Scale prevention method

Abstract

To provide a method for inhibiting the formation and growth of scale.SOLUTION: A scale prevention method includes capping a substance to be a factor of scale formation and / or scale itself with an oil solution.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for inhibiting the formation and growth of scale. [Background technology]

[0002] The Kraft process (KP process) is the predominant method of pulp production both in Japan and overseas. This is because the KP process can be used with a variety of wood types and produces pulp that is stronger than other pulps, as well as increased productivity through efficient recovery boilers and continuous digesters, and the development of continuous causticizing equipment has led to a dramatic improvement in the recovery rate of chemicals and energy and a significant reduction in production costs.

[0003] However, the types and ratios of resins and inorganic substances vary depending on the wood species and place of origin, and alkaline chemicals are used during cooking. As a result, water-insoluble scale is generated during the chemical recovery process, particularly in the black liquor concentration process. This scale adheres to the heat transfer plates in the tanks and evaporators, causing problems.

[0004] In the dilute black liquor tank where the black liquor produced in the pulp washing process is stored, the light calcium salts float when left to stand, and because the temperature inside the tank is around 80-90°C, the water evaporates. This causes lignin and other substances to coagulate around the calcium salts, growing scale, and concentrated lumps are generated one after another. If black liquor flows in from above and sends the scale to the next concentration process, it can cause blockages in the piping.

[0005] Conventional measures to address the above-mentioned problems associated with scale generation include the addition of scale inhibitors targeting inorganic substances, improvements to evaporator cleaning methods, the addition of viscosity reducers, etc. Conventional scale inhibitors aim to disperse scale using water-soluble components.

[0006] As scale inhibitors, Patent Document 1 proposes a water-soluble graft polymer obtained by graft-polymerizing a monoethylenically unsaturated monomer component onto a polyether compound, and Patent Document 2 proposes a composition using polyitaconic acid or a salt thereof and aminopolyacetic acid or a salt thereof. Patent Document 3 proposes the use of a polybasic aminocarboxylic acid compound in an aqueous system under alkaline conditions for cleaning scale from an evaporator in the black liquor concentration process. As viscosity reducers to be added in the black liquor concentration process, Patent Document 4 proposes urea, a quaternary ammonium salt, or an alkanolamine, and Patent Document 5 proposes a composition containing a radical scavenger. Patent Document 6 proposes a method for determining the scale accumulation level in a pulp mill evaporator or concentrator, and if the determined scale accumulation level is higher than a predetermined level, using an effective amount of a scale inhibitor composition, one or more compounds selected from the group consisting of monocarboxylic acids; polycarboxylic acids; fatty acids; low and high molecular weight aromatic aliphatic compounds and aromatic sulfonic acids; esters, anhydrides and amides thereof; low and high molecular weight amines; and combinations thereof, and monitoring the concentration of a scale inhibitor composition in a pulp waste liquor by using an inert fluorescent tracer. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 9-192691 [Patent Document 2] Japanese Patent Application Publication No. 7-119064 [Patent Document 3] JP 2007-63696 A [Patent Document 4] JP 2014-19993 A [Patent Document 5] JP 2019-11543 A [Patent Document 6] Special Publication No. 2010-527749 Summary of the Invention [Problem to be solved by the invention]

[0008] However, in Patent Documents 1 and 2, although it is effective against inorganic scale such as calcium carbonate, calcium phosphate, and silica, its effectiveness against organic salts such as lignin and fatty acids is not clear. In Patent Document 3, scale can be removed without stopping operation after scale generation, but scale generation cannot be suppressed. In Patent Documents 4 and 5, the operability in the concentration process is improved by reducing the black liquor viscosity, but the addition of a scale inhibitor, a pitch control agent, and the like is required. In Patent Document 6, a scale inhibitor composition is dissolved or dispersed in black liquor, which is pulp waste liquor, to capture and disperse calcium carbonate, calcium phosphate, and the like before they become scale, thereby inhibiting scale generation, but it is necessary to determine the scale accumulation level and monitor the concentration of the scale inhibitor composition in the pulp waste liquor.

[0009] In recent years, wood materials such as acacia have come to be used in the context of the need to reduce costs in pulp production, but low-cost wood materials such as acacia generate calcium salts, which are mainly organic calcium salts such as resin fatty acid salts, and the generation of scale has become common when such wood materials are used.

