US3699903A

US3699903A - Method for improving fuel combustion in a furnace and for reducing pollutant emissions therefrom

Info

Publication number: US3699903A
Application number: US118836A
Authority: US
Inventors: Oliver F King
Original assignee: Individual
Current assignee: Individual
Priority date: 1971-02-25
Filing date: 1971-02-25
Publication date: 1972-10-24
Anticipated expiration: 1989-10-24

Abstract

A method for improving fuel combustion in furnaces and the like and for reducing pollutant emissions therefrom, wherein primary air is used solely for fuel feed while commercially pure oxygen without any additives or other constituents is introduced for the combustion of the fuel in regulated amounts so as to provide sufficient oxygen for substantially complete combustion. The oxygen is preferably obtained by separating same from air so that the remaining nitrogen may be used as in inert gas applications.

Description

United States Patent King [ 51 Oct. 24, 1972 [54] METHOD FOR IMPROVING FUEL COMBUSTION IN A FURNACE AND FOR REDUCING POLLUTANT EMISSIONS THEREFROM Oliver F. King, 5422 Brae Burn Dn've, Bellaire, Tex. 77401 Filed: Feb. 25, 1971 Appl. N0.: 118,836

Inventor:

US. Cl. ..110/1 J, 110/28 R Int. Cl ..F23b 7/00 Field of Search ..1 10/1 H, l J, 28 R, 40; 122/479 A References Cited UNITED STATES PATENTS l/l94l De Baufre 122/479 3,048, i 31 Hardgrove ..1 10/28 2,820,438 l/1958 Andrews et al 122/479 2,980,082 4/1961 Firl ..122/479 Primary Examiner--Kenneth W. Sprague Attorney-Pravel, Wilson & Matthews [57] ABSTRACT 10 Claims, 1 Drawing Figure PATENTEDUBI24 I972 3,699,903

INVENTOR METHOD FOR IMPROVING FUEL COMBUSTION IN A FURNACE AND FOR REDUCING POLLUTANT EMISSIONS THEREFROM BACKGROUND OF THE INVENTION tures are higher, improved performance of the super- I BRIEF DESCRIPTION OF THE DRAWING The FIGURE of the drawings illustrates schematio cally a conventional boiler or steam generator having a produced and discharged to the atmosphere during combustion when air is used for supporting the combustion.

In US. Pat. No. 1,720,757, it was proposed that an oxidizing material such as copper oxide be used for supplying free oxygen to maintain complete combustion of the fuel in a secondary chamber. However, such procedure produced a residue of copper and also introduced additional components into the stack gases contributing to the pollution upon discharge through the stack.

In US. Pat. No. 2,980,082, it was proposed that the nitrogen in air be replaced with recirculated combustion gases, on the premise that oxygen alone, or air greatly enriched with oxygen, produced undesirably high furnace temperatures. However, by recirculating the high temperature combustion gases, the tempera tures are actually increased upon each recirculation, thus tending to defeat the purpose of using such combustion gases. Further, unnecessarily high volumes of inert inactive gases had to be handled, which meant that boiler or furnace sizes had to be accordingly larger than necessary if designed for just combustion purposes. Additionally, with such high volume flow, the pure oxygen was swept out of the stack with the gases that discharged therefrom, reducing the thermal efficiency, and so as to further accentuate the gas volume and flow velocity required.

SUMMARY OF THE INVENTION The present invention relates to a method wherein commercially pure oxygen is used alone, preferably in stoichiometric quantities, as the secondary or combustion gas, and with only enough primary air for fuel feed, adequate gas velocities, and fuel turbulence and distribution in the furnace firebox. The commercially, pure oxygen is preferably obtained by separating the oxygen from air so that the remaining nitrogen can be used for various applications where an inert gas is desirable. Thus, a twofold purpose is accomplished by removing the nitrogen from the oxygen in the air. The fuel, such as natural gas, oil, or coal is introduced into the furnace firebox in a compact, preferably circular configuration, and with the center or vortex thereof as the target area for the substantially pure oxygen stream used for combustion. The combustion zone is thus maintained as dense and compact as possible so that it does not impinge on the furnace walls or tubes. Because of the higher combustion temperatures, and more complete combustion, the flue or stack temperafurnace firebox in which fuel is burned for the generation of steam. I

DESCRIPTION OF THE PREFERRED EMBODIMENT In the drawings, the letter A designates generally a steam generator or boiler of conventional design having a furnace firebox or combustion chamber F in which the fuel is burned. Typically, the boiler or steam generator A has a furnace wall 10 which has a plurality of interconnected boiler tubes 12 extending vertically and disposed in a generally circular or peripheral arrangement on the inside of the wall 10 so as to leave the central combustion chamber or firebox F open for the flame of combustion, as will be more evident hereinafter. The tubes 12 are connected to a steam and water drum 14 in the conventional manner and also to a superheater section 16, which is also conventional. The superheated steam is available and is discharged at line 18 through any suitable control valve 19 in such line from the superheater 16. A mud drum 20 is connected with the steam and water drum 14 and also with the bottom of the furnace for collecting solids in the known manner.

