COMBUSTION SYSTEM WITH MIXING AND FLAME ARRESTING FOR POLLUTION REDUCTION

Abstract

Premixing fuel and oxidizer in a burner to form a flammable mixture is described. The burner is configured to reduce formation of a pollutant when the fuel and the oxidizer are combusted while deterring upstream propagation of the combustion reaction. The burner includes a mixer for premixing fuel and oxidizer to form a flammable mixture to be supplied to a reaction zone for a combustion reaction and a flame arrestor for deterring upstream propagation of the combustion reaction. In some embodiments, the mixer and the flame arrestor include a packing volume. In some embodiments, the mixer and the flame arrestor include at least a first packing volume for containing first packing, a second packing volume for containing second packing, and a packing gap in fluid communication between the first packing volume and the second packing volume.

Claims

1. A burner for premixing fuel and oxidizer to form a flammable mixture for a combustion reaction in a reaction zone, the burner configured to reduce formation of a pollutant when the fuel and the oxidizer are combusted while deterring upstream propagation of the combustion reaction out of the reaction zone, the burner comprising: a mixer for premixing fuel and oxidizer to form a flammable mixture to be supplied to a reaction zone for a combustion reaction, the mixer configured to reduce formation of a pollutant when the fuel and the oxidizer are combusted; a flame arrestor for deterring upstream propagation of the combustion reaction out of the reaction zone, the mixer and the flame arrestor including: a first packing volume for containing first packing, a second packing volume for containing second packing, a packing gap in fluid communication between the first packing volume and the second packing volume.

2. The burner as recited in claim 1, wherein the mixer and the flame arrestor occupy the same volume.

3. The burner as recited in claim 1, further comprising first packing in the first packing volume and second packing in the second packing volume.

4. The burner as recited in claim 3, wherein at least one of the first packing or the second packing comprises random packing.

5. The burner as recited in claim 4, wherein the random packing comprises a plurality of at least one of Pall rings or Raschig rings.

6. The burner as recited in claim 3, wherein at least one of the first packing or the second packing comprises structured packing.

7. The burner as recited in claim 6, wherein the structured packing comprises a plurality of rigid flow channels.

8. The burner as recited in claim 1, wherein the fuel comprises at least one of a flammable gas, a flammable liquid, or a flammable solid.

9. The burner as recited in claim 1, wherein the oxidizer comprises at least one of ambient air or oxygen from a pressurized oxygen source.

10. The burner as recited in claim 1, wherein the oxidizer comprises a vitiated oxidizer.

11. A method for premixing fuel and oxidizer in a burner to form a flammable mixture to be supplied to a reaction zone for a combustion reaction, the burner configured to reduce formation of a pollutant when the fuel and the oxidizer are combusted while deterring upstream propagation of the combustion reaction out of the reaction zone, the method comprising: introducing fuel and oxidizer to a first packing volume containing first packing; introducing the fuel and the oxidizer to a packing gap downstream of the first packing volume; and introducing the fuel and the oxidizer to a second packing volume containing second packing downstream of the packing gap.

12. The method as recited in claim 11, wherein a portion of the fuel bypasses the first packing volume, the packing gap, and the second packing volume and is combusted in a secondary reaction zone.

13. The method as recited in claim 11, wherein the oxidizer comprises vitiated oxidizer.

14. A burner for premixing fuel and oxidizer to form a flammable mixture for a combustion reaction in a reaction zone, the burner configured to reduce formation of a pollutant when the fuel and the oxidizer are combusted while deterring upstream propagation of the combustion reaction out of the reaction zone, the burner comprising: a mixer for premixing fuel and oxidizer to form a flammable mixture to be supplied to a reaction zone for a combustion reaction, the mixer configured to reduce formation of a pollutant when the fuel and the oxidizer are combusted; and a flame arrestor for deterring upstream propagation of the combustion reaction out of the reaction zone.

15. The burner as recited in claim 14, wherein the mixer and the flame arrestor occupy the same volume.

16. The burner as recited in claim 15, wherein the mixer and the flame arrestor include a packing volume.

17. The burner as recited in claim 14, wherein the mixer and the flame arrestor include: a first packing volume for containing first packing, a second packing volume for containing second packing, a packing gap in fluid communication between the first packing volume and the second packing volume.

18. The burner as recited in claim 17, further comprising first packing in the first packing volume and second packing in the second packing volume.

19. The burner as recited in claim 18, wherein at least one of the first packing or the second packing comprises random packing.

