Low Nox Burner with Targeted Gas Injection

This application is a continuation-in-part application of and claims priority to U.S. patent application Ser. No. 18/476,150 filed on Sep. 27, 2023, which claims priority to U.S. Provisional Patent Application No. 63/384,769 filed on Nov. 22, 2022, the entireties of which are incorporated herein by reference.

This invention relates generally to a gas burner, and more particularly to a gas burner that utilizes a targeted gas, such as a NOx reducing medium, to lower NOx production.

Petroleum refining and petrochemical processes frequently involve heating process streams in a furnace. The interior chamber of the furnace contains tubes which contain the process streams. The interior chamber is heated by a plurality of gas burners which receive a fuel which combusts to produce heat.

One area of concern for gas burners is the production of NOx gases. As would be appreciated, NOx refers to oxides of nitrogen, principally comprised of nitric oxide, NO, and nitric dioxide, NO. It is believed that there are at least three principal NOx formation mechanisms in combustion processes, 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).

It is known that NOx formation in gas burners can be mitigated by staging fuel and air and creating primary and secondary combustion (flame) zones. Staged air and staged fuel burners work primarily on the Thermal NOx and Prompt NOx formation processes. The highest flame temperatures, and thereby the greatest potential for Thermal NOx formation, is achieved when gaseous fuels and combustion air are thoroughly mixed and rapidly combusted in or near stoichiometric proportions.

Accordingly, the staged air and staged fuel burners seek to lower the temperature of the flame and thereby lower the NOx production. Classic staged fuel or staged air burners produce two combustions zones for off-stoichiometric combustion.

In the case of the staged fuel burner, all the combustion air passes through the primary combustion zone and into the secondary combustion zone with the partial combustion products of the primary combustion zone. In this case, the primary combustion zone is lean, having an excess amount of combustion air. Lean combustion reduces the flame temperature, in part, as all of the mass of the combustion air rapidly absorbs and commutes heat from the flame out of the primary combustion zone and thus allowing time (measurable in milliseconds) for heat to radiate out of the primary combustion zone to the surrounding environs including to the heater, boiler or furnace process tubes. The fully and/or partially combusted (reacted) products of combustion pass from the primary combustion zone to the secondary or staged combustion zone. This transit allows time (again measurable in milliseconds) for the primary combustion zone products to further radiate heat out to the surrounding environs and process tubes. Therefore, the somewhat cooled combustion products from the primary combustion zone act to conduct heat from and cool the secondary combustion zone. Further, the secondary combustion zone combustion reactions occur, on average, at relatively lean conditions as the typical process heater, boiler or furnace operates at lean conditions with an excess of 5% to 25% combustion air. Thereby the combustion process is complete to a fair degree, industrially acceptable level of efficiency, 5% to 25% excess air.

The classic staged air burner reverses the staging process and introduces all the fuel gas for combustion in the primary combustion zone and only a portion of the combustion air. In the case of the staged air burner, the primary combustion zone may operate sub-stoichiometrically and achieve industrially acceptable excess air levels, 5% to 25% excess air, as reactants and products pass through the secondary combustion zone. With the staged air burner, the reactants must pass through a region of near stoichiometry where flame temperatures, and thereby Thermal NOx formation, is high and therefore staged air burners can have difficulty delivering very low NOx emissions.

More recently, internal flue gas recirculation burners have utilized flue gas within the heater or furnace combustion chamber which is motivated by the fuel gas and mixed into the primary and secondary combustion zones. This flue gas, relatively cool, massive products of combustion (flue gas), pass into and through the combustion zones thereby further cooling the combustion zone and reducing Thermal NOx formation. The water vapor in the flue gas also serves to mitigate NOx created via the Prompt NOx mechanism by solvating and catalyzing hydrocarbon combustion by more recently understood Water Gas Shift Reaction (“WGSR”) mechanisms described in “A Paradigm Shift in Steam Assisted Elevated Flare Systems,” International Flame Research Foundation, July 2020, by Jan De Ren, Kurt Kraus and Chris Ferguson. These WGSR mechanisms are also present to a limited degree in classic or conventional staged fuel or staged air burners as products of combustion from the primary combustion zone to the secondary combustion zone includes some water vapor.

In some combustion systems, a Selective Catalytic Reduction (SCR) system is used for post-flue gas treatment to NOx emissions. A SCR system is an effective way of reducing NOx in a flue gas stream, with reductions up to 95%. However, such systems require space for the catalyst and structure, high capital and operating costs, formation of other undesirable emissions, and formation of undesirable species that may lead to catalyst poisoning and deactivation.

