Low nox, high rate, high temperature, staged recirculation combustor and radiant tube combustion system

Abstract

Embodiments of the present invention include high temperature staged recirculation combustors and radiant tube combustor assemblies that provide high efficiency, low NOx and CO emissions, and uniform temperature characteristics. One such staged recirculation combustor includes a combustion tube (47) having inner and outer helical fins forming opposing helical passages for combustion gases and combustion products, a combustion nozzle (32) coupled to the combustion tube, a gas tube (37) extending axially into the combustion tube, and a staged gas nozzle (51) coupled to the gas tube, wherein the staged gas nozzle includes radial outlet holes into the combustion tube and an axial gas staging tube (10) extending into the combustion nozzle to stage combustion.

Description

[0001] This application is a divisional application of the invention patent application filed on September 25, 2015, with application number 201580060242.2 and entitled "Low NOx, High Efficiency, High Temperature, Staged Recirculation Burner and Radiant Tube Combustion System".

[0002] Cross-reference to related applications

[0003] This application is a continuation of U.S. Application No. 14 / 863563, filed September 24, 2015, which claims the benefit of U.S. Provisional Application No. 62 / 055095, filed September 25, 2014. The entire teachings of the above application are incorporated herein by reference. Background Technology

[0004] The combustion of fossil fuels introduces emissions, such as nitrogen oxides (NOx), into the atmosphere. NOx emissions originate from nitrogen in, for example, combustion air and fuel-bound nitrogen in coal or fuel oil. The conversion of fuel-bound nitrogen into NOx depends on the amount and reactivity of nitrogen compounds in the fuel and the amount of oxygen in the combustion zone. The conversion of atmospheric nitrogen N2 present in the combustion air into NOx depends on temperature; the higher the flame temperature in the combustion zone, the greater the amount of NOx produced in the emissions. One way to reduce NOx levels is to create a fuel-rich combustion zone followed by a lean combustion zone, which can be achieved by staged air introduction into the combustion chamber. Recirculating fuel gases into the flame is another technique for limiting NOx emissions. Summary of the Invention

[0005] Embodiments of the present invention include high-temperature staged recirculation burner and radiant tube burner assemblies that provide high efficiency, low NOx and CO emissions, and uniform temperature characteristics. One such staged recirculation burner includes a combustion tube having inner and outer helical fins forming opposing helical passages for combustion gases and combustion products, a combustion nozzle coupled to the combustion tube, a gas tube extending axially into the combustion tube, and a staged gas nozzle coupled to the gas tube, wherein the staged gas nozzle includes a radial outlet orifice entering the combustion tube and an axial gas staged tube extending into the combustion nozzle for staged combustion.

[0006] Some embodiments of this staged recirculation burner may include a ceramic wall as part of the combustion tube, which separates the flow of combustion gases from the flow of combustion products, wherein the flow directions of the combustion gases and combustion products are opposite. In many embodiments, the combustion tube may be made of silicon carbide, and / or the combustion nozzle may be a conical combustion nozzle.

[0007] The staged recirculation burner may also include a heat exchanger coupled to the combustion tube, which uses combustion products from the combustion tube to heat the combustion gases supplied to the combustion tube. In such an embodiment, the combustion tube and the heat exchanger may be connected via specialized silicon carbide threads, allowing the combustion tube to be adjustable. The burner's gas pipe may extend through the central axis of the heat exchanger and into the combustion tube.

[0008] In some embodiments, the staged gas nozzle radially injects gas into a spiral flow of preheated air flowing through the combustion tube, and in this embodiment, the staged gas nozzle may inject only a portion of the gas through the radial orifice of the staged gas nozzle to create a substantially inclined gas mixture to suppress the temperature of the combustion products, and inject the remaining gas through the axial gas stage tube.

[0009] An exemplary radiant tube burner assembly includes a staged recirculation burner as described above, an outer radiant tube coupled to the burner, and an inner recirculation tube concentrically located within the outer radiant tube, wherein the outer radiant tube and the inner recirculation tube form an annular space between the inner and outer radiant tubes, and a rotating blade spacer is located within the outer radiant tube and between the distal end of the inner recirculation tube and the distal end of the outer radiant tube, so that combustion products flow through the annular space between the outer radiant tube and the inner recirculation tube. Attached Figure Description

[0010] The foregoing will be apparent from the more detailed description of exemplary embodiments of the invention shown in the following figures, wherein the same reference numerals refer to the same parts in different views. The figures are not necessarily drawn to scale, but rather focus on illustrating embodiments of the invention.

