Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN  A CARRIER GAS OR AIR 
  • F23C6/00—Combustion apparatus characterised by the combination of two or more combustion chambers or combustion zones, e.g. for staged combustion
  • F23C6/04—Combustion apparatus characterised by the combination of two or more combustion chambers or combustion zones, e.g. for staged combustion in series connection
  • F23C6/045—Combustion apparatus characterised by the combination of two or more combustion chambers or combustion zones, e.g. for staged combustion in series connection with staged combustion in a single enclosure
  • F23C6/047—Combustion apparatus characterised by the combination of two or more combustion chambers or combustion zones, e.g. for staged combustion in series connection with staged combustion in a single enclosure with fuel supply in stages
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN  A CARRIER GAS OR AIR 
  • F23C7/00—Combustion apparatus characterised by arrangements for air supply
  • F23C7/002—Combustion apparatus characterised by arrangements for air supply the air being submitted to a rotary or spinning motion
  • F23C7/004—Combustion apparatus characterised by arrangements for air supply the air being submitted to a rotary or spinning motion using vanes
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN  A CARRIER GAS OR AIR 
  • F23C9/00—Combustion apparatus characterised by arrangements for returning combustion products or flue gases to the combustion chamber
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23L—SUPPLYING AIR OR NON-COMBUSTIBLE LIQUIDS OR GASES TO COMBUSTION APPARATUS IN GENERAL ; VALVES OR DAMPERS SPECIALLY ADAPTED FOR CONTROLLING AIR SUPPLY OR DRAUGHT IN COMBUSTION APPARATUS; INDUCING DRAUGHT IN COMBUSTION APPARATUS; TOPS FOR CHIMNEYS OR VENTILATING SHAFTS; TERMINALS FOR FLUES
  • F23L7/00—Supplying non-combustible liquids or gases, other than air, to the fire, e.g. oxygen, steam
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN  A CARRIER GAS OR AIR 
  • F23C2202/00—Fluegas recirculation
  • F23C2202/20—Premixing fluegas with fuel

Definitions

• This invention relates to a burner having reduced N0 X emissions and, in particular, to a burner wherein flow and mix rates may be varied in accordance with the combustion characteristics and demand rate of the burner.
• the specific adjustments of an existing burner may be retrofitted to vary for optimization with demand.
• Combustion system burners have come under increased scrutiny for the toxic emissions which are a by-product of the combustion process. Depending upon the extent of combustion, carbon monoxide and NO x may be omitted at unacceptable levels. Carbon monoxide levels can normally be controlled through complete combustion resulting in carbon dioxide. However, three factors contribute to the formation of NO ⁇ in combustion systems. The first and most widely recognized is flame temperature. Most current systems incorporate some method of staging fuel and air to reduce flame concentration and resultant high temperatures. A second factor is excess 0 2 levels. Higher 0 levels tend to provide more oxygen for combination with nitrogen; however, the higher 0 2 levels results in excess air which tends to balance the effect of lower temperatures. The laminar mix in most current low NO ⁇ burners requires more 0 for complete combustion. If lower 0 2 levels are utilized the result is incomplete combustion in the form of carbon monoxide. The third factor is residence time in a critical temperature zone which is virtually ignored in modern burners because reduced time means higher velocities producing unacceptable temperatures.
• FGR external, induced or forced flue gas recirculation
• the present invention overcomes the disadvantages of the prior known burner systems by providing a low N0 ⁇ burner with an adjustable design for application in many different systems and in response to different operating conditions.
• the burner of the present invention may be installed as a retro-fit adapter for existing burner systems.
• the low N0 ⁇ burner of the present invention includes a plurality of coaxial passageways through which combustion gases flow.
• Primary air flows through an inner passageway within which a spin vane is positioned.
• the spin vane may be axially adjusted to optimize combustion.
• the flow of primary air from the forced air windbox into the burner is controlled by a damper having adjustable louvers to further improve combustion.
• As the primary air passes through the vane it is caused to spin and mix with the fuel supplied through a series of eductor nozzles radially spaced about the primary combustion zone.
• the nozzles mix the fuel with secondary combustion air from the windbox prior to eduction into the combustion chamber.
• recirculated flue gas may be mixed with the fuel in the eductor nozzles.
• a chamber throat formed of refractory materials forms a secondary combustion zone where reradiation from the refractory throat heats the fuel/air mix and speeds the burning process.
• a final tertiary burn takes place in a tertiary combustion zone beyond the refractory throat where laminar mixing occurs as a result of the tertiary air supply which bypasses the initial combustion zones.
• the system of the present invention provides improved reduction of N0 X emissions through three distinct means: (1) Recirculation of flue gases for mixing with combustion fuel prior to injection into the combustion chamber; (2) Use of eductor nozzles to mix combustion fuel with recirculated flue gases prior to combustion; and (3) Injection of a chemical or other secondary compound into flue gas inlet. With flue gas temperatures approximating 400°F the compound injected into the flue gas is vaporized which cools the flue gas resulting in more efficient operation of the eductors and lower flame temperatures. Possible injection compounds include chemicals such as methanol, steam or water, cool air or waste materials.
