DESCRIPTION
METHOD AND APPARATUS FOR TREATING HIGH TEMPERATURE SLAG
TECHNICAL FIELD
The present invention relates to a method of treatment and apparatus for treatment of high temperature slag discharged from a hot metal pretreatment furnace, converter, electric furnace, etc. in a hot metal pretreatment process or steelmaking process etc. at a 1200°C or more high temperature. Specifically, it relates to a treatment method and treatment apparatus efficiently cooling hot metal pretreatment slag, converter slag, electric furnace slag, or other slag containing CaO discharged from a hot metal pretreatment furnace, converter, electric furnace, etc. at a high temperature, efficiently separating and recovering the metal contained in the slag, and enabling the slag to be effectively utilized for road base materials, manmade underwater structures, etc.
BACKGROUND ART
The hot metal pretreatment process or steelmaking process (hot metal pretreatment furnace, converter, electric furnace, etc.) produces and discharges 12O0°C to 1600°C high temperature slag containing CaO in large amounts. The high temperature slag contains large amounts of iron metal. The slag is cooled and the metal recovered from the slag, then the slag is utilized as road base material or manmade underwater structures and the metal is utilized as steelmaking material etc. For this reason, in the past, slag has been treated as shown in FIG. 6 and FIG. 7.
First, the molten slag containing CaO is stored in a slag pan 1 carried on a car and conveyed to an outdoor slag treatment site. At the slag treatment site, a
lurality of cooling pits or yards 2 provided with sprinkler apparatuses 4 are aligned. As shown in FIG. 6(A), high temperature slag 3 is discharged to one cooling pit (yard) 2 among these. This discharge requires from 20 minutes to 1 hour. After this, the slag is slowly cooled (air cooled) for about 2 to 4 hours for preventing steam explosions.
After the danger of steam explosions is past, the slow cooled slag 6 is sprinkled with a large amount of cooling water 5 from the sprinkler apparatus 4 as shown in FIG. 6(B) to promote cooling for the primary cooling. This sprinkling is performed for at least 3 hours, in the case of slag for which water is hard to penetrate, for 2 to 3 days. For this reason, a large number of cooling pits 2 are provided and successively used.
The thus cooled slag 7, as shown in FIG. 6(C), is dug up by a construction machine 8 and, as shown in FIG. 6(D), is transported by a dump truck 9 to a crushing plant.
At the crushing plant, the cooled slag 7, as shown in FIG. 7, is first charged into a hopper 11 and conveyed by a primary conveyor 33 through a primary magnetic separator 34 to separate out large lumps of metal 35. Next, the slag is crushed by a primary crusher 36 and dropped onto a secondary conveyor 39. The secondary conveyor 39 is provided with a secondary magnetic separator 38 which separates out medium lumps of metal 37. Here, the slag is placed on a primary vibrating screen 40, then is conveyed by a tertiary conveyor 41 to a secondary crusher 42 for crushing. The crushed slag is conveyed by a quaternary conveyor 44 during which a tertiary magnetic separator 43 separates the small lumps of metal 45. A secondary vibrating screen 46 classifies the slag into medium lump grade slag 4 7 and small lump grade slag 48.
In this way, the high temperature slag is cooled, the metal is separated and recovered from the slag, then
the slag is effectively utilized as a road base material, manmade underwater structure, or other construction material.
However, cooling at a pit or yard by a large amount of sprinkling is poor in cooling efficiency, so the cooling requires a long time. Further, to prevent dust generated from the surface of the solidified slag from rising, there was the problem that the dust collection cost swells. Further, when the sprinkling becomes uneven, a CaO ingredient remains in the slag. This is liable to pose a problem when using the slag as a road base material.
Further, the unreacted CaO ingredient dispersed in the fine powder part of the slag disperses in water as Ca(OH)2- Further, this Ca(0H)2 deposits on the slag as a whole coming into contact with the water resulting as the entire slag ending up becoming strongly alkaline. When using the slag for a road base material or manmade underwater structure applications, the strong alkaline water caused when the slag contacts the water causes white turbidity, so neutralization is required.
Further, as explained above, slag is separated into metal and slag by being passed through a crusher and magnetic separator several times, but solidified slag has considerable hardness, so unless a powerful crusher is used, sufficient crushing is not possible. Further, the thus obtained metal is not sufficiently separated from slag, so is low in iron content. There is the problem that even if passing the slag through a two-stage crusher, only a 70 to 80% iron content is obtained and even if passing the slag through a three-stage crusher, only an 80 to 90% iron content is obtained.
In this regard, Japanese Patent Publication (B2) No. 5-42380 discloses a method of stable treatment of steelmaking slag comprising pouring molten state steelmaking slag into a shallow bottom broad dish, sprinkling it with water for primary cooling, then
sprinkling it with water in a slag removal car for secondary cooling and further immersing it in a water storage pit. However, this method has the above problem of generation of strongly alkaline water due to immersion of the slag in water.
Further, Japanese Patent Publication (A) No. 2003-247786 discloses a method of treatment of steelmaking slag comprising a first process of gradually cooling steelmaking slag in a container to obtain large lumps of high temperature slag containing cc'-Ca2SiO4 in large amounts and crushing the large lumps to produce small lumps of slag and a second process of placing these small lumps of slag into a rotary cooler for rapid cooling and utilizing the phase transformation where the α'-Ca2SiO4 in the slag changes to -Ca2Si04 for powderization.
