JP6286819B2 - How to suppress scale - Google Patents

Description

  The present invention relates to a method for suppressing scale in a pulp production facility.

  Pulp is produced by adding treated water containing sodium hydroxide to wood chips and cooking. Since wood chips contain a large amount of calcium salt, barium salt, phosphate, etc., a large amount of calcium ions, barium ions, and phosphate ions are eluted in the treated water during the pulp production process.

  These ions form scales due to the oxalate ions produced during the pulp cooking and bleaching stages and the chemicals used in those stages. The scale adheres to any part of the pulp production facility, causing a decrease in the flow rate of the treated water, a decrease in heat exchange efficiency or power consumption efficiency, and in some cases damages the pulp production facility.

  Therefore, it is necessary to prevent the scale from forming or sticking in the pulp production facility, or to remove the attached scale. Conventionally, chemical washing using acid, chelating agent, etc., physical washing with high pressure water, etc. It was.

  However, since chemical cleaning using an acid neutralizes sodium hydroxide contained in the treated water, high-pressure water needs to be applied directly to the part of the scale attached. For this reason, any of the washing methods needs to be performed with the pulp production facility stopped, and there are problems such as loss of pulp production, increase in labor for washing, etc., and necessity for post-treatment such as washing waste liquid.

  The present invention has been made in view of the above circumstances, and without stopping the pulp production equipment, a method for continuously suppressing scale, specifically, for example, preventing the formation and adhesion of scale, Alternatively, an object is to provide a method for removing attached scale.

  By adding a predetermined compound such as tetrasodium ethylenediaminetetraacetate (EDTA · 4Na) to the fluid of the pulp production facility, the inventor suppresses the formation and adhesion of scale in the pulp production facility in operation. As a result, the present invention has been completed. Specifically, the present invention provides the following methods.

  (1) A method for suppressing the scale of a pulp production facility, wherein the fluid in the operating facility comprises ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, ethylenediaminetetramethylenephosphonic acid, phosphonobutanetricarboxylic acid, and salts thereof. A method for suppressing scale, which comprises adding one or more compounds selected from the group.

  (2) The scale suppression method according to (1), wherein 0.05 wt / vol% or more of the compound is added to the fluid.

  ADVANTAGE OF THE INVENTION According to this invention, the scale in a production facility can be suppressed, without stopping the pulp production facility.

It is a schematic block diagram of the pulp production equipment which concerns on one Embodiment of this invention. It is a graph which shows the change of the flow volume of the black liquor in the digester 11 which concerns on one Embodiment of this invention. It is a graph which shows the change of the flow volume of the black liquor in the digester 11 which concerns on one Embodiment of this invention. It is a graph which shows the change of the flow volume of the green liquid in the flow path of the causticization system 41 which concerns on one Embodiment of this invention.

  Hereinafter, although embodiment of this invention is described, this invention is not restrict | limited by this.

<Pulp production facilities>
FIG. 1 is a schematic configuration diagram of a pulp manufacturing system 1 using wood chips 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. A path is formed and fluid in the pulp production system circulates. In addition, the cooking system 10, the black liquor processing system 20, the green liquor production system 30, and the green liquor processing system 40 further include 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 having heaters (not shown) at the upper part and / or the lower part, 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 (pulp slurry) is transferred to a pulp refining section, where it undergoes bleaching, papermaking processes, and the like in order to produce paper. 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 green liquor (smelt) from the bottom of the boiler 22. The discharged green liquid is transferred to the dissolution tank 31.

[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 green liquor is dissolved in the dissolution tank 31 with stirring. 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 causticization system 41, a white liquor clarifier 42, and a white liquor tank 43 in order from the upstream, and a kiln 44 downstream of the white liquor clarifier 42. 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 kiln 44 communicates with the causticizing system 41.

  The green liquor is mixed with calcium oxide supplied from the kiln 44 in the causticizing system 41. The causticizing system 41 includes a breaker 411 and a plurality of causticizing reaction tanks 412 located downstream thereof. 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.

[Introduction section]
The introduction part is in an appropriate part of the cooking system 10, the black liquor treatment system 20, the green liquor production system 30, or the green liquor treatment system 40, and a scale inhibitor to be described later is introduced. The cooking system 10, the black liquor treatment system 20, the green liquor production system 30, or the green liquor treatment system 40 contains ions that form scales in the fluids at all these locations, and there is a concern about problems due to scale. The scale inhibitor introduced from the introduction part suppresses the scale at the introduction site and downstream thereof. In the present invention, the suppression of the scale is not particularly limited, but means, for example, prevention of scale formation / attachment or removal of the attached scale.

