JPS60181392A - Direct causticizing method using fluidized bed - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a direct causticizing process using a fluidized bed, and more particularly to a process that can extend the service life of the metal oxides used.

In the pulp manufacturing process at a paper mill, chemicals, mainly caustic soda (NaOH), are used to separate the wood components cellulose and lignin and extract only the cellulose. A solution containing dissolved lignin and Na components that has passed through the cooking process is discharged as a waste liquid called black liquor, and a method of burning this black liquor to recover heat and recover NaOH has been conventionally practiced. The conventional method uses N during black liquor combustion.
a2. o o3 is reacted and produced, and this N at ,
Slaked lime (Oa (OH)2) produced from 003 in a separate process
) to recover NaOH, but the reaction process is complicated and the equipment becomes large, and the Ca00 generated during NaOH generation is converted to 0a(OH) through a slaked process.
There is a problem in that a large amount of energy is consumed to restore the For this reason, a primary aclH recovery method called a direct causticization method has been proposed for the purpose of energy saving and equipment simplification, and the inventor has proposed a method using a fluidized bed furnace as an example thereof. [Patent Application No. 57-4029] The direct causticizing method itself produces sodium ferrate (NaFe02) by adding an oxide metal such as Fe2O3 during the combustion process, and then recovers NaOH by hydrolyzing this NaFeO2. In this method, when a fluidized bed is used, FexOa is used as the fluidized medium to cause combustion and a reaction to generate NaFeOz.

As shown in Fig. 1, this method first forms a surface layer 5 of NaFeα on the surface of media particles 4 made of Fe20B through a combustion reaction with black liquor as shown in (a) in the figure. The media particles are extracted from the fluidized bed and hydrolyzed by adding water to recover N2LOH. During this time, the surface layer 5 dissolves into the water, and as a result, the particle diameter of the particles becomes smaller by the amount of the surface layer 5, and as the particles are used several times, they dissolve into the medium as shown in (0) and (d). The particles become smaller in diameter and eventually scatter into the sky tower, placing a heavy burden on the dust collector. Furthermore, particles whose diameter has been reduced in this way become unusable, and particles that can sufficiently react to NaFe0z are simply reduced in particle size and are discarded in large quantities, which is extremely uneconomical. be. In addition to the reasons mentioned above, it takes a certain amount of time for the black liquor directly supplied into the fluidized bed to completely react, but this also ignores the collisions between media particles and the reduction in particle size due to abrasion during this time. I can't.

An object of the present invention is to eliminate the above-mentioned problems, to provide a method in which even small-sized particles can be used sufficiently as a fluidizing medium, and the reduction in particle size itself can be reduced.

In short, this invention sprays a liquid mixture of black liquor and metal oxide particles from the upper part of the fluidized bed as particles (droplets) of a predetermined size, and at least part of the reaction with the black liquor is carried out in the lower part of the upper part of the upper part of the upper part of the upper part of the fluidized bed. When reaching the fluidized bed through vaporization combustion, sodium ferrate particles are used to form medium particles with a predetermined particle size.

Embodiments of the present invention will be described below with reference to the drawings.

In Fig. 2, 6 is a fluidized bed furnace, and when starting the fluidized bed furnace, metal oxide (hereinafter [Fe20s J
) is filled with a fluidized medium consisting of (described in ), and is fluidized by air A supplied from the perforated plate 7. Note that the particle size is approximately 100 to 1'oooμ. Conventionally, black liquor was supplied directly to this fluidized bed, but in this method, black liquor is supplied by spraying from the empty column. That is, the black liquor 9 and the iron oxide particles (Fe2O3) are mixed and stirred in the mixing tank 8, and the mixed liquid 11 of both is supplied via the pipe line 29 to the oscillator 12 disposed in the empty tower part 6a of the fluidized bed furnace.

A mixed liquid of black liquor and FI9203 is sprayed onto the oscillator 12, and in this case, the particle size of the sprayed liquid is set to be about several mm, so that the particle size of the fluidizing medium described later becomes an appropriate size.

FIG. 3 schematically shows how the particles of the sprayed liquid change. In the liquid particles (hereinafter referred to as "droplets") sprayed into the sky column by the oscillator 12, particles 4 made of Fe2O3 are located, for example, approximately in the center. The particles 4 may be, for example, small-diameter particles that should be disposed of as shown in FIG. 1(d). In such a state, the droplets sprayed into the empty column undergo a combustion reaction due to the heat H in the empty column, and the antibt formed by the following formulas (1) and (2) is generated.
; to form a layer 5 made of NaFeOz.

2NaOH+(!02Na, Co, 10H20-(1)
Na200s+Fe2o3-+2NaFflO+Co
2...(2) During this time, a cavity 13 is formed in the layer and the layer becomes porous. In this way, the reaction proceeds while falling, reaching the fluidized bed 14. Here, the reaction further progresses due to the temperature H2 in the layer, and the particles become NaFeO2 completely, and these particles become medium particles. On the other hand, Fe, which was previously introduced as a fluid medium, was 0. The particles react with the unreacted or unreacted black liquor that falls to form NaFeO2. Therefore, the particles in the fluidized bed are gradually replaced by NaFeO2 particles. Here, the true specific gravity of Fezes is heavy at 4.5 to 5.0, and the apparent specific gravity when fluidized is about 2.5 to 3.0, but on the other hand, the apparent specific gravity when made into media particles of 1 Ja Feoa is Specific gravity is about 1.0 to 1.5. Therefore, for example, when almost the entire amount is replaced with NaFeO2 particles, 50o~
800-1200m with pressure loss of looommAq only
Is it possible to form a fluidized bed as deep as 1000 ft for effective reaction? I can say te.

