Note: Descriptions are shown in the official language in which they were submitted.
8~6
PROCESS FOR THE PRODUCTION 0~ T~EATED LIME, TREATED LIME
PRODUCED THEREBY, AND A PROCESS FOR THE DESULPHURISATION
OF IRON USING SUCH TREATED LIME.
Field of the Invention
The present invention is concerned with a process for the
production of treated lime, sometimes also known as tempered lime,
and with the treated lime produced thereby. The invention is also
concerned with a process for ~he desulphurisation of iron using
such treated lime.
Review of the Prior Art
It is known to employ lime (CaO) in the desulphurisation of
iron by injecting a carefully controlled stream of the finely
divided lime, in admixture with other materials such as finely
divided magnesium, into the iron to form a sulphur-containing slag
that floats to the surface. By way of example the lime mixture
must be sufficiently finely divided that not more than 15% by
weight is retained by a +100 mesh sieve, while not less than 80%
by weight passes through a -200 mesh sieve. Such a finely divided
lime material i~ difficult to handle with limited flowability and
a marked tendency to bridge and plug in the apparatus in which it
i8 used.
Definition of the Invention
It is a principal object of the present invention to
provide a proces~ for the production of treated lime.
It is another object to provide a new product consisting of
a treated lime.
It is a further object to provide a new proce~s for the
desulphurisation of iron employing a treated lime.
il~O816
In accordance with the present invention there is provided
a process for the production of treated lime including the step of:
comilling together lime in lump form and a non-aqueous
liquid surfactant to produce a finely divided treated lime having
the particles thereof intimately mixed with and coated by the
liquid surfactant.
Also in accordance with the invention there is provided a
treated lime comprising finely divided lime produced from line in
lump form, the treated lime having the particles thereof inti-
mately mixed with and coated by a non-aqueous liquid surfactant
; by comilling together the said lime in llimp form and the said
surfactant.
Further in accordance with the invention there is pro-
vided a process for the desulphurisation of iron comprising adding
to the iron a mixture of finely divided treated lime and magnesium
; powder, the finely divided treated lime being produced from lime
in lump form and having the particles thereof intimately mixed
with and coated by a non-aqueous liquid silicone surfactant by
comilling together the said lime in lump form and the said sur-
faGtant.
Preferably the said lime in lump form is of dimension
not more than about 6 mm., and preferably the finely divided
treated lime is at a state of division such that not more than
15~ by weight is retained by a 100 mesh sieve and not less than
25 80~ by weight passes through a -200 mesh sieve. The crystal size
of the lime preferably is not more than about 5 microns.
. .
. . . . . .
,~ . ' : ' i ' ,:
. . ~ .. .
.. ..
,
.;. ,
.
Preferably the said surfactant is a silicone material,
preferably the treated surfactant is added in the amount of from
about 0.1~ to about 0.5~ by weight of the lime, and preferably
the said surfactant has a viscosity of between about 20 to about
100 centistokes at a temperature od 25C. The said surfactant
may be added to the lump lime at a temperature of from about 15C
to 38C (about 60F to 100F), and preferably is added at a
temperature of about 22C (90F).
The lump lime and the said surfactant may be comilled
together by a hammer mill, and the resultant treated lime pre-
ferably has an angle of repose of between 38 and 30.
:
' _ 3 _
i
~!
. .
. .
~ ' ~
.`., .
.'''''' ~', ` .
1140816
Description of the Drawin~s
Processes and products which are particular preferred
embodiments of the invention will now be described, by way of
example, with reference to the accompanying diagrammatic drawing,
wherein:
Figure 1 is a schematic diagram of apparatus for carrying
out the process,
Figure 2 is a diagram illustrating the measurement of the
angle of repose of the treated material, and
Figure 3 is a schematic diagram of iron desulphurisation
apparatus for use with a process of the invention.
Description of the Preferred Embodiments
The lime employed in the processes and product of the
invention is produced by the calcination of limestone by a method
such that the~lime crystals have a dimension of not more than
about 5 microns, for example by calcination in a rotary or
calcimatic kiln. Material of larger crystal size tends to be
more flowable, but is less reactive and is therefore not as
suitable for the particular intended end purpose. The }ime is
screened to remove lumps of dimension greater than about 6 mm.
and the screened small lump material is fed from a chute 10 to a
worm screw conveyor 12. A non-aqueous liquid silicone surfactant
stored in a tank 14 is fed by an accurately controllable
peristaltic-type pump 16 to the conveyor 12 in which it i8 mixed
with the lime material. The mixture is then transferred to
another worm screw conveyor/mixer 18 to a hammer mill 20, the
screen 22 of which discharges directly into a hopper 24, from which
the material can be fed via a valve 26 to a suitable transport 28.
