Note: Descriptions are shown in the official language in which they were submitted.
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APPARATUS FOR INJECTING GAS INTO A VESSEL
TECHNICAL FIELD
The present invention provides an apparatus for
injecting gas into a vessel. It has particular, but not
exclusive application to apparatus for injecting a flow of
gas into a metallurgical vessel under high temperature
conditions. Such metallurgical vessel may for example be
a smelting vessel in which molten metal is produced by a
direct smelting process.
A known direct smelting process, which relies on
a molten metal layer as a reaction medium, and is
generally referred to as the HIsmelt process, is described
in International application PCT/AU96/00197 (V~10 96/31627)
in the name of the applicant.
The HIsmelt process as described in the
International application comprises:
(a) forming a bath of molten iron and slag in a
vessel;
(b) injecting into the bath:
(i) a metalliferous feed material,
typically metal oxides; and
(ii) a solid carbonaceous material,
typically coal, which acts as a
reductant of the metal oxides and a
source of energy; and
(c) smelting metalliferous feed material to
metal in the metal layer.
The term °smelting" is herein understood to mean
thermal processing wherein chemical reactions that reduce
metal oxides take place to produce liquid metal.
The HIsmelt process also comprises post-
combusting reaction gases, such as CO and H2 released from
the bath in the space above the bath with oxygen-
containing gas and transferring the heat generated by the
post-combustion to the bath to contribute to the thermal
energy required to smelt the metalliferous feed materials.
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The HIsmelt process also comprises forming a
transition zone above the nominal quiescent surface of the
bath in which there is a favourable mass of ascending and
thereafter descending droplets or splashes or streams of
molten metal and/or slag which provide an effective medium
to transfer to the bath the thermal energy generated by
post-combusting reaction gases above the bath.
In the HIsmelt process the metalliferous feed
material and solid carbonaceous material 1S Injected into
the metal layer through a number of lances/tuyeres which
are inclined to the vertical so as to extend downwardly
and inwardly through the side wall of the smelting vessel
and into the lower region of the vessel so as to deliver
the solids material into the metal layer in the bottom of
the vessel. To promote the post combustion of reaction
gases in the upper part of the vessel, a blast of hot air,
Which may be oxygen enriched, iS Injected into the upper
region of the vessel through the downwardly extending hot
air injection lance. To promote effective post combustion
of the gases in the upper part of the vessel, it is
desirable that the incoming hot air blast exit the lance
with a swirling motion. To achieve this, the outlet end
of the lance may be fitted with internal flow guides to
impart an appropriate swirling motion. The upper regions
35 of the vessel may reach temperatures of the order of 2000°C
and the hot air may be delivered into the lance at
temperatures of the order of 1100-1400°C. The lance must
therefore be capable of withstanding extremely high
temperatures both internally and on the external walls,
particularly at the delivery end of the lance which
projects into the combustion zone of the vessel. The
present invention provides a lance construction which
enables the relevant components to be internally water
cooled and to operate in a very high temperature
environment.
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DISCLOSURE OF THE INVENTION
According to the invention there a.s provided
apparatus for injecting gas into a vessel, including:
a gas flow duct extending from a rear end to a
forward end from which to discharge gas from the duct;
an elongate central tubular structure extending
within the gas flow duct from its rear end to its forward
end;
a plurality of flow directing vanes disposed
about the central tubular structure adjacent the forward
end of the duct to impart swirl to a gas flow to the
forward end of a duct, the forward end of the central
structure and the forward end of the duct co-acting
together to form an annular nozzle for flow of gas from
the duct with swirl imparted by said vanes;
cooling water passages within the central tubular
structure for flow of cooling water forwardly through the
central structure from its rear end to its forward end and
to internally cool that forward end and thence to return
back through the central structure to its rear end.
The forward end of the duct may be formed as a
hollow annular tip formation and the gas flow duct may
include duct tip cooling water supply and return passages
for supply of cooling water forwardly along the duct into
the duct tip and return of that cooling water back along
the duct.
The interior peripheral surface of the duct may
be lined with refractory material.
Preferably the central tubular structure defines
a central water flow passage for flow of Water forwardly
through that structure directly to the forward end of the
central structure and an annular water flow passage
disposed about the central passage for return flow of
water from the forward end of the central structure back
to the rear end of that structure.
The central tubular structure may comprise a
central tube providing the central water flow passage and
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a further tube disposed around the central tube to define
said annular water flow passage between the tubes.
