Note: Descriptions are shown in the official language in which they were submitted.
S~6
APPARATUS FOR HEAT RECOVERY FROM MOLTEN SLAG
BACKGROUND OF THE INVENTION
This invention relates to apparatus for the recovery
of sensible heat from molten slag discharged from metal-
lurgical furnaces such as converters and blast furnaces.
Of a variety of schemes heretofore suggested and
practiced for heat recovery from molten slag, two typical
ones are disclosed in Japanese Patent Application Nos.
90932/1976 and 155448/1976 laid open to public inspection
as Nos. 16031/1978 and 78995/1978, respectively. The
former proposes the quenching of molten slag with an inert
gas and the recovery of heat from the inert gas by means
of a heat exchanger such as a cooler or boiler.
The latter application, on the other hand, teaches
the slurrying of molten slag with water. After being
pressurized to augment its sensible heat, the slurried
slag i5 introduced into a cooler tank to provide saturated
~. ~ `,
~'155~6
steam and heated water. The cooler tank has a heat exchanger
mounted therein for heating pure water with the heated water.
Heat is thus recovered from the molten slag in the form of
saturated steam.
Both prior art techniques have a deficiency in common:
they do not provide for the recovery of heat radiated from molten
slag. The efficiency of these and like conventional systems is
therefore not necessarily high. According to the second mentioned
application, in particular, the pressure within the cooler tank
sets a limit on recoverable heat, and mechanical limitations make
it difficult to handle large quantities of slag at one time.
SUMMARY OF THE INVENTION
The present invention aims at more efficient and
economical recovery of heat from molten slag than has been possible
heretofore.
The invention provides apparatus for the recovery of
heat from molten slag comprising:
combination agitating and heat recovery means at a first
heat recovery station for agitating molten slag to granulate the
slag and for recovering heat therefrom, said means having a slag
receptacle means for receiving the molten slag therein, a horizon-
tal rotatable shaft, and a plurality of agitator rods projecting
from axially spaced positions on the rotatable shaft and movable
into and out of the slag in said slag receptacle means during
rotation of said shaft, said rotatable shaft and said agitator rods
having passageway means therein and means for passing fluid to be
heated through said passageway means for heating the fluid at least
by radiation from the slag being agitated by said agitating and
1~55'~6
heat recovery means;
conveying means for conveying the granulated slag from
the first heat recovery station to a second heat recovery station;
and
heat recovery means at the second heat recovery station
for heating a gas by convection from the granulated slag.
Thus the invention advocates heat recovery from molten
slag by two successive, different processes, first by radiation
and then by convection. The agitation of molten slag at the first
heat recovery station assures highly efficient recovery of heat
radiated therefrom, because it prevents the gradual solidification
of the slag from its exposed surface. From the granulated slag
having a reduced temperature, moreover, heat is recovered by con-
vection. It is therefore evident that the invention succeeds in
practically full conversion of the heat content of molten slag into
useful heat energy.
Since the fluid heated by being passed through the
agitator rods can also be put to some useful purposes, heat is
actually recovered not only by radiation but also by direct con-
duction at the first heat recovery station.
The above and other features and advantages of this in-
vention and the manner of a-ttaining them will become more apparent,
and the invention itself will best be understood, from the follow-
ing description of the preferred embodiments taken in connection
with the attached drawings.
BRIEF DESCRIPTION O_ THE DRAWINGS
FIGURE 1 is a vertical sectional view, partly in
elevation and partly broken away for clarity, of the
l~S546
apparatus for heat recovery from molten slag construct-
ed in accordance with this inven-tion;
FIG. 2 is a vertical sectional view taken along
the line II-II of FIG. l;
FIG. 3 is an enlarged, fragmentary elevational view,
partly broken away and shown in section to reveal the
inner details, of the agitator mechanism in the apparatus
of FIG. l;
FIG. 4 is a horizontal sectional view taken along
the line IV-IV of FIG. 1;
FIG. 5 is a diagrammatic top plan view explanatory
of the arrangement of modified means at the first heat
recovery station, for combined use with the provisions
at the second heat recovery station in the apparatus of
FIG. l;
FIG. 6 is an enlarged vertical sectional view taken
along the line VI-VI of FIG. 5;
FIG. 7 is an enlarged vertical sectional view taken
along the line VII-VII of FIG. 5;
FIG. 8 is a further enlarged horizontal sectional
view taken along the line VIII-VIII of FIG. 7;
FIG. 9 is a top plan view, partly broken away for
clarity, of a further preferred form of the apparatus
according to the invention;
- FIG. 10 is an enlarged vertical sectional view taken
along the line X-X of FIG. 9; and
FIG. 11 is an enlarged vertical sectional view taken
~S5~
along the lin~ XI-~I of E'IG. 9.
