CHARGE FOR MANUFACTURING FERROSILICON

Abstract

 The present invention relates to metallurgy, manufacturing ferroalloys, in particular, to manufacturing ferrosilicon. The invention describes the charge composition for manufacturing ferrosilicon, which includes quartzite, a carbonaceous reducing agent and the ferruginous material, the ferruginous material being the pyrite cinder pellets with the following ratio of components, wt%: the quartzite - 34-50, the carbonaceous reducing agent - 30-34, the pyrite cinder pellets - the rest. The shavings of carbonaceous steels as a component of the charge are absent. At the same time, the carbonaceous reducing agent contains in wt%: the nut coke - 40-67 and the wood wastes -33-60, the wood wastes being the pellets or the chips. At the same time, the pellets contain the pyrite cinder and the liquid glass as a binder with the following ratio of components, wt.%: the pyrite cinder - 85-93, the liquid glass - 7-15, on a dry basis. The technical result is in expanding the charge compositions range, using the cheap and non-scarce raw materials and improving the operating performance of a furnace device by using in the process of the ferrosilicon manufacture the charge composition having low electrical conductivity, which leads to an increase in silica recovery, while increasing the charge filter layer and to a decrease in the formation of the non-technological slag and, as a result, to a possibility of the furnace transformer operation at a higher voltage level, which increases the electrical efficiency of the furnace device.

Description

TECHNICAL FIELD

[0001] The present invention relates to metallurgy, manufacturing ferroalloys, in particular, to manufacturing ferrosilicon.

Prior art

[0002] Ferrosilicon with the silicon content of 18-95 % is smelted in ferroalloy furnaces. The ore constituent of charge is quartzites containing more than 95% SiO₂ and a small amount of alumina (Al₂O₃). Quartzite is crushed and washed from clay. Metallurgical fine coke is used as a reducing agent. The reducing agent basic requirements:

• a low ash content;
• high electrical resistance;
• a low volatile content;
• the strength of the pieces when heated.

[0003] To prepare the desired concentration of silicon in an alloy, the crushed shavings of carbonaceous steels are introduced into charge. In the presence of iron, the progress of the process is facilitated. Silicon is reduced with carbon according to the reaction: SiO₂ + 2C = Si + 2CO.

[0004] With an excess of the reducing agent, silicon carbide is also formed: SiO₂ + 3C = SiC + 2CO.

[0005] The presence of silicon carbide is undesirable, since due to its refractory quality, the lower part of the furnace is cluttering up and its efficiency is decreased. In the presence of iron, silicon carbide is destroyed by free silica (SiO₂) according to the reactions:

        2SiC + SiO₂ = 3Si + 2CO Si + Fe = FeSi.

[0006] The more iron is in charge, the lower the temperature is at which ferrosilicon is prepared.

[0007] In the course of smelting, which is carried out continuously, electrodes are immersed deeply into charge. When loading charge materials, they try to create and maintain the charge in the form of cones around the electrodes. The purpose of the charge cones is to make it difficult for the gases that are formed in a reaction zone to escape, and to decrease heat losses. The wider the charge cone is, the larger the furnace active zone is, the better the charge settles down, the more stable the furnace operation is.

[0008] In the zone of arcs in the charge, a cavity at a very high temperature is formed. The walls of this cavity are being melted off continuously, silicon is being reduced and dissolved in liquid iron thus forming a ferrosilicon alloy. The alloy is lowering into the reaction zone.

[0009] During the normal furnace operation, the electrodes are lowering slowly, as soon as they are burnt out, and the charge is settling down evenly around the electrodes. The smelted ferrosilicon is run into a ladle 12-15 times per day and poured.

