RU2451098C2 - Melting method of ferrosilicon in ore heat-treatment furnace - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: method involves continuous loading to the furnace of charge with reducing carbon mixture and its electrothermic melting. At that, melting is performed in conditions of optimum compliance of electric operating mode to geometrical parameters of ore heat-treatment furnace as per ratios obtained during operation of furnaces, which use fossil coals in quantity of 50% as to carbon in composition of reducing carbon mixture.

EFFECT: invention allows melting ferrosilicon at minimum specific consumption of raw material and electric energy by optimising geometrical dimensions of ore heat-treatment furnace and electrical melting modes, which are determined depending on ratio of fossil coals in reducing carbon mixture.

3 cl, 3 tbl, 2 dwg

Description

The invention relates to the field of ferrous metallurgy, and in particular to a carbon thermal method for smelting ferrosilicon in an ore-thermal furnace.

A known method of smelting ferrosilicon in an ore-thermal furnace (hereinafter RTP), comprising continuously loading the mixture with a carbon reducing agent and its electrothermal smelting into a furnace, the geometric dimensions of the furnace and its electrical parameters for smelting ferrosilicon are calculated using formulas determined by statistical processing of actual data at provided that coke nut is used as a carbon reducing agent [1-4]. Attempts to use carbonaceous materials (fossil coals) as a reducing agent with a higher electrical resistivity led to a mismatch in the geometric dimensions of the furnace and the established electric melting mode.

In connection with this disadvantage of the known method of smelting is the limitation in the use of fossil coal as a carbon reducing agent.

The objective of the invention is to develop a method for smelting ferrosilicon with a minimum specific consumption of raw materials and electricity, allowing the use of fossil coals in the composition of the reducing mixture.

The problem is solved in that the carbon reduction mixture contains coke nut and fossil coals in an amount of 50% carbon, and the smelting is carried out under conditions of the optimal ratio of the parameters of the electric operating mode — reactive and active phase resistance, impedance and apparent phase power, phase voltage and force current from the low side of the transformer and the geometric parameters of the furnace internal diameter of the bath and its depth, diameter and length of the self-sintering electrode, the diameter of the decay of the electrodes.

At the same time, when using long-flame and brown coal in the reducing mixture, the carbon excess coefficient is maintained at 0.98, and the electrodes are immersed in the mixture during smelting of high-silicon ferrosilicon to a depth of 1.67 times the diameter of the electrode.

This allowed us to increase the power in the arc by increasing the resistance in the charge (R _W ) from 3 ÷ 5 mOhm (when working on coke) to 10 ÷ 5 mOhm (when working using fossil coal). Replacing the coke nut with coal by 50% for carbon made it possible to redistribute the power in the working space of the RTP: the proportion of power released in the arc increased from 44 to 61%; the share of power released in the charge decreased from 18 to 8%.

The selection of the geometric dimensions of the RTP and the electrical modes of its operation is carried out according to the ratios below.

1. The inner diameter of the bath is determined by the optimal density of active power in the cross section of the bath (p _in = 510 kW / m ² ) with a minimum specific energy consumption. The dependence is described by equation (1):

where: d _in - the inner diameter of the bath, m;

P is the active power of the furnace, kW.

2. The diameter of the decay of the electrodes is determined based on the optimal value of the specific power in the cross section of the diameter of the decay (p _p = 2465 kW / m ² ) with a minimum specific energy consumption. The dependence is described by equation (2):

where: d _p is the diameter of the decay of the electrodes, m;

P is the active power of the furnace, kW.

3. The choice of reactive and active resistances is made on the basis of the following laws:

- the reactance of the phase is determined by the dependence, which is described by equation (3):

where: P is the active power of the furnace, kW;

X _f - reactance phase, mOhm,

the optimal ratio of the phase resistance (R _f ) to reactance (X _f ) is determined by equation (4):

- phase impedance (Z _f ) - according to equation (5):

Cosφ = 0.8.

The total phase power will be:

, МВА

MBA

4. The diameter of the self-sintering electrode, depending on the total phase power, is described by equation (6):

where: S _f - full phase power, MVA;

X _f - reactance of the phase, mOhm.

5. The phase voltage on the low side of the transformer was determined by the dependence, which is described by equation (7):

where: S _f - full phase power, kVA;

U _f - phase voltage of the transformer from the low side, V.

6. The current strength on the low side of the transformer is determined by converting equation (7), according to equation (8):

where: I - current strength from the low side, kA.

