WO2000061992A1

WO2000061992A1 - Tunneled multi-blade swirler/gas injector for a burner

Info

Publication number: WO2000061992A1
Application number: PCT/US2000/009190
Authority: WO
Inventors: Hamid Sarv
Original assignee: McDermott Technology Inc
Current assignee: McDermott Technology Inc
Priority date: 1999-04-09
Filing date: 2000-04-07
Publication date: 2000-10-19
Anticipated expiration: 2001-10-09
Also published as: AU4451700A

Abstract

A swirler (10) for a fossil-fuel fired burner used in connection with a furnace or boiler has a hollow guide pipe (20) supporting several swirl blades (30) at an end (50) adjacent the furnace. Internal tunnels (34) within the swirl blades (30) connect the hollow guide pipe (20) to discharge openings (32) provided in the trailing edges of each swirl blade (30). Gaseous substances such as oxygen or natural gas are provided through the guide pipe (20) and tunnels (34) to the discharge openings (32) for pre-mixing at the burner throat to reduce NOX formation, and/or to improve ignition and flame stability.

Description

TUNNELED MULTI-BLADE SWIRLER/GAS INJECTOR FOR A BURNER

BACKGROUND OF THE INVENTION

1. FIELD OF THE INVENTION

The present invention relates generally to the field of industrial furnace and utility boiler fossil fuel burners and. in paπicular, to a new and useful burner swirler with tunnels in the swirler blades for injecting a gaseous substance such as natural gas or oxygen into the combustion mix.

2. DESCRIPTION OF THE RELATED ART Fossil fuel-burning industrial and utility power plants emit oxides of nitrogen (nitric oxide. NO and nitrogen dioxide. NO_:) - generally referred to as NO_x - by oxidizing the nitrogen contents of the combustion air and/or the fuel. NO_x is a known precursor to acid rain, photochemical smog and air pollution. Various methods have been formulated to reduce NO_x emissions. One such NO_x reduction method involves the use of natural gas in fossil fuel burners.

As taught by U.S. Patent No. 5.807.094 to Sarv. an air-premixed natural gas burner is provided which reduces NO_x formation resulting from partial pre-mixing of air and natural gas adjacent the burner throat. The entire disclosure of U.S. Patent No. 5.807.094 is hereby incorporated by reference as though fully set forth herein. U.S. Patent No. 5.470.224 to Bortz discloses a burner having natural gas injected between the blades of an air swirler for rapid mixing. A physical embodiment of the burner is sold by Todd Combustion Company under the name Rapid Mix Burner RMB™.

U.S. Patent No. 5.829.369 to Sivv et al. describes the use of axial natural gas elements for co-firing fuel gas with pulverized coal.

None of the prior improvements to burners incorporate a gas injection and mixing mechanism which is contained solely within the swirler.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an apparatus for use in burners used for the combustion of fossil fuels.

It is a further object of the invention to provide a swirler having an injection mechanism for supplying natural gas to a combustion zone to reduce NO_x formation. It is also an object of the invention to provide a swirler having an injection mechanism for supplying oxygen to a combustion zone to enhance ignition and flame stability for hard-to-burn solid fuels.

Another object of the invention is to provide a swirler for use with liquid fuel burning burners. Accordingly , a swirler with a hollow guide pipe supporting multiple blades adjacent a furnace end is provided. The swirler blades each include tunnels in fluidic communication with a transport passage located inside the hollow guide pipe and openings in the swirler blade edges facing the furnace combustion chamber. The tunnels may be used to transport oxygen, natural gas, or other combustible gaseous substances. The tunnels may comprise a single passage or multiple passages interconnecting the transport passage to one or more openings in the trailing edge of the swirl blade.

The particular orientations, size, angle, cross-sectional shape, and number of openings in each blade edge, as well as the number of swirl blades, can be varied depending on the application, including desired stoichiometry, extent of mixing, exit velocities, supply pressure, and overall burner design.

In an alternative embodiment, the swirler comprises an inner liquid fuel pipe inserted through the hollow guide pipe and forms an annular passage therebetween, and a liquid fuel atomizer is connected to the inner liquid fuel pipe and located at the furnace end of the hollow guide pipe. Again, one or more tunnels are provided to fluidically interconnect the annular passage to the openings.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is illustrated.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

Fig. 1 is a perspective view of a swirler according to the invention; Fig. 2 is a side elevational view of a natural gas burner employing the swirler of the invention;

Fig. 3 is a side elevational view of a pulverized coal burner using the swirler of the invention; and Fig. 4 is a perspective view of an alternate embodiment of the swirler used with liquid fuel fired burners.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings, in which like reference numerals are used to refer to the same or functionally similar elements, Fig. 1 shows a swirler 10 for a burner (not shown in Fig. 1) having a hollow guide pipe 20 which defines a transport passage 22 therein and which also supports several swirl blades 30 adjacent a furnace end 50 of the hollow guide pipe 20. The swirl blades 30 of swirler 10 impart a desired spin to air or mixtures of pulverized coal and air which are conveyed past the swirler 10, thereby improving the air or air/fuel mixing adjacent the burner throat (not shown in Fig. 1). Furnace end 50 of swirler 10 is typically positioned very close to the burner throat opening into the associated furnace and is oriented facing the furnace combustion region.

