Low NOx combustor with target gas injection

Abstract

A combustor configured to generate a flame in a combustion zone is provided, where the combustor includes a combustion air conduit providing combustion air to the combustion zone, a target gas conduit surrounded by the combustion air conduit, and a fuel gas conduit surrounding the combustion air conduit, the combustion system includes a target gas conduit surrounded by a target gas conduit that provides a target gas, such as a NOx reducing medium, to the combustion zone, and a fuel gas conduit surrounded by the target gas conduit that provides a fuel gas to the combustion zone where a portion of the fuel gas is mixed with a portion of the target gas and then mixed with combustion air in the combustion zone.

Description

[0001] Related Applications

[0002] This application claims priority to U.S. Provisional Patent Application Serial No. 63 / 384,769, filed on Nov. 22, 2022, the entire content of which is incorporated herein by reference. Technical Field

[0003] The present invention generally relates to a gas burner and, more particularly, to a gas burner that utilizes a target gas such as a NOx reduction medium to reduce NOx production. Background Art

[0004] Petroleum refining and petrochemical processes typically involve heating process streams in furnaces. The interior cavity of the furnace contains tubes that hold the process streams. The interior cavity is heated by a plurality of gas burners that receive fuel for combustion to generate heat.

[0005] One area of concern with gas burners is the production of NOx gases. It should be understood that NOx refers to nitrogen oxides, which mainly consist of nitric oxide NO and nitrogen dioxide NO2. It is believed that there are at least three main NOx formation mechanisms during combustion, namely thermal NOx, fuel NOx, and prompt NOx. See "Nitrogen Oxides (NOx), What and How They are Controlled", EPA Technical Bulletin, November 1999 (available at: https: / / www3.epa.gov / ttncatc1 / dir1 / fnoxdoc.pdf).

[0006] The formation of NOx in known gas burners can be mitigated by staging the fuel and air and creating a primary combustion (flame) zone and a secondary combustion (flame) zone. Staged air burners and staged fuel burners mainly act on the thermal NOx and prompt NOx formation processes. The highest flame temperature is achieved when the gaseous fuel and combustion air are thoroughly mixed and burned rapidly in stoichiometric or near-stoichiometric proportions, thereby realizing the maximum potential for thermal NOx formation.

[0007] Therefore, staged air burners and staged fuel burners seek to reduce the temperature of the flame, thereby reducing NOx production. Classic staged fuel burners or staged air burners form two combustion zones for non-stoichiometric combustion.

[0008] In the case of a staged fuel burner, all the combustion air passes through the primary combustion zone and then enters the secondary combustion zone together with a portion of the combustion products from the primary combustion zone. In this case, the primary combustion zone is lean, having an excess of combustion air. The lean combustion reduces the flame temperature to some extent because the mass of all the combustion air rapidly absorbs the heat in the flame and discharges it from the primary combustion zone, allowing time (measured in milliseconds) for the heat to radiate from the primary combustion zone to the surrounding environment, including heaters, boilers, or furnace process tubes. The combustion products of complete and / or partial combustion (reactions) are transferred from the primary combustion zone to the secondary combustion zone or the staged combustion zone. This transfer allows time (also measured in milliseconds) for the products from the primary combustion zone to further radiate heat to the surrounding environment and the process tubes. Thus, the slightly cooled combustion products from the primary combustion zone serve to conduct heat in the secondary combustion zone and cool the secondary combustion zone. Additionally, the combustion reaction in the secondary combustion zone generally occurs under relatively lean conditions because typical process heaters, boilers, or furnaces operate under lean conditions with 5% to 25% excess combustion air. Therefore, the combustion process is completed to an appropriate extent to achieve an industrially acceptable efficiency level, i.e., 5% to 25% excess air.

[0009] Classic staged air burners reverse the staging process and introduce all the fuel gas for combustion in the primary combustion zone and only introduce a portion of the combustion air. In the case of a staged air burner, the primary combustion zone can operate sub-stoichiometrically, and since the reactants and products pass through the secondary combustion zone, an industrially acceptable excess air level, i.e., 5% to 25% excess air, is achieved. For a staged air burner, the reactants must pass through a region close to stoichiometry where the flame temperature is high and thermal NOx is thereby formed, so it may be difficult for a staged air burner to achieve very low NOx emissions.

[0010] Recently, internal flue gas recirculation burners have utilized flue gas within a heater or furnace combustion chamber, which is actuated by fuel gas and mixed into the primary and secondary combustion zones. This flue gas (relatively cold, large quantities of combustion products (flue gas)) enters and passes through the combustion zone, thereby further cooling the combustion zone and reducing the formation of thermal NOx. Water vapor within the flue gas also serves to mitigate NOx generated via the prompt NOx mechanism through solvation and catalytic hydrocarbon combustion, which is achieved through the recently understood water-gas shift reaction ("WGSR") mechanism, as described by Jan De Ren, Kurt Kraus, and Chris Ferguson in "A Paradigm Shift in Steam-Assisted Elevated Flare Systems" at the International Flame Research Foundation in July 2020. Since the combustion products from the primary combustion zone to the secondary combustion zone include some water vapor, these WGSR mechanisms also exist to a limited extent in classical or conventional staged fuel or staged air burners.

[0011] In some combustion systems, selective catalytic reduction (SCR) systems are used for post-treatment of flue gas for NOx emissions. SCR systems are an effective way to reduce NOx in the flue gas stream, reducing it by up to 95%. However, such systems require space for the catalyst and structure, high capital investment and operating costs, form other undesirable emissions, and form undesirable substances that can cause catalyst poisoning and deactivation.

[0012] Both staged air burners and staged fuel burners may require and produce a large number of flames to achieve low NOx emissions. Modern heater and furnace designs must be designed for larger and more costly combustion chambers so that staged fuel burners and staged air burners can produce more low-NOx emission burner flames.

