INTERNAL REFRACTORY COOLER

REFROIDISSEUR REFRACTAIRE INTERNE

English Abstract

A wall lining for a furnace (10) includes a refractory layer (14) having a hot face (16) exposed to the interior of the furnace. A
plurality of elements of a high thermal conductivity material (18), such as copper wires or rods, extend from the outer shell (12) of the
furnace into the refractory lining (14). The elements (18) provide a continuous heat conduction path to the outer shell (12) of the furnace. A
cooling jacket (22) removes heat from the outer shell. The elements (18) are dispersed in the refractory lining (14) to provide a substantially
uniform temperature across the hot face of the furnace in the vicinity of the elements. The wall lining may be formed by fixing an array
of the elements to the inside wall of the outer shell of the furnace and applying a refractory material to the inside wall.

French Abstract

Revêtement destiné à la paroi d'un four (10) et doté d'une couche réfractaire (14) présentant une face chaude (16) tournée vers l'intérieur du four. Plusieurs éléments (18) en matériau à conductivité thermique élevée, par exemple des fils ou tiges de cuivre, s'étendent depuis la cuve externe (12) du four et pénètrent dans le revêtement réfractaire (14). Ces éléments (18) forment un chemin continu de conduction de chaleur vers la cuve externe (12) du four. Une chemise de refroidissement (22) évacue la chaleur de la cuve externe. Lesdits éléments (18) sont dispersés dans le revêtement réfractaire (14) de manière que la température sur toute la face chaude du four soit sensiblement homogène au voisinage des éléments. Le revêtement de la paroi peut être formé par fixation d'un groupe d'éléments à la paroi interne de la cuve externe du four, et application sur cette paroi interne d'un matériau réfractaire.

Claims

14
CLAIMS
1. A wall lining for a furnace having an outer shell and a source of external
coolant in
conjunction with the outer shell, said wall lining comprising a refractory
lining adjacent the
outer shell, the refractory lining having a hot face exposed to high
temperature during
operation of the furnace, the refractory lining including a plurality of
cooling elements of
high thermal conductivity material, the elements extending into the refractory
lining
towards the hot face, each of the elements providing a continuous heat
conduction path
from the end of the element located closer to the hot face to the outer shell
of the furnace,
characterised in that the elements are dispersed in the refractory lining such
that said
elements are relatively concentrated in hot spots in said furnace and a
relatively lesser
number of elements are located in cooler parts of said furnace, to provide a
substantially
uniform temperature across the hot face of the furnace in the vicinity of the
elements,
wherein the plurality of elements of a high thermal conductivity material
extend into the
refractory lining towards the hot face of the furnace but do not extend
through the
refractory lining.
2. A wall lining for a furnace as claimed in claim 1 wherein the high thermal
conductivity material is a metal or a metal alloy.
3. A wall lining for a furnace as claimed in claim 2 wherein said metal or
metal alloy
is copper.
4. A wall lining for a furnace as claimed in claim 2 wherein the elements of
high
thermal conductivity material comprise metal wires or metal rods.
5. A wall lining for a furnace as claimed in claim 4 wherein the metal wires
or metal
rods have a diameter of up to 25 mm.
6. A wall lining for a furnace as claimed in any one of claims 1 to 5 wherein
said
refractory lining is formed of refractory bricks and wherein the elements of
high thermal
conductivity material are formed by impregnating said refractory bricks with
molten metal
and allowing the molten metal to solidify.
7. A wall lining for a surface as claimed in claim 6 wherein the molten metal
impregnates only part-way into the refractory bricks.