However, this method is a method effective only for stainless steel slag involving the precipitation of large amounts of -Ca2Si04 and cannot be applied for slag generated from the general steelmaking process.
Further, as described in the examples of Japanese Patent Publication (A) No. 2003-247786, a cooling time extending over 24 hours is required for slow cooling, so there is the problem that the productivity is low.
Further, with this process, it is possible to use a screen to recover the large size metal ingredient, but the rotary cooler is not a pressure vessel and has no atomizing function or mechanical crushing process, so it is hard for a powderization phenomenon to occur by phase transformation. Therefore, the obtained metal becomes further lower in grade than the method of the later-mentioned Japanese Patent Publication (A) No. 6-346161 and cannot be used in a steelmaking furnace. Further, by limiting the basicity, the range of the applicable slag is also limited. This cannot be said to be a general method.
Further, Japanese Patent Publication (A) No. 6-
346161 discloses a method of recovering metal in steelmaking slag comprising atomizing steelmaking slag in water, then classifying it by a screen etc. by grain size, dropping the classified slag into a blower stream to separate it into high weight slag and low weight slag, and sending the high weight slag into the furnace to extract the metal. However, the atomization is a method requiring tremendous facilities and costs and unavoidably suffers from the trouble of steam explosions. Further, the obtained lumps of slag greatly vary in size. Further, mechanical crushing requires air separation. Further, the obtained metal is also a low grade one with an iron content of 50 to 90% and greatly varies and is hard to use in a steelmaking furnace.
Furthermore, Japanese Patent Publication (A) No. 6-281363 discloses a method comprising solidifying steelmaking slag on a slag pan, mechanically crushing this, placing the obtained high temperature roughly crushed slag in a hermetic pressure vessel, sprinkling cooling water from above, using the generated steam to set the inside of the pressure vessel at a predetermined pressure condition, and utilizing slag expansion due to rapid cooling and hydration for crushing. The obtained fine grain slag is used as it is, while the coarse grain part is mechanically crushed and magnetically graded for use as a steelmaking material. However, the method of using a high temperature pressure vessel requires tremendous facilities and costs and unavoidably suffers from the trouble of steam explosions. Further, the obtained lumps of slag greatly vary in size. Further, mechanical crushing requires air grading. The metal also is low in grade with an iron content of 50 to 90% and greatly varies, so is hard to use in steelmaking furnaces. There are therefore problems similar to the case of the above Japanese Patent Publication (A) No. 6-346161.
In this way, various methods have been proposed for
the method of treatment of high temperature slag, but none have been commercially applied due to the above reasons. Steelmaking slag containing CaO and other high temperature slag are actually being treated in the world by the inefficient, high cost method shown in FIG. 6 and FIG. 7. This conventional method still suffers from numerous problems such as the generation of dust after discharge from the slag pan, generation of a large amount of powder or flames, fast deterioration of facilities, and further the residual CaO in the slag obstructing effective utilization as a road base material etc.
Note that Japanese Patent Publication (A) No. 10-139502 discloses a method of recovery of heat from slag comprising moving slag by a conveying means from an inlet to an outlet of a housing, arranging the front end of an air pipe near the surface of or inside the moving slag, blowing out cooling air from the front end to evenly cool the slag, recovering the air raised in temperature by passing between the grains of the slag, and exhausting this as heating air from the housing. However, this art is for recovery of heat from slag. It does not suggest efficiently cooling the slag or recovering the metal in the slag.
DISCLOSURE OF THE INVENTION
The present invention has as its object the provision of a method of treatment and apparatus for treatment of high temperature slag able to solve the above conventional problems, free of the problem of generation of dust or generation of strongly alkaline water in the treatment process such as with the water cooling apparatus at a conventional slag yard, able to efficiently recover slag as a more preferable recyclable substance without requiring a long time for treatment, and able to efficiently recover the metal contained in the slag and obtain metal with a high iron content without causing any steam explosions or fire. Further, the present invention has as its object to enable these
without requiring excess facilities or cost.
The present invention was made to achieve the above objects and has as its gist the following:
(1) A method of treatment of high temperature slag performing primary cooling of high temperature slag containing CaO, then charging this primary cooled slag into a cooling apparatus and performing secondary cooling while making it move through the inside of the cooling apparatus, said method of treatment of high temperature slag characterized by making both the primary cooling and secondary cooling in a range not generating free water.
(2) A method of treatment of high temperature slag as set forth in (1) characterized by using, as a cooling apparatus for performing the secondary cooling, a rotary cooler provided therein with a cooling air blowing means and a cooling water feeding means for performing both water cooling and air cooling in a range not generating free water.
(3) A method of treatment of high temperature slag as set forth in (1) characterized by using, as a cooling apparatus for performing the secondary cooling, a apparatus provided with a casing having therein a cooling air blowing means, a cooling water feeding means, and a vibrating conveyor providing with vibrating plates for performing both water cooling and air cooling in a range not generating free water.
(4) A method of treatment of high temperature slag as set forth in (2) characterized by providing projections at the inside surface of the casing of the rotary cooler of said cooling apparatus, charging the rotary cooler with slag after primary cooling in a 500°C or more high temperature state, making the casing rotate so as apply a crushing action to said slag due to dropping impact over at least 10 minutes while cooling, and separating the metal contained in the slag.
