METHOD FOR PRODUCING MOLDED PRODUCT FOR FERROCOKE

Abstract

A method for producing a molded product for ferrocoke, wherein a high-strength molded product for ferrocoke can be produced advantageously without making particular investment in facilities and inviting the operating troubles. In a method for producing a molded product for ferrocoke by molding a mixed starting material of coal, an iron-source material, a high-softening point binder having a softening point of not lower than 150 C., and a low-softening point binder having a softening point of lower than 150 C., at least one of the iron-source material and the high-softening point binder is previously heated to not less than a temperature lower by 20 C. than a softening point of the high-softening point binder to perform molding of the mixture.

Claims

1-6. (canceled)

7. A method for producing a molded product for ferrocoke by molding a mixed starting material of coal, an iron-source material, a high-softening point binder having a softening point of not lower than 150 C., and a low-softening point binder having a softening point of lower than 150 C., characterized in that at least one of the iron-source material and the high-softening point binder is previously heated to not less than a temperature lower by 20 C. than a softening point of the high-softening point binder to perform molding of the mixture.

8. The method for producing a molded product for ferrocoke according to claim 7, wherein iron-source particles having an average particle size of not more than 2.0 mm are used as the iron-source material, heated to not less than a temperature lower by 20 C. than the softening point of the high-softening point binder, then mixed with the high-softening point binder, and thereafter mixed with the low-softening point binder having a softening point of lower than 150 C. to mold the mixed starting material.

9. The method for producing a molded product for ferrocoke according to claim 7, wherein iron-source particles having an average particle size of not more than 2.0 mm are used as the iron-source material, and the high-softening point binder is heated to not less than a temperature lower by 20 C. than the softening point of the high-softening point binder, then mixed with the iron-source material, and thereafter mixed with the low-softening point binder having a softening point of lower than 150 C. to mold the mixed starting material.

10. The method for producing a molded product for ferrocoke according to claim 7, wherein the iron-source material and the high-softening point binder are simultaneously charged into a kneading machine.

11. The method for producing a molded product for ferrocoke according to claim 8, wherein the iron-source material and the high-softening point binder are simultaneously charged into a kneading machine.

12. The method for producing a molded product for ferrocoke according to claim 9, wherein the iron-source material and the high-softening point binder are simultaneously charged into a kneading machine.

13. The method for producing a molded product for ferrocoke according to claim 7, wherein the iron-source material or the high-softening point binder is heated to not more than a temperature higher by 10 C. than the softening point of the high-softening point binder.

14. The method for producing a molded product for ferrocoke according to claim 8, wherein the iron-source material or the high-softening point binder is heated to not more than a temperature higher by 10 C. than the softening point of the high-softening point binder.

15. The method for producing a molded product for ferrocoke according to claim 9, wherein the iron-source material or the high-softening point binder is heated to not more than a temperature higher by 10 C. than the softening point of the high-softening point binder.

16. The method for producing a molded product for ferrocoke according to claim 7, wherein an average particle size of the iron-source material is 0.58-1.64 mm.

17. The method for producing a molded product for ferrocoke according to claim 8, wherein an average particle size of the iron-source material is 0.58-1.64 mm.

18. The method for producing a molded product for ferrocoke according to claim 9, wherein an average particle size of the iron-source material is 0.58-1.64 mm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] FIG. 1 is a graph showing a relation between a strength of a molded product and a heating temperature of a high-softening point binder.

[0023] FIG. 2 is a graph showing a relation between a strength of a molded product in use of a high-softening point binder having a softening point of 180 C. and a heating temperature of iron ore.

[0024] FIG. 3 is a graph showing a relation between a strength of a molded product in use of a high-softening point binder having a softening point of 160 C. and a heating temperature of iron ore.

[0025] FIG. 4 is a graph showing a relation among an oxygen concentration of a gas for heating coal, a temperature of coal in drying, and a strength of a molded product.

[0026] FIG. 5 is a graph showing a relation between a strength of a molded product and an average particle size of iron ore.

