WO2004099452A1

WO2004099452A1 - Iron ore pellets with reduction of abrasion, sticking, degradation and dust emission, and its production process

Info

Publication number: WO2004099452A1
Application number: PCT/BR2004/000060
Authority: WO
Inventors: Vinicius Oliveira Fonseca; Mauricio Marcos Otaviano; Mauricio Cota Fonseca; Flávio DA SILVA LOPES
Original assignee: Samarco Mineração S/A
Priority date: 2003-05-05
Filing date: 2004-04-30
Publication date: 2004-11-18
Also published as: PE20050300A1; RU2338799C2; SE0500001L; SE0500001D0; CA2524637C; BR0301250A; CA2524637A1; BRPI0410080B1; SE530211C2; CL2004000966A1; RU2005137684A; BRPI0410080A; MXPA05011814A

Abstract

Iron ore pellets are produced by a process in which the iron ore is mixed with additives necessary to adapt the desired chemical composition, and they are then pelletized in rotatory disks. The resultant elements are pellets which are taken to a straight grate furnace, where they undergo a thermal process, receiving additional mixtures of polymers or acrylic copolymers, polymers and vinyl acetate copolymers or synthetic oils which form a protective layer- to become resistant to abrasion, sticking, dust degradation and dust emission.

Description

Title: "IRON ORE PELLETS WITH REDUCTION OF ABRASION, STICKING, DEGRADATION AND DUST EMISSION, AND ITS PRODUCTION PROCESS"

This invention refers to iron ore pellets that incorporate special characteristics, such as: high resistance to abrasion, reduced tendency to sticking, reduced tendency to degradation and dust emission through the addition of polymers or acrylic copolymers and polymers or vinyl acetate copolymers and through the addition of synthetic oils.

Normally, iron ore pellets are produced through a process in whi- ch the iron ore is mixed with the necessary additives to adapt the desired chemical composition to be further pelletized in rotatory disks or drums.

The resultant elements are the pellets - iron ore agglomerates - of semi-spherical shape, which are transported to a straight grate furnace, where they undergo a thermal processing with temperatures up to about 1360°C. Right after the discharge of the pelletizing furnaces in the production process, the iron ore pellets undergo different handling stages. The first stage consists of stocking through piling. The second stage consists of shipping, through the reclaim and loading of vessels, followed by a marine transportation stage, which will take the pellets to the clients, who will accomplish the stage of discharge of pellets.

The pellet can undergo stocking stages in the user's patio and feeding of furnaces or reactors, where the reduction of iron ore will occur; or undergo an intermediary stage, and further stock load and discharge in barge or train, in order to transport the pellets to the user's patio. The necessary time so that the flux, from the exit of the straight grate furnace to reduction in blast furnace or reactors of direct reduction, be completed varies usually from 3 to 6 months and the stock stages are made in outdoors patios.

Concerning the physical aspect, the handling of pellets or of any other iron ore agglomerate, through the mechanical attrition forces between each pellet or agglomerate, leads to the generation of fine particles - smaller than 0,5 mm. In this granulometry range, these fine particles are dragged by any airflow stronger than 5m/s - winds -, very common during the handling while transporting - operations in apron conveyers, operations with trucks, operations with vessels, operations with tractors and power shovels -, or e- ven during the stock period in piles. The dragging of these fines is extremely undesirable and harmful to the environment since it is classified as a source of dust generation.

Due to its high specific surface, the amount of fines that is not dragged by the wind and is adhered to the pellets volume or other iron ore agglomerate, which are fed in the reduction reactors for the production of primary iron, jeopardizes the good performance of the reduction process t- hrough expressive production decrease, besides the increase of combustible consumption - coal, coke, natural gas -, high cost materials in these processes. In this case, a main contact of the fine with hot gases inside the reduction reactors allows the occurrence of bridges formation and conse- quently, the formation of great masses of pellets aggregate with fines characterizing the sticking. These aggregates prevent the adequate flux of gases in the reactors, causing preferential fluxes or even the airtigthtness of the reactors. Specifically in the process of direct reduction of iron ore pellets in the reactors of direct reduction - where melting does not occur -, at temperatures higher than 600°C, the sticking tendency is more expressive, since this sticking is related to a surface phenomenon in which fibrous iron is formed. Several invention patents relate the application of superficial oxides coverage and/or oxides mixtures in iron ore pellets to minimize the formation of fibrous iron and the sticking effect. However, the fixation of these oxides coverage and/or oxides mixtures during the handling of pellets are equally subject to abrasion efforts and the consequent generation of fines smaller than 0,5 mm. Another problem, concerning the degradation or aging of the iron ore pellets - process characterized by the degradation of the physical and metallurgical properties as time goes by and during the stock of pellets or another iron ore agglomerate, before its use in the reduction reactors. The mechanism of the iron ore agglomerates aging process - pellets, sinters and briquettes - is connected to the decomposition of some phases that contain calcium, and the formation of new compounds through reactions with water and carbon dioxide contained in the atmosphere. The water penetrates in the superficial pores of the iron ore agglomerates, reacting with the CaO present, forming calcium hydroxide [Ca(OH)₂]. The contact of the calcium hydroxide with the carbon dioxide (CO₂) in the atmosphere at ambient temperature leads to the formation of calcium carbonate (CaCO₃, free energy ΔG = -28,2270kcal/mol, at 25 °C). This process is followed by volumetric expansion, causing the degradation of the physical structure of the iron ore agglomerates. This mechanism is described in equations 1-4. CaO + H₂0 → Ca(OH)₂ (1)

