JP2007070784A - Method for treating black liquor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for treatment with which lignin or an alkali is efficiently separated from an alkaline black liquor discharged from the papermaking/paper pulp manufacturing industry and treated water is used as purified water. <P>SOLUTION: The method for treatment is carried out as follows: an acid is added to the black liquor to regulate the resultant liquor until the pH becomes 2.5-3.5; a flocculant is then added to sediment the lignin contained in the black liquor and separate the lignin from supernatant water; and ozone gas as micro-bubbles is preferably subjected to a contact reaction with the supernatant water. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  Currently, black liquor discharged from the paper and pulp and paper manufacturing industry contains a lot of harmful properties of black liquor. Concentration and incineration including energy use are performed, but a great deal of cost and air pollutants and odorous substances are released into the atmosphere. The present invention provides this black liquor treatment method. It is concerned.

  Black liquor is discharged from the wood cooking (lignin removal) process. The source of black liquor is cooking liquor, which uses caustic soda to dissolve lignin in water, and also uses sodium sulfide to promote delignification. In addition to lignin, it contains hydrogen sulfide, methyl mercaptan, dimethyl sulfide, dimethyl disulfide produced by hydrolysis of sodium sulfide, and is a harmful alkaline liquid that also contains carbohydrates, organic acids, and resins. .

In the conventional black liquor treatment method, the concentrated concentration is increased by using a large-scale multi-effect vacuum evaporator method in order to increase the solid content, and the concentration is further increased by oxidation with air. After adding sodium sulfide and sulfate waste liquid, it is burned and the inorganic chemicals sodium carbonate and sodium sulfide are recovered from the ash, and the incineration energy is used for heating the boiler feed water, but most of it is released into the atmosphere. Yes.
Then, sodium carbonate is dissolved in water, calcium hydroxide is converted into caustic soda, and caustic soda is used again as a cooking liquid for recycling.

  However, the equipment cost of the countermeasures in the conventional technology is large, malodorous substances are leaked outside the treatment facility, a lot of water is used, most of the lignin is incinerated, and discharged into the atmosphere as exhaust gas. The cost is very high.

  The unique smell around the paper and paper mills in Japan is due to sulfur compounds such as dimethyl sulfide, which uses a lot of water and discharges it after use. Since the displacement is extremely high, it is desired that black liquor treatment be performed in a more environmentally friendly manner.

The present invention solves the above-mentioned problems and is a black liquor treatment method having the following constitution.
(1) After diluting the alkaline black liquor discharged from the paper and paper pulp manufacturing industry with water, the acid is added to the liquor to adjust the pH to 2.5 to 3.5, and further slight aggregation A method for treating black liquor, comprising adding an agent, causing the lignin contained in the black liquor to be solidified to be settled or settled and floated, and separated into solid lignin and clean water.
In this case, the kind of acid to be added is hydrochloric acid, sulfuric acid, nitric acid, formic acid, hydrofluoric acid, etc., and by this treatment, most of the lignin contained in the black liquor precipitates, and the lignin can be easily separated.
(2) Ozone gas is contact-reacted with the clean water described in (1) above, and it is contained in unsedimented lignin contained in the clean water, organic acids and resins contained in the wood, and hemicellulose by the oxidizing power of ozone. A method for treating black liquor, comprising oxidizing or decomposing any one or more components selected from soluble carbohydrates or other sulfur compounds.
(3) A black liquor treatment method, wherein the ozone gas contact reaction according to (2) is performed after sand filtration of clean water.
(4) A black liquor treatment method, wherein ozone gas is supplied as microbubbles (microbubbles) to the clean water according to any one of (1) to (3) to cause a contact reaction.

