CN111826499A - A blast furnace molten iron decarburization treatment method based on converter LT dust removal - Google Patents

Abstract

The present invention relates to a blast furnace molten iron decarburization treatment method based on converter LT dust removal. , reduce the carbonaceous dust produced by the temperature drop of molten iron. The present invention reduces the carbon content in molten iron by adding converter LT dust as a decarburizer into the blast furnace tapped iron, and solves the problem of graphite dust pollution in the iron and steel plant inversion link from the root. The decarburizer is the converter LT dust removal ash in the steelmaking plant, which has an obvious effect on the decarburization of the blast furnace molten iron, which can reduce the amount of carbon sequestered in the molten iron and alleviate the pollution problem of graphite dust in the steelmaking plant. The iron, which improves the utilization value of the converter LT dust ash.

Description

A blast furnace molten iron decarburization treatment method based on converter LT dust removal

technical field

The invention belongs to the technical field of molten iron pretreatment in the steelmaking process, and in particular relates to a blast furnace molten iron decarburization treatment method based on converter LT dust removal.

Background technique

The energy consumption and environmental load of iron and steel enterprises are closely related to the technological process required for production. On the basis that the current iron and steel production process is basically mature and stable, continuous improvement of the "interface" technology between equipment is an effective measure to optimize production indicators. Among them, the "interface" between the blast furnace and the converter (mixed iron furnace) is particularly important, which is usually called the "iron-steel interface". "Iron-steel interface" includes many links such as molten iron from blast furnace, molten iron transportation and pretreatment. During this process, the temperature of the molten iron will drop sharply due to the loss of heat dissipation. According to the data provided by Baosteel Compound, the temperature drop of molten iron at the "iron-steel interface" can reach more than 150℃.

Through on-site observation, it is found that a large amount of high-temperature smoke and dust will be generated during the transportation of molten iron, especially in the process of inversion of molten iron. Through detection and analysis, the main components of this soot are carbon and iron. For example, the carbon and iron content in the soot of Wuhan Iron and Steel, Anshan Iron and Steel and Panzhihua Iron and Steel Co., Ltd. exceeds 70%; the carbon and iron content of the Shougang, Kunming Iron and Steel and Taigang Iron and Steel Co., Ltd. exceeds 80%. This is because when the temperature of the molten iron is lowered, the carbon in the molten iron is supersaturated and precipitated, and even a large amount of flake graphite can be seen in the settled dust. In addition, high temperature molten iron reacts with oxygen in the air to produce iron oxide dust particles. Studies have shown that when the temperature of molten iron decreases by 100 °C, the saturated solubility of carbon decreases by 0.24% on average, that is, about 2.4 kg of carbon is precipitated in 1 ton of molten iron. For the "iron-steel interface" with a daily turnover of 1,000 tons of molten iron, dozens of tons of carbonaceous dust will be produced.

The formation of this soot not only wastes carbon and iron resources, affects the air quality, but also causes great harm to equipment and human body. In particular, the graphite dust is flake-like, and when it falls on the road surface and the rail surface of the train, the vehicle is prone to skidding during operation. Affected by the precipitation of carbon supersaturation, some carbon and iron form Fe ₃ C and escape. When the graphite dust appears in the form of magnetic Fe ₃ C, it has a great impact on the electrical equipment with magnetic fields on the production site, and has a serious impact. The heat dissipation, insulation performance and service life of such appliances. In addition, graphite dust is smooth and easy to adhere, and when it comes into contact with human skin, it causes skin itching, redness and other symptoms.

At present, there are several ways to solve this problem. First, all major steel plants use the method of air extraction and dust removal to purify the air. The second is to reduce the heat loss of molten iron in the torpedo tanker by improving the external thermal insulation structure of the torpedo tanker, thereby reducing the temperature drop of the molten iron during transportation. Third, some iron and steel plants use capping on the top of the torpedo tanker to reduce the heat loss of the molten iron. The first dust removal method is restricted by the process operation. The main problem is that the dust removal hood conflicts with the operation of other equipment, the equipment layout is difficult, the maintenance and operation costs are high, the dust collection effect is not good, and the symptoms are not cured. The latter two methods have achieved certain results, but still cannot avoid the generation of a large amount of graphite dust. Because, the carbon-saturated molten iron produced by the blast furnace will inevitably cause carbon precipitation in the process of temperature reduction.