Both staged air and staged fuel burners can require and produce large,

voluminous flames to achieve low NOx emissions. Modern heater and furnace designs must be designed for larger, more costly combustion chambers to allow for larger low NOx emission burner flames of staged fuel and staged air burners.

Therefore, there remains a need for a burner that has low NOx production that does not suffer from these drawbacks.

A new burner and method of using same has been invented and utilizes targeted gas, namely a NOx reducing medium or mixture of NOx reducing media, to reduce NOx emissions generated during combustion in the burner. Specifically, the burner is configured so that the targeted gas and/or an internally recirculated flue gas flow between combustion air and fuel gas supplied to the combustion zone of the burner, which causes the targeted gas and/or the internally recirculated flue gas to mix with the fuel gas prior to subsequently mixing with the combustion air in the combustion zone. In this way, the “inert” components of the gas and/or NOx reducing media (CO, N, HO) are mixed in with the fuel gas to promote conductive heat transfer from the combustion reactants (fuel and air) from the onset of combustion and throughout the combustion reactants to reduce the incident or peak flame temperature in the combustion process. Reducing the peak flame temperature reduces oxidation of nitrogen in the combustion air or fuel gas in the reaction zone (flame) and thereby reduces the formation of thermal NOx, which is the NOx formed during combustion of fuel gas. Also, the water vapor from the gas (NOx reducing medium) serves to solvate and catalyze the combustion reaction to reduce the activation temperature of the combustion reactants to further reduce the peak flame temperature and thereby NOx emissions.

Thus, the present invention may be broadly characterized as providing a burner configured to produce a flame in a combustion zone, where the burner includes a combustion air conduit that provides combustion air to the combustion zone, a targeted gas conduit surrounded by the combustion air conduit, the targeted gas provides a gas, and more specifically, a NOx reducing medium, to the combustion zone and a fuel gas conduit surrounded by the targeted gas conduit, the fuel gas conduit provides fuel gas to the combustion zone, wherein a portion of the fuel gas is mixed with a portion of the targeted gas prior to mixing with the combustion air in the combustion zone.

In other embodiments, the fuel gas conduit includes an inlet that draws in additional flue gas from a combustion source. Also, the combustion air conduit may have a closed end and openings at the closed end, where the targeted gas (NOx reducing medium) flows across the closed end forming a fluid barrier between the combustion air and the fuel gas. Further, the targeted gas conduit may include a closed end and openings at the closed end for injecting the targeted gas into the combustion zone. Similarly, the fuel gas conduit may include a closed end and openings at the closed end for injecting the fuel gas into the combustion zone. In an embodiment, a portion of the fuel gas is injected through an inlet to the combustion air conduit and mixes with a portion of the combustion air prior to the combustion zone. In another embodiment, a portion of the targeted gas is mixed with a portion of the combustion air prior to entering the combustion air conduit with a balance of the targeted gas entering the targeted gas conduit. In a further embodiment, an amount greater than 0% to an amount equal to 95% of the targeted gas is mixed with the combustion air prior to entering the combustion air conduit with a balance of the targeted gas entering the targeted gas conduit. In an embodiment, the combustion air in the combustion air conduit is preheated to a predetermined temperature. Further in an embodiment, the combustion air in the combustion air conduit includes oxygen enriched or pure oxygen. The burner may also include a controller configured for controlling a flow rate of the combustion air in the combustion air conduit, a flow rate of the gas (NOx reducing medium) in the targeted gas conduit in a predefined proportion and flow rate of the fuel gas in the fuel gas conduit. In an embodiment, at least one aperture extends between the combustion air conduit and the targeted gas conduit. In another embodiment, at least one aperture extends between the targeted gas conduit and the fuel gas conduit.

In another aspect, the present invention may be characterized as providing a process for reducing production of NOx gases at a burner, where the process includes injecting a combustion air into a combustion zone, injecting a targeted 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 targeted gas prior to mixing with the combustion air in the combustion zone.

