JP7810258B2 - Sinter manufacturing method - Google Patents

Description

The present invention relates to a method for producing sintered ore for use in the steel industry.

The iron ore sintering process involves a mixture of iron ore, flux, and a carbonaceous material as solid fuel, which is then sintered in a sintering machine using the heat from the combustion of the carbonaceous material. Powdered coke is typically used as the carbonaceous material. However, other materials such as anthracite may also be used to diversify risks, such as fluctuations in the price of raw coal and problems with coke manufacturing equipment.

On the other hand, in response to growing awareness of environmental conservation in recent years, the diversification of carbon materials is progressing with the intention of reducing the burden on the environment, apart from considerations such as risk diversification.

For example, Patent Document 1 discloses a carbon material for sintering iron ore, intended for subbituminous coal and lignite, which has a reaction initiation temperature of 550°C or less, a volatile matter (VM) of 1.0% or more, a hydrogen to carbon atomic ratio (H/C) of 0.040 or more, and a pore volume of 0.1 to 10 μm in diameter measured by mercury intrusion porosimetry of 50 mm ³ /g or more.

Patent document 2 discloses a method in which 30% or more of high-crystallization-water iron ore containing 4.0% or more crystallization water is used, and 10% or more by mass of solid fuel having a combustion start temperature of less than 450°C is included.

Patent document 3 discloses a two-stage ignition sintering method in which a sintering bed is formed in two stages and the surface of each stage is ignited to carry out sintering. The raw materials used in the lower stage are coke or anthracite, along with a carbonaceous material with a lower combustion start temperature.

Patent document 4 discloses a method in which a carbonaceous material with a low combustion start temperature is blended with fine coke or anthracite as an agglomerating agent in an amount ranging from 25 to 75% of the total carbon content, and at least one of a low combustion start temperature carbonaceous material and a high combustion start temperature carbonaceous material is added in the latter half of the granulation process.

International Publication No. 2010/087468 International Publication No. 2010/106756 Japanese Patent Application Laid-Open No. 2020-186436 Japanese Patent Application Laid-Open No. 2022-033594

However, the conventional technology has the following problems.
The use of carbonaceous materials with low combustion initiation temperatures in the sintering process reduces the yield. The techniques disclosed in Patent Documents 1 and 2 describe the use of carbonaceous materials with low reaction initiation temperatures and combustion initiation temperatures. However, they do not describe the effect of using carbonaceous materials with low combustion initiation temperatures on the yield in the sinter ore manufacturing process, nor do they consider measures to improve the yield.

Furthermore, the technology disclosed in Patent Document 3 is based on the two-stage ignition sintering method, and cannot be used for general sintering methods. The technology disclosed in Patent Document 4 uniformly organizes materials by carbon content. However, it does not take into account that there are many types of carbonaceous materials with low combustion start temperatures, and that their combustion start temperatures vary, and therefore does not take into account the resulting impact on yield.

The present invention was made in consideration of the above circumstances, and aims to propose a method for producing sintered ore while improving yield when using carbonaceous material with a low combustion start temperature in the sintering process.

The method for producing sintered ore of the present invention, which advantageously solves the above-mentioned problems, is a method for producing sintered ore using carbonaceous material with a combustion start temperature of 550°C or less, and is characterized in that gaseous fuel supplied above the sintering machine's sintering bed is sucked in from below the sintering bed together with air and introduced into the sintering bed.

The method for producing sintered ore according to the present invention is as follows:
(a) sucking the gaseous fuel in a half-length range on the ore feeding section side on the sintering bed in the traveling direction of the sintering machine;
(b) The carbonaceous material having a combustion start temperature of 550°C or less is either or both of an organic resource excluding fossil fuels and a carbonaceous material produced using the organic resource as a raw material;
(c) adjusting the concentration of the gaseous fuel contained in the air introduced into the sintering bed to be less than the lower limit of flammability;
(d) when the gaseous fuel is supplied, the carbonaceous material is reduced by 10% or less in terms of calorific value equivalent to coke relative to the total amount of all carbonaceous materials when the gaseous fuel is not supplied;
This may be a more preferable solution.

In the sintered ore manufacturing method of the present invention, when carbonaceous material with a low combustion start temperature is used in the sintering process, the gaseous fuel supplied above the sintering machine's charging bed is sucked in from below the charging bed together with air and introduced into the charging bed, thereby improving the heat pattern and suppressing a decrease in yield.

1 is a graph showing the influence of biomass charcoal and gaseous fuel on sintering yield. 1 is a graph showing the effect of the gas fuel injection range on the sintering yield.

The following provides a detailed description of embodiments of the present invention. The following embodiments are intended to exemplify equipment and methods for embodying the technical concept of the present invention, and are not intended to limit the configuration to that described below. In other words, the technical concept of the present invention can be modified in various ways within the technical scope described in the claims.

