JP2007289817A - Washing method of process water system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a washing method of a process water system which can exhibit a sufficient washing effect against deposit containing barium sulfate and calcium sulfate in a short time. <P>SOLUTION: In the washing method of a process water system, a first washing liquid containing at least one of a carbonate, a phosphate, and a phosphonate, and having a pH of 8 or higher is circulated into the process water system in which the deposit containing barium sulfate and/or calcium sulfate exists (a first washing process), and then a second washing liquid containing hydrochloric acid, nitric acid, sulfamic acid, organic acids, etc. is circulated into the process water system (a second washing process). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a process water-based cleaning method in which a deposit containing barium sulfate or calcium sulfate is present.

In process water systems, deposits containing barium sulfate or calcium sulfate may become a problem due to adhesion. For example, dirt that adheres and accumulates in the paper / pulp manufacturing process water system is barium sulfate or calcium sulfate generated by barium or calcium derived from wood and sulfuric acid used in the papermaking process, pitch component of pulp, fine fibers, printing ink, It has a complicated composition consisting of sizing agents and the like. Recently, as the paper / pulp manufacturing process is closed and the paper making speed is increased, serious problems such as a decrease in product quality and a decrease in production efficiency due to these soil components are caused and become serious. Among these, barium sulfate and calcium sulfate are hard lump deposits as deposits, are insoluble in acids and alkalis, are difficult to remove, and cause various obstacles.
Further, in the manufacturing process water system of the outer wall material using gypsum such as gypsum board, the raw material gypsum (that is, calcium sulfate) adheres to the piping and the manufacturing apparatus, which causes a problem.
Furthermore, even in the manufacturing process water system in the salt industry, calcium sulfate adheres to the piping and the concentration kettle, which causes a problem.

  Conventionally, as process water-based cleaning liquids, alkali cleaning agents such as caustic soda and soda ash and aminocarboxylic acid chelating agents such as ethylenediaminetetraacetic acid sodium salt (EDTA-Na salt) have been used. And deposits made of calcium sulfate are not effective and have been problematic.

  For this reason, as cleaning liquids with further improved cleaning effects, cleaning liquids containing organic acids such as citric acid, malic acid, tartaric acid (Patent Document 1), cleaning liquids using diphosphonic acid and hydrogen peroxide in combination (Patent Document 2), A cleaning liquid (Patent Document 3) containing 1-hydroxyethylidene-1,1-diphosphonic acid or a salt thereof has been proposed for a paper / pulp manufacturing process.

Japanese Patent Laid-Open No. 62-141187 Japanese Patent No. 2543214 Japanese Patent No. 2746563

  However, even when using the cleaning solution of the above-mentioned patent document, a deposit containing barium sulfate or calcium sulfate has a problem that it cannot exhibit a sufficient cleaning effect or requires long-time cleaning. .

  The present invention has been made in view of the above-described conventional situation, and is a cleaning liquid for paper / pulp manufacturing process capable of exhibiting a sufficient cleaning effect in a short time for a deposit containing barium sulfate or calcium sulfate. Providing a system cleaning method is a problem to be solved.

  In the process water-based cleaning method of the present invention, the first cleaning solution containing at least one of carbonate, phosphate and phosphonate and having a pH of 8 or more is used as a deposit containing barium sulfate and / or calcium sulfate. A first cleaning step for circulating in the existing process water system; and a second cleaning step for circulating a second cleaning liquid containing an acid other than sulfuric acid in the process water system after the completion of the first cleaning process. .

  The actions of the first cleaning liquid and the second cleaning liquid in the present invention are considered as follows. That is, first, the carbonate, phosphate and phosphonate contained in the first cleaning solution undergo a substitution reaction on the surface of the sparingly soluble calcium sulfate or barium sulfate, and then the carbonate, phosphate and phosphonate. (First cleaning step). Further, calcium or barium salts generated by the substitution reaction are dissolved and removed by an acid other than sulfuric acid contained in the second cleaning liquid (second cleaning step). According to the test results of the inventors, an excellent cleaning effect can be obtained if the pH of the first cleaning liquid is 8 or more. Particularly preferred pH is 9 or more. Thereby, calcium sulfate and barium sulfate in the deposit are dissolved and removed in a short time.

