JPS6081016A - Method for recovering soda from waste liquor from pulp manufacturing stage - Google Patents

Abstract

PURPOSE:To reduce considerably the cost of fuel required to recover soda by feeding waste liquor from a pulp manufacturing stage and BaCO3 powder to a recovery boiler, calcining them, introducing the calcined products into a soda dissolving tank, producing NaOH and BaCO3 with water, and reusing the BaCO3 in the recovery boiler. CONSTITUTION:Highly concd. alkali waste liquor from a pulp manufacturing stage is blown into the bottom part of a recovery boiler 10 from burners 12 in the form of fine particles, and at the same time, heated air fed from air feeding pipes 13, 14 to produce smelted matter by combustion at a high temp. BaCO3 powder is also blown into the bottom part of the boiler 10 from feeding inlets 15, and it is converted into BaO and allowed to flow down into a soda dissolving tank 16 together with the smelted matter. The tank 16 contains water fed from a feeding pipe 17, and the smelted matter is dissolved in the water to produce NaOH and BaCO3. The NaOH is taken out of an outlet 18 for taking out white liquor, and it is stored in a white liquor tank 19. The BaCO3 is taken out of an outlet 21 and fed to a drying means 24. The dried BaCO3 is fed to the boiler 10 from the inlets 15.

Description

[Detailed description of the invention] In particular, it concerns measures to streamline the causticization process for recovered chemicals.

FIG. 1 is a schematic diagram showing an alkali pulp manufacturing process. Hereinafter, a conventional method for producing alkaline pulp will be explained with reference to FIG.

In Fig. 1, l is a pulp digester, 2 is a 7'-loop blow tank, P is pulp, 3 is an evaporator for concentrating waste liquid, 4 is a chemical recovery boiler (hereinafter referred to as recovery boiler), 5 is the sumeru and dissolution tank, 6 is the causticizing tank, and 7 is the causticizing tank.
8 is a white liquor tank, and 9 is an electrolyte machine.

Chemicals for bulb cooking are supplied to the digester 1 or the causticizing tank 6, which includes a blow tank 2, an evaporator 3, a recovery boiler 4, a smelt dissolving tank 5, a causticizing tank 6, and a white liquor tank 8.
The valves are circulated through the cooking chemical circulation system PL in this order. Cal/rum carbonate produced in the causticizing tank 6 is calcined in a rotary kiln 7 to become cal/rum oxide, which is recycled to the causticizing tank 6. In addition, some of the chemicals scatter as dust from the flue in the recovery boiler 4, but most of it is collected by the electrostatic precipitator 9 and returned to the black liquor line.
sent to and burned. In the conventional method, the alkaline pulp waste liquid is combusted in a recovery boiler 4. The smelt produced here is dissolved in water in a smelt dissolving hinoki 5 to produce a sodium carbonate aqueous solution. This carbonated soda is then sent to causticizing tank 6.
When it comes into contact with the supplied Ca(ω1)2 (or CaO and H2O), it is causticized into caustic soda, which is a cooking chemical, as shown in the following equation.

Na2COs-l-Ca(OH)2→2NaOH+Ca
On the other hand, ClIC0:l produced in the causticizing tank 6 is
CaO is calcined in a rotary kiln 7 and slaked with water to produce ca(o+q)2, which is circulated and used in a causticizing tank 6.

The disadvantage of the above conventional method is that the CaCO3 generated in the causticizing tank 6
The problem is that the amount of fuel used when firing the slurry in a kiln is large.

The purpose of the present invention is to provide a pulp waste soda recovery method that can save energy in the firing of the C a CO3 slurry produced in the causticizing tank 6 and streamline the causticizing process of the recovered chemicals. For this purpose, the present inventors first constructed a pulp waste liquid combustion section KCa of a recovery boiler.
Powder containing mainly CO3 is supplied to obtain CaO in the recovery boiler furnace, and the CaO burned in the furnace is led to the soda dissolution tank at the bottom of the recovery boiler, where it is generated by a causticizing reaction in the soda dissolution tank. The CaCO3 slurry is brought into contact with the exhaust gas of the boiler flue, dried, and then introduced into the recovery boiler furnace.
When eliminating the need for a rotary kiln for drying and firing CO3 slurry, a method has been proposed in which drying of acO3 slurry can be effectively carried out using boiler exhaust heat (Japanese Patent Application No. 149232/1982), but this paper The present invention further improves this by supplying barium carbonate or powder mainly containing barium carbonate and iron oxide to the pulp waste liquid combustion section of the recovery boiler instead of the powder mainly containing CaCO3 in the above method. It is characterized by a high causticization rate.