Therefore, it is necessary to solve the problem from the root on the basis of the existing technology, that is, to reduce the pollution of graphite dust by reducing the carbon content in the molten iron. To this end, Ding Yuehua et al. carried out laboratory research on the decarbonization of molten iron based on the water samples of Kunming Iron and Steel, using iron concentrate powders such as Diantan ore, Brazilian powder, premixed powder, and sintered ore as decarburizers. The No. 6 blast furnace of Kunming Iron and Steel Co., Ltd. was selected for the field test, and Diantan ore powder, which is low-cost and easy to organize and supply, was selected as the decarburizer. The mineral powder is put into a 25kg woven bag, and when the molten iron comes out of the blast furnace, the mineral powder is manually added from the iron ditch behind the small dam in front of the blast furnace. Although this technology has achieved remarkable results in the decarburization of molten iron, there are still the following problems: (1) it uses iron ore concentrate powder as a decarburizing agent, and the cost is relatively high; (2) it directly adds carbon dioxide at room temperature to molten iron. Diantan ore powder caused the molten iron to cool down by about 20℃, which caused a large heat loss and aggravated the production of carbonaceous dust. (3) When using iron ore concentrate on site, the Diantan ore powder packaged in woven bags is manually added to the iron ditch when the molten iron comes out of the blast furnace, which is easy to cause splashing of molten iron, material loss and safety hazards .

SUMMARY OF THE INVENTION

(1) Technical problems to be solved

In order to solve the above-mentioned problems of the prior art, the present invention provides a blast furnace molten iron decarburization treatment method based on converter LT dust removal. The cost of decarburization treatment of molten iron is reduced, and iron elements in converter LT dust ash are efficiently recovered, so that resources can be fully utilized.

(2) Technical solutions

In order to achieve the above-mentioned purpose, the main technical scheme adopted in the present invention includes:

A blast furnace molten iron decarburization treatment method based on converter LT dust removal. carbonaceous dust produced.

In a preferred embodiment of the present invention, the composition of the LT dust removal ash is as follows: by mass percentage, it includes S0.060%-0.075%, SiO ₂ 1.50%-2.90%, Al ₂ O ₃ 0.02%-0.05%, CaO 6.00%-9.10%, MgO3.5%-5.0%, MnO 0.40%-0.55%, _P2O5 0.15%-0.25%, FeO 27.0% _-32.0 %, Tfe total iron 56.00-63.40%, C 1.00% -2.00%, Fe ₂ O ₃ 50.0%-55.00%, and the remaining undetected parts are 1.00%-3.00%.

In a preferred embodiment of the present invention, the used amount of the converter LT dust removal is 2-5% by mass of molten iron.

In a preferred embodiment of the present invention, the converter LT dust ash is mixed with molten iron from the blast furnace in powder or block form; the size of the block is 0.3-5 cm.

Wherein, the shape of the block is not limited, and may be a regular cylindrical shape, a rectangular shape, an ellipsoid shape, or an irregular three-dimensional shape after a spherical shape. The purpose of pre-forming the powdered converter LT dust dust into a block is to increase the particle size of the converter LT dust dust when it is added to the molten iron, so as to prevent the loss and safety problems caused by high temperature splashing. Of course, the powdered converter LT dust can also be directly mixed with molten iron from the blast furnace, but if the dosing method is improper, it is easy to generate splashes, causing certain losses and poor safety, while the lumps can reduce the generation of splashes. If the size of the block is too small, the splash-proof effect will not be achieved and the workload of making the block and briquetting will be too large; if the size of the block is too large, the decarburization reaction speed will be too slow, the reaction time will be prolonged, and the carbon reduction will be reduced. The effect is poor, and the converter LT dust will remain after the reaction.

