FIELD OF THE INVENTION

The present invention relates to a method of testing the suitability of coke for blast furnace iron making involving a simple yet highly cost-effective process. More particularly, the present invention is directed to a cost effective method for evaluating suitability of different coal blend samples and importantly directed to prevent the mass production of bad coke unsuitable for blast furnace. The method according to the invention would entail carrying out tests on different blends of coal of different quality before it is charged in coke ovens for the bulk manufacture of coke. Advantageously, the method according to the invention would enable ready and faster identification of only those coal blends, which could produce the coke with required CRI and CSR and the thus identified suitable blends of coal can then be subjected to mass production in coke oven plant thereby saving cost of production, avoid interruption in production due to poor quality of coke and improving productivity in blast furnace.

BACKGROUND ART

In coke oven plants of the large steel plants, it is a normal practice to blend various types of coals viz. hard coking coal, semi-hard coking coal and non-coking coal in various proportions as input to coke making process to minimize the use of scarce resource (hard coking coal) and also to minimize the cost of coke produced as there is a direct dependence of cost of coke to profitability of a steel industry. It is common experience in the existing art of coke making process that coke produced from a particular blend of coal is rejected by blast furnace owing to poor quality. Such situation leads to rejection and wasting of substantial quantity of coke produced escalating cost of steel production. Charging an inferior coke inside the blast furnace poses problems such as high dust generation, poor permeability, hanging, slips, high fuel rate, reduction in the quantity of coal injection, low productivity etc. Only those coal blends, which produces the coke with required CRI and CSR should therefore be allowed for mass production in coke oven plant. Failing to adhere to this practice, at times, may result in the production of inferior coke, which when used in blast furnace poses operational problems in the blast furnace.

There has been thus a need for developing a method for simple and cost-effcetive manner of screening of suitability of coke for application in blast furnace iron making operation on a sampling basis, avoiding rejection and waste of large quantity of coke produced from a particular coal blend, due to poor quality before the starting of mass production of coke from that coal blend. It is also a requirement in the related art of determining suitable coke blend suitable for blast furnace iron making involving a method which would provide desired guideline based on CRI and CSR values of sample coke produced from a coal blend sample in real life oven environment to favor accept or reject decision for that particular coal blend to continue or discontinue in coke making, so that blast furnace operation and production can be efficient and economic.

OBJECTS OF THE INVENTION

It is thus the basic object of the present invention to provide for a method of screening the suitability of coke for blast furnace iron making by way of a simple, cost-saving and user friendly method.

A further object of the present invention is directed to said method of screening the suitability of coke for blast furnace iron making wherein only those coal blends, which produces the coke with required CRI and CSR could be readily identified and used for mass production in coke oven plant.

A still further object of the present invention is directed to said method of testing the suitability of coke for blast furnace iron making wherein said testing method would avoid the unwanted mass production of bad coke unsuitable for blast furnace.

A still further object of the present invention is directed to said method of testing the suitability of coke for blast furnace iron making wherein said method would avoid misuse of resources like the good quality coking coal being part of a bad coke.

A still further object of the present invention is directed to said method of testing the suitability of coke for blast furnace iron making wherein the testing method would ensure uninterrupted supply of good quality coke to blast furnace.

A still further object of the present invention is directed to said method of testing the suitability of coke for blast furnace iron making wherein the cost per ton of coke charged to blast furnace could be significantly reduced.

A still further object of the present invention is directed to a method of testing the suitability of coke for blast furnace iron making wherein coal blend could be subjected to screening before it is charged in coke ovens for the bulk manufacture of coke.

A still further object of the present invention is directed to said method of testing the suitability of coke for blast furnace iron making which would eliminate problems relating to high dust generation, poor permeability, hanging, slips, high fuel rate, reduction in the quantity of coal injection, low productivity in blast furnace due to poor quality of coke produced and charged in BF.

