Ferrocoke manufacturing method

Abstract

In a ferrocoke manufacturing method by shaping and carbonizing a mixture of coal and iron ore, a hardly softening coal having a button index (CSN) of not more than 2.0 is used as the coal. The coal can be a blend of hardly softening coal and easily softening coal, and the hardly softening coal can be a coal having a button index (CSN) of 1.0 and a volatile matter of not less than 17%, and the easily softening coal can be a coal satisfying that a value obtained by multiplying CSN of easily softening coal by a blending ratio of easily softening coal in all coals is a range of 0.3-5.2. The coal can also be a blend of hardly softening coal and easily softening coal, and the hardly softening coal can be a coal having a button index (CSN) of 1.5-2.0, and the easily softening coal can be a coal satisfying that a value obtained by multiplying CSN of easily softening coal by a blending ratio of easily softening coal in all coals is nit more than 5.0.

Claims

1. A ferrocoke manufacturing method comprising: (i) mixing a mixture of coal and iron ore, (ii) shaping the mixture into a shaped body, and (iii) carbonizing the shaped body, wherein the coal is a blend of a hardly softening coal and an easily softening coal, and the hardly softening coal has a button index (CSN) of 1.0 and a volatile matter of not less than 17%, and the easily softening coal satisfies a value obtained by multiplying CSN of the easily softening coal by a blending ratio thereof in all coals that is a range of 0.3-5.2, wherein the hardly softening coal has a maximum fluidity of less than 2 ddpm measured by Gieseler plastometer as described in Japanese Industrial Standard (JIS) M8801.

2. The ferrocoke manufacturing method according to claim 1, wherein the blending ratio of the easily softening coal in all coals is not more than 0.8.

3. A ferrocoke manufacturing method comprising: (i) mixing a mixture of coal and iron ore, (ii) shaping the mixture into a shaped body, and (iii) carbonizing the shaped body, wherein the coal is a blend of the hardly softening coal and the easily softening coal, and the hardly softening coal is a coal having a button index (CSN) of 1.5-2.0 and a volatile matter of not less than 17%, and the easily softening coal satisfies a value obtained by multiplying CSN of the easily softening coal by a blending ratio thereof in all coals that is not more than 5.0, wherein the hardly softening coal has a maximum fluidity of less than 2 ddpm measured by Gieseler plastometer as described in Japanese Industrial Standard (JIS) M8801.

4. The ferrocoke manufacturing method according to claim 1, wherein the hardly softening coal has a volatile matter of not less than 22.2%.

5. The ferrocoke manufacturing method according to claim 1, wherein the hardly softening coal is a coal having a volatile matter of not more than 26.5.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a graph showing a relation between CSN of an easily softening coal and a blending ratio of an easily softening coal exerting a strength after carbonization in the case of using a hardly softening coal with a button index (CSN) of 1.0.

(2) FIG. 2 is a graph showing a relation between CSN of an easily softening coal and a blending ratio of an easily softening coal exerting a strength after carbonization in the case of using a hardly softening coal with a button index (CSN) of 1.5 and 2.0.

(3) FIG. 3 is a photograph showing an appearance of fused ferrocoke.

(4) FIG. 4 is a diagram showing an influence of CSN of a hardly softening coal upon a fusion ratio.

(5) FIG. 5 is a schematic view of a shaft type carbonization furnace.

(6) FIG. 6 is a graph showing a heat pattern inside a shaft type carbonization furnace.

(7) FIG. 7 is a graph showing a change of ferrocoke strength with lapse of time.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

(8) The invention includes a ferrocoke manufacturing method having a high strength and a high reactivity without causing the decrease of the strength even if an inferior quality coal is used. That is, this method is characterized in that when a mixture of coal and iron ore is shaped and carbonized to manufacture ferrocoke, a coal having a button index (CSN) of not more than 2.0 is used as a hardly softening coal. The reason why the button index (CSN) of the hardly softening coal is limited to not more than 2.0 is due to the fact that when a coal having a CSN value of more than 2.0 is used, if a shaped body of this hardly softening coal and an iron ore (a weight ratio of the iron ore in the mixture of the hardly softening coal and the iron ore is 30 mass %) is carbonized, fusion between the mutual shaped bodies is generated inevitably and hence the effect of suppressing the fusion by the addition of the hardly softening coal cannot be obtained.

