JPS5950020A - Apparatus for recovering soda from pulp spent liquor - Google Patents

Abstract

PURPOSE:To save fuel for calcining CaCO3 and to facilitate the calcination by blowing air into a pipe connecting an Na2CO3 recovering boiler to a calciner for calcining CaCO3 with combustion gas sucked from the lower part of the boiler. CONSTITUTION:Waste liquor from an alkali pulping stage is burned in an Na2CO3 recovering boiler 10, and the resulting smelt is allowed to flow in an Na2CO3 dissolving vessel 16 contg. water from the bottom of the boiler 10. CaO is introduced into the vessel 16 from a CaCO3 calciner 23, and a reaction is caused to prepare NaOH as digesting chemicals. The NaOH is introduced into a white liquor tank 19 and fed to a system for circulating pulp digesting chemicals through a pipe 20. A CaCO3 slurry formed in the vessel 16 is predehydrated, fed to the calciner 23, and calcined. Hot combustion gas is sucked into the calciner 23 from the combustion zone of the boiler 10 with a device 27 and utilized to calcine the CaCO3 slurry, and it is fed to a flue 12. When the gas is sucked, preheated air is fed from an air feeding inlet 31 attached to a pipe 22 connecting the boiler 10 to the calciner 23. Combustible gas sucked into the calciner 23 is burned, so the calcination of the CaCO3 is facilitated.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in pulp waste soda recovery equipment, and in particular to measures to streamline the causticization process of 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), 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 causticizing tank 6, and then the pulp is fed to the blow tank 2, evaporator V-ta 3, recovery boiler 4, smelt dissolving tank 5, causticizing tank 6, and white liquor tank 8 in that order. The cooking chemicals circulate through the circulation system PL. The calcium carbonate produced in the causticizing tank 6 is transferred to the rotary 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 recovered 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 carbonated soda is then sent to causticizing tank 6.
It is brought into contact with the supplied Ca(OH)2 (or CaO and H2O) and causticized into caustic soda, which is a cooking chemical, as shown in the following formula.

NaICO3+ Ca(OH)2→2 Na0T(+
On the other hand, CaCO5 generated in the causticizing tank 6 is
It is calcined in a rotary kiln 7 to form CaO, and slaked with water to generate Ca(OH), 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 object of the present invention is to provide a valve waste liquid soda recovery device that can save energy in firing the CaC01 slurry produced in the causticizing tank 6 and streamline the causticizing process of recovered chemicals. Ca is discharged from the soda dissolving tank at the bottom of the recovery boiler or a separate causticizing device using high-temperature gas sucked from the bottom of the furnace.
One of the features is that the calcium carbonate calciner is installed near the bottom of the soda recovery boiler to dry and burn CO3, and the high-temperature gas generated by the soda recovery boiler is used as a heat source for the calcium carbonate calciner. Therefore, the second feature is that air is injected into the connecting pipe between the soda recovery boiler and the calcium carbonate calcining equipment, which can be considered as a fuel saving compared to the conventional rotary kiln installed separately. Combustible gas generated in the bottom combustion section of the recovery boiler is subjected to secondary combustion in a calcium carbonate calciner, and the temperature of the calciner is raised to facilitate firing and reduce the amount of suction gas. A large amount of cooling air is sucked in at the outlet of the calcium carbonate calcining device to control corrosion and dust adhesion of the suction fan.

The present invention provides a soda recovery boiler that sprays and burns valve waste liquid, in which an opening is provided in the valve waste liquid combustion section of the recovery boiler, and a connecting pipe connected to the opening is provided, and downstream of the connecting pipe, a soda dissolving tank is provided at the bottom of the recovery boiler. Or, it has a soda carbonate calcining device with a calcium carbonate supply port connected to a separate causticizing tank, a high-temperature gas suction device, and a connecting pipe connecting the high-temperature gas suction device and the recovery boiler flue. The present invention relates to a valve waste liquid soda recovery device characterized in that an air inlet is provided in a connecting pipe of a soda carbonate baking device.

The present invention is effective when applied to valve cooking chemical recovery boilers of pulp and paper mills, which are energy-intensive industries.

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

In the figure, 10 is the recovery boiler main body. 11 is a boiler bank part connected to the flue, 12 is a boiler flue, 13 is a valve waste liquid burner, 14 and 15 are primary and secondary air supply ports, respectively, and 16 is arranged at the bottom of the recovery boiler 10. 17 is a water supply port arranged to open at the top of the soda dissolving tank 16, 18 is a white liquid take-out pipe arranged to open to the soda dissolving tank 16, and 19 is the same white liquid dissolving tank. a white liquid tank to which a liquid take-out pipe 18 is connected;
20 is a white liquor supply pipe connected to the same white liquor tank 19; 21
is a calcium carbonate slurry take-out pipe connected to the bottom of the soda dissolving tank 16.

