JPS63171814A - Method for stabilizing condition of oxygen blast furnace during low rate of operation - Google Patents

Abstract

PURPOSE:To stably operate an oxygen blast furnace over a long period, by supplying sensible heat corresponding to the increase of heat loss with preheated gas blown from a shaft during the low rate of operation of the blast furnace. CONSTITUTION:When pig iron smelting operation is carried out at a low rate of operation at the time of occurrence of trouble or regulation of production, heat loss increases relatively from that during normal operation by the reduction of the amt. of pig iron tapped, so sensible heat corresponding to the increase of heat loss is supplied with preheated gas blown from a shaft. Iron smelting operation can be stably carried out at a low rate of operation.

Description

DETAILED DESCRIPTION OF THE INVENTION OBJECTS OF THE INVENTION (Industrial Field of Application) The present invention relates to a method for stabilizing furnace conditions during low operation in iron-making blast furnaces, particularly oxygen blast furnaces.

(Conventional technology) Originally, blast furnace operation was primarily concerned with excellent productivity, and by increasing the air blowing temperature, increasing the furnace top pressure, and increasing the air blowing amount, the operating efficiency of modern large blast furnaces has decreased. Maximum 2.5
”/day/d.

However, if there are troubles during operation or it is necessary to make production adjustments, production may be forced to operate at a stable, low operating rate for a relatively long period of time. In such a case, the operation rate will be lowered due to the reduction in the amount of air blown, but the lowest limit of the operation rate in a normal blast furnace that mainly blows hot air from the siding is approximately 1.4"/day/rrr. Conventionally, increases in heat loss were dealt with by increasing the fuel ratio, changing the charge distribution, or increasing the peripheral flow.
A further decrease in the operating rate will cause the furnace condition to become extremely unstable due to a decrease in the gas flow rate near the furnace wall (creating an inert zone or causing the growth of deposits on the furnace wall). It is known that long-term operation is impossible.Recently, in order to further improve the productivity of blast furnaces, oxygen blast furnaces have been developed, such as the one disclosed in Japanese Patent Application Laid-open No. 159104-1983, in which oxygen is the main component of the air blown from the tuyeres. However, oxygen blast furnaces are only now on the verge of being put into practical use, and there is almost no technology disclosed regarding stable operation methods at low operating rates.

(Problems to be solved by the invention) The present invention was created in view of the current situation,
In particular, the object of the present invention is to provide an operating method that enables long-term stable operation at a low iron production ratio in an oxygen blast furnace under low operating conditions.

"Structure of the Invention" (Means for Solving the Problem) In order to achieve the above object, the present inventors blow in sensible heat from the shaft that is approximately equal to the increase in heat loss due to the reduction in operating efficiency. A method for stabilizing furnace conditions during low operation in an oxygen blast furnace characterized by supplying with preheated gas.

Suggest to Ki.

This invention enables a furnace that can increase productivity by maintaining a much higher operating rate than a conventional blast furnace during normal operation, but when trouble occurs or production adjustment occurs, the operating rate is lower than that of a conventional blast furnace. It is possible to carry out multiple iron making operations.

(Function) In the present invention, an oxygen blast furnace refers to an oxygen concentration of 40% from the surface.
This is a blast furnace that operates by blowing the above-mentioned gas at room temperature and preheating gas from a shaft.

Although most of the highly productive practical blast furnaces perform some oxygen enrichment operation, most of the furnaces mainly use high-temperature air from the tuyere as the main source of ventilation. Therefore, although N8, which accounts for about 79% of the air, is not directly involved in the reduction of iron ore,
It plays the role of replenishing the amount of heat necessary to provide a huge amount of sensible heat to the charge from the tip of the tuyere to the stock line and actively perform gas reduction, so there is no need to replenish heat from sources other than the tuyere. However, in blast furnace operations where oxygen is the main component of air blown from the tuyere, as in the present invention, top gas or steam may be blown from the tuyere or near the tuyere as a temperature regulator to counter the temperature rise at the tip of the tuyere. Besides N!
Due to the reduction in the amount of gas due to the absence of the furnace, the gas reduction range above 700° C. is narrowed, and preheating gas must be blown into the shaft portion to compensate for the temperature drop at the top of the furnace. Under normal operation, the amount of preheated gas blown at about 700 to 1200° C. is approximately 35% or less of the amount of Bosch gas produced at the tip of the tuyere. The above-mentioned problem during low operation is due to the fact that the heat loss increases relative to that during normal operation as the iron output decreases, and the area near the furnace wall is cooled. Therefore, when it becomes necessary to perform low operation, stable operation is possible without increasing the fuel ratio by increasing the amount of preheated gas blown into the reactor.

In order to achieve the effects of the present invention, it is necessary to inject sensible heat as the preheating gas, which is at least equivalent to the increase in heat loss compared to normal operation. The lowest operating rate of a conventional blast furnace is 1.4? /day/rrl warmer than 1
．． Long-term stable operation is possible at low operating rates of up to 0'/day/rrr.

(Example) The following is a comparison between normal operation and low operation rate of an oxygen blast furnace in a blast furnace having a furnace capacity of 2828 rrl.

The air flow rate at the tuyere tip O8 is 35 ONn? /l, which was the same as in normal operation, and an amount corresponding to the difference in heat loss was supplemented with preheated gas from the shaft. In this example, about three times as much preheating gas as in normal operation is blown.

It should be noted that the amount of heat loss is assumed to be the same even if the operating rate decreases because there is no significant change in the amount of heat loss per hour, and then the increase in heat loss, which is inversely proportional to the decrease in the operating rate, is assumed to be equal to the amount of heat loss from the preheated gas. It was replenished by sensible heat. The table shows the operating conditions during normal operation and low operating speed. Stable operation continued by increasing only the amount of preheating gas without changing the fuel ratio, oxygen usage, etc.

FIG. 1 is a schematic diagram of a typical flow of an oxygen blast furnace implementing the present invention. The gas in the furnace when the charge is charged into the blast furnace 1 from the top of the furnace is sent to the gas holder 3 via the top gas cleaning mechanism 2, but is branched midway and passes through the booster 4 to the preheating gas generator 5 to generate high-temperature gas. is generated and blown into the furnace from a gas inlet 6 provided in the shaft. On the other hand, oxygen is sent from the oxygen source 7 to the preheating gas generator 5 and the tuyere 9, but normally, as a substitute for coke, pulverized coal from the pulverized coal storage tank 8 and top gas that has passed through the booster 4' are used. A portion of it is also blown into the furnace through the tuyere 9.

``Effects of the Invention'' As detailed above, when the present invention is used to operate an oxygen blast furnace under low operation rate, the fuel ratio etc. are not changed, so the furnace condition is not affected and the blast furnace is no longer louder than a normal blast furnace. It is an extremely excellent invention because it enables ironmaking operation at a low operating rate, and enables low-cost, long-term stable operation with almost minimum fuel costs, especially during production adjustments. Can be done.

[Brief explanation of the drawing]

The drawings show an example of the operational flow of an oxygen blast furnace in which the present invention is implemented. 1: Blast furnace 2: Furnace top gas cleaning mechanism 3: Gas holder 4 Nib-star 4' nib-star 5: Preheating gas generator 6: Gas blowing lower: Oxygen source 8: Pulverized coal storage tank 9 = Tuyere

Claims (1)

[Claims] Sensible heat is approximately equal to the increase in heat loss due to a decrease in operating efficiency.
A method for stabilizing furnace conditions during low operation in an oxygen blast furnace, which is characterized by replenishment using preheated gas blown in from a shaft.