[0010] From application for an invention RU 96113642 published on 20.10.1997, the charge for smelting ferrosilicon is known that contains quartzite, pitch coke, wood and metal wastes, which is characterized in that it contains additionally metallurgical coke, which is used in the form of a mixture with the pitch one, at the following ratio of components, wt%: the wood wastes - 4-50, the mixture of the pitch and metallurgical coke - 10-30, the metal wastes - 5-20, the quartzite - the rest, the metallurgical coke proportion being 5-50% of the total mass of the coke mixture. At the same time, Banichi quartzite is used as the quartzite. At the same time, the chips with a size of not more than 50 mm are used as the wood wastes. At the same time, the shavings of 14 A grade and the transformer steel scraps with a size of not more than 42 mm are used as the metal wastes.

[0011] From patent RU 2094518, published on 27.10.1997, an invention is known that relates to ferrous metallurgy, namely, to charges for manufacturing ferrosilicon alloys. The charge contains quartzite, wood and metal wastes, as well as metallurgical coke in the form of a mixture with the pitch one, at the following ratio of components, wt%: the wood wastes - 4-50, the mixture of the pitch and metallurgical coke - 10-30, the metal wastes - 5-20, the quartzite - the rest, the metallurgical coke proportion being 5-50% of the total mass of the coke mixture.

[0012] From patent RU 2106423, published on 10.03.1998, an invention is known that relates to ferrous metallurgy, namely, to charges for manufacturing ferrosilicon alloys. The charge for smelting ferrosilicon contains quartzite, coke, metal wastes and the pellets of the spent contact mass of the chemical manufacture at the following ratio of components, wt%: the coke - 10-40, the metal wastes - 6-30, the pellets - 0,3-20, the quartzite - the rest.

[0013] From author's certificate SU 618437, published on 05.08.1978, the charge for smelting ferrosilicon is known that contains quartzite, a carbonaceous reducing agent and iron shavings, which is characterized in that for the purpose of decreasing aluminum in the alloy, it contains additionally pyrite at the following ratio of components, wt.%: the quartzite - 40-70; the carbonaceous reducing agent - 15-45; the pyrite - 2-40; the iron shavings - the rest.

[0014] From author's certificate SU 765389, published on 23.02.1983, the charge for manufacturing low-silicon ferrosilicon is known that includes a ferruginous material and coke, which is characterized in that for the purpose of increasing manganese in the alloy, decreasing the release of graphite spill, excluding the use of scarce iron shavings, the charge contains additionally limestone and poor ferromanganese ore, and ferruginous quartzite as the ferruginous material at the following ratio of components, wt%: the ferruginous quartzite - 44-58; the poor ferromanganese ore - 19-20; the limestone - 6-9.

[0015] From author's certificate SU 998558, published on 23.02.1983, the charge for preparing ferrosilicon is known that includes a carbonaceous reducing agent, a metal additive, and quartzite, which is characterized in that for the purpose of increasing the silicon reduction degree and increasing the furnace efficiency, it contains additionally silicate slag and quartzite barite at the following ratio of components, wt%: the carbonaceous reducing agent - 20-35; the metal additive - 1-40; the silicate slag - 1-10; the quartzite barite - 0.5-10; the quartzite - the rest.

[0016] From author's certificate SU 998567, published on 23.02.1983, the charge for smelting low-silicon ferrosilicon is known that includes quartzite, iron shavings, coke, which is characterized in that for the purpose of decreasing its electrical conductivity on the furnace top and decreasing the silicon losses, it contains additionally carbonate manganese ore at the following ratio of components, wt%: the quartzite - 28-32; the iron shavings - 40-47,5; the carbonate manganese ore - 7-12; the coke - 16.5-18.

[0017] From author's certificate SU 1565913, published on 23.05.1990, the charge for smelting ferrosilicon is known that contains quartzite, fine coke and iron shavings, which is characterized in that for the purpose of increasing the mechanical strength and deoxidizing capacity of the resulting alloy and decreasing its smelting point, it contains additionally boron-bearing briquettes at the following ratio of components, wt.%: the quartzite - 20-58; the fine coke - 10-34; the iron shavings - 5-50; the boron-bearing briquettes - 3-20, while the boron-bearing briquettes have the following composition, wt%: the datolite concentrate - 63-70; the fine coke riddlings - 25-34; the sulfite-alcohol liquor- 3-5.

