JP2896982B2 - Method for increasing white liquor sulfidity and dissolving tank - 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 increasing the degree of sulfidation of white liquor used for obtaining pulp by cooking wood raw material as a raw material for papermaking in a kraft cooking process of papermaking, and to be used in this method. Related to the dissolution tank.

[0002]

2. Description of the Prior Art Kraft cooking has been widely used as a method for producing pulp by cooking wood raw materials.
This kraft cooking method uses wood materials such as conifers and hardwoods as papermaking materials, contains sodium hydroxide and sodium sulfide as active alkalis, and has a sulfidity of 23 to 2%.
7% to 8 kg / c at about 170 ° C. in a so-called white liquor which is a colorless or pale transparent liquid at 8%.
The papermaking raw material is steamed under heating and pressure of about m ² G for about 2 hours, and the cooking liquor obtained by digestion is separated into pulp and waste liquor called so-called black liquor.

[0003] The black liquor is concentrated, and a large amount of organic substances such as lignin contained therein are burned and removed by a recovery boiler, and the generated heat is recovered as waste heat, and a combustion residue (smelt) is obtained. Collect drugs. In this smelt, sodium is contained as sodium hydroxide, sodium sulfide and sodium carbonate. In this way, the sodium in the white liquor is eventually recovered. On the other hand, most of the sulfur components are discharged out of the system as waste gases from the recovery boiler in the form of various sulfur compounds such as hydrogen sulfide and various sulfur oxides (SO _X ), and the sulfur components are lost in large quantities. become.

A smelt containing sodium hydroxide, sodium sulfide, sodium carbonate and the like as a sodium compound is brought into contact with a weak liquid in a recovery boiler desalper, and sodium hydroxide, sodium sulfide and sodium carbonate are dissolved and unreacted. A green liquor clarified liquid is obtained by separation from sludge as a lysate. The desired amount of the green liquor clarified liquid is sent to the next causticizing step.
On the other hand, after the sludge is washed with water, solids are discharged out of the system, and the separated liquid after washing is used as a weak liquid. As the weak liquid, in addition to the separated liquid after the washing, the separated liquid after the lime mud washing in the next causticizing step is used.

[0005] The liquid obtained in this green liquor step is generally called green liquor. In this green liquor, as a sodium compound,
At least sodium hydroxide, sodium sulfide and sodium carbonate are dissolved. Sodium carbonate is roasted lime containing calcium oxide in the next causticizing step,
It is contacted in the presence of water and converted to sodium hydroxide to obtain a caustic solution. The so-called white liquor containing sodium sulfide and sodium hydroxide in a predetermined ratio is obtained by removing lime mud mainly containing an insoluble calcium compound such as calcium carbonate from the obtained caustic solution. This white liquor is stored in a white liquor tank, and a desired amount thereof is supplied to a wood raw material digestion process.

[0006] In the causticizing step, the lime mud separated from the causticizing liquid is washed, and the separated liquid after the washing is used as a weak liquid in the green liquor step. The obtained solid is recovered as limestone, roasted together with limestone replenished as required, and used as roasted lime containing calcium oxide for causticizing sodium carbonate in green liquor.
In this part of the process, most of the sulfur components are mainly contained in the waste gas from the recovery boiler and lost. On the other hand, the sodium component is also discharged out of the system as (1) sodium sulfate. (2) Part of the black liquor adheres to the pulp and is carried out of the system. (3) Contained in the separated liquid after lime mud washing in the causticizing process. It will be lost together with the sulfur component due to such factors. However, various preventive measures have been taken to minimize the loss of the sodium component, for example, by recovering it as a weak solution and sodium sulfate.

Therefore, in such a partial process,
Since the loss of the sulfur component is larger than the loss of the sodium component, the content of the sulfur component unilaterally decreases as the number of circulations of the white liquor increases. The degree of sulfidation of the liquid will decrease. Therefore, in order to increase and recover the degree of sulfidation, it is customary to replenish sodium sulfate in a recovery boiler. Recently, sodium sulfite (Na ₂ SO ₃ ) obtained by flue gas desulfurization instead of or together with sodium sulfate (hereinafter, sodium sulfate and sodium sulfite are sometimes referred to as sodium-sulfur compounds) Is sometimes used.

However, sodium sulfate and sodium sulfite are compounds containing not only a sulfur component but also a sodium component. Therefore, it is impossible to increase and restore the sulfidity of white liquor to a predetermined value only by such a sodium-sulfur compound. It was difficult. In addition, since various steps are interposed between the addition of the sodium-sulfur compound and the use of the white liquor, they greatly change due to unexpected fluctuations in operating conditions in each of the interposed steps. sulfur components, and optionally has to predict the respective content of the sodium component, the exact prediction also because it is difficult, in this conventional method increases accurately sulfide of the white liquor, It was difficult to recover.