[0013] Accordingly, there remains a need for a burner with low NOx production and without these drawbacks. SUMMARY OF THE INVENTION

[0014] A new type of burner and its method of use have been invented and utilize a target gas, i.e., a NOx reduction medium or a mixture of NOx reduction media, to reduce NOx emissions generated during combustion in the burner. Specifically, the burner is configured such that the target gas and / or the internal recirculation flue gas flows between the combustion air and the fuel gas supplied to the combustion zone of the burner, which causes the target gas and / or the internal recirculation flue gas to mix with the fuel gas and then mix with the combustion air in the combustion zone. Thus, the "inert" components (CO2, N2, H2O) of the gas and / or the NOx reduction medium are mixed with the fuel gas to promote conductive heat transfer of the combustion reactants (fuel and air) from the start of combustion to the entire combustion reaction, so as to reduce the incident flame temperature or the peak flame temperature during the combustion process. Reducing the peak flame temperature reduces the oxidation of nitrogen in the combustion air or the fuel gas in the reaction zone (flame), and thereby reduces the formation of thermal NOx, which is the NOx formed during the combustion of the fuel gas. Moreover, the water vapor in the gas (NOx reduction medium) is used to solvate and catalyze the combustion reaction to reduce the activation temperature of the combustion reactants, thereby further reducing the peak flame temperature and thus reducing the NOx emissions.

[0015] Accordingly, a broad feature of the present invention may lie in providing a burner configured to generate a flame in a combustion zone, wherein the burner includes a combustion air conduit, a target gas conduit, and a fuel gas conduit, the combustion air conduit supplying combustion air to the combustion zone, the target gas conduit being surrounded by the combustion air conduit and supplying a gas, and more specifically a NOx reduction medium, to the combustion zone, the fuel gas conduit being surrounded by the target gas conduit and supplying fuel gas to the combustion zone, wherein a portion of the fuel gas is mixed with a portion of the target gas and then mixed with the combustion air in the combustion zone.

[0016] In other embodiments, the fuel gas conduit includes an inlet that draws additional flue gas from a combustion source. Also, the combustion air conduit may have a closed end and an opening at the closed end, where the target gas (NOx reduction medium) flows across the closed end, thereby forming a fluid barrier between the combustion air and the fuel gas. Additionally, the target gas conduit may include a closed end and an opening at the closed end for injecting the target gas into the combustion zone. Similarly, the fuel gas conduit may include a closed end and an opening at the closed end for injecting the fuel gas into the combustion zone. In one embodiment, a portion of the fuel gas is injected through the inlet into the combustion air conduit and mixed with a portion of the combustion air before reaching the combustion zone. In another embodiment, a portion of the target gas is mixed with a portion of the combustion air and then enters the combustion air conduit, where the remaining portion of the target gas enters the target gas conduit. In additional embodiments, an amount greater than 0% to equal to 95% of the target gas is mixed with the combustion air and then enters the combustion air conduit, where the remaining portion of the target gas enters the target gas conduit. In one embodiment, the combustion air in the combustion air conduit is preheated to a predetermined temperature. Additionally in one embodiment, the combustion air in the combustion air conduit includes enriched oxygen or pure oxygen. The burner may also include a controller configured to control the flow rate of the combustion air in the combustion air conduit, control the flow rate of the gas (NOx reduction medium) in the target gas conduit at a predefined ratio, and the flow rate of the fuel gas in the fuel gas conduit. In one embodiment, at least one orifice extends between the combustion air conduit and the target gas conduit. In another embodiment, at least one orifice extends between the target gas conduit and the fuel gas conduit.

[0017] In another aspect, the features of the present invention may reside in providing a method for reducing the production of NOx gas at a burner, where the method includes injecting combustion air into the combustion zone, injecting a target gas into the combustion zone, and injecting fuel gas into the combustion zone, where a portion of the fuel gas is mixed with a portion of the target gas and then mixed with the combustion air in the combustion zone.

[0018] In another aspect, the features of the present invention may lie in a method for using a control system to control a burner to reduce the production of NOx gas during combustion, wherein the method includes enabling a purge program, and closing the inlet and outlet valves leading to the blower and the recirculation line to prevent the accumulation of combustible gas in the burner, and opening the inlet and outlet valves leading to the blower and the recirculation line when the purge program is completed, wherein, during the purge program, at least one blower in the burner is automatically started and supplies combustion air to the burner and the recirculation line. In one embodiment, completing the purge program includes replacing at least four full volumes of air in the burner. In another embodiment, the method further includes electrically interlocking to start the burner until the purge program is completed. In another embodiment, the method further includes controlling at least one motor of the blower, and the at least one motor is a variable frequency drive motor.

[0019] In another aspect, the features of the present invention lie in a method for using a control system to control a burner to reduce the production of NOx gas during combustion, wherein the method includes operating the burner in a standby mode until the temperature of the combustion chamber in the burner is at a predetermined minimum temperature, and when the temperature of the combustion chamber of the burner is at the predetermined minimum temperature, operating the burner in an operating mode.

[0020] In another aspect, the features of the present invention lie in a method for using a control system to control a burner to reduce the production of NOx gas during combustion, wherein the method includes directly injecting a NOx reduction medium into the combustion chamber in the burner and controlling the injection of the NOx reduction medium into the combustion chamber in proportion to the composition of the flue gas in the combustion chamber and the direct measurement result of the NOx emissions at the outlet of the burner. In one embodiment, the method includes controlling the rate of injection of the NOx reduction medium into the combustion chamber by changing the speed of the blower in the burner using a variable frequency drive motor.

