US2918267A - Pelletizing furnace - Google Patents

Description

Dec. 22, 1959 P. L.. sTEFFENsEN PELLETIZING FURNACE 2 Sheets-Sheet 1 Filed March 18, 1953 INVENTOR Perqy. Sie'enerz,

Dec. 22, 1959 P. STEFFENSEN PELLETIZING FURNACE 2 Shets-Sheet 2 Filed March 18, 1953 mw MT@ INVENTOR Per@ S'ff'rzla BY 20j@ ATTORNEY United States Patent O PELLETIZIN G FURNACE Percy Lea` Steffensen, Cornwall, Pa., assignor to Bethlehem Steel Company, a corporation of Pennsylvania Application March 18, 1953, Serial No. 343,138

1 Claim. (Cl. 263-29) My invention relates in general to a process and apparatusI for agglomerating line particles of iron oxide into pieces of sufficient size for proper charging into a blast furnace or open hearth furnace, and more particularly to a method, and furnace which have special advantages for performing the roasting operation of such process.

The starting ore material which I prefer to use in the practice of my invention is a moist tine concentrate of magnetite (Fe304), to which a small amount of finely dividedfuel has been added; andthe desired end product consists of fairly large and uniform dry pellets of hematite (F8203)- Accordingly, there arewrequired two principal operations, namely, the formation of the ore balls in a balling drum or thelike, and'then the roasting of these balls at a temperature sufliciently` high to give the necessary strength and hardness to withstand subsequent handling.

The operation of hardening these ore balls or pellets is.v preferably carried out in a furnacel of the vertical shaft type wherein the` heated ore charge forms a continuous column of downwardly-moving material in the stack.

Itis an object in this invention to provide means for maintaining uniform and continuous flow of the charge in such a furnace.

A further object is to provide agitator and Crusher means for assisting discharge and preventing stoppages in the bottom discharge opening.

In the attached two (2) sheets of drawings:

Fig. 1 is a vertical section taken through one shaft of a furnace having dual shafts and hoppers;

Fig. 2 is -a vertical section taken centrally through the lower portions of the furnace shafts and the hoppers; and

Fig. 3 is a detail view, partly in section, of the air inlet and pellet agitating mechanism of the furnace.

Referring more particularly to the drawings inclusive, the furnace has a rectangular outer shell 24 of steel plates, which shell is provided with conventional outer lstiffening members (not shown) and brick ties 25 adapted for supporting the necessary thickness of insulating and high temperature refractory brickwork 26. By means of a common dividing wall 27 of refractory brick which extends vertically upward and terminates in a sloping peak 27 near the top of the furnace for the full length of the furnace, said furnace is separated into twin shaft furnaces 28 and 29, which are operated and controlled practically as one.

Each of said shaft furnaces 28 and 29 is provided with combustion chambers 30 and 31 on opposite ends. Located centrally between the combustion chambers in each shaft furnace and in spaced vertical alignment the end walls of each shaft define a top stack 32 having a slight upward taper, and below it an intermediate zone 33 and a lower zone 34, terminating in a long steel hopper 35, all of which should be rectangular in cross-section as shown in Fig. 1.

Each of said combustion chambers 30 and 31 is provided with a fuel oil burner 36, manholes 37, sight holes 38, an arched roof 39, and a bottom dust leg 40. Lower 2,918,267 Patented Dec. 22, 1959 and upper passages 41 and 42 for admitting the air to be heated and for passing out the heated air connect each combustion chamber with the shaft below and above the zone 33. The zones 33 and 34 have each essentially the shape of an inverted truncated wedge with their respective side walls 43 and 44 sloping at an angle preferably not exceeding about 20 from vertical to facilitate discharge. In dimensions, zone 33 will vary in width from about twice the bottom width of the stack 32 at the top of said zone to not less than said bottom stack width at the bottom, and zone 34 may be made somewhat wider. A short brickwork extension 45 carrying the bottom of said stack 32 slightly below the level of the roof 39 permits the proper travel of the hot gases and yet prevents the ore pellets from entering the combustion chambers 30 and 31.

Air under pressure from a blower (not shown) is introduced centrally through horizontal lateral pipes 46 separated by partition plate 47 and through vertically arranged rows of louvres 48 on support members 49 at the bottom of each shaft, and travels upward through the heated pellets and lower passages 41 into the combustion chambers 30 and 31. An inverted V-shaped cover 50- protects the above-described air inlet means 46, 47 and 48 from the heavy downward pressure exerted by the descending charge and splits it centrally into two substantially equal parts.

Thermocouples 52 in passages 42 from the combustion chambers permit control of air Volume and oil tlow to maintain a uniform heat line near the top of the charge and a constant combustion chamber temperature.