(5) A method of treatment of high temperature slag as set forth in any one of (1) to (4) characterized by
placing a grizzly at the slag charging port side of said cooling apparatus, separating and recovering the large lumps of metal in the slag after primary cooling, then charging this into the cooling apparatus.
(6) A method of treatment of high temperature slag as set forth in (4) or (5) characterized by separating the metal contained in the slag by setting the residence time of the slag in said rotary cooler to 10 to 20 minutes.
(7) A method of treatment of high temperature slag as set forth in any one of (4) to (6) characterized by placing a vibrating screen and magnetic separator at the slag discharge port side of the rotary cooler and separating and recovering the slag and metal crushed inside the rotary cooler.
(8) A method of treatment of high temperature slag as set forth in any one of (1) to (7) characterized in that the temperature of the slag charged in the cooling apparatus after primary cooling is 700 to 1250°C.
(9) A method of treatment of high temperature slag as set forth in any one of (1) to (8) characterized in that the slag temperature at the slag discharge port of said cooling apparatus is maintained at 100°C or more.
(10) A method of treatment of high temperature slag as set forth in any one of (1) to (9) characterized in that said slag is steelmaking slag or hot metal pretreatment slag.
(11) An apparatus for treatment of high temperature slag comprising cooling high temperature slag containing CaO after primary cooling while moving the slag inside it, said apparatus for treatment of high temperature slag characterized by being a rotary cooler having a cylindrical casing rotating about a slanted axis and having a slag charging port at one end and a slag discharge port at the other end, support rollers rotatably supporting said casing at the outer surface, and a rotational drive device making the cylindrical
casing rotate about an axis, the inside of the casing having a cooling air blowing means for blowing cooling air on the slag and a cooling water feeding means for feeding cooling water to the slag.
(12) An apparatus for treatment of high temperature
slag comprising cooling high temperature slag containing
CaO after primary cooling while moving the slag inside
it, said apparatus for treatment of high temperature slag
characterized by being provided with a cylindrical casing
having a slag charging port at one end and a slag
discharge port at the other end, the inside of the casing
having a vibrating conveyor provided with vibrating
plates conveying slag in an axial direction of the casing
• while imparting vibration, a cooling air blowing means for blowing cooling air on the slag, and a cooling water feeding means for feeding cooling water to the slag.
(13) An apparatus for treatment of high temperature slag as set forth in (11) characterized in that the casing of said rotary cooler is provided with projections at inside surface thereof.
(14) An apparatus for treatment of high temperature slag as set forth in (13) characterized by being provided with a vibrating screen and magnetic separator for separating and recovering slag and metal at a slag discharge side of said treatment apparatus.
(15) An apparatus for treatment of high temperature slag as set forth in any one of (11) to (14) characterized in that said treatment apparatus is provided with a cooling water feeding means for water cooling of the outside surface of said casing.
(16) An apparatus for treatment of high temperature slag as set forth in any one of (11) to (15) characterized said treatment apparatus is provided with a grizzly at slag charging port thereof.
According to the present invention, when cooling the high temperature slag containing CaO discharged from the furnace from the high temperature state, both the primary
cooling and secondary cooling are performed by water cooling in a range not generating free water, so the CaO in the slag will no longer leach out into the cooling water like in the past and no strongly alkaline water will be generated. For this reason, the slag as a whole will no longer end up becoming alkaline. Further, the apparatus is not corroded by strongly alkaline water.
Further, in the cooling process, the high temperature slag contacts the water molecules whereby an aqueous gasification reaction proceeds between the carbon and water in the slag, a shift reaction proceeds whereby the CO produced by this reaction becomes C02, and the generated C02 changes the CaO in the slag to CaC03. As a result, the content of CaO in the cooled slag can be lowered.
Note that in the secondary cooling, cooling by only the cooling gas for preventing the generation of free water may be considered, but by cooling by water cooling like in the present invention, the cooling ability rises and the slag temperature at the outlet side of the cooling apparatus stabilizes. Note that in the steelmaking process, the size of the CaO added as a desulfurization agent or dephosphorization agent during the melting of the iron or melting of the steel is usually around 75 fim, so the size of the unreacted CaO remaining in the slag becomes less than that. For this reason, if classifying the cooled slag into coarse grains and fine grains, the unreacted CaO concentrates at the fine grain side and the content of unreacted CaO in the coarse grains becomes further lower. For this reason, by classification, it is possible to separate slag into slag with a low content of unreacted CaO and slag with a relatively high content of unreacted CaO and possible to easily effectively use the slags.
Further, by maintaining the slag temperature at the slag discharge port of the cooling apparatus at 100°C or more, it is possible to more reliably suppress free water
of the slag and possible to prevent the generation of strongly alkaline water.
Further, if recovering the large lumps of metal in the slag before the rotary cooler or other cooling apparatus, the recovery rate of the metal rises and it is possible to prevent damage to the cooling apparatus by large lumps of metal.
Further, according to the present invention, slag with a low hardness in the high temperature state is cooled while applying dropping impact inside the rotary cooler for 10 minutes or more. Due to this, the slag is easily broken up and is more reliably crushed than by the method of running it through a crusher for a few seconds as in the past. As a result, the efficiency of separation of the metal and slag becomes higher.
