Claims:We Claim:

1. A process for manufacture of granulated fuel sources for efficient conversion of 0.5 mm size fines into + 3 mm size suitable for sinter making comprising:
providing said fuel sources selected from coal and coke including combinations thereof of size below 3.15 mm including fines below 0.5 mm size coal/coke and selectively granulate the same with binder selected from coal tar and sodium silicate in a granulator whereby granulated coal/coke is produced with significant reduction in <0.5mm coal/coke size fraction based on the starting feed coal/coke fines of <0.5 mm size coal/coke in the range of 35to 40%.

2. The process as claimed in claim 1 wherein the said fuel source of coal/coke used comprised of size below 3.15 +2mm in amounts of 15 to 21% by wt, -2+1 mm in amounts of 20 to 25% by wt , -1+ 0.5 mm in amounts of 20 to 25% by wt and fines of <0.5 mm size coal/coke in amounts of 35 to 40 % by wt with said select binder with coal/coke: binder in proportions of 8 to 10: 12 to 14 % by wt. preferably 8 to 10 : 8 to 14% by wt respectively.

3. The process as claimed in anyone of claims 1 or 2 wherein said binder coal tar addition to said fuel sources selected from coal and coke including coal/coke fines of <0.5 mm size coal/coke in amounts of up to 14 % provided for the reduction of coal/coke size fines <0.5 mm from 37.4% to 0.1 and increase in the +3 mm size of coal/coke from 0% (base case) to 52.3%; and

wherein said binder sodium silicate addition to said fuel sources selected from coal and coke including coal/coke fines of <0.5 mm size coal/coke in amounts of up to 8 % provided for
the reduction of coal/coke size fines <0.5 mm from 37.35 % to 6.86% and increase in the +3 mm size of coal/coke from 0% (base case) to 26.18%.

4. Granulated coal/coke suitable for use in sintering of +3 mm size which is a granulated conversion product of combination of coal/coke of size below 3.15 +2mm in amounts of 15 to 21% by wt, -2+1 mm in amounts of 20 to 25% by wt , -1+ 0.5 mm in amounts of 20 to 25% by wt and fines of <0.5 mm size coal/coke in amounts of 35 to 40 % by wt.. and binder selected from coal tar and sodium silicate in amounts of 8 to 14 % by wt..including said fines of <0.5 mm size coal/coke in amounts of 35 to 40 % by wt converted into +3 mm size form for better access to oxygen for effective combustion.

5. A process for sinter production with reduced internal fine generation and efficient quality sinter produce comprising:

i) providing granulated fuel sources including anyone or more of granulated coal and coke including +3 mm size which is a granulated conversion product of combination of granulated fuel source involving coal/coke of size below 3.15 +2mm in amounts of 15 to 21% by wt, -2+1 mm in amounts of 20 to 25% by wt , -1+ 0.5 mm in amounts of 20 to 25% by wt and fines of <0.5 mm size coal/coke in amounts of 35 to 40 % by wt.. and binder selected from coal tar and sodium silicate in amounts of 8 to 14 % by wt.;
ii) providing a sinter feed mix comprising of iron ore fines along with other usual sinter feed along with said granulated fuel sources selected from coal/coke including combinations thereof in mixing drum;
iii) carrying out the sintering including said granulated coal/coke along with the sinter feed mix following standard/ regular sintering technology to thereby produce sinter with reduced internal fine generation by 6.4 to 22.1 % with respect to use of only coke fines and without said granulated coal/coke in sinter mix.

6.The process for sinter production as claimed in claim 5 wherein said step of providing granulated coal/coke include said coal/coke fines of <0.5 mm size coal/coke comprises:
granulated coal/coke including said coal/coke fines of <0.5 mm size coal/coke suitable for sinter making comprising:

providing said coal/coke including said fines of <0.5 mm size coal/coke and selectively granulate the same with binder selected from coal tar and sodium silicate in a granulator whereby granulated coal/coke is produced with significant reduction in <0.5mm coal/coke size fraction based on the starting feed coal/coke fines of <0.5 mm size coal/coke in the range of 35-40 %.

7. The process for sinter production as claimed in anyone of claims 5 or 6 wherein the fuel source including said coal/coke fines of <0.5 mm size coal/coke with said select binder is carried out including said coal/coke fines of <0.5 mm size with said fuel source coal/coke: binder in proportions of 8 to 10:12 to 14 % by wt. preferably with said fuel source coal/coke: binder in proportions of 8 to 10: 8 to 14 % by wt..

8. The process for sinter production as claimed in anyone of claims 5 to 7 comprising:
carrying out a primary dry mixing of sinter feed mix charge along with said granulated coal/coke in a primary mixing drum wherein said sinter feed mix include iron bearing materials 79 to 84% by wt., limestone 4 to 6 % by wt. dolomite 5 to 7 % by wt., quick lime 2.2 to 3.3 and coal fines amounts of up to5.2to 5.5%;
carrying out a secondary wet mixing of the said sinter mix charge mix with said granulated coal/coke
charging of green mix and carrying out sintering;
generating sinter products and cooling the same.

