Specialized metallurgical processes – compositions for use therei – Processes – Producing or treating free metal
Reexamination Certificate
1998-05-04
2001-04-10
King, Roy (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Processes
Producing or treating free metal
C075S468000, C075S489000, C075S501000, C075S502000, C075S529000, C095S139000, C095S140000
Reexamination Certificate
active
06214084
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the manufacture of iron and more particularly to the production of iron by smelting processes. Specifically, the invention relates to the introduction of carbon monoxide to the smelting furnace of an ironmaking plant.
BACKGROUND OF THE INVENTION
Iron is produced in furnaces into which iron ore, a fuel, usually coal or coal char, and oxygen are introduced. The ore, primarily Fe
2
O
3
, undergoes a preliminary reduction to FeO by contact with carbon monoxide and carbon in the top part of the furnace or in a chamber above the furnace, and the FeO is further reduced to metallic iron by contact with carbon monoxide and other reducing gases in the lower part of the furnace. The carbon monoxide is produced by partial combustion of the fuel, which is introduced into the lower part of the furnace together with oxygen. During the course of the process, a layer of molten iron forms at the bottom of the furnace and a layer of slag, produced from slagging agents introduced into the furnace with the fuel and from impurities contained in the ore, forms on top of the molten iron.
The hot waste gas exiting the furnace generally contains, by volume, about 10 to 35% carbon monoxide, about 2 to 15% hydrogen, about 40 to 55% carbon dioxide and the balance mostly nitrogen, water vapor, sulfur compounds (SO
x
, H
2
S, etc.) and nitrogen oxides NO
x
). Ore and ash solids are also entrained in the waste gas. The waste gas is generally passed through particle separator to remove the solids, then passed through a waste gas boiler to recover heat energy, then treated to remove sulfur and nitrogen oxides, then combusted to recover the fuel value of the carbon monoxide contained in the gas, and finally discharged into the atmosphere.
In order to improve the efficiency of the ironmaking process, a stream of inert gas, such as nitrogen, can be bubbled through the molten iron to agitate the melt and thereby improve contact between any unconverted FeO in the melt and the carbon monoxide and carbon. Introduction of nitrogen into the furnace has certain disadvantages. Since nitrogen is inert and has no fuel value; additional fuel must be introduced into the furnace to provide the energy necessary to heat the nitrogen to the desired operating temperature. Additionally, the nitrogen increases the volume of waste gas issuing from the top of the furnace, thus increasing the size requirements of the waste gas treating equipment used with the furnace. Furthermore, the high temperature inside the furnace causes some of the nitrogen to be converted to nitrogen oxides, thereby increasing the concentration of pollutants in the waste gas, and the presence of nitrogen in the waste gas lowers the combustible value of the gas.
Methods of improving the operating efficiency of ironmaking processes are continuously sought. The present invention provides a significant improvement in the operating efficiency of these processes by significantly reducing, or entirely eliminating, intentional introduction of nitrogen into the furnace, by enhancing the efficiency of fuel conversion in the furnace efficiency, and by reducing the amount of sulfur in the molten iron by reducing fuel consumption.
SUMMARY OF THE INVENTION
The invention comprises replacing part or all of the nitrogen stirring gas introduced into the molten iron phase and/or the slag phase formed in an ironmaking reactor with reducing gas.
In a broad embodiment, the invention comprises a process for producing iron from iron ore comprising the steps:
(a) combusting a carbonaceous fuel with oxygen in a reactor having a reservoir, thereby producing heat and carbon monoxide;
(b) contacting iron ore and slagging agent with the carbon monoxide in the reactor in the presence of heat, thereby converting iron oxides in the ore to molten iron and forming in the reservoir a molten iron phase and a slag phase; and
(c) periodically removing molten iron and slag from the reactor;
the improvement comprising introducing reducing gas into the molten iron phase, into the slag phase or into both the molten iron phase and the slag phase.
The invention is particularly applicable when used in a plant in which carbon monoxide-containing off gas is discharged from the reactor.
In a preferred embodiment of the invention, the reactor comprises an upper cyclone section and a lower converter section. In this preferred embodiment, high purity oxygen and the iron ore are injected tangentially into the cyclone section of the reactor. Additionally, the carbonaceous fuel and high purity oxygen are introduced into the converter section of the reactor.
In another preferred embodiment, at least part of the reducing gas is carbon monoxide-rich gas. The carbon monoxide-rich gas can be produced from the carbon monoxide-containing off gas. In this embodiment, this carbon monoxide-rich gas can be obtained by passing the carbon monoxide-containing off gas through a carbon dioxide-removal system. The carbon dioxide-removal system is preferably an adsorption system containing a carbon dioxide-selective adsorbent.
In another preferred aspect, water vapor, one or more nitrogen oxides, one or more sulfur oxides or combinations of any of these are removed from the carbon monoxide-containing off gas.
In another preferred embodiment of the invention, at least part of the reducing gas is obtained by passing the carbon monoxide-containing off gas through a gas separation system comprising means for separating nitrogen, argon or mixtures thereof from the carbon monoxide-containing off gas. In a more preferred embodiment, this gas separation system comprises one or more adsorbents. In another preferred embodiment, at least part of the reducing gas is obtained by passing the carbon monoxide-containing off gas through both a carbon dioxide-removal system and the above-mentioned gas separation system. In a preferred aspect of this preferred embodiment, the carbon monoxide-containing off gas is first passed through a carbon dioxide-removal system and then passed through the gas separation system.
In another preferred embodiment of the invention, at least part of the reducing gas is obtained by passing the carbon monoxide-containing off gas through a carbon monoxide removal system, which, in a more preferred embodiment, comprises a carbon monoxide-selective adsorbent. In another preferred embodiment, at least part of the reducing gas is obtained by passing the carbon monoxide-containing off gas through both a carbon dioxide-removal system and a carbon monoxide removal system. In a more preferred embodiment, the carbon monoxide-containing off gas is passed through a carbon dioxide-removal system and then passed through a carbon monoxide removal system.
In another preferred embodiment, a diluent gas selected from nitrogen, argon, carbon dioxide or mixtures of two or all of these is introduced into the molten iron phase, introduced into the slag phase or introduced into both the molten iron phase and the slag phase with or in addition to the reducing gas. In this preferred embodiment, the diluent gas can be obtained from the carbon monoxide-containing off gas. The reducing gas and the diluent gas can be introduced together or introduced separately into the molten iron phase, into the slag phase or into both the molten iron phase and said slag phase. The reducing gas and the diluent gas can be introduced into the molten iron phase, into the slag phase or into both the molten iron phase and the slag phase through one or more concentric conduits, with the reducing gas being introduced through the center conduit and the diluent gas being introduced through an outer concentric conduit.
In another preferred embodiment of the invention, hydrocarbon fuel is introduced into the molten iron phase, into the slag phase or into both the molten iron phase and the slag phase. The reducing gas and hydrocarbon fuel can be introduced as a mixture or they can be separately introduced into these phases. In a more preferred aspect of this preferred embodiment, the fuel is methane.
In another preferred embod
Kapoor Akhilesh
Saxena Neeraj
Sweeney Paul Alfred
King Roy
McGuthry-Banks Tima
Neida Philip H. Von
Pace Salvator P.
The BOC Group Inc.
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