SUMMARY OF THE INVENTION

Thus according to the basic aspect of the present invention there is provided a method of testing/screening the suitability of coke for blast furnace iron making comprising: i. providing samples of coal to be used as coke and crushing to desired size; ii. preparing the coal blend of said thus crushed samples of the coal and adding de-mineralized water such as to maintain desired moisture level followed by mixing for homogenization;

iii. filling the thus obtained coal blend in boxes adapted for enduring the carbonization process upto a desired bulk density enabling effective carbonization of the blend; iv. introducing the box filled with the sample coal blend as above into the coal cake prepared for regular production of coke and thereafter charging the coal cake alongwith the sample coal blend in said box inside the oven for regular carbonization; v.after carbonization the cake is taken out and quenched as usual; vi. removing the box and the resultant coke therein air dried , followed by crushing to desired sizes for CRI and CSR analysis to thereby determine the suitability of the coal blend for coke for use in blast furnace.

A further aspect of the present invention is directed to a method of testing/screening the suitability of coke for blast furnace iron making wherein in step i. above, the samples of coal to be used as coke are crushed to size below 3mm.

A still further aspect of the present invention is directed to a method of testing/screening the suitability of coke for blast furnace iron making wherein in step ii. above, the sample coal blends are mixed with de-mineralized water to maintain a moisture level of about 10% and thereafter subject the same to homogenization.

A still further aspect of the present invention is directed to a method of testing/screening the suitability of coke for blast furnace iron making wherein in step iii. above, the coal blend is filled inside stainless steel box ,mild steel box preferably anti-corrosive stainless steel box.

A still further aspect of the present invention is directed to said method of testing/screening the suitability of coke for blast furnace iron making wherein said coal blend is filled inside box in 3-4 increments and stamped with metal stamper until preferably about 18 Kgs of coal blend is stamped with bulk density 1.15 kg/cm2.

Yet another aspect of the present invention is directed to a method of testing/screening the suitability of coke for blast furnace iron making wherein said step iv. introducing the box filled with the sample coal blend as above into the coal cake prepared for regular production of coke comprises the steps of:

a. a small portion about the size of the box of the said coal cake for regular production of coke preferably at the center of its width and at about l/3rd of its length from the pusher side is removed to accommodate the box therein; and

b. placing therein said removed portion of the coal cake the box such that the top of the box is in level or about 20-25 mm below the surface of the coal cake.

A still further aspect of the present invention is directed to a method of testing/screening the suitability of coke for blast furnace iron making wherein in said step vi. above, the resultant coke from the box is air dried for a period of about 2 hrs.

A still further aspect of the present invention is directed to said method of testing/screening the suitability of coke for blast furnace iron making wherein in said step vi. Above, the coke from the box is crushed by means of jaw crusher to the required size of plus 19 mm to minus 21 mm for carrying out said CRI and CSR analysis.

A still further aspect of the present invention is directed to said method of testing/screening the suitability of coke for blast furnace iron making as claimed in anyone of claims 1 to 8 wherein the crushed coke having a CRI< 25% and CSR > 64 % is found acceptable for bulk production.

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

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURE

Figure 1: is the schematic flow chart Flow diagram depicting various steps in performing box test screening to predict the suitability of coke for blast furnace based on CRI & CRS analysis of coke sample produced.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANIED DRAWINGS

The present invention is directed to a cost effective method and, in particular, to a method for evaluating suitability of coke produced from different coal blend samples by converting coal blend to prepared samples of coke by filling coal blend of desired size fraction, duly moisturized and homogenized, in a cubic box of desired size made of sheet metal preferably Stainless Steel, stamped to desired bulk density, carbonized and then carrying out CRI(Coke Reactivity Index) and CSR(Coke Strength after Reactivity) analysis of the coke sample obtained to thereby determine the suitability of the coal blend for coke for use in blast furnace.

Charging an inferior coke inside the blast furnace poses problems such as high dust generation, poor permeability, hanging, slips, high fuel rate, reduction in the quantity of coal injection, low productivity etc. To avoid this, the coal blend is subjected to box test before it is charged in coke ovens for the bulk manufacture of coke. The coke obtained by box test is then tested for CRI and CSR to determine its suitability to blast furnace operation. Only those coal blends which produces the coke with required CRI and CSR are allowed for mass production in coke oven plant. Based on extensive trial and experiments, it was observed that, coke having a maximum of 25% CRI and a minimum of 64% CSR were found to be suitable for blast furnace operation (though it might differ from furnace to furnace).