• the present system reduces N0 ⁇ emissions without the trade off of increased CO emissions of prior known burners by optimizing the volume and mix of combustion air to the staged combustion zones.
• the burn temperature and residence time of the combustion gases are controlled through the various adjustments of the burner system.
• N0 X emission levels are reduced by controlling the 0 2 levels within the combustion zones, temperature of the recirculated combustion gases and residence time within burner. These parameters are controlled by varying the pitch angle of the diffuser blades, the length of the chamber from the vane diffuser to the fuel jets, and the ratio of primary combustion air flowing through the central passage to secondary and tertiary (if present) combustion air flowing to subsequent combustion zones.
• the present system includes internal flue gas recirculation which maintains the temperature of the recirculated gases while ensuring complete combustion. While the adjustable vane reduces CO levels, recirculation through the eductor nozzles reduces N0 ⁇ levels.
• FIGURE 1 is a cross-sectional view of a low N0 X burner embodying the present invention
• FIGURE 2 is an enlarged perspective of the eductor nozzles within circle 2 of Fig. 1;
• FIGURE 3 is a cross-sectional view of an alternative embodiment of the low N0 ⁇ burner
• FIGURE 4 is an end view thereof
• FIGURE 5 is an enlarged perspective of the eductor nozzles of Fig. 3 for injecting combustion fuel
• FIGURE 6 is an enlarged perspective of the eductor nozzles of Fig. 3 for injecting recirculated flue gases.
• FIG. 1 shows a high efficiency, low N0 X emission burner 10
• Figure 3 shows an alternative construction for optimizing recirculation and mix of combustion fuel with recirculated flue gases to reduce N0 X emissions.
• the embodiment of the present invention provide a high efficiency burner whereby flame temperature, burn rate, etc. are strictly controlled yet undesirable emissions are substantially reduced.
• the burner 10 of the present invention includes an outer housing 12 adapted to be bolted or welded to a wall of a boiler or similar structure.
• the housing 12 directs combustion air from a forced air windbox through adjustable louvers 14 into a central air passage 16.
• Axially positioned within the air passage 15 is a pipe 18 through which combustion fuel, such as refinery oil or natural gas, amy be supplied.
• a spin vane 20 attached to the pipe 18 imparts a rotational mix on the combustion air flowing across the vane 20 to ensure an optimum mix of combustion air and fuel.
• the axial position of the spin vane 20 and the angle of the vent blades may be selectively adjusted to optimize burn rates while minimizing emissions such as CO.
• the damper 14 may be selectively adjusted to control the volume of combustion air flowing into the combustion zones in the central passage 16 to further optimize combustion.
• the burner 10 includes passageways for delivery of both combustion fuel and recirculated flue gases to the combustion chamber 16.
• Flue gases are recirculated through an inlet 22 which communicates with the flue of the burner 10.
• the flue gases are directed through a plurality of passageways 24 which communicate with annular flue gas chambers 26 extending about the central passage 16.
• Combustion fuel is supplied through a fuel inlet 28 and diverted through a plurality of passageways 30 to annular combustion fuel chambers 32 extending about the central passage 16.
• the annular fuel chambers 32 are disposed within the annular flue gas chambers 26 to facilitate ready communications.
• the annular chambers are longitudinally spaced along the central passage 16 in accordance with the desired combustion zones of the burner 10. In the example depicted in Fig. 1, three longitudinally spaced chambers are utilized to create primary, secondary and tertiary combustion zones.
• a primary combustion zone is created by a first set of eductor nozzles 34 in fluid communication with both the combustion gas chamber 26 and the combustion fuel chamber 32.
• the first eductor nozzles 34 are circumferentially spaced about the air passage 16 to deliver the mixture of flue gas and fuel into the passage 16 just downstream of the spin vane 20 creating the primary combustion zone.
• a secondary combustion zone is created by a second set of eductor nozzles 36 in fluid communication with both the combustion gas chamber 26 and the combustion fuel chamber 32.
• the second eductor nozzles 36 are circumferentially spaced about the air passage 16 to deliver the mixture of the gas and fuel into the passage 16 downstream of the first eductor nozzles 34 creating the secondary combustion zone.
• a tertiary combustion zone is created by a third set of eductor nozzles 38 in fluid communication with both the combustion gas chamber 26 and the combustion fuel chamber 32.
• the third eductor nozzles 38 are circumferentially spaced at the mouth of the central air passage 16 to deliver the mixture of flue gas and fuel into a tertiary combustion zone.
• Refractory material 40 lines the combustion chamber 16 to direct combustion through the burner 10.
• the eductor nozzles 34,36,38 comprise tubular bodies with an outlet 42 in communication with the combustion chamber 16 and an inlet 44 in communication with both the flue gas chamber 26 and the combustion fuel chamber 32.
• the combustion fuel is supplied under pressure to the chamber 32.
• the chamber 32 includes an aperture 46 axially aligned with the eductor nozzle 36 and in close proximity to the inlet 44.
