CA1217032A - Method of producing silicon - Google Patents
Method of producing siliconInfo
- Publication number
- CA1217032A CA1217032A CA000468603A CA468603A CA1217032A CA 1217032 A CA1217032 A CA 1217032A CA 000468603 A CA000468603 A CA 000468603A CA 468603 A CA468603 A CA 468603A CA 1217032 A CA1217032 A CA 1217032A
- Authority
- CA
- Canada
- Prior art keywords
- briquets
- silicon
- furnace
- quartz
- method defined
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 229910052710 silicon Inorganic materials 0.000 title claims abstract description 35
- 239000010703 silicon Substances 0.000 title claims abstract description 35
- 238000000034 method Methods 0.000 title claims abstract description 22
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims abstract description 76
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 56
- 235000012239 silicon dioxide Nutrition 0.000 claims abstract description 51
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 31
- 239000010453 quartz Substances 0.000 claims abstract description 31
- HBMJWWWQQXIZIP-UHFFFAOYSA-N silicon carbide Chemical compound [Si+]#[C-] HBMJWWWQQXIZIP-UHFFFAOYSA-N 0.000 claims abstract description 23
- 229910010271 silicon carbide Inorganic materials 0.000 claims abstract description 23
- 239000000377 silicon dioxide Substances 0.000 claims abstract description 20
- 239000003638 chemical reducing agent Substances 0.000 claims abstract description 12
- 239000000571 coke Substances 0.000 claims abstract description 7
- 238000006243 chemical reaction Methods 0.000 claims description 24
- 229910052681 coesite Inorganic materials 0.000 claims description 14
- 229910052906 cristobalite Inorganic materials 0.000 claims description 14
- 229910052682 stishovite Inorganic materials 0.000 claims description 14
- 229910052905 tridymite Inorganic materials 0.000 claims description 14
- 238000004519 manufacturing process Methods 0.000 claims description 7
- 239000003245 coal Substances 0.000 claims description 6
- 239000002006 petroleum coke Substances 0.000 claims description 5
- RHZUVFJBSILHOK-UHFFFAOYSA-N anthracen-1-ylmethanolate Chemical compound C1=CC=C2C=C3C(C[O-])=CC=CC3=CC2=C1 RHZUVFJBSILHOK-UHFFFAOYSA-N 0.000 claims description 2
- 239000003830 anthracite Substances 0.000 claims description 2
- 239000003575 carbonaceous material Substances 0.000 claims description 2
- 229910002804 graphite Inorganic materials 0.000 claims description 2
- 239000010439 graphite Substances 0.000 claims description 2
- 239000003077 lignite Substances 0.000 claims description 2
- 229910052751 metal Inorganic materials 0.000 claims description 2
- 239000002184 metal Substances 0.000 claims description 2
- 229910021471 metal-silicon alloy Inorganic materials 0.000 claims description 2
- 229910045601 alloy Inorganic materials 0.000 claims 1
- 239000000956 alloy Substances 0.000 claims 1
- 239000011335 coal coke Substances 0.000 claims 1
- 230000001131 transforming effect Effects 0.000 claims 1
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 29
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 5
- 229960001866 silicon dioxide Drugs 0.000 description 5
- 229940124024 weight reducing agent Drugs 0.000 description 5
- 238000005265 energy consumption Methods 0.000 description 3
- 239000007788 liquid Substances 0.000 description 3
- 239000000463 material Substances 0.000 description 3
- 239000002994 raw material Substances 0.000 description 3
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 2
- 229910000519 Ferrosilicon Inorganic materials 0.000 description 2
- 239000006004 Quartz sand Substances 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 229910002091 carbon monoxide Inorganic materials 0.000 description 2
- 239000003610 charcoal Substances 0.000 description 2
- 238000004939 coking Methods 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 239000007789 gas Substances 0.000 description 2
- 229910052742 iron Inorganic materials 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 239000003415 peat Substances 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 229910000676 Si alloy Inorganic materials 0.000 description 1
- 238000005299 abrasion Methods 0.000 description 1
- 230000004913 activation Effects 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 239000011230 binding agent Substances 0.000 description 1
- 238000004364 calculation method Methods 0.000 description 1
- 239000000969 carrier Substances 0.000 description 1
- 239000007795 chemical reaction product Substances 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 238000004140 cleaning Methods 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000002349 favourable effect Effects 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 239000011044 quartzite Substances 0.000 description 1
- 238000010079 rubber tapping Methods 0.000 description 1
- 239000004576 sand Substances 0.000 description 1
- 238000012216 screening Methods 0.000 description 1
- 239000007858 starting material Substances 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C1/00—Making non-ferrous alloys
- C22C1/02—Making non-ferrous alloys by melting
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B33/00—Silicon; Compounds thereof
- C01B33/02—Silicon
- C01B33/021—Preparation
- C01B33/023—Preparation by reduction of silica or free silica-containing material
- C01B33/025—Preparation by reduction of silica or free silica-containing material with carbon or a solid carbonaceous material, i.e. carbo-thermal process
Landscapes
- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Inorganic Chemistry (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Mechanical Engineering (AREA)
- Metallurgy (AREA)
- Silicon Compounds (AREA)
- Carbon And Carbon Compounds (AREA)
- Crystals, And After-Treatments Of Crystals (AREA)
- Manufacture And Refinement Of Metals (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A method of producing silicon in a low-shaft electrical furnace in which reductant briquets having at least a 50% excess of carbon over that required to form silicon carbide from silicon dioxide in the briquets are provided at the upper portion of the furnace so that this excess carbon is transformed into activated carbon with a coke structure and participates in the subsequent reduction of molten quartz at a lower portion of this furnace.