20. The burner as recited in claim 19, wherein the random packing comprises a plurality of at least one of Pall rings or Raschig rings.

21. The burner as recited in claim 18, wherein at least one of the first packing or the second packing comprises structured packing.

22. The burner as recited in claim 21, wherein the structured packing comprises a plurality of rigid flow channels.

23. The burner as recited in claim 14, wherein the fuel comprises at least one of a flammable gas, a flammable liquid, or a flammable solid.

24. The burner as recited in claim 14, wherein the oxidizer comprises at least one of ambient air or oxygen from a pressurized oxygen source.

25. The burner as recited in claim 14, wherein the oxidizer comprises a vitiated oxidizer.

26. A method for premixing fuel and oxidizer in a burner to form a flammable mixture to be supplied to a reaction zone for a combustion reaction, the burner configured to reduce formation of a pollutant when the fuel and the oxidizer are combusted while deterring upstream propagation of the combustion reaction out of the reaction zone, the method comprising: introducing fuel and oxidizer to a mixer for premixing the fuel and the oxidizer to form a flammable mixture to be supplied to a reaction zone for a combustion reaction; and introducing the fuel and the oxidizer to a flame arrestor for deterring upstream propagation of the combustion reaction out of the reaction zone.

27. The method as recited in claim 26, wherein a portion of the fuel bypasses the mixer and the flame arrestor and is combusted in a secondary reaction zone.

28. The method as recited in claim 26, wherein the oxidizer comprises vitiated oxidizer.

29. The method as recited in claim 26, wherein introducing the fuel and the oxidizer to a mixer and introducing the fuel and the oxidizer to a flame arrestor comprise introducing the fuel and the oxidizer to a packing volume.

30. The method as recited in claim 29, wherein introducing the fuel and the oxidizer to a packing volume comprises: introducing the fuel and the oxidizer to a first packing volume containing first packing; introducing the fuel and the oxidizer to a packing gap downstream of the first packing volume; and introducing the fuel and the oxidizer to a second packing volume containing second packing downstream of the packing gap.

Description

DRAWINGS

[0003] The Detailed Description is described with reference to the accompanying figures. The use of the same reference numbers in different instances in the description and the figures may indicate similar or identical items.

[0004] FIG. 1 is a diagrammatic illustration of a combustion system including a burner with a mixer and a flame arrestor in accordance with example embodiments of the present disclosure.

[0005] FIG. 2 is a diagrammatic illustration of a combustion system including a burner with a mixer and flame arrestor in accordance with example embodiments of the present disclosure.

[0006] FIG. 3 is a diagrammatic illustration of a combustion system including a burner with a mixer and flame arrestor, a fuel supply conduit, and an air handling device in accordance with example embodiments of the present disclosure.

[0007] FIG. 3a is a diagrammatic illustration of a combustion system including a burner with a mixer and flame arrestor, a fuel supply conduit, an air handling device, and a mixing plenum, where some flue gas or other non-combustible gas is added to the air to reduce the concentration of oxygen (known as vitiated air), the vitiated air going to the burner in accordance with example embodiments of the present disclosure.

[0008] FIG. 4 is a diagrammatic illustration of a combustion system including a burner with a mixer and flame arrestor, a fuel supply conduit, and an air handling device, where secondary fuel bypasses the mixer and flame arrestor in accordance with example embodiments of the present disclosure.

[0009] FIG. 4a is a diagrammatic illustration of a combustion system including a burner with a mixer and flame arrestor, a fuel supply conduit, an air handling device, and a mixing plenum, where secondary fuel bypasses the mixer and flame arrestor, and where some flue gas or other non-combustible gas is added to the air to reduce the concentration of oxygen (known as vitiated air), the vitiated air going to the burner in accordance with example embodiments of the present disclosure.

[0010] FIG. 5 is an isometric view of a combustion system including a burner with a mixer and flame arrestor, a fuel supply conduit, and an air handling device in accordance with example embodiments of the present disclosure.

[0011] FIG. 6 is a partial cross-sectional isometric view of the combustion system illustrated in FIG. 5.

[0012] FIG. 7 is a partial cross-sectional side elevation view of a combustion system including a burner with a mixer and flame arrestor with random packing in a first packing volume and a second packing volume separated by a packing gap in accordance with example embodiments of the present disclosure.

[0013] FIG. 8 is a perspective view illustrating structured packing for a combustion system, where the structured packing is configured for mixing in an XZ direction in accordance with example embodiments of the present disclosure.

[0014] FIG. 9 is a partial perspective view illustrating a packing volume including structured packing, such as the structured packing illustrated in FIG. 8, in accordance with example embodiments of the present disclosure.

