US3400921A

US3400921A - Fuel burner

Info

Publication number: US3400921A
Application number: US493458A
Authority: US
Inventors: Fritz L Hemker
Original assignee: Babcock and Wilcox Co
Current assignee: Babcock and Wilcox Co
Priority date: 1965-10-06
Filing date: 1965-10-06
Publication date: 1968-09-10
Anticipated expiration: 1985-09-10

Description

F L.. HEMKER sept. 1o, 196s FUEL BURNER Filed Oct. 6, 1965 INVENTOR Fritz L. Hemker ATTORNEY United States Patent 0 3,400,921 FUEL BURNER Fritz L. Hemker, Wadsworth, Ohio, assigner to The Babcock & Wilcox Company, New York, N.Y., a corporation of New Jersey Filed Oct. 6, 1965, Ser. No. 493,458 11 Claims. (Cl. 266-29) ABSTRACT 0F THE DISCLOSURE A burner arrangement whereby the major portion of an ash containing fuel is burned in a combustion chamber prior to introduction into a blast furnace. This is accomplished by radially introducing all of the combustion air into the chamber through a plurality of regularly spaced openings covering the circumferential area of the combustion chamber. This radially introduced air forms a protective layer of air between the fuel stream and the inner surface of the combustion chamber thus protecting the chamber walls from the intense heat required for achieving this more complete burning of the fuel.

This invention relates generally to fuel burners and more particularly to a fuel burner specifically adapted for firing coal or other solid carbonaceous fuel in a blast furnace.

The merits of firing supplemental fuel in a blast furnace to decrease coke consumption are well known; moreover, it is generally appreciated that thermodynamically, coal is superior to oil or gas for this purpose. Recent experimental operation of a blast furnace using coil injection has indicated however that when coal is introduced into a blast furnace at high rates, heavy carry-over of carbon in the top gas results. This carry-over is believed to result from the hot blast air reacting preferentially with the coke in the blast furnace in lieu of reacting with the injected coal which is at a lower temperature. As a consequence, the hydrocarbons in the unburned coal break down into hydrogen and carbon fractions in the high ternperature reducing atmosphere of the blast furnace, with the carbon being carried over with the top gas. These recent experiments indicate that if coal is to be used as a supplemental fuel in blast furnaces, for economic operation it will have to be almost completely burned or at least devolatilized before being admitted to the blast furnace. This would require a fuel burner capable of containing the combustion process without being subject to slag accumulations. Moreover, since it is desirable to It is therefore an object of the present invention to provide a fuel burner, specifically adapted for burning particle-form carbonaceous fuel, such as pulverized coal, in a blast furnace, wherein a major portion of the fuel is burned within the burner itself prior to discharge into the blast furnace. It is a further object of the present invention that such burner be capable of operation without requiring water cooling of any type other than what is normally used in the vicinity of blast furnace tuyeres of present day design. It is a still further object of the present invention that the fuel burner be structurally adaptable for incorporation into existing blast furnaces.

These and other objects may be attained in a blast furnace having a boundary wall formed with a tuyere opening and a fuel burner arranged to fire through the tuyere opening. The burner includes an elongated refractory burner tube of generally circular cross-section in axial 3,400,921 Patented Sept. 10, 1968 alignment with the tuyere opening and having an inlet end and an open discharge end. The burner tube is formed with a plurality of relatively small, spaced openigs over substantially its entire inner surface, and is enclosed with in a windbox chamber to which high temperature blast air is delivered. A fuel stream containing particle-form carbonaceous fuel is introduced into the inlet end of the burner tube. The pressurized blast air supplied to the windbox chamber passes through the burner tube open ings and mixes with and burns a major portion of the fuel within the burner tube prior to discharge of the hot combustion products into the blast furnace. The openings in the burner tube are sized and arranged to insure an adequate, positive inflow of air through all of the openings during burner operation to effect a protective layer of air between the intensely hot burning fuel stream and the inner surface of the burner tube.

