Method of producing sintered ore

Abstract

A method of producing a sintered ore includes charging a sintering raw material containing a powder ore and a carbonaceous material onto a circulatory moving pallet to form a charged layer, igniting the carbonaceous material on a surface of the charged layer, introducing air above the charged layer containing a gaseous fuel diluted to not more than a lower limit of combustion concentration with wind boxes arranged below the pallet into the charged layer by suction, and combusting the gaseous fuel and the carbonaceous material in the charged layer, wherein more than 50% of a total supply of the gaseous fuel is supplied in a front portion of a region supplying the gaseous fuel.

Claims

1. A method of producing a sintered ore comprising: charging a sintering raw material containing a powder ore and a carbonaceous material onto a circulatory moving pallet to form a charged layer, igniting the carbonaceous material on a surface of the charged layer, introducing air above the charged layer containing a gaseous fuel diluted to not more than a lower limit of combustion concentration with wind boxes arranged below the pallet into the charged layer by suction, and combusting the gaseous fuel and the carbonaceous material in the charged layer, wherein the region supplying the gaseous fuel is a region wherein a high-temperature keeping time kept at not lower than 1200 C. but not higher than 1380 C. is less than 150 seconds when the area is sintered by combustion heat of only the carbonaceous material, and wherein more than 50% of a total supply of the gaseous fuel is supplied in a front portion of a region supplying the gaseous fuel.

2. The method according to claim 1, wherein the region supplying the gaseous fuel is not more than 40% of a machine length ranging from an ignition furnace to an ore removing portion.

3. The method according to claim 2, wherein the concentration of the gaseous fuel contained in air introduced in the charged layer is not more than the lower limit of combustion concentration.

4. The method according to claim 1, wherein the concentration of the gaseous fuel contained in air introduced in the charged layer is not more than the lower limit of combustion concentration.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic view illustrating a known sintering process.

(2) FIG. 2 is a graph showing a pressure loss distribution in a charged layer in the sintering.

(3) FIG. 3 is a graph showing a temperature distribution in a charged layer at a high productivity and a low productivity, respectively.

(4) FIG. 4 is a schematic view illustrating a change inside a charged layer with the advance of the sintering progress.

(5) FIGS. 5(a) and (b) are views illustrating a temperature distribution when a combustion zone is existent in each position of an upper portion, a middle portion and a lower portion of a charged layer and a yield distribution of a sintered ore in a widthwise section of the charged layer.

(6) FIG. 6 is a view illustrating a temperature change in a charged layer according to a change (increase) in an amount of a carbonaceous material.

(7) FIG. 7 is a view illustrating a sintering reaction.

(8) FIG. 8 is a phase diagram illustrating a process of producing a secondary hematite of a skeleton-crystal form.

(9) FIGS. 9(a) and (b) are schematic views illustrating an effect of a gaseous fuel supply on a high-temperature keeping time.

(10) FIG. 10 is a graph showing an influence of a gaseous fuel supply on a distribution of a high-temperature keeping time in a thickness direction of a charged layer.

(11) FIGS. 11(a) and (b) are graphs showing simulation results of a temperature history at a position of 50 mm depth from a surface of a charged layer according to a supplying way of a gaseous fuel.

(12) FIGS. 12(a) and (b) are views illustrating conditions of a sintering experiment simulating an actual sintering machine.

(13) FIG. 13 is a graph showing a temperature history at depth positions of 50 mm, 100 mm and 300 mm from a surface of a raw material charged layer in sintering experiments under conditions of FIG. 12, respectively.

(14) FIGS. 14(a)-(c) are graphs showing experimental results (sintering time, shatter strength, productivity) in sintering experiments under conditions of FIG. 12.

DESCRIPTION OF REFERENCE SYMBOLS

(15) 1: hopper for raw material

(16) 2, 3: drum mixer

(17) 4: hopper for floor-bedded ore

(18) 5: surge hopper

(19) 6: drum feeder

(20) 7: cutout chute

(21) 8: pallet

(22) 9: charged layer

(23) 10: ignition furnace

(24) 11: wind box (wind box)

(25) 12: cut-off plate

DETAILED DESCRIPTION

(26) As a technique to address the above issues, we proposed a technique wherein both of the maximum achieving temperature and the high-temperature keeping time in the charged layer are controlled within adequate ranges by decreasing the amount of the carbonaceous material added in the sintering raw material and introducing various gaseous fuels diluted to not more than the lower limit concentration of combustion into the charged layer from above the pallet in an area located at downstream side of the ignition furnace of the sintering machine and at a front half of the length of the sintering machine to perform combustion in the charged layer.

(27) We conducted the following experiments to study a method of supplying a gaseous fuel which is the most effective to raise a temperature during the sintering in an outermost surface portion of a sintering raw material charged layer in supplying the gaseous fuel of the same heat generation amount.

