Claims:I Claim:
1. A method of slag handling to control metallic losses in slag generated in steel making comprising:
i) Providing the slag along with leftover molten metal/steel in slag in a carrying container/thimble wherein the slag usually is on top of the leftover molten metal/steel;
ii) controlled pouring of the slag from said container/thimble for slag dumping such that only the top slag initially flows out and when the slag containing leftover molten metal/steel surface during pouring stopping said pouring such that substantial portion of only the top slag is dumped and the leftover molten metal/steel with slag layer floating on top is retained;
iii) Allowing the leftover molten metal/steel with slag layer floating on top to cool to thus solidify the slag with the solidified leftover molten metal/steel thereunder;
iv) Recovering the leftover molten metal/steel by removing the remnant solidified slag adhered thereto.

2.A method as claimed in claim 1 comprising:
i) Providing the slag alongwith leftover molten metal/steel in slag in a carrying container/thimble wherein the slag usually is on top of the leftover molten metal/steel;
ii) controlled pouring of the slag in the slag pit for slag dumping including titling the container/thimble on a side of its axis in the vertical plane such that only the top slag flows out and when the slag containing leftover molten metal/steel surface during dumping making the container/thimble upright such that substantial portion of the slag is dumped and the leftover molten metal/steel with slag layer floating on top is retained in said container/thimble;
iii) Allowing the leftover molten metal/steel with slag layer floating on top in the container/thimble to cool to thus solidify the slag with the solidified leftover molten metal/steel thereunder;
iv) Releasing the thus obtained solidified leftover molten metal/steel with some remnant solidified slag adhered thereto;
v) Recoveringthe leftover molten metal/steel by removing the remnant solidified slag adhered thereto.

3. A method as claimed in anyone of claims 1 or 2 wherein when during pouring the leftover molten metal/steel visually surface during said controlled slag pouring the pouring operation is stopped.
4. A method as claimed in anyone of claims 1 to 3 wherein a slag float on the top of the liquid metal and does not allow it to come in to contact with atmospheric oxygen and other gases thus preventing oxidation.

5. A method as claimed in anyone of claims 1 to 4 wherein the left over metal along with a top layer of slag is allowed to solidify in slag thimble itself and the solidified metal is then dumped by tilting the slag thimble upside down and thereafter whatever slag is adhered to the metal, is chipped off and the metal recovered is recharged.

6. A method as claimed in anyone of claims 1 to 5 wherein said molten slag from steel making itself provides for desired anti-sticking character and whenever molten slag is poured into slag pot, a thin layer of slag sticks to the inner surface of the Slag Pot which itself acts as an anti-sticking compound for the rest of the molten Slag, the first layer of slag which comes in contact with the slag thimble itself acts as an anti-sticking compound.

7. A method as claimed in anyone of claims 1 to 6 wherein said step of cooling preferably comprise natural cooling without any contact with air moisture or water.

8. A method as claimed in anyone of claims 1 to 7 wherein the container/thimble used is at room temperature.

9. A method as claimed in anyone of claims 1 to 8 wherein FeO content in slag is not more than 30%.

Dated this the 16th day of January, 2016
Anjan Sen
Of Anjan Sen & Associates
(Applicant’s Agent)

, Description:FIELD OF THE INVENTION
The present invention relates to a method of slag handling to control metallic loses in slag generated in steel making. The invention deals with recover of metal lost due to oxidation duringmolten Slag Handling and Scrap Metal Recovery in the Steel Making Industry. The present invention thus provide a simple process wherein controlled pouring of the slag from said container/thimble for slag dumping such that only the top slag initially flows out and when the slag containing leftover molten metal/steel surface during pouring stopping said pouring such that substantial portion of only the top slag is dumped and the leftover molten metal/steel with slag layer floating on top is retained and thus eliminate metallic losses that otherwise occur due to oxidation of the metal that comes in contact of atmospheric moisture and water when slag handling is done by conventional method.

BACKGROUND OF THE INVENTION

In Steel making process, there are various by-products which are formed during the various reactions that are being carried out in the Steel Making operation. In this process, Slag is one of the major by-products which is formed due to the impurities present in the hot metal that is obtained from iron making.