[0010] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for suppressing the occurrence and growth of scale. [Means for solving the problem]

[0011] In order to solve the above problems, the present inventors conducted extensive research and found that floating calcium salts are the cause of scale formation when using wood that generates the above-mentioned organic calcium salts. Calcium salts contain a large amount of organic salts such as fatty acid salts. The inventors discovered that by adding an oily component, it is possible to capture the floating scale containing organic salts with a large amount of fatty acid salts, and by forming an oil film on the top surface of the black liquor to prevent water evaporation, it is possible to suppress the scale from drying and hardening due to water evaporation, and further growth using the scale as a nucleus, thereby completing the present invention.

[0012] That is, the scale prevention method of the present invention is characterized by capping the scale and / or substances that cause scale generation with an oil agent. Effect of the Invention

[0013] According to the present invention, the occurrence and growth of scale can be suppressed. [Brief description of the drawings]

[0014] [Figure 1] This is a diagram showing an overview of the kraft pulp manufacturing process, including the cooking process, washing process, and the process in which the black liquor extracted in the washing process is concentrated and burned to recover the chemical solution and reuse it in the cooking process. [Diagram 2] FIG. 2 is a vertical cross-sectional view showing a schematic state in which an oil film is formed on the upper surface of black liquor in a tank of a system for handling black liquor. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, the embodiment of the present invention will be specifically described. The scale targeted by the method of the present invention is not particularly limited, but may be, for example, scale generated during the pulp production process, and the production method and type of pulp are not particularly limited. The pulp production method is not particularly limited, but may be, for example, a mechanical production method, a chemical production method, an intermediate production method between these, a production method using waste paper, etc.

[0016] Pulps produced by mechanical methods are not particularly limited, but examples thereof include mechanical pulps such as groundwood pulp and refiner ground pulp. Pulps produced by chemical methods are not particularly limited, but examples thereof include chemical pulps such as sulfite pulp and kraft pulp. Examples of the intermediate production method between mechanical and chemical methods include, but are not limited to, semi-chemical pulp and chemical ground pulp. Pulp produced using waste paper is not particularly limited, but examples thereof include waste paper pulp.

[0017] Among these, most of the pulp currently produced is chemical pulp, mainly kraft pulp, because it can be used with a variety of wood types, has high pulp strength, and can reduce production costs by improving chemical and energy recovery efficiency, etc. The method of the present invention is particularly suitable for use in chemical production methods, since it includes steps in which scale is particularly likely to occur (the cooking step and washing step, which will be described later), and among these, it is particularly suitable for use in the production process of chemical pulp, especially kraft pulp.

[0018] The kraft pulp manufacturing process includes the cooking and washing steps, and the black liquor extracted in the washing step is concentrated and burned to recover the chemicals and reuse them in the cooking step, as shown in Figure 1. In the cooking step, wood chips are fed into the cooking tank 1, where they are boiled with chemicals to extract wood fibers as pulp.

[0019] Next, in the washing process, the pulp is washed in a pulp washing device 2 to wash away the resin contained in the pulp. After that, the pulp is produced through a bleaching process. In the bleaching process, the pulp washed in the washing process is bleached to pure white pulp.

[0020] The resin that is washed off in the washing process is extracted as black liquor, which is concentrated and used as fuel for the boiler. In other words, the concentrated black liquor is burned to generate steam, which can be used to drive a generator to generate electricity. The thermal energy obtained by burning the black liquor can also be used for the paper drying process and other thermal energy used within the factory.

[0021] In the system that handles the black liquor generated in the pulp manufacturing process, the black liquor is transferred in sequence via piping to the diluted black liquor tank 3, evaporator 4, intermediate tank 5, evaporator 6, and raw liquor tank 7 in Fig. 1. The concentrated black liquor in the raw liquor tank 7 is supplied to a recovery boiler 8 and combusted, and the chemicals in the black liquor are recovered as a residue from the combustion. The chemicals are regenerated and supplied to the cooking tank 1 in the cooking process of the pulp plant for reuse.