- 4 -
;
)816
The resultant treated li~e exhibits ~ hi~hl~ improved
flowability to the extent that it is particularly suited for u~e
as the lime material in the desulphurising process described
above, in that it does not bridge or plug in the apparatus used
for delivering it to the iron bath, so that its delivery can be
effec~ed with the desired close control as to volume per unit
time. Moreover, the non-aqueous silicone surfactant inhibits the
absorbtion of water into the structure of the finely divided lime,
giving a longer tank life. ~he flowability is tested conveniently
: 10 by pouring the material through a funnel 30 (Fig. 2) so that it
impinges on a shelf 32 until its natural angle of repose R has been
established, the excess material running over the edge of the
shelf; the angle of repose of the material remaining on the shelf
is then measured. It was found that untreated lime had an angle
15 of 45, a treated lime including 0.1% by weight of surfactant had
an angle of 35, and a treated lime including 0.2~ by weight had
an angle of 32. ~t i8 preferred that the.angle be between 3B
and 30. An angle of at mo~t 38 is preferred to give the necessary
flowability, while an angle of les~ than 30 is not needed, and
indeed may result in a material that i8 SO flowable that it becomes
difficult to handle, exhibiting a flowability approaching that of
water.
Liquid silicone ~urfactants are non-aqueous materials that
are particularly suited for the operation of the invention, and
four especially preferred materials arey94lo6 or Q13563 qold by
Dow Chemical Co., SF96 sold by Canadian General Electric Co., and
Y9416 sold by Union Carbide Corporation, all being clear water-
like liquids. Silicone surfactants are relatively expensive
5 -
., .
,
. .
.. :
.
1140816
materials (e.g. at this ti~e pexhaps 75 tLmes as expensive as the
lime) and it is therefore preferred to use a~ little a~ pos~ible
that will provide the required flowability. We find that with the
cogrinding process of the invention the required flowability can
S be achieved with as little as 0.1% by weight of the mixture. Up
to 0.5% by weight can be employed, but no commercial value is noted
in using more than this amount, and in fact, as described above,
an excess may result in difficulty in handling the resultant
treated material.
We prefer to use a silicone surfactant having a viscosity
between 20 and 100 centistokes at 25C, and preferably one having
a viscosity of about 50 centistokes at this temperature. If the
viscosity is too highit becomes difficult to meter such small
amounts of liquid, while if the viscosity is too low there is a
lS tendency for the material to be absorbed into the crystalline
lime with a 108s of effectiveness an`d increase in the amount of
expensive surfactant required. The problem of metering the small
; quantities of liquid is considerably relieved by maintaining it
at a temperature in the tank 14 of between about 15C~60F) and
38C ~100F~, preferably at 27C (80F). We have found that a
controllable peristaltic pump is particularly suited for accurate
delivery of these materials.
; A hammer mill provides the necessary comilling with adequate
capacity and continuous operation, and the number of hammers and
the mesh of the screen 22 are adjusted to give a resultant
material of the desired particle size. For the intended
desulphurisation process this means that less than 15~ by weight
is retained by a 100 mesh sieve, while at least 80~ by weight
-, - 6 -
.
.
~ 6
passes throu~h a -200 mesh sieVc~ and this paxticle 5ize may be
obtained by use of a -48 mesh si~ve 2~.
The material obtai~ed is employed ~n a desulphurisation
process of the invention making use of the apparatus ~hown in
Figure 3. A so-called torpedo rail car 34 filled with about 200-
300 metric tons of molten iron while at a desulphurisation station
has a lance 36 inserted therein. Over a period of about
minutes a mixture of treated lime of the invention and finely
divided magnesium powder is fed continuously to the iron where it
reacts with the sulphur and sulphur-containing components to
form a slag which ~oats to the top to form a readily removable
layer 38. In a typical process there is added about 4.5 to 6.0
Kg. of lime per metric ton of iron, and about 0.5 Kg. or less of
powdered magneiium per metric ton. The use of the treated lime of
the invention ensures a more uniform flow and re-action throughout
the iron; it is possible with the invention to achieve sulphur
contents as low as .005%~ although the more usual value is about
0.01S. It also permits a substantial reduction in the amount of
magnesium that would otherwise be required e.g- about h~lf of the
amou~t previously required.
_.
~ ~ , ~ .. ...
