US1703518A - Blast furnace - Google Patents

Description

J. P. DOVEL BLAST FURNACE Feb. 26, 1929.

Filed July 28, 1927 I I I 1 z x I 1 1/ J-R D m/e1 Gau e Patented Feb. 26.1929.

UNITED STATES JAHES P. mm, 01' BIRMINGHAM, ALABAMA.

BLAST FURNACE.

Application filed Jul as, 1927. s mi'm. 209,074.

My invention relates to a new and improved method for the construction and operation of metallurgical blast furnaces.

The ob'ects of my invention are to so deent process involves the provision of means 5 sign the urnace as to materially increase its output, toinsure a longer continued operation, to obtain the desired adual, continuous downward movement 0 the stock in the furnace, thereby avoiding. any hanging of the stock on the furnace walls, and to reduce.

to a negli ible amount the valuable ore and cokethat is now carried out entrainedin the gas and represents not only a loss in stock but an added expense in the operation.

In approaching the solution of the prob-' lems that have confronted the designing of metallurgical blast furnaces, I find that en -v gineershave Sou ht to'prevent the hanging of the stock on t e inwall of the furnace by working on the theory that the rapid expansion of the area of furnace stack downwardly would cause the stock to move downwardly continuously without hanging. The application of this theory will result in a substantial contraction of the bore of the furnace and that in turn in an acceleration of the gas flow through the stock. Further, in the former standard-*design-of metallurgical blast furnaces effort has been made to conserve and protect the furnace lining by so eharging the stock that the zone of most intense heat was removed from the lining and therefore the practice has been to draw this most intensely heated zone toward the center of the furnace. The reason for this has been that no practical means has heretofore been found that would provide a furnace lining that would stand the utilization of the most intense heat around the column'of stock blocks in accordance with my plending a V pli-y cation, Serial Nof663,283, w erein- I a've shown and described amethod of "embedding in the furnacelining a multiplieityfof cool- 'ing' blocks which were detachably'sup orted by the furnace jacket and which won (1 operateto cause an agglomerate and h hly refractory lining to uild itself u wit in the furnace as the. original lining 'sintegrated nace diameter-at this point to e enlarged by substituting thin for thick linings heretofore and yet, accordin to my theory of designor burned away, which agglomerate lining will automatically maintain itself and resist the action of very intense heat The next step in the approach to my presing the subject matter of my pending appli:

cation, Serial No. 72,103, I have shown and described a furnace having its upper portion above the zone of highest heat formed by a. metallic shell with removable and replaceable wear 'lates which .would take all abrasive wear rom the stock and thus ermit the furconsidered necessary.

Having thus provided means to withstand vthe high temperatures and the wear of the stock I was ready to a proach the solution of the problem of per ecting the blast furnace design to the end that ideal operation "might be obtained. and this end is accomplished, briefly, (1) by the designing of the furnace to eliminate or reduce to a minimum the angle or batter of its inner wall, thereby increasing to the maximum ermissible extent the cross-scctional area 0 the up er portion of the furnace, and (2) by so c ar ing the stock that the zone of most intense eat is provided about the column of stock. The results of the change in furnace design and charging methods have been astomshing. In the first place, it has increased the capacity of the furnace from 30% to 50% and it has reduced the flue dust nuisance to a point where the out oing gases are practically carrying only is e ustentrained dur-' ing the charging of the stock whereby very fine unsintered stock can be furnaced. In a number of furnaces convertedto this new design I have reduced the output of flue dust from 538 lbs. to 58 lbs. per ton of iron produced, In attem tin to solve the reasons for this remarkab e reduction in the flue dust output, I have reached the conclusion thatit is the result of the increased stock lincrdiameter of the furnace which results in so slight, if any, an acceleration of the gases flowing upwardly through the stack that the latter;

' operation.

ing and fall of the stock in the furnace are have a rate of flow which permits them to filter through the natural voids in the stock column whereby the do not entrain the dust in them'but ten to leave such dust as may be entrained in the filtering mass of stock. Therefore, one important object of my furnace is todecelerate the gas flow, as contrasted with present practice.

The charging bell in my improved design of furnace is disposed and arranged so as to produce a distribution that will locate the larger and more open portion of the stock column in its center and about the outer periphery of the stock column. Tests by pyrometers in an operating furnace have shown a temperature which increases from the center to the periphery of the stock and this, notwithstanding that the larger stock par ticles collect bothin the center and about the periphery of the stock column. I am of opinion that the higher temperatures exist about the periphery of the stock colum'n due to the fact that it has relative movement to the fixed furnace walls which tends to open up the draft space, thereby accelerating the gas flow upwardly along the furnace lining and producing in this circumferential zone the highest rate of reduction. Obviously, where the column of stock is reducing fastest about its eripherythere will be no tendency for it to ang on the furnace walls and this theory has been substantiated in practice where the furnaces have operated for a long period without the slightest indication of any hanging at all, whereas before their design was changed I expected and encountered trouble from the hanging of stock almost daily in the furnace The disadvantages of the hangtoo well known to those skilled in the art to need further comment here to emphasize the importance from an operating point that will result from the elimination of hanging.

One very important fea ure of my present invention is that due to t e filtering action of the furnace and the slow gas travel, very fine stock may be successfully smelted without' sintering.

As typical of all blast furnace designs for the embodiment of the rinciples of design and operation forming the basis of my present application, I show in Fig. 1 is a blast furnace partly in side elevation and partly in vertical cross-section equipped with the thin water cooled block lining and with the metal lined'top with a portion of the cross-section of the stock illustrate'dto show both the stock distribution,

the theoretical rate of gas flow through the stock, and typical range of temperatures radially of the stock.