[0022] In the black liquor concentration process, various materials and chemicals are contained in the black liquor, and therefore there are many substances that cause scale generation, such as calcium phosphate and resin fatty acid salts. The concentration of these substances increases, and the viscosity also increases. This makes it easy for hard scale to occur. This can cause the scale to clog or stick to pipes, evaporators, filters, etc., resulting in poor concentration.

[0023] In the scale prevention method of the present invention, the generation and growth of scale is inhibited by capping the substances that cause scale generation and / or the scale with an oil agent.

[0024] Substances that cause scale formation include oily substances in black liquor, such as organic salts, particularly resin fatty acid salts, which are mainly calcium salts.

[0025] In the present invention, scale broadly includes water-insoluble aggregates generated in black liquor, strong hard scale, etc. It also includes adherents and precipitates on structures in the system handling black liquor generated in the pulp manufacturing process, such as tanks, piping, evaporators, filters, etc. Examples of water-insoluble aggregates generated in black liquor include suspended matter or sludge that is also called sludge and is suspended in water, and aggregates of calcium salts and hydrophilic black substances such as lignin, primary walls, and cell middle layers.

[0026] In the present invention, capping includes capturing substances that cause scale generation and / or scale in the oil phase of an oil agent that is added to black liquor and dispersed in water without dissolving, and also includes forming an oil film of the oil agent on the upper surface of the black liquor and capturing these between the oil film and the black liquor.

[0027] In the present invention, by adding an oil agent, which is an oily component, the substances and / or scale that cause scale generation are captured, or as shown in Fig. 2, an oil film 11 is formed on the top surface of black liquor 10, i.e., on the water surface, to prevent water evaporation, and the substances and / or scale that cause scale generation are captured and removed between the oil film 11 and black liquor 10, thereby preventing the substances and / or scale that cause scale generation, such as oily substances and / or aggregates containing calcium salts, from proceeding to the next process. When water evaporates, it dries and hardens, which causes sludge to be generated, but this can be suppressed by forming an oil film 11 on the water surface to prevent evaporation. If a large amount of calcium salts proceed to the next process, they can cause scale to form during concentration. However, by capping the substances that cause scale and / or the scale, the amount of calcium salts that proceed to the concentration process can be reduced, thereby suppressing the formation of scale in the tank. If the particle size of the water-insoluble aggregates becomes large, it can cause clogging of filters, piping, and the next process. Furthermore, if the wall surface scale becomes large and strong, it is difficult to remove the strong scale, and a large amount of water and time are required. However, according to the present invention, the particle size of the water-insoluble aggregates is small, and the amount of calcium salt that advances to the next process is small. The wall surface scale is small and soft, and forms soft calcium salt aggregates in the oil film or below, making it easy to remove. With the method of the present invention, it is possible to omit the addition of water or black liquor to remove the scale, thereby reducing the effort and time required for recovery and removal.

[0028] During the concentration process, in the dilute black liquor tank 3 in Figure 1, sludge that is insoluble in the black liquor is generated. For example, calcium salts such as resin fatty acid salts rise to the surface of the black liquor and coagulate due to evaporation of water, generating sludge. If this sludge further grows as scale, some of it will be caught in the next process, causing contamination of the tank walls and clogging of filters, piping, and the next process. By capping the top of the black liquor with an oil agent, which is a water-insoluble base, in the dilute black liquor tank 3, where the black liquor is temporarily stored before concentration, it is possible to capture organic calcium salts and other substances that cause scale while suppressing the solidification of scale due to evaporation, and to suppress the generation of strong scale in the tank and evaporator.

[0029] In the evaporators 4 and 6, various components are dispersed, and various components are aggregated by concentration, and the viscosity increases by concentration. As a result, hard scale is generated around calcium salts such as resin fatty acid salts, and the hard scale remains without dispersing. For example, the evaporators 4 and 6 use a type that uses a heat transfer plate in which the liquid is uniformly distributed from above to the heating element by a distributor, but such evaporators 4 and 6 suffer from reduced heat transfer, poor concentration, and shutdown due to cleaning, etc. The method of the present invention can suppress these by adding an oil agent to the black liquor and capping the substances and / or scale that cause scale generation, such as oily substances and / or aggregates, with the oil agent.

