Note: Descriptions are shown in the official language in which they were submitted.
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Title: "IRON ORE PELLETS WITH REDUCTION OF ABRASION, STICK-
ING, 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 ad-
dition of polymers or acrylic copolymers and polymers or vinyl acetate co-
polymers 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 ship-
ping, through the reclaim and loading of vessels, followed by a marine trans-
portation 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
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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 proc-
esses. In this case, a main contact of the fine with hot gases inside the re-
duction reactors allows the occurrence of bridges formation and conse-
quently, the formation of great masses of pellets aggregate with fines charac-
terizing the sticking. These aggregates prevent the adequate flux of gases in
the reactors, causing preferential fluxes or even the airtigthtness of the
reac-
tors. 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
stick-
ing is related to a surface phenomenon in which fibrous iron is formed. Sev-
eral 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 con-
nected to the decomposition of some phases that contain calcium, and the
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formation of new compounds through reactions with water and carbon diox-
ide contained in the atmosphere. The water penetrates in the superficial po-
res of the iron ore agglomerates, reacting with the Ca0 present, forming cal-
cium 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 (CaC03, free energy 0G = -28,2270kcal/mol,
at 25 °C). This process is followed by volumetric expansion, causing
the deg-
radation of the physical structure of the iron ore agglomerates. This mecha-
nism is described in equations 1-4.
Ca0 + H20 ~ Ca(OH)2 (1 )
C02 + H20 ~ H2CO3 (2)
2H2C03 + Ca(OH}2 -~ Ca(HC03)~ + 2H20 (3}
Ca(HC03)2 -~ CaC03~. + H20T + C02T (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, sticfcing, degradation by aging, dust emission, and its pro
duction process.
The innovative concept of the invention is based on the applica-
tion of polymers or acrylic copolymers and polymers or vinyl acetate copoly-
mers 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 ag-
glomerate to resist the abrasion efforts during handling, minimizing the gen-
eration of fines and consequently the reduction of 80 to 95 % of dust emis-
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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 proc-
ess, 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 ag-
glomerates, obstructing the penetration of humidity through the surface,
minimizing the advance of the degradation mechanism by aging and han-
dling, 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 ag-
glomeration 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 be-
fore 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 pel-
let 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-
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garding the polymers, copolymers and synthetic oils proposed as additives in
this invention. The main disadvantage, evidenced in table 1, is the effective-
ness 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,
5 or synthetic oils, or even petroleum paraffin should meet the following prem-
ises 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 ap-
plication 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 - IS03271 - lower than 2,0%;
Based on the information exposed so far, the inventor led theo-
retical studies and experiments in laboratory scale (in the facilities of
Samar-
co Minera~ao 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 follow-
ing procedure was used.
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Representative samples of finished iron ore pellets were col-
lected, 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 par-
affin. All samples were submitted to wear tests through abrasion - IS03271.
The table 1 shows the results of wear tests through abrasion -
IS03271 - for polymers, synthetic oil and petroleum paraffin respectively.
Table 1 - Resistance to Abrasion Indexes (Percentile smaller than 0,5 mm)
Vinyl
Petroleum AcrylicSynthetic
NaturalParaffinAcetate
PlymersOils
Polymers
brasion index of pellets
at ambien
temperature.
5,20 - - - -
brasion index after
pellets stratifica
tion at ambient temperature.
- 1,35 2,30 2,55 0,90
brasion index after
pellets stratifica
tion at a temperature - 1,20 - - -
of 50 C
brasion index after
pellets stratifica
tion at a temperature - 4,15 1,75 2,25 1,30
of 100 C
brasion index after
pellets stratifica
tion at a temperature - 4,40 1,45 1,75 1,75
of 200 C
In table 1, the data identified as NATURAL represents samples
of references composed of pellets without additives and at ambient tempera-
ture.
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
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the temperature of discharge of pelletizing furnaces (about 250°C)
until am-
bient temperature. In the case of polymers, this effect is more evident with
increase of pellets temperature, since the water loss contained in the poly-
mers 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
tem-
perature ranges tested, there is a tendency to efficiency reduction, if the
tem-
perature 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 petro-
leum paraffin lose its efficiency in the reduction of wear through abrasion,
result-
ing in values very close to the reference samples for this index and intense
va-
porization of this additive at this temperature range was once observed.
At the same time, sticking rehearsals were made, according to
standard IS011256, 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 differen-
tiated 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 tempera-
ture of test IS011256, reaches 850°C.
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Tables 2 and 3 show results obtained with petroleum and poly-
mers paraffin, respectively.
Table 2 - Sticking Evaluation tests (IS011256) for petroleum paraffin
Pellets condition Sticking Index
(%)
Natural 72,3
With Bauxite stratification 48,9
With Petroleum Paraffin stratification 69,1
ith Bauxite and Paraffin stratification 13,4
Table 3 - Sticking Evaluation tests (IS011256) for polymers
Pellets Condition Sticking Index
Natural 42,36
ith Bauxite stratification 20,15
ith Bauxite stratification, after abrasion44,05
ith Bauxite and Polymers stratification 11,64
ith Bauxite and Polymers stratification, 26,97
after abrasion
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 accom-
plishment 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 accom-
plished, 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
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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 la-
yer 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 accomplish-
ment 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 bau-
xite at different of bauxite nronortions.
Pellets Condition / Test Tem Stickin Index
erature
With Bauxite and Polymers stratification,with 0,45 %
of Bau
xite weight. 5,64
Tested at 850 C
ith Bauxite and Polymers stratification,with 0,25 %
of Bau
xite weight. 5,90
Tested at 850 C
ith Bauxite and Polymers stratification,with 0,45 %
of Bau
xite weight. 13.20
Tested at 950 C
With Bauxite and Polymers stratification,with 0,25 %
of Bau
xite weight. 37,20
ested at 950 C
Based on the conclusions of the analysis of table 3, concerning
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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 enou-
gh to guarantee very low values in the sticking index, even when the test is
5 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
10 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 pro-
cess 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 pro-
portion 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.
