JPS59146930A - Method for recovering soda from waste liquor from pulp manufacturing stage - Google Patents

Abstract

PURPOSE:To reduce the cost of fuel by feeding powder consisting of CaCO3 and iron oxide to the waste liquor burning section of a recovery boiler, forming calcium ferrate by calcination, introducing it into a soda dissolving vessel to recover soda, CaCO3 and iron oxide, bringing the CaCO3 and iron oxide into contact with flue gas, and reutilizing dried compounds. CONSTITUTION:Waste liquor from a pulp manufacturing stage is blown into a recovery boiler 10 as a mist from burners 12, heated air is fed from air feeding pipes 13, 14, and the waste liquor is burned to produce smelted matter. At the same time, powder contg. CaCO3 and iron oxide as principal components is fed to the waste liquor burning section of the boiler 10 from feeding inlets 15, and calcium ferrate is formed by calcination. The smelted matter and the calcium ferrate are introduced into a soda dissolving vessel 16 under the boiler to recover sodium, calcium and iron components, and a slurry contg. CaCO3 and iron oxide formed by caustification in the vessel 16 is introduced into a drying means 24 placed in a flue through a transferring pipe 25. The slurry is dried, and the resulting powder is fed to the feeding inlets 15 through a transferring pipe 26 and reutilized.

Description

[Detailed description of the invention] The present invention is an improvement of a pulp waste soda recovery method.

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 Figure 1, 1 is a valve digester, 2 is a blow tank for pulp material, P is pulp, 3 is an evaporator for concentrating waste liquid, 4 is a chemical recovery boiler (hereinafter referred to as recovery boiler 2), and 5 is a smelt. 6 is a causticizing tank, 7 is a rotary kiln, 8 is a white liquor tank, and 9 is a steam collector.

Chemicals for pulp cooking are supplied to the digester 1 or the causticizing tank 6, which includes a blow tank 2, an evaporator 3, a recovery boiler 41, a smelt bath tank 5, a causticizing tank 6, and a white liquor tank 8.
In this order, the pulp cooking chemical circulation system RP L is evacuated. The calcium carbonate produced in the causticizing tank 6 is transferred to the lorry kiln 7.
It is calcined to produce ipicalcium acid and 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 recovered by the electrostatic precipitator 9, returned to the black liquor line, sent to the recovery boiler 4, 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 tank 5 to form an aqueous solution of sodium carbonate.This soda is then brought into contact with the supplied cacoH)2 (or CaO and H2O) in a causticizing tank 6. Then, it is causticized with caustic soda, which is a cooking chemical, as shown in the following formula.

Na2CO3+0a(OH)2-+ 2NaOH+0a
On the other hand, O a 003 generated in the causticizing tank 6 is
It is calcined in a rotary kiln 7 to form OaO, slaked with water to generate Ca (OH)2, and recycled to the causticizing tank 6.

The disadvantage of the above conventional method is that Oa O0 generated in the causticizing tank 6
3. 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 firing the C a CO3 slurry produced in the causticizing tank 6 and streamline the causticizing process of recovered chemicals. For this purpose, the inventors first installed (ag) in the pulp waste liquid combustion section of the recovery boiler.
GaO is obtained in the recovery boiler furnace by supplying powder mainly containing o3, 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 fed into the recovery boiler furnace.
When drying CO3 slurry and eliminating the need for a rotary kiln for firing, a method has been proposed in which drying of CaC;Os slurry can be effectively carried out using boiler exhaust heat (
% Application No. 57-149232), the present invention is a further improvement on this, and instead of the powder mainly containing CaG Os in the above method, a powder mainly containing calcium carbonate and iron oxide is used in the pulp waste liquid combustion section of the recovery boiler. It is characterized in that the firing and causticizing rates are increased by supplying it.

In the present invention, when pulp waste liquid is spray-combusted in a soda recovery boiler, powder mainly containing calcium carbonate and iron oxide is supplied to the pulp waste liquid combustion section of the recovery boiler, and the powder is calcined into calcium ferrate in the recovery boiler furnace. Calcium ferrate calcined in the same furnace is led to a soda dissolution tank located at the bottom of the recovery boiler that recovers iron, calcium, and calcium, and calcium carbonate and iron oxide produced by the causticization reaction in the soda dissolution tank. The method is characterized in that the slurry is brought into contact with the flue gas at the rear of the recovery boiler to supply the dried calcium carbonate and iron oxide powder into the recovery boiler furnace.

The method of the present invention is effective when applied to the pulp cooking chemical recovery boiler of paper bargueyang, 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 the shape of a funnel so that the smelt 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 powder mainly containing calcium carbonate and iron oxide. For example, limestone is an example of calcium carbonate, and FeO is an example of iron oxide.

Fe2O3 and Fe3O4 are used. Calcium carbonate and iron oxide can be used on your own ship for most of the time against 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 1o;
7 is a water supply port arranged to open at the upper part of the soda dissolving tank 16, 18 is a white liquor take-out pipe that opens into the above-mentioned soda dissolving tank 16, and 19 is a white liquor take-out pipe 18. is the white liquor tank that was read directly, 2o is the same white liquor tank 1
9 is connected to the white liquor supply pipe, 21 is the above soda solution 'ps
This is a calcium carbonate slurry and iron oxide slurry take-out pipe connected to the bottom of the tank 16. 22 is a dust collection device installed in the flue at the rear of the boiler bank, and a Multichron or high-temperature electric industrial dust machine can be used. 23 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; 24 is a drying means for calcium carbonate and iron oxide slurry disposed in the rear flue; It is designed to dry by contact with exhaust gas. In this case, the slurry containing calcium carbonate and iron oxide may optionally be pre-dehydrated, and then the dehydrated cake may be dried. Reference numeral 24A denotes slurry supply means disposed above the drying means 24 for calcium carbonate and iron oxide, and for example, a spray nozzle, a belt conveyor, etc. can be used. 25 is a slurry transfer pipe connected on one side to the calcium carbonate and iron oxide slurry take-out pipe 21 and the other side is connected to the slurry supply means 24A, and 26 is a lower part of the calcium carbonate and iron oxide slurry drying means 24. It is a transfer pipe for dried calcium carbonate and iron oxide powder, connected on one side and connected on the other side to a supply port 15 for powder mainly containing calcium carbonate and iron oxide.

