RSPE “Karaganda State Technical University”

Karaganda, the Republic of Kazakhstan

D.K. Isin, À.Z. Isagulov,

D.À. Isagulova, S.Å. Oryngozhina, B.D. Isin

UDC 669.337.111:669.181.4

STUDYING COMBINED PROCESS OF SINTERING AND METALLIZATION OF IRON-ORE MATERIALS

One of the main directions of decreasing coke discharge intensity and increasing blast furnaces productivity is using metallized charge in the blast furnace melting.

Metallization efficiency can be achieved by different ways, but the main are the following:

a) decreasing the cost of iron-ore material subjected to metallization;

using in the process of metallization accessible, cheap solid or gaseous reducers.

Large resources of natural gas can be used for metallization of iron-ore materials including agglomerate. Studying the agglomerates sintered by hot air under pressure showed that they possess high reducibility caused by fuel low consumption for their sintering and high oxidation. The experiments for agglomerates reducing on the Linder set there were showed that these agglomerates metallization degree was 62,5%, as compared to 33,4% of a common agglomerate and 55,6% of oxidized fluxed pellets of SSMCC. It’s obvious that such agglomerates like the pellets can be metallized on the existing sets without worsening their work indicators.

One of the peculiarities of the agglomerates structure, unlike the pellets structure, is the presence of large pores Ø till 1 mm and larger. These pores presence is substantiated by the conditions of the agglomerate obtaining in which through the layer there continuously flows air for sintering. The agglomerate obtained possesses without its destroying a significant gas-permeability, and through it there can be supplied a reducing gas.

There has been suggested a technology of metallized agglomerate obtaining consisting of two stages: agglomerate sintering with heat till 1000-1100⁰Ñ and the following metallization of the hot undestroyed agglomerate by the converted natural gas with the temperature 1100-1200⁰Ñ. The experiments were carried out on the enlarged laboratory set of the retort type with the inner diameter of the lined bowl 250 mm and the height 350 mm. the set is a combination of an bowl and a burner.

The usability of such a set for working with increased pressure was designed by the fact that the gas-and-air and gas-and-oxygen burners operate with a compulsory mixing of gases from the gas networks of high pressure. To the set there are supplied: natural gas, technical oxygen and compressed air.

A unit for gases burning is characterized by the possibility to carry out various modes of natural gas burning with obtaining on its base the products of burning with different metallurgical properties (from oxidation till reducing) which is necessary in combining the processes of the charge sintering and the following agglomerate metallization.

In the experiments there was used the charge from the KMA, ores of Krivoi Rog, limestone and coke fines. In one of the experiments the charge consisted of the Olenegorsk concentrate and 2% of coke fines. The ore of Krivoi Rog was used as a return.

The composition of the charge with KMA concentrate was the following:

concentrate - 60%;

ore of Krivoi Rog - 20%;

limestone - 16,5 18,5%,

and the coke fines content varied from 1,5 till 5,0%.

The prepared dry charge was mixed within 3 minutes, then wetted till 7,0 – 7,5% and mixed again within 3 minutes in the unit of a concrete mixer type.

With practically equal weigh of the layer in the retort the height changed from 250 till 300 mm as in a part of experiments there was performed the charge compacting. At the stage of charge sintering there were used the products of burning natural gas with air with its rate factor 1,1–1,2. The products of burning were diluted with the secondary air or technical oxygen. There was obtained a gas mixture with oxygen content 8-10% in the first case and 20-23% in the second. The composition of the gas phase of the charge sintering are given in Table 1.

Table 1 – Gas phase composition at the stage of the charge sintering

Method of gases obtaining	Content, %
	ÑÎ2	Î2	N2
1. ÑÍ4 burning with air and diluting the products of burning with the secondary air	6,4 – 7,9	8,2 – 9,8	83,8 – 84,0
2. The same, but diluting with oxygen	5,0 – 8,8	20,0 – 22,7	70,0 – 73,3

Water content (by calculation) in the gas mixture varied from 8,0 till 12,5%. The gases temperature over the charge layer varied from 1000 till 1100^îÑ.

The presence of carbon dioxide and water steam at the gas stage braked the process of the charge sintering. By the moment of the sintering stage the temperature by the layer height was balanced and equal to 1020 – 1125^îÑ with the drop about 100^îÑ.