[0011] Figure 1 This is a schematic diagram illustrating a single-ended radiant (SER) tube burner assembly according to an exemplary embodiment of the present invention.

[0012] Figure 2 This is a schematic diagram illustrating a burner assembly according to an exemplary embodiment of the present invention.

[0013] Figure 3 This is a schematic diagram showing the inlet of a combustion air heat exchanger according to an exemplary embodiment of the present invention.

[0014] Figure 4 This is a schematic diagram illustrating a heat exchange surface according to an exemplary embodiment of the present invention.

[0015] Figure 5 This is a schematic diagram illustrating a gas pipe / gas nozzle assembly according to an exemplary embodiment of the present invention. Detailed Implementation

[0016] Exemplary embodiments of the present invention are described below.

[0017] Structure of Staged Recirculating Burner and Radiant Tube Burner Systems

[0018] Figure 1 An exemplary embodiment of a self-recuperative single-ended radiant tube burner system assembled in the chamber of a conventional heat treatment furnace is shown. Figure 1 The diagram shows a furnace wall 20, typically made of refractory material 21 with an outer metal skin 22 covering it. A self-regenerating single-ended radiant tube burner system includes an elongated (outer) radiant tube 23 disposed within the furnace chamber, made of silicon carbide, metal, or other suitable heat-resistant material. The outer radiant tube 23 extends through a cavity 25 within the furnace, its downstream end closed as shown in 24. The outer radiant tube 23 includes an outer flange 26, which is secured in place in a furnace mounting flange 14 on the furnace outer wall and can be held in place using an exhaust housing flange 28 for mounting a burner assembly 30 to the furnace. The burner assembly 30 is secured to and partially disposed within the radiant tube 23 to generate a high-velocity, high-temperature flame to adequately heat the furnace. An inner radiant tube 27, made of silicon carbide, is concentrically assembled within the outer radiant tube 23. The inner radiant tube 27 is appropriately positioned downstream (far end) (e.g., three inches) of the outer tube 23 using spacers (rotating blades) 29. The length of the inner tube 27 is furnace-specific, but the inlet face 31 coincides with the inner furnace refractory wall 20. Similarly, the outlet component (i.e., the combustion nozzle 32) of the burner assembly 30 is parallel to the inner wall of the refractory wall 20 and the surface of the inner radiant tube 31.

[0019] refer to Figure 2 The combustor may contain multiple components, including, for example, an exemplary staged recirculation combustor assembly 30: an inlet housing 34, a gas conduit 37, an exhaust housing 43, a heat exchanger 42 (e.g., the heat exchanger disclosed in U.S. Patent No. 8,162,040), a gas nozzle 51, and a combustion tube 47. Combustion air is guided by a conduit, enters the combustor inlet housing 34 via an orifice 36, and communicates with a blower (not shown) or other means for generating a forced flow of combustion air. A fuel supply line 35, communicating with the elongated gas conduit 37, is also connected to the combustor inlet housing 34.

[0020] Gas pipe 37 extends downstream through heat exchanger 42, across the central axis of the assembly, and into combustion pipe 47, where it supports gas nozzle 51. Inlet housing 34 and gas nozzle 51 can be specifically designed to communicate in such a way that spark plug 19 and flame sensor 18 (… Figure 1 It can be placed inside the gas tube 37. For example... Figure 5As shown, spark plug 19 can extend through gas nozzle 51 via 51B, and the electrode can be positioned approximately one inch downstream of 51B to ignite the fuel / air mixture exiting from it. Flame sensor 18, connected to an indicator, can extend through gas nozzle 51 via 51C and can be located approximately three inches downstream. Flame sensor 18 detects the presence of a flame and indicates when the flame extinguishes via appropriate indication. Gas tube 37 can be made of 1.5" process 80 stainless steel tubing to withstand the high temperatures generated by downstream combustion itself and the reheating of the combustion gases through combustion tube 47 and heat exchanger 42. Gas nozzle 51 can be made of silicon carbide to provide enhanced exposure to high-temperature environments and allow for a stable and consistent delivery of natural gas. Gas nozzle 51 can be assembled into gas tube 37 and secured using set screws (e.g., three set screws 37A spaced 120 degrees apart), as... Figure 3 As shown. The small gap 37B created by the inner diameter of the gas tube 37 and the outer diameter of the gas nozzle 51 can be sealed with ceramic putty to ensure that no gas flows through the gap space.

