CN1055977C

CN1055977C - Treatment and recovery process of black liquor in papermaking mill

Info

Publication number: CN1055977C
Application number: CN96118749A
Authority: CN
Inventors: 武秉哲
Original assignee: Individual
Current assignee: Individual
Priority date: 1996-08-20
Filing date: 1996-08-20
Publication date: 2000-08-30
Anticipated expiration: 2016-08-20
Also published as: CN1174268A

Abstract

The present invention relates to a technology for treating waste water by an electrochemical separation method, which mainly solves the problem that the prior art has the defects of excessive investment, overhigh treatment expense or low treatment capacity, easy occurrence of a film blocking phenomenon, complicated technology, etc. In the technology, black pulp liquid is simultaneously injected to both sides of a microporous film from one end of an ionization tank to form dense alkali liquid and neutral liquid which then respectively flows out from the other end. The dense alkali liquid is recovered; a coagulating agent is added to the neutral liquid to make lignin separated and recovered; then, the liquid from which the lignin is recovered is directly recovered to be used as pulp washing water or to be retreated. The technology can be widely suitable for recovering and treating black pulp liquid from paper mills using straw pulp to manufacture paper.

Description

Paper mill pulp black liquor treatment and recovery process

The invention relates to a process for treating wastewater by adopting an electrochemical separation method, in particular to a process for treating and recovering black liquor of paper pulp in a paper mill.

China is a big country for straw pulp paper making, the straw pulp paper making amount accounts for about 70% of the straw pulp paper making amount all over the world, and the specific gravity of wood pulp paper making is very low. Straw pulp papermaking produces a black pulp liquor containing a very large amount of impurities such as residual alkali, lignin, fibers, colloids, organic suspended matter, etc., but most importantly, the residual alkali and lignin, which are mixed together, make the black liquor difficult to handle, and the environmental pollution of the black liquor is very serious. In order to radically cure the black liquor, people advocate to adopt a method of burning dry black liquor for treatment, which neither discharges black liquor nor recycles residual alkali, but the proposal has huge construction investment and high burning operation cost, so the treatment facilities built by domestic straw pulp paper mills are basically shut down or are about to be shut down at present; in addition, a biochemical method is adopted to directly treat the black liquor in research experiments, but the black liquor cannot be popularized and applied due to the reasons of too low treatment speed, incapability of recovering residual alkali, poor treatment effect and the like; water purification technologies at home and abroad, such as electrodialysis, reverse osmosis, ultrafiltration and other methods, are only suitable for deep purification treatment of purified water and cannot be suitable for treating black liquor.

Chinese patent CN88102696.4 discloses a new process for treating ionic colloidal waste liquid suitable for treating black liquor from paper making, which comprises diluting the black liquor to 1% -14%, charging into a container with dc electric field for ionization, separating lignin from the waste liquor and recovering, charging the clear liquid after lignin recovery into a container with ion diaphragm for further ionization, forming alkaline liquid in cathode region and acidic liquid in anode region, finally discharging the alkaline liquid and acidic liquid respectively, thus achieving the purpose of recovering residual alkali. However, the disadvantages of this process are: firstly, an ion diaphragm is adopted in the process, the ion diaphragm is generally suitable for deep purification of solution with lower concentration and clean water and cannot be suitable for heavy dirty water and water with the temperature higher than 45 ℃, and the pulp black liquor belongs to the heavy dirty water and has higher temperature; secondly, for the reasons, the concentration of the pulp black liquor needs to be diluted to 1% -14% during treatment, which wastes a large amount of water purification resources and increases the treatment cost; thirdly, in order to reduce the degree of fouling, the process employs a method of first separating the lignin, i.e. ionizing the diluted black liquor in a vessel without an interposed ion membrane, separating the lignin from the solution, and recovering it by precipitation or filtration, which is not practical because it is not possible to do so in practiceTheoretically, the sodium lignin is a substance with good water solubility under alkaline conditions, is difficult to separate from water regardless of treatment, has a neutral pH of 7 or an acidic pH of 5-6, and does not contain or contains little water in liquidAmount of NaCO₃、NaHCO₃Under the conditions of (1), the lignin can be separated from the water by a method; fourthly, the ion diaphragm used in the process is easy to have the phenomenon of film blocking when in use; fifth, the process is complicated.

