JPS5913448B2 - Method for producing bulky calcium sulfate dihydrate needle crystals and apparatus used in the method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing bulky calcium sulfate gonate (hereinafter simply referred to as trihydrate) needle crystals from sulfur oxides in exhaust gas, and an apparatus used in the method. be.

Acicular crystals of α-type calcium sulfate hemihydrate (hereinafter simply referred to as hemihydrate) have recently been in the spotlight as gypsum whiskers, and various manufacturing methods have become known, and future applications are expected.

However, the α-type hemihydrate needle crystals have a high solubility in water and are unstable at low temperatures, and are easily hydrated to form trihydrate, thus making it difficult to produce α-type hemihydrate needle crystal fibers. In this method, the α-type hemihydrate salt needle crystals formed must be rapidly filtered or separated while hot, washed, and immediately dried, which caused many difficult problems in process control.

Conventional calcium sulfate dihydrate (hereinafter simply referred to as industrial water salt)
are short and small, have poor drainage properties, and are difficult to mechanically entangle, so they have rarely been used as raw materials for molded products.

Therefore, even though the above-mentioned drawbacks existed, α-type hemihydrate had to be used as a raw material for molded products.

However, the present inventors have discovered that bulky dihydrate needle crystals can be obtained by curing α-type hemihydrate under certain conditions, and have completed the present invention.

Such bulky dihydrate needle crystals are obtained by immersing α-type hemihydrate salt in warm water under certain conditions without drying it, and are made by papermaking.

The molding elements form a close mechanical intertwining with each other and can provide molded products with extremely high mechanical strength, making them excellent raw materials for molded products.

However, the method for producing bulky dihydrate acicular crystals according to the present invention includes step 1 of producing calcium sulfite in flue gas desulfurization using the lime-gypsum method: the slurry containing calcium sulfite is used as it is or as desired, Step 2 of adding a crystallizing agent and a metal salt and adjusting the pH to acidic; Step 3 of oxidizing the pH-adjusted treated solution under heat and pressure to convert calcium sulfite into α-type calcium sulfate hemihydrate; and Step 3 of the oxidized solution. Step 4 of obtaining bulky acicular crystals of calcium sulfate dihydrate by curing at a temperature range of 30 to 80 degrees Celsius and performing water utilization of α-type calcium sulfate hemihydrate. The method is carried out in an apparatus system in which an absorption tank for carrying out Step 1, a pH adjusting tank for carrying out Step 2, an oxidation reactor for carrying out Step 3, and a curing tank for carrying out Step 4 are connected in series.

A detailed explanation will be given below together with an apparatus for implementing the present invention shown in FIG.

In step 1, the combustion gas containing sulfur oxides from the boiler is passed through a cooling tower to lower the exhaust gas temperature to about 60°C, and then the exhaust gas is passed into an absorption tank 1 containing a solution or slurry of slaked lime or calcium carbonate. It is brought into contact with slaked lime or calcium carbonate through the air blowing pipe 1a to absorb sulfur oxides in the exhaust gas.

In this step, the sulfur oxide is absorbed by slaked lime or calcium carbonate to become calcium sulfite, and a calcium sulfite slurry is produced in the absorption tank.

After a certain period of time has elapsed, the calcium sulfite slurry is taken out from the outlet 1b of the absorption tank, and slaked lime or carbonate slurry is introduced from the raw material tank through the absorption tank input port 1c as a raw material for the next reaction.

In step 2, the calcium sulfite slurry produced and discharged in the absorption tank of step 1 is transferred to pH adjustment tank 2, and the slurry is made acidic by adding sulfuric acid or the like from acid tank 2a without stirring. Adjust the pH accordingly.

The pH value is preferably pH 3 to 4, but is not limited to this.

Furthermore, if desired, in order to shorten the time required for the subsequent oxidation reaction, a metal salt as an oxidation promoter and/or a crystal modifier as a gypsum crystallization promoter may be added in an amount of 0.01 to 1% by weight.
(hereinafter simply referred to as "person in charge").