[0030] Highly viscous black liquor scale occurs and grows in the intermediate tank 5 between the evaporators 4 and 6, and in the raw liquor tank 7 that stores concentrated black liquor. This causes contamination of the tank walls, which can lead to clogging of filters, piping, and subsequent processes. The scale prevention method of the present invention can suppress these problems by adding an oil agent to the black liquor to cap the scale.

[0031] In the above process, the oil film added to the black liquor can be collected by sucking it up from the top side. The scale in the collected matter becomes a soft calcium salt aggregate in the oil layer or in the lower layer, and is easy to remove because it does not become hard. The recovered material is in a liquid, semi-gel, or gel state at room temperature (25° C.). In terms of ease of handling as the oil is not incorporated into the scale, an oil that remains in a liquid state even when cooled to room temperature is preferred.

[0032] In the present invention, the oil agent is insoluble in water, or is poorly or slightly soluble in water. As an indicator, it forms an oil film on the upper surface of the black liquor. As an index of the insolubility of an oil agent in water, the n-octanol / water partition coefficient of the oil agent is not particularly limited, but is preferably 1.0 or more, more preferably 1.3 or more, even more preferably 1.8 or more, and particularly preferably 2.5 or more.

[0033] Since black liquor is used at temperatures ranging from about 80°C to the boiling point of water, the boiling point of the oil agent is preferably 100°C or higher, and more preferably 120°C or higher, so that the oil agent is not evaporated or lost when added to the black liquor.

[0034] When the oil is added to the black liquor, it is preferable that the oil is liquid and has low viscosity at the temperature, in order to further suppress the generation and growth of scale. 2 / sec or less is preferable, and 30 mm 2 / sec or less is preferable, and 20 mm 2 / sec or less is even more preferable. The kinematic viscosity here is a value measured using a Cannon-Fenske viscometer in accordance with JIS Z8803.

[0035] The oil agent is not particularly limited, but examples thereof include mineral oil, ester oil, glycol ether-based compound, higher fatty acid, higher alcohol, silicone oil, etc. These may be used alone or in combination of two or more.

[0036] Among these, mineral oil, ester oil, glycol ether compounds, and higher alcohols are preferred from the viewpoint of further suppressing the generation and growth of scale, and mineral oil and ester oil are more preferred. Furthermore, when recovering the oil film formed on the upper surface of the black liquor, the recovered material remains liquid even when cooled to room temperature, and the oil agent is not incorporated into the scale, making it easier to handle. Therefore, ester oil, glycol ether compounds, and higher alcohols are preferred.

[0037] It is preferable to use a combination of a mineral oil and one or more selected from an ester oil, a glycol ether compound, and a higher alcohol, in order to achieve both suppression of the generation and growth of scale and easier handling of the recovered oil film formed on the upper surface of the black liquor even when cooled to room temperature when the oil film is recovered.

[0038] The mineral oil is not particularly limited, but examples thereof include petroleum-based hydrocarbons, aromatic hydrocarbons, paraffin-based hydrocarbons, naphthenic hydrocarbons, and olefin-based hydrocarbons.

[0039] The ester oil is not particularly limited, but may be, for example, an ester of a fatty acid and an alcohol, or an ester of a fatty acid and an alkylene oxide having 3 or more carbon atoms. The fatty acid constituting the ester oil is not particularly limited, but may be, for example, linear or branched, saturated or unsaturated, or monobasic or polybasic. The alcohol constituting the ester oil is not particularly limited, but may be, for example, a monohydric alcohol or a polyhydric alcohol.

