Method for producing sintered ore

Abstract

Proposed is a method for producing a sintered ore by improving a yield when a carbonaceous material having a low combustion start temperature is used in a sintering step. The method for producing a sintered ore involves using a carbonaceous material having a combustion start temperature of 550°C or lower, wherein a gaseous fuel supplied above a charging layer in a sintering machine is introduced into the charging layer by suction from below the charging layer together with air. It is preferable that the gaseous fuel is suctioned within a range from an ore suppling part above the charging layer to 1 / 2 of the length in a traveling direction of the sintering machine; the carbonaceous material having the combustion start temperature of 550°C or lower is an organic resource excluding fossil fuel, a carbonaceous material produced from the organic resource as a raw material, or a combination thereof; the gaseous fuel included in the air to be introduced in the charging layer has a concentration below the lower flammable limit; and, in the supply of the gaseous fuel, the amount of the carbonaceous material is reduced by 10% or less, relative to the total amount of all carbonaceous materials when no gaseous fuel is supplied, in terms of heat quantity equivalent to coke.

Description

Technical Field

[0001] This invention relates to a method for producing a sintered ore used in steel industry.Background Art

[0002] In a process for sintering an iron ore, a mixture of iron ore, flux, and carbonaceous material as a solid fuel is sintered in a sintering machine using the combustion heat of the carbonaceous material. Coke breeze is generally used as the carbonaceous material. Anthracite coal or the like other than coke breeze may be used to diversify risks such as price fluctuation of raw coal, troubles of coke-producing equipment and the like.

[0003] Meanwhile, in response to a growing concern on the environmental conservation, diversification of carbonaceous materials is progressing with the intention of reducing the burden on the environment, apart from the idea of risk diversification.

[0004] For example, Patent Literature 1 discloses a carbonaceous material for the sintering of an iron ore, assuming subbituminous coal or brown coal. This carbonaceous material has a reaction start temperature of 550°C or lower, a volatile matter content (VM) of 1.0% or more, an atomic ratio of hydrogen to carbon (H / C) of 0.040 or more and a pore content having a pore size of 0.1 to 10 µm measured by a mercury intrusion porosimetry of 50 mm 3< / g or more.

[0005] Patent Literature 2 discloses a method in which a solid fuel having a combustion start temperature below 450°C is included by 10 mass% or more, when a high crystallization water iron ore containing 4.0 mass% or more of crystallization water is used by 30% or more.

[0006] Patent Literature 3 discloses a two-stage ignition sintering method involving forming sinter-charging layers in two stages and igniting each surface to initiate sintering, in which anthracite coal, and carbonaceous material with a combustion start temperature lower than that of the other two materials are used as raw materials on the lower stage side.

[0007] Patent Literature 4 discloses a method in which a carbonaceous material having a low combustion start temperature as a coagulation material is mixed with coke breeze or anthracite coal in an amount of 25 to 75% of a total carbon content, and at least one of a carbonaceous material having a low combustion start temperature and a carbonaceous material having a high combustion start temperature is added at a latter half of a granulation step.Citation ListPatent Literature

[0008] Patent Literature 1: WO-2010 / 087468 Patent Literature 2: WO-2010 / 106756 Patent Literature 3: JP-A-2020-186436 Patent Literature 4: JP-A-2022-033594 Summary of InventionTechnical Problem

[0009] However, these prior arts have the following problems.

[0010] The use of a carbonaceous material having a low combustion start temperature in a sintering step results in a reduced yield. While the methods disclosed in Patent Literature 1 and Patent Literature 2 address the use of a carbonaceous material having a low reaction start temperature or combustion start temperature, they do not describe the adverse impact on the yield in the production process of a sintered ore when the carbonaceous material having a low combustion start temperature is used, nor do they consider the countermeasure to increasing the yield, etc.

[0011] The method disclosed in Patent Literature 3 is based on the premise of the two-stage ignition sintering method and cannot be applied to the general sintering method. The method disclosed in Patent Literature 4 uses the carbon content for control. However, due to the wide variety of carbonaceous materials with low combustion start temperatures, there is significant variation in combustion start temperature. In Patent Literature 4, no consideration has been given to this significant variation and its effect on yield associated with this variation.

