Method of operating a pelletizing plant

Abstract

A method of operating a pelletizing plant for additional treatment of iron making, steelmaking and pellet plant residues, the plant including an indurating furnace in which green pellets are charged and fired to produce hard pellets, where the method includes: preparing iron ore green pellets; and charging and firing said green pellets in an indurating furnace, such that agglomerates of by-products are charged and fired with the green pellets in the indurating furnace, thereby producing hardened pellets and hardened agglomerates of by-products; a pelletizing plant is also presented including a pelletizing section, an indurating furnace, an agglomerating section for producing agglomerates of by-products, where a feeding arrangement is configured to charge agglomerates of by-products into said indurating furnace, together with the green pellets.

1 . A method of operating a pelletizing plant for iron making furnaces, said pelletizing plant comprising an indurating furnace in which green pellets are charged and fired to produce hard pellets, said method comprising:
 preparing iron ore green pellets using a balling drum and/or a disc pelletizer;   charging and firing said green pellets in an indurating furnace;   wherein agglomerates of by-products are prepared by compacting to form lumpy products; and wherein said lumpy agglomerates of by-products are charged and fired with said green pellets in said indurating furnace, thereby producing hardened pellets and hardened agglomerates of by-products.   
     
     
         2 . The method according to  claim 1 , wherein said agglomerates of by-products and said green pellets are loaded on a charge conveyor of said indurating furnace in two superposed layers, the upper layer mainly comprising the agglomerates of by-products and the lower layer mainly comprising said green pellets. 
     
     
         3 . The method according to  claim 2 , wherein charging of said charge conveyor is carried out by means of a segregating unit receiving said green pellets and agglomerates of by-products and distributing the latter into said upper and lower layers. 
     
     
         4 . The method according to  claim 1 , wherein the heat treatment in said indurating furnace is carried out in an oxidizing atmosphere, whereby the obtained hardened pellets and hardened, lumpy agglomerates of by-products have a metallization below 50%. 
     
     
         5 . The method according to  claim 1 , wherein said method comprises a step of preparing agglomerates of by-products, which includes processing by-products, in particular coarse-grained, with additives and optionally fines or other iron bearing material, in a compacting apparatus to form said lumpy agglomerates of by-products. 
     
     
         6 . The method according to  claim 5 , wherein said agglomerates of by-products are prepared from a mixture comprising:
 by-products including iron and/or steelmaking waste materials; and   fines collected from said segregating unit.   
     
     
         7 . The method according to  claim 6 , wherein said by-products are reverts from iron making plants selected from the list comprising: steelmaking slag, mill scale, scrap fines, oxide fines, dust and sludges collected in offgas lines, fines fractions from screening units, sludges iron- or flux-bearing blast furnace by-products, and their combinations. 
     
     
         8 . The method according to  claim 7 , wherein said reverts, during the compacting stage, have a particle size in the range of 0.045 to 5 mm. 
     
     
         9 . The method according to  claim 1 , wherein said agglomerates of by-products contain less than 50 wt. % iron ore. 
     
     
         10 . The method according to  claim 1 , wherein said agglomerates of by-products are formed as lumps or briquettes with a size above 16 mm. 
     
     
         11 . The method according to  claim 1 , wherein said step of preparing green pellets comprises preparing a mixture of raw materials including: fine grained iron ore and possible additives, in particular a binder, and processing said mixture to form substantially ball-shaped pellets. 
     
     
         12 . The method according to  claim 11 , wherein said possible additives include fine by-products with 70 wt. % of the particles having a minus 352 mesh. 
     
     
         13 . The method according to  claim 1 , wherein said pellets consist of more than 61 wt. % fine grained iron bearing particles, in particular particles of iron ore. 
     
     
         14 . The method according to  claim 1 , wherein said pellets have a diameter in the range of 9 to 18 mm. 
     
     
         15 . A pelletizing plant comprising:
 a pelletizing section for producing green pellets comprising fine iron ore by processing a fine iron ore containing mixture in a balling drum and/or a disc pelletizer;   an indurating furnace for firing said green pellets into hardened pellets;   a feeding arrangement configured to charge said green pellets onto a charge conveyor of said indurating furnace; and   an agglomerating section for producing lumpy agglomerates of by-products and/or of coarse iron ore, and in that said feeding arrangement is further configured to charge said lumpy agglomerates of by-products into said indurating furnace, together with said green pellets.   
     
     
         16 . The pelletizing plant according to  claim 15 , wherein green pellets formed in said pelletizing section and agglomerates of by-products formed in said agglomerating section are discharged onto a common conveyor, transferring the green pellets and agglomerates of by-products to said feeding arrangement. 
     
     
         17 . The pelletizing plant according to  claim 16 , comprising a first return route for undersized and oversized pellets, collected during transfer thereof on said common conveyor. 
     
     
         18 . The pelletizing plant according to  claim 15 , wherein said feeding arrangement is configured to charge the green pellets and agglomerates of by-products in two layers, with said agglomerates of by-products on top. 
     
     
         19 . The pelletizing plant according to  claim 15 , wherein said feeding arrangement comprises a set of superposed roller screens. 
     
     
         20 . The pelletizing plant according to  claim 15 , comprising a second return route for collecting undersized material and fines from said feeding arrangement and transferring the latter to said agglomerating section. 
     
     
         21 . A method of operating a pelletizing plant for iron making furnaces, said pelletizing plant comprising an indurating furnace in which green pellets are charged and fired to produce hard pellets, said method comprising:
 preparing iron ore green pellets using a balling drum and/or a disc pelletizer;   charging and firing said green pellets in an indurating furnace;   wherein agglomerates of coarse iron ore are prepared by compacting to form lumpy products; and in that said lumpy agglomerates of by-products are charged and fired with said green pellets in said indurating furnace, thereby producing hardened pellets and hardened agglomerates of by-products.   
     
     
         22 . The method according to  claim 4 , wherein the heat treatment in said indurating furnace is carried out in an oxidizing atmosphere, whereby the obtained hardened pellets and hardened, lumpy agglomerates of by-products have a metallization below 10% or 5%. 
     
     
         23 . The method according to  claim 10 , wherein said agglomerates of by-products contain less than 20 wt. % iron ore. 
     
     
         24 . The method according to  claim 10 , wherein said lumps or briquettes have a size above 20 or 24 mm. 
     
     
         25 . The method according to  claim 13 , wherein and preferably said pellets consist of at least 80 wt. % of particles having a minus 325 mesh.