The invention aims to overcome the defects of the prior art and provide a paper mill pulp black liquor treatment and recovery process which has the advantages of less investment, lower treatment cost, capability of recovering residual alkali and lignin, no need of diluting the pulp black liquor and difficulty in causing film blockage.

The technological scheme of the present invention is that the paper pulp black liquor treating and recovering process for paper mill features that ① includes injecting paper pulp black liquor into one ionizing tank with one microporous membrane in the middle, injecting paper pulp black liquor simultaneously from two sides of the microporous membrane, ② making the paper pulp black liquor flow along the ionizing tank and Na under the action of the electric field of the ionizing tank⁺Sodium ions are gathered to one side close to the negative electrode plate to form a concentrated alkaline solution area, so that Ro^-Collecting lignin ions to one side close to the positive electrode plate to form a neutral liquid zone or a slightly acidic liquid zone, ③ making concentrated alkali liquid and neutral liquid or slightly acidic liquid flow out from the other end of the ionization tank respectively to recover the concentrated alkali liquid, ④ adding coagulant into the neutral liquid or slightly acidic liquid and stirring to separate lignin therein and recover lignin, ⑤ recovering the liquid obtained after recovering lignin, directly using it as washing water or after reprocessing as washing water or discharging it.

The ionization tank used in the technical solution can be made of various corrosion-resistant and insulating materials such as plastics, glass fiber reinforced plastics and the like, the microporous membrane can be made of chemical fibers, glass fiber fibers, porous ceramic plates, porous plastic plates, porous chemical material plates, asbestos and the like, the size of the micropores is generally 10 nM-10 MuM, the size of the micropores can allow ions to pass through or lignin to pass through under the action of an electric field, but has the characteristic of preventing the ions from returning, and the strong alkali liquor can be effectively separated from neutral liquor or acidic liquor; the ionization grooves on two sides of the microporous membrane are provided with a positive electrode plate and a negative electrode plate.

The invention simultaneously injects the pulp black liquor into the ionization tank from two sides of the microporous membrane, and simultaneously leads the separated pulp black liquor to flow out from two sides of the microporous membrane at the other end of the ionization tank, and takes the special property of the pulp black liquor into consideration, namely the black liquor contains more fibers, thereby avoiding the serious blockage of the microporous membrane caused by the impurities such as the fibers when the pulp black liquor flows from one side of the microporous membrane to the other side.

Under the action of an electric field of an ionization tank, the pulp black liquor can fully separate and concentrate ions and lignin, and the process of separating and concentrating the ions and the lignin is as follows:

1. residual alkali

By the action of an electric field Na⁺Is concentrated to the negative electrode region

OH^-Concentrating to positive electrode region

2Na under the action of electric field⁺Is concentrated to the negative electrode region

CO₃ ^2-Concentrating to positive electrode region

HCO₃ ^-Concentrating to positive electrode region

2. Water glass colloid

Na₂SiO₃+H₂O→2Na⁺+SiO₃ ^2-+H₂O2 Na under the action of electric field⁺Is concentrated to the negative electrode region

SiO₃ ^2-Concentrating to positive electrode region

3. Sodium lignin

RO-Na+H₂O⇄Na⁺+RO^-+H₂O is acted on Na by electric field⁺Is concentrated to the negative electrode region

RO^-Concentrating to positive electrode region

Separating and concentrating the paper pulp black liquor to form concentrated alkali liquor on one side of the microporous membrane, and discharging the concentrated alkali liquor to obtain a pH value of 12-14, and forming neutral liquor or acidic liquor on the other side of the microporous membrane, wherein the pH value of the discharged neutral liquor or acidic liquor is 6-7. The discharged concentrated alkali liquor is stored in an alkali recovery tank for reuse, so that the alkali can be completely recovered, the zero discharge of the alkali is realized, and the discharged neutral liquor or the discharged acidic liquor is added with a coagulant to precipitate lignin in the liquor.

