CA1139940A

CA1139940A - Apparatus for producing water granulated slag

Info

Publication number: CA1139940A
Application number: CA000355391A
Authority: CA
Inventors: Kazumasa Taguchi; Masaharu Kitajima; Hiroshi Yamashita; Toshihiro Ideguchi; Toshio Ohyabu; Teruaki Okuo; Tsuyoshi Yasui
Original assignee: Rasa Corp
Current assignee: Rasa Corp
Priority date: 1979-07-03
Filing date: 1980-07-03
Publication date: 1983-01-25
Also published as: BR8008731A; AU6058980A; GB2066689B; DE3049683A1; JPS569253A; AU543678B2; GB2066689A; WO1981000103A1

Abstract

ABSTRACT OF THE DISCLOSURE
A water slag granulator adopts a slurry tank and a sedimentation tank each provided with a screw conveyor or dewatering a slag slurry as it is transferred from the bottom of each associated tank where it is precipitated towards the outside of the tank. Thus, dewatering tanks as used in the prior art equipment can be dispensed with. Also, the dewatering operation can be peformed continuously and efficiently in the apparatus using the screw conveyor for the dewatering purpose, instead of a batch type dewatering system of the prior art. Further, the blowing jet water can be controlled responsively to the molten slag feed and, thus, a relatively small water reservoir is sufficient for accomodating the molten slag feed variation, contributing to a reduction in the equipment cost.

Description

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BACXGROUND OF THE INVENTION
The present invention relates to an apparatus for producing water granulated slag and, more particularly, to such a slag granulator with associated equipment of smaller size and simplified construction, in which a slurry of water granulated slag can be dewatered con-tinuously and efficiently by a method capable of dewatering the slurry as it is trans~erled.
Recently, slag which is produced secondarily in blast furnaces, converters or other metal smelting furnaces is water-granulated to be utilized as useful materials for a veriety of applications including a cement material and fine aggregate of concrete. To obtain such water granulated slag, molten slag discharged from a furnace is fed intb a water jet and granulated thereby and recovered as a slurry of water granulated slag (hereinafter, referred to as slurry or slag slurry). Thus, it is necessary to pro~ide a dewatering process for separating the slurry into granulated slag and water.
Heretofore~ such a dewatering operation has been accomplished by using a slag granulator as typically shown in FIG. 1. In the arrangement of FIG. 1, the slag slurry S discharged from a water blowing unit 1 is first dxopped into a concentration tank 2 to be precipitated and concentrated on the botto~ of the tank 2. The con centrated slurry is then fed by a slurry pump Pl through a line Ll to a dewatering tank 3, where it is subjected ~3~

to a predetermined dewatering operation to be re-covered as a water granulated slag product~ The separated water is gathered in a collection tank 4. The water (containing a significant quantity of granulated slag) overflowing the concentration tank 2 is caught by and stored in a water reservoir 5 and, then, is fed by a pump P2 through a line L2 to the collection tank 4, and thence to a sedimentation tank 6. The granulated slag slurry precipitated and concentrated in the tank 6 is fed by a pump P3 through a line L3 to the dewatering tank 3, where it is subjected to a dewatering operation.
The water separated from the precipitate in the tank 6 is fed by a pump P4 to a cooling tower, where it is cooled to a predetermined temperature and stored in a cooled water tank 8. The cooled water is then-fed through a line L4 to the wa-te-r--bl-owing unit to be recycled as pressurized blowing jet water. However, the slag trea~ment processes using the aforementioned water slag granulator of the prior art have several drawbacks.
In the prior art equipment the slag slurry is transferred by the action of electrically driven slurry pumps or the like, and a large amount o~ electrical energy is required.
Also, operational efficiency of the prior art equipment is significantly limited because dewatering is done in a batch type dewatering tank needing 12 - 24 hours per one batch. Since it is often necessary to provide a plurality of large-sized dewatering tanks, electric energy costs are high. Further, in the prior art equipment, the cooled ~35~