  Therefore, according to the process water-based cleaning method of the present invention, a sufficient cleaning effect can be exhibited in a short time with respect to a deposit containing barium sulfate or calcium sulfate.

As a method for preparing the first cleaning liquid, (1) a method of adding a concentrated liquid (for example, 10 wt% to 50 wt%) in which at least one of carbonate, phosphate and phosphonate is dissolved, to the process water, (2) There is a method in which at least one of carbonate, phosphate and phosphonate is added and dissolved in the process water as it is, but the former method, which does not easily cause a difference in concentration depending on the location, has a uniform cleaning effect. This is more preferable. The pH can be adjusted using sodium hydroxide, potassium hydroxide, hydrochloric acid or the like. Since the pH of the first cleaning solution decreases as the cleaning progresses, measure the pH during the cleaning, and if the pH falls below 8, adjust the pH by adding the first cleaning solution or adding sodium hydroxide or potassium hydroxide. Do. The concentration of carbonate, phosphate and phosphonate as active ingredients in the first cleaning liquid is appropriately selected according to the type of carbonate, phosphate and phosphonate used, the type of deposit to be cleaned, etc. Usually, it is 0.1 wt% to 5 wt%.
In addition, a wet penetrant such as a surfactant, an antifoaming agent, a chelating agent, a corrosion inhibitor and the like may be used in combination as long as the effect of the first cleaning agent is not hindered.

In addition, as a method for preparing the second cleaning liquid, (1) a method of preparing a concentrated liquid of acid other than sulfuric acid (for example, 20% by weight to 50% by weight) with fresh water after discharging the first cleaning liquid, (2 ) After cleaning with the first cleaning liquid, without discharging the first cleaning liquid, a concentrated liquid of acid other than sulfuric acid (for example, 20 wt% to 50 wt%) is added to the first cleaning liquid as it is to make it acidic. There is a method for preparing a cleaning solution.
The concentration of the acid other than sulfuric acid as the active ingredient in the second cleaning liquid is determined based on the type of acid used, the type of the first cleaning liquid, the type of deposit to be cleaned, the required cleaning level, and the cleaning level with the first cleaning liquid. Although it may be selected as appropriate in consideration, it is usually 0.1% by weight to 5% by weight.
Moreover, you may use together wet penetrants, such as surfactant, an antifoamer, a chelating agent, a corrosion inhibitor, etc. in the range which does not prevent the effect of a 2nd cleaning agent.

  In the process water-based cleaning method of the present invention, it is preferable that after the first cleaning process is completed, the first cleaning liquid is discharged from the process water system and then the second cleaning process is performed. This is because, since the first cleaning liquid is alkaline, if the first cleaning liquid remains in the second cleaning step, the amount of acid consumed increases by the amount required for neutralization. In particular, when carbonate is contained in the first cleaning liquid, if an acid is added while leaving the first cleaning liquid in the process water system, a large amount of foaming may occur due to carbon dioxide, which may overflow.

  The first cleaning liquid is preferably an aqueous carbonate solution. When carbonate is contained in the first cleaning liquid, carbon dioxide bubbles are generated by an acid other than sulfuric acid circulated in the second cleaning step, and the deposit is physically removed by the foaming action. Because it is played.

  Furthermore, the second cleaning liquid is preferably an aqueous solution containing at least one of sulfamic acid, citric acid, and malic acid. These acids are relatively safe acids in handling, and it is easy to ensure work safety. Moreover, since citric acid and malic acid have the effect of forming a complex with barium and calcium to increase the dissolving power, the detergency is increased.

