[0001] The invention relates to a metallurgical vessel comprising a lower portion for accommodating
a molten metal bath and part of a slag layer in use, an upper portion for accommodating
the remainder of the slag layer in use and a plurality of lances which project into
the upper portion of the vessel and supply oxygen containing gas to the upper portion
of the vessel. The present invention also relates to a method of iron making.
[0002] The term metallurgical vessel refers to a vessel suitable for treating metal or metal
oxide, metal smelting, refining or reducing.
[0003] EP 0 735 146 describes a metallurgical vessel of the converter type, in which pre-reduced
iron compounds are further reduced. Oxygen is supplied by means of a plurality of
lances that project through the wall of the vessel and extend to above the slag layer.
It is known from this document to introduce a gas through the bottom of the vessel
into the molten metal in order to rinse the iron melt. This procedure is also known
as bottom stirring or bottom bubbling in the art and is performed to agitate the molten
metal in the lower portion of the vessel. Bottom stirring ensures sufficient heat
transfer to the molten metal bath beneath the slag layer and sufficient stirring of
the lower slag layer itself so that it does not become quiescent and so that heat
generated in the upper slag layer is also transferred to the lower slag layer. Bottom
stirring has considerable drawbacks such as, for example, increasing refractory erosion
along the walls of the vessel in the area of the hot metal as well as requiring injection
points beneath the tap level of the vessel that have a relatively short lifetime and
are difficult to maintain.
[0004] The object of the present invention is to provide a metallurgical vessel having reduced
refractory erosion and greater ease of maintenance without a reduction in production
efficiency.
[0005] The present invention overcomes the problems of the prior art as the metallurgical
vessel comprises a plurality of tuyeres arranged around the circumference of the lower
portion of the vessel suitable for supplying gas and/or liquid and/or solids and/or
plasma into the slag layer in the lower portion of the vessel.
[0006] The plurality of lances supply oxygen containing gas, and thereby heat, to the slag
in the upper portion of the vessel whilst the gas and/or liquid and/or solids and/or
plasma supplied by the tuyeres ensure that the lower slag layer does not become quiescent.
Quiescence results in a cooling of the lower slag layer and a loss of productivity.
The tuyeres supply gas and/or liquid and/or solids and/or plasma directly to the lower
slag layer whereas gas is injected through the bottom of the vessel into the molten
metal in bottom stirring. The present invention thus does not generate high flow velocities
in the molten metal thereby avoiding one of the major drawbacks of bottom stirring
namely the fast erosion of the vessel wall in the part of the vessel containing the
molten metal. The supply of gas and/or liquid and/or solids and/or plasma to the slag
layer in the lower portion of the vessel by the tuyeres thus does not cause erosion
of the refractory lining in the hot metal zone but it does maintain productivity by
stirring the lower slag layer. Stirring the lower slag layer maximises reactions within
the lower slag layer and ensures it does not become quiescent. The supply of combustible
gas and/or liquid and/or solids by the tuyeres also increases heat transfer from the
slag layer to the molten metal in the lower portion of the vessel. The tuyeres are
also easier to maintain as they are positioned above the tap level of the vessel.
[0007] The diameter of the lower portion of the vessel may preferably be smaller than the
diameter of the upper portion of the vessel. The tuyeres are arranged around the circumference
of the lower part of the vessel and therefore the jets emitted by the tuyeres will
penetrate into the slag layer in the lower portion of the vessel before rising through
the slag into the upper portion of the vessel. Any "hot spots" i.e. areas of higher
temperature, created by the gas and/or liquid and/or solids and/or plasma supplied
by the tuyeres, in the slag layer in the upper portion of the vessel will therefore
be sufficiently distant from the wall of the vessel to ensure that no increase in
corrosion and/or erosion of the wall occurs.
[0008] The tuyeres may preferably comprise oxy-fuel burners to act as a direct heat source
in the slag layer in the lower portion of the vessel. The oxy-fuel burners will increase
the productivity of the reactor by increasing the occurrence of the endothermic reduction
reactions and thereby increasing the reduction capacity of the slag layer.
[0009] The tuyeres preferably supply oxygen containing gas to the slag layer in the lower
portion of the vessel. The oxygen contained in the gas will combust char into carbon
monoxide thereby providing an additional source of heat in the slag layer and increasing
the productivity of the reactor as explained for oxy-fuel burners.
[0010] At least ten tuyeres may be positioned around the lower portion of the vessel to
ensure optimum distribution of the gas and/or liquid and/or solids and/or plasma,
supplied by the tuyeres, into the slag layer.
[0011] The metallurgical vessel of the present invention preferably comprises a melting
cyclone positioned above, and in open communication with, the vessel. Such a melting
cyclone is described in Dutch patent NL C 257692 and EP 0690136.
[0012] The metallurgical vessel of the present invention may be used for iron making and
steel making.
[0013] The present invention also relates to a method of reducing iron oxide to iron using
a metallurgical vessel in accordance with the invention, comprising the steps of supplying
iron oxide to the vessel, supplying oxygen containing gas to the interior of the metallurgical
vessel, supplying carbonaceous material to the iron oxide and supplying gas and/or
liquid and/or solids and/or plasma into the slag layer in the lower portion of the
vessel via the plurality of tuyeres.
