DESC:FIELD OF THE INVENTION

The present invention relates to a system for cooling and weathering of mixed steel slag for efficient metallic recovery and advancement in process of weathering of steel slag for easy metallic recovery and subsequent application of its varied contents including as civil construction aggregates. More particularly, the present invention is directed to a system and method for controlled cooling and weathering of steel slag stored in a pit directly from steel melting shop and controlled water spraying thereon and weathering slag by steam produced therefrom utilizing the heat of slag. Importantly, the present advancement is directed to providea techno-economical process for loosening the metal-slag bond and stabilizing the non metallic slag component with reduced expansion for being used as aggregates in civil construction requiring less time, space and energy for separation of metal from non metallic slag.

BACKGROUND OF INVENTION

Steel plants generate 200 kgs of steel slag for every tonne of steel produced. This slag is slowly cooled in pits and then subjected to crushing and magnetic separation for metal recovery. The non-metallic slag is usually dumped. These metal containing steel slags are very hard when air cooled and pose difficulties during crushing and metallic separation. The non-metallic component in chemically un-stable and has expansion characteristics, which restricts its usage in civil applications.

Steel industries generate huge amount of iron and steel slag through iron and steel making processes. The dumping of these slags is a major concern for the steel industry as well a very serious environmental concern. As steel production is increasing to meet the market demand of steel, substantial efforts and investments have been made into research over the years to develop the slag processing technologies which enable re-use of slag either directly or through enlargement of slag-based products. Due to rapid suburbanization and rising environmental concerns over sand quarrying and rock crushing, the construction industry is also facingenormousencounter to meet the accumulative demand of natural coarse and fine aggregates. Owing to the fact that the chemical and physical properties of iron and steel process slags counterpart the properties of natural aggregates, it is found that one of the major application areas where large quantities of slag can be consumed in road and civil constructions as replacement of natural aggregates. However, slags must be processed to match the requirements for use as aggregates.

First step of processing steel slags includes open cooling in air which takes 15-20 days. This slow cooling of metal containing steel slags results in large boulder formations which becomes difficult to handle.

Second step is to crush the slag boulders using crushers, impactors etc to break in smaller sizes and subject to metallic separation. The metallic component is recycled back in the steel making process and the non-metallic portion is dumped. This process consumes lot of energy due to hard slag metal bonding.

In spite of holding good mechanical properties, direct use of non metallic component of this processed slag as aggregates has not been successful due to its expansion characteristics especially steel slag which shows volumetric instability in the presence of water. Several expansive reactions are the primary reasons for steel slag expansion. The primary reason for volumetric expansion and structural instability of steel slags is the presence of free lime (CaO - [CaO + H2O ?Ca(OH)2]) and magnesium oxide (MgO - [MgO + H2O ? Mg(OH)2]) in its mineralogy which forms low density hydroxides in the presence of water and temperature. The swelling nature of steel slag is detrimental to almost all civil engineering applications. Hence, the main challenge to the researchers has been to develop a treatment process to decrease the volume instability caused by the expansive components of steel slag by changing its chemical and/or mineralogical properties and its accurate measurement.

The most primal weathering is only storing steel slag at outside. Moisture from rain gradually reacts with unreacted quicklime but reaction time is extremely long, i.e., about two years. This is termed as natural weathering and as daily steel slag production is huge so is not viable. Dry and wet cycle of steel slag is another weathering process of steel slag. This process needs large area for spreading slag of upto 2-3meter height in form of heaps. Water sprayed over the heaps and then held for drying it completely. This cycle run for 4-6 month, also depends on local climate conditions. Open steam weathering process is also one solution to stable steel slag. This process takes 6-7 days to finish the expansive nature. Recently, open yard steam weathering becomes popular, but its reaction time is at least 6-7 days. Furthermore, it needs large yard, which three walls are fenced with concrete walls. A cover sheet is often applied and put on the slag to have uniform reaction; even sheet covering work is heavy and dangerous. But the open steam weathering yard is so wide that obtaining of uniform reaction is difficult only with rough steam piping and cover sheets. This process is not cost effective as it requires huge maintenance and manpower for handling. Another solution to age the steel is pressurized steam weathering under controlled conditions. The process is aged under steamy atmosphere with high pressure and temperature shows weathering reaction time change by temperature. According to saturated steam temperature increase, pressurized steam weathering reaction speed increases 12 times as higher than open yard steam weathering. This phenomenon had confirmed by small autoclave at pilot scale. Then it was found that weathering reaction was completed within only 6-8 hours under 2 bar steamy atmosphere. This method gives very effective results as expansive properties of steel slag diminishes with 6-8 hours. The advantage of this technology is to receive uniform weathering of steel slag within a very short duration. The critical point of this process is, production of stable steel slag is very limited. This process operated in the range of 2-4 bar pressurized steam hence very dangerous. This process is not techno economical as the production cost of aged steel slag is too high and not feasible. Further, steam box technology is also available to age the steel slag to make it suitable for construction applications. This technology is proven but require huge capital investment. Though many techniques are available to finish the expansive characteristics of steel slag, all are having some drawbacks like need for huge area, high maintenance and manpower requirement.

