JPH04354810A - Method for blowing fine coal into blast furnace and device therefor - Google Patents

Abstract

PURPOSE:To improve combustibility of fine coal and to enable the blowing of a large quantity of fine coal for reducing coke ratio by preheating the fine coal blown into a blast furnace. CONSTITUTION:At the time of blowing the fine coal 14 supplied from a hopper 11 through a supplying piping 13 and a lance 12 into the blast furnace 40 from a tuyere 41, the fine coal 14 is preheated at >=200 deg.C with a preheating device 20 arranged in the supplying piping 13. The preheated fine coal 14 is blown into a raceway 42 from the tuyere 41 together with hot blast 31 fed from a blowing pipe 30. Therefore, the fine coal preheated at >=200 deg.C generates a hydrocarbon series gas. By this gas generation, combustion of the fine coal is quickly started. Further, since trace of the gas generation if remained as gas pores in the fine coal, specific surface area is increased and the combustibility is improved. In this result, the blown fine coal 14 is perfectly burnt in the raceway 42 and unburnt char 43 causing an undesirable furnace condition is not remained in the furnace.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pulverized coal injection method and apparatus for reducing a coke ratio by blowing pulverized coal together with hot air from a blast furnace tuyere.

0002

[Prior art] Pulverized coal is blown into a blast furnace through a tuyere.
It is consumed as a heat source in the furnace. This pulverized coal injection reduces the amount of expensive coke used and lowers the production cost of hot metal. Therefore, in recent years, an operating method in which pulverized coal is injected into the blast furnace has been implemented. Furthermore, the amount of pulverized coal injected is also increasing in order to reduce coke consumption.

[0003] Pulverized coal injected into a blast furnace reacts with oxygen in the furnace and burns, maintaining a high temperature atmosphere necessary for reducing iron ore and melting the reduced iron. However, pulverized coal has poor combustibility and tends to accumulate in the furnace. In order to improve this combustibility, it has been adopted to increase the oxygen enrichment rate of the hot air blown in with the pulverized coal.

0004

[Problems to be Solved by the Invention] When hot air with an increased oxygen enrichment rate is used as a carrier gas, a sufficient amount of oxygen is supplied, so that the combustion efficiency of pulverized coal is improved. However, significantly increasing the oxygen enrichment rate increases the oxygen consumption rate and does not lead to a reduction in hot metal cost. Therefore, in actual operation, there still remains a problem with the combustibility of pulverized coal.

[0005] When a large amount of pulverized coal is injected into a blast furnace, it is inevitable that unburned pulverized coal will accumulate in the furnace. As a result, even if the amount of pulverized coal injected is increased, it does not lead to a reduction in the coke ratio. Furthermore, when unburned pulverized coal accumulates in the furnace, the ventilation of the blast furnace decreases. Moreover, since the pulverized coal is deposited in an irregular manner, the hot air passing through the furnace is biased. As a result, blow-through occurs in areas with high air permeability, and an unstable operating state occurs in which the smelting reaction does not proceed sufficiently in areas with low air permeability. As a result, the effective internal volume of the blast furnace decreases, leading to a decrease in the amount of iron output.

The present invention was devised to solve these problems, and by preheating the pulverized coal that is injected into the blast furnace, the combustibility of the pulverized coal is increased and the coke ratio is reduced. The purpose of this project is to maintain stable furnace conditions even at low temperatures, and to produce hot metal at a low cost by injecting a large amount of pulverized coal.

[0007]

[Means for Solving the Problems] In order to achieve the purpose of the pulverized coal injection method of the present invention, pulverized coal is heated to 200°C in advance.
After being preheated as described above, the pulverized coal is brought into contact with hot air, and the pulverized coal is blown into the blast furnace together with the hot air. Preheating of the pulverized coal injected into the blast furnace is preferably 500°C or less.

[0008] Furthermore, the blowing device used in this method is
a pulverized coal supply pipe that connects a hopper that accommodates pulverized coal and a lance that passes through the blow pipe and faces into the blast furnace tuyere;
The pulverized coal supply pipe includes a preheating device installed in the middle of the pulverized coal supply pipe, and a temperature detector installed downstream of the preheating device to detect the temperature of the pulverized coal after preheating. The preheating capacity of the preheating device is adjusted based on the temperature of the pulverized coal.