water tank functioning as a source of the blowing jet water must necessarily have a large capacity, because it is necessary to provide a large quantity of pressurlzed blowing jet water during the startup period and because the water ratio, namely the ratio of pressurized blowing jet water versus slag, must be preset to a high level to adequately meet the variation of the molten slag quantity fed from the smelting furnace and various troubles occurring during operation after the startup. Alternatively, where the cooled water tank capacity is fairly limited, a rather complicated arrangement would be required to otherwise supply fresh ~ater.~rom the outside of the water recycling system. Under these circumstances, the prior art systems have required large--scale equipment as well as a high electric energy cost. .In addition, since ...... the dewatering operation is based on a batch-mode~
the dewatering effici.ency and the productivity of granulated slag have been much rest-ric~ed.
SUMMARY OF THE INVEN~ION
The present invention has been achieved with a view to overcoming the foregoing drawbacks of the prior art water slag granulator by providing an improved system in which a screw conveyor is used as a m~ans for trans-ferring the granulated slag slurry fed from the water 2S blowing unit and in which said screw conveyor performs a dual function of transferring and dewatering the water granulated slag slurry to dispense with the dewatering tank of the prior art and to permit continuous and efficient dewatering of the granulated slag slurry.

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Accordlngly, an object of the present invention is to provide an apparatus for producing water granulated slag comprising a slurry tank for storing a water granulated slag slurry discharged from a water blowing unit, and a screw conveyor provided in the slurry tank for transferring and dewatering the slag slurry, said screw conveyor being inclined upwardly, as viewed in the direction of slurry flow, from its near end d-ispo-sed on the bottom of the slurry tank and immersed in the slurry towards its far end extended above the liquid suxface of said slurry tank thereby to permit the slag slurry precipitated on the slurry tank bottom to be dewatered by the action of gravity as it is transferred on said screw conveyor from the tank bottom to the outside of the tank.
Another object of the present invention is to provide apparatus for producing water granuIated slag comprising a slurry tank for storing a water granulated slag slurry discharged from a water blowing unit, a sedimentation tank for precipitating and concentrating said slag slurry on the bottom thereof while permitt.ing at its one peripheral end an inflow of the liquid overflowing said slurry tank and an outflow of the supernatant liquid from other peripheral end at an upper part thereof, and a water xeservoir for storing said supernatant liquid flowing out of the sedimentation tank, the slurry tank and the sedimentation tank each being provided with a screw conveyor for trans-ferring and dewatering the slag slurry, each screw conveyor being inclined upwardly, as viewed in the direction ~3~9~

of slurry ~low, from its near end disposed on the bottom of its associated tank and immersed in the slurry towards its far end extended above the liquid surface of each associated tank thereby to permit the granulated slag slurry precipitated on said slurry tank and sedimentation tank bottoms to be dewatered by the action of gravity as the precipitated slurry is transferred on each screw conveyor from its associated tank bottom to the outside thereof.
Still another object of the present invention is to provide the aforementioned apparatus which further comprises a cooling tower and in which said water reservoir is composed of an intercommunicated hot water tank and cold water tank, said supernatant liquid flowing out of the sedimentation tank being stored in the hot water tank and then cooled to a predetermined temperature in a cooling tower to be stored in the cold wate~ tank for recycled use as the blowing jet water.
These and other objects and features of the present invention will become obvious ~rom the detailed description of the invention when read with the accompanying drawings.
BRIEF DESCRIPTION OF T~E DRAWINGS
FIG. 1 is a schematic sectional view of a typical water slag granulator according to the prior art;
FIG. 2(I) is a schematic sectional view of a preerred embodiment of the water slag granulator according to the present invention, and FIG. 2(II) is a section taken on the line A - A of FIG. 2(I); and ~3~

FIG. 3 (I) is a schematic sectional view of another preferred embodiment of the water slag granulator according to the present invention; and FIG. 3(II) is a section taken on the line B - B and C - C.
DETAIL~D DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawings, especially to FIG. 2, showing one preferred arrangement of the present invention, the reference numeral 1 ~enerally represents a water blowing unit, to which is connected a slurry tank 9 provided therein with a screw conveyor 10. The water blowing unit l is composed of a molten slag trough l.l, a cooling blower 1O2, a ~lowing bo~es 1.3 and 1.4 producing cold water jets C, and an exhaust duct 1.5.
The water jets produced under pressure by the blowing boxes 1.3 and 1.4 have a predetermined flow rate-and vPlocity, and act to fine the molten sla~ and then to coagulate the resultant fine parti~les into larger particles which are then formed into a slag slurry in the presence of water. This process is called a water slag granulation.
The resultant slurry S of the water granulated slag is fed through a slurry trough l n6 into the slurry tank 9, where it is precipitated, and the slag slurry separates into a concentrated slurry at the lower part of the tank 9 and clear supernatant water on the upper part. As shown in FIG. 2(II), the slurry tank 9 is provided therein with a screw conveyor 10 which is inclined upwardly from its near end towards its far end as viewed in the direction of slurry flow. As the screw conveyor 10 is rotated by ~L3~9~ `

