JPH0348127B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention also relates to a method for efficiently recovering caustic soda from pulp cooking waste liquor (also referred to as black liquor).

[Conventional technology]

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, 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 combustion of 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, when applying the above method to a fluidized bed furnace, it is necessary to use non-iron oxide materials such as sand and gravel as a dust collector downstream of the fluidized bed furnace. When using a granular type dust collector that uses granular materials as filter media, the fine powdered sodium ferrate collected by the dust collector that is used for hydrodispersion may contain worn filter media, and the recovered caustic soda may contain impurities. There was a problem.

The present invention was made in view of the above points, and an object of the present invention is to provide a method for recovering caustic soda from pulp waste liquid that can effectively recover waste heat and efficiently proceed with the reaction in a fluidized bed furnace. That is.

[Means and actions for solving the problem]

In order to achieve the above object, the method of recovering caustic soda from pulp waste liquid of the present invention will be described with reference to FIGS. 1 and 2. After concentrating pulp waste liquid, Fe ₂ O ₃ , TiO ₂ , FeTiO ₃ is added as a causticizing agent and combusted in a fluidized bed furnace 4, and then the product is poured into water to recover caustic soda and the causticizing agent, the method comprising: The exhaust gas from 4 is introduced into a filtration layer made of coarse particles of causticizing agent and passed through it to collect dust.
It is characterized in that the coarse causticizing agent in the filter bed, which has been preheated by exhaust gas, is supplied to the fluidized bed furnace 4.

As shown in FIGS. 1 and 2, a coarse causticizing agent is used as a filter material in the dust collector 15 downstream of the fluidized bed furnace 4, and the preheated coarse causticizing agent is transferred to the fluidized bed furnace 4. By using the waste heat, combustion and reactions in the fluidized bed furnace can be carried out efficiently.

〔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 supplied to a fluidized bed furnace 4. As a fluidizing agent for this fluidized bed furnace 4, a material selected from the group consisting of Fe ₂ O ₃ , TiO ₂ , and FeTiO ₃ is used (Fig. 1 shows an example in which high-quality iron ore is used as a causticizing agent). ) is used. The thick black liquor is combusted in the fluidized bed, and the reactions of the above-mentioned reaction formulas (1) and (2) take place. Thick black liquor is a solid substance
Concentrate to 50wt% or more, and reduce the reaction temperature to 700%.
~1100°C, preferably 850~1000°C.

Then, the product in the fluidized bed furnace 4 is extracted,
After being cooled in a cooler 5, it is introduced into a hydrolysis tank 6 and placed in water to carry out the reaction of the above reaction formula (3).
Generates NaOH _{and Fe2O3} . This NaOH and Fe ₂ O ₃ are sent to Clarifair 7.
NaOH and Fe ₂ O ₃ are separated, and NaOH is stored in a caustic soda tank 8. Fe ₂ O ₃ is in the cleaning tank 10,
It passes through a filter 11 and is recovered as Fe ₂ O ₃ . This Fe ₂ O ₃ is supplied to the fluidized bed furnace 4 . Note that 12 is a pure water tank, 13 is a boiler, 14 is a gas/air heater, 15 is a dust collector, 16 is an induction fan, and 17
is a chimney.

The dust collector has a structure in which coarse-grained causticizing agent (in the case of Figure 1, good quality iron ore) is movably filled between porous supports such as louvers, punched metal, and wire mesh. . Dust such as ferric acid soda discharged from the dust collector 15 is attached.
Fe ₂ O ₃ is introduced into a classifier 18 such as a vibrating sieve, and is separated from ferric acid soda and fine powder Fe ₂ O ₃ and coarse powder.
Fe ₂ O ₃ is classified into Fe 2 O 3 and coarse Fe ₂ O ₃ is transferred to the fluidized bed furnace 4.
is supplied to The fine powder can be used in the hydrolysis step or in the premixing step with black liquor.

In this embodiment, iron ore is used as the filter material for the dust collector 15 downstream of the fluidized bed furnace 4, and since preheated iron ore is supplied to the fluidized bed furnace 4, the waste heat can be used to reduce the flow rate. It has the advantage that combustion and reaction in a bed furnace can proceed efficiently.

FIG. 2 shows another embodiment of the invention. In FIG. 2, iron ore is first introduced as a causticizing agent into a classifier 20 and classified into fine powder and coarse particles, which have a particle size smaller than that of the fluidizing agent in the fluidized bed furnace 4, and the fine powder is transferred to a mixing tank 21. After being supplied and premixed with concentrated black liquor, this mixture is charged into the fluidized bed furnace 4 and combusted to carry out the reactions of the above reaction formulas (1) and (2). Dust collector 15 for coarse particles
It is used as a filter material. The concentrated black liquor is concentrated to a solid content of 50 wt% or more, and premixed so that the molar ratio of Fe and Na (Fe/Na) is 1 or more. In addition, the fluidizing agent in the fluidized bed furnace 4 has a particle size of
0.2~2.0mm, and the reaction temperature is 700~
The temperature is 1100°C, preferably 850 to 1000°C.