  The process water-based cleaning method of the present invention can be suitably used for a paper / pulp production process water system. In the pulp and paper industry, with the recent expansion of environment-friendly bleach-free (ECF) pulp, chlorine dioxide is used instead of chlorine, and sulfuric acid is used for bleaching under acidic conditions. Since the paper / pulp production process water system contains barium and calcium derived from wood, it tends to react with sulfuric acid used in the bleaching process to generate barium sulfate and calcium sulfate. Specifically, the preparation process, including equipment, piping, fan pumps, filters (including drum washers and diffusers) and screens around the acid hydrolysis tower in the previous stage of the ECF bleaching process and the chlorine dioxide tower in the ECF bleaching process It is easy to form deposits on screens, pipes and fan pumps, distributors and slice lips, white water silos and pit walls, pipes and fan pumps in the papermaking process, and they are applied to cleaning these parts. Further, the present invention is applied to washing and removing deposits containing barium sulfate and calcium sulfate in filters after pulp cooking (including drum washers and diffusers).

Examples of the carbonate, phosphate and phosphonate contained in the first cleaning liquid in the process water-based cleaning method of the present invention include sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, sodium phosphate, and hydrogen phosphate 2 Sodium salt of sodium, sodium dihydrogen phosphate, potassium phosphate, dipotassium hydrogen phosphate, potassium dihydrogen phosphate, 1-hydroxyethylidene-1, 1-diphosphonic acid (HEDP) 1-4 salt (HEDP · 1-4Na ), 1 to 4 potassium salt of 1-hydroxyethylidene-1, 1-diphosphonic acid (HEDP) (HEDP 1 to 4K), 1 to 5 sodium of 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC) 1 to 5 salts of salt (PBTC · 1-5Na), 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC) Um salt (PBTC · 1-5K), 1-6 sodium salt of nitrilotrismethylenephosphonic acid (NTP) (NTP · 1-6Na), 1-6 potassium salt of nitrilotrismethylenephosphonic acid (NTP) (NTP · 1 ˜6K), N, N, N ′, N′-tetrakis (phosphonomethyl) ethylenediamine (EDTMP) 1-8 sodium salt (EDTMP · 1-8Na), N, N, N ′, N′-tetrakis (phosphonomethyl) 1-8 potassium salt (EDTMP * 1-8K) etc. of ethylenediamine (EDTMP) etc. are mentioned. Among them, sodium carbonate, potassium carbonate, 1-hydroxyethylidene-1, 1-diphosphonic acid (HEDP) 3-4 sodium salt (HEDP-3-4Na), 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC) 3-4 sodium salt (PBTC · 3-4Na) is preferred. You may use these 1 type or in combination of 2 or more types.
Examples of the acid contained in the second cleaning liquid include acids other than sulfuric acid such as sulfamic acid, organic acids (citric acid, malic acid, tartaric acid, glycolic acid, etc.), methanesulfonic acid, hydrochloric acid, nitric acid, and the like. Of these, sulfamic acid, citric acid and malic acid are preferred. You may use these 1 type or in combination of 2 or more types.

Specific methods of the first cleaning process and the second cleaning process are, for example, as follows.
First washing step Sodium carbonate is stirred and dissolved in fresh water to prepare a 10% by weight aqueous sodium carbonate solution, and 10% by weight aqueous sodium carbonate solution is added while circulating the process water to be washed. A predetermined concentration in the range of 0.1 wt% to 5 wt% is used as the first cleaning liquid. Steam or the like is blown into the process water system while circulating the first cleaning liquid with a pump or the like, and the first cleaning liquid is heated. The heating target temperature of the first cleaning liquid is usually determined appropriately according to the target process, with 30 to 80 ° C. as a guide. For example, in the cleaning of the diffuser in the chlorine-free bleaching process, the temperature is increased to 70 ° C. to 80 ° C., and in the screen of the preparation process or the inlet of the paper making process, the temperature is increased to 30 to 50 ° C. The cleaning time by circulation of the first cleaning liquid is appropriately determined in consideration of the type of barium sulfate / calcium sulfate-containing deposit to be cleaned and the required cleaning level, but it is usually 1 hour to 3 hours. During the cleaning with the first cleaning liquid, the pH of the cleaning liquid is appropriately measured, and when the pH is 8 or less, an aqueous sodium hydroxide solution, an aqueous potassium hydroxide solution, or about 10% by weight sodium carbonate aqueous solution is added to the cleaning liquid. The pH is maintained at 8 or higher.

