.5 parts oxidizing gas to 1 part carbon-based fuel, 2 parts oxidizing gas to 1 part carbon-based fuel, 2.5 parts oxidizing gas to 1 part carbon-based fuel, or 3.0 parts oxidizing gas to 1 part carbon-based fuel, and / or at most 8 parts oxidizing gas to 1 part carbon-based fuel, at most 7 parts oxidizing gas to 1 part carbon-based fuel, at most 6 parts oxidizing gas to 1 part carbon-based fuel, or at most 5 parts oxidizing gas to 1 part carbon-based fuel.

[0055] The furnace has an atmosphere that is controlled so that the furnace has little or no nitrogen, for example, less than 5 volume percent, less than 3 volume percent, less than 2 volume percent, less than 1 volume percent, or 0 volume percent nitrogen.

[0056] As a result of burning the carbon-based fuel in the oxidizing gas, exhaust gas is formed. The exhaust gas is discharged from the furnace through one or more exhaust outlets. For example, the exhaust gas may be discharged from the furnace through at least two exhaust outlets, at least three exhaust outlets, at least four exhaust outlets, or more exhaust outlets. The exhaust outlets are positioned on the side walls of the furnace or on the roof or ceiling of the furnace. When there are two or more exhaust outlets, one of the exhaust outlets may be positioned on a first side wall of the furnace and the second exhaust outlet may be positioned on a second side wall of the furnace opposite the first side wall. There may also be a most downstream exhaust outlet and a most upstream exhaust outlet.

[0057] The exhaust outlet is in fluid communication with the flue. Exhaust gases can flow from the furnace into the flue. The flue can be positioned in approximately the same horizontal plane as the exhaust outlet, above the exhaust outlet, or below the exhaust outlet. The flue can be connected to the exhaust outlet by a downcomer. In such cases, the exhaust gases flow from the exhaust outlet down the downcomer and into the flue.

[0058] Ammonia is injected into the flue gas through one or more nozzles. The ammonia reacts with the exhaust gas. Specifically, the ammonia reacts with NOx in the exhaust gas to form water and nitrogen gas. The ammonia may be aqueous ammonia, anhydrous ammonia, urea, or a combination thereof.

[0059] The ammonia is injected at a rate calculated based on all nozzles. The ammonia may be anhydrous ammonia, aqueous ammonia, urea, or a combination thereof. The total flow rate of ammonia injected through all nozzles is at least 0.01 gallons per minute (GPM), at least 0.03 GPM, at least 0.05 GPM, at least 0.07 GPM, at least 0.09 GPM, at least 0.11 GPM, at least 0.13 GPM, or may be at least 0.15 GPM, and / or the rate may be at most 0.4 GPM, at most 0.35 GPM, at most 0.32 GPM, at most 0.3 GPM, at most 0.28 GPM, at most 0.25 GPM, or at most 0.22 GPM. The rate of ammonia discussed herein refers to the amount of ammonia being injected. This excludes any water that may simply be injected, for example. So, for example, if you want to inject 0.07 GPM of ammonia and your solution contains 20 percent ammonia by volume, the ammonia solution will be injected at a rate of 0.35 GPM, since at this rate the ammonia will be injected at a rate of 0.07 GPM.

[0060] Ammonia should be injected into the flue at a point where the exhaust gases are at reaction temperature, which can be between 850°C and 1200°C, or between 875°C and 1150°C, or between 900°C and 1100°C, or between 950°C and 1050°C.

[0061] The ammonia may be injected at one or both side walls of the flue, at the end wall of the flue, at the roof or ceiling of the flue, at the floor of the flue, or a combination thereof. The ammonia may be injected at the upstream end wall, which is the end wall where the most upstream downcomer connects to the flue, at the side wall, ceiling, or floor of the flue between the most upstream and most downstream downcomers, at the side wall or floor of the flue where the most downstream downcomer connects to the flue, or at the side wall, ceiling, or floor of the flue between the most downstream downcomer and the downstream end wall, connector flue, or chimney.

[0062] Ammonia may be injected at these locations through multiple nozzles. For example, there may be at least two, at least four, or at least six nozzles at each location, and / or there may be up to 14, up to 12, or up to 10 nozzles at each location. When ammonia is injected through multiple nozzles at a single location, the nozzles may be aligned horizontally and / or vertically relative to another nozzle. For example, ammonia may be injected through nozzles positioned in the top half of a side wall or end wall, the bottom half of a side wall or end wall, the left half of an end wall, or the right half of an end wall. In certain instances, ammonia is injected into the flue through four nozzles or eight nozzles.

[0063] Once injected into the flue, NOx in the exhaust gas reacts with the ammonia to form nitrogen gas and water, thereby reducing NOx emissions, which then travels through the remainder of the flue, optionally to a connector flue, and is discharged out the chimney.

[0064] "Example 1" 1 and 2 show an exemplary plant equipped with a NOx reduction system according to the present invention. The plant has a furnace 12 into which glass material can be fed or added through an input opening 14. The glass frit is fed into the furnace 12 from the input opening 14 as shown by arrow A in FIG. 1.

[0065] The furnace has multiple burners 16, which supply a mixture of carbon-based fuel and oxidizing gas and are configured to combust the carbon-based fuel with the oxidizing gas to form multiple oxy-fuel combustion flames 18. The burners 16 are positioned in openings in the sidewalls 24 of the furnace 12. The openings of each burner 16 in the sidewalls 24 are staggered with respect to the openings of the burners 16 in the opposing sidewalls 24, so that no burner 16 opening is directly opposite another burner. Each burner 16 is connected to an oxidizing gas source and a carbon-based fuel source by separate supply lines for each source. The oxidizing gas is primarily oxygen and has at least 95 volume percent oxygen. The oxidizing gas contained less than 1 volume percent nitrogen gas or no nitrogen gas. The carbon-based fuel in this example is natural gas. The oxidizing gas and carbon-based fuel are delivered to the furnace 12 through the burners 16. The oxidizing gas and carbon-based fuel are fed into the furnace 12 in a ratio of at least 1.5 parts oxidizing gas to 1 part carbon-based fuel to a maximum of 2.5 parts oxidizing gas to 1 part carbon-based fuel, or more preferably in a ratio of approximately 2 parts oxidizing gas to 1 part carbon-based fuel.

