US2877163A - Metallurgical coke and process for producing the same - Google Patents

Description

United States Patent METALLURGICAL COKE AND PROCESS FOR PRODUCING THE SAME Audr Frangois Boyer, Verneuil, France, assignor to Charbonnages de France, Paris, France, a public institution of France No Drawing. Application August 1, 1955 Serial No. 525,800

Claims priority, application France September 21, 1954 11 Claims. (Cl. 202-33) This invention relates to metallurgical cokes and to processes for producing such cokes.

It is an object of the present invention to provide means facilitating manufacture of a greatly improved metallurgical coke having a substantially higher thermal efficiency than previously known cokes of this type, whereby both fusible and infusible coking coals may be used for manufacturing said coke and supplementary additions of binder materials to said coking coals are obviated.

It is another object of the present invention to provide means affording a novel metallurgical coke of high mechanical stability in which the relatively infusible components may comprise a larger percentage of the total coking batch than the fusible components.

Another object of the present invention is to provide means contributing to relatively inexpensive and economically profitable production of metallurgical cokes Wherein a mixture of fusible and infusible bituminous coals having high percentages of volatile materials contained therein is employed in producing the cokes, said fusible coals serving as binders for said infusible coals, and both said fusible and said infusible coals providing relatively great quantities of commercially usable by-products.

A further object of the present invention is to provide means conducive to a simplified yet highly efiicacious metallurgical coke of the aforesaid type in which the particles or granules of the infusible bituminous coal component are larger in size and substantially heavier than the particles or granules of the fusible, normally fatty coking coal.

Still a further object of the present invention is the provision of means leading to a metallurgical coke of the aforesaid type in which the relatively large infusible coking coal granules have a pyrogenation temperature which is lower than the pyrogenation temperature of the granules of the relatively smaller fusible, fatty coking coals or mixture of such fatty coking coals.

More particularly, the invention is directed to a process of producing metallurgical cokes from mixtures of coals having, as shown in the table hereinbelow, high percentages of volatile materials contained therein. Such coals have heretofore been reputed to be inapt for use in the production of the aforesaid metallurgical cokes because of their relatively low degree of fusibility.

The process according to the invention, quite to the contrary, enables the utilization of such high volatile content non caking coals in larger percentages than has been the vogue in heretofore known coke manufacturing procedures. As a result, the high volatile non caking coals, which can thus be advantageously used in the coking process, no longer are restricted to the status of mere additives or supplements to the coking batch or mass, but may actually take the place of the conventional base coking coal as the principal constituent of the coking mass without preliminary mechanical separation of the petrographic components of said base coal.

The problem of the utilization of high volatile non 2,877,163 Patented Mar. 10, 1959 caking coals in the manufacture of metallurgical cokes has heretofore been resolved in an empirical manner by processes and procedures which are characterized by the use of a cokable base coal to which was added a so-called reducing or thinning agent constituted of non-cokable coals, coke or semi-coke. Other procedures have required mechanical separation of the fusible constituents of a relatively difiicultly cokable coal from the infusible constituents thereof and formulation of a coking mass of appropriate, predeterminedgranular size distribution prior to the coking operation.

It is to be noted that all of these known procedures are characterized by the two following inconveniences:

(a) The infusible coal has normally not been utilizable in quantities greater than approximately 15 or 20% of the total coking mass or batch.

(b) It has always been necessary to crush or pulverize to a relatively fine particle size the infusible constituent of the coking mass, even though such constituent, in general, is the harder of the coals employed (e. g., high volatile C bituminous coal, coke, semi-coke).

According to other known procedures it was possible to use coals only slightly or not at all fusible as the base constituent of the coking mass. However, this always necessitated addition of considerable quantities of hydrocarbonic binders to the coking mass, such quantities amounting at times to as much as 20% of the total coking mass.

Certain other known procedures permitted a reduction in the quantity of good coking coal to be utilized by addition to said coal of additives, called reducing or thinning agents, constituted by relatively inert substances having an extremely low volatile material content, such as anthracite, coke or semi-coke. However, these inert substances, which undergo a slight contraction during the course of the carbonization, must necessarily be finely crushed or pulverized if it is desired to obtain a coke of good quality.

