Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
w093/05354 2 118 7 9 0 PCT/SE92/00628
Drying process
The present invention relates to a process for the
drying of objects or bodies containing water and made of a
- 5 refractory material. By the expression "ob~ects or bodies"
there are also included such refractory constructions as
are constituted by linings of tundishes, the bot~om part
of ladles, chute furnaces for casting~ electric arc fur-
naces, etc. The expression also, of course, covers sepa-
rate objects or bodies such as bricks, larger constructio-
nal elements of different types of furnaces, lances etc.
The drying of constructions of refractory materials
intended for use in applications requiring a high tempe-
ra~ure requires the water present in the material to be
removed in an effective and safe manner. The techniques
hitherto prevailing are drying while supplying heat from
the outside or $n some other way. When drying self-suppor-
ting ob~ects or bodies such drying takes place in furnaces
of different types, and when drying linin~s of different
types the heat is supplied also from the outside by the
furnace being heated after drying temperature for the
purpose of removing the w ter to a sufficient degree so
that the lin~ng can be taken into use. The prior art in-
volves substantial draw-backs, such as high energy re-
quirement, extended and thereby costly drying, difficul-
ties in determin~ng when the drying is finished, etc. Fur-
thermore, there are risks involved in connection with the
drying while supplying external heat residing in the risk
for burstiny. In the heating the water present in the ma-
terial,will be evaporated under heavy volume increase, andthis result~ in obvious risks to the environment. This
problem is the foundation of the techni~es disclosed in
Swedish patents 7315942-8 and 8206043-5, wherein a solu-
tion is presented residing in the advance inclusion in the
material of channel-forming elements or fibres to facili-
tate release of the water in connection with the heating.
W093/05354 PCT/SE92/00628
211~790
The present invention has for its ob~ect to provide
new drying technigues, wherein the disadvantages of the
prior art are avoided. Thus, one ob;ect of the invention
is to provide a new drying process resulting in substan-
tially reduced drying costs at the same time as the dryingperiod will be substantially shortened.
Another ob~ect of the invention is to provtde a pro-
cess which in its preferred form invGlves eliminated or at
least substantially reduced risk for bursting.
These and other ob~ects that will be clear from the
following description of t~e t nvention are provided by a
process for the drying of ob~ects or bodies comprising al-
so fixed arrangements, such as linings of furnaces, con- -
tai~ing water and made of a refractory material by heating
to an increased temperature exceeding an~ preferably sub-
stantially exceeding the boiling point of water. ~he pro-
c~ss accordlng to the invention is characterized in that
the drying takes place from the interior of the materia~,
the heat necessary for the drying being supplied from the
inside of the material through holes or channels provided
in the material.
Even though the heat can be supplied through any hea-
ting medium it is preferred that the heating takes place
via electric resistor elements. These resistor elements
can be arranged in holes or channels $n the ref~actory ma-
r terial in different ways. Thus, the resistor elements can
be removable and thus renewed useful or they may be fixed-
ly casted to the material and thus left behind in the ma-
terial after finished drying.
I~ is particularly preferred in the process according
to the invention to carry out the drying of objects or bo-
dies made of a refractory material containing channel-for-
ming elements, which are substantially evenly distributed
in the material. These techniques known per se in connec-
tion with drying through externally supplied heat are de-
scribed in connection with such conventional techniques in
for example Swedish patent 7315942-8. Such channel-forming
w093/053~4 2 1 1 8 7 9 0 PCT/S~92/00628
elements suitably constitute a~bout 0.05 to 0.5~ by weight
of the material, and a particularly preferred range is
about O.l to 0.3~ by weight.
Preferred channel-forming elements are based on natu-
ral materials originating from plants, such as for examplestraw or stalks from ordinary cereals, grass, rice roots,
fibres from palm tree~, neadles from pine trees and simi-
lar. For the purpose of facili.tat$ng release from the xe-
fractory material the diameter of said channel-forming
elements can vary from some mlcrons up to several milli-
- meters. In practice palm tree fibres are preferred, since
such fibres have a small diameter, a high density and are
relatively rigid. This type of fibre is ofte~ sold under
the tradename "Bassinen.
Al~ernative materials for the channel-forming ele-
ments are pre-fabricated fibres made of suitable pl2stic
material~, such as polypropyl~. Such materials or ele-
ments may have a diameter Or from some tens of microns up
to a few millimeters, for example up to about S mm.
In order to provide for suitable exit paths for the
vaporized water ~n the refractory materials lt is essen-
tial that the channel-forming eleme~ts are elongate, i.e.
have high ratio length/diameter. Said ratio is suitably
above about 5 and the length of the elements may va~y
withln broad limits. In order to facilitate admixing these
elements into the refrac~ory material it is preferred that
the length has not too high a value.
