CN1989292A - Method for black liquor treatment - Google Patents

Abstract

This invention relates to a method for treating black liquor. The invention can effectively extract lignin and alkali separately from alkaline black liquor discharged from paper and pulp manufacturing industries, and produces purified water after treatment. Acid is added to the black liquor to adjust the pH to 2.5–3.5, and a coagulant is added to cause the lignin contained in the black liquor to precipitate, thus separating the lignin from the purified water. Ideally, ozone gas is used as microbubbles to react with the purified water.

Description

Treatment method of black liquor

technical field

At present, for the treatment of black liquor discharged from the paper and pulp manufacturing industry, since the properties of the black liquor contain many harmful substances, the countermeasures are to make a huge investment in equipment, recover the alkali, concentrate the black liquor, and carry out Incineration treatment using energy is included, but the cost of these treatments is very high and air pollutants and malodorous substances are discharged into the atmosphere. The present invention relates to providing a treatment method for the black liquor.

Background technique

Black liquor is discharged from the wood cooking (removal of lignin) process. The essence of the black liquor is the cooking liquor. Because the cooking liquor uses caustic soda to dissolve lignin in water, and then uses sodium sulfide to promote delignification, so the black liquor contains not only lignin, but also sodium sulfide produced by hydrolysis. Hydrogen sulfide, methyl mercaptan, dimethyl sulfide, dimethyl disulfide, and harmful alkaline liquid substances containing carbohydrates, organic acids, and resins.

The processing method of existing black liquor is, in order to concentrate it and improve the solid content concentration, use the large-scale multi-effect vacuum evaporator method to concentrate, further improve the degree of concentration through the oxidation of air, and then add sodium sulfide and sulfuric acid Salt waste liquid is added to this black liquor and burned to recover inorganic compounds such as sodium carbonate and sodium sulfide from the obtained ash. The energy of incineration is used for boiler water supply heating, but most of it is discharged into the atmosphere.

Also, sodium carbonate is dissolved in water, calcium hydroxide is converted into caustic soda, and caustic soda is reused and recycled for cooking liquor.

However, the equipment cost of the measures in the prior art is huge, and the malodorous substance leaks out of the treatment facility, uses too much water, and most of the lignin is incinerated and discharged into the atmosphere as exhaust gas, all of which require treatment costs. great.

A unique odor can be felt near paper and pulp factories in Japan, which is caused by sulfur compounds such as dimethyl sulfide, due to the use of a large amount of water and discharge after use, and the amount of exhaust gas emissions It is also extremely high, so it is desirable to have a more environmentally friendly method for black liquor treatment.

Contents of the invention

The present invention is a method for solving the above-mentioned problems, and is a black liquor processing method having the following configuration.

(1) A treatment method for black liquor, characterized in that, after diluting the alkaline black liquor discharged from the paper and pulp manufacturing industry with water, adding acid to the liquor to adjust the pH value to 2.5 to 3.5, and then Add a small amount of coagulant to make the lignin contained in the black liquor become solid and deposit, or deposit and float, and separate into solid lignin and clear water.

In this case, the kind of acid to be added is hydrochloric acid, sulfuric acid, nitric acid, formic acid, hydrofluoric acid, etc., and most of the lignin contained in the black liquor can be deposited by this treatment, and the lignin can be easily separated.

(2) A processing method for black liquor, characterized in that ozone gas is contacted with the clear water recorded in the above (1) to react, and the undeposited lignin and wood contained in the clear water are removed by the oxidation ability of ozone. Any one or two or more components selected from organic acids and resins contained in hemicellulose, soluble carbohydrates contained in hemicellulose or other sulfur compounds are oxidatively decomposed.

(3) a processing method of black liquor, characterized in that, after carrying out sand filtration to clear water, carry out the contact reaction of ozone gas recorded in above-mentioned (2) again.

(4) A method for treating black liquor, comprising supplying ozone gas as microbubbles (microbubbles) to the clean water described in any one of (1) to (3) above, and performing a contact reaction.

(5) A processing method for black liquor, characterized in that, in the step of contacting and reacting ozone gas with the clear water described in any one of the above (2) to (4), at first mixing ozone gas and a part of it with a high-speed mixer Clear water becomes a microbubble mixture of ozone gas, and the microbubble mixture is sent to the clean water.

In clear water such as solid-liquid separation, lignin, soluble carbohydrates contained in hemicellulose, organic acids and neutralized substances contained in wood, resins contained in wood and saponified substances, tall oil, Dimethyl sulfide, hydrogen sulfide, methyl mercaptan, dimethyl disulfide, etc. Although the decomposition of these organic substances requires strong oxidizing substances, the present invention has solved them.

Ozone gas as a powerful oxidizing substance is currently prepared by an ozone generator, but it contains about 90% of O ₂ , N ₂ , CO _{2 ,} etc., and about 10% is O ₃ . Therefore, in order to make the _O3 produce the maximum oxidation capacity, it is necessary to have the conditions to make _O3 easy to oxidize and decompose, that is, when the pH value of the black liquor is reduced to about 3 with acid, the oxidation capacity of _O3 is improved , And because the smaller the bubbles of O ₃ are, the larger the reaction area is, so the oxidation ability is greatly improved.