ef-W
A method of producing silicon in a low-shaft electrical furnace in which reductant briquets having at least a 50% excess of carbon over that required to form silicon carbide from silicon dioxide in the briquets are provided at the upper portion of the furnace so that this excess carbon is transformed into activated carbon with a coke structure and participates in the subsequent reduction of molten quartz at a lower portion of this furnace.
ef-W
Description
7~3~
METHOD OF PRODUCING SILICON
SPECIFICATION
Field of the Invention My present invention relates to a method of producing silicon from quartz and, more particularly, to a two-stage method of producing silicon from the reaction of qusrtz with carbon.
Backæround of the Invention Reference may be had, with respect to the production of silicon, to my U.S. Patents 4,364,974, 4,366,137 and 4,389,493 and to the prior German applications and other patent documents referred to therein.
It is known from these publications and others that it is possible to carry out a reaction between the silicon containing raw material, i.e. quartz and briquets of a reducing agent consistin~ predominantly of carbon at &
suitable temperature to ultimately reduce the quartz to silicon.
German Patent l9 15 905 and German Patent 30 32 720 describe briquets which are produced for this purpose.
The process is carried out in an electrical low-shaft furnace to which the quartz is supplied in granular or particulate form together with br;quets of the silicon-dioxide containing carbonaceous material so that the overall reaction proceeds in accordance with the equation Si02 + 3C = SiC + 2CO.
This reaction produces silicon ca~bide as a result of an excess of carbon and is carried out at an upper portion of the furnace at a temperature below 1600 C.
At a lower part of the furnace at a temperature above 1600 C and preferably in the range of 1800 to 2000 C, liquid quartz is reduced with the silicon carbide thus formed in accordance with the reaction scheme:
Si02 + 2SiC = 3Si + 2CO. The carbon monoxide gases are discharged from the furnace and molten silicon can be tapped from the furnace.
The briquets of the reducing medium are generally produced by hot briquetting and the raw material quartz which is used can be any of the silicon dioxide materials which have commonly been used as a source of silicon especially quartzite and quartz sand. For the production of the reducing agent briquets, quartz sand is ~enerally employed.
rj~
-- 1 ~
3~
The term "hot briquetting" as used herein is intended to refer to binderless briquetting in which the starting materials are heated to a temperature of ~30 C and 540 C and are pressed to form the briquets as in German Patent 19 15 905. ~owever, when briquets of a reducing aeent are described in this applicstion, it will be understood that they can be fabricated in other ways as well.
In the system of German Patent 30 32 720, the reduction-a~ent briquets which are used have only a slight stoichiometric excess of carbon with respect to the reaction SiO2 + 3C = SiC t 2CO.
Indeed, one of the goals of this system is to ma~imize the completeness of the reaction without leavin~ si~nificant carbon excess so that the subsequent reduction of the quartz can be effected in the liquid state with only SiC a5 the reductant.
Any carbon excess which is present is provided to compensate for the loss of carbon by the reaction with o~ygen from sources other than the SiO2.
Such carbon is of course lost insofar as the reduction of SiO2 is concerned.
The reducing briquets, after the initial stage, thus consist practically entirely of silicon carbide snd do not have any significant content of free carbon.
~hile the method tescribed in this last-mentioned patent and in my above-mentioned U.S. patents have generally been satisfactory, they can still be improved with respect to the yield of silicon and the energy efficiency, i.e. the energy consumption per unit of silicon produced.
Ob.iects of the Invention It is, therefore, ths principal object of the present invention to provide an improved method of producing silicon in a low-shaft electrical furnace in accordance with the principles described whereby the energy consumption per unit of silicon produced is markedly increased.
Another object of my invention is to provide a process of the class described but with an increased yield of silicon.