The transport passage 22 is used to carry gaseous substances, generally referred to as 40, into the combustion region to improve the combustion process. The gaseous substance 40 may advantageously comprise oxygen to facilitate combustion, or it may itself comprise a combustible gas such as, but not limited to, natural gas, propane, methane, refinery gas, etc. The swirl blades 30 are fixedly mounted to the outside of the hollow guide pipe 20 in a known manner and orientation, but the number of swirl blades 30 and their orientation can be varied as required depending on the application of the swirler 10 to a given burner.

Each swirl blade 30 is provided with at least one hole or opening 32 in a trailing edge of the swirl blade 30 adjacent the furnace end 50 of the hollow guide pipe 20. Preferably, a plurality of openings 32 is provided in each swirl blade 30. The opening(s) 32 are fluidically connected to the transport passage 22 by at least one tunnel 34 provided within the body of the swirl blade 30. In the simplest form of the invention, a single tunnel 34 may be provided in each swirl blade 30, fluidically connecting the transport passage 22 with a single opening 32 so that the gaseous substances 40 within the transport passage 22 can be conveyed through the swirl blades 30 and out through the openings 32. However, various combinations, shapes, and configurations of the tunnel 34 may be provided in each swirl blade 30. For example, each tunnel 34 could define a substantially straight flow passage from the transport passage 22 to a given opening 32, or the tunnel 34 could be provided with segments or be curved or provided with what could be defined as an inlet portion 36 and an outlet portion 38 as illustrated in Fig. 1. Multiple, independent tunnels 34 could be provided, one for each opening 32. Alternatively, as shown in Fig. 1, a tunnel 34 could be provided with a single inlet portion 36 that could serve essentially as a manifold which feeds multiple outlet portions 38 and their associated openings 32. If desired, the inlet portions 36 could extend substantially radially outwards from a longitudinal axis A of the hollow guide pipe 20, with the outlet portions 38 extending substantially parallel to the longitudinal axis A. In any event, and regardless of their configuration, the important feature of any of the tunnels 34 is that each defines a fluidic passage within the swirl blade 30 which fluidically conveys a gaseous substance 40 from the transport passage 22 to and at through the openings 32. Fig. 2 shows the swirler 10 of the invention used in a gas-fired burner 90 for a furnace. Combustion air 100 is provided to the outlet end of the burner 90 via conventional elements including a core air damper 92 and adjustable spin vanes 94 within a burner barrel 96. The burner 90 itself would not be located within a windbox 98. The swirler 10 has hollow guide pipe 20 supported along a central longitudinal axis A of the gas-fired burner 90. Swirl blades 30 are adjacent the furnace end 50 of the hollow guide pipe 20 and are positioned in close proximity to a burner throat 60 defined by burner quarl 62. In this case, the gaseous substance 40 is advantageously natural gas, and is supplied through the transport passage 22 in the guide pipe 20 to the tunnels 34 in the swirl blades 30. When the swirler 10 is used in this configuration, it is thus possible to create a locally pre-mixed, fuel-rich zone which suppresses flame temperature and oxygen concentration adjacent the burner throat 60. These conditions result in lower NO_x formation. Further NO_x reduction can also be achieved by recirculating a portion of the combustion products from the furnace exit and mixing the recirculated combustion product gases with the combustion air 100 prior to entering the windbox 98.

Fig. 3 illustrates use of the swirler 10 of the invention in a pulverized coal-fired burner 120. As is known to those skilled in the art, a mixture of primary air and pulverized coal 122 is provided to a coal supply nozzle 124. A distribution cone or primary air /pulverized coal (PA/PC) mixing device, schematically shown at 126, is generally provided therein to prevent coal roping within the nozzle 124. Secondary air 128 is provided via a control damper 130 to fixed and adjustable spin vanes 132, 124, respectively, located within a burner barrel 136. The swirler 10 and its swirl blades 30 swirls the PA/PC mixture passing thereacross. The swirler 10 positioned within the coal supply nozzle 124 adjacent the furnace throat 60 can be used to provide either natural gas or oxygen 40 through the hollow guide pipe 20 and tunnels 34 within the swirl blades 30 to the openings 32 at the furnace end 50 of the coal supply nozzle 124. The furnace end 50 of the hollow guide pipe 20 is again positioned near the end of the coal nozzle 124 and adjacent the furnace. Natural gas co-firing using the swirler 10 not only reduces NO_x formation and unburned carbon emissions, but also improves flame stability at πiinimum firing rates. Other benefits include lower SO₂ and CO₂ emissions from the furnace. Injecting fuel gas 40 near the exit of the coal supply nozzle 124 from the swirler 10 scavenges oxygen from the NO_x and converts it to N₂ (elemental nitrogen).

