US3865084A

US3865084A - Inner furnace air chamber

Info

Publication number: US3865084A
Application number: US431243A
Authority: US
Inventors: Poister David C De
Original assignee: Foster Wheeler Inc
Current assignee: Foster Wheeler Inc
Priority date: 1974-01-07
Filing date: 1974-01-07
Publication date: 1975-02-11
Anticipated expiration: 1992-02-11
Also published as: JPS50101928A; JPS563482B2; CA1014459A; ES433620A1

Abstract

A furnace assembly and method in which an air-fuel mixture is supplied to a burner which is associated with at least one of the walls of the furnace assembly with an auxiliarly supply of air being discharged toward said burner for mixing and combusting with the unburnt fuel from the burner.

Description

a 7 limited States Fatwa 1 1 3,865,084 De Paister 1 Feb. 11, 11975 4] INNER FURNACE AFR CHAMBER 2,022,512 11/1935 Macchi 431/10 X 1 Invent David De Power, Morristown, 5:31;??? 2/1332 1132.?7111131113331111: 311333131 33141? NJ. 3,699,903 10/1972 King 110/28 X [73] Assignee: Foster Wheeler Corporation,

L'vmgswn Primary EXaminer-Kenneth W. Slprague 22 Filed; 7 1974 Attorney, Agent, or Firm-Marvin A. Naigur; John E.

Wilson [21] App]. No.: 431,243

[52] US. Cl. 122/235 B, 110/1 K, 110/28 R, [57] ABSTRACT 110/75 R, 431/10 [51] Km. C1. F22b A furnace assembly and method In which air-fuel 53 Field f Search 0/1 K 23 R, 23 A 23 F, mixture is supplied to a burner which is associated 0 2 122 235 R, 235 431 0; 119 72 with at least one of the walls of the furnace assembly R, 75 R, K, J with an auxiliarly supply of air being discharged toward said burner for mixing and combusting with the 5 R f r Cited unburnt fuel from the burner.

UNITED STATES PATENTS 5 Claims, 3 Drawing Figures 1,889,031 11/1932 Bell 122/235 X e4 M w l2\ L82 Mg)-l H!74 4o 24 1 1 .1 g 24 4 ;I

@f ea-{a 4 -Tif 6* -LQ. J Z: 54 $3 *1: 1 42 -41 To ::5; i2 I 1 PATENTEDFEBI H875 SHEET '2 OF 2 FIG. 2.

INNER FURNACE AIR CHAMBER BACKGROUND OF THE INVENTION This invention relates to a furnace assembly and method and, more particularly, to an improved furnace assembly and method in which the formation of nitric oxides as a result of fuel combustion is reduced.

A great deal of attention has recently been directed to the reduction of nitric oxides resulting from the combustion of fuel at burners, and especially in connection with the furnace sections of relatively large installations such as vapor generators and the like.

In these type of arrangements, one or more burners are usually disposed in communication with the interior of the furnace and operate to combust either oil or gas in air. Since nitrogen is present in the air and, in most cases, in the fuel, a relatively high level of nitric oxide, or nitric oxides, are produced which causes severe air pollution problems.

Since the formation of nitric oxides increases with increases in the burner temperatures, several attempts have been made to suppress the latter temperatures and thus reduce the formation of nitric oxides. However, previous attempts have often resulted in added expense in terms of costs, etc., and lead to other related problems.

SUMMARY OF THE INVENTION It is, therefore, an object of the present invention to provide a furnace assembly and method in which the level of nitric oxides is considerably reduced.

It is a more specific object of the present invention to provide a furnace assembly and method in which a two-stage combustion process is achieved which lowers the flame temperature in order to reduce the formation of nitric oxides.

Toward the fulfillment ofthese and other objects, the furnace assembly of the present invention comprises a housing formed by a plurality of interconnected walls, at least one burner associated with at least one of said walls, means for supplying an air-fuel mixture to said burner for combusting in said furnace, and means disposed within said housing and in a spaced relation to said walls for discharging air towards said burner for mixing and combusting with the unburnt fuel from said burner.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view depicting the furnace assembly of the present invention shown in conjunction with a vapor generator;

FIG. 2 is an enlarged cross-sectional view taken along the line 22 of FIG. 1; and

FIG. 3 is an enlarged partial elevational view ofa portion of the furnace assembly of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS. 1 and 2 of the drawings, a furnace incorporating features of the present invention is shown in general by the reference numeral as installed in a vapor generator 12. The furnace I0 is rectangular shaped, elongated, and extends from a bottom hopper portion 14 to an upper outlet area 16 which is enclosed by a penthouse 18 for the vapor generator 12.

