JPH0239478B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for drying and granulating raw materials supplied to a kiln in a method for producing potassium silicate fertilizer using fly ash as a raw material.

As is well known, fly ash is a fine powder that floats in waste gas generated from a pulverized coal combustion furnace such as a thermal power plant, is discharged together with the waste gas, and is mainly collected by an electrostatic precipitator. This fly ash is mainly composed of silicon dioxide, which is a relatively stable substance chemically, but as mentioned above, since it is a fine powder, potassium salt is added to it and it is heated in a kiln.
It is known that when fired at 600 to 1100°C, potassium reacts with silicon in the fly ash to become citric acid-soluble potassium silicate, which can be used as potassium silicate fertilizer.

When firing a mixture of fly ash and potassium salt, it is easier to handle the mixture in the form of granules of appropriate particle size than in the form of powder, and the firing efficiency is higher. Potassium silicate fertilizer is also easy to handle as a fertilizer.

Potassium hydroxide is usually used as the potassium salt, but the usual raw material used is an aqueous solution of about 48%. Therefore, when this is mixed with the fly ash, the mixture becomes a slurry with a moisture content of approximately 19%, which must be dried before it can be fed into the kiln, and at the same time, from the point mentioned above, the dried material must be turned into granules. There is a need.

By the way, in the past, an aqueous solution of potassium hydroxide was added to the fly ash, and a small amount of pulverized coal and magnesium hydroxide were added to this to form a slurry, which was then sent to a dryer and dried while being granulated. method was tried. However, slurry is extremely easy to adhere to the inner wall surface of the dryer, stirring blades, etc., and once it has adhered, it is hardened by the hot air sent into the dryer, so it cannot be granulated or dried. The drawback was that it was difficult to continue operating the machine under certain conditions.

Therefore, in JP-A No. 55-104987, the present applicant proposed two-stage drying in which a part of the potassium hydroxide aqueous solution is first mixed and dried with other powder, the remaining potassium hydroxide aqueous solution is mixed therewith, and the mixture is dried again. proposed a method. Although this proposed technique itself is effective, the drying efficiency is low because it performs two stages of drying.

On the other hand, Japanese Patent Application Laid-open No. 51-54097 discloses a technique for obtaining particulate solid calcium hypochlorite having a smooth round surface by spraying an aqueous slurry of calcium hypochlorite onto falling particles. In addition, the special public
Publication -13051 discloses that slurry is continuously sprayed into a heating furnace and heated, the liquid is evaporated and granular powder is dropped into the furnace, a particle layer is formed at the bottom of the furnace, and the continuous spraying Techniques have been shown to obtain particles by enlarging the particles in the furnace extension. However, these known techniques relate to granulation and do not solve the above-mentioned problems.

Therefore, an object of the present invention is to provide a granulation and drying method in which a dryer can be suitably operated in a granulation and drying step in a method for producing citric acid-soluble potassium silicate fertilizer using fly ash as a starting material. .

As a result of researching the conditions under which the above-mentioned slurry can be continuously dried, the inventor of the present invention made it into granules with a size of about 1 to 5 mmψ, and set the average moisture content of the granules to about 6 to 9%. It has been found that there is no problem in continuous operation of the dryer if the amount is reduced to . This average moisture content is 6~
It has been found that a granular material having a weight ratio of about 9% can be obtained by coating a pre-dried granular raw material with the slurry in an amount of about 1/2 to 1/3 by weight. The granular raw material for coating the slurry is a dried granular product that is a raw material for citric acid-soluble fertilizer produced in advance and is fed back during the process.

If the average moisture content is 9% (by weight) or more, the adhesiveness increases and it tends to clump, and over time the clumps turn into stone and become hard, making it impossible to operate the dryer. Moreover, if it is less than 6% (weight), the amount of feedback increases and production efficiency decreases.

Embodiments of the present invention will be described below based on the drawings.

In the following example, the amount of product per hour is 3000 kg.