In Fig. 2 I show diagrammatically the effect of changing a standard refractory lined furnace according to existing practice, shown in dotted lines, to the design accordance furnace top, 11 the lower charging hopper, 12

the main bell which is of such diameter that the stock distributed from it will collect in larger particles at the center and about the periphery of the stock column. The furnace jacket is reinforced by vertical structural iron beams 13 which support and maintain positively the alignment of the top construction.

The bustle pipe 14 delivers air to the tuyeres 15 in accordance with furnace practice and the bosh is water cooled by elements 16 and cooling blocks 17 The crucible is surrounded by a cast iron jacket 18 which is set in a well 19 adapted to be filled with water. This water will filter into the brick bottom 20 of the crucible and foundations thus serving to protect them from excessive heat.

I It will be observed in Fig. 1 that the lining or inwall 5 is much'thinner than the usual practice. The thickness of this wall will run from 3. to 4 feet in present practice, whereas in my new design these walls need not be more than from 22" to 27". I can employ so thin a lining because as it wears away or disintegrates, which is expected to occur promptly, it is replaced by an agglomerate and highly refractory lining built up from stock particles or semi-fused stock particles and minerals deposited by the gases. An analysis of this built up agglomerate lining shows it to be formed largely of carbon, principally in graphitic form, and alkali minerals, principally potash.

By reference to Fig. 2, the dotted lines indicate the design of the inwall of a standard furnace having a bosh diameter of 22 6", a top diameter .of 16 6", and an angle or batter to the inwall of about 1 to the foot. Such a furnace when redesigned in accordance with my lmproved method of construction will have smallest diameter of the's haft. The existing bell having a 12 6? diameter could be .used and its marginal edge b'ein more remote from the shaft inwall it woul hold the zone of fine material at the same distance from the axis of the shaft and the added space between this zone and. the shaft would permit the heavier stock particles to roll down and 001- I lect a ainst the inwall of the shaft, thereby providing a more porous arrangement of stock surrounding the stock column.

In a furnace of the type described, I have shown by the arrows in Fig. 1 the rate of gas flow, the length of the arrow indicating the rate of flow through each portion of the stock, and below these arrows I have arranged pyrometer readings with a center temperature of 1200 F. and about one-third of the way out to the shaft increasing to 1260 F., and then in the next one-third increasing to about 1500 F., and along the shaft inwall the temperature is increased to 15309 F.

It is to be noted that the increased mass of stock provided at the top of the stock column has another advantage, namely, it will effect a rapid cooling of the gases, thereby reducing their volume and reducing their rate of flow, which obviously will assist the filtering action and will have the important result of materially decreasing the temperature of the outgoing gases, thereby reducing the coke consumption of the furnace.

An important object of my invention lies in the readiness with which it is available for the redesigning of existing furnaces to obtain the improved operating results above pointed out, as the existing shells can be retained and the lining readjusted and inserted to suit the conditions of such furnaces yet to roduce therefrom the operation contemplated by my invention.

In the operation of this furnace, due to the retarded rate of gas flow and the filtering ac: tion of the stock, the production capacity of this furnace after change in design will be increased from 30% to 50%, and it is operated with the greatest ease and will produce a very uniform product, using fine unsintered ore i desired. In the operation of four furnaces of this type up to March, 1927, onl .19 of one per cent of the total output was off grade.

. Another advantage of my improved method of construction and operation of thefurnace wherein the maximum reduction occurs adj acent' to the wall of the shaft is that I avoid the formation of pockets of molten metal which tend to run down the wall and cut the bronze, bosh plates, coolers and tuyeres.

The size of the bell and of stock used should be calculated to produce an increased ratio of voids through the center and about the periphery of the stock column so that the more rapid central and marginal reduction occurring would not only prevent the stock hanging on the inwall but would also avoid an Imreduced center mass of the stock wedging against the converging walls of the bosh. For ideal operation the stock column should have a balanced rate of reduction between its central and marginal portions. Satisfactory results are obtained where the area at the base of the bell is approximately one-third of the stock line area. The ratio of voids, which governs the ratio of reduction, at the margin and center can be controlled by the percentage of coarse to fine material in the charge which must be determined empirically, having regard to the available raw material.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent, is

1. The method of operation of a blast furnace which comprises maintaining the upflow of gases through the furnace stock column adjacent the wall of thestack at a velocity as high as through any other portion of the stock column, and chilling the stock elements touching the wall to form a selfreplaceable stack lining.

2. The method of operating a blast furnace which comprises maintaining the furnace stock column with relatively large void areas adjacent the wall of the stack and in the center forming a relatively dense annulus of material remote from the furnace wall whereby the higher rate of gas flow is along the wall of the stack and through the center of the stock column, and chilling the stock elements touching the wall to form a selfreplaceable stack lining. a

3. The method of operating a blast furnace which comprises so charging the stock thereinto that a higher temperature exists adjacent the wall of the furnace stack than exists farther interiorly of the furnace, and maintaining a self-replaceable stack wall from refractory materials in the furnace charge.

4. The method of operating a blast furnace which comprises maintaining the furf nace charge in a column having a relatively dense annulus of material interiorly of the furnace and lessening in density toward the inner wall of the furnace stack, and chilling the material touching said wall to form a self-replacing lining.

5. The method of operating a blast fur nace which comprises maintaining the furnace charge in a relatively dense annular column bearing loosely against the inner walls of the furnace stack, supplying air upwardly through the stack for combustion whereby a higher temperature and higher rate of gas flow occurs through the center and along the walls of the stack than through the dense annular'column, and cooling the walls of the the descending stock and to maintain the wall of the stack at a substantially uniform thickness.

In testimony whereof I aflix my signature.

JAMES P. DOVEL.

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