The drawing also illustrates a gas flow duct 25 having a conventional economizer section or unit 30 therein for further utilizing the heat in the exhaust gases. The duct 25 connects with a conventional vertically extending exhaust stack 35 which is open at the upper end for the exhausting of the exhaust gases to the atmosphere. The height of the stack 35 of course varies in accordance with the location and condition of draft desired, and it will be understood that the illustration in the drawings is merely illustrative and is not intended to be limiting as to size.

In the method of the present invention, the fuel which is introduced into the firebox or combustion chamber F may be any one of a number of common fuels such as natural gas which is principally methane, or pulverized coal. Also, the fuel may be a liquid such as oil of the bunker C-grade. The fuel is introduced into the combustion chamber or firebox F by means of one or more fuel burner heads 50 of conventional construction. If the fuel is lump coal, it would be stoker fed as is well known. The particular construction for each of such fuel burner heads is dependent upon the particular kind of fuel, i.e., whether it is gaseous, liquid or a solid in the form of small particles.

With the present invention, each of such heads has a port or port means for introducing primary air as indicated at 51 with the fuel. In the typical installation, each fuel burner head has air aspirating ports so as to draw the air in with the fuel as the fuel is injected into the firebox or combustion chamber F.

The quantity of the primary air which is introduced is specifically limited in the method of this invention so that it serves mainly to properly feed the fuel into a compact dense pattern in substantially the central portion of the fire chamber F between the burner heads 50 so that the fuel is in a position for burning away from the furnace wall and the tubes 12. Such primary air also serves to control the theoretical flame temperature, and to provide fuel turbulence and distribution within the compact but substantially circular pattern of the fuel. Also, the volume of the air which is introduced may be regulated to obtain adequate firebox, boiler flue and exhaust stack velocities and volumes.

Oxygen is introduced in substantially pure form at an oxygen inlet head 61 which is connected to a line 62 leading to a source of oxygen which is substantially pure. Oxygen is sold in commercially pure form, which means that the oxygen has a purity of about 99.99 percent. However, commercial oxygen in tonnage quantities may have a purity as low as 80 percent. For the purposes of this invention, the oxygen should be substantially pure, which means it is within the range of from about 80 percent to 100 percent pure.

in the preferred form of the invention, the substantially pure oxygen is obtained by separating the oxygen from the nitrogen in air so that the nitrogen is also available for use as an inert gas in various applications such as a nitrogen blanket for disposition over materials or substances which might have a tendency to burn or explode in an air or oxygen atmosphere. Other uses for the nitrogen will readily occur to those skilled in the art. It will be appreciated that the separation of the nitrogen accomplishes a two-fold purpose since it removes the nitrogen from the air which would otherwise be a pollutant in the combustion within the furnace and it also makes the nitrogen available for use at a point remote from the furnace. The particular manner of separating the oxygen and the nitrogen from each other is of course well known.

The oxygen is introduced from the head or nozzle 61 so that it feeds into the center or vortex of the fuel pattern formed by the introduction of the fuel through the burner heads 50. Such control over the introduction of the oxygen into the fuel tends to confine the flame within the central portion of the firebox F so that it does not create hot spots on the furnace wall 10 or the tubes 12. Thus, even though the theoretical flame temperature is higher than when air alone is used for combustion, the higher temperatures are controlled-so that they are not damaging to the furnace itself. In fact, the higher temperatures produce many advantages. For example, with the higher combustion temperatures and more complete combustion, the flue or stack temperatures are higher and the performance of the superheater and preheater sections of the furnace or generator A are improved. The actual size of the furnaces may be reduced as a result of smaller volumes of gas which are moved through the furnace with the present invention, and this can result in reduced stack heights and ultimately in improved thermal efficiency. When the existing furnaces are used with the method of this invention, a smaller flame pattern is created by regulating the burner heads 50. The smaller flame pattern is desirable so that the furnace wall 10 and the surround- 6 ing tubes 12 are not subjected to the extremely hot combustion temperatures in the flame.

As pointed out above, the method of this invention involves a control of the quantity of the substantially pure oxygen and the quantity of the primary air which are introduced intothe firebox so that the oxygen normally constitutes the principal gas for the combustion of the fuel, and the primary air serves essentially only for controlling the flame temperature, for feeding the I fuel into the firebox in the desired pattern, for discharging the exhaust gases at adequate stack velocities and volumes, andfor creating fuel turbulence and distribution.

By way of specific example, when the fuel is methane, a theoretical flame temperature of about 5 ,500 F. is obtained when the substantially pure oxygen supplies slightly above 50 percent of the oxygen and the primary air supplies slightly less than 50 percent of the oxygen in stoichiometric relationship to the quantity of the methane. When the substantially pure oxygen supplies at least 25 percent of the oxygen and the primary air supplies the rest, the theoretical flame temperature is about 4,400 E, as compared to only about 3,700 F. with all primary air. If flame temperatures above 5,500 F. can be tolerated in a furnace, the amount of oxygen supplied in pure oxygen form is increased to supply as much as percent of the oxygen while the primary air supplies only 25 percent thereof. Under such conditions, the theoretical flame temperature is about 6,500" F. Thus, the advantages of the higher temperatures, plus less pollutants from nitrogen and the other enumerated advantages over the prior practices are illustrated by such examples.