[0018] From patent RU 2109836, published on 27.04.1998, an invention is known that relates to metallurgy, more specifically to manufacturing ferroalloys, in particular, to preparing ferrosilicon. The essence of the invention is in the fact that the charge for preparing ferrosilicon contains additionally a mixture of fluxed iron-ore pellets and iron scale in the ratio of 1 : (1-3) at the following ratio of components, wt%: the quartzite - 35-55; the carbonaceous reducing agent - 20-30; the mixture of the fluxed iron ore pellets and the iron scale - 10-30; the steel shavings - the rest. When using the mixture of the pellets and scale in the charge composition for smelting ferrosilicon, the silicon escaping with waste gases is decreasing. In addition, an increase in the depth of the electrodes' immersion into the charge is noted, which allows exercising smelting at higher voltage on a low side of a transformer, as well as exercising smelting without using expensive semi-coke.

[0019] Thus, various charge compositions for smelting ferrosilicon are known from the prior art. However, the disadvantages of the prior art are using scarce steel shavings in the charge composition.

[0020] Due to the manufacture cuts at machine building plants, there is currently a significant lack of raw materials for a sale of charge.

[0021] In addition, when using steel shavings, the electrical conductivity of the charge increases, which leads to a decrease in the depth of the electrodes' immersion into the charge or a need for increasing the amount of fine coke in the charge composition. Due to this fact, the losses of silicon monoxide together with the waste gases are increasing and a gas operating regime of closed furnaces is deteriorating. This circumstance has an especial impact on the operation of the furnaces having a low arrangement of an arch, since a space under the arc is becoming clogged.

[0022] The closest solution to the claimed invention is the charge composition disclosed in patent RU 2109836.

[0023] Thus, as a prototype, the charge composition disclosed in patent RU 2109836 is adopted, where the charge contains quartzite, a carbonaceous reducing agent (nut coke), steel shavings and additionally a mixture of fluxed pellets and iron scale in the ratio of 1 : (1-3) at the following ratio of components, wt%: the quartzite - 35-55, the carbonaceous reducing agent - 20-30, the mixture of the fluxed iron ore pellets and the iron scale in the ratio of 1 : (1-3) - 10-30, the steel shavings - the rest.

[0024] The prototype significant disadvantage is the presence in the charge composition of the scarce and expensive steel shavings of grade 14 A GOST 2787-75 "Ferrous Secondary Metals" and the iron scale, which is prone to caking and freezing down in winter conditions due to the presence of moisture, which makes its transporting and loading-unloading difficult, including on the charge-feeding conveyor lines of the furnaces.

[0025] The said disadvantages of the solution represented in the prototype are remedied by the further development of the qualitative and quantitative charge composition for manufacturing ferrosilicon.

DISCLOSURE OF THE INVENTION

[0026] According to the present invention, the charge for manufacturing ferrosilicon does not contain the scarce metal shavings from carbonaceous steels as a ferruginous component, but it contains the pellets prepared from the pyrite cinder (technogenic wastes) having the exemplary composition given in Table 1 and liquid glass as a binder.

Table 1

Pyrite cinder composition
Component	Content, wt%
CaO	0.26
CaCO3	1.18
CaF2	1.12
MgO	0.91
SiO2	15.7
Al2O3	2.55
FeO	5.9
Fe2O3	70.9
S, total	1.36
As	0.12
Total:	100%

[0027] The essence of the invention is in that the pellets prepared from a mixture of pyrite cinder and liquid glass form a porous structure, which accelerates the processes of an indirect reduction (with the help of CO) of the iron of the pellets by the components of a ferroalloy gas (these processes are developed in the upper horizons of the furnace):

Fe₂O₃ + 3CO = 2Fe + 3CO₂

Fe₂O₃ + 3H₂ = 2Fe + 3H₂O

Fe₂O₃ + 3SiO (gas) = 2Fe + 3SiO₂ (solid)

and prevents the formation of iron silicates that create disturbances in the normal operation of the ferroalloy furnace (this process occurs in the lower horizons of the furnace):

        Fe₂O₃ + SiO₂ + C = Fe₂SiO₄ (slag) + CO,

that is, the progress of this negative reaction is difficult due to the lack of iron oxides in the lower horizons of the furnace.

