Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Background of the Invention:
l. Field of the Invention:
This invention relates to a process for manufac-
turing a granular compound fertilizer.
2. Description of the Prior Art:
It has been known to the public to prepare a
solution o-f an ammonium phosphate, ammonium sulfate or a
mixture thereof, which serves as a raw material for
granular compound fertilizers, -from ammonia and phosphoric
acid or sulfuric acid or a mixture of these acids while
making use of a tubular reac-tor. Reference may be made,
for example, to a report written by B. R. Parker, M. N.
Norton and D. G. Salladay (reported at FAI-IFDC Seminar
1977 in New Delhi, India). Compared with carrying out the
above reaction in a neutralizing reaction tank equipped
with an agitator, the above method has such merits that
the reactor is simple in structure and easy in maintenance
and the reaction heat may be effectively utilized -for the
evaporation of water and the granulation and drying
operations .
The thus-obtained solution is then fed to a
drum-shaped granulator or blunger, mixed with a large
quantity of recycled solid particles as well as, optionally
another solid fertilizer substance and/or solid diluent
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into granules, thereby providing a granular subs~ance
having a water content of 2 - 5% by weight. This granular
substance is thereafter dried with hot air in a rotary
drier and subjected to classification in a classifier,
thereby obtaining a final product, i.e., compound -Eertilizer
of a desired particle size range. Excessively large
particles are recycled to the granulator after pulverization
and excessively small particles are recycled to the
granulator as they are.
The above process generally requires making the
quantity o~ solid particles recycled to the granulation
apparatus 2 - 8 times that of the final product drawn out
of the system in order to maintain the granulator and rotary
drier under good operation conditions with respect to the
granulatability of each compound fertilizer or the water or
energy balance in the granulation system? although the
above figures vary depending on the components contained
in the compound fertilizer. Thus, it is generally required
to recycle to the recycling line even a part of particles
oE the desired particle size which are obtained in the
classifier.
Summary of the Invention:
An object of this invention is to provide an
improved process for efficiently manufacturing a granular
compound fertilizer which contains at least -two agronomically
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effective components selected from N (nitrogen), P (phosphor)
and K (potassium).
According to this invention, the following process
for manufacturing a granular compound fertilizer is provided:
A process -for manu~acturing a granular compound
fertilizer containing at least two agronomically ef-fective
components selected form N, P and K, which comprises reacting
phosphoric acid, sulfuric acid or nitric acid or a mixture
thereof and ammonia in a tubular reactor to form a solution
containing diammonium hydrogenphosphate, ammonium dihydro-
genphosphate, ammonium sulfate, ammonium nitrate or a
mixture thereof; introducing the solution into a mixing
tank and either evaporating the water contained therein to
obtain a high temperature slurry having a liquid content of
40 - 90% by volume or evaporating the water contained
therein and, at the same time, mixing a solid -fertilizer
substance or solid diluent having particle sizes of 50 -
1,000 ~m or a molten liquid or aqueous solution of a
fertilizer substance with the solution to obtain a high
temperature slurry having a liquid content of ~0 - 90% by
volume spraying the thus-obtained high temperature slurry
into the spacing of a granulation zone of a spouted bed
granulation apparatus or fluidized bed granulation apparatus,
thereby causing the thus-sprayed slurry to stick to priming
particles floating in the spacing and thus forming enlarged
granules; and drying and/or cooling the thus-enlarged granules.
~Z~
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Brief Descrlption of the Drawing:
/ The accompanying drawing is a flow sheet illus-
trating one embodiment of the invention.
Detailed Description of the Invention:
In a process according to this invention, ammonia
and phosphoric acid, nitric acid, sulfuric acid or a mixture
thereof are reacted in a tubular reactor. As an acid to be
reacted with ammonia, it is preferred to employ phosphoric
acid or a mixed acid of phosphoric acid and nitric acid or
sulfuric acid. These acids and their proportions can be
selected in accordance with the agronomica~ly effec~ive
components contained in each intended compound fertilizer
and the concentrations thereof.
Where phosphoric acid or a mixed acid of phosphoric
acid and another acid is used, the resulting ammonium
phosphate has maximum solubility when its molar ratio of
ammonia to phosphoric acid is 1.~ to 1. If the molar ratio
exceeds 1.4 to 1, the solubility of the ammonium phosphates
drops abruptly and solid ammonium phosphates deposit,
resulting in the clogging of the tubular reactor. Accord-
ingly, it is desirable to maintain the molar ratio of ammonia
to phosphoric acid in a tubular reactor within 1.3 - 1.6 to
1, particularly, within 1.3 - 1.5 to 1. Ammonia, which is
reacted further with phosphoric acid, is added in a
subsequent step as will be described later in this specifi-
cation.