[0040] Among the acids constituting the ester oil, fatty acids having 2 to 24 carbon atoms are usually used as the monobasic acids, and such fatty acids may be either linear or branched, and may be either saturated or unsaturated. Specifically, acetic acid, propionic acid, linear or branched butanoic acid, linear or branched pentanoic acid, linear or branched hexanoic acid, linear or branched heptanoic acid, linear or branched octanoic acid, linear or branched nonanoic acid, linear or branched decanoic acid, linear or branched undecanoic acid, linear or branched dodecanoic acid, linear or branched tridecanoic acid, linear or branched tetra ... saturated fatty acids such as linear or branched pentadecanoic acid, linear or branched hexadecanoic acid, linear or branched heptadecanoic acid, linear or branched octadecanoic acid, linear or branched hydroxyoctadecanoic acid, linear or branched nonadecanoic acid, linear or branched icosanoic acid, linear or branched heneicosanoic acid, linear or branched docosanoic acid, linear or branched tricosanoic acid, and linear or branched tetracosanoic acid; acrylic acid, linear or branched butenoic acid, linear or branched pentenoic acid, linear or branched hexenoic acid, linear or branched heptenoic acid, linear or branched octenoic acid, linear or branched nonenoic acid, linear or branched decenoic acid, linear or branched undecenoic acid, linear or branched dodecenoic acid, linear or branched tridecenoic acid, linear or branched tetradecenoic acid, linear or branched pentadecenoic acid, linear or branched Examples of unsaturated fatty acids include branched hexadecenoic acid, linear or branched heptadecenoic acid, linear or branched octadecenoic acid, linear or branched hydroxyoctadecenoic acid, linear or branched nonadecenoic acid, linear or branched icosenoic acid, linear or branched henicosenoic acid, linear or branched docosenoic acid, linear or branched tricosenoic acid, linear or branched tetracosenoic acid, and mixtures thereof.

[0041] Among the alcohols constituting the ester oil, the monohydric alcohol generally has 1 to 24 carbon atoms, preferably 1 to 12 carbon atoms, and more preferably 1 to 8 carbon atoms. Such an alcohol may be either linear or branched, and may be either saturated or unsaturated. Specific examples of the alcohol having 1 to 24 carbon atoms include methanol, ethanol, linear or branched propanol, linear or branched butanol, linear or branched pentanol, linear or branched hexanol, linear or branched heptanol, linear or branched octanol, linear or branched nonanol, linear or branched decanol, linear or branched undecanol, linear or branched dodecanol, linear or branched tridecanol, linear or branched tetradecanol, linear or branched pentadecanol, linear or branched hexadecanol, linear or branched heptadecanol, linear or branched octadecanol, linear or branched nonadecanol, linear or branched icosanol, linear or branched henicosanol, linear or branched tricosanol, linear or branched tetracosanol, and mixtures thereof.

[0042] Among the alcohols constituting the ester oil, the polyhydric alcohol is usually one having a hydric to decahydric alcohol, preferably one having a hydric to hexahydric alcohol. Specific examples of the dihydric to decahydric polyhydric alcohol include dihydric alcohols such as ethylene glycol, diethylene glycol, polyethylene glycol (trimer to pentamer of ethylene glycol), propylene glycol, dipropylene glycol, polypropylene glycol (trimer to pentamer of propylene glycol), 1,3-propanediol, 1,2-propanediol, 1,3-butanediol, 1,4-butanediol, 2-methyl-1,2-propanediol, 2-methyl-1,3-propanediol, 1,2-pentanediol, 1,3-pentanediol, 1,4-pentanediol, 1,5-pentanediol, and neopentyl glycol; glycerin, polyglycerin (dimer to octamer of glycerin, such as diglycerin and triglycerin); polyhydric alcohols such as glycerol, tetraglycerin, etc., trimethylolalkanes (trimethylolethane, trimethylolpropane, trimethylolbutane, etc.) and dimers to octamers thereof, pentaerythritol and dimers to tetramers thereof, 1,2,4-butanetriol, 1,3,5-pentanetriol, 1,2,6-hexanetriol, 1,2,3,4-butanetetrol, sorbitol, sorbitan, sorbitol glycerin condensates, adonitol, arabitol, xylitol, mannitol, etc.; sugars such as xylose, arabinose, ribose, rhamnose, glucose, fructose, galactose, mannose, sorbose, cellobiose, maltose, isomaltose, trehalose, sucrose, etc., and mixtures thereof.

[0043] Among alcohols, trihydric or lower alcohols are preferred, and dihydric or lower alcohols are more preferred, since they have low viscosity and are more suitable for suppressing the occurrence and growth of scale.

[0044] The total number of carbon atoms of the fatty acid and alcohol in the ester oil is preferably large in order to prevent the oil from becoming miscible with water when decomposed at the heating temperature in the black liquor handling system and to more effectively suppress the generation and growth of scale. From this point of view, the total number of carbon atoms is preferably 4 or more, and more preferably 8 or more.

[0045] Examples of linear ester oils include, but are not limited to, ethyl butyrate, butyl butyrate, hexyl butyrate, ethyl laurate, butyl laurate, hexyl laurate, ethyl stearate, butyl stearate, hexyl stearate, ethyl oleate, butyl oleate, and hexyl oleate.