~ suitable drive means M at a predetermined speed about its longitudinal axis, the concentrated slurry predipitated on the bottom of the tank 9 is transferred at a predetermined rate from the near end of the conveyor 10 to its far end extended above the liquid surface (f) of the tank 9.
Further, as the screw conveyor 10 is rotated, the slag slurry reaching the liquid surface (f) is then subjected to a dewatering action called "hydro-extractlon" by gravity. The separated water may be caught and returned to the slurry tank 9 by a suitable means, e.g. a chute 13.
Upon reaching the far end of the screw conveyor 10, the thus dewatered slurry, namely granulated slag, is dropped through a duct 11 onto a belt conveyor 12 provided immediately below the duct 11, thence it is continuously carried on the belt conveyor 12 to a predetermined yard (not shown).
Thus, the screw conveyor lO functions not only as a carrying means for transferring the ~re-cipitated slurry S from the bottom of the tank 9 to the outside thereof, but also as a dewatering means for hydro-extracting the slurry as it is moved from the surface level of the tank 9 to the far end of the belt conveyor. It has ~een experimentally shown that the moisture content of the granulated slag fed out to the yard is reduced to about 15 - 20% or less.
In the meantime, transfer of a fluidic substance on a screw conveyor generally requires a trough~like guide member to be provided longitudinally along the underside of the screw conveyor. According to the present invention, 3g~

however, since as the screw conveyor i5 rotated the slag granules are deposited below the screw conveyor to such an extent that the gra~ulated slag deposition itself provides a function of a "material guide" for the slurry under being transferred, as indicated at S' in FIG. 2 (II), the screw conveyor according to the present invention can transfer the slurry smoothly without otherwise providing such a guide member.
If a metal screen conveyor of a suitable mesh size is used as the belt conveyor 12 for transferring the granulated slag taken out of the slurry tank to the yard, an added hydro-extracting effect is obtained during the course of transfer to the yard which will improve the dewatering effect.
Although the foregoing FIG. 2 shows only the water blowing unit, sluEry tank and screw-conveyor provi-ded~
therein, it is to be noted that the water slag granulator is provided, as re~uired, with other associated equipment including those for feeding the blowing jet water or for draining the slurry tank. Further, there may be provided, as required, a sedimentation tank for precipitating and separating the granulated slag entrained by water over-flowing the slurry tank, or various equipment required to recycle the separated water as the blowing jet water.
Referring now to FIG. 3 ~I), showing another preferred arrangement of the water slag granulator according to the present invention, the slurry tank 9 for storing the slag slurry discharged from the water blowing unit l is further ~3~

provided with a sedimentation tank 14 and a cooling tower 19 which promotes separation of the granulates slag from the slurry in the sedimentation tank 14 and which cools clean supernatant water from the tank 14 for recycling the same to the blowing jet water.
In this preferred equipment, a part of the slag slurry in the slurry tank 9 overflows into the sedimentation tank 14 from its one peripheral end. ~he slag slurry fed from the water blowing unit into the slurry tank 9 is treated therein in the same manner as in the slurry tank shown in FIG. 2, to be transferred and dewatered as a concentrated slurry by a screw conveyor 10.1 for recovery in the form of dewatered slurry, namely, granulated slag. The slag slurry overflowing the slurry tank 9 into the sedi-mentation tank 14 is further subjected therein to slag-water separation. Preferably, the sedimentation tank 14 may be provided with a slag mud collector 15. As shown in FIG. 3(II), the slag mud collector :L5 has a tray-like shape in its vertical section containing its center axis. As it is rotated about the center axis, the slag mud collector 15 acts on the slurry to collect the same into the slag mud collecting chamher 16 at the bottom of the sedimentation tank 14. Although the slag mud collector is provided singly in the example illustrated in FIG. 3(II), there may be a plurality of slag mud collectors so as to distribute among them any large load imposed by an input of a large quantity OL slurry. However, it is to be noted that use of a large plurality of slag mud collectors ~ 10 -.