[0028] This circumstance allows replacing the steel shavings completely, while using a non-scarce material - pyrite cinder, which is a sulfuric acid manufacture waste.

[0029] In view of the fact that these manufacturing wastes create a negative impact on the environment, the implementation of the claimed invention will alloy solving the problem of disposal of the harmful manufacturing waste.

[0030] Thus, the task of the present invention is to remedy the disadvantages of the prior art, to develop the charge composition for manufacturing ferrosilicon, which is not inferior in quality, but which allows replacing without the losses for the manufacture scarce steel shavings with the low-quality waste from the sulfuric acid manufacture, while solving a double task, reducing the expenses for the raw materials and disposing the technogenic product.

[0031] The technical result is in expanding the charge compositions range, using the cheap and non-scarce raw materials and improving the operating performance of a furnace device by using in the process of the ferrosilicon manufacture the charge composition having low electrical conductivity, which leads to an increase in silica recovery, while increasing the charge filter layer and to a decrease in the formation of the non-technological slag and, as a result, to a possibility of the furnace transformer operation at a higher voltage level, which increases the electrical efficiency of the furnace device.

[0032] The said technical result is achieved with the help of the charge composition for manufacturing ferrosilicon, which includes quartzite, a carbonaceous reducing agent and a ferruginous material, while the ferruginous material is pyrite cinder pellets at the following ratio of components, wt%: the quartzite - 34-50, the carbonaceous reducing agent - 30-34, the pyrite cinder pellets - the rest.

[0033] The carbonaceous reducing agent contains the nut coke - 40-67 wt% and the wood wastes - 33-60% wt%, while the wood wastes are pellets or chips.

[0034] The pellets contain pyrite cinder and liquid glass as a binder in the amount of 7-15 wt% on a dry basis.

[0035] The above and other tasks, peculiarities, advantages, as well as the technical significance of this invention will be more clear from the following detailed description of the invention with the references to the accompanying figures.

BRIEF DESCRIPTION OF THE FIGURES

[0036] 

Figure 1 shows an electronic image of the pyrite cinder taken by a microscope at 320 times magnification.

Figure 2 shows an electronic image of the ferrosilicon taken by a microscope at 320 times magnification.

Figure 3 shows a semi-industrial furnace being the ore reduction electric furnace with three graphitized electrodes and a graphite lining (RKO 0.2).

Figure 4 shows an X-ray image of the ferrosilicon, where an experimental line is red, a calculated line is blue, and the difference between the experimental and calculated lines of the X-ray images is pink.

Figure 5 shows an X-ray image of the ferrosilicon, where the experimental line (red) is indicated with the assignment of the peaks to the phases.

Figure 6 shows an electronic image of the phase ferrosilicon composition taken by a microscope.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0037] From the conducted laboratory studies on smelting the ferrosilicon, where the metal shavings were replaced completely with the pyrite cinder pellets, it can be concluded that this replacement method is quite possible. However, in order to prevent an increase in specific energy consumption and carbon for reducing iron oxides and heating slag, it is necessary to select both an electrical operating regime of the furnace and a percentage content of the charge components.

[0038] The studies of the claimed charge composition according to the present invention were conducted with the use of the laboratory furnace and the semi-industrial furnace.

[0039] Figure 1 shows an electronic image of the pyrite cinder taken by a microscope. The average composition is Spectrum 1.

[0040] Table 2 below shows an analysis of the composition of the pyrite cinder of the spectra shown in Figure 1.