  The introduction part may be an arbitrary part of the fluid flow path described above, and is preferably a part where suppression of occurrence of a problem due to scale is required or upstream thereof. For example, it can be introduced into the digester 11, the boiler 22, the dissolution tank 31, the slaker 411 green liquor, or can be introduced into water for dissolving the smelt.

[Scale inhibitor]
The scale inhibitor of the present invention is selected from the group consisting of ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), ethylenediaminetetramethylenephosphonic acid (EDTMP), phosphonobutanetricarboxylic acid (PBTC), and salts thereof. One or more compounds that are not decomposed even in a high-temperature, high-alkaline environment, and can suppress scale in an operating pulp production facility. In addition, these scale inhibitors can restore the flow rate through which the pulp production facility is partially or wholly in operation to a flow rate close to the flow rate during the cleaning. These scale inhibitors do not change kappa number and whiteness before and after washing and do not adversely affect pulp quality. The scale inhibitor preferably includes tetrasodium ethylenediaminetetraacetate, pentasodium diethylenetriaminepentaacetic acid, pentasodium ethylenediaminetetramethylenephosphonate, and phosphonobutanetricarboxylic acid.

  The introduction amount of the scale inhibitor can be appropriately set according to the abundance of ions forming the scale, a decrease in the flow rate due to adhesion of the pulp to the production facility, and the like. In order to sufficiently suppress the formation and adhesion of scale, the amount introduced is not particularly limited, but is preferably 0.05 wt / vol% or more, more preferably 0.10 wt% with respect to the fluid (for example, black liquor or green liquor). / Vol% or more, more preferably 0.25 wt / vol% or more. In order to suppress undesired reactions, the amount introduced is not particularly limited, but is 5.0 wt / vol% or less, 4.0 wt / vol% or less, 3.0 wt / vol% or less, 2.0 wt% with respect to the fluid. / Vol% or less, 1.0 wt / vol% or less, 0.5 wt / vol% or less, and more than 5.0 wt / vol% unless an undesired reaction occurs. When the amount of the scale inhibitor added is less than 0.05 wt / vol%, the scale inhibitor is consumed by the metal ions in the pulp or flowing fluid. On the other hand, when the amount of the scale inhibitor introduced exceeds the amount at which an undesirable reaction occurs, the pulp quality may be lowered although the scale formation / attachment prevention and the scale removal efficiency are high. Note that the volume of the fluid flowing can be calculated based on the measured value, for example, by providing a flow meter at an appropriate location in the fluid flow path.

  The method for introducing the scale inhibitor is not particularly limited, and for example, it can be added mechanically or artificially in the introduction part. When removing the scale, for example, from when the flow rate of the fluid in the pulp production facility falls below a predetermined value, until the flow rate recovers to a clean value or a value that does not cause a problem in pulp production. Scale inhibitors can be added continuously or intermittently. In addition, when aiming at prevention of scale formation / attachment, for example, a scale inhibitor can be added continuously or intermittently, and the amount of the scale inhibitor is particularly limited. Any amount can be used, and a constant amount may continue to be added or may be added in a modified manner. By introducing the scale inhibitor in this way, scale formation and adhesion can be prevented or the adhered scale can be removed.

As long as the inhibitor of a scale does not inhibit the effect | action which suppresses the scale, 1 or more other chemical | medical agents can be mixed and used. The other drug is not particularly limited, but is, for example, a chelating agent or a polymer compound, and the chelating agent is hydroxyethylethylenediaminetriacetic acid (HEDTA), glutamic acid diacetic acid (CMGA), hydroxyethylidene diphosphonic acid (HEDP) , Aminotrimethylenephosphonic acid (ATMP), ethylenediaminetetramethylenephosphonic acid (EDTMP), phosphonobutanetricarboxylic acid (PBTC), citric acid, succinic acid, phthalic acid, malic acid, tartaric acid, and salts thereof. It may be one or more selected. The amount of chelating agent other than ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, ethylenediaminetetramethylenephosphonic acid, phosphonobutanetricarboxylic acid and their salts is 3 times or less, 2 times or less, 1 time or less of the scale inhibitor of the present invention. 0.5 times or less, 0.3 times or less, or 0.1 times or less, and may not be included.

  The polymer compound may be one or more selected from the group consisting of known compounds. The amount of the polymer compound introduced is not particularly limited, but may be any amount as long as it does not inhibit the action of the scale inhibitor.