15
8. A wall lining for a furnace as claimed in any one of claims 1 to 7 wherein
the
plurality of elements are integrally formed with the outer shell.
9. A wall lining for a furnace as claimed in any one of claims 1 to 8 wherein
the
plurality of elements are attached or affixed to the outer shell.
10. A wall lining for a furnace as claimed in any one of claims 1 to 9 wherein
the
plurality of elements are presented throughout substantially all of the wall
lining.
11. A wall lining for a furnace as claimed in claim 3 wherein said high
thermal
conductivity material elements comprise a copper wire mesh proximate the inner
surface of
said outer shell, said copper wire mesh having further copper wires mounted at
points of
intersection on the mesh and extending substantially at right angles to the
plane of the
mesh into the refractory lining.
12. A method for lining a furnace with a wall lining comprising a refractory
lining
having a plurality of elements of high thermal conductivity, the elements
extending from
an outer shell of the lining into the refractory lining, characterised in that
said method
comprises:
a) calculating heat flux through the wall lining required to obtain a
temperature
at a hot face of the wall lining at which corrosion reactions cease or
freezing of process
material occurs;
b) determining a thermal conductivity of the wall lining required to obtain
said
heat flux calculated in step (a);
c) determining positioning and spacing of said plurality of elements in said
wall lining required to obtain said heat flux in step (a) and a substantially
uniform
temperature across the hot face of the furnace in the vicinity of said
elements during
operation of said furnace; the elements being concentrated in hot spots of
said furnace and
a relatively lesser number of elements being positioned in cooler parts of
said furnace; and
d) providing said furnace with said wall lining, said elements being in
thermal
contact with the outer shell and extending into the refractory lining towards
the hot face of
the furnace but do not extend through the refractory lining

16
13. A method as claimed in claim 12 wherein said heat flux is calculated from
the
equation:
<IMG>
where
Q = heat flux
T f = furnace temperature
T c = temperature of coolant used to cool the outer shell
R tot = total thermal resistance of the wall lining and the total thermal
resistance of
the walling lining. R tot is approximated by.
<IMG>
where
L = thickness of the wall lining; and
.lambda. = thermal conductivity of the wall lining.
14. A method as claimed in claim 12 or 13 further comprising fixing an array
of said
elements to an inside wall of the outer shell of the furnace such that the
elements are in
thermal contact with the inside wall and applying a refractory containing
material to the
inside wall of the outer shell to form a coating on the inside wall.
15. A method as claimed in claim 14 wherein the refractory lining has a
thickness to
fully cover the array of elements.
16. A method as claimed in claim 15 wherein the step of fixing the array of
elements
comprises affixing a copper wire mesh to the inside wall of the outer shell,
said copper
wire mesh having further copper wires mounted at points of intersection on the
mesh and
extending substantially at right angles to the plane of the mesh.

Description

WO 95/22732 PCT/AU95/00074
218350
TITLE: INTERNAL REFRACTORY COOLER
The present invention relates to refractory wall linings used in furnaces. In
particular, the present invention relates to cooling arrangements for
refractory wall
linings.
s Furnaces operating at high temperatures are used in a number of different
processes, including the smelting of metals. Most furnaces are constructed
from an
outer shell made of a metallic material, which is usually steel. The outer
shell is
lined with a layer of refractory bricks to insulate the outer shell from the
extreme
temperatures in the interior of the furnace and also to prevent the very hot
materials
contained in the furnace from contacting the outer shell. Refractory linings
should
have a long life in order to minimise the considerable down time associated
with
relining a furnace.
Refractory linings are generally made from materials that are fairly
unreactive
with the contents of the furnace. However, erosion and destruction of
refractory
a linings does occur and it has been found that the rate of erosion and
destruction of
the lining increases as the temperature of the hot face of the lining (that
is, the face
of the lining exposed to the interior of the furnace) increases. Therefore,
numerous
attempts have been made to decrease the temperature of the hot face of the
lining
in order to increase the life of the refractory lining.
One construction proposed for use in decreasing the temperature of the hot
face involves the installation of a water-cooling circuit in the refractory
lining. As
water flows through the cooling circuit, it extracts heat from the refractory
lining and
acts to decrease the temperature of the hot face of the lining. Although such
constructions operate to satisfactorily reduce the temperature of the lining,
they
zs involve the use of cooling water circuits within the lining. Any leakage of
water
from the cooling circuit has the potential to seep into the furnace and cause
explosions and hydration of the refractory. This is obviously an extremely
hazardous
situation and it is now believed that internal water-cooling of refractory
linings
should be avoided.
Another approach that has been adopted by industry involves the placement
of solid cooling members of high thermal conductivity through the wall of a
furnace