[0066] The furnace 12 does not include any burners 16 that combust a carbon-based fuel in the presence of a different oxidizing gas, specifically air or a gas having more than 5 volume percent nitrogen gas. Thus, the furnace 12 is an oxy-fuel furnace or an oxy-fuel furnace. Thus, the combustion chamber has less than 5 volume percent nitrogen gas in its atmosphere.

[0067] Within furnace 12, a carbon-based fuel is combusted in the presence of an oxidizing gas to form a flame 18. The flame melts the glass frits to form molten glass 44. The combustion of the carbon-based fuel and the oxidizing gas produces exhaust gases.

[0068] The furnace 12 in this example has four exhaust outlets: two upstream exhaust outlets 20, one on each side wall 24, and two downstream exhaust outlets 22, one on the first side wall and one on the second side wall 24. The exhaust outlets 20, 22 allow communication between the furnace 12 and two flues 26 (a first flue and a second flue).

[0069] The first and second flues 26 are connected to the exhaust outlets 20, 22 by downcomers 27, 28. Two downcomers 27, 28 connect to the first flues 26 and two other downcomers 27, 28 connect to the second flues 26 to the exhaust outlets 20, 22. Exhaust gases flow out of the furnace 12 through the exhaust outlets 20, 22 and along exhaust path B to the first and second flues 26, 26.

[0070] Referring to Figures 3-5, each flue 26 has a NOx reduction device, which includes at least one nozzle 30, or multiple nozzles 30. In this example, four nozzles 30 are positioned on the first sidewall 32, four nozzles 30 are positioned on the second sidewalls 34 of the first and second flues 26, and four nozzles 30 are disposed on the upstream end walls 36 of the first and second flues 26. Thus, each flue includes 12 nozzles in three locations. Each nozzle 30 can be independently turned on or off to control the location of ammonia addition. An ammonia pump controls the flow rate of the ammonia supply. Thus, an operator can control the location of ammonia delivery into the flue 26 and the amount of ammonia delivered into the flue 26.

[0071] Specifically, eight nozzles were installed on each of the side walls 32, 34 of the flue 26 where the most downstream downcomer 28 connects to the flue 26. As shown in Figures 3-4, each side wall 32, 34 of each flue 26 has two nozzles 30 on the upper side and two nozzles 30 on the lower side of the side wall 32, 34. Thus, each flue 26 has four nozzles 30 on the first side wall 32 and four nozzles 30 on the second side wall 34. In total, each flue 26 has eight nozzles 30 between both side walls 32, 34 at approximately the location where the most downstream downcomer 28 connects to the flue 26.

[0072] The number of nozzles 30 is not critical and was used in each instance simply as a means to control the flow rate of ammonia. It is foreseeable that a single nozzle 30 in any location described herein should be sufficient, as long as that nozzle 30 is capable of delivering an appropriate volume of ammonia relative to the amount of exhaust gas in the flue.

[0073] Each nozzle 30 was connected to an ammonia pump via ammonia piping, not shown in the figures. The nozzles 30 were also connected to a local air supply, also not shown in the figures. Ammonia was injected into the exhaust gas at a rate of 37.85 ml / min (0.01 GPM) to 3028.33 ml / min (0.8 GPM). This injection rate was the rate at which ammonia was added across all nozzles 30. Preferably, the ammonia flow rate should be between 189.27 ml / min (0.05 GPM) and 832.79 ml / min (0.22 GPM).

[0074] The first and second flues 26 connect to a connector flue 40 at or near the downstream end walls 38 of the first and second flues. The connector flue 40 allows communication between the first and second flues 26 and a chimney 42. The exhaust outlets 20, 22, downcomers 27, 28, the first and second flues 26, the connector flue 40, and the chimney 42 are configured to discharge gases exhausted from the furnace 12 out of the plant through the chimney 42. The exhaust gases discharged from the chimney 42 have a reduced amount of NOx compared to the exhaust gases found in the furnace 12.

[0075] While this example presents specific locations of the nozzles 30 and a specific number of nozzles 30 at each location, it should be readily apparent to one skilled in the art that the locations and number of nozzles 30 may be modified to other locations or other numbers of nozzles 30. For example, only one nozzle may be used at each location, or the locations may be between the most downstream downcomer 28 and the downstream end wall 38, the downstream end wall 38, between the most downstream downcomer 28 and the upstream end wall 36, or the sidewall 32 or 34 where the most upstream downcomer 27 connects to the flue 26. Furthermore, the NOx reduction device and / or nozzles 30 may be located at one or more of these locations, or may be located only in the first flue 26, or may be located only in the second flue 26. Alternatively, the nozzles 30 may be located on the ceiling (or roof) or floor of the first flue 26 and / or the second flue 26.

[0076] Glass frit was fed into furnace 12 via a charging device at an opening or charging end 14. Inside furnace 12, burners 16 provided oxy-fuel gas and a carbon-based fuel, the carbon-based fuel combusting in the presence of the oxy-fuel gas. Little or no nitrogen was intentionally added to the atmosphere of furnace 12. Because furnace 12 was not hermetically sealed, nitrogen would have entered furnace 12 to the extent that it was present.

[0077] Combustion of the carbonaceous fuel and oxygen results in the formation of molten glass 44 and exhaust gases. Because some nitrogen must have entered the furnace 12, the exhaust gases contained some NOx. The exhaust gases would be discharged from the furnace 12 through left and right exhaust outlets 20 and 22 to left and right downcomers 27 and 28. The exhaust gases would proceed along path B to the first and second flues 26.

[0078] Within the flue, ammonia will be injected by nozzles 30 installed in the flue 26 at the locations described above. The ammonia will react with the NOx to form nitrogen and water, thereby reducing the NOx emissions produced by the oxy-fuel furnace 12.

[0079] Examples 1-22 refer to the side walls 32, 34 of the flue 26 and where the nozzles 30 are located on the side walls 32, 34. Unless expressly stated, it is understood that the nozzles 30 on the side walls 33, 34 may be located anywhere on the side walls 32, 34 of the flue 26, and that the roof of the flue 26 and the floor of the flue 26 are suitable substitutes for the side walls 32, 34.

[0080] "Example 2" In this example, the plant is configured similarly to Example 1, except that NOx abatement device nozzles are positioned only at the upstream end walls 36 of the first and second flues 26. As long as NOx abatement device nozzles 30 are present anywhere else, these nozzles are turned off, and therefore ammonia cannot be pumped into the flues at other locations. Thus, ammonia is injected into the flues at the upstream end walls 36 of the first and second flues 26, or only at the upstream end walls 36 of the first and second flues 26.

