Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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METHOD FOR CONDITIONING FERTILIZER GRANULES
Description:
The invention relates to a method for conditioning fertilizer granules. Within
the scope of the
present invention, the phrase "fertilizer granules" refers in particular to
potassium fertilizer
granules and especially preferably potassium chloride fertilizer granules or
potassium sulfate
fertilizer granules. However, the invention also includes the conditioning of
other fertilizer
granules, e.g., ammonium sulfate granules.
Fertilizer granules, e.g., potassium sulfate fertilizer granules or potassium
chloride fertilizer
granules, are produced, for example, by press granulation (compacting) in
roller presses where
the starting material (e.g., fine-grained salts) is compacted in roller
presses and consequently
pressed to form so-called slabs. These flat slabs are then pulverized (e.g.,
in impact mills) and
classified.
In the production of potassium chloride fertilizer granules, the starting
material (for example,
potassium chloride salts) is usually charged to the roller press in a hot dry
condition. Then the
granules are conditioned by moistening them with water and then exposing the
moistened
granules to a stream of air and solidifying them by utilizing the inherent
heat of the granules.
This should improve the abrasion resistance, so that unwanted production of
dust and/or fine
particles is reduced. To do so, for example, DD 136 956 proposes that the dust
and fines should
first be removed from the (raw) granules in a fluidized bed, then wetted with
water, and next the
surface of the granules is solidified by recrystallization processes utilizing
the thermal capacity
of the granules. The moistened granules are then dried with a strong stream of
air and next
cooled with air, where both the drying and the cooling may take place in the
fluidized bed (cf.
DD 136 956).
On the other hand, in the production of potassium sulfate fertilizers, the
starting materials are
not pressed while dry in practice but instead the finely crystalline potassium
sulfate is usually
pressed with the addition of water in the roller press to form the slab. Next
the slab can be dried
in a dryer according to a first process variant and then granulated. No
conditioning of the
granules is provided. In this case, the granules have a low final moisture
content but the
abrasion resistance is also low. In a second process variant, there is no
drying of the slab
before granulation, so the slab is granulated while moist. To increase the
quality of the raw
granules, they can be moistened by adding water after granulation. The
moistened granules are
then stored in large product storage devices for a period of several weeks so
that the surface of
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the granules, which is partially dissolved due to the addition of water,
becomes crystallized and
solidified. This yields an end product with a higher moisture content but also
with a greater
abrasion resistance.
__ The methods used in practice to produce fertilizer granules, e.g.,
potassium chloride ¨ or
potassium sulfate fertilizer granules ¨ have proven to be fundamentally
successful in practice
but they could be improved upon. That is where the present invention begins.
DE 28 10 640 Al also discloses a method for producing granular products from a
fine-grained
__ material consisting essentially of sulfatic potassium or ammonium salts by
using a high-pressure
roller press, wherein the material to be pressed is treated with water and/or
water vapor at
elevated temperatures before being introduced into the roller press. This
should adjust a
moisture content of 0.5 to 2.0% by weight and a temperature of 40 C to 50 C in
the material to
be pressed. The temperature of the material to be pressed should be kept below
the
__ condensation temperature of water vapor during the entire pressing
operation. The product
removed from the high-pressure roller press, preferably at a temperature of 55
to 95 C, consists
of slabs which are then milled. Next the correctly sized particles are
separated from the milled
product, in particular separating particles with an average grain diameter of
1 mm to 4 mm as
the product from the coarse grain and fine grain and cooled to room
temperature.
Furthermore, DE 39 18 523 Al describes a method for preventing dust from
forming when
loading or transporting granules or pellets, in particular fertilizer
granules, wherein such
granules are prepared by dry press granulation. The formation of dust during
loading or shipping
is prevented by the use of a conditioning agent, such that a liquid mixture
(dust binding mixture)
__ consisting of at least two organic substances that are completely soluble
in one another is
added.
The invention is based on the object of creating a method with which
fertilizer granules and
potassium fertilizer granules in particular, especially preferably potassium
chloride fertilizer
__ granules or potassium sulfate fertilizer granules can be conditioned with
little effort in terms of
plant technology and economically, such that a storable product with low
production of
undersized grain and fine dust and with a high abrasion resistance is made
available.
To achieve this object, the invention teaches according to a first aspect a
method for
__ conditioning fertilizer granules, for example, potassium chloride
fertilizer granules, wherein first
granules are made available at a temperature of more than 40 C,
wherein the granules are moistened with water, and
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wherein the moistened granules are next exposed to a stream of air and
solidified utilizing the
inherent heat of the granules. It is provided according to the invention that
the moistened
granules (for solidification) are dehydrated with an air flow rate of at least
100 m3 (cubic meters)
per metric ton of granules (i.e., specific air flow rate of 100 m3/t) at an
air temperature of less
than 45 C. The reference to weight is based on the moistened granules exposed
to air.