[0009]

As described above, in the conventional paper making by the kraft digestion method using white liquor, when the white liquor is circulated and used, the sulfidity of the white liquor can be increased only by replenishment of the sodium-sulfur compound. It was difficult to accurately increase and recover. The present inventors have found that in the paper by click rough <br/> preparative digestion methods using white liquor, when recycled white liquor, sulphide of the white liquor, easily increased, and accurately As a result of earnest and praise for the method of obtaining a predetermined degree of sulfidation, instead of adding a sodium-sulfur compound to a recovery boiler, by adding elemental sulfur to white liquor before using it in the kraft cooking process Has obtained new knowledge that the sulphidity of white liquor to be recycled and reused can be maintained at a predetermined value without adversely affecting the papermaking itself by kraft digestion, and has reached the present invention based on this new knowledge. did.

[0010]

That is, the first invention is a papermaking raw material cooking liquor in a papermaking kraft cooking step, which increases the degree of sulfidation of a white liquor containing sodium hydroxide and sodium sulfide as active alkalis. In the method, prior to use in the cooking of papermaking raw materials, molten sulfur as single element sulfur in white liquor is formed into fine droplets by pressure spraying.
No added sulfide from the added elemental sulfur in the white liquor
It is a method to expand the white liquor sulfidity, wherein Rukoto yielding sodium. In other words, instead of adding the sodium-sulfur compound to the recovery boiler in the conventional paper making including the kraft cooking step, the first invention of the present invention provides at least white liquor before adding to the kraft cooking. Depending on the lowered degree of sulfurization , molten sulfur is added as elemental sulfur.
It is added as fine droplets by pressure spraying and added in the white liquor.
Sodium sulfide is generated from the added elemental sulfur ,
This is a method of increasing the degree of sulfidation of white liquor to a predetermined value. In the present invention, a white liquor is defined as an aqueous solution containing at least sodium hydroxide and sodium sulfide as active alkalis, as conventionally defined.

The method for increasing the degree of sulfidation of white liquor of the present invention is a so-called
Process of cooking papermaking raw material by cooking papermaking raw material in white liquor
It is applied to papermaking including at least a so-called kraft cooking step. That is, instead of replenishing the sodium-sulfur compound in the recovery boiler, this papermaking is different from the conventional papermaking in the kraft cooking process except that simple sulfur is added to the white liquor before being added to the kraft cooking process. Is essentially different, as long as it has at least a kraft digestion step, a recovery boiler, a green liquor step and a causticizing step, as in conventional papermaking, and furthermore, as in the conventional method. Deformation in each process and addition of process,
Includes all deletions.

In the first aspect of the present invention, the simple substance added to the white liquor is
Body sulfur is inexpensive, highly safe, and handled
ButBecause it ’s easyMolten sulfurIt is said. Molten sulfur,
It depends on the pressure, but for example, under almost normal pressure, temperature
Liquid having a viscosity of about 5 to 8 centipoise
Can be used as it is. In addition,
As body sulfurThe commercially available molten sulfur to be added is, Its sources,
There are no particular restrictions on the manufacturing method, production center, and the like.

The amount of added elemental sulfur is determined by analyzing the respective concentrations of sodium hydroxide and sodium sulfide in the white liquor having reduced sulphidity before use, and calculating the difference between the sulphidity calculated from these and a predetermined sulphidity. Can be obtained as an amount corresponding to The sulphidity of the white liquor in the present invention is a so-called Canadian sulphidity, and according to the usual definition,
[Sodium sulfide (Na ₂ S) / Sodium sulfide (Na ₂ S) +
Sodium hydroxide (NaOH)] × 100%. In this formula, both sodium sulfide and sodium hydroxide are values converted into sodium oxide (Na ₂ O) (weight). The degree of sulfidation of this white liquor is usually about 23-28% as in conventional papermaking. The sulfidity of this white liquor can be determined by the Tappi method widely used as a standard method in the paper industry (for example, “Japanese edition TA
PPI standard ") It is determined in accordance with T624os-68. The amount of sulfur added to the white liquor having a reduced degree of sulfidity supplied from the causticizing process is as follows:
This is a white liquor 1m ³ per about 1~1.5kg.

This elemental sulfur is usually added to the white liquor whose sulphidity has been reduced in the preceding dissolving tank and has a predetermined sulphidity (the same applies to the sulphidity of the white liquor used in the kraft digestion step). A liquid adjusted to a higher sulfuration degree than
It is preferable to add this pre-dissolved solution to a white liquor having a reduced degree of sulfidation before being used in the kraft cooking step. However, it is also possible to adjust the sulphidity of the white liquor to a predetermined sulphidity by directly adding this elemental sulfur to the white liquor having a reduced sulphidity before being used in the kraft cooking step. In the conventional method, the pre-dissolved solution and the white liquor to which elemental sulfur is added are usually stored in a white liquor tank installed on the upstream side of the kraft digestion process. It can be white liquor in a tank or white liquor in a white liquor supply pipe for supplying the white liquor to the kraft cooking process.