[0009]

[Operation] The reason why the combustibility of pulverized coal is improved by preheating is presumed to be as follows. The temperature of pulverized coal is 200℃
If the temperature is higher than that, thermal decomposition will easily occur. At the initial stage of thermal decomposition, gases such as CO2 and H2O are generated. As the temperature of pulverized coal rises, hydrocarbon tar and gas are gradually generated. Due to the generation of these gases, the time it takes for preheated pulverized coal to ignite is much shorter than for pulverized coal that is not preheated. Moreover, since the hydrocarbon gas burns preferentially over the pulverized coal, the temperature of the pulverized coal rises rapidly and the thermal decomposition reaction proceeds at high speed.

[0010] Pulverized coal explodes due to high-speed thermal decomposition,
Refine grains. As the pulverized coal becomes finer, the gas produced by thermal decomposition is released from the pulverized coal, and the remaining solid mainly composed of carbon,
In other words, traces of gas release in the char become many pores,
Makes the char porous. As a result, the specific surface area of the char increases compared to the case without preheating. This also improves combustibility.

[0011] The combustibility of pulverized coal is significantly improved at a preheating temperature of 200°C or higher. The higher the preheating temperature is set, the better the combustibility becomes. However, if the preheating temperature exceeds 500°C, a large amount of tar will be generated from the pulverized coal. When the tar is cooled, it aggregates and accumulates inside the pulverized coal supply pipe, potentially clogging the pipe. Therefore, it is preferable to attach a heat retaining device or a heating device to the supply pipe to prevent the temperature of the pulverized coal from decreasing until it is blown into the blast furnace. Alternatively, it is also effective to set the preheating temperature to 500° C. or lower to suppress the generation of tar.

The present invention will be specifically explained below with reference to the drawings. For example, the pulverized coal injection device 10 is shown in FIG.
As shown in the figure, a hopper 11 containing pulverized coal and a lance 12 are connected by a supply pipe 13. The hopper 11 stores pulverized coal 14 that has been finely crushed by a mill or the like. A carrier gas supply pipe 16 faces a cutting opening 15 provided at the bottom of the hopper 11 . Pulverized coal 14 is cut out from hopper 11 by carrier gas 17 sent through carrier gas supply pipe 16 and fed into supply pipe 13 .

A preheating device 20 is provided in the middle of the supply pipe 13. In the illustrated case, a heat medium conduit 21 is wound around the outer periphery of the supply pipe 13, and high temperature gas 22 is sent into the heat medium conduit 21. The heat of the high-temperature gas 22 is transferred to the pulverized coal 14 flowing in the supply pipe 13 via the heat medium conduit 21 and the pipe wall of the supply pipe 13, raising the temperature of the pulverized coal 14. As the high temperature gas 22, combustion exhaust gas, blast furnace exhaust gas, etc. can be used. Note that the present invention is not limited to the heating method shown in FIG. A direct heating method using a beam irradiation, etc. can be adopted as appropriate.

A temperature detector 2 is provided downstream of the preheating device 20.
3 is provided. The detection terminal 24 of the temperature detector 23 faces the inside of the supply pipe 13 and directly measures the temperature of the pulverized coal 14 or carrier gas 17 flowing through the supply pipe 13. At this time, since the pulverized coal 14 has a very fine particle size, it has substantially the same temperature as the carrier gas 17. The measurement results are displayed using an appropriate control circuit (not shown).
The flow rate of the hot gas 22 that is sent to the hot gas supply system through the heat medium conduit 21 is controlled. Thereby, the pulverized coal 14 is preheated to a constant temperature of 200° C. or higher. Note that the temperature measurement of the pulverized coal 14 can be performed by indirect measurement via the pipe wall of the supply pipe 13 instead of directly measuring the temperature of the pulverized coal 14 flowing in the supply pipe 13.

The preheated pulverized coal 14 may be cooled by the atmosphere before it is blown into the furnace from the tuyere 41 of the blast furnace 40 through the lance 12. Therefore, a heat insulating material 25 is wrapped around the outer periphery of the lance 12 to prevent the temperature of the pulverized coal 14 from decreasing. This prevents the tar generated from the pulverized coal 14 from coagulating and depositing in the supply pipe 13 or the lance 12, making it possible to feed the pulverized coal 14 into the furnace under stable conditions.

The tip of the lance 12 passes through the wall of the blow pipe 30 and faces the tuyere 41. The pulverized coal 14 is blown into the furnace from the tuyere 41 together with the hot air 31 sent through the blow pipe 30.

