Claims:I/WE CLAIM:

1. A method for developing a cold-bonded micro-pellets, the method comprising:
forming a mixture of a dried blast furnace sludge with an organic binder, the organic binder being in 0.2 – 1 wt.% of blast furnace sludge; and
pelletizing the mixture in a disk pelletizer for residence time of 1-1.5 minutes.

2. The method as claimed in claim 1, wherein the organic binder is sodium lignosulphate or calcium lignosulphate.

3. The method as claimed in claim 1, wherein the cold-bonded micro-pellets size 90% is passing 10 mm.

4. The method as claimed in claim 1, wherein the amount of water sprayed during pelletizing in the mixture is 25-30 wt% of the total weight of the mixture.

5. The method as claimed in claim 1, wherein the cold bonded micro pellet is air dried for 24 hours.

6. The method as claimed in claim 1, wherein RPM of the disk pelletizer is 16 rpm or 20 rpm or 24 rpm.

7. The method as claimed in claim 1, wherein inclination of the disk pelletizer is 55 or 60 or 65.

8. The method as claimed in claim 1, wherein the blast furnace sludge is dried by means of pressure filter to make dried blast furnace sludge.

9. The method as claimed in claim 1, wherein specific gravity of the dried blast furnace sludge is 2.71 g/cc.

10. The method as claimed in claim 1, wherein the size of the dried blast furnace sludge is d10 1.29 µm.

11. The method as claimed in claim 1, wherein the size of the dried blast furnace sludge is d50 13.84 µm.

12. The method as claimed in claim 1, wherein the size of the dried blast furnace sludge is d90 58.79 µm

13. The method as claimed in claim 1, wherein the composition of the dried blast furnace sludge is Fe-33.78, SiO2-4.86, Al2O3-3.84, FeO-8.26, MgO-0.25, MnO2-0.07, Na2O-0.16, ZnO-2.77, K2O-0.17, CaO-1.62, Fe(M)-0.35, Combustible 35.6.
, Description:
TECHNICAL FIELD
The present invention relates to sinter making process to be used in blast furnace. More particularly, the present invention relates to development of cold-bonded micro-pellets.
BACKGROUND
During the hot metal production from blast furnaces, huge quantity of dusts and sludges are generated. These sludges contain major quantity of water, which are further processed through the pressure filters. These filtered blast furnace sludges contains huge ultrafine particles.
At present, as a practice these sludges are used in sinter making process by mixing with other steel plant wastes (process solid wastes). But direct usage of these ultra-fines is restricted due to the permeability limitation of the sinter plant.
Few attempts were taken to re-utilize the blast furnace sludge in steel making process.
In the patent IN201400365I2, the process was developed for generating the micro-pellets using steel plant wastes i.e. blast furnace sludge, LD Sludge etc. The binders used are dextrin; molasses; mixtures of dextrin and molasses; LD sludge etc. For proper strength the micro pellets have to kept at a particular temperature (80-110°C) for range between 10-50 minutes. This involves separate induration unit which adds to energy consumption and time.
Su, Lampinen and Robinson 2004 attempted to reuse the fine sludge and dust in the form of cold bonded pellets using cement as binder in laboratory and pilot scale pelletizing plant. It was established that with coarser particle size BF flue dust, it has a negative effect for increasing both the cold strength and capacity for levels of over 25% of the mixture. Rather, fine BOF sludge has the positive effect on cold strength, while its interaction with BF flue dust has the negative effect on reduction degree.
J Pal et al, 2015 attempted to develop micro pellets of carbon composites using blast furnace flue dust. They have attempted to develop carbon composites using blast furnace dust and sludge with coke fines and iron ore fines. They used lime fines and molasses as binders. Subsequently, for achieving better strength they had treated the pellets using CO2 gas which adds additional cost and time.
Ammasi and J Pal, 2017 attempted to develop indurated pellets using the blast furnace flue dusts. They had used iron ore fines, coal, coke powder along with blast furnace flue dust for making the pellets using bentonite as inorganic binder. After generation of the pellets they had achieved the pellet strength by induration process at 1280°C temperatures which also adds additional cost and time.
P K Singh et.al, 2017 developed the indurated pellets for utilization in the sintering process. They conducted pot sinter tests and found these can be used as the replacement of coke breeze in sinter making process. The induration adds additional cost and time.

OBJECTIVES
It is therefore an object of the invention to generate cold-bonded green micro pellets using blast furnace sludge as feed.
Another objective of invention is to generate cold-bonded micro-pellets with comparable DSN (drop strength number) and DCS (dry crushing strength).