[0014] The present invention also relates to a method of iron making comprising the steps
of:
- conveying iron-oxide containing material into the melting cyclone,
- pre-reducing said iron-oxide containing material by means of a partially post-combusted
reducing process gas originating from the metallurgical vessel,
- at least partly melting the iron-oxide containing material in the melting cyclone
by supplying oxygen containing gas to the melting cyclone and effecting a post-combustion
in said reducing process gas,
- permitting the pre-reduced and at least partly melted iron-oxide containing material
to pass downwardly from said melting cyclone into the metallurgical vessel in which
final reduction takes place and
- effecting the final reduction in the metallurgical vessel in a slag layer, by supplying
oxygen containing gas to the interior of the metallurgical vessel via a plurality
of lances, by supplying coal to the interior of the metallurgical vessel and by supplying
gas and/or liquid and/or solids and/or plasma to the lower slag layer via a plurality
of tuyeres, and thereby forming said reducing process gas and effecting a partial
post-combustion in said reducing process gas in said metallurgical vessel by means
of said oxygen containing gas supplied thereto.
BRIEF INTRODUCTION TO THE DRAWINGS
[0015] Figure 1 shows an apparatus in accordance with the invention.
DESCRIPTION OF A PREFERRED EMBODIMENT
[0016] The apparatus in figure 1 comprises a metallurgical vessel 1 and a melting cyclone
8. Details of the melting cyclone are not shown. The metallurgical vessel itself comprises
a lower portion 2 which accommodates the iron bath 9 and part of the slag layer 6
and comprises at least one tap hole 11 for tapping off molten iron and slag. The vessel
also comprises an upper portion 3, which accommodates the remainder of the slag layer
6, and a roof portion 4. The slag layer 6 thus rests on top of the iron bath 9 and
extends from the lower portion of the vessel 2 into the upper portion 3. Pre-reduced
iron oxide 10 falls or flows from the melting cyclone into the metallurgical vessel
and is finally reduced in the slag layer. A plurality of lances 5 supply oxygen containing
gas to the slag layer 6 in the upper portion 3 of the vessel. Two lances are shown
in the figure but more may be present depending on, for example, the size of the vessel
and the performance parameters of the lances. A plurality of tuyeres 7 are arranged
around the circumference of the lower portion of the vessel. The tuyeres are suitable
for supplying gas and/or liquid and/or solids (such as recycled dust) and/or plasma
to the slag layer in the lower portion 2 of the vessel. The number of tuyeres arranged
around the circumference of the lower part of the vessel can be varied depending on
the size of the vessel and the performance parameters of the tuyeres. The tuyeres
may comprise oxy-fuel burners. During the final reduction of the pre-reduced iron
oxide a process gas comprising reducing CO is produced that is partially post-combusted
above the slag layer 6 in the vessel 1, whereby heat needed for the final reduction
is released. The reducing process gas rises and is further post-combusted in the melting
cyclone 8 with oxygen containing gas supplied to the melting cyclone. Iron oxide supplied
to the melting cyclone is pre-reduced approximately to FeO and at least partly melted
in the melting cyclone. The pre-reduced iron oxide 10 then falls or flows down into
the metallurgical vessel 1.
[0017] While the invention has been illustrated by a particular embodiment, variations and
modifications are possible within the scope of the inventive concept.
1. Metallurgical vessel comprising a lower portion for accommodating a molten metal bath
and part of a slag layer in use, an upper portion for accommodating the remainder
of the slag layer in use and a plurality of lances which project into the upper portion
of the vessel and supply oxygen containing gas to the upper portion of the vessel
characterised in that a plurality of tuyeres are arranged around the circumference of the lower portion
of the vessel suitable for supplying gas and/or liquid and/or solids and/or plasma
into the slag layer in the lower portion of the vessel.
2. Metallurgical vessel according to claim 1 characterised in that the diameter of the lower portion of the vessel is smaller than that of the upper
portion.
3. Metallurgical vessel according to claims 1 or 2 characterised in that the tuyeres comprise oxy-fuel burners.
4. Metallurgical vessel according to any of the previous claims comprising a melting
cyclone positioned above and in open communication with the metallurgical vessel.
5. Method of reducing iron oxide to iron using a metallurgical vessel in accordance with
any one of claims 1-4, comprising the steps of supplying iron oxide to the vessel,
supplying oxygen containing gas to the upper portion of the metallurgical vessel via
the plurality of lances, supplying carbonaceous material to the iron oxide and supplying
gas and/or liquid and/or solids and/or plasma into the slag layer in the lower portion
of the vessel via the plurality of tuyeres.
6. Method of reducing iron oxide according to claim 5 characterised in that the tuyeres supply oxygen containing gas into the lower slag layer.
7. Method of iron making comprising the steps of:
- conveying iron-oxide containing material into the melting cyclone,
- pre-reducing said iron-oxide containing material by means of a partially post-combusted
reducing process gas originating from the metallurgical vessel,
- at least partly melting the iron-oxide containing material in the melting cyclone
by supplying oxygen containing gas to the melting cyclone and effecting a post-combustion
in said reducing process gas,
- permitting the pre-reduced and at least partly melted iron-oxide containing material
to pass downwardly from said melting cyclone into the metallurgical vessel in which
final reduction takes place and
- effecting the final reduction in the metallurgical vessel in a slag layer, by supplying
oxygen containing gas to the interior of the metallurgical vessel via a plurality
of lances, by supplying coal to the interior of the metallurgical vessel and by supplying
gas and/or liquid and/or solids and/or plasma to the lower slag layer via a plurality
of tuyeres, and thereby forming said reducing process gas and effecting a partial
post-combustion in said reducing process gas in said metallurgical vessel by means
of said oxygen containing gas supplied thereto.