22 is a high-temperature combustion gas take-off pipe provided in the combustion section of the soda recovery boiler, 23 is a calcium carbonate firing device connected to the combustion gas take-off pipe 22, and 27 is a gas drive that provides a force for sucking high-temperature combustion gas from the combustion section of the soda recovery boiler. A device such as an induced draft fan or an ejector, 24 a high temperature flue connecting the calcium carbonate calcining device 23 and the gas drive device 27, and 28 a connecting pipe connecting the gas drive device 27 and the boiler flue 12. child\
25 is an air intake pipe for cooling and dilution installed when the gas drive device 27 is an induced draft fan, and 26 is an air intake pipe 250.
This is a temperature adjustment mechanism that adjusts the inlet temperature of the gas drive device 27 by adjusting the opening degree. 29 is pre-dehydrated calcium carbonate slurry discharged from the soda dissolving tank 16 or calcium carbonate slurry discharged from the causticizing device,
This is a supply port for supplying calcium carbonate to the calcining device 23. 30 is a connecting pipe for dropping calcium oxide calcined in the calcium carbonate calcining device 23 into the soda dissolving tank 16. 31 is an air supply port provided in the combustion gas extraction pipe 22.

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 valve waste liquid is sprayed in the form of fine particles from the burner 13, and primary and secondary air supply pipes 1 are connected to the bottom of the furnace.
The heated air supplied from 4.15 causes high temperature combustion to produce smelt (mainly Na2CO3). This smelt is allowed to flow down from the bottom of the furnace to the soda dissolving tank 16 at the bottom of the recovery boiler.

In the soda dissolving tank 16, smelt (NaCOs) is dissolved in the water previously supplied from the water supply pipe 17, and calcium oxide (NaCOs) from the calcium carbonate calcining device 23 is dissolved.
CaO) and the following reaction occurs.

Na1CO1+ CaO+ H2O→2NaOH+Ca
The cooking chemical NaOH is made with CO3.

The NaOH generated in the soda dissolving tank 16 is removed from the white liquor outlet 18.
The white liquor is led from there to the white liquor tank 19, and then sent from the white liquor supply pipe 20 to the valve cooking chemical circulation system PL as shown in FIG.

On the other hand, CaCO3 generated in the soda dissolving tank 16 is taken out from the calcium carbonate slurry outlet 21, subjected to preliminary dehydration, and then supplied to the calcium carbonate supply port 29 of the calcium carbonate calcining device 23. Firing in the firing device 23 (CaCO3→C
The aO+CO2) CaO is dropped from the connecting pipe 30 into the soda dissolving tank 16 at the bottom.

The preheated air input from the air supply port 31 is transferred from the combustion section of the soda recovery boiler 10 to the calcium carbonate firing device 23.
The combustible gas sucked into the combustible gas is combusted, and the radiation of the combustion flame and the high-temperature gas facilitate the calcination of calcium carbonate in the calcium carbonate calcination device 23.

Combustion gas sucked from the recovery boiler combustion section through the high-temperature combustion gas take-off pipe 22 burns calcium carbonate into calcium oxide in the calcium carbonate burner 1i23, passes through the high-temperature flue 24, and is then sucked into the cold air intake pipe 25. After being diluted and cooled with air, it is sent to the recovery boiler flue 12 through a connecting pipe 28 by a gas drive device 27. The temperature adjustment mechanism 26 detects the gas temperature in the gas drive device 27 and adjusts the damper opening degree of the air intensifier tube 25 to adjust the gas temperature in the gas drive device 27. The gas temperature must be maintained at a suitable temperature to avoid corrosion of the gas drive material and adhesion of dust in the gas.

The present invention provides the following effects.

■ The device of the present invention sucks high-temperature gas from the pulp waste combustion section of the soda recovery boiler and supplies it to the calcium carbonate baking device installed downstream to burn calcium carbonate. It is possible to reduce the amount of fuel oil used for auxiliary combustion for calcium carbonate calcination.

(a) Since the high-temperature combustion gas discharged from the calcium carbonate calcining equipment is diluted and cooled with air, the induced draft fan that sucks the high-temperature combustion gas in the soda recovery boiler furnace can be used to prevent material corrosion and soda ash dissolution. High-temperature gas can be sucked while avoiding stains and adhesion.

(b) Since the calcium carbonate calciner sucks flammable gas from the combustion section of the soda recovery boiler and injects preheated air from the air supply port 31, the temperature inside the furnace near the inlet of the calcium carbonate calciner increases, causing It made firing easier.

[Brief explanation of the drawing]

FIG. 1 is a flow sheet showing a conventional alkali pulp manufacturing process, and FIG. 2 is a schematic diagram showing the method and apparatus of the present invention. Sub-agents 1) Meifuku agent Ryo Hagiwara - Figure 2

Claims (1)

[Claims] In a soda recovery boiler that sprays and burns pulp waste liquid, an opening and a connecting pipe connected to the opening are provided in the pulp waste liquid combustion section of the recovery boiler, and a soda dissolving tank at the bottom of the recovery boiler or a separate pipe is installed downstream of the connecting pipe. It has a sodium carbonate calcining device with a calcium carbonate supply port connected to the causticizing tank, a high-temperature gas suction device, and a connecting pipe connecting the high-temperature gas suction device and the recovery boiler flue. A pulp waste liquid soda recovery device characterized by having an air inlet in the connecting pipe.