This is, of course, a major inconvenience, causing excessive expenditures of both time and labor. Moreover, the yield of gases or tars during the carbonization operation is considerably reduced, it being well known, as pointed out above, that these inert substances contain only negligible quantities of volatile materials.

The process, according to the invention, of manufacturing metallurgical cokes obviates the aforesaid major inconveniences and presents the following important advantages:

(a) It permits utilization, in the batch of coking coal, of a greater percentage of relatively infusible bituminous coals than the maximum percentage heretofore attainable in accordance with known procedures, and, in accordance with the invention, this percentage may be as high as (b) It permits utilization of the most fusible and consequently the least hard coal as the most finely ground constituent of the coking batch.

(c) No addition of any binder material is necessary.

(d) The coking operation is rendered financially and economically highly profitable, on the one hand because of the greater quantities of gaseous and coal tar byproducts obtainable during the carbonization, and on the other hand because of the particular quality of the tars which are obtained during coking of a batch of coal containing large quantities of volatile materials, such coal V stituents, one of which is a slightly fusible or relatively,

infusible bituminous coal or coal mixture in granular form with granules of relatively large average size and which has a pyrogenation temperature distinctly lower than the pyrogenation temperature of the other constituent, the latter being a fusible fatty or bituminous coal or a mixture of such fatty or bituminous coals. By way of definition, the term pyrogenation temperature is employed to designate the small temperature range within which a coal with a high content of volatile materials will undergo its rapid thermal decomposition and, accordingly, will contract. For best results, the difference between these pyrogenation temperatures of the two constituents should be so chosen that at the moment of resolidification of the second constituent, the protocoke of the first constituent will have reached the end of its phase of rapid contraction.

'By Way of example, the following table illustrates the resolidification temperatures and the temperatures corresponding to the end of the rapid contraction for various grades of bituminous coals. These temperatures, which normally vary with the rate of heating, have been determined for a heating rate of 2 C. per minute, a heating rate commonly employed in industrial carbonization operations.

From the table it will be seen that only the medium volatile bituminous grade of coal fully satisfies the condition of equality between the resolidification temperature and the temperature corresponding to the end of the rapid contraction. Effectively, thus, the coal of this grade is the only one which, without being mixed with coals of other grades, enables a good coke to be produced.

Of the other grades of coal listed, the 30% volatile bituminous coals result in a mediocre type of coke, while the A and B high volatile bituminous coals result in extremely cracked or fissured cokes. In fact, the high volatile B bituminous coals are substantially noncokable, as are the high volatile C bituminous coals.

With coals of these last four grades, the condition of equality between the respective temperatures characterizing the various components of a mixed coking batch or composition cannot always be attained. In that event, said condition is replaced by the aforesaid condition that the rapid contraction of the infusible component shall have been completed when the fusible component reaches its resolidification temperature.

From the table it may, therefore, be seen that an acceptable, mechanically strong coke may be produced by employing a batch consisting of a mixture of high volatile C bituminous coal and 30% volatile bituminous coal, the latter, of course being the fusible constituent of the batch. Alternatively, high volatile A bituminous coal may be selected as the fusible constituent to be mixed with the infusible high volatile C bituminous coal. In each of these cases, the infusible constituent reaches the termination of its phase of rapid contraction at 475 C., while the resolidification temperature of the fusible constituent is 480-485 C. in the former case and 475-480 C. in the latter case. However, a combination of high volatile A and B bituminous coals or of high volatile B and C bituminous coals will prevent attainment of satisfactory results, i. e., manufacture of cokes having the requisite superior mechanical and thermal properties, because the resolidification temperature of the more fusible constituent will be reached before the temperature corresponding to the end of the 4' rapid contraction phase of the relatively infusible constituent.

A further characteristic of the process according to the invention is that the granules of the relatively infusible coal are substantially large in size while the fusible coking coal granules are relatively small or fine in size.

One effect of these two characteristics is that during the coking of the mixture the total surface contact area between the granules of the infusible and fusible constituents is reduced as much as possible. This lessens the tendency of the mixture to diffuse or. spread apart. Such diffusion, which is avoided bythe process of the invention, would have the disadvantageous eifect (as in the known processes) of lowering the resolidification temperature of the coking coals which, in turn, would unfavorably influence the fluidity of the mixture during its fusion and would augment cracking or fissnration during contraction of the protocoke.

