Specialized metallurgical processes – compositions for use therei – Processes – Process control responsive to sensed condition
Reexamination Certificate
1997-03-21
2001-01-09
Andrews, Melvyn (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Processes
Process control responsive to sensed condition
C075S384000, C075S385000, C075S386000, C075S387000, C075S501000, C075S502000
Reexamination Certificate
active
06171364
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to improvements in methods of producing molten iron. More particularly, the invention concerns a method for stabilizing the operation of a post-combustion smelting process for producing hot, molten iron from iron ores and/or other iron-bearing oxides. The Government of the United States of America has rights in this invention pursuant to Cooperative Agreement No. DE-FC07-94ID13284, awarded by the U.S. Department of Energy.
Methods of producing iron by smelting reduction, utilizing post-combustion technology with iron ore and coal-based fuels, are well known in the art. In such processes, it is preferable to use process controls that maintain a stable smelting operation, while maximizing the molten iron production rate. In addition, it is preferable to simultaneously minimize the fuel and oxygen consumption rates. However, in direct ironmaking processes there are numerous operating parameters that affect both the rate of iron production and the rate of fuel consumption. Moreover, these same parameters generally affect the quality of the molten iron produced. Within the smelter reactor, the material feed rates, the oxygen flow rate, the bottom stirring gas flow rate, the oxygen lance and tuyere configuration, the oxygen lance height, the system pressure, and the slag weight are all examples of variables that generally affect the operating performance of the smelter reactor.
Prior art process control methods can fail to effectively maintain control of the molten iron temperature and/or the chemical composition of the hot metal produced. Moreover, prior methods of control can cause the slag to foam out of the smelter reactor. It is an object of the present invention to design a method for the stable operation of a smelter reactor that overcomes one or more of those deficiencies of the prior art.
SUMMARY OF THE INVENTION
The present invention relates to a method of producing molten iron in a stable manner in a direct smelting process in which a source of iron oxide, flux, and a source of carbon and hydrogen are charged to a smelter reactor. Oxygen and nitrogen are also charged to the smelter reactor, with at least some of the oxygen being continuously introduced via an overhead lance. Conditions are maintained within the smelter reactor to cause at least some of the iron oxide to be chemically reduced. A bath of molten iron is thus created in the bottom of the smelter reactor, surmounted by a layer of foaming slag. Carbon monoxide is generated within the smelter by the reaction of carbon with iron oxide. The carbon monoxide rises through the slag, as does the hydrogen. At least some of the carbon monoxide and hydrogen react within the smelter with the continuously charged oxygen, thereby generating heat for endothermic reactions taking place within the reactor. An offgas is released that contains CO, CO
2
, H
2
, and H
2
O. At least some of the molten iron produced is removed from the reactor. This is the process, well known in the art, that is improved by the present invention.
In the method of the present invention, a certain group of conditions is repeatedly measured during the process. (By “repeatedly” we here mean that the condition is either continuously measured or is measured at regular or irregular time intervals.) Those conditions are the slag height, the temperature of the molten iron, the content of CO, CO
2
, H
2
, and H
2
O in the offgas, the carbon content of the molten iron, and the FeO content (weight percent) in the slag. One or more process variables are subsequently adjusted (after the measurements) so as to help keep one or more of those conditions (slag height, etc.) within a predetermined range. Preferably, the process variable or variables that are adjusted are selected from the group consisting of the addition rate of the carbon and hydrogen source, the addition rate of the source of iron oxide, the addition rate of flux, the addition rate of oxygen, the height of the oxygen lance relative to the slag, the rate at which the bath of molten iron is stirred, and the rate at which molten iron and slag are removed from the smelter reactor.
By utilization of the method of the present invention, one can effectively maintain control of the molten iron temperature and the molten iron carbon content, as well as prevent the slag from foaming out of the smelter reactor. In addition, the present method enables one to create a stable iron smelting process that maximizes the molten iron production rate, while minimizing the fuel and oxygen consumption rates.
By “slag height” is meant the level in the reactor where the upper surface of the slag layer is. Suitable methods of measuring slag height are known in the art. For example, slag height can be measured by an acoustic technique or by using a conductivity probe. If the slag height is not measured continuously, then it preferably is measured at least as often as once every 30 minutes.
Methods of measuring the temperature of the molten iron are also known in the art. For example, a thermocouple device or an optical pyrometer can be used. If the temperature of the molten iron is not continuously monitored, then it, too, is preferably measured at least as often as once every 30 minutes.
Means of measuring the content of CO, CO
2
, H
2
, and H
2
O in the offgas are also known in the art. For example, a mass spectrometer or gas chromatography equipment can be used. If the offgas's content of each of these four chemicals is not continuously measured, then it is preferred that they be measured at least once every 15 minutes.
Means of measuring the carbon content of the molten iron are likewise known in the art. For example, a sample of hot metal can be taken using a sub-lance, and that sample can then be analyzed using infra-red absorption techniques. If the carbon content of the molten iron is not continuously measured, then preferably it is measured at least as frequently as once every 30 minutes.
Methods of measuring the FeO content of the slag during the smelting reduction of iron oxide are likewise known in the art. For example, a sample of the slag can be taken using a sub-lance, and that sample can be analyzed using an x-ray spectrophotometer. If the FeO content of the slag is not continuously measured, then preferably it will be measured at least as frequently as once every 30 minutes.
For each of the above-mentioned process conditions there is a range within which it is preferred that the condition be held during the process. For example, it is preferable for the slag height to be kept more than one meter below the cone of the smelter reactor. (By the “cone” is meant the top-most portion of the reactor, where the walls slant inwardly. In the reactor shown in
FIG. 2
of the drawings accompanying this specification, the cone is the “Gun/Cooled” section.) Similarly, the temperature of the molten iron is preferably maintained within the range of approximately 1450° C. to approximately 1550° C. during operation. The carbon content of the molten iron preferably falls within the range of approximately 4% to approximately 4.5% (weight basis). In addition, it is preferable to have a FeO content in the slag within the range of approximately 2% to approximately 5% (weight basis).
The amount of CO, CO
2
, H
2
, and H
2
O in the offgas determines the post-combustion degree in the offgas. By post-combustion degree (PCD) is meant the following ratio:
PCD
=
100
×
(
%
CO
2
+
%
H
2
O
)
(
%
CO
+
%
CO
2
+
%
H
2
+
%
H
2
O
)
Preferably, the PCD is maintained within the range of approximately 30% to approximately 60%. If the majority (dry weight basis) of the carbonaceous fuel is coal, the PCD will preferably be kept within the range of about 30% to about 50% (e.g., about 30% to about 40%). If the majority of the fuel is coke, the PCD preferably will be kept with the range of about 45% to about 60% (e.g., about 50% to about 60%).
After the aforementioned process conditions are all measured, if any condition is outside the
Downing Kenneth B.
Sarma Balu
Andrews Melvyn
Fitzpatrick ,Cella, Harper & Scinto
Steel Technology Corporation
LandOfFree
Method for stable operation of a smelter reactor does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for stable operation of a smelter reactor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for stable operation of a smelter reactor will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2525827