Claims:WE CLAIM:

1. Coal blend including non-coking coal for making blast furnace (BF) grade coke comprising:

5-11wt.% of non-coking coals, 6-7 wt.% of semi soft coking coals, 23-33 wt.% of medium coking coals and 59-61 wt.% of hard coking coal favouring CSR in the range of 64.60 – 66.60%.

2. Coal blend as claimed in claim 1 having compacted bulk density in the range of 1.10 to 1.15 T/m³, wherein said compacted bulk density is comprised of coal blend of crushed separately 90 wt% of coal particle having less than 3.15 mm size and 45-50 wt% of coal particles having less than 0.5 mm size.

3. Coal blend as claimed in anyone of claims 1 or 2 favouring CRI values 24.10 to 26.16 %.

4. Coal blend as claimed in anyone of claims 1 to 3 wherein one or more non-coking coals having ash content (dry basis) in the range of 7-10 weight %, volatile matter (dry basis) in the range of 25-30 weight%, and Crucible Swelling Number (CSN) value zero.

5. Coal blend as claimed in anyone of claims 1 to 4 comprising semi soft coking coals having ash content (dry basis) in the range of 5-10 weight %, volatile matter (dry basis) in the range of 30-40 weight%, CSN in the range of 2.5-3.5 and maximum fluidity in the range of 50-90 dial division per minute (ddpm).

6. Coal blend as claimed in anyone of claims 1 to 5 comprising one or more medium coking coals having ash content (dry basis) in the range of 8-10 weight %, volatile matter (dry basis) in the range of 26-30 weight%, CSN in the range of 6-7.5 and maximum fluidity in the range of 300-450 ddpm.

7. Coal blend as claimed in anyone of claims 1 to 6 comprising one or more hard coking coal having ash content (dry basis) in the range of 7-13 weight %, volatile matter (dry basis) in the range of 20-25 weight%, CSN in the range of 7-8.5 and maximum fluidity in the range of 150-2500ddpm.

8. A process for the manufacture of coal blend as claimed in anyone of claims 1 to 7 comprising:
involving a coal blend of 5-11wt.% non-coking coals, 6-7 wt.% of semi soft coking coals, 23-33 wt.% of medium coking coals and 59-61 wt.% of hard coking coal;

carrying out blend preparation comprising selective crushing of different coals and proportionate mixing to maximize the coal blend bulk density in the range of 1.10 to 1.15 T/m3

9. A process as claimed in claim 8 comprising step of achieving said bilk density by selectively crushing individual coals separately to obtain 90 wt% of coal particle having less than 3.15 mm size and 45-50 wt% of coal particles having less than 0.5 mm size followed by thorough dry mixing and adding appropriate quantity of water;
Homogenising the mixture, ensuring the final blend moisture in the range of 9 to 11%, preferably 10%;
compacting the blend to reach desired bulk density.

10. A process as claimed in anyone of claims 8 or 9 wherein the process is targeted at achieving coal blend to ensure coke properties comprising CSR in the range of 64.60 – 66.60% and CRI 24.10-26.16 %.

Dated this the 17th day of September, 2019

Anjan Sen
Of Anjan Sen & Associates
(Applicants Agent)
IN/PA-199

, Description:FIELD OF THE INVENTION
The present invention relates to coal blend including using non-coking coals and a process for preparing coal blend through selective crushing and optimized blending of coals for making blast furnace (BF) grade coke. More particularly, the present invention is directed to a process for making blast furnace (BF) grade coke using different types of non-coking coals in coal blend with no deterioration in high temperature properties of coke, e.g., Coke Strength after Reaction (CSR) and Coke Reactivity Index (CRI). The coke properties achieved by the process ensure CSR value of 64.60–66.60 % and (CRI) in the range of 24.10–26.16 % which can be charged in any blast furnace, i.e., mini blast furnace to larger blast furnace. This aforesaid coke CSR value can be achieved through partial replacement of coking coal by non-coking coal as high as 11%. The coal blend for coke making according to the process of the invention consists of 5-11 weight percentage of non-coking coals, 6-7 weight% of semi soft coking coals, 23-33 weight% of medium coking coals and 59-61 weight %of hard coking coal to produce blast furnace (BF) grade coke.