Table 2

Spectrum	O	Na	Mg	Al	Si	S	Ca	Fe	Zn	Ba
Spectrum 1	35	1.0	1.0	2.7	10.2	1.9	0.9	44.7	0.6	1.4
Spectrum 2	45	2.1	7.1	16.6	18.8	0.0	0.1	8.3	0.3	1.8
Spectrum 3	19	0.1	0.1	0.4	0.6	27.5	0.2	51.6	0.2	0.0

[0041] All results are in wt%.

[0042] Spectrum 1 is removed from the highlighted area, the rest are pointwise.

Na2O	MgO	Al2O3	SiO2	CaO	FeO	Fe2O3	BaO
1.4%	2%	5%	23%	1%	2.7%	62.9%	1.6%

[0043] In order to confirm the claimed technical result, the microscopic and X-ray phase analyses were conducted. The ferrosilicon microphotographs (see Figure 6) obtained from the charge using the pyrite cinder show a low slag content.

[0044] Figure 2 shows an electronic image of the ferrosilicon taken by a microscope. The average composition is Spectrum 5.

[0045] Below, there is an analysis of the ferrosilicon composition shown in Figure 2.

[0046] From the analysis of the spectra shown in Table 3, it can be seen that the silicon is being reduced, and with the small amount of loss.

Table 3

Spectrum	Si	Fe	Total:
Spectrum 1	32.7	67.3	100.0
Spectrum 2	37.4	62.6	100.0
Spectrum 3	18.1	81.9	100.0
Spectrum 4	18.6	81.4	100.0
Spectrum 5	30	70	100.0 average

[0047] Figure 4 shows an X-ray image of the ferrosilicon, where the experimental line is red, the calculated line is blue, and the difference between the experimental and calculated lines of the X-ray images is pink. Figure 5 shows an X-ray image of the ferrosilicon, where the experimental line (red) is indicated with the assignment of the peaks to the phases. These X-ray images also confirm obtaining the ferrosilicon at the complete replacement of a ferruginous material in the charge with the pyrite cinder pellets.

[0048] Thus, after the studies with the use of the laboratory furnace showed a possibility of using the pyrite cinder in the charge composition, the studies with the use of the semi-industrial furnace RKO 0.2 were conducted (see Figure 3).

[0049] The studies of the said charge with the use of the pyrite cinder were conducted with the use of the experimental ore reduction electric furnace with three graphitized electrodes and the graphite lining. The nominal power of the transformer of the furnace device was 160 KVA at a voltage on the electrodes of 48V.

[0050] During conducting the studies, the charges that provide obtaining the ferrosilicon of FS-45, FS-65 grades were used:
Embodiment 1. A typical portion ("charge batch") of the charge for smelting the ferrosilicon of the following composition:

Component	Fraction	Content in kg	Content in wt%
Quartzite	20-40 mm	15	34
Nut coke	10-25 mm	7	16
Wood pellets or chips	-	8	18
Pyrite cinder pellets	5-30 mm	14	32
Total:		44	100

Embodiment 2.

Component	Fraction	Content in kg	Content in wt%
Quartzite	20-40 mm	15	50
Nut coke	10-25 mm	4	13
Wood pellets or chips	-	6	20
Pyrite cinder pellets	5-30 mm	5	17
Total:		30	100

Embodiment 3.

Component	Fraction	Content in kg	Content in wt%
Quartzite	20-40 mm	15	36
Nut coke	10-25 mm	8	20
Wood pellets or chips	-	4	10
Pyrite cinder pellets	5-30 mm	14	34
Total:		41	100

[0051] The embodiments of the charge compositions 1-3 confirm the achievement of the technical result in the specified ranges of the content of the components, namely: the quartzite - 34-50 wt%, the carbonaceous reducing agent (the nut coke and the wood wastes) - 30-34 wt%, the pyrite cinder pellets - the rest.

[0052] The method for manufacturing the charge.