It is well known that the hot metal is charged with a few percent of scrap as coolant, the process starting by blowing/arcing the hot metal and then the slag formation takes place, after many chemical reactions, the steel is made either with the help of L D Converter or with the help of Arc Furnace by complete removal of impurities to make steel. After the steel is produced with slag floating over the steel due to the density difference, the steel is tapped through a hole called Tap Hole. After the completion of Tapping (means metal is collected in a Steel Ladle), some product is leftover in the furnace which is called Slag. Then the leftover slag is completely dumped in the slag thimble provided. There will be metallic remains/particles that also flow with slag into slag thimble due to the slag metal mixture. This loss of metallic content directly affects the yield of the steel making because it is a processed steel and recovering this metal from that slag adds up to the cost of the steel making and also makes the slag handling difficult due to oxidation of the metal. The presence of metal content in slag makes it very hard to break or disintegrate. Also the metal content in the slag means loss in money and recovering it makes the process complicated.Various processes have been developed to recover the iron that inevitably goes with the slag. These processes typically recover the iron after the mixture of slag and metal has been cooled and solidified. For example, the separated slag from steel making process is poured in the slag pit and is subsequently allowed to solidify naturally or by spraying the cold water on the dumped slag. As a result, boulders are formed by entrapment of the iron particles within slag due to the development of mechanical and chemical bonds between them. The entrapped iron is recovered from the solidified slag by first crushing the boulders to suitable size and magnetic separation of the iron particles from the non-magnetic slag. However it is not possible to liberate all the iron particles from the slag. A part of iron is attached to the bulk of solidified slag. Further, during cooling and solidification of the slag, some part of iron is lost due to oxidation.

PRESENT PROCESS OF SLAG HANDLING
Generally two major processes of steel making are used for making the steel on large scale, where both slag and refined steel are produced in clear molten state, namely Basic Oxygen Furnace (BOF) and Electric Arc Furnace (EAF). In BOF at the end of the steel making process the refined molten steel is tapped through tap hole while leaving the slag inside the furnace along with a small amount ofmolten steel. The molten slag along with the leftover steel is poured in to the slag thimble for its eventual disposal. The small amount of molten steel so sacrificed during tapping goes with the slag. The small amount of steel sacrificed to go with the slag is recovered by employing crushing and magnetic separation of the Slag/Metal mix after cooling and solidification of the slag.

In EAF process the slag is allowed to flush out of furnace during the refining process itself. However, small amount of the molten steel gets mechanically entrapped and drained with the flushing slag. The small amount of the molten steel thus ends up with the slag that is collected. Additionally, the small amount of iron entrapped during slag flushing is recovered by the process described above.

In both the processes, the molten steel and the slag are not clearly obtained as two physically distinct products. The slag along with the small amount of molten iron in the form of the molten steel, is collected in the slag thimble and transported to the slag handling yard for subsequent solidification and separation of the iron from the slag. The slag thimble is tilted to pour the slag iron mixtures in to the slag pit prescribed for slag dumping. It is tilted on one side on its axis in the vertical plane upside down such that the slag and the metal mixtures flows in to the slag pit.

Hence poured slag and iron mixture is allowed to solidify either naturally or by spraying cold water. Subsequently, once the slag is solidified the slag and iron mixture bonds up chemically and mechanically forming a boulder mass.This boulder is broken in to smaller size by using the excavators/heavy earth movers in to the manageable size. This process of breaking is so called the loosening.During loosening some amount of metal that is visible by naked eye is recoveredusing excavators itself.

Once the loosening of the slag is complete the solidified and the loosened slag is taken out of the slag pit and whatever iron particlesare present in the slag are separated magnetically as per the capacity of the magnet.

Usually the metal is recovered from the secondary steel making by allowing the metal and the slag to cool and solidify naturally and mechanically liberate the steel that is visible to the naked eye and the remaining steel left over which is present under the slag is eventually disposed-off because there is no other method present for theseparation of the steel.

In present process of slag handling, slag from the steel furnace is bought to the yard and dumped in allocated area called PIT. After dumping of few numbers of slag thimbles of some prescribed quantity as per the capacity of the slag pit that is how much it can hold, up to that much amount of slag is dumped then that slag is cooled with the help of water. (Ferric oxideis formed by the oxidation reaction of Steel with atmospheric moisture and oxygen which is very difficult to process in order to recover iron from it.It makes the processing even harder and lengthy which is avoided since it is an expensive process). Then the slag is loosened after the cooling with the help of heavy earth movers but with many difficulties. This adds up the cost of processing of slag and steel making because even disposal of gangue material is very important, and even if the metal present comes in contact with the cooling water there are possibilities for oxidation of the metal which is uneconomical to reuse.

