The production of steel involves a number of processing steps in which iron-containing ores and particles are refined into iron metal. One step that is very important in that process is using a blast furnace to consume iron oxides in a number of forms and reduce these input materials into metallic iron. Iron oxides can be provided to the blast furnace in the form of raw ore, pellets or sinter. Raw ore comprises iron ore (Hematite (Fe2O3) or Magnetite (Fe3O4)) that is mined and then sized into pieces from about 0.5 to about 1.5 inches diameter. Such ore can have relatively high iron content between about 50% and 70%. This raw ore is considered to be of high quality since it can generally be fed directly into a blast furnace without further processing.
Iron ore that has lower iron content is typically processed to eliminate waste material and increase iron content. In particular, iron-rich pellets can be produced by crushing and grinding the low iron content ore into a powder so that waste material, sometimes called gangue, can be eliminated. The remaining powder is then formed into small pellets and fired in a furnace. The finished pellets have about 60% to 65% iron content.
As noted above, iron sinter may also be used to feed the blast furnace. Sinter is an irregular porous material, generally in the form of small pieces, that is produced by firing a combination of granular raw ore, coke, and limestone with iron-containing steel processing waste materials. Coke is a particulate form of processed coal, and limestone is a mineral used as a flux to remove impurities from the mixture. These materials are mixed in desired proportions and introduced into a sintering production line.
Of the three feed types for a blast furnace, sinter is typically the least expensive, and thus it is desirable to use a larger portion of sinter in the blast furnace feed mix when possible. In addition, some amount of sinter is generally desired in order to adjust the metallurgy of the finished iron product. However, one significant limitation on the use of sinter is the efficiency and effectiveness of the sintering process. In particular, known sinter processing systems have limitations which impede sinter production rates and adversely affect the quality of the sinter. As a result of these limitations, sinter cannot be used to feed blast furnaces as much as would otherwise be desirable.
The foregoing background discussion is intended solely to aid the reader. It is not intended to limit the invention, and thus should not be taken to indicate that any particular element of a prior system is unsuitable for use within the invention, nor is it intended to indicate any element, including solving the motivating problem, to be essential in implementing the innovations described herein. The implementations and application of the innovations described herein are defined by the appended claims.