WO2004090421A1

WO2004090421A1 - Nox reduction in burners

Info

Publication number: WO2004090421A1
Application number: PCT/CA2004/000553
Authority: WO
Inventors: John D. Chato
Original assignee: Chato John D
Priority date: 2003-04-14
Filing date: 2004-04-14
Publication date: 2004-10-21
Also published as: CA2425777A1

Abstract

It has now been discovered that NOX generation can be curtailed by ensuring that substantially all of the burning gases are subjected to a sufficient degree of turbulence. The present invention is directed to a method of burning a gaseous fuel with air, utilizing an apparatus (8) defining a mixing chamber (28), a combustion chamber (12) and an access opening (30) through which the fuel/air mixture can pass into the combustion chamber, the method comprising the steps of mixing the fuel and air and passing the mixture through the access opening in such a way as to eliminate laminar flow and to subject the mixture to turbulent flow.

Description

NOX Reduction in Burners

This invention relates generally to fuel burners, and has to do particularly with a burner design which can be operated in such a way as to greatly reduce the presence of Nitrogen/Oxygen compounds (NOX) in the downstream combustion gases.

Background of the Invention

NOX compounds have been a problem of long standing in burner technology. Attempts have been made to control the formation of NOX compounds by adjusting the air-fuel ratio in the combustible mixture, but with only limited success.

The Prior Art

The essential components of a conventional gaseous fuel burner can be summarized as including a mixing chamber where the gaseous fuel and oxidant (air) can be mixed and maintained under pressure, a combustion chamber at lower pressure than the mixing chamber, and means defining a restricted opening which allows the mixture to pass from the mixing chamber to the combustion chamber. Ignition means are also provided, for initiating or maintaining combustion.

Because of the high Nitrogen content of the air (about 80%), a problem of long-standing is encountered in most burners of conventional design, relating to the formation of various Nitrogen/Oxygen compounds (collectively referred to as NOX). These compounds are regarded as toxic to animal life and deleterious to the environment.

General Description of the invention

The inventor has discovered that a striking reduction in the NOX content of the products of combustion can be attained by ensuring that substantially all of the combustible mixture (fuel/air) exhibits turbulent flow as it enters the combustion chamber. As will appear more clearly below, the provision of sharp edges on the portions defining the opening into the combustion chamber, and the design of the opening to ensure that no part of the inflowing gaseous fuel mixture is too far away from a sharp edge (readily established by simple experiment), appear to establish the necessary conditions for subjecting virtually all of the air-fuel mixture to the mechanical agitation needed to promote the formation of carbon oxides and suppress the formation of NOX.

While not wishing to be bound by theory, it is speculated that, when a portion of the mixture enters the combustion chamber without turbulence, the steady or "laminar" flow of that portion favors the chemical formation of NOX at the expense of carbon/oxygen compounds. Consequently, in order to promote the burning of carbon in the fuel mixture, and the suppression of NOX formation, the way to proceed is to establish conditions in which the full cross-section of the entering fuel is subjected to mechanical agitation and turbulence. The inventor has discovered that this can be attained through the design of the opening.

To more fully convey this concept, let it be imagined that a gaseous fuel burner incorporates a mixing chamber at high pressure where the fuel and oxidant are mixed together, and also incorporates a combustion chamber at lower pressure. The two chambers are adjacent opposite faces of a metal partition, and an access passageway or opening in the partition allows the burnable mixture to flow from the mixing chamber to the combustion chamber. More particularly, the opening is in the form of a slot in the partition through which the gaseous fuel mixture can pass. The width of the slot can be finely adjusted. At a narrow setting for the slot, all portions of the entering gas are subjected to mechanical agitation, thus favoring the suppression of NOX. At a wide setting, a portion (the central part) of the gas passing through the slot does so under laminar flow conditions, with only the edge portions of the gaseous flow being subject to the shear forces that generate turbulence. The laminar-flow region results in NOX formation and may be compared to a river which flows relatively steadily and smoothly at midstream, but is subject to turbulence, agitation and eddy currents next to the riverbank. The turbulent flow is due to the shearing interaction between the moving water and the stationary embankment. By contrast, at a narrow setting for the slot, all portions of the entering gas are subjected to mechanical agitation, thus favoring the suppression of NOX.

More particularly, this invention provides an apparatus for burning a gaseous fuel with air in such a way as to reduce NOX compounds in the products of combustion, the apparatus defining:

- a mixing chamber where the fuel is mixed with air,

- a combustion chamber where the fuel is burned, and

- an access opening through which the fuel/air mixture can pass into the combustion chamber, the opening being configured so as to substantially eliminate any laminar flow of the fuel/air mixture, and to subject substantially all of the mixture to turbulent flow, thereby suppressing the formation of NOX.

