Specialized metallurgical processes – compositions for use therei – Processes – Producing or treating free metal
Reexamination Certificate
1998-07-28
2001-01-16
Andrews, Melvyn (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Processes
Producing or treating free metal
C075S446000, C075S491000
Reexamination Certificate
active
06174346
ABSTRACT:
FIELD
The present invention relates to a method and an apparatus for producing metals and metal alloys, in particular, although by no means exclusively iron and iron alloys, from metal oxides, such as ores and partly reduced ores.
BACKGROUND
There are a number of known methods of smelting iron ore to produce molten iron which are based on the use of a metallurgical vessel (hereinafter referred to as a “smelt reduction vessel”) containing a molten bath of iron and slag.
In general terms, these known methods comprise injecting iron ore or partially reduced iron ore and a source of a carbonaceous material into a molten bath of iron and slag. In the molten bath the iron ore or partially reduced iron ore is reduced to metallic iron and melted. The carbonaceous material (in solid or gaseous form) is required as a source of reductant and thermal energy and to carburise the molten bath to produce pig iron (typically 1 to 4 wt. % carbon in metal).
In a number of known processes, reaction gases that are discharged from the smelt reduction vessel are used to preheat and to partially reduce iron ore in a pre-reduction vessel, such as a shaft furnace, prior to transferring the partially reduced iron ore into the smelt reduction vessel. These known processes are commonly described as being two-stage linked processes.
SUMMARY
An object of the present invention is to provide a method and an apparatus for producing molten iron which is an improvement over the known two-stage linked processes.
According to the present invention there is provided a method of producing metals and metal alloys from metal oxides which comprises the steps of:
(i) partially reducing metal oxides and/or partially reduced metal oxides and at least partially devolatilising a solid carbonaceous material, by injecting metal oxides and/or partially reduced metal oxides and the solid carbonaceous material into a pre-reduction vessel and maintaining a temperature of at least 550° C. in the pre-reduction vessel; and
(ii) reducing further the partially reduced metal oxides to produce molten metal by injecting the partially reduced metal oxides and the at least partially devolatilised solid carbonaceous material from step (i) into a smelt reduction vessel containing a molten bath of metal and slag.
The at least partially devolatilised solid carbonaceous material produced in pre-reduction step (i) is a source of carbon for use in the subsequent smelt reduction step (ii). As is discussed above, the carbon is needed in the smelt reduction step (ii):
(a) to reduce the pre-reduced metal oxides to metal;
(b) to provide a source of thermal energy to melt the metal oxides; and
(c) to carburise the bath to provide levels of dissolved carbon in metal that may be required to produce metal alloys in the molten bath.
The invention does not preclude injection into the smelt reduction vessel of carbonaceous materials in addition to the at least partially devolatilised solid carbonaceous material that is produced in the pre-reduction vessel.
For example, the invention extends to the injection of coal or other suitable solid carbonaceous materials or any suitable gaseous carbonaceous materials into the smelt reduction vessel in addition to the injection of the at least partially devolatilised solid carbonaceous material produced in the pre-reduction vessel.
It is preferred that the at least partially devolatilised solid carbonaceous material be char.
The term “char” is understood herein to mean the product of heating coal without burning the coal.
It is preferred that the pre-reduction step (i) partially reduces the metal oxides and/or partially reduced metal oxides to a pre-reduction degree of at least 50%.
The term “pre-reduction degree” is understood herein to mean the percentage of oxygen removal starting from Fe
2
O
3
.
It is preferred particularly that the pre-reduction step (i) partially reduces the metal oxides and/or partially reduced metal oxides to a pre-reduction degree of at least 60%.
It is preferred more particularly that the pre-reduction step (i) partially reduces the metal oxides and/or partially reduced metal oxides to a pre-reduction degree of at least 70%.
Typically, the pre-reduction step (i) partially reduces the metal oxides and/or partially reduced metal oxides to a pre-reduction degree of 80%.
The purpose of the solid carbonaceous material injected into the pre-reduction vessel in the pre-reduction step (i) is to provide:
(a) a source of the char or other at least partially devolatilised solid carbonaceous material for use subsequently in the smelt reduction step (ii); and
(b) a source of reductant to pre-reduce the metal oxides in the pre-reduction vessel.
It is preferred that the solid carbonaceous material injected into the pre-reduction vessel be coal.
In that event, it is preferred that the temperature in the pre-reduction vessel be maintained at a temperature, typically less than 1000° C., at which the fixed carbon component of the coal does not act readily as a reductant. In such a situation, the volatiles, such as hydrocarbons, in the coal are the main source of reductant. Specifically, the hydrocarbons crack to form the reductants CO and H
2
O (and other products).
It is noted that the invention does not preclude the use of fixed carbon in the coal as a reductant in the pre-reduction vessel.
It is preferred that the pre-reduction step (i) comprises forming a fluidised bed of the metal oxides and/or partially reduced metal oxides and the solid carbonaceous material in the pre-reduction vessel.
It is preferred particularly that the fluidised bed be formed by injecting air into the pre-reduction vessel either directly or indirectly.
It is preferred that the temperature be maintained at the temperature of at least 550° C. in the pre-reduction vessel by:
(i) combusting coal and/or other carbonaceous materials (including gaseous carbonaceous materials) in the pre-reduction vessel; and/or
(ii) providing heat energy by indirect heat exchange.
It is preferred that the temperature in the pre-reduction vessel be maintained at a temperature of at least 600° C.
It is preferred particularly that the temperature in the pre-reduction vessel be maintained at a temperature of at least 750° C.
It is preferred more particularly that the temperature in the pre-reduction vessel be maintained at a temperature of at least 800° C.
It is preferred that the temperature in the pre-reduction vessel be maintained at a temperature of less than 1000° C.
It is preferred particularly that the temperature in the pre-reduction vessel be maintained at a temperature of less than 1000° C.
The preferred temperature range for the pre-reduction vessel is 750 to 950° C.
The reduction and melting reactions in the smelt reduction step (ii) described above are endothermic and, therefore, it is preferred that the method includes a step of maintaining the temperature of the molten bath in the smelt reduction vessel above a minimum temperature.
It is preferred that the minimum temperature of the molten bath be in the range of 1350° C.-1500° C.
It is preferred that the step of maintaining the temperature of the molten bath in the smelt reduction vessel above the minimum temperature comprises post-combusting reaction gases, such as CO and H
2
, released from the molten bath by injecting oxygen-containing gas into a gas space in the smelt reduction vessel above the molten bath and transferring energy generated by the post-combustion to the molten bath.
It is preferred that the oxygen-containing gas be air.
It is preferred particularly that the air be preheated to a temperature of at least 1000° C.
It is preferred that the pre-reduction step (i) comprises pre-reducing the metal oxides and/or partially reduced metal oxides in two or more pre-reduction stages.
It is preferred particularly that the pre-reduction step (i) comprises:
(i) a first pre-reduction stage of injecting metal oxides and reaction gases from the smelt reduction vessel and/or a second pre-reduction vessel into one pre-reduction vessel to dry, pre-heat, and partially reduce the metal oxides and,
Dry Rodney James
Innes John Alexander
Andrews Melvyn
Merchant & Gould P.C.
Technological Resource Pty. Ltd.
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