[0015] The white liquor tank and the preceding dissolving tank when the elemental sulfur is added to the white liquor in the white liquor tank may be collectively referred to as a dissolving tank. In the method of the first invention, unlike the prior art which uses sodium-sulfur compounds such as sodium sulfate and sodium sulfite, which necessarily accompany sodium with sulfur, each of the pre-dissolved solution and the white liquor supplied to the kraft digestion step Can be accurately adjusted to any desired value. In the preceding dissolution tank, in order to adjust the degree of sulfidation of the white liquor, since it must be higher than the above-mentioned predetermined degree of sulfidation, it is necessary to use an excessive amount of sulfur than the above-mentioned addition amount. This is also possible in the present invention.

In order to increase the degree of sulfidation of a white liquor having a reduced degree of sulfuration, sulfur must be dissolved and reacted with a part of sodium hydroxide in the white liquor to form Na ₂ S. However, the temperature of the white liquor is therefore practically
It is usually operated at about 80-95C. Temperature before Symbol white liquor during sulfidity increased is less than about 120 ° C. the temperature of the molten sulfur to be added. Therefore, the molten sulfur added to such white liquor is brought into contact with white liquor having a temperature lower than its melting point, so that the sulfur added as a liquid crystallizes immediately in this white liquor, and further aggregates. And 1-2cm
It becomes a sphere of a degree and cannot be uniformly dispersed in the white liquor. This is essentially unavoidable no matter how vigorously the white liquor itself is agitated during the sulfur addition.

In order to uniformly increase the sulfidity of the white liquor, it is necessary to disperse the molten sulfur added to the white liquor as uniformly as possible in the white liquor. In order to uniformly disperse the molten sulfur added to the white liquor into the white liquor, the molten sulfur is formed into fine droplets having a diameter of about 300 to 500 μm by pressure spraying or two-fluid spraying. It is possible by adding and dispersing in a white liquor which is being agitated. Pressurized spraying is a method in which pressurized molten sulfur is ejected in the form of mist from a nozzle at the tip of a supply pipe.

In this pressurized spray, the magnitude of the pressure is
It varies depending on the amount of liquid to be ejected and the effective diameter of the nozzle. In the present invention, the number of nozzles is not particularly limited, but a plurality is preferable. The effective diameter of the nozzle is, for example, usually about 2.0 to 4.0 mm, preferably 2.0.
It is about 3.0 mm. The magnitude of the pressure is usually about 4 to 5 kg / cm ² G. Here, the effective diameter of the nozzle is defined as the diameter when the entire area of the nozzle is assumed to be a circle.

In the pressurized spray, the shape of the droplet spray, which is a group of fine droplets of molten sulfur sprayed and ejected, differs depending on the shape of the nozzle, and (1) a film having a narrow width; There are 2) conical shapes distributed throughout the cone and (3) conical shapes with a hollow part in the center. A commercially available nozzle can be used as it is.

In the two-fluid spraying, a high-speed fluid (hereinafter sometimes referred to as an atomizing fluid) is caused to flow while discharging molten sulfur from a nozzle, and the molten sulfur is ejected as fine mist droplets. It is a way to let it go. In the present invention, a high-temperature inert gas is preferably used as the atomizing fluid, but it does not prevent the use of steam. The temperature of each of the inert gas and steam is
There is no particular limitation as long as the temperature is the temperature of the molten sulfur, for example, 120 ° C. or higher, but it is preferably about 120 to 150 ° C. For example, as a high temperature inert gas, 130
Approximately 4 kg / cm ² G compressed gas at ± 5 ° C. is used. When steam is used, about 4 kg / cm ² G (about 151 ° C.) is used as steam. The inert gas is not particularly limited as long as it is an inert gas with respect to various reactions related to the degree of sulfidation of the white liquor. However, in practice, a nitrogen gas and a nitrogen-containing gas such as air are usually used. Is preferred.
In this case, the effective diameter of the nozzle and the like are the same as those in the nozzle for the pressurized spray described above.

The flow rate of the atomizing fluid is appropriately selected depending on the kind of the fluid, the effective diameter of the nozzle, the outflow rate of the molten sulfur, and the like. The fine droplets of molten sulfur sprayed by pressurized spraying or two-fluid spraying are usually jetted into a space above the white liquor surface in the dissolving tank (hereinafter sometimes referred to as a tank space).