In order to make the O ₃ bubble particles as small as the micron order, the size of the O ₃ bubbles can be made extremely small by, for example, stirring clean water and O ₃ at high speed. The small bubbles do not break and disappear until they reach the surface of the clear water. At the instant of breaking and disappearing, although it can be said that the internal temperature of the bubbles reaches a high temperature of several thousand degrees and a high pressure of thousands of atmospheres, it is ideal to carry out Processing, by adding acid in this way to adjust the pH value makes O ₃ gas into small micron-sized bubbles. At this time, it is more preferable to irradiate ultrasonic waves at the same time because the cracking and disappearing effects can be accelerated.

(6) a treatment method for black liquor, characterized in that the structure of the high-speed stirrer described in (5) above is made of stainless steel, and clear water is entered into the blade-type stirrer rotating at a high speed of 3000～20000 revolutions, And into the ozone. Clean water and ozone are mixed in the mixer. At this time, the ozone becomes micro-bubbles, and the mixture of the micro-bubbles and upper water is discharged from the bottom into the clean water stored in the reaction tank and stays in the clean water for a long time.

(7) A treatment method for black liquor, characterized in that the clear water obtained by the above (1) or the clear water that is oxidized by the ozone obtained in any one of the above (2) to (6) is used as the black liquor Dilution water or water used in pulp manufacturing is used.

(8) A treatment method for black liquor, characterized in that, after the clear water having undergone the contact reaction of ozone gas described in any one of the above-mentioned (2) to (6) is neutralized, the process of contacting activated carbon is carried out. Adsorption treatment.

The organic matter contained in the clear water is completely decomposed into CO ₂ and H ₂ O, and finally the purified water can be obtained by removing impurities by adsorption of activated carbon. The obtained purified water (clear water) can be used for dilution or for pulp manufacturing of water use.

Thus, according to the present invention, the removal (separation) of lignin in black liquor can be easily realized by adjusting the pH of dissolved lignin so that it becomes a suspension.

Moreover, this can be carried out at normal temperature and pressure, and the electricity cost of using O ₃ can be further greatly reduced due to the effect of acid and microbubbles.

Usually, although the oxidative decomposition ability of ozone (O ₃ ) is based on the oxidation ability of the oxygen atom possessed by ozone, the pH value in the black liquor is lowered to about 3 by the addition of acid, so that the hydrogen atom possessed by the acid and the ozone atom Combined, active oxygen having a strong oxidizing power exceeding that of oxygen atoms is generated. Since the oxidizing ability of this active oxygen has a decomposition ability far greater than that of oxygen atoms, acid is added to the clean water of the object to be treated to make the pH value about 3, and the decomposition ability is greatly improved by adding ozone.

Description of drawings

FIG. 1 is a system configuration diagram of an embodiment of the present invention.

Fig. 2 is a flowchart of an embodiment of the present invention.

Fig. 3 is a flowchart of an embodiment of the present invention.

In the picture:

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

Detailed ways

Next, embodiments of the present invention will be described using examples.

Example 1

FIG. 1 shows a system configuration diagram of the embodiment, and FIG. 2 shows its flowchart.

First, in Fig. 1, the number 1 from the left is a black liquor storage tank, in which black liquor is stored.

Next, reference number 2 is a pH adjustment tank, in which black liquor and dilution water are filled, acids such as hydrochloric acid and sulfuric acid are added, and a coagulant is added and slowly stirred to deposit lignin and other substances. At this time, it is desirable to add a trace amount of hydrofluoric acid as an acid.

Subsequently, reference numeral 3 is a dehydrator 3 in which lignin is taken out as a solid by, for example, pressure filtration.

Reference numeral 4 is an ozone reaction tank, and a liquid from which lignin has been removed by pressure filtration is introduced, and ozone is used as microbubbles to perform a contact reaction.

At this stage, since ozone gas, which is a powerful oxidizing substance, maximizes the oxidizing ability, and the smaller the O _bubbles , the larger the reaction area, so the oxidizing ability is greatly improved.

Since the particles of the O ₃ bubbles are down to the micron level, the size of the O ₃ bubbles can be made into extremely small bubbles by stirring clean water and O ₃ at a high speed. At the moment when the bubbles disappear, it can be said that the internal temperature of the bubbles reaches thousands. The high temperature of 100 degrees Celsius and the high pressure of thousands of atmospheres allow the reaction to proceed intensely.

Number 5 is a neutralization tank, in which lye is added for neutralization, and then introduced into the activated carbon tower 6 to absorb and remove all impurities to become purified treated water.

The treated water is stored in the treated water storage tank 8, and then (1) introduced into the pH adjustment tank 2 as dilution water, or (2) used as other industrial water or the like.

In addition, in the flow chart of FIG. 2, a more specific description is given with an additional character.

Example 2

The processing of black liquor is carried out according to the flowchart shown in FIG. 3 .