In a preferred embodiment of the present invention, the converter LT dust and iron concentrate powder are further mixed to form a decarburizer, which is mixed with molten iron from the blast furnace; the iron concentrate powder contains 50-67wt% of total iron TFe.

Preferably, the mixing mass ratio of converter LT dust removal and iron ore concentrate powder is 50-100:1-50; Use carbon.

In a preferred embodiment of the present invention, the treatment method: when the molten iron from the blast furnace is mixed and decarburized using the converter LT dust removal or the mixture of the converter LT dust removal and iron concentrate powder, the molten iron temperature is 1330-1500 °C. °C, the optimum temperature is 1400-1500 °C. It was found in the research that if the molten iron is lower than 1400℃, the decarburization reaction speed will be slow, and the required reaction time will be longer, resulting in some residual dust in the converter LT dust, and the reaction is not complete.

In a preferred embodiment of the present invention, the processing method includes: after each time the molten iron is poured back from the torpedo car to the converter or the ladle of the steelmaking plant, removing the dust from the lump converter LT or the dust from the converter LT with the iron The mixture of concentrate powder is loaded to the bottom of the torpedo tanker, and the decarburizer is preheated by the waste heat of the torpedo tanker during the process of returning the torpedo tanker from the steel plant to the iron plant to reduce the direct mixing of the decarburizer with the blast furnace molten iron. hot metal heat loss.

Load the bulk converter LT dust ash or the mixture of converter LT dust ash and iron concentrate into the emptied torpedo tanker for preheating. When the water is poured into the torpedo tanker, the decarburizer is located at the bottom of the molten iron, and it is fully mixed and reacted with the molten iron under the impact of the molten iron, which improves the decarburization effect without special stirring; Heat loss due to molten iron.

In a preferred embodiment of the present invention, the processing method includes: before the molten iron from the blast furnace, laying powdered converter LT dust or converter LT dust in the molten iron ditch connecting the hot metal outlet from the blast furnace and the torpedo tanker The mixture with iron concentrate powder makes molten iron flow through the powdery decarburizer and react with each other to realize decarburization.

By laying a small amount of powdered converter LT dust or a mixture of converter LT dust and iron concentrate powder into the molten iron ditch, a large amount of splashing will not occur, and the blast furnace molten iron flowing through will have a partial decarburization effect, reducing The workload of briquetting all decarburizers.

In a preferred embodiment of the present invention, the processing method includes:

S1: briquetting: the mixture of converter LT dust removal or converter LT dust removal and iron ore concentrate is fully mixed with binder and water to make pulp, pressed into blocks, and dried to obtain block decarburizers;

S2: Fill the bulk decarburizer to the bottom of the emptied torpedo tanker, and preheat the decarburizer with the help of the residual heat of the torpedo tanker;

S3: Before the molten iron from the blast furnace, lay powdered decarburizer in the molten iron ditch connecting the molten iron from the blast furnace and the torpedo truck, so that the molten iron from the blast furnace flows through the molten iron ditch and enters the torpedo truck with decarburization. After the molten iron is poured into the torpedo tanker, it contacts and reacts with the bulk decarburization agent pre-filled at the bottom of the torpedo tanker to further realize decarbonization.

Preferably, in step S1, the binder is an inorganic binder to prevent the organic binder from introducing carbon into the molten iron. Preferably, the inorganic binder is bentonite. Further preferably, the amount of the binder added is 5%-8% of the mass of the converter LT dust or the mixture of the converter LT dust and the iron concentrate powder.

Preferably, in step S1, the drying temperature is 110-120° C., and the time is 3-5 hours.

Preferably, the decarburizing agent used twice in step S2 and step S3 is 2-5% of the molten iron capacity of a single torpedo tanker; if the amount of decarburizing agent is too large, it will not only lead to excessive heat loss and excessive temperature drop of molten iron , which intensifies carbon precipitation, and also causes the decarburizer to react incompletely within a limited time.