[0046] Examples of branched ester oils include, but are not limited to, esters of fatty acids having a branched carbon chain length and alcohols having a linear carbon chain length, such as ethyl 2-ethylhexylate, butyl 2-ethylhexylate, octyl 2-ethylhexylate, ethyl isooctylate, butyl isooctylate, octyl isooctylate, ethyl isostearate, butyl isostearate, octyl isostearate, and isooctyl isostearate; 2-ethylhexyl butyrate, 2-ethylhexyl laurate, 2-ethylhexyl oleate, Examples of such esters include esters of fatty acids having a straight carbon chain length and alcohols having a branched carbon chain length, such as isooctyl butyrate, isooctyl laurate, isooctyl oleate, isostearyl butyrate, isostearyl laurate, and isostearyl oleate, and esters of fatty acids having a branched carbon chain length and alcohols having a branched carbon chain length, such as 2-ethylhexyl 2-ethylhexylate, isooctyl 2-ethylhexylate, isostearyl 2-ethylhexylate, 2-ethylhexyl isostearate, and isooctyl isostearate.

[0047] Examples of saturated ester oils include, but are not limited to, ethyl butyrate, butyl butyrate, hexyl butyrate, ethyl laurate, butyl laurate, hexyl laurate, ethyl stearate, butyl stearate, hexyl stearate, butyl 2-ethylhexylate, octyl 2-ethylhexylate, ethyl isooctylate, butyl isooctylate, octyl isooctylate, ethyl isostearate, butyl isostearate, octyl isostearate, and isooctyl isostearate.

[0048] The unsaturated ester oil is not particularly limited, but examples thereof include ethyl oleate, butyl oleate, hexyl oleate, 2-ethylhexyl oleate, oleyl butyrate, oleyl laurate, and oleyl stearate.

[0049] Among these, unsaturated ester oils are preferred because the viscosity of the oil does not become too high and handling is easier.

[0050] The number of ester bonds in one ester oil molecule is not particularly limited, but examples include 1 to 4 (monoester, diol monoester, diester, diol diester, triester, tetraester), etc. The number of ester bonds in one ester oil molecule is preferably 3 or less (monoester, diester, triester), and more preferably 2 or less (monoester, diester), in order to prevent the viscosity of the oil from becoming too high and to facilitate handling.

[0051] Examples of monoesters include, but are not limited to, alkyl butyrate esters such as ethyl butyrate, butyl butyrate, and octyl butyrate; alkyl 2-ethylhexate esters such as ethyl 2-ethylhexylate, butyl 2-ethylhexylate, and octyl 2-ethylhexylate; alkyl isostearate esters such as ethyl isostearate, butyl isostearate, octyl isostearate, and isooctyl isostearate; and alkyl oleate esters such as octyl octylate, butyl oleate, octyl oleate, and isooctyl oleate.

[0052] The diol monoester is not particularly limited, but examples thereof include propylene glycol fatty acid esters, neopentyl glycol fatty acid esters, etc., which are esters of the above dihydric alcohols and fatty acids having 4 to 30 carbon atoms. Specific examples thereof include propylene glycol caprylic acid ester, propylene glycol capric acid ester, propylene glycol lauric acid ester, propylene glycol palmitic acid ester, propylene glycol stearate, propylene glycol oleic acid ester, neopentyl glycol lauric acid ester, neopentyl glycol palmitic acid ester, neopentyl glycol stearate, neopentyl glycol oleic acid ester, etc.

[0053] The diester is not particularly limited, but examples thereof include propylene glycol fatty acid diester, neopentyl glycol fatty acid diester, etc., which are diesters of the above dihydric alcohols and fatty acids having 4 to 30 carbon atoms. Specific examples thereof include propylene glycol caprylic acid diester, propylene glycol capric acid diester, propylene glycol lauric acid diester, propylene glycol palmitic acid diester, propylene glycol stearic acid diester, propylene glycol oleic acid diester, propylene glycol caprylic acid capric acid diester, propylene glycol capric acid diester, neopentyl glycol lauric acid diester, neopentyl glycol palmitic acid diester, neopentyl glycol stearic acid diester, neopentyl glycol oleic acid diester, etc. The fatty acid may be used alone or in combination of two or more.