[0027] FIG. 6 is a graph showing a relation between a strength of a molded product and a temperature of iron ore.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

[0028] The inventors have made various examinations and found that when a molded product for ferrocoke is produced by molding a starting material containing coal, an iron-source material and a binder, a high-softening point binder is previously heated up to a temperature close to a softening point thereof and thereafter charged into the starting material in a kneading machine and then a low-softening point binder is added thereto and kneaded, whereby a strength of a molded product in the kneading is increased. Also, it has been found that the strength of the molded product is increased by a method wherein the iron ore causing no problems in the safety and quality even in the heating to not less than the softening point of the high-softening point binder is heated instead of the high-softening point binder and coal is charged into the kneading machine and then the iron ore and high-softening point binder are simultaneously charged into the kneading machine and the low-softening point bonder is added thereto. As a result, the invention has been accomplished. Here, the softening point of the binder can be measured by a ring-and-ball method (JIS K2425).

[0029] Each of various component members used in the production method of the molded product for ferrocoke according to the invention will be described, and a relation between each component member and a strength of a molded product will be explained below.

[0030] As the nature of coal used in the invention, an average maximum reflectance Ro (JIS M8816) is 1.3%, and an ash content (JIS M 8812) is 9.3 mass %. As the nature of iron ore as an iron-source material, a total iron content is 57.1 mass % (JIS M8212). As a high-softening point binder is used a petroleum pitch having a softening point of 180 C. (volatile matter: 38 mass %) or 160 C. (volatile matter: 45 mass %). As a low-softening point binder is used a coal-based soft pitch having a softening point of 40 C. A mixing ratio of coal, iron ore, high-softening point binder, and low-softening point binder is 66.5 mass %, 28.5 mass %, 2 mass %, and 3 mass %, respectively. The adjustment of the particle size is performed by pulverizing into not more than 2.8 mm in full dosage of coal, not more than 3 mm in full dosage of iron ore (average particle size of 1.04 mm, which is calculated from a sum of product of a residual ratio in each sieve and an average value of adjoining sieve sizes), and not more than 1 mm in full dosage of high-softening point binder, respectively. The water content in the high-softening point binder after the pulverization is 0.3%.

[0031] Although the main iron-source material is iron ore, the term iron-source material used herein means to use not only the iron ore but also the other iron-source material such as iron-making dusts and so on. As the high-softening point binder can be used ASP (asphalt pitch) or the like, while SOP (soft pitch), PDA (propane deasphalted asphalt) and so on can be used as the low-softening point binder.

[0032] The kneading machine used in the invention is a high-speed agitating type mixer having an effective volume of 75 L. A molding machine is a double-roll type molding machine having a roll size of 650 mm104 mm. The feeding of the starting material to the rolls is performed by gravity charging, in which a flow rate of the starting material into the rolls is adjusted by up-and-down movement of an adjusting plate disposed on the top portion between the rolls to control a molding pressure. The molding is performed under a circumferential speed of 0.2 m/s and a linear pressure of 4-5 t/cm in the rolls. The molded product has a size of 30 mm25 mm18 mm (6 cc) and an egg-type form.

[0033] The strength of the molded product is evaluated from a residual ratio of not less than 16 mm after the rotation of 30 times at a rate of 20 rotations per 1 minute with an I-type drum testing machine (cylinder of 130 mm in inner diameter700 mm) (ID strength 30/16).

[0034] In the production method according to the invention, a relation between a heating temperature of the high-softening point binder and a strength of the molded product is examined in the case of previously heating the high-softening point binder. The drying and heating of the starting material is performed as follows. The pulverized coal is heated up to 150 C. in an atmosphere having an oxygen concentration of 1%. The iron ore is heated up to 150 C. in an air atmosphere. Each material is charged into a kneading machine at a predetermined amount. The high-softening point binder heated to four temperature levels of 160 C. (20 C. lower than the softening point of the high-softening point binder), 170 C. (10 C. lower than the softening point), 180 C. (same as the softening point) and 190 C. (10 C. higher than the softening point) is charged into the kneading machine immediately while rotating main rotation blades of the kneading machine. As the high-softening point binder is used a binder having a softening point of 180 C. A low-softening point binder heated up to 160 C. is added at a predetermined amount and kneaded. A kneaded mass is discharged from the kneading machine after the end of the kneading, in which a time from the addition of the low-softening point binder to the discharge is 90 seconds. The discharging temperature in the kneading machine is 170-175 C. The kneaded mass is immediately charged into a double roll type molding machine to produce briquettes.