BACKGROUND OF THE INVENTION

Coke is one of the major raw materials for blast furnace (BF) and the quality of coke is one of the most important factors affecting BF performance with respect to the productivity and coke rate. Consistency of coke quality is also required for higher productivity and smooth functioning of BF. Coke Strength after Reaction (CSR) and Coke Reactivity Index (CRI)tests were performed to evaluate the high temperature properties of coke. CSR specification limit varies from furnace to furnace based on BF height, working volume and operating conditions.

The coal blend, consisting of various coals in predefined proportions, is charged into the coke oven for carbonization to produce BF grade coke.Carbonization is the process of transforming coking coal into metallurgical coke in the absence of air at a temperature of ~1050°C. In this process, the coal loses all its volatile matters and the solid residue gets recrystallized into hard mass, called coke. Among the entire range of coal from lignite to anthracite, bituminous coals possess coking property. Only some kind of bituminous coals soften, then solidify into a strong, porous coke structure. Mostly medium volatile (20 - 30%) bituminous coals are used in coke making. Scarcity of coking coal reserves worldwide has necessitated to think for non-coking coal usage in coke making.

However, non coking coal is not used in coal blend having some adverse characteristics which has detrimental impact on coke properties. Non-coking coal does not exhibit any rheological properties such as Free Swelling Index (FSI) and Fluidity, which contributes in carbonization and are essential for coke making. In absence of these rheological properties, the non-coking coal does not transform into plastic state during carbonisation. The absence of rheological properties in non-coking coal leads to deterioration in coke properties when blended whereas the coking coal transforms into plastic state, swells, and then solidifies to form coke during carbonisation.

The difference between properties of non-coking and coking coal are as follows:
Properties Non-coking coal Coking coal
Free Swelling Index, No. 0 >6
Maximum Fluidity, ddpm 0 >50
Vitrinite, % 10 – 30 60 – 80
Exinite, % 2 – 6 0 – 5
Inertinite,% 55 – 75 20 – 30
Mineral matter, % 5 – 20 5 – 10
Mean Maximum Reflectance (MMR), % 0.4 - 0.6 0.9 - 1.1

Non-coking coal does not exhibit any rheological properties (i.e., zero free swelling index and zero maximum fluidity). So, the non-coking coal does not transform into plastic state during carbonisation. However, the coking coal transforms into plastic state, swells and then solidifies to form coke during carbonisation. The absence of rheological properties in non-coking coal leads to deterioration in coke properties, when blended. By increasing non-coking coal above 11%, coke properties deteriorated resulting in inferior CSR & CRI values. Coke with CSR value of < 64.5% and CRI value of >27% is not a suitable feed for the blast furnace.

Chinese Patent No.CN103965929 dated 15th April 2014 by Diao Yuechuanet al. (Nanjing Iron & Steel Co. Ltd.) describes method for increasing use amount of high-volatile non-caking bituminous coal during coking process by using modifying agent in the tune of 0.08-0.12% of the total weight of the coking coal and maximum CSR achieved was 46.73%.The present invention differs in the sense that the non-coking coal use can be increased without any binder or coal property-modifying agent. The achieved CSR is 64.60 - 64.70 % for 11% non-coking coal fines blend.

Indian Patent No. 866/KOL/2013 dated 22nd July 2013 by Debjani Nag et al. (Tata Steel Ltd.),discloses the use of organo-refined coal by blend design, where 50-80 weight % medium coking coal is used and maximum CSR achieved was 53.90 %. However, in present invention, 5-11 weight % of non-coking coals, 5-10 weight% of semi soft coking coals, 20-35 weight% of medium coking coals were used achieving CSR in the range of 64.60 – 66.60%.

United States Patent No. US9845439 B2 dated 19th December 2017 by Shimoyama et al. (JFE Steel Corporation), provides a technique to check the compatibility between coals for coke making by surface tension difference of coals, where several coking coals are used other than non-coking coal. However, in present invention, 5-11 weight % of non-coking coals and 5-10 weight% of semi soft coking coals were used achieving CSR in the range of 64.60 – 66.60%.

United States Patent No. US10240092 B2 dated 26th March 2019 by Yusuke Dohi et al. (JFE Steel Corporation), provides a coal mixture comprising large-permeation-distance coal (~0.80% MMR) and permeation-distance-decreasing coal (>=1.25% MMR) for coke making, where several coking coals are used other than non-coking coal (0.40-0.60% MMR).