[0021] In another aspect, the features of the present invention lie in a method for using a control system to control a burner in a burner system to reduce the production of NOx gas during combustion, wherein the method includes directly injecting a NOx reduction medium into the combustion chamber in the burner and controlling the injection of the NOx reduction medium into the combustion chamber in proportion to at least one of the amount of NOx at the outlet of the burner, the temperature at the outlet of the burner, the amount of oxygen in the flue gas, the flow rate and pressure of the flue gas in the combustion chamber, and the composition of the flue gas in the combustion chamber. In one embodiment, the method further includes controlling the rate of injection of the NOx reduction medium into the combustion chamber by changing the speed of the blower in the burner system using a variable frequency drive motor. In another embodiment, the method includes controlling the rate of injection of the NOx reduction medium into the combustion chamber by adjusting the position of the flow control valve in the burner system by adjusting the controller.

[0022] Additional aspects, embodiments, and details of the present invention (all of which may be combined in any manner) are set forth in the following detailed description of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] One or more exemplary embodiments of the present invention will be described below with reference to the following drawings, in which:

[0024] Figure 1A is a perspective view of a burner according to the present invention;

[0025] Figure 1B is Figure 1A a cross-sectional view of the burner shown;

[0026] Figure 2 is a cross-sectional view of another embodiment of a burner according to the present invention.

[0027] Figure 3 is associated with Figure 1A , Figure 1B and Figure 2 a schematic view of an embodiment of a control system associated with the burner in the embodiment shown. DETAILED DESCRIPTION

[0028] As described above, the present invention solves the problem of producing low NOx emissions in high-temperature furnace and heater systems, particularly in the case of burning fuel gases with a high hydrogen content and fuel gases that fluctuate from a high hydrogen content to a low hydrogen content. Specifically, the burner of the present invention utilizes a target NOx reduction medium such as N2, CO2, H2O, recycled flue gas, or any suitable combination of these gases to reduce NOx emissions to a level sufficient to eliminate the need for a selective catalytic reduction (SCR) system, thereby reducing the capital investment, operating costs, and carbon footprint of the high-temperature furnace and heater systems during installation and long-term operation. With these general principles in mind, one or more embodiments of the present invention will be described with the understanding that the following description is not intended to be limiting.

[0029] As Figure 1A and Figure 1B shown, the burner of the present invention (generally designated 30) includes a combination of a combustion air duct 32, a target gas duct 34, and a fuel gas duct 36.

[0030] The fuel gas conduit 36 is centered within the burner 30 and has a longitudinal axis 38 and a first diameter. The first end 40 of the fuel gas conduit 36 includes an inlet 42 for receiving fuel gas, and the opposite second end 44 is closed by a cap 46. The cap 46 can be formed separately and attached to the fuel gas conduit 36 by welding or other suitable attachment methods, or it can be formed integrally with the fuel gas conduit. As shown, at least one gas opening, preferably a plurality of spaced gas openings 48, extends or is formed along the circumference of the fuel gas conduit 36 at the second end 44 to inject the fuel gas into the primary combustion zone 50 within a combustion chamber (not shown), which can be a chimney or a furnace. The contemplated sources and / or compositions of the fuel gas include refinery fuel gas, synthetic fuel gas, process exhaust gas, natural gas, propane, butane, LPG, hydrogen up to 100% by volume, and any combination of the foregoing. The pressure of the fuel gas can vary between 0.07 bar and 2.07 bar (1 psig to 30 psig).

[0031] The target gas conduit 34 has a second diameter and extends along the longitudinal axis 38, wherein the second diameter of the target gas conduit 34 is greater than the first diameter of the fuel gas conduit 36 such that the target gas conduit surrounds the fuel gas conduit. The first end 52 and the opposite second end 54 of the target gas conduit 34 are both closed. Specifically, the first end 52 of the target gas conduit 34 includes a flange 56 that is fixed to the conduit 34 by a fastener. The second end 54 includes a cap 58 similar to the cap 46 of the fuel gas conduit 36 and has at least one gas opening, preferably a plurality of spaced gas openings 60, that extend along the circumference of the target gas conduit 34 at the second end 54. As Figure 1A and Figure 1B shown, the gas openings 60 are spaced from the fuel gas openings 48 and inject the target gas (NOx reduction medium) into the combustion zone 50. The target gas conduit 34 includes an inlet 62 at the first end 52 that is transverse to the longitudinal axis 38 and supplies the target gas and / or NOx reduction medium from a gas source such as a NOx reduction medium source to the target gas conduit 34.

[0032] The combustion air duct 32 has a third diameter and extends along a longitudinal axis 38, wherein the third diameter of the combustion air duct 32 is greater than the second diameter of the target gas duct 34 and the first diameter of the fuel gas duct 36 such that the combustion air duct 32 surrounds the target gas duct 34 and the fuel gas duct 36. Similar to the target gas duct, the combustion air duct 32 includes a first end 64 closed by a flange 66 and an opposite second end 68 closed by a cap 70, the flange being fixed to the duct by fasteners, the cap being formed separately and fixed to the duct 32 by welding or other suitable attachment means, or being integrally formed with the duct. The combustion air duct 32 also includes at least one air opening, preferably a plurality of spaced apart air openings 72, at the second end 68, wherein the air openings 72 extend around the circumference of the duct 32 and are spaced apart from the fuel gas openings 48 and the gas openings 60. In the illustrated embodiment, the combustion air duct includes two rows of air openings. It is contemplated that the combustion air duct 32 may have a single row or multiple rows of air openings 72. Additionally, the combustion air duct 32 includes an inlet 74 at the first end 64 of the duct that is transverse to the longitudinal axis 38 and receives air, also referred to as combustion air, wherein the air flows along the combustion air duct 32 as shown by arrow 76 and injects the combustion air into the combustion zone 50 through the air openings 72.