DEFECIENCIES/DISADVANTAGES OF THE CONVENTIONAL SLAG HANDLING PROCESS
In the present process, there are many flaws which not only make the process difficult but also increases the cost of steel making and makes the process too much unsafe. Some of them are listed below:
1. Since the slag is dumped and cooled in a very vast area,the molten slag which comes in contact with entrapped metal, bonds up and forms a hard cake of mass/bolder. Before its disposal it must be broken into small pieces. This is very difficult to loosen/break in to small pieces because of the hardness.
2. Due to the metal entrapped in molten slag, the metal gets mixed with molten slag. After cooling this mixture, the process of loosening becomes very much difficult.
3. Due to the metal entrapped in molten slag, the metallic losses will be more and as a result, the Yield is decreased.
4. Due to the hardness of slag& metal mixture, the use of heavy earth mover is required for longer periods of time which results in greater pollution, noise and dust. Besides, fuel consumption is also more in this process. Since more cooling is required, there will be more dust formation which results in equipment and machines requiring more maintenance.
5. As the slag is loosened, it is disposed/sent to MRP (metal recovery plant) to recover any metallic content that is present in the slag.In order to minimize the metallic losses, the cost of processing slag adds up to the overall Cost of Steel Making. In MRP, first the steel mix slag is charged in a hopper and passed through crushers, screens and number of conveyers. Then the crushed particles are passed over the magnetic separator where magnetic particlesare recovered. The recovered metal will be in the form of coarse particles and also contains some particles of slag. This slag has some amounts of impurities like sulphur (S), phosphor (P), silica (SiO2), alumina (Al2O3) etc. which is uneconomical for reuse.If used it adds up to the cost of steel making.
6. This conventional Metal Recovery Plant (MRP) is a very lengthy process. It takes more time and requires more area. In this process dust generation is more. Which is not environmental friendly and also uses more electricity, water, land, fuel, manpower and other heavy equipment and earth movers.
7. Safety parameter wise, conventional slag handling/process is very much unsafe.
8.The main problem in metal recovery is that while cooling, the metal that is to be recovered, comes in contact with atmospheric air/moisture or water resulting in the formation ferrous oxides of FeO and Fe2O3. Recovering back the metal from this mixture is extremely difficult.

Various processes have been developed to recover the iron that inevitably goes with the slag. These processes typically recover the iron after the mixture of slag and metal has been cooled and solidified. For example, the separated slag from steel making process is poured in the slag pit and is subsequently allowed to solidify naturally or by spraying the cold water on the dumped slag. As a result, boulders are formed by entrapping of iron particles within the slag due to the development of mechanical and chemical bonds between them. The entrapped iron is recovered from the solidified slag by first crushing the boulders to a suitable size and magnetic separation of the iron particles from the non-magnetic slag. However it is not possible to liberate all the iron particles from the slag. A part of iron is attached to the bulk of solidified slag. Further, during cooling and solidification of the slag, some part of iron is lost due to oxidation.

There has been thus a need in the field of iron and steel production to develop a simple and safe method of slag handling which would save metal loss due to oxidation and separate slag and residual metal in thimble in a easy and environment friendly manner without needing use of electricity, water, land, fuel, manpower and other heavy equipment /earth movers. This invention thus aims at eliminating loss of metal that is inevitably lost presently because of oxidation.

OBJECTS OF THE INVENTION

The basic object of the present invention is directed to a method of slag handling to control metallic loses in slag generated in steel making.

A further object of the present invention is directed to a method of slag handling to control metallic loss in slag generated in steel making that is inevitably lost due to oxidation of metal.

A still further object of the present invention is directed to a method of slag handling to control metallic loss in slag generated in steel making involving controlled pouring of the slag from said container/thimble for slag dumping such that leftover molten metal/steel with slag layer floating on top is retained and thus eliminating metallic losses that otherwise occur due to oxidation of the metal that comes in contact of atmospheric moisture and water when slag handling is done by conventional method.

A still further object of the present invention is directed to a method of slag handling to control metallic loss in slag generated in steel making wherein non-sticky nature of slag layer on inner wall of thimble is utilized to recover the solidified slag covered metal after solidification by slow natural cooling inside the thimble.