[0081] "Example 3" In this example, the plant is configured similarly to Example 1, except that NOx abatement device nozzles are positioned only on the first and second side walls 32, 34 of the first and second flues 26. To the extent that NOx abatement device nozzles 30 are present anywhere else, these nozzles 30 are turned off, and therefore ammonia cannot be pumped into the flues at other locations. Thus, ammonia is injected either at the first and second side walls 32, 34 of the first and second flues 26, or only at the first and second side walls 32, 34 of the first and second flues 26.

[0082] "Example 4" In this example, the plant is configured similarly to Example 1, except that the NOx abatement device nozzles are positioned only on the upstream end wall 36 of only one flue 26 or only the first flue 26, and not on both flues. As long as NOx abatement device nozzles 30 are present at any other location, they are turned off, and therefore ammonia cannot be pumped into the flues at other locations. Thus, ammonia is injected into either one flue or the first flue 26 at the upstream end wall 36, or into only one flue or the first flue 26 at the upstream end wall 36.

[0083] "Example 5" In this example, the plant is configured similarly to Example 1, except that the NOx abatement device nozzles are positioned only on the first sidewall 32 and second sidewall 34 of one flue 26, or only the first flue 26. As long as NOx abatement device nozzles 30 are present at any other location, these nozzles 30 are turned off, and therefore ammonia cannot be pumped into the flue at other locations. Thus, ammonia is injected into the first flue 26 at the first sidewall 32 and second sidewall 34, or only the first flue 26 at the first sidewall 32 and second sidewall 34.

[0084] "Example 6" In this example, the plant is configured similarly to Example 1, except that NOx abatement device nozzles are positioned only at the downstream end walls 38 of the first and second flues 26. As long as NOx abatement device nozzles 30 are present anywhere else, these nozzles are turned off, and therefore ammonia cannot be pumped into the flues at other locations. Thus, ammonia is injected into the flues 26 either at the downstream end walls 38 of the first and second flues 26, or only at the downstream end walls 38 of the first and second flues 26.

[0085] "Example 7" In this example, the plant is configured similarly to Example 1, except that NOx abatement device nozzles are positioned only at the downstream end wall 38, first side wall 32, and second side wall 34 of the first and second flues 26. As long as NOx abatement device nozzles 30 are present anywhere else, these nozzles are turned off, and therefore ammonia cannot be pumped into the flues at other locations. Thus, ammonia is injected into the flues 26 either at the downstream end wall 38, first side wall 32, and second side wall 34 of the first and second flues 26, or only at the downstream end wall 38, first side wall 32, and second side wall 34 of the first and second flues 26.

[0086] "Example 8" In this example, the plant is configured similarly to Example 1, except that NOx abatement device nozzles are positioned only at the downstream end wall 38 and the upstream end wall 36 of the first and second flues 26. As long as NOx abatement device nozzles 30 are present anywhere else, these nozzles are turned off, and therefore ammonia cannot be pumped into the flues at other locations. Thus, ammonia is injected into the flues 26 either at the downstream end wall 38 and the upstream end wall 36 of the first and second flues 26, or only at the downstream end wall 38 and the upstream end wall 36 of the first and second flues 26.

[0087] "Example 9" In this example, the plant is configured similarly to Example 1, except that the NOx abatement nozzles are positioned only at the downstream end wall 38 of one flue 26, or only the first flue 26. As long as NOx abatement nozzles 30 are present at any other location, they are turned off, and therefore ammonia cannot be pumped into the flues at other locations. Thus, ammonia is injected into one flue 26 at the downstream end wall 38, or into only one flue 26 at the downstream end wall 38.

[0088] "Example 10" In this example, the plant is configured similarly to Example 1, except that the NOx abatement device nozzles are positioned only on the downstream end wall 38, the first side wall 32, and the second side wall 34 of one flue 26, or only the first flue 26. As long as the NOx abatement device nozzles 30 are present at any other locations, these nozzles are turned off, and therefore ammonia cannot be pumped into the flue at other locations. Thus, ammonia is injected into the flue 26 only at the downstream end wall 38, the first side wall 32, and the second side wall 34 of one flue 26, or only the first flue 26, or only at the downstream end wall 38, the first side wall 32, and the second side wall 34 of one flue 26, or only the first flue 26.

[0089] "Example 11" In this example, the plant is configured similarly to Example 1, except that NOx abatement device nozzles are positioned only on the downstream end wall 38, first side wall 32, second side wall 34, and upstream end wall 36 of the first and second flues 26. As long as NOx abatement device nozzles 30 are present anywhere else, these nozzles are turned off, and therefore ammonia cannot be pumped into the flues at other locations. Thus, ammonia is injected either at the downstream end wall 38, first side wall 32, second side wall 34, and upstream end wall 36 of the first and second flues 26, or only at the downstream end wall 38, first side wall 32, second side wall 34, and upstream end wall 36 of the first and second flues 26, 26.

[0090] "Example 12" In this example, the plant is configured similarly to Example 1, except that NOx abatement device nozzles are positioned only on the downstream end wall 38, first side wall 32, second side wall 34, and upstream end wall 36 of the first and second flues 26. As long as NOx abatement device nozzles 30 are present anywhere else, these nozzles are turned off, and therefore ammonia cannot be pumped into the flues at other locations. Thus, ammonia is injected either at the downstream end wall 38, first side wall 32, second side wall 34, and upstream end wall 36 of the first and second flues 26, or only at the downstream end wall 38, first side wall 32, second side wall 34, and upstream end wall 36 of the first and second flues 26, 26.

[0091] "Example 13" In this example, the plant is configured similarly to Example 1, except that the NOx abatement device nozzles are positioned on only one sidewall (only first sidewall 32 or only second sidewall 34) of the first and second flues 26. As long as the NOx abatement device nozzles 30 are present anywhere else, these nozzles 30 are turned off, and therefore ammonia cannot be pumped into the flues at other locations. Thus, ammonia is injected into the flues on only one sidewall (only first sidewall 32 or only second sidewall 34) of the first and second flues 26, or ammonia is injected into the flues on only one sidewall (only first sidewall 32 or only second sidewall 34) of the first and second flues 26.