[0021] Once combustion air enters the inlet housing 34 through inlet port 36, it fills the void 38 around gas pipe 37. Figure 2 A gasket 39 between the burner inlet housing 34 and the heat exchanger spacer flange 40 seals the combustion air into the gap and forces air into the inlet portion of the heat exchanger 42 (e.g., about three inches long), where air begins to be drawn into a single port forming a rounded rectangular channel. In some exemplary embodiments, there may be six separate ports. Figure 3 An exemplary inlet of heat exchanger 42 is shown.

[0022] The heat exchanger 42 can be held in place between the burner inlet housing 34 and the exhaust housing 43 (e.g., an inlet with a concentrically inserted heat exchanger flange) by compression of the spacer flange 40. The exhaust housing 43 is lined with a high-temperature insulating sleeve 44 that fills the space between the inner diameter of the exhaust housing 43 and the outer diameter of the heat exchanger 42. This insulation acts as a barrier between the physical structures of the heat exchanger 42 and the exhaust housing, keeping the temperature sufficiently low for it to be made, for example, of ordinary low-carbon steel.

[0023] The insulating sleeve 44 is locked in the spiral annular space 42E on the outer surface created by the spiral heat exchanger air passage 42D. Figure 4 Combustion air travels axially and spirally up to 7 inches per revolution, for example, through a rounded rectangular channel. For example, after approximately nine revolutions, all the air is in the transition zone 42B between heat exchanger 42 and combustion tube 47. Figure 2 The combustion tube 47 can be, for example, about 3.25 inches long.

[0024] The heat exchanger 42 and the combustion tube 47 can be connected via a dedicated silicon carbide thread 47A. Figure 2 The heat exchanger 42 may have a special female thread, while the combustion tube 47 may have a special male thread. This connection allows the heat exchanger to be of standard length and the combustion tube to be adjusted to fit the furnace application. Once combustion air enters the combustion tube 47, it enters through the outer diameter 50 of the gas pipe. Figure 2 ), combustion tube 47 ( Figure 2 The inner diameter of the combustion air and the inner diameter of the spiral fin passage 47B create another spiral annular space, which extends axially downstream at a speed of, for example, about 1.67 inches per revolution, and terminates at the combustion nozzle 32. For example, as the combustion air moves 5 revolutions axially and radially, the air is drawn through the staged gas nozzle 51, where natural gas passes through, for example, eight small holes 51A spaced about 45 degrees circumferentially. Figure 5 The gas / air mixture is then injected into the combustion air. The gas / air mixture then continues to move axially and radially at a speed of 1.67 inches per revolution, for example, approximately two full revolutions before entering the combustion nozzle 32. Simultaneously, the staged gas extension tube 51D ( Figure 5 The gas downstream of the centrifugal air and gas mixture is injected into the combustion nozzle 32 and enters the inner radiant tube 27 for intentional staged combustion. The cross-sectional area ratio of the radial orifice to the axial orifice ranges from 1:1 to 10:1, such that the amount of radially discharged gas is between 50% and 90% of the total gas.

[0025] The gas / air mixture then enters the outlet end of the combustion tube 47 and is delivered through the combustion nozzle 32, which is arranged as a tapered converging tube (this term may be used interchangeably with combustion nozzle 32 herein), and is designed so that when the orifice 32A directs the flame toward the inner radiating tube 27 ( Figure 1 The flame velocity is increased during combustion. Combustion is completed inside the inner radiant tube 27, and the heat products of combustion flow downwards along the tube towards the downstream end of the outer tube 24, where the hot gas is rotated 180 degrees and forced to flow in the opposite direction to the first end of the inner radiant tube 31 through the annular gap between the outer radiant tube 23 and the inner radiant tube 27. As combustion products near the first end of the inner radiant tube 31, the high-speed flame generated by the tapered converging tube entrains some of the gas that is recycled back into the ongoing combustion.