DESCRI~TIO~I OF THE PREFERRED EMBODIMENTS
The heat recovery apparatus according to the present
invention will now be described more specifically in
terms of its first preferable form illustrated in its
entirety in FIG. 1. Seen at 1 is a well known ladle car
which transports molten slag as from a blast furnace or
converter, not shown, to a charging station C. At this
charging station the ladle car pours the molten slag into
a suitable open-top receptacle such as a pan or pot 6,
which carries the slag to a first heat recovery station
2. Heat radiating from the molten slag is recovered at
this first heat recovery station while at the same time
the slag is being agitated and granulated. The pan 6
subsequently carries the granulated slag to a discharge
station D, from which the slag travels on a suitable
conveyor such as a skip hoist 3 to a second heat recovery
station 4. At this second heat recovery station the
granulated slag heats a gas, normally air, by convection
as such air is forced upwardly into the piled mass of
slag granules or grains.
The ladle car 1 moves along a pair of rails 5 orient-
ed perpendicular to the drawing sheet. Conveyed from the
furnace (not shown), the molten slag has a temperature
in the range of, say, 1,350 to 1,400C as it is poured
from the ladle car 1 into the pan 6 at the charging
station C.
S5L~
As will be seen also from FIG. 2, the pan 6 of
semicylindrical shape is mounted on a wheeled carriage
7 via a pair of trunnions 14 for pivotal motion about a
horizontal axis. The carriage 7 moves along a horizontal
track formed by a pair of rails 8 and extending, in a
direction at right angles to the axis of pivotal motion
of the pan 6 thereon, between the charging station C and
the discharge station D via the first heat recovery
station 2. A pair of sprocket wheels 9 and 10 are
rotatably supported at the opposite ends of the rails 8.
Wrapped around and engaged with these sprocket wheels,
a chain 11 has its opposite ends fastened to the carriage
7. One of the sprocket wheels 9 and 10 is coupled to a
drive mechanism, not shown, for driving the carriage 7
together with the pan 6 thereon back and forth along the
rails 8.
Charged with molten slag at the charging station C,
the pan 6 is fed into the space under a fixed cover 19
at the first heat recovery station 2. The cover 19 is
shown as being box shaped, closed at the top and open
at the bottom, forming a substantially confined space 15
in combination with the pan 6 held in place at the first
heat recovery station. The entire inside surface of the
cover 19 is lined with piping 20 providing passageways
for water or any other suitable fluid to be heated by
radiation from the molten slag in the pan 6.
An agitator mechanism 12 is mounted within the cover
iS~
19 for stirring and granulating the molten slag in the
pan 6. The agitator mechanism 12 comprises a rotatable
shaft 16 supported horizontally by the cover 19, two
staggered sets of agitator rods 17 projecting in
diametrically opposite directions from axially spaced
positions on the rotatable shaft, and a drive mechanism
18 mounted on some suitable support, not shown, outside
of the cover 19 for imparting rotation to the shaft 16.
Thus, upon rotation of this shaft, the two sets of agi-
tator rods 17 alternately thrust into and out of the molten
slag in the pan 6 thereby agitating and granulating same.
All the agitator rods 17 on the rotatable shaft 16 are
in coplanar relationship to each other. During the travel
of the pan 6 to and away from the first heat recovery
station 2, therefore, the agitator rods 16 may be held in
a horizontal plane so as not to impede the passage of the
pan.