Next, FIG. 4 shows another state of droplet change.

These droplets are a mixture of a plurality of extremely small particles 4a, which are almost the same as Fe20s, which is the core of the particles that formed the fluidized medium in Fig. 3, and usually have different particle sizes like this. It is more common for it to contain multiple particles. Even in the case of a mixture with particles of extremely small diameter, the particle size of the droplets themselves is approximately several mm, so the fluidized bed 1
4, it can be fully used as a fluidized medium particle.

Therefore, virtually all Fe2O collected by the dust collector can be used.

The molar ratio of F e /N a is an important factor in the generation of NaFeO2, but when the Fe20s particles are thin, F e
It was confirmed that the reaction rate remained almost unchanged even when the e/Na molar ratio was increased to 1.1 or more. On the other hand, the generated NaFe
oz is Fe/N, and the larger the molar ratio of a, the higher the melting point. However, from the point of view of reaction rate, the molar ratio o is 9 to 1.
．． It is preferable to operate at a temperature of about 1, and the softening point of NaFeO2 produced in this range is about 1100°C. For this reason, the operating temperature of the fluidized bed is set to 1100°C or less.

The NaFeO2 particles formed by the above method are overflowed from the fluidized bed and supplied to the dissolution tank 15.

In this case, the small diameter particles scattered together with the exhaust gas G are also collected in the dust collector 1.
6 is collected and supplied to the same tank.

Water W is supplied to this dissolution tank 15, and the following formula (3)
Hydrolysis is carried out as follows.

2NaFeOz +H202NaOH+Fe20g =
(3) In this case, it is preferable to heat the inside of the tank with a heating medium such as steam S to increase the reaction rate. NaOHll produced by hydrolysis! : The mixed liquid of Fe20s reaches the sedimentation tank 17 via the pipe 16, and the Fe20s mixture is sedimented and separated.
Oa reaches a dehydrator 19 via a pipe 18. In this case, since the 20 g of Fe to be separated contains a large amount of particles of considerably small diameter, filter cloths for dehydrators such as vacuum type, pressure type, belt press type, etc. used in conventional methods are insufficient. Therefore, in this invention, a filter with a filter aid (in this case, it is preferable to use Fe2O particles to be filtered) is filtered in advance to form an aid layer on the filter surface, and a filter with a small diameter is used. It is preferable to configure the structure to prevent an extreme increase in cake resistance due to particles. Cake after dehydration (
Fe20g) is supplied to the dryer 21 and dried. In this case, it is economical to use the exhaust gas G of the fluidized bed furnace 6 as the heating medium for drying.

On the other hand, the NaOH solution enters the filter 23 via the pipe 22.

It is preferable that the filter medium in this case also has an auxiliary agent layer made of Fe, O, and particles formed on the filtering surface as in the case of the dehydrator 19 described above. In this case, filtered Fed Os fine particles may also be supplied to the dryer 21 for use. The NaOH separated from the dehydration 519 and the filter 23 is stored in the NaOH storage tank 24.
It is stored in and supplied to the cooking process as needed.

Further, the Fe20x particles 1o dried in the dryer 21 are supplied to the hopper 25 and stored therein. The stored Fθgos particles are supplied to the stirring tank 8 through the pipe line 26, mixed with the black liquor 9, and supplied to the ongilator 12 through the pipe line 27, where they are subjected to the above-described combustion. In addition, it is preferable to use a heating medium to promote mixing during mixing and stirring.

By carrying out this invention, it is possible to form a fluidized medium of almost a predetermined particle size regardless of the particle size of the metal oxide particles such as iron oxide particles, so the metal oxide can be used until the end, which is extremely economical. .

In addition, since the heat in the empty column can be used for the reaction, the reaction time within the bed can be shortened, and media particles can be quickly discharged from the bed, thereby minimizing particle collisions and reduction in diameter due to abrasion. This makes it possible to delay the size reduction of metal oxide particles themselves.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view showing the state of change in particles of a conventional fluidized medium, Fig. 2 is a system diagram of a plant implementing the method according to the present invention, and Figs. 3 and 4 show the relationship between iron oxide particles and black liquor. FIG. 3 is a cross-sectional view showing the changing state of mixed liquid particles in the furnace. 4.10...Iron oxide particles 5...Sodium ferrate layer 6...Fluidized bed furnace 6a... Sky tower section 9... Black liquor 11... Mixture of black liquor and iron oxide particles 12...
...oscillator (0) (b) (c) (d) Figure 3 I2

Claims (1)

[Scope of Claims] 1. In a method for recovering sodium content in black liquor by reacting black liquor and metal oxide in a fluidized bed furnace, a mixture of black liquor and metal oxide is passed through the cavity of the fluidized bed furnace. A direct causticizing method using a fluidized bed, characterized in that the particles are sprayed from the bed, at least a part of the reaction is carried out in the empty column, and the particles that have fallen into the fluidized bed are used as a fluidized medium. 2. The direct causticizing method using a fluidized bed according to claim 1, characterized in that the particle size of the sprayed particles of the mixture is about 1 mm or more. 3. Claims 1 or 2, characterized in that the metal oxide is iron oxide, the reaction product is sodium ferrate, and the fluidized medium at the time of starting the fluidized bed is iron oxide particles. Direct causticization method using a fluidized bed as described. 4. Adjust the molar ratio of iron and sodium from about 0.9 to about 1.1.
4. A direct causticizing method using a fluidized bed according to claim 3, characterized in that the temperature in the fluidized bed is controlled to be between about 1,100° C. or less.