JP2884870B2 - Calcium carbonate production equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing calcium carbonate, and more particularly, to fluctuations in the concentration of an aqueous suspension of calcium hydroxide, the temperature at the start of the reaction, the amount of supplied carbon dioxide, and the concentration of carbon dioxide. The present invention relates to a method for producing calcium carbonate which is not easily affected by water and is excellent in water dispersibility.

[0002]

2. Description of the Related Art A typical industrial production method of calcium carbonate is to blow carbon dioxide gas into a suspension of calcium hydroxide solution having a concentration of about 5 to 20% by weight from a fixed jet port such as a nozzle or a straight pipe. Is a method for causing a carbonation reaction.

[0003] In the method for producing calcium carbonate, when the blowing of carbon dioxide gas into the aqueous suspension of calcium hydroxide is continued,
The viscosity of the suspension increases, and conversely decreases as the carbonation proceeds, until it becomes lower than the original suspension. Further, when the carbonation is further advanced and the pH of the suspension becomes 7.0 to 8.0, the end point of the carbonation is determined, and then the generated calcium carbonate is filtered, dried and crushed.

[0004] That is, in the above-mentioned method, the average particle diameter (length of the long side) obtained by observation with an electron microscope is 1 to 1 by appropriately adjusting the concentration, temperature, amount of carbon dioxide gas blown, and the like of the suspension of calcium hydroxide. Light calcium carbonate composed of calcite crystals or aragonite crystals of spindle-shaped particles or columnar particles of about 5 μm or average particle diameter (length of one side of a cube) 0.03 to 0.3.
Colloidal calcium carbonate composed of calcite crystals of cubic particles of about 3 μm is produced.

[0005]

However, in the above-mentioned method, when the concentration of calcium hydroxide suspension, the temperature, the amount of carbon dioxide gas blown, and the concentration of carbon dioxide gas are changed, the crystal form of calcium carbonate formed and the particle size thereof are changed. The variation is enormous.

[0006] The reaction time is determined by the amount of carbon dioxide gas blown or the specifications of the apparatus. However, the conventional method has a drawback that the production efficiency is low because the reaction time is usually as long as 5 to 24 hours.

Even if the amount of carbon dioxide gas is increased for the purpose of shortening the reaction time, the dispersibility of bubbles of carbon dioxide gas is poor, the particle diameter becomes large, and the effective contact area with the aqueous calcium hydroxide suspension is reduced. In addition, the bubbles are fused during the ascent, and the particle diameter is further increased and rapidly rises to the liquid surface, so that the residence time in the calcium hydroxide aqueous suspension is shortened. Of the carbon dioxide gas, the proportion of the carbon dioxide that participates in the carbonation reaction (hereinafter referred to as the carbon dioxide utilization rate) is reduced, so it is necessary to increase the installed capacity of the carbon dioxide blowing blower more than necessary, and its power consumption is also reduced. There is a disadvantage that the production cost is increased due to the increase.

[0008] Further, as a carbon dioxide gas source, exhaust gas from a lime burning kiln of a pulp mill, for example, an alkaline pulp or kraft pulp manufacturing plant (hereinafter referred to as lime kiln exhaust gas).
When lime kiln exhaust gas is used, heat is recovered in the lime mud dewatering process, which is usually circulated, but due to air leaking at that time, the carbon dioxide concentration in the subsequent process is 10 to 20% by volume.
May go down.

Conventionally, in the production of calcium carbonate, the reaction is carried out at a carbon dioxide gas concentration of 25 to 35% by volume in the lime kiln exhaust gas. However, when the concentration becomes less than 25% by volume, the conventional method reduces the amount of gas. Even if you inject carbon dioxide in the same way,
The reaction time increases and the production capacity decreases. Further, when a large amount of carbon dioxide gas is blown, there is a disadvantage that the carbon dioxide gas utilization rate decreases as described above.

The lime kiln exhaust gas of a pulp manufacturing plant contains trace amounts of sulfur oxides, unburned carbon or lime dust, etc., and if these dusts are mixed during the carbonation reaction, the generated calcium carbonate However, there is a problem that calcium carbonate grows due to a decrease in whiteness of the powder and the dust as a nucleus, which causes a variation in particle size, resulting in an uneven calcium carbonate.