With regard to the compo~t~on of the refractory ma-
terial any common refractory oxides can be included. Thus,
refrac~ory compositions conta:Lning essentially SiO2 or
Zr2 may be used, and also neutral refractory composltions
containing mainly A12O3 or Cr2O3 or a basic refractory
mixture containing essentially MgO or CaO, can be used
when applying the techniques according to the present in-
vention.
W093/0~354 PCT/SE92/00628
211~790
The refractory oxida const:itutes the ma~or part ofthe material and the weight rat:io thereof su~tably lies
within the range about 75 to about 95% by weight of the
material as a whole. It may also contain a minor amount of
binder such as high grade alum~inumoxide cement, phosphoric
acid or clay.
The refractory material used in the drying process
according to th~ invent:ion is prepared in a conventional
ma~ner by mixing o f ~he constil:uents, such as in a mixing
container containing a mixer, ~md the container can be
heated if desirable, and when used the channel-forming
elements are introduced into the material during some
phase of its manufacture.
The inven~ion will in the foll~wing be further illus~
trated by non-l ~ miting examples. In said examples the per-
centages rela~e to weight lf not otherwise stated. Example
2 refers to the appended drawillg wh~ch in two different
v~ews shows the design of a block for a foundry.
EXAMPLE 1
The present e~ample relates to drying in accordance
with the present invention of a so called in~ection lance
intended for the feeding of gas or other material into a
molten metal. The lance consis~ts of a central steel tube
surrounded by a mantle made of a refractory material, in
the present example Victor Korund WR, Hogan~s, Sweden.
This refractory material has a composition of 96%
A1203, 0.5~ SiO2 and 0.1% Fe203. The apparent density
according to Din 51065 is 2.800 kg per m3. The quantity of
ref~ac~ory material in the lance is about 330 kg. The re-
fractory material contains evenly distributed palm tree
fibres of the t-ype Bassine hav.ing a length varying from
about 15 to about 20 mm. The f.ibres constitute about 0.2%
of the refractory material.
After completing the lanc~e the water contained in the
material is expelled while using the techni~ues according
to the present invention. Drying takes place by introdu-
W093/053~4 2118 7 9 0 PCT/~E92/0062X
cing an elongate electric resistor element in the center
of the steel tube and energy is supplied at a power of
about 3 KW. The drying time is about 24 hours, and no
signs of burstin~ or other problems could be observed
S durlng drying. A normal dryins time for such a lance in a
furnace while supplying extern,al heat is multlfariously
longer and normally requires three days or more. In addi-
tion to the advantage of short drying time there is also,
of course, obtained the advant:age of substantially lower
energy consumption, since the energy losses to the envi-
ronment are su~stantially reduced.
EXAMPLE 2
The present invent$on xelates to the manufacture and
dry~ng of a block for a found~, the block having the de-
sign as is clear from the draw~g. The block is made of a
refractory material, Ultracas1; CD 4 SR, Bohlin & Lofgren,
Sweden, and ~ts weight is about 1.350 kg. The refractory
material contains channel-form~ng fibres in the same man-
ner as stated in Example 1. Isl connection with casting 14through-going holes having a diameter of about 20 mm even-
ly distributed over the block are arranged.
The drylng ta~es place by insertion of electric re-
sistor elements in tubular form, one into each hole, and
an added power of 12 KW is supplied for the drying. The
drying time is about 12 hours for the complete removal of
contained water.
Compared to conventional drying in a gas-heated fur-
nace the energy required can be reduced by 8 to 9 times.
EXAMP~E 3
The present example relates to the drying of a so
called heart body for an LB-furnace. The heart body is
cast starting from Victor Korund ES, Hoganas, Sweden, as a
refractory material and the quantity of the material is
750 kg. The chemical analysis for the refractory material
is 94% A1203, 0.5% SiO2 and 0.1% Fe203. Its apparent den-
W093/0~354 PCT/SE92/00628
2118790
3 ~
sity according to Din 51065 is 2.750 kg per m . The ma-
terial is supplied with channel-forming fibres in the same
way as in Example ~. In connection with the casting there
are arranged 12 through-goin~ holes in the heart body in-
tended for electric resistor elements.
After finished casting an electric resistor element
of tubular type having an effect of about 1 KW is intro-
duced into each of the 12 holes. The drying time while
using a total power of thus about 12 KW $s 33 hours and
the drying takes place without problems.
It should be observed that the present invention is
not limited to the embodiments illustrated above. Thus,
the process according to the invention can be applied to
the drying of refractory masses irrespective of shape and
device. Even if the examples relate to the drying of self-
supported bodies or ob~ects the invention may egually well
be applied to permanent refractory constructions, such as
furnace linings and the like. The drying can take place
using reusable electric resistor elements or using resis-
tor elements permanently cast into the material.
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