Patent EA-004611-B1 (EA)
Title: Arrangement and method for reducing build-up a roasting furnace grate
Inventor: NYBERG JENS
IPC: F27D25/00
Filed: 2002-03-08
Abstract: 1. An arrangement to reduce build-up in a roasting of fine-grained material in a fluidized bed furnace, said arrangement comprising a gas distribution unit situated in the lower part of the furnace, connected to a large number of jets, via which gas is fed through the bottom of the grate into the fluidized bed space, into which fine-grained solid material is fed via a feed unit located in a furnace wall and made to fluidize, said furnace wall being equipped with an overflow aperture for calcined material and with a discharge aperture located in the upper part of the furnace, characterized in that the part of the grate beneath the fine-grained material feed point is equipped with extra gas jets, which are connected to a separate gas feed line, wherein the amount of extra gas jets at the feed grate point is at least 5% of the number of normal gas jets in the feed grate area. 2. An arrangement according to claim 1, characterized in that the percentage of the grate beneath the concentrate feed point i. e. the feed grate, is at least 5% of the total cross-sectional area of the grate. 3. An arrangement according to claim 1, characterized in that the percentage of the grate beneath the concentrate feed point i. e. the feed grate, is 10-15% of the total cross-sectional area of the grate. 4. An arrangement according to claim 1, characterized in that the amount of extra gas jets at the feed grate point is10-20% of the number of normal gas jets in the feed grate area. 5. An arrangement according to claim 1, characterized in that the extra gas jets are located above the grate level. 6. An arrangement according to claim 1, characterized in that the extra gas jets are directed horizontally. 7. An arrangement according to claim 1, characterized in that the extra gas jets are preferably multi-branched so that the nozzle at the end of the nozzle tube extending above the grate level opens out essentially horizontally in several directions. 8. A method for reducing build-up in the roasting of a fine-grained material in a fluidized bed furnace, in which the material to be roasted is fed into the fluidized bed space via a feed unit located in a furnace wall and made to fluidize by roasting gas blown through a grate in the bottom of the furnace, and at least some of the calcined material is removed via an overflow aperture at the height of the top of the fluidized bed as the gases and some of the solids exit the upper section of the furnace, characterized in that the section of the grate below the feed point of the fine-grained material is equipped with additional gas jets, which are connected to a separate gas feed line, and that roasting gas is fed into the furnace via the additional gas jets with an oxygen content which is at least equal to the oxygen content of the roasting gas in the rest of the grate. 9. A method according to claim 8, characterized in that roasting gas is fed into the furnace via the additional gas jets with an oxygen content which is higher than the oxygen content of the roasting gas in the rest of the grate.