JPH0411673B2 - - 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.

[Conventional technology]

BACKGROUND ART Conventionally, the lime method has been put into practical use when recovering caustic soda from pulp cooking waste liquor (hereinafter referred to as pulp waste liquor) 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 discharged from the process of cooking and bleaching cellulose materials, which is substantially free of sulfur compounds, is concentrated and then burnt with the addition of iron oxide to produce sodium ferrate. A method has been proposed in which caustic soda is recovered directly 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 probably caused by the combustion of the waste liquid, which decomposes the organic matter contained in the waste liquid, and the resulting products are soda carbonate and/or soda oxide, which are It is thought that by reacting with iron oxide to produce sodium ferrate as shown in equations ) and (2), and treating this in water, caustic soda and iron oxide can be obtained as shown in equation (3). .

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→ 2NaON+Fe ₂ O ₃ ...(3) On the other hand, JP-A-58-132191 describes a process of mixing iron oxide and black liquor in a mixing tank and then supplying the mixture to a combustion furnace, and a process of mixing iron oxide and black liquor in a mixing tank and then supplying the sodium ferrate produced by combustion. A direct solubilization method in the pulp manufacturing process, which comprises a step of supplying a powder containing powder to a dissolution tank, a step of separating iron oxide and recovering caustic soda, and a step of supplying the separated iron oxide to the mixing tank. is listed.

Furthermore, in Japanese Patent Application Laid-Open No. 58-132192, black liquor and iron oxide powder are mixed in advance in a mixing tank, then burned in a fluidized bed furnace, and the powdered sodium ferrate in the combustion exhaust gas is collected in a dust collector. A direct causticizing method using a fluidized bed furnace is described in which iron oxide is collected, then hydrolyzed into caustic soda and iron oxide, and the recovered iron oxide and black liquor are mixed in the mixing tank.

[Problem to be solved by the invention]

However, when applying the method described in the above-mentioned Japanese Patent Publication No. 51-12724 to a fluidized bed furnace, the general principle is that iron oxide (iron ore) is regenerated and recycled in the direct causticizing method, and a dust collector or other (The replenishment rate is on the order of a few percent at most). On the other hand, as the number of times granular iron ore is recycled and used increases, the amount of pulverization in the furnace increases (approximately 10% is pulverized), and there is also some pulverization during handling of iron ore in the feeder, causticization process, etc. can be seen. In addition, since the fluidized bed method basically uses a granular causticizing agent, it is not possible to set the reaction molar ratio Fe/Na close to 1.0 (as shown in reaction equations (1) and (2), equimolar On the other hand, there were problems with powdered causticizing agents, such as tin being thrown out of the furnace, making it impossible to expect the reaction to proceed sufficiently.

In addition, the above-mentioned Japanese Patent Application Laid-Open No. 58-132191,
Publication No. 58-132192 describes the feature of the present invention as follows: ``Ferrous acid soda from a fluidized bed furnace and dust from a boiler, cyclone, and electrostatic precipitator are introduced into a hydrolysis device to convert them into caustic soda and recovered iron oxide. There is no mention of the technical concept of "after separation, the granular iron oxide is fed to a fluidized bed furnace, the powdered iron oxide is mixed with black liquor, and then this mixture is fed into the fluidized bed furnace."

The present invention was made in view of the above points, and involves circulating recovered granular iron oxide directly to a fluidized bed furnace.
By premixing powdered iron oxide recovered from boilers, cyclones, and electrostatic precipitators with black iron and circulating it, the reaction surface area increases and the reaction rate between black liquor and iron oxide improves. The purpose of this invention is to provide a method that can reduce the amount of replenishment.