There has been thus a need to develop anindustrially scalable process for cooling and weathering of steel slag in cost effective and energy efficient manner to separate metal from non-metallic slag components by direct treatment of hot steel slag in less time requiring less space while also stabilizing expansion characteristics in a reliable manner making the treated slag suitable for use as aggregate in civil construction.

OBJECTS OF THE INVENTION

The basic object of the present invention is directed toa process of controlled cooling and weathering of steel slag for easy metallic recovery and subsequent application of non metallic slag as civil construction aggregates and a system to carry out such process.

A further object of the present invention is directed toa system and process of controlled cooling and weathering of steel slag to stabilize steel slag in a very economic method for use as construction aggregates meeting required physical property requirements specially the expansion which is required to be consistently below a given standard threshold.

A still further object of the present invention is directed to a system and process of controlled cooling and weathering of steel slag to stabilize steel slag involving transportation of hot steel slag to specially designed pits and periodically sprinkling water uniformly over the filled slag.

A still further object of the present invention is directed to a system and process of controlled cooling and weathering of steel slag to stabilize steel slag that can process steel slag coming directly from the steel making shop without prior separation of metallic and non-metallic slag.

Another object of the present invention is directed to a process of controlled cooling and weathering of steel slag wherein controlled cooling allows differential expansion of slag and metal and allowing it to separate with each other.

Yet another object of the present invention is directed to a process of controlled cooling and weathering of steel slag wherein the heat of slag converts the water into steam and which percolates into the slag pores and allows hydration of free lime and Pericles resulting in its weathering.

A still further object of the present invention is directed to a process of controlled cooling and weathering of steel slag wherein mixed slag comes into contact with steam and non-metallic part expand due to hydration reaction, thus allowing self-cracking of slag lumps, that helps to separate metallic and non- metallic part due to loosening effect.

A still further object of the present invention is directed to a process of controlled cooling and weathering of steel slag to stabilize steel slag whereby cooled and aged slag is easy to handle in metallic separation circuit reducing the energy requirement and can be directly used as replacement of natural aggregates in civil construction.

SUMMARY OF THE INVENTION
The basic aspect of the present invention is directed to a process for facilitating separation of metallic and non-metallic from mixed steel slag comprising step of weathering including:
providing a closed pit with a slag charging and discharging opening;
charging mixed slag of both metallic and non-metallic contents slag for stabilization directly from steel making unit into said pit;
sprinkling water over said mixed slag to carry out cooling and weathering of the mixed slag utilizing the heat of the mixed slag directly charged from said steel making unit;
covering the pit containing the mixed slag post sprinkling of water by heat resistant cover thereby keeping the steam locked into the slag for accelerating the weathering process with desired loosening of the slag lumps for favouring separation of metallic and non-metallic fractions of said slag.

A further aspect of the present invention is directed to a process comprising repeating the process of water sprinkling, steam generation and weathering and stabilizing all the expansive components and reduce the expansion of the slag aggregates.
A still further aspect of the present invention is directed to a process comprising carrying out spreading and uniform levelling of the said mixed slag in the pit prior to uniform water sprinkling on the mixed slag.
A still further aspect of the present invention is directed to a process comprising subjecting the thus weathered slag to slag crushing to separate metallic and nonmetallic fractions of slag wherein due to weathering process, the slag lumps becomes losses and are easy to handle. The metallics recovered from the magnetic separator is next sent to the steel making and the non-metallic are screened and piled in different size fractions for use in construction industry as aggregates.
Another aspect of the present invention is directed to a process wherein said step of weathering of slag is carried out by periodically sprinkling water over the slag for 50 to 70 minutes preferably about 60 minutes after every 10 to 14 hours preferably about twelve hours for 9 to 11 days preferably about 10 days such as to achieve volumetric expansion, whereby big lumps of slag undergo self-cracking due to hydration reaction.

Yet another aspect of the present invention is directed to a process wherein large metal pieces are taken out from the pit directly.
A further aspect of the present invention is directed to a process which is free of any required additional balling process and the energy consumption in metallic separation process is reduced by 10% and expansion of steel slags reduce from 4% to <1.5 %.
A still further aspect of the present invention is directed to a system for carrying out process for facilitating separation of metallic and non-metallic from mixed steel slag as described above comprising:

atleast one steam weathering pit for accommodating the hot mixed steel slaglayered into the pit uniformly;

each said steam weathering pit having sprinklers for sprinkling water on the said hot mixed steel slag; and

heat resistant releasable covering for the whole of each said steam weathering pit.