Second washing step After washing with the first washing solution, the first washing solution is discharged, fresh water is added and the process water system to be washed is circulated while gradually adding a 20 wt% aqueous sulfamic acid solution. The second cleaning liquid is prepared so that the concentration of the liquid reaches a predetermined concentration within the range of 0.1 wt% to 5 wt%. As a concentration method of sulfamic acid, there is a diazotization titration method of the Japanese Pharmacopoeia. By gradually adding the sulfamic acid aqueous solution, the fresh water in the process including the remaining liquid of the first cleaning liquid becomes gradually acidic, and the sodium carbonate remaining in the process can be decomposed by the sulfamic acid to generate fine bubbles. . Due to the bubbles, the barium sulfate and / or calcium sulfate-containing deposit is cracked or the deposit is partially peeled off from the adhesion surface. The second cleaning liquid is continuously circulated, and the barium sulfate and / or calcium sulfate-containing deposit is peeled and dissolved and cleaned. During the cleaning with the second cleaning liquid, the pH of the cleaning liquid is appropriately measured, and when the pH is near neutral of 6.5 or more, an aqueous sulfamic acid solution is added to keep the pH of the second cleaning liquid acidic. The cleaning time with the second cleaning liquid is usually 1 hour to 3 hours. After the cleaning is finished, the second cleaning liquid is discharged and the cleaning is finished.
Further, when the first cleaning liquid is an aqueous solution of phosphate and / or phosphonate, the 20% by weight sulfamic acid aqueous solution is gradually added while circulating the first cleaning liquid without discharging the first cleaning liquid, The second cleaning liquid can be prepared while neutralizing the first cleaning liquid with sulfamic acid. Usually, the first cleaning liquid that has been subjected to the cleaning treatment is discharged, neutralized with hydrochloric acid or sulfuric acid, and then discharged into a river after being subjected to drainage treatment. The first cleaning liquid is neutralized with sulfamic acid while the first cleaning liquid is being neutralized. 2. By preparing the cleaning solution, neutralization treatment costs are reduced by hydrochloric acid or sulfuric acid.

Examples in which the present invention is further embodied will be described below in comparison with comparative examples.
Examples 1-9 and Comparative Examples 1-6
<Preparation of first cleaning liquid and second cleaning liquid>
In Examples 1-9 and Comparative Examples 1-6, as shown in Table 1, 1% sodium carbonate aqueous solution, 1% sodium phosphate aqueous solution and 0.9% 2-phosphonobutane-1 as the first cleaning liquid, It was selected from tetrasodium 2,4-tricarboxylate aqueous solution and adjusted to various pH with hydrochloric acid (pH 8 or more in Examples 1 to 9, pH 6 or less in Comparative Examples 1 to 6). The second cleaning liquid was selected from hydrochloric acid, malic acid, sulfamic acid, and citric acid, and the concentration was 1% by mass.

<Barium sulfate dissolution test>
1st washing | cleaning process 200 ml of 1st washing | cleaning liquid prepared in the said Examples 1-9 and Comparative Examples 1-6 is taken, and it puts into a 300 ml Erlenmeyer flask, and also adds 0.2 g of reagent barium sulfate. And after setting to a rotary shaker, it was shaken at 150 rpm for 90 minutes.
Second Washing Step After standing for 5 minutes, the supernatant liquid is discarded by decantation, 200 ml of the second washing liquid is added, and the same operation is performed. And No. of known weight. The mixture was filtered with 5C filter paper, washed with water, dried and weighed to determine the weight of the residue. As a result, as shown in Table 1, in Examples 1 to 9, dissolution of barium sulfate was observed, whereas in Comparative Examples 1 to 6, dissolution was not recognized. In particular, when the pH was 10 or more, barium sulfate was rapidly dissolved. From these facts, it was found that the pH of the first cleaning liquid needs to be 8 or more.