[Means to solve 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 involves, as shown in FIG. 1, adding iron oxide as a causticizing agent after concentrating the pulp waste liquid. The product is combusted in a fluidized bed furnace 3, and then the product is poured into water to recover caustic soda and a causticizing agent.The fluidized bed furnace exhaust gas is heat recovered in a boiler 5, and then collected in a cyclone 6, an electrostatic precipitator 7, etc. In the method of collecting dust through a device, granular new iron oxide is supplied to the fluidized bed furnace 3, and ferric acid soda from the fluidized bed furnace 3 and dust from the boiler 5, cyclone 6, and electrostatic precipitator 7 are added with water. After being introduced into the decomposition device 8 and separated into caustic soda and recovered iron oxide, the recovered iron oxide is classified into powdered iron oxide and granular iron oxide, and the granular iron oxide is supplied to the fluidized bed furnace 3 to be separated into powdered iron oxide. The method is characterized in that iron oxide and concentrated pulp waste liquid are mixed, and then this mixture is charged into a fluidized bed furnace 3.

Moreover, as shown in FIG. 2, the method of the second invention of the present application supplies granular new iron oxide to the fluidized bed furnace 3, and converts the granular sodium ferrate from the fluidized bed furnace 3 into the first hydrolysis device. 8a to separate caustic soda and recovered granular iron oxide, and the recovered granular iron oxide is supplied to the fluidized bed furnace 3, and the dust from the boiler 5, cyclone 6, and electrostatic precipitator 7 is transferred to the second hydrolysis device. 8b to separate into caustic soda and recovered powdered iron oxide,
The method is characterized in that the recovered powdered iron oxide and the concentrated pulp waste liquid are mixed, and then this mixture is charged into the fluidized bed furnace 3.

Further, as shown in FIG. 3, the method of the third invention of the present application is to supply granular new iron oxide to the fluidized bed furnace 3, collect dust from the boiler exhaust gas in the first cyclone 6a, and then collect at least one part of the exhaust gas. A portion of the mixture of concentrated pulp waste liquid and powdered iron oxide is introduced into the dryer 12 to be preheated and dried, and this dried product is introduced into the fluidized bed furnace 3, and the exhaust gas from the dryer 12 is transferred to the second cyclone 6b, The dust is collected through an electrostatic precipitator 7, and the ferric acid soda from the fluidized bed furnace 3, the boiler 5, and the dust from the first cyclone 6a are introduced into a hydrolysis device 8 and separated into caustic soda and recovered iron oxide. After classifying the recovered iron oxide into granular iron oxide and powdered iron oxide, the granular iron oxide is supplied to the fluidized bed furnace 3, and the powdered iron oxide and the dust from the second cyclone 6b and the electrostatic precipitator 7 are collected. The method is characterized in that it is mixed with a concentrated pulp waste liquid, and then this mixture is supplied to the dryer 12.

Furthermore, as shown in FIG. 4, in the method of the fourth invention of the present application, granular new iron oxide is supplied to the fluidized bed furnace 3, and after the boiler exhaust gas is collected in the first cyclone 6a, at least A portion of the mixture of concentrated pulp waste liquid and powdered iron oxide is introduced into the dryer 12 to be preheated and dried, and this dried product is introduced into the fluidized bed furnace 3, and the exhaust gas from the dryer 12 is transferred to the second cyclone 6b, Dust is collected through an electrostatic precipitator 7, and sodium ferrate from the fluidized bed furnace 3 is passed through the first hydrolysis device 8a.
to separate into caustic soda and recovered granular iron oxide, and supply the recovered granular iron oxide to a fluidized bed furnace 3,
The dust from the boiler 5 and the first cyclone 6a is introduced into the second hydrolysis device 8b and separated into caustic soda and recovered powdered iron oxide, and the recovered powdered iron oxide, the second cyclone 6b, and the electrostatic precipitator 7 It is characterized in that the dust from the dryer and the concentrated pulp waste liquid are mixed, and then this mixture is supplied to the dryer 12.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 shows an example of an apparatus for carrying out the method of the invention. The dilute black liquor is introduced into an evaporator 1 such as a vacuum evaporator or a rotary disk type evaporator, and is evaporated and concentrated to obtain a 60 to 80% concentrated black liquor.Then, the concentrated black liquor is sent to a mixing tank 2. Meanwhile, granular iron oxide is supplied to the fluidized bed furnace 3. The bed temperature of fluidized bed furnace 3 is 700~
1100℃, preferably 900~1000℃, Fe/Na
should be greater than or equal to 1.0. Examples of fluidized bed forming materials include pure iron, iron ore (Fe ₂ O ₃ , Fe ₃ O ₄ ), sintered ore,
Granular iron-based compounds such as reduced pellets and granulated steel dust, SiO ₂ , AI ₂ O ₃ , Cr ₂ O ₃ ,
Particulate compounds such as MgO and CaO are used.
In this example, iron ore is used as iron oxide,
Replenishment is done with granular iron ore. The supplementary granular iron ore used has the same particle size as the fluidized bed forming material (0.2 to 3.0 mm) or coarser than the fluidized bed forming material (maximum 5.0 mm). 4 is a fluidized bed forming material supply tank. Fluidized bed furnace 3
The ferric acid soda from the boiler 5, the cyclone 6, and the dust from the electrostatic precipitator 7 are introduced together into the hydrolysis device 8, where they are extracted and separated into caustic soda and recovered iron oxide, and the recovered iron oxide is dried and classified. Device 1
After dry classification into powdered iron oxide and granular iron oxide by contacting with combustion exhaust gas at 0, granular iron oxide and supply tank 4
The powdered iron oxide and the concentrated pulp waste liquid (concentrated black liquor) are mixed in the mixing tank 2, and then this mixture is brought into contact with combustion exhaust gas in the drying device 11 to dry it. , and put it into the fluidized bed furnace 3.

