CA1262044A - Rotary calciner with stationary discharge scroll - Google Patents

Abstract

ABSTRACT

A discharge scroll for a rotary calcining furnace comprises an open top and bottom frame fixed between the discharge end of the furnace soaking pit and the rotary discharge table. The scroll wall has a gap in its lower edge through which material discharged into the scroll flows out onto the discharge table. The scroll may be cylindrical or polygonal in plan, the gap may be uniform or graduated in depth, and its depth or its peripheral extent may be adjustable.

Description

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Field of the Invention This invention relates to rotary ~urnaces used for the calcining of solid materials such as coke. It is more particularly concerned with apparat~s useable with such furnaces which overcomes furnace discharge problems arising from treatment of material having a large proportion of fine particles.

Background of the Invention Rotary hearth furnaces with non-rotating rabbles are commonly used for the continuous coking, devolatilizing and/or calcining of carbonaceous materials such as non-caking coals, anthracite coal, wood products, green petroleum coke, pellets or briquettes containing controlled percentages of bituminous coking coal and other carbonaceous materials or inerts, either with or without a bituminous binder. They may also be used for the calcining of dolomite, limestone and cement rock, the reclaiming of calcium oxide from carbonate sludge, the decomposition of carbonates, sul~onates and chlorides, the reactivation of activated carbon and-the like.
Examples of such furnaces are found in U.S. patents 3,448,012, 3,470,068, 3,475,286, 3,5g4,2~7, 3,612,497, 3,652,426~ and 3,763,013. Generally the furnace comprises a hearth rotating about a vertical axis with its bottom sloping down to a central outlet, a cylindrical chamber known as a soaking pit extending below tha-t outlet to a restricted discharge opening, and a horizontal rotary discharge table therebelow~ ~abbles above the hearth are positioned to move the charge inwardly toward the soaking pit and plows above the discharge table are positioned to move the material on the table toward a discharge port.

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~2~ 1874-732 A number of operators of rotary hearth calciners have observed a phenomenon called "flooding", that is, a spontaneous rapid discharge of ma-terial from the soaking pit onto -the discharge table. Flooding occurs during a time when the rotary hearth furnace is treating a material containing an unusually large proportion of fine particles. The term "fine particles"
as here used comprehends particles which pass through a screen having square openings one-sixteenth oE an lnch or less on a side. The phenomenon of flooding presents operating problems and may also present safety problems.
Summary of the Invention The invention is in a rotary calciner having a rotary hearth and rabbles a soaking pit centrally affixed to said rotary hearth and depending therefrom and a rotary discharge table positioned to receive materials discharged from said soak-ing pit, the improvement comprising a non-rotating scroll posi-tioned between the discharge end of said soaking pit and said discharge table said scroll being greater in periphery than said discharge end but less than said discharge table and having at least one discrete unobstructed gap in its wall through which material discharged within said scroll onto said rotating dis-charge table flows out on said table beyond said scroll said scroll and gap being dimensioned to contain intermittently discharge material from said soaking pit and cause i-t to be carried out through said gap and over said discharge table at a substantially uniform ra-te by rotation of said discharge table.
Figure l is a schematic vertical cross section of a portion of a rotary hearth furnace equipped with one embodiment of the scroll of our invention. For clarity no plow is shown.
F'igure 2 is a schematic plan of the discharge -table and scroll of Figure l on -the plane II-II and including a plow ,".~t~ 2.

~ ~% ~ ~ 187~-732 and outlet for the discharge table.
Figure 3 is an elevation of the scroll of Figure 1 showing the extent and width of the gap therein.

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~ 4 Figure 4 is a vertical section through the scroll of Figure 3 taken on the plane IV-IV.
Figure 5 is an elevation of another form of scroll of our insentlon.
Figure 6 is an elevation of a double gap scroll otherwise like that of Figure 3.
Figure 7 is a schematic plan of a discharge table co-axial with the soaking pit of the rotary hearth furnace and having two plows with which the double gap scroll of Figure 6 can be used.
Figure 8 is a schematic plan of a discharge table with its axis offset from the axis of the soaking pit and having two outlets and two plows, with which a wide gap scroll can be used.
Figure 9 is a schematic plan of a discharge table co-axial with the soaking pit of a rotary hearth urnace and a square scroll.
Figure 10 is a schematic plan of a discharge table co~axial with the soaking pit of rotary hearth furnace and a scroll formed from individual segments so as to have a gap of adjustable width.
Figure 11 is an elevation of a scroll like that of Figure 5 and mounting therefor which allows angular adjustment of the scroll around its vertical axis.
Figure 12 is a schematic elevation of a cylindrical scroll having a vertically adjustable gap.
Figure 13 is a schematic elevation of a cylindrical scroll having a peripherally adjustable gap.