[0015] FIG. 10 is a perspective view illustrating structured packing for a combustion system, where the structured packing is configured for mixing in a YZ direction in accordance with example embodiments of the present disclosure.

[0016] FIG. 11 is a partial perspective view illustrating another packing volume including structured packing, such as the structured packing illustrated in FIG. 10, in accordance with example embodiments of the present disclosure.

[0017] FIG. 12 is a partial perspective view illustrating a mixer and flame arrestor including a first packing volume, such as the packing volume illustrated in FIG. 9, and a second packing volume, such as the packing volume illustrated in FIG. 11, where the first packing volume and the second packing volume are separated by a packing gap in accordance with example embodiments of the present disclosure.

[0018] FIG. 13 is a flow diagram illustrating a process for premixing fuel and oxidizer in a burner to form a flammable mixture to be supplied to a reaction zone for a combustion reaction in accordance with example embodiments of the present disclosure.

[0019] FIG. 14 is another flow diagram illustrating a process for premixing fuel and oxidizer in a burner to form a flammable mixture to be supplied to a reaction zone for a combustion reaction in accordance with example embodiments of the present disclosure.

[0020] FIG. 15 is a further flow diagram illustrating a process for premixing fuel and oxidizer in a burner to form a flammable mixture to be supplied to a reaction zone for a combustion reaction in accordance with example embodiments of the present disclosure.

[0021] FIG. 16 is another flow diagram illustrating a process for premixing fuel and oxidizer in a burner to form a flammable mixture to be supplied to a reaction zone for a combustion reaction in accordance with example embodiments of the present disclosure.

DETAILED DESCRIPTION

[0022] Industrial burners typically produce a flame by mixing a hydrocarbon fuel such as natural gas with an oxidant such as air to form a flammable mixture, and then provide a source of ignition to initiate a combustion reaction. Usually, the fuel mixes downstream of the burner. Such burners are generally known as diffusion burners because they do not mix air and fuel in the body of the burner itself, but instead rely on external mixing of the fuel and air. Flames from such burners are known as diffusion flames. Diffusion flames contain zones of incomplete mixing and inhomogeneous fuel-air mixtures that are prone to produce high local flame temperatures and attendant NOx emissions. For example, a flame may be defined as an area of high chemical and temperature gradients, and such gradients are known to abet formation of NOx, a regulated criteria pollutant.

[0023] To the extent the oxidation of fuel occurs without a flame, or in as short a flame as possible, NOx may be minimized. NOx may also be reduced by premixed combustion with a high excess of oxygen, by combusting diffusion combustion with an excess of fuel, and/or by employing both premixed high-excess air and diffusion combustion with an excess of fuel such that air is in excess overall, which may be referred to as staged combustion. Adding flue gas or another non-combustible gas to either the diffusion or premixed combustion can also lower NOx by diluting species that form NOx, and/or by reducing the temperature of the reaction due to the increase of inert mass flow through the oxidation zone.

[0024] To avoid inhomogeneities that contribute to NOx formation, some burners premix the fuel and air within the body of the burner prior to ignition. This may result in lower NOx. However, premix burners are prone to a phenomenon known as flashback, where the combustion zone propagates upstream and into the burner. High temperatures in the body of a burner can destroy the burner in short order and/or create a hazard. However, if the fuel and oxidant are substantially premixed, and if the flame is prevented from propagating upstream and into the burner, the results are low NOx and reliable operation.

[0025] A technique for reducing the combustion volume is to remove a portion of fuel from a flame zone and direct it elsewhere in a hot furnace or against a hot surface in order to oxidize a portion of the fuel without such oxidation producing a flame. Fuel removed from the primary flame zone and directed elsewhere is known as secondary fuel. Traditionally, secondary fuel is allowed to mix with non-combustible flue gas in the furnace before interacting with the primary flame. This reduces NOx, though to a lesser extent than oxidizing the secondary fuel without a flame. It is also possible to oxidize the fuel on any hot surface with or without a flame. If fuel is oxidized on a hot surface without a flame, it can produce relatively low NOx.

[0026] Ignition of a fuel may be accomplished by exposing a portion of a flammable mixture to a sufficiently high temperature. This may be accomplished by a pilot flame, a high energy spark, or other techniques sufficient to bring the fuel-oxidant mixture above a critical minimum temperature known as the autoignition temperature. Once ignition is achieved, the combustion generates sufficient energy to support self-sustained combustion, which may be referred to as propagation of the oxidation reaction.