[0054] The triester is not particularly limited, but examples thereof include tri-fatty acid trimethylolpropane esters, tri-fatty acid pentaerythritol esters, etc., which are triesters of the above-mentioned polyhydric alcohols and fatty acids having 4 to 30 carbon atoms. Specific examples thereof include tricaprylic acid trimethylolpropane ester, tricapric acid trimethylolpropane ester, trilauric acid trimethylolpropane ester, tripalmityl acid trimethylolpropane ester, tristearate trimethylolpropane ester, trioleic acid trimethylolpropane ester, tricaprylic acid capric acid trimethylolpropane ester, tricapric acid lauric acid trimethylolpropane ester, trilauric acid pentaerythritol ester, tripalmityl acid pentaerythritol ester, tristearate pentaerythritol ester, trioleic acid pentaerythritol ester, rapeseed oil, palm oil, coconut oil, and other vegetable oils, beef tallow, lard, and other animal oils, and fish oils. The fatty acids may be used alone or in combination of two or more.

[0055] The tetraester is not particularly limited, but examples thereof include tetrafatty acid pentaerythritol esters of fatty acids, which are tetraesters of the above polyhydric alcohols and fatty acids having 4 to 30 carbon atoms. Specific examples thereof include tetralauric acid pentaerythritol ester, tetrapalmitic acid pentaerythritol ester, tetrastearic acid pentaerythritol ester, tetraoleic acid pentaerythritol ester, tetracaprylcapric acid pentaerythritol ester, etc. The fatty acids may be used alone or in combination of two or more.

[0056] The glycol ether compound is not particularly limited, but may be, for example, a straight-chain, branched, or cyclic compound that contains carbon atoms, hydrogen atoms, and ether bonds.

[0057] Examples of glycol ether compounds include alkylene glycol, alkylene glycol monoalkyl ether, alkylene glycol dialkyl ether, etc. The number of carbon atoms in the alkylene unit is preferably 2 to 5.

[0058] The alkylene glycol is not particularly limited, but from the viewpoint of being insoluble in water and further suppressing the occurrence and growth of scale, it is preferable that the alkyl group is 3 or more. Specific examples include polypropylene glycol and polybutylene glycol.

[0059] The alkylene glycol monoalkyl ether and the alkylene glycol dialkyl ether are not particularly limited, but from the viewpoint of being insoluble in water and further suppressing the occurrence and growth of scale, for example, it is preferable that the alkyl group is 3 or more. The number of carbon atoms of the alkyl group is preferably 4 to 30. Specific examples include an oleyl alcohol PO (4 mol) adduct, an oleyl alcohol PO (8 mol) adduct, an oleyl alcohol PO (12 mol) adduct, a 2-ethylhexyl alcohol PO (4 mol) adduct, a 2-ethylhexyl alcohol PO (8 mol) adduct, a 2-ethylhexyl alcohol PO (12 mol) adduct, an oleyl alcohol BO (4 mol) adduct, an oleyl alcohol BO (8 mol) adduct, an oleyl alcohol BO (12 mol) adduct, a 2-ethylhexyl alcohol BO (4 mol) adduct, a 2-ethylhexyl alcohol BO (8 mol) adduct, a 2-ethylhexyl alcohol BO (12 mol) adduct, and the like.

[0060] The higher fatty acid is not particularly limited, and may be, for example, either linear or branched, and may be either saturated or unsaturated. The number of carbon atoms of the higher fatty acid is preferably 6 to 24, more preferably 8 to 20, from the viewpoint that the solubility in water is lower.

[0061] The higher fatty acid is not particularly limited, but examples thereof include caproic acid, 2-ethylhexyl acid, isostearic acid, oleic acid, linolenic acid, and linoleic acid.

[0062] The higher alcohol is not particularly limited, but examples thereof include saturated alcohols such as 2-ethylhexyl alcohol, lauryl alcohol, palmityl alcohol, stearyl alcohol, and isostearyl alcohol, and unsaturated alcohols such as oleyl alcohol. Unsaturated alcohols are preferred because they are liquid at low temperatures and easier to handle.