It is an object of the present invention to provide a method for producing calcium carbonate which improves the above-mentioned conventional disadvantages, and in particular, makes effective use of the exhaust gas of a lime kiln.

[0012]

Means for Solving the Problems The first invention is directed to calcium carbonate
In an apparatus for producing asium, the reaction tank is a vertical type ,
The upper surface of the gas reservoir in the lower part of the vertical reaction tank is located at the center of the vertical reaction tank.
A large number of small holes in a conical shape having a vertex
Is a configuration of a calcium carbonate production apparatus in which is formed .

[0013] A second invention is a method for producing calcium carbonate.
The equipment used to make the lime kilns, wet scrubbers,
And a tube-type heat exchanger and the vertical according to claim 1.
Lime kiln kiln
Is a wet scrubber, shell and tube heat exchange
The flow is sequentially conducted to the shell side of the exchanger and the vertical reaction tank,
On the other hand, shell and tube heat exchanger tubes
A calcium carbonate producing apparatus in which a cooling medium is conducted .

Further, according to a third aspect of the present invention, there is provided the lime calcination of the second aspect.
Kiln exhaust gas is used for shell and tube heat exchange
Is connected to the shell side of the
Coolant flows through the tubes of the heat exchanger
Calcium carbonate production equipment that has been used .

[0015]

The present invention is configured as described above, and the concentration of the aqueous calcium hydroxide suspension used in the reaction is 5 to 15% by weight. If the content exceeds 15% by weight, the viscosity of the suspension becomes high, so that the fine bubbles of the lime kiln exhaust gas are not sufficiently dispersed, and large bubbles are formed to float, thereby lowering the utilization rate of carbon dioxide gas.

If the content is less than 5% by weight, the dispersion of carbon dioxide is good, and the utilization rate of carbon dioxide is good, but the production capacity is reduced.
Many of the generated calcium carbonate crystals are coarse and undesirably mixed with fine crystals to form an inhomogeneous mixture.

Further, the lime kiln exhaust gas containing carbon dioxide gas reacting with the calcium hydroxide is supplied as fine bubbles. Means for forming fine bubbles of the lime kiln exhaust gas may be obtained by attaching a gas reservoir having a large number of small holes on the upper surface below the carbonation reaction tank and bubbling the lime kiln exhaust gas from the large number of small holes.

The shape of the gas reservoir is to raise the center portion of the anti応槽, tilt down side to the reaction vessel periphery. or,
Shape when this is conical, pyramidal Jomata may be either hemispherical shape. The shape of many small holes may be any of a circle, a square, an ellipse, a rectangle, and the like. However, it is preferable that the hole has a circular shape without corners where calcium carbonate is easily removed, and the opening ratio of the holes is 2 to 15%. Preferably it is 3 to 13%.

By bubbling the fine bubbles of the exhaust gas as described above, the fine bubbles can sufficiently come into contact with the aqueous solution of calcium hydroxide, and the mechanical strength of the gas reservoir becomes high.
Since the amount of air blown can be increased and the time for floating to the liquid surface becomes longer, the utilization rate of carbon dioxide gas can be improved.

Further, the lime kiln exhaust gas of a pulp manufacturing plant as a carbon dioxide gas source has a high temperature and contains dust, so that cooling and dust removal are required during the carbonation reaction.

In the present invention, at least one of the means for cooling and removing dust is a gas-liquid contact type scrubber. By this gas-liquid contact type scrubber, the high temperature gas of about 200 ° C is primarily cooled to about 60 ° C,
In addition, dust contained in the exhaust gas is removed.

Next, the exhaust gas is cooled from about 60 ° C. to about 40 ° C. by a shell and tube heat exchanger (hereinafter, referred to as a shell heat exchanger). However, the cooling temperature at this time is appropriately changed according to the quality design because of one factor of the quality design of the calcium carbonate.

According to the present invention, the exhaust gas is conducted to the shell side of the shell-type heat exchanger, while the cooling medium is conducted to a large number of tubes mounted inside the heat exchanger.