WO 95/22732 PCT/AU95100074
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and into a lining. The outer portion of the solid cooling members remain
outside the
refractory lining. The portions of the cooling members located external to the
furnace are cooled by a water cooling circuit. Accordingly, if leaks develop
in the
water-cooling circuit, water cannot come into contact with the hot contents of
the
s furnace, which eliminates hydration and reduces the danger of explosion. The
solid
cooling members are generally spaced about half a metre apart from each other.
This leads to large temperature gradients in the refractory lining. Areas of
high
temperature in the lining wear much more quickly than areas of relatively
lower
temperature and wear of the lining is very uneven. Furthermore, the large
temperature gradients in the lining set up large thermal stresses in the
refractory
lining.
United Kingdom Patent No. 1,585,155 describes an arc-furnace that is
provided with a composite lining that includes an exposed inner layer of
refractory
material facing the furnace interior. An outer layer of refractory material
that backs
a onto the inner layer is provided, with this outer layer of refractory
material being in
thermal contact with the inner layer. The outer layer is made of a material
that has
a higher thermal conductivity than the inner layer. The outer layer may be in
contact with the furnace casing, which dissipates heat to the surroundings or,
more
usually, to a forced air or water-cooling medium. The composite construction
of
the refractory lining acts to increase the heat flow through the side wall
lining to
thereby reduce the extent of refractory wear. This construction suffers from
the
disadvantage of requiring a composite refractory wall structure to be
installed in the
furnace. Furthermore, although the outer layer of the refractory lining is
described
as being made from a high conductivity refractory material, the conductivity
of such
a refractory materials is relatively low and this acts to somewhat limit the
amount of
heat that can be removed from the furnace. Composite linings are also
expensive
and may be reactive.
A further solution to the erosion and penetration of refractory linings in
high
temperature furnaces is described in United States Patent No. 3,849,587
assigned to
Hatch Associates Limited. This patent discloses protecting refractory linings
of
furnaces operating at high temperatures by placing solid cooling members of
high

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thermal conductivity through the wall of a furnace and into the lining. The
outer
portions of the solid cooling members remain outside the refractory lining.
The
cooling members embedded in the lining are substantially devoid of water-
cooled
channels in the portions located in the lining of the furnace which avoids
water leaks
into the furnace. The portions of the cooling members located outside the
furnace
are generally cooled by a water-cooling circuit. The length, cross-sectional
area,
spacing and a material of the cooling members are selected to avoid melting of
the
cooling members and to conduct sufficient heat from the lining to limit
erosion of
the lining.
to The cooling members inserted in the lining are preferably made from copper.
The cooling members described in this patent are of a large diameter,
typically of
about four inches ( 100 mm) diameter, and are spaced a relatively large
distance apart
from each other. This leads to the formation of a temperature gradient across
the
hot face of the refractory lining, with the attendant uneven wear and thermal
stresses
is associated with such temperature gradients.
The present invention provides a refractory lining that overcomes or at least
ameliorates one or more of the disadvantages of the above prior art.
In a first aspect, the present invention provides a wall lining for a furnace
having an outer shell and a source of external coolant in conjunction with the
outer
2o shell, said wall lining comprising a refractory lining adjacent the outer
shell, the
refractory lining having a hot face exposed to high temperature during
operation of
the furnace, the refractory lining including a plurality of elements of a high
thermal
conductivity material, the elements extending into the refractory lining
towards the
hot face, each of the elements providing a continuous heat conduction path
from the
zs end of the element located closer to the hot face to the outer shell of the
furnace, the
plurality of elements being dispersed and spaced in the refractory lining to
provide
a substantially uniform temperature across the hot face of the furnace in the
vicinity
of the elements during operation of the furnace.
By "substantially uniform temperature", it is meant that the temperature
across
3o the hot face does not vary by more than 100°C. Preferably, the
temperature across
the hot face does not vary by more than 50°C.
The plurality of elements may be present throughout substantially all of the
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wall lining in order to achieve the desired uniform temperature across the hot
face.
Alternatively, the plurality of elements may be arranged in the wall linings
such that
they are more concentrated in what would otherwise be hot spots in the
furnace.
Similarly, cooler parts of the furnace may have a relatively lesser number of
s elements and it is possible that the elements may not extend to all parts of
the
furnace. This is especially so in cases where furnace design and operation
would,
in the absence of the plurality of elements, lead to pronounced hot and cold
spots
in the furnace, it being appreciated that the further heat extraction provided
by the
plurality of elements may not be required in cooler areas of the furnace.
The furnace lining of the present invention may be used to ensure that a
substantially uniform temperature is attained across the hot face of the
furnace in the
vicinity of the elements. Alternatively, the lining may be designed to ensure
that a
substantially uniform temperature is attained across the entire hot face of
the furnace.
This is preferable as undesirable temperature gradients will be prevented from
being
a formed on the hot face. In either case, the substantially uniform
temperature may
be below a temperature at which the rate of destruction and/or erosion of the
refractory lining will occur at an unacceptably high rate. It will be
appreciated that
in furnaces that, in the absence of the plurality of elements, would have
pronounced
hot and cold spots, the elements may only be required in or near what would
utherwise be the hot spots.
Preferably, the high thermal conductivity material is a metal or metal alloy.
Copper is especially preferred.
In a preferred embodiment of the present invention, the plurality of elements
of high thermal conductivity material extend into the refractory lining
towards the
hot face but are not sufficiently long to extend to the hot face. This results
in the
ends of the elements being separated from the hot face by a refractory layer,
which
reduces the heat flux through the wall and acts to insulate the elements from
the
very high temperatures experienced at the hot face during operation of the
furnace.
This protects the elements and reduces the possibility of degration of and
thermal
damage to the elements.
The plurality of elements of high thermal conductivity material extend from

