JPS59146933A - Method for recovering soda from waste liquor from pulp manufacturing stage - Google Patents

Abstract

PURPOSE:To recover sodium and magnesium components by feeding MgCO3-base powder to the waste liquor burning section of a recovery boiler, forming MgO by calcination, and introducing most of the MgO and smelted matter into a soda dissolving vessel under the boiler. 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. MgCO3- base powder is fed to the waste liquor burning section from feeding pipes 15, and MgO is formed by calcination. Most of the MgO is introduced into a soda dissolving vessel 16 under the boiler 10 together with the smelted matter flowing downward along the wall of the boiler. They are dissolved in water from a feeding pipe 17 and reacted to recover sodium and magnesium components.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a valve waste soda recovery method, and in particular to a measure for rationalizing the causticization process of recovered chemicals.

A conventional method for producing alkali pulp will be explained using the schematic explanatory diagram of FIG. 1 showing the process for producing an alkali pulp.

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

Pulp cooking chemicals are supplied to the digester 1 or the causticizing tank 6, and the valve cooking chemicals are supplied to the digester 1 or the causticizing tank 6 in the following order: the blow tank 2, the evaporator 3, the recovery boiler 4, the smelt dissolving tank 5, the causticizing tank 6, and the white liquor tank 8. Circulate through the circulation system PL. The calcium carbonate produced in the causticizing tank 6 is transferred to the lorry kiln 7.
It is calcined to form calcium oxide 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 collected by the electrostatic precipitator 9 and returned to the black liquor line.
is 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 tank 5 to produce a sodium carbonate aqueous solution. This sodium carbonate is made of Ca(OH), which is supplied in the causticizing tank 6.
2 (or CaO and H2C) to be causticized into caustic soda, which is a cooking chemical, as shown in the following formula.

Na2 co3+Ca (OH)2 →2 NaO[(
On the other hand, the CaCO3 generated in the causticizing tank 6 is calcined in a rotary kiln 7 to form CaO, and is slaked with water to generate Ca(OH)2, which is recycled to the 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 present invention aims to provide a pulp waste liquid soda recovery method that can save energy in firing the aCO3 slurry produced in the causticizing tank 6 and streamline the causticizing process of recovered chemicals. For the same purpose, the present inventors first introduced Ca into the pulp waste liquid combustion section of the recovery boiler.
Powder mainly containing CO3 is supplied and CaO is calcined in the recovery boiler furnace, and the Ca0O dog portion calcined in the furnace is guided to the soda melting tank at the bottom of the recovery boiler along with the smelt flowing down the furnace wall to dissolve soda and calcium. As a result, the CaC03 powder in the causticizing equipment that was conventionally used can be fed into the combustion section of the recovery boiler unburned, so the CaCO3 burning means, such as a rotary kiln, can be eliminated and fuel costs can be saved. However, the present invention uses a powder containing magnesium carbonate as a base instead of a powder containing raw calcium carbonate in the above method, thereby increasing the firing rate. It is characterized by an increased causticization rate.

The present invention, when spraying and burning pulp waste liquid in a soda recovery boiler, feeds a powder containing raw magnesium carbonate to the pulp waste liquid combustion section of the recovery boiler and burns magnesium oxide in the recovery boiler furnace. The main feature of this system is that most of the magnesium oxide fired in the boiler is guided along with the smelt flowing down the furnace wall to the soda molten wood at the bottom of the recovery boiler, where soda and magnesium are recovered.

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

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

In the figure, 1o is the main body of the recovery boiler, 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 magnesium carbonate. 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; 17 is a soda dissolving tank disposed at the top of the M tub 16;
Reference numeral 18 indicates a white liquor take-out pipe arranged to open into the soda dissolving tank 16, 19 indicates a white liquor tank to which the white liquor take-out pipe 18 is connected, and 2o indicates a white liquor supply connected to the white liquor tank 19. Pipe 21Fi is a magnesium carbonate slurry take-out pipe connected to the bottom of the above-mentioned melting shell 16.

In such a 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 burned into the burner 1.
The primary and secondary components are sprayed in fine particles from 2 and supplied to the bottom of the furnace.
The heated air supplied from the secondary air supply pipes 13 and 14 is combusted at high temperature to produce smelt (raw Na2 CO3). 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, powder containing mainly magnesium carbonate is injected into the furnace from the supply port 15 at the bottom of the furnace.

M fired in a furnace (M, co3 → M, O + CO2),
Most of the O is carried on the smelt flowing down the furnace wall and is caused to flow down to the soda dissolving tank 16 at the bottom. In the soda dissolving tank 16, smelt (Na2CO3, M, O) is dissolved in water previously supplied from the water supply pipe 17, and the following reaction occurs.

Naz co3+ M, O+ H2C→2 Na, Ol
(+ MyCO3 In this way, the cooking chemical NaO
Make H.

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 valve cooking chemical circulation system PL as shown in FIG.
sent to.

Furthermore, the present invention provides the following effects on the MP CO3 produced in the soda dissolving tank 16 and the magnesium carbonate slurry taken out from the outlet 21.

(7) In the method of the present invention, in a soda recovery boiler that sprays and burns valve waste liquid, powder containing mainly magnesium carbonate is supplied to the valve waste liquid combustion section of the recovery boiler, and magnesium oxide is fired in the recovery boiler furnace. ,
Since causticization is achieved 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 conventional methods, and this has the advantage of significantly reducing fuel costs.

(b) Figure 3 shows 1. Barin, O, Knack
e”Thermo-chemical prop
ertj-es of inorganic 5ubs
1o at each temperature of the method of the present invention and the comparative reaction calculated using the thermodynamic data of Tance' (1975).
This is a plot of gKp (logarithm of the equilibrium constant of the reaction), and indicates that the larger pIOgKI) is, the easier the reaction is to proceed. In the figure, curve A is M, co3
→MSl=O+ CO2, curve B is CaCO3→Ca
The temperature change of 1 ogKp was determined for each O+CO2 reaction.

Curve A, which is the method of the present invention, has 1 ogKp higher than Ca predetermined (curve B), which indicates that it is superior to the others in terms of reactivity. In other words,
This means that in curve A, M0 is easier to generate than CaO, and a higher causticization rate can be obtained.

(1) Since there are few technical problems, it can be implemented in a reasonable process.

) The furnace structure of the recovery boiler is almost the same as that of the alkaline valve waste liquid recovery boiler, and has the advantage that the technological development elements are limited to a part of the bottom of the furnace.

[Brief explanation of the drawing]

FIG. 1 is a flow sheet 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. 3 is a graph showing the temperature dependence of 10 gKp for the method of the present invention and comparative reactions. Sub-agents 1) Meifuku agent Ryo Hagiwara - 2

Claims (1)

[Claims] (1) When spraying and burning valve waste liquid in a soda recovery boiler, powder containing raw magnesium carbonate is supplied to the pulp waste liquid combustion section of the recovery boiler, and magnesium oxide is burned in the recovery boiler furnace. A valve waste liquid soda recovery method characterized in that most of the magnesium oxide calcined by the smelt flowing down the furnace wall is guided to a soda dissolving tank at the bottom of a recovery boiler to recover soda and magnesium components.