Preferably the central structure includes a heat
insulating outer shield to retard heat transfer from gas
in the gas flow duct into the cooling water passages in
the central structure.
The heat insulating shield may be comprised of a
plurality of tubular segments of heat insulating material
disposed end to end to form the heat shield as a
substantially continuous tube extending from the rear end
to the front end of the central structure about an annular
air gap disposed immediately within the heat shield.
Said air gap may be formed between the tubular
heat shield and the further tube defining the outer wall
of the annular water return flow passage.
Preferably said tubular segments of the heat
shield are supported to accommodate longitudinal expansion
of each segment independently of the other such segments.
The forward end of the central structure may
include a domed nose portion provided internally with a
single spiral cooling water passage to receive water from
the central water flow passage in the central structure at
the ti.p of the nose and direct that water in a single flow
around and backwardly along the nose to cool the nose with
a single coherent stream of cooling water.
The apparatus may include a gas inlet for
introduction of hot gas into the rear end of the duct, the
gas inlet comprising a refractory body defining a first
tubular gas passage aligned with and extending directly to
the rear end of the duct and a second tubular gas passage
transverse to the first passage to receive hot gas and
direct it to the first passage so that the hot gas and any
particles entrained therein impinge on refractory wall of
the first passage, the gas flow undergoing a change of
direction in passing from the first passage to the second
passage.
The first and second gas flow passages may be
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essentially normal to one another.
The central tubular structure may extend
centrally through the first gas flow passage of the gas
inlet means and rearwardly beyond the gas inlet. The rear
5 end of the central structure may then be located
rearwardly of the gas inlet and be provided With water
couplings for the flow of cooling water to and from the
central structure.
BRIEF DESCRIPTION OF THE DRAWINGS
In order that the invention may be more fully
explained one particular embodiment will be described in
detail with reference to the accompanying drawings in
which:
Figure 1 is a vertical section through a direct
smelting vessel incorporating a pair of solids injection
lances and a hot air blast injection lance constructed in
accordance with the invention;
Figure 2 is a longitudinal cross-section through
the hot air injection lance;
Figure 3 is a longitudinal cross-section to an
enlarged scale through.a front part of a central structure
of the lance;
Figures 4 and 5 illustrate the construction of a
forward nose eud of the central structure;
Figure 6 is a longitudinal cross-section through
the central structure;
Figure 7 shows a detail in the region 8 of
Figure 6;
Figure 8 s a cross-section. on the line 8-8 in
Figure 7; and
Figure 9 is a cross-section on the line 9-9 in
Figure 7.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Figure 1 illustrates a direct smelting vessel
suitable for operation by the Hlsmelt process as described
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in International Patent Application PCT/AU96/00197. The
metallurgical vessel is denoted generally as 11 and has a
hearth that includes a base 12 and sides 13 formed from
refractory bricks; side walls 14 which form a generally
cylindrical barrel extending upwardly from the sides 13 of
the hearth and which includes an upper barrel section 15
and a lower barrel section 16; a roof 17; an outlet 18 for
off-gases; a forehearth 19 for discharging molten metal
continuously; and a tap-hole 21 for discharging molten
slag.
In use, the vessel contains a molten bath of iron
and slag which includes a layer 22 of molten metal and a
layer 23 of molten slag on the metal layer 22. The arrow
marked by the numeral 24 indicates the position of the
nominal quiescent surface of the metal layer 22 and the
arrow marked by the numeral 25 indicates the position of
the nominal quiescent surface of the slag layer 23. The
term °quiescent surface" a.s understood to mean the surface
when there is no injection of gas arid solids into the
vessel.
The vessel is fitted with a downwardly extending
hot air injection lance 26 for delivering a hot air blast
into an upper region. of the vessel and two solids
injection lances 27 extending downwardly and inwardly
through the side walls 14 and into the slag layer 23 for
injecting iron ore, solid carbonaceous material, and
fluxes entrained in an oxygen-deficient carrier gas into
the metal layer 22. The position of the lances 27 is
selected so that their outlet ends 28 are above the
surface of the metal layer 22 during operation of the
process. This position of the lances reduces the risk of
damage through contact with molten metal and also makes it
possible to cool the lances by forced internal water
cooling without significant risk of water coming into
contact with the molten metal in the vessel.
