Note: Descriptions are shown in the official language in which they were submitted.
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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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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.
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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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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
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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.
