CA1145546A - Apparatus for heat recovery from molten slag - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

Molten slag fresh from a smelting or refining furnace is ladled into a pan on a wheeled carriage and is thereby transported to a first heat recovery station, where water is heated by radiation from the slag while the latter is being agitated and granulated.
On granulation the slag is conveyed as by a skip hoist to a second heat recovery station, where the residual heat of the slag is utilized to heat air by convection.
The heated air is directed into a utility device such as a boiler, from which the cooled air is fed back to the second heat recovery station for reheating. Several embodiments are disclosed.

Description

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 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.

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 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 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.

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.

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 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.

Claims (17)

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

1. Apparatus for the recovery of heat from molten slag com-prising:
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 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.

2. The apparatus according to claim 1 further comprising piping disposed above the agitating means and means for passing fluid to be heated through said piping.

3. The apparatus according to claim 1, further comprising means for removing slag from the agitator rods.

4. The apparatus according to claim 3, wherein the removing means comprises a plurality of fixed tines arranged in inter-digitating relation with the agitator rods.

5. The apparatus according to claim 4, wherein the tines are angled downwardly.

6. The apparatus according to claim 1, 2 or 3, wherein the first heat recovery means comprises piping disposed over the agitating means for the passage of the fluid to be heated.

7. The apparatus according to claim 1, in which said slag receptacle means is constituted by an open top slag receptacle, and said apparatus further comprising:
(a) a track extending between a charging station and a discharge station via the first heat recovery station;
(b) a carriage reciprocally movable along said track, said open-top slag receptacle being on the carriage for being charged with molten slag at the charging station and carrying the slag to the first heat recovery station and thence, after the slag is granulated, to the discharge station; and (c) discharge means for causing the receptacle to dis-charge the granulated slag at the discharge station.

8. The apparatus according to claim 7, wherein the receptacle is mounted on the carriage for pivotal motion about an axis at right angles with the track, and wherein the discharge means com-prises:

(a) a pinion rotatable simultaneously with the receptacle relative to the carriage; and (b) a rack disposed at the discharge station and extending parallel to the track for engagement with the pinion;
whereby the receptacle is automatically pivoted to dis-charge the granulated slag as the carriage moves to the discharge station.

9. The apparatus according to claim 7, wherein the receptacle is mounted on the carriage for pivotal motion about an axis parallel to the track, and wherein the discharge means is mounted on the carriage for pivotally moving the receptacle relative to the carriage.

10. The apparatus according to claim 7, further comprising means for feeding part of the granulated slag from the second heat recovery station back into the receptacle at said discharge station to line its inside surface.

11. The apparatus according to claim 1, wherein the second heat recovery means comprises:
(a) an enclosure for accommodating the granulated slag;
and (b) means for introducing the gas under pressure into and through the granulated slag within the enclosure.

12. The apparatus according to claim 11, wherein the second heat recovery means further comprises:
(a) means for directing the heated gas from within the enclosure into a heat exchange device; and (b) means for directing the cooled gas from the heat exchange device back into the enclosure through the introducing means.

13. The apparatus according to claim 11, wherein the bottom of the enclosure is constituted at least in part by a plurality of spaced-apart rollers for permitting the controlled passage of the granulated slag therethrough.

14. The apparatus according to claim 1, 11 or 12, in which said slag receptacle means is a receptacle stationarily mounted at the first heat recovery station for being charged with molten slag, the receptacle having the combination agitating means and heat recovery means mounted therein, and having an outlet at the bottom of the receptacle for the discharge of granulated slag to be transported to the second heat recovery station by the conveying means, and means for opening and closing the outlet of the recep-tacle.

15. The apparatus according to claim 1, 11 or 12, in which said receptacle means is a pair of slag receptacles stationarily mounted side by side at the first heat recovery station, each receptacle having combined agitating means and heat recovery means mounted therein, and having an outlet at the bottom of each recep-tacle for the discharge of granulated slag to be transported to the second heat recovery station by the conveying means, and means for opening and closing the outlet of each receptacle; and said apparatus further comprising means for charging molten slag into either of the receptacles.

16. Apparatus for the recovery of heat from molten slag, com-prising:

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 heat recovery means;
receptacle emptying means for emptying agitated cooled slag from said receptacle means;
conveying means for conveying the granulated slag from the first heat recovery station to a second heat recovery station;
heat recovery means at the second heat recovery station for heating a gas by convection from the granulated slag; and granulated slag feed means for feeding part of the granulated slag from said second heat recovery station back into said receptacle means in said first heat recovery station after the agitated and cooled slag has been removed therefrom for lining the inside of the receptacle means with the granulated slag.

17. The apparatus according to claim 16, wherein the charg-ing means comprises:
(a) a two-way tiltable trough mounted between the pair of slag receptacles for pivotal motion about a horizontal axis in either of opposite directions, the trough being capable of charging molten slag into either of the receptacles depending upon the direction in which it is tilted; and (b) means for tilting the trough in either of the opposite directions.