Converter LT dust removal:

The converter LT dust ash comes from the converter gas dry method (LT method) purification and recovery technology. The LT method system was jointly developed by the German company Lutsch and Thyssen in the late 1960s. It is mainly composed of flue gas cooling, purification and recovery and dust briquetting. The temperature of the flue gas generated during the converter steelmaking process is reduced from about 1450 °C to 800 to 1000 °C through the cooling flue, and then enters the flue gas purification system. . The flue gas purification system is composed of an evaporative cooler and a cylindrical electrostatic precipitator. The flue gas temperature drops to 180-200°C after passing through the evaporative cooler. At the same time, through quenching and tempering treatment, the resistivity of the flue dust is reduced and coarse dust is collected. After this preliminary treatment, the flue gas enters the cylindrical electrostatic precipitator for further purification, so that the dust concentration is reduced to below 10mg/m ³ , so as to achieve the best dust removal efficiency. The coarse dust collected by the evaporative cooler and the dust collected by the cylindrical electrostatic precipitator constitute the converter LT dust collection. It can be sent to the briquetting station through the conveyor, and the dust is heated to 500-600 ℃ in the rotary kiln, and the dust is pressed and formed by hot briquetting.

(3) Beneficial effects

The beneficial effects of the present invention are:

The invention reduces the carbon content in the molten iron by adding the converter LT dust as a decarburizer into the blast furnace tapped iron, and solves the problem of graphite dust pollution in the iron and steel plant inversion link from the root. The decarburizer is the converter LT dust removal ash in the steelmaking plant, which has an obvious effect on the decarburization of the blast furnace molten iron, reduces the amount of carbon sequestered in the molten iron, alleviates the pollution problem of graphite dust in the steelmaking plant, makes full use of waste resources, and recovers the waste in the converter LT dust removal ash. Iron, which improves the utilization value of converter LT dust ash.

The present invention also innovates the application method of the decarburizer, including: (1) pre-laying the powder decarburizer in the molten iron ditch between the blast furnace and the torpedo tanker, and pre-decarburizing the molten iron flowing through, Because the molten iron flows through the molten iron ditch in a flowing state, it fully contacts with the decarburizer and reacts to decarburize, eliminating the need for stirring operations; (2) Place the block decarburizer in the torpedo tanker that has been emptied of molten iron, and put it in the torpedo tanker. In the process of returning from the steelmaking plant to the ironmaking plant, the decarburizer is preheated by the waste heat of the torpedo tanker, and the temperature is raised to 800-1000°C, reducing the contact between the bulk decarburizer and the high-temperature molten iron (about 1480°C). The heat loss, slow down the decarbonization phenomenon.

The blast furnace molten iron decarburization treatment method of the present invention is simple and easy to operate, and compared with the preparation of dust removal equipment for removing graphite dust, the present invention has less investment and lower cost, solves the problem of graphite dust from the source, and has an ideal decarburization effect.

Detailed ways

In order to better explain the present invention and facilitate understanding, the present invention will be described in detail below with reference to the specific embodiments.

At present, the iron-steel interface transportation process is as follows: the molten iron from the blast furnace of the iron-making plant is filled into the torpedo tanker, and then the molten iron is transported to the iron-mixing furnace or the converter ladle of the iron-making plant through the torpedo tanker. The temperature of molten iron coming out of the blast furnace is about 1500℃, and when it is poured into the iron mixing furnace or the converter ladle, the temperature drops to about 1320℃, during which there is a temperature drop of more than 100℃. The solubility drops sharply, resulting in the precipitation of a large amount of carbon powder, which has become one of the main pollution sources of steel mills.