As described above, the temperature of the white liquor itself filled in the dissolving tank is lower than the temperature of the molten sulfur, that is, lower than the melting point of sulfur. Is also lower than the melting point of sulfur. Therefore,
When the molten sulfur is sprayed and supplied to the inside of the melting tank, the molten sulfur adheres to the outer peripheral surface of the pipe for supplying the molten sulfur and the rotating shaft of the stirrer to solidify and lose the molten sulfur.
There is a great risk that the nozzle of this supply pipe will be blocked by the solidified sulfur. Further, the molten sulfur also adheres to the upper bottom and the inner surface of the peripheral wall near the melting tank in which the pipe for supplying the molten sulfur is disposed, and solidifies, thereby losing the molten sulfur.

The present inventors have found that the molten sulfur supplied into the melting tank is supplied to the outer peripheral surface of a pipe for supplying the molten sulfur, a nozzle,
As a result of diligent and intensive studies on measures to prevent solidification by adhering to the rotating shaft of the stirrer and the inner peripheral surface of the dissolving tank, the present invention has been achieved. That is, the second invention of the present invention is a melting tank characterized in that a molten sulfur supply pipe whose at least a front end is surrounded by a heating guide pipe is disposed in a tank body. In the dissolving tank of the second aspect of the present invention, the molten sulfur supply pipe is a pipe for supplying molten sulfur into the tank of the dissolving tank, for example, a pipe for supplying molten sulfur alone in pressurized spray. (Hereinafter sometimes referred to as a single molten sulfur supply pipe) and a pipe for supplying molten sulfur in a two-fluid spray together with an atomizing fluid (hereinafter sometimes referred to as a two-fluid supply pipe).

In the dissolving tank according to the second aspect of the present invention, the molten sulfur supply pipe is provided on the upper bottom plate of the dissolving tank or on a peripheral wall above the surface of the white liquor in order to blow the molten sulfur into the tank space of the dissolving tank. You.

In the melting tank according to the second aspect of the present invention, the tip of the molten sulfur supply pipe including the nozzle is surrounded by a heating guide pipe. It is preferable that the molten sulfur supply pipe is surrounded by the heating guide pipe as long as possible, and it is particularly preferable that the pipe is surrounded by the rear end (the end opposite to the nozzle, and so on). Further, the heating guide tube may be further extended beyond the tip of the molten sulfur supply tube, and is more preferable.
In the melting tank of the second aspect of the present invention, the heating guide tube may have a peripheral wall and an upper bottom plate, and at least the peripheral wall may form a cylindrical body having a cavity through which the heat transfer medium passes.
The upper bottom plate of the heating guide tube may also form a cavity connected to the cavity of the peripheral wall.

The heating guide tube is provided so as to position the nozzle of the molten sulfur supply tube substantially at the center of a cross section substantially orthogonal to the long axis direction. Also, the distance from the nozzle to the inner peripheral surface of the peripheral wall of the heating guide tube depends on the shape of the droplet spray ejected from the nozzle, the amount of molten sulfur ejected from the nozzle, the arrangement position of the molten sulfur supply pipe, the atomizing fluid And the speed of the atomizing fluid are 20 kg / min. For example, when the speed of the atomizing fluid is 20 kg / min, about 100 to 150 mm
It is said.

The length of the extended portion of the heating guide tube depends on the shape of the droplet spray ejected from the nozzle, the amount of molten sulfur ejected from the nozzle, the arrangement position of the molten sulfur supply tube, the nozzle and the white liquor level. , The amount and speed of the atomizing fluid, and various other factors, and cannot be specified unconditionally. For example, the speed of the atomizing fluid is 20 kg /
In the case of min, it is about 200 to 250 mm. The distance between the nozzle and the white liquor level depends on the shape of the droplet spray ejected from the nozzle, the amount of molten sulfur ejected from the nozzle, the location of the molten sulfur supply pipe, and various other factors. For example, when the speed of the atomizing fluid is 20 kg / min, it is about 500 mm. The distance between the nozzle and the liquid level of the white liquor can be adjusted by changing the length of the insertion portion of the nozzle of the molten sulfur supply pipe into the tank and / or the height of the liquid level.

The height of the surface of the white liquor in the dissolving tank is changed by a conventional method.
A chamber provided with a partition having a hole formed in a lower part thereof, and a discharge port provided below the top of the partition plate, and a discharge port provided with a solution through a hole in the lower part of the partition plate (hereinafter referred to as discharge). Room
And sometimes overflows from the discharge pipe,
The liquid level of the dissolving tank can be maintained at the height of the discharge pipe, and this is performed by adjusting the height of this discharge port.

In the dissolving tank, the white liquor is maintained at the above-mentioned temperature. For this purpose, the white liquor in the tank must be kept warm. The heat retention is performed by coating the outer surface of the tank body with a heat retaining material such as glass wool and rock wool in a usual manner. The solution in the dissolution tank is preferably agitated in order to keep the temperature and the sulfidity as uniform as possible. Stirring is not particularly limited with respect to the stirring means, but usually it is preferable to use a mechanical stirrer. Further, a baffle can be provided in the dissolving tank in order to improve the stirring efficiency.