(28) At first, when the sintering is conducted by depositing a raw sintering material added with 5.0 mass % of a carbonaceous material (powdery coke) at a thickness of 400 mm onto a pallet of a sintering machine, igniting a surface portion thereof in an ignition furnace and then sucking air under a negative pressure of 1000 mmH.sub.2O with wind boxes installed below the pallet, assuming that a natural gas (LNG) as a gaseous fuel is supplied for 6 minutes after 30 seconds of the ignition (corresponding to about 35% of the total sintering time), the temperature change in the sintering at a depth position of 50 mm from the surface of the charged layer is simulated using a sintering one-dimensional model.

(29) Moreover, when the total amount of the gaseous fuel supplied is same as shown in FIG. 11(a), the simulation is conducted under 3 conditions: i.e. a condition that the concentration of the gaseous fuel supplied is constant of 0.25 vol % for the above gaseous fuel supplying time (6 minutes) (condition A); a condition that the concentration of the gaseous fuel supplied is decreased sequentially to 0.31 vol %, 0.25 vol %, 0.19 vol % from the upstream side toward the downstream side for the above gaseous fuel supplying time (6 minutes) (condition B); and a condition that the gaseous fuel is intensively supplied at a high concentration (0.4 vol %) for the first 2 minutes when the sintering reaction proceeds in the outermost surface portion of the raw material charged layer and then supplied at a low concentration (0.18 vol %) for subsequent 4 minutes (condition C).

(30) FIG. 11(b) shows simulation results of condition A supplying the gaseous fuel at a constant concentration and condition C intensively supplying the gaseous fuel at the upstream side. As seen from this figure, in condition C intensively supplying the gaseous fuel at the upstream side, the maximum achieving temperature is 1296 C., which is 21 C. higher than 1275 C. in condition A, and the time kept at not lower than 1200 C. (high-temperature keeping time) is also prolonged from 85 seconds to 105 seconds. In condition B gradually decreasing the concentration of the gaseous fuel supplied, the maximum achieving temperature is raised as compared to that in condition A, and the high-temperature keeping time is prolonged, but both the conditions are not much different. From these results, it is assumed that to raise the sintering temperature in the outermost surface portion of the raw material charged layer, if the amount of the gaseous fuel supplied (heat generation amount) is the same, it is effective to intensively supply the gaseous fuel especially in the front half portion (upstream side portion) of the gaseous fuel supplying region.

(31) Next, for the purpose of confirming the results of the above simulations, we conducted a sintering experiment wherein the sintering is conducted by filling sintering raw material at a layer thickness of 380 mm into a test pot having an inner diameter of 300 mm and a height of 400 mm shown in FIG. 12(b) to form a charged layer, igniting the surface of the charged layer with an ignition burner, and sucking air with a blower disposed below the test pot and not shown under a negative pressure of 700 mmH.sub.2O.

(32) Assuming that the gaseous fuel is supplied from three gaseous fuel supplying apparatuses installed in the actual sintering machine, the supply of the gaseous fuel (LNG) from a nozzle disposed above the charged layer is conducted under three conditions after 30 seconds of the ignition as shown in FIG. 12(a), i.e. a condition A that LNG of 0.25 vol % is supplied for 2 minutes from each apparatus (for 6 minutes in total), a condition B that LNG is supplied from each apparatus while gradually decreasing from 0.31 vol % to 0.25 vol % and further 0.19 vol %, and a condition C that LNG of a high concentration (0.4 vol %) is supplied from the first apparatus and LNG of a low concentration (0.18 vol %) is supplied from each of the remaining two apparatuses.

(33) In the above sintering experiment, a thermocouple is inserted at each position of 50 mm, 100 mm and 300 mm from the outermost surface of the raw material charged layer to measure the temperature history at each position during the sintering. In the sintering experiment, the time required for sintering is also measured, while the shatter strength SI of the obtained sintered ore (mass % of particles having a particle size of not less than 10 mm when being sieved after the drop test) is measured according to JIS M8711, and the productivity of the sintered ore is determined from these measured values.

(34) In FIG. 13 are shown the temperature results measured on condition A and condition C at each position of 50 mm, 100 mm and 300 mm from the outermost surface of the raw material charged layer. Moreover, the results of condition B are superior to those of condition A, but both the conditions are not much different. As seen from this figure, in condition A supplying the gaseous fuel at a constant concentration and condition B sequentially decreasing the concentration of the gaseous fuel supplied from the upstream side to the downstream side, the maximum achieving temperature at a position of 50 mm from the surface is lower than 1200 C. (the high-temperature keeping time=0), while in condition C intensively supplying the gaseous fuel on the upstream side, the maximum achieving temperature is 1265 C. and the high-temperature keeping time is ensured to be approximately 1 minute (50 seconds). Moreover, in condition C, the maximum achieving temperature at a position of 100 mm from the surface is raised and the prolongation of the high-temperature keeping time is attained.