Description oE Preferred Embodiments In Figure 1 is shown a portion of sloping hearth 10 of a rotary hearth furnace as described generally hereinabove eguipped with ~abbles llo An inverted frusto-conical soaking pit 12 is centrally attached to hearth 10 which rotates about axis 15. A circular discharge table 13 is positioned below soaking pit 12 and rotates about its axis 14 which is offset from axis 15 of the furnace. As will be shown our invention is also suitable for rotary furnaces in which hearth and discharge table rotate about the same axis.
A non-rotating frame 16 having a top element 17 surrounds discharge table 13 as well as the discharge end 18 of soaking pit 12. Top element 17 carries a circumferential trough 19 and discharge end 18 of soaking pit 12 carries a depending flange 20 which forms a seal with trough 19. Scroll 21 is affixed to top element 17 so as to be co-axial with soaking pit 12. Top element 17 may be a series of ribs or o~
other construction.
As shown in Figure 2 discharge table 13 is provided with a discharge chute 22 and plow 23 which deflects material discharged through scroll 21 onto table 13 into chute 22 when table 13 is rotated counter-clockwise.
One embodiment of our scroll is illustrated in elevation and section in Figures 3 and ~. A cylindrical shell 26 is formed with outwardly extending flange or rim 25 which is preferably circular. ~ gap or opening 27 is cut in the lower edge of shell 26 extending through a portion of its circumference. We call the circumferential ex-tent of the gap its width. The vertical dimension of the gap we call its depth. The upper edge 28 of the gap in Figures 3 and 4 is 4.

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parallel to the discharge table surEace. The side edges 29 of the gap may be vertical or may incline away from lts upper edge 28.
In operation a rotary hearth furnace equipped with our scroll discharges its heated burden into its soaking pit 12 from which the particles fall into scroll 21 and onto that portion of the rotary discharge table 13 which is momentarily below the scroll wall. Scroll 21 is adjusted by moving it about its axis to position its gap 27 so that the material in the scroll will be earried out through the gap by the rotation of the discharge table. There must be clearance of course between the scroll and the table, and some fines may escape therethrough, but the bulk of the discharge is through the gap, and therefore as long as the discharge table rotates at a constant rate the discharge talces place at a reasonably constant volumetric rate which is not greatly affected by the particle size distributionO The diseharged material on the discharge table is direeted by plow 23 into discharge chute 22.
Our scroll may take various Eor~s and the plow and diseharge ehute arrangement on the discharge table may be adjusted accordingly. Figure 5 illustrates the distinctive portion of a scroll having a gap which extends around its entire eireumference with a depth increasing uniformly from zero to its maximum value through 360 and then abruptly dropping to zero. The ~croll wall 31 if unrolled to a flat strip would have a width 32 at one end narrower than its width 33 at the other end and a lower edge 3~ substantially a straight line.
The seroll shown in Figure 6 has two gaps 36 and 37 which are shown as having the same general shape as the gap 27 of Figure 3 but ga~s 36 an~ 37 may have any desired width and depth and could be of different configurations. A double gap scroll would be used with a discharge table arrangement indicated in Figure 7. Two plows 38 and 39 are positioned to direct ~he discharge from gaps 36 and 37 into two discharge chutes 40 and 41 respectively. In Figure 7 the scroll and discharge table of the furnace are co-axial. Figure 8 illustrates an apparatus arrangement similar to that of Figure 7 but with the axis of the discharge table offset from the axis of the scroll. The arrangements of both figures permit the use o two separate material cooling devices.
As we have mentioned our scroll need not be circular in plan. Figure 9 shows a square scrolL 43 positioned co-axially with its discharge table ~. The gap of scroll 43 may be in any wall. A non-circular scroll of our invention may take the shape of a polygon~ perferably a regular polygon.
Our scroll may be integral or comprise several elements which elements may be modules. A modular scroll co-axial with its discharge table is shown schematically in Figure 10. The scroll comprises a number of modules 46 each with an arcuate wall segment ~7 forming a portion of the wall o~ a circular scroll and an arm 48 extending radially outwardly from each segment 47 to supporting means fixed beyond the circumference of discharge table 4g. Modules 46 are assembled as is shown in Figure 10 so that the scroll wall segments 47 are contiguous. ~ scroll gap may be formed by the omission of one or more modules ~6. Alternatively, the scrolL wall segments 47 may form a complete circle bu-t one or more may have a gap or a portion of a gap in its lower edge.