CO₂ + H₂0 → H₂CO₃ (2)

2H₂CO₃ + Ca(OH)₂ - Ca(HCO₃)₂ + 2H₂O (3) Ca(HCO₃)₂ → CaCO₃4 + H₂Ot + CO₂t (4)

The water - H₂0 - cited in equations 1 and 2 can originate from the water added in the agglomerates right after the discharge of the furnace for dust contention or from rainy water, air humidity, among others. As an example, we can say that in iron ore pellets stored for long periods of time, it is possible to observe the appearance of white dots in their surfaces which are the calcium carbonate precipitated mentioned in equation 4 - the contact of these white dots with hydrochloric acid causes effervescence and shows evident presence of CaCO₃.

This invention deals with a new type of iron ore agglomerate or other type of material - pellets, sinters, briquettes - with reduced generation of abrasion fines, sticking, degradation by aging, dust emission, and its pro- duction process.

The innovative concept of the invention is based on the application of polymers or acrylic copolymers and polymers or vinyl acetate copolymers or synthetic oils, ranging from 0,14 to 1% in agglomerate mass, to form a protective layer - coating - in the surface of the substratum agglomerate -, whose physical, chemical and mechanical properties enable the new agglomerate to resist the abrasion efforts during handling, minimizing the generation of fines and consequently the reduction of 80 to 95 % of dust emis- sion. With the reduction of the quantity of fines, the deleterious effect of the sticking inside the reactors decreases. In the case of direct reduction process, the protective layer increases the fixation of the oxides and/or of oxides mixtures added, significantly reducing the formation of fibrous iron and stick- ing. The protective layer also provides superficial waterproofing of the agglomerates, obstructing the penetration of humidity through the surface, minimizing the advance of the degradation mechanism by aging and handling, characterized by the generation of a maximum weight of 1 % of smaller agglomerate particles of 6,3 mm. The protective layer is constituted of acrylic polymers or vinyl a- cetate - structures composed of carbon, hydrogen and other elements as radicals, formed from small units called "mers" , or acrylic copolymers or vinyl acetate - polymers constituted of different units of repetition or "mers" -, or synthetic oils that can have esters basis. The use of polymers and copolymers is widely spread in the agglomeration area, especially in the iron ore pelletizing process, as in patent US 5,171 ,781 where Farrar et al teaches the use of polymers as agglomera- tive. The agglomerative is added to the iron ore with the other additives before the pelletizing in rotatory disks or drums, as described previously. Other application known to technicians related to the subject, described for example in patent US 5,271 ,859, where Roe teaches us how to use polymers as dust suppressor when applied in surfaces at temperatures up to 316 °C. But, in none of them he taught or evaluated the effects that the incorporation in the surface and in polymers pores and acrylic copolymers, polymers and vinyl acetate copolymers or synthetic oils, after the formation of the protective layer, provide the iron ore pellets with characteristics claimed in this invention. We will further discuss and evidence abrasion, degradation, dust emission and reduction of sticking tendency indexes reached by the pellet of this invention. The addition of saturated hydrocarbons - petroleum paraffin -, to the surface of the iron ore pellets is also presented as a good constituent for the formation of the protective layer, however with some disadvantages re- garding the polymers, copolymers and synthetic oils proposed as additives in this invention. The main disadvantage, evidenced in table 1 , is the effectiveness for fixation of the additive to the pellet when its surface is above 100 °C. The use of copolymers and/or acrylic polymers or vinyl acetate, or synthetic oils, or even petroleum paraffin should meet the following premises to guarantee the efficiency of the protective layer:

• To not completely vaporize during the application of the protective layer, considering that the temperature of the pellets during the application is between 150 and 300°C; • To be able to fixate the oxides and/or mixture of oxides used to a- void the formation of fibrous iron, and that are in the surface of the iron ore pellets in proportions that vary from 2 to 5 parts for every 1000 parts of pellets, guaranteeing a sticking level lower than 10% measured through procedure IS011256 at 850°C, and lower than 15% measured through the same procedure at 950°C;

• To enable the application through spray or immersion;

• To not contain sulfur, chlorine, heavy metals, benzene, potassium, sodium or phosphorus;

• In the case of iron ore pellets, to check resistance to abrasion after the application, measured through the resistance level to wear though abrasion - ISO3271 - lower than 2,0%;

Based on the information exposed so far, the inventor led theoretical studies and experiments in laboratory scale (in the facilities of Samar- co Mineracao S.A.), besides in industrial production scale experiments with iron ore pellets, with the addition of copolymers and polymers, henceforth generically denominated polymers, and synthetic oils of esters basis in low percentile, to block the effects of degradation by aging, to increase pellets resistance to wear through abrasion, to reduce the generation of fines smaller than 0,5mm, to reduce dust emission, to reduce sticking tendency, and to drastically minimize the use of water during its handling.

In the experiments accomplished in laboratory scale, the following procedure was used. Representative samples of finished iron ore pellets were collected, that is, after the burning thermal processing, for the accomplishment of rehearsals of wear through abrasion, according to procedure IS03271. To simulate the temperature conditions of pellets in the discharge of pelletizing furnaces, and to evaluate the behavior of additives in these conditions, the samples were heated in hothouses at different temperature levels.

To generate reference data, fifty percent of the samples were submitted to wear tests through abrasion without the addition of polymers, synthetic oils or petroleum paraffin. The other fifty percent of the remaining samples received applications of polymers, synthetic oils and petroleum paraffin. All samples were submitted to wear tests through abrasion - IS03271.

The table 1 shows the results of wear tests through abrasion - ISO3271 - for polymers, synthetic oil and petroleum paraffin respectively. Table 1 - Resistance to Abrasion Indexes (Percentile smaller than 0,5 mm)

In table 1 , the data identified as NATURAL represents samples of references composed of pellets without additives and at ambient temperature.

After analysis of the curves we can conclude that: 1) With the addition of polymers and/or synthetic oils it is possible to obtain data on the resistance index to wear through abrasion lower than 2,0%, and these results are repeated with pellets temperature varying from the temperature of discharge of pelletizing furnaces (about 250°C) until ambient temperature. In the case of polymers, this effect is more evident with increase of pellets temperature, since the water loss contained in the polymers emulsion collaborates to the rise of the temperature of vitreous transi- tion of the polymers adhered to the surface of pellets and more concentrated, allowing the formation of the protective layer as soon as the pellets cool off. For synthetic oils one can notice that, in spite of the good results in the temperature ranges tested, there is a tendency to efficiency reduction, if the temperature increase continues. In fact, vaporization of the oil during the tests was observed, although much less expressive than in petroleum paraffin, which will be commented next.

2) After the addition of petroleum paraffin it is possible to obtain values of the resistance index to wear through abrasion lower than 2,0%. However, this result is only obtained for pellets in temperatures between 50°C and ambient temperature. For temperatures higher than 50°C, the petroleum paraffin lose its efficiency in the reduction of wear through abrasion, resulting in values very close to the reference samples for this index and intense vaporization of this additive at this temperature range was once observed.

At the same time, sticking rehearsals were made, according to standard ISO11256, to evaluate the behavior of pellets during reduction in direct reduction reactors, regarding this phenomenon. In these tests bauxite was used as oxide to minimize the formation of fibrous iron.

The data identified as natural belongs to the reference samples, that is, without addition of bauxites, polymers, petroleum oils or paraffin. The sequence of rehearsals and the accomplishment of differentiated tests among additives were based on the individual behavior of each additive during rehearsals. With this focus, it sticking tests with synthetic oils were not accomplished, since the vaporization behavior in temperatures higher than 200°C had already been detected and, therefore, the paraffin re- suits were adopted, presenting a more critical situation of vaporization than the oils, as well as a good reference for the synthetic oils, once the temperature of test ISO11256, reaches 850°C. Tables 2 and 3 show results obtained with petroleum and polymers paraffin, respectively. Table 2 - Sticking Evaluation tests (IS011256) for petroleum paraffin

Table 3 - Sticking Evaluation tests (ISO11256) for polymers

Through tests whose results are represented in tables 2 and 3, it was possible to obtain the following conclusions: A) Observing the data in table 2, we can notice that the efficiency of the protective layer with petroleum paraffin increases when the mixture of this additive with bauxite is processed. This conclusion confirms the theory that the protective layer has a property to fixate the oxide used to inhibit the formation of fibrous iron. However, during tests, the effect of high tempera- ture on the petroleum paraffin led to intense vaporization of this additive, causing blockage in the exhaustion pipes of the apparatus set for the accomplishment of tests, which was enough to begin tests with polymers.