In order to solve the above problems, the main technical means adopted by the present invention include: adding a decarburizing agent to the molten iron from the blast furnace to perform decarburization treatment to reduce the generation of carbon dust from the source. When choosing a decarburizer, choose converter LT dust ash, or converter LT dust ash with iron ore concentrate. The Fe ₂ O ₃ content of the converter LT dust ash is more than about 50%, and it has strong oxidizing property at high temperature, which can oxidize the C contained in the molten iron into CO or CO ₂ to remove it, while the converter LT dust ash has a strong oxidizing property. Iron is also efficiently recovered. In the timing and manner of adding the decarburizing agent, the present invention selects the powder and block decarburizing agent. The application method mainly includes two improvements: first, the powdery decarburizer is preferably spread a layer of powdery decarburizer into the molten iron ditch (the molten iron flow channel connecting the blast furnace and the torpedo tanker) before the molten iron is released from the blast furnace, When the molten iron flows through the powder decarburizer, the decarburizer oxidizes the carbon in the molten iron to achieve partial pre-decarburization. Second, after the torpedo tanker pours the transported molten iron into the converter ladle or the iron mixing furnace, the torpedo tanker is in an empty state. At this time, the bulk decarburization agent that plays the main role of decarburization can be loaded into the tank of the torpedo tanker. , Use the waste heat of the torpedo tanker to heat up the decarburizer. When the fish tanker returns to the ironworks to transport the molten iron again, the decarburizer in the tanker has been heated to about 800-1000℃. After the blast furnace molten iron is poured into the tanker, the impact The decarburizer is fully mixed and contacted with the molten iron, and the decarburizer oxidizes and removes the carbon in the molten iron, eliminating the need for stirring operations. Since the decarburizer is preheated to a high temperature, even if it is mixed with molten iron discharged from the blast furnace, excessive heat loss will not occur.

In order to further illustrate the features and technical effects of the solution of the present invention, the following description is given in conjunction with specific embodiments.

Example 1

In this example, the converter LT dust ash is used as a decarburizer, which is mixed with blast furnace molten iron to realize decarburization. In this embodiment, the composition of the converter LT dust removal sample is:

Element mass percentage Element mass percentage S 0.069 Tfe full iron 59.49 SiO₂ 1.63 C 1.53 Al₂O₃ 0.36 Mfe magnetic iron -- CaO 8.12 Fe₂O₃ 52.23 MgO 4.19 ZnO trace MnO 0.426 Na₂O trace P₂O₅ 0.199 K₂O trace FeO 29.48 The rest of the undetected part 1.77

The particle size of the converter LT dust ash is 10-50 microns. A certain amount of the above converter LT dust ash is fully mixed with bentonite and water to be uniformly pulped, pressed into blocks, and dried at 110-120 ° C for 3-5 hours, a cylindrical block of decarburizer was obtained with a diameter of 1 cm and a height of 1.5 cm. Among them, bentonite accounts for 5% of the dust quality of converter LT.

The initial value of carbon measurement is sampled from the iron and steel plant, and the composition of each iron nugget sample (about 500g) is slightly different. In order to make the test results more accurate, each sample was tested three times, and the average value of the three times was taken, and the carbon content in the iron samples was tested repeatedly in each experiment. The average content of Si and Mn in the iron sample is 0.28% and 0.20%, respectively

In this example, the influence of different amounts of decarburizers on the decarburization effect of molten iron was studied, specifically adding 3%, 4%, and 5% (based on the quality of molten iron) of converter LT dust-removing block decarburizer to molten iron. (Converted to the mass of converter LT dust removal), the molten iron temperature was kept at 1450°C. The experimental results are recorded in Table 1.

Table 1

It can be seen from Table 1 that with the increase of the amount of dust removal in the converter LT, the carbon reduction amount in the molten iron gradually increases, and the decarburization effect is remarkable. Compared with the prior art using 3% of Diantan mine to achieve about 0.30% carbon reduction at the same experimental temperature, the decarburization agent used in the present invention has higher decarburization efficiency.

Example 2

This example uses converter LT dust as a decarburizer, which is mixed with blast furnace molten iron to achieve decarburization, and the composition, specification, and briquetting steps of converter LT dust are the same as in Example 1. During the measurement, each sample was tested three times and the average value was taken.