In a further aspect, the present invention may be characterized as a process for controlling a burner using a control system to reduce the production of NOx gases during combustion, where the process comprises initiating a purge sequence in which at least one blower in the burner is automatically activated and supplies combustion air to the burner and recirculation lines, and closing inlet and outlet valves to the blower and recirculation lines to prevent combustible gases from accumulating in the burner and opening the inlet and outlet valves to the blower and recirculation lines when the purge sequence is complete. In an embodiment, the completion of the purge sequence includes changing at least four complete volumes of air in the burner. In another embodiment, the process further comprises electrically interlocking activating the burner until the purge sequence is complete. In another embodiment, the process further comprises controlling the at least one motor the blower, which is a variable frequency drive motor.

In another aspect, the present invention is characterized as a process for controlling a burner using a control system to reduce the production of NOx gases during combustion, where the process comprises operating the burner in standby mode until the temperature of a combustion chamber in the burner is at a predetermined minimum temperature, and operating the burner in run mode when the temperature of the combustion chamber of the burner is at the predetermined minimum temperature.

In another aspect, the present invention is characterized as a process for controlling a burner using a control system to reduce the production of NOx gases during combustion, where the process comprises directly injecting a NOx reducing medium in a combustion chamber in the burner and proportionately controlling the injection of the NOx reducing medium in the combustion chamber with a composition of a flue gas in the combustion chamber and a direct measurement of NOx emissions at an outlet of the burner. In an embodiment, the process includes controlling an injection rate of the NOx reducing medium in the combustion chamber by varying a speed of a blower in the burner using a variable frequency drive motor.

In a further aspect, the present invention is characterized as a process for controlling a burner in a burner system using a control system to reduce the production of NOx gases during combustion, where the process comprises directly injecting a NOx reducing medium in a combustion chamber in the burner and proportionately controlling the injection of the NOx reducing medium in the combustion chamber with at least one of an amount of NOx at an outlet of the burner, a temperature at the outlet of the burner, an amount of oxygen in the flue gas, a flow rate and pressure of a flue gas in the combustion chamber and a composition of the flue gas in the combustion chamber. In an embodiment, the process further comprises controlling an injection rate of the NOx reducing medium in the combustion chamber by varying a speed of a blower in the burner system using a variable frequency drive motor. In another embodiment, the process includes controlling an injection rate of the NOx reducing medium in the combustion chamber by varying the position of a flow control valve in the burner system by modulating a controller.

In another aspect of the invention, a burner is configured to produce a flame in a combustion zone is provided where the burner includes a combustion air conduit that provides combustion air to the combustion zone, a primary targeted gas conduit surrounded by the combustion air conduit that provides a targeted gas to the combustion zone, a secondary targeted gas conduit that provides additional targeted gas to the combustion zone, a primary fuel gas conduit surrounded by the targeted gas conduit that provides fuel gas to the combustion zone and a secondary fuel gas conduit that provides additional fuel gas to the combustion zone, where a portion of the fuel gas from at least one of the primary fuel gas conduit and the secondary fuel gas conduit is mixed with a portion of the targeted gas prior to mixing with the combustion air in the combustion zone.

In a further aspect, the present invention is characterized as a process for reducing production of NOx gases at a burner, where the process includes injecting a combustion air into a combustion zone, injecting a targeted gas into the combustion zone via a primary targeted gas conduit, injecting additional targeted gas into the combustion zone via a secondary targeted gas conduit, injecting a fuel gas into the combustion zone via primary fuel gas conduit, injecting additional fuel gas into the combustion zone via secondary fuel gas conduit where a portion of the fuel gas from at least one of the primary fuel gas conduit and the secondary fuel gas conduit is mixed with a portion of the targeted gas prior to mixing with the combustion air in the combustion zone.

Additional aspects, embodiments, and details of the invention, all of which may be combinable in any manner, are set forth in the following detailed description of the invention.

As described above, the present invention addresses the problem of producing low NOx emissions in high temperature furnace and heater systems, especially when firing high hydrogen content fuel gasses and fuel gas that fluctuate from high hydrogen to low hydrogen content. Specifically, the present burner utilizes a targeted NOx reducing medium such as N2, CO2, H2O, a recirculated flue gas or any suitable combination of these gases, to reduce NOx emissions low enough to eliminate the need for Selective Catalytic Reduction SCR systems thereby reducing capital and operating expenses and the carbon footprint of high temperature furnace and heater systems during both 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.

As shown in the, the present burner generally indicated as, includes a combination of a combustion air conduit, a targeted gas conduitand a fuel gas conduit.