9. The process for sinter production as claimed in anyone of claims 5 to 8 wherein sinter feed mix and pre-granulated coal/coke 5.2-5.5% by wt. is added in mixer drum and first carrying out said dry mixing for a period of 4 to 6 minutes, preferably about 5 minutes and at 19 -21 rpm preferably about 20 rpm and after the completion of dry mixing, water in amounts of 6.66-7.33% by wt. is added for nodulization in wet mixing and again rotated for 4 -6 min preferably 5 minutes and at 19 - 21 rpm preferably about 20 rpm such as to maintain moisture in the mix in the range of 8.1-8.2%.

10. The process for sinter production as claimed in anyone of claims 5 to 9 wherein
coal/coke fines of < 0.5 mm size coal/coke which lead to adhering layer of sinter granules are converted into granules of size +3 mm for better access to oxygen and improving the coal combustion in sinter bed resulting in improvement in sinter properties including improved sinter yield from 83.0% to 83.7% with sodium silicate & from 79.0 to 83.8% with coal tar; similarly, Tumbler Index increases from 59.5% to 61.6% with sodium silicate & from 57.1% to 61.7% with coal tar with the use of coal tar binder in granulated coal/coke of 14 % the sinter yield increases by 6.1%, tumbler index by 4.4% and internal fine generation decreased by 22.3%, while with the use of sodium silicate binder in granulated coal/coke of 8.0% the sinter yield increased by ~1 %, tumbler index by 3.5 % and internal fine generation decreased by 6.4%.

Dated this the 8th day of September, 2021
Anjan Sen
Of Anjan Sen & Associates
(Applicant’s Agent)
IN/PA-199
, Description:FORM 2
THE PATENT ACT 1970
(39 OF 1970)
&
The Patent Rules, 2003
COMPLETE SPECIFICATION
(See Section 10 and Rule 13)

1 TITLE OF THE INVENTION :
A METHOD FOR SINTER MAKING USING GRANULATED COAL/COKE FOR ACHIEVING IMPROVED SINTER PROPERTIES.



2 APPLICANT (S)

Name : JSW STEEL LIMITED.

Nationality : An Indian Company.

Address : Dolvi Works, Geetapuram, Dolvi, Taluka Pen, Dist. Raigad, Maharashtra-402107,India; Having the Registered Office at
JSW CENTRE,BANDRA KURLA COMPLEX,BANDRA(EAST), MUMBAI-400051, STATE OF MAHARASHTRA,INDIA.




3 PREAMBLE TO THE DESCRIPTION

COMPLETE

The following specification particularly describes the invention and the manner in which it is to be performed.

FIELD OF THE INVENTION:

The present invention relates to a method of sinter making, and more particularly, to sinter making with addition of pre-granulated fuel source like coal and coke including combinations thereof prepared in a granulator (disc pelletizer/mixer drum)using selective binder, along with other sinter feed mix to produce a feed mix for sintering process. Importantly, the present invention is directed to a simple, cost effective, and environment friendly process for sinter production ensuring improved sinter yield, and higher productivity by utilizing pre-granulated coal.

BACKGROUND OF THE INVENTION:

The existing system in sinter making utilizes raw material like iron ore fines, limestone, dolomite, mill scale, GCP dust, quicklime, flue dust and coal/coke fines as a fuel to produce the sinter for use as input raw material to blast furnace. The said sinter feed mix is mixed in a mixing drum to produce granules. Out of the above sinter feed mix, coke fines is the major source of heat in sintering process and provides more than 80% of heat for sintering(L. Xiong, Powder Technology,340 (2018), 131).

During sinter feed mix preparation with as–received un-sieved coke, micrographs of coke particles were taken to illustrate the position of coke particles during granulation.
Coke fines traditionally used in sintering process are classified as coarse (coke size>1 mm), intermediate (1-0.25 mm) and fines (<0.25 mm)(C.S. Teo, ISIJ Int. vol.32, (1992), 1047).It was observed that coarse coke particle does not participate in granulation because of its hydrophobic nature. Intermediate coke particles attached on the outside of adhering layer of granules while the fine coke particles disperse well in the adhering fine layer of granules. This phenomenon occurs because fine coke particles have very good adhering properties and can be incorporated into the adhering fine layers easily and early. Location of coke particles on granules formed after granulation has a direct effect on sintering process. Coarser coke particles are free and hence have a direct access to oxygen will increase the combustion rate but affects the combustion efficiency. The coke fines (<0.25 mm size) which are embedded in adhering fine layer of granules have poor access to oxygen and this coke particle extends the trailing edge of the combustion zone.

Granulation of coke fines is not new, researchers like F.M Mohammed (Science of Sintering • May 2010) and M. Niesler (METALURGIJA 53 (2014) 1, 37-39) have used a particular size of coke to granulate and used in sintering process. F.M Mohammed and M. Niesler granulated only -<0.5 mm size coke with binder molasses and hydrated lime. Both the work shows improvement in sinter quality with the use of granulated coke using molasses and hydrated lime. However, both of these works have a limitation that they add additional processing steps: 1. screening/ separation, 2. Granulation. Further, use of molasses has additional step of drying of the granules.