[0026] Both helical inserts in heat exchanger 42 and combustion tube 47 can be made of silicon carbide. The helical fluid channel design increases the conductive heat transfer surface area of ​​the outer ceramic walls of the two heat exchange surfaces. The advantage of the silicon carbide composition is that the thermal expansion of the two components is smaller when subjected to significant temperature changes than if they were made of other materials. This also enhances the compatibility and connection of the helical heat exchanger with the rest of the burner system, reducing thermal stress that may be associated with the inter-component connections under high-temperature operating conditions.

[0027] When the heat-generating products leave the annular space, a portion of the heat-generating products are recycled, while most of them enter the inner diameter 15 of the outer radiant tube 23. Figure 1 The combustion tube 47 has an outer diameter of 16 and an annular channel formed by a spiral fin passage (e.g., 1.67 inches per turn) extending along the length of the combustion tube 47 toward the exhaust housing 43. A cross-section of this spiral fin passage 47B is shown in... Figure 2 The fins extend from the inner side of the combustion tube 47; therefore, fluid paths are sequentially arranged on both sides of the combustion tube to conduct heat transfer through the ceramic walls that separate the fluid. The increased heat transfer surface area generated by the inner and outer finned combustion tube 47 sufficiently reduces the exhaust gas temperature, allowing the high-efficiency heat exchanger 42 to be installed outside the single-ended radiant tube burner system (exhaust housing 44) while maintaining a sufficiently low temperature so that it can be made of, for example, ordinary low-carbon steel.

[0028] As the combustion products leave the first regenerative section generated by the combustion tube 47, the products are transferred to the exhaust housing 43, where they enter the heat exchanger 42, the spiral combustion air passage 42D, and the insulating sleeve 44. Figure 2 The spiral gap 42E formed by ) Figure 4 Combustion gases pass through an annular gap of approximately 0.8 inches per revolution, covering the entire axial length of the heat exchanger, and ultimately exit through the exhaust casing outlet 33. Figure 1 The heat exchange fluid at the exhaust casing outlet 33 is so hot that heat that would otherwise be lost to the atmosphere has been transferred to the combustion air, heating it to a temperature between 1050°F and 1250°F, and significantly improving the efficiency of the self-regenerating single-ended radiant tube burner system.

[0029] The aforementioned exemplary features include a combustion tube with helical fins on both the inner and outer surfaces, forming helical fin passages (e.g., which may extend at 1.67 inches per turn), sequentially setting the fluid paths for combustion air (inner) and combustion heat products (outer) for conductive heat transfer through a ceramic wall separating the fluids. The increased heat transfer surface area generated by the inner and outer finned combustion tubes sufficiently lowers the exhaust gas temperature, allowing a high-efficiency heat exchanger to be installed in the exterior (exhaust housing) of a single-end regenerative (SER) burner, maintaining a sufficiently low temperature to allow the exhaust housing to be made, for example, from ordinary low-carbon steel. The inner helical fins also provide improved mixing characteristics as natural gas is dispersed into the already rotating combustion air through a gas nozzle strategically located downstream of the combustion nozzle. This improved mixing results in reduced combustion losses as the gas / air mixture is accelerated through a tapered converging tube (combustion nozzle) and the flame is ignited.

[0030] Another exemplary feature includes the specific selection and assembly of the combustion tubes and heat exchangers. An advantage of the silicon carbide composition is that the thermal expansion of the combustion tubes and heat exchangers is less when subjected to significant temperature variations than if they were made of other materials. This also enhances the ability of the spiral heat exchanger to be matched and connected to the rest of the burner system, reducing thermal stress that may be associated with inter-component connections under high-temperature operating conditions. The combustion tubes and heat exchangers can be connected via specialized silicon carbide threads, where the heat exchanger has a special female thread and the combustion tube has a corresponding male thread. This thread allows the heat exchanger to be of standard length, and the combustion tube length to be adjusted for specific furnace applications.

[0031] Another exemplary feature includes a heat exchanger for a unique channel orientation. Combustion air can be introduced into individual ports (e.g., six ports) in the inlet section, forming rounded rectangular channels that allow the combustion air to pass through axially and helically, for example, at approximately 0.8 inches per turn. The combination of short cycles and helical structure significantly increases the heat transfer surface area and allows for maximum heat transfer between the incoming combustion air and the outgoing combustion products. The heat exchanger can operate without requiring the provision of an oversized blower or expansion method, thereby generating forced air at an increased rate to overcome the pressure drop caused by the channel design.