Examples of metal salts as oxidation promoters include soluble inorganic acid salts such as ferric sulfate and nickel sulfate.

In addition, as crystal modifiers, sodium citrate, ammonium citrate, sodium fumarate, sodium tartrate,
Organic acid salts such as sodium succinate and aluminum sulfate, aluminum chloride.

Examples include inorganic acid salts such as alum.

These examples are not intended to limit the invention.

In step 3, the calcium sulfite slurry treatment liquid whose pH has been adjusted in the pH adjustment tank of step 2 is sent to the oxidation reactor 3, and is catalytically oxidized under heating and pressure while introducing oxygen-containing gas or air from the aeration pipe 3a. .

The oxidation conditions are such that the slurry is heated at a temperature of 120 to 150°C, preferably 120 to 130°C, and under a pressure of 2 kg/i or more, and calcium sulfite in the slurry is oxidized to form needle-like crystals of α-type hemihydrate.

In step 4, the acicular crystal slurry of α-type hemihydrate produced by the air catalytic oxidation in the oxidation reactor in step 3 is directly sent to the curing tank 4.

In the curing tank 4, the acicular crystal slurry of α-type hemihydrate salt is
The acicular crystals of α-type hemihydrate are kept in a temperature range of 30 to 80°C, and as they undergo a hydration reaction, they grow while maintaining their acicular form to become even bulkier acicular crystals of industrial water salt. Become.

Desirable curing conditions at this time are to maintain the slurry of the α-type hemihydrate salt needle crystals at 30 to 80°C, more preferably at 35 to 75°C, and the temperature treatment is preferably carried out for 30 minutes or more, and more preferably for 1 to 30 minutes. The heating process should be continued for a period of time or longer, and it is desirable to perform slow stirring during the heating process.

Note that the amount of slurry mixed in the curing tank 4 is preferably about 20% or less of needle-like crystals of α-type hemihydrate based on water.

When the slurry is cured at a temperature of 30°C or lower, the α-type hemihydrate salt needle crystals are converted into a short, thick plate-like or columnar form, and when the slurry is cured at a temperature of 80°C or higher, it becomes α-type hemihydrate. Salt needles are converted into fine needles.

Finally, the slurry is filtered with suction and dried to obtain bulky trihydrate needle crystals.

In the present invention, the α-type hemihydrate slurry produced in step 3 is continuously subjected to water utilization reaction and crystal growth. Therefore, the water in the system is saturated with calcium sulfate, and the α-type hemihydrate slurry is saturated with calcium sulfate. Since the shaped crystals do not elute into water any more, it is possible to prevent the crystals from becoming thinner due to crystal elution, and in the above curing temperature range, the crystals grow while maintaining their needle-like morphology and become extremely bulky. Acicular crystals of high trihydrate salt can be obtained quickly.

The reason for this crystal growth is that the calcium sulfite slurry changes from the α-type hemihydrate needle crystals through the above process to trihydrate needle crystals while maintaining the needle shape, and then dissolves in water. It is conceivable that calcium sulfate, which is present in the water, precipitates as a trihydrate using the needle-shaped crystals as nuclei.

Such needle-like crystals are therefore considerably bulkier and longer than the needle-like crystals of the alpha hemihydrate salt.

Since the trihydrate obtained by the method of the present invention is a bulky acicular crystal with a major axis of 150 to 1000 μm and a minor axis of about 3 to 20 μm, it is difficult to form strong mutually in products such as sheets and plates. A product with high structural strength is obtained by forming entanglements, and in the case of paper-making, the paper product becomes coarse, so it has extremely good freeness and a high yield.

Furthermore, trihydrate has a low solubility in water and does not incorporate any more water into its crystals, so it has excellent stability.

