US3217781A

US3217781A - Gas mixer for blast furnace stoves

Info

Publication number: US3217781A
Application number: US270850A
Authority: US
Inventors: Gerald R Curtis; Neal T Kurfiss
Original assignee: Armco Inc
Current assignee: Armco Inc
Priority date: 1963-04-05
Filing date: 1963-04-05
Publication date: 1965-11-16
Anticipated expiration: 1982-11-16

Description

Nov. 16, 1965 G. R. CURTIS ETAL GAS MIXER FOR BLAST FURNACE STOVES Filed April 5, 1963 INVENTOR. GERALD R. CURTIS AND NEAL T KURFISS ATTORNEYS United States Patent 3,217,781 GAS MIXER FOR BLAST FURNACE STOVES Gerald R. Curtis and Neal T. Kurfiss, Middletown, Ohio, assignors to Armco Steel Corporation, Middletown, Ohio, a corporation of Ohio Filed Apr. 5, 1963, Ser. No. 270,850 8 Claims. (Cl. 158-109) This invention relates to burners for blast furnace stoves, and more particularly to a device for thoroughly mixing a gaseous fuel and air therein.

A modern blast furnace installation will include two or more stoves, each of which is a large structure substantially filled with refractory checkerwork. At any given time, one of these stoves is on the line; that is, cold air is passed through the checkerwork, and fed into the blast furnace. At the same time, the other stoves are on gas. This means that fuel gas and air are burned in a combustion chamber, and the products of combustion are directed through the checkerwork to heat up the stove. At suitable time intervals, the various stoves are alternated so that the supply of air to the blast furnace is maintained at a high temperature.

Burners for such stoves generally utilize blast furnace gas as fuel, primarily because of its ready availability. However, such gas is characterized by a relatively low calorific value. This of course means that a large volume of gas must be burned; as a result, the burners are generally operated at a rather high speed. A common problem in such an operation is what may be called backfiring. This is due in very large part to an insufficient mixing of the gaseous fuel and combustion air, so that the gases do not ignite at the mouth of the burner. Hence there is a delayed ignition, occurring probably when the gas reaches the begining of the checkerwork, with a resulting explosion and flash back. At that time, the flame will go out until the gas again returns to the beginning of the checkerwork.

Accordingly, a primary object of this invention'is to provide a mixing device which will improve the mixing of gas and air, and prevent pulsating explosions at high burning rates.

Another object of this invention is the provision of such a device which will accomplish the thorough mixing Without using any moving parts or requiring additional energy.

While it is very desirable to have ignition occur at the mouth of the burner, it will immediately be apparent that combustion cannot be permitted within the mixer itself. For this reason, prior art devices maintain the gas and air in separate conduits until they enter the combustion chamber, and then attempt to induce sufficient turbulence to accomplish the necessary mixing at that point.

It is therefore still another object of the present invention to provide a device in which mixing is accomplished within the mixer, but in which combustion is prevented until the gases reach the entrance to the combustion chamber.

Still a further object of this invention is the provision of a mixer configuration which, while very eificient in producing violent turbulence, is very easy to fabricate.

Other objects of this invention will become apparent as this specification proceeds. Reference will be made from time to time to the accompanying drawings forming a part hereof, and in which:

FIGURE 1 is a vertical cross-sectional view through the device of this invention, and

FIGURE 2 is a perspective view showing a portion of the device illustrated in FIGURE 1.

Broadly considered, the mixer of this invention includes two concentric conduits, with a high pressure gas (either fuel or air) flowing through the inside conduit,

and a lower .pressure gas (again either fuel or air) carried by the outside conduit. This invention also includes a stationary whirler which utilizes the pressure differential between the two gas streams to supply the energy to accomplish the complete admixture of the gases.

Referring now to FIGURE 1, the inside conduit has been designated at 10, and the outside conduit at 11. In the embodiment shown, the outside conduit includes a portion 11a which is suitably joined to the portion 11 with an air-tight seal as at 12. This two-piece construction is preferred'in order that the portion 11a may be removed and a door (not shown) may be placed over the entrance to the combustion chamber when the stove is on the line. In any event, it will certainly be understood that the out-' side conduit can be made in one piece, in which a suitable valve, preferably water cooled, must be provided to close the opening into the combustion chamber.