The coagulant addition in the technical scheme of the invention can be aluminum trichloride AICl₃Or polyaluminium chloride, the two can be used independently or mixed, the mixing proportion is not limited, the dosage is 1/200-1/700 of neutral liquid or subacid liquid generally, the colloid in the degradation liquid enables lignin to be easily precipitated, so that the dosage of the coagulant is reduced, the liquid can be aerated, and then the coagulant is added, wherein the dosage is 1/500-1/1000 of the weight of the liquid generally, and the lignin can be precipitated or filtered out. The coagulant of aluminium trichloride and polyaluminium chloride is used as one kind of self-decomposing water circulating agent, and can be eliminated from water without ion accumulating effect. In order to increase filterability of lignin, a small amount of polyacrylamide as coagulant aid can be added after adding coagulant, and the dosage is about middleThe content of the acidic liquid or the slightly acidic liquid is below 1/10000.

The liquid obtained after recovering the lignin in the invention can be directly recovered as the water for washing the pulp for reuse, or can be properly treated, such as aeration, contact oxidation or anaerobic treatment and filtration, so as to obtain white clear water, and the clear water can also be recovered as the water for washing the pulp or discharged, and at the moment, the discharge standard is reached, so that the environment can not be polluted.

The figure is a schematic diagram of the structure of an ionization chamber used in one embodiment of the present invention.

The ionization tank shown in the attached figure is provided with a square plastic tank body 1, the size of the tank body 1 is 400mm long, 380mm wide and 350mm high, a microporous membrane 3 made of corrosion-resistant polyester fiber is arranged in the middle of the tank body 1, the micropore size of the microporous membrane 3 is generally 10 nM-10 mu M, a positive pole plate 2 and a negative pole plate 4 are respectively arranged in the tank body 1 on two sides of the microporous membrane 3, the positive pole plate 2 is made of a stainless steel plate, the negative pole plate 4 is made of a stainless steel mesh, two liquid inlets 7 and 8 are arranged on the lower portion of one end of the tank body 1, two liquid outlets 5 and 6 are arranged on the upper portion of the other end, and the two liquid inlets 7 and 8 and the two liquid outlets 5 and 6 are respectively located on two.

A specific embodiment of the present invention will be described in detail below.

The process comprises the steps of ①, injecting the pulp black liquor into an ionization tank shown in the figure, introducing direct current with the voltage of 30-40V and the current of 15-20A into two

electrode plates

2 and 4 on the ionization tank, injecting the pulp black liquor into two liquid inlets 7 and 8 at two sides of a microporous membrane 3 at the same time, injecting 30-40 Kg of pulp black liquor per hour, allowing the pulp black liquor to flow along the ionization tank at two sides of the microporous membrane 3 while injecting ②, and allowing Na to flow along the ionization tank at two sides of the microporous membrane 3 under the action of the electric fields of the two electrode plates in the ionization tank⁺The ions are gathered to one side close to the negative electrode plate 4 to form a concentrated alkaline solution area Ro ^-③ allowing the concentrated alkali solution and the neutral or acidic solution formed in the ionization tank to flow out from the two outlets 5 and 6 at the other end of the ionization tank at the same speed as the pulp black liquor④ flowing the neutral or acidic solution into a tank, aerating (bubbling with air) for 4-6 hr, and adding AICl₃The coagulant is used in an amount of 1/500-1/1000 of the total amount of the liquid, and is stirred for 30 seconds⑤ aerating the light yellow liquid after recovering lignin, precipitating, and recovering it as water for washing pulp or discharging it after reaching standard.