The construction of the hot air injection lance
26 is illustrated is Figures 2 - 9. As shown in these
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figures lance 26 comprises an elongate duct 31 which
receives hot gas through a gas inlet structure 32 and
injects it into the upper region of vessel. The lance
includes an elongate central tubular structure 33 which
extends within the gas flow duct 31 from its rear end to
its forward end. Adjacent the forward end of the duct,
central structure 33 carries a series of four swirl
imparting vanes 34 for imparting swirl to the gas flow
exiting the duct. The forward end of central structure 33
has a domed nose 35 which projects forwardly beyond the
tip 36 of duct 31 so that the forward end of the central
body and the duct tipped tip co-act together to form an
annular nozzle for divergent flow of gas from the duct
with swirl imparted by the vanes 34. Vanes 34 are
disposed in a four-start helical formation and are a
sliding fit within the forward end of the duct.
The wall of the main part of duct 31 extending
downstream from the gas inlet 32 is internally water
cooled. This section of the duct is comprised of a series
of three concentric steel tubes 37, 38, 39 extending to
the forward end part of the duct where they are connected
to the duct tip 36. The duct tip 36 is of hollow annular
formation and it is internally water cooled by cooling
water supplied and returned through passages in the wall
of duct 31. Specifically, cooling water is supplied
through an inlet 41 and annular inlet manifold 42 into an
inner annular water flow passage 43 defined between the
tubes 38, 39 of the duct through to the hollow interior of
the duct tip 36 through circumferentially spaced openings
in the tip. Water is returned from the tip through
circumferentially spaced openings into an outer annular
water return flow passage 44 defined between the tubes 37,
38 and backwardly to a water outlet 45 at the rear end of
the water cooled section of duct 31.
The water cooled section of duct 31 is internally
lined with an internal refractory lining 46 that fits
within the innermost metal tube 39 of the duct and extends
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through to the water cooled tip 36 of the duct. The inner
periphery of duct tip 36 is generally flush with the inner
surface of the refractory lining which defines the
effective flow passage for gas through the duct. The
forward end of the refractory lining has a slightly
reduced diameter section 47 which receives the swirl vanes
34 with a snug sliding fit. Rearwardly from section 47
the refractory lining is of slightly greater diameter to
enable the central structure 33 to be inserted downwardly
through the duct on assembly of the lance until the swirl
vanes 34 reach the forward end of the duct where they are
guided into snug~engagement with refractory section 47 by
a tapered refractory land 48 which locates and guides the
vanes into the refractory section 47.
The front end of central structure 33 which
carries the swirl vanes 34 is internally water cooled by
cooling water supplied forwardly through the central
structure from the rear end to the forward end of the
lance and then returned back along the central structure
to the rear end of the lance. This enables a very strong
flow of cooling water directly to the forward end of the
central structure and to the domed nose 35 in particular
which is subjected to very high heat flux a.n operation of
the lance.
Central structure 33 comprises inner and outer
concentric steel tubes 50, 51 formed by tuba segments,
disposed end to end and welded together. Inner tube 50
defines a central water flow passage 52 through which
water flows forwardly through the central structure from a
water inlet 53 at the rear end of the lance through to the
front end nose 35 of the central structure and an annular
water return passage 54 defined between the two tubes
through which the cooling water returns from nose 35 back
through the central structure to a water outlet 55 at the
rear end of the lance.
The nose end 35 of central structure 33 comprises
an inner copper body 61 fitted within an outer domed nose
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shell 62 also formed of copper. The inner copper piece 61
is formed with a central Water flow passage 63 to receive
water from the central passage 52 of structure 33 and
direct it to the tip of the nose. Nose end 35 is formed
with projecting ribs 64 which fit snugly within the nose
shell 62 to define a single continuous cooling water flow
passage 65 between the inner section 61 and the outer nose
shell 62. As seen particularly in Figures 4 and 5. The
ribs 64 are shaped so that the single continuous passage
65 extends as annular passage segments 66 interconnected
by passage segments 67 sloping from one annular segment to
the next. Thus passage 65 extends from the tip of the
nose in a spiral which, although not of regular helical
formation, does spiral around and back along the nose to
exit at the rear end of the nose into the annular return
passage formed between the tubes 51, 52 of central
structure 33.
The forced flow of cooling water in a single
coherent stream through spiral passage 65 extending around
and back along the nose end 35 of central structure
ensures efficient heat extraction and avoids the
development of "hot spots" on the nose which could occur
if the cooling water is allowed to divide into separate
streams at the nose. In the illustrated arrangement the
cooling water is constrained in a single stream from the
time that it enters the nose end 35 to the time that it
exits the nose end.