(9) The lower limit of the button index (CSN) of the hardly softening coal is not particularly limited. However, when the button index (CSN) of the hardly softening coal is 1.0, a target strength may not be attained in accordance with a volatile matter of the hardly softening coal as seen from examples mentioned later, so that the button index (CSN) of the hardly softening coal is preferable to be 1.5-2.0.

(10) In examples according to the invention that the coal is a blend of hardly softening coal and easily softening coal and the hardly softening coal is a coal having a button index (CSN) of 1.5-2.0, it is preferable that the easily softening coal satisfies that a value obtained by multiplying CSN of the easily softening coal by a blending ratio thereof in all coals is not more than 5.0. Furthermore, in examples according to the invention that the coal is a blend of hardly softening coal and easily softening coal and the hardly softening coal is a coal having a button index (CSN) of 1.0, it is preferable that the hardly softening coal is a coal having a volatile matter of not less than 17% and the easily softening coal satisfies that a value obtained by multiplying CSN of the easily softening coal by a blending ratio thereof in all coals is within a range of 0.3-5.2. Moreover, the volatile matter is measured according to JIS M8812 and represented by dry ash free base.

EXAMPLES

(11) There will be described preferable examples using a blend of a hardly softening coal and an easily softening coal below.

(12) This experiment is performed according to the following process. A shaped body is manufactured by changing each CSN of a hardly softening coal and an easily softening coal (carbon content and MF are varied with the change of CSN) to evaluate strength after carbonization (ferrocoke strength). The hardly softening coal and the easily softening coal are blended so as to render coals of plural brands into predetermined CSN and carbon content. As a quality of the coal used, Table 1 shows a grade of the easily softening coal and Table 2 shows a grade of the hardly softening coal. As an iron ore are used ones having a total iron content of 57 mass %. A pulverized grain size of each of the coal and iron ore is not more than 3 mm in total. Also, a maximum fluidity MF in Table 2 is measured by a Gieseler plastometer. A sensitivity is low at a lower range of MF. In this time, MF measurement of the hardly softening coal is performed five times, and an average value thereof is determined as MF value.

(13) TABLE-US-00001 TABLE 1 Brand CSN (-) MF (ddpm) Ash content (%) A 2.5 30 21.5 B 3.0 4 9.7 C 3.5 2 18.1 D 4.5 33 8.8 E 5.0 29 8.0 F 5.5 82 7.8 G 6.0 81 8.9 H 6.5 85 7.3 I 7.0 2 8.8

(14) TABLE-US-00002 TABLE 2 Brand MF (ddpm) CSN (-) VM (%) Ash content (%) J 0.00 1.0 12.5 12.7 K 0.00 1.0 14.6 10.8 L 0.60 1.0 17.2 10.9 M 0.40 1.0 17.2 11.3 N 1.00 1.5 17.4 9.9 O 0.80 1.5 27.5 22.5 P 1.40 2.0 22.2 10.4 Q 1.60 2.0 23.6 15.2 R 1.60 2.5 25.5 11.1 S 1.80 2.5 26.5 14.5 T 1.80 3.0 26.5 9.7 U 1.80 3.0 25.5 10.7

(15) Moreover, the shaping treatment is performed by the following method. That is, the coal, iron ore and binder are mixed so that blending ratios are set to 65.8 mass %, 28.2 mass % and 6 mass % to the total weight of raw materials, respectively. As to the coal, the easily softening coal and the hardly softening coal are blended. A mixture of these raw materials is kneaded in a high-speed mixer at 140-160° C. for about 2 minutes, and the kneaded material is shaped into briquettes in a double roll type shaping machine. A size of the roll is 650 mm in diameter and 104 mm in width, and shaping is performed at a peripheral speed of 0.2 m/s and a linear pressure of 4 t/cm. A shaped body has a size of 30 mm×25 mm×18 mm (6 cc) and is oval.

(16) Then, the thus obtained shaped bodies are carbonized according to the following carbonization process of a laboratory scale. That is, 3 kg of the shaped bodies are filled in a carbonization can of 300 mm in both length and 400 mm in height, kept at a furnace wall temperature of 1000° C. for 6 hours and then cooled in nitrogen atmosphere. The carbonized material cooled to room temperature is taken out to measure strength and evaluate a fusion ratio. The measurement of the strength is performed as a drum strength (DI.sup.150.sub.6) In this regard, DI.sup.150.sub.6 means a value obtained by measuring a mass ratio of coke having a grain size of not less than 6 mm under a condition of 15 rpm, 150 revolutions by a revolution strength testing method of JIS K2151. A target strength is set to not less than 82. The fusion ratio is evaluated by a weight percentage of a fused material to a total weight of the carbonized material.