In this case, since the exhaust gas is treated by a gas-liquid contact type scrubber, the relative humidity is almost 100%, and the cooling medium comes into contact with the outer surfaces of a large number of tubes through which the cooling medium is conducted. The tube is condensed and condensed, and as the condensation progresses, the outer surface of the tube becomes wet and eventually drops as a drop.

At this time, dust in the lime kiln exhaust gas which is not treated by the scrubber is repeatedly caught with moisture condensed on the outer surface of the densely packed tube, so that the dust is efficiently removed.

Condensation of water on the outer surface of the tube, formation of droplets,
The falling behavior is performed continuously, so that dust does not adhere to the outer surface of the tube, the outer surface of the tube is always kept clean, and an excellent cleaning action can be exhibited.

Further, since the outer surfaces of a large number of tubes through which the cooling medium is conducted are kept clean without dust sticking and are always kept in a wet state, the overall heat transfer coefficient is 400 Kcal / cm. Since the temperature can be maintained at about m ² · hr · ° C., the heat exchange rate is extremely high and continuous operation is possible.

According to the present invention, the dust is removed by the above-mentioned method. However, when the dust in the exhaust gas exceeds 0.030 g / Nm ³ dry, the amorphous dust is converted into calcium carbonate during the carbonation reaction. It becomes a nucleus at the time of formation, the particle size of calcium carbonate increases, and the variation also increases, the specific scattering coefficient decreases, the whiteness of calcium carbonate decreases, and it is used as a coating pigment or filler during paper production. In such a case, the whiteness is reduced and exceeds a suitable range. When the dust in the exhaust gas is 0.030 g / Nm ³ dry or less, a suitable calcium carbonate can be obtained.

According to the present invention, the secondary particles of calcium carbonate formed are weak, uniform and relatively fine, so that they do not undergo a drying or crushing step, and are used as a filler in paper suspension as a suspension. Even when used, a paper having high whiteness and opacity can be obtained.

In some cases, the suspension may be wet-pulverized and used, or the suspension may be dehydrated to a concentration of about 60% by weight of calcium carbonate, concentrated, and blended into a pigment for coated paper to provide a smooth surface. A matt coated paper with good properties can be obtained.

On the other hand, the carbon dioxide in the lime kiln exhaust gas is usually 25 to 35% by volume, but if the fine bubbles of the exhaust gas are reacted as in the present invention, those having a low carbon dioxide gas concentration, for example, Concentration after flash dryer process 10 ~
Exhaust gas of about 25% by volume can be used, and the reaction efficiency at that time does not decrease so much. Therefore, the lime kiln exhaust gas can be effectively used, and the utilization rate of carbon dioxide gas can be improved.

Although stable quality can be obtained even if the carbon dioxide concentration is less than 10% by volume, the carbon dioxide concentration is desirably 10% by volume or more because the reaction time is prolonged and the power consumption of the blower is increased.

Since the calcium carbonate obtained in the present invention has a uniform crystal form, it can be used in addition to paper fillers and pigments,
It can also be used to produce ink, plastic, rubber, etc.
Further, the calcium carbonate obtained in the present invention can be used as it is in the paper making process without going through a drying or crushing process.

Furthermore, the calcium carbonate obtained in the present invention has a good dispersion state and relatively fine secondary particles in a weakly agglomerated state can be obtained. When used as a filler for papermaking, the yield in the wire part of a paper machine is high. And has excellent scattering ability in the internally added paper sheet, which can contribute to increasing the whiteness of the paper.

In the conventional method, when the amount and concentration of carbon dioxide gas blown, the concentration of the aqueous calcium hydroxide suspension, and the reaction start temperature are the same, the reaction time becomes longer, and the particle size of the generated calcium carbonate becomes larger. It tends to be slightly coarse, and when internally added to paper, the effect of increasing whiteness and opacity is small.

[0036]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described more specifically with reference to the drawings and experimental examples and examples, but the present invention is not limited to these.

FIG. 1 is a flow chart of a carbonation reaction using the apparatus of the present invention .
The waste gas is sent to a wet scrubber 3 and the exhaust gas is further sent to a shell heat exchanger 4 combined with the wet scrubber 3, and the exhaust gas is supplied to a carbonation reaction tank 6 by a blower 5.