Changes when barium sulfate is immersed in an aqueous potassium carbonate solution In order to investigate the role of carbonates in the present invention, 1% and 5% potassium carbonates are prepared. And add 0.2 g of reagent barium sulfate. And after setting to a rotary shaker, it was shaken at 150 rpm for 1 hour. And No. The mixture was filtered with 5C filter paper, washed with water and centrifuged four times, dried, and then subjected to IR measurement. As a result, as shown in FIG. 1, by shaking with an aqueous potassium carbonate solution, the absorption due to barium sulfate was reduced and the absorption due to the carbonyl group of potassium carbonate was increased. The effect was greater at 5% than at 1%.
From the above results, the effects of the first cleaning step and the second cleaning step in the process water-based cleaning method of the present invention are considered as follows. That is, in the first cleaning step, the potassium carbonate contained in the first cleaning liquid undergoes a substitution reaction with the sulfate radical for barium sulfate and changes to potassium carbonate. In the second cleaning step, it is presumed that the barium carbonate produced by the substitution reaction is dissolved by the acid of the second cleaning solution. In addition, it is estimated that calcium sulfate is dissolved and removed from the same action.

Dissolution test for deposits collected from actual machine Examples 10-16 and Comparative Examples 7-16 shown in Table 2 below using deposits mainly composed of barium sulfate collected from the chlorine dioxide bleaching step of the actual paper and pulp manufacturing process The barium sulfate dissolution test described above was performed using the first and second cleaning solutions.
Examples 10-16 are selected from sodium carbonate, sodium phosphate, 2-phosphonobutane-1,2,4-tricarboxylate tetrasodium and 1-hydroxyethylidene-1,1-diphosphonate tetrasodium as the first wash. did. The second cleaning liquid was selected from hydrochloric acid, malic acid, sulfamic acid, and citric acid, and the concentration was 1% by mass.
On the other hand, in Comparative Examples 7 to 16, as shown in Table 2, the combination of the acidic first cleaning liquid and the acidic second cleaning (Comparative Examples 7 and 14), the combination of the alkaline first cleaning liquid and the alkaline second cleaning. (Comparative Examples 8 to 11), a combination of an acidic first cleaning liquid and an alkaline second cleaning (Comparative Example 12), a combination of an alkaline first cleaning liquid and an alkaline second cleaning (Comparative Examples 13, 15, and 16) did.

  As a result, as shown in Table 2 above, deposits were almost dissolved in Examples 10 to 16, whereas in Comparative Examples 8 to 12 and Comparative Examples 14 to 16, the dissolution rate was 14% or less, which was extremely low. . Further, Comparative Example 11 containing EDTA sodium salt as a chelating agent had a dissolution rate of 49%, and was found to be superior to the cleaning method of Comparative Example 11 conventionally used as a deposit cleaning method.

It is a spectrum which shows the change of IR when a barium sulfate is immersed in potassium carbonate aqueous solution.

Claims (5)

A first cleaning that includes at least one of carbonate, phosphate, and phosphonate and has a pH of 8 or more flowing through a process water system in which a deposit containing barium sulfate and / or calcium sulfate is present. Process,
And a second cleaning step in which a second cleaning liquid containing an acid other than sulfuric acid is circulated in the process water system after the completion of the first cleaning step.   A process water-based cleaning method, wherein after the first cleaning process, the second cleaning process is performed after the first cleaning liquid is discharged from the process water system.   3. The process water-based cleaning method according to claim 1, wherein the first cleaning liquid is an aqueous carbonate solution.   The process water-based cleaning method according to claim 1 or 2, wherein the second cleaning liquid is an aqueous solution containing at least one of sulfamic acid, citric acid, and malic acid.   The process water system cleaning method according to claim 1, wherein the process water system is a paper / pulp manufacturing process water system.

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