[0035] FIG. 1 shows an influence of the heating temperature of the high-softening point binder upon the strength of the molded product. As the heating temperature of the high-softening point binder is increased, the strength of the molded product is increased. The temperature of the kneaded mass is not more than the softening point of the high-softening point binder. However, once the high-softening point binder is heated to a temperature approximately equal to or higher than the softening point, the high-softening point binder is somewhat softened, so that it is guessed that the swelling or dissolving of the high-softening point binder is promoted in the mixing with the low-softening point binder and the interaction of both the binders is increased to improve the function of the binders.

[0036] The low-softening point binder is dissolved (120 C. due to the restriction of the test device) and 33 mass % of the high-softening point binder is added to the weight of the dissolved low-softening point binder to perform hot filtration. When the filtrate is analyzed by a high-frequency induction coupled plasma (ICP), a metallic nickel not included in the low-softening point binder but being an ingredient of the high-softening point binder is detected from the filtrate. That is, it is cleared that the ingredient of the high-softening point binder is eluted into the low-softening point binder. In this analysis, it is considered that although the temperature of the low-softening point binder is low, the dissolution of the high-softening point binder is promoted as the mixed temperature of the high-softening point binder and the low-softening point binder is increased. Therefore, it is considered that the strength of the molded product is increased as the heating temperature of the high-softening point binder shown in FIG. 1 is increased.

[0037] Next, the iron ore showing no nature change even in the heating in air at a higher temperature is heated to five temperature levels of 160 C. (20 C. lower than the softening point of the high-softening point binder), 170 C. (10 C. lower than the softening point), 180 C. (same as the softening point), 190 C. (10 C. higher than the softening point), and 200 C. (20 C. higher the softening point) instead of previously heating the high-softening point binder. As the high-softening point binder is used a binder having a softening point of 180 C. The iron ore heated to a predetermined temperature is mixed with a predetermined amount of the high-softening point binder for 30 seconds, which is charged into a kneading machine together with a coal material previously heated to 150 C. Then, a predetermined amount of a soft pitch is added thereto and kneaded immediately. A kneaded mass is discharged from the kneading machine after the end of the kneading, in which a time from the addition of the low-softening point binder to the discharge is 90 seconds. The discharging temperature of the kneaded mass is 170-175 C.

[0038] FIG. 2 shows an influence of the heating temperature of the iron ore upon the strength of the molded product. As the heating temperature of the iron ore is increased, the strength of the molded product is increased. When the discharging temperature of the kneaded mass is 170-175 C., the viscosity of the low-softening point binder remains unchanged, so that it is considered that there are no differences in the dispersibility of the low-softening point binder. The temperature of the high-softening point binder previously mixed with the iron ore is increased by increasing the temperature of the iron ore, so that the swelling or dissolving of the high-softening point binder is promoted in the mixing with the low-softening point binder, and it is guessed that the interaction between both the binders is increased to improve the function of the binders. When a target value of the strength of the molded product is set to 85, it can be seen that the iron ore is necessary to be heated to not less than a temperature lower by 20 C. than the softening point of the high-softening point binder.

[0039] A test is conducted by changing the high-softening point binder having a softening point of 180 C. with a petroleum-based binder having a softening point of 160 C. The iron ore is heated to five temperature levels of 140 C. (20 C. lower than the softening point of the high-softening point binder), 150 C. (10 C. lower than the softening point), 160 C. (same as the softening point), 170 C. (10 C. higher than the softening point) and 180 C. (20 C. higher than the softening point). The discharging temperature of the kneaded mass is 155-160 C. FIG. 3 shows an influence of the heating temperature of the iron ore upon the strength of the molded product. Although the discharging temperature of the kneaded mass is somewhat lower than the softening point of the high-softening point binder, as the heating temperature of the iron ore is increased like in FIG. 2, the strength of the molded product is increased. It can be seen that when the iron ore heated to a temperature lower by 20 C. than the softening point of the high-softening point binder is used, the strength of the molded product is decreased, while a target vale of the strength of the molded product (ID strength 30/16) of not less than 85 is kept. Even in the case of using the binder having a softening point of 160 C., it is considered that the interaction of the high-softening point binder and the low-softening point binder is increased by mixing the iron ore heated to a temperature equal to or higher than the softening point with the binders.

