Process and plant for reducing solids containing iron oxide
This invention relates to a process for reducing solids containing iron oxide, such as iron ore, in which fine-grained solids are heated and at least partly calcined in a pre-heating stage ( 2, 9 ). In a first fluidized-bed reactor ( 14 ) downstream of the preheating stage ( 2, 9 ), the solids are prereduced and reduced further in a second fluidized-bed reactor ( 16 ). Downstream of the second reactor ( 16 ) a briquetting stage ( 20 ) is provided, in which the solids are briquetted at a temperature above 500 ° C. To increase the energy efficiency of the process and improve the flowability of the solids in the briquetting stage ( 20 ), magnesite is added to the preheating stage ( 2, 9 ) together with the solids containing iron oxide, which magnesite is at least partly calcined in the preheating stage ( 2, 9 ) to obtain magnesium oxide. Furthermore, the invention relates to a corresponding plant.
1 . A process for reducing solids containing iron oxide, in particular iron ore, in which fine-grained solids are heated and at least partly calcined in a preheating and/or calcining stage, are prereduced in a first fluidized-bed reactor downstream of the preheating and/or calcining stage, and are reduced in a second fluidized-bed reactor and briquetted in a briquetting stage downstream of the second reactor at a temperature above 500° C., wherein magnesite together with the solids containing iron oxide is added to the preheating and/or calcining stage, which magnesite is at least partly calcined in the preheating and/or calcining stage to obtain magnesium oxide.
2 . The process as claimed in claim 1 , wherein the magnesite together with the solids containing iron oxide is calcined in the preheating and/or calcining stage at temperatures of 400 to 1250° C., in particular at 540 to 1000° C.
3 . The process as claimed in claim 1 , wherein more than 50%, in particular about 90%, of the magnesite added to the preheating and/or calcining stage together with the solids containing iron oxide has a grain size between 300 pm and 3 mm, in particular between 400 pm and 1 mm.
4 . The process as claimed in claim 1 , wherein between 0.1 and 5 wt-%, in particular about 0.5 wt-% of magnesite are added to the solids containing iron oxide before and/or during the supply into the preheating and/or calcining stage.
5 . The process as claimed in claim 1 , wherein the solids supplied to the briquetting stage from the second reactor contain between 0.1 and 5 wt-%, in particular about 0.5 wt-%, of magnesium oxide.
6 . The process as claimed in claim 1 , wherein in a heating stage upstream of the briquetting stage the solids reduced in the second reactor together with the magnesium oxide are heated to a temperature above 600° C., in particular about 700° C., and are introduced into the briquetting stage in the hot condition.
7 . The process as claimed in claim 1 , wherein the solids containing iron oxide are reduced in the first and second reactors at temperatures below 700° C., in particular at about 630° C., to obtain metallic iron with a degree of metallization of more than 75%, in particular more than 90%.
8 . Use of magnesite as flux material which in a process for producing sponge iron briquets, in particular as claimed in claim 1 , is charged together with solids containing iron oxide, in order to increase the flowability of hot sponge iron during the supply from a reduction stage into a briquetting stage.
9 . A plant for reducing solids containing iron oxide, in particular for performing a process as claimed in, claim 1 , comprising a preheating and/or calcining stage, a first and a second reactor each constituting a fluidized-bed reactor, and a briquetting stage, wherein the preheating and/or calcining stage includes means for the simultaneous continuous or discontinuous introduction of iron-oxide-containing solids and magnesite, and that upstream of the briquetting stage a heating stage is provided.
10 . The plant as claimed in claim 9 , wherein at least one of the two reactors is a fluidized-bed reactor with a circulating fluidized bed and/or an annular fluidized bed.
11 . The plant as claimed in claim 10 , wherein the first and second reactors have a plurality of nozzles or inlet openings for supplying a heated gaseous reducing agent such as hydrogen.
12 . The plant as claimed in claim 9 , wherein the preheating and/or calcining stage includes a first Venturi preheater with a downstream first cyclone and a second preheater with a downstream second cyclone, the first and/or the second cyclone being connected with the first Venturi preheater via conduit for recirculating dust separated from waste gas.