US2368270A - Lining rotary furnaces - Google Patents

Description

Jan, 30, 1945. "E. B. STORY 2,368,270

LINING ROTARY FURNACE 4 Filed July 23, 1942 2 Sheets-Sheet l INVENTOR EGWa "OBSfO/y Patented Jan. 30, 1945 2,368,270 LINING ROTARY FURNACES Edward B. Story, Bethel Township, Allegheny County, Pa., assignor to A. M. Byers Company, Pittsburgh, Pa., a corporation of Pennsylvania Application July 23, 1942, Serial No. 452,033

Claims.

This invention relates to lining rotary furnaces. It relates more particularly to an improved method of forming a lining in a rotary furnace having a generally horizontal axis of rotation.

Rotary furnaces having a generally horizontal axis of rotation are used for various purposes, finding a large part of their utility in the metallurgical field. For example, such furnaces are used as melting furnaces for reducing a solid charge to molten form. As a specific example, rotary furnaces of the type mentioned are used for melting iron silicate slag used for admixture with molten ferrous material in the manufacture of wrought iron by the Aston process.

Rotary furnaces of the type above. mentioned commonly consist of a metal shell of generally cylindrical shape, usually with frusto-conical ends, lined with a refractory material to protect the shell during operation. An example of such a rotary furnace is shown in my Patent No. 2,258,632. Heretofore such furnaces have been lined either by building a laid-up lining of refractory brick into the furnace or by centrifugally applying lining material. The building of a brick lining in a rotary furnace is highly undesirable as the furnace must be cooled before commencement of the work so that workmen may enter it, the old lining mustv be removed and the new lining must be built up brick by brick. A great deal of time is Wasted in the shut-down, the cost of the brick is great and the cost of laying the brick in the furnace. is also high. In an effort to obviate the disadvantages of lining rotary furnaces with built-up refractory brick linings it has heretofore been proposed to introduce into the furnace lining material in molten form and rotate the furnace at high speed to cause the lining material to form by centrifugal force a molten lining completely covering the interior of the furnace wall and to chill or cool such molten lining so that it willremain in place when the furnace is slowed down to operating speeds. However, this manner of lining is not feasible as furnaces of the type in question are not designed for operation at such speed that a molten linin material will be caused to form a lining on the interior of the furnace by centrifugal force. Operation of such a furnace at such high speeds for even a limited time imposes great strains and heavy wear on the furnace and greatly shortens its life. Moreover, when the lining formed by centrifugal action cools strains are set up therein which often result in cracks causing spalling and consequent failure of the lining.

This method of lining rotary furnaces-is: so im-.

practical that the first mentioned method of lining with brick is still universally resorted. to despite its great disadvantages mentioned above.

I have devised a method of forming a lining in a rotary furnace having a generally horizontal axis. of rotation which obviates the disadvantages of both prior methods. According. to my im proved method it is unnecessary to cool the furnace so that workmen may enter it. No expensive brick. is used. The time of shut-down is very short. In applying the lining the furnace is not operated at speeds in excess of normal operating speeds. The lining which is formed is tenacious and comparatively free from strains which are likely to result in cracks causing spalling when the lining cools.

I form a lining in a rotary furnace of the type in question by introducing into the furnace linin material in molten form and with such lining material therein rotating the furnace so that a pool of the liningmaterial lies in the bottom of the rotating furnace and portions of the lining material progressively solidify by freezing as accretions on the interior of the wall of the furnace.

Purely for purposes of explanation and illustration I shall describe the invention in connection with the lining of a rotary furnace havinga generally horizontal axis of rotation with slag. As above mentioned, rotary furnaces having a generally horizontal axis of rotation are used for melting iron silicate slag for admixture with molten ferrous material to form wrought iron by the Aston process. It-is desirable to line such a furnace with a slag having a composition like that of the slag to be melted in the furnace. I provide asource of such molten slag other than the furnace to be lined. The slag to be used for lining the furnace in question may be melted in another rotary furnace or in an open hearth furnace or otherwise. By way of example, the molten slag for liningthe rotary furnace will be considered as being formed or melted in anopen hearth furnace. The temperature of the slag as itcomes from the open hearth furnace will ordinarily be in the neighborhood of 2400 to 2500 F. The slag is tapped into a ladle and the ladle is transferred to the rotary furnace where it pours the. slag into the rotary furnace. The temperature of the slag as poured into the rotary furnace may be in the neighborhood of 2300 to 2400 F. The melting temperature of the slag is in the neighborhood of 2150 to 2250 F., depending on its: composition. i