For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the following description which refers to the accompanying drawing in which FIG. 1 is a sectional side elevation of a fuel burner according to the present invention mounted in the boundary wall of a blast furnace.

Referring to the drawing7 a burner 10 according to the present invention is mounted to fire into the upper hearth area of a blast furnace chamber 12 which is cylindrical in horizontal cross-section and is bounded by a refractory wall 14 encased on its outside by a metallic shell plate 16. The burner 10 is mounted on a flange member 17 which is suitably welded to the plate 16 and circumscribes the outer periphery of an inwardly tapered tuyere opening 18. A water-cooled inwardly tapered frustoconical tuyere cooler casting 20 lines the inner surface of the tuyere opening 18.

Suitable connections

20A and 20B are provided for effecting the circulation of cooling water through the tuyere cooler casting 20. A water-cooled tuyere 22 projects into the furnace chamber 12 and engages at its rearward end with the forward end of the tuyere cooler casting 20. Suitable threaded

connections

22A and 22B are provided for the circulation of cooling water through the tuyere 22. The inner wall of the tuyere 22 defines an unobstructed discharge passage or port 24 that is axially aligned with the tuyere opening 18. The

above-described tuyere opening 18 and water jacketed members 20 and 22 are of standard blast furnace construction.

The burner 10 includes a windbox casing 26 enclosing a windbox chamber 28. The casing 26, the forward end of which fits within the recess formed by the tuyere cooler casting 20, includes an inwardly tapered frusto-conical wall portion 29 which is spaced from and substantially parallel with the inner wall of the tuyere cooler casting 20, an inner end plate 30 that is formed with an opening axially aligned with the ydischarge passage 24 of the tuyere 22, and an outer end plate 31. The outer end plate 31 engages a flanged portion of a tuyere stock elbow 32, the elbow 32 being connected for flow of high temperature blast air therethrough from a bustle pipe (not shown) of the usual type common to blast furnaces. The inner walls of the elbow 32 and the casing 26 are lined with heat resistant refractory material 33, in view of the fact that the blast air flowing through the elbow 32 into the windbox chamber is normally in the order of 1800- 2000 F.

At the junction 30A of the inner flange plate 30 and the tuyere 22, and at the junction 31A of the outer end plate 31 and the elbow 32, the engaging surfaces are spherical in shape so `as to allow nominal amounts of relative movement between the elbow 32, windbox casing 26 and tuyere 24. These elements are maintained in proper position by means of a spring tensioned bridle assembly 33 which resiliently interconnects a bracket 34 rigidly attached to the elbow 32 with the shell plate 16.

The main component of the burner is an elongated cylindrical burner tube 40 that is 'arranged within the windbox chamber 28 and has its central axis in alignment with the axis of the discharge port 24 of the tuyere 22. The bumer tube 40 is positioned and supported by means of radially projecting struts 45 attached at their inner ends to a pair of spaced support rings 46 which embrace the tube 40 and at their outer ends to the windbox casing 26. The forwardmost end of the tube 40 is maintained in ialignment with the tuyere port 24 by means of ra support ring 47 which is wel-ded to the inner end plate 30 and embraces the end of the tube 40. The outer (inlet) end of the burner tube 40 is closed by a circular plate 42, and the open discharge end is in direct communication wi-th, and the same diameter as, the discharge passage 24 of the tuyere 22. The burner tube 40 is formed over its entire cylindrical area with a plurality of substantially regularly spaced openings 41, the details of which will be discussed here- 'inaften Projecting rearwardly from the elbow 32 is an access tube 35 which is closed at its end by a removable plate 36. A shielding tube 37 extends through and is welded to the plate 36. Extending within the shielding tube 37 is a fuel supply pipe `44 which has its open discharge end projecting through the plate 42 so that a fuel stream is introduced into the burner tube generally along its axis. The function of the shielding tube 37 is to prevent overheating of the fuel in the supply line 44 by the hot blast air owing through the elbow 32. The outer end of the shielding tube 37 is closed by a seal cap 38 through `which the fuel pipe 44 passes. The fuel pipe 44 connects with a fuel source (not shown).