[0032] Another exemplary feature includes a silicon carbide axial tube through the gas pipe nozzle. Silicon carbide provides enhanced exposure to high-temperature environments with minimal thermal expansion, allowing for stable and consistent dispersion of natural gas. Radial orifices in the nozzle inject gas into a helical flow of preheated combustion air, thereby increasing mixing characteristics and resulting in reduced combustion losses. The axial orifices allow the spark and flame rod to be located inside the gas pipe and inserted into the ignition point. The axial tube through the gas pipe nozzle allows gas to flow axially into the downstream combustion nozzle and into the inner radiant tube before the centrifugal air and gas mixture for intentionally staged combustion.

[0033] The disclosed exemplary embodiments offer advantages over existing systems, such as increased efficiency, more customizable combustion tube length, above-average hot spot (HSOA) uniformity of less than 50 degrees Fahrenheit (which provides more uniform heating of the load and longer tube life when using an alloy outer tube), NOx emissions of less than 240 ppm and CO emissions of less than 10 ppm at all fire rates with 3% oxygen, and optional all-ceramic designs (e.g., gas nozzles, inner tubes, outer tubes, heat exchangers, and combustion tubes), which enable high-temperature applications and reduce maintenance cycles compared to existing alloy and ceramic single-end regenerative (SER) burners.

[0034] Operation of staged recirculation burner and radiant tube burner systems

[0035] As described above, exemplary specific embodiments may include, for example, Figure 2 The components shown include a gas pipe 37, an exhaust housing 43, a preheating flow reducer 42A, an exhaust insulation sleeve 44, a threaded combustion pipe connector 47A, an inner and outer finned combustion pipe 47, a staged gas nozzle 51, a combustion nozzle 32, a centering spacer 29, an air / gas inlet housing 34, an air inlet 36, a gas inlet 35, a gas stager 10, and a heat exchanger 42. This staged recirculation burner can operate in a radiant tube combustion system, which may include, for example, a gas stager 10. Figure 1 The inner furnace wall 20, furnace refractory material 21, outer refractory wall / shell 22, outer radiant tube 23, outer radiant tube cap and support 24, refractory furnace opening 25, outer radiant tube flange 26, support flange 14, inner recirculation pipe 27, flame rod 18 and igniter 19 are shown.

[0036] As an example of operation, gaseous fuel enters gas inlet 35 and air / gas inlet housing 34, while air enters air inlet 36 of air / gas inlet housing 34 at an air-to-gas ratio, for example, between about 5:1 and 15:1, sufficient to produce a flame and combustion products upon ignition. The gaseous fuel travels downward along gas pipe 37, where it enters staged gas nozzle 51, which may include radial outlet orifices and axial gas stage pipes 10. The cross-sectional area ratio of the radial orifice to the axial pipe may be, for example, 1:1 to 10:1, such that the amount of radially discharged gas is between 50% and 90% of the total gas. Simultaneously with the gaseous fuel, air enters the fluid inlet of heat exchanger 42 and the internal spiral passage of heat exchanger 42, which may have a substantially rectangular cross-section. The air receives energy from the outer wall of the spiral passage and is preheated to a temperature greater than 400 degrees Celsius before leaving the spiral passage of heat exchanger 42 as preheated air, and then flows into preheating converging tube 42B. The outer wall of the spiral channel receives energy from the heat-generating products flowing through the surrounding fluid path, and the outer spiral channel forms a fluid path with a generally rectangular cross-section through the outer wall. As energy is transferred to the outer wall and further to the air flowing through the heat exchanger 42, the heat-generating products are cooled. The heat-generating products are discharged through the exhaust casing 43. The exhaust casing 43 includes an exhaust insulating sleeve 44, which minimizes heat loss to the atmosphere and allows the maximum amount of heat to be transferred to the outer spiral wall, and thus to the air.

[0037] Preheated air enters a preheating flow converging tube attached to the inner and outer finned combustion tube 47, which itself can be attached to the preheating flow converging tube via a threaded ceramic combustion tube connector 47A. Within the inner and outer finned combustion tube 47, the preheated air is further heated to a highly preheated air temperature exceeding 500 degrees Celsius by heat-generating products flowing over the exterior of the inner and outer finned combustion tube 47, which contains one or more helical fins. The inner and outer finned combustion tubes cool the heat-generating products, where the outer radiating tube 23 and the outer radiating tube flange 26 can be mounted between the stepped flange 14 and the exhaust housing flange 43 without using excessively high-temperature materials.