The vapor generator 12 includes a convection section 20 which has an inlet portion enclosed by the penthouse 18 and an outlet portion connected to an air heater 22 to be described in detail later.

The furnace 10 is formed by front and

rear walls

24 and 26, respectively, and a pair of

side walls

28 and 30. As shown in FIG. 3 in connection with the wall 24, the walls are formed by welding together a plurality of tinned tubes 32 along their lengths so that the enclosure formed by the walls is substantially gas tight. In a normal installation an insulating wall of a suitable insulating material would be provided adjacent each of the

walls

24, 26, 28, and 30 and externally thereof. However, for the convenience of presentation these insulating walls have been omitted from the present drawings.

Water is passed through the tubes 32 of the

walls

24, 26, 28 and 30 and is routed in a. predetermined flow path by means of suitable headers, downcomers, etc., in a manner so that it is gradually turned into steam by virtue of the heat generated in the furnace 10, after which the steam is superheated and collected in drums or the like in a conventional manner. Hot gases flowing upwardly in the furnace 10 exit through the outlet area 16 and pass downwardly through the convection section 20 and into the air heater 22 for further treatment in a manner to be described in detail later.

A windbox 40 encloses the lower portion of the furnace 10 for supplying air to the furnace. The windbox 40 includes front and rear walls 412 and 44, which are spaced from the

walls

24 and 26, respectively, of the furnace 10. A plurality of burners, shown in general by the reference numeral 46, are supported by the windbox 40 and discharge through openings formed in the

walls

24 and 26.

The burners 46 associated with the front wall 24 of the furnace 10 are shown in detail in FIG. 3. In particular, the burners 46 are supported by the wall 42 of the windbox 40 and are shown as being arranged in two vertical walls of four burners per row, it being understood that the number of burners 46 and their particular pattern can vary. Since the burners 46 are of a conventional design and form no portion of the present invention, they are shown only in general with it being understood that they include an inlet for receiving fuel, which can be in liquid or gaseous form or which can be a mixture of pulverized coal and primary air. A series of openings 48 are formed through the wall 24 in alignment with the burners 46 for allowing air from the windbox 40 to pass into the furnace 10 where it combines with the fuel from the burners 46 which, upon ignition, combusts in a primary combustion zone formed in the interior of the furnace immediately adjacent the openings 48, in a conventional manner.

Air from an external source (not shown) is introduced to the system through a duct 50 with a portion of it passing into the air heater 22 which is adapted to effect a heat exchange between the latter air and the combustion gases from the convection section 20 in a conventional manner. These gases, after passing through the air heater 22, discharge via a duct 54 to a stack, or the like, while the heated air discharging from the air heater 22 is routed through a duct 56 and into the lower portion of the windbox 40 for passage through the openings 48. The duct 56 has a venturi portion for the purpose of measuring the amount of air flow,.which flow is regulated by means of a damper 58 formed in the duct 56 downstream of its venturi portion.

According to a main feature of the present invention, a quantity of supplemental air is discharged directly toward the burner openings 48 in the

walls

24 and 26 which aids in reducing the formation of nitric oxides. To this end, an enclosure 60 is provided within the furnace l and is formed by four

interconnected walls

62, 64, 66, and 68 each of which are formed by a plurality of interconnected finned tubes similar to the

walls

24, 26, 28, and 30 of the furnace 10.

A plurality of openings 70 are formed through the

walls

62 and 64 of the enclosure 60 with a portion of the openings being located directly opposite corresponding openings 48 formed in the

walls

24 and 26 of the furnace assembly 10. Although only the

walls

24 and 62 of the furnace 12 and the enclosure 60 are shown in detail in FIG. 2, it is understood that the

Walls

26 and 64, respectively, are formed identically.

As shown in FIG. 1, the finned tubes forming the walls of the enclosure 60 are connected to upper headers 74 and lower headers 76, it being understood that downcomers, etc., can also be provided to route water through the walls in a manner to generate steam and pass same into the steam drum, or the like, which also serves the main system.

The air duct 50 is also connected, via

ducts

80, 82 and 84, to the enclosure 60 to supply air to the latter enclosure for discharge through the openings '70 provided in the

walls

62 and 64. A damper 86 is provided in the duct 80 to regulate the quantity of air supplied to the enclosure 70.