Here described is a process for producing silicon in a low-shaft electrical furnace to which quartz and reducing-agent briquets are supplied and which effects an initial reduction at an upper portion of the furnace at a temperature below 1600 C to transform silicon dio~ide in these briquets to silicon carbide which forms a reducing agent for the quartz at a lower high 3~
temperature region of the furnace, operating at 1800 C to 2000 C and in which the molten quartz reacts ~ith the silicon carbide to form molten silicon.
The reducin~-a~ent briquets which nre uged have a si~nificant excess of carbon, i.e. an e~cess over stoichiometric requirements of more than 50% by weight above that required for the reaction SiO2 ~ 3C = SiC + 2CO.
Furthermore, in this upper portion of the electrical furnace operatin~ at a temperature below 1600 C, the briquets are transformed at least in part to an activated carbon by a cokin~ operation so that the e~cess carbon of the briquets assumes a cokelike structure which remains until the briquets enter the liquid quartz phase so that the quartz in the lower part of the furnace is reduced not only by the silicon carbide which is quantitatively produced in the briquets, but also by the coke-structured activated carbon of the briquets.
Preferably, the briquets are provided so that the e~cess of carbon is less than 90% by wei~ht and generally is about 80% by wei~ht.
I have found that optimal results can be obtained when the total e~cess carbon of the briquets is sufficient by itself to reduce at least 50~ by weight of the quartz in the aforementioned lower portion of the low-shaft electrical furnace. This may be accomplished by properly proportioning the various components of the burden or char~e of the ~urnace.
Obviously I need not utilize exclusively the high~carbon e~cess briquets described and these briquets can be partly combined with briquets containing lesser amounts of carbon provided there is a substantial proportion of the sctivated carbon. In addition, I can make up part of the carbon requirements by the use of a classical charge or burden which can contain, for e~ample, 3 metric tons of quartz, 0.4 metric ton of charcoal, 0.4 metric ton of peat coke, 0.3 metric ton of petroleum coke and 0.5 metric ton of ash-free coal as long as sufficient activated carbon is provided by the reducin~ briquets described.
As has already been indicated, the manner and means for producing the red~cing briquets is optional and any conventional method of equipment csn be used for this purpose as long as the briquets are stable and can be introduced in the described manner as part of the burden or charge of the low-shaft electrical furnace, together with the quartz raw material.
In a preferred or best mode embodiment of the invention, however, hot briquetting is used and the briquets are of eg~ or pillow shape having a 7(1~
volume of 15 to 60 cm3. The carbon content of the reducing briquets which are to be fabricated by hot briquecting should preferably be predominantly caking coal and can include comparatively inert carbon carriers such as petroleum coke, anthracite, graphite, lignite co~e and pit coal or bituminous coke.
When it is desired to convert the silicon which is for~ed to other end products such as ferrosilicon and silicon-metal alloys of other compositions, suitable metal-containing substances such as iron chips or ~ranulated iron may be added.
The process is based upon my discovery that the activated carbon described above can promote a si~nificantly higher degree of reduction of the silicon dioxide in the lower portion of the furnace beyond that which would be expected merely from the addition of an equivalent amount of carbon as part of the burden and with a substantially reduced energy input.
More particularly in accordance with the invention there is provided, a method for producing silicon in an electrical-shaft furnace comprising the steps of:
(a) introducing into said furnsce reductant briquets containing silicon dioxide and a carbonaceous reducin~ agent together with quartz, said carbonaceous reducing agent being present within said briquets in more than 507~ and less than 90~ by weight excess of that stoichiomet~ically required for the reaction SiO2 + 3C = SiC + 2C0 in said briquets;
(b) reacting at a temperature below about 1600C said briquets at an upper portion of said furnace to transform the sllicon aioxide therein to silicon carbide and produce an activated carbon with a coke structure within said briquet, said briquets having an internal surface of between 20 and 230 m /g:
tc) reacting the silicon carbide thus produced with molten quartz at a lower portion of said furnace at a temperature above 1600C to reduce the quartz to siiicon; and (d) reducing with said activated carbon a further amount of molten quartz in said lower portion of said furnace.
Brief Description of the Drawin~
The above and other objects, features and advantages of the present invention will become more readily apparent from the following description and , ., ~ 4 -< .. , ~
~'7~32 examples, reference being made to the accompanyin~ drawing, the sole FIGURE of which is a diagra~matic vertical section through a low-shaft electrical furnace for carrying out the process embodying the present invention.
Specific ~escri~tion In the drawin~ I have shown a low-shaft electrical furnace 10 which has an upper portion 11 and a lower portion 12 located above the hearth 13 from which the molten silicon can be tspped through a tapping hole 14.
