JPH0551537B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for efficiently recovering caustic soda from pulp cooking waste liquor (also referred to as black liquor) and reducing the amount of causticizing agent supplied. It is something.

[Prior Art] Conventionally, the lime method has been put into practical use when recovering caustic soda from pulp cooking waste liquid (hereinafter referred to as pulp waste liquid) generated when wood chips are digested. However, this lime method has drawbacks such as a complicated process, the production of waste, which requires measures against odor and drainage, and a poor causticization rate.

In order to eliminate these shortcomings, the special public
As shown in Publication No. 12724, the alkaline waste liquid, which is substantially free of sulfur compounds, discharged from the process of cooking and bleaching cellulose materials is concentrated, then combusted with the addition of iron oxide, and the resulting sodium ferrate is produced. A method has been proposed in which caustic soda is directly recovered as an extracted aqueous solution by pouring it into water, and the iron oxide obtained as an extraction residue is recycled and reused. In this method, the production of caustic soda from alkaline waste liquid is
The organic matter contained in the waste liquid is probably decomposed by the fuel in the waste liquid, and the resulting products, sodium carbonate and/or soda oxide, react with iron oxide as shown in equations (1) and (2) below. It is thought that caustic soda and iron oxide can be obtained as shown in equation (3) by producing sodium ferrate and treating it in water.

Na ₂ CO ₃ +Fe ₂ O ₃ →Na ₂ Fe ₂ O ₄ +CO ₂ (1) Na ₂ O + Fe ₂ O ₃ →Na ₂ Fe ₂ O ₄ (2) Na ₂ Fe ₂ O ₄ +H ₂ O → 2NaOH + Fe ₂ O ₃ (3) [Problem to be solved by the invention] However, in order to apply the above method to a fluidized bed furnace,
(1) When recovering NaOH by hydrolyzing the generated sodium ferrate, coarse iron oxide tends to gradually become fine powder. (2) Iron ore is generally used as Fe ₂ O ₃ , and iron ore There are 5 to 5 fine particles (0.149 mm or less) inside.
Contains 30wt% and also contains several impurities such as SiO ₂ and Al ₂ O ₃ .
(3) Pulp waste liquid becomes concentrated and swells easily as the solid content concentration increases, and the apparent specific gravity decreases. The resistance to combustion gas increases, making it difficult to feed into the fluidized bed.
There were problems such as these, which were problems when putting it into practical use.

The present invention was made in view of the above points, and consists of pre-classifying a causticizing agent into fine powder and coarse particles, premixing the fine powder causticizing agent and black liquor, and then dividing the recovered causticizing agent into fine powder and coarse particles. By classifying the fine powder into black liquor and premixing this fine powder with black liquor, combustion of black liquor outside the fluidized bed, that is, in the freeboard inside the fluidized bed furnace, is reduced compared to when only black liquor is input. By suppressing the combustion of the caustic agent and dispersing it uniformly in the fluidized bed, increasing the amount of reaction per unit volume, and effectively using the finely powdered caustic agent, the amount of replenishment of the caustic agent can be reduced. The object of the present invention is to provide a method for recovering caustic soda from pulp waste liquid.

[Means and actions for solving the problem]

In order to achieve the above object, the method for recovering caustic soda from pulp waste liquid according to the first invention of the present application will be described with reference to FIG. 1. After concentrating pulp waste liquid (also called black liquor), Fe ₂ O ₃ , TiO ₂ ,
A method in which a substance selected from the group consisting of FeTiO ₃ is added as a causticizing agent and combusted in a fluidized bed furnace 6, and then the product is poured into water to recover caustic soda and the causticizing agent, the causticizing agent being pulverized. After premixing the concentrated pulp waste liquid and a finely powdered causticizing agent, this mixture is charged into the fluidized bed furnace 6, and the coarse particles are charged into the fluidized bed furnace 6. The product produced in step 6 is directly extracted from the fluidized bed furnace 6 and poured into water to recover caustic soda and causticizing agent.The causticizing agent is then classified into coarse particles and fine powder, and the coarse particles are transferred to the fluidized bed furnace 6.
It is characterized in that the fine powder is mixed with the concentrated pulp waste liquid and charged into the fluidized bed furnace 6.

In addition, compared to when only black liquor is added, combustion of black liquor outside the fluidized bed is suppressed, it is easier to disperse uniformly within the fluidized bed, and the reaction surface area is increased, resulting in a larger reaction amount per unit volume. Become.

