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  Fuel dilution for reducing nox productionUSPTO Application #: 20070048679Title: Fuel dilution for reducing nox production Abstract: A combustion device and combustion method for mixing a fuel and a fluid to form a diluted fuel mixture and passing the diluted fuel mixture through a nozzle. The nozzle comprises a nozzle body having an inlet face, an outlet face, and an inlet flow axis passing through the inlet face and the outlet face, and one or more slots extending through the nozzle body from the inlet face to the outlet face, each slot having a slot axis. (end of abstract) Agent: Air Products And Chemicals, Inc. Patent Department - Allentown, PA, US Inventors: Mahendra Ladharam Joshi, Xianming Jimmy Li, Aleksandar Georgi Slavejkov USPTO Applicaton #: 20070048679 - Class: 431008000 (USPTO) Related Patent Categories: Combustion, Process Of Combustion Or Burner Operation, Flame Shaping, Or Distributing Components In Combustion Zone The Patent Description & Claims data below is from USPTO Patent Application 20070048679. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application is a continuation-in-part of U.S. patent application Ser. No. 10/713,232, filed Nov. 14, 2003 and also a continuation-in-part of U.S. patent application Ser. No. 10/786,281, filed Feb. 25, 2004, which is a Division of U.S. patent application Ser. No. 10/353,683, filed Jan. 29, 2003, U.S. Pat. No. 6,866,503, each incorporated herein by reference. BACKGROUND [0002] Nozzles are used in a wide variety of applications to inject one fluid into another fluid and promote efficient mixing of the two fluids. Such applications include, for example, chemical reactor systems, industrial burners in process furnaces, fuel injectors in gas turbine combustors, jet engine exhaust nozzles, fuel injectors in internal combustion engines, and chemical or gas injection in wastewater treatment systems. Industrial burners may be used in heating reformers, process heaters, boilers, ethylene crackers, or other high temperature furnaces. The objective in these applications is to promote vortical mixing and rapid dispersion of the injected fluid into the surrounding fluid. It is usually desirable to achieve this efficient mixing with a minimum pressure drop of the injected fluid. [0003] The proper design of injection nozzles for burners in industrial furnaces and boilers is important for maximizing combustion efficiency and minimizing the emissions of carbon monoxide and oxides of nitrogen (NO.sub.x). In particular, tightening regulations on NO.sub.x emissions will require improved and highly efficient nozzle and burner designs for all types of fuels used in industrial furnaces and boilers. Burners in these combustion applications utilize fuels such as natural gas, propane, hydrogen, refinery offgas, and other fuel gas combinations of varying calorific values. Air, preheated air, gas turbine exhaust, oxygen-depleted air, industrial oxygen, and/or oxygen-enriched air can be used as oxidants in the burners. [0004] Conventional turbulent jets can be used in a circular nozzle tip to entrain secondary or surrounding combustion gases in a furnace by a typical jet entrainment process. The entrainment efficiency can be affected by many variables including the primary fuel and oxidant injection velocity or supply pressure, secondary or surrounding fluid flow velocity, gas buoyancy, primary and secondary fluid density ratio, and the fuel nozzle design geometry. Efficient low NO.sub.x burner designs require nozzle tip geometries that yield maximum entrainment efficiency at a given firing rate or at given fuel and oxidant supply pressures. Higher entrainment of furnace gases followed by rapid mixing between fuel, oxidant gas, and furnace gases produce lower average flame temperatures, which reduce thermal NO.sub.x formation rates. Enhanced mixing in the furnace space also can reduce CO levels in the flue gas. If the nozzle design geometry is not optimized, the nozzle may require much higher fuel and/or oxidant supply pressures or higher average gas velocities to achieve proper mixing in the furnace and yield the required NO.sub.x emission levels. [0005] In many processes in the chemical industry, the fuel supply pressure is limited due to upstream or downstream processes. For example, in the production of hydrogen or synthesis gas from natural gas by steam methane reforming (SMR), a reformer reactor furnace fired by a primary natural gas fuel produces a raw synthesis gas stream. After optional water gas shift to maximize conversion to hydrogen, a pressure swing adsorption (PSA) system is used to recover the desired product from the reformer outlet gas. Combustible waste gas from the PSA system, so-called PSA offgas, which typically is recovered at a low pressure, is recycled to the reformer as additional or secondary fuel. High product recovery and separation efficiency in a PSA system requires that blowdown and purge steps occur at pressures approaching atmospheric, and typically these pressures are as low as practical to maximize product recovery. Therefore, most PSA systems typically produce a waste gas stream at 5 to 8 psig (135 kPa to 155 kPa) for recycle to the reformer