Example 1: Preferable CSN and Volatile Matter of Hardly Softening Coal and Nature of Easily Softening Coal in a Coal Blend

(17) As to the results of the above experiment, ferrocoke strength to a value obtained by multiplying CSN of the easily softening coal by a weight ratio of the easily softening coal to the total coal weight is plotted in a graph of FIG. 1. As the hardly softening coal is used a coal having CSN of 1.0 and a volatile matter of 13.6% and 17.2%. Table 2 describes two kinds of coals having CSN of 1.0 as brands J and K of the hardly softening coal. In the case that the volatile matter is 13.6%, the brands J and K are blended in an each amount of 50 mass %, while in the case that the volatile matter is 17.2%, brands L and M are blended in an each amount of 50 mass %.

(18) Table 3 shows a blending condition of the easily softening coal blended with the hardly softening coal, value obtained by multiplying CSN of the easily softening coal by a weight ratio of the easily softening coal to the total coal weight, and strength of ferrocoke obtained from a mixed coal blended with a coal having CSN of 1.0 as the hardly softening coal as data in the graph of FIG. 1. Even when any easily softening coal is used, if the hardly softening coal has CSN of 1.0 and a volatile matter of 13.6%, it can be seen that the strength after the carbonization largely falls below the target strength different from that of the examples described in the above patent documents. Since ferrocoke contains an iron ore having no compatibility with carbon materials, it is considered that the ferrocoke strength is apt to be largely decreased when being blended with a hardly softening coal hardly fused by softening and showing no swellability.

(19) In FIG. 1, the plot having 0 as the value of abscissa axis shows the result in the blending of only hardly softening coals. When the volatile matter is 13.6%, the strength is largely decreased. On the other hand, when the volatile matter is 17.2%, the strength is near to the target value in the blending of only the coals. In the case that the blending ratio of the easily softening coal is 0.1-0.8, the strength exceeds the target value when the value obtained by multiplying CSN of the easily softening coal by the blending weight ratio of the easily softening coal is 0.3-5.2. Even when the volatile matter is 17.2%, it is considered that the swellability is low at CSN of 1.0, but since the coal is at a state of somewhat promoting carbonization as compared to strong caking coal, mitigation of carbon structure associated with heating is easily caused as compared to the case that the volatile matter is 13.6%. To this end, it is guessed that the coal is slightly softened under carbonization condition through rapid heating as in this experiment (rapid heating condition even in the actual shaft furnace) and hence the strength is recognized to be in a range exceeding the target value. Moreover, the reason why the optimum range is existent in the value obtained by multiplying CSN of the easily softening coal by the blending weight ratio of the easily softening coal is considered due to the fact that when the value is small, swelling of the coal is small and the adhesion between the grains is deteriorated, while when the value is large, the strength after the carbonization is decreased by increase of porosity associated with the swelling of the carbonized material.

(20) TABLE-US-00003 TABLE 3 Blending condition of easily softening coal Brand Blending CSN*Blending DI.sup.150.sub.6 (-) used CSN ratio ratio VM 13.6% VM 17.2% — — 0 0 16.0 76.0 A 2.5 0.05 0.13 18.0 77.0 B 3.0 0.1 0.30 25.1 82.0 C 3.5 0.2 0.70 38.0 82.0 D 4.5 0.3 1.35 43.2 82.6 D 4.5 0.6 2.70 60.0 83.2 E 5.0 0.6 3.00 58.0 84.0 F 5.5 0.8 4.40 64.0 83.5 G 6.0 0.6 3.60 68.0 84.5 H 6.5 0.8 5.20 71.0 83.0 I 7.0 0.8 5.60 69.0 80.0

Example 2: Preferable CSN of Hardly Softening Coal and Nature of Easily Softening Coal in a Coal Blend

(21) Hardly softening coals having CSN of 1.5 and 2.0 are examined below. That is, the examination is performed by blending coals N and O having CSN of 1.5 and coals P and Q having CSN of 2.0 as shown in Table 2 in an each amount of 50 mass %. Table 4 shows a blending condition of an easily softening coal blended with the hardly softening coal, value obtained by multiplying CSN of the easily softening coal by a weight ratio of the easily softening coal to the total coal weight, and strength of ferrocoke obtained from a coal blend combined with the hardly softening coal having CSN of 1.5 and 2.0 as the examination results. Based on the results of Table 4 are plotted ferrocoke strengths to the value obtained by multiplying CSN of the easily softening coal by the weight ratio of the easily softening coal to the total coal weight in the graph of FIG. 2.