Note that iron oxide may be supplied in either granular or powdered form by premixing it with black liquor. Further, the iron oxide and black liquor may be simply mixed into an irregular shape or may be granulated. In this case, black liquor can be used as the granulating agent, and no new binder is particularly required. That is, by mixing in the mixing tank 2, when the amount of black liquor is large, the powdered iron oxide aggregates and becomes an irregularly shaped aggregate, and when the amount of black liquor is small, the black liquor becomes a binder and is granulated. Things arise. In this case, the mixing tank 2 also functions as a granulation tank. Although FIG. 1 shows a case in which the entire amount of black liquor is mixed with iron oxide, it is also possible to separate and supply the black liquor into an individual supply and a premixed supply.

FIG. 2 shows a case where two hydrolysis devices are provided. That is, granular sodium ferrate from the fluidized bed furnace 3 is introduced into the first hydrolysis device 8a, extracted and separated into caustic soda and recovered granular iron oxide, and the recovered granular iron oxide is brought into contact with combustion exhaust gas in the drying device 10a. After drying, the fluidized bed forming material is supplied to the fluidized bed furnace 3 via the fluidized bed forming material supply tank 4, and the dust from the boiler 5, cyclone 6, and electrostatic precipitator 7 is introduced into the second hydrolysis device 8b, and caustic soda is After extracting and separating the recovered powdered iron oxide from
It is sent to a mixing tank 2 and mixed with concentrated pulp waste liquid (concentrated black liquor), and then this mixture is dried and then charged into a fluidized bed furnace 3. As mentioned above, the particle size of the granular iron oxide is about 0.2 to 5 mm, and the particle size of the powdered iron oxide is 0.2 mm or less, which is a particle size that can be carried over in the furnace. The other configurations are the same as in the case of FIG.

FIG. 3 shows a case where a dryer such as a flash dryer (hereinafter referred to as a flash dryer) and one hydrolysis device are provided. That is, after the exhaust gas from the boiler 5 is collected by the first cyclone 6a, part or all of the exhaust gas is introduced into the flash dryer 12, where it is mixed with the concentrated black liquor and powdered iron oxide sent by the slurry pump 13. The mixture is spray-dried and granulated, and this granulated material is charged into the fluidized bed furnace 3, and the exhaust gas from the flash dryer 12 is passed through the second cyclone 6b and the electrostatic precipitator 7 to collect dust. The ferric acid soda from 3, the boiler 5, and the dust from the first cyclone 6a are introduced into the hydrolysis device 8, where they are extracted and separated into caustic soda and recovered iron oxide, and the recovered iron oxide is passed through the dry classification device 14.
After drying it by contacting it with combustion exhaust gas and classifying it into granular iron oxide and powdered iron oxide, the granular iron oxide is supplied to the fluidized bed furnace 3 via the fluidized bed forming material supply tank 4, and the powdered iron oxide is iron and second cyclone 6b,
Dust from an electrostatic precipitator 7 and concentrated black liquor are mixed in a mixing tank 2, and then this mixture is supplied to a flash dryer 12. Third
The evaporator 1a in the figure is a vacuum evaporator, which evaporates and concentrates the dilute black liquor to a 60-65% concentrated black liquor. The other configurations are the same as in the case of FIG.