WO 95/22732 PCTIAU95/00074
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-s-
the inner wall of the outer shell of the furnace and into the refractory
lining to
provide a continuous heat conduction path from the ends of the elements closer
to
the hot face to the outer shell. Heat is conducted along the elements to the
outer
shell. An external cooling circuit may be associated with the outer shell to
remove
s heat from the furnace wall. Therefore, the plurality of elements assist in
removing
heat from the furnace and enable the hot face of the refractory lining to be
maintained at a temperature that allows a long service life for the refractory
lining.
The plurality of elements are dispersed through the refractory lining such
that the hot
face has a substantially uniform temperature in the vicinity of the elements.
This
avoids the formation of hot spots in the furnace, reduces the formation of
thermal
stresses in the refractory layer and produces stable conditions at the hot
face. In this
regard, it is noted that the furnace described in U.S. Patent No. 3,849,s87,
which
utilises relatively large cooling bodies widely spaced throughout the lining,
is
incapable of achieving these desirous conditions.
a The elements of high thermal conductivity material may be formed as metal
wires or metal rods, with copper being the preferred metal of choice. The rods
or
wires may range in diameter from parts of a millimetre up to 2s mm. Larger
diameters are not recommended as it becomes difficult to obtain the desired
heat
removal from the furnace whilst retaining a substantially uniform temperature
across
zo the hot Face of the refractory lining.
Alternatively, the elements may be formed by impregnating refractory bricks
with molten metal and allowing the molten metal to solidify. When refractory
bricks
are impregnated with molten metal, the molten metal moves into the bricks
along the
pores of the refractory bricks. Upon solidification of the molten metal, solid
bodies
of metal extending from one face of the brick into the brick are formed, and
these
solid bodies of metal act as the plurality of elements of high thermal
conductivity
material when the bricks are used to line the furnace. It will be appreciated
that the
face of the bricks that is exposed to the impregnating molten metal will be
the face
of the brick that is placed adjacent the inner wall of the outer shell of the
furnace.
The molten metal should also impregnate only part way through the bricks to
ensure
that a refractory layer remains between the metal and the hot face of the
furnace.

