Specialized metallurgical processes – compositions for use therei – Processes – Process control responsive to sensed condition
Reexamination Certificate
2000-04-24
2001-10-16
Andrews, Melvyn (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Processes
Process control responsive to sensed condition
C075S467000, C266S080000, C266S088000
Reexamination Certificate
active
06302941
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for operating a blast furnace in which a heat conditions in the furnace is controlled.
BACKGROUND OF THE INVENTION
In producing molten iron by a blast furnace, iron ore as iron raw material, coke as fuel, lime stone as by-product, etc. are introduced into the furnace from the top thereof, and hot blast is blown into the furnace from a tuyere in the lower portion thereof to burn the coke, so that the iron ore is reduced by the generated reducing gases mainly comprising CO and heat energy. As a result, the iron content of the iron ore becomes the main component of molten iron, while the gangue minerals of the iron ore, and the ashes of the coke become slag together with the limestone, both of which are periodically discharged from a tap hole and a slag hole, respectively, of the lower portion of the furnace. In the blast furnace, the molten iron is produced by the process of high-temperature reaction of the raw material and the reducing gases, and thus it is very important to maintain a stationary state while maintaining a material balance and a heat balance. There is a strong demand for maintaining the stability of furnace conditions in the operation of the blast furnace.
Therefore, in order to maintain the stable conditions of the blast furnace, it is an essential condition to sufficiently control heat conditions in the furnace.
The heat conditions in the blast furnace is divided into the level of heat conditions and the transition of heat conditions, and is one of items regarded as the most important information which reflects the in- furnace conditions such as reaction in the furnace, etc. The level of heat conditions and the transition of the heat conditions basically significantly affect the temperature of molten iron. Therefore, in order to stabilize the operation of the blast furnace and in order to decrease the unit fuel consumption, and in order to improve productivity and quality of molten iron, it is very important to measure, correctly and precisely, the temperature of the molten iron with a short time delay, to control the heat conditions in the furnace, on the basis of the information of the temperature measurement, and adjust, correctly and precisely, the temperature of the molten iron, to a target level. However, for the heat conditions in the blast furnace, conventionally, the level of the heat conditions in the furnace is evaluated by the temperature of the molten iron after tapping, and the heat conditions transition is evaluated and inferred from information from the various sensors arranged in the blast furnace.
(1) The Level of Heat Conditions.
Generally, in tapping in a blast furnace, molten iron is injected from the tap hole, passed through a long runner having a length of as long as about 20 m, and flows into a skimmer. As the position and method of measuring the temperature of the molten iron, a method is conventionally employed in which the molten iron and slag are separated by the skimmer on the basis of the difference in a specific gravity so that the slag floats on the molten iron, and then the temperature of the molten iron is measured. The temperature is measured by using an immersion type thermocouple thermometer. On the inner surface of the runner is formed a runner comprising a monolithic refractory. Therefore, the temperature of the tapped molten iron is decreased due to heat extraction by heat conduction to the runner and heat radiation to air in the course of passage through the runner. In tapping, the diameter of the tap hole is increased due to wearing by the slag, and thus the tapping rate changes with the passage of the tapping time.
The temperature of the molten iron measured in the skimmer is affected by heat extraction from the molten iron in the runner and a change in the tapping rate (t/min) to greatly change during the time from the start to end of tapping. The temperature is generally low in the initial stage of tapping, and then gradually increases to the highest temperature in the last stage of tapping. Conventionally, the highest temperature is used as the temperature of the molten iron.
The blast furnace is generally operated so that the tapping rate is slightly higher than the production rate of the molten iron in the furnace. Therefore, tapping from the predetermined tap hole is performed for about 3 to 4 hours at a time, and then the tap hole is closed to wait until a molten iron is produced and again accumulated in the vicinity of the tap hole. However, during this waiting time, another tap hole is opened for tapping in the same way. Generally, tapping is carried out through an opposite tap hole of the furnace for about 3 to 4 hours at a time. During tapping through the other tap hole, the temperature of the runner provided on the predetermined tap hole is decreased. Therefore, when measuring the temperature of the molten iron in the skimmer during next tapping, the temperature changes in such a manner that it is low in the initial stage, and reaches the highest temperature in the last stage. However, such changes in the temperature of the molten iron measured in tapping are not constant, and greatly vary from one tapping to another, as shown later in FIG.
11
.
FIG. 11
shows an example of measurement results of the temperature of a molten iron by a conventional method.
FIG. 8
shows the results of measurement only in tapping in which the highest temperature was actually 1500 to 1510° C. in 8 to 12 temperature measurements of the molten iron at one tapping. This graph indicates that in the conventional method of measuring the temperature of the molten iron, even in cases at the same level of highest temperature, variations occur in the first temperature measurements, and the rising patterns from the initial stage to the last stage at the highest temperature are not constant. Therefore, it is difficult to not only infer the highest temperature from the first temperature measurement, but also infer the highest temperature from the temperature measurement in the course from second measurement to later measurement.
Also, since the runner of the spout comprising a monolithic refractory is worn by a slag flow, the runner is generally changed for every 2 to 3 weeks. In first tapping after the runner is
7
repaired, the sensible heat of the tap runner is small, and thus heat extraction from the molten iron to the tap runner is further increased. In measuring temperature of the molten iron in first tapping after the tap runner is constructed, the initial measurement is further decreased.
In accordance with conventional temperature measurement of the molten iron in the skimmer, the temperature of the molten iron changes in such a manner that it increases with the passage of time from the start of tapping, and reaches the highest temperature in the last stage. However, for the above-mentioned reasons, the rising curve of temperature greatly varies from one tapping to another.
In the temperature of the molten iron in the skimmer in the initial stage of tapping, the temperature of the molten iron in the furnace greatly decreases with low precision, and a long time is required until the temperature of the molten iron in the skimmer reaches the tapping temperature and is stabilized. Furthermore, even if the measurement in the skimmer is corrected by data from many operations, it is difficult to correctly infer the temperature of the molten iron in the furnace. It is also difficult to know the temperature with a short time delay.
For the above reasons, in the conventional method of measuring the temperature of a molten iron, for the temperature of the molten iron permitting evaluation of t he level of the heat conditions, only 1 item of data can be obtained in 3 to 4 hours required for one time of measurement. Therefore, the conventional method has problems as means for evaluating the heat conditions in the furnace.
(2) Heat Conditions Transition
As described above, the transition pattern of the temperature of the molten iron varies from one tapping to another, and large
Hayasaka Yasukazu
Oya Kenji
Wakai Hajime
Wakita Shigeru
Andrews Melvyn
Frishauf, Holtz Goodman, Langer & Chick, P.C.
NKK Corporation
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