A still further object of the present invention is directed to a method of slag handling to control metallic loss in slag generated in steel making to enable slag metal separation and metal recovery in aeasy, safe and environment friendly manner without needing use of electricity, water, land, fuel, manpower and/or other heavy equipment /earth movers.

SUMMARY OF THE INVENTION

The basic aspect of the present invention is directed toa method of slag handling to control metallic loses in slag generated in steel making comprising:
i) Providing the slag along with leftover molten metal/steel in slag in a carrying container/thimble wherein the slag usually is on top of the leftover molten metal/steel;
ii) controlled pouring of the slag from said container/thimble for slag dumping such that only the top slag initially flows out and when the slag containing leftover molten metal/steel surface during pouring stopping said pouring such that substantial portion of only the top slag is dumped and the leftover molten metal/steel with slag layer floating on top is retained;
iii) Allowing the leftover molten metal/steel with slag layer floating on top to cool to thus solidify the slag with the solidified leftover molten metal/steel thereunder;
iv) Recovering the leftover molten metal/steel by removing the remnant solidified slag adhered thereto.

A further aspect of the present invention is directed tosay method comprising:
i) Providing the slag along with leftover molten metal/steel in slag in a carrying container/thimble wherein the slag usually is on top of the leftover molten metal/steel;
ii) controlled pouring of the slag in the slag pit for slag dumping including titling the container/thimble on a side of its axis in the vertical plane such that only the top slag flows out and when the slag containing leftover molten metal/steel surface during dumping making the container/thimble upright such that substantial portion of the slag is dumped and the leftover molten metal/steel with slag layer floating on top is retained in said container/thimble;
iii) Allowing the leftover molten metal/steel with slag layer floating on top in the container/thimble to cool to thus solidify the slag with the solidified leftover molten metal/steel thereunder;
iv) Releasing the thus obtained solidified leftover molten metal/steel with some remnant solidified slag adhered thereto;
v) Recovering the leftover molten metal/steel by removing the remnant solidified slag adhered thereto.

A still further aspect of the present invention is directed to said method wherein when during pouring the leftover molten metal/steel visually surface during said controlled slag pouring the pouring operation is stopped.

A still further aspect of the present invention is directed to saidmethod wherein a slag float on the top of the liquid metal and does not allow it to come in to contact with atmospheric oxygen and other gases thus preventing oxidation.

A still further aspect of the present invention is directed to saidmethod wherein the left over metal along with a top layer of slag is allowed to solidify in slag thimble itself and the solidified metal is then dumped by tilting the slag thimble upside down and thereafter whatever slag is adhered to the metal, is chipped off and the metal recovered is recharged.

Another aspect of the present invention is directed to saidmethod wherein said molten slag from steel making itself provides for desired anti-sticking character and whenever molten slag is poured into slag pot, a thin layer of slag sticks to the inner surface of the Slag Pot which itself acts as an anti-sticking compound for the rest of the molten Slag, the first layer of slag which comes in contact with the slag thimble itself acts as an anti-sticking compound.

Yet another aspect of the present invention is directed to saidmethod wherein said step of cooling preferably comprise natural cooling without any contact with air moisture or water.

A further aspect of the present invention is directed to saidmethod wherein the container/thimble used is at room temperature.

A still further aspect of the present invention is directed to saidmethod wherein FeO content in slag is not more than 30%.

The above and other objects and advantages of the present invention are described hereunder in greater details with reference to the following accompanying non limiting illustrative drawings.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

Figure 1(a):showing the titled position of thimblewith molten slag layer over the molten metal about to be poured.
Figure 1(b) showing the thin slag layer that sticks on inner wall of the thimble.
Figure 2(a): shows how the most of the molten slag is poured from slag thimble with remaining molten metal under the cover of slag layer preventing atmospheric oxidation.
Figure 2(a): shows the position of slag thimble in upright position to allow the remaining metal under the cover ofa thin slag layer to cool and solidify within the thimble by slow natural cooling.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS

The present invention is directed to a method of slag handling to control metallic loss in slag generated in steel making involving controlled pouring of the slag from said container/thimble for slag dumping such that leftover molten metal/steel with slag layer floating on top is retained and thus eliminate metallic losses that otherwise occur due to oxidation of the metal that comes in contact of atmospheric moisture and water when slag handling is done by conventional method.