At the stage of metallization there were used the products of natural gas conversion with technical oxygen with the former rate factor 0,39 – 0,41. The composition of the dry products of conversion (average within the period of studying) was a s follows, % (volum.):

ÑÎ2	ÑÎ	Í2	N2
5,2	35,0	55,0	4,8

Thus, the composition of the oxygen conversion products for natural gas was characterized by an increased content of oxidation components. The technological parameters of carrying out the experiments varied depending on the problem posed. The conditions of the experiments carrying out on the agglomerate metallization are shown in Table 2.

In the process of metallization of the hot agglomerate there takes place a gradual, though negligible, decreasing the temperature of the gas phase and agglomerate. In most experiments the temperature drop by the layer height obtained by the moment of transition from the sintering stage to the metallization stage was pertained till the end of the experiment.

Table 2 - Conditions of experiments carrying out on the agglomerate metallization

Metallization stage duration, min	Concentrate type in the charge	Carbon content in the charge	Natural gas rate, m/hour
20	con. ÊÌÀ+agglo-ore	1,5	22,
20	con. ÊÌÀ+agglo-ore	3,0	21,0
25	con. ÊÌÀ+agglo-ore	1,5	23,0
30	con. ÊÌÀ+agglo-ore	5,0	24,0
30	con. ÊÌÀ+agglo-ore	2,0	25,0
30	con. ÊÌÀ+agglo-ore	1,5	23,0
30	con. ÊÌÀ+agglo-ore	2,5	19,0
40	con. ÊÌÀ+agglo-ore	2,0	20,0
30	Olenegorsk concentrate	2,0	20,0

The experiments showed that there can be achieved the degree of the agglomerate metallization 46-58% (on average by the layer). A relatively small temperature drop by the layer height ensures obtaining rather a uniform in the quality the agglomerate pie even with a short duration of the experiment (Table 3).

The metallized agglomerate strength in all the cases was high. After testing in the drum according with the standard methodology the fraction yield – 5 mm didn’t exceed 16%.

The increasing of the fuel content in the charge in all the cases leads to increasing iron protoxide content in the agglomerate related with silica, which decreases the agglomerate reducibility. Consequently, the fuel increased consumption leads to slowing the processes of metallization with gases. The experimental data show that the fuel consumption in the limits 2,0 to 2,5 is quite sufficient for obtaining strong metallized agglomerate.

Table 3 - The experiment duration effect on the agglomerate metallization degree

Experiment duration, min.	Layer zone	Agglomerate chemical composition, %				Metallization degree, %
		Fåîáù	Fåìåò	FåÎ	Få2Î3
20	top middle bottom	67,88 65,50 63,03	41,32 39,1 24,6	31,6 32,6 48,3	2,97 1,70 1,40	60,0 59,7 38,8
30	top middle bottom	63,44 66,12 66,12	24,9 45,1 45,34	54,03 31,6 28,6	- -	36,2 68,2 68,5

At the temperature i8n the layer lower that 1000^îÑ and metallization stage duration 30 minutes the degree of the agglomerate metallization didn’t exceed 40%. A higher degree of metallization with the same duration of the process is achieved with the temperature rising in the layer up to 1030 – 1100^îÑ. Over this temperature the process of sintering is slowed as a result of a partial agglomerate melting and its structure worsening. Thus, for a successful process of metallization of the hot agglomerate it’s necessary to provide the temperature in the layer within the limits 1030 – 1100^îÑ.

With increasing the metallization stage duration from 20 till 30 minutes, the degree of metallization increases very little (from 49,4 till 52,8%). A probable reason of the metallization process slowing can be considered the fact that with the metallization degree over 40% there takes place a blocking of not completely reduced iron oxides with the formed film of metallic iron, as well as due to decreasing the agglomerate porosity as a result of a partial melting of the material and pores coagulation.

CONCLUSIONS

1. By the combined process of sintering and metallization with the products of natural gas conversion under the increased pressure of the gas phase there was obtained metallized by 50-68% agglomerate. The metallization stage duration was 20-30 min.

2. The extent of using the reducing capability of ÑÎ and Í₂ conversion products in the agglomerate metallization was 80-100 and 50-55% of the balanced one, respectively.

3. The optimal temperature of the hot agglomerate metallization was 1030-1100⁰Ñ.

4. The fraction content (-5mm) in the samples of the metallized agglomerate after testing in the Linder drum was 12%, which is 4-5 times less than in a common agglomerate.