[0092] "Example 14" In this example, the plant is configured similarly to Example 1, except that the NOx abatement device nozzles are positioned on only one sidewall (first sidewall 32 or second sidewall 34) of only one flue 26 (first flue 26). As long as NOx abatement device nozzles 30 are present anywhere else, these nozzles 30 are turned off, and therefore ammonia cannot be pumped into the flue at other locations. Thus, ammonia is injected into the flue at only one sidewall (first sidewall 32 or second sidewall 34) of only one flue 26 (first flue 26), or at only one sidewall (first sidewall 32 or second sidewall 34) of only one flue 26 (first flue 26).

[0093] "Example 15" In this example, the plant is configured similarly to Example 1, except that NOx abatement device nozzles are positioned only at the upstream end wall 36, first side wall 32, and second side wall 34 of the first and second flues 26. As long as NOx abatement device nozzles 30 are present anywhere else, these nozzles are turned off, and therefore ammonia cannot be pumped into the flues at other locations. Thus, ammonia is injected into the flues 26 either at the upstream end wall 36, first side wall 32, and second side wall 34 of the first and second flues 26, or only at the upstream end wall 36, first side wall 32, and second side wall 34 of the first and second flues 26.

[0094] "Example 16" In this example, the plant is configured similarly to Example 1, except that the NOx abatement device nozzles are positioned only on the upstream end wall 36, first side wall 32, and second side wall 34 of only one flue 26 (first flue 26). As long as NOx abatement device nozzles 30 are present at any other locations, these nozzles are turned off, and therefore ammonia cannot be pumped into the flue 26 at other locations. Thus, ammonia is injected into the flue 26 at the upstream end wall 36, first side wall 32, and second side wall 34 of only one flue 26 (first flue 26), or only at the upstream end wall 36, first side wall 32, and second side wall 34 of only one flue 26 (first flue 26).

[0095] "Example 17" In this example, the plant is configured similarly to Example 1, except that the NOx abatement device nozzles are positioned only on the upstream end wall 36 and only one side wall (first side wall 32 or second side wall 34) of the first and second flues 26. As long as the NOx abatement device nozzles 30 are present anywhere else, these nozzles are turned off, and therefore ammonia cannot be pumped into the flues at other locations. Thus, ammonia is injected into the flues 26 only on the upstream end wall 36 and only one side wall (first side wall 32 or second side wall 34) of the first and second flues 26, or only on the upstream end wall 36 and only one side wall (first side wall 32 or second side wall 34) of the first and second flues 26, 26.

[0096] "Example 18" In this example, the plant is configured similarly to Example 1, except that the NOx abatement device nozzles are positioned on only the upstream end wall 36 and only one side wall (first side wall 32 or second side wall 34) of only one flue 26 (first flue 26). As long as NOx abatement device nozzles 30 are present anywhere else, these nozzles are turned off, and therefore ammonia cannot be pumped into the flue 26 at any other location. Thus, ammonia is injected into the flue 26 at only the upstream end wall 36 and only one side wall (first side wall 32 or second side wall 34) of only the first flue 26, or is injected into the flue 26 at only the upstream end wall 36 and only one side wall (first side wall 32 or second side wall 34) of only the first flue 26.

[0097] "Example 19" In this example, the plant is configured similarly to Example 1, except that the NOx abatement device nozzles are positioned only at the downstream end wall 38 and the upstream end wall 36 of only one flue 26 (the first flue 26). As long as the NOx abatement device nozzles 30 are present at any other locations, they are turned off, and therefore ammonia cannot be pumped into the flue at any other locations. Thus, ammonia is injected into the flue 26 only at the downstream end wall 38 and the upstream end wall 36 of the first flue 26, or only at the downstream end wall 38 and the upstream end wall 36 of the first flue 26.

[0098] "Example 20" In this example, the plant is configured similarly to Example 1, except that NOx abatement device nozzles are positioned only on the downstream end wall 38, only one side wall (first side wall 32 or second side wall 34), and upstream end wall 36 of the first and second flues 26. As long as NOx abatement device nozzles 30 are present anywhere else, these nozzles are turned off, and therefore ammonia cannot be pumped into the flues at other locations. Thus, ammonia is injected either at the downstream end wall 38, only one side wall (first side wall 32 or second side wall 34), and upstream end wall 36 of the first and second flues 26, or at the downstream end wall 38, only one side wall (first side wall 32 or second side wall 34), and upstream end wall 36 of the first and second flues 26, 26.

[0099] "Example 21" In this example, the plant is configured similarly to Example 1, except that the NOx abatement device nozzles are positioned only on the downstream end wall 38, only on one side wall (first side wall 32 or second side wall 34), and only on the upstream end wall 36 of only one flue 26 (first flue 26). As long as NOx abatement device nozzles 30 are present anywhere else, these nozzles are turned off, and therefore ammonia cannot be pumped into the flue at other locations. Thus, ammonia is injected only on the downstream end wall 38, only on one side wall (first side wall 32 or second side wall 34), and only on the upstream end wall 36 of only the first flue 26, or only on the downstream end wall 38, only on one side wall (first side wall 32 or second side wall 34), and only on the upstream end wall 36 of only the first flue 26.

[0100] "Example 22" Using any of Examples 1-21, aqueous ammonia was injected into the exhaust gas and flue at the specified flow rates. The flow rates are presented in Figure 5. Surprisingly, when ammonia was injected into the exhaust gas from an oxyfuel combustion furnace, a significant reduction in NOx occurred. Significant and surprising NOx reductions were observed with 19 volume percent aqueous ammonia at a flow rate of only 0.19 GPM (i.e., an ammonia flow rate of 0.036 GPM) into the exhaust gas. Although more significant reductions were observed at higher flow rates, ammonia slip became an issue with 19 volume percent aqueous ammonia at flow rates above 1.0 GPM (i.e., an ammonia flow rate of 0.19 GPM).

[0101] The invention is further described in the following numbered clauses.

[0102] Clause 1: A plant for a combustion process, the plant comprising: a furnace for heating a material; a burner configured to combust an oxidizing gas and a carbon-based fuel in the furnace, the oxidizing gas having at least 80 volume percent oxygen, particularly at least 85 volume percent, more particularly at least 90 volume percent, more particularly at least 92 volume percent, more particularly at least 94 volume percent, or at least 95 volume percent oxygen; an exhaust outlet configured to allow communication between the furnace and a flue and to remove exhaust gases produced during the combustion process from the furnace to the flue; and a nozzle positioned in the flue and configured to inject ammonia into the flue and / or the exhaust gases, the ammonia being selected from the group consisting of aqueous ammonia, anhydrous ammonia, urea, or combinations thereof.