Selectively granulating only <0.5 mm size coke particle is not feasible in actual industrial process in integrated steel plant as it generally contains moisture (10-16%) which makes the separation (sieving) difficult. Separating a particular size fraction of coke adds an additional processing step and requires capital investment. Separate granulation and briquetting plant has been established which granulates and briquettes the waste fine (size majorly 150 microns) to be used after keeping it for drying for several days. This requires additional space and capital expenditure.

Since coal/coke is the major source of heat input to the sintering process and contains approximately 35%, <0.50 mm fines. A pressing requirement for better granulation of coal/ coke with suitable binder is felt, which can increase the coal combustion efficiency with minimum capital and inventory requirement.

Sintering process requires fuel as a part of process requirement to provide required heat for the reactions. Most of the time, this heat requirement is met with the help of coke breeze and many sinter plants uses coal fines, whereas, some uses combination of the both in some proportion. Although there is some difference in calorific value & volatile matter content of coal & coke, the decision to select the type of fuel mostly depends on the availability & cost. Xin Zhang et al (Nature research 11, (2021), 1540) has reported that granulation behaviour of coke is similar to that of coal.

The present advancement is thus targeted at meeting need in the art to develop new methods of sintering involving such coal and coke based fuel sources in sinter feed mix to improve the quality of sinter.

OBJECTS OF THE INVENTION:

The basic object of the present innovation is thus directed to a process for sintering iron ore involving pre-granulated fuel source like coal and coke including combinations thereof in sinter feed mix during granulation in mixer drum to improve sinter yield and reduce return fine generation.

A further object of the present innovation is to provide a process for granulating such fuel sources like coal ,coke with binder sodium silicate and coal tar such that the <0.5 mm % size of coal/coke is reduced.

A further object of the present innovation is to provide a process for sinter production using pre-granulated coal/coke in sinter mix, favored decrease of<0.5 mm coal size from 37.4% to 6.8, 3.2, 0.9 & 0.5% using 8, 10, 12 & 14% sodium silicate and 37.4% to 11.9, 4.1, 1.2 and 0.1%using 8, 10, 12 & 14% coal tar binder respectively. The decreased % of <0.5 mm size of coal/coke will lead to increase of +3 mm coal fine after granulation in a granulator.

A still further object of the present innovation is to provide a process for sinter production using pre-granulated coal/coke in sinter mix, favored increase in sinter strength. The increase in sinter strength is mainly due to use of sodium silicate & coal tar binder, which leads to the decrease in <0.5 mm size coal/coke and restricted its entry in adhering fine layer of granules formed during sinter feed mix preparation.

A still further object of the present innovation is to provide a process for sinter production using pre-granulated coal. Coke in sinter mix, favored increase in sinter strength. The increase in sinter strength results in reduction of fines from 17.3 % to 16.2% with 8% sodium silicate addition for granulating coal, coke as no significant change is observed beyond 8%. Similarly, with coal tar addition to coal fines, internal fine generation is reduced from 20.8 to 16.2% with 14% coal tar addition.

A further object of the present innovation is to provide a process for sinter production using pre-granulated coal, coke in sinter mix, for optimizing the % of coal binder. A maximum of 8% sodium silicate binder performed better for sinter strength. Further increase in sodium silicate % indicates no significant change in sinter properties.

A further object of the present innovation is to provide a process for sinter production using pre-granulated coal, coke in sinter feed mix with sodium silicate as a binder, with no significant change in alkali % in chemical composition. The alkali load in blast furnace causes scaffolding and hanging in blast furnace.

SUMMARY OF THE INVENTION

The basic aspect of the present invention is directed to a process for manufacture of granulated fuel sources for efficient conversion of 0.5 mm size fines into + 3 mm size coal/coke suitable for sinter making comprising:
providing said fuel sources selected from coal and coke including combinations thereof of size below 3.15 mm including fines below 0.5 mm size coal/coke and selectively granulate the same with binder selected from coal tar and sodium silicate in a granulator whereby granulated coal/coke is produced with significant reduction in <0.5mm coal/coke size fraction based on the starting feed coal/coke fines of <0.5 mm size coal/coke in the range of 35 to 40 % by wt.

A further aspect of the present invention is directed to said process wherein the said fuel source of coal/coke used comprised of size below -3.15 +2mm in amounts of 15 to 21% by wt, -2+1 mm in amounts of 20 to 25% by wt, -1+ 0.5 mm in amounts of 20 to 25% by wt and fines of <0.5 mm size coal/coke in amounts of 35 to 40 % by wt with said select binder with coal/coke: binder in proportions of 8 to 10 : 12 to 14 % by wt. preferably 8 to 10 : 8 to 14% by wt respectively.