The sulfidity of the white liquor in the dissolving tank of the second invention is usually adjusted by measuring the sulfidity of the white liquor and adding an amount of sulfur corresponding to the lowered sulfidity. The measurement of the degree of sulfidation of the white liquor is usually performed at the causticizing step or at the outlet thereof. Adjustment of each supply amount of white liquor, molten sulfur and optionally used atomizing fluid, adjustment of the liquid level of the solution, adjustment of the discharge amount of the solution and temperature adjustment of the solution, and adjustment of each of the white solution and the solution Confirmation of the degree of sulfuration can also be performed manually. However, an automatic analyzer and a computer are used to check the degree of sulfide of each of the white liquor and the solution, and an automatic temperature measuring device and an automatic liquid level meter are used as terminals. The flow can be transmitted to a flow control valve or an opening / closing valve disposed in each supply pipe via the above, and these can be automatically operated to automatically adjust the degree of sulfidation of the solution.

A molten sulfur storage tank may be connected upstream of the above-described dissolution tank of the present invention, and a dissolved liquid storage tank may be connected downstream thereof, if desired, to provide a white liquor sulfur degree adjusting device. . The molten sulfur storage tank and the melting tank are connected via a pump.

The molten sulfur storage tank cools and cools the molten sulfur in the tank.
In order to prevent solidification, the temperature is preferably kept the same as in the melting tank. Further heating may be performed if desired. In addition, in order to prevent the molten sulfur accompanying the atomized fluid such as a large amount of air injected and released into the dissolving tank from being lost outside the apparatus, the evaporation of the vapor from the dissolving liquid in the dissolving tank in the dissolving tank in the dissolving tank is controlled. In order to prevent this, the tank space of the dissolving tank and the tank space of the dissolving solution storage tank are preferably connected to each other. It is preferable that the temperature of the solution storage tank is kept the same as in the above-described solution tank in order to prevent a temperature drop due to heat loss of the solution in the tank. In order to prevent the molten sulfur from cooling and solidifying in the pipes connecting the tanks and to prevent heat loss of the solution due to cooling, it is preferable to keep the pipe covered with a heat insulating material to keep the temperature.

When the dissolving tank is a preceding dissolving tank, it is particularly preferable to provide a dissolving solution storage tank downstream thereof. When the dissolution tank is a pre-dissolution tank, the pre-dissolution liquid from the pre-dissolution tank is temporarily stored in the dissolution liquid storage tank, and the desired amount of the pre-dissolution liquid in the dissolution liquid storage tank is the white liquor in the white liquor tank or The liquor is added to the white liquor in the white liquor supply pipe to the cooking step, adjusted to a predetermined degree of sulfidation, and then supplied to the kraft cooking step. Also, the white liquor tank can be used as a dissolution tank,
In this case, the white liquor in the white liquor tank is adjusted to a predetermined degree of sulfurization to form a solution, and the solution is directly supplied to a desired amount via a solution storage tank in some cases. But,
It is supplied to the next kraft cooking process.

[0034]

BEST MODE FOR CARRYING OUT THE INVENTION The first invention is a method for increasing the sulfidity of white liquor. In a conventional papermaking method including a kraft cooking step, a sodium-sulfur compound such as sodium sulfate and / or sodium sulfite is added to a recovery boiler. Instead of adding it, instead of adding it to the white liquor having a lower sulphidity before using it in the kraft digestion process, increase or recover the sulphide to a predetermined sulphidity, or Partial sulfur is added to obtain a pre-solution having a higher sulfidity than the predetermined sulfidity, and this pre-solution is added to the white liquor having a lower sulfidity to increase to a predetermined sulfidity. This white liquor is a conventional white liquor in which the sulfidity is increased and recovered by adding sodium-sulfide such as sodium sulfate and / or sodium sulfite in the conventional method in the next kraft cooking step. the same as , It can be used without any trouble.

Further, the second invention is a dissolving tank for adding molten sulfur to the white liquor as fine droplets by pressurized spraying or two-fluid spraying and dissolving it in the white liquor, which is surrounded by a heating guide tube. The obtained molten sulfur supply pipe is disposed in the tank body, and any of a preceding melting tank and a white liquor tank can be used as a tank body of the melting tank. This will be described more specifically in the following examples.