The essential novelty and advantages of the process according to the present invention will be more fully understood in the light of the following explanation. Coals which contain relatively great quantities of volatile materials generally result in highly fissured or cracked cokes, even if the latter are well fused, because such coals undergo very rapid contractions subsequent to their resolidification.

The physical characteristics of the .coke produced may be improved either by elevating the resolidification temperature of the fusible constituent of the coking batch, as is conventionally being done through addition of large quantities of medium or low volatile bituminous coal, or by lowering the temperature at which the rapid contraction of the infusible constituent occurs, keeping the resolidification temperature constant, of course.

It has been found, however, that among the coals having a very high volatile material content, those coals which contract at the lowest temperatures are the ones which are least cementatory or agglutinant. According to the invention, therefore, it is proposed to diminish the tendency of cokes so produced to crack by employing a large proportion of non-cokable coals.

This proposal could ordinarily not be put into effect without special artifices, because cokes containing a large proportion of substantially infusible coals, such as high volatile C bituminous coals or lignites, normally have very inferior mechanical strength characteristics. Research has shown that if the relatively infusible coals are mixed with fusible coals there is produced, during the coking operation, a superficial dissolution of the infusible coals, e. g., the high volatile C, in the fusible coals.

The resulting mixed phase of the coke has completely undesirable physical properties. Among these are slight fluidity and consequent inferior agglutination, and lower resolidification temperature with a consequent relatively great degree of fissuration or cracking. Thus, it is at this point that a way of eliminating the aforesaid undesirable properties must be found.

Since the problem involved is essentially one of surface action, it is proposed to reduce the formation of the above-mentioned mixed phase by diminishing the total surface area of the infusible coals which the fusible coals must contact to agglutinate said infusible coals. This object may be realized in practice by utilizing only relatively large granules of the infusible coals.

On the other hand, it is not necessary that there be a very thick layer of fusible coal between each adjacent pair of infusible coal granules. For all practical purposes, it is sufficient if the interposed layer of fusible coal is a few tenths of a millimeter thick. This, of course, makes it desirable to crush or pulverize the fusible coals, which are usuallythe more expensive as well as the softer and more grindable coals, to as fine a degree as possible so'as to reduce the overall quantity of fusible coal which is1 required to completely embed the infusible coal granu es.

The substantial advantages of this procedure according to the invention may be immediately seen by comparison with the previously known procedures, in accordance with which it was not possible to utilize more than about 15 to 20% of infusible coals and in accordance with which it was necessary to finely pulverize the harder coals.

Specifically, therefore, a coking batch to be used in accordance with the present invention consists of a large proportion of granules of infusible bituminous coals having a high volatile material content and relatively large granules. Coal dust is usually eliminated by suitable sifting or screening of the batch. The remainder of the batch consists of finely ground granules of fusible bituminous coal, the average weight of each of the latter type of granules ranging from approximately ,4 to M of the average weight of each of the infusible coal granules.

Thus, to practice the process of the invention there is merely required a suitable crushing or pulverizing and sifting installation and, perhaps, a mechanism for compacting or tamping the coking batch, in addition to the coking system. The latter may be a continuous or discontinuous furnace, for example, an industrial furnace 380 mm. in width, operating at predetermined high or low temperatures, according to the desired operating conditions.

The fusible coal constituent is susceptible to the same operations and modifications as the complete coking batches described above. Thus, this constituent may be varied by mixing of different grades of fusible coals and by regrinding of certain fractional portions of the fusible mixture, for example.

It is to be noted that the coking batches or compositions prepared in accordance with the process of the present invention are capable of yielding much greater amounts of gaseous by-products due to the possibility of using coals containing as much as 40% of volatile materials. On the other hand, the densities of the charges of coking coals are greater than the densities heretofore available in known coking batches or charges due to the more favorable size distribution of the coal granules and due to the greater density of the high volatile C bituminous or other infusible coals.

Other advantages and special features resulting from the practice of the process according to the present invention may be realized from the following examples of coking batches or compositions.

