Title of Invention

AN IMPROVED METHOD OF PREPARING BLENDED COALS FOR CARBONISATION IN COKE OVENS

Abstract

An improved method of preparing blended coals for carborisation in coke ovens to produce coke with improved strength characteristics which will result in reduced coke rate i.e. consumption of coke per ton of molten metal produced and increased productivity of molten metal in blast furnaces, characterised in that the method comprises the following steps in sequence : a) coals of different grades from source (1) are supplied to screen (2) which allows grains of size -40 mm or -80 mm to pass through it and accumulate in storage yard/bunker (4); b) the coals of grain size +40 mm or +80 mm which do not pass through screen (2) are fed into crusher (3) which converts the grain size to -40 mm or -80 mm and allows the crushed grains to accumulate in storage yard/bunker (4); c) the coal grains in storage yard/bunker (4) are segregated into softer and harder groups in a known manner; d) the grains of softer group are supplied to screen (5) which allows grains of size -10 mm to pass through it and enter into mixer (9), and allows the grains of size +10 mm, which do not pass through screen (5) to enter into crusher (6) which crushes the grains to an extent so that 90% of the crushed grains are of size -3 mm, and the crushed grains are fed into mixer (9); e) the grains of harder group are supplied to screen (7) which allows grains of size -3 mm to pass through it and enter into mixer (9), and allows the grains of size +3 mm, which do not pass through screen (7) to enter into crusher (8) which crushes the grains to an extent so that 9096 of the crushed grains are of size -3 mm, and the crushed grains are fed into mixer (9); and f) mixer (9) is operated to mix the grains fed into it, thoroughly to produce the blended coals for carborisation in coke ovens. Reference: Figure 1 of the accompanying drawings.