[0027] By removing sufficient heat from a flame, a flame may be extinguished, which may be referred to as termination of the oxidation reaction. Flame arrestors function mainly by removing sufficient heat from a flame to reduce its temperature below the temperature required for ignition and propagation, resulting in termination of the oxidation process. This is typically achieved by dividing the flow through thermally conductive passages so that sufficient heat can be removed from the fluid, causing it to fall below the temperature required for propagation of the fuel's oxidation.

[0028] Prior to combustion, devices may be used to mix fuel and oxidant so that at least a portion of the mixture is between an upper and lower flammability limit capable of supporting combustion. One simple device for doing so is a fuel conduit containing fuel at an elevated pressure relative to its surroundings that allows the fuel to pass through the conduit and across an orifice or nozzle into the surrounding air. The fuel jet issuing from such a nozzle entrains surrounding air to create a flammable mixture. A flame supported by such an arrangement is known as a diffusion flame. If the mixing occurs within the burner itself prior to ignition by means of a Venturi body or other device, the flame resulting from the premixed fuel and air is known as a premix flame.

[0029] Other mixing devices may also be used in non-combustion applications to mix two fluid streams. Static mixers can be used to enhance the mixing of fluids. Static mixers generally include stationary rigid bodies that direct or enhance fluid mixing. There is a wide variety in types and kinds of static mixers, including helical mixers, plate mixers, baffle mixers, intersecting-channel mixers, and so forth. Random packing can be used as another kind of fluid mixer. For example, random packing can be used in distillation columns, absorption columns, and other equipment and to enhance fluid mixing. Examples of random packing include Pall rings, Raschig rings, and so on. Structured packing is another kind of mixer arrangement used in distillation and other mass-transfer processes to enhance fluid mixing. Structured packing can use rigid-flow channels that cause flowing streams to collide and mix with one another. Various types and kinds of structured packing employ solid channels, perforated channels, mesh channels, and so forth.

[0030] Referring generally to FIGS. 1 through 16, combustion systems 100 with burners 102 for premixing fuel 104 and oxidant/oxidizer 106 to form a flammable mixture for a combustion reaction in a reaction zone are described. In embodiments of the disclosure, the burners 102 are configured to reduce formation of one or more pollutants when the fuel 104 and the oxidizer 106 are combusted. The burners 102 are also configured to deter upstream propagation of the combustion reaction. In some embodiments, the fuel 104 can be one or more flammable materials, such as flammable gases, flammable liquids, flammable solids, and so forth. In some embodiments, the oxidizer 106 can be ambient air that is drafted into the burner by the natural buoyancy of hot flue gases (e.g., gases exiting a combustion chamber). In some embodiments, the oxidizer 106 can be air that is induced or forced into the burner 102 by mechanical equipment, such as a fan and/or another device to import oxidizer. For example, the oxidizer 106 can be oxygen (e.g., pure oxygen from a pressurized oxygen source), oxygen-enriched air, chlorine, or any other oxidizing species.

[0031] With reference to FIG. 1, a combustion system 100 includes a burner 102 having a mixer 108 and a flame arrestor 110 arranged in seriatim or one after another. The combustion system 100 is connected to a source of fuel 104 and to a source of oxidizer 106. The fuel 104 and the oxidizer 106 are admitted to the mixer 108, where the fuel 104 and the oxidizer 106 are premixed (e.g., substantially mixed) to produce a flammable mixture. The flammable mixture continues from the mixer 108 through the flame arrestor 110, after which it is ignited by an ignitor 112 to react in a reaction zone 114 for the combustion reaction. As described herein, the flame arrestor 110 deters upstream propagation of the reaction zone 114. For example, the flame arrestor 110 prevents the oxidation reaction from migrating upstream and propagating into the flame arrestor 110 or the mixer 108.

[0032] In some embodiments, a combustion system 100 includes one or more fuel passages configured to emit a flow of fuel, a mixer in the path of the fuel flow and in proximity to the fuel passage(s) to mix the fuel with an oxidant, and an arresting element positioned between the fuel-air mixture and an ignition source. As described herein, the mixing and/or arresting may be performed in communication with a thermally conductive medium. In some embodiments, a hot surface of the burner may be used to oxidize all or a portion of the fuel without a flame.