Further, inside the rotary cooler, cooling water and cooling air are jointly used for the slag, so breakage occurs due to phase transformation and the difference in the shrinkage rate due to rapid cooling by blowing these and the crushing efficiency can be further improved.
This crushing is safe since it is performed inside the rotary cooler. There is no danger of fire or rising powder. No high pressure container is required either, so the facility costs also become cheaper and the required area also can be reduced. Furthermore, no wide area is required as in the past and the transport costs of the slag also can be slashed.
Further, if making the temperature of the slag
charged inside the rotary cooler 700 to 1250°C, it is possible to cause crushing by utilizing the change in volume due to the phase transformation inherent to the slag containing CaO and iron in the cooling process. For this reason, it is possible to more efficiently promote the crushing by the crushing action due to dropping impact and the crushing action due to phase transformation.
Further, if making the residence time of the slag
inside the rotary cooler 10 to 20 minutes, it becomes possible to recover high grade metal. If increasing the residence time, the crushing effect is improved, but the facility becomes larger in size and damage to the facility also becomes greater. The repair costs and other running costs also rise. Therefore, a time of over 20 minutes is not preferred.
Further, by setting a vibrating screen and magnetic separator at the outlet side of the rotary cooler, it is possible to separate and recover the iron metal from the crushed slag and obtain high iron content metal and obtain slag from which the metal has been separated. Utilization for a road base material etc. becomes possible.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an explanatory view showing an embodiment of the present invention.
FIG. 2 is an explanatory view showing another embodiment of the present invention.
FIG. 3 is a flowchart showing an example of the processes of the present invention.
FIG. 4 is an explanatory view showing still another embodiment of the present invention.
FIG. 5 is a cross-sectional view of a rotary cooler used for the embodiment of the present invention.
FIG. 6(A) to (D) is explanatory view of a conventional slag treatment method.
FIG. 7 is an explanatory view of a conventional slag treatment method (continuation of FIG. 6).
BEST MODE FOR CARRYING OUT THE INVENTION
Below, a preferred embodiment of the present invention will be shown.
<1> First, the example of cooling high temperature slag containing CaO will be explained.
FIG. 1 is an explanatory view showing an example of an embodiment of the present invention. High temperature molten slag 3 containing CaO is poured from a slag pan 1
to a pit (yard) 2 where it is first subjected to primary cooling. The high temperature slag treated by the present invention is steelmaking slag or hot metal pretreatment slag discharged from the furnace or pot. The steelmaking slag contains converter blow refining slag, hot metal pretreatment slag, molten iron dephosphorized slag, molten iron desulfurized slag, etc.
The steelmaking slag or hot metal pretreatment slag contains part of the fine powder of CaO blown into the molten iron (as explained above, around 75 urn) as unreacted free CaO. Note that the temperature of the slag discharged from the furnace or pot differs depending on the type of the slag, but in general is 1400 to 16O0°C with steelmaking slag and is 1200 to 1400°C with hot metal pretreatment slag.
The structure of the pit (yard) 2 for the primary cooling is not particularly limited. Here, a structure laying steel slabs of thicknesses of 0.25 mm over a layer of crushed stone is employed. In addition, a cooling box may be used for the primary cooling. The high temperature slag is raked to an even thickness on the pit (yard) 2 whereby large lumps of metal are removed. Further, cooling water is sprayed from the sprinkling nozzles of the sprinkler apparatus 4 to an extent not generating free water. At this time, the sprayed cooling water must instantaneously evaporate to rob heat of vaporization from the slag and not remain in the state of free water. If generating free water, the problem of leaching of alkali from the slag as a whole arises, so this is not preferred. Due to this primary cooling, the slag temperature is reduced to 700 to 1250°C or so. Note that as explained later, when considering efficient separation of metal from slag, 700 to 1000°C is preferable.
Here, "not generating free water" means not allowing the presence of water deposited on the slag surface or in recesses. This means, at the time of cooling, prevention
of sprayed moisture from not being evaporated and remaining at the slag surface or recesses or flowing down to the bottom of the yard or pit. For this reason, by setting the sprinkling rate in accordance with the amount or temperature of the slag and adjusting the sprinkling rate in accordance with the change of temperature of the slag accompanying cooling, water is sprinkled while confirming smooth evaporation.
Next, a power shovel or other suitable construction machine 8 is used to take out the slag after primary cooling from the pit (yard) 2, then the slag is charged into the cooling apparatus 10 of the high temperature slag treatment apparatus for secondary cooling.
At the front of the cooling apparatus 10, a hopper 11 is placed. On the top surface of this, a lattice for screening called a "grizzly" 12 is provided in a slanted state. The large metal lumps in the slag after the primary cooling are separated by this screening use lattice grizzly 12. Only the small sized slag 7' passing through the grizzly 12 is charged by the feed apparatus (vibrating feeder) 13 to the cooling apparatus 10.
As the cooling apparatus 10 for the secondary cooling, various types may be used, but in the embodiment of FIG. 1, a rotary cooler 10ic* is used.
A cylindrical casing 14 is made to rotate about an axial line inclined slightly from the horizontal plane. Inside this, a cooling air blowing means 18 and a later explained cooling water feeding means 19 are provided. That is, the casing 14 is usually a cylinder made of a steel having a slag charging port 15 at one end and a slag discharge port 16 at the other end. It is supported rotatably by support rollers 17 and can rotate about the axial line by a rotary drive apparatus (not shown).
