JPH0372756B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for recovering smelt whose main component is high-temperature soda carbonate flowing out from the lower part of a black liquor recovery furnace in a kraft pulp manufacturing process.

Conventionally, in the kraft pulp manufacturing process, the washing waste liquid (black liquor) discharged from the cooking, oxidation and evaporation processes is supplied to a recovery furnace, such as a recovery boiler.
Here, the organic matter in the black liquor is burned, and the dissolved salts (sodium sulfate, caustic soda, soda sulfide, etc.) in the black liquor are reduced to become smelt (molten salt). This smelt is discharged from the bottom of the recovery furnace, dissolved in a weak acid (waste from washing during the causticizing process), and becomes a solution (green liquor). Since this green liquor has soda carbonate as its main component, it is causticized using the following formula.

Na ₂ CO _{3 +} Ca(OH _{) 2} → _2Na

Therefore, when the causticizing process and the calcium carbonate decarboxylation process are combined, or when the green liquor is brought to another factory for treatment, it is necessary to transport the green liquor. However, when transporting the green liquor, it is necessary to adjust the concentration of the green liquor to an appropriate concentration for transportation, so a large amount of the liquor must be transported, and there is also the problem of corrosion of tanks and the like.

In order to solve these problems, the solution is separated into solid and liquid by means such as a centrifugal dehydrator, and the solid is supplied to the desired equipment. However, this method has problems in that the solid recovery rate is low and sufficient dehydration treatment (for example, water content of 9.0% or less) is impossible.

The purpose of the present invention is to solve the above-mentioned problems of the prior art, and to recover smelt discharged from a recovery furnace as a powdery solid, so that the smelt can be transferred to the secondary causticizing treatment and decarboxylation treatment processes. It is an object of the present invention to provide a smelt recovery method that can simplify the treatment process, and also recover the thermal energy possessed by the smelt and reuse it for combustion in a black liquor recovery furnace.

The present invention involves crushing and solidifying the smelt flowing out from the lower part of the black liquor recovery furnace in the kraft pulp manufacturing process using high-pressure air, cooling the solidified smelt in a fluidized bed state, recovering it as a powder, and converting it into solidified powder. The high-temperature air obtained by heat exchange with fluidized air that cools the solidified powder can be used as combustion air in the black liquor recovery furnace.

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

In the figure, high-temperature smelt M ₁ (approximately
840°C to 900°C) is flowed into the wind-crushed cooling furnace 3. During this inflow process, high-pressure air at room temperature forced in from the cooling fan 4 is injected into the blast cooling furnace 3 from a plurality of blast nozzles 5. As a result, the high-temperature smelt is atomized by the kinetic energy of high-pressure air at room temperature, and is instantaneously cooled (0.02-0.1 seconds) at 700-800°C to become a solidified powder, which is suspended in airflow.

The air injection speed required for this wind crushing and atomization is 30
~120 m/sec, the coagulated powder particle size can be 10 mm or less. The soda carbonate powder particles that have been crushed and solidified by the wind crushing nozzle 5 float in the cooling furnace, and some of the small-diameter particles _M2 are entrained in the airflow and discharged out of the furnace, but the large-diameter particles _M3 are Crushing cooling furnace 3
The powder falls to the bottom and forms a particle layer of soda carbonate powder. The temperature of this particle layer is lowered to approximately 500 to 700°C by the air injected from the wind crushing nozzle 5, but the cooling air pushed in from the bottom of the wind crushing cooling furnace 3 by the cooling fan 6 causes the particle layer to flow. The heat is exchanged, and the powder is discharged from the discharger 7 at the bottom of the furnace as powder M ₃ at a temperature of 100°C or less. High temperature after fluid heat exchange (250
~350°C) The air is discharged from the cooling furnace together with the air and suspended particles M ₂ injected from the blasting nozzle 5, and after the suspended particles are separated and collected by the separation cyclone 8, it is attracted by the exhaust fan 9, and is then transferred to the recovery boiler 1.
The air is pushed into the furnace and is recovered and used as combustion air, and the floating particles contained in this combustion air that cannot be completely collected by the cyclone 8 are sent to the recovery boiler 1.
Since it is melted and absorbed by the high temperature smelt _M1 inside, it is not released into the atmosphere as dust. In addition, the fine particles M ₂ captured by the separation cyclone 8 are transferred to the discharger 1
0.

The amount of air required for blowing the smelt by the blowing nozzle 5 and for initial cooling of the smelt is 1.5 to 3.0 Nm ³ /
KgNa ₂ CO ₃ is sufficient, and 1.5 to 1.8 Nm ³ /KgNa ₂ CO ₃ is also sufficient if the smelt can reach the optimum particle size (2 mm or less) by the blasting nozzle 5.

According to this embodiment, air having a high temperature level can be recovered by effectively utilizing the sensible heat of the smelt. In addition, the atmosphere is used as cooling air, and after the sensible heat of the smelt is recovered, it is used directly as combustion air, so the concentration of suspended particles can be kept below a certain level without letting dust out of the system. This prevents clogging and allows the equipment to operate continuously for a longer period of time.

As described above, according to the present invention, smelt can be recovered as a powder at room temperature, so secondary handling equipment can be simplified, transportation processing can be facilitated, and corrosion etc. can be prevented. Maintenance is easy because it prevents damage to the smelt, and the thermal energy obtained during the cooling process of the solidified smelt powder can be reused for combustion in the black liquor recovery furnace, improving the thermal efficiency of the equipment. The concentration of suspended particles in the combustion air path can be suppressed without emitting dust outside the system.
The device can be operated continuously for a longer period of time.

[Brief explanation of drawings]

The drawing is a system diagram of smelt recovery equipment for implementing the present invention. 1...Recovery boiler, 3...Flag cooling furnace, 4,6
...Cooling fan, 5...Blow crushing nozzle, 7...Ejector, 8...Separation cyclone.

Claims (1)

[Claims] 1 The smelt flowing out from the lower part of the black liquor recovery furnace in the kraft pulp manufacturing process is blown with high pressure air to solidify and atomize the smelt, and then the resulting solidified powder is cooled with fluidized air and collected, and the solidified powder is High-temperature air obtained by heat exchange between the powder and fluidized air is introduced into a separating means to separate and collect floating particles of smelt generated during solidification of smelt contained in the high-temperature air, and then the black liquor is A method for recovering smelt in a black liquor recovery furnace, characterized in that it is used as combustion air in the recovery furnace.