[0033] In operation, the target gas duct 34 of the burner 30 of the present invention receives a target gas such as a NOx reduction medium or a mixture of NOx reduction media through an inlet 62 such that the target gas flows along the outer surface of the fuel gas duct 36 as shown by arrow 78, such that the target gas (NOx reduction medium) is located between the combustion air and the fuel gas to effectively form a barrier between the combustion air and the fuel gas, whereby the target gas can mix with the fuel gas and then mix with the combustion air in the combustion zone 50. Moreover, the fuel gas is injected at a specific location where it also draws flue gas from a combustion source such as a surrounding furnace (not shown). Thus, as Figure 1A and Figure 1BAs shown, at least a portion of the target gas and at least a portion of the fuel gas are mixed together and then mixed with at least a portion of the combustion air in the combustion zone. The burner 30 of the present invention thus effectively surrounds the fuel gas with both the internally recirculated flue gas and / or the externally recirculated target gas (NOx reduction medium), thereby forcing the internal flue gas and the target gas to mix with the fuel gas and then with the combustion air. In this way, the "inert" components of the target gas and / or the NOx reduction medium such as CO2, N2, H2O are physically mixed with the fuel gas to promote conductive heat transfer of the combustion reactants (fuel and air) from the start of combustion to the entire combustion reaction, thereby achieving the maximum effect of reducing the incident flame temperature or the peak flame temperature during the entire combustion process in the combustion zone 50. Reducing the peak flame temperature reduces the oxidation of nitrogen entering the combustion zone (flame) in the combustion air or fuel, thereby reducing the formation of thermal NOx.

[0034] In addition, the water vapor in the NOx reduction medium, or steam injected as the NOx reduction medium, is used to solvate and catalyze the combustion reaction, thereby reducing the activation temperature of the combustion reactants and thereby reducing the incident flame temperature and the peak flame temperature formed in the combustion zone, which further reduces the NOx emissions.

[0035] By making the NOx emissions low enough (usually below 5 ppmvd to 20 ppmvd) without the need for SCR or other similar NOx reduction equipment, the capital investment and operating costs required to achieve regulatory NOx emissions are greatly reduced. For example, a burner with the target flue gas recirculation system (TFGR system) of the present invention can reduce the total installation cost by more than 50% to 90%. Additionally, of course, the amount of steel, refractory materials, and other materials required for the construction of the burner on a new burner system or a modified system, as well as the carbon footprint, are greatly reduced. The additional NOx reduction system using a catalyst, catalyst bed, housing, ammonia injection system, ammonia supply truck transportation, receiving, tank storage, and delivery system is entirely replaced by the burner 30 and the TFGR system of the present invention.

[0036] See Figure 2 , which shows another embodiment of the burner 30 according to the present invention, where the same reference numerals are used for the same features.

[0037] Figure 2The burner 30 is configured with an opening, hole, or orifice 80 in the wall 82 of the fuel gas conduit 36 between the fuel gas conduit and the target gas conduit 34. Moreover, the wall 84 of the target gas conduit 34 includes an opening, hole, or orifice 86 between the target gas conduit 34 and the combustion air conduit 32. It is contemplated that the wall 82 of the fuel gas conduit 36 and the wall 84 of the target gas conduit 34 may include a single opening, hole, or orifice, or multiple openings, holes, or orifices 80, 86. In addition, as Figure 2 shown, the openings 80, 86 may be in the walls 82, 84 of both the fuel gas conduit 36 and the target gas conduit 34, or only in the wall 82 of the fuel gas conduit 36 or the wall 84 of the target gas conduit 34.

[0038] In any configuration described in this embodiment, if the target gas (NOx reduction medium) in the target gas conduit 34 is supplied at a pressure higher than the pressure of the combustion air or fuel gas, then a portion of the target gas (or other NOx reduction medium) will enter and mix with the combustion air and / or fuel gas, thereby pre-mixing with the combustion air and / or fuel gas and then being ejected from the burner combustion in the combustion zone 50, which further enhances the NOx reduction mechanism such that the combustion produces low NOx emissions. This pre-mixing can also enhance the burner flame stability, thus enabling continuous and stable combustion.

[0039] Alternatively, if the combustion air pressure or fuel gas pressure is higher than the pressure of the target gas, then the fuel gas or combustion air can flow into the target gas (or NOx reduction medium), thereby pre-mixing with the target gas and then being ejected from the burner 30 in the combustion zone 50 to achieve a similar NOx reduction effect and / or flame stability in the combustion zone 50.

[0040] As described above, it has been found that further control of NOx production can be achieved by providing a NOx reduction medium via the target gas conduit 34. The NOx reduction medium can include, but is not limited to, fluids such as flue gas from the combustion zone 50, flue gas from the exhaust of a heater, boiler, or furnace surrounding or associated with the burner 30 of the present invention, steam (water vapor), nitrogen, carbon dioxide, or even fuel gas such as methane. It is known that inert gases such as steam, nitrogen, and carbon dioxide injected into the fuel gas stream or air stream of the burner can contribute to reducing NOx emissions by reducing the partial pressures of the reactants (both fuel and air), cooling, and by transferring heat out of the combustion section of the combustion zone 50. In addition, steam and gases containing steam (NOx reduction medium) are beneficial for catalyzing and solvating combustion reactions. Thus, in some of the various configurations of the present invention, a portion or all of the NOx reduction medium (or a mixture of NOx reduction media) is supplied to the target gas conduit 34 to facilitate selectively and desirably setting the proportion of the NOx reduction medium at an optimal location in the flame zone in the combustion zone 50.

[0041] Although there can be many different sources of the NOx reduction medium, one preferred source is the flue gas from the combustion zone 50 itself. External flue gas recirculation is well known and practiced in the industry and involves typically moving flue gas from the exhaust stack or chimney of the burner to the inlet of the burner via an electrically powered fan. From the perspective of capital investment and operating costs, external flue gas recirculation is costly. The convective section of the heater, boiler, or furnace must be made larger to accommodate the addition of recirculated flue gas to the system, pipes and fans must be purchased and installed, and the fan must be powered and operated. In addition, when the flue gas is mixed with the combustion air, a relatively large amount of external flue gas (about 30% of the flue gas volume) must be recirculated to achieve a significant reduction in NOx.