The present invention is based on the finding that it is quite advantageous to
moisten the (raw)
granules and to expose them to a stream of air by utilizing the inherent heat
so that the surface
is solidified and smooth if necessary and so that the abrasion and the
unwanted formation of
undersized grain and/or fine dust is reduced. However the invention has
recognized that is not
necessary to dry the moistened granules (with hot air) and then cool them
(with cool air) but
instead that a product of high quality and with an excellent storage capacity
can be obtained if
(only) dehydration is carried out with very strong streams of air. Whereas
with a traditional
installation, for example, drying with hot air and then cooling with air first
take place with hot air
in a fluidized bed when the (cooling) air at room temperature and a very high
air flow rate of at
least 100 m3 per metric ton of granules, preferably at least 300 m3, for
example, at least 600 m3
per metric ton is selected. In terms of the installation technology, it is
therefore not necessary to
set up both a drying zone and a cooling zone in a fluidized bed installation,
for example, but
instead the [dehydration] can take place in a single zone in the fluidized bed
and/or in several
(identical) zones in which only air at room temperature and/or at ambient
temperature with a
very strong stream of air is supplied. The water vapor escaping from the moist
granules (i.e., the
vapors) is removed with strong streams of air, so that the moisture is
effectively removed from
the granules and the desired solidification takes place. The fact that the air
used for dehydration
is at a relatively low temperature in the range of room temperature is
especially important, so
that it is possible in particular to omit complex burners and/or burner stages
for heating the air.
Only when such an installation is operated in an extremely cold environment
and consequently
it is necessary to intake air at very low temperatures (e.g., close to or
below the freezing point)
may it be expedient to have a slight preheating of the air within the scope of
the invention, but
without exceeding temperatures of 45 C. Consequently, on the whole, the
installation operates
very favorably in terms of energy and plant technology. Within the scope of
the invention, the air
for dehydration especially preferably has a maximum temperature of up to 35 C.
The air flow
rate can be selected as a function of the air temperature and the relative
atmospheric humidity
(i.e., that of the air supplied).
It is provided that the moistened granules are preferably dehydrated in a
fluidized bed
installation. Basically, however, the dehydration may also take place in
installations of another
type.
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If working with a fluidized bed system, the invention proposes that the
moistened granules are
dehydrated in a dehydration zone of the fluidized bed system with a stream of
air that has been
described here and without an upstream drying zone using hot air.
The moistening may be carried out in a fundamentally known way in a drum
and/or a drum
mixer. Such mixing in the drum should at the same time ensure rounding of
particles. However,
in a preferred further embodiment, the present invention has recognized that
moistening need
not necessarily be carried out in a drum but instead, for example, moistening
may also take
place in a shaft mixer, for example, a dual-shaft mixer. This makes it
possible to further reduce
the complexity of the system.
Due to the dehydration, the water content of the granules is reduced to less
than 1%, preferably
less than 0.5%, for example, less than 0.2% (based on weight).
The subject matter of the invention is also a device for conditioning
fertilizer granules with a
method of the type described here. Such a device has a mixing device for
moistening the (raw)
granules and a dehydration device in which the moistened granules are
dehydrated with an air
flow rate of at least 100 m3 per metric ton of granules at an air temperature
of less than 45 C.
The dehydration device is especially preferably designed as a fluidized bed
system and the
dehydration consequently takes place in the fluidized bed.
According to a second aspect, the invention discloses a method for
conditioning fertilizer
granules, for example, potassium sulfate fertilizer granules, wherein moist
granules produced by
granulation of a moist slab emerging from a roller press are made available
first,
wherein the granules are moistened with water, for example, and
wherein the moistened granules are next treated with a stream of air and
thereby dehydrated
and solidified. Moist granules produced from the slab within the scope of the
invention
preferably refers to granules with a moisture content of 0.5% by weight to
2.0% by weight.
According to this invention, however, these granules which are already moist
are moistened
(again) by the addition of water, namely preferably with the addition of 0.5%
by weight to 5.0%
by weight, especially preferably 1% by weight to 3% by weight water, each
based on the weight
of the granules. The granules produced from the slab has a relatively low
temperature because
the starting material charged previously to the press is not (actively) heat
and at any rate
heating takes place (passively) due to the pressing and/or granulating process
in the wake of
press granulation.
