JPS58132193A - Recovery of caustic soda using fluidized layer - 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 method for recovering chemicals from black liquor, and in particular, the recovery effect is enhanced by effectively reacting the Na content in black liquor with iron oxide powder during the combustion stage. Regarding the method.

In the pulp manufacturing process at paper mills, chemicals such as caustic soda (NaOH) are used to separate the wood components cellulose (fiber) and lignin (resin) and extract only the cellulose. The solution containing dissolved lignin and Na components that passes through the culm during cooking is discharged as a waste liquid called black liquor, and heat is recovered by burning this black liquor.
In addition, a method of recovering and reusing NaOH has been conventionally practiced. However, the conventional method uses a burner for black liquor combustion and sprays it into the furnace or sprays it onto the furnace wall and burns it as char at the bottom of the furnace to react and generate Na2CO3.
Slaked lime (Oa(OH)2) produced from 003 in a separate process
This method recovers NaOH by reacting with NaOH, and the reaction process requires complicated equipment and is difficult to control. There is a problem in that a large amount of energy, such as fuel, is consumed to return the water. For this reason, an NaOH recovery method called a direct causticization method has been attempted in order to simplify the equipment and reduce energy consumption. 1st
To explain the outline of this direct causticizing method using a diagram, the lignin of wood chips is separated by NaOH in the cooking process 1, and the black liquor containing lignin and Na components is separated by adding Fe2O3 in the combustion process 2. Carry out the reaction of Eq.

2 Na OH+ 002->Na 2 Q 03
+H20...(1)Na2C03+Fe203->
2NaFeO2+OO2-(2) Of these, sodium ferrate (NaFeO2) is hydrolyzed in the next dissolution step 3 to recover NaOH.

2NaPeOg+ H2O -2NaOH+ Fe2O
3...-(3) In other words, in the direct causticization method (ingredients (2 people (3
) By performing the reaction, NaOH can be recovered, and the Fe2O3 used for this recovery can be recycled and reused, reducing equipment costs and costs compared to conventional methods.
It has the advantage that energy consumption can be significantly reduced.

In order to make the direct causticizing method outlined above more efficient, it is necessary to pay attention to the following points: (1) Reaction (combustion) between iron oxide and Na content in black liquor.
The longer the time, the better; if a long reaction time cannot be ensured, it is necessary to use a reactor type with strong catalytic action.

(2) In order for the sodium ferrate produced by the above reaction to undergo subsequent hydrolysis efficiently, its crystal structure must be changed to β.
It is necessary to keep it in a mold, and for this purpose it is necessary to control the reaction temperature.

(3) Furthermore, the sodium ferrate needs to be in powder form to facilitate its handling, and for this reason, it is also necessary to control the reaction humidity.

Further, although it is not directly involved in the L distribution method, it is necessary to make efforts to reduce as much as possible the intake of nitrogen oxides (NOx) generated during black liquor combustion.

The purpose of the present invention is to propose a direct causticizing method that is constructed in view of the above-mentioned requirements and is capable of increasing the recovery rate of chemicals in black liquor and reducing the amount of nitrogen oxides generated.

In short, this invention uses a black liquor combustion (reaction) apparatus as a fluidized bed furnace, and the reaction is carried out in the fluidized bed, and the reaction is controlled by a control box.

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

In FIG. 2, reference numeral 5 denotes a fluidized bed furnace, in which black liquor is combusted and sodium ferrate is produced by reaction. For the black liquor 6 supplied to the fluidized bed furnace 5, F is added as iron oxide powder.
e2O3 is mixed in advance, and the reactions shown in formulas (1) and (2) above are carried out in the furnace to produce iron oxide).
Jium (NaFeO3) is produced by the reaction. N a F
e There are three types of O2 based on this crystal structure: α, β, and γ, but in order to effectively hydrolyze it, the β type is preferable, and in order to obtain the β type, the reaction temperature should be about 800 to 1000°C.
It is necessary to do so. In addition, in order for this NaFeO2 to form a powder, the reaction temperature must be lower than the melting point of the ash produced by combustion and at least 1100°C with a safety margin. is the reaction temperature of 1000
It must be kept below ℃.

Here, the reaction within the fluidized bed of the fluidized bed furnace 5, that is, Fe2O3
The generation reaction of NaFeO2 by combustion of black liquor containing black liquor depends on the temperature in the layer, and it is important that NaFeO2 is in the form of powder.