The present invention provides a method for spraying and burning pulp waste liquid in a soda recovery boiler, by supplying barium carbonate or powder mainly containing barium carbonate and iron oxide to the pulp waste liquid combustion section of the recovery boiler, and converting barium oxide in the recovery boiler furnace. Alternatively, the barium oxide or barium ferrate is calcined into barium ferrate, and the barium oxide or barium ferrate calcined in the same furnace is led to the soda dissolving tank at the bottom of the recovery boiler where soda, barium, and iron are recovered, and the causticizing reaction in the soda dissolving tank is carried out. This method is characterized in that barium carbonate or barium carbonate and iron oxide slurry produced are brought into contact with the exhaust flue gas at the rear of the recovery boiler to supply the dried barium carbonate and iron oxide powder into the recovery boiler furnace.

The method of the present invention is effective when applied to a pulp cooking chemical recovery boiler of a filter paper pulp mill, which is an energy-intensive industry.

The present invention will be explained below with reference to FIG.

In the figure, 10 is a recovery boiler main body, the lower part of which is sloped in a funnel shape so that the sysmelt can easily flow down. 11 is a boiler bank connected to the flue, 12 is a pulp waste liquid burner, and 13 and 14 are primary and secondary, respectively.
The secondary air supply port 15 is a supply port for barium carbonate or a powder mainly containing barium carbonate and iron oxide. Fed, Fe2O3, and Fear4 are used as iron oxides. Barium carbonate and iron oxide may be used in approximately equivalent amounts to the amount of smelt. Note that the above powder may be added to the pulp waste liquid supply system. 16 is a soda dissolving tank disposed at the bottom of the recovery boiler 10, 17 is a water supply port which is specially arranged to open at the top of the soda dissolving tank 16, and 18 is a water supply port which is opened to the soda dissolving tank 16. Completely installed white liquid outlet pipe, 19
20 is a white liquor supply pipe connected to the white liquor tank 19; 21 is barium carbonate connected to the bottom of the soda dissolving tank 16; or, This is a barium carbonate and iron oxide slurry extraction pipe. 22
is a dust collection device installed in the flue at the rear of the boiler back, and a multi-clone or high-temperature electrostatic precipitator can be used. 2
3 is a collected dust transfer pipe connected to the dust collecting device 22 on one side and opened to the soda dissolving tank 16 on the other side, and 24 is a barium carbonate or barium carbonate and iron oxide slurry disposed in the rear flue. This drying method is used to dry the boiler by contacting with the boiler exhaust gas. In this case, barium carbonate,
Alternatively, the slurry containing barium carbonate and iron oxide may be pre-dehydrated as the case may be, and then the dehydrated cake may be dried. 24Δ is a slurry supply means disposed above the barium carbonate or barium carbonate and iron oxide drying means 24,
For example, a spray nozzle, a belt conveyor, etc. can be used. 25 is a slurry transfer pipe whose one side is connected to the slurry increase pipe 21 of the barium carbonate or barium carbonate and iron oxide, and the other side is connected to the slurry supply means 24A, and 26 is the barium carbonate or barium carbonate and iron oxide slurry transfer pipe. One side is connected to the lower part of the drying means 24 for iron slurry, and the other side is connected to the feed port 15 for powder mainly containing barium carbonate or barium carbonate and iron oxide, and dried barium carbonate or barium carbonate and iron oxide. This is a powder transfer tube.

In such a configuration, the operation of the present invention will be explained. At the bottom of the furnace, which is the valve waste liquid combustion section of the recovery boiler 10, highly concentrated alkaline valve waste liquid is burned in the burner 12.
The heated air supplied from the primary and secondary air supply pipes 13 and 14 is supplied to the bottom of the furnace in the form of fine particles, and is combusted at high temperature to produce smelt (mainly Na2COx). At this time, the bottom of the furnace is tilted like a funnel as shown in the figure to improve the flow of the smelt.

Furthermore, barium carbonate or a powder mainly containing barium carbonate and iron oxide is sprayed into the furnace from the supply port 15 at the bottom of the furnace. Firing at the furnace gate (13a C03-B a 0-+-c
o2, or BaCO3-1-Fe20a→BaO*F
e20z+COz) BaO or BaO-
Most of the Fe20'a is carried by the snort flowing down the furnace wall and is caused to flow down into the soda dissolving tank 16 at the bottom. In the soda dissolving tank 16, smelt (NazCOa, BaO, or BaO1'ezO,+) is dissolved in the water previously supplied from the water supply pipe 17, and the following reaction occurs.

