WO2024116778A1

WO2024116778A1 - Method for producing sintered ore

Info

Publication number: WO2024116778A1
Application number: PCT/JP2023/040407
Authority: WO
Inventors: 友司岩見; 慎平藤原; 隆英樋口
Original assignee: Ｊｆｅスチール株式会社
Priority date: 2022-12-02
Filing date: 2023-11-09
Publication date: 2024-06-06
Also published as: TW202428888A

Abstract

Proposed is a method for producing a sintered ore, in which yield is improved when a carbon material with a low combustion initiation temperature is used in a sintering step. The present invention is a method for producing a sintered ore using a carbon material with a combustion initiation temperature of 550°C or below, wherein a gaseous fuel supplied above a charging layer of a sintering machine is drawn in from below the charging layer, together with air, and introduced into the charging layer. It is preferable that: the gaseous fuel is drawn in, in a direction of advancement of the sintering machine, in a one-half length range on a feed unit side over the charging layer; the carbon material with a combustion initiation temperature of 550°C or below is a non-fossil-fuel organic-based resource and/or a carbon material produced using the non-fossil-fuel organic-based resource as a raw material; the gaseous fuel included in the air introduced into the charging layer has a concentration below the lower limit of concentration for combustion; and when the gaseous fuel is being supplied, the amount of the carbon material is cut back to 10% or less, on a coke-equivalent calorie basis, of the total amount of all of the carbon material when the gaseous fuel is not being supplied.

Description

Sinter manufacturing method

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

In the iron ore sintering process, a mixture of iron ore, flux, and carbon material as solid fuel is sintered in a sintering machine using the heat from the combustion of the carbon material. Coke powder is generally used as the carbon material. In order to spread the risk of price fluctuations in raw coal and problems with coke manufacturing equipment, anthracite and other coals are sometimes used instead of coke powder.

On the other hand, in response to the 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 the idea of risk diversification, etc.

For example, Patent Document 1 discloses a carbon material for sintering iron ore, assuming subbituminous coal or 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 water of crystallization iron ore containing 4.0% or more water of crystallization is used, and 10% or more of solid fuel with 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 charge layer is formed in two stages and sintering is carried out by igniting the surface of each stage, using coke or anthracite and a carbonaceous material with a lower combustion start temperature as the raw material in the lower stage.

Patent Document 4 discloses a method in which a carbonaceous material with a low combustion start temperature is mixed with fine coke or anthracite as an agglomeration agent in an amount ranging from 25 to 75% of the total carbon content, and at least one of the low combustion start temperature carbonaceous material and the 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 JP 2020-186436 A JP 2022-033594 A

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

Furthermore, the technology disclosed in Patent Document 3 is premised on a 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. On the other hand, there are many types of carbonaceous materials with low combustion start temperatures, and this does not take into account the fact that their combustion start temperatures vary, and the associated impact on yield is not taken into account.

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

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

The method for producing sintered ore according to the present invention is as follows:
(a) sucking the gaseous fuel in a range of 1/2 of the length of 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 other than fossil fuel and a carbonaceous material produced using the organic resource as a raw material;
(c) maintaining the concentration of the gaseous fuel contained in the air introduced into the sintering bed at less than the lower flammable limit concentration;
(d) when the gaseous fuel is supplied, the amount of the carbonaceous materials is reduced by 10% or less in terms of heat equivalent to coke relative to the total amount of all the 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 together with air from below the charging bed and introduced into the charging bed, improving the heat pattern and preventing a decrease in yield.

1 is a graph showing the effect 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.

Below, the embodiments of the present invention are specifically described. The following embodiments are intended to exemplify equipment and methods for embodying the technical ideas of the present invention, and are not intended to specify the configuration as described below. In other words, the technical ideas of the present invention can be modified in various ways within the technical scope described in the claims.

In diversifying carbon materials to reduce the environmental burden, attention is being paid to organic resources other than fossil fuels and carbonaceous materials produced using these organic resources as raw materials (hereinafter referred to as biomass charcoal). Biomass charcoal absorbs carbon dioxide gas while the plants that are its raw material grow, so fuels made from biomass charcoal can be counted as having no carbon dioxide gas emissions outside the system from the perspective of carbon neutrality. As a result, the use of biomass charcoal is being considered in iron ore sintering processes, which normally use coke powder. A characteristic of biomass charcoal is that it starts to burn at a lower temperature than coke. While the starting temperature for coke to burn is in the range of 650 to 750°C, the starting temperature for biomass charcoal to burn is generally below 550°C.

In this embodiment, flux and carbonaceous material are added to the iron ore as auxiliary raw materials during the sintering process, and the materials are continuously charged onto the sintering machine to form a sintering bed (charging layer). The sintering bed is ignited at the top end, and then exhaust gas is sucked in from the bottom end, 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. A blower is used to suck in the exhaust gas from the bottom end. The sucked in exhaust gas passes through a duct, passes through a dust collector and desulfurization and denitrification equipment, and is then discharged from the chimney.

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

The combustion reaction of carbon materials is a gas-solid reaction. The solid carbon material reacts with oxygen in the surrounding gas and burns. In gas-solid reactions under conditions of gas flow, such as sintering, there is a very thin area called a gas film on the surface of the solid. The gas film is not affected by the turbulent flow outside and maintains a laminar flow. The combustion of carbon materials is used when oxygen diffuses from the outside of the gas film through the gas film and reaches the surface of the carbon material. Here, if the burning speed of the carbon material is very fast, even if the oxygen concentration in the surroundings is high, the oxygen consumption rate at the surface due to the burning of the carbon material is greater than the oxygen supply rate due to oxygen diffusion in the gas film, and the oxygen concentration in the gas film decreases. As a result, the carbon material undergoes incomplete combustion and the amount of carbon monoxide generated increases. Therefore, if the burning speed is very fast, part of the combustion heat of the carbon material is not used and is discharged outside the system as carbon monoxide. Therefore, it is thought that the yield decreases due to the decrease in reaction heat used for sintering. In addition, a fast burning speed indicates that the time from the start of combustion to the end of combustion is short. It burns out immediately after the start of combustion, and cooling begins with the air coming from above. Therefore, the sintering bed in the sintering machine forms a heat pattern in which the temperature rises rapidly and then drops in a short time. This effect means that the sintering reaction in the high-temperature area only occurs for a short period of time, which can result in insufficient bonding between the ores.