furnace. After a surge tank to even out cyclic pressure fluctuations and necessary flow control equipment for firing control, the waste gas supply pressure available for secondary fuel to the reformer furnace burners may be less than 3 psig (120 kPa). [0006] For cost-effective control of NO.sub.x emissions from SMR process furnaces, the burners should be capable of firing at these low secondary fuel supply pressures. If the burners cannot operate at these low pressures, the secondary fuel must be compressed, typically using electrically-driven compressors. For large hydrogen plants, the cost of this compression can be a significant portion of the overall operating cost, and it is therefore desirable to operate the reformer furnace burners directly on low-pressure PSA waste gas as the secondary fuel. [0007] Some commercially-available low NO.sub.x burners use active mixing control methods such as motor-driven vibrating nozzle flaps or solenoid-driven oscillating valves to produce fuel-rich and/or fuel-lean oscillating combustion zones in the flame region. In these burners, external energy is used to increase turbulent intensity of the fuel and oxidant jets to improve mixing rates. However, these methods cannot be used in all low NO.sub.x burner designs or heating applications because of furnace space and flame envelope considerations. Other common NO.sub.x control methods include dilution of fuel gas with recirculated flue gas or the injection of steam. By injecting non-reactive or inert chemical species in the fuel-oxidant mixture, the average flame temperature is reduced and thus NO.sub.x emissions are reduced. However, these methods require additional piping and costs associated with transport of flue gas, steam, or other inert gases. In addition, there is an energy penalty due to the required heating of dilution gases from ambient temperature to the process temperature. [0008] It is desirable that new low NOx burner designs utilize cost-effective passive mixing techniques to improve process economics. Such passive techniques utilize internal fluid energy to enhance mixing and require no devices that use external energy. In addition, new low NO.sub.x burners should be designed to operate at very low fuel gas pressures. Embodiments of the present invention, which are described below and defined by the claims which follow, present improved nozzle and burner designs which reduce NO.sub.x emissions to very low levels while allowing the use of very low pressure fuel gas. BRIEF SUMMARY [0009] In various embodiments, the invention relates to a nozzle comprising a nozzle body having an inlet face, an outlet face, and an inlet flow axis passing through the inlet face and the outlet face, and two or more slots extending through the nozzle body from the inlet face to the outlet face, each slot having a slot axis. The slot axis of at least one of the slots is not parallel to the inlet flow axis of the nozzle body. The nozzle may further comprise a nozzle inlet pipe having a first end and a second end, wherein the first end is attached to and in fluid flow communication with the inlet face of the nozzle body. The slot axes of at least two slots in the nozzle may or may not be parallel to each other. The ratio of the axial slot length to the slot height may be between about 1 and about 20. [0010] At least two of the slots in the nozzle may intersect each other. The nozzle may have three or more slots and one of the slots may be intersected by each of the other slots. In one configuration, the nozzle has four slots wherein a first and a second slot intersect each other and a third and a fourth slot intersect each other. [0011] In various embodiments, the invention relates to a nozzle comprising a nozzle body having an inlet face, an outlet face, and an inlet flow axis passing through the inlet face and the outlet face, and two or more slots extending through the nozzle body from the inlet face to the outlet face, each slot having a slot axis and a slot center plane. None of the slots intersect other slots and all of the slots are in fluid flow communication with a common fluid supply conduit. The center plane of at least one slot may intersect the inlet flow axis. [0012] In various embodiments, the invention relates to a nozzle comprising a nozzle body having an inlet face, an outlet face, and an inlet flow axis passing through the inlet face and the outlet face, and two or more slots extending through the nozzle body from the inlet face to the outlet face, each slot having a slot axis and a slot center plane. A first slot of the two or more slots may be intersected by each of the other slots and the slot center plane of at least one of the slots may intersect the inlet flow axis of the nozzle body. The center plane of the first slot may intersect the inlet flow axis at an included angle of between 0 and about 30 degrees. The center plane of any of the other slots may intersect the inlet flow axis at an included angle of between 0 and about 30 degrees. The center planes of two adjacent other slots may intersect at an included angle of between 0 and about 15 degrees. The two adjacent other slots may intersect at the inlet face of the nozzle body. [0013] In various