(5) In the step of contacting ozone gas with clean water according to any one of (2) to (4) above, first, ozone gas and a part of clean water are mixed with a high-speed stirrer, A method for treating black liquor, characterized in that it is a microbubble mixed solution, and the microbubble mixed solution is discharged into tap water.
Water for solid-liquid separation, etc. includes lignin, soluble carbohydrates contained in hemicellulose, organic acids and neutralized products in wood, resins and saponified products in wood, tall oil, dimethyl sulfide , Hydrogen sulfide, methyl mercaptan, dimethyl disulfide, and the like, and the decomposition of these organic substances requires a strong oxidizing substance, but the present invention solves this.
Although ozone gas, which is a powerful oxidizing substance, is currently produced by an ozone generator, nearly 90% of the ozone gas contains O ₂ , N ₂ , CO ₂ , etc., and about 10% is O ₃ . Therefore it is necessary condition for O ₃ tends recommend oxidative decomposition in the O ₃ capitalize on its full oxidizing power, it is when the black liquor is lowered to pH3 longitudinal by acid, oxidation of O ₃ The smaller the bubbles of O ₃ gas are, the larger the reaction surface becomes, so that the oxidizing power increases dramatically.
In order to reduce the O ₃ gas bubble particles to the micro level, for example, by stirring the water and O ₃ at high speed, the size of the O ₃ gas bubble can be made extremely small. It was. This small bubble breaks and disappears by the time it reaches the surface of the water supply, but at the moment when it breaks and disappears, the internal temperature of the bubble is said to be high, several thousand degrees, and high pressure of several thousand atmospheres. Thus, after adjusting the pH by adding acid, it is preferable to process the O ₃ gas into small micro-level bubbles. At this time, it is more preferable to irradiate ultrasonic waves at the same time because the destruction / extinction action is promoted.

(6) The high-speed stirrer according to (5) is made of stainless steel, and has a structure in which clean water is introduced into a blade-type stirrer rotating at a high speed of 3000 to 20000 rotations, and ozone is blown. Water and ozone are mixed in the stirrer, and at this time ozone becomes microbubbles. The mixture of the microbubbles and water is discharged from below into the water stored in the reaction tank. A method for treating black liquor, characterized in that it is retained in tap water for a long time.
(7) The diluted water or paper pulp of black liquor obtained from the above-obtained purified water obtained in (1) above or the ozone-treated upper water obtained in any one of (2) to (6) above. A method for treating black liquor, characterized by being used as water for production.
(8) Black, characterized in that, after neutralizing the clean water subjected to the ozone gas contact reaction described in any one of (2) to (6) above, it is brought into contact with activated carbon and subjected to an adsorption treatment. Liquid processing method.
The organic matter contained in the clean water is completely decomposed into CO ₂ and H ₂ O, and finally purified water can be obtained by adsorbing and removing impurities by activated carbon, and this purified water (clean water) obtained is It can also be used for dilution, and can also be used as water for paper pulp production.
Thus, according to the present invention, removal (separation) of lignin in black liquor can be easily achieved by making dissolved lignin into suspension (SS) by adjusting pH.
And it can be carried out at room temperature and normal pressure, and the electricity cost associated with the use of O ₃ can be drastically reduced by the effect of acid and microbubbles.

In general, the oxidative decomposition power of ozone (O ₃ ) is based on the oxidizing power of oxygen atoms in ozone, but the pH in black liquor is lowered to around 3 by the addition of acid, and the hydrogen atoms in acid have Ozone atoms are combined to generate active oxygen with a stronger oxidizing power than oxygen atoms. Since the oxidizing power of this active oxygen has a decomposing power far exceeding the oxidizing power of oxygen atoms, acid is added to the top water of the object to be treated, and ozone is added at a pH of about 3 to dramatically decompose. Power is improved.

  According to the present invention, lignin and alkali can be efficiently separated from black liquor, and the treated water can be used as purified water for various uses such as black liquor dilution water and paper pulp manufacturing water.

The embodiment of the present invention will be described with reference to examples.
Example 1:
FIG. 1 shows a system configuration diagram of the embodiment, and FIG. 2 shows a flowchart thereof.
First, in FIG. 1, black liquor is stored in the storage tank at 1 from the left.
Next, the black liquor and the diluted water are put into the pH adjusting tank 2, acid such as hydrochloric acid and sulfuric acid is added, and a flocculant is added and the mixture is slowly stirred to precipitate lignin and others. At this time, it is preferable to add a small amount of hydrofluoric acid as the acid.
Next, in the dehydrator 3, lignin is taken out as a solid substance, for example, with a filter press.
The liquid from which the lignin has been removed by the filter press is introduced into the ozone reaction tank 4, and ozone is contacted and reacted as microbubbles.
At this stage, ozone gas, which is a strong oxidizing substance, has the maximum oxidizing power and the smaller the bubbles of O ₃ gas, the larger the reaction surface, so that the oxidizing power increases dramatically.
In order to reduce the O ₃ gas bubble particles to the micro level, it is possible to make the O ₃ gas bubble size extremely small by stirring the clean water and O ₃ at a high speed. At the moment when the bubbles disappear, the internal temperature of the bubbles becomes a high temperature of several thousand degrees and is said to be a high pressure of several thousand atmospheres, and the reaction proceeds strongly.

