Apparatus for feeding gases into a smelting furnace

The present invention relates to a method and apparatus for feeding reaction gases, advantageously oxygen and air or a mixture thereof, into a smelting furnace so that the cross-sectional area wherethrough the reaction gases are fed can be adjusted. Thus the velocity of the gases when they are discharged into the smelting furnace can be maintained sufficiently high while the quantity and quality of the gas varies.

BACKGROUND OF THE INVENTION 
The present invention relates to a method and apparatus for feeding 
reaction gases, advantageously oxygen and air or a mixture thereof, into a 
smelting furnace so that the cross-sectional area through which the gases 
are fed can be adjusted. Thus the velocity of the gases when they are 
discharged into the smelting furnace can be maintained sufficiently high 
with a varying quantity and quality of the gas. 
When reaction agents and reaction gases are fed into a suspension smelting 
furnace, these are brought into contact with each other and mixed only in 
the reaction zone of the furnace. Now the mass transfer between the 
reacting solid particle and surrounding gas is rendered as high as 
possible in the reaction space itself, because the velocity difference 
between the reaction gas and the powdery solid matter also is made as 
great as possible. 
From the U.S. Pat. No. 4,210,315 there is known an apparatus where the 
suspension of a powdery solid substance and a reaction gas is formed by 
feeding the solid substance into the reaction space centrally with respect 
to the reaction gas supply. Inside the solid substance feed pipe, there is 
coaxially installed a gas supply pipe wherethrough part of the gas is fed, 
and the bottom end the gas supply pipe is made conical so that gas is 
discharged through apertures provided at the bottom end of the cone. The 
gas emitted through the discharge apertures directs the solid substance 
falling along the conical surface towards the reaction gas zone proper, 
coming from outside the solid substance flow, i.e. towards the periphery 
of the reaction space. 
From the U.S. Pat. No. 3,392,885 there is known a method and apparatus 
whereby the direction of the main reaction gas flow described in the above 
patent can be flexibly changed. By means of this apparatus, a horizontally 
supplied gas flow is divided to sub-flows radially with the aid of 
partition walls, and simultaneously the direction of the gas flow is 
turned to be parallel to the central axis of the reaction shaft of the 
smelting furnace, so that the velocity of the sub-flows increases at the 
same time. The sub-flows are discharged into the reaction space as an 
annular flow, thus encircling the concentrate flow supplied from the 
inside. 
The U.S. Pat. No. 4,392,885 describes a method and apparatus whereby the 
major part of the reaction gas flow according to the U.S. Pat. No. 
4,210,315 is fed symmetrically in several turbulent jets from around the 
pulverous substance flow into the reaction space. The discharge pipes, 
wherethrough the turbulent jets flow, are adjustable so that the degree 
and direction of turbulence therein can be adjusted. 
The above described apparatuses designed for feeding pulverous substances, 
mainly concentrates, are perfectly usable as long as the amount of the 
material to be fed into the smelting furnace remains more or less the 
same. If the amount of concentrate to be fed into the smelting furnace is 
for some reason essentially reduced, the amount of supplied reaction gas 
must likewise be reduced. Generally there are no serious problems in 
feeding the concentrate; both measured and smaller amounts can normally be 
easily fed in through the same supply devices. However, a bigger problem 
arises with respect to the reaction gas to be supplied, for if the amount 
of gas is essentially reduced, its velocity in the discharge aperture also 
is reduced, because the transversal surface wherethrough it is fed still 
remains the same. 
If the gas discharge velocity in the concentrate distributor and thus in 
the reaction zone of the furnace is essentially reduced, this causes 
difficulties in creating a good suspension in the reaction shaft, and as a 
consequence the reactions between concentrate and gas take place in an 
irregular and unsatisfactory manner. These difficulties are somewhat 
alleviated by means of the apparatus according to the U.S. Pat. No. 
4,392,885, where the gas turbulence is intensified, but if the amount of 
gas falls for instance to half of the measured values, a good suspension 
is difficult to achieve even with this method. Another important reason 
for the diminishing of the reaction gas amount is that there is a growing 
tendency towards an intensified oxygen enriching, which naturally 
decreases the amount of employed gas. 