[0053] The charge mixture was prepared by loading in layers into a "flexible disposable container" (FDC) having a bottom unloading gate, placing in layers at first the light-weight components of the charge (the nut coke, the pellets), then the heavy-weight ones (the pyrite cinder pellets and the quartzite) within one "charge batch." In total, 4 charge batches were placed per FDC. The FDC was unloaded to a working site through the bottom unloading gate, thereby exercising the charge components mixing. This charge was then fed into the furnace manually with shovels. In the furnace, the charge cones were maintained around the electrodes to block the radiation of the burning arcs. If necessary, the fragments of the sintered charge were sewn with wood battens and pushed into the hot zones of the furnace closer to the electrodes.

[0054] The taphole of the furnace was pierced every 2-3 hours and the melt was released directly into a flat casting-form lined up with the fireclay bricks covered with a nonstick sand mixture. The amount of the slag coming out of the furnace was negligible, and the majority of the surface of the ferrosilicon ingot was free from non-metallic inclusions.

[0055] The silicon content in the obtained ferrosilicon varied from 41 to 64%, depending on the selected composition of the particular charge formulation.

[0056] An example of the ferrosilicon sample phase composition, wt%:

Formula	%
Si	6
FeSi2	94

[0057] Figure 6 shows an electronic image of the phase ferrosilicon composition taken by a microscope.

[0058] According to Figure 6, the chemical composition of the ferrosilicon confirms its phase composition. From the represented electronic images, it can be seen that a fairly homogeneous phase of FeSi₂ is obtained. The average impurity content in wt% is coherent with the X-ray images shown in figures 4 and 5.

[0059] The typical composition of the ferrosilicon impurities is shown in Table 4 below:

Table 4

Component	Content in wt%
Al	0.25
C	0.017
S	0.026
P	0.023
Mn	0.11
Cr	0.069

[0060] A weak sensitivity of the electrode position in the furnace to the level of the charge loading was noted: before the start of smelting, the electrode position was fixed according to the gear batten of a lifting appliance drive. An upward manoeuvre of the electrode was not more than 100 mm, while the thickness of the charge loading was 400 mm. At the same time, the transformer working tap was the same (48V between the electrodes), and the current of the electrode corresponded to a nominal value (1900±50A). This means that the electrical conductivity of the charge was negligible. The level of the charge loading was determined by the forecast of the integrity of the electrode body within the duration of one smelting.

[0061] Thus, the alloy corresponding to the ferrosilicon was obtained.

[0062] In the prototype, it was not possible to replace completely the expensive and scarce shavings due to the fact that, in the process of smelting without using the shavings, the large amount of the fayalitic slag was formed and the furnace operation was disturbed. In the obtained charge according to the present invention, it was possible to replace completely the expensive and scarce shavings with the sulfuric acid manufacture waste that is practically free-of-charge and available in huge amounts, namely, with the pyrite cinders, and to obtain the process with the slag low yield, to make it cost-effective and continuous.

[0063] At the same time, in addition to the economic effect gained from the use of the charge using the pyrite cinders, the improvement of the operating performance of the furnace device is achieved due to the use in the process of the ferrosilicon manufacture the charge composition having low electrical conductivity, which leads to an increase in the silica recovery, while increasing the charge filter layer and, as a result, to a possibility of the furnace transformer operation at a higher voltage level, which increases the electrical efficiency of the furnace device.

Claims

1. The charge for manufacturing ferrosilicon includes quartzite, a carbonaceous reducing agent and a ferruginous material, wherein the ferruginous material is pyrite cinder pellets with the following ratio of components, wt%: the quartzite - 34-50, the carbonaceous reducing agent - 30-34, the pyrite cinder pellets - the rest.

2. The charge according to claim 1, wherein the carbonaceous reducing agent contains in wt%: the nut coke - 40-67 and the wood wastes -33-60, the wood wastes being the pellets or the chips.

3. The charge according to claims 1-2, wherein the pellets contain the pyrite cinders and the liquid glass as a binder with the following ratio of components, wt.%: the pyrite cinders - 85-93, the liquid glass - 7-15, on a dry basis.

Drawing