Intha rotary: furnacet'o belined. is of thetilting type the furnace may be tilted slightly to facilitate pouring in the molten slag. Preferably the furnace is rotated while the slag is being poured in. The slag is preferably poured in at a rate in the general neighborhood of six or seven tons per minute. With a furnace 28 feet long and 8 feet in diameter this rate is found to be most satisfactory. The slag should be poured fast enough so that it will not solidify and form a thick encrustation at the end of the furnace where it is poured in before it can flow down to the opposite end of the furnace but on the contrary will form a pool of molten slag in the bottom of the furnace extending throughout the entire length of the furnace.

Either before or upon completion of the pouring of the slag into the rotary furnace the furnace, if originally tilted, is returned to horizontal position. It is rotated at a speed which is preferably no faster than the normal operating speed of the furnace and may be considerably slower. The speed of rotation of the furnace is such that the molten slag which has been poured in lies in the bottom of the furnace in a pool. As the furnace rotates portions of the molten slag progressively solidify and form as accretions on the interior wall of the furnace.

At the beginning of the lining operation the furnace may have a bare metal shell or it may have an old lining or it may have a partial lining. Sometimes during operation large portions of the lining fall away entirely, baring large areas of the metal shell. If all or substantial portions of the metal shell is or are bare at the beginning of the lining operation the molten slag will rapidly adhere to and solidify on the metal. After a thin layer of slag has solidified on the metal the remaining slag is much slower to adhere to the original thin slag lining. Rotation of the furnace is continued and little by little portions of the slag which lies as a pool in the bottom of the furnace solidify by freezing on the furnace wall and form progressive accretions. Thus the lining consists of many thin layers of slag deposited one upon another. As the slag cools and is progressively deposited on the inner wall of the furnace the pool of slag lying in the bottom of the furnace becomes smaller and smaller until it finally disappears entirely and the slag is all uniformly disposed upon the inner wall of the furnace as a lining.

It is desirable to form a lining from 3 to 4 inches thick as such a lining, although it may crack to some extent, will maintain its integrity when cold. A thinner lining may when cold crack and spall off. A lining to 1 inch thick is formed in the first two or three revolutions of the furnace, that is, in a matter of three or four minutes, but the formation of the remainder of the lining to build up its thickness to, say, 3 inches, requires considerably longer as the slag is highly insulating. A total time of perhaps fifteen to twenty minutes is required to complete the lining, The speed of rotation of the furnace during formation of the lining is preferably slow enough so that a thick enough lining will be formed on the first revolution or, in any event, the first two or three revolutions, so that it will bridge over the top of the furnace as the furnace rotates without falling off. For a furnace 8 feet in diameter the best rotational speed during formation of the lining is not greater than one revolution per minute and desirably somewhat All in a furnace 8 feet in diameter and'28 feet long is about twenty to twenty-five tons.

It is preferable, where possible, to cool the furnace shell while lining it as above described. Many furnaces of the type in question are externally water cooled. A common provision for water cooling is to dispose a water spray pipe directly above the furnace and parallel to its axis of rotation and to deliver Water therethrough upon the outside of the furnace shell throughout the length of the shell. Such a cooling arrangement is particularly desirable when lining the furnace in the manner which I have described above as the cooling water sprayed onto the furnace cools the slag and assists in its solidification into the lining. The cooling spray does not solidify the pool of molten slag lying in the bottom of the furnace, but when portions of such molten slag adhere to the furnace wall during rotation of the furnace and emerge from the pool they are cooled to or below the melting point. As these portions approach the top of the furnace they are progressively further cooled and solidified. Cooling during lining is also desirable to avoid the danger of buckling or burning of the shell,

The lining formed as above described is highly tenacious and is comparatively free from strains which are likely to result in serious cracks during operation of the furnace. The entire operation may be performed in a few minutes time as compared with several days time required for relining a furnace with brick. The cost of relining by my method is a very small fraction of the cost of relining a furnace with brick. The furnace is not subjected to abnormal conditions as is the case when such a furnace is rotated rapidly to apply the lining by centrifugal force. My process has been actually used in lining a furnace in operation and has proved highly successful.