[0038] Highly preheated air exits the fins of the inner and outer finned combustion tubes 47 in a helical flow path, wherein the staged gas nozzle 51 is positioned to radially inject gas into the helical flow of the highly preheated air. The position of the staged gas nozzle 51 and its radial orifices ensures that the air-gas mixture is properly mixed to form a mixture ignitable by the tip of the igniter 19, and flows into the combustion nozzle 32 for further combustion, which is attached to the inner and outer finned combustion tubes 47, for example, via a high-temperature ceramic threaded connection. Not all gas is injected through the radial orifices of the staged gas nozzle 51. The ignited mixture is substantially lean to suppress the temperature of the exothermic products, which suppresses the formation of nitrogen oxides. The exothermic products exit the combustion nozzle 32 at a velocity sufficient to entrain the exothermic products flowing through the annular space formed by the inner recirculation tube 27 and the outer radiating tube 23 and further through the opening formed between the combustion nozzle outlet 32A and the interior of the inner recirculation tube 27. The heat-generating products are at a sufficiently low temperature to ensure that the heat-generating products leaving the combustion nozzle are sufficiently diluted, so as to further reduce the formation of nitrogen oxides before the heat-generating products are completely burned in the internal recirculation pipe 27 through exhaust gas recirculation.

[0039] The final amount of gas is injected into the partially combusted heat products through an axial tube that extends from the staged gas nozzle 51 and enters the combustion nozzle 32. The gas is completely combusted before leaving the end of the inner recirculation tube 27. The combination of lean combustion, recirculation of heat products, and gas staging of combustion products is sufficient to suppress the formation of nitrogen oxides, minimize the combustion temperature to suppress nitrogen oxide formation, and improve the temperature uniformity of the heat released from the outer radiant tube 23.

[0040] The heating products can be oriented by a centering spacer (rotating blade) between the annular spacer formed by the outer radiant tube 23 and the inner recirculation tube 27. This centering spacer (rotating blade) can include at least two uniform fins and promotes the flow reversal from the heating products into the formed annular space. As the heating products flow within the formed annular space, a significant amount of energy is transferred to the wall of the outer radiant tube 23 through convection and radiative heat transfer. Energy is also transferred through the wall of the outer radiant tube 23 via conduction. A significant amount of energy is transferred from the outer radiant tube 23 to the inner furnace wall 20 via radiative heat transfer. When the heating products leave the annular space, a portion of the heating products is recirculated, while the majority enters the outer fins of the inner and outer finned combustion tubes 47. As described above, the heating products are cooled by flowing through the inner and outer finned combustion tubes 47 and the heat exchanger 42 before leaving the system at the outlet of the exhaust shell 33.

[0041] While exemplary embodiments have been specifically shown and described above, those skilled in the art will understand that various changes in form and detail may be made without departing from the scope of the invention. For example, the outer tube 23 may be finned, bladed, and / or twisted to improve heat transfer. The inner tube 27 may be finned, bladed, and / or segmented to improve heat transfer uniformity, combustion, and recirculation. The combustion nozzle 32 may include a single or multiple nozzles, which are not necessarily circular, and may include orifice extensions for air staging. The gas nozzle 10 may include radial, axial, tangential, and / or inclined orifices, which are not necessarily circular, and may include orifice extensions for gas staging. Orifices may, for example, be circular, elliptical, square, slotted, or porous. The combustion tube 17 may be finned, bladed, and / or twisted to improve heat transfer. The rotating blade 29 may be helical or U-shaped with an inlet point to separate the flow. The inner tube 27 and outer tube 23 may use staging helices (rifling) or staging fins to reduce variations in above-average hot spots (HSOA) and lower HSOA values. For example, the first third of the tube may be smooth, while the latter two-thirds may have fins. The outer tube 23 may be an alloy tube with a demodulated silicon carbide air heater, which would be a low-pressure, reduced-efficiency system, allowing for the installation of a higher-pressure, higher-efficiency air heater. The heat exchanger 42 may have fins, blades, and / or segments to improve heat transfer uniformity and combustion. The gas nozzle 10 may extend or retract, and its length is variable, combined with variations in the shape and diameter of the tapered constrictor 32 and the orifice 32A to alter the emissions and thermal characteristics of the radiant tube heating system.

