Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02213738 1997-08-19
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PROCESS FOR THE PRODUCTION OF
GRANULATED POTASSIUM CHLORIDE
This invention relates to the manufacture of inorganic
fertilizers, and more particularly to the production of
granulated potassium chloride.
Potassium chloride is an inorganic fertilizer component.
It is used in granulated form and various processes are
known in the art for preparing it in such a form. One
such process consists in feeding particulate potassium
chloride to calendering rollers, whereby to produce a
sheet which is then ground to granules. However, this
process has a low efficiency and only about 300 of the
prcduct is satisfactc=ily granulated by passage between
calendering rollers. Further, a significant amount of
the material (3-So) is lost and t~;e resistance of the
granules to compressicn is relati~.re~y low, specifically
they have a crushing load - the ccmpression load which
destroys the granules by crushing them - of about 2-
2.5 kg.
Another method of prcducing potassium chloride granules
involves preparing a mixture of the raw material with 3-
i0 a of ammonium chloride, humidifying the mixture by the
addition of water, passing it through a sieve and drying
the resulting granules. This process, however, is
relatively expensive, and does not permit the use of
high temperatures and therefore necessarily comprises a
relatively long drying phase.
CA-A-212650 discloses a process for producing granulated
potassium chloride from powdered KC1 salt by melting
said powdered salt in a melting furnace, and solidifying
the liquified salt into granules by spraying said
liquified salt into a cooling chamber.
ANIEI~I~t~ SHEET
IPEA~~Q
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It is also been attempted to increase the strength of the potassium chloride
granules by the addition of secondary products formed in the manufacture of '
said chloride, particularly magnesium chloride in the amount of about 3.~%
and calcium chloride in the amount of about 1.5%. In this way, however, a
more by groscopic material is produced and the necessity of using a relatively
low drying temperatures (e.g., about 200°C) increases the duration of
the
drying and the expense of energy.
It is particularly difficult to obtain hCl granules having dimensions of about
3-
4 mm and adequate compression strength, e.g. of 3 to 7 kg and such production
is not possible by the methods and apparatus of the prior art.
It is a purpose of this invention to overcome the defects of the known
processes
and to provide a process for the production of granulated potassium chloride
which produces the desired product in granulated form, without substantially
increasing manufacturing costs.
It is another purpose of this invention to provide such a process w hick
produces potassium chloride granules having a high resistance, in particular a
resistance to compression or crushing load of 3 to 7 kg.
It is a further purpose of this invention to provide such a process which
permits to produce granules having dimensions of 1.5 mm and more. ,
a
It is a further purpose of this invention to provide Such a process «-hich
reduces the by groscopicity of the final product.
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It is a still further purpose of this invention to provide such a process
which
' affords a saving in the energy required for carrying it out.
These and other purposes and advantages of the invention will appear as the
description proceeds.
The process according to the invention comprises the steps of
- forming a mixture of potassium sulfate and potassium chloride;
- melting said mixture;
- bringing said molten mixture into physical contact with a cooling surface
provided with recesses, said recesses being substantially of dimension and
shape of the granules to be produced. said surface being cooled, whereby
solidification of the molten mi.Yture is obtained: and
-collecting the solid granules from the said surface.
T'refer< <~ly, the amount of h,~SO~ used is about 1 to ~% by weight of the hCl-
Ii.,SO~ mi.~ture.
Generally, the granules obtained from the solidification of the molten drops
have sizes comprised between 1.o and 6 mm.
The granulation process is characterized by a cooling method which was
discovered to be very efficient. according to said method, the molten mi.Yture
is poured on a cooling surface having recesses thereon, the recesses
substantially of dimension and shape of the granules to be produced.
according to a preferred embodiment of the invention, said surface is provided
SUBSTITUTE SHEET (RULE 26)
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by a drum capable of rotational movement. Heat is transferred from the
molten drops collected in the recesses to the substance of which the drum is
made of (preferably iron), while the drum being continuously cooled by water.
Granules are therefore obtained in the recesses, and may then be collected in
a
container wherein heat exchanger is placed to complete the cooling procedure,
while the heat is recycled.