[0042] It has also been found that flue gas from a fluid catalytic cracking (FCC) unit is another source of NOx reduction medium that can be used to reduce NOx generated by the burner flame. Exemplary FCC units are described in U.S. Patent Publications 2021 / 0009904 and 2020 / 0325087, both of which are incorporated herein by reference. Although it is believed that using FCC flue gas alone will reduce NOx production, if used in a burner with the TFGR system of the present invention, the production of NOx gas will be further reduced.

[0043] In the above-described embodiments, a control system including a controller or control unit (which may be a processor) is used to control the operation of the burner 30 such that the control unit communicates with the burner and is designed to actively control the injection rate, position, local stoichiometry, and the NOx reduction medium introduced into the combustion process, the flame, and reduce the NOx production to a very low value of less than 10 ppmvd using a relatively appropriate amount of the NOx reduction medium such as flue gas. Increasing the rate of flue gas recirculation while further reducing NOx emissions may cause burner instability and / or flame loss. By designing and actively controlling the injection rate, position, local stoichiometry, and the NOx reduction medium introduced into the combustion process, the formation of flame and NOx can be reduced while maintaining good burner and flame stability and continuous operation.

[0044] Figure 3 An embodiment of a control system 90 that communicates with the burner 30 is shown. More specifically, the control system 90 communicates with a burner control system that is associated with the burner and controls the operation of the burner. The control system 90 performs different control operations on the burner 30, including open-loop control operations, partial closed-loop control operations, and closed-loop control operations.

[0045] The main focus of the control system is to reduce thermal NOx emissions from the burner 30. The level of excess air, the temperature of this air, and the way the air is mixed with the gas affect the production of NOx during combustion. The control system communicates with the burner 30 and a blower, and controls the burner and the blower, which has isolation valves at the inlet and outlet of the burner. In this way, the control system controls the injection of the target gas (NOx reduction medium) to significantly reduce the NOx emissions generated during the combustion process.

[0046] The control system includes a control panel and communicates via Modbus TCP / IP with a burner control system (burner) 92 with DCS. The control panel is located in the control room of the facility including the burner 30 or at a remote site at a facility or location different from the burner. During operation, the control system starts, operates, and shuts down the burner in an orderly and safe manner. The design of the burner incorporates a blower, isolation valves, key analyzers, and sensors to perform the start-up, stop, and shutdown of the burner. All necessary permits, program status, and alarms related to the burner will be displayed on the HMI installed on the control panel of the control system.

[0047] In one embodiment, the burner system includes a low NOx burner, a blower with a variable frequency drive (VFD), blower inlet 93 and outlet 94 isolation valves, three (3) mandatory instruments (i.e., the firebox temperature sensor 101, the firebox O2 analyzer 102, and the fuel gas pressure gauge 103), an optional instrument system (i.e., the stack NOx analyzer 104, the stack temperature transmitter 105, the recirculation flow meter 106, the oxygen (O2) gauge 107, and the pressure gauge 110), and a NOx control performance curve programmed in a dedicated programmable logic controller (PLC) (or other suitable computer controller). The unique design of the burner system and control system of the present invention uses a target NOx reduction medium to significantly reduce the emissions generated by the burner 30.

[0048] The control system 90 performs different control operations associated with the burner 30, including but not limited to a purge operation or purge program, an open-loop control operation, a partial closed-loop control operation, and a closed-loop control operation.

[0049] The purpose of the purge program is to remove any combustible vapors and gases that have entered any part of the target gas burner system during burner shutdown, including the burner and the ductwork from the burner outlet, such as the stack. The purge time is set to ensure that at least four volume replacements of the entire burner system have been completed.

[0050] In the purge operation / program, the purge assembly, including the blower inlet and outlet isolation valves, and the recirculation purge assembly are directly connected to the burner assembly, i.e., the burner 30. The purge program initiates a purge cycle in coordination with the burner control system, while the purge program is an independent program and does not require any operator input or intervention. Including this feature enables the burner system to operate fully automatically by maintaining safe operating conditions, even when not in use due to the use of isolation technology. Moreover, the unique purge program helps remove the recirculation flue gas in the recirculation duct before enabling the ignition of the burner 30.

[0051] The purge program is started by activating the "Purge Start" switch. Operating this switch enables the purge program for the process heater (i.e., the burner 30). Upon completion, the blower speed is controlled by the variable frequency drive (VFD) (i.e., the VFD motor) and begins to ramp up to full speed to provide sufficient flow within the burner system to replace the combustible gas in one or more recirculation lines with fresh air from the combustion air duct 32.

[0052] When the purge cycle is completed, the blower, recirculation line, and inlet and / or outlet valves are closed, which prevents combustible gases from the stack from flowing into the burner injection until the pilot flame and the main burner flame are ignited. The main burner flame safeguard is electrically interlocked with the control system to provide proof of purge that the piping purge within the burner system has been successfully completed.

[0053] In the standby / run program, the control system 90 enables the operator to operate the target gas burner system in a safe standby mode or a run mode, where the mode depends on plant requirements. One or more safety interlocks associated with the firebox / burner temperature, fuel gas pressure, process heater oxygen percentage (O2%), flame failure, and other process heater trip conditions will keep the target gas burner system in the standby mode to prevent any thermal shock, undesired operation, and / or flame instability until the burner (process heater) combustion chamber is properly preheated at minimum load.

[0054] During the run mode, a specified amount of NOx reduction medium is directly injected into the burner, and the specified amount of NOx reduction medium is proportionally controlled with three or more mandatory key sensors (i.e., firebox / burner temperature, firebox / burner oxygen percentage, and analyzer and fuel gas pressure) using an auxiliary controller in the target gas burner system. The injection rate is achieved by changing the speed of the blower in the target gas burner system through a variable frequency drive (VFD) control. After conducting an actual performance test of the burner, a performance curve between the VFD speed of the target gas burner system and the above sensors is uniquely formed. There can be different NOx reduction media, such as target NOx reduction gas 108, CO2, nitrogen, and steam, where control valves with flow control loops are used to control these NOx reduction media to reduce NOx emissions.