In this example, the effect of converter LT dust removal as a decarburizer on the decarburization effect of molten iron was studied at different temperatures. Specifically, the temperature of molten iron for maintaining the decarburization reaction was 1420°C, 1450°C, and 1480°C, respectively, and in each set of temperature experiments, the amount of dust removal from converter LT was 4% of the mass of molten iron. The experimental results are recorded in Table 2.

Table 2

It can be seen from the above table that when the amount of dust removal in the converter LT is constant, the carbon reduction effect has little to do with the temperature of the molten iron during the decarburization reaction, that is, the temperature has little effect on the decarburization effect, and the amount of carbon reduction depends largely on the converter LT. Amount of dust decarburizer. Therefore, considering the complete reaction and cost saving, when the converter LT dust is used as the decarburizer, the decarburization requirement of the molten iron after the blast furnace is tapped can be met when the dosage is 3-4%; when the decarburizer is used at 4%, The carbon reduction rate is 0.42%.

Example 3

In this example, converter LT dust-removing ash and iron ore concentrate powder (Brazilian iron ore concentrate powder) are mixed as decarburizer in a mass ratio of 80:20, and the composition, specification and briquetting step of converter LT dust-removing ash are all the same as those in Example 1. same. The composition of iron ore concentrate is as follows:

In this example, the influence of different amounts of decarburizers on the decarburization effect of molten iron was studied, specifically adding 3% and 4% (converter LT dust removal + iron concentrate powder quality and the percentage of molten iron mass) to molten iron respectively. Mass decarburizer (made from converter LT dust removal + iron concentrate powder, 5% bentonite briquette), keeping the temperature of molten iron at 1450°C. The experimental results are recorded in Table 3.

table 3

It can be seen from the above table that the ideal carbon reduction effect can also be achieved by using the mixture of converter LT dust removal and iron concentrate powder as the decarburizer. This embodiment directly utilizes the decarburization of iron concentrate powder and the production of molten iron, and no special pelletizing treatment is required for the iron concentrate powder (usually, special pelletizing is required before the iron concentrate powder is added to the blast furnace).

The above examples 1-3 are all verified in the laboratory using converter LT dust as the decarburizer, or the converter LT dust as the base material and the decarburization agent mixed with iron concentrate powder, and mixed with blast furnace molten iron to the ideal carbon reduction effect.

When used on site in a steelmaking plant, the present invention also includes at least one of the following improvements in the dosing method and dosing timing of the decarburizer:

① Every time after the molten iron is poured from the torpedo tanker to the converter or ladle of the steelmaking plant, the lump converter LT dust or the mixture of converter LT dust and iron ore concentrate is filled to the bottom of the torpedo tanker to make the torpedo tanker In the process of returning from the steel plant to the iron plant, the decarburizer is preheated by the waste heat of the torpedo tanker, which reduces the heat loss of the molten iron caused by the direct mixing of the decarburizer with the blast furnace molten iron, and also eliminates the need for special stirring operations.

②Before the molten iron coming out of the blast furnace, lay powdered converter LT dust removal or a mixture of converter LT dust removal dust and iron concentrate powder in the molten iron ditch connecting the molten iron outlet from the blast furnace and the torpedo tanker, so that the molten iron flows through the powdered Decarburizers and react with each other to achieve decarburization. The powdery decarburizer can quickly react with the molten iron in the molten iron ditch without splashing.

It should be understood that the above description of the specific embodiments of the present invention is only to illustrate the technical route and characteristics of the present invention, and its purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly, but the present invention Not limited to the specific embodiments described above. Any changes or modifications made within the scope of the claims of the present invention should be covered within the protection scope of the present invention.

Claims (10)

1. A blast furnace molten iron decarburization treatment method based on converter LT fly ash is characterized by comprising the following steps: the converter LT dedusting ash is used as a decarbonizer to be mixed with molten iron from a blast furnace, and carbon in the molten iron is oxidized to achieve the decarbonization effect, so that carbon-containing dust generated by the temperature drop of the molten iron is reduced.