According to conventional practice, a blast furnace is operated at super-atmospheric pressure; hence the top gas coming from the furnace is under pressure when it reaches the burner. In the embodiment illustrated, the fuel gas under relatively high pressure is shown by full line arrows as passing through the inside conduit 10; but it will be understood that if desired the gaseous fuel could be passed through the outside conduit, and the air for combustion through the inside conduit. Further in the embodiment shown, air for combustion will be fan driven through the outer conduit 11, and its passage is indicated by the dotted arrows. A fan has not been shown in the drawing, but it will be understood that it is conventional in construction, and as such, forms no part of this invention. It is only necessary to provide a pressurized supply of gas through the inside conduit 10, and a supply of gas under somewhat lower pressure through the outer conduit 11.

The mixing device itself includes two principal parts. The first of these is a frustum shaped deflector ring indicated at 13. As shown in the drawings, the ring 13 is mounted within the inside conduit 10, and serves two important functions. First, it acts to deflect a portion of the high pressure gas stream outwardly, and secondly, it defines an orifice which serves to increase the velocity of the high pressure stream. This of course ultimately results in better mixing.

The stationary whirler can best be described by referring at this time to FIGURE 2. As seen therein, it includes four mixing vanes indicated at 14, although the number of vanes is not critical. Each of these vanes is formed to provide a curved surface, but it will be noted that the curved surface is bounded by three straight lines. That is, each vane has a straight base 15, a straight leading edge 16, and a straight trailing edge 17. The opposite side edge 18 of each vane is curved, but it will be noted that the shortest distance from every point along the opposite side edge to the base is constant. This particular construction of the mixing vane has two primary advantages. In the first place, it is very efiicient in imparting a swirling or rotary motion to the high pressure stream of gas and directing a portion of it outwardly into the low pressure stream of gas, and in the second place, it is very easy to fabricate.

As clearly shown in FIGURE 2, the four vanes are joined together at their bases 15, and spaced approximately of rotation apart. The spaced apart

circular rings

19 and 20 are secured to the opposite side edges of all four of the vanes. Each of these rings is provided with a number of outwardly projecting flanges 21, by means of which the stationary whirler may be secured within the outside conduit 11a. It will be apparent that at high operating rates, the whirler develops a great deal of torque, and certain reinforcements in the mounting arrangement are desirable. For example, straps 22 (FIG- URE 2) may be mounted tangentially between the bases Patented Nov. 16,. 1965 9 of the flanges 21 and the outer conduit 11a. These straps Simply act as tension members to prevent rotation.

At this time, it should be noted that the inside conduit terminates a short distance in back of the stationary whirler. It will therefore be apparent that beyond the end of the inside conduit, yet still within the outside conduit 11a, there can be a complete admixture of the gaseous fuel and the air for combustion.

Optimum performance requires that the gases be ignited at the mouth of the burner as soon as the mixture enters the combustion chamber at a point indicated in FIG. 1 generally at 23. The combination of the frustum deflector ring 13 and the mixing vanes 14 produce a violent turbulence which will insure complete mixing of the gases prior to leaving the mixer, and insures ignition at the mouth of the burner 23.

To prevent the flame from backing up into the burner, the gas mixture, while in the mixer itself, must be maintained at a velocity which is greater than the flame propagation rate. By operating the mixture at a high velocity, it is not necessary to keep the gas and air separated until they enter the combustion chamber. With this invention, mixing can be accomplished within the mixing device itself, and combustion will not occur until the velocity of the mixture drops at the entrance to the combustion chamber.

Numerous modifications in this invention will readily present themselves to the skilled worker in the art. Hence, although the invention has been described in terms of an exemplary embodiment, no limitation is intended except insofar as set forth in the following claims.