A sighting tube 39 is welded to and extends through the plate 36 and into the burner tube 40 so that combustion conditions can be visually monitored.

The fuel to be delivered to the above-described burner 10 via pipe 44 is preferably pulverized coal in dense phase transport, i.e. pulverized coal entrained in a stream of carrier gas, the mixture having 'a carrier gas to solids ratio no greater than 5 cubic feet of carrier gas (at standard conditions) for each pound of solids. A preparation and conveying system for delivering such a dense phase coal stream to a blast furnace is disclosed in U.S. -Patent 3,204,942, issued Sept. 7, 1965, in the name of I H. Kidwell et al. 'It is contemplated that the phase dense phase transport will also include a solid fuel/ liquid slurry, e.g. a mixture of pulverized coal and fuel oil. It is further intended that crushed as well as pulverized coal or char entrained in -a carrier fluid be within the purview of the present invention, and the phase particle-form carbonaceous fuel is used herein as being inclusive of these forms of lfuels.

-In the operation of the burner 10, hot blast air is supplied to the windbox 28 via elbow 32, and coincidentally a stream of fuel is introduced axially into the burner tube 40 through pipe 44. The air, after passing through the openings 41, mixes with lthe fuel, and since the blast air temperature is Well above the ignition temperature of some of the fuel stream components, ignition takes place within the burner tube almost immediately. By properly spacing yand sizing the openings 41 in the burner tube 40, air is introduced into the tube along its entire length so that a substantial portion of the fuel is burned before -discharge into the blast furnace chamber 12.

The sizing of the burner tube 40 and openings 41 is critical in the design of this burner. As above stated, ya substantial amount of combustion takes place within the |burner tube 40, and it should be recognized that the combustion gas temperatures resul-ting from this burning approach temperature levels of 4000 F. By properly sizing the burner tube 40 and the openings 41, it has been found that a protective layer of air can be maintained along the entire inner surface of the burner tube 40 .to prevent impingement of the hot gases on the inner wall of the burner tube 40. rFhis same influx of air along the entire length of the 'burner tube 40 also prevents the deposition of slag on the inner wall of the tube. It should be noted that the windbox chamber 28 is forwardly tapered to enhance the distribution of air to the openings 41 along the length of the burner tube 40.

An experimental burner of the type Idescribed above has been operated in the test facilities of the assignee of the present invention to determine the design perimeters and limitations of this burner. In the test burner, the burner tube 40 was 341/2 inches long and 6 inches (inside) in diameter. Satisfactory operation was obtained by providing evenly spaced openings 41, the cumulative area of which was between 6 and 7% of the total area of the inner surface of the burner tube 40. As a result of these tests, it was concluded that the ratio of cum-ulative area of the spaced openings 41 to the area of the discharge area at the end of the tube 40 should lbe no greater than approximately 1.5. The higher ratios were found to result in llame impingement on the burner tube 40 and its rapid failure. The lower ratios were found to be operable; lhowever, excessive pressure drop resulted. It was `further found that the diameter of the openings 41 should not exceed approximately 3/s-inch, since large openings resulted in excessive spacing between openings with consequent breaking down of the layer of cooling air `and localized hot spots between openings.

Both a stainless steel burner tube and a ceramic burner tube were tested during the abovedescribed experimental operation of this burner. The stainless steel tube demonstrated good characteristics in that it was light and structurally adequate; however, it has an obvious limitation of about 1800 F. blast air temperautre. Burning within the ceramic refractory tube was observed to be slightly superior, probably because of better mixing of the fuel and air due to the jet action imparted to the air because of the increased thickness of the ceramic tube wall.