The gist of the present invention is to prevent black liquor from burning in the freeboard part of the fluidized bed in the fluidized bed furnace 6.
By premixing a finely powdered causticizing agent with black liquor, preventing the finely powdered causticizing agent from flying out of the furnace, and burning the black liquor in a fluidized bed, the finely powdered causticizing agent can be used effectively. be.

Further, the method of the second invention of the present application will be explained with reference to FIG. 3, after concentrating the pulp waste liquid,
A substance selected from the group consisting of Fe ₂ O ₃ , TiO ₂ , and FeTiO ₃ is added as a causticizing agent and combusted in a fluidized bed furnace 6, and then the product is poured into water to recover caustic soda and the causticizing agent. In the method, the causticizing agent is classified into fine powder and coarse particles, and after the concentrated pulp waste liquid and the fine powder of the causticizing agent are mixed in advance, this mixture is charged into a fluidized bed furnace 6, and the coarse particles are fed into the fluidized bed furnace. 6, and the product produced in the fluidized bed furnace 6 is directly extracted from the fluidized bed furnace 6, and put into water to recover caustic soda and causticizing agent.The causticizing agent containing the recovered ash is then subjected to deashing treatment. The causticizing agent is separated into a causticizing agent and ash, and the causticizing agent is then classified into coarse particles and fine particles.The coarse particles are circulated to the fluidized bed furnace 6, and the fine particles are mixed with the concentrated pulp waste liquid and sent to the fluidized bed furnace. It is characterized by being inserted into 6.

In the case of deashing, impurities in the causticizing agent can be removed, so a causticizing agent with low purity can be used.

〔Example〕

Embodiments of the present invention will be described below based on the drawings. FIG. 1 shows an embodiment of an apparatus for carrying out the method of the invention. In FIG. 1, dilute black liquor in a dilute black liquor tank 1 is introduced into an evaporator 2 and evaporated.
The concentrated black liquor is stored in a concentrated black liquor tank 3, and this black liquor is sent to a mixing tank 4. On the other hand, a substance selected from the group consisting of Fe ₂ O ₃ , TiO ₂ , and FeTiO ₃ (Fig. 1 shows an example in which high-quality iron ore is used as a causticizing agent) is passed through a classifier 5. The fine powder is introduced into a mixing tank and classified into fine powder, which has a finer particle size than the fluidizing agent and causticizing agent in the fluidized bed furnace 6, and coarse particles, which have a larger particle size than the fluidizing agent and causticizing agent. 4 and pre-mixed with concentrated black liquor, this mixture is fed to fluidized bed furnace 6.
The coarse particles are fed to the fluidized bed furnace 6 where they are combusted and the reactions shown in equations (1) and (2) are carried out. Although not shown, fluidizing air is supplied to the lower part of the fluidized bed furnace 6 (see FIG. 2). Thick black liquor has a solid content
It is concentrated to 50 wt% or more, and premixed so that the molar ratio of Fe and Na (Fe/Na) is 1 or more. In addition, the particle size of the fluidizing agent and causticizing agent in the fluidized bed furnace 6 is set to 0.2 to 2.0 mm, and the reaction temperature is controlled.
The temperature is 580 to 1100°C, preferably 900 to 1000°C.

Then, the product in the fluidized bed channel 6 is extracted,
After being cooled in the cooler 7, it is introduced into the hydrolysis tank 8 and placed in water to carry out the reaction of the above reaction formula (3).
Generates NaOH _{and Fe2O3} . As a hydrolyzing agent, in addition to H ₂ O, it is also possible to use a weak alkaline solution from the washing step. This NaOH and Fe ₂ O ₃ are sent to the Clarifier 10 and converted into NaOH and Fe ₂ O ₃
NaOH is separated into caustic soda tank 11.
is stored in Fe ₂ O ₃ is in cleaning tank 12, filter 1
3 and is recovered as Fe ₂ O ₃ . This Fe ₂ O ₃ is further introduced into a classifier 14 and classified into coarse particles and fine particles, with the coarse particles being supplied to the fluidized bed furnace 6 and the fine particles being supplied to the mixing tank 4 . Note that 15 is a pure water tank, 16 is a boiler, 17 is a gas/air heater, 18 is a dust collector,
20 is an induction fan, and 21 is a chimney.