In BOF at the end of the steel making process the refined molten steel is tapped through tap hole while leaving the slag inside the furnace along with small amount ofmolten steel. The molten slag along with the leftover steel is poured in to the slag thimble for its eventual disposal. The small amount of molten steel so sacrificed during tapping goes with the slag. This molten steel is recovered by using magnetic separation after cooling and solidification of the slag.

In EAF process the slag is allowed to flush out of furnace during the refining process itself. However, small amount of the molten steel gets mechanically entrapped and drained with the flushing slag. The small amount of the molten steel thus ends up with the slag that is collected. Additionally, the small amount of iron entrapped during slag flushing is recovered by the process described above.

In both the processes, the molten steel and the slag are not clearly obtained as two physically distinct products. The slag along with the small amount of molten iron in the form of the molten steel is collected in the slag thimble and transported to the slag handling yard for subsequent solidification and separation of the iron from the slag. The slag thimble is tilted to pour the slag iron mixtures in to the slag pit prescribed for slag dumping. It is tilted on one side of its axis in the vertical plane till only slag flows in to the slag pit.

According to the present process of preventing metal loss due to oxidation by controlled pouring, at the time of collecting slag, when metal starts falling/sparks of metal are visible, then the thimble is again tilted upright. Thus, only metal along with minute amounts of slag will be left in the thimble. This slag floats on the top of the liquid metal and does not allow it to come in to contact with atmospheric oxygen and other gases thus preventing oxidation. Accompanying Figure 1(a) shows the method of pouring slag by tilting the thimble where the thimble(1) is tilted through an angle to remove the molten slag(3) layer from top of molten metal(2). Accompanying Figure 1(b)shows the tilted position of thimble when a thin slaglayer(1) is found to sticks to the walls of thimble.

Accompanying Figure 2(a) shows the further tilted position of the thimble(1) when most of the molten slag(3) layer is removed or dumped and only a small portion of slag is retained to cover the remaining molten metal/steel(2) inside the thimble.

The left over metal(2) along with a top layer of slag(3) is allowed to solidify in slag thimble(1) itself and the solidified metal is then dumped by tilting the slag thimble upside down as shown in accompanying Figure 2(b),then whatever slag is adhered to the metal, it is chipped off and the metal recovered is recharged.

Molten slag from steel making itself has an anti-sticking character. Whenever molten slag is poured into slag pot, a thin layer of slag sticks to the inner surface of the Slag Pot as shown in the Figure 1(b). Then, this layer itself acts as an anti-sticking compound for the rest of the molten Slag. The first layer of slag which comes in contact with the slag thimble itself acts as anti-sticking compound.

The best solution to avoid the loss of metal due to oxidation will be to avoid the external cooling and to allow the slag (with metal) to cool naturally. Once the molten iron attains the solidification temperature range with a top slag layer over it, then there is no chance of oxidation. Thus, it is better to solidify the molten metal by cooling it naturally without any contact with air moisture or water.

As per the experiments and trials carried out under the present invention, the applicants have noted the following requirements for satisfactory implementation of the process:
1. The Thimble supplied to the furnace should be at room temperature.
2. FeO content in slag should not be more than 30%.

The experimental trials as illustrated in following Table I indicates the quantum of metal loss due to oxidation going by the conventional slag handling method vis-à-vis the saving in metal loss following slag handling process according to the present invention avoiding oxidation.

Metal losses in conventional slag handling/processing method Saving in metal when using Present invention without oxidation loss
Plant capacity 1 Million Tonne steel Plant capacity 1 Million Tonne steel
Metal included in steel mixed slag generated -10,000t Metal included in steel mixed slag generated -10,000t
No. of trials Metal recovery from slag Metal loss
No. of trials Metal recovery from slag Metal loss
1 67% 33% 1 98% 2%
2 69% 31% 2 99% 1%
3 70% 30% 3 100% Nil

It is thus possible by way of the present invention to provide a for method of slag handling to control metallic losses in slag generated in steel making involving controlled removal of slag from top of molten metal such that there remain a cover of slag over remaining molten metal during pouring that protects the metal from oxidation and resultant loss. The metal is recovered by solidifying the slag covered metal by slow cooling within the thimble, dumping the solidified mass by turning over the thimble and then chipping off the slag layer.The process is simple, cost effective, environment friendly without needing much of space, handling equipments or power.