~criau 9 5 / 0 0 0 7 G.
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The wall lining of the present invention allows for cooling of the refractory
lining without internal cooling of the lining being required. The plurality of
elements conducts heat to the outer shell of the furnace and external cooling
circuits
can remove the heat from the outer shell. The external cooling circuit may be
a
forced or natural convection air cooling arrangement or, more preferably, be a
cooling water circuit. For example, the outer shell may be encased in a water
jacket,
although other cooling water arrangements may also be used.
The plurality of elements provide a continuous path for heat conduction to the
outer shell. They also allow for minimisation of contact resistances to heat
transfer
to from the refractory lining. More effective heat transfer can be achieved
than in
composite linings described in some prior art documents, because the wall
lining of
the present invention exhibits a higher overall effective thermal
conductivity.
In one embodiment, the plurality of elements may be integrally formed with
the outer shell. In another embodiment, the plurality of elements may be
attached
15 or affixed to the outer shell.
The wall lining of the present invention may be retro-fitted to existing
furnaces or it may be designed as part of new furnaces. In the case of retro-
fitting
existing furnaces, the plurality of elements may be inserted into holes
drilled through
the furnace and into the refractory lining, although this has the potential to
weaken
zo the furnace structure. More preferably, the wall lining is fitted at the
same time as
replacement of the refractory lining is to occur. The lining may be fitted at
such a
time by using metal impregnated refractory bricks to line the furnace or by
using
refractory bricks previously fitted with rods or wires.
In another aspect, the present invention provides a method for lining a
furnace
zs with a wall lining comprising a refractory lining having a plurality of
elements of
high thermal conductivity elements extending from an outer shell of the lining
into
the refractory lining, said method comprising:
(a) calculating heat flux through the wall lining required to obtain a desired
temperature at a hot face of the wall lining;
30 (b) determining a thickness of the wall lining and a thermal conductivity
of the
wall lining required to obtain said heat flux calculated in step (a);
(c) determining positioning and spacing of said plurality of elements in said
wall
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AMENDED SHEET
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_ 6a _
lining required to obtain said thermal conductivity; and
(d) providing said furnace with said wall lining, said elements being in
thermal
contract with the outer shell, said wall lining providing a substantially
uniform temperature across the hot face of the furnace during operation to
said furnace.
The present invention may also enable a furnace to be fitted with a refractory
lining without using refractory bricks at all.
In a further aspect, the present invention provides a method for lining a
furnace with a refractory lining, said furnace including an outer shell, which
method
to compasses:
- fixing an array of elements of a high thermal conductivity material to an
inside wall of the outer shell such that the array of elements is in thermal
contact with the outer shell, and
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WO 95/22732 PCT/AU95/00074
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- applying a refractory-containing material to the inside wall of the outer
shell
to form a coating on the inside wall.
The refractory-containing material may be applied in a substantially dry state
or in the form of a slurry or a paste.
s The refractory-containing material may include a refractory material and one
or more further components that result in a composite refractory lining being
obtained, or the refractory-containing material may contain purely refractory
material only.
The refractory lining may be a composite lining formed by sequentially
applying, in any desired order, separate layers of a refractory-containing
material
and layers of non-refractory or low refractory materials.
If a slurry or paste of a refractory-containing material is used, it may be
necessary to apply the refractory or paste to the inside wall in a series of
stages in
which a first thin coating is applied and allowed to set, followed by the
application
a of one or more further coatings of slurry or paste. This step-wise building
up of the
refractory lining may be necessary when thick refractory linings are required,
it
being appreciated that difficulties may be experienced with drying and
cracking of
a thick lining if it is applied as a single coat.
The complete refractory lining should be of a thickness that is sufficient to
fully cover the array of elements. This will provide a layer of insulating
refractory
material between the ends of the elements and the hot face of the furnace
which will
act to prevent melting of the elements during use of the furnace.
The refractory-containing material may be applied to the inside wall by any
suitable method known to those skilled in the art. For examole_ the refra~tn,~-
containing material may be applied by spraying, gunning or trowelling. The
invention should be understood to include all methods of applying the
refractory-
containing material to the inside wall of the furnace.
If a slurry or paste is used, the slurry or paste should be sufficiently thick
or
viscous to enable it to remain in place on the inside wall whilst it is
setting. Routine
trials will easily establish the required slurry or paste viscosity to achieve
this aim.
The array of elements preferably comprises an array of metallic elements. In

