JP4453707B2 - Scale formation inhibitor, scale formation suppression method, and green liquid production system in green liquid production system - Google Patents

Description

  The present invention relates to a scale formation inhibitor that suppresses scale formation in a green liquor production system, a scale formation inhibition method, and a green liquor production system.

  Paper is manufactured by preparing pulp by adding treated water containing sodium hydroxide to wood chips and cooking, bleaching this pulp, and making paper. Since wood chips and pulp contain abundant calcium salts, barium salts, oxalates, etc., a large amount of calcium ions, barium ions, and oxalate ions are eluted in the treated water during the paper manufacturing process.

  When these oxalate ions and sulfate ions are combined with calcium ions and barium ions, substances extremely insoluble in water such as calcium sulfate, barium sulfate, and calcium oxalate are generated as scales. The scale adheres to every part of the green liquor production system, induces a decrease in the flow rate of the treated water and a reduction in power consumption efficiency, and in some cases damages the equipment constituting the green liquor production system.

  Therefore, it is necessary to reduce the scale attached to the green liquor production system. Conventionally, it is common to remove the adhered scale by periodic cleaning or acid cleaning. However, in such a removal operation, the operation of the green liquor production system must be temporarily stopped, and the paper production efficiency is greatly reduced.

For this reason, the technique which suppresses formation of a scale is requested | required by throwing a predetermined composition into the green liquid manufacturing system in operation. As such a composition, Patent Document 1 discloses a multi-component copolymer having monomer units of 1,2-dihydroxy-3-butene, maleic acid, acrylic acid and the like.
Special table 2003-520117 gazette

  However, since the composition described above employs multiple components as monomer units, there is a problem that the production cost of the composition increases and the production system becomes complicated.

  The present invention has been made in view of the above circumstances, and using a material that can be manufactured in an inexpensive and simple manufacturing system, a scale formation inhibitor and scale formation that can sufficiently suppress the formation of scale in a green liquor manufacturing system. It aims at providing the suppression method and a green liquor manufacturing system.

  The present inventors have found that the formation of scale in the green liquor production system can be drastically suppressed by using a copolymer having maleic acid and acrylic acid as monomer units and having a weight average molecular weight of 3000 or more. The headline and the present invention were completed. Specifically, the present invention provides the following.

  (1) A scale formation inhibitor in a green liquor production system containing a copolymer having a monomer unit substantially consisting of maleic acid and acrylic acid and having a weight average molecular weight of 3000 or more.

  (2) By introducing a copolymer having monomer units substantially consisting of maleic acid and acrylic acid and having a weight average molecular weight of 3000 or more into a fluid in a green liquor production system containing scale forming ions, A method for suppressing scale formation in a green liquor production system for suppressing formation.

  (3) The scale formation suppression method in the green liquor production system according to (2), wherein the copolymer is introduced so that the concentration of the copolymer with respect to the fluid is 0.1 to 1000 mg / L.

  (4) The scale formation suppression method in the green liquor production system according to (3), wherein the copolymer is introduced so that a concentration of the copolymer with respect to the fluid is 0.1 to 100 mg / L.

(5) A green liquor production system comprising a fluid flow path through which a fluid containing scale-forming ions flows,
A green liquor production system further comprising introducing means for introducing a scale formation inhibitor containing a copolymer having monomer units substantially consisting of maleic acid and acrylic acid and having a weight average molecular weight of 3000 or more into the fluid channel. .

  According to the present invention, since the scale formation inhibitor is composed of a copolymer in which the monomer unit is substantially composed of maleic acid and acrylic acid and the weight average molecular weight is 3000 or more, the scale formation inhibitor is inexpensive and simple. Can be manufactured in a manufacturing system. Further, a scale formation inhibitor containing a copolymer having a monomer unit substantially consisting of maleic acid and acrylic acid and having a weight average molecular weight of 3000 or more is added to the fluid in the green liquor production system containing the scale-forming ions. Since it was introduced, the binding of scale-forming ions is inhibited. Thereby, scale formation can be sufficiently suppressed.

  Hereinafter, although embodiment of this invention is described, this invention is not specifically limited to this.