In operation, the amount of air supplied to the wind box 40 via the duct 56 is regulated by the damper 58 so that it is less than the theoretical combustion air requirements for the fuel supplied to the burners 46. This delays the complete combustion of the fuel in the primary combustion zones located in the furnace l0 adjacent the openings 48, and results in a relatively low flame temperature, which reduces the formation of nitric oxides. The amount of air supplied by the enclosure 60 via the openings 70 is regulated by the damper 86 to insure that it is sufficient to combust the remaining unburnt fuel from the burners 46 in a secondary combustion zone formed between the openings 48 and the openings 70. Since the openings 70 are aligned with the openings 48 and since air from the enclosure 60 is discharged in a direction directly opposite that of the fuelair mixture from the burners 46, it can be appreciated that optimum mixing occurs between the respective fluids to facilitate complete combustion of the unburnt fuel with a minimum quantity of excess air from the enclosure 60.

The water passing through the

walls

62, 64, 66, and 68 of the enclosure 60 maintains the enclosure at a relatively low temperature to protect it from damage, and, in addition, cools the flame temperature at the secondary combustion zone.

It is noted from a view of FIG. 1 that a portion of the openings 70 extend above the upper burners 46 to insure that air is available to mix with any unburnt fuel rising towards the top of the furnace by natural convection.

Of course, other variations of the specific construction and arrangement of the furnace assembly disclosed above can be made by those skilled in the art without departing from the invention as defined in the appended claims.

What is claimed is:

1. A furnace assembly comprising a housing formed by a plurality of interconnected walls, a plurality of burners associated with at least one of said walls, means for supplying an air-fuel mixture to said burners for combusting in said housing, an enclosure extending within said housing and formed by interconnected walls, a wall of said enclosure extending parallel to said one wall of said housing and having a plurality of openings respectively facing said burners, said latter enclosure wall being formed by a plurality of interconnected finned tubes, and means for supplying air to said enclosure for discharging through said openings and towards said burners for mixing and combusting with the unburnt fuel from said burners, and means for passing water through said tubes to cool said tubes and the air discharging through said openings.

2. The furnace assembly of claim 1 wherein the walls or said housing are formed by a plurality of interconnected finned tubes for receiving water to be heated by said furnace.

3. The furnace assembly of claim 1 wherein the air portion of said air-fuel mixture is less than that required to achieve complete combustion and wherein the air discharged through said openings is sufficient to achieve complete combustion.

4. A method of burning a fuel air mixture in a furnace to produce a minimum amount of nitrogen oxides in the combustion gases leaving the furnace, which comprises the steps of introducing the fuel into the furnace through a burner port in a furnace wall, introducing a portion of the combustion air into said furnace through said burner port in mixing relationship with said fuel, regulating the amount of air supplied through said burner port to an amount which is less than the theoretical combustion air requirements for the corresponding fuel to delay the complete combustion of said fuel and thereby reduce the maximum flame temperature in the furnace and the formation of nitrogen oxides below the values which would occur if all of the air required for complete combustion were introduced with the fuel, discharging the remaining amount of air required to insure complete combustion of the fuel through openings extending through a wall of an enclosure disposed within said furnace, said remaining amount of air being directed towards said burner port and in a direction opposite the direction of discharge of said fuel and air so as to mix said remaining amount of air with the unburnt portion of said fuel to complete the combustion of said fuel, and cooling the wall of said enclosure through which said openings extend to cool said remaining amount of air.

5. The method of claim 4 wherein said wall of said enclosure is formed by a plurality of interconnected finned tubes, said step of cooling comprising the step of passing water through said tubes.

Claims

4. A method of burning a fUel-air mixture in a furnace to produce a minimum amount of nitrogen oxides in the combustion gases leaving the furnace, which comprises the steps of introducing the fuel into the furnace through a burner port in a furnace wall, introducing a portion of the combustion air into said furnace through said burner port in mixing relationship with said fuel, regulating the amount of air supplied through said burner port to an amount which is less than the theoretical combustion air requirements for the corresponding fuel to delay the complete combustion of said fuel and thereby reduce the maximum flame temperature in the furnace and the formation of nitrogen oxides below the values which would occur if all of the air required for complete combustion were introduced with the fuel, discharging the remaining amount of air required to insure complete combustion of the fuel through openings extending through a wall of an enclosure disposed within said furnace, said remaining amount of air being directed towards said burner port and in a direction opposite the direction of discharge of said fuel and air so as to mix said remaining amount of air with the unburnt portion of said fuel to complete the combustion of said fuel, and cooling the wall of said enclosure through which said openings extend to cool said remaining amount of air.