The cooling air blowing means 18 is set so as to run along the axial line of the center of the casing 14. This is a cooler of a structure ejecting cooling air from this cooling air blowing means 18 to cool the slag charged
into it. Note that in the example of FIG. 1, as a preferable mode, a cooling water feeding means (external sprinkling pipe) 20 is arranged at the outer circumference of the casing 14. Cooling water is injected from this cooling water feeding means 20 for external cooling of the casing.
Note that this cooling water feeding means 20 can be made the same configuration as the later mentioned cooling water feeding means 19.
At the front of the slag charging port 15 of this cooling apparatus 10 (10a), as explained above, a hopper 11 provided with a grizzly 12 is provided whereby a high temperature slag treatment apparatus is formed.
The slag cooled by the primary cooling to 700 to 1250°C is charged from the hopper 11 at the top end of the casing 14. Along with rotation of the casing 14, the slag gradually moves in the direction of the slag discharge port 16.
Further, FIG. 2 shows another embodiment of the invention. As the cooling apparatus 10 for secondary cooling, in addition to such a rotary type cooling apparatus, as shown in FIG. 2, it is possible to use a conveyor type cooling apparatus 10b provided with a cylindrical casing 14 provided with a slag charging port 15 at one end and a slag discharge port 16 at the other end, a vibrating conveyor provided inside it with vibrating plates 24 and extending in the axial direction of the casing, a cooling air blowing means 18, and a later explained cooling water feeding means 19.
In the example of this cooling apparatus 10b shown in FIG. 2, the cooling air blowing means 18 feeds cooling air from a cooling air feed pipe 18a, extending along the axial direction of the casing at the outside of the casing 14, through branch pipes 18b into the casing 14. Due to the cooling air blown upward from below the vibrating plates 24 of the conveyor 23, the slag is conveyed in the direction of the slag discharge port 16
while in a flowing state.
At the front of the slag charging port 15 of this cooling apparatus 10b (10), as explained above, a hopper 11 provided with a grizzly 12 is provided to form a high temperature slag treatment apparatus.
Further, above the outside of the casing 14 of the cooling apparatus 10b, in the same way as the case of the cooling apparatus 10a, a cooling water feeding means 20 (not shown) is preferably provided.
Note that the cooling air blowing means 18 in the cooling apparatus 10 (10a, 10b) is provided with a cooling use air pipe 18a. The side facing the slag may be configured provided with cooling air ejection holes (not shown), or, for example, as shown in FIG. 5, ejection use branch pipes 18b, at suitable intervals along the longitudinal direction of the cooling air feed pipe.
Further, the cooling water feeding means 19 of the cooling apparatus 10 (10a, 10b) is provided with a cooling water feed pipe 19a along the axial direction of the casing. The side facing the slag may be configured provided with cooling water sprinkling holes 19c (for example, see FIG. 2), or, for example, as shown in FIG. 5, sprinkling use branch pipes 19b at suitable intervals along the axial direction of the casing.
In either case, the cooling apparatus 10 (10a, 10b) is used for effectively utilizing the held heat of the slag to promote the aqueous gasification reaction or shift reaction. Further, by using the cooling apparatus 10, it is possible to prevent the danger of the CO produced by the aqueous gasification reaction from being released into the surrounding atmosphere.
In this way, in the present invention, the cooling apparatus 10 is used for secondary cooling of the slag, but is characterized by using water cooling to an extent not generating free water not only for the primary cooling, but also the secondary cooling. For this reason, inside the cooling apparatus 10, a cooling water feeding
means 19 is arranged as explained above and sprinkles water on the slag moving through the inside of the cooling apparatus 10. However, this amount of sprinkling is made an amount whereby the water will instantaneously vaporize when the high temperature slag and sprinkling water come into contact and whereby no free water is allowed to be generated.
At this time, a large amount of heat of vaporization is robbed from the slag and the slag is cooled down to 300°C or less, preferably 250°C or less. Note that the sprinkling rate from the cooling water feeding means is adjusted while considering the changes in the amount of slag, temperature, etc. needless to say. Note that to reliably prevent the generation of free water, the slag temperature at the outlet of the cooling apparatus 10 is preferably maintained at 100°C or more.
In this way, in the present invention, in the primary cooling and secondary cooling processes, the slag and free water do not come into contact, so no alkali water is generated like in the past. Therefore, the slag as a whole will never end up becoming alkaline. Further, corrosion of the apparatus by strongly alkaline water can be prevented. Further, due to the aqueous gasification reaction and shift reaction being promoted, it is possible to reduce the free-CaO in the slag.
The slag cooled by secondary cooling to 300°C or less is discharged from the slag discharge port 16 of the cooling apparatus to the conveyor 22.
As described above, the CaO remaining in the slag in this way is almost always about 75 urn or less. It is dispersed as fine grains in the cooled slag without generation of free water, so if classifying the discharged slag by a screen (not shown) etc., the unreacted CaO will concentrate at the fine grain side and will not be contained much at all at the coarse grain side. For this reason, it is possible to obtain coarse
grains with a low CaO content and fine grains with a high CaO content.
Note that inside the cooling apparatus 10, dust is generated due to the pulverization accompanying cooling of the slag or pulverization accompanying mechanical agitation, so the inside air is passed through a cyclone dust collector 21 to collect the dust, then is exhausted to the outside by an exhaust fan 29.