The fuel gas conduitis centrally located within the burnerand has a longitudinal axisand a first diameter. A first endof the fuel gas conduitincludes an inletfor receiving fuel gas and an opposing second endis closed by a cap. The capmay be independently formed and attached to the fuel gas conduitby welding or other suitable attachment method or integrally formed with the fuel gas conduit. As shown, at least one gas opening, and preferably, a plurality of spaced gas openingsextend or are formed along a circumference of the fuel gas conduitat the second endto inject the fuel gas into a primary combustion zonewithin a combustion chamber (not shown) that may be a stack or furnace. Contemplated sources and/or compositions of the fuel gas include refinery fuel gas, synthetic fuel gas, process off gas, natural gas, propane, butane, LPG, hydrogen including up to 100% by volume, and any combination of the foregoing. The pressure of the fuel gas may vary from 0.07 to 2.07 Barg (1 to 30 psig).

The targeted gas conduithas a second diameter and extends along the longitudinal axis, where the second diameter of the targeted gas conduitis greater than the first diameter of the fuel gas conduitsuch that the targeted gas conduit surrounds the fuel gas conduit. A first endand an opposing second endof the targeted gas conduitare both closed. Specifically, the first endof the targeted gas conduitincludes a flangethat is secured to the conduitby fasteners. The second endincludes a capsimilar to the capof the fuel gas conduitand has at least one gas opening, and preferably a plurality of spaced gas openingsextending along a circumference of the targeted gas conduitat the second end. As shown in, the gas openingsare spaced from the fuel gas openingsand inject targeted gas (NOx reducing medium) into the combustion zone. The targeted gas conduitincludes an inletat the first endthat is transverse to the longitudinal axisand supplies the targeted gas and/or a NOx reducing medium, to the targeted gas conduitfrom a gas source, such as a source of a NOx reducing medium.

The combustion air conduithas a third diameter and extends along the longitudinal axis, where the third diameter of the combustion air conduitis greater than the second diameter of the targeted gas conduitand the first diameter of the fuel gas conduitsuch that the combustion air conduitsurrounds the targeted gas conduitand the fuel gas conduit. Similar to the targeted gas conduit, the combustion air conduitincludes a first endthat is closed by a flangesecured to the conduit by fasteners, and an opposing second endthat is closed by a capthat is independently formed and secured to the conduitby welding or other suitable attachment method, or integrally formed with the conduit. The combustion air conduitalso includes at least one air opening, and preferably a plurality of spaced air openingsat the second end, where the air openingsextend about a circumference of the conduitand are spaced from the fuel gas openingsand the gas openings. In the illustrated embodiment, the combustion air conduit includes two rows of the air openings. It is contemplated that the combustion air conduitmay have a single row or a plurality of rows of the air openings. Further, the combustion air conduitincludes an inletat the first endof the conduit that is transverse to the longitudinal axisand receives air, also called combustion air, where the air flows along the combustion air conduitas shown by arrowsand injects the combustion air into the combustion zonethrough the air openings.

In operation, the targeted gas conduitof the present burnerreceives targeted gas, such as a NOx reducing medium or a mixture of NOx reducing media, through the inletsuch that the targeted gas flows along the outer surface of the fuel gas conduitas indicated by arrows, such that the targeted gas (NOx reducing medium) is positioned between the combustion air and the fuel gas to effectively create a barrier between the combustion air and the fuel gas thereby enabling the targeted gas to mix with the fuel gas prior to mixing with the combustion air in the combustion zone. Also, the fuel gas is injected at a location where it also draws in a flue gas from a combustion source, such as a surrounding furnace (not shown). Thus, as shown in, at least a portion of the targeted gas and at least a portion of the fuel gas mix together prior to mixing with at least a portion of the combustion air in the combustion zone. The present burnerthereby effectively surrounds the fuel gas with both an internally recirculated flue gas and/or an externally recirculated and targeted gas (NOx reducing medium), forcing mixing of the internal flue gas and the targeted gas with the fuel gas prior to subsequently mixing with the combustion air. In this way, the “inert” components of the targeted gas and/or a NOx reducing medium, such as CO2, N2, H2O, are physically mixed in with the fuel gas to promote conductive heat transfer from the combustion reactants (fuel and air) from the very onset of combustion and throughout combustion reactions thereby having a maximum effect to reduce the incident or peak flame temperature throughout the combustion process in the combustion zone. Reducing the peak flame temperature reduces oxidation of nitrogen entering the combustion zone (flame) from the combustion air or fuel thereby reducing thermal NOx formation.