A still further aspect of the present invention is directed to said process wherein said binder coal tar addition to said fuel sources selected from coal and coke including coal/coke fines of <0.5 mm size coal/coke in amounts of up to 14 % provided
for the reduction of coal/coke size fines <0.5 mm from 37.4% to 0.1 and increase in the +3 mm size of coal/coke from 0% (base case) to 52.3%; and
wherein said binder sodium silicate addition to said fuel sources selected from coal and coke including coal/coke fines of <0.5 mm size coal/coke in amounts of up to 8 % provided for
the reduction of coal/coke size fines <0.5 mm from 37.35 % to 6.86% and increase in the +3 mm size of coal/coke from 0% (base case) to 26.18%.

A still further aspect of the present invention is directed to Granulated coal/coke suitable for use in sintering of +3 mm size which is a granulated conversion product of combination of coal/coke of size below 3.15 +2mm in amounts of 15 to 21% by wt, -2 +1 mm in amounts of 20 to 25% by wt , -1+ 0.5 mm in amounts of 20 to 25% by wt and fines of <0.5 mm size coal/coke in amounts of 35 to 40 % by wt. and binder selected from coal tar and sodium silicate in amounts of 8 to 14 % by wt. including said fines of <0.5 mm size coal/coke in amounts of 35 to 40 % by wt converted into +3 mm size form for better access to oxygen for effective combustion.

A still further aspect of the present invention is directed to a process for sinter production with reduced internal fine generation and efficient quality sinter produce comprising:
i) providing granulated fuel sources including anyone or more of granulated coal and coke including +3 mm size which is a granulated conversion product of combination of granulated fuel source involving coal/coke of size below 3.15 +2mm in amounts of 15 to 21% by wt, -2 +1 mm in amounts of 20 to 25% by wt , -1+ 0.5 mm in amounts of 20 to 25% by wt and fines of <0.5 mm size coal/coke in amounts of 35 to 40 % by wt.. and binder selected from coal tar and sodium silicate in amounts of 8 to 14 % by wt.;
ii) providing a sinter feed mix comprising of iron ore fines alongwith other usual sinter feed alongwith said granulated fuel sources selected from coal/coke including combinations thereof in mixing drum;
iii) carrying out the sintering including said granulated coal/coke alongwith the sinter feed mix following standard/regular sintering technology to thereby produce sinter with reduced internal fine generation by 6.4 to 22.1 % with respect to use of only coke fines and without said granulated coal/coke in sinter mix.

A still further aspect of the present invention is directed to said process for sinter production wherein said step of providing granulated coal/coke include coal/coke fines of <0.5 mm size coal/coke comprises:
granulated coal/coke including said coal/coke fines of <0.5 mm size coal/coke suitable for sinter making comprising:
providing said coal/coke including said fines of <0.5 mm size coal/coke and selectively granulate the same with binder selected from coal tar and sodium silicate in a granulator whereby granulated coal/coke is produced with significant reduction in <0.5mm coal/coke size fraction based on the starting feed coal/coke fines of <0.5 mm size coal/coke in the range of 35 to 40% .

Another aspect of the present invention is directed to said process for sinter production wherein the said fuel source including coal/coke fines of <0.5 mm size coal/coke with said select binder, experiment is carried out including said coal/coke fines of <0.5 mm size with said fuel source coal/coke : binder in proportions of 8-10%&12-14 % by wt. preferably with said fuel source coal/coke: binder in proportions of 8 to 10: 8-14 % by wt.
Yet another aspect of the present invention is directed to said process for sinter production comprising:
carrying out a primary dry mixing of sinter feed mix charge alongwith said granulated coal/coke in a primary mixing drum wherein said sinter feed mix include iron bearing materials 79-84% by wt., limestone 4-6 % by wt. dolomite 5-7 % by wt., quick lime 2.2-3.3 and coal 5.2-5.5 % by wt.
carrying out a secondary wet mixing of the said sinter mix charge mix with said granulated coal/coke;
charging of green mix and carrying out sintering;
generating sinter products and cooling the same.

A further aspect of the present invention is directed to said process for sinter production wherein sinter feed mix and pre-granulated coal/coke5.2 to 5.5% by wt. is added in mixer drum and first carrying out said dried mix for a period of 4 to 6 preferably about 5 minutes and at 19 to 21 rpm preferably about 20 rpm and after the completion of dry mixing, water in amounts of 6.66 to 7.33 % by wt. is added for nodulization and wet mixing and again rotated for 4 to 6 min preferably 5 minutes and at 19 to 21 rpm preferably about 20 rpm such as to maintain moisture in the mix in the range of 8.1 to 8.2%.

A still further aspect of the present invention is directed to said process for sinter production wherein
coal/coke fines of < 0.5 mm size coal/coke which lead to adhering layer of sinter granules are converted into granules of size +3 mm for better access to oxygen and improving the coal combustion in sinter bed resulting in improvement in sinter properties including improved sinter yield from 83.0% to 83.7%with sodium silicate &from 79.0 to 83.8% with coal tar; Similarly, Tumbler Index increases from 59.5% to 61.6% with sodium silicate & from 57.1% to 61.7% with coal tar and wherein
with the use of coal tar binder in granulated coal/coke of 14 % the sinter yield increased by 6.1%, tumbler index by 4.4% and internal fine generation decreased by 22.3% while with the use of sodium silicate binder in granulated coal/coke of8 % the sinter yield increased by 1 %, tumbler index by 3.5 % and internal fine generation decreased by 6.4%.