The slag treated by the method of the present invention is low in content of CaO, so can be used for example for manmade underwater structures such as fishing reefs as is or with just slight treatment by carbon dioxide.
Further, in the past, aging was reguired at the time of using slag as the road base material, but the coarse grain slag obtained according to the present invention is low in free CaO content, so it becomes possible to eliminate aging or shorten the aging period.
<2> Next, the example of the case of cooling high temperature slag containing CaO and recovering metal will be explained.
FIG. 3 is a view showing the work flow of the present invention, FIG. 4 is an explanatory view of an embodiment of the present invention, and FIG. 5 is a schematic view showing a cross-section of a rotary cooler.
The 1200 to 1600°C high temperature slag containing CaO discharged from the steelmaking processes of the hot metal pretreatment furnace, converter, electric furnace, etc. is discharged from the slag pan 1 to the cooling pit or yard 2. Here, the high temperature slag is allowed to stand for primary cooling for a short time of 10 to 30 minutes until changing from a molten state to a high temperature solid. Any large lumps of metal are removed. Sprinkling is not essential at the time of primary cooling at the pit or yard 2, but for efficient cooling and metal recovery, primary cooling including cooling by
sprinkling cooling water is performed.
Note that in the present invention, as explained above, at the time of the sprinkling cooling at the primary cooling and the later mentioned secondary cooling, cooling is necessary so that no free water is generated. That is, in the primary cooling, sprinkling cooling (water cooling) is not necessarily required, but to increase the treatment efficiency and reduce the amount of generation of dust, water cooling is preferable in the primary cooling as well. At that time, water cooling so as not to generate free water is necessary.
The solidified slag is dug up by a construction machine 8 and charged through the hopper 11 to the rotary cooler 10a of the cooling apparatus. Preferably, at the inlet of the hopper 11, a lattice-like screen called a "grizzly" 12 is arranged to recover large lumps of metal in the slag before the rotary cooler 10a. The slag passing through the grizzly 12 is charged by a vibrating conveyor or vibrating feeder or other feed apparatus 13 in a 500°C or more, preferably 700 to 1250°C, more preferably 700 to 1000°C high temperature state into the rotary cooler 10a.
The rotary cooler 10a is usually structured supporting a steel cylindrical casing (shell) 14 inclined slightly in axial direction from the horizontal plane by support rollers 17 and rotating the casing at a speed of 1 to 10 rpm or so. That is, the steel cylindrical casing 14 has a slag charging port 15 at one end and a slag discharge port 16 at the other end, is supported in a rotatable manner by support rollers 17, and can rotate about the axial line by a rotary drive apparatus (not shown).
As shown in FIG. 4, the inside surface of the casing (shell) 14 is provided with a large number of projections 25. Slag charged from the part of the slag charging port (inlet cover) 15 to the inside of the casing (shell) 14 is raised up and dropped repeatedly along with rotation
of the casing (shell) 14. The projections 5 have the function of raising the dropping impact effect. The projections 25 may be any shapes such as plate shapes, angle shapes, cylindrical shapes, rod shapes, track shapes, L-shapes, and H-shapes. Further, they may be made combinations of these shapes.
At the outside of the cylindrical casing (shell) 14, a cooling water feeding means (external sprinkling pipe) 20. is provided for cooling the casing (shell) 14 from the outside. Note that this cooling water feeding means 20 can be configured in the same way as the later explained cooling water feeding means 19.
Further, at the center part of the casing (shell) 14, a cooling air feed pipe 18a extending along the axial direction of the casing is fixed as a cooling air blowing means 18. Cooling air is fed from a blower fan 26.
As shown in FIG. 5, the cooling air feed pipe 19a is provided with a large number of branch pipes 19b which blow cooling air from their front ends toward the slag. The air rate is for example 100 to 1400 m3/min.
By making the casing (shell) 14 rotate in this way, the slag is cooled by cooling air while subjected to a crushing action due to the dropping impact. Unlike slag cooled to ordinary temperature, the 500°C or more slag charged into the casing (shell) 14 is low in hardness, so crushing is promoted. In addition, by rapid cooling, it is possible to simultaneously cause breakage by the phase transformation and difference in shrinkage rates.
This rapid cooling can also be performed by just the cooling air feed pipe 18a of the cooling air feeding means 18 or the branch pipes 18b provided at it, but in an embodiment of the present invention, below the cooling air feed pipe 18a used as the cooling air blowing means 18, a cooling water feed pipe 19a used as the cooling water feeding means 19 is arranged and, as shown in FIG. 5, cooling water is sprinkled from the branch pipes 19b of the cooling water feed pipe 19a to enhance the rapid

cooling effect.
Note that the cooling water instantaneously evaporates by contact with the high temperature slag, so no free water is generated.
In this way, the slag is crushed by the crushing action due to the dropping impact and the breakage effect due to the rapid cooling of the air cooling and water cooling and resultant phase transformation of the slag and difference in shrinkage rates at cooling and is discharged from a chute 16a of the slag discharge port 16 on to a conveyor 22. In the present invention, it is necessary to apply the crushing action due to dropping impact to the slag inside the rotary cooler 10a for at least 10 minutes.
However, to make the residence time of the slag over 20 minutes, the facility becomes large in size and the damage to the facility becomes larger. The repair costs and other running costs also rise. Therefore, 10 to 20 minutes is suitable.
