Title of Invention

A METHOD FOR PREPARATION OF COAL BLEND FOR BF COKE MAKING.

Abstract

There is disclosed an improved method for preparation of coal blend for use in coke making which comprises preparing a coat blend by mixing low ash hard coal and other coats in equal proportions in a slot oven in a conventional manner, then subjecting the blend to a crushing step in a conventional manner to obtain crushed coal blend with at least 80% of the particles passing through a 3.2 mm BSS and there after mixing 15 to 25% based on the weight of the crushed coal, a further amount of non-crushed low ash hard coal and blending the same thoroughly such that the overall crushed coal in the final blend is of particles of less than 80% passing through a 3.2 mm BSS before feeding same to the coke oven.

Full Text

Introduction to the Field of Invention: This invention relates to an improved method for the preparation of coal blend for coke making purposes. Prior Art and Drawbacks: It is well known to prepare a blend of several types of coals at desired quantities and subject the same to a crushing step before charging in a slot oven to produce coke for blast furnace. In the known art, the practice throughout the world is more or less uniform. Normally coal blend (prepared by mixing several types of coals) for carbonization in a slot oven is crushed to 80% through 3.2 mm prior to charging in coke ovens. This practice is practically universal for coke making from coal/coal blend viz. USA, Japan, Russia, UK, India, South Africa etc. Numerous publications (coke and chemistry, fuel) including test/reference books (chemistry of coal utilization edited by Lowry, Elliot etc.) available throughout the world are available. However, in these processes, the final blend exhibits fine fraction of considerable amount, which is not desired. The more the fines, the less the coking property of the coal blend. Another drawback is that the bulk density of the blend is adversely affected which affects the oven throughout. We further noticed that the known practice consumes high amount of electrical energy due to the fines production. Yet another drawback is that the blend offered certain coke oven charging problem from the battery of ovens due to the presence of fines. Further, the presence of fines encourages these fines to be carried over in the gas lines and affect the coke oven operation. Yet another drawback is that the carry over fines is liable to cracking and there is a tendency for deposition of graphite (roof carbon) and low tar quality. 2 Objects of the Invention: It is therefore a primary object of this invention to propose an improved process for the manufacture of coal blend suited to coke oven operation in a manner better than possible so far. It is another object of this invention to propose such a process, which will reduce the production of fines in the crushed coal blend before charging to the coke oven. It is a further object of the invention to propose such a process, which will decrease the carry over of fines in the gas lines of the slot oven. It is stilt further object of the invention to propose such a process, which will provide a coal blend with improved bulk density. It is yet another object of the invention to propose such a process in which the overall consumption of electrical energy will be less compared to the conventional process of preparing coal blend. It is a still further object of the invention, which will help in the production of coke with reduced possibilities of cracking of fines and less graphite generation while improving the tar quality. These and other objects of the invention will be apparent from the following paragraphs. Brief Statement of the Invention: Thus, according to this invention, there is provided a method for preparation of coal blend for BF coke making comprising preparing said coal blend first by introducing low ash, having ash content of less than 10% by weight, hard coal having average reflectance (RoR, v/v%) 1.10 to 1.30 and volatile matter between 22-25% on air dried basis with other types of coal in aliquot(predetermined) proportions to obtain coal blend in crushed form in a crusher such that at least 80% of the particles passing through a 3.2mm BSS and thereafter mixing 15-25% of a further amount of uncrushed low