Note: Descriptions are shown in the official language in which they were submitted.
llZS53,4
The present invention relates to a process for pro-
ducing citric acid soluble potassium silicate fertilizer in a
high yield and with a high heat efficiency, and to an apparatus
for use in said process.
As is well known, a citric acid soluble potassium ferti-
lizer can be solubilized by the citric acid excreted by the roots
of plants, but only a certain amount of the fertilizer is solu-
bilized and absorbed into the plant. Unlike the usual water-
soluble potassium fertilizers, the citric acid soluble potassium
fertilizer is resistant to rain water. Further, it neutralizes
acid in soil caused by the citric acid excreted by plant roots.
Although such a citric acid soluble potassium fertilizer is
suitable for Japanese agriculture where the climate is relatively
warm and rainy and the acidification of soil is already at an
advanced stage due to the use of chemical fertilizers, such as
ammonium sulfate, its practical use is only rare. This is
mainly attributableto the fact that if a citric acid soluble
potassium silicate fertilizer is produced by the conventional
process from fly ash as a silicic acid source, a continuous
operation is quite difficult to conduct because of the high
temperature necessary for calcination, which inevitably results
in high cost as compared with other fertilizers. In addition,
such fertilizers produced using known techniques lack uniform
product quality.
Earnest studies have been conducted with the aim of
overcoming the above-mentioned difficulties encountered with
citric acid soluble potassium fertilizers. As a result, it has
been discovered that an inexpensive potassium fertilizer of high
quality can be produced with a high efficiency by utilizing fly
ash, such as that formed in power stations operated with coal,
together with inexpensive crude caustic potash .
Fly ash is contained in waste gases formed in boilers
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and furnaces operated with pulverized coa], such as those in
thermal power stations. The fly ash contains a large quantity
of silicon. If the fly ash is admixed with a potassium source,
such as caustic potash (KOH) or potassium carbonate and calcined
at a temperature of about 600 to l,100C, the potassium reacts
with the silicon present in fly ash to form a citric acid soluble
potassium silicate. The chemical reactions that occur can be
expressed by the following chemical equations:
If caustic potash is used as potassium source,
2KOH + SiO2 ~ K2O.SiO2 + H2O
(water-soluble potassium)
2KOH + nSiO2 - ~ K2O.nSiO2 n = 2-6
(citric acid soluble potassium
silicate),
If potassium carbonate is used as potassium source,
2 3 io2 ~ K2O.Sio2 + CO2
(water-soluble potassium)
K2CO3 + nSiO2 > K2O.nSiO2 n = 2-6
(citric acid soluble potassium
silicate)
As is well known, fly ash has a size of micron order,
so that if one wishes to calcine it, such as by means of a fluid
calcining furnace, it scatters in the hot air used as the calcina-
tion medium, and the calcination cannot be carried out.
In view of the above, the problems have been earnestly
studied, and it has been discovered that calcination can be
carried out with high efficiency if the starting materials, such
as fly ash, potassium source and other required materials are
kneaded with a binder, such as caustic potash solution and then t
the kneaded mixture is formed into granules having a size of
about 3 to about 5 mm. The granules can then be calcined to
form a product that is usually cooled, pulverized, further granu-
lated and dried, after which it is shipped as a final product.
1~25~3~
More particularly, the present invention provides a
process for producing citric acid so:Luble potassium silicate fre-
tilizer, which process comprises:
~ a) forming a mixture comprising a solution of 40 to
50% caustic potash as a binder in an amount of 20 to 25 parts by
weight based on the mixture, potassium carbonate in an amount of
9 to 12 parts by weight based on the mixture, fly ash in an amount
of 50 to 70 parts by weight based on the mixture and pulverized
coal in an amount of 5 to 30 parts by weight based on the mixture;
tb) kneading the mixture by means of a continuous kneader;
(c) forming the resulting kneaded mixture into granules
by means of an extruder;
(d) drying said granules to a state of substantially
absolute dryness by means of a fluidized dryer; and
(e) calcining the resulting dried granules at a tempera-
ture fron 900C to 1100C, by means of a fluidized calcining fur-
nace in order to chemically react the potassium with silicon pre-
sent in the fly ash and thereby form a citric acid soluble potas-
sium silicate.