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unduly adds to the size of the sedimentation tank.
Normally, two slag mud collectors as shown in FIG. 3(I) are sufficient for achieving satisfiable results.
Alternatively, the sedimentation tank may dispense with the slag mud collector, leaving the slag granules to naturally precipitate under gravity onto the tank bottom.
Further, screw conveyors 10.2 and 10.3 are provided at the bottom of the sedimentation tank 14. Each of these conveyors is inclined upwardly, as viewed in the direction of slurry flow, from its near end disposed in the slag mud collecting chamber 16 where the precipitated sluxry is collected towards its far end extended above the liquid surface of the sedimentation tank.
The granulated slag slurry flowing in the sedimentation tank 14 undergoes precipitation and concentration to be ef~iciently collected in the slag mud collecting chamber 16 by the slag mud collectors I5.1 and lS.a. Like the slurry precipitated on th-e b~ttom of the slurry tank 9, the concentrated slurry thus collected is dewatered as it is transferred on the rotating screw conveyor from the liquid surface to the outside of the tank and, upon reaching the far end of the screw conveyor, the dewatered slurry or granulated slag is passed through the duct 11' onto the belt conveyor 12, which in turn carries the granulated slag to the yard. The clear supernatant liquid separated from the slurry in the sedimentation tank 14 is then fed through a passage 17 to a water reservoir In the conventional equipment, sedimentation tanks have almost a circular shape in plan view with their slurry feed port located at the center and their supernatant liquid discharge ports at the periphery. Thexefore, since they must have a diameter at least twice the natural precipitation distance of slag granules and since a plurality of sedi-mentation tanks must be provided when large loads are to be treated, large eqipme~t coats are incurred. To the contrary, in the preferred equipment of the present inven-tion, for example as shown in FIG. 3(I), since the wateroverflowing the slurry tank is fed into the sedimentation tank from its one peripheral end, the water flow or liquid flow cased thereby permits a use of slag mud collectors of smaller diameter. Further, the sedimentation tank can be of compact design by adopting a rectangular configura-- tion with a due consideration paid to its effecti~e area------and by distributing a large load capacity to two slag mud collectors.
As shown in FIG. 3(I), it is pxeferable that the water reservoir 18 for storing the clear supernatant water from the sedimentation tank is composed of a hot water tank 18.1 and a cold wa~er tank 18.2 which are combined with a cooling tower l9. In this arrangement the cleaE supernatant water naturally flowing from the sedimentation tank 14 is first stored in the hot water tank 18.1 to be fed by a feed pump Pa into the cooling tower, where it is cooled to a predetermined temperature to be stored in the cold water tank 18.2. The cold water .

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is fed, from time to time, through a line L to the water blowing unit 1 by a feed pump Pb to be used as a recycled blowing jet water.
Further, the hot water tank 18.1 of the water reservoir 18 has the same water level as that of -the seaimentation tank 14 and is communlcated with the cold water tank 18.2, so that unbalanced water supply or flow rate may be prevented when starting or stopping the water slag granulator or in case of any emergency and so that a required quantity of the pressurized jet water may always be secured.
In this connection, the molten slag quantity fed into the water blowing unit 1 generally varies with the slag production in the associated blast ~urnace or other smelting furnace, and its maximum variation reaches a level higher than or equal to twofold or three fold its average level. To maintain an adequate water ratio under such changeable circumstances, a sufficient quantity of cooling water must be secured for feeding the pressurized jet water responsive to the variation. For accomplishing this, the prior art has preset a considerably high water ratio by always feeding a large ~uantity of pressurized jet water for accommodating an expected maximum variation of the molten slag ~eed, without controlling the water feed responsively to the variation at all. Thus, according 2S to the prior art, a large sized cold water tank must necessarily be provided together with its associated equipment of correspondingly larger size. According to the present invention, the water feed is controlled ~3~