[0103] Clause 2: The plant of clause 1, wherein the combustion process is used to make glass and the material heated in the furnace is a glass batch material.

[0104] Clause 3: The plant of clause 1 or 2, wherein the flue has an upstream end wall, and the nozzle is positioned in the flue at the upstream end wall.

[0105] Clause 4: The plant of clauses 1 to 2, wherein the flue has a first sidewall and the nozzle is positioned in the flue at the first sidewall.

[0106] Clause 5: The plant of clause 4, wherein the flue has a second side wall and a second nozzle is positioned in the flue at the second side wall generally opposite or opposite the first nozzle.

[0107] Clause 6: The plant of clause 1 or 2, wherein the nozzle is positioned in a downstream end wall of the flue.

[0108] Clause 7: The plant of any of clauses 1 to 6, further comprising a downcomer connecting the flue to the exhaust outlet.

[0109] Clause 8: The plant of clause 7, wherein the nozzle is positioned in the flue at the end wall or side wall where the downcomer joins the flue.

[0110] Clause 9: A plant according to any of clauses 1 to 6, wherein the exhaust outlet is an upstream exhaust outlet, the plant further having a downstream exhaust outlet, and the upstream exhaust outlet and the downstream exhaust outlet are in communication with the flue.

[0111] Clause 10: The plant of clause 9, further comprising a downstream most downcomer connecting the downstream exhaust outlet to the flue and an upstream most downcomer connecting the upstream exhaust outlet to the flue.

[0112] Clause 11: The plant of clause 9 or 10, wherein the nozzle is positioned on the side wall at a position downstream of the most downstream downcomer or the downstream exhaust outlet, at a position between the downstream end wall of the flue and the most downstream downcomer or the downstream exhaust outlet, and / or at a position between the most downstream downcomer or the downstream exhaust outlet and the most upstream downcomer or the upstream exhaust outlet.

[0113] Clause 12: A plant according to any of clauses 1 to 11, wherein the nozzle is configured to open or close.

[0114] Clause 13: The plant of any of clauses 1 to 12, wherein the nozzle is configured to increase or decrease the flow rate of the ammonia.

[0115] Clause 14: The ammonia is at a total flow rate of at least 0.01 gallons per minute (GPM), at least 0.03 GPM, at least 0.05 GPM, at least 0.07 GPM, at least 0.09 GPM, at least 0.11 GPM, at least 0.13 GPM, or at least 0.15 GPM. 14. The plant of any of clauses 1 to 13, wherein ammonia is injected into the exhaust gas at a flow rate and / or rate that can be up to 0.4 GPM, up to 0.35 GPM, up to 0.32 GPM, up to 0.3 GPM, up to 0.28 GPM, up to 0.25 GPM, or up to 0.22 GPM.

[0116] Clause 15: A plant according to any of clauses 1 to 14, wherein the nozzle is positioned in the flue where the exhaust gas has a reaction temperature of between 850°C and 1200°C, or between 875°C and 1150°C, between 900°C and 1100°C, or between 950°C and 1050°C.

[0117] Clause 16: A plant according to any one of clauses 1, 2, 4, 5 and clauses 7 to 15, wherein the plant is configured to inject ammonia only into the sidewall of the flue.

[0118] Clause 17: The plant of clause 16, wherein the nozzle is positioned in the side wall of the flue approximately between the most downstream downcomer or the downstream exhaust outlet and the flue, or at a junction between the most downstream downcomer or the downstream exhaust outlet and the flue.

[0119] Clause 18: The plant of clause 16, wherein the nozzle is positioned in the side wall of the flue between the most downstream downcomer or the downstream end wall of the flue.

[0120] Clause 19: A plant according to any of clauses 1 to 3 or clauses 7 to 15, wherein the plant is configured to inject ammonia only into the upstream end wall of the flue.

[0121] Clause 20: The plant of any of clauses 1, 2, or clauses 6 to 15, wherein the plant is configured to inject ammonia into only the downstream end wall of the flue.

[0122] Clause 21: A plant according to any one of clauses 1 to 20, wherein the plant does not include a catalyst for reacting the ammonia with the exhaust gas.

[0123] Clause 22: A plant according to any one of clauses 1 to 21, wherein the furnace is an oxygen-fueled furnace.

[0124] Clause 23: A plant according to any of clauses 1 to 22, wherein the exhaust gases are removed by an induced draft stack effect or an induced draft fan positioned in the flue.

[0125] Clause 24: A plant according to any one of clauses 1 to 22, wherein the exhaust gases are removed by induced stack effect.

[0126] Clause 25: A plant for a combustion process, the plant comprising: a furnace for heating a material; a burner configured to combust an oxidizing gas and a carbon-based fuel in the furnace, the oxidizing gas having at least 80 volume percent oxygen, particularly at least 85 volume percent, more particularly at least 90 volume percent, more particularly at least 92 volume percent, more particularly at least 94 volume percent, or at least 95 volume percent oxygen; an exhaust outlet configured to allow communication between the furnace and a flue and to remove exhaust gases produced during the combustion process from the furnace to the flue; and a plurality of nozzles positioned in the flue and configured to inject ammonia into the flue and / or the exhaust gases, the ammonia being selected from the group consisting of aqueous ammonia, anhydrous ammonia, urea, or combinations thereof.

[0127] Clause 26: The plant of clause 25, wherein the combustion process is used to make glass and the material heated in the furnace is a glass batch material.

[0128] Clause 27: The plant of clause 25 or 26, wherein the flue has an upstream end wall, a first side wall, a second side wall, and a downstream end wall, and the plurality of nozzles are positioned in the upstream end wall, the first side wall, the second side wall, the downstream end wall, or any combination thereof.

[0129] Clause 28: A plant as described in any of clauses 25 to 27, further comprising a downcomer pipe connecting the flue to the exhaust outlet, and at least some of the plurality of nozzles are positioned in the side wall and / or the upstream end wall of the flue at the location where the downcomer pipe connects to the flue.

[0130] Clause 29: A plant according to any of clauses 25 to 27, wherein the exhaust outlet is an upstream exhaust outlet, the plant further having a downstream exhaust outlet, the upstream exhaust outlet and the downstream exhaust outlet communicating with the flue.

[0131] Clause 30: The plant of clause 29, further comprising a downstream most downcomer connecting the downstream exhaust outlet to the flue and an upstream most downcomer connecting the upstream exhaust outlet to the flue.