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In this second aspect, the invention is directed first to the finding that it
is not (always)
necessary following the production of fertilizer granules, for example,
potassium sulfate fertilizer
granules, to dry the slab before granulation, so that expensive drying
equipment can be omitted
according to the invention. The granules produced by press granulation are
consequently
5 available in a moistened condition. Nevertheless, according to the
invention, there is (additional)
moistening due to the addition of water in order to trigger partial
dissolution of the surface of the
granules. Then there is cold hardening of the surface of the granules due to
crystallization of the
dissolved salts. According to the invention, this is supported and accelerated
by the fact that the
granules are exposed to a stream of air and thereby solidified without input
of heat and
consequently the granules are conditioned. Due to this exposure to air, the
granules are
dehydrated without being dried out due to a supply of heat. Such an exposure
to air and
consequent dehydration can preferably take place in a fluidized bed system and
consequently
dehydration can preferably take place in a fluidized bed system, namely
especially preferably
with relatively high air flow rates. Thus, the moistened granules are
preferably dehydrated in an
air flow rate of at least 100 m3, preferably at least 300 m3, for example, at
least 600 m3 per
metric ton of granules. In doing so, the process is carried out at relatively
air temperatures so
that drying with hot air is avoided and instead preferably air at room
temperature is used, so this
makes it possible to eliminate the use of burners and/or burner stages for
heating the air. Only
when such an installation can be operated in an extremely cold environment and
consequently
air at very low temperatures must be taken in (for example, temperatures close
to the freezing
point or even lower) may a slight preheating of the air be expedient within
the scope of the
invention, but still without exceeding temperatures of 45 C. Consequently,
such a plant can
operate very favorably with regard to plant technology. The air to which the
moistened granules
are exposed and with which they are consequently dehydrated especially
preferably is at a
temperature of up to 35 C. The air flow rate can be selected as a function of
the air temperature
and the (relative) atmospheric humidity (of the air supplied).
The conditioning of the granules according to the invention, for example, in a
fluidized bed
apparatus without input of heat, results in the abrasion resistance being
improved by 30% to
50% in comparison with traditional methods in which the (moistened) granules
are stored in
large product storage devices over a period of several weeks. Furthermore, the
storage times,
which may optionally still be necessary until achieving a market-ready product
with a moisture
content of 50.5(Y0 by weight, can be reduced greatly and then the required
storage capacities
can also be reduced accordingly.
According to the second aspect of the invention, the subject matter of the
invention is in
particular not only the method described here for conditioning but also a
method for producing
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fertilizer granules, for example, potassium fertilizer granules, especially
preferably potassium
sulfate fertilizer granules. Within the scope of this production process,
- starting material, for example, fine-grained potassium salt is moistened
with the addition
of water for example,
- the moistened starting material is compacted in a roller press to form a
slab, and
- the slab is pulverized (i.e., granulated) to form the granules and is
optionally classified.
Next the granules are then conditioned in the manner described above, i.e.,
the granules are
moistened with water and the moistened granules are then exposed to a stream
of air and
thereby solidified.
The starting material is preferably not heated before being compacted, so that
it preferably has
temperatures of less than 40 C. In the wake of press granulation, i.e.,
compacting, on the one
hand, and granulation, on the other hand, there is also no (active) heating of
the material but
instead there is at any rate a (passive) heating due to the pressing operation
and/or the
granulation process. The starting material is preferably moistened by adding
water in an amount
of 0.5% by weight to 2% by weight, for example, 0.5% by weight to 1.5% by
weight, based on
the weight of the starting material. The slab formed by compacting is
especially preferably
pulverized in a moist condition without first drying it so that moist granules
are made available
and can then be moistened in the manner described above within the context of
conditioning
(additionally). Fundamentally, however, the invention also includes production
processes in
which the slab is optionally dried before being granulated.
The (conditioned) granules are stored in a storage device, for example, a
storage building, in air
for a predetermined period of time, as needed. According to the invention,
this period of time
can be reduced significantly in comparison with the known methods, so that the
storage
capacities can also be reduced on the whole.
The starting material is preferably moistened immediately before being charged
to the roller
press, namely in a mixer, for example, a drum mixer or a dual-shaft mixer.
For moistening of the granules produced by press granulation, preferably a
mixer, for example,
a drum mixer is also used. Such mixing in the drum can at the same time ensure
rounding of the
particles. However, in a preferred further embodiment, the invention has
recognized that
moistening in a drum is not absolutely necessary but that instead the
moistening may also take
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place in a shaft mixer, for example, a dual-shaft mixer. The complexity of the
installation can be
further reduced in this way.
The water content of the granules is especially preferably reduced to less
than 1%, preferably
less than 0.5%, for example, less than 0.2% based on weight, in the wake of
conditioning by
exposing the granules to the stream of air. If the desired levels are not
reached directly due to
the air exposure within the context of conditioning, the value can then be
reached by relatively
short storage times.
