Specialized metallurgical processes – compositions for use therei – Processes – Producing or treating free metal
Reexamination Certificate
1999-06-01
2001-05-29
Kastler, Scott (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Processes
Producing or treating free metal
C266S221000, C266S267000
Reexamination Certificate
active
06238457
ABSTRACT:
The present invention relates to a method for feeding reaction gas and finely divided solids to a suspension smelting furnace, so that the flow velocity and flowing direction of the reaction gas and solids are adjusted at a point where the reaction gas and solids are discharged into the suspension smelting furnace. The invention also relates to a multiadjustable burner for realizing the method.
The reaction shaft of a suspension smelting furnace is vertical, and it is necessary to form a good, i.e. controlled and adjustable suspension in between the finely divided solids and reaction gas to be fed downwardly in at the top part thereof, in order to achieve for the solids a combustion that is as complete as possible. A prerequisite for the formation of a good suspension is that the suspension is not formed until the reaction space, i.e. the reaction shaft.
The finely divided solids to be fed into the suspension smelting furnace can be dispersed and distributed into the reaction shaft for instance by using a central jet distributor described in the GB patent 1,569,813. By means of said distributor, the orientation of the solids that first flow freely downwards is turned to an almost horizontal, outwardly direction prior to discharging solids into the reaction shaft. The solids are directed outwards by using a curved glide surface in the distributor and dispersion air jets directed outwardly from underneath said surface. Reaction gas is fed into the outwardly directed solids flow. The finely divided solid material is most often a concentrate.
In a normal situation, said central jet distributor with fixed perforations is sufficient; however, the use of concentrates that are difficult to make react is becoming increasingly common, and therefore a need has arisen to change dispersion also in other ways than by altering the amount of dispersion air. Because the dispersion air perforation in the concentrate distributor proper is located in the reaction space, i.e. in the reaction shaft itself, the conditions are fairly demanding, and because the perforations are also located far away and at the end of narrow channels, it is not sensible to adjust the sizes of perforations—at least not in continuous operation.
In the prior art there is known a method described in the U.S. Pat. No. 5,133,801, where on the central axis of a central jet distributor there is applied a vertical oxygen lance, through which oxygen is fed 5 . . . 15% of the total amount of oxygen. Said lance is tubular in shape, so that therein the discharge velocity and orientation of the oxygen into the furnace are, owing to the straight, stationary model, determined according to the quantity of oxygen only. Oxygen is mainly used as additional oxygen for the concentrate, to boost the reactions from the middle of the cloud of concentrate distributed by the concentrate distributor.
Generally the oxygen or oxygen-bearing gas, such as air, serving as the reaction gas, is first fed into the furnace in horizontal direction, but the gas direction must be turned to vertical prior to its feeding to the reaction shaft. The changing of the direction of the reaction gas is described in the U.S. Pat. No. 4,392,885. According to this patent describing a directional burner, the reaction gas is fed from around a pulverous solid material in an annular flow to the furnace reaction shaft through a discharge orifice with a fixed cross-sectional area.
In a normal situation it suffices to have a burner with a stationary discharge orifice for the reaction gas, but because current usage increasingly favors nearly 100% oxygen, gas quantities have been reduced to a roughly fifth part of the previous air supply. Consequently, in order to reach a given velocity for the reaction gas there is required an increasingly diminishing cross-sectional flow area for the discharge orifice of the burner. It is a fairly common requirement for the burner that it must be feasible for running a relatively wide range as for capacity and oxygen-enrichment. Because the reactions and conditions in the furnace require a certain velocity range for the reaction gas in the reaction shaft, the use of a burner with a fixed orifice leads to outside said range of acceptability. Consequently, current technology requires that the cross-sectional area of the reaction gas orifice in the burner is adjustable.
The adjusting of the reaction gas discharge orifice as such is not a problem, and there are several different ways to perform the task. The problem is to find a way of adjustment which, in addition to working in a desired fashion, also endures the rough furnace conditions, i.e the temperature (about 1400° C.), has good mechanical strength (for instance for the removal of possible build-ups with a rod), etc.
A stepwise adjustment is performed for example in a fashion described in the U.S. Pat. Nos. 5,362,032 and 5,370,369 or in the FI patent application 932458. In the first of said patents, around the concentrate distributor there are provided two cocentric annular rings of different sizes for the reaction gas. By conducting the gas to either or both rings, there are obtained three fixed discharge velocity areas. In the second patent, a desired number of discharge pipes of a desired size are closed or put to use. In the third there are “dropped” a suitable number of funnel-shaped open cones according to the case. All embodiments, however, are characterized by their stepwise nature, which means that it is not possible to bind the adjustment for instance to capacity in a continuous process.
Continuously operated systems of adjustment are described in the U.S. Pat. Nos. 4,490,170 and 4,331,087. In both systems, adjusting is based on changing the rotation power of the reaction gas, and is thus not suitable for adjusting linear velocity only.
The Japanese patent application 5-9613 utilizes a continuously operated adjustment for the reaction gas. In this application, the adjustment is a closed cone structure that moves vertically around the concentrate pipe. A reducing cone that leads reaction gas into the cylindrical discharge orifice of the burner serves as the counterpiece of said closed cone. The cones that form the flow channel are both straight (i.e. the surface wall is straight) and equiangular, so that the gas is directed to the concentrate falling in the cylinder before it reaches the distributor cone attached to the oil lance installed inside the concentrate pipe. Thus the adjusting operations are clearly carried out before the concentrate and the reaction gas are discharged into the furnace, and while discharging into the furnace, the reaction gas that is partly mixed into the concentrate has lost the velocity (and direction) it achieved through the adjustment, i.e. the discharge velocity into the furnace is determined according to the fixed discharge orifice of the burner. The direction of the adjustment is always the same: powerfully towards the middle axis, never parallel to the axis or outwards therefrom.
The above described mixing of reaction gas and concentrate carried out inside the burner is not possible with pure oxygen or with a high oxygen-enrichment, if the concentrate is easily reacting, because in that case the result is the blocking of the burner due to the sintering of the concentrate. From the point of view of adjustment, the burner operates, with respect to the furnace space, in similar fashion as any burner with a fixed orifice. Said patent application also introduces the use of oxygen and/or oil in a concentrate burner in the middle of the concentrate flow, but it does not describe in more detail any features affecting the discharge of said oxygen and/or oil.
In the method according to the present invention, the adjusting of the reaction gas velocity, and particularly of its direction as well, takes place in a reaction gas channel located around the finely divided solids flow, in which channel there is installed a vertically moving, annular and custom-shaped adjusting member. The adjusting member is connected to an adjusting device proper, which reacts to
Holmi Ismo
Jokinen Tuomo
Lilja Launo
Sipilä Jussi
Törölä Vesa
Kastler Scott
Morgan & Finnegan , LLP
Outokumpu Oyj
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