FI77278B - FOERFARANDE OCH ANORDNING FOER FOERBRAENNING AV SODASVARTLUT. - Google Patents

Description

1 77278

Method and apparatus for burning soda ash liquor -Förfarande och anordning för förbränning av sodasvartlut

The invention relates to a method and an apparatus for burning soda liquor and to an apparatus for applying the method. In particular, the invention relates to a process for burning sulfur-free soda-black liquor in a fluidized bed reactor in the presence of iron oxide, to bind sodium in .

It is known from Finnish patent application 791287 that sulfur-free soda-black liquor can be burned in a bubbling fluidized-bed reactor using an iron oxide bed above the melting point of sodium carbonate. Incineration leads to the formation of sodium ferrite. The sodium hydroxide used in the cooking process is regenerated by immersing the sodium ferrite in hot water. The iron oxide precipitate formed is separated and recycled to the fluidized bed.

The disadvantages of bubbling fluidized bed combustion are e.g. the following factors: - The grain size of the iron oxide / sodium ferrite must be such that it does not travel out of the reactor with the gas stream (> 1 mm).

- Because recycled iron oxide is heterogeneous in grain size (1 mm to <10 μm), some of the iron oxide immediately follows the gas flow (<200 μm) without reacting completely.

2 77278 - When using a coarse feed, the diffusion of alkali into the iron oxide particles is so slow that it has to be used extensively, so that only the surface layer reacts. In this case, the required Fe / Na molar ratio is> 2.0.

- When black liquor is injected into the bed, it cools as a result of the evaporation of water and a temperature profile is created in which the bed is colder than the free-board sector.

It has been found in the combustion tests that the alkali content of the product ash depends on the particle size according to Figure 1, with the fine material containing substantially more alkali than the coarse material.

The object of the invention is to provide a method and a device by means of which the amount of iron oxide required can be reduced.

The process according to the invention is characterized in that the gas stream is passed to a particle separator, where a particle fraction with a particle size of mainly less than 50 μm with a higher sodium content is discharged from the reactor with a gas stream, and only .

For example, by separating the grain size class from 200 to 100 μ m from the flue gas and returning it to the reactor, its reaction time can be extended so that the amount of iron oxide required for combustion can be reduced to Fe / Na - 1.5.

However, the separator must be designed to pass a fine fraction of less than 50 μm for which a short reaction time is sufficient to saturate with alkali. If the Fe / Na molar ratio of 3 77278 approaches 1.0, the ash becomes sticky and causes deposition problems in the heat separator.

The device specifically intended for the application of the method is characterized in that upwardly directed nozzles are arranged at or below the lower end of the cone of the cyclone separator.

The invention will now be described in more detail with reference to the accompanying drawings, in which Figure 1 shows the alkalinity of product ash as a function of particle size, Figure 2 schematically shows an apparatus for applying the method according to the invention and Figure 3 a vertical sectional view of a cyclone separator.

The circulating mass reactor 1 shown in Fig. 2 is fed with black liquor and via lines 2 and 3. In addition, the oxygen-containing gas required for combustion and fluidization, such as air, is fed to it. The gas flow rate in the reactor is kept so high that the smaller particles follow the gas flow and travel with the gas flow out of the reactor.

The reactor is equipped with a separator 4, which is designed to pass through a fine fraction of less than 50. The coarser solid, most preferably in the particle size range of 200 to 100, is separated from the gas and returned to the reactor up to line 5 so that iron oxide particles which have not yet been saturated with alkali are re-exposed to black liquor and can react with sodium compounds in the liquor. The sodium ferrite generated in the combustion is removed from the bottom of the reactor via line 6 and the sodium hydroxide is regenerated by immersing the sodium ferrite compound in hot water.

4 77278

Fig. 3 shows a cyclone separator (7) suitable for the method according to the invention, to which the gases leaving the reactor 1 of Fig. 2 are led to the upper part 8 thereof via an inlet line 9 connected tangentially. The separated solid is removed through an outlet pipe 11 connected to the bottom of the conical lower part 10 of the separator. The gas is discharged through an outlet pipe 12 centrally arranged at the top. Below the bottom of the cone, upwardly directed nozzles 13 are arranged, which are connected to an annular supply chamber to which an air supply line (not shown) is connected. By blowing air in upward jets at the lower end of the cone, small particles can be separated from the solid therein, which passes out of the separator with the gas stream leaving through the pipe 12. By changing the amount of air fed to the separator, it is possible to influence the size and number of particles following the gas flow and thus adjust the resolution of the separator.

The invention is not limited to the exemplary embodiment, but various modifications and applications are defined by the claims. within the scope of the inventive idea are possible.

Il

Claims (5)

A process for combusting sulfur-free black liquor from soda pulp cooker in fluidized bed in a circulating bed reactor in the presence of iron oxide, for transferring sodium to sodium ferrite, wherein to the reactor with circulating bed, black liquor from soda pulp boiler and iron oxide, as well as iron oxide and iron oxide, are measured. gas, and the gas flow rate in the reactor is poured so that the smaller particles are transported with the gas stream out of the reactor, characterized in that the gas stream is led to a particle separator, at which a particle fraction in which the size of the particles is less than 50 µm and which contains a higher amount of sodium, is discharged with the gas stream from the reactor, and only a particle fraction in which the size of the particles exceeds 50 µm and which contains iron oxide particles which have not reacted with the sodium compounds is returned to the fluidized bed. Process according to claim 1, characterized in that the solid particles separated from the flue gases have a particle size of 200-100 µm. Process according to Claim 1 or 2, characterized in that the solid particles are separated by a cyclone separator. 4. A method according to claim 3, characterized in that the separating capacity of the cyclone separator is controlled with a tapered gas stream supplied to the conical bottom of the separator. Apparatus for carrying out a process according to any of the preceding claims, comprising a cyclone separator reactor with a circulating bed, known in the art.