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

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

Figure 1: shows the flow chart for existing sintering process.
Figure 2: shows the flow chart for the sintering process according to present invention a) modified process b) flow chart for granulating coal involving granulation of coal fines using binder coal.
Figure 3: illustrates schematic of pot sinter unit utilized for experimental trials according to the present invention.
Figure 4: Sorting of binder after granulation a) Size analysis without shatter test b) Size analysis after shatter test.
Figure5:Change in sinter properties a) sinter yield b) Tumbler Index and c) Productivity and d) internal fine with the use of pre-granulated coal using coal tar as a binder.
Figure 6: Change in granulometry of coal after granulation with coal tar a) <0.5 mm size coal and b) + 3 mm size coal (0% is base case).
Figure 7: Change in sinter properties a) sinter yield b) Tumbler Index and c) Productivity and d) internal fine with the use of pre-granulated coal using sodium silicate as a binder.
Figure 8: Change in granulometry of coal after granulation with sodium silicate a) <0.5 mm size coal and b) + 3 mm size coal (0% is base case).

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS

The present invention is directed to a process for sinter production with improved quality of coal and/or coke granulation using granulator and its addition in sinter feed mix for higher sinter yield and reduce internal fine generation.
While the process of the present advancement is illustrated hereunder based on the advancement in involving pre-granulated coal as the fuel source for sintering process and its unique and surprisingly special advantages, the same is equally applicable involving pre-granulated coke or combinations of coal and coke as the fuel source for the advanced sintering method of the present invention.
Sintering is a technology for agglomeration of iron ore fines and other material such as limestone, dolomite, quicklime, and coal fines into useful Blast furnace burden material for hot metal production. The raw materials used for sintering are of different sizes such as iron ore fines (-10 mm), coke breeze, limestone, dolomite, and return sinter (-5 mm). The proportioned raw material is then mixed and moistened using normal process water in a mixer drum. The mix is then loaded on sinter machine through a feeder on a moving grate to produce product sinter. Accompanying Figure 1 shows the flow chart for existing sintering process.

More particularly, the present innovation relates to a new method for sintering wherein the addition of coal fines in sinter feed mix is replaced by addition of “pre-granulated coal” in a granulator to reduce the <0.5 mm fraction of coal fines and improve sinter yield and internal fine generation.
In the new method, coal fines as received from sinter plant is granulated in a granulator with varying % of binder, sodium silicate and coal tar separately and added in sinter mix for wet mixing and granulation in mixer drum in place of adding coal fines without granulation in mixer drum.
Therefore, such as herein described is a new method of sintering process for achieving higher sinter yield comprising the steps: providing sinter raw mix such as iron ore fines, and other material such as limestone, dolomite, quicklime, and coal fines in weighed proportion and then transfer of the sinter raw mix through conveyer in the primary mixer drum first, where dry mixing of sinter feed mix takes place and then it is transferred to nodulizer (or secondary mixer drum) where water for moistening the feed mix is added to obtain granulated sinter feed mix. Accompanying Figure 2 shows the flow chart for the sintering process according to present invention involving granulation of coal fines using binders.
When coal fines are granulated in a granulator, the coal fines surface is wetted and subsequently coated with sodium silicate and coal tar binder. At the point of contact between particles, sodium silicate and coal tar binders causes bridges to form. Subsequent rotation inside a granulator and contact of individual coal fines wetted with sodium silicate &coal tar each containing one or many ore grains resulting in granulation.
In the new method, addition of sodium silicate or coal tar binder (8, 10, 12 & 14% of coal mass) in a granulator along with coal fines, the added binder facilitates the easy wettability and improves the granulation of coal fines. This has resulted in reduction of coal fines (<0.5 mm) size from 37.4 to 0.5 with binder sodium silicate and to 0.1% with coal tar binder. This decreased amount of <0.5 mm coal fines have led to the formation of +3 mm size coal granule due to the granulation process. The +3 mm coal granule increased from 0 % (as received coal) to 34.8% with addition of sodium silicate binder and to 52.3% with coal tar binder with 14% binder mass % in coal fines. When this granulated coal is added in sinter feed mix, an improvement in sinter properties is observed which might be due to better access of coal fines to oxygen which in earlier cases a major fraction of coal (<0.5 mm) size gets absorbed in adhering fines layer. The presence of <0.5 mm coal fines in adhering fines layer of sinter granules has a poor access to oxygen. Thus, affecting the combustion behavior in sinter bed affecting sinter properties.
The disclosed method of addition of “pre-granulated” coal fines in sinter feed mix for effective combustion with increase in sinter yield and reduction in internal fine generation has been successfully designed, developed and established through laboratory based pot sintering trials. Pre – granulated coal with 8,10, 12, and 14% sodium silicate and coal tar binder have been added to sinter feed mix in sintering process and pot sintering test were done to find out the effect of “pre-granulated” coal fines addition on sinter properties like sinter yield and tumbler index and its effect on sinter chemistry.
Pot sintering was carried out on a laboratory scale pot sinter equipment as shown in accompanying Fig.3, with the actual sinter feed mix used for making sinter in sinter plant. Conventional process uses coal fines as –received un-sieved coal in sinter feed mix for making sinter.Continuous rotation of material was carried out for five minutes in nodulizer for producing agglomerates of sinter feed mix. Sufficient number of pot sintering experiments were carried out after granulating coal with varying % of sodium silicate and coal tar as a binder addition. Binder was used to granulate coal as it contains approximately 37.5% of <0.5 mm size coal. These coal fines because of smaller size during granulation are present in adhering fines layer of sinter granules which has poor access of oxygen and cause delayed combustion.
To granulate the <0.5 mm size coal in a granulator, various binders like coal tar, sodium silicate, Portland cement and quicklime were used. After allowing for overnight drying, size analysis and shatter test (5 drops from height of 1 meter) were done to analyze the abrasion. Figure 4 shows that size analysis done without shatter test shows that <0.5 mm size of coal is reduced more with sodium silicate and coal tar compared to Portland cement. Quick lime use as a binder makes the coal sluggish and hence cannot be sieved, therefore, rejected. Furthermore, shatter test was done for coal fines granulated with sodium silicate and coal tar to analyze its abrasion resistance. Shatter test results shows that coal tar and sodium silicate led to significant reduction in <0.5mmcoal size fraction.
Therefore, pot sinter experiments were conducted using granulated coal with coal tar& sodium silicate binder. Various process data during pot sintering test were collected for analysis to understand the technological benefits/changes in sinter properties due to addition of “pre-granulated” coal with different % of binder sodium silicate and coal tar.
The following procedure was followed in the experimental trials of pot sintering tests:

POT SINTERING TESTS
a) Preparation of samples for physico-chemical analysis:
All the raw material samples are subjected to both chemical and physical analysis tests. In the physical analysis test the raw materials are screened to different size fractions shown in Table -1, and chemical analysis of the feed mix is done by using XRF shown in Table-2.
Table 1 Size distribution of raw materials (mass%)
Sieve size (mm)
Raw material -10+8 -8+6 -6+3 -3+1 -1+0.5 -0.5+0.15 -5
Iron ore 16.5 35.5 26.5 10 9.5 2
Limestone 35 30 35
Dolomite 35 30 35
Return fine 100
Coal 40 30 30
Also, Quicklime is used as -3 mm

Table-2 Chemical analysis of sinter feed mix
Raw materials Fe(T) SiO2 Al2O3 CaO MgO Moisture LOI
Iron ore 59.8-64.5 2.5-5.4 1.8-4.1 0.08-1.29 0.03-0.39 6.0-11.2 2.1-4.8
Limestone 0.6-4.0 0.8-1.9 0.2-0.4 47.3-54.9 0.8-7.2 1.1-3.9 38.9-42.5
Dolomite 0.1-4.5 0.2-5.2 0.3-0.8 32.8-50.5 5.7-19.0 0.9-4.5 39.6-45.1
Quicklime 0.5-1.5 2.3-4.6 0.2-0.8 73.4-90.7 1.8-4.6 -- 3.1-18.3
Coal 0.4-0.6 4.6-7.7 3.0-4.4 0.4-0.7 0.1-0.2 5.9-7.3 81.1-84.1
Return fine 52.2-56.3 4.3-5.5 2.7-3.9 9.68-13.1 1.8-3.5 -- --

b) Charge calculations for pot sinter experiments:
Charge calculations for pot sinter experiments were done on the basis of four equations:
• FeO%
• LOI balance
• Total Fe
• MgO balance
Once the required compositions percentage of different raw materials are found out using the above mass balance equations, the raw material is weighed using electronic balance. Sinter feed mix distribution (mass%) is shown in following Table 3:

Table 3:Sinterfeed mix distribution (mass%)
Sr.No. Raw material mass%
1 Iron bearing material 79-84
2 Limestone 4-6
3 Dolomite 5-7
4 Quicklime 2.2-3.3
5 Coal 4.5-5.2

Pot sinter experiment plan were designed with three repeat trials. Pot sinter test conditions are shown in following Table-4.
c) Granulation of coal fines with binders

As received unsieved coal below 3.15 mm size is provided and granulated it with the help of binders.
Typical size distribution of coal is as shown below:

Sieve size (mm)
5
-5+4
-4+3.15
-3.15+2
-2+1
-1+0.5
-0.5
Wt% 15 to21 20 to25 20 to25 35 to 40