When the fuel is carbon, the theoretical flame temperatures are somewhat higher than when the fuel is methane and the pure oxygen to primary air is the same. For example, when the pure oxygen supplies about 50 percent of the oxygen and the primary air supplies the other 50 percent of the oxygen, the theoretical flame temperature is about 5,680 F. When the pure oxygen supplies about 25 percent of the oxygen, the theoretical flame temperature is about 4,400 F., whereas such temperature is only about 3,800 F. with all primary air. When the pure oxygen supplies about 75 percent of the oxygen and the primary air supplies the other 25 percent, the theoretical flame temperature is about 7,500 F. which is higher than can be tolerated in many furnaces.

It will be understood that the ratio of pure or substantially pure oxygen to the primary air will vary depending upon the fuel used, and the temperatures which the particular furnace can stand without damage, and therefore, the foregoing examples are not intended to be limiting.

The foregoing disclosure and description of theinvention are illustrative and explanatory thereof, and various changes in the size, shape, and materials as well as in the details of the illustrated construction may be made without departing from the spirit of the invention.

I claim:

1. A method for improved fuel combustion in a furnace firebox or the like, comprising the steps of:

injecting fuel into a furnace firebox with primary air to an area of fuel combustion in the furnace firebox;

feeding substantially pure oxygen in gaseous form into the furnace firebox separately from said primary air and at the area of the fuel combustion; and

controlling the quantity of said oxygen and the quantity of said primary air introduced into the firebox so that said oxygen supplies at least about 25 percent of the oxygen for the combustion of the fuel and said primary air serves to control the flame temperature, feed the fuel into said firebox in said pattern, discharge the exhaust gases at adequate stack velocities and volumes, and create fuel turbulence and distribution.

2. The method set forth in claim 1, wherein:

the quantity of said substantially pure oxygen and primary air is substantially equal to the stoichiometric amount necessary for complete combustion of said fuel.

3. The method set forth in claim 1, wherein:

the oxygen provided by said quantity of primary air is less than the quantity of oxygen provided by said substantially pure oxygen.

4. The method set forth in claim 1, wherein said fuel is either gaseous, liquid, or a solid in lump or panicle form when injected into said firebox.

5. The method set forth in claim 1, wherein said fuel is natural gas.

6. The method set forth in claim 1, wherein said fuel is pulverized coal.

7. The method set forth in claim 1, including:

directing said fuel into the furnace away from the furnace walls or tubes so that localized hot spots do not develop at the elevated combustion temperature by direct contact of any part of the furnace with the flame.

8. The method set forth in claim 1, including:

separating nitrogen from air to obtain said substantially pure oxygen prior to feeding said oxygen into said fuel in said fumace.

9. The method set forth in claim 8, including:

distributing the nitrogen at a point remote from the furnace to form an inert nitrogen blanket.

10. The method set forth in claim 1, wherein:

said substantially pure oxygen is in the range of about 80-100 percent oxygen.

Claims

1. A method for improved fuel combustion in a furnace firebox or the like, comprising the steps of: injecting fuel into a furnace firebox with primary air to an area of fuel combustion in the furnace firebox; feeding substantially pure oxygen in gaseous form into the furnace firebox separately from said primary air and at the area of the fuel combustion; and controlling the quantity of said oxygen and the quantity of said primary air introduced into the firebox so that said oxygen supplies at least about 25 percent of the oxygen for the combustion of the fuel and said primary air serves to control the flame temperature, feed the fuel into said firebox in said pattern, discharge the exhaust gases at adequate stack velocities and volumes, and create fuel turbulence and distribution.

2. The method set forth in claim 1, wherein: the quantity of said substantially pure oxygen and primary air is substantially equal to the stoichiometric amount necessary for complete combustion of said fuel.

3. The method set forth in claim 1, wherein: the oxygen provided by said quantity of primary air is less than the quantity of oxygen provided by said substantially pure oxygen.

4. The method set forth in claim 1, wherein said fuel is either gaseous, liquid, or a solid in lump or particle form when injected into said firebox.

5. The method set forth in claim 1, wherein said fuel is natural gas.

6. The method set forth in claim 1, wherein said fuel is pulverized coal.

7. The method set forth in claim 1, including: directing said fuel into the furnace away from the furnace walls or tubes so that localized hot spots do not develop at the elevated combustion temperature by direct contact of any part of the furnace with the flame.

8. The method set forth in claim 1, including: separating nitrogen from air to obtain said substantially pure oxygen prior to feeding said oxygen into said fuel in said furnace.

9. The method set forth in claim 8, including: distributing the nitrogen at a point remote from the furnace to form an inert nitrogen blanket.

10. THe method set forth in claim 1, wherein: said substantially pure oxygen is in the range of about 80-100 percent oxygen.