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PreEerably our scroll, though it does not rotate, ma~
be mounted to permlt angular adjustment around its central axis as is shown in Figure 11. There a scroll wall 31 as is shown in Figure 5 is affixed at its top edge to a circular ring 51 which extends beyond wall 31. Ring 51 is supported by a number of supporting arms 52 the inside ends of which terminate in grooved members 53 f;tting ring 510 Arms 52 may be attached to any non-rotating portion of the frame or may have their own foundation. Ring 51 is rotated in the grooves oE members 53 to position the gap o~ scroll wall 31 in its desired relation wi~h the discharge chute for the discharge table and may be locked in that orientation with any convenient locking device.
Our modular scroll described hereinabove and illustrated in Figure 10, permits incremen~al adj~lstment o~ the peripheral extent of th gap. Figure 12 illustrates a scroll oE
our invention having a gap adjustable in its vertical dimension. The scroll wall 55 has a circumferentially extending gap 56, the upper portion of which is shown to be covered by a plate 57 contoured to fit against wall 55~ In the figure the lower edge 60 of plate 57 is held at a level above -the bottom edge o~ scroll wall 55 so as to leave that portion of gap 56 unobstructed. Vertically elongated slots 58 in plate 57 accommodate bolts 59 affixed in wall 55 so that when the upper ends o~ those slots are in contact with bolts 59 gap 56 is open to the extent above described. Plate 57 can be raised to the extent permitted by its slots 58 and held in a raised position by nuts 61, screwed on bolts 59.
A scroll of our invention with a peripherally adjustable gap is illustrated in Figure 13. The scroll wall 62 has a lower edge 67 parallel with its upper edge 68 and extending around the major portion of its clrcumference. The lower edge 63 of the minor portion of scroll wall 62 is elevated above eage 67 so as to form a gap between edge 63 and the discharge table. Plate 64, which is curved to match -the radius of wall 62, is attached to wall 62 by a pair of bolts 66 which pass through wall 62 in horizontal circumferential slot 65 so that the posi-tion of plate 64 can be adjusted to vary the effective circumferential extent of the above-mentioned gap.
Although we have described our invention hereinabove as used with rotary hearth calcining furnaces it is also useful with calcining furnaces in which the hearth is stationary and the rabbles rotate with respect to the hearth.
In the foregoing speciication we have described presently pererred embodiments oE our invention; however it will be understood that our invention may be otherwise embodied within -the scope of the following claims.

Claims (5)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a rotary calciner having a rotary hearth and rabbles a soaking pit centrally affixed to said rotary hearth and depending therefrom and a rotary discharge table positioned to receive materials discharged from said soaking pit, the improvement comprising a non-rotating scroll positioned between the discharge end of said soaking pit and said discharge table said scroll being greater in periphery than said discharge end but less than said discharge table and having at least one dis-crete unobstructed gap in its wall through which material dis-charged within said scroll onto said rotating discharge table flows out on said table beyond said scroll said scroll and gap being dimensioned to contain intermittently discharge material from said soaking pit and cause it to be carried out through said gap and over said discharge table at a substantially uniform rate by rotation of said discharge table.

2. Apparatus of Claim 1 in which the scroll is polygonal in plan.

3. Apparatus of Claim 1 including means for adjusting said gap said means comprising an element overlying said wall at said gap and extending beyond its periphery at an end, and also vertically, horizontal slots in said element, first fasten-ing means affixed to said wall extending through said slots in said element and second fastening means cooperating with said first fastening means to hold said element against said wall.

4. Apparatus of Claim 1 including means for adjusting said gap in the vertical direction comprising an element over-lying said wall and said gap and extending beyond it peripherally at both ends, and above it vertically, vertical slots in said 9.

element, first fastening means affixed to said wall and extending through said slots and second fastening means cooper-ating with said first fastening means to hold said element against said wall.

5. Apparatus of Claim 1 in which said wall comprises a plurality of wall sections each comprising a fractional part of the periphery of said wall and including supporting means affixed to said frame for positioning said wall sections in adjoining relation so as to form a scroll with a predetermined discrete gap in its periphery.

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