To carry out the box test method according to the present invention for evaluating quality of coke produced and its suitability for use in blast furnace, following experiments have been carried out:

(a) Experiments performed with boxes made of steel sheet for filling and stamping of prepared fresh coal blend sample for converting to coke in a regular batch heating in coke oven. Standardized box of size and thickness of the box as 250mm x 250mm x 250mm with 10 mm thickness', was found to be optimum owing to manual handling of the boxes and found to provide improved and consistent results. Boxes of other dimensions are not able to ensure consistent result. Though the sizes of the box are not critical, it is better to have the box dimension at least 10 times the size of coke used for CRI & CSR analysis (which is 19-21 mm).

(b) Following sequential steps have been followed in the method of testing according to the present invention involving carbonization of coal blend sample stamped in box made preferably of stainless steel sheet.

i. providing samples of coal to be used as coke and crushing to desired size, preferably crushed to size below 3mm;

ii. preparing the coal blend of said thus crushed samples of the coal and adding de-mineralized water such as to maintain desired moisture level of about 10% followed by mixing for homogenization;

iii. filling the thus obtained coal blend in boxes, stainless steel box ,mild steel box preferably anti-corrosive stainless steel box, adapted for enduring the carbonization process upto a desired bulk density enabling effective carbonization of the blend; coal blend is filled inside said box in 3-4 increments and stamped with metal stamper until preferably about 18 Kgs of coal blend is stamped with bulk density 1.15 kg/cm2, iv. introducing the box filled with the sample coal blend as above into the coal cake prepared for regular production of coke following the steps of

a. a small portion about the size of the box of the said coal cake for regular production of coke preferably at the center of its width and at about l/3rd of its length from the pusher side is removed to accommodate the box therein; and

b. placing therein said removed portion of the coal cake the box such that the top of the box is in level or about 20-25 mm below the surface of the coal cake; and thereafter charging the coal cake alongwith the sample coal blend in said box inside the oven for regular carbonization; v.after carbonization the cake is taken out and quenched as usual;

vi. removing the box and the resultant coke therein air dried in an air oven at 150 °C for a period of about 2 hrs , followed by crushing in a jaw crusher to desired sizes ranging from plus 19 mm to minus 21 mm for CRI and CSR analysis to thereby determine the suitability of the coal blend for coke for use in blast furnace wherein the crushed coke having a CRI< 25% and CSR > 64 % is found acceptable for bulk production.

The above mentioned steps of conducting the box test according to the present invention to ascertain the suitability of coke for blast furnace operation, produced from a coal blend sample, are illustrated in the accompanying schematic flow diagram as per accompanying Figure 1.

The following examples further illustrate the manner of screening the coal blends in accordance with the present invention:

Example I:

According to this example , the method according to the present invention was carried out by way of one box test experiment involving above steps with a coal blend comprising 40% Hailcreek coal, 30% Kestral coal, 20% Alpha coal and 10% Riverside coal. The resultant coke showed a value of CRI-31% and CSR-60.86%, which did not meet the requirement. Further investigation revealed that, Hailcreek coal was contaminated at the loading port itself. Thus by way of the test according to the invention, the tested coal blend was rejected for bulk production.

Example II:

Under this example a further box test was carried out as per the present invention detailed above with coal blend comprising 50% Illawara coal, 30% Gregory coal and 20% Anthracite coal. The resultant coke showed a value of CRI-30% and CSR-60%, which was found not upto the desired requirement. Further investigation revealed that, Gregory coal was contaminated with other non-coking coals at the unloading port. Thus, the coal blend thus tested was rejected for bulk production.