In this way, Fe ₂ O ₃ and black liquor are introduced in a pre-mixing method, and the Fe ₂ O ₃ used for mixing is a fine powder smaller than the particle size of the fluidizing agent and causticizing agent.
Even if Fe ₂ O ₃ is fed alone into the fluidized bed, it will not be accompanied by the combustion gas and will not immediately jump out of the furnace, and it will not reach the fluidized bed, which would be expected if only black liquor was supplied. Due to the volatilization of volatile matter, ash, etc. due to the combustion of the black liquor, loss of Na ₂ O to be recovered by reacting with Fe ₂ O ₃ can be suppressed as much as possible. The black liquor must be burned in a fluidized bed. In addition, the specific gravity of Fe ₂ O ₃ is 4.5 to 4.9,
On the other hand, when only black liquor is supplied, as the black liquor is concentrated and the solid content increases, the organic matter tends to volatilize and swell, so the apparent specific gravity decreases and the combustion gas increases. The resistance force against Na 2 O increases, and Na 2 O is easily carried over to the outside of the system without reaching the fluidized bed, resulting in a loss of Na ₂ O. In addition, since black liquor is a viscous liquid, it is difficult to mix with granular Fe ₂ O ₃ , but it is relatively easy to mix with granular Fe ₂ O ₃ , and the mixture is used as a fluidizing agent and causticizing agent. It has a larger shape (lump-like or candy-like) and has a larger specific gravity (as mentioned above).
The specific gravity of Fe ₂ O ₃ is 4.5 to 4.9), and there is no leakage out of the furnace. In addition, the production reaction of sodium ferrate (Na ₂ Fe ₂ O ₄ ) is a reaction between Fe ₂ O ₃ and Na ₂ CO ₃ , and the larger the reaction surface area of Fe ₂ O ₃ (thus, the finer the powder) ,
The amount of reaction per unit volume increases, and further recovery of Na ₂ O by the reaction of Fe ₂ O ₃ + Na ₂ O within the mixture can be expected. Furthermore, as mentioned above, when recovering NaOH by hydrolyzing the generated sodium ferrate,
Coarse grains of Fe ₂ O ₃ tend to gradually become fine powder, and iron ore contains 5 to 30 wt of fine powder (0.149 mm or less).
%, and contains several wt% of impurities such as SiO ₂ and Al ₂ O _3. If iron ore is received in a fluidized bed with a wide particle size distribution, the fine powder will fly out and cannot be used by itself. , As in the present invention, the method of mixing fine powder Fe ₂ O ₃ with black liquor in advance is as follows:
Black liquor can be combusted in a fluidized bed to effectively react Na ₂ CO ₃ and Fe ₂ O ₃ , and it can also be used for the recovery reaction of Na ₂ O, leading to a reduction in raw material costs. It makes perfect sense.

FIG. 2 shows a case where a fluidized bed type cooler is used as the cooler. That is, as a cooler while extracting sodium ferrate produced in the fluidized bed furnace 6 through an overflow pipe and supplying it to the hydrolysis process,
A fluidized bed cooler 22 is used, air is supplied to the cooler 22 by a fan 23, and the hot air that directly cools the ferric acid soda is used as preheated air, and the hot water for indirect cooling is used as the hydrolyzed liquid. It is composed of The recovery of caustic soda through hydrolysis progresses more favorably in warmer water, preferably at 60 to 100°C.
Adjust to this temperature. This embodiment has the advantage of being able to save energy, such as by utilizing waste heat.

FIG. 3 shows another embodiment of the invention. That is, the recovered Fe ₂ O ₃ containing impurities (ash) such as SiO ₂ and Al ₂ O ₃ is introduced into a deashing device 24 using a gravity separation method or a flotation method to separate it into Fe ₂ O ₃ and ash. Then, Fe ₂ O ₃ is introduced into a classifier 14 and classified into coarse particles and fine powder, the coarse particles are supplied to a fluidized bed furnace 6, and the fine powder is supplied to a mixing tank 4. When a flotation method is adopted as the deashing device 24, Fe ₂ O ₃ containing ash is mixed with water, a scavenger, and a foaming agent, and air is blown from the bottom of the device to generate bubbles to remove Fe _{2 O 3} . Only O ₃ is separated by selectively adhering to bubbles and floating.

As a collecting agent for adjusting the surface properties of Fe ₂ O ₃ , heavy oil such as C heavy oil, atmospheric distillation residue oil, etc.
Fatty acids, petroleum sulfonates, and ether amines are used as foaming agents to adjust the surface properties of bubbles. Nonionic surfactants are surfactants that adsorb to the water-air interface and change the surface tension. agent,
Anionic surfactants, cationic surfactants or combinations thereof, or a number of well-known traditional flotation techniques, such as pine oil (approximately 60% terpene), camphor oil (terpenes and cineole 20-30%), cresol,
Methyl isobutyl carbinol and the like are used. The other configurations are the same as in the case of FIG. This embodiment has the advantage that impurities in the iron ore can be removed and iron ore with low purity can be used.