DISCLOSURE OF THE INVENTION
The present invention provides a method for developing a cold-bonded micro-pellets, the method comprising:
forming a mixture of a dried blast furnace sludge with an organic binder, the organic binder being in 0.2 – 1 wt.% of blast furnace sludge; and
pelletizing the mixture in a disk pelletizer for residence time of 1-1.5 min.
The organic binder is sodium lignosulphate or calcium lignosulphate.
The cold-bonded micro-pellets size obtained is 90% with passing 10 mm.
The preferred amount of water sprayed during pelletizing in the mixture is 25-30 wt% of the total weight of the mixture.
The cold bonded micro pellet is air dried for 24 hours.
In an embodiment, RPM of the disk pelletizer is 16 rpm or 20 rpm or 24 rpm.
In another embodiment, inclination of the disk pelletizer is 55 or 60 or 65.
In an embodiment, the blast furnace sludge is dried by means of pressure filter to make dried blast furnace sludge.
In a preferred an embodiment, specific gravity of the dried blast furnace sludge is 2.71 g/cc.
In a preferred an embodiment, the size of the dried blast furnace sludge is d10 1.29 µm.
In a preferred an embodiment, the size of the dried blast furnace sludge is d50 13.84 µm.
In a still another embodiment, the size of the dried blast furnace sludge is d90 58.79 µm
In a still another embodiment, the composition of the dried blast furnace sludge is Fe-33.78, SiO2-4.86, Al2O3-3.84, FeO-8.26, MgO-0.25, MnO2-0.07, Na2O-0.16, ZnO-2.77, K2O-0.17, CaO-1.62, Fe(M)-0.35, Combustible 35.6.

BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 shows a method for developing cold-bonded micro-pellets in accordance with an embodiment of the invention.
FIG. 2 shows an XRD spectrum of a dried blast furnace sludge/PF feed sample in accordance with an embodiment of the invention - H: Hematite, M: Magnetite, C: Iron carbide, Q: quartz.
FIG. 3 shows an SEM analysis of a dried blast furnace sludge in accordance with an embodiment of the invention.
Fig. 4 shows the effect of pelletization time on particle size distribution of micropellets for 1.0% sodium lignosulphate in accordance with an embodiment of the invention
FIG. 5 and FIG. 6 shows the effect of pelletisation time on DSN and DCS in accordance with an embodiment of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS
With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity. The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the disclosure to achieve one or more of the desired objects or results. Throughout this specification, the word “comprise”, or variations such as “comprises” or “comprising” or “containing” or “has” or “having”, or “including but not limited to” wherever used, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment may be included in at least one embodiment of the present disclosure. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification may not necessarily all refer to the same embodiment. It is appreciated that certain features of the disclosure, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the disclosure, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination.
In accordance with an embodiment of the invention, a method (100) for developing cold-bonded micro-pellets is shown in FIG. 1. The method (100) comprises:
step (104) for forming a mixture of a dried blast furnace sludge with an organic binder, the organic binder being in 0.2 – 1 wt.% of blast furnace sludge; and
step (108) for pelletizing the mixture in a disk pelletizer for residence time of 1-1.5 min.
In an embodiment, the organic binder is sodium lignosulphate or calcium lignosulphate. The preferred range of the organic binder is 0.8-1wt.%.
The blast furnace sludge contains a lot of moisture which needs to be dried for pelletising by means of pressure filter to make dried blast furnace sludge. The BF sludge is dried in a dryer. The moisture content of the dried blast furnace sludge is below 5% of wt. of the dried blast furnace sludge.
The size of the dried blast furnace sludge is mostly ultra-fine particles of less than 45 µm in size. The size is d10 is 1.29 µm, d50 is 13.84 µm and d90 is 58.79 µm. The assay of the blast furnace sludge used is given in Table 1 below.

Table 1 Assay analysis of blast furnace sludge
Fe SiO2 Al2O3 FeO MgO MnO2 Na2O ZnO K2O CaO Fe(M) Combustible Rest
33.78 4.86 3.84 8.26 0.25 0.07 0.16 2.77 0.17 1.62 0.35 35.6 Non-traceable impurities
The chemical assay shows the dried blast furnace sludge has substantial iron and combustible values and with negligible metallic iron. Specific gravity of the dried blast furnace sludge is 2.71 g/cc.
XRD spectrum (shown in FIG. 2), indicates that the blast furnace sludge contains iron mostly in hematite, and magnetite phase. Further, it is observed that iron carbide phase also exists along with quartz phase in the sample.
SEM analysis (shown in FIG. 3) indicates significant quantity of carbon particle present in the sample along with iron. Further analysis is shown in Table 2 below.