[0033] Referring now to FIG. 2, another combustion system 100 includes a burner 102 having a combined mixer and flame arrestor (e.g., a mixer and a flame arrestor that occupy the same volume), which may be referred to as a mixarrestor (e.g., mixer and flame arrestor 116). In this example, fuel 104 and oxidizer 106 are admitted to the mixer and flame arrestor 116, where the fuel 104 and the oxidizer 106 are premixed (e.g., substantially mixed) to produce a flammable mixture. The flammable mixture continues through the mixer and flame arrestor 116, after which it is ignited by an ignitor 112 to react in a reaction zone 114 for the combustion reaction. As described herein, the mixarrestor/mixer and flame arrestor 116 deters upstream propagation of the combustion reaction out of the reaction zone 114. For example, the mixer and flame arrestor 116 prevents the oxidation reaction from migrating upstream and propagating into the mixer and flame arrestor 116, e.g., preventing sustained combustion inside the mixarrestor.

[0034] With reference to FIG. 3, a combustion system 100 includes a burner 102 having a mixer and flame arrestor 116. In this example, an oxidizer 106 such as air (e.g., ambient air) is conducted to the mixer and flame arrestor 116 by an air handling device, such as a fan 118. Fuel 104 from a supply 120 is conveyed through a fuel supply conduit 122 to one or more orifices 124 and into the mixer and flame arrestor 116 to substantially mix the fuel 104 and the oxidizer 106. The fuel 104 and oxidizer 106 are admitted to the mixer and flame arrestor 116, where the fuel 104 and the oxidizer 106 are premixed (e.g., substantially mixed) to produce a flammable mixture. The flammable mixture continues through the mixer and flame arrestor 116, after which it is ignited by an ignitor 112 to react in a reaction zone 114 in an oxidation reaction between the fuel 104 and the oxidizer 106.

[0035] Referring to FIG. 3a, in another example a combustion system 100 includes a burner 102 having a mixer and flame arrestor 116, a fuel supply conduit 122, an air handling device 118, and a mixing plenum 118a to produce vitiated air originating from a flue-gas zone 128a. For example, flue gas is withdrawn from a furnace and mixed with incoming air in the mixing plenum 118a. The vitiated air is then conducted to the mixer and flame arrestor 116 by an air handling device, such as a fan 118. Fuel 104 from a supply 120 is conveyed through a fuel supply conduit 122 to one or more orifices 124 and into the mixer and flame arrestor 116 to substantially mix the fuel 104 and the oxidizer 106. The fuel 104 and oxidizer 106 are admitted to the mixer and flame arrestor 116, where the fuel 104 and the vitiated oxidizer 106 are premixed (e.g., substantially mixed) to produce a flammable mixture. The flammable mixture continues through the mixer and flame arrestor 116, after which it is ignited by an ignitor 112 to react in a reaction zone 114 in an oxidation reaction between the fuel 104 and the oxidizer 106.

[0036] While supplying flue gas from a flue-gas zone 128a is described with some specificity herein, in other embodiments flue gas may be supplied from anywhere outside of the reaction zone 114, e.g., to vitiate the air, dilute the fuel-air mixture, reduce flame temperatures and species concentrations, and thereby suppress NOx. Further, any non-combustible gas may be supplied to the mixing plenum 118a, including, but not necessarily limited to: water vapor, CO.sub.2, nitrogen, and so forth. For example, flue gas can be a mixture of the above, with whatever remains of the uncombusted oxygen. In some embodiments, up to twenty-five percent (25%) of flue gas produced may be recirculated (e.g., without affecting normal burner operation). As described, this amount of flue gas recirculation may reduce NOx from about fifty to one hundred parts per million (50-100 ppm) to about twenty-five to thirty parts per million (25 to 30 ppm).

[0037] Referring now to FIG. 4, a combustion system 100 includes a burner 102 having a mixer and flame arrestor 116. In this example, an oxidizer 106 such as air (e.g., ambient air) is conducted to the mixer and flame arrestor 116 by an air handling device, such as a fan 118. Fuel 104 from a supply 120 is conveyed through a fuel supply conduit 122 to one or more orifices 124 and into the mixer and flame arrestor 116 to substantially mix the fuel 104 and the oxidizer 106. The fuel 104 and oxidizer 106 are admitted to the mixer and flame arrestor 116, where the fuel 104 and the oxidizer 106 are premixed (e.g., substantially mixed) to produce a flammable mixture. The flammable mixture continues through the mixer and flame arrestor 116, after which it is ignited by an ignitor 112 to react in a reaction zone 114 in an oxidation reaction between the fuel 104 and the oxidizer 106. In this example, a secondary fuel 126 bypasses the mixing zone/mixer and flame arrestor 116 to oxidize with or without a flame in a secondary reaction zone 128. For instance, the secondary fuel 126 can be oxidized directly by the premixed flame. In another example, the secondary fuel 126 can be oxidized without a flame.