Thus non-coking coal was not used previously without any modifier in coal blend along with hard coking coal or semi coking coal. By using non-coking coal, coke properties deteriorate resulting inferior CSR & CRI, and coke with CSR value of < 64.5% and CRI value of >27% is not a suitable feed for blast furnace.However, in present invention, 5-11 weight % of non-coking coals and 5-10 weight% of semi soft coking coals were used achieving CSR in the range of 64.60 – 66.60%.

The present invention deals with the process of using non-coking coal fines in coal blend maintaining the coke CSR value greater than 64.5%. The said process is directed to mixing of coking coal, semi soft coking coal and non-coking coal with selective granulation involving blend preparation with selective crushing of different coals to desired fineness and proportionate mixing to achieve homogeneous mixture using intensive mixer with controlled moisture level in final blend and compacting to maximize the coal blend bulk density prior to coking.

OBJECTS OF THE INVENTION

The basic object of the present invention is directed to coal blend including non coking coal and a process for coke making involving preparingsaid coal blend with partial replacement of hard coking coal by non-coking coalin coal blend to produce the blast furnace grade coke.

A further object of the present invention is directed to said process involving use of non-coking coal in blend through selective crushing to maintain the proper particle size distribution followed by mixing and compacting to achieve desired bulk density of coal cake prior to coking.

A still further object of the present invention is directed to said process for coke making involving use of non-coking coal in blend without impacting the high temperature properties of coke.

A further object of the present invention is directed to said process of coke making from coal blend containing non coking coal toreduce the dependency of coking coal import.

SUMMARY OF THE INVENTION
The basic aspect of the present invention is directed to provide Coal blend including non-coking coal for making blast furnace (BF) grade coke comprising:

5-11wt.% of non-coking coals, 6-7 wt.% of semi soft coking coals, 23-33 wt.% of medium coking coals and 59-61 wt.% of hard coking coal favouring CSR in the range of 64.60 – 66.60%.

A further aspect of the present invention is directed tosaid Coal blend having compacted bulk density in the range of 1.10 to 1.15 T/m³ wherein said compacted bulk density is comprised of coal blend of crushed separately 90 wt% of coal particle having less than 3.15 mm size and 45-50 wt% of coal particles having less than 0.5 mm size.

A still further aspect of the present invention is directed to provide Coal blend favouring CRI values 24.10 to 26.16 %.

A still further aspect of the present invention is directed to provide said Coal blend wherein one or more non-coking coals having ash content (dry basis) in the range of 7-10 weight %, volatile matter (dry basis) in the range of 25-30 weight%, and Crucible Swelling Number (CSN) value zero.

A still further aspect of the present invention is directed to provide Coal blend comprising semi soft coking coals having ash content (dry basis) in the range of 5-10 weight %, volatile matter (dry basis) in the range of 30-40 weight%, CSN in the range of 2.5-3.5 and maximum fluidity in the range of 50-90 dial division per minute (ddpm).

Another aspect of the present invention is directed to provide Coal blend comprising one or more medium coking coals having ash content (dry basis) in the range of 8-10 weight %, volatile matter (dry basis) in the range of 26-30 weight%, CSN in the range of 6-7.5 and maximum fluidity in the range of 300-450 ddpm.

Yet another aspect of the present invention is directed to provide Coal blend comprising one or more hard coking coal having ash content (dry basis) in the range of 7-13 weight %, volatile matter (dry basis) in the range of 20-25 weight%, CSN in the range of 7-8.5 and maximum fluidity in the range of 150-2500ddpm.

A further aspect of the present invention is directed to provide a process for the manufacture of coal blend as described above comprising:
involving a coal blend of 5-11wt.% non-coking coals, 6-7 wt.% of semi soft coking coals, 23-33 wt.% of medium coking coals and 59-61 wt.% of hard coking coal;

carrying out blend preparation comprising selective crushing of different coals and proportionate mixing to maximize the coal blend bulk density in the range of 1.10 to 1.15 T/m3

A still further aspect of the present invention is directed to provide said process comprising step of achieving said bulk density by selectively crushing individual coals separately to obtain 90 wt% of coal particle having less than 3.15 mm size and 45-50 wt% of coal particles having less than 0.5 mm size followed by thorough dry mixing and adding appropriate quantity of water;
Homogenising the mixture, ensuring the final blend moisture in the range of 9 to 11%, preferably 10%;
compacting the blend to reach desired bulk density.

A still further aspect of the present invention is directed to provide a process wherein the process is targeted at achieving coal blend to ensure coke properties comprising CSR in the range of 64.60 – 66.60% and CRI 24.10-26.16 %.