Table 2
Spectrum Carbon Oxygen Aluminum Silicon Sulfur Calcium Iron Zinc
1 23.8 30.75 NA 0.14 NA NA 45.31 NA
2 24.15 32.01 NA NA NA NA 43.84 NA
3 96.16 3.28 NA NA NA NA 0.56 NA
4 35.61 26.97 1.61 NA 0.35 0.2 31.71 3.24
Mean 44.93 23.25 1.61 NA 0.35 0.2 30.35 3.24
The RPM of the disk pelletizer is maintained at 16-24. The preferred RPM being 16, 20 and 24.
The inclination of the disc pelletizer is maintained at 55-65 degrees. The preferred inclination of the disc pelletizer being 55, 60, 65.
During pelletization, amount of water sprayed is 25-30% of the total weight of the mixture. The water sprayed aids in bonding. The desired amount of water is sprayed throughout the processing time in a gradual manner. The water is preferred at 30 wt% of the mixture.
Post pelletization, the cold bonded micro pellet is air dried for 24 hours.
The cold-bonded micro-pellets size obtained as per the method (100) is 90% with 10 mm passing.

Experimental Analysis:
Here, an attempt is made to develop cold-bonded micro-pellets using blast furnace sludges. The feed (blast furnace sludge) is mixed and the green micro pellets are prepared and at different operating conditions varying the palletization time, lignosulphate %, etc. as mentioned in Table 3.
Table 3
Expt. No. Time, mins Moisture (%) Organic binder % Avg. DSN Avg. GCS D50, mm
1 1 25 0.2 4 60 0.9
2 1.5 30 0.2 27 105 5.2
3 1 25 0.6 27 105.3 3
4 1.5 30 0.6 50 143.7 6.5
5 1 25 1 43 106.3 3.2
6 1.5 30 1 35 132.7 5.4
7 1 10 0.2 generated green pellets (couldn’t be screened not enough strength)
8 1.5 12 0.6 generated green pellets (couldn’t be screened not enough strength)

A mixture is formed of the dried blast furnace sludge with sodium lignosulphate as binder. The sodium lignosulphate is 0.2 to 1.0 wt.% of the dried blast furnace sludge. The mixture is pelletized in the disk pelletizer for residence time of 1-1.5 min.
The cold bonded micro pellet is air dried for 24 hours.
RPM and angle of the disk pelletizer was maintained between 16-24 degrees.
The mixture contains a minimum moisture content of 25% to 30% for effective micro-pellet formation.
The conventional cold bonded micro pellets have the avg. Drop Strength No (DSN) and avg. Green Crushing Strength (GCS), using bentonite as binder, as shown below in Table 4.
Table 4
Expt. No. Time, mins Avg. DSN Avg. GCS %(-6.3+2) D50, mm
T2 2 12 77 22.15686 1.0
T3 3 18 109 74.55268 3.4
T4 4 12 76 31.44531 2.1
T5 5 9 98 70.04132 3.25
T6 6 7 67 28.33333 1.8
It’s evident that there is an increment of Avg. GCS as well as Avg. DSN when compared the conventional (in Table 4) with claimed process (100) to produce cold bonded micro pellet.
Fig. 4 shows the effect of pelletization time on particle size distribution of micropellets for 1.0% sodium lignosulphate. It is evident that most of the cumulative wt% passing is achieved between 6-7 mm micropellet size when pelletized either for 1 min or 2 min.
Fig. 5 shows the effect of pelletisation time on DSN with micro pellet size varying from -6.3+4, -5+4, -4+3.15, -3.15+2 for time 1 min and 2 min.
Fig. 6 shows the effect of pelletisation time on DCS with micro pellet size varying from -6.3+4, -5+4, -4+3.15 for time 1 min and 2 min.

It is to be understood that the foregoing descriptive matter/preferred embodiments is illustrative of the disclosure and not a limitation. While considerable emphasis has been placed herein on the particular features of this disclosure, it will be appreciated that various modifications can be made, and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. Those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein. Similarly, additional embodiments and features of the present disclosure will be apparent to one of ordinary skill in art based upon description provided herein.
Descriptions of well-known/conventional methods/steps and techniques are omitted so as to not unnecessarily obscure the embodiments herein. Further, the disclosure herein provides for examples illustrating the above described embodiments, and in order to illustrate the embodiments of the present disclosure certain aspects have been employed. The examples used herein for such illustration are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the following examples should not be construed as limiting the scope of the embodiments herein.

INCORPORATION BY REFERENCE
All references, articles, publications, patents, patent publications, and patent applications cited herein are incorporated by reference in their entireties for all purposes. However, mention of any reference, article, publication, patent, patent publication, and patent application cited herein is not, and should not be taken as, an acknowledgment or any form of suggestion that they constitute valid prior art or form part of the common general knowledge in any country in the world.