Further, this invention provides a method of burning a gaseous fuel with air in such a way as to reduce NOX compounds in the products of combustion, utilizing an apparatus defining a mixing chamber where the fuel is mixed with air, a combustion chamber where the fuel is burned, and an access opening through which the fuel/air mixture can pass into the combustion chamber from the mixing chamber, the method comprising the steps of: a) mixing the fuel with air in the mixing chamber, and b) passing the fuel/air mixture through the access opening in such a way as to substantially eliminate laminar flow of the fuel/air mixture where it passes into the combustion chamber, and to subject substantially all of the mixture to turbulent flow, thereby suppressing the formation of NOX. General description of the drawings:

The invention will now be described in greater detail with reference to the attached drawings, in which like numerals denote like parts throughout the several views, and in which:

Figure 1 is a vertical axial sectional view through a vortical fuel burner constructed in accordance with this invention; and

Figure 2 is a perspective view of the apparatus of Figure 1 , with a portion of the outer wall broken away to reveal the internal structure.

Detailed description of the drawings

Referring now to the drawings, an apparatus 8 for burning a gaseous fuel with air has a cylindrical outer housing 10 surrounding an nternal combustion chamber 12, a circular bottom wall 14, and an annular ntermediate wall 16 above and parallel with the bottom wall 14. The intermediate wall 16 is not shown in Figure 2, in order to avoid cluttering the drawing. As seen in Figure 1 , the intermediate wall 16 defines, with the bottom wall 14, a secondary air chamber 18. Further, the intermediate wall has a circular inner edge 20.

Centrally located in the combustion chamber 12 is a cylindrical inner housing 22 which includes a cylindrical side wall 24 and a circular top wall 26, the inner housing containing and defining a mixing chamber 28. The top wall 26 is securely but adjustably mounted to the side wall 24, and a circular slot 30 between them serves as an opening allowing the gaseous fuel/air mixture to flow from the mixing chamber into the combustion chamber 12. As an example, the top wall 26 could have an externally threaded lower extension (not illustrated) threadably engaging an internal thread (not illustrated) defined by the side wall 24, along with a mechanism by which the top wall 26 could be locked in any desired position, thus allowing for on-site adjustability of the configuration of the slot 30. It will be noted in Figure 1 that the internal edge 20 of the annular wall 16 is spaced outwardly away from the cylindrical side wall 24 of the housing 22, thereby leaving a gap 32 which allows air in the secondary air chamber to gain access to the combustion chamber 12.

To bring combustion air to the mixing chamber 28, there is provided an air inlet pipe 34 extending horizontally from the wall 24 to a location external to the outer housing 10. Standard connections (not illustrated) connect the pipe 34 to a source of pressurized air. An opening 36 in the pipe 34 allows air to enter the secondary air chamber 18.

To bring gaseous fuel to the mixing chamber 28, there is provided a fuel inlet pipe 38, located coaxially inside the air inlet pipe 34, with standard connections (not illustrated) to a source of pressurized gaseous fuel.

In use, pressurized air and fuel are fed along the pipes 34 and 38, respectively, and a portion of the entering air is allowed to pass through the opening 36 into the secondary air chamber 18. The size of the slot (its vertical dimension in the embodiment illustrated) is adjusted to ensure that - virtually all of the mixture entering the combustion chamber is subjected to turbulent flow conditions.

While one embodiment of this invention has been described hereinabove and illustrated in the attached drawings, it will be evident to those skilled in the art that changes and modifications may be made thereto, without departing from the essence of this invention, as set forth in the appended claims.

Claims

1. An apparatus for burning a gaseous fuel with air in such a way as to reduce NOX compounds in the products of combustion, the apparatus defining:

- a mixing chamber where the fuel is mixed with air,

- a combustion chamber where the fuel is burned, and

2. The apparatus claimed in claim 1 , further comprising portions defining the opening, the portions being adjustable, so that the size and configuration of the opening can be adjusted.

3. The apparatus claimed in claim 1 , in which the opening has the form of a slot.

4 A method of burning a gaseous fuel with air in such a way as to reduce NOX compounds in the products of combustion, utilizing an apparatus defining:

- a mixing chamber where the fuel is mixed with air, - a combustion chamber where the fuel is burned, and

- an access opening through which the fuel/air mixture can pass into the combustion chamber from the mixing chamber,

- the method comprising the steps of: c) mixing the fuel with air in the mixing chamber, d) and passing the fuel/air mixture through the access opening in such a way as to substantially eliminate laminar flow of the fuel/air mixture where it passes into the combustion chamber, and to subject substantially all of the mixture to turbulent flow, thereby suppressing the formation of NOX.

5. The method claimed in claim 4, in which the apparatus comprises portions defining the opening, the portions being adjustable, the method further involving c) adjusting the said portions, thereby adjusting the size and configuration of the opening to achieve the suppression of NOX.