Above the conveyor 22, a magnetic separator 31 is set for separating the metal from the crushed material.
The slag passed through the magnetic separator 31 is separated by the vibrating screen 32 into large grain slag and small grain slag. In the present invention, the slag is sufficiently crushed and separation of the slag and metal is promoted, so the metal recovered by the magnetic separator 31 is high in grade and has a stable iron content of the level of 85% or more.
In this way, in the present invention, the slag is crushed inside the rotary cooler 10a, so no steam explosion or fire is caused. Further, no excessive facilities or cost are required such as with a pressure vessel, and rising dust can be reliably suppressed. Note that the dusty gas generated inside the rotary cooler 10a is sucked in by the exhaust fan 29 and guided through the exhaust duct 28 to the cyclone dust collector 21 for purification.
. The advantages of cooling and metal recovery in the present invention may be summarized as follows:
(i) In the present invention, unlike a short time passage type crusher such as a conventional jaw crusher, the method of applying dropping impact over a long period of time is employed, so it is possible to break up lumps of slag and possible to improve the recovery efficiency of metal and the iron content of the recovered metal.
(ii) According to the present invention, the lumps of slag become resistant to powderization and the amount of powder unsuitable for civil construction becomes smaller.
(iii) No crusher is required, so the power costs become smaller. Further, deterioration of the facilities is small, so the repair costs are also small. The metal recovery cost also becomes less expensive.
(iv) No expensive facilities such as atomizers are required.
(v) There is no deterioration of the surrounding environment such as noise or dust.
(vi) It is possible to discharge the slag from the furnace, then recover high purity metal within 1 hour, so it is possible to quickly resend it to a furnace for reuse.
EXAMPLES
Below, examples will be used to further explain the present invention.
Example 1
About 20 tons of about 1300°C hot metal pretreatment slag containing CaO produced when blowing in CaO powder to dephosphorize and desulfurize the molten iron was transferred to a pit lined with steel slabs as shown in FIG. 1, raked to an even thickness, and sprinkled with water on its surface for primary cooling to 1000°C. The thickness of the slab layer was 0.25 m, while the area was about 6 m x 5 m. The cooling water instantaneously
evaporated, so no free water was generated.
The slag primary cooled in this way was charged into the hopper, the grizzly separated and removed the large lumps of metal, then the remainder was supplied to a rotary cooler of an approximately 2 m diameter and an approximately 8 m length as shown in FIG. 1 for secondary cooling. The slag temperature at the slag charging port of the rotary cooler was 850°C. This slag was blown with 142 m3/hr of cooling air for air-cooling inside the rotary cooler.
Further, the outer circumference of the rotary cooler was supplied with 30 tons/h of cooling water for water cooling, and the slag was sprinkled with 1 tons/hr of cooling water from an internal cooling water feeding means to water cool the slag to an extent not generating free water. The average residence time of the slag in the rotary cooler was 20 minutes.
As a result, slag cooled to about 220°C was discharged from the slag discharge port of the rotary cooler. The temperature drop of the slag passing through the inside of the rotary cooler was 630°C. The slag was pulverized while being conveyed through the inside of the rotary cooler and became pulverized slag. Note that the content of the unreacted CaO contained in the original slag is 6 to 9%, but falls to 2.5 to 4% at the slag discharge port of the rotary cooler. This slag was able to satisfy the characteristic of an expansion ratio of 1.5% or less required for a road base material in JIS-5015 even after post treatment.
On the other hand, when cooling the internal gas of the rotary cooler for gas, the drop in temperature of the slag while passing through the inside of the rotary cooler is only 450°C. While no free water is generated, there was clearly a drop in cooling ability.
Example 2
The present invention was performed using 1000 tons
of steelmaking slag discharged from the steelmaking process. The slag temperature discharged from the furnace was about 1400°C giving a molten state. The slag was allowed to stand for 20 minutes to cause it to solidify in a cooling pit as shown in FIG. 4. Rather than conventional cooling sprinkling, to prevent the generation of free water, sprinkling cooling at 3.0 m3/hr for 5 minutes was performed. Next, this slag was dug up by a power shovel and charged into the rotary cooler. The charging speed was 10 tons/hr, and the slag temperature at the time of charging was about 1000°C.
The casing (shell) of the rotary cooler was rotated at 5 rpm. The residence time of the slag at the inside was 20 minutes. Inside the casing (shell), 400 m3/min of cooling air and 5 m3/hr of cooling water were fed. In this water cooling, no free water was generated. Inside the casing (shell), the projections shown in FIG. 5 were formed. The slag was crushed by the crushing action by dropping impact and the crushing action by the rapid cooling and discharged from the casing (shell) at about 100°C. The extracted matter was run through a magnetic separator to recover the metal.
As a result, 150 tons of metal was recovered. That is, 150 kg of metal was recovered from 1 ton of slag. The iron content in the metal was 85%. Overall, 127.5 tons of iron was recovered.
On the other hand, 1000 tons of steelmaking slag was treated by the conventional method shown in FIG. 6 and FIG.7 . The resultant amount of the magnetically picked up metal per ton of slag, amount of generation of fine powder slag per ton of slag, concentration of pure iron contained in the magnetically picked up metal, and amount of pure iron recovered by ton of slag are shown in Table 1 compared with the invention method. As shown by this data, according to the present invention, it was possible to recover a large amount of high purity iron compared
with the conventional method.