Reference numerals 1 to 4 in the figure are storage tanks in which potassium hydroxide aqueous solution (48% aqueous solution) fly ash, pulverized coal, and magnesium hydroxide are stored, respectively. Reference numeral 5 is a mixing tank, and this mixing tank 5 contains 1774 kg of potassium hydroxide (48% aqueous solution).
hr fly ash (moisture 0.4%) 2408Kg/hr, pulverized carbon (moisture 4%) 480Kg/hr and magnesium hydroxide (moisture 3%) 144Kg/hr are charged and mixed. That is, a good weight ratio is 1.36 parts of fly ash, 0.27 parts of pulverized coal, and 0.08 parts of magnesium hydroxide to 1 part potassium hydroxide. Since pulverized coal and magnesium hydroxide do not cause a chemical reaction, it is more convenient to mix a predetermined amount together in advance.
This mixture becomes a slurry of 4776Kg/hr (moisture 19%), so this slurry is then sent to the supply tank 6, and this slurry is further pumped through the metering pump 7 to 4776Kg/hr (moisture 19%).
It is pumped out at a speed of hr and supplied to a mixer 8, where it is dispersed over the nuclide to be fed back as described below. In this case, if there is a fluctuation in the amount of feedback from the line _L1 , it goes without saying that the amount of feed back from the pump 7 can be controlled by detecting the amount of feedback. The reason why the mixing tank 5 is provided in front of the supply tank 6 is to continuously perform processes such as granulation drying and calcination, which will be described later, and the mixing tank 5 also serves as a reserve tank for the supply tank 6. There is. The supply tank 6 is equipped with a measuring device 9 to detect the amount of slurry in the tank 6, and when this slurry decreases to a certain amount, it is transferred from the mixing tank 5 and new material is put into the mixing tank 5. It is designed to perform mixing.

If the slurry is left in the mixing tank 5 and the supply tank 6 for too long, it will solidify, so it is preferable to keep the slurry in the mixing tank 5 and the supply tank 6 for 10 to 20 minutes and to constantly renew it with new slurry. The mixer 8 sprays and coats the surface of the powdery raw material, which has been dried to a moisture content of 1% in advance and is mostly granulated into granules with a grain size of 1 to 4 mmψ, with the slurry supplied from the supply tank 6. The model is not particularly limited as long as it is a new granular material and has such a function. For example, as shown in the figure, a horizontal trough 10 may be provided with a rotating shaft 11 therein, and a number of stirring hands 12 may be protruded from this to rotate the rotating shaft 11.

It has been experimentally confirmed that the higher the temperature during this mixing operation, the faster the solidification rate of the slurry material becomes. FIG. 2 shows viscosity (centipoise) on the vertical axis, time on the horizontal axis, and temperature as a parameter. As can be seen from this figure, either the material to be fed back is cooled or the casing wall of the mixer 8 is cooled to bring the temperature of the material inside the mixer to about 60°C.
By keeping the temperature below ℃, the material does not petrify or solidify even after long-term continuous operation, making it very effective.

In this state, ₉₅₅₂
Kg/hr (moisture 1%) of powdery raw material is introduced, and the raw material is pumped from the pump 7 while stirring the raw material.
Pour 4776Kg/hr of slurry and continue stirring. Then, the slurry coats the surface of the granular raw material from line _L1 , and the particles adhere to each other to form a lump of about 10 to 30 mmψ. At this time, the fed-back powder raw material becomes a nuclide and adheres to the slurry, and flows smoothly on the inner wall of the dryer, preventing the slurry from adhering to the inner wall of the dryer and the stirring blades, and also prevents the slurry from adhering to the inner wall of the dryer and the stirring blades. grow into things. The granular raw material has been dried in advance, and since it is a bolus, some of the water contained in the slurry penetrates into the granular raw material, reducing the average moisture content to about 7%, making the particles suitable for granulation and drying. It will become.

Next, this lump (14328Kg/hr) is fed to a feeding device.
Supplied to the dryer 13 via F ₁ , and further supplied with 400
Dry by blowing hot air at a temperature of about 500°C to 500°C. This dryer 13 is not particularly limited as long as it dries the input lumps without crushing them, and may be any suitable drying device that applies mechanical force to disperse and scatter particles, such as rotation, rotary aeration, or a fluidized bed. Can be used. At this time, the degree of exhaust gas from the dryer 13 is preferably 170° C. or higher, so that the granules do not solidify.
Moreover, the hot air sent into this is the hot air (800° C. to 1000° C.) discharged from the firing furnace 14, which will be described later.
The auxiliary furnace 15 is used at the start of operation or when the hot air temperature is insufficient. Dryer 13 removes moisture 1
As a result, the granules (13158Kg/hr) are transported together with 2768Kg of crushed powder from the crusher 17 via the transfer device C (15926Kg/hr) to the sieve 16. 9688 to
Kg/hr is supplied, and the other particulate matter (6238 Kg) is led to the feedback tank 18 without being sieved.
The granules introduced into the sieve machine 16 are sieved and have a grain size of 4.
More than mmψ (2768Kg/hr) and particle size 1-4mm
It is sieved into ψ (3875Kg/hr) and 1mmψ or less (3015Kg).

