US3684483A

US3684483A - Directly reducing iron oxide in a rotary kiln with pellitized carbonaceous material

Info

Publication number: US3684483A
Application number: US2949A
Authority: US
Inventors: Gerhard Reuter; Dietrich Werner
Original assignee: Metallgesellschaft AG
Current assignee: GEA Group AG
Priority date: 1969-02-28
Filing date: 1970-01-14
Publication date: 1972-08-15
Anticipated expiration: 1989-08-15
Also published as: DE1910147C3; GB1264452A; SE354081B; DE1910147A1; DE1910147B2; NL6919134A

Abstract

IN A PROCESS OF DIRECTLY REDUCING AN IRON ORE IN ADMIXTURE WITH A CARBONACEOUS MATERIAL IN A ROTARY KILN, AT LEAST THAT PORTION OF THE UNCONSUMED CARBONACEOUS MATERIAL REMOVED FROM THE KILN PRODUCT HAVING A PARTICLE SIZE BELOW 1 MILLIMETER IS PELLETIZED, PREFERABLY WITH THE ADDITION OF A HYDROCARBONACEOUS BINDER, AND RECYCLED.

Description

United States Patent Office 3,684,483 Patented Aug. 15, 1972 DIRECTLY REDUCING IRON OXIDE IN A ROTARY KILN WITH PELLITIZED CARBO- NACEOUS MATERIAL Gerhard Renter, Frankfurt, and Dietrich Werner, Offenthal, Germany, assignors to Metallgesellschaft Aktiengesellschaft, Frankfurt am Main, Germany No Drawing. Filed Jan. 14, 1970, Ser. No. 2,949 Claims priority, application Germany, Feb. 28, 1969, P 19 10 147.4 Int. Cl. C21b 11/06, 13/08 U.S. Cl. 75-33 Claims ABSTRACT OF THE DISCLOSURE In a process of directly reducing an iron ore in admixture with a car-bonaceous material in a rotary kiln, at least that portion of the unconsumed carbonaceous material removed from the kiln product and having a particle size below 1 millimeter is pelletized, preferably with the addition of a hydrocarbonaceous binder, and recycled.

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.

To ensure a substantial metallization and a protection of the resulting sponge iron against re-oxidation, 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.

For economic reasons, 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.

It is difiicult, however, to recycle fuel having a particle size below about 1 millimeter in this manner because such fuel would be entrained in the rotary kiln and a considerable part of such fuel would be carried out by the exhaust gases leaving the kiln.

In the previously known processes, considerable losses were caused by the fact that the exhaust gases contained solid carbonaceous material. Also any subsequent treatment or use of the exhaust gases would be plagued by the entrained solids. For this reason, the previously used carbonaceous materials were selected so that the resulting amount of unconsumed carbonaceous material having a particle size below about 1 millimeter in the matter discharged from the kiln was as small as possible.

While the surplus carbonaceous fines in the matter discharged from the kiln can be utilized by burning said fines in separate furnaces, this measure is not economical in many cases.

THIS INVENTION 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.

According to the invention, 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.

If 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.

In a preferred embodiment of this invention, only that 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.

In a further embodiment of this invention, the surplus carbonaceous fuel to be pelletized in comminuted so that 50-80 percent, preferably about 60 percent thereof, has a particle size below 0.04-0.06 millimeter, preferably below 0.05 millimeter. The required state of fineness will depend on the desired strength of the pellets and on the properties of the carbonaceous material. In an embodiment of the invention, 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. Alternatively, 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.

EXAMPLE A rotary kiln was charged with fresh coal in the form of Rheinische lignite having the following composition:

Percent Water Ash 4.8 fixed 45.5 Volatiles 39.5

Net calorific value 5,150 kcal./ kg.

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.

In another test, the entire fraction below 1 millimeter was ground. Thereafter, 2 kilograms of this fraction were separated and discarded. The results were virtually the same.

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.

We claim:

1. In a process of directly reducing an iron oxidecontaining material charged into one end of a rotary kiln in admixture with a solid carbonaceous material as a reducing agent wherein unconsumed carbonaceous material recovered from the kiln product is recycled, the improvement comprising: separating said unconsumed carbonaceous material from said kiln product, treating the material so recovered to remove at least a substantial part of the ash therefrom, separating from the balance of the resulting material that portion having a particle size above about 1 millimeter and directly recycling it to the kiln, pelletizing the balance of the resulting material having a particle size belowabout l millimeter into pellets having a particle size in the range of 8 to 20 millimeters and charging the resulting pellets into said rotary kiln at the charging end thereof.

2. The process of claim 1 wherein said resulting material is comminuted prior to pelletizing.

3. The process of claim 2 wherein said resulting material is comminuted so that in the range of 50 to 80 percent thereof has a particle size below about 0.06 millimeter.

4. The process of claim 1 wherein the pellets are made with an addition of water amounting up to about 40 percent by weight.

5. The process of claim 1 wherein the pellets are made with an addition of up to about 15 weight percent of a heavy hydrocarbonaceous binder.

References Cited UNITED STATES PATENTS 3,235,375 2/ 1966 Meyer et al. 7'5-36 X 3,425,824 2/1969 Heitmann -33 3,469,970 9/1969 Heitmann 75-33 2,834,044 5/1958 Antonson et al. 23-314 UX 3,294,567 12/ 1966 Dobbin et al. 23-314 X 3,391,234 7/ 196 8 Walenciak et al. 23-314 X 2,880,083 3/1959 Wienert 75-33 3,097,090 7/1963 Aamot 75-33 3,180,725 4/ 1965 Meyer et al. 75-33 3,462,262 8/1969 Koch 75-33 2,687,290 8/ 1 954 Garoutte et a1. 75-25 'UX 3,326,669 6/ 196-7 Stirling 75-25 X HEN-RY W. TAR-RING 11, Primary Examiner US. Cl. X.R. 23-314