[0132] Clause 31: The plant of clause 29 or 20, wherein the plurality of nozzles are positioned on the side wall at a position downstream of the most downstream downcomer or the downstream exhaust outlet, at a position between the downstream end wall of the flue and the most downstream downcomer or the downstream exhaust outlet, and / or at a position between the most downstream downcomer or the downstream exhaust outlet and the most upstream downcomer or the upstream exhaust outlet.

[0133] Clause 32: Plant according to any of clauses 25 to 31, wherein the nozzle is configured to open or close.

[0134] Clause 33: The plant of any of clauses 25 to 32, wherein the nozzle is configured to increase or decrease the flow rate of the ammonia.

[0135] Clause 34: The ammonia is at a total flow rate of at least 0.01 gallons per minute (GPM), at least 0.03 GPM, at least 0.05 GPM, at least 0.07 GPM, at least 0.09 GPM, at least 0.11 GPM, at least 0.13 GPM, or at least 0.15 GPM. 34. The plant of any of clauses 25 to 33, wherein ammonia is injected into the exhaust gas at a flow rate and / or rate that can be up to 0.4 GPM, up to 0.35 GPM, up to 0.32 GPM, up to 0.3 GPM, up to 0.28 GPM, up to 0.25 GPM, or up to 0.22 GPM.

[0136] Clause 35: A plant according to any of clauses 25 to 34, wherein the nozzle is positioned in the flue where the exhaust gas has a reaction temperature of between 850°C and 1200°C, or between 875°C and 1150°C, between 900°C and 1100°C, or between 950°C and 1050°C.

[0137] Clause 36: A plant according to clauses 25 to 34, wherein the plant is configured to inject ammonia only into the sidewall of the flue.

[0138] Clause 37: The plant of clause 36, wherein the nozzle is positioned in the side wall of the flue approximately between the most downstream downcomer or the downstream exhaust outlet and the flue, or at the junction between the most downstream downcomer or the downstream exhaust outlet and the flue.

[0139] Clause 38: The plant of clause 36, wherein the nozzle is positioned in the side wall of the flue between the most downstream downcomer or the downstream end wall of the flue.

[0140] Clause 39: A plant as described in clauses 25 to 34, wherein the plant is configured to inject ammonia only into the side wall of the upstream end wall of the flue.

[0141] Clause 40: The plant of clauses 25 to 34, wherein the plant is configured to inject ammonia only into the side wall of the downstream end wall of the flue.

[0142] Clause 41: A plant according to any of clauses 25 to 40, wherein the plant does not include a catalyst for reacting the ammonia with the exhaust gas.

[0143] Clause 42: A plant according to any one of clauses 25 to 41, wherein the furnace is an oxygen-fueled furnace.

[0144] Clause 43: A plant according to any of clauses 25 to 42, wherein the exhaust gases are removed by an induced draft stack effect or an induced draft fan positioned in the flue.

[0145] Clause 44: A plant according to any of clauses 25 to 42, wherein the exhaust gases are removed by induced stack effect.

[0146] Clause 45: A plant for a combustion process, comprising: a furnace for heating a material; and a burner configured to combust an oxidizing gas and a carbon-based fuel in the furnace, the oxidizing gas having at least 80 volume percent oxygen, particularly at least 85 volume percent, more particularly at least 90 volume percent, more particularly at least 92 volume percent, more particularly at least 94 volume percent, or at least 95 volume percent oxygen; the burner allowing communication between the furnace and a first flue, and discharging exhaust gases generated during the combustion process into the furnace. a first exhaust outlet configured to remove exhaust gases produced during the combustion process from the furnace into the first flue; one or more first flue nozzles positioned in the first flue and configured to inject ammonia into the first flue and / or the exhaust gases, the ammonia being selected from the group consisting of aqueous ammonia, anhydrous ammonia, urea, or combinations thereof; and a second exhaust outlet enabling communication between the furnace and a second flue and configured to remove the exhaust gases produced during the combustion process from the furnace into the second flue.

[0147] Clause 46: The plant of clause 45, wherein the second flue does not include any nozzles configured to inject the ammonia into the second flue.

[0148] Clause 47: The plant of clause 45, wherein the second flue has one or more second flue nozzles, and the second flue nozzles are configured in an off position such that ammonia cannot be injected into the second flue.

[0149] Clause 48: The plant of clause 45, wherein the second flue has one or more second flue nozzles configured to inject the ammonia into the second flue.

[0150] Clause 49: Plant according to any of clauses 45 to 48, wherein the combustion process is used to make glass and the material heated in the furnace is a glass batch material.

[0151] Clause 50: The plant of any of clauses 45 to 49, wherein the first flue has an upstream end wall, a first side wall, a second side wall, and a downstream end wall, and the one or more nozzles are positioned in the upstream end wall, the first side wall, the second side wall, the downstream end wall, or any combination thereof.

[0152] Clause 51: A plant as described in any of clauses 45 to 50, further comprising a downcomer connecting the first flue to the first exhaust outlet, and wherein the one or more nozzles are positioned in the side wall of the first flue and / or the upstream end wall of the first flue.

[0153] Clause 52: A plant as described in any of clauses 45 to 51, wherein the first exhaust outlet is a first upstream exhaust outlet, and the plant further has a first downstream exhaust outlet, and the first upstream exhaust outlet and the first downstream exhaust outlet are in communication with the first flue.

[0154] Clause 53: The plant of clause 52, further comprising a first most downstream downcomer connecting the first downstream exhaust outlet to the first flue, and a first most upstream downcomer connecting the first upstream exhaust outlet to the flue.

[0155] Clause 54: The plant of any of clauses 45 to 53, wherein the one or more nozzles are positioned on the side wall at a position downstream of the most downstream downcomer or the downstream exhaust outlet, at a position between the downstream end wall of the flue and the most downstream downcomer or the downstream exhaust outlet, at a position between the most downstream downcomer or the downstream exhaust outlet and the most upstream downcomer or the upstream exhaust outlet, or any combination thereof.

[0156] Clause 55: Plant according to any of clauses 45 to 54, wherein the one or more nozzles are configured to open or close.

[0157] Clause 56: The plant of any of clauses 45 to 55, wherein the one or more nozzles are configured to increase or decrease the flow rate of the ammonia.

