Exploration of Smelting Chromium Ore to Smelt High Carbon Ferrochrome

I. Introduction

China is a region with scarce chrome ore resources, and most of the chrome ore is imported from abroad. Therefore, the study adequate supply of cheap powdered chrome ore production of high-carbon ferrochrome process is important.

At present, the process of smelting high carbon ferrochrome in powdered chrome ore mainly includes direct smelting and pretreatment-smelting. The former one has two different processes: smelting furnace and plasma smelting according to different smelting equipments ; the latter one has three different processes: sintering-smelting, ball-smelting and briquetting-smelting according to different pretreatment methods.

In comparison, the sintered chrome ore has better thermal stability and reductibility, the sintering-smelting process is mature, the mine consumption and energy consumption are low, and the economic benefits are good. The physicochemical properties of the sintering process and sinter are discussed in detail; this paper focuses on the test conditions of different proportioning schemes. And on this basis. An analysis of the furnace conditions of smelting chrome ore to smelt high carbon ferrochrome.

Second, the basic situation of the high-carbon ferrochrome furnace in the smelting furnace

(1) Characteristics of the material in the furnace

In the case of normal smelting, there are eight material characteristics areas in the high-carbon ferrochrome furnace in the smelting furnace. Top to bottom are bulk layer, melt layer, the residual layer bears with coke slag layer, the slag layer, the residual seam, and a metal layer baked product of the iron layer. The chemical reaction type intensity of each zone, the composition and state of the charge and furnace gas are different, and the change is a function of time during a smelting cycle.

(2) Main chemical reactions in the furnace

The main chemical reactions involved in the smelting of high-carbon ferrochrome in submerged arc furnace can be summarized into three types: they are the reduction reaction of mineral oxidation components, the slagging reaction and the decarburization and desiliconization reaction of molten metal.

1, reduction reaction

2, slag reaction

3, decarburization, desiliconization reaction

(3) Law of charge and furnace gas movement

In the submerged arc furnace, the charge and the gas phase of the furnace move toward each other, and they are mutually dependent, and depend on each other, which is mutually weak.

1, the furnace material decline depends on the following mechanical relationship

P=P _effective - â–³P

Where P is the force that determines the drop of the charge;

P is _effective for effective gravity and is determined by:

P _{has taught} = P _material - ( _PMo + P _liquid )

P _material is the gravity of the charge _material itself;

P is the _friction lining of the friction between the gob and the internal charge resistance;

â–³P is the total pressure difference of the furnace gas passing through the charge, which approximates the resistance or supporting force of the rising furnace gas to the charge, and the influencing factors can be summarized as follows:

f is the drag coefficient, which is a dimensionless constant under the condition of a submerged arc furnace;

w is the actual flow rate of the furnace gas through the furnace layer under a certain temperature and pressure, m / s;

ρ is the actual gas density, Kg/m ³ ;

H is the height of the charge layer, m;

D is the equivalent diameter of the interparticle particle channel and is determined by:

D=4ε/s, (m)

S is the total surface area of ​​the bulk material per unit volume, ie this surface area:

ε is the void ratio of the layer, that is, the ratio of the void volume of the layer to the volume of the bulk material.

2, the furnace gas rises because the furnace column has a pressure difference ΔP. It can be seen from the deformation of the formula (3) that the factors affecting the rise of the furnace gas are the equivalent diameter D of the furnace and the height H of the charge layer.

Third, the test

(1) Test conditions

1, the main parameters of the equipment

Production test is carried out in a 3000KVA submerged arc furnace

Table 1 Main parameters of electric furnace equipment

2, raw material chemical composition and particle size

Table 2 Chemical composition and particle size of the main raw materials involved in the test

Note: Mine 1, Mine 2, Mine 3 and Mine 4 are sintered chrome ore, high grade massive chrome ore, low grade massive chrome ore and powdered chrome ore.

(2) Test plan

Table 3 Arrangement of trials by factor conversion method

Note: The ratio of chrome ore is based on 500kg.

(3) Test process parameters

Table 4 Main operating parameters and average slag composition of the test process

(4) Test results

Table 5 Average alloy composition and technical and economic indicators of each scheme

Note: 1. Cost refers to the sum of the electricity consumption, mine consumption and coke consumption per ton of iron, that is, the process cost.

2. The units of Nissan, electricity consumption, mine consumption, coke consumption and cost are ton/day, kws/t, t/t, t/t and yuan/t, respectively.

Fourth, discussion

(1) Characteristics of smelting chrome ore to smelt high carbon ferrochrome

The process of smelting high-carbon ferrochrome in submerged arc furnace is full of contradictions. For example, the contradiction between the downward flow of the charge and the upward flow of the furnace gas; the contradiction between the furnace temperature and the reaction rate; the contradiction between the coke ore ratio and the effective working end of the electrode; the contradiction between the smelting strengthening and the antegrade. Under certain conditions of equipment and raw materials, these contradictions restrict the enhancement of smelting, productivity and comprehensive benefits.