[0012] The present invention is made in view of the above background and aims to propose a method for producing a sintered ore including improving a yield when a carbonaceous material with a low combustion start temperature is used in a sintering step.Solution to Problem

[0013] The method for producing a sintered ore according to the invention that advantageously solves the above problems utilizes a carbonaceous material having a combustion start temperature below 550°C, and characterized by introducing a gaseous fuel supplied above a charging layer of a sintering machine into a charging layer by suction from below the charging layer together with air.

[0014] The method for producing a sintered ore according to the invention have the following preferable solution means: (a) the gaseous fuel is suctioned within a range from an ore supplying part above the charging layer to 1 / 2 of the length in a traveling direction in the sintering machine; (b) the carbonaceous material having a combustion start temperature of 550°C or lower is an organic resource excluding fossil fuel, a carbonaceous material produced from the organic resource as a raw material, or a combination thereof; (c) the gaseous fuel included in the air to be introduced into the charging layer has a concentration below a lower flammable limit; (d) when the gaseous fuel is supplied, the amount of the carbonaceous material is reduced by 10% or less relative to the total amount of all carbonaceous materials when no gaseous fuel is supplied, in terms of heat quantity equivalent to coke. Advantageous Effects of Invention

[0015] In the method for producing a sintered ore according to the invention, when the carbonaceous material having the low combustion start temperature is used in the sintering step, the gaseous fuel supplied to the upper side of the charging layer in the sintering machine is introduced into the charging layer by suction from below the charging layer together with air, which can improve the heat pattern to suppress the decrease in yield.Brief Description of Drawings

[0016] Fig. 1 is a graph showing an influence of biomass coal and gaseous fuel on a sinter yield. Fig. 2 is a graph showing an influence of a blowing range of a gaseous fuel on a sinter yield. Description of Embodiments

[0017] An embodiment of the present invention will be specifically described below. The following embodiment presents examples of a device and a method for embodying the technical idea of the present invention, and is not intended to restrict the configuration to the one to be described below. Thus, various changes can be made to the technical idea of the present invention within the technical scope described in the claims.

[0018] In the diversification of carbonaceous materials to reduce environmental burden, attention is paid to organic resources excluding fossil fuel or a carbonaceous material produced from the organic resource as a raw material (hereinafter referred to as biomass coal). Since biomass coal absorbs carbon dioxide during the growth of the plant as a raw material, the fuel using the biomass coal can be considered as having no carbon dioxide emissions to the external environment, based on the concept of carbon neutrality. Thus, the use of biomass coal in a sintering process of an iron ore, which normally uses coke breeze, is also being considered. The characteristic of biomass coal is that it has a low combustion start temperature compared to coke. Specifically, the combustion start temperature of coke is in the range of 650 to 750°C, while the combustion start temperature of biomass coal is approximately 550°C or lower.

[0019] In this embodiment, a flux and a carbonaceous material are added to an iron ore as auxiliary materials during the sintering step and continuously charged onto the sintering machine to form a sinter bed (charging layer). After the sinter bed is ignited at its upper end face, the exhaust gas is suctioned from the lower end face, whereby the combustion of the carbonaceous material is propagated from the upper end face to the lower end face of the bed to conduct the reaction and agglomeration between the iron ore and the flux by using the heat. A blower is used to suction the exhaust gas from the lower end face. The suctioned exhaust gas is passed through a duct and discharged through a chimney via a dust collector and desulfurization-denitration equipment.

[0020] Biomass coal is characterized by having a low combustion start temperature. This is considered due to the fact that biomass coal is porous and has a very large specific surface area compared to coke breeze (derived from fossil fuel), which is normally used in a sintering step, and a high combustion rate is achieved even at a low temperature. Therefore, biomass coal not only has a low combustion start temperature but also tends to have a high combustion rate after the start of combustion.