[0036]

EXAMPLES The present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples. Example 1 Dissolution tank The dissolution tank of the second invention will be described with reference to FIGS. 1 and 2. FIG. 1 is a longitudinal sectional view showing an embodiment of the dissolving tank of the second invention, and FIG. 2 is a sectional view of the dissolving tank shown in FIG.
It is sectional drawing of the -A cutting part. The dissolution tank 1 includes a tank body 11 having a peripheral wall 110, an upper bottom plate 111 and a bottom plate 112, and an upper bottom plate 11 of the tank body 11.
1, a stirrer 12 disposed so as to penetrate its rotary shaft, a two-fluid supply pipe 13 disposed so as to penetrate an upper bottom plate 111 from the center of the tank body 11 toward the peripheral wall 110, and a two-fluid supply pipe. 13
And a white liquor supply pipe 15 disposed close to the heating guide pipe 14 and the peripheral wall 110 of the tank body 11 so as to penetrate the upper bottom plate 111. Further, the entire outer peripheral surface of the peripheral wall 110 of the tank body 11 is covered with a heat insulating material layer 113. The inside of the tank body 11
A partition plate 114 fixed to the inner peripheral surface of the peripheral wall 110 forms a melting chamber 115
And a discharge chamber 116. A hole 1141 is formed in the lower part of the partition plate 114, and the melting chamber 115 and the discharge chamber 1 are formed.
16 are connected to each other through this hole 1141.

The two-fluid supply pipe 13, the heating guide pipe 14, and the white liquor supply pipe 15 are all disposed on the upper bottom plate 111 above the melting chamber 115, and the stirrer 12 has its shaft Is disposed so as to penetrate the upper bottom plate 111 above the melting chamber 115. Further, on the peripheral wall 110 of the tank body 11, a solution discharge port 117 is provided below the top of the partition plate 114 so as to be connected to a discharge chamber 116 inside the tank body 11. The two-fluid supply pipe 13 is a double pipe, and its inside and outside are a molten sulfur channel 130 and an atomized fluid channel 131, respectively. The two-fluid supply pipe 13 has a nozzle 132 at the tip inside the tank body 11 and a molten sulfur supply port 133 at the rear end outside the tank body. An atomizing fluid inlet 134 connected to the atomizing fluid channel 131 is opened outside the outer fluid tank body of the two-fluid supply pipe 13. The atomizing fluid flow path 131 is closed at the rear end of the two-fluid supply pipe 13.

A heating guide tube 14 surrounding the two-fluid supply tube 13 is provided outside the two-fluid supply tube 13. The heating guide tube 14 has a cylindrical peripheral wall 140 and an upper bottom plate 141. The peripheral wall 140 is provided with a cavity 142 through which the heat transfer medium passes. The cavity 142 is connected to each of the heat transfer medium supply port 143 and the heat transfer medium discharge port 144. The peripheral wall 140 of the heating guide tube 14 is further extended beyond the nozzle at the tip of the two-fluid supply tube. The two-fluid supply pipe 13 is provided so as to penetrate substantially the center of the upper bottom plate 141 of the heating guide pipe 14.

In this dissolving tank 1 , white liquor having a reduced degree of sulfide from the preceding causticizing step is supplied from the white liquor supply pipe 15 into the dissolving chamber 115 of the tank 11. The white liquor in the tank 11 is stirred by the stirrer 12. In order to improve the stirring efficiency in the tank, a flat bottomless inverted cone having a large number of holes formed in the peripheral surface is provided substantially horizontally as the baffle 16. Molten sulfur and atomizing fluid are supplied in two fluid supply pipes
Through the molten sulfur supply port 133, the molten sulfur flow path 130, the atomizing fluid inlet 134, and the atomizing fluid flow path 131, respectively, the nozzle 132 at the tip of the two-fluid supply pipe 13 jets into the space in the tank body 11 together. At this time, the molten sulfur is sprayed as fine droplets.

The sprayed molten sulfur spouted is dispersed in the white liquor, dissolved in the white liquor, and reacted with a part of sodium hydroxide in the white liquor to form Na ₂ S _x. As a result, a solution having a desired degree of sulfidation is obtained. The lysing solution in the lysing chamber 115 is
From the discharge chamber 116 in the tank body 11 to be stored therein, the liquid level in the discharge chamber 116 rises, reaches the solution discharge pipe 117, and the solution in the discharge chamber 116 The liquid is overflowed from the discharge port and discharged out of the tank, and the level of the solution in the dissolving chamber 115 of the dissolving tank 1 is maintained at substantially the same level as the dissolving solution discharge pipe 117.

Embodiment 2 White liquor sulphidity adjusting apparatus A white liquor sulphidity adjusting apparatus using the dissolving tank of the second invention will be described with reference to FIG. FIG. 3 is a system diagram of the white liquor sulphidity adjusting device. In FIG. 3, each tank is shown in a longitudinal section end view. A molten sulfur storage tank 2 and a dissolved liquid storage tank 3 are disposed on the upstream side (the same applies to the left side below in the drawing) and downstream side of the dissolution tank 1 , respectively.

The outer peripheral surface of the peripheral wall of the molten sulfur storage tank 2 is covered with a heat insulating material layer 22. Further, a heating coil 21 is provided in the inside thereof so that heating can be performed when the temperature of the molten sulfur decreases. The dissolving tank 1 is as shown in the first embodiment. The outer surface of the peripheral wall of the solution storage tank 3 is covered with a heat insulating material layer 31. The outlet 23 of the molten sulfur tank 2 and the molten sulfur supply port 133 of the two-fluid supply pipe 13 of the melting tank 1 are connected by a molten sulfur transfer pipe 4 via a pump 41. The molten sulfur transfer pipe 4 is covered with a heat insulating material.