2. According to claim1, the blast furnace molten iron decarburization treatment method is characterized in that the LT fly ash comprises the following components: comprises 0.060 to 0.075 percent of S and SiO by mass percent₂1.50％-2.90％、Al₂O₃0.02％-0.05％、CaO6.00％-9.10％、MgO 3.5％-5.0％、MnO 0.40％-0.55％、P₂O₅0.15 to 0.25 percent of iron, 27.0 to 32.0 percent of FeO, 56.00 to 63.40 percent of Tfe total iron, 1.00 to 2.00 percent of C and Fe₂O₃50.0% -55.00% and the rest is 1.00% -3.00% of the undetected part.

3. The method for decarbonizing molten iron of a blast furnace according to claim 1, wherein the amount of fly ash of the converter LT used is 2 to 5% by mass of the molten iron.

4. The method for decarbonizing molten iron of a blast furnace according to claim 1, wherein the converter LT fly ash is mixed with the molten iron discharged from the blast furnace in a powdery or lump form; the size of the block is 0.3-5 cm.

5. The method for decarbonizing molten iron of a blast furnace according to claim 1, wherein converter LT fly ash is mixed with fine iron ore powder to form a decarbonizer, and the decarbonizer is mixed with molten iron discharged from the blast furnace; the iron ore concentrate powder contains 50-67 wt% of total iron TFe.

6. The method for decarbonizing the blast furnace molten iron according to any one of claims 1 to 5, wherein when the molten iron from the blast furnace is subjected to mixed decarbonization by using the converter LT fly ash or the mixture of the converter LT fly ash and the iron concentrate powder, the temperature of the molten iron is 1330 ℃ to 1500 ℃; the preferred temperature is 1400-1500 ℃.

7. The decarburization method for molten iron in a blast furnace of claim 5, wherein the decarburization method comprises: after molten iron is poured into a converter or a ladle of a steel plant from the torpedo car, the blocky decarbonizing agent is filled to the bottom of the torpedo car, so that the decarbonizing agent is preheated by means of the waste heat of the torpedo car in the process of returning the torpedo car from the steel plant to the steel plant, and the heat loss of the molten iron caused by directly mixing the decarbonizing agent with the molten iron of the blast furnace is reduced.

8. The decarburization method for molten iron in a blast furnace of claim 5, wherein the decarburization method comprises: before the molten iron from the blast furnace, a powdery decarbonizing agent is paved in a molten iron ditch connecting a molten iron outlet of the blast furnace with a torpedo car, so that the molten iron flows through the powdery decarbonizing agent and reacts to realize decarbonization.

9. The method for decarbonizing molten iron in a blast furnace according to claim 1, comprising:

s1, briquetting: fully mixing converter LT fly ash or a mixture of the converter LT fly ash and iron ore concentrate powder with a binder and water for pulping, pressing into blocks and drying to obtain a block decarbonizer;

mixing the converter LT fly ash and iron concentrate powder to prepare a powdery decarbonizer;

s2, filling the blocky decarbonizing agent to the bottom of the emptied torpedo ladle car, and preheating the decarbonizing agent by using the waste heat of the torpedo ladle car;

s3, before the molten iron from the blast furnace, paving a powdery decarbonizing agent into a molten iron ditch connecting a molten iron outlet of the blast furnace with a torpedo ladle car, so that the molten iron from the blast furnace reacts with the decarbonizing agent to realize decarbonization in the process of flowing through the molten iron ditch and entering the torpedo ladle car;

and after the molten iron is poured backwards to the torpedo ladle car, the molten iron is contacted with a blocky decarbonizer which is filled at the bottom of the torpedo ladle car in advance and reacts, so that decarbonization is further realized.

10. The method for decarbonizing the blast furnace molten iron according to claim 9, wherein the binder is an inorganic binder, and the amount of the binder added is 5 to 8 percent of the mass of the converter LT fly ash or the mixture of the converter LT fly ash and the iron ore concentrate powder in step S1.