Example HI:

A further example involving box test was performed as per the detailed steps given above according to the present invention with coal blend comprising 20% Illawara coal, 35% Hailcreek coal, 35% Gregory coal, 10% Anthracite coal. Corresponding CRI of 24% and CSR of 65.13% was observed in the resulting coke sample. The resultant coke showed a value of CRI less than 25% and CSR more than 64%, which was found satisfactorily meeting the requirement of coke characteristics suitable for application in blast furnace operation. The coal blend under this exemplary test was thus screened as allowed for bulk production of coke.

It is thus possible by way of the present invention to providing a simple, user friendly and cost-effective method of testing the suitability of coke for blast furnace iron making by conducting coal blend screening involving box test for producing coke from a particular coal blend and evaluating the suitability by observing the CRI and CSR in the desired range that ensure satisfactory uninterrupted blast furnace performance with higher productivity in a cost effective manner, avoiding the possibility of mass scale production of bad quality coke and also save wastage of scarce resource such as the hard coking coal.

We Claim:

1. A method of testing/screening the suitability of coke for blast furnace iron making comprising:

i. providing samples of coal to be used as coke and crushing to desired size; ii. preparing the coal blend of said thus crushed samples of the coal and adding de-mineralized water such as to maintain desired moisture level followed by mixing for homogenization;

iii. filling the thus obtained coal blend in boxes adapted for enduring the carbonization process upto a desired bulk density enabling effective carbonization of the blend; iv. introducing the box filled with the sample coal blend as above into the coal cake prepared for regular production of coke and thereafter charging the coal cake along with the sample coal blend in said box inside the oven for regular carbonization; v. after carbonization the cake is taken out and quenched as usual; vi. removing the box and the resultant coke therein air dried , followed by crushing to desired sizes for CRI and CSR analysis to thereby determine the suitability of the coal blend for coke for use in blast furnace.

2. A method of testing/screening the suitability of coke for blast furnace iron making as claimed in claim 1 wherein in step i. above, the samples of coal to be used as coke are crushed to size below 3mm.

3. A method of testing/screening the suitability of coke for blast furnace iron making as claimed in anyone of claims 1 or 2 wherein in step ii. above, the sample coal blends are mixed with de-mineralized water to maintain a moisture level of about 10% and thereafter subject the same to homogenization.

4. A method of testing/screening the suitability of coke for blast furnace iron making as claimed in anyone of claims 1 to 3 wherein in step iii. above, the coal blend is filled inside stainless steel box ,mild steel box preferably anti-corrosive stainless steel box.

5. A method of testing/screening the suitability of coke for blast furnace iron making as claimed in anyone of claims 1 to 4 wherein said coal blend is filled inside box in 3-4 increments and stamped with metal stamper until preferably about 18 Kgs of coal blend is stamped with bulk density 1.15 kg/cm2.

6. A method of testing/screening the suitability of coke for blast furnace iron making as claimed in anyone of claims 1 to 5 wherein said step iv. introducing the box filled with the sample coal blend as above into the coal cake prepared for regular production of coke comprises the steps of:

a. a small portion about the size of the box of the said coal cake for regular production of coke preferably at the center of its width and at about l/3rd of its length from the pusher side is removed to accommodate the box therein; and

b. placing therein said removed portion of the coal cake the box such that the top of the box is in level or about 20-25 mm below the surface of the coal cake.

7. A method of testing/screening the suitability of coke for blast furnace iron making as claimed in anyone of claims 1 to 6 wherein in said step vi. above, the resultant coke from the box is air dried for a period of about 2 hrs.

8. A method of testing/screening the suitability of coke for blast furnace iron making as claimed in anyone of claims 1 to 7 wherein in said step vi. above, the coke from the box is crushed by means of jaw crusher to the required size of plus 19 mm to minus 21 mm for carrying out said CRI and CSR analysis.

9. A method of testing/screening the suitability of coke for blast furnace iron making as claimed in anyone of claims 1 to 8 wherein the crushed coke having a CRI< 25% and CSR > 64 % is found acceptable for bulk production.

10. A method of testing/screening the suitability of coke for blast furnace iron making substantially as hereindescribed and illustrated with reference to the accompanying figures.