WO2003052149A1

WO2003052149A1 - Iron-ore pellets with reduced abrasion, sticking, degradation and dust emission, and a process for producing them

Info

Publication number: WO2003052149A1
Application number: PCT/BR2002/000183
Authority: WO
Inventors: Vinicius Oliveira Fonseca; Mauricio Marcos Otaviano; Mauricio Cota Fonseca; Flávio DA SILVA LOPES
Original assignee: Samarco Mineração S/A.
Priority date: 2001-12-17
Filing date: 2002-12-13
Publication date: 2003-06-26
Also published as: AU2002350294A1; BR0106149A

Abstract

The iron-ore pellets are produced by a process in which the iron ore is mixed with additives necessary to achieve the desired chemical composition, and then pelletized on rotary discs; the resulting elements are formed pellets that are carried into a straight grate furnace, where they undergo a burning process, with addition of a mixture of saturated hydrocarbons in low percentages, such as oil paraffins - structure composed of carbon and hydrogen, with simple chemical bond between carbon atoms - to make them resistant to abrasion, sticking, degradation and emission of dust.

Description

Title: "IRON-ORE PELLETS WITH REDUCED ABRASION, STICKING, DEGRADATION AND DUST EMISSION, AND A PROCESS FOR PRODUCING THEM"

The present invention relates to iron-ore pellets having special characteristics, such as: high resistance to abrasion, reduced tendency to sticking, reduced tendency to degradation and reduced dust emission, by virtue of the addition of saturated hydrocarbons, as oil paraffins.

Background of the invention

Usually, iron-ore pellets are produced by a process in which iron ore is mixed with additives necessary to achieve the desired chemical composition, and then pelletized on balling discs.

The resulting elements are pellets that are carried into straight grate furnace, where they undergo a burning process.

On the processes of producing primary iron, the handling of the iron-ore pellets, throughout the history of pelletizing, entails the generation of fine particles - smaller than 6.3mm, which are undesirable for affecting the production process in a negative manner.

In addition to the aspects harmful to the environment, due to generation of dust, these particles smaller than 6.3mm contribute to an ex- pressive drop in production of the reactors. Moreover, they cause an increase in fuel, which is an expensive input in these processes.

Many researches have been developed with a view to minimizing the harmful effects of degradation and wear out of the pellets by abrasion while they are handled and used in the reduction reactors, but always without acting directly onto the mentioned problem.

After intensive and innovatory technological development, the pellet sticking - a metallurgical phenomenon by which fibrous iron is formed on the surface of the pellets, with the consequent sintering among the particles in contact with one another, forming localized and undesirable pellet ag- glomerates during the direct-production process - is now being treated by adding bauxite (rock constituted by a mixture of hydrated aluminum oxides and iron) in the form of slurry with water.

Also, it is very usual to eliminate the dust generated by the wear out of the pellets due to abrasion by spraying water. A number of other studies show that applying water or aqueous mixtures onto the pellets while they are being handles is undesirable. This practice increases the inner energy of the pellets, causing accumulation of tensions and formation of cracks. The occurrence of chemical dissociation of some scorified compounds has been proved. Such compounds have the function of guaranteeing cohesion of the pellets, thus preventing them from degradation. This dissociation is linked to the thermodynamic conditions, which are favorable to chemical-bond breaking, and to the occurrence of reactions that form hydrated compounds, with the consequent generation of empty spaces within the pellets. As a result, the pellets become weak, which is also called aging. Summary of the invention

In view of the above problems of the state of the art mentioned above, it is an object of the present invention to provide iron-ore pellets with reduced abrasion, sticking, degradation and dust emission.

The invention also aims to provide a process of producing said iron-ore pellets with the above characteristics.

Such objects of the invention are achieved by means of an iron- ore pellet incorporating, a mixture of saturated hydrocarbons in low percentages, as for example oil paraffin or synthetic oil - structures composed of carbon and hydrogen, with simple chemical bonds between carbon atoms - to make them resistant to abrasion, sticking, degradation due to handling, and low tendency to dust emission.

