GB2117507A - Burner - Google Patents

Abstract

A high velocity burner 10 suitable for use with heated combustion air has inner and outer housings 20, 18 with a fuel gas inlets 12 into one end of the combustion chamber 30 within the inner housing and an air inlet 16 into the annular chamber between the housings. The inner housing 20 is made of refractory material. A baffle 32 is arranged to direct the fuel entering the combustion chamber outwardly, and a first and second series of holes 48, 50 extend through the inner housing to provide combustion air to the combustion chamber. A refractory flame shield 28 is positioned in the combustion chamber between the inlet and the first series of holes through the inner housing, the inner housing converging at its exit end 44 to provide an exit of a preselected diameter so that the combustion chamber diameter is twice the exit diameter and the combustion chamber length is three times the exit diameter. A series of holes 52 extend through the inner housing 20 to provide flow of combustion air to the exit portion of the inner housing. <IMAGE>

Description

SPECIFICATION Burner Furnaces have long been fired with high velocity burners. Such burners are used to achieve large heat releases and to assure circulation of the products of combustion in the furnace at sufficient velocity to improve the heat exchange therein. Many of such burners utilized air entering tangentially in an annular chamber surrounding the housing which contains the combustion chamber. U.S. Patent No.

3,265,113 discloses an example of such burner design. Other burners have utilized an outer housing with an inner housing containing the combustion chamber and with the annular chamber having the air inlet connected thereto and being open to the fuel inlet side of the combustion chamber as shown in U.S. Patent No. 1,791,561. Some burners have suggested the use of a refractory shell with a plurality of holes therethrough and through which the fuel and air mixture passes for burning on the interior of the shell as shown in U.S. Patent No.

3,227,201.

Some prior patents have suggested that burners have deflecting plate at the end of their inlet to deflect the fuel-air flow outwardly, such as shown in U.S. Patent Nos. 3,475,240; 2,497,321; 2,642,131; and 2,851,092.

The present invention is directed to providing an improved burner suitable for using hot combustion air which has a fuel inlet at one end which diverges outwardly from the inlet into a combustion chamber within an inner refractory housing. Hot combustion air is supplied to an annular chamber around the combustion chamber with a first series of combustion air holes extending from the annular chamber into the combustion chamber at a position near the fuel inlet and protected by a refractory flame shield and a second series of such holes into the center portion of the combustion chamber. The combustion chamber converges to an exit with additional combustion and cooling air being supplied through a third series of holes into the exit from the annular chamber.

An object of the present invention is to provide an improved high velocity burner using hot combustion air and having a high turndown ratio.

Another object is to provide an improved high velocity burner which can operate with a stable flame on preheated combustion air.

Afurther object is to provide an improved high velocity burner using hot combustion air which can be operated to have both high and low heat release rates with a stable flame.

These and other objects and advantages of the present invention are hereinafter set forth and explained with respect to the drawing wherein: The figure is a longitudinal sectional view of the preferred form of the improved burner of the present invention.

Burner 10 includes fuel inlet duct 12 which is secured to end closure 14, air inlet duct 16 which is secured to outer tubular housing 18 and inner tubular housing 20 which is supported within housing 18 by flanges 22 and 24 at opposite ends. Outer hosuing 18 is suitably lined with a refractory material 26 and inner housing 20 is composed of a suitable refractory material. Flame shield 28 is supported within the inlet end of inner housing 20 in alignment with inlet duct 12 and forming the entrance to combustion chamber 30. Baffle 32 is supported in close spaced relationship to the inner end of fuel inlet duct 12 to deflect the fuel gas radially outward.

Refractory material 34 is positioned within end closure 14 as shown and has an outwardly diverging surface 36. Flame shield 28 of suitable refractory material is secured within the inner periphery of flange 22, has converging entrance portion 38 and tubular portion 40 extending axially of inner housing 20. The exit 42 from combustion chamber 28 is formed by converging portion 44 of inner housing 20 and exit converges slightly and then diverges as shown.

Fuel gas is delivered through duct 12, is directed outwardly by baffle 32 and passes through the interior of flame shield 28. Combustion is initiated in combustion chamber 30 by suitable ignition means (not shown). Air to support combustion is delivered through duct 16to annularchamber46between inner and outer housings 20 and 18. Combustion air enters into combustion chamber 30 through first series of holes 48 through inner housing in the area immediately behind flame shield 28 and through second series of holes 50 through inner housing 20 at a position downstream from flame shield 28 and upstream of the mid point of combustion chamber 28. Air also flows from chamber 46 and holes 52 into exit 42.The airflowing around inner housing 20 provides cooling of housing 20 and the air flowing through holes 52 into exit is discharged into the high velocity combustion gases to provide the final quantity of combustion air to assure complete combustion of the fuel gas.

A typical burner of the present invention is a burner having a heating capacity of 5,000,000 Btu/ hour and an exit diameter of 6-1/2 inches converging to 6-1/4 inches to 2-3/4 inches in length and diverging to 6-1/2 inches in 10 inches of length, which would provide an exit velocity of combustion gases approximately one-half the speed of sound to thereby minimize the noise created by the burner. It is preferred that the combustion chamber diameter be approximately twice the exit diameter (12-1/8 inches) and that its length be approximately three times the exit diameter (20-1/4 inches) from flame shield 28 to exit 42.The holes 48, 50, and 52 are selected to provide the preselected amount of back pressure and in the example it would be a back pressure of 14 to 15 ounces per square inch with the burner 10 running on hot air at a temperature of approximately 1000"F supplied to air inlet 16. With 24 holes in the first and second series 48 and 50, the diameter of the holes is preferred to be 5/8 inch and 24 holes 52 are preferred to be 5/16 in diameter.

Flame shield 28 is believed to allow operation of burner 10 on constant air and to provide a stable flame when operating on ratio. Flame shield 28 has an inner diameter of 8-1/2 inches. Holes 48 have their centerlines positioned 3/4 of an inch from the end of flame shield 28. Holes 50 have their centerlines positioned 5 inches from the centrelines of holes 48.

Tubular portion 40 of flame shield 28 is 2-3/8 inches long. Inlet 12 is 3 inches in diameter and air inlet is 9 inches in diameter. This provides an air to fuel gas ratio with suitable controls such as are well known of 11 to 1 or approximately 10% excess air over the stoichiometric ratio.

Claims (6)

1. A burner suitable for use with high temperature combustion air having an outer housing on inner housing positioned within the outer housing and spaced radially therefrom to form an annular chamber, an inlet through the outer housing to supply hot combustion air to said annular air chamber, the inner housing defining a combustion chamberwith aflame shield at one end and a reduced diameter exit at the opposite end, a fuel inlet for delivering fuel to the flame shield and characterized by said inner housing and said flame shield being made of a refractory material, said inner housing having an internal diameter approximately twice its exit diameter and a length approximately three times the exit diameter, holes extending through said inner housing to supply combustion air to the combustion chamber within said inner housing, at least some of the holes communicating with the initial portion of the exit from said combustion chamber.

2. A burner according to claim 1 wherein a portion of said combustion air holes extend through said inner housing at a position surrounding the flame shield.

3. A burner according to claim 1 or 2 wherein said inner housing has an exit passage having a short slight initial covergence and a longer divergence with the end diameters thereof being substantiallythe same.

4. A burner according to claim 3 wherein the combustion air holes communicating with said exit are in the initial converging portion of said exit.

5. A burner according to any of the preceding claims wherein said combustion air holes include a first, second and third circumferential series of holes with the first and second series being upstream of the mid portion of the combustion chamber and the third series of holes extending into the exit.

6. A burner substantially as described and shown in the drawing.