  The method for introducing the scale inhibitor is not particularly limited. For example, a solid inhibitor can be directly added to the fluid, or a solution (for example, an aqueous solution) of the inhibitor can be added to the fluid. Since the scale inhibitor of the present invention can be used in an aqueous solution, the reaction time with the scale attached to the production equipment for the ions forming the scale and the pulp, even for differences in the dissolution rate of the scale inhibitor, etc. Can be adjusted.

  Further, the scale inhibitor is added to the pulp slurry, and, for example, a bleaching process, a papermaking process, and the like can be sequentially performed to produce paper.

<Other pulp production facilities>
The pulp production facility in another embodiment of the present invention is a pulp production system using waste paper pulp. The pulp manufacturing system using waste paper pulp was de-inking system to remove the ink component by adding deinking agent, deinking system to make pulp slurry with mechanical force while mixing waste paper as raw material with water, deinked A washing system for washing the pulp slurry with a screen is provided.

  There is a case where calcium carbonate is added as a filler to the waste paper pulp and calcium chloride is added as a deinking aid, which causes a problem due to scale in the waste paper pulp manufacturing system. The scale suppression method of the present invention can also be used in a scale suppression method in a used paper pulp production system.

  The present invention will be described more specifically with reference to the following examples. However, the present invention is not limited to the following examples as long as the gist thereof is not exceeded.

The compounds used to suppress the scale used in the examples are as follows.

<Examples 1-4 and Comparative Examples 1-10>
The compound was added to a stainless steel autoclave containing 100 mL of black liquor and 1 g of calcium carbonate having a particle size of 1.5 mm in a pulp production facility so as to be 10 mmol / L or 20 mmol / L, respectively. A time simulated cooking test was conducted. Thereafter, the calcium ion concentration (mg / L) in the black liquor was measured to determine the calcium ion sequestration rate. The acidic compound used was neutralized to pH 7 with sodium hydroxide.

<Control 1>
The concentration of calcium ions in the black liquor before heating was measured.

<Control 2>
A simulated cooking test was conducted in the same manner as in Examples 1 to 4 except that the compound was not added to the autoclave.

１）化合物添加せず、２）ｐＨ７のナトリウム塩

1) No compound added 2) Sodium salt at pH 7

  In Examples 1 to 4, ethylenediaminetetraacetic acid tetrasodium, diethylenetriaminepentaacetic acid pentasodium, ethylenediaminetetramethylenephosphonic acid pentasodium, sodium salt of phosphonobutanetricarboxylic acid, the concentration of calcium ions in black liquor at high temperature It was able to be enlarged, and the calcium ion sequestration rate was also high. It was found that these compounds do not decompose even at high temperatures, can decompose scale, and can form chelates with calcium ions. In contrast, the compounds in Comparative Examples 1 to 10 have a lower function of decomposing scale than the compounds in Examples 1 to 4, and it is known that they can be used effectively while the production facility is stopped. Some cannot be used effectively.

<Example 5 and Comparative Example 11>
The flow rate of black liquor during cleaning is 350 m ³ / hr, and the production capacity of LBKP (hardwood bleached kraft pulp) is 850 t / day. In a continuous digester, the black liquor flow rate is reduced to 120 m ³ / hr due to scale. First, 0.4 wt / vol% trisodium citrate (40 mass% aqueous solution) with respect to the flow rate of 350 m ³ / hr of black liquor at the time of cleaning is added to the circulating suction pump portion of the heater at the bottom of the continuous digester. The addition continued for an elapsed time of 0.5-2.5 hours. Subsequently, 0.4 wt / vol% tetrasodium ethylenediaminetetraacetate (40% by mass aqueous solution) was added for an elapsed time of 4.0 to 6.0 hours with respect to a black liquor flow rate of 350 m ³ / hr during cleaning. I kept doing it. The flow rate of the black liquor was measured every 30 minutes to evaluate the inhibitory effect of the scale of each compound, the measured values are shown in the following table, and the change in the flow rate of the black liquor with respect to the elapsed time is shown in FIG.

ａ）化合物の添加を中止
ｂ）表中の「↓」は各化合物を２時間添加し続けたことを示す。

a) Discontinuation of compound addition b) “↓” in the table indicates that each compound was continuously added for 2 hours.