[0158] Clause 57: The ammonia is at a total flow rate of at least 0.01 gallons per minute (GPM), at least 0.03 GPM, at least 0.05 GPM, at least 0.07 GPM, at least 0.09 GPM, at least 0.11 GPM, at least 0.13 GPM, or at least 0.15 GPM. 57. The plant of any of clauses 45 to 56, wherein ammonia is injected into the exhaust gas at a flow rate and / or rate that can be up to 0.4 GPM, up to 0.35 GPM, up to 0.32 GPM, up to 0.3 GPM, up to 0.28 GPM, up to 0.25 GPM, or up to 0.22 GPM.

[0159] Clause 58: A plant as described in any of clauses 45 to 57, wherein the one or more nozzles are positioned in the first flue at which the exhaust gases have a reaction temperature of between 850°C and 1200°C, or between 875°C and 1150°C, between 900°C and 1100°C, or between 950°C and 1050°C.

[0160] Clause 59: A plant as described in clauses 45 to 58, wherein the plant is configured to inject ammonia into only the sidewall of the first flue.

[0161] Clause 60: The plant of clause 59, wherein the one or more nozzles are positioned in the side wall of the flue approximately between the first most downstream downcomer or the first downstream exhaust outlet and the first flue, or at a junction between the first most downstream downcomer or the first downstream exhaust outlet and the first flue.

[0162] Clause 61: The plant of clause 59, wherein the one or more nozzles are positioned in the side wall of the first flue between the first most downstream downcomer or the first downstream end wall of the first flue.

[0163] Clause 62: The plant of clauses 45 to 61, wherein the plant is configured to inject ammonia only into a side wall of a first upstream end wall of the first flue.

[0164] Clause 63: The plant of any one of clauses 45 to 62, wherein the plant is configured to inject ammonia only into a side wall of a first downstream end wall of the first flue.

[0165] Clause 64: A plant according to any of clauses 45 to 63, wherein the plant does not include a catalyst for reacting the ammonia with the exhaust gas.

[0166] Clause 65: A plant according to any one of clauses 45 to 64, wherein the furnace is an oxyfuel furnace.

[0167] Clause 66: A plant according to any of clauses 45 to 65, wherein the exhaust gases are removed by an induced draft stack effect or by an induced draft fan positioned in the flue.

[0168] Clause 67: A plant according to any of clauses 45 to 66, wherein the exhaust gases are removed by induced stack effect.

[0169] Clause 68: A plant as described in any of clauses 45 to 67, wherein the furnace has a second upstream exhaust outlet and a second downstream exhaust outlet enabling communication between the second flue and the furnace, and optionally a second upstream downcomer connecting the second upstream exhaust outlet to the second flue, and optionally a second downstream downcomer connecting the second downstream exhaust outlet to the second flue.

[0170] Clause 69: The plant of Clause 68, wherein the second flue has an upstream end wall, a first side wall, a second side wall, and a downstream end wall, and the one or more nozzles are positioned in the upstream end wall, the first side wall, the second side wall, the downstream end wall, or any combination thereof.

[0171] Clause 70: A plant as described in any of clauses 68 to 69, wherein the one or more nozzles of the second flue are positioned such that the exhaust gas has a reaction temperature in the second flue of between 850°C and 1200°C, or between 875°C and 1150°C, between 900°C and 1100°C, or between 950°C and 1050°C.

[0172] Clause 71: A method for reducing NOx emissions in an oxyfuel combustion furnace, the method comprising the steps of burning a carbon-based fuel in an oxidizing gas having at least 80 volume percent oxygen, specifically at least 85 volume percent, more specifically at least 90 volume percent, more specifically at least 92 volume percent, more specifically at least 94 volume percent, or at least 95 volume percent oxygen; discharging the exhaust gas from an exhaust outlet to a flue; reacting the exhaust gas with ammonia in the flue; and discharging the exhaust gas from the flue.

[0173] Clause 72: The method of clause 71, wherein the oxygen-fired furnace is an oxygen-fired glass melting furnace.

[0174] Clause 73: The method of clause 71 or 72, further comprising melting feedstock in the oxyfuel furnace.

[0175] Clause 74: The method of clause 73, wherein the raw material is a glass batch.

[0176] Clause 75: The method of any of clauses 71 to 74, wherein the ammonia is injected into the flue at an upstream end wall, a first side wall, a second side wall, a downstream end wall, or a combination thereof.

[0177] Clause 76: The method of any of clauses 71 to 75, wherein the ammonia is injected into the flue at the first side wall.

[0178] Clause 77: The method of any of clauses 71 to 76, wherein the ammonia is injected into the flue at the first side wall and at the second side wall at a point approximately opposite or opposite to an injection location on the first side wall.

[0179] Clause 78: The method of any of clauses 71 to 74, wherein the ammonia is injected into the flue at a downstream end wall of the flue.

[0180] Clause 79: The method of any of clauses 71 to 78, wherein the exhaust gas exits the furnace through the exhaust outlet and is discharged through a downcomer into the flue.

[0181] Clause 80. The method of clause 79, wherein the ammonia is injected into the flue at the end wall or the side wall where the downcomer joins the flue.

[0182] Clause 81: The method of any of clauses 71 to 78, wherein the exhaust outlet is an upstream exhaust outlet, the exhaust gas is further discharged from a downstream exhaust outlet and a most downstream downcomer, and from the upstream exhaust outlet through an upstream downcomer to the flue, and ammonia is injected into the flue at a position downstream of the most downstream downcomer or the downstream exhaust outlet, a position between a downstream end wall of the flue and the most downstream downcomer or the downstream exhaust outlet, a position between the most downstream downcomer or the downstream exhaust outlet and the most upstream downcomer or the upstream exhaust outlet, or a combination thereof.

[0183] Clause 82: The method of any of clauses 71 to 81, wherein the injection of ammonia is injected at a flow rate that can be increased or decreased.

[0184] Clause 83: The ammonia is at a rate of at least 0.01 gallons per minute (GPM), at least 0.03 GPM, at least 0.05 GPM, at least 0.07 GPM, at least 0.09 GPM, at least 0.11 GPM, at least 0.13 GPM, or at least 0.15 GPM. 83. The method of any of clauses 71 to 82, wherein a total ammonia flow rate is injected into the exhaust gas and / or rate can be up to 0.4 GPM, up to 0.35 GPM, up to 0.32 GPM, up to 0.3 GPM, up to 0.28 GPM, up to 0.25 GPM, or up to 0.22 GPM.