In this configuration, the operation of the present invention will be explained. At the bottom of the furnace, which is the pulp waste liquid combustion section of the recovery boiler 10, highly concentrated alkaline pulp waste liquid is stored in the burner 12.
The heated air supplied from the primary and secondary air supply pipes 13 and 14 is sprayed in the form of fine particles and supplied to the bottom of the furnace, and is combusted at high temperature to produce smelt (mainly Na2Go3).

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.

Further, powder containing mainly calcium carbonate and iron oxide, such as limestone Ca G Os powder and ferric oxide powder, is sprayed into the furnace from the supply port 15 at the bottom of the furnace. Calcined in a furnace (CaCO3+Fe2O3→CtL○・Fe2O3+0
Most of the CaO.Fe2O3 produced in 02) is carried by the smell) K 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 (Na2Go3.
aao-Fe2o5) is dissolved and the following reaction occurs.

NaCo+CaO・FaO−+ 2NaOH+C
aCO3+Fe2032 3 23 In this way, NaOH, which is a cooking chemical, is made.

On the other hand, NaOH generated in the soda dissolving tank 16 is led from a white liquor outlet 18 to a white liquor tank 19, and from a white liquor supply pipe 20 to a pulp cooking chemical circulation system PL as shown in FIG.
sent to.

In addition, C a CiO3 and Fe2O3 generated in the soda dissolving tank 16 are transferred to the calcium carbonate and iron oxide slurry outlet 2.
1, this slurry is sent to the drying means 24 in the rear flue as described above, and the dried material is fed to the recovery boiler at the feed port 1.
Supply from 5.

In the present invention, the following effects are achieved.

(To) The method of the present invention is to supply powder mainly containing calcium carbonate and iron oxide to the pulp waste liquid combustion section of the recovery boiler at a soda recovery point where pulp waste liquid is spray-combusted, and to convert calcium ferrate in the recovery boiler furnace. Since the method is calcined and causticized by applying high temperature in the furnace, there is no need for heating in a rotary kiln, which requires a large amount of fuel compared to the conventional method (therefore, there is an advantage that the fuel cost can be greatly reduced). be.

(b) Since the rotary kiln will be abolished, it will be necessary to dry the calcium carbonate and iron oxide slurry, but after preliminary dehydration of the calcium carbonate and iron oxide slurry produced in the soda dissolving tank, the slurry will be dried by bringing it into direct contact with the flue gas. for drying.

The heat required for drying can be obtained from the exhaust gas, improving thermal efficiency.

ri) Figure 3 shows r, Barin, O, Knacke.
'Thermo-chemical prope
rties of inorganic 5ubsta
log'K at each temperature of the method of the present invention and the comparative reaction calculated using the thermodynamic data of
This is a plot of p (logarithm of the horizontal constant of the reaction), and indicates that the larger the value (logK]), the easier the reaction is to proceed. In the figure, curve A is Caaos +Fe2e
3→CaO-Fe2O3+co21 curve B is CaC0→
CaO+Go2 curve C curve NaCo+Fe2O3→Na
20-Fe2O3+002 and 3 The curve shows the temperature change in logKp for the reaction of Na2CO3→Na2O+CO2.

Curve A, which is the method of the present invention, shows that logiCI) is at a higher position than the Ca method (curve B) and the Fe method (curve C), indicating that it is superior to the others in terms of reactivity. There is. In other words, this means that in curve A,
CaO' Fe3205 is a product of other reactions, e.g.
This shows that CaO, Na20-Fe2O3 is produced in a larger amount than other methods (Ca method, Fe method), which means that a higher causticization rate can be obtained in the soda solution M bath than other methods (Ca method, Fe method). Demonstrate that the method is useful.

2) Since dried calcium carbonate and iron oxide are supplied into the furnace, the temperature inside the furnace does not decrease compared to the case where they are dried in the furnace (the calcination of CaO-Fe2O3 becomes easier).

[Brief explanation of drawings]

FIG. 1 is a flow silt showing a conventional alkali valve manufacturing process, and FIG. 2 is a schematic diagram showing an apparatus to which the method of the present invention can be applied. FIG. 6 is a graph showing the temperature dependence of log and Kp of the method of the present invention and comparative reactions. Sub-agents 1) Meikoku Agent Ryo Hagiwara - Figure 1, 2nd flash

Claims (1)

[Claims] (1) When the pulp waste liquid is spray-combusted in the soda recovery boiler, a powder mainly containing calcium carbonate and iron oxide is supplied to the pulp waste liquid combustion section of the recovery boiler, and the powder is calcined into calcium ferrate in the recovery boiler furnace. The calcium ferrate calcined in the same furnace is led to the soda dissolution tank at the bottom of the recovery boiler to recover soda, calcium and iron, and the calcium carbonate slurry and iron oxide slurry produced by the causticization reaction in the same soda dissolution tank. A pulp waste liquid soda recovery method characterized in that the pulp waste soda is dried by being brought into contact with the rear flue gas of a recovery boiler, and then the dried calcium carbonate and iron oxide powders are supplied into a recovery boiler furnace.