In an effort to diversify carbon materials to reduce environmental impact, attention is being focused on organic resources other than fossil fuels and carbonaceous materials produced using these organic resources (hereinafter referred to as biomass charcoal). Because biomass charcoal absorbs carbon dioxide while the plants that make up its raw material grow, fuels made from biomass charcoal can be counted as carbon-neutral, with no carbon dioxide emissions outside the system. As a result, the use of biomass charcoal is being considered in iron ore sintering processes, which typically use coke breeze. A distinctive feature of biomass charcoal is its lower combustion start temperature compared to coke. While the combustion start temperature of coke is in the range of 650-750°C, the combustion start temperature of biomass charcoal is generally below 550°C.

In this embodiment, during the sintering process, flux and carbonaceous material are added as auxiliary raw materials to the iron ore and continuously charged onto the sintering machine to form a sintering bed (charging layer). After the sintering bed is ignited at the top, exhaust gas is drawn in from the bottom, causing the combustion of the carbonaceous material to spread from the top to the bottom of the bed, and the heat is used to cause the iron ore and flux to react and form into agglomerates. Exhaust gas is drawn in from the bottom using a blower. The drawn exhaust gas passes through a duct, passes through a dust collector and desulfurization and denitrification equipment, and is then discharged from a chimney.

A distinctive feature of biomass charcoal is its low combustion initiation temperature. This is thought to be because biomass charcoal is porous and has a very large specific surface area compared to the fine coke (derived from fossil fuels) commonly used in the sintering process, allowing for a high combustion rate even at low temperatures. Therefore, biomass charcoal not only has a low combustion initiation temperature, but also tends to have a high combustion rate once combustion has begun.

The combustion reaction of carbonaceous materials is a gas-solid reaction. Solid carbonaceous materials react with oxygen in the surrounding gas and burn. In gas-solid reactions under flowing gas conditions, such as sintering, a very thin layer called a gas film exists on the solid surface. The gas film maintains a laminar flow unaffected by external turbulence. Oxygen diffuses from the outside of the gas film through the gas film and reaches the surface of the carbonaceous material, where it is used for combustion. However, if the combustion rate of a carbonaceous material is very fast, even in cases where the ambient oxygen concentration is high, the rate of oxygen consumption at the surface due to combustion of the carbonaceous material is greater than the rate of oxygen supply due to oxygen diffusion within the gas film, resulting in a decrease in the oxygen concentration within the gas film. This causes incomplete combustion of the carbonaceous material and increases the amount of carbon monoxide generated. Therefore, if the combustion rate is very fast, some of the heat of combustion of the carbonaceous material is not utilized and is emitted outside the system as carbon monoxide. This is thought to result in a decrease in yield due to a decrease in the reaction heat used for sintering. Furthermore, a fast combustion rate indicates a short time from the start to the end of combustion. The sintered material burns out immediately after combustion begins, and then begins to cool down due to the air coming from above. As a result, the sintered material in the sintering machine forms a heat pattern in which the temperature rises rapidly and then drops in a short time. This effect causes the sintering reaction in the high-temperature region to occur only in a short time, which can result in insufficient bonding between the ores.

In this embodiment, gaseous fuel is supplied above the sintering machine's charging bed, and together with air, it is sucked in from below the sintering bed and introduced into the sintering bed. The introduced gaseous fuel burns above the position where the carbonaceous material is burning in the height direction of the sintering bed, mitigating the cooling effect of the air flowing in from the upper layer. This prevents the temperature of the sintering bed from dropping. This effect extends the time the sintering bed is maintained at a high temperature, i.e., the sintering reaction time. This also strengthens the bonding between the ores. This effect is also achieved under conditions using conventional coke powder, etc. In particular, with carbonaceous materials with a low combustion start temperature, such as biomass charcoal, the sintering reaction time in the high-temperature region of the base heat pattern before the gaseous fuel is injected is short. Therefore, the effect of injecting gaseous fuel in extending the sintering reaction time in the high-temperature region is greater than when coke, etc. is used.

Furthermore, gaseous fuel burns above the point where the carbonaceous material in the sintering bed begins to burn, consuming oxygen and reducing the oxygen concentration supplied to the carbonaceous material burning below in the sintering bed. This has the effect of slowing the combustion rate of the carbonaceous material. As a result, there is a possibility of reduced production of coke breeze due to the slower combustion rate. On the other hand, this adverse effect can be mitigated with biomass charcoal, which has a high combustion rate.

In general, in sintering machines, the upper layer tends to have a lower yield due to a lack of heat, while the lower layer tends to have an excess of heat. This is because cold air flows directly into the upper layer from above the sintering bed. The upper layer is more susceptible to the effects of a lack of heat caused by the use of biomass coal. Therefore, it is preferable that the suction of gaseous fuel also be carried out within half the length of the ore feed section above the sintering bed where the reaction zone is located in the upper layer. It is more preferable that the suction of gaseous fuel be carried out within at least one-quarter of the length of the ore feed section of the sintering machine, and even more preferably within one-third of the length.