Reference numeral 7 denotes a control box for storing memory and issuing command signals, and an in-bed temperature detector 8 constantly detects the temperature of the fluidized bed 5a. Based on this detection result, the black liquor supply adjusts the amount of combustion air supplied to control the temperature in the bed. For example, when the temperature in the bed is low, the opening of the valve 9 is increased to increase the amount of black liquor supplied, and correspondingly, the opening of the damper 10a is increased to increase the amount of combustion air supplied. As a result, the fluidized state of the fluidized medium becomes active, which is favorable for combustion. If the temperature inside the layer is too high, perform the reverse operation to the above. In addition, the control box 7 detects NOx by the NOx detection 511 arranged in the empty tower part 5b.
The density is detected, and the above-mentioned control i1: is performed using the detection result as a correction value.

FIG. 3 shows another embodiment.

In this embodiment, an intrabed heat exchanger tube 1 arranged in a fluidized bed is used.
The temperature in the fluidized bed is adjusted by regulating the flow rate of the fluid in the pipe No. 3 by a valve 13.

In this device, if the temperature in the bed is too high, the valve 9 is throttled to reduce the amount of black liquor supplied, and the opening of the valve 14 is increased to increase the flow of cooling medium such as water supply, thereby lowering the temperature in the bed. . On the other hand, when the temperature in the bed is low, the opening degree of valve 9 is large and the opening degree of valve 1 is large.
4 narrows down and increases the opening degree of the damper lOa. Also N
When the NOx concentration increases as determined by the Ox detector 11, the damper 10c is opened and a part of the combustion exhaust gas G is mixed with the fluidized air and supplied from the lower part of the fluidized bed 5a to lower the bed temperature and reduce NOx. Measure.

NaFe generated in the fluidized bed furnace 5 by the above method
O2 is collected as dust by a dust collector (not shown) installed in the exhaust gas pipe and sent to the next step of the dissolution process, where it is hydrolyzed by the dissolved water into NaOH and Fe2O3 as shown in equation (3), and NaOH is Fe and 03 is reused in the chip cooking process to be mixed with black liquor and combusted.

The fluidized medium forming the fluidized bed 5a is preferably magnesia clinker (MgO) or electroformed alumina (A1203) in order to avoid fusion bonding with sodium components and minimize wear of the media particles.

By carrying out this invention, the temperature within the fluidized bed can be maintained appropriately, and the reaction between the caustic soda contained in the black liquor and the iron oxide powder can be effectively carried out, and the generated sodium ferrate can be made into a powder form that is easy to handle. Moreover, the crystal structure can be made into the β type, and in addition, by controlling the temperature within the fluidized bed, the concentration of nitrogen oxides in the combustion exhaust gas can be significantly reduced.

[Brief explanation of drawings]

Fig. 1 is a system diagram showing an outline of the direct causticizing method, Fig. 2 is a control system diagram of a fluidized bed furnace showing the first embodiment of the present invention, and Fig. 3 is a fluidized bed furnace showing the second embodiment. It is a control system diagram of a furnace. 5...Fluidized bed furnace 5a...Fluidized bed 5b...Sky tower section 6...Black liquor 7...Control box 13...In-bed heat transfer tube agent patent attorney Oka Tagobe Ω No. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1. In a method for recovering caustic soda by reacting black liquor and iron oxide powder in a combustion furnace and hydrolyzing the reaction product, the combustion furnace is a fluidized bed furnace, and the temperature in the bed is lowered. A method for recovering caustic soda using a fluidized bed, characterized in that the product is mainly powdered sodium ferrate and has a β-type crystal structure by controlling the product. 2. Set the temperature inside the fluidized bed to about 800℃ to 1000℃ and β
A method for recovering caustic soda using a fluidized bed according to claim 1, wherein the main product is sodium ferrate. 3. Placing an intrabed heat exchanger tube in the fluidized bed of the fluidized bed furnace,
The temperature in the bed is adjusted by supplying black liquor to the fluidized bed by adjusting the density of the medium supplied to the heat exchanger tubes in the bed. Method for recovering caustic soda. 4. Claims 1 to 3, characterized in that the control is performed by a control box that emits a memory and a command signal.
A method for recovering caustic soda using a fluidized bed according to any one of paragraphs. 5. Using the fluidized bed according to any one of claims 1 to 4, characterized in that the fluidized medium in the fluidized bed furnace is powder of magnesia alinker or electroformed alumina. Method for recovering caustic soda.