The sintered chrome ore structure is loose and porous, has a large surface area, and has good reaction performance, and has a certain residual coke content (see Table 2). Therefore, when smelting chrome ore to smelt high-carbon ferrochrome, the utilization rate of coke is high, the amount of blending is small, and the ratio of coke ore is low, which is beneficial to the control of smelting load.

At the same time, the sintered chrome ore has a certain high temperature strength and a large amount of micropores are present inside, and the porosity of the material layer is large. It can be known from the formula (4) that the equivalent diameter D of the intergranular channel is large, and the gas permeability of the material layer is good. Under the conditions of intensified smelting, it is conducive to the stability of the furnace.

These performance characteristics of sintered chrome ore provide the possibility to enhance the comprehensive grade of chrome ore for enhanced smelting. According to the test situation, due to the addition of sintered chrome ore, the average synthesis of chrome ore in Scheme 1, Scheme 2 and Scheme 3 is compared with Scheme 4 while maintaining low apparent power and high power factor. Grade and average daily output increased by 1.62% and 9.08%, respectively. The smelting and strengthening effect is obvious.

In addition, the surface area of ​​sintered chrome ore is large, according to the heat transfer equation:

Dq=a×F×△T×d

Under a certain initial temperature difference ΔT, the heat exchange Q of the furnace gas and the charge per unit time is large, the temperature of the furnace gas discharged outside the furnace is low, the energy utilization rate is high, and the load demand and power consumption of the smelting are low ( See Tables 4 and 5).

(2) The problem of the amount of sintered chrome ore

The results of Scheme 1 and Scheme 2 show that the proportion of sintered chrome ore in the chrome ore ratio cannot be too large. The sintered chrome ore has good gas permeability and the equivalent diameter D of the interparticle passage is large. It can be seen from the formula (3) that under the smelting condition of the submerged arc furnace, when D is increased, the flow rate w of the furnace gas is increased, and the residence time of the furnace gas in the furnace is shortened. This results in insufficient heat exchange between the furnace gas and the charge, and the temperature of the furnace gas discharged outside the furnace is high, and the total amount of heat energy is increased, and the power consumption is increased.

Similarly, from the formula (3), the amount of sintered chrome ore is increased. The rate W of the furnace gas is increased, and the density ρ of the furnace gas is decreased. In addition, the heat exchange between the furnace gas and the charge is insufficient, and the temperature of the upper charge is too low. The reaction mainly carried out in the bulk layer and the upper part of the molten layer is actually carried out in two steps:

3(FeO-Cr ₂ O ₃ )+3CO=3Fe+3Cr ₂ O ₃ )+3CO ₂

3CO ₂ +3C=6CO

In the case where the temperature is low and the density of the furnace gas (the main component is CO) is small, the rate and limit of the reaction are greatly reduced. This aggravates the reaction burden of areas such as the residual coke layer, and even a large amount of residual ore and residual coke reach the lower reaction zone of the furnace, so that the coke-bearing layer, the slag layer and the residual ore layer become a mixed slag layer.

Because of the large amount of residual solids and residual coke in the form of solid particles, the mixed slag has a high melting point and poor fluidity, the reaction conditions in the lower reaction zone are deteriorated, the ore and coke are largely lost, and the mineral consumption is increased.

In addition, since the sinter has a certain C content and a large surface area with good reaction performance, the amount of the sinter is too large, and the coking ratio of the furnace is lowered. In comparison, the load is insufficient, and the apparent power and the active power are reduced. (See Table 4).

(3) Problems related to chrome ore

On the basis of Scheme 1, on the basis of Scheme 1, the high-grade powdered chrome ore is used instead of 50% of the low-grade bulk chrome ore. The daily output and recovery rate are increased by 13.68% and 4.71%, respectively, and the power consumption is reduced by 16.40%. Technical and economic indicators. This indicates that the gas permeability index of the first scheme is more than the reaction strength in the furnace.

Compared with the first scheme, the comprehensive grade of the chrome ore in the scheme 3 is increased by 4.06%, which is beneficial to increase the reaction intensity in the furnace and increase the flow of the furnace gas in the same unit, thereby reducing the excess of the smelting and strengthening the gas permeability performance index. It is conducive to the active and stable furnace conditions. At the same time, the comprehensive grade of chrome ore into the furnace is increased, the amount of slag is reduced, the total amount of chromium and heat taken away by the slag is reduced, and the mine consumption and power consumption are reduced (see Table 5).

The powdered chrome ore replaces the bulk chrome ore, the equivalent diameter D of the inter-particle channel is reduced, the furnace gas velocity is decreased, and the furnace gas and the charge are sufficiently exchanged to reduce the power consumption. In addition, the addition of low-priced powdered chrome ore, in the case of ensuring normal furnace conditions, is also beneficial to reduce costs and improve overall efficiency.

V. Conclusion

(1) Sintering chrome ore is feasible in smelting high carbon ferrochrome.

(2) Sintering chrome ore to smelt high-carbon ferrochrome, with a certain amount of lump ore and fine ore is necessary for obtaining good economic benefits.

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