The Fe ₂ O ₃ recovered through the filter 11 is further introduced into the classifier 22 and classified into coarse particles and fine particles.The coarse particles are supplied to the dust collector 15 as a filter material, and the fine particles are sent to the mixing tank 21. Supplied. In addition, Fe ₂ O ₃ with dust attached, such as sodium ferrate, discharged from the dust collector 15 is introduced into a classifier 18 such as a vibrating sieve, where it is separated into sodium ferrate and fine Fe ₂ O ₃ and coarse particles.
The coarse particles are classified into Fe ₂ O ₃ and fed to the fluidized bed furnace 4 as a causticizing agent. The other configurations are the same as in the case of FIG.

As described above, in this example, Fe ₂ O ₃ and black liquor are introduced using the premixing method, and are used for mixing.
Since Fe ₂ O ₃ uses fine powder smaller than the fluidizing agent particle size, even if fine powder Fe ₂ O ₃ alone is put into the fluidized bed, it will prevent it from immediately jumping out of the furnace.
In addition, Na 2 to be recovered by reacting with Fe ₂ O ₃ due to the volatilization of volatile matter, ash, etc. due to the combustion of black liquor before it reaches the fluidized bed, which is expected when only easily combustible black liquor is input _. The loss of O 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,
This is approximately twice as large as that of silica sand, etc. On the other hand, when only black liquor is supplied, the specific gravity itself increases as the black liquor becomes concentrated and the solid content increases;
Due to the property of organic matter to volatilize and swell, the apparent specific gravity decreases, and the resistance to rising combustion gas increases, making it easier for Na ₂ to be carried over to the outside of the system without reaching the fluidized bed. O will suffer a loss. In addition, black liquor is a viscous liquid, so it is difficult to mix with granular Fe ₂ O ₃ , but it is relatively easy to mix with powdered Fe ₂ O ₃ , and the mixture has a shape larger than the superplasticizer particle size. (lumpy or candy-like)
Therefore, there is no chance of it jumping out of the furnace. In addition, the reaction that produces sodium ferrate (Na ₂ Fe ₂ O ₄ ) is the reaction between Fe ₂ O ₃ and
This is _a solid phase reaction with Na ₂ CO _{3 ,} and the larger the reaction surface area of Fe ₂ O ₃ (and thus the finer the powder), the larger the amount of reaction per unit volume. Recovery of Na ₂ O through the reaction of ₂ O can also be expected. Furthermore, as mentioned above, when recovering NaOH by hydrolyzing the generated sodium ferrate, coarse particles are
Fe ₂ O ₃ tends to gradually become fine powder, and iron ore contains 5 to 30 wt% of fine powder (0.149 mm or less), so when iron ore is received in a fluidized bed with a wide particle size distribution Since the fine powder cannot be used alone because it jumps out, the method of mixing fine powder Fe ₂ O ₃ with black liquor in advance as in this example is as follows:
It is possible to effectively react Na ₂ CO ₃ and Fe ₂ O ₃ by burning black liquor in a fluidized bed, 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.

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, in the method of the present invention, a substance selected from the group consisting of Fe ₂ O ₃ , TiO ₂ , and FeTiO ₃ is used as a causticizing agent, and a coarse causticizing agent is added downstream of a fluidized bed furnace. By supplying the filter material preheated in the dust collector to the fluidized bed furnace, waste heat can be effectively recovered, making the reaction in the fluidized bed furnace more efficient. This has the effect of making progress easier.

[Brief explanation of drawings]

FIGS. 1 and 2 are flow sheets showing one embodiment of an apparatus for carrying out the method of the present invention. 1... Dilute black liquor tank, 2... Evaporator, 3
... Concentrated black liquor tank, 4 ... Fluidized bed furnace, 5 ... Cooler, 6 ... Hydrolysis tank, 7 ... Clarifier, 8 ... Caustic soda tank, 10 ... Washing tank,
11... Filter, 12... Pure water tank, 13...
...boiler, 14...gas/air heater, 15...
Dust collector, 16...Induction fan, 17...Chimney,
18... Classifier, 20... Classifier, 21... Mixing tank, 22... Classifier.

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 4, and then the product is poured into water to recover caustic soda and the causticizing agent from the fluidized bed furnace 4. The exhaust gas of
A method for recovering caustic soda from pulp waste liquid, characterized in that a coarse causticizing agent in a filter bed preheated by exhaust gas is supplied to a fluidized bed furnace 4.