embodiments, the invention relates to a burner comprising: [0014] (a) a central flame holder having inlet means for an oxidant gas, inlet means for a primary fuel, a combustion region for combusting the oxidant gas and the primary fuel, and an outlet for discharging a primary effluent from the flame holder; and [0015] (b) a plurality of secondary fuel injector nozzles surrounding the outlet of the central flame holder, wherein each secondary fuel injector nozzle comprises [0016] (1) a nozzle body having an inlet face, an outlet face, and an inlet flow axis passing through the inlet face and the outlet face; and [0017] (2) one or more slots extending through the nozzle body from the inlet face to the outlet face, each slot having a slot axis and a slot center plane. [0018] Each secondary fuel injector nozzle of the burner assembly may have two or more slots and the slot axes of at least two slots may not be parallel to each other. Each secondary fuel injector nozzle may have two or more slots and at least two of the slots may intersect each other. The nozzle body may have four slots, wherein a first and a second slot intersect each other, and wherein a third and a fourth slot intersect each other. [0019] Alternatively, the nozzle body may have three or more slots and a first slot may be intersected by each of the other slots. The center plane of the first slot may intersect the inlet flow axis at an included angle of between 0 and about 15 degrees. The center plane of any of the other slots may intersect the inlet flow axis at an included angle of between 0 and about 30 degrees. The center planes of two adjacent other slots may intersect at an included angle of between 0 and about 15 degrees. The two adjacent slots may intersect at the inlet face of the nozzle body. [0020] In various embodiments, the invention relates to a combustion process comprising: [0021] (a) providing burner assembly including: [0022] (1) a central flame holder having inlet means for an oxidant gas, inlet means for a primary fuel, a combustion region for combusting the oxidant gas and the primary fuel, and an outlet for discharging a primary effluent from the flame holder; and [0023] (2) a plurality of secondary fuel injector nozzles surrounding the outlet of the central flame holder, wherein each secondary fuel injector nozzle comprises [0024] (2a) a nozzle body having an inlet face, an outlet face, and an inlet flow axis passing through the inlet face and the outlet face; and [0025] (2b) one or more slots extending through the nozzle body from the inlet face to the outlet face, each slot having a slot axis and a slot center plane; [0026] (b) introducing the primary fuel and the oxidant gas into the central flame holder, combusting the primary fuel with a portion of the oxidant gas in the combustion region of the flame holder, and discharging a primary effluent containing combustion products and excess oxidant gas from the outlet of the flame holder; and [0027] (c) injecting the secondary fuel through the secondary fuel injector nozzles into the primary effluent from the outlet of the flame holder and combusting the secondary fuel with excess oxidant gas. [0028] The primary fuel and the secondary fuel may be gases having different compositions. The primary fuel may be natural gas and the secondary fuel may comprise hydrogen, methane, carbon monoxide, and carbon dioxide obtained from a pressure swing adsorption system. The secondary fuel may be introduced into the secondary fuel injector nozzles at a pressure of less than about 3 psig (122 kPa). The primary fuel and the secondary fuel may be gases having the same compositions. [0029] As defined herein, an oxidant gas is an oxygen-containing gas, for example air, oxygen-depleted air, oxygen-enriched air, and industrial oxygen. [0030] In various embodiments, the invention relates to a combustion method comprising: [0031] (a) mixing a first substantially gaseous fuel having a first fuel index and a fluid having a second fuel index which is different from the first fuel index in a conduit thereby forming a diluted fuel mixture; and [0032] (b) passing the diluted fuel mixture through a nozzle, the nozzle comprising: [0033] (1) a nozzle body having an inlet face, and outlet face, and an inlet flow axis passing through the inlet face and the outlet face; and [0034] (2) one or more slots extending through the nozzle body from the inlet face to the outlet face, each slot having a slot axis. [0035] A residence time for the diluted fuel mixture in the conduit is defined as the volume of the conduit divided by the volumetric flow rate of the combined fuel and fluid streams. The residence time may be 0.1 to 10 milliseconds. [0036] The nozzle may comprise two or more slots extending through the nozzle body from the inlet face to the outlet face. The second fuel index may be less than the first fuel index by at least by at least 0.1, or by at least 0.25, or by at least 0.75. Continue reading... Full patent description for Fuel dilution for reducing nox production Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Fuel dilution for reducing nox production patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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