(1) The first and infusible constituent of the batch is high volatile C bituminous coal containing 40% volatile materials having a crucible swelling index of approximately zero (0), the average size of the particles or granules being between 2 and 3 mm. or such as to enable them to pass through a No. 5, 6, 7, 8 or 10 sieve. The second and fusible constituent is medium volatile bituminous coal containing 25% volatile materials and having a crucible swelling index of 9. The average size of the granules of the latter is approximately 0.2 mm. or such as to enable them to pass through a No. 70 sieve. The batch itself consists of 60% of the first constituent and 40% of the second constituent.

(2) The first constituent is the same as in Example 1 above. The second constituent is a mixture, in equal parts, of medium volatile bituminous coal with 25% volatile materials and an expansion index of 9, and high volatile A bituminous coal with 35% volatile materials and a crucible swelling index of 8. The average size of the granules of the latter is 0.5 mm. or such as to enable them to pass through a No. 30 or 35 sieve. As before, 60%of the first constituent and 40% of the second constituent make up the batch to be coked.

The metallurgical cokes produced by appropriately heating the coal batches or mixtures of the two cited examples have the qualities and characteristics of high grade metallurgical cokes.

(3) The first constituent is as in Example 1 above.

6 The second constituent is a high volatile A bituminous coal with 35% volatile materials and a crucible swelling index of 8 and an average granular size such as to enable the granules to pass through any sieves between Nos. 30 to 70.

The metallurgical coke produced from this mixture is only slightly inferior in quality to the cokes obtained in the above example.

In these three examples the coke may be improved in quality by moistening the first constituent with water or with oil, the second constituent being kept relatively dry. This will result in a substantially uniform embedding of the first constituent in the second.

As indicated hereinabove, experiments have shown that if the high volatile C component of the third of the above examples is replaced by high volatile B" bituminous coal, the coke produced is definitely inferior in quality; its quality as determined by the shatter-test is at best only slightly above 50% as good as that of the cokes produced in accordance with either of said examples.

Thus it will be realized that there has been provided, in accordance with the invention, a process for the preparation of a metallurgical coke which comprises mixing an infusible coal having a high content of volatiles and of relatively large particle size with a fusible coking coal of finely divided particle size, the pyrogenation temperature of said infusible coal being distinctly lower than that of said fusible coal, the resolidification temperature of said fusible coal during coking being at least equal to the temperature corresponding to the end of the rapid contraction of the infusible coal when heated alone, heating said mixture to coke said fusible coal.

Various changes and modifications may be made without departing from the spirit and scope of the present invention and it is intended that such obvious changes and modifications be embraced by the annexed claims.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent, is:

l. A composition of matter comprising a homogeneous mixture of granules of an infusible coal having a high content of volatiles and an average particle size corresponding approximately to the sieve openings in No. 5 to 10 sieves, with granules of a fusible bituminous coal having a high content of volatiles and an average particle size corresponding approximately to the sieve openings in No. 30 to 70 sieves, the pyrogenation temperature of said infusible coal being distinctly lower than that of said fusible coal, and the resolidification temperature of said fusible coal during coking being at least equal to the temperature corresponding to the end of the rapid contraction of the infusible coal when heated alone.

2. A composition of matter according to claim 1, wherein said infusible coal is present in an amount at least equal to that of said fusible coal.

3. A composition of matter according to claim 1, wherein said average particle size of said granules of said fusible coal is less than 0.5 mm. in diameter and the weight of said granules of said infusible coal ranges from about to 1000 times the weight of said granules of said fusible coal.

4. The process of preparing a metallurgical coke, which comprises the steps of mixing granules of an infusible coal having a high content of volatiles and an average particle size corresponding to the sieve openings in No. 5 to 10 sieves with granules of a fusible bituminous coal having a high content of volatiles and an average particle size, corresponding to the sieve openings in No. 30 to 70 sieves and further having a pyrogenation temperature distinctly higher than that of said infusible coal as well as a resolidification temperature during coking at least equal to the temperature corresponding to the end of the rapid contraction of said infusible coal when heated alone and heating the resultant mixture to coke said fusible coal.