[0040] In FIG. 2, the high-softening point binder is indirectly heated by heating the iron ore. Then, coal is heated instead of the iron ore. FIG. 4 show s a relation among an oxygen concentration in a gas for heating coal, a coal temperature in drying, and a strength of a molded product. The heating time is 30 minutes. As a heating gas is used a mixed gas of nitrogen and oxygen. When the oxygen concentration is made up to 5% at a coal temperature of 150 C., the strength of the molded product can be kept at a target value of not less than 85. However, when the coal temperature is not lower than 160 C., the target strength of the molded product cannot be attained at an oxygen concentration of 2%. The reason why the strength of the molded product is decreased by increasing the oxygen concentration and the coal temperature is considered due to the fact that the coal surface is oxidized by the heating treatment and the wettability between the binder and coal is deteriorated by oxidation of the coal surface to lose the adhesion function of coal by the binder. In the actual process, it is difficult to always keep the oxygen concentration of not more than 2%, so that it is desirable to heat the iron ore or the high-softening point binder.

[0041] When heat is transferred from the high-temperature iron ore to the high-softening point binder, it is necessary to consider the heat transfer of a short time, so that a value of k.Math.A/r[J/s/K] in the following heat conduction and transfer equation (1) is important:

Q=(K.Math.A/r).Math.T=k.Math.(6.Math.w//D)/r.Math.T(1),

wherein Q is a heat transferring rate [J/s], k is a heat conductivity [J/s/m/K], A is an area per unit weight of iron ore [m.sup.2], r is a radius of a high-softening point binder [m], T is a temperature difference between iron ore and high-softening point binder, w is a weight of iron ore [kg], p is a density of iron ore [kg/m.sup.3], and D is a diameter of iron ore [m].

[0042] From the equation (1), it is anticipated that the heat transferring rate is primarily decreased with the increase of the iron ore diameter, so that the increase of the iron ore diameter becomes disadvantageous in the heating of a short time. Now, the kneading and molding test is conducted by changing a pulverizing particle size of iron ore. The test is performed in eight particle size levels within a range of 0.42-2.17 mm as an average particle size of iron ore. Table 1 show s sieve mesh used (JIS) and each particle size composition. Coal previously heated to 150 C. is charged into a kneading machine, and then a high-softening point binder having a softening point of 180 C. and iron ore heated to the softening point of the high-softening point binder are simultaneously charged into the kneading machine while rotating main rotation blades in the kneading machine at a low speed. A predetermined amount of a low-softening point binder is added immediately after the completion of the charging, agitated for 90 seconds, and then discharged from the kneading machine to perform molding (Case-A). As a comparison for the test, the iron ore, binder and iron ore are separately heated to 180 C. and charged into the kneading machine (Case-B).

TABLE-US-00001 TABLE 1 Sieve mesh Weight ratio on sieve (%) (mm) No.1 No.2 No.3 No.4 No.5 No.6 No.7 No.8 5.6 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 4.75 0.0 0.0 0.0 0.0 0.0 0.0 7.0 12.0 4.0 0.0 0.0 0.0 0.0 3.1 9.0 10.0 13.0 2.8 0.0 0.0 0.0 4.9 6.9 8.0 7.0 12.0 2.0 0.0 0.0 8.1 9.9 13.0 8.0 7.0 9.0 1.4 0.0 10.2 13.0 14.2 11.7 10.0 9.0 7.0 1.0 6.3 12.8 17.2 14.0 13.1 15.0 8.0 7.0 0.71 13.1 12.0 14.8 12.7 12.2 12.0 9.0 8.0 0.5 16.6 9.5 7.0 9.1 10.5 10.0 7.0 6.0 0.3 17.0 10.3 6.9 7.2 6.3 5.0 8.0 7.0 0.15 14.0 11.2 8.5 5.5 7.1 7.0 7.0 5.0 0.106 11.2 7.0 6.2 5.2 4.8 5.0 6.0 4.0 0.09 7.8 6.0 5.0 5.1 4.3 4.0 6.0 4.0 0.075 4.2 6.7 5.1 4.7 2.8 3.0 4.0 3.0 0.045 5.0 7.2 5.1 4.3 2.1 2.0 3.0 2.0 0.045 4.8 7.1 3.1 3.2 2.1 2.0 2.0 1.0 Average 0.42 0.58 0.86 1.04 1.26 1.42 1.64 2.17 particle size (mm)

[0043] Coal previously heated to 150 C. is charged into a kneading machine, and a high-softening point binder having a softening point of 180 C. and iron ore heated to the softening point of the high-softening point binder are simultaneously charged into the kneading machine. A predetermined amount of a low-softening point binder is added immediately after the completion of the charging, agitated for 90 seconds, and discharged from the kneading machine to perform molding (Case-A). As a comparison for the test, the iron ore, binder and iron ore are separately heated to 180 C. and charged into the kneading machine (Case-B).