(35) FIG. 14 shows the results of sintering time, shatter strength and productivity obtained under each of conditions A and C. Moreover, the results of condition B are superior to those of condition A, but there is no difference from condition A. As seen from FIG. 14, the sintering time is somewhat prolonged in condition C intensively supplying the gaseous fuel on the upstream side as compared to condition A supplying the gaseous fuel at a constant concentration and condition B sequentially decreasing the concentration, while the strength of the sintered ore (shatter strength) is increased to cause an improvement of about 3% in the productivity. From these results, it can be seen that if the amount of the gaseous fuel supplied (heat generation amount) is same, the high-quality sintered ore can be produced with a high productivity by intensively supplying the gaseous fuel at the front half portion (upstream side portion) of the gaseous fuel supply region.

(36) It is necessary that the gaseous fuel is supplied in a region wherein the time kept at the maximum achieving temperature of not lower than 1200 C. during the sintering in the raw material layer cannot be ensured for not less than 150 seconds, that is, a region wherein the high-temperature keeping time is less than 150 seconds. The length of this region is varied depending on the specification of the sintering machine or the operational conditions of the sintering, but is generally about 30% of the front side (upstream side) of a machine length ranging from the ignition furnace to the ore removing portion (effective machine length).

(37) Even in the region wherein the high-temperature keeping time is less than 150 seconds, the high-temperature keeping time tends to be more decreased on the front side (the upstream side). Therefore, when the gaseous fuel is supplied from a viewpoint of compensating heat generation amount intensively on a region having a short high-temperature keeping time, it is required to supply more than 50% of the total supply of the gaseous fuel on a front portion of the gaseous fuel supply region, and preferably it is desirable to supply not less than 65% on such a portion.

(38) When the gaseous fuel is supplied intensively on the upstream side, to more enhance the effect, the region supplying the gaseous fuel at a high concentration is preferable to be a front portion of the gaseous fuel supply region instead of the front portion. In this case, it is more preferable to supply more than 40% of the total supply of the gaseous fuel in such a portion.

(39) Also, the supply of the gaseous fuel is preferable to start on a downstream side of not less than 3 m from the outlet side of the ignition furnace (not less than 75 seconds after the ignition). When it is too close to the ignition furnace, the gaseous fuel is supplied at a state of existing a source of fire on the outermost surface of the charged layer so that there is a fear that combustion occurs before the introduction into the raw material charged layer.

(40) The gaseous fuel is not limited to the aforementioned LNG (natural gas), and can preferably be, for example, a by-product gas of an ironworks such as blast furnace gas (B gas), coke oven gas (C gas), a mixed gas of blast furnace gas and coke oven gas (M gas) or the like, a flammable gas such as town gas, methane gas, ethane gas, propane gas or the like and a mixture gas thereof. Moreover, unconventional natural gas (shale gas) collected from a shale layer and different from the conventional natural gas can be used like LNG.

(41) The gaseous fuel contained in air introduced into the charged layer is necessary to have a concentration of not more than the lower limit of combustion concentration of the gaseous fuel. When the concentration of the diluted gaseous fuel is higher than the lower limit of combustion concentration, it is combusted above the charged layer, so that there is a fear of losing the supplying effect of the gaseous fuel or causing explosion. On the other hand, when the concentration of the diluted gaseous fuel is high, it is combusted in a low-temperature zone. Hence, there is a fear that the gaseous fuel may not contribute to the prolongation of the high-temperature keeping time effectively. The concentration of the diluted gaseous fuel is preferably not more than of the lower limit of combustion concentration at room temperature in air, more preferably not more than of the lower limit of combustion concentration, further preferably not more than 1/10 of the lower limit of combustion concentration. However, when the concentration of the diluted gaseous fuel is less than 1/100 of the lower limit of combustion concentration, heat generation amount by the combustion is lacking and the effects of increasing the strength of sintered ore and improving the yield cannot be obtained so that the lower limit is set to be 1/100 of the lower limit of combustion concentration. With regard to the natural gas (LNG), since the lower limit of combustion concentration of LNG at room temperature is 4.8 vol %, the concentration of the diluted gaseous fuel is preferably 0.053.6 vol %, more preferably 0.01.0 vol %, further preferably in a range of 0.050.5 vol %. As the method of supplying the diluted gaseous fuel may be used either of a method of supplying air containing a gaseous fuel previously diluted to not more than the lower limit of combustion concentration or a method of ejecting a gaseous fuel with a high concentration into air at a high speed to instantly dilute to not more than the lower limit of combustion concentration.