Preferably, the drum makes a continuous rotational movement, through which
the granules obtained in the recesses fall to a container for collection,
because
due to the cooling process their dimensions become smaller than these of the
recesses. Of course, any other convenient procedure which allows cycling
process, such as conveyer belt, may be adapted, and further means to allow the
falling of said granules from said recesses to said container may be added.
~s stated, the surface provided with recesses thereon mad- be of any desired
structure: the recesses. for example, may have a rectam ular or hexagonal
cross section, and their bottom is usually rounded. _' ccording to one
embodiment of the invention, the drum is coated with a porous coating to
provide a protection for the drum. . according to another embodiment of the
invention, a second roller may be coupled to the drum to break the material
crvstalized outside the recesses. By the use of said second roller, eYCess of
material is removed from the recesses, leveling the upper face of the granules
produced, and thus obtaining well defined shapes of the granules.
a
The apparatus according to the invention comprises
- means for forming a mi.Yture of potassium sulfate and potassium chloride:
- means for bringing said mi.Yture to an oven;
SUBSTITUTE SHEET (RULE 26)
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means for melting said mixture in the oven:
- means for obtaining the crystals by bringing said molten mixture into a
physical contact with a cooling surface provided with recesses, said recesses
being substantially of dimension and shape of the granules to be produced,
said surface being cooled, whereby solidification of the molten mixture is
obtained; and
means for collecting the solidified granules from the surface and further
cooling them, and for recy cling the heat.
In a preferred embodiment of the invention, means for improving the energt-
use are provided. in order to make the process more industrially attracti~-e.
~s may be clear to one skilled in the art, several ways for improving the
consumption of energy may be applied in the above described process and
apparatus, two of which are exemplified in the drawings.
In the drawings:
Fig. 1 illustrates one preferred embodiment of the invention.
Fig.2 illustrates another preferred embodiment of the invention based on the
use of cyclone heat exchanger.
Fig. 3 shows a preferred embodiment of the drum and its cooling sy stem.
Fig. ~ shows another preferred embodiment of the drum, when coupled to a
second roller ( a view of the rotary axis).
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Detai end Description of Preferred embodiments
Referring to Fig. 1, the solid material to be treated, comprising a mixture of
about 95 to 9996 0~ KCl and 1 to 6°6 of K.zS04, indicated at (1), is
chargred into a
container or like apparatus ~. By any coxtvenient feeder (3), such as screw-
feeder, the mixture is fed, ~ a controlled manner, to conduit (4). Numeral
(4a)
indicates a reservoir containing a fuel, such as mazout. A different fuel
could,
of course, be usEd. The pxeb~eated fuel is fed, together with preheated air
(according to one embodiment of the invention, the loot six is obtained from
heat exchanger (10), to be described hereinafter) to a burner, whiclx is
schematically indicated as 4b. The product of the burning of the fuel and the
hot air, i.e., combustion gases, flow through conduit (4) and drive the salt
mixture to melting oven (5), which is a cyclone oven. The salt mixture
completely melts in oven (5) ( at about 8$0-8b0 °C). Numeral (6)
indicates a
container in which the melted salt mixture is collected, and numeral (6a)
stands for the Ievel of the molten salt in said cox~taxner. This mixture is
now
brought into contact with the granulation system. The granulation system is
composed of a drum, (16), made of a material which is a good heat conductor,
such as iron., capable of making a rotational movement. V~ater (20) is pumped
by a pump (7.9), in order to cool the sotating drum, in a manner specifically
shown in figure 3. The surface of said drum has recesses on, and the molten
mixture is poured from, container ~ to the recesses of said surface. Due to
the
rotational movement of the drum, crystals obtai~aed in the recesses fall,
being
collected in a container (17a), in which heat exchanger (1'~ is placed, to
further
carry out the cooling process of the granules anal to recycle the heat
absorbed.
As stated, the apparatus described above may be further modified, in order to
make it more attractive from the economical and i,xxdustrial points of view,
For
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example, it may be coupled to another system, in order to improve the energy
use and to avoid possible loses of heat and material. Particularly, the
combustion gases have a temperature of about 880-950°C at their exit
from
oven ~, az~d in addition they carry some small amounts of the salt mixture in
the form of very small drops or in the dorm of molecules which are in the
gaseous phase. Thus, the suspension of molten salt drops in the combustion
gases flows through gas conduit ('T) into a gas separator ($), walls of which
are
cooled by water. KCl-K~S04 particles, formed as a result of the cooling of the
suspension, fall to the bottom of the separator and therefrom into a vessel
($b).