Compared with the prior art, the invention has the following advantages:

1. the method avoids the adoption of a dry-burning method for treating the black liquor of the paper pulp, reduces the investment, if the method is used for treating 25 tons per hour, the investment is about 320 ten thousand yuan, which is about 1/4 of the dry-burning method, and the treatment and operation cost is very low;

2. the invention adopts the method that the paper pulp black liquor is injected from two sides of the microporous membrane at the same time, and the concentrated alkali liquor and the neutral or slightly acidic liquor are discharged from two sides of the microporous membrane at the same time, and adopts the microporous membrane which is not easy to have the membrane blocking phenomenon, even under the condition that the microporous membrane is blocked by the fiber, the ions can still pass through to carry out acid-base separation, thereby fundamentally solving the most serious membrane blocking problem of the process, not only leading the application of the process in the production practice to be possible, but also directly treating the paper pulp black liquor with the concentration of 100 percent, and saving a large amount of water purification resources for dilution;

3. the capacity of treating black liquor can be greatly improved because the treatment capacity is not limited by the water passing amount of the microporous membrane, and in addition, the utilization rate of electric energy reaches the optimal state by adjusting the injection amount of the black liquor to be matched with the ionization current, so that the power consumption can be reduced, the temperature in the tank can be reduced, and the treatment capacity can be improved;

4. because the invention solves the problem of film blockage, the method of firstly recovering residual alkali and then recovering lignin can be adopted for treatment, thus not only leading the invention to be feasible in theory and practice, but also leading the treatment and recovery process to be simpler;

5. the microporous membrane is used in the invention, so that the condition that the temperature of the paper pulp black liquor is lower than 45 ℃ when the ionic membrane is used can be avoided;

6. the invention can effectively treat the paper pulp black liquor, recover the residual alkali, recover the lignin and recover the water, and realize two zero discharge of the alkali and the sewage, thereby not only generating good social benefit and preventing the environmental pollution caused by the paper pulp black liquor, but also generating great economic benefit, calculated by 1 ten thousand tons of paper making per year, 3 tons of residual alkali can be recovered each day, 400 tons of water can be saved, and about 100 ten thousand yuan can be obtained per year except the treatment cost.

Claims

1. A paper mill pulp black liquor treatment and recovery process is characterized in that:

① injecting the black pulp liquor into an ionization tank with a microporous membrane in the middle part, and injecting the black pulp liquor from two sides of the microporous membrane simultaneously;

② making the black liquid flow along the ionization tank on both sides of the microporous membrane to make Na under the action of electric field in the ionization tank⁺Sodium ions are gathered to one side close to the negative electrode plate to form a concentrated alkaline solution area, so that Ro^-The lignin ions are gathered to one side close to the anode plate to form a neutral liquid area or a meta-acid liquid area;

③ allowing concentrated alkali solution and neutral solution or acidic solution to flow out from the other end of the ionization tank respectively, and recovering concentrated alkali solution;

④ adding coagulant into neutral or acidic liquid, stirring to separate lignin, and recovering lignin;

⑤ the liquid obtained after lignin recovery is recovered and used as washing water directly or after reprocessing or discharged.

2. The paper mill pulp black liquor treatment and recovery process of claim 1, characterized in that: and aerating the neutral liquid or the acidic liquid for 4-6 hours before adding the coagulant into the neutral liquid or the acidic liquid.

3. A paper mill pulp black liquor treatment and recovery process according to claim 1 or 2, characterized in that: the coagulant addition refers to the addition of aluminum trichloride or/and polyaluminium chloride.

4. The paper mill pulp black liquor treatment and recovery process of claim 3, characterized in that: the retreatment of the liquid obtained after the lignin is recovered refers to the retreatment of aeration and precipitation.