7. The length of the electrode and the depth of the bath (H), which corresponds to the length of the electrode, is determined by equation (9)

where: R is the electrical resistance of the electrode, Ohm;

ρ - electrical resistivity of the coked portion of the electrode, Ohm · mm ² / m;

L is the length of the electrode, m;

S = π · d _e ^2/4 - cross-section area of the electrode ² mm;

d _e - the diameter of the electrode, mm

8. Calibration calculation of the diameter of the electrode was made according to the permissible current density according to equation (10):

where: I is the current strength in the electrode, A;

d _e - electrode diameter, cm;

j is the current density in the electrode, A / cm ² .

The optimal geometric and electrical parameters of the furnaces obtained on the basis of the developed method are presented in table 1.

Table 1 Optimal geometric and electrical parameters R kW X _f , mOhm Z _f , mOhm Cosφ S, kVA U _f , B I _f , A d _e , M N, m d _p , m d _in , m J, A / cm ² 15,000 0.87 1,449 0,8005 18738 95.2 65639 1,166 2.77 2,784 6,121 6.16 16000 0.887 1,478 0,8005 19987 99,2 67139 1,179 2.84 2,876 6,322 6.16 17000 0,903 1,505 0,8005 21236 103,2 68579 1,191 2.90 2,964 6,516 6.16 18000 0.919 1,531 0,8005 22485 107.1 69964 1,203 2.96 3,050 6,705 6.16 19000 0.934 1,556 0,8005 23734 111.0 71300 1,215 3.01 3,134 6,889 6.16 20000 0.948 1,581 0,8005 24984 114.7 72592 1,226 3.07 3,215 7,068 6.16 21000 0.962 1,603 0,8005 26233 118.4 73843 1,236 3.12 3,294 7,243 6.16 22000 0.976 1,626 0,8005 27482 122.1 75055 1,246 3.17 3,372 7,413 6.16 23000 0.989 1,648 0,8005 28731 125.6 76232 1,256 3.22 3,448 7,580 6.16 24000 1.001 1,669 0,8005 29980 129.2 77376 1,265 3.27 3,522 7,743 6.16 25000 1.014 1,689 0,8005 31229 132.6 78489 1,275 3.32 3,594 7,902 6.16

The method of smelting ferrosilicon is implemented in an ore-thermal furnace, which is illustrated by drawings, namely: in Fig. 1 - section AA of Fig. 2; figure 2 shows a vertical diametrical section of the furnace.

The furnace includes a steel cylindrical casing 1, made of masonry, equipped with a bottom tub 2 with carbon lining. Three self-sintering carbon electrodes 3 are vertically placed in the inner cavity of the bath, displaced around the circle by 120 ° relative to each other. The movement of the electrodes is carried out by electric winches or hydraulic hoists, while the adjustment of the specified current in the electrode is carried out by moving the electrode in a vertical plane, namely: to increase the current, the electrode is lowered, and to reduce the current, the electrode is raised. The furnace is loaded from above through tubules. The charge is delivered to the tubes using a transfer trolley. At the bottom of the bath, ice 4 is provided for releasing the melt. The furnace is powered by an individual 3-phase transformer, which is equipped with a device for switching stages of transformation under load.

The commissioning of the furnace is carried out in the traditional way by preliminary sintering of the electrodes by burning the coal mixture in barbecue in the air supply mode. Next, load the mixture into a furnace with a carbon reducing agent and carry out its electrothermal smelting. The main parameter for controlling the electric mode, for a specific composition of the reducing mixture, is the total phase resistance on the low side of the transformer, which is maintained by an automatic process control system (APCS) of an ore-thermal furnace, consisting of the following subsystems:

- control of the movement and bypass of the electrodes;

- control of the oil switch and protection of the furnace transformer;

- management of the dosing process of raw materials and targeted loading of the furnace;

- control of electrical and thermal parameters and metering of raw materials.

The automated system allows flexible restructuring of the process control model depending on current tasks.

The proposed design of an ore-thermal furnace for smelting ferrosilicon can increase productivity by 15.0-17.0%, reduce specific energy consumption by 12.0-15.0%, increase the extraction of silicon in the alloy by 5.0-7.0%

The proposed ore-thermal furnace with a usable capacity of 18 and 21 MW was tested in the conditions of OJSC Kuznetsk Ferroalloys and was proposed for implementation at ferroalloy plants in the smelting of ferrosilicon.

The measurements performed on the existing furnace, when it is working with 100% coke nut loading and with 50% coke nut replacement by fossil coals, are presented in table 2.

table 2 No. p / p Parameter Name Unit of measurement The share of replacement of coke with coal, 0% The share of replacement of coke with coal, 50% one Current strength in the electrode BUT 65,000 62500 2 Phase voltage at the electrode AT 98 101.3 3 Furnace impedance mOhm 1.51 1,62 four Impedance in the charge mOhm 3.2 12.8 5 Phase active power in an arc kw 2400 3300 6 Specific Power Consumption kWh / t 10330 8104 7 Daily furnace productivity t / day 35.7 47.9 8 Cosφ 0.813 0.851

The measurements were performed with the same input parameters.