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A tubular reactor is similar to a short piping
in its structure and therefore, it has a very small volume.
It is thus unsuitable to employ such a tubular reactor
for adding and mixing a solid, molten liquid or aqueous
solution to and with a solution of ammonium phosphates J
ammonium sulfate or ammonium nitrate resulting from a
reaction between ammonia and the above-described acid.
Therefore, a reaction mixture ~ormed in the tubular reactor
is then introduced into a mixing tank, where it is reacted
further with ammonia in order to increase the molar ratio
of ammonia to phosphoric acid further. The water is caused
to evapo~ate from the reaction mixture owing -to its sensible
heat and reaction heat given off in the mixing tank. It is
unnecessary to add that it is also possible to heat the
mixing tank with steam and to evaporate the water if no
sufficient heat quantity is available for the evaporation
of the water from the reaction mixture. Furthermore, it is
also possible to add while stirring various kinds of
fertilizer substances in the form of a solid, molten liquid
or aqueous solution to the reaction mixture in order to
adjust the proportion of each component in ~he intended
compound fertilizer and its concentration in the mixing
tank. It may be feasible to add a solid diluent together
with such fertilizer substances or as their substituent.
The particle sizes of these solids should range from 50 -
1,000 ~m.
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The liquid content of the thus-formed slurry
ranges ~0 - 90~ by volume, and preferably, 40 - 60~ by
volume. If the liquid content does not reach 40% by volume,
it is di-fficult to achieve smooth transportation of the
slurry -from the mixing tank to the granulation apparatus
by means of a pump. On the other hand, if the water
content of the slurry exceeds 30~ by volume, it is necessary
to have more water evaporate in the granulation apparatus,
thereby leading to an increased energy demand. Such a high
water content is accompanied by another drawback in that
the water content of the granular substance to be obtained
will be high and a separate drier will be required.
Although fine solid particles are contained in
the thus-obtained high temperature slurry, these solid
particles have particle sizes within the above range and
are uniformly dispersed in the slurry, thereby making it
possible to feed the slurry to a spouted bed or fluidized
bed granulation apparatus, which will be described below,
by means of a pump. Owing to the nature of the slurry,
spray nozzles of the granulation apparatus will be protected
from clogging. It is pre-ferred to conduct the agitation of
the reaction mixture in the mixing tank at a speed of 150 -
500 r.p.m. It is generally preferred to maintain the slurry
at 80 - 130C in the mixing tank, although it varies depending
on the composition and the like of the intended compound
fertilizer. The residence time of the slurry in the mixing
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tank is preferably 20 minutes or less, and particularly,
10 minutes or less. A residence time exceeding 20 minutes
is not preferred because it tends to induce a quality
alteration to the compound fertilizer due to interactions
among the raw material fertilizer substances.
The high temperature slurry prepared in the
mixing tank is then sprayed into a granulation spacing of
a spouted bed or fluidized bed granulation apparatus by a
pump through s?ray nozzles and is allowed to stick to
priming pa.-ticles floating in the granulation spacing. As
such priming particles, may be employed excessively large
granules (after pulverization) and excessively small
granules, both of which granules are discharged from the
granulation apparatus and separated from granules of the
desired particle size range by a classifier. Any known
spouted bed granulation apparatus or fluidized bed granu-
lation apparatus may be employed in the present invention.
The embodiment of this invention will hereinafter
be described with reference to the accompanying drawing.
Raw material phosphoric acid, sulfuric acid, nitric acid
or a mixture thereof is charged into a tubular reactor 1
through a line 5 or 6. A part of the whole ammonia required
to make the molar ratio of ammonia to phosphoric acid 1.4
to 1, is supplied through a line 7 to carry out a reaction.
The reaction mixture from the tubular reactor 1 is introduced
into a mixing tank 2 by coupling an outlet nozzle of the
tubular reactor l directly to the mixing tank 2. The mixing
tank 2 is provided with a high-speed agitator 3 which may
be rotated at 150 - 500 r.p.m., whereby completing in a
short period of time -the mixing of the reaction mixture
with a solid raw material containing agronomically e-ffective
components such as N, P and/or K, or an aqueous solution or
molten liquid thereof, or a solid diluent -fed into the mixing
tank 2 via a line 8 or 9. On the other hand, the remaining
part of the whole ammonia which is excessive to the above-
mentioned ratio, is supplied into the mixing tank 2 through
a line 10, whereby achieving the desired molar ratio. While
carrying out these mixing or reaction operations, the water
is evaporated from the reaction mixture by virtue of reac~ion
heat generated in the tubular reactor 1 and/or mlxing tank 2.