As shown in FIG. 2, the shell type heat exchanger 4 of the present invention is a quadrangular prism type, and has a number of small-diameter tubes 8 connected in parallel in a horizontal direction inside a shell 7.
Is attached. As an example, the cross-sectional area of the shell is about
In 2.2 m ^2, the diameter of the case tube has an outer diameter of about 15.9m
m, the number of tubes is 3120.

An exhaust gas inlet 9 is formed below the shell 7, and an exhaust gas outlet 10 is formed at the top of the shell 7 so that the exhaust gas is introduced into the shell type heat exchanger 4 on the side of the shell 7. And a small-diameter tube 8
The cooling water is introduced from a cooling water inlet 11 and discharged from a cooling water outlet 12 while being sequentially sent to a large number of tubes 8 connected and arranged. Reference numeral 13 in FIG. 2 denotes a shower for cleaning the outer surface of the tube 8 when the shell heat exchanger 4 is stopped.

As shown in FIG. 1, the exhaust gas from the wet scrubber 3 is supplied from the exhaust gas inlet 9 of the shell heat exchanger 4 combined with the scrubber 3 to the inside of the shell 7, and the tube 8 of the shell heat exchanger 4 It is cooled by the cooling water supplied inside. Since the exhaust gas supplied from the wet scrubber 3 has a relative humidity of 100%, the moisture in the exhaust gas comes into contact with the tube 8 of the shell heat exchanger 4 to cause dew condensation, which drops and drops. Therefore, the dust contained in the exhaust gas is trapped and removed by the condensed moisture, and the dust is remarkably reduced in dust.
To the carbonation reaction tank 6.

Since the exhaust gas is made lower by removing the dust in the shell heat exchanger 4 of the present invention, the blower 5 for sending the exhaust gas to the carbonation reaction tank 6 has a small volume of shaft power. Roots blower can be used and power saving is achieved.

FIG. 3 is a cross-sectional view of the carbonation reaction tank of the present invention. A blow valve 14 is attached to a lower portion of a carbonation reaction tank (hereinafter, simply referred to as a reaction tank) 6. A gas reservoir 15 is mounted above the blow valve 14. The upper surface of the gas reservoir 15 is formed in a conical shape having an apex at the center of the reaction tank 6, and a number of small holes 16 are formed in the upper surface of the gas reservoir 15 as shown in FIG. . The aperture ratio of this hole 16 is 5%, and the vertex angle is 90%.
Degrees.

When an aqueous solution of calcium hydroxide is supplied to the reaction tank 6 from the suspension supply port 18 and the exhaust gas is supplied from the exhaust gas supply pipe 17, the exhaust gas is
6 and slowly float in the suspension as fine bubbles, and during the floating, sufficiently contact the calcium hydroxide in the suspension to achieve the carbonation reaction. In this case, although illustration is omitted, a pipe for supplying fresh water is provided at the lower part of the exhaust gas supply pipe 17 to supply fresh water before supplying exhaust gas, and the hydroxide suspension is supplied from the gas reservoir 15. If it is located at the top, partial unreaction can be prevented.

After the completion of the carbonation reaction, the blow valve 1
Open 4 to take out the suspension of calcium carbonate formed. At this time, since the calcium carbonate adhering to the many holes 16 of the gas reservoir 15 is washed away by the reverse flow of the suspension of calcium carbonate, the many holes 16 hardly clog.

On the other hand, as a method for controlling the carbonation reaction, means such as measuring the pH of the suspension during the reaction and adjusting the amount of carbon dioxide gas to be introduced are used. In this method, the suspension in the middle of the reaction in the reaction tank is passed through the lower part of the reaction tank 6 through the conduit 20 and the liquid sending pump 2.
After passing through 1 to a pH measuring device 22 equipped with a pH electrode, measuring the pH, and returning to the reaction tank 6 via a conduit 23,
The acidic waste water or fresh water is passed through a conduit 24 and a liquid sending pump 21 to have a pH.
After being sent to the measuring device 22 for cleaning, it is discharged from the discharge port 25 to the outside of the system.

The pH measurement of the reaction solution and the washing of the system with acidic waste water or fresh water can be automated by sequence control, and the interval can be appropriately selected. It is desirable to wash the double with acidic drainage or fresh water.