First, add 50t of dilution water to the stock solution of 10t black liquor (containing 20% solid content) to obtain a total of 60t of treated liquid, add 900kg of hydrochloric acid therein, add 1.8kg of polymer coagulant while stirring, then place, Separation into a liquid part and a solid part.

The obtained liquid part 48t is subjected to sand filtration, microbubble ozone gas is introduced into the filtered water obtained through sand filtration for oxidation treatment, and then 300 kg of caustic soda is added for neutralization treatment. Next, the neutralized water was passed into an activated carbon tower to perform adsorption treatment of impurities to obtain purified water.

This purified water is used as the above-mentioned dilution water or pulp manufacturing water.

On the other hand, 12 t of solids obtained from the above solid-liquid separation process were filtered by pressure filtration, and separated into 610 kg of dehydrated liquid 11 and 390 kg of dehydrated blocks (water content 78%). Furthermore, 1 ton of filter cloth cleaning water and 3 kg of coagulant were used for filtration.

The above detachment liquid and filter cloth washing water are added to the liquid part before sand filtration.

In addition, 39 kg of quicklime was added and mixed to the above-mentioned dehydrated block to obtain 429 kg of a dry and loose coarse-grained processed product. Since this processed product contains a large amount of lignin, it is easy to handle and becomes a water-insoluble composition.

In addition, in Table 1, the analysis value of the raw liquid of black liquor and the processing liquid of each process is shown.

Table 1

project Detected body A B Original sample (stock solution of black liquor) BOD 180000 160000 COD 68000 65000 SS - - Sand filter (inlet) BOD - - COD 870 780 SS 90 110 PH 2.8 2.9

continued on next page

Table 1, continued from previous page

Sand filter (export) BOD - - COD 830 660 SS 12 11 PH 2.9 2.9 O ₃ reaction tower (inlet) BOD - - COD 830 660 SS 12 11 PH 2.9 2.9 O ₃ reaction tower (outlet) BOD - - COD 84 110 SS Below 10 Below 10 PH 2.9 3.0 Activated carbon adsorption (inlet) BOD - - COD 84 110 SS Below 10 Below 10 PH 7.5 7.2 Activated carbon adsorption (export) BOD twenty two 5.2 COD 16 11 SS Below 10 Below 10 PH 7.6 7.2 Treated water quality (purified water) BOD twenty two 5.2 COD 16 4.0 SS Below 10 Below 10 PH 7.6 7.2

Unit: BOD, COD is mg/L, SS is mg/kg

As can be seen from the numerical values shown in the table, the water quality of the finally obtained treated water (purified water) has excellent values for BOD, COD, SS, etc., and it can be seen that it is purified water with excellent water quality.

The black liquor treatment method of the present invention can be used as an effective treatment method for lignin-containing black liquor in the field of papermaking and pulp production.

According to the present invention, lignin and alkali can be efficiently extracted separately from black liquor, and the treated water becomes purified water, which can be used for various purposes such as dilution water of black liquor and water for pulp production.

Claims (8)

1. A processing method for black liquor, characterized in that, after diluting the alkaline black liquor discharged from papermaking and pulp manufacturing with water, adding acid in the liquor to adjust the pH value to 2.5～3.5, and then adding a small amount of The coagulant makes the lignin contained in the black liquor become solid and deposit, or deposit and float, and separate into solid lignin and clear water. 2. the processing method of black liquor according to claim 1, it is characterized in that, make ozone gas and above-mentioned clear water contact reaction, utilize the oxidizing power of ozone to from the undeposited lignin contained in clear water, contained in wood Organic acids and resins, soluble carbohydrates contained in hemicellulose or any one or two or more components selected from other sulfur compounds are oxidatively decomposed. 3. the processing method of black liquor according to claim 2, is characterized in that, After sand filtering the clean water, the contact reaction of ozone gas is carried out. 4. according to the processing method of the black liquor described in any one in claim 1～3, it is characterized in that, Ozone gas is supplied to the above-mentioned clean water as microbubbles (microbubbles) to cause a contact reaction. 5. according to the processing method of the black liquor described in any one in claim 2～4, it is characterized in that, In the process of contacting the ozone gas with the clear water, first mix the ozone gas and a part of the clear water with a high-speed mixer to form a microbubble mixture of the ozone gas, and then put the microbubble mixture into the clean water. 6. the processing method of black liquor according to claim 5, is characterized in that, The structure of the above-mentioned high-speed mixer is made of stainless steel, and the clear water is introduced into a blade-type mixer rotating at a high speed of 3000 to 20000, and ozone is passed into; the clear water and ozone are mixed in the mixer, and at this time, the ozone becomes microbubbles, The mixed solution of the tiny air bubbles and clear water is released from the bottom into the clear water stored in the reaction tank and stays in the clear water for a long time. 7. a processing method of black liquor, is characterized in that, The clear water obtained by the above claim 1 or the clear water obtained by oxidation treatment with ozone in any one of claims 2 to 6 is used as dilution water for black liquor or water for pulp production. 8. according to the processing method of the black liquor described in any one in claim 2～6, it is characterized in that, After the clean water subjected to the contact reaction with ozone gas was neutralized, adsorption treatment by contacting activated carbon was performed.

Images