Full Text

The present .invention relates to an impioved method of prcpming coals for carbonisation in Coke Ovens. The existing method of preparation of coals for carbonisation in coke ovens comprises crushing of coals of different grades together, irrespective of variations in their grain size, hardness and caking/coking properties. The abrasion strength (M10) of the coke produced from the coals prepared in the existing method is interior resulting in higher coke consumption and reduced productivity in blast furnaces. The main objective of the present invention is to provide an improved method of preparing coals from different sources with optimum grain size distribution in coal blend. The other objective is to lower the cost of blending operations. Another objective is to increase the abrasion strength of the coke produced by carbonisation of the blended coals in coke ovens which will result in reduction in coke consumption and increase in the productivity of the blast furnaces. The invented method basically comprises first segregating the coals obtained from different sources into two or more separate groups according to their grain size and hardness, and then crushing the coals of the groups separately and optimally, prior to their mixing in a mixer machine. A number of steps are followed in sequence before producing the final blend of the coals for carbonisation in coke ovens. The groups containing the softer and harder coals are crushed to different extents with a view to optimistothe grain size distribution and improviagabrasion strength of Ihc coke produced by carbonisation of the blend in coke oven. It is known that an increase in abrasion strength of-the coke lowers the consumption of coke in blast furnaces for producing a given quantity of molten metal. Since coke consumption is a major component of cost in the production of molten metal in blast furnaces, an appreciable economy in the production of molten metal can be achieved by increasing the abrasion strength of the coke. Moreover the invented process comprises the various steps in sequence which lead to a reduction in the cost of production of the blended coals compared with the existing method of preparing blended coals. The quality of the coals obtained from different sources is assessed in terms of the following parameters : (a) Average grain size, (b) Grindability index, (c) Ash content, (d) Fluidity, (e) Dilatation and (f) Rank. These parameters of coals are determined in known standard methods. The grinclability of coals is determined by heating coals in the absence ol air and noting the change in volume. As the heating is continued in a known Ruhr Dilaiometer in which a coal pencil is held in position at a specified temperature and for a specified time, there is at first a reduction in the volume of the pencil owing to escape of volatile matters from it and then there is an increase in the volume of the pencil owing to its dilatation i.e. swelling. If the final volume is greater than the initial volume, then there is a positive dilatation of coals. The value of dilatation depends on the combined effect of the average size, ash content and rank of the coal sample. The typical quality parameters of the coals obtained from a number of different sources are presented in Table 1. It is noted from Table I that the coals obtained from sources - Dugda, Munidih and Imported having relatively a high grindabilily index (HGI) in the range of 72.1 - 81.2 are easy-to-grind and possess improved caking properties, while those obtained from sources Kathara, Gidi, Assam and Kargali having relatively a low grindability index (HGI) in the range of 48.7 - 60.2 are difficult-to-grind and posses poor caking properties. The abrasion strength index (M10) of the cokes produced by carbonisation of blended coals in coke ovens is determined in the known standard Micum Drum Tests, in which 50 kg of coke containing grins of size +50mm is rotated at 25 rpm for 4 minutes i.e. for 100 revolutions of the drum and then the coke is screened on a screen having round holes of diameter 10mm each. The weight % of the coke granules passing through the screen holes is the abrasion strength index (M10) of the coke tested. An empirical relationship used for estimating the abrasion strength index (M10) of a cokasample is also given below : M10 = K + k1a1 in which, K, k1 , k2 and k3 are constants a1 is the weight % of coal grains of size +3mm a2 is the ratio of content of -1.4 sp.gr. fraction (pure coal) in +3 mm grains and total coal blend a3 is the coefficient of ash distribution in different size fractions of coal defined in a known manner. Exlensivc experiments /were curried out by carboni/ing samples of blended coals prepared in different methods and determining the M10 value of the cokes produced, in the Micum Drum tests. The carboni/alion of the blended coal samples was done in a pilot oven of 250 kg capacity. The following three methods were followed in producing blended coais for carbonisation in the pilot oven in carrying out the experiments : (1) Hxisting method in which coals obtained different sources were mixed and crushed together. (2) Modified method (A) in which coals obtained from different sources were crushed separately, and crushed coals were mixed together. (3) Modified method (B) in which coals obtained from different sources were pre-screencd to segregate the grains coarser than the size of the screen holes, the coarser grains thus segregated were crushed and then mixed with the finer grains. The M10 indices obtained in the above three methods are presented in Table II, from which it is noted that the MIO index improves^from the Existing Method to Modified Method (A) and from Modified Method (A) to Modified Method (B), indicating thereby that the abrasion strength of the coke increases from the Hxisting Method to Modified Method (A) and from Modified Method (A) to Modified Method (B). It is known that unit decrease in MIO index leads to 2% reduction in the coke rate i.e. consumption of dry coke in blast furnaces per ton of hot metal produced and 2.5% increase in the productivity of blast furnaces. The invented method of producing blended coals is based on the Modified Method (B), as described hereinafter fully and particularly, in an unrestrictive manner by way of an example only with reference to the accompanying drawings in which - Figure 1 is a flow diagram showing the various steps followed in sequence for producing blended coal from coals of different grades for carbonisation in coke oven into cokes of improved quality, which will result in reduction in the coke rate and increase in blast furnace productivity. Referring to Fig. 1, the coals of different grades from sources (1) are supplied to screen (2) which allows grains of size -40mm or -80mm to pass through it and accumulate in the storage yard/bunker (4). The grains of size +40mm or +80mm which do not pass through the screen (2) are fed into the crusher (3) which converts the grains into size -40mm or -80mm. The crushed coals are allowed to accumulate in (he storage yard/hunker (4). The coal grains in storage yard/hunker (4) are segregated into soller and harder groups in a known manner. The soller grains are supplied to the screen (5) which allows (he grains of size -10mm to pass through it and enter into the mixer (9), The grains of size -f 10mm which do not pass through the screen (5) are fed into the crusher (6) which crushes the grains to an extent so that 90% of the crushed grains are of size -3mm. The grains crushed in the crusher (6) are fed into the mixer (9). The harder grains are supplied to the screen (7) which allows the grains of size -3mm to pass through it and enter into the mixer (9). The grains of size +3mm which do not pass through the screen (7) are fed into the crusher (8) which crushes the grains to an extent so that 90% of the crushed grains are of size -3mm. The grains crushed in the crusher (8) are fed into the mixer (9). The mixer (9) mixes the grains fed into it thoroughly to produce the blended coals in which 80% of the grains are of size -3mm. The crushers used comprise each a number of hammers and a number of side plates, each hammer being disposed with a gap between it and a corresponding side piate. The gap is adjusted to produce crushed grains of the required size. Quality parameters of coals obtained from different sources (Table Removed) Abrasion Strength Index (M10) of coke from coal blends produced in different methods Different Methods 1. Existing Method 2. Modified Method (A) 3. Modified Method (B) Abrasion Strengthlndex (M101) 11.3 10.0 We claim :- I. An improved method of preparing ~ «. coals lor carbonisation in coke ovens to produce coke with improved strength characteristics which will result in reduced coke rate i.e. consumption of coke per ton of molten metal produced and increased productivity of molten metal in blast furnaces, characterised in that the method comprises the following steps in sequence : a) mixing coals received from different sources; b) screening the mixture in a screen which allows the coal grains of size -40mm or - 80mm to pass through it and accumulate in a storage yard/bunker; c) crushing the coal grains of size +40mm or +80mm, which do not pass through the said screen to convert the grains into size -40mm or -80mm and allow the crushed grains to be accumulated in the said storage yard/bunker; d) segregating the incoming coals in a known manner into/two groups, namely one group containing relatively soil coals and the other group containing relatively hard coals; e) screening the group containing soil coals in a screen which allows the grains of size -10mm to pass through it and enter into a mixer; 1) crushing the soft coals of size +10mm which do not pass through the said screen into grains, 90% of which are of size -3mm and allowing the crushed grain to enter into the said mixer; g) screening the group containing hard coals in a screen which allows the grains of size -3mm to pass through it and enter into the said mixer; h) crushing the hard grains of size +3mm, which do not pass through the said screen into grains, 90% of which are of size -3mm and allowing the crushed grains to enter into the said mixer; i) mixing tiie grains thoroughly in the said mixer to produce the blended coals containing grains, of which 80% are of size -3mm. 2. The method as claimed m nauu I, wherein the grains are crushed using a crusher comprising a number ofhammers and a number of side plates, each hammer being disposed with an adjustablc ;.sap between it and a corresponding side plate.

Documents:

2468-del-1996-abstract.pdf

2468-del-1996-claims.pdf

2468-del-1996-complete specification (granted).pdf

2468-del-1996-correspondence-others.pdf

2468-del-1996-correspondence-po.pdf

2468-del-1996-description (complete).pdf

2468-del-1996-drawings.pdf

2468-del-1996-form-1.pdf

2468-del-1996-form-19.pdf

2468-del-1996-form-2.pdf

2468-del-1996-form-4.pdf

2468-del-1996-gpa.pdf