Additionally, this invention provides an apparatus for
producing a citric acid soluble potassium silicate fertilizer ac-
cording to the processes of this invention, which apparatuscomprises:
(a) a plurality of continuous quantitative feeders for
supplying the binder, potassium source, fly ash and pulverized
coal for formlng the mixture;
(b) a continuous kneader for contlnuously kneading the
mixture;
(c) an extruder for forming the resulting kneaded mixture
into granules;
(d) a fluidized dryer for drying the granules to a state
of substantlally absolute dryness;
(e) a fluidized calcining furnace for calcining dried
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~ranules in o~der to chemically react pot~ssium with silicon
present in the ~ly ash and the~eby ~or~ ~ citXic acid soluble
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potassium silicate; and
(f) a cooling device for cooling the resulting calcined
product.
In practicing this invention, the pulverized coal gen-
erates heat throughout the period during which the kneaded and
granulated product is calcined in the fluid calcining furnace,
and thereby acts so as to maintain the granular product at a
high temperature over a long period of time.
In another embodiment of this invention, the calcined
product is cooled by means of a high speed cooling device, and
then pulverized into powder by means of a pulverizer, after which
it is transferred to a product storage tank.
When the calcined and pulverized product is to be
shipped in the form of a powdery product, it can be taken out of
the product storage tank by means of a screw feeder and trans-
ported to a package station.
When the calcined and pulverized product is to be ship-
ped in a granular form, it can be fed by means of a screw feeder
into a granulator where it can be kneaded together with an added
water-soluble binder, granulated and dried, after which it can
be transported to a package station.
In order to prepare a calcined product in a granular
form, the apparatus of the invention can additionally be equipped
with a pulverizer for pulverizing the calcined and cooled product,
a storage tank for storing the pulverized product, a granulator
for kneading and granulating the product carried out of the
storage tank and a second fluid dryer for drying the granulated
product.
Preferably waste gas that is discharged from the first
fluid dryer is introduced into a dry dust chamber to remove
floating dust, and then the removed floating dust is returned to
the continuous kneader.
~lZ5531~
Preferably, waste gas that is discharged from the fluid
calcining furnace is introduced into a heat exchanyer, and the
waste heat is transmitted to low temperature air from a secondary
line. The air heated thereby can then be supplied to the first
fluid dryer for use as a drying medium.
Further, it is preferable to supply waste gas discharged
from the cooler directly into a second fluid dryer for use as a
drying medium.
It is also preferable to introduce waste gas from the
second fluid dryer into a dry dust chamber where floating dust
present therein is removed. The removed floating dust can then
be returned to a product storage tank.
In another embodiment of this invention, there is pro-
vided a hot air generating device where natural gas or a fuel oil
is burned in order to supply a calcining medium of high tempera-
ture to the fluidized calcining furnace used for the calcination
of granulated product. Preferably, waste gas discharged from the
fluidized calcining furnace is returned to said hot air generat-
ing device via a heat exchanger.
It is also preferable that waste heat is waste gas dis-
charged from the fluid calcining furnace be transmitted to the
low temperature air via the first and second heat exchanger, and
the air heated thereby then supplied to the second dryer as a
drying medium.
The present invention will be further illustrated by
way of the accompanying drawing in which:
Figure 1 is a flow sheet for the production of citric
acid soluble silicate fertil'zer according to one embodiment of
the present invention.
As shown in the left upper part of the Figure, there are
provided quantitative feeders la to lf for continuously measuring
and feeding materials. The first continuous quantitative feeder
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la continuously measures 48% caustic potash (KO~I) and feeds it
into continuous kneader 2 via line La-1. Similarly, second feeder
lb handles potassium carbonate (K2CO3), third feeder lc handles
magnesium hydroxide [Ma(OH)2], fourth feeder ld handles pulverized
coal and sixth feeder lf handles fly ash. The fifth feeder le is
a reserve. It should be noted that the above-mentioned magnesium
hydroxide is not indispensable in the invention but when present
is preset in an amount of 3 to 4 parts by weight based on the
mixture.
The materials supplied by the continuous quantitative
feeders la-lf are kneaded in continuous kneader 2 to give a slime,
which passes line La-2 and reaches extruder 3. The slimy material
is formed by extruder 3 into granules of about 3 to about 5 mm size,
and the granules are then supplied to fluid dryer 4 via line La-3.
Fluid dryer 4 is a fluidized bed type of dryer equipped
with a porous plate. One blows hot air, recovered in heat exchan-
ger 18 mentioned later, via line Lb-4, whereby granules on the
porous plate are fluidized and dried to a state of absolute dry-
ness where no water is contained at all. The drying temperature
is in the range of about 200 to about 300C, and the drying time
is about 10 minutes. This is for the reason that if drying tem-
perature is higher than about 300C, there occur cracks in the
granule and if it is lower than about 200C an absolute dryness
is quite difficult to reach.