[0021] The combustion reaction of the carbonaceous material is a gas-solid reaction, where the carbonaceous material as a solid reacts with oxygen in surrounding gas for combustion. In the gas-solid reaction under a gas flow condition such as sintering, a very thin region called gas boundary layer forms on the surface of the solid. This gas boundary layer maintains a laminar flow, unaffected by external turbulent flow. In the combustion of the carbonaceous material, oxygen is used in such a way that it diffuses from the outside of the gas boundary layer through its inside to reach the surface of the carbonaceous material. When the combustion rate of the carbonaceous material is very high, the oxygen consumption rate on the surface caused by the combustion of the carbonaceous material exceeds the oxygen supply rate via diffusion within the gas boundary layer, even when the surrounding oxygen concentration remains high. This results in a reduction of the oxygen concentration within the gas boundary layer. As a result, the carbonaceous material causes incomplete combustion, leading to an increased production of carbon monoxide. Accordingly, at a very high combustion rate, some of the heat from the combustion of the carbonaceous material is not used and is released outside the system as carbon monoxide. This is considered to reduce the reaction heat used in sintering and reduce the yield. Further, the high combustion rate corresponds to a short time from start to finish of combustion. The combustion concludes shortly after it begins, followed by cooling initiated by air flown from above. This creates a heat pattern in which the temperature of the charging layer in the sintering machine rises abruptly and falls within a short time. This effect causes the sintering reaction at high temperatures to be completed in a short time, leading to insufficient bonding between the ores.

[0022] In this embodiment, the gaseous fuel supplied above the charging layer in the sintering machine is introduced into the charging layer by suction from below the charging layer together with air. The gaseous fuel thus introduced is combusted above a position where the carbonaceous material is combusted in a height direction of the charging layer and mitigates the cooling effect of air flown from above, thus suppressing the decrease in the temperature in the charging layer. This effect allows the charging layer to maintain a high temperature for a long time, i.e., a long sintering reaction time, resulting in a strong bonding between the ores. Such an effect develops even under conditions using typical coke breeze or the like. In particular, carbonaceous materials having a low combustion start temperature, such as biomass coal, have a short sintering reaction time in a high temperature range in the base heat pattern before the gaseous fuel is blown in. Therefore, the effect of prolonging the sintering reaction time in the high temperature range by blowing the gaseous fuel is largely developed as compared to the use of coke or the like.

[0023] Furthermore, oxygen is consumed when the gaseous fuel is combusted above the position where the carbonaceous material in the charging layer ignites, thus reducing the concentration of oxygen supplied to the carbonaceous material to be combusted in the lower portion of the charging layer. This has an effect of reducing the combustion rate of the carbonaceous material. This effect may reduce production due to the lower combustion rate when coke breeze is used. However, such a negative effect can be mitigated by using biomass coal having a high combustion rate.

[0024] In a typical sintering machine, the yield tends to be lower in the upper layer portion due to heat deficiency, while overheating tends to occur in the lower layer portion. This is due to the fact that cold air is flown directly into the upper layer portion from above the charging layer. The upper layer portion is more susceptible to the heat deficiency by the use of biomass coal. Therefore, the suction of the gaseous fuel should be conducted within a range from an ore supplying part above the charging layer to 1 / 2 of the length in a traveling direction in the sintering machine, where the reaction zone remains in the upper layer portion. Preferably, the suction of the gaseous fuel should be conducted within a range of 1 / 4 of the length or more, more preferably within a range of 1 / 3 of the length or more.

[0025] The gaseous fuel should be diluted below the lower flammable limit. This is because if combustion starts outside above the charging layer by residual fire on the charging layer in the sintering machine, the effect of blowing the gaseous fuel cannot be sufficiently achieved, which may lead to fire or the like. Further the gaseous fuel may be any gas such as city gas, natural gas, propane gas, coke-oven gas and so on; non-toxic city gas, natural gas, propane gas, etc. are preferable. The lower flammable limit of each gaseous fuel with respect to air is, for example, city gas: 4.5 volume%, natural gas: 4.4 volume%, propane gas: 2.4 volume%, etc. The lower concentration limit of the gaseous fuel is defined by the required heat quantity. From a viewpoint of effectively utilizing the gaseous fuel, the lower concentration limit of the gaseous fuel should be more than 0 volume%, and preferably 1 / 20 or more of the lower flammable limit.