Further, water vapor from the NOx reducing medium, or steam injected as a NOx reducing medium, serves to solvate and catalyze the combustion reaction thereby reducing the activation temperature of the combustion reactants and thereby the resulting incident and peak flame temperatures in the combustion zone, which further reduces NOx emissions.

By producing NOx emissions that are low enough (often lower that 5 to 20 ppmvd) to eliminate the need for SCRs or other similar NOx reducing equipment, the capital and operating expenses required to achieve regulatory NOx emissions is greatly reduced. For example, burners with the present Targeted Flue Gas Recirculation system (TFGR system) can reduce total installation costs by over 50% to 90%. Additionally, the amount of steel, refractory materials and other materials needed for construction in a burner installation on a new burner system or retrofit system is, of course, greatly reduced, as well as the carbon footprint. Additional NOx reducing systems that utilize a catalyst, a catalyst bed, a housing, an ammonia injections system, ammonia supply trucking, receiving, tank storage and delivery system are all replaced with the present burnerand TFGR system.

Referring to, another embodiment of the burneraccording to the present invention is shown in which the same reference numbers are used for the same features.

The burnerofis configured with an opening, hole or aperturein a wallof the fuel gas conduitbetween the fuel gas conduit and the targeted gas conduit. Also, the wallof the targeted gas conduitincludes an opening, hole or aperturebetween the targeted gas conduitand the combustion air conduit. It is contemplated that the wallof the fuel gas conduitand the wallof the targeted gas conduitmay include a single opening, hole or aperture, or a plurality of openings, holes or apertures,. Further, the openings,may be in the walls,of both the fuel gas conduitand the targeted gas conduitas shown in, or only in the wallof the fuel gas conduitor the wallof the targeted gas conduit.

In any of the configurations described in this embodiment, if the targeted gas (NOx reducing medium) in the targeted gas conduitis supplied at a pressure higher than that of the combustion air or the fuel gas, then a portion of the targeted gas (or other NOx reducing media) will enter and mix with the combustion air and/or the fuel gas, thereby premixing with the combustion air and/or fuel gas before ejection from the burner combustion in the combustion zone, which further enhances NOx reducing mechanisms resulting in low NOx emissions from combustion. This premixing may also enhance burner flame stability delivering continuously stable combustion.

Additionally, if the combustion air pressure or the fuel gas pressure is greater than that of the pressure of the targeted gas, then fuel gas or combustion air can flow into the targeted gas (or NOx reducing media), thereby premixing with the targeted gas prior to ejecting out the burnerin the combustion zonefor similar NOx reducing effects and/or flame stabilization in the combustion zone.

As noted above, it has been discovered that further control of the NOx production may be achieved by providing a NOx reducing medium via the targeted gas conduit. The NOx reducing media may include, but are not limited to, fluids such as flue gas from the combustion zone, flue gas from the exhaust of a heater, boiler or furnace surrounding or associated with the present burner, steam (water vapor), nitrogen, carbon dioxide or even a fuel gas such as methane. It is known that inert gases such as water vapor, nitrogen and carbon dioxide injected in the fuel gas or air stream of a burner can help reduce NOx emissions by reducing the partial pressure of reactants, both fuel and air, cooling and by transferring heat out of the combustion section of the combustion zone. Further, water vapor and a gas (NOx reducing medium) containing water vapor facilitate catalyzing and solvating the combustion reactions. Accordingly, in some of the various configurations of the present invention, a portion or all the NOx reducing medium (or a mixture of NOx reducing media) is supplied to the targeted gas conduitto facilitate selective and designed proportioning of the NOx reducing medium in the optimal location(s) in the flame zone(s) in the combustion zone.

While there may be many and various sources for the NOx reducing medium, one preferred source is the flue gas from the combustion zoneitself. External flue gas recirculation of flue gas is well known and practiced in the industry and involves the movement of flue gas from an exhaust chimney or stack of the burner to the inlet of the burner, usually by a powered fan. External flue gas recirculation is costly from both capital and operating cost perspectives. The convection sections of the heater, boiler, or furnace must be made larger to accommodate the addition of the recycled flue gas in the system, the ducting and fan must be purchased and installed, and the fan must be powered and operated. Further, relatively large quantities of external flue gas, around 30% of the flue gas volume, must be recycled to achieve significant NOx reduction when the flue gas is mixed with the combustion air.

