Charging coke oven blended coal and an overlay of briquettes

Abstract

This specification discloses a carbonization method of coal briquette which made from non-coking coal and poor coking coal. According to this method, a formed coke for blast furnace can be produced economically by using conventional coke oven.

Description

This invention relates to a carbonization method of coal briquette consisting of poor coking coal and non-coking coal, by using a conventional coking oven.

According to the growth of the iron and steel industry all over the world, the metallurgical coking coal is getting increasingly difficult to obtain, and this trend is becoming increasingly severe. To cope with this trend, the blend of non-coking coal to the coal blend for metallurgical coke and the production of metallurgical coke using non-coking coal as the main raw material instead of the coking coal have been investigated.

As one manner to make the metallurgical coke from non-coking coal, there is formed coke method. In this method, the non-coking coal is formed into briquette prior to high temperature carbonization. However, the high temperature carbonization of the coal briquette in this method cannot be done with the conventional coke oven, and a exclusive equipment for the carbonization of the coal briquette is required. In addition to that, the exclusive equipment which is presently available, economically inferior to the conventional coking oven.

In another method, the coal briquette consisting of poor coking coal and soft coking coal is used as part of coking coal charging to the conventional cokeoven (as disclosed in Japanese patent publication No. 16484/1960). In this method, the caking material content in the coal briquette is set high (with the caking material index of 66 to 90 percent) to result in fusing of the coal briquette with the surrounding coking coal, so that no trace of briquette can be found in the product coke at all. In an example disclosed in the Japanese patent publication No. 16484/1960, 40 percent coal briquette are charged together with the usual coking coal into a 1/4-ton experimental coking oven. However, the bulk density of the charging coal included the coal briquette (with 40 percent) is increased to 0.78 ton per cubic meter compared to 0.72 to 0.74 ton per cubic meter in case of the 100 percent usual coking coal. Therefore, in the operation of the practical coke oven, the discharge of the product from the coke oven get into trouble.

In practice, therefore, in the disclosed method, the proportion of the coal briquette in the charging coal for the conventional coke oven is 25 to 30 percent at the most, and the poor coking and the non-coking coal cannot use more than about 20 percent.

In the method according to the invention, it is possible to use the poor coking and the non-coking coal by 20 percent or more of the total charge into the conventional coke oven. Also, it is essentially different from the above method (disclosed in the Japanese Pat. publication No. 16484/1960) in that a formed coke can produce with the conventional coke oven.

An object of the invention is to provide a carbonization method, in which high temperature carbonization of coal briquette and usual coking coal can be done separately in the same conventional coke oven without requiring any exclusive coking equipment and without causing fusion of the briquette one with another or the briquette with the usual coking coal.

According to the invention, the usual coking coal and the coal briquette charged into the coke oven may be carbonized at the same time.

More particularly, in the carbonization method of the coal briquette according to the invention, the usual coking coal, which consist of 20 to 60 percent of hard coking coal, 0 to 40 percent of soft coking coal and 0 to 50 percent of semi-hard coal so that its coke strength index (15 mm index in accordance with JIS, K-2151-1962) is 91 or greater, is charged in a range between 70 and 94 percent of the effective height of the conventional coke oven, and then the coal briquette coal which mainly is consisted of the poor coking coal and the non-coking coal or non-caking carbonacious substance such as petroleum coke is charged in a range between 6 to 30 percent of the effective oven height for high temperature coking to obtain the metallurgical coke.

According to the invention, it is also possible to charge the usual coking coal from the charging hole of the pusher side on the coke oven and then charge only the briquette coal from another changing hole (on the coke guide side).

The following example is made prior to tests using actual coke oven.

EXAMPLE

This example used a standard experimental coke oven with a charging capacity of 25 kg. The quality of coals used in this example are as shown in Table 1 and Table 2 below:

Table 1 __________________________________________________________________________ Name of coal Proportion Quality of blended coal __________________________________________________________________________ Keystone (hard coking coal) 15 % Total moisture: 7.7 % Inhercent moisture: 2.0 % Free swelling index: 61/2 Ash: 7.2 % Balmer (hard coking coal) 20 % Volatile matter: 28.8 % Fixed carbon: 62.0 % Devis Blend (semi-hard 15 % coking coal) Wollondilly (semi-hard 20 % Total sulfur: 0.51 % coking coal) Akabira (soft coking 30 % Size distribution coal) (-3 mm): 73.3 % __________________________________________________________________________

Table 2 ______________________________________ Name of coal Proportion Quality of blended coal ______________________________________ Poor caking coal 60 % Inherent moisture: 1.9 % Ash: 7.2 % Petroleum coke 30 % Volatile matter: 28.9 % (non-caking) Fixed carbon: 62.10% Coal tar pitch 10 % Total sulfur: 0.62% Free swelling index: 1 ______________________________________

The blended coal shown in Table 1 is usual for producing blast furnace coke. The blend for the coal briquette coal shown in Table 2 consists of the poor coking coal (with 3.2 percent inherent moisture, 11.8 percent ash, 32.3 percent volatile matter, 52.7 percent fixed carbon and free swelling index of 1) and the petroleum coke having no caking property. The coke produced from this poor coking coal is inadequate as blast furnace coke since the coke strength index is very low, being 30.9; (the 15 mm index according to JIS is 30.9 and the stability factor according to ASTM D 294-64 is 7.5).