A still further aspect of the present invention is directed to a system wherein each said pit is closed from three sides and open in one side for charging and discharging of the mixed slag.

A still further aspect of the present invention is directed to a system comprising plurality of said steam weathering pit with accompanying sprinklers and heat resistant cover arranged in rows with passage for approach of machineries in between the rows in a manner to favour easy loading and unloading of slag therein.

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

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1: is a simplified schematic diagram (Top view) of full scale steam weathering plant used for stabilization of steel slag according to present invention comprisingarrangement of water sprinkling system and its design.

Figure 2: is a simplified schematic three dimensional steam weathering slag pit and arrangement of water sprinkling.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO ACCOMPNAYING DRAWINGS

The present invention is directed toa system and process of controlled cooling and weathering of steel slag for easy metallic recovery and subsequent application of non metallic slag as civil construction aggregates. The process include transportation of hot steel slag directly from steel making plant to specially designed pits and periodically sprinkling water uniformly over the filled slag. The controlled cooling allows differential expansion of slag and metal and allowing it to separate with each other. The heat of slag converts the water into steam and which percolates into the slag pores and allows hydration of free lime and Pericles resulting in its weathering.

With reference to Figure 1, a simplified schematic view of complete steam weathering plant used for stabilization of LD slag. Steam weathering pit 1 is having assembly of total ten numbers of pits. Every pit is having water sprinklers 2 on the either side all along the length. As there is an arrangement of two rows of steam weathering pits, passage 4 has been made for loading and unloading of steel slag. Machineries 3 are involved for slag placing into pit.

In reference to Figure 2, the steam weathering pit 1 having dimension of 3*4*5. Water sprinkling system 2 also configured within.

Accordingly, the invention resides in a unique and direct process where steel can have transported to steam weathering site besides a slag processing/crushing plant. Steel slag directly dumped into pit. There are total 8 pits have been created. The dimensions of each pits are 20 meter in length, 12 meters in width and 7-8 meter in depth. All these pits are specially created to place hot steel slag directly coming from steel melt shop. These pits are having capacity to accumulate 1day production of LD steel slag ie. 6000T /day. This helps to track the all the processing parameter of steel melt shop and properties of steel slag that has been produced and arrived for steam weathering process. These pits are capable of handling any size of steel slag lumps. Steel slag layered into the pit uniformly. Steam weathering trials has been taken with different processing parameters. Initially slag pit has been simply filled with steel slag and water spayed over the pit in regular intervals. Water spay on the pit has been in cyclic in nature. Slag weathering trials has been taken while keeping steel slag from 4-6-8-10 and 12 days. Samples have been collected for different processing duration. Samples has been collected and tested for further expansion. This apparatus for expansion testing of slag samples, e.g. steel slag samples, comprising: has a doubled walled stainless steel chamber having an insulator packing in between which acts as the container capable of holding water/steam or any liquid under pressurized and high temperature conditions. The apparatus sits on four bottom stands and has a drainage valve connected to its bottom. It has been observed that when top surface is open to atmosphere, steam escaped and steam channeling takes place. The results those have been received are not satisfactory as few samples finishes expansion characteristics but few failed in this. As steam distribution is not uniform throughout the pit resulted non-uniformity of steel slag weathering. Further it has been decided to pack the pit from the top to avoid escape of steam. This has been done via packing the pit surface with waste conveyers. Slag has been processed through this technique and found that steam is not coming out. Further trials have been done for different weathering duration like 4-6-8-10 and 12 days. Sampling has been done for every cycle of the weathering and undergone through expansion testing as stated previously. Results are quite satisfactory as steel slag finishes expansion in 8-10 days. Coning-quartering method has been adopted for proper sampling. As stated there is requirement of packing the pit to avoid steam escape, causing huge manpower involvement and tough conditions for processing.To resolve this issue, brainstorming has been done with the technical officials/researchers and it has been decided to cover the top surface with -10mm LD slag that is having finer fraction more. This helps out to stop the escape of steam as top surface of the pit covered with fine material and water sprayed over. Rolling of the top surface also contributes to stop the steam coming out. This method giving very positive results as the entire pit is covered to stop steam channeling. In combination of the all the above said technique, the process has been adopted for further trials of weathering. Again trials have been performed for 4-6-8-10 and 12 days weathering. Sampling has been done and tested under expansion test apparatus. The expansion results are fully satisfactorily and expansion of steel slag found within the range of prescribed limit.