B) Preliminary tests showed that the protective layer processed with the polymers mixture with bauxite is more efficient than when only the polymers is added. Base on this affirmation, sticking tests were accomplished, with samples undergoing two situations:

1) Right after the processing of coverage with oxide or the poly- mers+ oxide mixture;

2) Right after the resistance test to wear of pallets through abrasion with oxide coverage or the polymers+ oxide mixture;

The goal in these tests is to test the resistance of the protective layer in fixating the oxides, the bauxite in this case, even under aggressive handling conditions.

With this focus, table 3 shows the efficiency of the protective layer in fixating the bauxite, since the result of the sticking test resulted in 26,97%, which is considered a very satisfactory result in the circumstances of the test, comparing to the natural sample or to the bauxite sample after the abrasion test which was of 44,05%.

In none of the tests with polymers any blockage or obstruction in the exhaustion pipes was detected in the apparatus set for the accomplishment of tests.

To confirm sticking results of the protective layer using polymers mixture with bauxite, tests were accomplished varying the quantity of bauxite added, maintaining the same polymers amount and the results are shown in table 4.

Table 4 - Sticking Evaluation tests (IS011256) for polymers mixture with bauxite at different of bauxite ro ortions.

Based on the conclusions of the analysis of table 3, concerning the good capacity of the protective layer with polymers for fixating bauxite, the evaluation of table 4 shows that the increase of bauxite added, keeping the same polymers quantity, allows the protective layer to be resistant enough to guarantee very low values in the sticking index, even when the test is led outside normal temperature conditions, that is, in higher temperatures which in this case was of 950°C.

Other tests were conducted, such as chemical analyses, using chromatography and X-ray spectrometry methodology, and the presence of sulfur, chlorine, heavy metals, benzene, potassium, sodium or phosphorus in the polymers as well as in the petroleum paraffin was not detected. These tests were not accomplished for the synthetic oil with ester base.

The addition of polymers and synthetic oils, in the industrial process is best accomplished through the preparation of the polymers or acrylic copolymers solution, polymers or vinyl acetate copolymers or synthetic oils diluted in 50 to 80 % in water, comprehending mixture and homogenization, and further transport of the solution until the application site, where the stratification of iron ore pallets through aspersion is obtained, in the proportion of 0,7 to 2% in mass of the agglomerate flux or ore, inside transfer chutes or through screening process, not limited to these points.

Claims

1- Agglomerates of sintered ores, pelletized, briquetted, pressed, or ores as found in their natural state, in any granulometry, ferrous or non- ferrous ore, especially iron ore pellets characterized by the fact that they in- corporate, on its surface and in its pores, acrylic polymers or copolymers, polymers or copolymers of vinyl acetate or synthetic oils, from 0,14 to 1% in agglomerate mass, and also by the fact that they present resistance level to abrasion smaller than 2%, tendency to maximum sticking of 10% (tested at 850 °C) or maximum of 15% (tested at 950 °C), tendency to degradation t- hrough handling with generation of particles smaller than 6,3 mm less than 1% in agglomerate weight and reduction from 80 to 95% of dust emission.

2- Agglomerates production process of sintered ores, pelletized, briquetted, pressed, in any granulometry, ferrous or non-ferrous ore, especially iron ore pellets, characterized by the inclusion, before or after reduc- tion, of stages of: a) Prepare of the acrylic polymer or copolymer solution, polymers or copolymers of vinyl acetate or synthetic oils diluted at 50 to 80 % in water, comprehending mixture, homogenization; b) Transport of the solution to the inspection site of the solution; c) Aspersion of the solution in the proportion of 0,7 to 2 % in mass over the flux of the agglomerate, preferably in transfer chutes and or in the sifting process, shaped as a cone and filled with minimum pressure of 1 ,5 kgf/cm².

3- Process, according to claiming 2, characterized for also being used in the ores manipulation as found in their natural state, ferrous or non- ferrous ore, especially lump-ore.