Specialized metallurgical processes – compositions for use therei – Processes – Producing or treating free metal
Reexamination Certificate
2001-07-30
2003-12-30
Andrews, Melvyn (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Processes
Producing or treating free metal
C075S010630, C075S500000, C266S177000, C266S195000
Reexamination Certificate
active
06669756
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a discharge apparatus for a movable hearth type heat treatment furnace and its operation method. The present invention also relates to a method of manufacturing molten iron by reducing raw material formed from at least powdered iron oxide-containing material and powdered carbonaceous reducing agent to manufacture reduced iron using a rotary hearth type reduction furnace and the like as a movable hearth type heat treatment furnace, and then reducing and melting the reduced iron in a molten iron-manufacturing furnace.
2. Description of the Invention
Recently, a movable hearth type heat treatment furnace, for example, a rotary hearth type reduction furnace has been widely used for manufacturing reduced iron or metallic iron by reducing raw material which comprises iron ore or dust of an iron foundry, the other waste, coal and the like as components. The movable hearth type heat treatment furnace for manufacturing reduced iron or metallic iron reduces raw material on the movable hearth or additionally heats raw material after reduced, thereby melting and separating iron and slag. And, although a discharge apparatus is provided for discharging reduced iron that is highly reoxidizable or metallic iron that has no reoxidation problem (to be referred as heat-treated products), carbonaceous powder, and slag mixture, which are discharged from a discharge port out of the furnace, various types of such a discharge apparatus for movable hearth type heat treatment furnace have been known.
For example, a known discharge apparatus consists of a chute located between a discharge port for heat-treated products of movable hearth type heat treatment furnace and a downstream side facility, and high temperature switching valves having two or more stages for preventing outflow of high temperature gas from the movable hearth type heat treatment furnace, the valves having a well-known construction. That is, the discharge apparatus is constructed to feed heat-treated products discharged from the furnace into the downstream side facility simultaneously with discharging heat-treated products out of the furnace, while preventing outflow of high temperature gas from the movable hearth type heat treatment furnace by mutual on-off operations of high temperature switching valves.
In addition, another known discharge apparatus consists of a chute located between the discharge port for discharging heat-treated products of the movable hearth type heat treatment furnace and a detachable sealed container, and high temperature switching valves of well-known construction in the way of chute.
Yet another known discharge apparatus consists of a chute, of which one end is connected to the discharge port for discharging heat-treated products of the movable hearth type heat treatment furnace, and the other end is provided with a quantitative discharge apparatus such as a vibration feeder, a screw conveyor, or a pan conveyor.
Conventionally, molten pig iron was manufactured mainly by a blast furnace method. The blast furnace method is a method in which raw material of massive iron ore and coke are charged from the top portion of furnace and hot reducing gas is produced by blowing hot blast from a tuyere provided in the bottom portion of furnace to burn the coke, thereby reducing and melting the iron oxide. Although the blast furnace method is a process having a very good efficiency, it has a drawback in that it requires massive raw material and reducing agent. That is, because the feeding of massive ore as raw material is tight, it is inevitable to use powdered ore after forming it into sintered ore or pellets and thus a sintering machine or a facility for manufacturing pellets is needed. In addition, because reducing agent is used after carbonized and coked, strongly caking coal that is expensive is needed as coal for manufacturing coke besides a coke furnace. Furthermore, in these facilities, because it is supposed that cost for measuring pollution will be increased suddenly as environmental regulation is strengthened from now on, thereby cost needed for processing raw material and reducing agent in advance will be increased, and as a result, there will be a problem that cost of molten pig iron will be increased.
Recently, methods of manufacturing molten pig iron directly from powdered iron ore and coal material which do not require or simplify a facility for processing such raw material and fuel in advance, have been developed. Among them, it is noted that various methods of manufacturing molten pig iron have been proposed and paid attention, in which a mixture of powdered iron ore and coal material is pre-reduced in the aforementioned movable hearth type heat treatment furnace, for example, a rotary hearth type heat treatment furnace, so that reduced iron is manufactured, and the reduced iron is discharged by the aforementioned discharge apparatus and the like, and then reduced and molten in a smelting furnace.
For example, finely powdered iron ore and finely powdered carbonaceous material are formed into a briquette shape and these formed products are pre-reduced into reduced iron in a rotary hearth furnace as a pre-reduction furnace and are discharged from the furnace at least at a temperature which is not lower than 1000° C. Meanwhile, a smelting furnace, within which metallic bath exists and which blows oxygen into the furnace simultaneously introducing finely powdered carbonaceous material onto the surface of bath, is prepared, the aforementioned reduced iron is charged into the smelting furnace, and reducing and melting are performed. In this case, the exhaust gas of smelting furnace is recovered and introduced into a rotary hearth furnace, which is a pre-reduction furnace, as fuel for pre-reducing the formed products.
Also, powdered iron oxide and powdered solid-reducing agent are mixed, the mixture obtained thereby is pre-reduced in the powdered state as it is without being conglomerated thereby producing reduced iron, and then discharged from the furnace at a temperature of at least 500° C. Meanwhile, a filled-in layer of coal material exists in the furnace, conglomerated granular coal material is charged from the top portion of the furnace, and the reduced iron is charged into a shaft furnace that generates reducing gas by blowing oxygen-containing gas from a tuyere provided in the bottom portion of the furnace to burn coal material in front of the tuyere, whereby reducing and melting are performed. An this time, some cases recover produced gas of the shaft furnace and charge a part of it into the rotary hearth furnace, which is a pre-reduction furnace, as fuel.
Furthermore, some cases pre-reduce raw pellets consisting of iron ore, carbon-containing reducing agent and slag-forming material to form self-fluxing reduced iron, charge the self-fluxing reduced iron into a submerged arc furnace, and perform reduction and melting while melting and separating slag during a temperature-rising process, thereby manufacturing molten pig iron, of which the concentration of carbon is 1? 5%.
Although the above prior arts are excellent, at first, there are problems in connection with the means for feeding reduced iron discharged from the rotary hearth furnace into the smelting furnace as follows:
Firstly, as to the discharge apparatus of movable hearth type heat treatment furnace, because the heat-treated products discharged from the exhaust port of movable hearth type heat treatment furnace have a high temperature maximum above 1000° C. and in addition thereto powder (carbonaceous powder) is also discharged, troubles such as blockage and adherence are liable to be occurred in the high temperature switching valves and it is difficult to continue stable operation. In addition, the discharge of heat-treated products by the high temperature switching valve is intermittent, and in particular there is a problem to be solved in that continuous melting is impossible if a melting furnace is located in the downstream side, whereby improveme
Hashimoto Sumito
Tetsumoto Masahiko
Uchida Toshikatsu
Umeki Takao
Urabe Yoshihiro
Andrews Melvyn
Kabushiki Kaisha Kobe Seiko Sho
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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