(42) To obtain a sintered ore having an excellent reduction degradation index (RDI), a high strength and an excellent reducibility, it is important that calcium ferrite produced at a temperature of not lower than 1200 C. is not decomposed into calcium silicate and secondary hematite. To this end, it is important that the temperature in the charged layer is kept at not lower than 1200 C. (solidus temperature of calcium ferrite) for a long time without exceeding the maximum achieving temperature in the charged layer during sintering over 1400 C., preferably 1380 C. In the method of producing the sintered ore, therefore, it is preferable that the region supplying the gaseous fuel is applied to a region where the high-temperature keeping time kept at not lower than 1200 C. but not higher than 1380 C. is less than 150 seconds when the sintering is performed by combustion heat of only the carbonaceous material to thereby attain the prolongation of the high-temperature keeping time.

EXAMPLE

(43) By using an actual sintering machine with a pallet width of 5 m and a length ranging from an ignition furnace to an ore removing portion (effective machine length) of 82 m and provided at a position of about 4 m downstream side of the ignition furnace with three gaseous fuel supplying apparatuses of 7.5 m in length (about 30% of effective machine length) in series is conducted a sintering experiment wherein LNG as a gaseous fuel is supplied from the gaseous fuel supplying apparatuses at a concentration of not more than the lower limit of combustion concentration into the charged layer for combustion.

(44) The concentration of LNG is varied as shown in Table 2. T1 is the conventional sintering condition wherein the sintering is conducted only by combustion heat of carbonaceous material (Comparative Example 1), T2 is a condition wherein LNG of 0.25 vol % being not more than the lower limit of combustion concentration is supplied from all of the three gaseous fuel supplying apparatuses (Comparative Example 2), T3 is a condition wherein LNG is supplied at a rate of 0.40 vol % from the most upstream gaseous fuel supplying apparatus and at a rate of 0.175 vol % from the remaining two gaseous fuel supplying apparatuses, respectively (Example 1), T4 is a condition wherein LNG is supplied at a rate of 0.50 vol % from the most upstream gaseous fuel supplying apparatus, 0.15 vol % from the subsequent gaseous fuel supplying apparatus, and 0.10 vol % from the most downstream gaseous fuel supplying apparatus, respectively (Example 2), and T5 is a condition wherein LNG is supplied at a rate of 0.60 vol % from the most upstream gaseous fuel supplying apparatus, 0.075 vol % from the subsequent gaseous fuel supplying apparatus and 0.075 vol % from the most downstream gaseous fuel supplying apparatus, respectively (Example 3). In the conventional sintering condition (Comparative Example), the amount of the carbonaceous material supplied into the sintering raw material is 5.0 mass %, and when the diluted gaseous fuel is supplied, the amount of the carbonaceous material is reduced to 4.7 mass % to prevent the maximum achieving temperature from exceeding over 1400 C.

(45) TABLE-US-00002 TABLE 2 Experiment level T1 T2 T3 T4 T5 Amount of 5.0 4.7 4.7 4.7 4.7 carbonaceous material (coke) (mass %) No. of gaseous fuel 1 2 3 1 2 3 1 2 3 1 2 3 supplying apparatuses (from the upstream side) Concentration of 0.25 0.25 0.25 0.40 0.175 0.175 0.50 0.15 0.10 0.6 0.075 0.075 gaseous fuel (LNG) supplied (vol %) Supply rate of gaseous 33.3 33.3 33.3 53.0 23.5 23.5 66.7 20.0 13.3 80.0 10.0 10.0 fuel (%) 50 50 65 35 76.7 23.3 85.0 15.0 Strength SI of product 89.2 89.7 92.0 92.3 92.5 sintered ore (%) Yield of product 76.8 78.1 80.3 80.5 81.0 sintered ore (%) Generation rate of 23.2 20.1 19.3 18.8 18.2 returned ore (%) Remarks Comparative Comparative Invention Invention Invention Example 1 Example 2 Example 1 Example 2 Example 3

(46) In the above sintering experiment, the time required to sinter is measured and at the same time the shatter strength SI of the obtained sintered ore (mass % of particles having a particle size of not less than 10 mm when being sieved after a drop test) according to JIS M8711, the yield of the product sintered ore, and the generation rate of the returned ore are determined, results of which are also shown in Table 2. From these results, it is confirmed that the strength of the sintered ore (shatter strength) is increased and the yield is improved under the condition of intensively supplying the gaseous fuel on the upstream side even in the actual sintering machine.

INDUSTRIAL APPLICABILITY

(47) The sintering method is useful as a method of producing a sintered ore used for iron-making, particularly as a raw material for a blast furnace, but also can be utilized as the other method for forming ore agglomerate.