Table 1 (Table Removed)
INDUSTRIAL APPLICABILITY
In this way, the method of treatment of high temperature slag of the present invention performs primary cooling on high temperature slag, then performs secondary cooling while moving the slag through a cooling apparatus, so a conventional large slag yard becomes unnecessary and a giant dust collector becomes unnecessary. Further, the cooling is performed without the slag contacting free water, so no strongly alkaline water is generated in the treatment process and no corrosion of the apparatus occurs. Further, a forced cooling system using water cooling is employed, so the treatment does not require a long time.
Further, according to the treatment method of the present invention, the slag is sufficiently crushed and the slag and metal are separated in an advanced fashion, so the metal recovered by the magnetic separator can be made a high grade one of a stable iron content of a level of 85% or more.
Further, in the present invention, the slag cooling and crushing are mainly performed inside the cooling apparatus, so no steam explosion or fire is caused. Further, it is possible to eliminate the need for the excessive facilities and costs of a pressure vessel and reliably suppress floating of powder.

WE CLAIMS :-
1. A method of treatment of high temperature slag performing primary cooling of high temperature slag containing CaO, then charging this primary cooled slag into a cooling apparatus and performing secondary cooling while making it move through the inside of the cooling apparatus, said method of treatment of high temperature slag characterized by making both the primary cooling and secondary cooling in a range not generating free water.
2. A method of treatment of high temperature slag as set forth in claim 1 characterized by using, as a cooling apparatus for performing the secondary cooling, a rotary cooler provided therein with a cooling air blowing means and a cooling water feeding means for performing both water cooling and air cooling in a range not generating free water.
3. A method of treatment of high temperature slag as set forth in claim 1 characterized by using, as a cooling apparatus for performing the secondary cooling, a apparatus provided with a casing having therein a cooling air blowing means, a cooling water feeding means, and a vibrating conveyor providing with vibrating plates for performing both water cooling and air cooling in a range not generating free water.
4. A method of treatment of high temperature slag as set forth in claim 2 characterized by providing projections at the inside surface of the casing of the rotary cooler of said cooling apparatus, charging the rotary cooler with slag after primary cooling in a 500°C or more high temperature state, making the casing rotate so as apply a crushing action to said slag due to dropping impact over at least 10 minutes while cooling, and separating the metal contained in the slag.
5. A method of treatment of high temperature slag as set forth in any one of claims 1 to 4 characterized by placing a grizzly at the slag charging port side of said cooling apparatus, separating and recovering the large
lumps of metal in the slag after primary cooling, then charging this into the cooling apparatus.
6. A method of treatment of high temperature slag as set forth in claim 4 or 5 characterized by separating the metal contained in the slag by setting the residence time of the slag in said rotary cooler to 10 to 20 minutes.
7. A method of treatment of high temperature slag as set forth in any one of claims 4 to 6 characterized by placing a vibrating screen and magnetic separator at the slag discharge port side of the rotary cooler and separating and recovering the slag and metal crushed inside the rotary cooler.
8. A method of treatment of high temperature slag as set forth in any one of claims 1 to 7 characterized in that the temperature of the slag charged in the cooling apparatus after primary cooling is 700 to 1250°C.
9. A method of treatment of high temperature slag as set forth in any one of claims 1 to 8 characterized in that the slag temperature at the slag discharge port of said cooling apparatus is maintained at 100°C or more.
10. A method of treatment of high temperature slag as set forth in any one of claims 1 to 9 characterized in that said slag is steelmaking slag or hot metal pretreatment slag.
11. An apparatus for treatment of high temperature slag comprising cooling high temperature slag containing CaO after primary cooling while moving the slag inside it, said apparatus for treatment of high temperature slag characterized by being a rotary cooler having a cylindrical casing rotating about a slanted axis and having a slag charging port at one end and a slag discharge port at the other end, support rollers rotatably supporting said casing at the outer surface, and a rotational drive device making the cylindrical casing rotate about an axis, the inside of the casing having a cooling air blowing means for blowing cooling
air on the slag and a cooling water feeding means for feeding cooling water to the slag.
12. An apparatus for treatment of high temperature
slag comprising cooling high temperature slag containing
CaO after primary cooling while moving the slag inside
it, said apparatus for treatment of high temperature slag
characterized by being provided with a cylindrical casing
having a slag charging port at one end and a slag
discharge port at the other end, the inside of the casing
having a vibrating conveyor provided with vibrating
plates conveying slag in an axial direction of the casing
while imparting vibration, a cooling air blowing means
for blowing cooling air on the slag, and a cooling water
feeding means for feeding cooling water to the slag.
13. An apparatus for treatment of high temperature
slag as set forth in claim 11 characterized in that the
casing of said rotary cooler is provided with projections
at inside surface thereof.
14. An apparatus for treatment of high temperature
slag as set forth in claim 13 characterized by being
provided with a vibrating screen and magnetic separator
for separating and recovering slag and metal at a slag
discharge side of said treatment apparatus.
15. An apparatus for treatment of high temperature
slag as set forth in any one of claims 11 to 14
characterized in that said treatment apparatus is
provided with a cooling water feeding means for water
cooling of the outside surface of said casing.
16. An apparatus for treatment of high temperature
slag as set forth in any one of claims 11 to 15
characterized said treatment apparatus is provided with a
grizzly at slag charging port thereof.