The raw materials for coal briquette mixed according to the proportion of Table 2 was pulverized less than 3 mm., and fed on to a kneader. The coal tar pitch in the mixture is method by the heat of hot steam blown into the kneader and the mixture is kneaded sufficiently, and then the mixture was supplied to the briquetting machine, which is a double roll type and has a briquette pressure of about 950 kg/cm (line pressure).

The coal briquette produced in the aforementioned way has dimensions of 28 mm .times. 19 mm and a weight of 10.1 grs. For the carbonization by the experimental coke oven, 184 kg of the blended coal shown in Table 1 was first charged uniformly within the carbonization chamber of the experimental coke oven and then 45 kg of the coal briquette produced under the above conditions charged on the blended coal. Then, the charge was carbonized with a flue temperature of 1,160.degree.C and a coking time of 15 hours and 46 minutes. After carbonization, the hot coke was discharged out of the oven by a pusher and quenched with water.

In the above manner, it was not recognized that the formed coke fused with the coke made from the usual blended coal. Table 3 below shows various properties of these cokes. Both cokes can be used as blast furnace coke.

Table 3 ______________________________________ Composition and properties of cokes Proximate Analysis Conventional Formed coke coke ______________________________________ Ash (%) 10.0 9.8 Volatile matter (%) 0.9 0.8 Fixed carbon (%) 89.1 89.4 Total sulfur (%) 0.48 0.56 Coke strength 15 mm index by JIS 92.2 94.6 25 mm index by JIS 86.7 -- 50 mm index by JIS 27.8 -- Stability factor by ASTM* 53.4 64.4 Hardness factor by ASTM* 62.2 71.6 Average size of coke (mm) 89.0 27 .times. 27 .times. 18 Porosity (%) 50.5 38.5 Crushing Strength (kg/cm.sup.2) 212 319 ______________________________________ *The ASTM stability and hardness factors were measured according to ASTM 294-1964.

In the coke oven usually used in the iron making industry, the coking coal is charged into the oven from a charging hole at the top of the carbonization chamber, and after the carbonization it is mechanically pushed out of the oven in the horizontal direction. Also, the coking coal charged into the coke oven should have good caking property and should be carbonized in the form of masses.

If coal briquette chiefly consisting of poor coking coal and non-caking material like that shown in FIG. 2, is solely charged into the coking oven, at the time of pushing the coke out of the oven the forward component of force exerted to the coke (formed coke) from the pusher is reduced, so that the pushing eventually becomes impossible.

FIG. 4 lists of a galvanometer of pusher in pushing tests carried out by using a industrial coke oven with an oven height of 4 m, which the efective dimension of carbonization chamber is 3.67 m in height, 13.68 m in length and 0.70 m in width, and effective inner volume of 19.2 m.sup.3 (charging capacity of 13.4 tons per oven). The usual blended coal and the coal briquette according to the invention charged into the oven chamber, and then the charged material carbonized at a flue temperature of 1,245.degree.C for a coking time of 14 hours and 06 minutes.

Table 4 ______________________________________ Kind of charged coal Electric current at pusher ______________________________________ Usual blended coal 70 to 72 amperes 90 percent usual blended coal and 73 to 74 amperes 10 percent coal briquette 70 percent usual blended coal and 75 to 77 amperes 30 percent coal briquette ______________________________________

As is apparent from Table 4, the electric current at the pushe is lowest in case of the sole usual blended coal. The electric current is slightly increased in case of 90 percent, that is, 12 tons of the usual blended coal and 10 percent, that is, 1.4 tons of the coal briquette. In this case, however, the pushing operation itself was found to be the same as in the above case. In case of 30 percent, that is, 4 tons of the coal briquette the electric current at the pusher is further increased. In this case, due to increased resistance of the coke within the oven the pusher stopped several times during the pushing operation, but the discharging of the coke was possible.

However, in tests conducted by charging 30 percent or more of the coal briquette the number of stoppage of the pusher was increased, and the discharging of the coke was difficult. Accordingly, according to the invention the proportion of the coal briquette to be charged is restricted to be 30 percent or less. According to the invention, the lower limit of the proportion of the coal briquette to be charged is made to be 6 percent, because with less than 6 percent of the proportion of the poor coking coal wide reduction of the coke cost cannot be expected.

As has been described in the foregoing, according to the invention the usual coking coal is charged in a range between 70 and 94 percent of the effective height of the coke oven while the coal briquette is charged in a range between 6 and 30 percent of the effective oven height on the usual coking coal for separately carbonizing the usual coking coal and coal briquette in the same coke oven by the usual high temperature carbonization method. Thus, it is possible to economically and inexpensively produce formed coke for blast furnace from poor coking coal with the conventional coke oven, and save the hard coking coal.

The coal briquette on the usual coking coal either slightly fuses or does not fuses at all depending upon the bituminous substance content (with less bituminous substance content the fusion being weaker). Therefore, when the oven lid is removed at the time of pushing out the coke it is possible that coal briquette in contact with the oven lid drops, which is very hazandous. To prevent this, it is better to use an oven lid slanted toward the oven chamber.

Claims

What is claimed is:

1. A method for carbonizing coal briquettes utilizing a conventional coking oven comprising:

charging said oven with a sufficient amount of a blended coal to fill the oven to a level within the range of between 70 and 94 percent of the effective height of the oven, said blended coal being capable of conversion into blast furnace coke upon carbonization thereof;

thereafter placing, on top of said blended coal, a sufficient amount of coal briquettes to fill the remainder of the effective height of the oven, said briquettes comprising an admixture of a soft coking coal and a non-coking carbonaceous substance; and

subjecting the contents of the oven to carbonization to thereby simultaneously produce blast furnace coke and coke briquettes.