Subsequently, in the neutralization tank 5, it neutralizes by adding an alkaline liquid, and then introduce | transduces into the activated carbon tower 6, adsorbs and removes all impurities, and it is set as the purified treated water.
The treated water is stored in the treated water storage tank 8, and then (1) used as dilution water to the pH adjustment tank 2 or (2) used for other industrial water.
In the flowchart of FIG. 2, more specific explanation is made by adding characters.

Example 2:
The black liquor was processed according to the flowchart shown in FIG.
First, 50t of dilution water was added to 10t of black liquor (containing 20% solids) to make a total of 60t of liquid to be treated, 900kg of hydrochloric acid was added thereto, and 1.8kg of polymer flocculant was added while stirring. Then, it was left to separate into liquid and solid contents.
The obtained liquid 48t was subjected to sand filtration, and microbubble-like ozone gas was introduced into the filtered water obtained by sand filtration for oxidation treatment, and then neutralized by adding 300 kg of caustic soda solution. Subsequently, the neutralized water was passed through an activated carbon column, and impurities were adsorbed to obtain purified water.
This purified water is used as the diluting water or paper pulp manufacturing water.
On the other hand, the solid content 12t obtained in the solid-liquid separation step was filtered through a filter press, and separated into 11,610 kg of desorbed liquid and 390 kg of dehydrated cake (water content 78%). At the time of filtration, 1 t of filter cloth washing water and 3 kg of flocculant were used.
The desorbed liquid and filter cloth washing water were added to the liquid before sand filtration.
In addition, 39 kg of quick lime was added to and mixed with the dehydrated cake, and 429 kg of a rough and coarse processed product was obtained. This treated product contained a large amount of lignin, was easy to handle, and was a composition insoluble in water.
Table 1 shows the analysis values of the black liquor stock solution and the treatment liquid in each step.
As can be seen from the numerical values shown in the table, the final treated water (purified water) quality of the BOD, COD, SS, etc. are all excellent values, and the purified water has excellent water quality. I understand.

  It can be employed as an effective treatment method for black liquor containing lignin in the papermaking field and paper pulp manufacturing field.

System configuration diagram of an embodiment of the present invention Flowchart of an embodiment of the present invention Flowchart of an embodiment of the present invention

Explanation of symbols

1: Black liquor storage tank 2: pH adjustment tank 3: Dehydrator 4: Ozone reaction tank 5: Neutralization tank 6: Activated carbon tower 7: Treated water storage tank

Claims (8)

  After diluting the alkaline black liquor discharged from the paper and paper manufacturing industries with water, add acid to the liquor to adjust the pH to 2.5-3.5, and add a slight flocculant. A method for treating black liquor, characterized in that the lignin contained in the black liquor is solidified to settle or settle and float, and is separated into solid lignin and clean water.   Ozone gas is contact-reacted with the clean water according to claim 1, and the oxidative power of ozone causes unprecipitated lignin contained in the clean water, organic acids and resins contained in the wood, soluble carbohydrates contained in hemicellulose, or A black liquor treatment method comprising oxidizing and decomposing any one or two or more components selected from other sulfur compounds.   3. A black liquor treatment method, wherein the ozone gas contact reaction according to claim 2 is performed after sand filtration of clean water.   A black liquor treatment method, wherein ozone gas is supplied as microbubbles (microbubbles) to the clean water according to any one of claims 1 to 3 to cause a contact reaction.   In the step of contacting ozone gas with clean water according to any one of claims 2 to 4, first, ozone gas and a part of clean water are mixed with a high-speed stirrer, and a microbubble mixed solution of ozone gas and No, a method for treating black liquor, characterized in that the microbubble mixture is discharged into tap water.   The high-speed stirrer according to claim 5 is made of stainless steel, has a structure in which clean water is introduced into a blade-type stirrer rotating at a high speed of 3000 to 20000, and ozone is blown, Ozone mixes in the stirrer, and at this time the ozone becomes microbubbles. The mixture of the microbubbles and clean water is discharged from the bottom into the clean water stored in the reaction tank and remains on for a long time. A method for treating black liquor, characterized by being retained in water.   Utilizing the clean water obtained in claim 1 or the clean water oxidized by ozone obtained in any one of claims 2 to 6 as black liquor diluted water or water for paper pulp manufacture And a black liquor treatment method.   A method for treating black liquor, comprising: neutralizing the clean water subjected to the ozone gas contact reaction according to any one of claims 2 to 6 and then bringing the activated water into contact with activated carbon to perform an adsorption treatment.

Images