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 and example.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig. 1: shows Coke CSR variation with different coal blend.
Fig. 2: shows Coke CRI variation with different coal blend.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO ACCOMPANYING DRAWINGS

The present invention relates to coal blend including non coking coal and a process for making blast furnace (BF) grade coke involving said coal blend including non-coking coals by proper mixing and compacting after appropriate crushing of coal particles.The said process consists of a coal blend comprising 5-11 weight % of non-coking coals, 5-10 weight% of semi soft coking coals, 20-35 weight% of medium coking coals and 55-65 weight % of hard coking coal. The process ensures no deterioration in high temperature properties of coke, e.g., Coke Strength after Reaction (CSR) and Coke Reactivity Index (CRI). The coke with CSR value of 64.5 - 66.5% and CRI value of 23 - 27% can be charged in any blast furnace, i.e., mini blast furnace to larger blast furnace.

The steps of preparing the coal blend according to present invention and evaluating the coke properties obtained thereof are illustrated with examples as follows:

Example I:
In present invention, nine coals were used for preparing the coal blend. Out of nine coals, there were four hard coking coals, two medium coking coals, one semi-soft coking coal and two non-coking coals or thermal coals, marked as A to I as detailed in following Table 1. The coals were subjected to complete characterization and carbonisation study. Lab tests were carried out to know the physico-chemical properties by following ASTM standards D720 – 91, D3173– 11, D3174–11, D3175-11, D2639 – 04, D2797M– 11a, D2798– 11a, D2799– 05a, D5341 – 99.

Table 1: Characterization of coals
Coal Name Coal Details Volatile matter (db)
(weight %) Ash (db)
(weight %) Crucible Swelling Number (CSN) Maximum fluidity dial division per minute (ddpm) Vitrinites(%) Mean Maximum Reflectance (MMR) (%)
A Hard coking coal 21.80 7.50 7.00 150 53.2 1.28
B Hard coking coal 23.10 12.70 7.50 1048 86.0 1.25
C Hard coking coal 24.20 9.70 7.50 860 61.0 1.18
D Hard coking coal 24.12 8.70 8.50 2456 58.9 1.17
E Medium coking coal 27.70 8.20 7.50 445 70.8 0.99
F Medium coking coal 26.60 8.11 7.50 393 67.0 1.03
G Semi soft coking coal 39.90 5.30 3.50 84 45.4 0.60
H Non-coking coal 28.74 9.06 0 0 25.5 0.50
I Non-coking coal 29.20 7.20 0 0 18.6 0.55

Example II:

Under this example, different blends were developed using different combinations of various coals as shown in Table 1. The coal blend preparation involves crushing of coals and measurement of crushing fineness at 0.5mm and 3.15mm respectively. The major invention in blend preparation is the selective crushing of different coals and proportionate mixing to maximize the coal blend bulk density to the tune of 1.15 T/m³. In order to achieve higher coal blend bulk density, the individual coals were crushed separately so as to obtain 90 wt% of coal particle having less than 3.15 mm size and 45-50 wt% of coal particles having less than 0.5mm size followed by thorough dry mixing and adding appropriate quantity of water. The homogeneous mixture was achieved using intensive mixer. Moisture analysis was done to ensure the final blend moisture in the range of 9 to 11%, preferably 10%. Then the blend was compacted using hydraulic press and the bulk density was measured. The coal cake bulk density is maintained in the range of 1.10 to 1.15 T/m³.

The four hard coking coals (A-D) are having 20-25% volatile matter content (drybasis), 7-13 % ash content (dry basis), 7.0-8.5 Crucible Swelling Number (CSN) and 150-2500dial division per minute (ddpm)maximum fluidity. The petrography analysis of these hard coking coals show 53-86% vitrinites and 1.17- 1.28% Mean Maximum Reflectance (MMR). These characterization results confirm coals A-D as hard coking coal.

The two medium coking coals (E-F) 26-30% volatile matter content (dry basis), 8-10 % ash content (dry basis), 6.0-7.5 CSN, 300-450 ddpm fluidity, 65-71% vitrinites and 0.95-1.05% MMR. The semi soft coking coal is having lower ashcontent, but higher volatilematter content, 2.5-3.5 CSN and 50-90ddpm fluidity, 45% vitrinite and 0.60% MMR. The non-coking coalsare having 7-10%ash content (dry basis),25-30% volatile matter (dry basis), 18-25% vitrinites, 0.50-0.55% MMR, zero CSN and zero fluidity.