Attention is now called to the details of the agitator
mechanism 12 shown in FIG. 3. Preferably, and as shown,
the rotatable shaft 16 and agitator rods 17 are all of
double-tube construction, including inner tubes 21 divid-
ing their interiors into inner 22 and outer 23 passageways
for a fluid such as water. The inner and outer passage-
ways intercommunicate at the tips of the agitator rods 17.
The fluid flowing through these passageways serves the
dual purpose of cooling the rotatable shaft 16 and agitator
rods 17 and of itself being heated by conduction, as well
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11~55~
as by radiation, from the slag in the 6 for heat recovery.
As may have been seen from the foregoing, at the
first heat recovery station 2, heat is recovered from the
molten slag as the fluid flowing through the piping 20,
and possibly through the agitator mechanism 12, is heated
by radiation (and conduction) from the slag, while the
slag is being agitated into granular form. The tempera-
ture of the slag may drop to, say, l,100C upon granulation.
As shown in FIGS. l and 2, a pinion 24 is fixedly
mounted on one of the trunnions 14 of the pan 6 for unitary
rotation therewith relative to the carriage 7. A rack 26
is immovably mounted at the discharge station D for engage-
ment with the pinion 24. Consequently, as the carriage 7
together with the pan 6 thereon travels to the discharge
station D following the completion of heat recovery and
slag granulation at the first heat recovery station 2, the
pinion 24 rotates in mesh with the rack 26 thereby causing
the pan to revolve on the trunnions 14. The construction
and disposition of the rack-and-pinion mechanism is such
that the pan 6 completes a 180-degree angular displacement
on reaching the discharge station D, thereby discharging
the granulated slag into a chute 25 on a bracket 27. This
chute directs the slag into a bucket 28 of the skip hoist
3, when the bucket is in its lowermost position indicated
by the solid lines.
Close to the discharge station D, and over the rails
8, a hopper 29 is disposed in which there is held in storage
11'~5546
the granulated slag fed back from the second heat recovery
station 4 by a belt conveyor 30. When the pan 6 is
pivoted back to its normal position on the carriage 7
following the discharge of the granulated slag, the hop-
per 29 drops a suitable amount of slag into the pan to
create a lining 31, FIG. 2, on its inside surface. The
slag lining 31 performs the functions of preventing the
adhesion of molten slag to the inside surface of the pan
and protecting it against overheating.
Driven by a motor drive unit 32, the bucket 28 of
the skip hoist 3 travels up and down on an incline having
a pair of guide rails 33. The bucket 28 has a gate 34
pivoted at 36 for opening and closing its discharge open-
ing. The gate 34 is held against and slides over another
piar of guide rails 37, parallel to the first recited
rails 33, thereby holding the discharge opening closed
during the up-and-down motion of the bucket 28 along the
incline. The upper extremities 37a of these guide rails 37
are curved away from the skip hoist incline. Thus, when
the bucket 28 reaches its uppermost position as indicated
by phantom line, the gate 34 automatically opens to permit
the discharge of the granulated slag into a convection
cooler 35 at the second heat recovery station 4.
With reference directed to both FIGS. 1 and 4 the con-
vection cooler 35 comprises an enclosure 38 in the shape
of an upstanding cylinder for accommodating the granulated
slag, and a chute 39 integral with the enclosure for
~ss~
directing the slag from the skip hoist 3 into the
enclosure. The temperature of the slag may drop 50C
or so during its transportation from the first heat
recovery station 2 to the second 4, so that it will
have a temperature of approximately 1,100C on entering
the convection cooler 35.
The bottom of the enclosure 38 is formed in part
by four radial rows of rollers 40 arranged at angular
spacings of 90 degrees about the center of the bottom.
Each row of rollers 40 is disposed horizontally, with
constant spacings therebetween. Any two adjacent rollers
are revolved in opposite directions by a suitable drive
mechanism, not shown, in order to permit the passage of
the granulated slag therebetween with its grain sizes
appropriately controlled. The spaces between the four
roller rows 40 are closed by bottom plates 41 of sectorial
shape. Although these bottom plates may be flat, it is
preferable that they bulge upwardly to assure smooth flow
of the slag granules onto the roller rows 40.