According to the present invention, there is now developed a method and 
apparatus where the cross-sectional flow area, wherethrough the reaction 
gas flows, can be adjusted so that the flowing velocity of the reaction 
gases can be maintained sufficiently high, and thus a good suspension 
between the particles of the pulverous solid substance and the gas can be 
ensured in the reaction shaft of the furnace, in which case the desired 
reactions between the solid substance and the gas proceed rapidly. 
Accordingly, the method of the invention for feeding reaction gases to the 
reaction shaft of a suspension smelting furnace is based on the fact that 
the gas distribution chamber is divided into several nested parts, so that 
gas can be fed in either through all annular sub-chambers, or only through 
one chamber, for example, depending on the amount of gas, and thus a 
sufficient gas velocity can be maintained all the time at the gas 
discharge aperture. Gas can be brought into the gas distribution chamber 
from one or several directions. 
The pulverous material, such as concentrate, and fluxes may be fed 
centrally from inside the gas distribution chamber, by means of for 
instance the central jet distributor according to the U.S. Pat. No. 
4,210,315 or the apparatus according to the U.S. Pat. No. 5,133,801. By 
means of the method of the invention, for example the air/oxygen ratio of 
the reaction gas can be adjusted steplessly, because the gas quantity is 
decreased while the oxygen ratio is increased, and this decreased amount 
of gas can now be fed in without using all sub-chambers.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
The concentrate distributor 1 is installed in the arch 2 of a smelting 
furnace, such as a suspension smelting furnace, so that the pulverous 
solid substance, such as concentrate, and reaction gases discharged from 
the distributor are supplied through separate channels and meet only in 
the reaction shaft located underneath the arch to form a suspension there. 
The concentrate is brought into the distributor through concentrate pipes 
3, and is made to flow down the pouring pipe 4 to the reaction shaft. 
Inside the concentrate pouring pipe 4, there is arranged a supply pipe 5 
for the gas, generally air, which is supplied in order to disperse the 
concentrate, and the bottom end of the supply pipe 5 extends lower than 
the bottom part of the pouring pipe 4 and is made conical and provided 
with perforations at the terminal edge. The dispersion air is discharged 
through the perforations nearly horizontally and thus disperses the 
concentrate curtain that flows around in an annular configuration, Inside 
the dispersing air supply pipe, there can also be arranged another gas 
supply pipe 6, wherethrough part of the required reaction gas is conducted 
into the reaction space. Advantageously this gas is oxygen. 
The major part of the reaction gas is conducted via the gas distribution 
chamber 7 surrounding the concentrate pouring pipe 4, to which gas 
distribution chamber 7 the gas is conducted through at least one feed pipe 
8. In the drawing there are two feed pipes. At its other end, prior to 
ending in the gas distribution chamber, the feed pipe is divided into at 
least two separate parts 9 and 10 by means of partition walls 11. The 
direction of the partition wall is turned to be parallel to the central 
axis of the reaction shaft, i.e. vertical, and it is formed to continue in 
an annular fashion inside the essentially cylindrical gas distribution 
chamber as far as the bottom end of the chamber. Thus the gas distribution 
chamber is formed of several nested annular members 12, 13, and the gas 
discharge aperture to the reaction shaft thus comprises two or more 
compartments. 
The gas supply to the gas distribution chamber is fed by means of supply 
valves 14 provided in the feed pipes 8, which valves can be manually or 
automatically adjustable. Thus the process gas is conducted to each of the 
nested chambers 9, 10 through a separate channel provided with an 
adjusting valve. The partition walls 11 of the sub-chambers extend as far 
as the discharge edge 15 of the gas distribution chamber, i.e. as far as 
the bottom edge of the furnace arch. While running with maximum load, the 
gas is discharged from every nested chamber at a velocity which is most 
advantageous for the process in question. While running with minimum load, 
the required amount of process gas is conducted through one chamber only, 
while the rest are closed.