A pneumatic system (15) is used to transfer it to the container (6), to be
melted therein. and further to be subjected to the granulation procedure, as
described above. The gases are brought into contact with heat exchangers.
Outside air (11) is driven from fan (9) to said heat exchanger, it is heated
therein from ambient temperature to about 450°C. According to one
preferred
embodiment of the invention, this heated air may now be used in the burner
(4b), fox the combustion process, as described above. 'fb~e cooled gases,
together
with the materials that have not separated from them, pass through a
separator (I2), and from it to mechanical filters (13), from which they are
drawn by exhauster fan (14), while the salt granules settle to the bottoux of
said second separator (12) and said filters (13) and reach said pneumatic
system (15), from which they are collected in vessel (8b) and transferred to
Container (6), as described above.
Another important aspect of the it~vention, which is considered to be a great
advantage, is the composition of the gases when they leave the melting oven
(5). Typically, the compositio~a of said gases coptain only small amounts of
oxides of nitrogen, sulfur and vanadium, and therefore fuel which is rich of
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sulfur and/or vanadium may be used. As can be appreciated by one skilled in
the art, this comprises both economical and ecological advantages, since these
gases may be further used in other industrial applications.
Referring to Fig.2, According to another embodiment of the invention, the
energy use is improved by using heat exchanger of cyclone type. Numeral 26
indicates a drying oven or the like, wherein said initial salt mixture is
subjected to some small extant of heating to remove humidity. The mixture is
collected ixx a container (2~5 , and is then fed 24 , in a controlled manner,
into
an ejector (~, and then transferred, by the use of an air stream 23a), to the
cyclone heat exchanger. The oven for carrying out the melting is indicated by
numeral 21 , wherein burners 30 are provided. The salt mixture is passing
through the cyclone heat exchanger 22 in the way to the oven, and the gases
produced during the melting axe driven into the heat exchanger, where they
flow in. a direction opposite to that of the air and salt, thus heating said
salt
mixture, in their way to the drying oven and from said drying oven to
mechanical filters (~. Salt that was carried over by the gases is collected at
the filters and transferred 28 to the oven.. The molten salt mixture obtained
at the oven is transferred (~ to the granulation process as described above.
Referring to Fig. 3, the drum is illustrated. The surface o~ the drum U is
provided ~uvith recesses (~, dimension of which is substantially of the
granules
tv be formed. Numeral, 33 indicates the internal water cooling.
Referring to Fig. 4, a preferred embodiment o~ the drum is illustrated
schematically (the view is of the rotary axis). The drum 34 coupled to a
roller
35 , their axes being parallel and they touch each other along a line. When
the
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rotational movemex~t of the drum is taking place (36], the roller is
performing
an opposite rotational movement 3? by which material that was solidi~~.ed on
the surface of the drum is removed, the upper face of the granules in the
recesses are leveled and the granules are brought ~,to a uniform shape.
~ a
Table I sum~ztarizes the results of the granulation process according to the
embodiment of Fig. 1, for varaious initial compositions and conditions (i.e,
dimensions of recesses in the drum). Initial KCl and K2S04 were obtained from
Dead Sea Works Ltd., in the form of a powder. The amount of mazout needed
is about 42 kg per tone of salt.
initialinitial total weight dimension of compression load
KCl K2S04 of final granules (kg)
K K final granules mm
K
50.0 1.5 5 i.5 ~.5-~.5 5.0-~.0
50.0 0.75 50.75 S.5-4.5 4.0-6.0
50.0 0.75 50.75 2.0-3.0 3.0-4.5
It will be apparent that the above-described apparatuses show only some
preferred embodiments of the invention and that xt zs possible to carry out
the
invention by using different means for feeding the initial salt mixture,
various
kinds of ovens to melt said mixture, etc. It is surprising that, as long as
the
initial mixture comprises an addition of K~S04, se set forth hereinbefore, and
the cooling of the molten drops is carried out as set forth hereinbEfore, the
granules thus obtained have properties, in particular compressive strength,
not attainable by any weans known in the art.