<Pulp production system>
FIG. 1 is a schematic configuration diagram of a pulp manufacturing system 1 including a green liquor manufacturing system according to an embodiment of the present invention. The pulp production system 1 includes a cooking system 10, a black liquor treatment system 20, a green liquor production system 30, and a green liquor treatment system 40, which are communicated with each other through a pipe indicated by a solid line in FIG. As a whole, it constitutes a circulation path. The green liquor production system 30 further includes an introduction section as introduction means (not shown). Hereinafter, each component will be described in detail.

[Cooking system]
The cooking system 10 has a digester 11, and a pulp refining section is provided downstream of the digester 11. In the digester 11, wood chips that are raw materials for pulp and white liquor containing sodium hydroxide are charged to digest the wood chips. The resulting pulp is transferred to the pulp refining section, where it is subjected to bleaching, paper making processes, etc., and paper is produced. On the other hand, the black liquor, which is a waste liquid, is transferred to an evaporator 21 described later for recovery of sodium hydroxide and the like.

[Black liquor treatment system]
The black liquor processing system 20 includes an evaporator 21 and a boiler 22 in order from the upstream. The black liquor is concentrated by the evaporator 21, transferred to the boiler 22, and burned in the boiler 22. Then, the inorganic sodium salt contained in the black liquor is melted and discharged as smelt from the bottom of the boiler 22. The discharged smelt is transferred to the dissolution tank 31.

  The boiler 22 may be provided with a heat recovery system for recovering thermal energy. As such a heat recovery system, a conventionally known one can be used (for example, see JP-A-6-212586).

[Green liquid production system]
The green liquor production system 30 includes a dissolution tank 31, a green liquor clarifier 32, and a green liquor tank 33 in order from the upstream. The smelt is stirred and dissolved in water in the dissolution tank 31. Thereby, in addition to sodium hydroxide, a green liquor rich in sodium carbonate is produced. The dissolution tank 31 is provided with a liquid feed pump (not shown), and the green liquid is sucked into the liquid feed pump and transferred to the green liquid clarifier 32. In the green liquor, the remaining undissolved components are removed by the green liquor clarifier 32. Thereafter, it is transferred to the green liquor tank 33 and stored, and is eventually transferred to the causticizing system 41.

[Green liquid treatment system]
The green liquor treatment system 40 includes a causticizing system 41, a white liquor clarifier 42, a white liquor tank 43, and a kiln 44 located downstream of the 43. The causticizing system 41, the white liquor clarifier 42, and the white liquor tank 43 are in communication with each other and constitute a circulation path as a whole.

  The green liquor transferred to the causticizing system 41 is mixed with calcium oxide supplied from the kiln 44 in the causticizing system 41. This mixing will be described in more detail.

  The causticizing system 41 includes a slaker 411 and a plurality of causticizing reaction tanks 412 located downstream of the slaker 411. The green liquor (usually 90 to 100 ° C., pH 13 to 14) transferred to the breaker 411 is mixed with calcium oxide supplied to the breaker 411 as well. Then, calcium oxide is dehydrated with water to produce calcium hydroxide. Thereafter, when transferred to the causticizing reaction tank 412, sodium carbonate in the green liquor reacts with calcium hydroxide to produce sodium hydroxide and calcium carbonate.

  The white liquor thus obtained is transferred to the white liquor clarifier 42. In this white liquor clarifier 42, after insoluble calcium carbonate is settled and separated, the white liquor is stored in the white liquor tank 43 and eventually circulated to the digester 11 for reuse. On the other hand, the separated calcium carbonate is recovered into the kiln 44, roasted, returned to calcium oxide, and reused in the causticizing system 41.

  In the present embodiment, the dissolution tank 31, the green liquor clarifier 32, the green liquor tank 33, and the pipes that communicate these constitute the fluid flow path through which the fluid in the green liquor production system containing scale-forming ions circulates. To do.

  Here, the scale-forming ions mean a group of ions that combine with each other to form a scale, and specifically include calcium ions, barium ions, sulfate ions, oxalate ions, and the like.

[Introduction section]
The introduction unit introduces a scale formation inhibitor, which will be described later, into an appropriate site in the green liquor production system 30 where suppression of scale formation is required. In the green liquor production system 30, scale forming ions exist everywhere in the fluid flow path, and there is a concern about the problem of scale adhesion. Since the scale formation inhibitor introduced by the introduction part inhibits the binding of scale forming ions at the introduction site and downstream thereof, scale formation can be sufficiently suppressed.