As the acidic wastewater generated from the pulp manufacturing plant, there are chlorinated wastewater in the bleaching process, sulfuric acid-containing wastewater from the chlorine dioxide manufacturing process, and the like, but from the bleaching process in order to prevent the formation of calcium precipitates. Chlorinated wastewater is desirable.

Since the pH measuring device is located outside the reaction tank 6 and measures the pH of the suspension during the reaction, it is immediately washed and the pH electrode is always kept clean. In addition, the frequency of maintenance can be reduced.

Experimental Example A reaction vessel was charged with 600 liters of a calcium hydroxide aqueous suspension having a concentration of 9.0 to 14.5% by weight, and while diluting carbon dioxide from a carbon dioxide gas cylinder with air, the diluted gas was supplied at a flow rate of 1500 liters / min. (15 ° C).

As means for forming fine bubbles of carbon dioxide gas,
Microbubbles of carbon dioxide gas were bubbled from small holes (round shape, diameter 20 mm; opening ratio 5%) formed in a conical gas reservoir (vertical angle 90 °) at the lower part of the reaction vessel. Table 1 shows the reaction conditions and the results of measuring the paper quality of the internally added paper. Also, the carbon dioxide concentration
At 20% by volume, the reaction time is 120 minutes (No. 2), 160 minutes (No.
3) Similarly, when the carbon dioxide concentration is 10% by volume, the reaction time is 22
It was 5 minutes (No. 1).

[0051]

[Table 1]

The measuring methods adopted in Tables 1 to 4 are as follows. (Dust amount) According to JIS Z 8808 "Method of measuring dust concentration in exhaust gas". (Average particle size) Shimadzu centrifugal sedimentation type particle size distribution analyzer SA-CP
It was measured with type 2. The sample was prepared by dissolving 3 g of Aron T-40 (manufactured by Toagosei Co., Ltd.) in an aqueous solution in which 0.015 g (solid content) was dissolved.
(Solid content) Dissolved and dispersed with an ultrasonic disperser for 5 minutes.
The average particle shape was represented by the median cumulative value (median diameter). (Crystal grain size; long diameter) Using a scanning electron micrograph,
The representative diameter of spindle-shaped or needle-shaped crystals was measured.

(Powder Whiteness) US TAPPI Standard Method T-646 OS-
Compliant with 75. The whiteness of the calcium carbonate suspension is
After dehydration using a No. 2 filter paper (manufactured by Toyo Roshi Kabushiki Kaisha) with a Buchner funnel, the mixture was dried at 40 ° C. for 24 hours. A household mixer was used to disintegrate and homogenize the sample.

(Dry pick) Printing was repeated (about three times) until the paper was peeled off using an RI-1 type printing test machine (manufactured by Mei Seisakusho), and the pattern on the rubber roll was transferred to a white paper.
Measure the ink density with an ink density meter (ink density meter DM-273
Mold, manufactured by Dainippon Screen Mfg. Co., Ltd.).

(Wet Pick) After water is applied to the sample with a sleeve-wound roll (containing water), printing is repeated, and the pattern on the rubber roll is transferred to white paper, and then the ink density is measured. (Ink set) After printing, overlay white paper on the printing surface, transfer the ink to the white paper after 30 seconds and 60 seconds with the presser roll, and measure the ink density. (Lose water) Pipette water between the metal roll and rubber roll.
Place 2 ml, slightly separate the rolls, transfer the pattern on the paper and rubber roll to white paper, and measure the ink density.

(Printed Surface Glossiness) Printing was performed by changing the amount of ink, and the glossiness when the ink density on the printed surface was 1.40 was measured. (Smoothness, air permeability) Measured by Oken type air permeability and smoothness tester (manufactured by Asahi Seiko Co., Ltd.).

(Specific scattering coefficient and specific absorption coefficient of filler) The specific scattering coefficient (s value) and the specific absorption coefficient (k value) of a sheet having a filler content of 60 g / m ² and an ash content of 10% are determined. On the other hand, determining the ratio scattering coefficient of a sheet having a basis weight of 60 g / m ² without internally adding the filler in the same pulp (S _P value) and specific absorption coefficient (K _P value). S value and k value of the internal paper is assumed to additive property between the ratio scattering coefficient fillers and S _P values and K _P value of the pulp (S _A value) and specific absorption coefficient (K _A value) is satisfied Then, the following relational expression is established.