Underlying the four roller rows 40 are chutes 42
leading to one and the same hopper 47 open to a belt
conveyor 48. The slag that has passed the roller rows 40
is thus chuted into the hopper 47 and thence onto the belt
conveyor 48, for delivery to a suitable storage or dis-
charge location. Part of the slag issuing from the hopper
47 is fed back to the aforesaid hopper 29 by the belt
conveyor 30, for use as a lining material for the pan 6.
--10--
5546
A wind box 45 is mounted centrally on the bottom
of the enclosure 38 to introduce air under pressure into
and throuyh the mass of granulated slag therein. In the
form of stacked cones, the wind box 45 has several
annular air outlets 46 which are angled downwardly to
prevent intrusion of the slag. The wind box communicates
with an annular header or manifold 44. Also in communi-
cation with this header are four short inlet conduits 43
projecting into and opening to the respective chutes 42,
so that air is also forced into the enclosure 38 through
the rollers 40 at its bottom.
The top end of the enclosure 38 is open to a conduit
54 in communication with any utility device, such as a
boiler 50, that can derive full benefits from the heated
air produced by the convection cooler 35. The conduit 54
has a built-in dust separator 49 which is shown to
comprise twisted rotary vanes 51 for centrifugally separ~t-
ing solid particles from the heated air stream. The air
outlet at the bottom end of the boiler 50 communicates
with the header 44 by way of a conduit system 53 having a
built-in circulator fan 52. A closed system of air circu-
lation is thus formed between the convection cooler 35
and boiler 50.
Thus, at the second heat recovery station 4, the air
pressurized by the circulator fan 52 is introduced into
the enclosure 38 of the convection cooler 35 through the
wind box 45 and through the gaps between the rollers 40.
~1~55~6
Streaming upwardly through the piled mass of granulated
slag within the enclosure 38, the air is heated to a
temperature of, say , 850C. The slag, on the other
hand, is cooled to a temperature range of, say 200 to
250C by heat exchange with the air. As the rollers 40
rotate in opposite directions as aforesaid, the cooled
slag passes the gaps therebetween at a controlled rate,
with its grain sizes reduced to values within a specific
maximum, and is chuted down to the hopper 47.
Heated by convection within the enclosure 38, the
air stream into the conduit 54, is removed of solid
particles by the dust separator 49, and then is guided
into the boiler 50. This boiler operates in the well
known manner to convert water into steam by the heat
carried by the incoming air. The air emerging from the
boiler may have a temperature ranging from 80 to 100C.
Again pressurized by the circulator fan 52, the cooled
air flows into the header 44 for recirculation through
the convection cooler 35 and boiler 50.
FIGS. 5 through 8 illustrate another preferred
embodiment of this invention, which differs from the
preceding embodiment only in the configuration of its
first heat recovery station 2a. As will be seen from
FIG. 5 in particular, this second embodiment has a pair
of immovable slag receptacles or containers 57a and 57b
of rectangular shape disposed side by side, with a
spacing therebetween, at the first heat recovery station
~1~5546
2a. A two-way tiltable trough 56, lying between the
eontainers 57a and 57b, is charged with molten slag
from the ladle car 1 and alternately pours the slag into
the two containers. Within each container, as in the
foregoing embodiment, heat is recovered by radiation,
and preferably by eonduetion as well, from the molten
slag while it is being agitated and granulated. The
granulated slag is fed by ehutes 59 into the bucket 28
of the skip hoist 3. This skip hoist and the means at
the seeond heat reeovery station ean be identical in
construction with those set forth in eonjunetion with
FIGS. 1 through 4.
Referenee is now direeted more specifically to FIGS.
6 and 7 in order to describe in detail the construetion
and operation of the means at the first heat recovery
station 2_. The tiltable trough 56 is supported by a
pair of trunnions 61 for pivotal motion about a horizontal
axis. A drive mechanism 60 is eoupled to one of the
trunnions 61 for imparting pivotal motion to the trough 56.
Normally held in a level attitude depieted by the solid
lines in FIG. 7, the trough 56 ean be tilted to either of
the opposite positions shown by phantom line for pouring
molten slag into the eorresponding one of the containers
57a and 57_.