The blown pulverized coal 14 is heated to 200°C in advance.
Since it has been heated to the above temperature, the generation and combustion of hydrocarbon gas starts as soon as it reaches the raceway 42. The resulting char also burns quickly within the raceway 42. That is, unburned char is less likely to occur, and a stable furnace condition is maintained. By preheating the pulverized coal 14 in this way, the combustion of the pulverized coal or char in the tuyere 41 and raceway 42 is carried out quickly, and unburned char is prevented from remaining in the furnace. As a result, it becomes possible to operate the blast furnace by reducing the coke ratio and injecting a large amount of pulverized coal.

On the other hand, in an operation in which pulverized coal 14 is injected without preheating, it was observed with a probe inserted into the furnace that a large amount of unburned char 43 was generated. When unburned char 43 rises inside the furnace, a coke layer 4
4 and reduces the ventilation inside the furnace. Furthermore, if unburned char 43 accumulates in the core 45, the air permeability and liquid permeability of the core 45 will deteriorate. Therefore, there is an upper limit to the amount of pulverized coal injected, and even if the amount of pulverized coal is increased, the coke ratio will not be reduced.

[0019]

EXAMPLE The method of the present invention was verified using a coke combustion oven having a fan-shaped cross section with a radius of 1.5 m. preheating device 20,
The blow pipe 30 etc. are arranged in the same manner as in Fig. 1, and the pulverized coal 14
An electric heater was used for preheating. Also, Raceway 4
A probe for collecting unburned char 43 discharged to the outside of the coke combustion furnace was inserted into the coke combustion furnace.

[0020] The unburned char obtained through the probe was analyzed, and the combustion efficiency of the pulverized coal 14 injected into the coke combustion furnace was calculated from the analyzed value and the amount collected. The calculation result,
Table 1 shows the operating conditions. Note that Table 1 lists the pulverized coal ratio in the actual furnace corresponding to the ratio between the amount of pulverized coal injected and the amount of hot air air under each operating condition. In addition, a case where pulverized coal without preheating was injected was also shown as a comparative example.

[0021]

[Table 1]

As is clear from Table 1, in Comparative Example 1, which adopted the same operating conditions as Examples 1 to 3 except that the pulverized coal was not preheated, the combustion efficiency of pulverized coal was an extremely low value of 68%. It shows. On the other hand, in Examples 1 to 3 in which pulverized coal was preheated, a high combustion efficiency of 96% or more was obtained. Furthermore, in order to obtain substantially the same combustion efficiency as Examples 1 to 3, it was necessary to increase the oxygen enrichment rate to 6%, as seen in Comparative Example 2. This comparison shows that combustion efficiency is improved by preheating pulverized coal, and the blast furnace can be operated at a high pulverized coal ratio with a lower coke ratio.

[0023]

[Effects of the Invention] As explained above, by preheating the pulverized coal that is injected into the blast furnace, the combustibility of the pulverized coal is improved and the pulverized coal is combusted in the tuyeres and raceways. Therefore, unburned char does not rise in the furnace and accumulate in the coke layer, or in the core, thereby deteriorating the air permeability, liquid permeability, etc. in the furnace. Therefore, a large amount of pulverized coal can be injected without making the furnace conditions unstable, the coke ratio can be reduced, and the production cost of hot metal can be lowered.

[Brief explanation of drawings]

FIG. 1 shows an example of a pulverized coal injection device according to the present invention.

[Explanation of symbols]

11 Hopper 12 Lance 13 Pulverized coal supply pipe 14 Pulverized coal 20 Preheating device 23 Temperature detector 30 Blow pipe 40 Blast furnace
41 Tuyere

Claims (2)

[Claims] 1. A method for injecting pulverized coal into a blast furnace, which comprises preheating pulverized coal to 200° C. or higher, bringing it into contact with hot air, and blowing the pulverized coal together with the hot air into the blast furnace. 2. A pulverized coal supply pipe that connects a hopper containing pulverized coal and a lance that passes through a blow pipe and faces into the blast furnace tuyere, a preheating device provided in the middle of the pulverized coal supply pipe, It is equipped with a temperature detector that is installed downstream of the preheating device and detects the temperature of the preheated pulverized coal.
A pulverized coal injection device, characterized in that the preheating capacity of the preheating device is adjusted based on the temperature of the pulverized coal detected by the temperature detector.