Referring to Fig. 3, agitator segments 53 having a plurality of breaker teeth 54 of Stellite or other hard alloy spaced at regular intervals on their upper faces are mounted at regularly spaced intervals on hollow air or water-cooled rocker shafts S5 extending horizontally in termediate between the cover 50 and bottom side walls 44 and parallel thereto. Said rocker shafts 55 are journaled through suitable air seals in the side walls of the furnace as at 56 and adapted to be reciprocated at intervals to break up any obstructing chunks of pellets by means of the arms 57 pivotally connected as at 58 to the connecting rod 59, which in turn is pivotally connected by link 60 to crank 61 rotated by motor 62.

The long steel hoppers 35 at the bottoms of the shaft furnaces have the form of inverted pyramids with substantially the same downward slope (about 20) as the lower side walls 44, and are provided near their discharge openings 63 with crusher discs 64 having evenly spaced hard-alloy teeth 65 entirely around their peripheries and with hard-alloy conical projections 66 on the side surfaces of the outer discs. Said discs are mounted for continuous rotation on a pair of transverse shafts 67 which are joined by a coupling 68 and journaled in an air-tight manner in bearings 69 suspended by cross-beams '70 and 71 and brackets 72. Gears 73 and 74 are driven by a gear reducer 75 connected by a belt 76 or the like to a motor 77 mounted on l-beams 78.

It is preferable that the formation of large masses of` pellets be prevented, or that at least the size of any such masses be limited to relatively thin weak slabs which readily break apart as they move down through the: furnace, and are then easily broken down to individual pellets by agitator means 53 and 64.

I have found in practice that the formation of large; continuous masses or cakes of cohering pellets in the.- upper part of the charged material in the furnace may be: quite effectively prevented by the exclusion of fines from between the pellets in designated areas of the charged material. Suitable means for this purpose are the hori zontal angle bars 174 shown in Fig. 1, disposed transversely across the furnace stack 32 a slight. distance above the top level of the charged pellets so as to intercept and direct the fall of the material being charged. The large ore pellets tend to roll before coming to rest, while the nes tend to collect where they fall, so that in practice the desired distribution is obtained.

The operation of the furnace is continuous, the moist ore pellets being charged at the top of the shafts and moving slowly downward as the fused and agglomerated product is discharged from the bottom hoppers. The blowers (not shown) introduce through the pipes 46 the main volume of air, which may be estimated approximately in the proportion of l2 cubic feet of air to one pound of pellets, into the cooling zone 34 near the bottom. Here it meets the descending hot pellets and absorbs much of their heat. This ascending preheated air, at a temperature of about 1200 F., divides when it reaches a point level with the bottom of the combustion chambers 30 and 31,

part of it continuing on up through the shafts and part being diverted laterally through the lower passages 41 and upward through said combustion chambers, wherein it is further heated to a temperature of about 1750 to 1850 F. The heated air then returns by means of the upper passages 42 from the tops of the combustion chambers to the shafts, where it rejoins the air which has ascended through the shafts and heats the incoming pellets up to near the tops of the shafts. At the very tops of the shafts, much of the heat remaining in this ascendingv air is expendedin removing moisture from the raw pellets introduced at the top, and air temperature drops to about 600 F.

The hard pellets at their discharge from the bottom of the furnace may be regarded as cold for all practical purposes, since their temperatures will not be much in excess of 150 F., constituting further proof of the eciency of the furnace as a heat interchanger between the hot pellets and the incoming air.

If a furnace of rather limited capacity, say up to 275 tons per day, is desired, a single stack and heating chamber p 4 tribution of the charge will afford much better results than a single chamber of apparently equivalent capacity.

Although I have thus shown and described my invention hereinabove in considerable detail, I do not wish to be limited narrowly to the exact and specic details mentioned, but I may also use such substitutes, modifications or equivalents thereof as are embraced within the scope and spirit of the invention and of the appended claim.

I claim:

An ore pellet roasting furnace comprising a substantially rectangular furnace shaft having inwardly sloping opposite side walls, air inlet means near the bottom of said furnace shaft intermediate the side walls, inverted V-shaped cover `means for protecting said air inlet means from the weight of the descending charge and dividing said charge into substantially equal parts, horizontally extending rocker shafts intermediate said cover means and the side walls, a plurality of toothed segments secured on said rocker shafts., and means for intermittently oscillating said rocker shafts with the segments thereon to break up the descending charge.

References Cited in the le of this patent UNITED STATES PATENTS 182,419 Cummings Sept. 19, 1876 742,037 Kearns Oct. 20, 1903 791,660 Walzel June 6, 1905 865,658 Scott Sept. 10, 1907 1,164,761 Simmons Dec. 21, 1915 1,235,740 Terrace Aug. 7, 1917 2,280,571 Dionisotte Apr. 21, 1942 2,451,024 Ellerbeck Oct. 12, 1948 2,470,543 Azbe May 17, 1949 2,624,560 Craig et al. Jan. 6, 1953 2,628,829 Ruiz Feb. 17, 1953 2,650,814 Howden Sept. 1, 1953 2,670,946 Royster Mar. 2,1954 2,676,095 DeVaney et al Apr. 20, 1954 2,744,743 Beggs et al May 8, 1956 FOREIGN PATENTS 501,249 Great Britain Feb. 23, 1939

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