Furthermore, since trihydrate contains a large amount of crystal water, even at high temperatures, the latent heat of evaporation of the crystal water cools the surrounding atmosphere until it completely loses the crystal water, making it extremely fireproof. It is something.

The present trihydrate needle crystals are thus formed into sheets, plates, etc., and are extremely useful as building materials, fillers for plastics, and various other uses.

Example 1 5 kg of calcium sulfite obtained by passing combustion gas through calcium carbonate slurry was added to 457 water to obtain calcium sulfite slurry, and an appropriate amount of sulfuric acid was added to this to adjust the pH to 3.
In an autoclave at a temperature of 130℃ and a pressure of 2.5K.
Pressurize at g/crix (gauge pressure) to reduce air oxidation to 1
．． I went for 5 hours.

Further, the slurry is taken out from the autoclave and cooled while being gently stirred.

At this time, the cooling rate is adjusted so that the temperature range of 60 to 50°C is passed in 1.5 hours.

After that, it is filtered and dried, with a long axis of 180 to 900μ and a short axis of 5.
Bulky trihydrate needles of ~25μ are obtained.

Example 2 In a desulfurization device using the lime-gypsum method in the same manner as in Example 1, the aqueous solution containing calcium sulfite produced was adjusted to 8% as calcium sulfite, and an appropriate amount of sulfuric acid was added to the solution.
At the same time as H4, add 0.2% ferric sulfate, fill in an autoclave, and heat at 125°C 120kg/Cll1
Heat and pressurize to (gauge pressure) and stir for 1 hour while blowing air.

After the oxidation reaction is completed, the slurry is removed from the autoclave, transferred to a hydration tank, and left to cool.

When the internal temperature reached 60°C, it was heated and maintained at this temperature for 2 hours, and then filtered and dried to obtain bulky trihydrate needle crystals with a major axis of 160 to 850 μm and a minor axis of 3 to 20 μm.

Example 3 The aqueous solution containing 8% calcium sulfite used in Example 2 was adjusted to pH 3, and sodium citrate was added to 0.
．． 1% and 0.1% of copper sulfate were added and charged into an autoclave at 130°C and 22 kg/cri.

70 while heating and pressurizing to (gauge pressure) and blowing air.
Stir for a minute.

Next, the slurry is taken out from the autoclave, maintained at 45° C. while being gently stirred, and subjected to a water conservation reaction for 2 hours.

After that, it is filtered and dried, with a long axis of 150 to 1000μ and a short axis of 5.
Bulky trihydrate needles of ~30μ are obtained.

[Brief explanation of the drawing]

FIG. 1 is a system diagram of an embodiment of the present invention. In the figure, 1... absorption tank, 2... pH adjustment tank, 3... oxidation reactor, 4... curing tank.

Claims (1)

[Claims] 1 Step of producing calcium sulfite in flue gas deflow by lime-gypsum method 1゜ The slurry containing the calcium sulfite is used as it is or as desired, a crystal modifier and a metal salt are added and the pH is made acidic. Adjustment step 2゜ Oxidize the pH-adjusted treatment liquid under heat and pressure to convert calcium sulfite into α-type calcium sulfate hemihydrate Step 3゜ Keep the oxidized liquid in the temperature range of 30 to 80 ° C. A bulky calcium sulfate trihydrate consisting of steps 1, 2, 3, and 4 of 4° or more Method for producing salt needle crystals. 2. An absorption tank that generates a slurry containing calcium sulfite by absorbing oxides in slaked lime or calcium carbonate emulsion; a pH adjustment tank that adjusts the pH of the slurry; and a pH adjustment tank that oxidizes the pH-adjusted calcium sulfite in the slurry. Production of bulky calcium sulfate trihydrate acicular crystals comprising an oxidation reactor to convert α-type calcium sulfate hemihydrate into α-type calcium sulfate hemihydrate, and a curing tank in which the slurry containing α-type calcium sulfate hemihydrate undergoes hydration reaction and crystal growth. Device.