ash aforesaid hard coal to said coal blend, based on the weight of the crushed coal, and blending the same thoroughly such that the overall crushed coal in the final blend obtained having 80% of the particles passing through a 3.2 mm BSS with advantageously lesser fines generated (-0.5mm), and an improved bulk density of the prepared coal blend due to better blend homogeneity, before feeding the same to the coke oven for making of BF coke used in high capacity blast furnaces. In this process, the following details are important for the success of the process. a. The uncrushed low ash hard coal added has an ash content of less than 10% by weight. 3 b. The particle size of the uncrushed low ash hard coal has top size of -50 mm BSS. c. The low ash hard uncrushed coal has 20-30% of its particle of -10 mm BSS and 55-65% less than 3mm BSS. d. The low ash uncrushed coal has vitrinite >50 and rank Ro max of 1.15 to 1.35 and rank of the final blend lies between Ro max of 1.15 to 1.25. e. The coarse size fraction of the low ash hard coal of -10 to +6 mm and -6 to +3 mm has positive dilatation, which helps in producing good coke. f. The overall crushing index (-3.2 mm) of the final coal blend charge is'64% to 82%. g. The final blend charge contains about 21% to 45% of particles of -0.6 mm BSS. h. The bulk density of the final blend charge is up to 810 kg/m3 depending on the granulometry (size consistencies) of the blend, and preferably 680 to 780 kg/m3. In our process, we add a certain amounts of uncrushed coal to the crushed coal blend. After intensive study, analysis and experiments, we have decided to add a certain amount of lowest ash hard coal in the uncrushed form to the crushed coal blend to be charged in the slot oven. The ash content and particle size of the addition is as follows: Ash: Particle Size: all passing through - 50 mm British Standard Screen (BSS) of which 60 to 70% is below 10 mm Low ash hard coal of -10 to +6 mm and -6 to +3 mm also show positive dilatation. The addition of uncrushed coal is preferably 15-25% of the total of low ash hard coal (which may vary 40% to 70% of the blend). The blend itself subjected to crushing is made of 50% low ash hard coal and 50% other coals. The low ash hard coal and other coals blend is crushed in a crusher such that at least 80% of the particles passing through 3.2 mm BSS. In view of addition of a certain amount of uncrushed low ash hard coal, the overall crushing level is such that the final blend obtained having 80% of the particles passing through 3.2 mm BSS and changes depending upon the quantity of low ash uncrushed hard coal used in the blend. Due to this addition of uncrushed low ash hard coal, the overall fines generated (-0.5 mm) is also less and the fines carry over in the gas is also reduced. 4 We have observed that the addition of uncrushed low ash hard coal does not affect the coke quantity since coarser size fractions of low ash hard coking coal show positive dilatation. Furthermore, the bulk density of this blend (mixture of part uncrushed low ash hard coal and crushed mixture of other part) would improve since the average size increases at the same moisture level in the blend. This will help in improved oven throughput. Experimental Study and Verification of the Invention: The following example more fully illustrates the features of the invention, A pilot plant study was carried out in strict confidence in a pilot oven (Carbolite make, 250 kg, variable width, electrically heated movable wall type) carbonizations on one of the steel plants coal blend in India showed the following: Blend : 50% low ash hard coal + 50% other coats Blend C0 100% of low ash hard coal added uncrushed C1 75% of low ash hard coal added uncrushed C2 50% of low ash hard coal added uncrushed C3 0% of low ash hard coal added uncrushed Table: Physical characteristics of test blends Blend C0 C1 C2 C3 % low ash hard coal in the blend 50 50 50 50 % low ash hard coal uncrushed in the charge 100 75 50 0 Overall crushing index (through 3.2 mm) 64.0 70.5 917 82.6 -0.6 mm in the charge 21.1 29.3 37.2 44.9 Bulk density, Kg/m3 782 731 688 685 Temperature condition: Blend moisture 8% Rate of heating 3° C/min. End coke mass temperature 1000°C+10 Carbonization period 18 hrs. Amount of charge per test 270 Kg. 5 We also verified