The dissolving tank 1 and the dissolving liquid storage tank 3 are connected by connecting the dissolving liquid discharge pipe 117 of the dissolving tank 1 and the dissolving liquid transfer pipe 5 connected to the inlet 32 of the dissolving liquid storage tank 3 . . The solution inlet 32 of the solution storage tank 3 is lower than the solution discharge pipe 117 of the solution tank 1 . The solution supply pipe 6 is connected to the outlet 33 of the solution storage tank 3 . The solution supply pipe 6 is provided with a pump 61. Dissolution tank 1
The tank space is connected to the tank space of the solution storage tank 3 by a ventilation pipe 7. Further, the upper base plate 34 of the solution storage tank 3, an exhaust pipe 8 which is caused to connect the tank space of the dissolution liquid storage tank 3 is provided. The solution transfer pipe 5 and the solution supply pipe 6 are each covered with a heat insulating material to keep the temperature.

The molten sulfur transported by the tank lorry or the tank truck is temporarily stored in the molten sulfur storage tank 2 . In the molten sulfur storage tank 2 , the molten sulfur is heated by a heating coil 21 as required, and further maintained at a predetermined temperature by a heat insulating material layer 22.
In 2 , the molten sulfur does not cool and solidify. The molten sulfur in the molten sulfur storage tank 2 is pressurized by the pump 41 and reaches the molten sulfur supply port 133 of the two-fluid supply pipe 13 of the melting tank 1 via the molten sulfur transfer pipe 4. Since the molten sulfur transfer pipe 4 is kept warm, the molten sulfur transfer pipe 4
Sulfur does not cool and solidify inside.

Further, the molten sulfur supplied through the molten sulfur supply port 133 of the two-fluid supply pipe 13 of the melting tank 1 and the molten sulfur through the molten sulfur flow path 130 is supplied to the atomizing fluid inlet 134 of the two-fluid supply pipe 13.
And the atomizing fluid that has passed through the atomizing fluid flow channel 131 is sprayed out of the nozzle 132 as fine droplets into the space of the dissolving tank 1 in the form of a spray, and further contacted with the white liquor in the dissolving tank 1 having reduced sulfide degree. And a white liquor, which is dissolved and reacted in a white liquor to obtain a dissolved liquid which is increased and adjusted to a desired degree of sulfurization. Dissolving tank discharge pipe 117 of this solution is the dissolving tank 1, the via sequential solution inlet 32 of the dissolving liquid flow pipe 5 and solution storage tank 3 temporarily caused to the reservoir and sent to the solution storage tank 3.

The solution storage tank 3 solution which is allowed to stored in the desired, solution storage tank 3 solution outlet 33 via a pump 61 and dissolving liquid supply pipe 6 sequentially fed to the next step. Further, the tank space of the dissolving tank 1 and the tank space of the dissolving liquid storage tank 3 are connected to each other by a vent pipe 7, and an exhaust pipe 8 is provided on the upper bottom plate of the dissolving liquid storage tank 3 . Then, the atomizing fluid such as a large amount of air in the tank space of the dissolving tank 1 which is injected into and discharged from the dissolving tank 1 and accompanies the molten sulfur, passes through the ventilation pipe 7 into the tank space of the dissolving liquid storage tank 3. migration was once stored in the tank space, preventing the generation of vapor from the liquid surface of the lysis solution storage tank 3, and then a bath of solution storage tank 3 from the exhaust pipe 8 disposed on the upper base plate of the solution tank 3 It is discharged out of the device together with the gas in the space. Dissolver discharge pipe 117, Dissolver transfer pipe
5, Since the solution storage tank 3 and the solution supply pipe 6 are all kept warm, the temperature of the solution supplied to the next step substantially maintains the temperature of the solution discharged from the solution tank. doing.

Example 3 Adjustment of Sulfur Degree of White Liquor Using the dissolving tank of the second invention shown in Example 1 as a pre-dissolving tank, the sulfidity supplied from the causticizing step was reduced. Obtain a solution that has been increased and adjusted from white liquor to the desired degree of sulfidation,
This solution was added to the white liquor supplied from the causticizing step and having a low degree of sulfidity to adjust to a predetermined degree of sulfidation, and the white liquor with the adjusted degree of sulfidation was used in the kraft cooking step.