[0063] Silicone oils include, but are not limited to, for example, linear, cyclic, or branched polymers or oligomers of monomeric silicon / oxygen (organosiloxane) monomers, optionally with some additional functional groups. The polymer backbone is typically composed of alternating silicon and oxygen atoms. The silicon atoms may have various substituents, which may be the same or different. The functional endblocking groups may have nitrogen or hydroxyl moieties.

[0064] Examples of silicone oils include silicone compounds such as dimethylpolysiloxane, methylhydrogenpolysiloxane, methylphenylpolysiloxane, stearoxymethylpolysiloxane, polyether-modified organopolysiloxane, fluoroalkyl-polyoxyalkylene-co-modified organopolysiloxane, alkyl-modified organopolysiloxane, terminal-modified organopolysiloxane, fluorine-modified organopolysiloxane, amino-modified organopolysiloxane, silicone gel, acrylic silicone trimethylsiloxysilicate, and cyclopentasiloxane.

[0065] In the method of the present invention, when an oil agent is added to the black liquor, the oil agent may be added alone or as a composition containing the oil agent. When the composition containing the oil agent is added, the components other than the oil agent are not particularly limited, and examples thereof include water, a surfactant, a defoaming agent, a chelating agent, and the like.

[0066] In the method of the present invention, the amount of oil added to the black liquor is preferably 1% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more, based on the black liquor in the tank, from the viewpoint of further suppressing the generation and growth of scale. The upper limit is not particularly limited, but is preferably 40% by mass or less, more preferably 30% by mass or less, and even more preferably 20% by mass or less, from the viewpoint of reducing the amount of oil used and suppressing the generation and growth of scale. EXAMPLES

[0067] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. <Examples 1-1 to 1-6 and Comparative Examples 1 to 3> The oils added to the black liquor were those listed in Table 1. Table 1 shows the solubility of the oils in water and their n-octanol / water partition coefficients. The black liquor was mixed with 5% by mass of sediment, which corresponds to the mass of scale, and dispersed by ultrasonic waves. The mixture was then filtered through a 100-mesh filter cloth to prepare a black liquor sample. 300 mL of the black liquor sample and the amount of oil solution shown in Table 1 were added to a stainless steel beaker with a diameter of 7.2 cm and a height of 11.0 cm, and the mixture was heated at approximately 85°C for 3 hours. After that, the discharge rate was reduced to approximately 50 g / min, and the black liquor solution (black liquor portion: approximately 290 ml, oil solution portion: remaining 20 to 40 ml) was extracted from the bottom, and the dirt on the wall and the condition of the collected sample were checked, and the mass of scale, which is the residue in the beaker, was measured. Wall stains were evaluated based on the scale mass according to the following criteria. ◎+: Scale mass is less than 3g ◎: Scale mass is 3g or more and less than 6g ○: Scale mass is 6g or more and less than 8g △: Scale mass is 8g or more and less than 10g ×: Scale mass is 10g or more

[0068] The results of the above measurements and evaluations are shown in Table 1.

[0069] [Table 1]

[0070] <Examples 2-1 to 2-18, Comparative Example 1> In the same manner as above, the black liquor sample and oil were added to the beaker and heated, then the black liquor solution was removed and the mass of the scale remaining in the beaker was measured. The amount of oil added was 30 mL. The kinetic viscosity of the oil at 40°C is shown in Table 2. The wall fouling was evaluated based on the scale mass using the above criteria, and the condition of the recovered oil at room temperature was also confirmed. The condition of the collected samples at room temperature was evaluated according to the following criteria. ◎: Liquid ○: Semi-gel △: Gel-like

[0071] The results of the above measurements and evaluations are shown in Table 2.

[0072] [Table 2] [Explanation of symbols]

[0073] 1 Digester 2 Pulp washing equipment 3. Dilute black liquor tank 4. Evaporator 5. Intermediate Tank 6. Evaporator 7. Concentrate tank 8 Recovery Boiler 9 Tank wall 10 Black liquor 11 Oil slick

Claims

1. A method for preventing scale by capping scale-causing substances and / or scale with an oil agent.

2. 2. The method for preventing scale formation according to claim 1, wherein the oil agent is at least one selected from the group consisting of mineral oil, ester oil, glycol ether compound, higher fatty acid, higher alcohol, and silicone oil.

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