Claims

1. A staged recirculation burner assembly, comprising: The inlet housing is configured to receive fuel and combustion gases; A heat exchanger having a first end and a second end, wherein the heat exchanger communicates with a gap at its first end to receive combustion gases from the inlet shell; A combustion tube, adjustablely connected to a second end of a heat exchanger, includes helical fins forming a helical path, the helical path including a first helical path extending axially downstream for combustion gases and a second helical path extending axially upstream for combustion products, and the combustion tube also includes a combustion nozzle having an outlet. A gas tube, arranged within the inlet housing and extending axially from a first end to a second end of the heat exchanger within a combustion tube, wherein a first helical path is confined between the gas tube and the combustion tube; and A staged gas nozzle connected to the outlet end of a gas tube to receive fuel from the gas tube includes a radial outlet orifice near the outlet end of the gas tube, the radial outlet orifice being configured to inject only a portion of the fuel in the gas tube into a helical flow of combustion gases flowing through a first helical path to form a fuel mixture that continues to travel along the first helical path before moving into the combustion nozzle; the staged gas nozzle also includes an axial gas stager downstream of the radial outlet orifice and extending into the combustion nozzle, the axial gas stager having an outlet upstream of the outlet of the combustion nozzle, wherein the axial gas stager is configured to simultaneously inject the remaining fuel in the gas tube into the combustion nozzle downstream of the ignited fuel mixture; The heat exchanger includes a combustion passage configured to use combustion products to heat the combustion gases.

2. The burner assembly of claim 1, wherein, The heat exchanger remains in place between the inlet casing and the exhaust casing.

3. The burner assembly as claimed in claim 1, wherein, The combustion nozzle is detachably attached to the combustion tube via a high-temperature ceramic threaded connection.

4. The burner assembly as claimed in claim 1, wherein, The combustion tube includes a ceramic wall that separates the first and second helical paths.

5. The burner assembly of claim 1, wherein, The combustion tube is made of silicon carbide.

6. The burner assembly of claim 1, wherein, The combustion nozzle is a tapered converging tube.

7. The burner assembly of claim 1, wherein, The inlet shell, heat exchanger, combustion tube, gas tube, staged gas nozzle, and axial gas stager are coaxial.

8. The burner assembly of claim 2, further comprising an insulating sleeve located between the inner diameter of the exhaust housing and the outer diameter of the heat exchanger.

9. The burner assembly of claim 8, wherein, The combustion passage of the heat exchanger is defined by the insulating sleeve.

10. The burner assembly of claim 1, wherein, The heat exchanger includes a plurality of inlets at its first end, the plurality of inlets being configured to receive combustion gases from the void.

11. The burner assembly of claim 10, wherein, Each of the plurality of inlets is connected to one of the combustion channels.

12. The burner assembly of claim 1, wherein, The heat exchanger includes a transition section at its second end, the transition section being configured to deliver combustion gases to the combustion tube.

13. The burner assembly of claim 1, wherein, The first and second ends of the heat exchanger are coaxial.

14. The burner assembly of claim 1, wherein, The inlet housing is configured to receive combustion gas and fuel in a ratio between 5:1 and 15:

1.

15. The burner assembly of claim 1, wherein, The combustion tube is adjustablely connected to the second end of the heat exchanger via a silicon carbide thread.

16. A radiant tube burner system, comprising: The staged recirculation burner assembly as claimed in claim 1; An external radiating tube is connected to the burner assembly; An inner recirculation tube is concentrically located inside the outer radiation tube, and the outer radiation tube and the inner recirculation tube form an annular space therebetween; as well as Rotate the blade spacer, located inside the outer radiator and positioned between the distal end of the inner recirculation tube and the distal end of the outer radiator, so that combustion products flow through the annular space between the outer radiator and the inner recirculation tube.

17. The burner system of claim 16, wherein, The external radiation tube is made of silicon carbide.

18. The burner system of claim 16, wherein, The internal recirculation tube is made of silicon carbide.

19. The burner system of claim 16, wherein, The combustion nozzle carries a portion of the combustion products through the annular space between the outer radiating tube and the inner recirculation tube.

20. The burner system of claim 16, wherein, The heat exchanger, combustion tube, gas tube, staged gas nozzle, axial gas stager, external radiant tube, internal recirculation tube, and rotating blade spacer are coaxial.

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