Inner structure 33 is provided With an external
heat shield 69 to shield against heat transfer from the
incoming hot gas flow in the duct 31 into the cooling
water flowing within the central structure 33. If
subjected to the very high temperatures and high gas flows
required in a large scale smelting installation, a solid
refractory shield may provide only short service. In the
illustrated construction the shield 69 is formed of
tubular sleeves of ceramic material marketed under the
name UMCO. These sleeves are arranged end to end to form
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a continuous ceramic shield surrounding an air gap 70
between the shield and the outermost tube 51 of the
central structure. In particular the shield may be made
of tubular segments of UMCO 50 which contains by Weight
.05 to .12% carbon, .5 to 1% silicon, a maximum of .5 to
1% manganese, .02% phosphorous, .02% sulphur, 27 to 29%
chromium, 48 to 52% cobalt and the balance essentially of
iron. This material provides excellent heat shielding but
it undergoes significant thermal expansion at high.
temperatures. To deal with this problem the individual
tubular segments of the heat shield are formed and mounted
as shown in Figures 6 - 9 to enable them to expand
longitudinally independently of one another while
maintaining a substantially continuous shield at all
times. As illustrated in those figures the individual
sleeves are mounted on location strips 71 and plate
supports 72 fitted to the outer tube 51 of central
structure 33, the rear end of each shield tube being
stepped at 73 to fit over the plate support with an end
gap 74 to enable independent longitudinal thermal
expansion of each strip. Anti-rotation strips 75 may also
be fitted to each sleeve to fit about one of the location
strips 71 on tube 52 to prevent rotation of the shield
sleeves.
Hot gas is delivered to duct 31 through the gas
inlet section 32. The hot gas may be oxygen enriched air
provided through heating stoves at a temperature of the
order of 1200°C. This air must be delivered through
refractory lined ducting and it will pick up refractory
grit which can cause severe erosion problems if delivered
at high speed directly into the main water cooled section
of duct 31. Gas inlet 32 is designed to enable the duct
to receive high volume hot air delivery with refractory
particles while minimising damage of the water cooled
section of the duct. Inlet 31 comprises a T-shaped
body 81 moulded as a unit in a hard wearing refractory
material and located within a thin walled outer metal
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shell 82. Body 81 defines a first tubular passage 83
aligned with. the central passage of duct 31 and a second
tubular passage 84 normal to passage 83 to receive the hot
airflow delivered from stoves (not shown). Passage 83 is
aligned with the gas flow passage of duct 31 and is
connected to it through a central passage 85 in a
refractory connecting piece 86 of inlet 32.
The hot air delivered to inlet 32 passes through
tubular passage 84 of body 81 and impinges on the hard
wearing refractory wall of the thick refractory body 82
which is resistant to erosion. The gas flow then changes
direction to flow at right angles down through passage 83
of the T-shaped body 81 and the central passage 85 of
transition piece 86 and into the main part of the duct.
The wall of passage 83 may be tapered in the forward flow
direction so as to accelerate the flow into the duct. It
may fox example be tapered to an included angle of the
order of 7°. The transition refractory body 86 is tapered
in thickness to match the thick wall of refractory body 81
at one end and the much thinner refractory lining 48 of
the main section of duct 31. It is accordingly also water
cooled through an annular cooling water jacket 87 through
which cooling.water is circulated through an inlet._88 and
an outlet 89. The rear end of central structure 33
extends through the tubular passage 83.of gas inlet 32.
zt is located within a refractory liner plug 91 which
closes the rear end of passage 83, the rear end of central
structure 33 extending back from gas inlet 32 to the water
flow inlet 53 and outlet 55.
The illustrated apparatus is capable of injecting
high volumes of hot gas into the smelting vessel 26 at
high temperature. The central structure 33 is capable of
delivering large volumes of cooling water quickly and
directly to the nose section of the central structure and
the forced flow of that cooling water in an undivided
cooling flow around the nose structure enables very
efficient heat extraction from the front end of the
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central structure. The independent water flow to the tip
of the duct also enables efficient heat extraction from
the other high heat flux components of the lance.
Delivery of the hot air flow into an inlet in which it
impacts with a thick wall of a refractory chamber or
passage before flowing downwardly into the duct enables
high volumes of air contaminated with refractory grit to
be handled without severe erosion of the refractory lining
and heat shield in the main section of the lance.