The black liquor flow rate did not change when trisodium citrate was added, but the black liquor flow rate was recovered to 310 m ³ / hr when tetrasodium ethylenediaminetetraacetate was added. And it confirmed that there was no change in the kappa number and the whiteness before and after washing, and the pulp quality was not adversely affected. Therefore, it was found that tetrasodium ethylenediaminetetraacetate can not only effectively sequester calcium ions at high temperatures, but also can decompose scales without decomposition even under high alkalinity.

<Example 6 and Comparative Example 12>
Flow of black liquor during cleaning is 150 meters ³ / hr, the production capacity of NBKP (softwood bleached kraft pulp) is reduced in a continuous digester, which is a 200t / day, by the scale, the flow rate of the black liquor to ^{40 m} 3 / hr First, in the circulating suction pump portion of the heater at the top of the continuous digester, 0.5 wt / vol% triethylsodium hydroxyethylethylenediamine triacetate (40% by mass aqueous solution) with respect to the black liquor flow rate of 150 m ³ / hr during cleaning ) Continued to be added for an elapsed time of 0.5-2.5 hours. Subsequently, 0.5 wt / vol% diethylenetriaminepentaacetic acid pentasodium (40 mass% aqueous solution) was added for an elapsed time of 4.0 to 6.0 hours with respect to the black liquor flow rate of 150 m ³ / hr during cleaning. I kept doing it. The flow rate of the black liquor was measured every 30 minutes to evaluate the effect of inhibiting the scale of each compound, the measured values are shown in the following table, and the change in the flow rate of the black liquor with respect to the elapsed time is shown in FIG.

ａ）化合物の添加を中止
ｂ）表中の「↓」は各化合物を２時間添加し続けたことを示す。

a) Discontinuation of compound addition b) “↓” in the table indicates that each compound was continuously added for 2 hours.

Although the black liquor flow rate was not changed by adding hydroxyethylethylenediamine triacetic acid trisodium salt, the black liquor flow rate was restored to 140 m ³ / hr when diethylenetriaminepentaacetic acid pentasodium salt was added. And it confirmed that there was no change in the kappa number and the whiteness before and after washing, and the pulp quality was not adversely affected. Therefore, it has been found that diethylenetriaminepentaacetic acid pentasodium not only effectively sequesters calcium ions at high temperatures, but also can decompose scales without decomposition even under high alkalinity.

<Example 7 and Comparative Example 13>
The flow rate of green liquid during cleaning is 150 m ³ / hr. In the crude green liquid supply piping, the green liquid flow rate is reduced to 90 m ³ / hr due to the scale. the so smelt a 0.5 wt / vol% with respect to the flow 150 meters ³ / hr of, firstly, 0.5 wt / vol% of hydroxyethyl ethylene diamine triacetic relative flow 150 meters ³ / hr of clean during the green liquor Trisodium acetate (40% by weight aqueous solution) was continuously added for an elapsed time of 0.5 to 2.5 hours. Subsequently, 0.5 wt / vol% of ethylenediaminetetramethylenephosphonate pentasodium (50 mass% aqueous solution) with respect to a flow rate of 150 m ³ / hr of the green liquor at the time of cleaning was changed to an elapsed time of 4.0 to 6.0 hours. The addition continued. The flow rate of black liquor was measured every 30 minutes to evaluate the effect of inhibiting the scale of each compound, the measured values are shown in the following table, and the change in flow rate of black liquor with respect to elapsed time is shown in FIG.

ａ）化合物の添加を中止
ｂ）表中の「↓」は各化合物を２時間添加し続けたことを示す。

a) Discontinuation of compound addition b) “↓” in the table indicates that each compound was continuously added for 2 hours.

The addition of hydroxyethylethylenediaminetriacetic acid trisodium did not change the flow rate of the green liquor. However, when ethylenediaminetetramethylenephosphonate pentasodium was added, the flow rate of the green liquor recovered to 140 m ³ / hr. And before and after washing | cleaning, it confirmed that there was no bad influence on the quality of the quicklime produced | generated in a kiln and the pulp quality produced by a cooking system. Therefore, it has been found that pentasodium ethylenediaminetetramethylenephosphonate can not only effectively sequester calcium ions at high temperatures, but also can decompose scales without decomposition even under high alkalinity.

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

Claims (1)

A method for controlling the scale of a pulp production facility, wherein the circulating fluid in the operating facility is composed of ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, ethylenediaminetetramethylenephosphonic acid, phosphonobutanetricarboxylic acid, and salts thereof. adding one or more compounds selected from Monodea is, equipment for adding the compound is a facility black liquor is flowing, scale suppression method.

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