The pair of eontainers 57a and 57b are disposed
symmetrically with respect to the vertical plane eontaining
the axis of the tiltable trough 56. Since these eontainers
-13-
554~
are of identical make, only the first container 57a,
shown in FIG. 6 and seen to the left in FIG. 7, will be
described in detail, it being understood that the same
description applies to the second container 57_.
Various parts of the second container will be identified
in the drawing by the same reference numerals as used
to denote the corresponding parts of the first container
but with only the subscript _ substituted for a.
The representative container 57_ has a pair of
outlets 62_ formed centrally at its bottom. Openably
closing these outlets, a pair of gates or doors 63_ are
both mounted on one end of a rod 64a which is coupled at
a point intermediate its opposite ends to the bottom of
the container 57_ by a pivot pin 65_, for pivotal motion
about a horizontal axis. The other end of the rod 64_ is
pin jointed to a fluid actuated cylinder 66_. ~pon con-
traction of this cylinder, therefore, the pair of gates
63a move downwardly to open the outlets 62a. The cylinder
is shown extended in FIG. 7 to close the outlets with the
gates.
Each outlet 62a of the container 57a is bounded by
upstanding walls 67a, the top ends of which are bent inward-
ly to provide rims 78_. Each gate 63a also has upstanding
walls 69a, located inside the walls 67a with working
clearance, for movement into and out of abutment against
the rims 78_. The bottom of the container 57a, as well as
the gate 63_, is covered with a preformed lining of
-14-
ll~SS46
granulated slag piled with an angle of repose ~.
Mounted within the container 57_ is an agitator
mechanism 72a comprising a rotatable shaft 70_ ex-
tending horizontally, and two rows of agitator rods 71a
projecting in diametrically opposite directions from
axially spaced positions on the rotatable shaft. A
drive mechanism 73 is coupled to the rotatable shaft 70a
for driving the same in a prescribed direction, so that
the two rows of agitator rods 71a are alternately drip-
ped into and out of the molten slag within the container
for agitating and granulating same. As in the preceding
embodiment the rotatable shaft 70a and agitator rods 71_
are both of double tube construction, with their interiors
partitioned by inner tubes 74_ into intercommunicated
inner and outer passageways for the circulation of water
or like fluid. The circulating water serves not only to
cool the agitator mechanism but also as a fluid medium
for the recovery of heat from the molten slag by both
radiation and conduction.
The cover portion 75a of the container 57_ has its
inside surface covered with piping 76a for the passage of
water to be heated by radiation from the slag within the
container. A vertical slot 84_ in the cover por-tion 75a
permits one end of the tiltable trough 56 to intrude into
the container for pouring molten slag therein.
As shown in FIG. 7 and in more detail in FIG. 8, the
agitator mechanism 72_ is provided with means 77_ for
55~6
removing slag from the agitator rods 71a. The slag
removing means include a set of fixed, coplanar tines
80_ projecting from one of the opposite side walls of
the container 57_ so as to be in interdigitating
relation with the agitator rods 71_. Preferably, the
tines 80a are also of double tube construction,
communicating with a header 81a, for the circulation of
cooling water therethrough. The cooling water serves,
of course, for the recovery of heat by radiation from
the slag within the container.
One of the most pronounced features of the second
embodiment set forth above resides in the fact that the
pair of containers 57a and 57_ are immovably disposed at
the first heat recovery station 2a. Compared with the
embodiment shown in FIGS. 1 through 4, therefore, this
second embodiment requires a considerably lower installation
cost as it dispenses with the means for the transportation
of the containers from the charging to the discharge
location. Moreover, since the lining slag 68 semiperma-
nently remains within the containers with the repose angle
~, it is unnecessary to feed back part of the slag from
the second to the first heat recovery station. This
feature makes it possible not only to correspondingly
reduce the processing capacity of the convection cooler
at the second heat recovery station, but also to eliminate
the conveyor for the feedback of the slag from the second
to the first heat recovery station.