The main results of FS75 grade ferrosilicon heats are presented in table 3.

Table 3 INDICATORS OPTIONS BASE SUGGESTED Productivity of the furnace in the smelting of alloy grade FS75, base. t / h

Specific energy consumption, kW · h / t

The extraction of silicon,% 84.6 90.7

Information sources

1. Oldzievsky S.A., Kravchenko V.A., Nezhurin V.I., Borisenko I.A. Mathematical modeling of electric fields of ore electrothermy furnaces. - M.: Metallurgy, 1990. - 112 p.

2. Zhuchkov V.I., Rosenberg V.L., Elkin K.S., Zelberg B.I. Electrical parameters and design of ore-reducing electric furnaces. - Chelyabinsk: Metallurgy, 1994 .-- 192 p.

3. Strunsky B.M. Calculations of ore-thermal furnaces. - M.: Metallurgy, 1982. - 192 p.

4. Gavrilov V.A., Polyakov I.I., Polyakov O.I. Optimization of the operating conditions of ferroalloy furnaces - M .: Metallurgy, 1996. - 176 p.

5. Recovery mixture for smelting ferroalloys. RF patent for invention No. 2236481, priority of 10/10/2002

6. A multi-component reducing mixture for smelting ferrosilicon. RF patent for the invention No. 2366740, priority from 02.10.2006

Claims (3)

1. A method of smelting ferrosilicon in an ore-thermal furnace, comprising continuously loading a mixture of a carbon with a reducing mixture into the furnace bath and its electrothermal melting, characterized in that the carbon reducing mixture contains coke nut and fossil coal in an amount of 50% carbon, and melting is carried out under conditions the optimal ratio of the parameters of the electric mode of operation - reactive and active phase resistance, impedance and apparent phase power, phase voltage and current with low sides of the transformer, and the geometrical parameters of the furnace - the inner diameter of the bath and its depth, the diameter and length of the self-sintering electrode, the diameter of the decay of the electrodes, which are calculated according to the following relationships:
- the inner diameter of the bath is determined by the optimal density of active power in the cross section of the bath (p _in = 510 kW / m ² ) with a minimum specific energy consumption:

where d _in - the inner diameter of the bath, m,
P is the active power of the furnace, kW;
- the diameter of the decay of the electrodes is determined based on the optimal value of the specific power in the cross section of the diameter of the decay (p _p = 2465 kW / m ² ) with a minimum specific energy consumption:

where d _p is the diameter of the decay of the electrodes, m,
P is the active power of the furnace, kW;
- determine the reactance of the phase
X _f = 0,0486 · R ^0,3 ,
where P is the active power of the furnace, kW,
X _f - reactance of the phase, mOhm;
- determine the optimal ratio of the phase resistance (R _f ) to reactance (X _f ):
R _F / _F X = 1.334,
- phase impedance (Z _f ):
Z _f = 1,667 · x _f
Cosφ = 0.8,
- total phase power:

, MBA,
- the diameter of the self-sintering electrode, depending on the total phase power:

where S _f - full phase power, MVA,
X _f - reactance of the phase, mOhm;
- phase voltage on the low side of the transformer:
U _f = 1.2912 · (S _f · X _f ) ^0.5 ,
where S _f - full phase power, kVA,
U _f - phase voltage of the transformer from the low side, V;
- current strength from the low side of the transformer:

where I is the current strength from the low side, kA;
- the length of the self-sintering electrode (L) and the depth of the bath (H), which corresponds to the length of the electrode:
L = R · π · d _e ^2/4 · ρ = 1,0205 · d _e ² · 10 ^-4 / ρ,
where R is the electrical resistance of the electrode, Ohm,
ρ is the electrical resistivity of the coked portion of the electrode, Ohm · mm ² / m,
L is the length of the electrode, m,

- the cross-sectional area of the electrode, mm ² ,
d _e - the diameter of the self-sintering electrode, mm 2. The method according to claim 1, characterized in that the verification calculation of the diameter of the self-sintering electrode is carried out according to the permissible current density according to the equation:

where I is the current strength in the electrode, A;
d _e - the diameter of the self-sintering electrode, cm;
j is the current density in the electrode, A / cm ² . 3. The method according to claim 1, characterized in that the main parameter for controlling the electric mode of a particular type of charge is the total phase resistance on the low side of the transformer, the value of which is maintained by an automatic process control system (ACS TP) of an ore-thermal furnace.

Images