Figure 4 shows a dryer such as a flash dryer, 2
This figure shows the case where a hydrolysis device is provided. That is, the ferric acid soda from the fluidized bed furnace 3 is introduced into the first hydrolysis device 8a, where it is extracted and separated into caustic soda and recovered powdered iron oxide, and the recovered granular iron oxide is brought into contact with combustion exhaust gas in the drying device 10a. After drying, the dust is supplied to the fluidized bed furnace 3 via the supply tank 4, and the dust from the boiler 5 and the first cyclone 6a is introduced into the second hydrolysis device 8b, where it is converted into caustic soda and recovered powdered iron oxide. After extraction and separation, the recovered powdered iron oxide is dried by contacting with combustion exhaust gas in the drying device 10b, and then the recovered powdered iron oxide, the dust from the second cyclone 6b, the electrostatic precipitator 7, and the black liquor are combined. are mixed in a mixing tank 2, and then this mixture is supplied to a flash dryer 12. The other configurations are the same as in the case of FIG.

〔Effect of the invention〕

Since the present invention is configured as described above, it has the following effects.

(1) Used as a causticizing agent for iron oxide (iron ore), the recovered granular iron oxide is circulated as it is to the fluidized bed furnace, and the powdered iron oxide recovered from the boiler, cyclone, and electrostatic precipitator is mixed with black liquor. Since it is mixed and used in circulation, the reaction surface area is increased and the reaction rate between black liquor and iron oxide is improved, and the amount of iron oxide to be replenished is reduced, making it more economical.

(2) The Na content carried over from the fluidized bed is
It depends on the operating conditions, but it is 30-40%. This Na
Almost 100% of the amount can be recovered. In addition,
In order to recover nearly 100% of the Na content as granular material as overflow from the fluidized bed, it is necessary to shorten the residence time of iron ore in the fluidized bed and reduce pulverization. connection, increasing running costs.

[Brief explanation of drawings]

The drawings show an apparatus for carrying out the method of recovering caustic soda from pulp waste liquid according to the present invention. Figure 1 is a flow sheet when one hydrolysis apparatus is installed, and Figure 2 is a flow sheet when two hydrolysis apparatuses are installed. 3 is a flow sheet when a flash dryer and one hydrolysis device are installed, and FIG. 4 is a flow sheet when a flash dryer and two hydrolysis devices are installed. 1, 1a... Evaporator, 2... Mixing tank, 3... Fluidized bed furnace, 4... Fluidized bed forming material supply tank, 5... Boiler, 6, 6a, 6b... Cyclone, 7... Electric collector Dust machine, 8, 8a, 8b...Hydrolysis device, 1
0... Dry classification device, 10a, 10b, 11...
Drying device, 12... Dryer (flash dryer), 13... Slurry pump, 14... Drying classification device.

Claims (1)