[0058]

(Equation 1)

(Equation 2)

The S _A and K _A of the filler were determined from this relational expression (see Paper and Paper Technical Journal, Vol. 33, No. 4, (April 1979) pages 34-45).

The particle size (the major axis of the spindle-shaped crystal) of the generated calcium carbonate is 2 to 5 μm, and the filler when the calcium carbonate is internally added to paper as a suspension without a drying and crushing step. Has a specific scattering coefficient of 2200 to 2600 cm ² / g, and the whiteness of paper having a basis weight of 60 g / m ² containing 15% by weight of ash is lower than that of the paper having a basis weight of 60 g / m ² containing no calcium carbonate. Whiteness increased significantly by 3-4 points, and opacity increased by 9-10 points.

In general, the paper strength of a paper containing a filler tends to be lower in tensile strength, bursting strength and bending strength because the smaller the particle size of the filler is, the more the inter-fiber bonds of the pulp are inhibited. However, in the case of bubbling carbon dioxide gas as fine bubbles as in the present invention, the generated calcium carbonate has a uniform shape and particle size, and the number of fine particles is reduced.

Light calcium carbonate (No. 3) obtained by bubbling carbon dioxide gas as fine bubbles has an average particle diameter almost equal to that of commercially available light calcium carbonate (PCX-850, manufactured by Shiroishi Kogyo Co., Ltd.). Equally, the paper strength of the present invention having a uniform shape and particle size is slightly higher.

Example 1 A reaction tank having the same structure as that of the experimental example was charged with 750 liters of a calcium hydroxide aqueous suspension having a concentration of 5 to 11% by weight, and the lime kiln exhaust gas from the kraft pulp production process was subjected to a gas-liquid contact type. Conducted through a scrubber, cooled and dedusted from a temperature of 210 ° C to 65 ° C, then conducted a lime kiln exhaust gas on the shell side of the shell-type heat exchanger, conducted water in a tube as a cooling medium, and conducted the temperature from 65 ° C. Cooled to 45 ° C. The dust in the exhaust gas is 0.022 to 0.026 g / Nm ³ dry, and the exhaust gas flow rate is 1000
The air was blown at a constant flow rate between 2500 liters / minute. The concentration of carbon dioxide in the exhaust gas was about 16% by volume. Table 2 shows the reaction conditions and the paper quality of the paper to which the generated calcium carbonate was internally added.

[0064]

[Table 2]

The reaction time fluctuated between 80 and 225 minutes by changing the flow rate of the carbon dioxide gas or the concentration of the aqueous solution of calcium hydroxide.
There 2000 cm ² / g or more, rise of whiteness and opacity of filled papers become respectively 3 points and 10 points or more, improvement was satisfactory.

The concentration of the aqueous calcium hydroxide suspension was adjusted to 5.
When the temperature was raised from 8% by weight (No. 4) to 10.2% by weight (No. 6), and the temperature at the start of the reaction was 50 ° C (No. 8) to 30 ° C.
When reduced to (No. 7), the particle size of the generated calcium carbonate became smaller,
Even when the amount was increased to 2,500 liters / minute from No. 9 (No. 9), the particle size of calcium carbonate hardly changed.

If the shape of the gas reservoir is a conical shape,
The mechanical strength of the gas reservoir is increased, increasing the gas injection volume
Is prevented clogging order to be attained, generated without varying greatly the quality of the calcium carbonate, it is possible to shorten the reaction time, the control of particle size and shape of the calcium hydroxide aqueous suspension This can be dealt with by changing the concentration or the reaction time.

Next, coated papers are produced from the calcium carbonate obtained in the present invention and commercially available calcium carbonate, and the properties of each coated paper are compared. Manufacture of coated paper: The calcium carbonate aqueous suspension (concentration 8.5% by weight) obtained in No. 7 of Example 1 was dehydrated to 100% by weight of a pigment having a concentration of 65% by weight, and a paint having the following composition Was dispersed with a Cowles disperser to prepare a coating color having a concentration of 61% by weight.