[0055] Additionally, in an alternative operation, the control system enables a "closed-loop" mode, in which the NOx reduction medium is directly injected into the burner 30 and is controlled to be proportional to the composition of the NOx reduction medium, where it is measured using direct NOx measurement at the stack or using indirect oxygen measurement. The injection rate is achieved by changing the speed of the blower of the burner system through VFD control.

[0056] In another alternative operation, the control system directly injects the NOx reduction medium into the burner 30, which is controlled to be proportional to the NOx reduction medium, the temperature at the stack, the flow rate and pressure of the fuel gas, and the fuel gas composition. The injection rate is achieved by changing the speed of the blower through VFD control. This mode of the control system is used to operate the controlled variables to achieve a significant reduction in NOx emissions.

[0057] In the above embodiments, the target gas controller is unique in the manner of injecting the NOx reduction medium into the burner using both "open" and "closed" control loops to control NOx emissions. Specifically, the unique features and technical advantages of the control system over other flue gas or other earlier NOx reduction medium control systems are as follows for control system 90:

[0058] 1. Integrate the purge procedure for injecting the NOX reduction medium with the purge procedures of the burner and heater systems for safe startup, as outlined in various regulatory materials such as, for example, the 85 Boiler and Combustion System Hazards Code.

[0059] 2. After the pre-combustion purge procedure, automatically shut down and isolate the NOx reduction medium injection system by closing any control valves or isolation valves and shutting down any fans, compressors, or pumps for the NOx reduction medium and entering the standby / operating procedure of the target gas burner system to wait for a service request.

[0060] 3. When the firebox (combustion chamber) temperature of the burner is low during startup / initial ignition of the burner flame, and the oxygen in the combustion chamber is high (21% by volume) and the temperature is low (i.e., close to ambient temperature), shut down and cut off the target gas burner system. Under these conditions, very little NOx will be produced at the time of ignition and immediately after ignition, and no or little NOx reduction medium is required.

[0061] 4. As the burner firing rate increases from the ignition level to the normal operating level, the firebox temperature increases and approaches the normal level (700 °C to 1275 °C), depending on the type and service of the heater or furnace, and the oxygen level decreases from ambient (21% by volume of oxygen) to the normal operating oxygen level of 1% to 5% by volume of oxygen in the combustion chamber, and the fuel pressure increases from the down-regulated level to the normal operating level. At a certain combination of an increase in the firebox temperature (above 760 °C) and an increase in the fuel gas pressure (above 5 psig in some cases) and a decrease in the oxygen level (possibly less than 5% by volume of oxygen), NOx formation will approach the regulatory limit. At pre-determined firebox temperature limits, oxygen limits, and fuel pressure limits, the target gas burner system starts delivering the NOx reduction medium to the burner and ramps up the injection rate to a pre-determined injection rate, thereby proportionally reducing NOx production during combustion.

[0062] The following are examples of how to proportionally adjust the target gas injection rate with various inputs:

[0063] · When the fuel gas pressure increases, increase the target gas (NOx reduction medium) flow

[0064] · When the firebox temperature increases, increase the flow rate of the target gas (NOx reduction medium).

[0065] · When the oxygen decreases, adjust the flow rate of the target gas (NOx reduction medium) according to other pre-determined conditions, which increases or decreases the flow rate to correct the abnormal oxygen condition;

[0066] · When the fuel composition changes, increase the flow rate of the target gas (NOx reduction medium) to achieve a higher hydrogen content;

[0067] · When the NOx concentration is too high, increase the flow rate of the target gas (NOx reduction medium) until the NOx emissions are met, i.e., the closed-loop operating mode;

[0068] · When the temperature of the target gas is higher than the specified limit or pre-defined limit, infiltrate more fresh air into the target gas.

[0069] · When the oxygen concentration in the target gas (NOx reduction medium) changes, such as a low oxygen concentration, less target gas is required, and if the oxygen concentration is high, more target gas is required to achieve the NOx emissions reduction target;

[0070] · When the flow rate of the target gas is directly measured, this flow rate can be used for closed-loop control to maintain consistent low NOx emissions by directly controlling the chimney NOx conditions

[0071] · The pressure of the target gas (NOx reduction medium) can replace the flow meter of the target gas, or indicate the flow rate used for loop control of the target gas to maintain consistent low NOx emissions.

[0072] Although the lowest NOx emissions may be produced when the burner 30 receives the NOx reduction medium at the highest flow rate, this may also be the initial point of burner instability. This initial instability can be detected by a high-speed pressure transmitter and associated instability detection software similar to that described in U.S. Patent 7,950,919. However, different from U.S. Patent 7,950,919 which mainly controls and adjusts the combustion chamber oxygen to respond to instability, in the present invention, the rate and position of the NOx reduction medium can be controlled.

[0073] Generally, sensors such as flow rate sensors and / or temperature sensors mounted at different positions within the heater, as well as flue gas oxygen and combustion chamber pressure or draft, can be used to monitor the NOx emissions of the burner 30. The rate, amount, or both of the NOx reduction medium delivered at the desired location in the flame zone can be increased until the desired NOx reduction is achieved. Once the desired NOx level is achieved, no additional NOx reduction medium need be introduced. If the burner becomes unstable, the rate and / or position of the NOx reduction medium can be controlled, or the excess air and oxygen levels can be adjusted as suggested in U.S. Patent 7,950,919 until burner stability is achieved.

[0074] It can further be envisioned that a field of view or infrared camera can be used to monitor aspects of flame stability and quality using artificial intelligence AI, as described in U.S. Patent Publication 2020 / 0386404, which is incorporated herein by reference. When instability or other anomalies are detected in the flame image using AI, the amount and position of the NOx reduction medium and / or other control aspects of the heater control system, such as excess oxygen, can be adjusted and controlled to simultaneously achieve the lowest level of NOx (or at least the desired level) with good burner flame stability.

