WO2003062477A2

WO2003062477A2 - Iron ore macropellets and a process for producing them

Info

Publication number: WO2003062477A2
Application number: PCT/BR2003/000007
Authority: WO
Inventors: Ricardo VESCOVI DE ARAGÃO; Denilson RODRIGUES DE ARAÚJO; Maurício COTA FONSECA
Original assignee: Samarco Mineracao SA
Current assignee: Samarco Mineracao SA
Priority date: 2002-01-22
Filing date: 2003-01-21
Publication date: 2003-07-31
Anticipated expiration: 2004-07-22
Also published as: AU2003201227A1; WO2003062477A3; BR0200157A

Abstract

Pellets and a process for producing them, the pellets having sizes that range from 14 to 25mm and aggregating coal, limestone and bentonite as additives, the process of producing the pellets comprising the steps of: a) adding to a ground (88%<325&num;) iron ore concentrate additive: H2O, coal, limestone and bentonite; b) causing said concentrate to roll on a balling disc, bringing about agglomeration of the material and forming the green pellets; c) sorting the pellets by sizes, selecting those with sizes ranging from 14 to 25 mm; d) returning the pellets smaller than 14mm and bigger than 25mm to the balling disc; e) firing the pellets in a straight grate, where sintering of the pellets take place between the oxides.

Description

Title: "MACROPELLETS AND A PROCESS FOR PRODUCING THEM"

The present invention relates a new type of iron-iron pellets with size distribution ranging from 14 to 25mm, an average size of 17mm, minimum tumble index of 90%, and minimum compression strength of 200 kgf/pellet.

State of the Art

The raw materials used for manufacturing pig-iron and/or sponge-iron, are: granulated iron ore or "lump ore', "sinter" and pellets, described herein on rising order of price. The highest price of the pellet may be a deci- sive factor in composing charge for reactors, leading to the reduction thereof in the charge of the reactor with a view to reducing costs.

Among the drawbacks in the firing process of said lump ore, there is the "decrepitation", one of the main items of quality control requirements of said material, which refers to the lump ore degradation by generating fine grains in the reactor due to some alteration mechanisms, such as anisotropy of the crystals and release of crystallization water, when heated. An important factor for the composition of the price of the pellet is its production cost. In order to minimize the productions costs, the employ of energetic inputs, such as fuel oil and electric power should be reduced. Objects of the invention

The present invention aims to provide pellets with metallurgical quality in relation to the lump, wherein the pellets of the invention also provides a lower productions cost, being, therefore, less expensive and resulting in better operational conditions. Summary of the invention

The above objects are acheived by means of a pellet having a size ranging from 14 to 25 mm and aggregate coal, limestone and bentonite. Another object of the present invention reside in a process for producing pellets which comprises: adding to a ground (88%<325#) iron ore concentrate additive: H₂0, coal, limestone and bentonite; causing said concentrate to roll on a balling disc, bringing about agglomeration of the material and forming the green pellets; sorting the pellets by sizes, selecting those with sizes ranging from 14 to 25 mm; returning the pellets smaller than 14mm and bigger than 25mm to the balling disc; and firing the pellets in a straight grate, where sintering of the pellets take place between the oxides, resulting in pellets having a strength required for the production of pig-iron and spon- ge-iron.

In view of these technical peculiarities, these macropellets can be used as basic input both in the process of manufacturing pig iron - produced in blast furnace - and in the manufacture of sponge iron, produced in direct reduction reactors, as well as in any other process to produce primary iron.

The pellets of the invention have lower production cost, being less expensive, and they can be used in reactors providing better operational conditions, due to the defined size distribution, as well as their geometric shape. Another advantage of pellets of the invention is that they undergo a burning process under high temperatures and do not present the decrepitation present in the production of lump ore as commented above.

In terms of metallurgical quality, macropellets are superior to the granulated iron ore, or "lump ore", as shown in Table 1 , which presents the metallurgical quality of the invented pellets, in tests carried out in the laboratories of Samarco Mineracao S. A. TABLE 1

The pellets of the invention are produced by a pelletizing process in which pellet feed (iron-ore concentrate 88% < 325#) is mixed with neces- sary additives to achieve the desired chemical composition and physical quality. Besides being fed to the balling disc, the mixture containing iron ore, moisture (H₂0), coal, limestone and bentonite, undergoes a "rolling" within the balling disc in circular motion, which brings about agglomeration of the mixture, forming what is called "green pellets". The green pellets formed on the discs undergo a screening process on roller screenings, where the fractions smaller than 14mm and bigger than 25mm return to the balling disc after application of the disintregation system.

Pellets with a diameter ranging from 14 to 25 mm are carried by conveyors to the Straight Grate, where they undergo a firing process, in which sintering reactions occur among elements (oxides) presented in the mixture. These reactions promote the strength required to the pellets for the next steps of producing pig-iron and sponge-iron. Such pellets differ from others found on the market mainly regarding mean diameter, size distribution, production cost and quality. In function of the greater size of the pellets, there is an increase in the empty spaces between pellets, which leads to better permeability of the green pellets during the firing burning process. This brings about an increase in productivity and a reduction in the consumption of electric power and fuel oil.

At the end of the firing process, the pellets undergo a screening process, in which pellets with size ranging from 14 to 25 mm are carried to the storage yard. The combination of the described factors lead to the production of the so-called macropellets with a lower production cost and consequently a lower end sale price, which can replace the "lump" in the reactors either partly or totally. An important factor for the composition of the price of the pellet is its production cost. In order to minimize the production costs, experimental processes were developed aim to reducing the employ of energetic inputs, such as fuel oil and electric power. Experimental procedure: 1 - balling test on a pilot disc for the production of macropellets with size distribution identical to that determined in industrial tests;

2 - firing test in Pot Grate (pilot installation in which one carries out tests of burning said iron-ore pellets for appraisal of the physical and metallurgical quality).

3 - evaluation of the consumption of electric power and combustible oil, in function of the productivity and physical quality of the macropellets.

Figure 1 is a graph showing the grain distribution of the standard pellets and macropellets.

The firing test and the production of the macropellets produced on pilot disc were carried out in the Pot Grate.

Table 2 shows the reduction in the consumption of air and of LPG (Liquid Petroleum Gas) achieved in the tests. TABLE 2

Thus, this is a comparison between the results of consumption of LPG and Air for different levels of quality.

These results illustrate the possibility of reducing cost by reducing the consumption of fuel oil and electric power. Another factor to be considered is the productivity that, with the increase in permeability (empty spaces between the pellets, which facilitate the passage of gases during the processes of drying and firing) of the green pellet bed, can be raised, as described in the Table 3 TABLE 3

Claims

1. Pellets comprising aggregate coal, limestone and bentonite, characterized in that they have sizes ranging from 14 to 25 mm.

2. A process of producing macropellets, comprising the steps of: a) adding to a ground (88%<325#) iron ore concentrate additive:

H₂O, coal, limestone and bentonite; b) causing said concentrate to roll on a balling disc, bringing about agglomeration of the material and forming the green pellets; characterized in that it comprises the steps: c) sorting the pellets by sizes, selecting those with sizes ranging from 14 to 25 mm; d) returning the pellets smaller than 14mm and bigger than 25mm to the balling disc; e) firing the pellets in a straight grate, where sintering of the pe- Nets take place between the oxides.

3. Process as defined in the claim 2, characterized in that after step (e), water is sprayed over the pellets.

4. Process as defined on claim 1 or 2, characterized in that the pellets obtained after step (e) with a size between 14 to 25 mm are sent to a storage yard.