  The introduction part may be an arbitrary part of the fluid flow path described above, and is preferably a part where suppression of scale formation is required or upstream thereof. For example, it can be introduced into the dissolution tank 31 or the green liquor clarifier 32, or can be introduced into water for dissolving the smelt.

  The amount of the scale formation inhibitor introduced may be appropriately set according to the amount of scale-forming ions present, the amount of fluid flowing, and the like. The introduction amount is preferably 0.1 to 1000 mg / L, more preferably 0.1 to 1000 mg / L, as described later, with respect to the fluid (for example, green liquor) in that the formation of scale can be sufficiently suppressed and is economical. It is set to be 1 to 100 mg / L. Note that the volume of the fluid flowing can be calculated based on the measured value by providing a flow meter at an appropriate location in the fluid flow path, for example.

<Scale formation inhibitor>
[composition]
The scale formation inhibitor of the present invention contains a copolymer having monomer units substantially consisting of maleic acid and acrylic acid and having a weight average molecular weight of 3000 or more.

  The phrase “consisting essentially of maleic acid and acrylic acid” means that compounds other than maleic acid and acrylic acid are not contained as monomer units in an amount that can suppress scale formation.

  In addition, the content ratio of maleic acid and acrylic acid is not particularly limited, and may be, for example, 30:70 to 70:30 (mol%).

  The scale formation inhibitor is usually used in a state where the copolymer is dissolved in water in consideration of the transfer efficiency, but is not limited thereto, and may be used in a slurry form or a powder form.

[Production method]
The scale formation inhibitor of the present invention can be produced by a conventionally known method, for example, a solution polymerization method or a bulk polymerization method. Specifically, di-t-butyl peroxide is added little by little while refluxing maleic anhydride, acrylic acid, methanol, and xylene with stirring. The mixture is stirred and then cooled to about 90 ° C. Subsequently, pure water is added and the mixture is further stirred for hydrolysis. Thereafter, xylene is separated by steam distillation to obtain a scale formation inhibitor as an aqueous solution of the copolymer.

  Polymers A to X shown in Table 1 were prepared in order to select useful components as a constituent of the scale formation inhibitor. Since the production procedure is the same except that the addition amount and the reaction time are appropriately changed, only the production method of the polymer C will be described in this specification.

  First, 49 g (0.5 mol) of maleic anhydride, 36 g (0.5 mol) of acrylic acid, 30 g (0.94 mol) of methanol, and 232 g (2.2 mol) of xylene were refluxed with stirring. -6.6 g (0.045 mol) of butyl peroxide was added in small portions over 3 hours. The mixture was stirred at 140 ° C. for about 2 hours and then cooled to about 90 ° C. Subsequently, 350 g of pure water was added and the mixture was stirred at 50 ° C. for 2 hours for hydrolysis. Then, xylene was isolate | separated by steam distillation, and the aqueous solution of the polymer C was obtained. In addition, as a result of adding a part of this aqueous solution to methanol and measuring the mass of the precipitated polymer, the yield was 92%.

  About each of produced polymer AX, the scale formation inhibitory ability from the calcium ion as a scale formation ion was evaluated as follows.

(Test Example 1)
First, calcium chloride dihydrate was added to the green liquor (pH 13.5, total alkalinity (Na ₂ O conversion value) 135 g / L, sodium concentration 9 mass%, calcium concentration 10 mg / L) generated in the kraft pulp manufacturing process. 185 mg / L was dissolved and test water was prepared. The test water was filtered through a filter paper (5C), and the calcium concentration in the filtrate was measured by an atomic absorption method, and found to be 65 mg / L.

  100 mL of test water added with 10 mg / L of polymer A (polymaleic acid) was poured into a stainless steel container and immersed in an oil bath at 95 ° C. for 1 hour. Then, it filtered through the filter paper (5C), and it was 14 mg / L when the calcium concentration in a filtrate was measured by the atomic absorption method. On the other hand, the calcium concentration in the filtrate obtained by the same procedure except that 100 mL of test water to which polymer A was not added was used was 13 mg / L. This value was taken as a blank value.

  Based on these two measured values, the precipitation inhibition rate of the calcium component present in the test water was calculated as {1- (65-14) / (65-13)} × 100 = 2 (%).