It is preferable to dilute gaseous fuel below its lower flammable concentration. This is because if residual fires on the sintering bed ignite outside above the sintering bed, it could not only prevent the full benefits of gaseous fuel injection but could also lead to a fire. Furthermore, any gas can be used as the gaseous fuel, including city gas, natural gas, propane gas, and coke oven gas. Non-toxic city gas, natural gas, and propane gas are preferred. For example, the lower flammable concentration of each gaseous fuel relative to air is 4.5 vol.% for city gas, 4.4 vol.% for natural gas, and 2.4 vol.% for propane gas. The lower flammable concentration limit for the gaseous fuel is determined by the required calorific value. From the perspective of effective use of gaseous fuel, the lower flammable concentration limit of the gaseous fuel contained in the air introduced into the sintering bed is preferably greater than 0 vol.%, and more preferably at least 1/20 of the lower flammable concentration limit.

In addition, if the introduction of gaseous fuel into the sintering bed increases the yield, the amount of carbonaceous material may be reduced by up to 10% of the total amount of all carbonaceous materials. This is because the injection of gaseous fuel eliminates the heat shortage in the upper layer of the sintering bed, thereby reducing the excess heat in the lower layer.

Example 1
The effects of the present invention were verified using a batch-type sintering test apparatus. T1 was a test using only commonly used coke, while T3 was a test using 20% biomass charcoal instead of the coke. In T2, T4, and T7, city gas was used as the gaseous fuel, adjusted to a concentration of 0.4% by volume relative to the intake air, and injected for 30 seconds to 7 minutes after the ignition furnace was extinguished. The same amounts of ore and auxiliary materials were used. The test conditions and results are shown in Table 1 and Figure 1. Compared to T1, which uses only coke (a reference example), T2, which also injected city gas, showed an approximately 3% improvement in yield. Meanwhile, T3, which replaced 20% of the coke with biomass charcoal, showed an approximately 8% decrease in yield compared to the base (T1). In contrast, T4, which injected city gas, showed an approximately 10% improvement in yield. A greater effect was confirmed in T4 than in T2, which injected city gas under the same calorific value conditions as T1. On the other hand, T5, T6, and T7 are levels where the amount of coke equivalent heat equivalent to T4 was reduced by 0.2% each. The reductions were made so that the ratio of coke to biomass coal did not change. As the reduction amount increased for T5, T6, and T7, the yield decreased. T7, which reduced the total coke amount by 12%, resulted in a yield lower than the base (T1) yield.

Example 2
Next, the gaseous fuel injection range was examined. Since this test was a batch-type test, injection over the entire length of the sintering bed was simulated as injection over the entire sintering time. The town gas was injected at a concentration of 0.4% by volume relative to the aspirated air. The same amounts of ore and auxiliary materials were used. The test conditions and results are shown in Table 2 and Figure 2. Based on T3 in Example 1, T4 involved 7 minutes of gaseous fuel injection, accounting for 25% of the total sintering time. In T8 to T10, the gaseous fuel injection time was 50%, 75%, and 100% of the total sintering time. The results showed that the yield increased when the gaseous fuel injection time was up to 50% of the total sintering time, but remained almost unchanged at 75% and 100%. It is believed that the effect of town gas injection was less pronounced in the latter half of the sintering time because the reaction zone had already reached the lower layer of the sintering bed and sufficient heat was already being generated.

Claims (4)

A method for producing sintered ore using a carbonaceous material having a combustion start temperature of 550°C or less, wherein the gaseous fuel supplied to the upper part of the sintering machine's sintering bed is sucked together with air from below the sintering bed and introduced into the sintering bed,
The gaseous fuel is introduced by diluting it to a concentration below the lower limit of combustion in an amount sufficient to ensure a sintering reaction time in a high temperature range that is reduced by using the carbonaceous material instead of the coke powder in the heat pattern ,
The gaseous fuel is any one of city gas, natural gas, and propane gas .
Here, the heat pattern refers to a temperature change in which the temperature of the charging bed in the sintering machine rises sharply and then falls in a short time.
A method for producing sintered ore. The method for producing sintered ore described in claim 1, wherein the gaseous fuel is sucked in within half the length of the ore feeding section above the sintering bed in the direction of travel of the sintering machine. The method for producing sintered ore described in claim 1, wherein the carbonaceous material having a combustion start temperature of 550°C or less is either or both of an organic resource excluding fossil fuels and a carbonaceous material produced using the organic resource as a raw material. A method for producing sintered ore as described in claim 1, wherein, when the gaseous fuel is supplied, the amount of carbonaceous material is reduced by 10% or less, in terms of the calorific value equivalent to coke, relative to the total amount of all carbonaceous material when the gaseous fuel is not supplied.