[0075] If there is a loss of the NOx reduction medium at any time or instance, the burner 30 of the present invention will still operate safely as a conventional low-NOx burner. The NOx emissions may increase, but the burner 30 will otherwise remain stable and continue to reliably deliver heat to the process in the heater, boiler, or furnace. Additionally, from the perspective of the burner operator, the burner 30 will operate just as a conventional burner does, without special operating problems.

[0076] Those of ordinary skill in the art should recognize and understand that various other components such as valves, pumps, fans, filters, coolers, etc. are not shown in the drawings because it is believed that their specific details are entirely within the knowledge of those of ordinary skill in the art and their description is not necessary for the implementation or understanding of the embodiments of the present invention.

[0077] Any of the foregoing pipelines, conduits, units, devices, containers, surroundings, zones, or the like may be equipped with one or more monitoring components, including sensors, measurement devices, data capture devices, or data transmission devices. Signals, methods, or state measurements, and data from the monitoring components may be used to monitor conditions in, around, and related to the method devices. Signals, measurements, and / or data generated or recorded by the monitoring components may be collected, processed, and / or transmitted via one or more networks or connections, which may be private or public, general or dedicated, direct or indirect, wired or wireless, encrypted or unencrypted, and / or combinations thereof; the present specification is not intended to be limiting in this regard.

[0078] Signals, measurements, and / or data generated or recorded by the monitoring components may be transmitted to one or more computing devices or systems. The computing device or system may include at least one processor and a memory storing computer-readable instructions that, when executed by the at least one processor, cause the one or more computing devices to perform a method that may include one or more steps. For example, one or more computing devices may be configured to receive data related to at least one device associated with the method from one or more monitoring components. One or more computing devices or systems may be configured to analyze the data. Based on the data analysis, one or more computing devices or systems may be configured to determine one or more recommended adjustments to one or more parameters of one or more of the methods described herein. One or more computing devices or systems may be configured to transmit encrypted or unencrypted data that includes one or more recommended adjustments to one or more parameters of one or more of the methods described herein.

[0079] The computing device of the system unit may include, for example, any type of general-purpose microprocessor or microcontroller, digital signal processing (DSP) processor, central processing unit (CPU), integrated circuit, field programmable gate array (FPGA), reconfigurable processor, other suitable programmed or programmable logic circuit, or any combination thereof.

[0080] The memory can be any suitable known or other machine-readable storage medium. The memory may include non-transitory computer-readable storage media such as, but not limited to, electronic, magnetic, optical, electromagnetic, infrared, or semiconductor systems, devices, or apparati, or any suitable combination of the foregoing. The memory may include a suitable combination of any type of computer memory located either inside or outside the device, such as random access memory (RAM), read-only memory (ROM), compact disc read-only memory (CDROM), electro-optical memory, magneto-optical memory, erasable programmable read-only memory (EPROM), and electrically erasable programmable read-only memory (EEPROM), ferroelectric RAM (FRAM), etc. The memory may include any storage device (e.g., apparatus) adapted to retrievably store computer-executable instructions executable by a controller or computing device.

[0081] The methods and steps described herein can be implemented in a high-level procedural or object-oriented programming or scripting language, or a combination thereof, to communicate with or assist in the operation of a controller or computing device. Alternatively, the methods and systems described herein can be implemented in assembly or machine language. The language can be a compiled or interpreted language. The program code for implementing the methods and systems described herein for controlling the gas flow to a burner can be stored on a storage medium or apparatus such as a ROM, disk, optical disc, flash drive, or any other suitable storage medium or apparatus. The program code can be readable by a general or special purpose programmable computer for configuring and operating the computer when the storage medium or apparatus is read by the computer to perform the processes described herein.

[0082] Computer-executable instructions can be in many forms executed by one or more computers or other devices, including program modules. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types. Typically, the functionality of program modules can be combined or distributed as needed in various implementations.

[0083] Specific implementation examples

[0084] Although the following is described in conjunction with specific embodiments, it should be understood that the description is intended to illustrate and not limit the scope of the foregoing description and the appended claims.

[0085] A first embodiment of the present invention is a burner configured to generate a flame in a combustion zone, the burner comprising: a combustion air duct that supplies combustion air to the combustion zone; a target gas duct that is surrounded by the combustion air duct and supplies target gas to the combustion zone; a fuel gas duct that is surrounded by the target gas duct and supplies fuel gas to the combustion zone, wherein a portion of the fuel gas is mixed with a portion of the target gas and then mixed with the combustion air in the combustion zone. An embodiment of the present invention is one embodiment, any embodiment, or all embodiments from the first embodiment to the previous embodiments of this paragraph, wherein the inlet of the fuel gas duct draws flue gas from a combustion source. An embodiment of the present invention is one embodiment, any embodiment, or all embodiments from the first embodiment to the previous embodiments of this paragraph, wherein the combustion air duct includes a closed end and an opening at the closed end, and the target gas flows across the closed end to form a fluid barrier between the combustion air and the fuel gas. An embodiment of the present invention is one embodiment, any embodiment, or all embodiments from the first embodiment to the previous embodiments of this paragraph, wherein the target gas duct includes a closed end and an opening at the closed end. An embodiment of the present invention is one embodiment, any embodiment, or all embodiments from the first embodiment to the previous embodiments of this paragraph, wherein the fuel gas duct includes a closed end and an opening at the closed end. An embodiment of the present invention is one embodiment, any embodiment, or all embodiments from the first embodiment to the previous embodiments of this paragraph, wherein a portion of the fuel gas is injected through the inlet into the combustion air duct and mixed with a portion of the combustion air and then reaches the combustion zone. An embodiment of the present invention is one embodiment, any embodiment, or all embodiments from the first embodiment to the previous embodiments of this paragraph, wherein a portion of the target gas is mixed with a portion of the combustion air and then enters the combustion air duct, and the remaining portion of the target gas enters the target gas duct. An embodiment of the present invention is one embodiment, any embodiment, or all embodiments from the first embodiment to the previous embodiments of this paragraph, wherein from greater than 0% to equal to 95% of the amount of the target gas is mixed with the combustion air and then enters the combustion air duct, and the remaining portion of the target gas enters the target gas duct. An embodiment of the present invention is one embodiment, any embodiment, or all embodiments from the first embodiment to the previous embodiments of this paragraph, and this embodiment further includes at least one orifice extending between the combustion air duct and the target gas duct.One embodiment of the present invention is one embodiment, any embodiment, or all embodiments among the first embodiment to the previous embodiments of this paragraph, and this embodiment further includes at least one orifice extending between the target gas conduit and the fuel gas conduit. One embodiment of the present invention is one embodiment, any embodiment, or all embodiments among the first embodiment to the previous embodiments of this paragraph, and this embodiment further includes at least one orifice extending between the target gas conduit and the fuel gas conduit. One embodiment of the present invention is one embodiment, any embodiment, or all embodiments among the first embodiment to the previous embodiments of this paragraph, wherein the target gas is a NOx reduction medium or a mixture of NOx reduction media.