WO 95/22732 PCT/AU95/00074
-s- 21~3~~0
one embodiment, the array of elements comprises a copper wire mesh having
further
copper wires mounted at the points of intersection on the mesh and extending
substantially at right angles to the plane of the mesh. When the mesh is fixed
to the
inside wall of the shell of the furnace, the copper wires mounted on the mesh
extend
s generally inwardly into the furnace. In use of the furnace, these copper
wires act as
cooling elements that provide a continuous heat conduction path from the end
of the
wires to a source of external coolant that is in contact with the outer shell
and the
cooling elements thereby assist in removing heat from the furnace.
In another embodiment, the step of fixing the array of elements to the inside
wall of the outer shell comprises integrally forming the array of elements
with the
inside wall of the outer shell. The array of elements may alternatively be
formed
by casting molten metal onto the inside wall of the outer shell.
Preferably, the array of elements is arranged such that a substantially
uniform
temperature is achieved across the hot face of the furnace in the vicinity of
the
a elements during operation of the furnace.
If a substantially uniform temperature across the entire hot face of the
refractory lining of the furnace is desired or required, it may be necessary
to have
an uneven distribution of elements of high thermal conductivity material
throughout
the wall lining. For example, the number of elements located at known hot
spots
zo of an operating furnace may be increased to remove proportionally greater
amounts
of heat per square metre when compared to cooler areas of the furnace.
Preferred embodiments of the present invention will be described in greater
detail with reference to the Figures, in which:
FIGURE 1 shows a cross-section of a wall lining of a furnace in
a accordance with the present invention;
FIGURE 2 shows a plot of temperature profile through the wall lining;
FIGURE 3 is a cross-sectional view of a cooling element design in
accordance with the present invention;
FIGURE 4 is a schematic diagram showing the set-up used for a plant trial
incorporating the cooling element design of Figure 3;
FIGURE S is a plot of the temperature profile through the cooling element

WO 95/22732 PCT/AU95I00074
218.320
from the plant trial; and
FIGURE 6 is a plot of the variation, with time, of the hot face heat transfer
coefficient during the plant trial.
Referring to Figure 1, the wall 10 of the furnace includes outer shell 12. The
s outer shell is generally made of steel. The furnace includes refractory
lining 14.
Hot face 16 is expos~td to the intense temperatures generated within the
furnace. The
wall lining includes a plurality of copper rods or wires 18 in thermal contact
with
the outer shell 12 and extending into refractory lining 14. As can be seen
from
Figure 1, copper rods 18 do not extend right through refractory lining 14 but
rather
end some distance away from hot face 16. This ensures that there is a layer of
refractory material located between the ends of copper rods 18 and the hot
face 16
and this layer of refractory material insulates the rods from the high
temperatures in
the furnace, thereby preventing degradation of and thermal damage to the rods.
During operation of the furnace, heat is transferred from hot face 16 through
a refractory lining 14 and to copper rods 18. The rods are in thermal contact
with
outer shell 12 and act to rapidly transfer heat to the shell. Cooling water
20, which
flows through cooling jacket 22, subsequently removes heat from the shell.
The copper rods 18 are dispersed through the refractory lining to provide a
substantially uniform thermal gradient across the hot face. The rods are
preferably
arranged such that essentially one-dimensional heat transfer through the wall
is
produced. This cools the hot face very evenly, effectively eliminating wall
hot spots
evident with prior art designs that cause uneven wear of the hot face. One-
dimensional heat transfer has also been shown to be more efficient i.e. less
high
conductivity material is required to remove the same heat flux.
a The purpose of the wall lining is to reduce the refractory temperature at
the
hot face to a specified temperature (either that at which corrosion reactions
cease or
freezing of process material occurs). The cooler must be designed so as to
achieve
this while minimising furnace heat losses (heat flux through the wall). The
heat flux
Q (W/m~, through the wall in Figure 1 can be calculated by
where Tf is the furnace temperature (°C), T° is the coolant
temperature (°C), and