• the pressure of the combustion fuel directs the fuel through the apertures 46 into the eductor nozzles 36.
• the nozzles 36 are spaced from the chamber 32 creating a gap placing the inlet in direct communication with the flue gas chamber 26.
• combustion fuel flows into the eductor nozzles, recirculated combustion gas is drawn into the eductor nozzles 36 and mixed with the fuel under compression.
• a mixture of combustion gas and combustion fuel will be injected into the central air passage 16 by the eductor nozzles 34,36,38.
• the flue gas temperature is approximately 400°F, the temperature of the combustion fuel will be increased prior to combustion. The resulting mix and increase in temperature optimizes the burn rate while substantially reducing noxious emissions such as N0 X and CO.
• the secondary compound is injected at the flue gas inlet 22 for mixture/vaporization in the recirculated flue gases.
• the raised temperature of the flue gas causes vaporization of the secondary compound injected therein.
• Examples of possible secondary compounds include chemicals such as methanol, steam or water, and chemical waste materials which are combustible.
• the injection of water has a cooling effect on the flue gas resulting in more efficient operation of the eductors and a lower flame temperature for a more even or complete burn.
• the flue gas/compound mixture then proceeds to the annular passages 26 for mixture with the combustion fuel as previously described.
• FIGs 3 through 6 show a retrofit version of a burner 100 embodying the principles of the present invention.
• the retrofit assembly 100 is utilized in replacement of exiting burners on older boilers and the like.
• the central air passage 116 includes a spin vane 120 mounted to tube 118.
• Recirculated flue gas is delivered through inlet 122 to an annular flue gas chamber 126 which is in fluid communication with both first eductor nozzles 134 and second eductor nozzles 136.
• Combustion fuel is supplied through inlet 128 to annular chamber 132 to force combustion fuel through apertures 146 into the eductor nozzles 134,136, recirculated flue gas is drawn into the nozzles for injection into the combustion chamber 116.
• the principles of a newly constructed burner can be applied to a retrofit version for installation in existing boiler construction.
• the adjustable aspects of the burner system of the present invention are designed to be adjusted for the specific combustion system being employed.
• the diffuser vane angle, the axial position of the diffuser, and the damper opening can all be individually set in accordance with known parameters of the burner system, namely fuel type, desired temperature, burn rate, etc. This is particularly significant in the retrofit conversion system where the operating parameters have been established.
• primary combustion occurs at the fuel nozzles 34,134 where initial mix of fuel and air occurs.
• the products of the primary combustion which is approximately 60% combustible, enter the refractory lined combustion zone 16,116 where further mix occurs with combustion air from the central air passage 16,116 and the diffuser 20,120.
• a secondary burn is accomplished in this highly controlled area where the reradiation from the refractory heats the products thereby speeding the burning process which consumes approximately 80% of the remaining combustible products.
• a final tertiary burn takes place in the furnace area where laminar mixing occurs.
• the distinct combustion zones are created through the creation of low pressure areas within the burner, namely directly downstream of the vent diffuser 20,120 and at the exhaust of the circumventing air.
• the low pressure area proximate the diffuser is affected by the pitch of the vane blades — as the vane diffuser is opened the pressure behind the flame is reduced.
• the several adjustments of the burner system of the present invention creates a N0 X trim system wherein the emission levels can be optimally controlled along the complete range of demand levels of a modulating burner.
• the N0 X trim system automatically adjusts the angular and axial position of the vane diffuser to vary the swirl number of the combustion air mix, the ratio of core air to annular air and the 0 2 levels in the burner across all the demand levels of the burner.
• These adjustments may be optimally determined across all demand levels of the burner such that as these levels are attained the trim system automatically adjusts the components of the system to reduce emission levels.
• Typical prior known burners have their emission levels set for operation in a nominal operating range sacrificing emission levels when demand levels fall outside of this range.
• the several adjustments of the present invention allows continuous automatic control of emission levels at all operating demand levels. Modern burners require continuous monitoring of N0 ⁇ levels from the burner. The data from these monitoring systems can be utilized to automatically adjust the NO ⁇ trim system according to the present invention.
• steps can be taken to further reduce emission levels or, alternatively, to reduce emission levels in fixed or non-adjustable burner systems.
• prior known systems have attempted to recirculate flue gases through the combustion chamber, it has been determined that combustion is optimized when flue gases are mixed with combustion fuel prior to introduction into the combustion zones. In the present invention, this mixture occurs through the eductor nozzles which communicate with both the combustion fuel chamber and the flue gas recirculation chamber.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Combustion & Propulsion (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)

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• 1994
  • 1994-03-22 JP JP6521316A patent/JPH08501143A/ja active Pending
  • 1994-03-22 EP EP94912832A patent/EP0640003A4/de not_active Withdrawn
  • 1994-03-22 CA CA002135772A patent/CA2135772A1/en not_active Abandoned
  • 1994-03-22 WO PCT/US1994/003072 patent/WO1994021357A1/en not_active Application Discontinuation
  • 1994-03-22 RU RU9494046129A patent/RU2089785C1/ru active

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