[0044] FIG. 5 shows a relation between a strength of a molded product and an average particle size of iron ore. In Case-B, when the average particle size of iron ore is not more than 1.26 mm, the strength of the molded product is increased as the average particle size becomes larger, while when the average particle size exceeds 1.26 mm, a tendency of somewhat decreasing the strength is observed. In Case-A, when the average particle size of iron ore is not less than 1.64 mm, the strength of the molded product is largely decreased, and the difference to Case-B becomes large. Assuming that the average particle size of iron ore purely exerts on the strength of the molded product in Case-B, the reason why the difference of the strength between Case-A and Case-B becomes larger at the average particle size of iron ore of not less than 1.64 mm is considered due to the fact that the temperature rising of the high-softening point binder is small and the interaction with the low-softening point binder becomes small.

[0045] As seen from the results in FIG. 5, the average particle size of iron ore is necessary to be not more than 2 mm in the invention. When the average particle size is as fine as 0.42 mm, total outer surface area of iron ore particles becomes larger, and the outer surfaces are covered with the binder, and hence the amount of the binder is lacking, and the strength may be decreased. The average particle size of iron ore of not more than 2 mm has no problem from a viewpoint of heating the high-softening point binder, but is preferable to fall into 0.58-1.64 mm.

EXAMPLE

[0046] A high-speed agitating type mixer having an effective volume of 375 L is used as a kneading machine in this example. A molding machine is a double-roll type molding machine having a roll size of 715 mm424 mm. The feeding of the starting material to the rolls is performed by gravity charging, in which a flow rate of the starting material into the rolls is adjusted by up-and-down movement of an adjusting plate disposed on the top portion between the rolls to control a molding pressure. The molding is performed under a circumferential speed of 0.2 m/s and a linear pressure of 3-4 t/cm in the rolls. The molded product has a size of 30 mm25 mm18 mm (6 cc) and an egg-type form. A mixing ratio of coal, iron ore, high-softening point binder, and low-softening point binder to the total weight of the materials is 65.8 mass %, 28.2 mass %, 2 mass %, and 3 mass %, respectively. The particle size of coal is not more than 2.8 mm in a full dosage, and an indirect heating type kiln is used in the dry heating of coal, and a direct heating type kiln is used in the iron ore. A temperature of coal is 150 C. in an outlet of the kiln and 148 C. prior to the charging into the kneading machine. An oxygen concentration in an atmosphere of the kiln is 0.8%. A rotation number of the kiln and a flow rate of a heating gas flowing in the kiln are determined so as to render a time from an inlet of the kiln to a discharge from the kneading machine into about 30 minutes.

[0047] The iron ore before the charging to the kneading machine is heated to seven temperature levels of 150 C. (30 C. lower than the softening point of the high-softening point binder), 160 C. (20 C. lower than the softening point), 170 C. (10 C. lower than the softening point), 180 C. (same temperature as the softening point), 190 C. (10 C. higher than the softening point), 200 C. (20 C. higher than the softening point), and 210 C. (30 C. higher than the softening point). As the high-softening point binder is used a binder having a softening point of 180 C. An average particle size of iron ore is 1.04 mm. After the addition of the iron ore and low-softening point binder, a low-softening point binder is charged and kneaded for 90 seconds. After the end of the kneading, molding is conducted immediately. FIG. 6 shows a relation between a strength of a molded product and a temperature of iron ore. When the heating temperature of iron ore is not lower than 160 C. (a temperature 20 C. lower than the softening point of the high-softening point binder), the strength of the molded product is confirmed to be higher than the target value.

INDUSTRIAL APPLICABILITY

[0048] According to the production method of the molded product for ferrocoke according to the invention, it is made possible to produce a high-strength molded product without using a particular facility and to provide a high-strength molded product suitable as a molded product used in the production of ferrocoke.