Oxidized starch (Oji Ace B, manufactured by Oji Constarch) 5.0 parts by weight Styrene butadiene latex (JSR 0691, manufactured by Nippon Synthetic Rubber Co., Ltd.) 12.0 parts by weight Calcium stearate (FCO Dispar, manufactured by Adeka Fine Chemical Co., Ltd.) 1.0 parts by weight Polyamide Polyurea resin (Sumireze 636, manufactured by Sumitomo Chemical Co., Ltd.) 0.5 parts by weight Sodium acrylate (Aron T-40, manufactured by Toagosei Co., Ltd.) 0.2 parts by weight

Next, this color was applied to the base paper for coating (basis weight 64
g / m ² , thickness 90 μm) at a coating speed of 30 m / min and a solid content of 13 g / m ²
With a test blade coater so that
Dry at ℃, pass twice through a super calender (linear pressure 190
Kg / cm) Coated paper was obtained.

Separately, as a comparative example, the following commercially available coating grade calcium carbonate and kaolin were prepared in the same manner as described above to prepare a coating color having a concentration of 63% by weight to obtain the same coated paper. Table 3 shows the paper quality of these various coated papers and the reaction conditions of calcium carbonate.

Escalon 2000 (dry milled calcium carbonate, manufactured by Sankyo Seiko Co., Ltd.) Carbital 90 (wet milled calcium carbonate, manufactured by Fuji Kaolin Co., Ltd.) Brilliant 15 (light calcium carbonate, manufactured by Shiroishi Kogyo Co., Ltd.) Ultracoat (imported kaolin, Engelhard Company)

[0073]

[Table 3]

The calcium carbonate produced in the present invention belongs to light calcium carbonate. However, unlike the fine cubic crystal (side length 0.15 μm) of Brilliant 15 of the same light calcium carbonate, coarse spindle-shaped or needle-shaped crystals (long diameter) In Table 3, although the white paper glossiness and the printed surface glossiness are low, the smoothness is high. Therefore, it can be said that the pigment is suitable for matte (matte) coated paper.

On the other hand, heavy calcium carbonate escalon 20
00 (average particle size 2.2 μm) and Carbital 90 (average particle size 1.
8 μm), as the pulverization proceeds and the particle size becomes finer, the glossiness of the coated paper, the glossiness of the printed surface, and the smoothness tend to increase.

The calcium carbonate produced according to the present invention has a low glossiness on white paper and a glossiness on a printed surface similarly to Escalon 2000, but gaps are formed between pigment particles at the time of coating, and they are compressed and leveled by a super calender. Therefore, since the particle shape and the particle size were uniform, the smoothness was extremely high, and was close to the smoothness of Ultracoat (kaolin). Higher smoothness is advantageous because printability is improved.

The wet pick and the dry pick were inferior to Escalon 2000, but at a level that could be prevented by the addition of a coating color binder (latex and starch) or by mixing with other pigments. is there.

As described above, in order to compare the coating suitability of the pigments, 100 parts of each pigment was blended and coated, and the paper quality of the coated paper was examined. It has been found that excellent properties are exhibited when the pigments of the coated paper are used in total or in a mixture with other pigments.

COMPARATIVE EXAMPLE Concentration was measured in a reaction tank (hereinafter referred to as a simple reaction tank) in which carbon dioxide gas was blown downward from a cylindrical blowing pipe and a reaction tank provided with a stirrer in the simple reaction tank (hereinafter referred to as a stirring reaction tank). 6.0
2,000 liters of an aqueous suspension of calcium hydroxide of about 10.1% by weight was charged, and the lime kiln exhaust gas from the kraft pulp manufacturing process was treated with a wet scrubber and an electrostatic precipitator without passing through a shell-type heat exchanger. Infused in minutes. The temperature of the exhaust gas at that time was 60 ° C and the dust content was 0.042
0.00.060 g / Nm ³ dry, carbon dioxide concentration was about 16% by volume. Table 4 shows the properties of the calcium carbonate produced in the present invention, the simple reaction vessel and the agitation reaction vessel, and the properties of the calcium carbonate produced with the internally added paper.

[0080]

[Table 4]

The calcium carbonate produced in the simple reaction vessel had a coarser particle size and an uneven shape as compared with the calcium carbonate produced in the present invention. The calcium carbonate produced in the stirred reaction tank had a uniform shape as compared with the simple formula, but the particle shape was not so different.