(22) TABLE-US-00004 TABLE 4 DI.sup.150.sub.6 (-) Hardly Hardly Blending conditions of easily softening coal softening softening Brand Blending CSN*Blending coal coal used CSN ratio ratio CSN:1.5 CSN:2.0 — — 0 0 82.0 82.0 A 2.5 0.1 0.25 82.1 82.4 A 2.5 0.2 0.50 82.1 82.0 B 3.0 0.2 0.60 82.3 83.3 C 3.5 0.8 2.80 84.1 84.3 D 4.5 0.4 1.80 83.8 83.0 D 4.5 0.8 3.60 85.6 85.0 E 5.0 0.4 2.00 82.4 82.0 E 5.0 0.8 4.00 84.5 85.5 F 5.5 0.6 3.30 84.5 85.8 F 5.5 0.8 4.40 84.6 84.1 G 6.0 0.6 3.60 84.0 84.1 G 6.0 0.8 4.80 83.3 82.2 H 6.5 0.2 1.30 82.5 83.0 H 6.5 0.8 5.20 81.7 81.8 I 7.0 0.4 2.80 84.6 84.0 I 7.0 0.6 4.20 83.1 84.0

(23) As seen from the results shown in Table 4 and FIG. 2, when the blending ratio of the easily softening coal is not more than 0.8, the strengths higher than that in the case that CSN of the hardly softening coal shown in FIG. 1 is 1.0 are obtained even in any values obtained by multiplying CSN of the easily softening coal by the blending weight ratio of the easily softening coal. Also, it can be seen that the strength is made to not less than the target value when the value obtained by multiplying CSN of the easily softening coal by the blending weight ratio of the easily softening coal is not more than 5.0. Moreover, the reason why the optimum range is existent in the value obtained by multiplying CSN of the easily softening coal by the blending weight ratio of the easily softening coal is considered due to the fact that if the value is larger, the strength after the carbonization is decreased due to the increase of the porosity associated with the swelling of the carbonized material.

Example 3: Preferable CSN of Hardly Softening Coal in a Coal Blend

(24) A fear of fusing the carbonized material is caused in the case that CSN of the hardly softening coal is 2.5. In FIG. 3 is shown a photograph of a fused case. Table 5 and FIG. 4 show results of fusion test when two kinds of hardly softening coals having CSN of 2.0 and 2.5 are carbonized in a laboratory scale to the value obtained by multiplying CSN of the easily softening coal by a blending weight ratio of the easily softening coal. In Table 2 are shown two kinds of coals having CSN of 2.5 as hardly softening coals P and Q. In this test, these coals are blended in an each amount of 50 mass %. As seen from the results of FIG. 4, the fusion ratio is not more than 10% when CSN of the hardly softening coal is 2.0. On the other hand, when CSN of the hardly softening coal is 2.5, the fusion ratio is not less than about 20%. Moreover, the term “fusion ratio” means a mass ratio of fused ferrocoke as shown in FIG. 3 in mass of ferrocoke produced.

(25) TABLE-US-00005 TABLE 5 Fusion ratio (%) Hardly Hardly Blending conditions of easily softening coal softening softening Brand Blending CSN*Blending coal coal used CSN ratio ratio CSN:2.0 CSN:2.5 A 2.5 0.2 0.5 3.0 12.0 A 2.5 0.6 1.5 3.0 14.0 B 3.0 0.8 2.4 6.1 15.8 D 4.5 0.8 3.6 7.1 20.5 E 5.0 0.8 4.0 8.2 22.0 F 5.5 0.2 1.1 5.3 15.0 F 5.5 0.6 3.3 4.0 19.0 G 6.0 0.2 1.2 6.1 17.0 G 6.0 0.8 4.8 7.0 20.0 H 6.5 0.8 5.2 8.7 25.0 I 7.0 0.4 2.8 5.0 16.0 I 7.0 0.8 5.6 8.8 33.0

