Treatment of flue gas

Claim 1

A dry method of removing an acid gas from hot flue gas, wherein an absorption agent in the form of a fine powder is introduced and dispersed in a stream of the hot flue gas in a tubular reaction zone (1) having a central vertical axis, whereby the acid gas is absorbed by and reacts with the absorption agent at a temperature within the range 500-900°C to produce a powder comprising reaction products and unreacted absorption agent suspended in the flue gas, whereafter the powder is separated from the flue gas in a separate separating zone (7), characterized by introducing, dispersing and suspending the absorption agent in a rising swirling stream of the hot flue gas at the lower part of the reaction zone, introducing at least a part of the hot flue gas axially at the bottom of the reaction zone as a stream which is subjected to a rapid reduction in axial velocity at the lower part of the reaction zone; and removing the resulting powder from the upper part of the reaction zone suspended in and entrained by the flue gas.

Claim 5

A method according to any one of the preceding claims, characterized in that the rapid reduction in axial velocity is provided by directing the rising axially introduced stream of hot flue gas through a divergent annular frustoconical bottom part (2) of the reaction zone, preferably having an apex angle greater than 12°, e.g. within the range 12-120°, in particular 40-90°.

Claim 6

A method according to any one of the preceding claims, characterized in that the swirling flow of the hot flue gas in the reaction zone is 'provided by bringing the gas into rotation before it is introduced axially into the reaction zone (Figure 2).

Claim 7

A method according to any one of claims 1 to 4, characterized in that the swirling flow of the hot flue gas in the reaction zone is provided by introducing a second stream of the hot flue gas tangentially into the reaction zone (Figure 1).

Claim 8

A method according to claims 6, characterized in that the swirling flow of the hot flue gas in the reaction zone is provided by introducing a second stream (5) of the hot flue gas tangentially at one or several positions at the lower part of the reaction zone (1).

Claim 9

A method according to any one of the preceding claims, characterized in that the absorption agent is a powder with a particle size within the range 20-150 micron, and is selected from the group comprising oxides, hydroxides and carbonates of calcium, magnesium and alkali metals.

Claim 10

A method according to any one of the preceding claims, characterized in that the absorption agent is soft burned lime, preferably at a temperature within the range 500-900°C.

Claim 12

A method according to any one of the preceding claims, characterized in that the gas retention time in the reaction zone (1) is withinl the range 1-5 seconds, preferably 2-3 second, and that the material retention time time in the reaction chamber is within the range 1-8 minutes, preferably 3-5 minutes.

Claim 13

A method according to any one the preceding claims, characterized in that a part of the powder precipitated in the separating zone is recirculated to the reaction zone, and that the external powder recirculation rate is equal to 10-70 times, preferably 15-30 times, the input rate of absorption agent and solid particles present in the hot flue gas.

Claim 15

A method according to any one of the preceding claims, characterized in that the separating zone comprises two subzones, a first subzone for precipitation of coarse particles and a second subzone for precipitation of fine particles, a heat recovery zone preferably being installed between the first and the second subzones.