These characteristics enable these iron-ore pellets to be employed as basic inputs, both in the process of manufacturing pig-iron - produced in blast furnaces - and in the manufacture of sponge-iron, which is produced in direct-reduction reactors, as well as in any other process of manufacturing primary iron.

Detailed description of the invention

On the basis of the information set forth, experimental theoretical studies on a laboratory scale were conducted (in the facilities of Samarco S.A.), in addition to experiments on an industrial scale of iron-ore pellets production, by adding paraffinic saturated hydrocarbons in low percentages, with a view to blocking the effects of degradation, lower the tendency to abrasion wear out of the pellets, reducing the tendency to sticking, reducing the emission of dust, effectively eliminating the use of water while handling the pel- lets.

For this purpose, in the experimental studies on a laboratory scale, the one has employed the procedure described below.

Within the scope of the laboratory tests, representative samples of the pelletization process were collected, in order to carry out essays for wear out of pellets by abrasion, according to the procedure ISO3271 , which is accepted all over the world as a standard procedure by producers and buyers of iron-ore pellets.

Fifty percent of the samples were subjected to the essays for abrasion wear, without addition of saturated hydrocarbons, and the remaining fifty percent were subjected to the essays for abrasion wear after addition of saturated hydrocarbons. By simulating the discharge of the straight grate furnace, the pellets were subjected to a process of heating up to the temperature of 250°C in oven, and then the saturated hydrocarbon was added, also heated to 250°C, thus preventing formation of cracks in the pellets.

Table I below shows the comparison of results between pellets with addition of hydrocarbons and pellets without addition of hydrocarbons. These are abrasion essays (ISO3271) on iron-ore pellets with addition of saturated hydrocarbons (range bigger than 6.3mm):

TABLE I

In a parallel manner, essays for sticking were conducted, already described, according to the standard ISO11256, which is accepted worldwide as a standard procedure by producers and buyers of iron-ore pellets to appraise the sticking of the pellets during the reduction in direct-reduction reactors, as shown in Table II below. TABLE II

Essays for appraising sticking (ISO11256)

These results confirm the capacity of saturated hydrocarbon to occupy the pore volumes of the iron-ore pellet, thus forming a protection layer on the surface of the pellets and inside their pores.

This layer prevents contact with compounds present in the at- mosphere, thus preventing their degradation.

Since saturated hydrocarbon has high adherence to the pellets, its mixture with bauxite provides greater fixation of this surface, thus preventing losses in the form of dust, improving the efficiency of the covering as far as the decrease in the tendency to sticking is concerned, and eliminating the use of water, the harmful effects of which have already been explained before.

The rigidity of the layer of saturated hydrocarbons, both on the surface and inside the pores of the pellets, is also sufficient to reduce the wear out of the pellets by abrasion to a minimum, reducing the emission of dust and eliminating the need of spraying water.

Other benefits resulting from these procedures are:

(a) increase in the useful life of the equipment, as a result of minimization of the wear out by virtue of the reduction of dust; and also by virtue of the lubricating effect of the satu- rated hydrocarbon;

(b) reduction in the electric-energy consumption, as a result of the possibility of turning off the gas scrubbers;

(c) increase in the rate of loading and unloading in the ships, because of the abrasion indexes; (d) reduction in fuel consumption in the processes of manufacturing primary iron ore, as a result of the combustion of the saturated hydrocarbon;

(e) reduction of environmental impact of the emission of dust during the handling of the pellets; and (f) modification of the data history of intrinsic characteristics of quality for iron-ore pellets.

Claims

1. Iron-ore pellet characterized by incorporating saturated hydrocarbons.

2. Iron-ore pellet as defined in claim 1 , characterized in that it comprises saturated hydrocarbons in low percentages.

3. Iron-ore pellet as defined in claim 1 or 2, characterized in that said saturated hydrocarbons are for example oil paraffins or synthetic oil.

4. Process for producing iron-ore pellets, characterized in that it comprises the application of saturated hydrocarbons in the pellets.

5. Process according to the claim 4, wherein the saturated hydrocarbons are for example oil paraffins or synthetic oil.