our findings in a running coke oven plant. Sustained industrial trials conducted for about 2 months in one of the Indian steel plants coke ovens where total quantity of tow ash hard coal (constituted about 70% of the blend) was added in uncrushed form. No deterioration in coke quality observed. Slight improvement in fines content (4% less fines generated) and coke cold strength improved M10 improved by 0.2 points. Advantages of the invention: i. Less generation fines, ii. Improved bulk density of the blend i.e. more oven throughput. iii. Saving in electrical energy since some amount of coal added uncrushed in the blend. iv. Ease of battery operation i.e. smoother charging in the oven due to less fines in the blend, v. Less fines carry over to gas lines. vi. Reduced possibilities of cracking and less graphite generation. vii. Improved tar quality. 6 We Claim: 1. A method for preparation of coal blend for BF coke making comprising preparing said coal blend first by introducing low ash, having ash content of less than 10% by weight, hard coal having average reflectance (RoR, v/v%) 1.10 to 1.30 and volatile matter between 22-25% on air dried basis with other types of coal in aliquot (predetermined) proportions to obtain coal blend in crushed form in a crusher such that at least 80% of the particles passing through a 3.2mm BSS and thereafter mixing 15-25% of a further amount of uncrushed low ash aforesaid hard coal to said coal blend, based on the weight of the crushed coal, and blending the same thoroughly such that the overall crushed coal in the final blend obtained having 80% of the particles passing through a 3.2 mm BSS with advantageously lesser fines generated (-0.5mm), and an improved bulk density of the prepared coal blend due to better blend homogeneity, before feeding the same to the coke oven for making of BF coke used in high capacity blast furnaces. 2. A method as claimed in claims 1, wherein said low ash hard uncrushed coal has a top size of -50 mm BSS, with 20-30% of its particle of -10mm BSS and 55-65% less than 3mm . 3. A method as claimed in claims 1 and 2, wherein, the low ash hard uncrushed coal has vitrinite content greater than 50 and rank Ro max of 1.15 to 1.35 and the rank of the final blend lies between Ro max of 1.15 to 1.25. 4. A method as claimed in claims 1 to 3, wherein, the coarse size fraction of the low ash hard coal of -10 to +6 mm and -6 to +3 mm has positive dilatation which helps in producing good coke. 5. A method as claimed in claims 1 to 4, wherein, the overall crushing index (-3.2 mm) of the final coal blend charge is 64% to 82%. 6. A method as claimed in claims 1 to 5, wherein, the final blend charge contains about 21% to 45% of particles of -0.6 mm BSS. 7 7. A method as claimed in claims 1 to 8, wherein, the bulk density of the final blend charge is up to 810 kg/m3 depending on the granulometry (size consistencies), preferably 680 to 780 kg/m3. 8. A method substantially as herein described with reference to the examples. Dated this the 21st day of January, 2002. 8 There is disclosed an improved method for preparation of coal blend for use in coke making which comprises preparing a coat blend by mixing low ash hard coal and other coats in equal proportions in a slot oven in a conventional manner, then subjecting the blend to a crushing step in a conventional manner to obtain crushed coal blend with at least 80% of the particles passing through a 3.2 mm BSS and there after mixing 15 to 25% based on the weight of the crushed coal, a further amount of non-crushed low ash hard coal and blending the same thoroughly such that the overall crushed coal in the final blend is of particles of less than 80% passing through a 3.2 mm BSS before feeding same to the coke oven.

Documents:

00036-cal-2002 abstract.pdf

00036-cal-2002 claims.pdf

00036-cal-2002 correspondence.pdf

00036-cal-2002 description(complete).pdf

00036-cal-2002 form-1.pdf

00036-cal-2002 form-13.pdf

00036-cal-2002 form-18.pdf

00036-cal-2002 form-2.pdf

00036-cal-2002 form-3.pdf

00036-cal-2002 latters patent.pdf

00036-cal-2002 p.a.pdf

00036-cal-2002 reply f.e.r.pdf

36-cal-2002-granted-abstract.pdf

36-cal-2002-granted-claims.pdf

36-cal-2002-granted-description (complete).pdf

36-cal-2002-granted-form 2.pdf

36-cal-2002-granted-specification.pdf