Several blends were designed using these coals to attain BF grade coke in laboratory.

Example III:

Under this example, carbonisation of coal cake obtained of different coal blend was carried out to produce coke in laboratory:

The blended coal cake of 120 kg weight was then charged into a pilot scale coke oven. The average carbonization cycle is around 20 hours. The coke mass, upon completion of carbonization cycle, was pushed out from the oven once the temperature of the centre mass exceeds 1050°C for three hours. The coke mass was quenched with water and left for drying. Subsequently the coke properties were tested.

Following Table 2 shows the coal blend and coke properties achieved in laboratory scale trials.

Table 2: Coal blend and Coke properties for the blends with/without non-coking coal
Blend No. Blend proportion Coal blend properties Coke properties
Ash (wt.%) V. M.
(wt%) Ash
(wt.%) V. M. (wt.%) CSR (%) CRI (%)
Blend -1 Hard coking coal - 61%, Coal E - 15%, Coal F - 18%, Coal G - 6% 8.95 26.38 12.08 0.88 66.60 24.15
Blend -2 Hard coking coal - 59%, Coal E - 15%, Coal F - 14%, Coal G - 7%, Coal H - 5% 8.90 26.44 12.03 0.86 65.96 24.10
Blend -3 Hard coking coal - 59%, Coal E - 15%, Coal F - 12%, Coal G - 7%, Coal H - 7% 8.92 26.53 12.05 0.91 65.68 24.96
Blend -4 Hard coking coal - 59%, Coal E - 15%, Coal F -10%, Coal G - 7%, Coal H - 9% 8.96 26.52 12.07 0.85 65.38 25.41
Blend -5 Hard coking coal - 59%, Coal E - 15%, Coal F - 8%, Coal G - 7%, Coal H - 11% 9.00 26.58 12.10 0.87 64.60 26.16
Blend -6 Hard coking coal - 59%, Coal E - 15%, Coal F -14%, Coal G - 7%, Coal I - 5% 8.85 26.57 12.01 0.84 65.22 25.21
Blend -7 Hard coking coal - 59%, Coal E - 15%, Coal F - 8%, Coal G - 7%, Coal I - 11% 8.90 26.63 12.07 0.88 64.70 26.08
Blend -8 Hard coking coal - 59%, Coal E - 15%, Coal F - 6%, Coal G - 7%, Coal H - 13% 9.02 26.61 12.13 0.86 63.82 27.09
Blend -9 Hard coking coal - 59%, Coal E - 15%, Coal F - 6%, Coal G - 7%, Coal I - 13% 8.94 26.65 12.10 0.89 63.95 27.06

The lab results show that, CSR value is decreasing with increase in non-coking coal (Coal Hand Coal I) percentage in the blend as shown in Figure 1. The CSR values of 64.60% and 64.70% were achieved with 11% coal H and Coal I in the blend respectively. It is found that with increase in non-coking coal above 11% in blend, the CSR values dropped below 64.5%, which is not suitable for smooth blast furnace operation.

Similarly, the lab results show that the CRI value is increasing with increase in non-coking coal (Coal Hand Coal I) percentage in the blend as shown in Figure 2. The CRI values of 26.16% and 26.08% were achieved with 11% coal H and Coal I in the blend respectively. It is found that with increase in non-coking coal above 11% in blend, the CRI values went up above 27%, which is not suitable for smooth blast furnace operation.

After successful lab trials, similar blends are applied in practice on industrial scale for both recovery and non-recovery coke ovens and yielded positive results.

It is thus possible by way of the present invention to provide a process for making blast furnace (BF) grade coke using non-coking coals in coal blend by proper blending and appropriate crushing of coal particles to desired fineness, homogeneous mixing, maintaining desired moisture level and compacting to achieve desired bulk density of coal cake followed by coking to obtain coke having desired properties suitable for use in BF. The said process consists of a coal blend comprising 5-11 weight % of non-coking coals, 5-10 weight% of semi soft coking coals, 20-35 weight% of medium coking coals and 55-65 weight % of hard coking coal. The process ensures no deterioration in high temperature properties of coke, e.g., Coke Strength after Reaction (CSR) and Coke Reactivity Index (CRI). The coke with CSR value of 64.6 - 66.6% and CRI value of 24.10 – 26.16% achieved by the process can be charged in any blast furnace, i.e., mini blast furnace to larger blast furnace for iron production on industrial scale.