WO 95/22732 PCT/AU95/00074
to - z ~ s35~o
T~ T
Rte.
R.roi. is the total thermal resistance of the wall section (m2K/V~. Therefore
to
control the refractory temperatures and heat flux the thermal resistance of
the wall
section must be altered. The total thermal resistance is the sum of the
conduction
resistance of each material layer and the convection resistance at the hot and
cold
s faces. However the convection resistances are either unchangeable or
insignificant
so the heat flow can only be controlled by the value of the conduction
resistance of
the actual element. A thermal conduction resistance R~,,,D (mZK/VV~, is given
as
_ L
RCOND
where L is the thickness of the layer (m), and is ~, is the thermal
conductivity of the
material (W/mI~. Changing the conductivity and thickness of the material
layers
~o in Figure 1 then allows the refractory temperatures and the heat flux to be
controlled.
The temperature profile throughout the wall section can be easily calculated
by
separate consideration of each thermal resistance using Equation 1. As
mentioned
previously the element is most efficient and the design procedure is most
accurate
when a uniform high conductivity material layer is employed as one-dimensional
a heat transfer is produced. However the method can still be applied to non-
homogeneous wall layers with reasonable accuracy.
A thermal resistance model, based on the above procedure, has been used in
an experimental study to predict the temperature distribution through a
refractory
cooler of the form shown in Figure 1. The experimental and model results are
so shown in Figure 2 for the case where the copper rods are 20 mm in diameter
and
60 mm apart. The model produces a reasonably accurate prediction of the
temperature profile and heat flux (experimented 24.0 kw/m2; model 21.2 kw/m~,
thereby showing the validity of this approach for element design.
Therefore, the present invention also provides for a relatively simple yet
s rigorous design procedure that is not available with prior art designs.

CA 02183520 2004-09-17
WO 95!22732 PCTlAI19~100074
-11-
Figure 3 shows a cross-section of a cooling element 30 in accordance with
the invention. The element consists of a copper base plate 32 integrally cast
with
copper rods 34 to form the main element body. An external wafer jacket 36 is
bolted to the base plate 32, for. example, by cap screws 38. A
s polytetrafiuoroethyiene gasket 40 is used to provide a fluid-tight seal
between base
plate 32 and water jacket 36 and to prevent wafer leaks from water flow
passage 42_
Refractory is cast around rods 34 to form the wall. As can be seen from Figure
3, refractory
44 extends from base plate 32 to slightly beyond the ends of copper rods 34.
m The main features of This cooling element design are the external water
jacket,
closely spaced copper rods and the use of castable refractory to form the
wall. The
external water jacket effectively eliminates the possibility of damaging water
leaks
into the furnace. The small pitch between adjacent copper rods (60 mm) should
greatly reduce the temperature gradients perpendicular to the hot face which
are
is evident with conventional cooling elements. This should result in a much
more
evenly cooled wall which will in turn produce more even wear of the hot face.
The
use of castabIe refractory should reduce the thermal resistances due to air
gaps that
commonly occur between refractory bricks. All these factors should contribute
to
a more efficient cooling system.
Plant trials of the cooling element design were undertaken using the cooling
element shown in Figure 3. The set-up used in the plant trials is shown in
Figure
4. Cooling element 30 was installed in the settler roof SO of the furnace. The
roof
is exposed to the mildest furnace conditions (i_e. relatively low temperatures
and no
slag washing) and was thought to be most suitable for this trial. The cooling
element 30 was suspended from supporting beams (not shown) by support brackets
52, S4 and the face of the cooling element was positioned flush with the hot
face S6
of the furnace. The cooling element 30 was fitted with water inlet 58 that
included
rotameter 60 for measuring the water flow rate and valve 62 for controlling
the
water flowrate. Cooling water is removed from the cooling element via cooling
water outlet line 64. Type K immersion thermocouples 65,b6 were connected to
the
water jacket to measure inlet and outlet water temperature, respectively.
Twenty-