After weighing of coal fines, the moisture of coal fines is maintained to 10% and then all the material is fed to a granulator. A weighed amount (8, 10, 12 & 14% of coal mass) of binders such as coal tar, quick lime, cement and sodium silicate binders are used for granulating the coal in a granulator. The granulator is rotated at 20 rpm for a period of 10 minutes for a through mechanized mixing. This has led to an increase of +3 mm size of coal and decrease in <0.5mm size coal. The 0.5 mm size coal which has converted into +3 mm size has now had better access to oxygen for carrying out the combustion. Once the coal fines are granulated, a shatter test from a height of 1 m is given for each binder addition case and change in <0.5 mm fraction is calculated after sieving. The result of shatter test (5 drops) shows that coal tar and sodium silicate binder is more effective in reducing the coal fines <0.5 mm size fraction. Both the binders are used for granulating coal and used in pot sinter experiments for analysis of its effect on sinter properties.

d) Mixing of pre-granulated coal along with sinter feed mix in mixing drum
The weighed amount of sinter feed mix and pre-granulated coal is added in mixer drum and first dry mixed for a period of 5 minutes and at 20 rpm. After the completion of dry mixing, water is added for nodulization and again rotated for 5 minutes and at 20 rpm.
After confirmation of required moisture in sinter feed mix, the sinter feed mix (approximately 75 kg) is then fed into sinter pot manually in tray after weighing in digital weighing machine.
e) Sintering process on sinter mix:
The sinter pot is geometrically cylindrical in shape with 600 mm height and 300 mm internal diameter. The bed height chosen here is as per the actual bed height maintained at the respective sinter plant. It is done so as to simulate the actual sinter plant conditions, so that the test results can be correlated.
The sinter pot with charge is mounted on top of wind box and the gap between sinter pot and wind box is sealed by nuts and bolts. Air blower of capacity 2700 mm WC is switched on to create the necessary suction beneath the grate bar. A suction of around 900 mm WC maintained during ignition (one minute) and then the suction is increased gradually to 1250 mm WC for the rest of the sintering process. During the sintering process, the suction and temperature of wind box is continuously monitored. When the wind box temperature reaches peak, it starts to decline, considering the sintering temperature. This peak wind box temperature is defined as break through point (BTP) marked as end of sintering process. Normally, in pot sinter trials the sintering time takes around 19-22 minutes.
After sintering is completed, it is kept for overnight cooling since it is very hot to handle manually. The sinter pot is then stripped to get sinter cake with the help of hoist crane. The sinter is than subjected to shatter test from a height of 2 m to simulate the star crusher activity in actual sinter plant. The sinter cake in shatter test is allowed to fall on a metal base plate of thickness 0.02 m. this test is carried out for two times to confirm the return sinter balance. After this the sinter samples are subjected to physical screening process. In this the process the sinter is classified as +40 mm, +20 mm, +10 mm, +8 mm and +5 mm fractions to estimate their percentage in the total material. The +5 mm size fractions of sinter are considered as final product of the sintering process.
Tumbler index is calculated using IS: 6495 - 1984
Table-4: Pot sinter test conditions used for pot sinter experiments.
Sr. No. Parameters Value
1 Bed height 0.60 m
2 Hearth layer/weight 0.06 m/ 7.5 kg
3 Ignition time 60 s
4 Suction during ignition 900 mm WC
5 Suction during sintering 1250 mm WC
6 Moisture 7.5 +/- 0.2 %

The process is implementable in industrial scale and all the test condition shown in Table-3 is similar to plant scale.
The following parameters were measured during the experiments:
• Sintering time
• BTP temperature
• Suction pressure
The following parameters were calculated through the experiments:
• Sinter yield
• Tumbler index (T.I)
• Productivity
Pot sinter results with pre-granulated coal fines with binder coal tar
No change in sintering time has been observed with the usage ofpre-granulated coal, using both coal tar and sodium silicate binder.
Table 5: Pot sinter test results
Expt. No. Coal tar (%) Productivity
(t/m2/hr.) Sinter yield T. I Internal fine generation
1 0 2.3 79.0 57.1 20.8
2 8 2.4 80.8 57.5 19.3
3 10 2.4 81.4 57.4 18.6
4 12 2.4 81.8 58.8 18.2
5 14 2.4 83.8 59.6 16.2

Table-6 Chemical analysis of pot sinter test results
Coal tar (%) T. Fe FeO CaO MgO SiO2 Al2O3 Na2O+K2O
0 54.7 11.65 11.43 2.01 5.07 3.83 0.07
8 54.7 11.72 11.45 1.90 4.84 3.52 0.06
10 54.4 11.83 11.38 1.98 4.82 3.57 0.10
12 54.8 12.01 11.65 1.92 4.93 3.81 0.10
14 54.4 12.30 11.47 1.95 4.94 3.85 0.09