In this embodiment, the gaseous fuel supplied above the sintering machine's charging bed is sucked in from below the sintering bed together with air 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 makes it possible to extend the time during which the sintering bed is maintained at a high temperature, that is, the time of the sintering reaction. Therefore, the bonds between the ores can be strengthened. This effect is also manifested under conditions where ordinary coke powder is used. In particular, with carbonaceous materials such as biomass charcoal that have a low combustion start temperature, the sintering reaction time in the high temperature region in the base heat pattern before the gaseous fuel is injected is short. Therefore, the effect of extending the sintering reaction time in the high temperature region by injecting the gaseous fuel is greater than when coke is used.

Furthermore, by burning gaseous fuel above the point where the carbonaceous material in the sintering bed starts to burn, oxygen is consumed, making it possible to reduce the concentration of oxygen supplied to the carbonaceous material burning below in the sintering bed. This has the effect of slowing down the burning rate of the carbonaceous material. As a result, there is a possibility of reduced production of coke powder due to the slower burning rate. On the other hand, with biomass charcoal, which has a high burning rate, this adverse effect can be mitigated.

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 charging layer. 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 is also carried out within a range of 1/2 the length of the ore feeding section above the charging layer where the reaction zone is located in the upper layer. It is more preferable that the suction of gaseous fuel is carried out within a range of 1/4 or more of the length of the ore feeding section of the sintering machine, and even more preferable that it is carried out within a range of 1/3 or more of the length.

It is preferable to dilute the gaseous fuel below the lower limit of flammability. This is because if residual fires on the sintering bed ignite the outside above the sintering bed, not only will the effect of gaseous fuel injection not be fully achieved, but it may also lead to a fire. Any gas may be used as the gaseous fuel, such as city gas, natural gas, propane gas, or coke oven gas. Non-toxic city gas, natural gas, or propane gas is preferable. For example, the lower limit of flammability of each gaseous fuel relative to air is city gas: 4.5 vol.%, natural gas: 4.4 vol.%, propane gas: 2.4 vol.%, etc. The lower limit of the concentration of the gaseous fuel is determined by the required amount of heat. From the viewpoint of effective use of the gaseous fuel, the lower limit of the concentration of the gaseous fuel contained in the air introduced into the sintering bed is preferably more than 0 vol.%, and more preferably 1/20 or more of the lower limit of flammability.

In addition, if the yield increases due to the introduction of gaseous fuel into the sintering bed, 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, making it possible to reduce the excess heat in the lower layer.

Example 1
The effect of the present invention was verified using a batch-type sintering test device. T1 was a level where only commonly used coke was used, and T3 was a level where 20% of the coke was replaced with biomass charcoal. In T2, T4 to T7, city gas was adjusted to a concentration of 0.4 volume% relative to the intake air as the gaseous fuel, and was 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 is a reference example where only coke was used, T2, where city gas was injected, had a yield improvement of about 3%. On the other hand, in T3, where 20% of the coke was replaced with biomass charcoal, the yield decreased by about 8% compared to the base (T1). In contrast, in T4, where city gas was injected, the yield improved by about 10%. It was possible to confirm a greater effect in T4 than the effect of T2, which is a level of city gas injection for T1 under the same heat quantity conditions. On the other hand, T5, T6, and T7 are levels where the amount of coke equivalent heat equivalent to T4 is reduced by 0.2% each. The reduction was made so that the ratio of coke to biomass coal would not change. As the reduction amount increased from T5 to T6 to T7, the yield decreased. In T7, where the total amount of coke was reduced by 12%, the yield was lower than that of the base (T1).

Example 2
Next, the gas fuel injection range was verified. Since this test was a batch type test, injection over the entire length above the sintering bed was simulated as injection during the entire sintering time. The city gas was adjusted to a concentration of 0.4 volume % relative to the suction air and injected. The same amount 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 was 7 minutes of gas fuel injection, which is 25% of the entire sintering time. In T8 to T10, the gas fuel injection time was 50%, 75%, and 100% of the entire sintering time. As a result, the yield increase effect was observed up to 50% of the entire sintering time, but the effect was almost flat at 75% and 100%. It is considered that the effect of city gas injection was difficult to manifest because the reaction zone reached the lower layer of the sintering bed in the latter half of the sintering time and sufficient heat was already obtained.

Claims

A method for producing sintered ore using carbonaceous material with a combustion start temperature of 550°C or less, in which 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.
The method for producing sintered ore according to claim 1, in which the gaseous fuel is sucked in within a range of 1/2 the length of the ore feeding section on the charging bed in the direction of travel of the sintering machine.
The method for producing sintered ore according to claim 1, wherein the carbonaceous material having a combustion start temperature of 550°C or less is either or both of an organic resource other than fossil fuel and a carbonaceous material produced using the organic resource as a raw material.
The method for producing sintered ore according to claim 1, in which the gaseous fuel contained in the air introduced into the sintering bed has a concentration below the lower limit of combustion.
The method for producing 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, in terms of heat equivalent to coke, relative to the total amount of all the carbonaceous materials when the gaseous fuel is not supplied.