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55~
Still another preferred embodiment of -the invention
shown in FIGS. 9 through 11 dispenses with the conventional
ladle car used in the two foregoing embodiments and
employs, instead, a pan 85 mounted on a wheeled carriage
87. This carriage travels along the pair of rails 5
between tlle location of a smelting or refining furnace
and the discharge station D via the first heat recovery
station 2_. Molten slag is directly poured into the pan
85 from the furnace.
As best shown in FIG. 10, the pan 85 is mounted on
the carriage 87 via a pair of trunnions 97 for pivotal
motion about a horizontal axis parallel to the track of
the carriage. A drive mechanism 96 is coupled to one of
the trunnions 97 for pivoting the pan 85. FIGS. 10 and 11
reveal that the pan 85 is semielliptic in shape as viewed
in a vertical plane parallel to the carriage trac~, and
semicircular as viewed in a vertical plane at right angles
therewith.
Disposed at the first heat recovery station 2_, just
over the rails 5, is an agitator mechanism 89 comprising
a rotatable shaft 90 extending parallel to the rails, and
two sets of agitator rods 91 projecting in opposite
directions from axially spaced positions on the rotatable
shaft. The rotatable shaft 90 and agitator rods 91 are
both of double tube design, providing passageways for the
circulation of water, as in the preceding embodiments of
the invention. A drive mechanism 92 is coupled to the
ll~SS4~i
rotatable shaft 90 for rotating t~le same in a prescrib-
ed direction. A cover 93 encloslng the upper portion
of the agitator mechanism 8g has its inside surface
covered with piping 94 for the passage of water.
After molten slag has been charged into the pan 85
directly from the furnace, the carriage 87 travels along
the rails 5 to the first heat recovery station 2b and
stops under the agitator mechanism 89, with the pan in
vertical register with the cover 93. As in the forego-
ing embodiments of the invention the water flowing through
the piping 94 is heated by radiation from the molten slag
in the pan 85 while the slag is being agitated into
granular form.
Two rows of tines 95 project from the opposite side
walls of the cover 93, in interdigitating relation with
the agitator rods 91, for removal of the slag that may
adhere thereto during the agitation of the slag in the pan
85. Unlike the tines 80_ and 80b shown in FIGS. 7 and 8,
the tines 95 are angled downwardly to remove the slag from
the agitator rods more positively and further to allow the
removed slag to drop more readily back into the pan 85.
During the operation of the agitator mechanism 89 the slag
tends to heap up on the downstream side of the pan 85 with
respect to the direction of rotation of the agitator rods
91. Angled downwardly, the tines 95 perform the additional
function of ohstructing any undue accumulation of the slag
on one side of the pan.
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1~5546
Upon completion of heat recovery and slag granu-
lation at the first heat recovery station 2_, the
carriage 87 transports the pan 85 to the discharge
station D, as illustra~ed in FIG. 9. At this discharge
station the drive mechanism 96 on the carriage 87
operates to turn the pan 85 about the trunnions 97 there-
by causing the pan to discharge the granulated slag into
the bucket 28 of the skip hoist 3 via a chute 98. The
skip hoist and the means at the second heat recovery
station 4 can be analogous in construction with those
set forth in connection with FIGS. 1 through 4.
As the convection cooler 35 at the second heat re-
co.very station 4 discharges the cooled slag after heat
recovery therefrom, a belt conveyor 99 returns part of
the slag to a hopper 100 lying between the first heat
recovery station 2b and the discharge station D. The
carriage 87 with the empty pan 85 thereon is held at a
temporary standstill under the hopper 100 during its
return travel from the discharge station D to the furnace.
The hopper 100 introduces the slag into the pan 85 to
form a lining shown at 101 in FIGS. 10 and 11.
Thus, in this third embodiment of the invention,
molten slag is charged directly into the pan 85 on the
wheeled carriage 87 from the furnace, instead of through
the conventional ladle car used in the two preceding
embodiments. Such direct introduction of molten slag
into the pan is preferred for reasons of smaller heat
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i5~,
loss and greater heat recovery. :Further, the agitation
of the slag in the pan itself precludes the Eormation
of skull, which is unavoidable with the use of the ladle
car as in the first two embodiments. Substantial
economy in installation costs will accrue from the use
of existing ladle car rails for the pan carriage 87.
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