Table-7 Change in granulometry of coal with coal tar binder
Sieve size coal size without granulation (mm) Granulated Coal size (mm, mass%)
0% 8% 10% 12% 14%
+5 19.94 28.05 31.29 42.84
-5+4 1.67 2.50 3.73 4.33
- 4+3.15 2.95 4.03 5.96 5.65
-3.15+2 18.03 16.21 16.43 18.40 19.77
-2+1 22.41 25.34 25.17 23.64 20.53
-1+0.5 22.21 22.00 19.69 15.73 6.78
-0.5 37.35 11.89 4.13 1.24 0.09

Accompanying Figure 5shows change in sinter properties a) sinter yield b) Tumbler Index and c) Productivity and d) internal fine with the use of pre-granulated coal using coal tar as a binder.
Accompanying Figure 6 shows Change in granulometry of coal after granulation with coal tar a) <0.5 mm size coal and b) + 3 mm size coal (0% is base case).
It is observed (fig.5) that the sintering properties such as sinter yield and tumbler index increases with increase in % of coal tar addition for granulating the coal fines. Sinter yield increases by 6.1%, tumbler index by 4.4% and internal fine generation decreases by 22.3% when coal tar % in granulated coal is 14%. A minor increase in productivity was observed for coaltar binder, whereas no such increase was found with sodium silicate binder is also observed. Figure 6 shows the granulometry of coal using coal tar as a binder. The coal size fines <0.5 mm reduced from 37.4% to 0.1 with 14 % coal tar addition. This decrease in <0.5 mm size coal has led to increase of +3 mm size of coal. The +3 mm size of coal has increased from 0% (base case) to 52.3% with 14% coal tar addition. Thus the% of fines which were present in adhering layer of sinter granules without coal granulation are now converted into granules of size +3 mm and has now better access to oxygen. This might has improved the coal combustion in sinter bed resulting in improvement in sinter properties.
Pot sinter results with pre-granulated coal fines with binder sodium silicate
The following pot sinter results obtained using pre-granulated coal with binder sodium silicate:
Table 8: Pot sinter test results
Expt. No. Sodium silicate (%) Productivity
(t/m2/hr.) Sinter yield T. I Internal fine generation
1 0 2.2 83.0 59.5 17.3
2 8 2.2 83.7 61.6 16.2
3 10 2.2 82.9 61.8 17.0
4 12 2.2 80.8 61.5 19.1
5 14 2.2 83.1 61.7 16.5

Table-9: Chemical analysis of pot sinter test results
Sodium silicate (%) T.Fe FeO CaO MgO SiO2 Al2O3 Na2O+K2O
0 54.4 11.5 12.0 1.91 5.2 3.6 0.09
8 54.5 11.7 11.9 1.92 5.2 3.6 0.09
10 54.2 10.9 12.1 1.95 5.3 3.6 0.10
12 54.4 12.1 11.9 1.92 5.2 3.6 0.10
14 54.0 11.6 12.2 1.90 5.3 3.6 0.10

Table-10: Change in granulometry of coal with sodium silicate binder
Sieve size coal size without granulation (mm) Granulated Coal size (mm, mass%)
0% 8% 10% 12% 14%
+5 21.82 21.71 27.89 26.07
-5+4 0.62 0.76 1.74 3.38
- 4+3.15 3.74 3.7 5.46 5.31
-3.15+2 18.03 13.65 17.78 31.61 26.07
-2+1 22.41 28.37 33.92 27.31 17.58
-1+0.5 22.21 24.94 18.9 5.11 21.1
-0.5 37.35 6.86 3.23 0.87 0.48

Accompanying Fig.7shows change in sinter properties a) sinter yield, b) Tumbler Index, c) Productivity and d) internal fine with the use of pre-granulated coal using sodium silicate as a binder
Accompanying Fig. 8showsChange in granulometry of coal after granulation with sodium silicate a) <0.5 mm size coal and b) + 3 mm size coal (0% is base case).

It is observed that all the sintering properties such as sinter yield and tumbler index increased when coal was granulated with 8% sodium silicate compared to base case. Tumbler index increased by 3.5% and sinter yield by ~1%. Internal fine generation reduced by 6.4%. However, no significant change in sinter properties is observed beyond 8% sodium silicate binder used for coal granulation.
When sodium silicate was used as a binder to granulate the coal, the 0.5 mm fraction of coal is reduced from 37.4% to 6.8% with 8% sodium silicate addition. Thus the % of fines which were present in adhering layer of sinter granules without coal granulation are now converted into granules of size +3 mm and has now better access to oxygen. This might have improved the coal combustion in sinter bed resulting in improvement in sinter properties.

It is thus possible by way of the present invention to provide a process for sinter production using pre granulated coal along with sinter feed mix with sodium silicate and coal tar as a binder, results in improved granulation of coal fines and leading to increase in sinter properties. Moreover, the above process has not led to any change in sinter chemical composition especially alkali content. Thus, this process of using pre granulated coal fines and its usage in sinter feed mix is found to be useful in decreasing the return fine generation.
As mentioned earlier in the prior art [Xin Zhang et al (Nature research 11, (2021), 1540)], coal & coke has similar granulation characteristics, hence above findings can be extrapolated to the coke also and these binders are expected to give similar improvement with the coke fine also.