In the accompanying drawing I have shown a present preferred apparatus upon which my invention maybe carried out, in which Figure 1 is a diagrammatic elevational view of a rotary slag melting furnace and associated equipment; and

Figure 2 is a plan View of the furnace and equipment shown in Figure 1.

Referring now more particularly to the drawings, the rotary slagmelting furnace is shown at 2. It rotate about a horizontal axis and has frusto-conical ends both of which are open. The

less than that. The weight of a complete lining 76 left-hand end viewing the drawings is the charging end and the ri ht-hand end is the tapping end. The furnace is tiltable about a pivot 3 to discharge its contents, the tapping end of the furnace being shown in tilted position in dotted lines in Figure 1. As the specific form of the furnace per se forms no part of the present invention, and as the furnace may be of standard type, the details thereof need not here be described.

The charging receptacle normally employed during operation of the furnace for charging it is shown at 4, being disposed in charging position in Figure 1 and in filling position in Figure 2. The fuel employed for heating the charge in the furnace durin normal slag melting operations is preferably coal. The coal is brought in on railroad tracks 1 and dumped into a hopper 8, whence it passes up a conveyer 9 into a pulverizer H), where the coal is reduced to pulverized form. The pulverized coal together with primary air passes through the conduit H to the burner 12. A fan I3 blows primary air through a conduit I4 to the pulverizer l and blows secondary air through a conduit l to the burner l2. The burner I2 has a swivel mounting l6 so that it may readily be swung into and out of operative position relatively to the rotary furnace 2. Flame and products of combustion pass through the rotary furnace 2 from left to right viewing the drawings while the furnace i rotating about its horizontal axis and pass thence through a movable stack connection I!- and a fixed stack flue l8 and up and out through a stack l9..

A pit 24 is provided in which are tracks 25 on which is a truck 26 adapted to receive a molten slag ladle 21. The movable stack connection I! is also mounted on tracks 28 so that when it is time to tap the furnace it can be moved out of the way along such tracks. A spray pipe 30 is mounted atop the furnace through which water is sprayed onto the furnace shell, the water pass-- ing down around the shell into a pit (not shown).

An overhead crane 6 carries a molten s ag ladle 5 adapted for transferring molten slag for lining the furnace 2 from the source of molten slag which, as above mentioned, is considered as being an open hearth furnace (not shown) to the fur nace 2. The manner in which my process is carried out has been explained above and its application to the apparatus shown in the drawings will be understood from the above description.

While I have described a present preferred method of practicing the invention it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously practiced within the scope of the following claims.

I claim:

1. A method of forming a lining in a rotary furnace having a generally horizontal axis of rotation comprising introducing into the furnace accretions on the interior wall of the furnace.

2. A method of forming a lining in a rotary furnace having a generally horizontal axis of rotation comprising introducing into the furnace lining material in molten form and with such lining material therein rotating the furnace so that a pool of lining material lies in the bottom of the rotating furnace and cooling the furnace wall, portions of the lining material progressively solidifying by freezing as accretions on the interior of the wall.

3. A method of forming a lining in a rotary furnace having a generally horizontal axis of rotation comprising introducing into the furnace lining material in molten form and with such lining material therein rotating the furnace so that a pool of lining material lies in the bottom of the rotating furnace and delivering a liquid coolant to the outside of the rotating furnace, whereby portions of the lining material progressively solidify by freezing as accretions on the interior wall of the furnace.

4. A method of lining with slag a rotary furnace having a generally horizontal axis of rotation comprising melting slag externally of such furnace, pouring molten slag into the furnace and with such slag therein rotating the furnace so that a pool of slag lies in the bottom of the rotating furnace and portions of the slag progressively solidify by freezing as accretions on the interior wall of the furnace.

5. A method of lining with slag a rotary furnace having a generally horizontal axis of rotation-

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