An installation for producing fertilizer granules of the type described here
will have at least one
(high-pressure) roller press (compacting press) and a pulverizing device
(e.g., impact mill)
downstream from the roller press. A moistening device, for example, a mixer,
may be arranged
upstream from the roller press. For conditioning of the granules produced by
press granulation,
a mixing device is then preferably also made available for moistening the
granules, for example,
a shaft mixer (e.g., a dual-shaft mixer). This is then preferably followed by
a device with which
the moistened granules can be exposed to a stream of air, for example, a
dehydration device
which is preferably designed as a fluidized bed system, i.e., the dehydration
takes place in the
fluidized bed, especially preferably without an upstream hot air drying zone.
The invention will now be explained in greater detail below on the basis of a
drawing which
shows only one exemplary embodiment, in which:
Fig. 1 shows a device for conditioning fertilizer granules, in
particular potassium
chloride fertilizer granules in a highly simplified schematic diagram, in
particular
according to the first aspect of the invention and
Fig. 2 shows a device for producing and conditioning fertilizer
granules, in particular
potassium sulfate fertilizer granules, in particular according to the second
aspect
of the invention.
Fig. 1 shows a device for conditioning fertilizer granules, in particular
potassium chloride
fertilizer granules in a greatly simplified schematic diagram. Fig. 1 relates
in particular to the first
aspect of the invention.
The device according to the invention has a mixing apparatus 1 and a
dehydration apparatus 2
downstream from a mixing device 1, which is designed as a fluidized bed system
2, in the
exemplary embodiment shown here.
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In the inventive process, first granules (and/or raw granules) are made
available, namely from a
granulation system 4, which is merely indicated. This usually consists of one
(or more) roller
presses with downstream milling and classification stages. The starting
material, for example,
fine dried salt, is compacted in this roller press and thereby pressed to form
so-called slabs.
These slabs are then pulverized, i.e. ground and classified, so that the
granules, i.e., raw
granules, are made available for the subsequent conditioning. After press
granulation, the raw
granules have relatively high temperatures of more than 40 C. This residual
heat is utilized as
part of the following conditioning. This conditioning is represented in the
figure. The (hot) raw
granules G are moistened in the mixing device 1. This moistening mixer 1 is
designed as a dual-
shaft mixer in the exemplary embodiment. This is followed by the dehydration
device 2 and
consequently also the fluidized bed system. The moistened granules B are
dehydrated in this
fluidized bed system 2 with an air flow rate of at least 100 m3 per metric ton
of granules at an air
temperature of less than 45 C and thereby solidified. The air L thereby
supplied consequently
has a temperature in the range of room temperature. The step of drying with
hot air is
eliminated, so that not even a subsequent cooling is required. The fluidized
bed system 2, which
is used within the scope of the invention, can consequently be shortened,
i.e., reduced in size,
in comparison with traditional fluidized bed systems, which have a drying
zone, on the one
hand, and also have a cooling zone, on the other hand, so that the system
complexity is
reduced. Then corresponding hot gas generators for heating the drying air can
also be omitted.
With the method according to the invention, a product P, i.e., conditioned
granules with a high
quality and long storage life are obtained by a simple method in terms of the
plant technology.
Fig. 2 shows schematically in a highly simplified diagram a device for
producing (and
conditioning) fertilizer granules, in particular potassium sulfate fertilizer
granules. Fig. 2 relates
in particular to the second aspect of the invention.
The essential component of such a plant is a roller press 5 in which the
starting material (e.g.,
potassium sulfate) is pressed and consequently compacted. The starting
material A supplied to
the roller press however is moistened first with water, namely in a mixing
device 6, which is
arranged upstream from the roller press 5.
The moist slab S emerging from the roller press 5 is pulverized and granulated
in a granulating
device 7, which may be designed as an impact mill, for example. It is
especially preferably
provided that the slab S is pulverized in a moist condition without prior
drying. This is usually
followed by a classification (not shown here).
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The (moist) granules G produced in this way are then conditioned according to
the invention ¨
optionally after storage and/or temporary storage. To do so, the granules G
are moistened with
water in a mixing device 1 to partially dissolve the surface of the granules.
Next the moistened
granules B are sent to a device 2, which is designed as a fluidized bed system
in this exemplary
embodiment, and in which the moistened granules B are exposed to a stream of
air L and
thereby dehydrated and solidified. Drying with hot air is not necessary here,
so that then cooling
is not necessary either. Consequently, the fluidized bed system 5, which is
used within the
scope of the invention, can be shortened, i.e., reduced in size in comparison
with traditional
fluidized bed systems, which have a drying zone, on the one hand, and have a
cooling zone, on
the other hand, so that the system complexity is reduced. Corresponding hot
gas generators
may then also become unnecessary for heating the air for drying.
The granules conditioned in this way as the product P have a very low moisture
content, so that
they are directly available and market ready. If the moisture does not meet
requirements, there
is the possibility of storing the granules from the fluidized bed system 2 in
air in a storage
device, for example, a storage building, so that a saleable product is
available after a relatively
short period of time.