[0038] Referring to FIG. 4a, in a further example a combustion system 100 includes a burner 102 having a mixer and flame arrestor 116. In this example, an oxidizer 106 such as air (e.g., ambient air) is mixed in a mixing plenum 118a with flue gas from a flue-gas zone 128a to produce vitiated air, which is then conducted to the mixer and flame arrestor 116 by an air handling device, such as a fan 118. Fuel 104 from a supply 120 is conveyed through a fuel supply conduit 122 to one or more orifices 124 and into the mixer and flame arrestor 116 to substantially mix the fuel 104 and the oxidizer 106. The fuel 104 and vitiated oxidizer 106 are admitted to the mixer and flame arrestor 116, where the fuel 104 and the oxidizer 106 are premixed (e.g., substantially mixed) to produce a flammable mixture. The flammable mixture continues through the mixer and flame arrestor 116, after which it is ignited by an ignitor 112 to react in a reaction zone 114 in an oxidation reaction between the fuel 104 and the oxidizer 106. In this example, a secondary fuel 126 bypasses the mixing zone/mixer and flame arrestor 116 to oxidize with or without a flame in a secondary reaction zone 128. For instance, the secondary fuel 126 can be oxidized directly by the premixed flame. In another example, the secondary fuel 126 can be oxidized without a flame.

[0039] With reference to FIGS. 5 through 7, in some embodiments, the mixer 108 and the flame arrestor 110 (e.g., as described with reference to FIG. 1) or the mixer and flame arrestor 116 include a first packing volume 130 containing first packing 132. The mixer 108 and the flame arrestor 110 or the mixer and flame arrestor 116 may also include a second packing volume 134 containing second packing 136. The mixer 108 and the flame arrestor 110 or the mixer and flame arrestor 116 further include a packing gap 138 in fluid communication between the first packing volume 130 and the second packing volume 134. In some embodiments, the first packing 132 and/or the second packing 136 include random packing 140 (e.g., as described with reference to FIG. 7). For example, the first packing 132 and/or the second packing 136 can include Pall rings, Raschig rings, and so forth. In embodiments, the random packing 140 can be thermally conductive random packing. As described with reference to FIGS. 6 and 7, the first packing volume 130, the second packing volume 134, and/or the packing gap 138 can be defined by a number of perforated plates 146, which can be supported by a longitudinal support 148.

[0040] Referring now to FIGS. 8 through 12, in some embodiments, the first packing 132 and/or the second packing 136 include structured packing 142. For instance, the first packing 132 and/or the second packing 136 can include rigid flow channels 144. In some embodiments, the structured packing 142 can be thermally conductive structured packing. As described, the first packing 132 can direct airflow in a first direction (e.g., an X-direction) and redirect the airflow in a second direction different to, but substantially in the same plane as, the first direction (e.g., a Z-direction). Similarly, the second packing 136 can direct airflow in a third direction (e.g., a Y-direction) and redirect the airflow in a fourth direction different to, but substantially in the same plane as, the third direction (e.g., a Z-direction). In embodiments, the plane of the directed airflows for the first packing 132 (e.g., an XZ-plane) can be substantially different from the plane of the directed airflows for the second packing 136 (e.g., a YZ-plane). For instance, the XZ-plane of the directed airflows for the first packing 132 can be generally perpendicular to the YZ-plane of the directed airflows for the second packing 136.

[0041] In some embodiments, the first direction and/or the second direction for the airflow through structured packing material are not necessarily linear directions. For example, first and second directions can be different from one another and also continuously change along the length of the structured packing. For example, the rigid flow channels with structured packing can be helical as illustrated in the accompanying drawing. Additionally, it should be noted that random packing 140 and structured packing 142 are provided by way of example and are not meant to limit the present disclosure. In other embodiments, the first packing volume 130 and/or the second packing volume 134 may contain other packing, such as mesh packing, fine and flexible sharp-edged steel filaments bundled together (e.g., steel wool), and so forth. For instance, first and/or second packing volumes can include mesh packing.

[0042] It should be noted that while the accompanying figures illustrate the same types of packing in the first packing volume 130 and the second packing volume 134 (i.e., random packing and random packing, structured packing and structured packing), the packing volumes can include different types packing (e.g., random packing in the first packing volume 130 and structured packing in the second packing volume 134, structured packing in the first packing volume 130 and random packing in the second packing volume 134, and so forth). There may also be more than two packing volumes separated by more than one packing gap. For example, a second packing gap may be provided downstream of the second packing volume 134, and a third packing volume may be provided downstream of the second packing gap.