Note that it is of course possible to use TiO ₂ or FeTiO ₃ instead of iron ore.

〔Effect of the invention〕

As explained above, the method of the present invention uses Fe ₂ O ₃ ,
Using a substance selected from the group consisting of TiO ₂ and FeTiO ₃ as a causticizing agent, classifying the causticizing agent into fine powder and coarse particles in advance, and classifying the recovered causticizing agent into fine powder and coarse particles, These causticizing agents and black liquor are premixed, and since the causticizing agent used for mixing uses a fine powder smaller than the particle size of the fluidizing agent and causticizing agent, only the easily combustible black liquor is used. Compared to the case where the black liquor is added to the fluidized bed, combustion of the black liquor outside the fluidized bed is suppressed, and it is easier to disperse the black liquor uniformly within the fluidized bed without carrying over, and the reaction surface area is increased, so the amount of reaction per unit volume is reduced. becomes larger and becomes Na ₂ O
This has the effect that the amount of causticizing agent to be replenished can be reduced by effectively utilizing the finely powdered causticizing agent.

In addition, when deashing is performed, impurities in the causticizing agent can be removed, so there is an effect that a causticizing agent with low purity can be used.

[Brief explanation of the drawing]

Fig. 1 is a flow sheet showing an example of an apparatus for carrying out the method of the present invention, Fig. 2 is an explanatory diagram when a fluidized bed type cooler is used as the cooler in Fig. 1, and Fig. 3 is an illustration of the present invention. 3 is a flow sheet showing another embodiment of an apparatus for carrying out the method of the invention. 1... Dilute black liquor tank, 2... Evaporator, 3
... Concentrated black liquor tank, 4 ... Mixing tank, 5 ... Classifier, 6 ... Fluidized bed furnace, 7 ... Cooler, 8 ... Hydrolysis tank, 10 ... Clarifier, 11 ... Caustic soda Tank, 12...Cleaning tank, 13...Filter, 14...Classifier, 15...Pure water tank, 1
6...Boiler, 17...Gas/air heater, 18
... Dust collector, 20 ... Induction fan, 21 ... Chimney, 22 ... Fluidized bed cooler, 23 ... Fan,
24... Deashing device.

Claims (1)

[Claims] 1. After concentrating the pulp waste liquid, Fe ₂ O ₃ , TiO ₂ ,
A method in which a substance selected from the group consisting of FeTiO ₃ is added as a causticizing agent and combusted in a fluidized bed furnace 6, and then the product is poured into water to recover caustic soda and the causticizing agent, the causticizing agent being pulverized. After premixing the concentrated pulp waste liquid and a finely powdered causticizing agent, this mixture is charged into the fluidized bed furnace 6, and the coarse particles are charged into the fluidized bed furnace 6. The product produced in step 6 is directly extracted from the fluidized bed furnace 6 and poured into water to recover caustic soda and causticizing agent.The causticizing agent is then classified into coarse particles and fine powder, and the coarse particles are transferred to the fluidized bed furnace 6.
A method for recovering caustic soda from pulp waste liquid, characterized in that the fine powder is mixed with the concentrated pulp waste liquid and charged into a fluidized bed furnace 6. 2 After concentrating the pulp waste liquid, Fe ₂ O ₃ , TiO ₂ ,
A method in which a substance selected from the group consisting of FeTiO ₃ is added as a causticizing agent and combusted in a fluidized bed furnace 6, and then the product is poured into water to recover caustic soda and the causticizing agent, the causticizing agent being pulverized. After premixing the concentrated pulp waste liquid and a finely powdered causticizing agent, this mixture is charged into the fluidized bed furnace 6, and the coarse particles are charged into the fluidized bed furnace 6. The product produced in step 6 is directly extracted from the fluidized bed furnace 6 and poured into water to recover caustic soda and a causticizing agent.The recovered causticizing agent containing ash is deashed to separate the causticizing agent and ash. The causticizing agent is then classified into coarse particles and fine powder, the coarse particles are circulated to the fluidized bed furnace 6, and the fine powder is mixed with concentrated pulp waste liquid and charged into the fluidized bed furnace 6. A method for recovering caustic soda from pulp waste liquid.