On the other hand, the calcium carbonate produced in the present invention has a spindle-shaped calcite-type crystal and a needle-like aragonite-type crystal partially mixed therein. The specific scattering coefficient was also equal or slightly higher. When used as a filler for paper, there is no problem even if aragonite-type crystals are mixed.

[0083]

As described in detail above, the invention of claim 1
Indicates that the gas reservoir upper surface of the vertical reaction tank has a conical shape,
Increasing the amount of blowing greatly increases the carbon dioxide gas utilization rate
It is possible to wash the generated calcium carbonate adhering to the pores
Can be Further, the invention of claim 2 uses the lime kiln exhaust gas.
Wet scrubber, shell heat exchanger and claim
Cooling and dust removal can be achieved by combination with the vertical reaction tank described in Item 1.
Efficiently performed, excellent dispersibility, uniform carbon dioxide
It is easy to get sium. Further, according to claim 3
Ming has a lime kiln exhaust gas on the shell side of the shell heat exchanger.
Through the cooling medium through the tube.
Dust removal in lime kiln exhaust gas has been greatly improved.
Wear.

In addition, when used as a filler for paper, since the filler has a large scattering ability, the whiteness and opacity of the internally-added paper have a large increase range, and are agglomerated to an appropriate size. Since the binding was not inhibited, the decrease in paper strength was smaller than when calcium carbonate obtained by pulverizing calcium carbonate or limestone obtained by the conventional method to the same average particle size was internally added.

When the calcium carbonate obtained in the present invention is blended with a pigment for coating, the smoothness is superior to that when calcium carbonate for a pigment obtained by dry-grinding limestone is blended.
A matt coated paper with good printability is obtained.

Further, calcium carbonate could be produced efficiently by using the lime kiln exhaust gas of an alkaline pulp or kraft pulp production plant of a paper pulp mill, and the concentration of carbon dioxide in the exhaust gas after heat recovery or dust removal was reduced. Even with these methods, the remarkable effect that the reaction can be completed in a shorter time than in the conventional method, and the paper can be internally added or coated without drying and crushing can be obtained.

Further, according to the present invention, even if the concentration of the reaction solution or the temperature of the reaction solution fluctuates, there is an effect that the change in the particle shape of calcium carbonate is small.

[Brief description of the drawings]

FIG. 1 is a flowchart of a carbonation reaction using lime kiln exhaust gas.

FIG. 2 is a sectional view of a shell-type heat exchanger.

FIG. 3 is a sectional view of a carbonation reaction tank used in the present invention.

FIG. 4 is a plan view of a gas reservoir.

[Explanation of symbols]

 1: Lime kiln 2, 5: Blower 3: Wet scrubber 4: Shell heat exchanger 6: Carbonation reaction tank 7: Shell 8: Tube 9: Exhaust gas inlet 10: Exhaust gas outlet 11: Cooling water inlet 12: Cooling water outlet 13: Shower 14: Blow valve 15: Gas reservoir 16: Hole 17: Exhaust gas supply pipe 18: Suspension supply port 19: Gas outlet 20, 23: Conduit 21: Liquid pump 22: pH meter 24: Conduit 25 : Vent

Claims (3)

(57) [Claims] 1. An apparatus for producing calcium carbonate.
And the reaction tank is of a vertical type,
The upper surface has a conical shape with a vertex at the center of the vertical reaction tank,
And a large number of small holes are formed in the upper surface.
Calcium carbonate production equipment . 2. An apparatus for producing calcium carbonate, comprising: lime
Firing kiln, wet scrubber, shell and chew
Combined with the vertical heat exchanger according to claim 1.
Exhaust gas from a lime kiln is a wet scrubber
-Shell side of shell and tube heat exchanger
And the vertical reactor, while the shell
Coolant is introduced into the tubes of the standard tube heat exchanger.
Calcium carbonate production equipment characterized by being passed through
Place . 3. The exhaust gas of a lime burning kiln is provided by a shell
Is connected to the shell side of the tube heat exchanger.
On the other hand, the shell and tube heat exchanger
Characterized in that a cooling medium is conducted in the tube.
The calcium carbonate production apparatus according to claim 2 .