What is claimed as new and what it is desired to secure by Letters Patent is:

1. A gas mixer for blast furnace stoves comprising a first conduit for the passage of gas under pressure, a second conduit surrounding said first conduit to form an annular chamber for the passage of gas under pressure, said second conduit extending beyond the end of said first conduit, means including a ring shaped deflector concentrically disposed within said first conduit at the outer end thereof to direct a portion of said gas under pressure outwardly, and a stationary whirler means mounted within said second conduit and beyond the end of said first conduit, said stationary whirler means being aligned coaxially with said first conduit and including a plurality of mixing vanes disposed to impart rotary movement to said gas leaving said first conduit, and to effect the mixing of said gases leaving said first and second conduits respectively.

2. The gas mixer claimed in claim ll, wherein said mixing vanes of said stationary whirler means each comprise a curved surface having a straight base, a straight leading edge, a straight trailing edge, and a curved opposite side edge.

3. The gas mixer claimed in claim 1, wherein said ring shaped deflector comprises a frustum ring, the larger end of said ring being mounted within and spaced from the inner wall of said first conduit.

4. The gas mixer claimed in claim 2, wherein said stationary whirler means includes four mixing vanes, said vanes being joined together along said straight bases and spaced substantially apart.

5. The gas mixer claimed in claim 2, wherein the shortest distance between every point along said curved opposite side edge and said straight base of each of said vanes is constant.

6. A gas mixer for blast furnace stoves comprising a first conduit for the passage of gas under high pressure, a second conduit surrounding said first conduit to form an annular chamber for the passage of gas under low pressure, said second conduit having an end portion thereof extending beyond the end of said first conduit, and a stationary whirler means mounted in said second conduit beyond the end of said first conduit and coaxial therewith, said whirler means having a plurality of mixing vanes disposed to impart rotary movement to said high pressure gas and to divert a portion of said high pressure gas outwardly for admixture with the low pressure gas flowing through the said extending end portion of said second conduit, each said vanes comprising a curved surface having a straight base, a straight leading edge, a straight trailing edge, and a curved opposite side edge.

7. The gas mixer claimed in claim 6, wherein the shortest distance between every point along said curved opposite side edge and said straight base of each of said vanes is constant.

8. The gas mixer claimed in claim 1 wherein the outermost edges of said vanes are secured to a ring the diameter of which is approximately equal to the diameter of said first conduit.

References Cited by the Examiner UNITED STATES PATENTS 850,996 4/1907 Cooley 158118 1,071,053 8/1913 Hunter 158l09 1,360,981 11/1920 Witt 158118 1,885,067 10/1932 Woodeson -104 1,893,533 1/1933 Barber 158l18 JAMES W. WESTHAVER, Primary Examiner.

Claims

1. A GAS MIXER FOR BLAST FURNACE STOVES COMPRISING A FIRST CONDUIT FOR THE PASSAGE OF GAS UNDER PRESSURE, A SECOND CONDUIT SURROUNDING SAID FIRST CONDUIT TO FORM AN ANNULAR CHAMBER FOR THE PASSAGE OF GAS UNDER PRESSURE, SAID SECOND CONDUIT EXTENDING BEYOND THE END OF SAID FIRST CONDUIT, MEANS INCLUDING A RING S HAPED DEFLECTOR CONCENTRICALLY DISPOSED WITHIN SAID FIRST CONDUIT AT THE OUTER END THEREOF TO DIRECT A PORTION OF SAID GAS UNDER PRESSURE OUTWARDLY, AND A STATIONARY WHIRLER MEANS MOUNTED WITHIN SAID SECOND CONDUIT AND BEYOND THE END OF SAID FIRST CONDUIT, SAID STATIONARY WHIRLER MEANS BEING ALIGNED COAXIALLY WITH SAID FIRST CONDUIT AND INCLUDING A PLURALITY OF MIXING VANES DISPOSED TO IMPART ROTARY MOVEMENT TO SAID GAS LEAVING SAID FIRST CONDUIT, AWND TO EFFECT THE MIXING OF SAID GASES LEAVING SAID FIRST AND SECOND CONDUITS RESPECTIVELY.