The thus-evaporated water is sent together with a small
quantity of ammonia gas via a line 12 to a gas scrubber 11,
where it is washed with water, phosphoric acid, sulfuric
acid or a mixture thereof supplied through a line 2~. Water,
phosphoric acid, sulfuric acid or a mixture thereof which
has absorbed ammonia is fed to the tubular reactor l through
a line 29. The thus-washed gas is released into the
atmosphere.
The above-described solid raw material containing
the agronomically effective components includes, for example,
urea, ammonium sulfate, ammonium nitrate, ammonium phos-
phates, ammonium chloride, potassium phosphates, calcium
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superphosphate, calcined phosphate fertilizer, potassium
sulfate, potassium chloride, potassium metaphosphate, a
urea-aldehyde condensate Eertilizer, magnesium silicate,
calcium silicate, various trace elements such as Zn, Mn,
Mo, Cu, Fe and B, etc. Examples of molten liquids containing
agronomically effective components include urea, ammonium
nitrate and the like. Examples of raw material solid
diluents include gypsum, bentonite, etc. The aqueous
solution containing agronomically effective components
includes, for example, an aqueous solution containing
water-soluble substances out o-f the above-described -fertilizer
substances.
A predetermined amount of priming particles is
supplied through a line 17 into a spouted bed granulation
apparatus 15. An upwardly-directed spouted bed o-f the
priming particles is formed within the granulation apparatus
15 by a flow o-f the heated air supplied through a Iine 16.
At the same time, the high temperature slurry is supplied
-from the mixing tank 2 through a pump ~ and line 13 to the
granulation apparatus 15 and sprayed upwardly through slurry
spray nozzles 1~ provided in the spouting bed granulation
apparatus 15 at a lower location thereof, thereby causing
the thus-sprayed liquid droplets to stick to the -floating
priming particles and to become larger while drying the
thus-enlarged granules with the air flow.
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The water evaporated from the high temperature
slurry and the air flow generated in the granulation
apparatus 15 and containing fine particles are sent through
a line 1~ to a separator 19, where the fine particles are
removed, and then released into the atmosphere. The fine
particles caugh-t by the separator 19 are conveyed to a
storage tank 22,
After enlargement in the granulation apparatus
15, the resulting granules (having a wide variety o-f
particle sizes -from large to small) are fed through a line
20 to a classifier 21, where they are classified into three
groups, i.e., those having diameters within -the desired
particle size range and to be finished to a final prodùct,
those having particle sizes larger than the upper limit of
the desired particle size range and those having par-ticle
sizes smaller than the lower limit of the desired particle
size range. Excessively large granules are fed to a
pulverizer 25 while excessively small particles are tempo-
rarily stored in the storage tank 22. The final product
is cooled down in a cooler 23 and sent outside the system
through a line 24. The excessively large particles are
pulverized by the pulverizer 25 and then recycled to the
classifier 21 through a line 26. The excessively small
particles, which have been temporarily stored in the
storage tank 22, are recycled via a line 17 to the granu-
lation apparatus 15. In order to control the particle size
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distribution at the outlet o:E the granulation apparatus
15, the amount of excessively small particles to be recycled
is controlled by a feeder 27.
According to this invention, a granular compound
fertilizer containing at least two components selected :Erom
N, P and K can be effectively manufactured from a reaction
mixture which has been obtained by reacting phosphoric
acid, sulfuric acid, nitric acid or a mixture thereof with
ammonia in a tubular reactor. Since a slurry prepared from
the above-mentioned reaction mixture is subjected to
granulation in a spouted bed or Eluidized bed, it is
possible to lower the load of the drying step in the granu-
lation process. In addition~ the evaporation of water` from
the reaction mixture can be effected in the course of the
preparation of the slurry by virtue of the reaction ~eat
between ammonia and the acid. Since the reaction mixture
is supplied in the slurry form to the granulation step, it
is -feasible to add, upon preparation of the slurry, any
desired fertilizer substance containing desired agronomically
effective components in desired concentrations or a solid
diluent to the reaction mixture so as to adjust the compo-
sition of the intended final product. Accordingly, the
process of this invention can be applied to manu~acture
granular compound -fertilizers of any composition. Further-
more, the deposition of ammonium monohydrogen phosphate and
clogging in the tubular reactor are avoided in the present
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process, since ammonia is reacted with phosphoric acid in
two steps, that is, in the tubular reactor and the mixing
tank.
The invention will be described further in the
following examples.
Example 1:
A manufacture test of a granular compound
fertilizer containing N and P in amounts of 18% by weight
and 46% by weight (in terms of P2O5), respectively, and
having diameters in a range of from 1 to 3.5 mm was carried
out as follows in accordance with the process illustrated
in the accompanying drawing: The test was conducted using
a tubular reactor of 50 mm in inner diameter and Z,000 mm
in length and a mixing tank with an effective volume of
50 Q and equipped with an agitator rotatable at 200 r.p.m.
I'he spouted- bed granulation apparatus was generally of a
cylindrical shape and was formed at a lower part thereof
into an inverted truncated conical shape. Its diameter
was 1,000 mm at the cylindrical part and its e-ffective
volume was 250 Q.