[0043] FIG. 13 depicts a process 200, in accordance with example embodiments, for premixing fuel and oxidizer in a burner to form a flammable mixture to be supplied to a reaction zone for a combustion reaction, where the burner is configured to reduce formation of a pollutant when the fuel and the oxidizer are combusted while deterring upstream propagation of the combustion reaction out of the reaction zone, using, for example, the combustion systems 100 described with reference to FIGS. 1 through 12 and discussed above. In the process illustrated, fuel and oxidant are mixed to form a substantially homogenous flammable mixture (Block 210). For example, a combustion system 100 is connected to a source of fuel 104 and to a source of oxidizer 106. The fuel 104 and the oxidizer 106 are admitted to a mixer 108, where the fuel 104 and the oxidizer 106 are mixed to produce a substantially homogenous flammable mixture. In another example, fuel 104 and oxidizer 106 are admitted to a mixer and flame arrestor 116, where the fuel 104 and the oxidizer 106 are mixed to produce a substantially homogenous flammable mixture.

[0044] Next, the flammable mixture is exported to an oxidation zone (Block 220). For instance, the flammable mixture continues from the mixer 108 through the flame arrestor 110 to a reaction zone 114. In another example, the flammable mixture continues through the mixer and flame arrestor 116 to a reaction zone 114. Then, oxidation of the reactive mixture is initiated (Block 230). For example, the flammable mixture is ignited by an ignitor 112 to react in the reaction zone 114. In embodiments of the disclosure, propagation of an oxidation reaction from the oxidation zone into an upstream zone containing a flammable mixture is prevented (Block 240). For instance, the fuel 104 and the oxidizer 106 are introduced to the first packing volume 130 containing first packing 132. Then, the fuel 104 and the oxidizer 106 are introduced to a packing gap 138 downstream of the first packing volume 130. Next, the fuel 104 and the oxidizer 106 are introduced to a second packing volume 134 containing second packing 136 downstream of the packing gap 138.

[0045] FIG. 14 depicts another process 300, in accordance with example embodiments, for premixing fuel and oxidizer in a burner to form a flammable mixture to be supplied to a reaction zone for a combustion reaction, where the burner is configured to reduce formation of a pollutant when the fuel and the oxidizer are combusted while deterring upstream propagation of the combustion reaction out of the reaction zone, using, for example, the combustion systems 100 described with reference to FIGS. 1 through 12 and discussed above. In the process illustrated, a portion of fuel and oxidant are mixed to form a substantially homogenous flammable mixture (Block 310). For example, an oxidizer 106 such as air is conducted to a mixer 108 or to a mixer and flame arrestor 116 by an air handling device, such as a fan 118. Fuel 104 from a supply 120 is conveyed through a fuel supply conduit 122 to one or more orifices 124 and into the mixer 108 or into the mixer and flame arrestor 116 to substantially mix the fuel 104 and the oxidizer 106. At the mixer 108 or the mixer and flame arrestor 116, the fuel 104 and the oxidizer 106 are mixed to produce a substantially homogenous flammable mixture.

[0046] Next, the flammable mixture is exported to an oxidation zone (Block 320). For instance, the flammable mixture continues from the mixer 108 through the flame arrestor 110 or through the mixer and flame arrestor 116 to a reaction zone 114. Then, oxidation of the reactive mixture is initiated (Block 330). For example, the flammable mixture is ignited by an ignitor 112 to react in the reaction zone 114. In embodiments of the disclosure, propagation of an oxidation reaction from the oxidation zone into an upstream zone containing a flammable mixture is prevented (Block 340). For instance, the fuel 104 and the oxidizer 106 are introduced to the first packing volume 130 containing first packing 132. Then, the fuel 104 and the oxidizer 106 are introduced to a packing gap 138 downstream of the first packing volume 130. Next, the fuel 104 and the oxidizer 106 are introduced to a second packing volume 134 containing second packing 136 downstream of the packing gap 138. Next, some of the fuel is conveyed to a secondary reaction zone and allowed to oxidize with or without a flame (Block 350). For instance, a secondary fuel 126 bypasses the mixer 108 and the flame arrestor 110 or the mixer and flame arrestor 116 to oxidize with or without a flame in a secondary reaction zone 128.