Floating dust leaving fluid dryer 4 passes lines Lb-5
and Lc-2 and reaches dry dust chamber 17 where it is recovered.
Recovered material is returned to continuous kneader 2 via line
Ld-l. A part of the hot air leaving fluid dryer 4isrecycled to
fluiddryer 4 via linesLb-5 andLb-6 with the aid of recycling fan 19.
The granular product, which has been dried to the state
of absolute dryness in fluid dryer 4, passes line La-4 and is
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supplied to fluid calcininy furllace 6 by screw fecder 5. Fluid
calcining furnace 6 is a fluidized bed type equipped with a
porous plate. The granular product on the porous plate is cal-
cined and brought into a fluidized state by the action of hot
air, which has been introduced from hot air generator 16 via
line Lb-l. Silicon present in fly ash reacts with potassium to
form a citric acid soluble potassium silicate. The calcining
temperature in fluid calcining furnace 6 is in the range of about
900 to about l,100~C and the time period of calcination is about
15 minutes. This is for the reason that if calcining temperature
is lower than about 900C, no reaction takes place. If it is
higher than about l,100C, the granules soften to form plate-like
matter.
Hot air generator 16 has an adjacent liquefied gas tank
14 from which liquefied gas is fed into hot air generator 16 via
line Le by pump 15. The higher temperature waste gas leaving
fluid calcining furnace 6 passes line Lb-2 and reaches heat ex-
changer 18 where it releases its heat by means of heat exchange,
after which it passes line Lb-3 and reaches hot air generator 16
again. On the other hand, air supplied from blower 20 into heat
exchanger 18 via line Lc-l and heated there passes line Lb-4
and reaches fluid dryer 4.
The product, which has completely been calcined in fluid
calcining furnace 6, passes line La-5 and is sent to high speed
cooling device 8 by screw feeder 7. High speed cooling device 8
is a fluidized bed type of cooler equipped with a porous plate.
Cold air supplied by cooling fan 21 via line Lb~7 fluidizes the
calcined product and rapidly cools it. Hot air leaving the high
speed cooling device 8 passes line Lb-8 and reaches second fluid
dryer 13 mentioned later where it is used as a drying medium for
fluid dryer 13. The residence time of calcined product in the
high speed cooling device 8 is about 10 minutes.
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Product cooled in hiyh speed cooling device 8 passes
line La-6 and reaches pulverizer 9 where it is pulverized into
powder, after which it is transportecl to product storage tank 10
via line La-7. Floating dust leaving product storage tank 10
passes line Lc~3 and is recovered, after which it is returned
to pulverizer 9 via Lc-4 by transporting fan 22. The product in
storage tank 10 is shipped as a powdery product A-l via screw
feeder 11 and line La-8. Otherwise, the product is sent to granu-
lator 12 where it is kneaded together with a binder, i.e., water
or other water-soluble binder fed from binder tank 23 via line
Lf and granulated, after which is passes line La-9, is dried in
second fluid dryer 13, passes line La-10 and is then shipped as
a granular product A-2. Floating dust leaving second fluid dryer
13 passes line Lc-5, is recovered in dry dust chamber 24, then
passes line Ld-2 and is finally recovered in line La-7.
Waste gas leaving dry dust chamber 17 is driven by waste
gas gan 25 and passes lines Lc-6 and Lc-8 to be released into
the atmosphere from chimney 27, while waste gas leaving dry dust
chamber 24 is driven by waste gas fan 26 and passes lines Lc-7
and Lc-9 to be released into the atmosphere via chimney 27.
A concrete example of the above-mentioned process is
described below.
Starting materials were measured in continuous quanti-
tative feeders la-lf in the following proportions:
0.88 T/H of 45% caustic potash solution as a binder,
0.436 T/H of potassium carbonate,
0.136 T/H of magnesium hydroxide,
0.4 T/H of pulverized coal, and
2.148 T/H of fly ash.
The materials were sent to continuous kneader 2 and kneaded
therein. After kneading, the slimy starting mixture was supplied
to extruder 3 where it was granulated into cylindrical granules
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having a diameter of 3 mm and a length of 5 mm.
Then, the granules were sent to fluid dryer 4 where
they were dried at 250C for 10 minutes until they reached
absolute dryness. Subsequently, the granules were sent to
fluid calcining furnace 6 where they were calcined at 1,000C
for 15 minutes. After calcination, the product was sent to high
speed cooler 8 where it was cooled with cold air for 15 minutes.