[Claims] 1. After concentrating the pulp waste liquid, iron oxide is added as a causticizing agent and burned in a fluidized bed furnace 3, and the product is then poured into water to recover caustic soda and the causticizing agent. In a method in which heat is recovered from bed furnace exhaust gas in a boiler 5 and dust is collected through a dust collector such as a cyclone 6 or an electrostatic precipitator 7, granular new iron oxide is supplied to a fluidized bed furnace 3. Ferric acid soda from 3 and dust from boiler 5, cyclone 6, and electrostatic precipitator 7 are introduced into hydrolysis device 8 and separated into caustic soda and recovered iron oxide, and then the recovered iron oxide is converted into powdered iron oxide. and granular iron oxide, the granular iron oxide is supplied to a fluidized bed furnace 3, the powdered iron oxide and concentrated pulp waste liquid are mixed, and this mixture is then charged into the fluidized bed furnace 3. A method for recovering caustic soda from pulp waste liquid. 2 After concentrating the pulp waste liquid, add iron oxide as a causticizing agent and combust it in a fluidized bed furnace 3. Then, the product is poured into water to recover caustic soda and the causticizing agent, and the fluidized bed furnace exhaust gas is sent to a boiler 5. In this method, granular new iron oxide is supplied to the fluidized bed furnace 3, and the granular iron oxide from the fluidized bed furnace 3 is Soda is transferred to the first hydrolysis device 8
a, the recovered granular iron oxide is separated into caustic soda and recovered granular iron oxide, and the recovered granular iron oxide is supplied to the fluidized bed furnace 3, and the dust from the boiler 5, cyclone 6, and electrostatic precipitator 7 is transferred to the second hydrolysis device. 8b to separate caustic soda and recovered powdered iron oxide, the recovered powdered iron oxide and concentrated pulp waste liquid are mixed, and then this mixture is introduced into a fluidized bed furnace 3. How to recover caustic soda from. 3 After concentrating the pulp waste liquid, add iron oxide as a causticizing agent and combust it in a fluidized bed furnace 3. Then, the product is poured into water to recover caustic soda and the causticizing agent, and the fluidized bed furnace exhaust gas is sent to a boiler 5. In this method, granular new iron oxide is supplied to the fluidized bed furnace 3, and the boiler exhaust gas is passed through the first cyclone 6a to recover heat and collect dust through a dust collector such as cyclones 6a and 6b and an electrostatic precipitator 7. After collecting dust in the fluidized bed furnace 3, at least a part of the exhaust gas is introduced into the dryer 12 to preheat and dry the mixture of concentrated pulp waste liquid and powdered iron oxide, and this dried product is fed into the fluidized bed furnace 3, and 12 exhaust gas to the second cyclone 6b,
The dust is collected through an electrostatic precipitator 7, and the ferric acid soda from the fluidized bed furnace 3, the boiler 5, and the first cyclone 6a are collected.
The dust is introduced into a hydrolysis device 8 to be separated into caustic soda and recovered iron oxide, and the recovered iron oxide is classified into granular iron oxide and powdered iron oxide, and then the granular iron oxide is transferred to a fluidized bed furnace 3. caustic soda from the pulp waste liquid, which is characterized in that the powdered iron oxide and the dust from the second cyclone 6b and the electrostatic precipitator 7 are mixed with the concentrated pulp waste liquid, and then this mixture is fed to the dryer 12. How to recover. 4 After concentrating the pulp waste liquid, add iron oxide as a causticizing agent and combust it in a fluidized bed furnace 3. Then, the product is poured into water to recover caustic soda and the causticizing agent, and the fluidized bed furnace exhaust gas is sent to a boiler 5. In this method, granular new iron oxide is supplied to the fluidized bed furnace 3, and the boiler exhaust gas is passed through the first cyclone 6a to recover heat and collect dust through a dust collector such as cyclones 6a and 6b and an electrostatic precipitator 7. After collecting dust in the fluidized bed furnace 3, at least a part of the exhaust gas is introduced into the dryer 12 to preheat and dry the mixture of concentrated pulp waste liquid and powdered iron oxide, and this dried product is fed into the fluidized bed furnace 3, and 12 exhaust gas to the second cyclone 6b,
Dust is collected through the electrostatic precipitator 7, and the ferric acid soda from the fluidized bed furnace 3 is introduced into the first hydrolysis device 8a to separate it into caustic soda and recovered granular iron oxide. The dust from the boiler 5 and the first cyclone 6a is introduced into the second hydrolysis device 8b and separated into caustic soda and recovered powdered iron oxide.
A method for recovering caustic soda from pulp waste liquid, characterized in that the dust from the cyclone 6b and the electrostatic precipitator 7 and the concentrated pulp waste liquid are mixed, and then this mixture is supplied to the dryer 12.