[0185] Clause 84: The method of any of clauses 71 to 83, wherein the ammonia is injected into the flue at a reaction temperature of the exhaust gas between 850°C and 1200°C, or between 875°C and 1150°C, between 900°C and 1100°C, or between 950°C and 1050°C.

[0186] Clause 85: A plant as described in clauses 71 to 84, wherein the ammonia is injected into a side wall of the flue.

[0187] Clause 86: The method of any of clauses 71 to 85, wherein ammonia is injected approximately only between the most downstream downcomer or the downstream exhaust outlet and the flue, or at the junction between the most downstream downcomer or the downstream exhaust outlet and the flue.

[0188] Clause 87: The method of any of clauses 71 to 86, wherein the ammonia is injected into the side wall of the flue between the most downstream downcomer or the downstream end wall of the flue.

[0189] Clause 88: The method of any of clauses 71 to 87, wherein the ammonia is injected into only a first side wall of the flue, only a second side wall of the flue, only a downstream end wall of the flue, only an upstream end wall of the flue, or only the first side wall and the second side wall of the flue.

[0190] Clause 89: The method of any of clauses 71 to 88, wherein the exhaust gas is discharged into a second flue, and the first flue and the second flue communicate with a chimney.

[0191] Clause 90: The method of clause 89, wherein ammonia is not injected into the second flue.

[0192] Clause 91: The method of clause 89 or 90, wherein ammonia is injected into the second flue at an upstream end wall, a first side wall, a second side wall, a downstream end wall, or a combination thereof, of the second flue.

[0193] Clause 92: The ammonia is at least 0.01 gallons per minute (GPM), at least 0.03 GPM, at least 0.05 GPM, at least 0.07 GPM, at least 0.09 GPM, at least 0.11 GPM, at least 0.13 GPM, or at least 0.15 GPM. 92. The method of claim 91, wherein ammonia is injected into the exhaust gas at a total ammonia flow rate of up to 0.4 GPM, up to 0.35 GPM, up to 0.32 GPM, up to 0.3 GPM, up to 0.28 GPM, up to 0.25 GPM, or up to 0.22 GPM.

[0194] Clause 93: The method of any of clauses 71 to 92, wherein a catalyst is not used to react the ammonia with the exhaust gas.

[0195] Clause 94: The method of any of clauses 71 to 93, wherein the furnace is an oxygen-fueled furnace.

[0196] Clause 95: A method according to any of clauses 71 to 94, wherein the exhaust gases are removed by an induced draft stack effect or an induced draft fan positioned in the flue.

[0197] Clause 96: The method of any of clauses 71 to 94, wherein the exhaust gases are removed by induced stack effect.

Claims

1. 1. A plant for a combustion process, comprising: a furnace for heating the material; a burner configured to combust an oxidizing gas and a carbon-based fuel in the furnace, the oxidizing gas having at least 80 volume percent oxygen; an exhaust outlet providing communication between the furnace and a flue, the exhaust outlet configured to remove exhaust gases generated during the combustion process from the furnace to the flue; a nozzle positioned within the flue and configured to inject ammonia into the flue and / or the exhaust gas, the ammonia being selected from the group consisting of aqueous ammonia, anhydrous ammonia, urea, or combinations thereof; and the nozzle is positioned within the flue where the exhaust gases are at a reaction temperature between 900°C and 1100°C; the plant further comprising a downcomer connecting the flue to the exhaust outlet; the nozzle is positioned within the flue where the downcomer communicates with the flue; The plant further comprises an additional nozzle connected to an air supply, the additional nozzle injecting air into the flue where the exhaust gas is at a temperature different from the reaction temperature, between 900°C and 1100°C.

2. The plant of claim 1 , wherein the nozzle is configured to be open or closed.

3. 3. The plant of claim 1 or 2, wherein the nozzle is configured to increase or decrease the flow rate of the ammonia.

4. 4. The plant of claim 1, wherein the ammonia is injected into the exhaust gas at a total ammonia flow rate of at least 0.01 gallons per minute (GPM).

5. 5. The plant of claim 1, wherein the plant is configured to inject ammonia into the sidewall of the flue only.

6. 5. A plant according to any one of claims 1 to 4, wherein the plant is configured to inject ammonia only into the upstream end wall of the flue.

7. 5. A plant according to any one of claims 1 to 4, wherein the plant is configured to inject ammonia only into the downstream end wall of the flue.

8. 8. The plant of claim 1, wherein the plant does not include a catalyst for reacting the ammonia with the exhaust gas.

9. 9. A plant according to any one of claims 1 to 8, wherein the furnace is an oxyfuel furnace.

10. 10. A plant according to any one of claims 1 to 9, wherein the exhaust gases are removed by the induced stack effect.

11. 1. A method for reducing NOx emissions in an oxyfuel furnace, comprising: burning a carbon-based fuel in an oxidizing gas having at least 80 volume percent oxygen; Discharging the exhaust gases through an exhaust outlet into a flue; reacting the exhaust gas with ammonia in the flue; Discharging the exhaust gas from the flue. and a nozzle positioned within the flue where the exhaust gas is at a reaction temperature between 900°C and 1100°C; A method wherein air is injected into the flue where the exhaust gas is at a temperature different from the reaction temperature, between 900°C and 1100°C.

12. 12. The method of claim 11, wherein the ammonia is injected into the flue at an upstream end wall, a first side wall, a second side wall, a downstream end wall, or a combination thereof.

13. 13. The method of claim 11 or 12, wherein the exhaust gases are discharged from the furnace through the exhaust outlet and into the flue through a downcomer.

14. 12. The method of claim 11, wherein the ammonia is injected into the flue at an end wall or side wall where a downcomer connects to the flue.

15. 15. The method of any one of claims 11 to 14, wherein the ammonia is injected into the exhaust gas at a total ammonia flow rate of at least 0.01 gallons per minute (GPM), and the flow rate may be up to 0.4 GPM.

16. 16. The method of any one of claims 11 to 15, wherein the ammonia is injected into a sidewall of the flue.

17. 17. The method of any one of claims 11 to 16, wherein no catalyst is used to react the ammonia with the exhaust gas.

18. 18. The method of any one of claims 11 to 17, wherein the furnace is an oxygen-fueled furnace.

19. 19. A method according to any one of claims 11 to 18, wherein the exhaust gases are removed by an induced stack effect.

20. 2. The plant of claim 1, wherein the air is injected into the flue where the exhaust gases are at a temperature below the reaction temperature.

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