Particles having a size of 4 mm ψ or more are sent to a crusher 17 and pulverized, and then mixed with the dry granules from the dryer 13 and transported. Particle size of 1mmψ or less (3015Kg/
hr) is put into the feedback tank 18. On the other hand, the exhaust gas discharged from the dryer 13 is sent to the cyclone dust collector 19 and back filter 21 to separate and collect fine particles floating there.The exhaust gas is sent to the exhaust gas treatment equipment and fine particles (234Kg/
hr) is put into the feedback tank 18. The granules put into the feedback tank 18 are sent to the mixing tank 8 as raw granules. Particles sieved by the sieving machine 16 with a particle size of 1 to 4 mmφ are line L ₂
Then, it is sent to the firing furnace 14 via the supply device F ₂ and fired. A bypass to a feedback tank may be provided between the sieving machine 16 and the firing furnace 14 as required.

As this kiln 14, a known kiln can be used, and since the grain size of the granules is arranged in the range of 1 to 4 mm, it is appropriate to use a fluidized bed kiln. 3875 kg/hr of granular material is charged into this firing furnace 14 and fired at a temperature in the range of 600 to 1100°C.
At the start of operation, the temperature rises to a predetermined temperature in the starter furnace 20, and from then on the coal in the components, ie, pulverized coal, becomes the fuel.
Under these temperature conditions, the potassium and silicon in the particles chemically react and turn into potassium silicate, which is soluble in citric acid.At the same time, the coal used as a fuel becomes _CO2 and evaporates from the particles, making the particles extremely porous. As a result, it becomes suitable as fertilizer.
The fired granules (3000 kg/hr) are taken out as a product, and the exhaust gas is used as a drying heat source for the dryer 13. Furthermore, part of this exhaust gas can also be used for drying pulverized coal through heat exchange.

As described above, according to the present invention, a pre-prepared dried granular product is used as a nuclide, and a mixed slurry of potassium hydroxide aqueous solution, fly ash, fine granular coal, and magnesium hydroxide is sprinkled on it, and dried and granulated. It is extremely easy to control the content, and this type of mixer maintains a moisture content of 6 to 9%, which prevents the granules from solidifying or turning into stone. This has the effect that it does not adhere to the surface of the substrate and allows continuous operation.

[Brief explanation of drawings]

FIG. 1 is a flow sheet diagram showing an embodiment of the present invention, and FIG. 2 is a graph showing the relationship between viscosity and time in a mixer using temperature as a parameter. 1, 2, 3, 4...Storage tank, 5...Mixing tank, 8
... mixer, 10 ... trough, 13 ... dryer,
_L1 ...Feedback line, 18...Feedback tank, 16...Sieving machine, 14...Calcining furnace.

Claims (1)

[Claims] 1. A method for producing a potassium silicate fertilizer in which an aqueous potassium hydroxide solution, fly ash, pulverized coal, and magnesium hydroxide are measured and mixed in a predetermined ratio to form a granular dry product, which is then calcined to produce a potassium silicate fertilizer. In the dry granulation method, the granulated dried product is fed back at a weight ratio of 2 to 3 to 1 part of the mixed slurry of potassium hydroxide aqueous solution, fly ash, pulverized coal, and magnesium hydroxide, and the mixed slurry is coated. A dry granulation method in a method for producing potassium silicate fertilizer that is used as a nuclide for dry granulation. 2. In a rotary dryer in which the supply amount of the mixed slurry is controlled by a slurry pump based on the feedback amount of the nuclide, and the mixed slurry is sprayed onto the nuclide from multiple locations,
It is dried with hot air at about ℃ and has a moisture content of about 1%.
A dry granulation method in the method for producing potassium silicate fertilizer according to claim 1, wherein the dried granules have a diameter of 4 mm. 3. In the step of dispersing slurry on the surface of the feedback particles, the feedback particles are cooled in advance with air or water, or the mixer is cooled with a water-cooled jacket, etc. to maintain the material temperature inside the mixer at 60°C or less during mixing. A dry granulation method in the method for producing a potassium silicate fertilizer according to item 1.