The extent of natural gas co-firing can range from 10% to 100% of the combined heat release by natural gas and pulverized coal. At 10% natural gas co-firing, 90% of the heat release is supplied by coal.

In the case of difficult to burn anthracitic and low- volatile coals, the gaseous substance 40 would preferably be oxygen and would be injected through the tunnels 34 in the swirl blades 30 to enhance the ignition and flame stability over a wide load range. A small amount of oxygen 40 can be injected through the transport passage 22 and conveyed via the tunnels 34 to the openings 32 in the swirl blades 30 to raise the elemental oxygen concentration to about 25-35 % by volume. Typically, oxygen concentration in atmospheric combustion air is only about 21 % by volume. The higher oxygen concentration improves the combustion reactions, fuel ignition, and flame stability.

An alternate embodiment of the swirler, generally referred to as 200, can be used with liquid fuel burners and is shown in Fig. 4. The swirler 200 is again provided with a hollow guide pipe 20, but in this case the hollow guide pipe 20 surrounds an inner liquid fuel supply pipe 210. An annular passage 212 is thus formed between the hollow guide pipe 20 and the inner liquid fuel supply pipe 210. Natural gas, oxygen or suitable gaseous substance 40 (as described above) can be supplied through the annular passage 212 to the openings 32 in the swirl blades 30 via the tunnels 34. The tunnels 34 are again formed as described above in connection with the first embodiment shown in Fig. 1. Inner liquid fuel supply pipe 210 is used to carry liquid fuel (such as fuel oil) and an atomizing medium, collectively designated 214, to a liquid fuel atomizer 216 provided in the furnace end 50 of the swirler 200.

As described earlier, different configurations and orientations of the tunnels 34 are possible and which can be used to transport any gaseous substance 40 to the openings 32 in a manner consistent with this invention. The size, shape, angle, number and orientation of the openings 32, as well as the size, shape, angle, number, and orientation of the swirl blades 30 can be varied to further improve NO_x reduction, fuel ignition, and flame stability in the furnace when a burner is provided with the swirler 10 of the present invention. The present invention can be used with both staged (substoichiometric) and unstaged (stoichiometric or above) combustion. Significantly, the present invention can be employed in retrofit applications to existing burners, as well as in new burner constructions.

While a specific embodiment of the invention has been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing" from such principles.

Claims

CLAIMS I CLAIM:

1. A swirler for a burner, comprising: a hollow guide pipe having a furnace end, the inside of the hollow guide pipe defining a transport passage; a plurality of swirl blades mounted on the hollow guide pipe adjacent the furnace end, each swirl blade having a trailing blade edge nearest the furnace end; at least one opening in each of the trailing blade edges; and each swirl blade having at least one tunnel fluidically connecting the at least one opening to the transport passage.

2. The swirler according to claim 1 , wherein the at least one tunnel comprises an inlet portion fluidically connected to the transport passage and an outlet portion fluidically connected thereto and to the at least one opening.

3. The swirler according to claim 1 , wherein the at least one tunnel comprises an inlet portion fluidically connected to the transport passage and plural outlet portions fluidically connected thereto and to plural openings.

4. The swirler according to claim 1, comprising an inner liquid fuel pipe inserted through the hollow guide pipe and forming an annular passage therebetween, and a liquid fuel atomizer connected to the inner liquid fuel pipe at the furnace end.

5. A fossil-fuel fired burner, comprising: a burner barrel having a central passageway surrounded by at least one annular passageway, the burner barrel having a furnace throat end; a swirler oriented concentric within the central passageway of the burner barrel, the swirler having a plurality of swirl blades at a swirler furnace end; and means for providing a gaseous substance through the swirler to at least one opening in each of the plurality of swirl blades.

6. The burner according to claim 5, wherein the at least one opening in each of the plurality of swirl blades is located in a trailing edge of each swirl blade.

7. The burner according to claim 5 , wherein the means for providing a gaseous substance through the swirler comprises a hollow guide pipe supporting the plurality of swirl blades within the central passageway, the hollow guide pipe defining a transport passage, and tunnel means provided in each of the swirl blades fluidically connected to the transport passage and to the at least one opening in each of the plurality of swirl blades.

8. The burner according to claim 5, wherein the burner is a pulverized coal burner and the central passageway comprises a coal supply nozzle.

. The burner according to claim 8 , wherein the means for providing a gaseous substance through the swirler comprises a hollow guide pipe supporting the plurality of swirl blades within the coal supply nozzle, the hollow guide pipe defining a transport passage, and tunnel means provided in each of the swirl blades fluidically connected to the transport passage and to the at least one opening in each of the plurality of swirl blades.

10. The burner according to claim 7, wherein the burner is a liquid fuel fired burner and further comprising an inner liquid fuel pipe inserted through the hollow guide pipe and forming an annular passage therebetween, and a liquid fuel atomizer connected to the inner liquid fuel pipe at the furnace end.