5. A metallurgical coke produced in accordance with the process of claim 4.

6. A metallurgical coke according to claim 5, said average particle size of said infusible coal granules being approximately 10 times said average particle size of said fusible coal granules.

7. A metallurgical coke according to claim 6, the average weight of each of said fusible coal granules being approximately A to of the average weight of each of said infusible coal granules.

8. The process of producing a metallurgical coke, comprising the steps of preparing a mixture of granules of a substantially infusible coal having a high content of volatile materials with granules of a substantially fusible bituminous coal having a high content of volatile materials, the average size of said granules of said substantially infusible coal being such as to enable them to pass through No. 5 to sieves while the average size of said granules of said substantially fusible coal is such as to enable them to pass through No. 30 to 70 sieves, the pyrogenation temperature of said substantially fusible coal being higher than the pyrogenation temperature of said substantially infusible coal, heating said mixture to cause said substantially infusible coal granules to pass through a phase of rapid contraction, and further heating said mixture to coke said substantially fusible coal granules upon termination of said rapid contraction of said substantially infusible coal granules, whereby said granules of said substantially infusible coal are agglutinated by said coked granules of said substantially fusible coal, to thereby produce a metallurgical coke of high quality with regard to its mechanical strength and thermal characteristics.

9. The process of claim 8, said substantially infusible coal granules constituting from 50% to 85% of said mixture, and said substantially fusible coal granules constituting from 50% to of said mixture.

10. A metallurgical coke composition; comprising a coked mixture of a first bituminous coal having a predetermined temperature range relating to the end of rapid contraction inherent in said first coal, with a secondbituminous coal with apredetermined resolidification temperature range, said first and second coals present in said mixture being selected so that the temperature relating to said end of rapid contraction of said first coal is lower than that of the resolidification temperature of said second coal, whereby both said bituminous coals yield a unitary product of high mechanical strength and thermal properties advantageous for metallurgical purposes, said first coal being a substantially non-fusible coal with a particle size ranging between number 5 and number 10 sieve openings and wherein said second coal is a fusible coal with an average particle size of approximately 35 to mesh.

11. A metallurgical coke composition; comprising a coked mixture of a first bituminous coal having a predetermined temperature range relating to the end of rapid contraction inherent in said first coal, with a second bituminous coal with a predetermined resolidification temperature range, said first and second coals present in said mixture being selected so that the temperature relating to said end of rapid contraction of said first coal is lower than that of the resolidification temperature of said second coal, whereby both said bituminous coals yield a unitary product of high mechanical strength and thermal properties advantageous for metallurgical purposes, the average particle size of said second coal being less than 0.5 mm. in diameter, the average particle size of said first coal ranging from to 1000 times the weight of the average particle size of said second coal.

References Cited in the file of this patent UNlTED STATES PATENTS 1,334,180 Smith Mar. 16, 1920 1,471,647 Chance Oct. 23, 1923' 1,667,906 Strafiord May 1, 1928 1,815,918 Knowles July 28, 1931 FOREIGN PATENTS 187,336 Great Britain Oct. 20, 1922

Claims (1)

1. A COMPOSITION OF MATTER COMPRISING A HOMOGENEOUS MIXTURE OF GRANULES OF AN INFUSIBLE COAL HAVING A HIGH CONTENT OF VOLATILES AND AN AVERAGE PARTICLE SIZE CORRESPONDING APPROXIMATELY TO THE SIEVE OPENINGS IN NO. 5 TO 10 SIEVES, WITH GRANULES OF A FUSIBLE BITUMINOUS COAL HAVING A HIGH CONTENT OF VOLATILES AND AN AVERAGE PARTICLE SIZE CORRESPONDING APPROXIMATELY TO THE SIEVE OPENINGS IN NO. 30 TO 70 SIEVES, THE PYROGENATION TEMPERATURE OF SAID INFUSIBLE COAL BEING DISTINCTLY LOWER THAN THAT OF SAID FUSIBLE COAL, AND THE RESOLDIFICATION TEMPERATURE OF SAID FUSIBLE COAL DURING COKING BEING AT LEAST EQUAL TO THE TEMPERATURE CORRESPONDING TO THE END OF THE RAPID CONTRACTION OF THE INFUSIBLE COAL WHEN HEATED ALONE.