Calculations indicate that burners according to the present invention, as described above, can be installed in existing blast furnaces without any major redesign or rearrangement of equipment, and without any appreciable increase in pressure drop over what is normally experienced through a blast furnace tuyere opening.

What is claimed is:

1. A fuel burner comprising an elongated burner tube of generally circular cross-section having a closed inlet end and an open discharge end, said burner tube being formed over substantially its entire area with a plurality of substantially yregularly spaced openings, said openings being arranged to direct air substantially radially into said burner tube, wall means enclosing said burner tube to form thereabout a windbox chamber, said windbox chamber being an annular chamber diminishing in cross-section in the direction of the discharge end of said burner tube, means for supplying air to said burner tube, means for substantially axially introducing into the inlet end of said burner tube a stream of ash containing fuel, and means for introducing all of said air into said windbox chamber to mix with and burn said fuel within said burner tube, the openings in said burner tube being sized and arranged to provide a positive inflow of air through all of said openings when said burner is in operation so as to provide a protective layer of air between the burning fuel stream and the inner surface of said burner tube.

2. A fuel burner according to claim 1 wherein said fuel stream is a dense two-phase mixture, one phase of which includes particle-form carbonaceous fuel.

3. A fuel burner according to claim 2 wherein means are provided for preheating said air to a temperature above the ignition temperature of said fuel stream, and wherein said burner tube is formed of a heat resistant refractory material.

4. A fuel burner according to claim 2 wherein said burner tube is cylindrical.

5. A fuel burner according to claim 3 wherein the cumulative open area of the `openings in said burner tube is no greater than approximately 1.5 times the area of the discharge opening of said burner tube.

6. In combination, a blast furnace having a boundary wall formed with a tuyere opening, a fuel burner arranged to lire through said tuyere opening, means for supplying a stream of ash containing fuel to said burner, means for supplying blast air to said burner, and means for preheating said yblast air to a temperature greater than the ignition temperature of said fuel, said fuel burner including an elongated burner tube of generally circular cross-section having a closed inlet end and an open discharge end and being in axial alignment with said tuyere opening, said burner tube being formed over substantially its entire area with a plurality of substantially regularly spaced openings, said openings being arranged to direct air substantially radially into said burner tube, wall means enclosing said burner tube to form thereabout a W-indbox chamber, said windboX chamber being an annular chamber diminishing in cross-section in the direction of the discharge end of said burner tube, means for substantially axially introducing said stream of fuel into the inlet end of said burner tube, and means for introducing all of said blast air into said Windbox chamber to pass through the burner tube openings and mix with and burn a major portion of said fuel within said burner tube prior to discharge therefrom, the openings in said burner tube being sized and arranged to provide a positive inflow of air through all of said openings when said burner is in operation so as,

to provide a protective layer of air between the burning fuel stream land the inner surface of said burner tube.

7. The `combination according to claim 6 wherein said fuel stream is a dense two-phase mixture, one phase of which includes particle-form carbonaceous fuel.

8. The combination according to claim 7 wherein said burner tube is formed of a heat resistant refractory material.

9. The combination according to claim 8 wherein said burner tube is cylindrical.

10. The combination according to claim 9 wherein the cumulative open area of the opening in said burner tube is no greater than approximately 1.5 times the area of the discharge opening of said burner tube.

11. The combination according to claim 10 wherein the cumulative open area of the openings in. said burner tube is approximately 6-7% of the internal surface area of said -burner tube.

References Cited UNITED STATES PATENTS 1,450,229 4/ 1923 Robinson. 609,744 8/ 1898 Hennig. 2,725,929 12/ 1955 Massier. 3,209,810 10/ 1965 Schuvart 266-*29 X FOREIGN PATENTS 351,768 7/ 1931 Great Britain.

I. SPENCER OVERHOLSER, Primary Examiner. E. MAR, Assistant Examiner.