WO 95122732 PCT/AU95100074
2183~~p
- 12-
four thermocouples were placed within cooling element 30 to measure the
temperature profile within the cooling element. Output from these
thermocouples
(shown schematically at 68) was connected to a datalogger 70 which logged
readings
every five minutes.
s The new cooling element was found to operate successfully in the plant
trials.
Figure 5 shows a sample temperature profile through the element from the hot
face
to the cold face recorded during a period of steady furnace operation. There
are two
separate profiles (copper and refractory) shown on Figure 5. The copper
profile is
taken from the cold face, passing through the centre of a copper rod into the
~o refractory past the tip of the rod to the hot face. The refractory profile
runs through
the refractory, midway between adjacent rods, to the hot face. There is a very
low
temperature gradient, 0.2°C/mm, through the solid copper plate (0 to 80
mm). The
temperature gradient increases to 0.7°C/mm through the copper rod (80
to 300 mm).
This is still a relatively low gradient with the tip of the rod only reaching
216°C.
a The low temperature at the rod tip shows that the external water jacket was
able to
effectively cool the internal copper rods. The temperature gradient through
the rods
is linear showing that heat transfer is largely one-dimensional along the
rods. In the
refractory adjacent to the rods the temperatures are similar to the copper
temperatures up to a distance of about 25 mm from the cold face. However,
towards
~o the tips of the copper rods (225 to 30~ mm from the cold face), the
refractory
temperatures are significantly higher than the copper temperatures at the same
depth.
This indicates the presence of multi-dimensional heat transfer and temperature
gradients in the element between the copper and refractory. These gradients
are due
to the uneven cooling (not one-dimensional) that occurs at the rod tips
because of
a the large difference in conductivity between the copper and refractory. It
is desirable
to minimise these uneven temperature gradients as higher refractory
temperatures can
cause increased wear, as discussed previously. However, the temperatures
throughout the remainder of the element section, and most importantly on the
hot
face, are reasonably similar from both profiles. This shows the new element
design
o is effective in cooling the wall fairly evenly in all areas apart from the
zone around
the rod tips.

WO 95/22732 PCT/AU95I00074
_ 13 _ 218352)
The temperature gradient through the refractory from the tip of the copper rod
to the hot face (305 to 330 mm) in Figure 7 is much higher than through the
copper
rods and refractory (80 to 305 mm). This gradient is approximately linear and
ranges from 11 °C/mm for the refractory between the copper rods to
17°C/mm for
s the refractory along the line of the copper rod with the hot face reaching a
temperature of 752°C. The high temperature gradient near the hot face
shows the
large insulating effect that a small thickness (25 mm) of refractory has due
to its low
conductivity. This layer of refractory on the hot face protects the copper
rods from
the high furnace temperatures and limits the heat flux through the element.
An accretion layer of frozen process material built up on the hot face of the
cooling element during the plant trial. The accretion layer introduced an
additional
thermal resistance which reduced the heat removed by the cooling water
significantly. The hot face heat transfer coefficient was similarly affected
(as shown
in Figure 6) because the thermal resistance of the accretion was incorporated
into the
a calculated heat transfer coefficient. Some of the variation displayed in
Figure 6 is
due to irregular furnace operation and the transient nature of the accretion
layer;
however, the effects of the accretion build-up can clearly be seen by the
gradual
decrease in the heat transfer coefficient. The heat transfer coefficient fell
from an
initial value of around 50 to 60 W/m2K to virtually zero. The hot face
temperature
w (ac the end of the element) was also reduced from 700°C to under
100°C due to the
insulating effect of the accretion layer. The thickness of the accretion layer
was
estimated to be 250 mm by pushing a large Type-K thermocouple down beside the
element and through the accretion. The extent and stability of any accretion
layer
depends not only on the extent of cooling but also on the internal furnace
conditions
is and process material characteristics. Accretion build-un ac~;~t~ ;n
.,~.,~;,~;",.
refractory protection.
Those skilled in the art will appreciate that the invention is susceptible to
variations and modifications other than those specifically described. It is to
be
understood that the present invention encompasses all such variations and
modifications that fall within its spirit and scope.

Representative Drawing