[0047] FIG. 15 depicts a process 200a, in accordance with example embodiments, for premixing fuel and vitiated oxidizer in a burner to form a flammable mixture to be supplied to a reaction zone for a combustion reaction, where the burner is configured to reduce formation of a pollutant when the fuel and the oxidizer are combusted while deterring upstream propagation of the combustion reaction out of the reaction zone, using, for example, the combustion systems 100 described with reference to FIGS. 1 through 12 and discussed above. In the process illustrated, a noncombustible gas (e.g., flue gas) is mixed with an oxidant to vitiate the oxidant (Block 210a).

[0048] Next, the fuel and vitiated oxidant are mixed to form a substantially homogenous flammable mixture (Block 210b). For example, a combustion system 100 is connected to a source of fuel 104 and to a source of oxidizer 106. The fuel 104 and the oxidizer 106 are admitted to a mixer 108, where the fuel 104 and the oxidizer 106 are mixed to produce a substantially homogenous flammable mixture. In another example, fuel 104 and oxidizer 106 are admitted to a mixer and flame arrestor 116, where the fuel 104 and the oxidizer 106 are mixed to produce a substantially homogenous flammable mixture.

[0049] Next, the flammable mixture is exported to an oxidation zone (Block 220). For instance, the flammable mixture continues from the mixer 108 through the flame arrestor 110 to a reaction zone 114. In another example, the flammable mixture continues through the mixer and flame arrestor 116 to a reaction zone 114. Then, oxidation of the reactive mixture is initiated (Block 230). For example, the flammable mixture is ignited by an ignitor 112 to react in the reaction zone 114. In embodiments of the disclosure, propagation of an oxidation reaction from the oxidation zone into an upstream zone containing a flammable mixture is prevented (Block 240). For instance, the fuel 104 and the oxidizer 106 are introduced to the first packing volume 130 containing first packing 132. Then, the fuel 104 and the oxidizer 106 are introduced to a packing gap 138 downstream of the first packing volume 130. Next, the fuel 104 and the oxidizer 106 are introduced to a second packing volume 134 containing second packing 136 downstream of the packing gap 138.

[0050] FIG. 16 depicts another process 300a, in accordance with example embodiments, for premixing fuel and vitiated oxidizer in a burner to form a flammable mixture to be supplied to a reaction zone for a combustion reaction, where the burner is configured to reduce formation of a pollutant when the fuel and the oxidizer are combusted while deterring upstream propagation of the combustion reaction out of the reaction zone, using. for example, the combustion systems 100 described with reference to FIGS. 1 through 12 and discussed above. In the process illustrated, a noncombustible gas (e.g., flue gas) is mixed with an oxidant to vitiate the oxidant (Block 310a).

[0051] Next, a portion of fuel and vitiated oxidant are mixed to form a substantially homogenous flammable mixture (Block 310b). For example, an oxidizer 106 such as air is conducted to a mixer 108 or to a mixer and flame arrestor 116 by an air handling device, such as a fan 118. Fuel 104 from a supply 120 is conveyed through a fuel supply conduit 122 to one or more orifices 124 and into the mixer 108 or into the mixer and flame arrestor 116 to substantially mix the fuel 104 and the oxidizer 106. At the mixer 108 or the mixer and flame arrestor 116, the fuel 104 and the oxidizer 106 are mixed to produce a substantially homogenous flammable mixture.

[0052] Next, the flammable mixture is exported to an oxidation zone (Block 320). For instance, the flammable mixture continues from the mixer 108 through the flame arrestor 110 or through the mixer and flame arrestor 116 to a reaction zone 114. Then, oxidation of the reactive mixture is initiated (Block 330). For example, the flammable mixture is ignited by an ignitor 112 to react in the reaction zone 114. In embodiments of the disclosure, propagation of an oxidation reaction from the oxidation zone into an upstream zone containing a flammable mixture is prevented (Block 340). For instance, the fuel 104 and the oxidizer 106 are introduced to the first packing volume 130 containing first packing 132. Then, the fuel 104 and the oxidizer 106 are introduced to a packing gap 138 downstream of the first packing volume 130. Next, the fuel 104 and the oxidizer 106 are introduced to a second packing volume 134 containing second packing 136 downstream of the packing gap 138. Next, some of the fuel is conveyed to a secondary reaction zone and allowed to oxidize with or without a flame (Block 350). For instance, a secondary fuel 126 bypasses the mixer 108 and the flame arrestor 110 or the mixer and flame arrestor 116 to oxidize with or without a flame in a secondary reaction zone 128.

[0053] Although the subject matter has been described in language specific to structural features and/or process operations, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.