  In the same procedure, the precipitation suppression rate of the calcium component was calculated for each of the polymers B to X. The results are shown in FIGS. FIG. 2 is a diagram showing the precipitation inhibition rate of the calcium component by the polymers A to R, and FIG. 3 is a diagram showing the precipitation inhibition rate of the calcium component by the polymers C to E and S to X.

  As shown in FIG. 2, the polymers D to H exhibited a significantly higher precipitation suppressing effect than the polymers A and I to R. This suggests that the monomer unit is substantially composed of maleic acid and acrylic acid to improve the ability to suppress scale formation.

  Further, the polymers D to H exhibited a significantly higher precipitation suppressing effect than the polymer C. This suggests that a weight average molecular weight of 3000 or more is necessary for improving the ability to suppress scale formation.

  On the other hand, as shown in FIG. 3, the copolymer whose monomer units are substantially composed of maleic acid and acrylic acid, as long as the maleic acid / acrylic acid molar ratio is in the range of 3/7 to 7/3. Thus, it was confirmed that the precipitation suppressing effect does not depend on the molar ratio.

(Test Example 2)
In the above-described green liquor production system 30 (green liquor production amount: 50 m ³ / hour), the ability of the polymers B and E to inhibit scale formation was evaluated. First, the polymer was introduced into the dissolution tank 31 via the introduction part so that the polymer concentration was 10 mg / L with respect to the green liquor. In this state, the green liquor production system 30 was operated for 3 months. In addition, the conditions of the green liquor at the time of operation were as follows.
pH: 13.5 to 13.8
Total alkalinity (Na ₂ O conversion value): 125 to 140 g / L
Sodium ion concentration: 7-9% by mass
Calcium ion concentration: 5-15mg / L

During the three months, the scale and the liquid feed pump provided in the dissolution tank 31 adhered, and the time and number of times when the liquid feed pump had to be washed were determined. This result is shown in Table 2 together with the result of the control group in which the polymer was not introduced.

  As shown in Table 2, in the green liquid production system 30 in which the untreated control group and the polymer B were introduced, it was necessary to frequently remove the scale by washing due to the scale adhering to the liquid feed pump. . On the other hand, in the green liquor production system 30 into which the polymer E was introduced, there was no noticeable scale adhesion over 3 months, and there was no need to perform cleaning.

  Thus, since the result of Test Example 2 using the green liquor production system 30 has a correlation with the result of Test Example 1, the polymers D to H that exhibited excellent functions in Test Example 1 It is suggested that both can exhibit an excellent ability to suppress scale formation in an actual green liquor production system.

It is a schematic block diagram of the pulp manufacturing system provided with the green liquor manufacturing system which concerns on one Embodiment of this invention. It is a figure which shows the scale formation effect by the scale formation inhibitor which concerns on the Example of this invention. It is a figure which shows the scale formation effect by the scale formation inhibitor which concerns on the Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Pulp production system 10 Digestion system 11 Distilling pot 20 Black liquor processing system 21 Evaporator 22 Boiler 30 Green liquor production system 31 Dissolution tank 32 Green liquor clarifier 33 Green liquor tank 40 Green liquor treatment system 41 Causticizing system 42 White liquor clarifier 43 White liquor tank 44 Kiln 411 Slaker 412 Caustic reaction tank

Claims (5)

  A scale formation inhibitor in a green liquor production system comprising a copolymer having a monomer unit substantially consisting of maleic acid and acrylic acid and having a weight average molecular weight of 3000 or more.   Inhibition of scale formation by introducing a copolymer having monomer units substantially consisting of maleic acid and acrylic acid and having a weight average molecular weight of 3000 or more into a fluid in a green liquor production system containing scale forming ions A method for suppressing scale formation in a green liquor production system.   The method for inhibiting scale formation in a green liquor production system according to claim 2, wherein the copolymer is introduced so that the concentration of the copolymer with respect to the fluid is 0.1 to 1000 mg / L.   The method for inhibiting scale formation in a green liquor production system according to claim 3, wherein the copolymer is introduced so that the concentration of the copolymer with respect to the fluid is 0.1 to 100 mg / L. A green liquor production system comprising a fluid flow path through which a fluid containing scale-forming ions flows,
A green liquor production system further comprising introducing means for introducing a scale formation inhibitor containing a copolymer having monomer units substantially consisting of maleic acid and acrylic acid and having a weight average molecular weight of 3000 or more into the fluid channel. .

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