The present designed process is capable of efficient weathering the steel slag. The pit formation has been done as per the slag quantity produced daily to accommodate the full day production slag. So critical issue of slag dumping has been resolved here.Further aged steel slag sends to slag crushing plant to separate metallic and nonmetallic fractions of slag. As weathering of slag resulted in volumetric expansion, hence big lumps of slag undergone through self-cracking due to hydration reaction. This phenomenon helps to reduce the power consumption of slag crushing. Stock yard of aged steel slag has been well designated for different size fractions. This provides better handling and scope for further civil applications.
Due to ageing process, the slag lumps becomes losses and are easy to handle. Metallic separation also becomes easier and faster leading to saving in power. Due to expansion, the metallic boulders and slag gets separated automatically. Large metal pieces can be taken out from the pit directly. The additional balling process can be avoided.

The energy consumption in metallic separation process reduces by 10% and expansion of steel slags reduce from 3-4% to <1.5 % through this process.

It is thus possible by way of the present invention to provide a process for controlled cooling and stabilization of steel slag in a very economic method and a system thereof. The slags expand when exposed to moisture due to presence of free CaO and MgO. Slags when intended to be used as construction aggregates must meet some physical property requirements specially the expansion which is required to be consistently below a given standard threshold. Among all previous techniques, new steam weathering approach has been adopted to stabilize steel slag with very low cost, easy to handle, and hardly require manpower with low maintenance to receive uniform properties of steel slag to apply in civil applications. Most importantly, in this steam weathering technique, steel slag directly coming from the steel making shop can be processed. Generally, other steam weathering techniques do weathering after separation of metallic and non- metallic slag. Only non-metallic slag processed through conventional techniques of weathering. This method process direct steel slag coming from the steel making shop. The unique advantage of this process is, the extraction of metallic part becomes very easy due to prior weathering of mixed slag. Mixed slag come into contact with steam and non-metallic part expand due to hydration reaction. This allow self-cracking of slag lumps, helps to separate metallic and non- metallic part due to loosening effect. Further process of crusher requires less energy for crushing of hard steel slag lumps. The present invention thus provide an easy and techno-economic solution for steam weathering that finishes expansive characteristics of steel slag which can be adopted universally.

,CLAIMS:We Claim:
1. A process for facilitating separation of metallic and non-metallic from mixed steel slag comprising step of weathering including:
providing a closed pit with a slag charging and discharging opening ;
charging mixed slag of both metallic and non-metallic contents slag for stabilization directly from steel making unit into said pit;
sprinkling water over said mixed slag to carry out cooling and weathering of the mixed slag utilizing the heat of the mixed slag directly charged from said steel making unit;
covering the pit containing the mixed slag post sprinkling of water by heat resistant cover thereby keeping the steam locked into the slag for accelerating the weathering process with desired loosening of the slag lumps for favouring separation of metallic and non-metallic fractions of said slag.

2. A process as claimed in claim 1 comprising repeating the process of water sprinkling, steam generation and weathering and stabilizing all the expansive components and reduce the expansion of the slag aggregates.

3. A process as claimed in anyone of claims 1 or 2 comprising carrying out spreading and uniform levelling of the said mixed slag in the pit prior to uniform water sprinkling on the mixed slag.

4. A process as claimed in anyone of claims 1 to 3 comprising subjecting the thus weathered slag to slag crushing to separate metallic and nonmetallic fractions of slag wherein due to weathering process, the slag lumps becomes losses and are easy to handle and the metallics recovered from the magnetic separator is next sent to the steel making and the non-metallic are screened and piled in different size fractions for use in construction industry as aggregates.

5. A process as claimed in anyone of claims 1 to 4 wherein said step of weathering of slag is carried out by periodically sprinkling water over the slag for 50 to 70 minutes preferably about 60 minutes after every 10 to 14 hours preferably about twelve hours for 9 to 11 days preferably about 10 days such as to achieve volumetric expansion, whereby big lumps of slag undergo self-cracking due to hydration reaction.

6. A process as claimed in anyone of claims 1 to 5 wherein large metal pieces are taken out from the pit directly.

7. A process as claimed in anyone of claims 1 to 6 which is free of any required additional balling process and the energy consumption in metallic separation process is reduced by 10% and expansion of steel slags reduce from 4% to <1.5 %.

8. A system for carrying out process for facilitating separation of metallic and non-metallic from mixed steel slag as claimed in anyone of claims 1 to 7 comprising:

atleast one steam weathering pit for accommodating the hot mixed steel slaglayered into the pit uniformly;

each said steam weathering pit having sprinklers for sprinkling water on the said hot mixed steel slag; and

heat resistant releasable covering for the whole of each said steam weathering pit.

9. A system as claimed in claim 8 wherein each said pit is closed from three sides and open in one side for charging and discharging of the mixed slag.

10. A system as claimed in anyone of claims 8 or 9 comprising plurality of said steam weathering pit with accompanying sprinklers and heat resistant cover arranged in rows with passage for approach of machineries in between the rows in a manner to favour easy loading and unloading of slag therein.

Dated this the 11th day of September, 2017
Anjan Sen
Of Anjan Sen & Associates
(Applicants Agent)