[0086] A second embodiment of the present invention is a method for reducing the production of NOx gas at a burner, the method including injecting combustion air into a combustion zone; injecting a target gas into the combustion zone; and injecting a fuel gas into the combustion zone, wherein a portion of the fuel gas is mixed with a portion of the target gas and then mixed with the combustion air in the combustion zone. One embodiment of the present invention is one embodiment, any embodiment, or all embodiments among the second embodiment to the previous embodiments of this paragraph, and this embodiment further includes mixing a portion of the fuel gas with the combustion air and then allowing it to reach the combustion zone. One embodiment of the present invention is one embodiment, any embodiment, or all embodiments among the second embodiment to the previous embodiments of this paragraph, and this embodiment further includes mixing a portion of the target gas with the combustion air. One embodiment of the present invention is one embodiment, any embodiment, or all embodiments among the second embodiment to the previous embodiments of this paragraph, and this embodiment further includes mixing from more than 0% to 95% of the target gas with the combustion air. One embodiment of the present invention is one embodiment, any embodiment, or all embodiments among the second embodiment to the previous embodiments of this paragraph, wherein the target gas is a NOx reduction medium or a mixture of NOx reduction media.

[0087] A third embodiment of the present invention is a method for controlling a burner using a control system to reduce the production of NOx gas during combustion. The method includes: enabling a purge program in which at least one blower in the burner automatically starts and supplies combustion air to the burner and a recirculation line; closing inlet and outlet valves leading to the blower and the recirculation line to prevent accumulation of combustible gas in the burner; and opening the inlet and outlet valves leading to the blower and the recirculation line when the purge program is completed. One embodiment of the present invention is one, any, or all of the third embodiment to the previous embodiments in this paragraph, wherein completing the purge program includes replacing at least four full volumes of air in the burner. One embodiment of the present invention is one, any, or all of the third embodiment to the previous embodiments in this paragraph, and this embodiment further includes electrically interlocking to start the burner until the purge program is completed.

[0088] Although no further detailed description is provided, it is believed that those skilled in the art can make the most of the present invention by using the foregoing description and can easily determine the basic features of the present invention without departing from the essence and scope of the present invention to make various changes and modifications and adapt it to various uses and conditions. Therefore, the foregoing preferred specific embodiments should be understood as illustrative only and not limiting the remainder of the disclosure in any way, and are intended to cover various modifications and equivalent arrangements included within the scope of the appended claims.

[0089] In the foregoing, all temperatures are shown in degrees Celsius, and all parts and percentages are by weight unless otherwise specified.

Claims

1. A burner (30) configured to generate a flame in a combustion zone (50), the burner comprising: a combustion air duct (32) that supplies combustion air to the combustion zone (50); a target gas duct (34) surrounded by the combustion air duct (32), the target gas duct supplying a target gas to the combustion zone (50); a fuel gas duct (36) surrounded by the target gas duct (34), the fuel gas duct (36) supplying fuel gas to the combustion zone (50), wherein a portion of the fuel gas is mixed with a portion of the target gas and then mixed with the combustion air in the combustion zone (50).

2. Burner (30) according to claim 1, wherein, An inlet (42) of the fuel gas duct (36) draws flue gas from a combustion source.

3. The burner (30) according to claim 1, wherein, The combustion air duct (32) includes a closed end (68) and an opening (72) at the closed end, the target gas flowing across the closed end (68) to form a fluid barrier between the combustion air and the fuel gas.

4. Burner (30) according to claim 1, wherein, A portion of the fuel gas is injected through an inlet (74) into the combustion air duct (32) and mixed with a portion of the combustion air and then reaches the combustion zone (50).

5. The burner (30) according to claim 1, wherein, A portion of the target gas is mixed with a portion of the combustion air and then enters the combustion air duct (32), wherein the remaining portion of the target gas enters the target gas duct (34).

6. The burner (30) according to claim 5, wherein, An amount of the target gas greater than 0% to equal to 95% is mixed with the combustion air and then enters the combustion air duct (32), wherein the remaining portion of the target gas enters the target gas duct (34).

7. The burner (30) according to claim 1, the burner further comprising at least one orifice (86) extending between the combustion air duct (32) and the target gas duct (34).

8. The burner (30) according to claim 7, the burner further comprising at least one orifice (80) extending between the target gas duct (34) and the fuel gas duct (36).

9. The burner (30) according to claim 1, the burner further comprising at least one orifice (80) extending between the target gas duct (30) and the fuel gas duct (36).

10. The burner (30) according to claim 1, wherein, The target gas is a NOx reduction medium or a mixture of NOx reduction media.

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