Na2COa +BaO-1-820-2Na01-1
+ BaC0+ -(1) or Na2COa+Ba0
Fe20s+1(20-2NaQ(+BaC0a+Fe
20a - (21 In this way, the cooking chemical NaO
Make H.

On the other hand, NaOll generated in the soda dissolving tank 16 is led from the white liquor outlet 18 to the white liquor tank 19, and then from the white liquor supply pipe 20 to the valve cooking chemical circulation system PL as shown in FIG. Sent. In addition, BaCO3 or BacO3, F C203 generated in the soda dissolving tank 16 is transferred to the barium carbonate, barium carbonate, or iron oxide slurry outlet 21.
This slurry is sent to the drying means 24 in the rear flue as described above, and the dried material is sent to the recovery boiler supply port 15.
Supplied from.

The present invention provides the following effects.

(g) In a soda recovery boiler that spray-combusts valve waste liquid, the method of the present invention is to supply barium carbonate or a powder mainly containing barium carbonate and iron oxide to the valve waste liquid combustion section of the recovery boiler and oxidize it in the recovery boiler furnace. Since barium or barium ferrate is calcined, there is no need for heating in a rotary kiln, which consumes a large amount of fuel, compared to conventional methods, and this has the advantage of significantly reducing fuel costs.

(a) Table 1 shows the solubility of calcium and barium carbonates and hydroxides in water. In this table, the solubility of calcium and barium is greater for barium, and the solubility of hydroxide is greater for barium. On the other hand, the details of the above-mentioned causticizing reaction formula (1) are as shown in the following formula, BaO→-)120- Ba(OH)z...f31N
a2C○3 + Ba(OH)2-2NaOH+Ba
The greater the solubility of CO3-f41 hydroxide and the lower the solubility of carbonate, the easier the reaction will proceed and the higher the causticization rate will be. Therefore, a method using calcium (Japanese Patent Application No. 57-142)
138), the method of the present invention using barium provides a higher causticizing rate.

Table 1 (T) Figure 3 is a plot of 109Kp (logarithm of the equilibrium constant of the reaction) at each temperature, and 10gKp
The larger the value, the easier the reaction progresses. In the figure, curve A is MgCO3-MgO+CO2° curve B
is MgCO3+Fe2O3→MgO-Fc203+CO
22 curve C is CaCO3-+ CaO+ CO21 curve is CaCO3+Feze3-+ CaO-Fe2O
3+ CO2, curve E is B a CO3 = 13aO-
The temperature dependence of j'ogKp for 1-CO2 is determined.

In this way, alkaline earth metals (Mg, Ca, Ba, etc.)
In the thermal decomposition of the carbonate, the thermal decomposition of the mixture with iron oxide (curves B, C,
D) has a larger 10 gKp and is superior in terms of reaction.

The same can be said for the thermal decomposition of barium carbonate (curve E); when iron oxide is added to barium carbonate, the reaction progresses more easily and a high causticization rate can be obtained.

(1) Since dry barium carbonate or barium carbonate and iron oxide are fed into the furnace, compared to drying in the furnace,
No decrease in furnace temperature, BaO1 or BaO・Fe2O
3. Firing becomes easier.

[Brief explanation of drawings]

Figure 1 is a flow note showing the conventional alkali pulp manufacturing process, Figure 2 is a schematic diagram showing an apparatus to which the method of the present invention can be applied, and Figure 3 is a flow note showing the conventional alkali pulp manufacturing process.
It is a graph showing the temperature dependence of gKp. Figure 1 Flute Figure 2

Claims (1)

[Claims] (1) When spraying and burning pulp waste liquid in a soda recovery boiler, barium carbonate,
Alternatively, a powder containing mainly barium carbonate and iron oxide in l ~ is supplied and fired into barium oxide or barium ferrate in a recovery boiler furnace, and the barium oxide or barium ferrate fired in the same furnace is converted into barium oxide or barium ferrate. The barium carbonate slurry or barium carbonate slurry and iron oxide slurry produced by the causticizing reaction in the soda dissolving tank are collected as smoke at the rear of the recovery boiler. A method for recovering soda from pulp waste liquid, characterized by supplying dried barium carbonate or barium carbonate and iron oxide powder into a recovery boiler furnace after drying by contacting with road exhaust gas.