(1) Specifications of preceding melting tank Size of tank body: inner diameter 2200 mm height 3000 mm Two-fluid supply pipe: inner diameter (diameter) of outer pipe 50 mm inner diameter (diameter) of inner pipe 25 mm (inner diameter) of nozzle 2mm heating guide tube: inner diameter (diameter) of peripheral wall 300mm Length from upper bottom plate to nozzle tip 400mm Distance from nozzle tip to liquid level 500mm

Stirrer: Model Pitched paddle Diameter of rotating surface 850 mm Number of stages of stirring blades 2 stages White liquor supply pipe: Inner diameter (diameter) 50 mm Length from upper bottom plate to tip 100 mm Effective volume of melting chamber: 5 m³  Effective volume of discharge chamber: 4m ³

(2) Operating specifications in the preceding melting tank Supplied white liquor: Sulfidity 23% Supply rate 0.5 m ³ / hr Temperature 90-93 ° C. Molten sulfur: Supply rate 0.1 m ³ / hr Pressure 4 kg / cm ² G Temperature 130 ° C. Viscosity 8 cp Atomizing fluid: Type 135 ° C. heated air Supply rate 0.04 kg / hr Pressure 4.5 kg / cm ² G Prior solution in tank: Temperature 90-95 ° C. Sulfur dissolved concentration (sulfur content 250-350 g / l

(3) Adjustment of sulfidity of white liquor supplied to kraft cooking process White liquor to which preceding solution is added: amount 4.5 m ³ / hr Sulfidity 23% (sulfur content 11 g / l) Temperature 85-90 ° C Lead solution: 300 l / hr White liquor after adjustment: Sulfidity 28% (14 g / l as sulfur) Temperature 80-90 ° C

(4) Kraft cooking step Using the white liquor adjusted to a predetermined degree of sulfidity as described above, kraft cooking was performed in the same manner as in the conventional method of adding sodium sulfate to the recovery boiler. Pulp was obtained at a papermaking raw material yield, and the quality of the obtained pulp was almost equal to that of the conventional method.

[0053]

According to the present invention, the change of the decrease in the degree of sulfidation of the white liquor can be naturally performed even when the operation is abnormal and the decrease in the degree of sulfidation of the white liquor is abnormally large. Accordingly, it is possible to easily and accurately adjust the sulphidity of the white liquor to a desired sulphidity as well as a predetermined sulphidity. Further, even if kraft digestion is performed using white liquor adjusted to a predetermined degree of sulfuration according to the present invention, the papermaking material can be digested in the same manner as in the conventional method without any adverse effect.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a dissolving tank of the second invention.

FIG. 2 is a sectional view taken along the line AA of the dissolving tank shown in FIG. 1;

FIG. 3 is a system diagram of a white liquor sulphidity adjusting apparatus using the dissolving tank of the second invention.

[Explanation of symbols] 1 Dissolution tank 11 Tank body 110 Perimeter wall 111 Top bottom plate 112 Bottom plate 113 Heat insulation material layer 114 Partition plate 1141 hole 115 Dissolution chamber 116 Discharge chamber 117 Dissolution liquid discharge pipe 12 Stirrer 13 Two-fluid supply pipe 130 Melting sulfur flow path 131 Atomized fluid flow path 132 Nozzle 133 Molten sulfur supply port 134 Atomized fluid inlet 14 Heating guide tube 140 Perimeter wall 141 Top bottom plate 142 Cavity 143 Heat transfer medium supply port 144 Heat transfer medium discharge port 15 White liquor supply pipe 16 Baffle 2 Molten sulfur storage tank 21 Heating tube 22 Heat insulation layer 23 Outlet 3 Dissolvent storage tank 31 Heat insulation layer 32 Dissolvent inlet 33 Dissolvent outlet 34 Bottom plate 4 Dissolved sulfur transfer pipe 41 Pump 5 Dissolvent transfer pipe 6 Dissolvent supply pipe 61 Pump 7 through Trachea 8 exhaust pipe

Claims (6)

(57) [Claims] 1. A method for increasing the degree of sulfidation of a white liquor, which is a cooking liquor for a papermaking kraft cooking step and contains sodium hydroxide and sodium sulfide as active alkalis, prior to use in the cooking of the papermaking raw material. And pressurized spray of molten sulfur as elemental sulfur in white liquor
And added pressure to form a minute droplet, a single vulcanized added in the the white liquor
A method to expand the white liquor sulfidity, wherein Rukoto yielding sodium sulfide yellowish. 2. A method to expand white liquor sulfidity of claim 1 Symbol placement molten sulfur is added is a minute droplets by the two-fluid spray. 3. A method to expand white liquor sulfidity of claim 2 wherein the inert gas stream is hot used for two-fluid spray. 4. A melting tank characterized in that a molten sulfur supply pipe, at least a tip of which is surrounded by a heating guide pipe, is disposed in a tank body. 5. The melting tank according to claim 4 , wherein the molten sulfur supply pipe is provided on an upper bottom plate of the melting tank. 6. heating guide tube, dissolving tank according to claim 4 or 5, wherein is further extended beyond the tip of the molten sulfur supply pipe.