responsively to the mol.ten slag feed variation and the hot water tank 18~1 is communicated with the cold water tank 18.2 for maintaining the latter to a required water level, so that an a~uate quantity of the pressurized jet water can always be fed responsively to the molten slag feed variation. Further, even if the water level of ~he cold water tank drops during the startup time, water naturally flowing therein from the hot water tank can compensate the level decrease, and feed pump water supply problems are avoided.
As a means for determining the variation of the molten slag feed, an amrneter may be connected to the power circuit of the slag mud collector 15 provided in the sedimentation tank 14, so that it can detect the various loads on the slag mud collector 15. Alternatively, a variation of the indication of an armme-te-r--connected to the slurry pump circuit, a water temperature variation in the slurry tank or water level variation in the sedimentation tank may be utilized to detect the rnolten slag feed variation.
20 In the preferred equipment illustrated in FIG~ 3, the slurry tank 9, sedimentation tank 14 and water reservoir 18 may be provided in one integral outer wall structure with common partition walls. If the water reservoir is to be provided adjacent to the sedimentation tank, the latter may be cornmunicated with the hot water tank of the water reservoir directly through the partition wall.
In such an arrangement, if any trouble occurs, for example, in the water feed system to cause a water level decrease ~l3~

in the sedimentation ~ank and water reservoir, the blowing water feed can be secured by causing the water to flow directly from the sedimentation tank into the water reservoir as an emergency measure.
As described herein according to the present invention, the slag slurry can be dewatered continuously and efficiently in a shorter time, because a screw conveyor for transferring the slurry is used also for the dewatering purpose, as compared with the batch type processing using a dewatering tan~ according to the prior art. In the p-rior art system using the dewatering tank, since a plurality of dewatering tanks and equipment must be providedl a large cost is incurred. Also, the prior art equipment was extremely inefficient, in that a long time was needed to achieve a required dewatering level.
- - According to the---present invention, an improved apparatus ~ - --~--is pro~ided in which all such problems of the prior art can be solved. For example, while the prior art system using a dewatering tank consumed about l,000 KW of electric power per one ton of slag slurry the power con-sumption of the equipment according to the present invention is reduced to about 400 KW under the same conditions.
The moisture content of the water granulated slag processed by the equipment of the present invention is in the range of about 15 - 20% or less, showing that the present equipment equals or imp~oves the dewatering effect of the prior art equipment.

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Finally, an organic combination of the slurry tank, sedlmentation tank and water reservoir according to the present invention provides an lmproved processing capacity and permits an automatic control over the water feed responsive to the molten slag feed variation as well as a reduction of the equipment size.

Claims

WHAT IS CLAIMED IS:

1. An apparatus for producing water granulated slag comprising a slurry tank for storing a water granulated slag slurry discharged from a water blowing unit and a screw conveyor provided in said slurry tank for transferring said slag slurry precipitated on the bottom of the slurry tank and for dewatering the same as it is transferred thereon, said screw conveyor being inclined upwardly, as viewed in the direction of slurry flow, from near end thereof disposed on the bottom of the slurry tank and immersed in the slag slurry towards a far end thereof extended above the liquid level of the slurry tank.

2. An equipment for producing water granulated slag comprising a slurry tank for storing a water granulated slag slurry discharged from a water blowing unit, a sedimentation tank permitting at one peripheral end thereof an inflow of said slag slurry overflowing said slurry tank and an outflow of a clear supernatant liquid from other peripheral end, and a water reservoir for storing said supernatant liquid from the sedimentation tank, the slurry tank and the sedimentation tank each being provided with a screw conveyor for transferring and dewatering the slag slurry precipitated on the bottom of each tank, each screw conveyor being inclined upwardly, as viewed in the direction of slurry flow, from a near end thereof disposed on the bottom of each associated tank and immersed in the slag slurry towards a far end thereof extended above the liquid level of each associated tank.

3. An apparatus for producing water granulated slag comprising a slurry tank for storing a water granulated slag slurry discharged from a water blowing unit, a sedimentation tank permitting at one peripheral end thereof an inflow of said slag slurry overflowing said slurry tank and an outflow of a clear supernatant liquid from other peripheral end thereof, a water reservoir for storing said supernatant liquid from sedimentation tank, and a cooling tower for cooling the supernatant liquid, said water reservoir being composed of a hot water tank into which the supernatant liquid flows from the sedimentation tank and a cold water tank for storing the cooled water from said cooling tower, the hot water tank being communicated with the cold water tank, the slurry tank and the sedimenta-tion tank each being provided with a screw conveyor for transferring and dewatering the slag slurry precipitated on the bottom of each tank, each screw conveyor being inclined upwardly, as viewed in the direction of slurry flow, from a near end thereof disposed on the bottom of each associated tank and immersed in the slag slurry towards a far end thereof extended above the liquid level of each associated tank.