[0026] When the yield was increased by introducing the gaseous fuel into the charging layer, the mixing amount of the carbonaceous material may be reduced within a range of 10% or less of the total amount of all carbonaceous materials. This is because the heat deficiency in the upper layer portion of the charging layer can be solved by blowing the gaseous fuel to reduce the excess amount of heat in the lower layer portion.Examples(Example 1)

[0027] The effect of the present invention was verified by using a batch-type sintering test apparatus. T1 was a level at which only commonly used coke was used, and T3 was a level at which biomass coal was used instead of 20% of the amount of coke. In T2 and T4 to T7, city gas as gaseous fuel was adjusted to the concentration of 0.4 volume% with respect to the suctioned air and was blown in for 7 minutes, starting 30 seconds after the extinction of an ignition furnace. The ore and auxiliary materials used for each level had the same mixing amount. The test conditions and results are shown in Table 1 and Fig. 1. In T2, where city gas was blown in, the yield is increased by about 3%, with respect to T1 as Reference Example, where only coke was used. In T3, where 20% of coke was replaced by biomass coal, the yield decreased by about 8% with respect to the baseline (T1). Meanwhile, the yield was increased by about 10% in T4 where city gas was blown in with respect to T3. A greater effect was observed in T4 compared to T2, where city gas was blown in T1 with the same amount of heat. On the other hand, T5, T6 and T7 were levels where the heat quantity was reduced incrementally by 0.2% from T4, in terms of heat quantity equivalent to coke, while maintaining the same ratio of coke to biomass coal. The yield decreased more as the heat quantity was more reduced in the order of T5, T6 and T7. In T7, where the heat quantity was reduced by 12% with respect to the total coke amount, the yield fell below the base level (T1). [Table 1]No.CokeBiomass coalCity gasYieldRemarksmass%*Presence or absencemass%T15.000Absence76.1Reference ExampleT25.000Presence79.2Reference ExampleT34.001.00Absence68.3Comparative ExampleT44.001.00Presence78.3Invention ExampleT53.840.96Presence77.5Invention ExampleT63.680.92Presence76.3Invention ExampleT73.520.88Presence75.2Invention Example*Mass% in terms of heat quantity equivalent to coke relative to raw material. (Example 2)

[0028] The blowing range of the gaseous fuel was verified. Since this test was a batch-type test, the blowing over an entire length above the charging layer was simulated to the blowing for the total sintering time. The blowing was conducted by adjusting the concentration of the city gas to 0.4 volume% with respect to the suction air. Moreover, the ore and auxiliary materials used for each level had the same mixing amount. The test conditions and the results are shown in Table 2 and Fig. 2. With respect to T3 of Example 1 as a base, gaseous fuel was blown in T4 for 7 minutes, which corresponded to 25% of the total sintering time. In T8 to T10, the blowing time of the gaseous fuel were 50%, 75% and 100% of the total sintering time, respectively. As a result, the effect of increasing the yield was observed at the blowing time of the gaseous fuel up to 50% of the total sintering time, but the effect was substantially saturated under the conditions of 75% and 100%. It is considered that the effect by the blowing of the city gas was hardly developed since the reaction zone reached the lower layer portion of the charging layer in the last half of the sintering time and sufficient heat had been already provided. [Table 2]No.CokeBiomass CoalSuction range [%] of city gasYieldRemarksmass%*Percentage to entire lengthmass%T34.001.00068.3Comparative ExampleT44.001.002578.3Invention ExampleT84.001.005079.5Invention ExampleT94.001.007579.3Invention ExampleT104.001.0010079.4Invention Example*Mass percentage in terms of heat quantity equivalent to coke relative to raw material.

Claims

1. A method for producing a sintered ore comprising using a carbonaceous material having a combustion start temperature of 550°C or lower, characterized in that a gaseous fuel supplied above a charging layer in a sintering machine is introduced into the charging layer by suction from below the charging layer together with air.

2. The method for producing a sintered ore according to claim 1, wherein the gaseous fuel is suctioned within a range from an ore supplying part above the charging layer to 1 / 2 of the length in a traveling direction in the sintering machine.

3. The method for producing a sintered ore according to claim 1, wherein the carbonaceous material having a combustion start temperature of 550°C or lower is an organic resource excluding fossil fuel, a carbonaceous material produced from the organic resource as a raw material, or a combination thereof.

4. The method for producing a sintered ore according to claim 1, wherein the gaseous fuel included in the air to be introduced into the charging layer has a concentration below a lower flammable limit.

5. The method for producing a sintered ore according to claim 1, wherein when the gaseous fuel is supplied, the amount of the carbonaceous material is reduced by 10% or less relative to the total amount of all carbonaceous materials when no gaseous fuel is supplied, in terms of heat quantity equivalent to coke.

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