(26) In this carbonization test, the shaped bodies are carbonized at a fixed state (fixed layer). In the case of a continuous production, it is a continuous system wherein the shaped bodies are charged from a top of a furnace such as shaft type furnace and the carbonized material is continuously discharged from a bottom of the furnace. It is commonly considered that the fusion is apt to be caused in the carbonization at the fixed layer as compared to the continuous system. Then, the inventors have made a test in a carbonization furnace of a laboratory scale on the shaped bodies causing poor discharge associated with fusion inside the furnace in the continuous shaft type carbonization bench plant in order to evaluate the difference of fusion ratios between the carbonization in the fixed layer and the continuous carbonization. In this carbonization test, the shaped bodies showing the fusion ratio of not less than 10% cause the poor discharge associated with the fusion inside the furnace in the continuous carbonization furnace. The dotted line in FIG. 4 shows a lower limit of the fusion ratio causing the poor discharge in the continuous carbonization furnace. When CSN of the hardly softening coal is 2.5, a fear of fusion becomes large in the continuous carbonization, so that the upper limit of CSN in the hardly softening coal is revealed to be 2.0.

Example 4: Other Preferable Cases

(27) In this example, coal, iron ore and binder are mixed so as to render each blending ratio into 65.8 mass %, 28.2 mass % and 6 mass % to the total weight of these raw materials, respectively. A coal A in Table 1 is used as an easily softening coal and a coal O in Table 2 is used as a hardly softening coal. A blending ratio of the easily softening coal to the hardly softening coal is 1/9 and 7/3. Thus, a value obtained by multiplying CSN of the easily softening coal by a weight ratio of the easily softening coal to the total coal weight is 0.25, which is obtained by multiplying CSN of 2.5 of the coal A by the blending ratio of 0.1 of the easily softening coal in the case of 1/9. In the case of 7/3, the value is 1.75, which is obtained by multiplying CSN of 2.5 of the coal A by the blending ratio of 0.7 of the easily softening coal.

(28) In the carbonization test is used a shaft type carbonization furnace of 0.3 t/d shown in FIG. 5. It is a continuous countercurrent type furnace made of SUS and having a size of 0.25 m in diameter×3 m in height and provided with a cooling equipment for generated gas. Thermocouples are disposed at an interval of about 10-20 cm in a center of a reaction tube from the top of the furnace toward a cooling zone at a bottom of the furnace to determine heating conditions for a predetermined heat pattern. In this example, an upper stage electric furnace is set to 700° C. and a lower stage electric furnace is set to 850° C., and further a high-temperature gas of 850° C. is passed from the bottom of the furnace at a flow rate of 60 L/min. FIG. 6 shows a heat pattern when the temperature in the lower stage electric furnace and the high temperature gas is set to 850° C. A highest achieving temperature in the center of the reaction tube is 852° C., and a time keeping this temperature is about 60 minutes. Green briquettes are charged into the inside of the furnace from the top of the furnace through a double valve, while carbonized ferrocoke is continuously discharged from the bottom of the furnace. Ferrocoke discharged at an interval of 30 minutes is taken out to measure a strength. The results are shown in FIG. 7.

(29) The followings are understood from the results of FIG. 7. Firstly, a carbonized material is discharged from the start of ferrocoke discharge up to 2 hours under a condition that a carbonization temperature of a shaped body is not sufficient, so that the ferrocoke strength is low. However, the discharge of ferrocoke becomes steady at a time exceeding 2 hours from the start of the discharge. In the case that CSN*blending ratio of easily softening coal is 1.75, the target strength is stably held at a time exceeding 2 hours from the start of the discharge. In the case that CSN*blending ratio of easily softening coal is 0.25, the strength becomes constant at a state of falling down the target value.

(30) From the above is understood that the preferable conditions of hardly softening coal and easily softening coal for manufacturing a high-strength ferrocoke are as follows.

(31) In order to manufacture a high-strength ferrocoke, it is important on the premise of using a blend of easily softening coal and hardly softening coal that a coal having a button index (CSN) of 1.0 and a volatile matter of not less than 17.0% or a button index (CSN) of 1.5-2.0 is used as the hardly softening coal and the easily softening coal satisfies that a value obtained by multiplying CSN of the easily softening coal by a blending ratio thereof to the total coal is within a range of 0.3-5.2.

(32) Also, in order to manufacture a high-strength ferrocoke, it is important on the premise of using a blend of easily softening coal and hardly softening coal that a coal having a button index (CSN) of 1.5-2.0 is used as the hardly softening coal and the easily softening coal satisfies that a value obtained by multiplying CSN of the easily softening coal by a blending ratio thereof to total coal weight is not more than 5.0.

(33) According to the ferrocoke manufacturing method according to the invention can be manufactured ferrocoke having a high strength and being low in cost and high in the reactivity, and it is possible to operate a blast furnace at a low reducing material ratio by using the thus obtained ferrocoke as a coal material.