Classifications

• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21B—MANUFACTURE OF IRON OR STEEL
  • C21B13/00—Making spongy iron or liquid steel, by direct processes
  • C21B13/08—Making spongy iron or liquid steel, by direct processes in rotary furnaces
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21B—MANUFACTURE OF IRON OR STEEL
  • C21B13/00—Making spongy iron or liquid steel, by direct processes
  • C21B13/0066—Preliminary conditioning of the solid carbonaceous reductant

Definitions

• PREAMBLE It is known to directly reduce iron oxide-containing materials in a rotary kiln in admixture with solid carbonaceous materials. Unconsumed carbonaceous material recovered from the kiln product is usually recycled.
• the solid carbonaceous materials serve as reducing agents and produce all or part of the heat which is required in the process. If only part of the heat requirement is met by the combustion of the carbonaceous materials, the remaining quantity of heat is supplied to the process with the aid of burners.
• the matter discharged from the kiln must contain a certain amount of surplus or unconsumed carbonaceous material. Unless the entire matter discharged from the kiln is directly subjected to further processing, e.g., in an electric furnace, this unconsumed carbonaceous material must be separated from the matter which has been discharged from the kiln.
• the surplus fuel which has been separated must be re-used. If the surplus fuel has a particle size in excess of about 1 millimeter, it can be recycled to the process without difficulty and can be charged into the rotary kiln at the charging end, together with the charge, or at a subsequent point further in the kiln.
• This invention provides a process of directly reducing iron oxide-containing materials in a rotary kiln wherein the unconsumed carbonaceous fines contained in the matter discharged from the kiln and having a particle size below about 1 millimeter are recycled to the rotary kiln and any entraining of the recirculated carbonaceous material by the exhaust gases is substantially eliminated. It is possible, according to this invention, to process solid carbonaceous material which has disintegrated in large part in the rotary kiln to a particle size of less then 1 millimeter.
• the surplus carbonaceous material which has been separated from the matter discharged from the kiln is treated to remove part of the ash therefrom and is then pelletized by a rolling operation with the addition of water and/or binders, and only the resulting pellets are recycled and charged to the rotary kiln.
• Part of the ash which has been produced from the carbonaceous material must be removed before the material is pelletized because the ash content would otherwise continuously increase. It is suitable to remove that fraction which has the highest ash content from the surplus.
• the surplus carbonaceous material is generally not directly available in the particle size which is required for a pelletization so that the material should be comminuted.
• the surplus carbonaceous material is preferably comminuted to the particle size which is required for the pelletization after part of the ash has been removed because in this case the costs of comminuting the amount of ash which has been removed is eliminated.
• the surplus carbonaceous material has to be present in a small particle size before the ash can be removed, the entire surplus is comminuted to the particle size which is required for the pelletization and then part of the ash is separated before the pelletization is effected.
• surplus carbonaceous fuel which has a particle size below about 1 millimeter and is contained in the matter discharged from the kiln is pelletized.
• the surplus having a particle size above about 1 millimeter canbe recirculated to the kiln without being pelletized becuse the losses of that particle size fraction caused by the exhaust gases are much smaller than with the fine fraction.
• the required state of fineness will depend on the desired strength of the pellets and on the properties of the carbonaceous material.
• the pellets are produced in a size up to about 20 millimeters, preferably 8-12 millimeters.
• Water in an amount up to about 40 percent by weight is preferably added in the production of the pellets.
• the binders which can be added to the pellets consist preferably of heavy organic binders, such as pitch and tar, which have preferably been recovered from the same carbonaceous material. These binders are added in an amount up to 15 percent by weight.
• the binder ma'y alternatively consist, e.g., of inorganic materials, such as bentonite in an amount up to 3 percent by Weight, or boiler ash in an amount up to 10 percent by weight. A mixture of these binders can also be used.
• the strength of the pellets will be sufiicient if they do not disintegrate while travelling through the first 2-4 meters of the rotary kiln into which they are charged.
• the pellets can be made in such a strength that they can travel along the entire length of the kiln substantially without disintegration. These strengths can be readily achieved without a thermal hardening process.
• the matter discharged from the rotary kiln contained surplus carbon in an amount of 10 percent by weight based on the charge ore.
• This low-temperature coke contained 83.7 percent fixed carbon.
• the matter discharged from the furnace was subjected to electrostatic magnetic separation whereby 167 kilograms of non-magnetic material were separated per metric ton of sponge iron.
• the separated non-magnetic material was separated into a fraction below 1 millimeter, amounting to 50 kilograms, and a fraction above 1 millimeter, amounting to 117 kilograms, 2 kilograms were separated from the fraction below 1 millimeter and discarded
• the remainder of 48 kilograms was ground in a mill until 60 percent of it had a particle size below 0.04 millimeter. It was then mixed with 3.5 kilograms pitch and 12.5 kilograms water and pelletized on a pelletizing plate to form pellets having an average diameter of 10 millimeters. 5 kilograms of fixed carbon were lost during the grinding, mixing and pelletizing operations so that the 5-8 kilograms of green pellets produced contained 35 kilograms of fixed carbon from the recirculated carbon. These pellets and the fraction above 1 millimeter were charged into the charging end of the rotary kiln. The entire recirculated coke contained 133 kilograms of fixed carbon.
• the saving compared to a recirculation of the surplus carbon without the pelletizing according to the invention amounted to 26 kilograms of fixed carbon, corresponding to 90 kilograms fresh coal.
• the heat consumption was reduced from 3,960,000 to 3,600,000 kcal. per metric ton of sponge iron.
• the process according to the invention has the advantage that solid carbonaceous materials can be used which disintegrate to a large extent in the kiln and that the surplus in the matter discharged from the furnace can be recirculated to the rotary kiln so that an economic benefit is obtained.
• Solid carbonaceous materials which disintegrate to a large extent in the kiln are, e.g., lignite or high-ash coal.
• a special advantage resides in that these materials can even be charged at the charging end of a rotary kiln to which the charge is supplied at a high temperature. In such process, the velocity of the exhaust gases at the end where the charge is received is particularl'y high and fine-grained materials are entrained by the exhaust gases to a large extent.
• pellets are made with an addition of up to about 15 weight percent of a heavy hydrocarbonaceous binder.

Landscapes

• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Manufacturing & Machinery (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Manufacture And Refinement Of Metals (AREA)
• Processing Of Solid Wastes (AREA)
• Muffle Furnaces And Rotary Kilns (AREA)

Applications Claiming Priority (1)

Publications (1)

Family

ID=5726638

Family Applications (1)

Country Status (5)

Families Citing this family (3)

• 1969
  • 1969-02-28 DE DE1910147A patent/DE1910147C3/de not_active Expired
  • 1969-12-19 NL NL6919134A patent/NL6919134A/xx unknown
• 1970
  • 1970-01-09 GB GB1264452D patent/GB1264452A/en not_active Expired
  • 1970-01-14 US US2949A patent/US3684483A/en not_active Expired - Lifetime
  • 1970-02-27 SE SE02646/70A patent/SE354081B/xx unknown

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