Into the tubular reactor 1, were directly charged
373 kg/hour of liquid ammonia at 0C through the line 7,
800 kg/hour (in terms of P2O5) o~ 5~ wt.% phosphoric acid
at 25C via the line 5 and 99 kg/hr of 98 wt.% of sulfuric
acid at 25C through the line 6. In addition, the reactor
1 was fed with 2,247 kg/hr ~in terms of P2O5) of 32.4 wt.%
of phosphoric acid at 30C through the line 28. The latter
phosphoric acid was first used as an absorbent in the gas
scrubber 11 to recover ammonia gas accompanied with steam
which had been separated in the mixing tank 2 and then
charged into the reactor 1 via the line 29. The reaction
mixture was then introduced into the mixing tank 2, where
it was reacted with 192 kg/hr of liquid ammonia at 0C
supplied through the line lO, thereby providing 2,985 kg/hr
of slurry at 110C which contained 15% by weight of water
and 46% by weight of solid components and consisting
principally of diammonium hydrogenphosphate and ammonium
sulfate. The resultant slurry was transported through the
slurry pump 4 and line 13 and sprayed through the spray
nozzles 14 disposed in the spouted bed granulation apparatus
15 which were operated under the following operation condi-
tions:
Amount of air blown in the 8,300 Nm3/hr
granulation apparatus
Temperature of air blown into O
the granulation apparatus 170 C
Temperature in the granulation 70 - 75C
apparatus
Amount of priming particles 2,710 - 2,760 kg/hr
Enlarged granules of a compound fertilizer were
obtained at the outlet of the line 20 at a rate of 5,180
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5,240 kg/hr. The water content in the enlarged granules
was 1.5 - 2~5% by weight.
The thus-granulated compound fertilizer was
classified at the classifier 21 into those having diameters
within the desired particle size range for the -final product,
those having excessively large particle sizes and those
having excessively small particle sizes which amounted on
average to 48.0%, 5.3% and 46.7%, respectively. Ihe final
product was obtained at a rate of 2,460 - 2,510 kg/hr. The
granular -final product was cooled in the cooler 23 to 45C,
which is a temperature suitable for storage, and discharged
out of the system through the line 24.
Example 2:
A manufacture test of a granular compound
fertilizer containing N, P and K in amounts of 19% by
weight, 19% by weight ~in terms of P2O5) and 19% by weight
(in terms of K2O), respectively, and having diameters in
a range of from 1 to 4 mm was carried out as follows in
accordance with the same process as that employed in Example
Into the tubular reactor 1 in the same manner as
that followed in Example 1 were supplied 259 kg/hr of liquid
ammonia at 0C through the line 7, 1,253 kg/hr (in terms of
P2O5) of 54 wt.% of phosphoric acid at Z5C via the line 5,
65 kg/hr of 98 wt.% of sulfuric acid at 25C through -the
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line 6, and 583 kg/hr ~in terms of P2O5) of 21.7 wt.% of
phosphoric acid at 30C via the line 28, The resulting
reaction mixture was introduced into the mixing tank 2 and
combined with 1,267 kg/hr of potassium chloride having
particle sizes of 1,000 ~m or smaller and maintained at
room temperature and 1,196 kg/hr of a 96 wt.% aqueous
solution of urea supplied at 110C through the line 9,
thereby obtaining a slurry having a temperature of 105C
and containing 6% by weight of water and 30.5% by weight
of solid components at a rate of 4,161 kg/hr. The thus-
obtained slurry was conveyed through the slurry pump 4
and line 3 and sprayed through the spray nozzles 14 of ~he
spouted bed granulation apparatus 15 operated under the
following operation conditions:
e Amount of air blown into the 8 500 Nm3/hr
granulation apparatus
Temperature of air blown into 50C
the granulation appaTatus
Temperature in the granulation 55 - 60C
apparatus
Amount of priming particles 4,030 - ~,270 kg/hr
supplied
Enlarged granules of a compound -fertilizer were
obtained at a rate of 7,865 - 8,345 kg/hr. These granules
had a water content of 1 - 1.5% by weight.
I'he thus granulated compound fertilizer was
classified at the classifier 21 into those having diameters
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within the desired particle size range for the Einal
product, those having excessively large particle sizes and
those having excessively small particle sizes which amounted
on average to 49.6%, 1.0% and 49.4%, respectively. The
final product was obtained at a rate of 3,840 - 3,920 kg/hr.
The final product was cooled to 45C in the cooler 23 and
then discharged out of the system.
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