It has also been discovered that flue gas from a fluidized catalytic cracking (FCC) unit is another source of the NOx reducing medium that may be used to reduce NOx production from a burner flame. An exemplary FCC unit is described in U.S. Pat. Pub. Nos. 2021/0009904 and 2020/0325087, both incorporated herein by reference. While the use of the FCC flue gas, alone, is believed to reduce the NOx production, if used in a burner with the present TFGR system, the production of NOx gases will be further reduced.

In the above embodiments, a control system including a controller or a control unit, which may be a processor, is used to control the operation of the burnersuch that the control unit communicates with the burner and is designed to actively control the injection rates, locations, localized stoichiometry and NOx reducing medium introduced to the combustion process, the flame, the NOx production can be mitigated to extremely low values, less thanppmvd with relatively modest amounts of NOx reducing media such as flue gas. Increasing rates of flue gas recirculation, while further reducing NOx emissions, can lead to burner instability and/or loss of flame. By designing for and actively controlling the injection rates, locations, localized stoichiometry and NOx reducing medium introduced to the combustion process, the flame and the NOx formation can be mitigated while maintaining good burner and flame stability and continuous operation.

An embodiment of the control systemin communication with burneris shown in. More specifically, the control systemcommunicates with a burner control system associated with the burner and controls the operation of the burner. The control systemperforms different control operations for the burnerincluding an open loop control operation, a partially closed loop control operation and a closed loop control operation.

The primary focus of the control system is to reduce thermal NOx emissions from the burner. The levels of excess air, the temperature of that air, and the way that the air is mixed with the gas affects the production of NOx during combustion. The control system communicates with and controls the burnerand a blower with isolation valves at inlet and outlet to the burner. In this way, the control system controls the injection of the targeted gas (NOx reducing medium) to significantly reduce NOx emissions generated during the combustion process.

The control system includes a control panel located in a control room at the facility including the burneror at a remote site that is at a different facility or location from the burner, and communicates with the burner control system (burner)with DCS via Modbus TCP/IP communications. During operation, the control system provides orderly and safe startup, operation, and shutdown of the burner. The design of the burner incorporates blowers, isolation valves, critical analyzer, and sensors to execute the start, stop and shutdown of the burner. All necessary permissive, sequence status and alarms related to the burner will be displayed on the HMI Installed on the control panel of the control system.

In an embodiment, the burner system includes a low NOx burner, a blower with a variable frequency drive (VFD), blower inletand outletisolation valves, three (3) mandatory instruments (i.e., firebox temperature sensor, firebox Oanalyzerand fuel gas pressure meter), optional instrumentation (i.e., stack NOx analyzer, stack temperature transmitter, a recirculation flow meter, an oxygen (O) meterand a pressure meter, and a NOx control performance curve programmed in a dedicated Programable Logic Controller (PLC) (or other suitable computer controller). The unique design of the present burner system and control system uses a targeted NOx reducing medium to significantly reduce NOx emissions produced by burner.

The control systemperforms different control operations associated with the burner, including but not limited to, a purge operation or purge sequence, an open loop control operation, a partially closed loop control operation and a closed loop control operation.

The purpose of the purge sequence is to remove the flammable vapors and gases that has entered any portion of the targeted gas burner system including the burner and ducting from the burner outlet such as a stack, during the shutdown of the burner. The purge time is set to ensure that at least four volume changes through the burner system have been completed.

In the purge operation/sequence, a purge assembly including blower inlet and outlet isolation valves and a recirculation purge assembly directly connect to the burner assembly, i.e., the burner. The purge sequence activates a purge cycle that is in concert with the burner control system, while being independent and not requiring any operator input or intervention. The inclusion of this features allows the burner system to operator fully automatically by maintaining safe operating conditions, even when not in use because of the isolation technique employed. Also, the unique purge sequence helps to remove the recirculated flue gas from recirculating ducting before initiating ignition of the burner.

The purge sequence starts by activating a ‘Purge Start’ switch. The operation of this switch initiates the purge sequence of a process heater, i.e., the burner. Upon completion, the blower speed is controlled by a variable frequency drive (VFD), i.e., VFD motor, and starts to ramp up to full speed to provide sufficient flow within the burner system to replace combustible gas in one or more recirculation lines with fresh air coming from the combustion air conduit.

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

In a standby/run sequence, the control systemallows an operator to operate the targeted gas burner system in a safe standby mode or a run mode, where the mode depends on the plant requirements. One or more safety interlocks associated with the firebox/burner temperature, fuel gas pressure, process heater oxygen percentage (O%), flame failure and other process heater trip conditions, will hold the targeted 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 warmed up with minimum load.