The burden or charge is introduced at 15 and can consist of silicon dioxide containing reductant briquets 16 which are formed by hot brlquetting as previously dsscribed with a minimum of 50% excess oP carbon above the stoichiometric quantity required for the conversion of all of the SiO2 of these briquets into silicon carbide.
The temperature at the upper portion 11 of the furnace is above the coking temperature of the carbon excess and is also above the temperature required for activation of the reduction of the silicon d~oxide of the briquets to silicon carbide in accordance with the equations presented earlier. The coking ~ases and the carbon monoxide which are formed are discharged at 17.
- 4a -z ~ phir of electrodes 18 extend into the furnace to pro~ide the heat required for meltin~ the quartz which is introduced together with the briquets as part of the burden so that at the lower portion 1~ or high tempernture bosh of the furnace, the silicon carbide from the fully reacted briquets and the e~cess activated carbon thereof can pass into the molten quartz and effect a further reduction. The molten silicon collects at 13 as previously noted and can be tapped from the furnace.
Specific Examples E~ample l For the production of about 600 metric tons of silicon, 1200 metric tons of briquets were produced which were introduced into the electrical low-shaft furnace together with an almost similar amount of lump quartz.
In the first step of the process, the briquets were produced from a mixture consisting of:
30% caking coal, 32% petroleum coke, and 38~ quartz and (99.8% SiO2) by the hot-briquetting process, i.e. the ~oal was used at temperatures of about 500 C as 8 binder. The finished cooled briquets were egamined. They contained 42(~ 0.4~% SiO2 and 52(~ 0.7~ Cfi .
A strength test showed that point pressure crushing strengths of 150 to 200 kg had been obtained, which are accounted for by the imbedding of the inert substances such as petroleum coke and sand in the fused and resolidified coal. Measurement of the internal surface of the briquets showed 0.5 to l.0 m ~g, indicating that no significant reaction surface is present on which heterogeneous reections between gases such as SiO and carbon can take place at high conversion efficiency.
In 8 second step of the process, the briquets were introduced into an electrical low-shaft furnace. Before introduction to the furnace the material arising from abrasion and fracture during transport was separated by screening. These fines amounted to less than 4~. This is a very good result. Indeed, charcoal, peat, and coals are destroyed to a much higher u 7~
degree. Values of more than 10~ are known.
A mi~ture of continuously fed lump quartz and briquets, statistically well distributed by shakin~, was heated in the electrical low-shaft furnace and brou~ht to reaction.
Considering the General reaction of the production of silicon SiO2 ~ 2C = Si + 2C0, one can see from the analysis o~ the briquets that carbon is present in substantial e~cess and that only the further renction with the lump quartz assures complete conversion. Since, however, before the formation of silicon, silicon carbide arises accordinG to the e~uation SiO2 + 3C = SiC + 2C0, there remains the question, whether sufficient carbon is present in the briquets for this reaction. Calculation shows that just less than twice as much carbon (about 80% e~cess) is present as is required for the reaction.
That is a molar ratio of 1 : ~ to 1 : 6. This has been aimed for, to maintain the coke-structures resulting from the hot-briquettin~, even if losses occur by the reaction to silicon carbide.
This theory was tested by use of thermocouples to determine the temperature zone at which the carbide reaction occurs. Samples were taken from the hot material havin~ a temperature of between 1500 and 1600 C, and showed clearly that the briquets still had their oriGinal shape, althou&h the conversion between carbon and silicon already had started or was even complete.
Most of the briquets showed a white surPace, indicatin~ that reaction had here occurred. Of more significance, however, was the measurement of the internal surface of the cooled briquets, which showed a considerably increased internal surface of between 20 and 230 m /g. The briquets were found to consist essentially of SiC and activated carbon with the coke structure.
This leads to a considerable decrease of the SiO2 precipitate in the ~as-cleaning. Closely connected therewith are the enerGy consumption Pnd the silicon yield. The consumption of electrical power in the furnace decreased by about 14%, whereas the silicon yield increased by more than 20%. An unexpected, but important economical advantaGe was the halving of the consumption of the electrodes, which dropped from 128 kg/T. Si to 59 k~/T. Si. The movements of the electrodes were minimized.
~'7~l3q~
Examole 2 In the production of ferrosilicon the situation is more favourable. Here the lo~ses by the formation of SiO are less.
If one proceeds as described in the foregoing e~ample such that the input of lump qusrtz and briquets rcmains in the ratio of 50 to 50, and scrap iron is added so that a 75% silicon alloy results, the advanta~es of the briquets are still clearly apparant, i.e. the consumption of electrisal power decreases by 8~ and the yield of silicon increases by 12~.
9061-~
METHOD OF PRODUCING SILICON
SPECIFICATION
Field of the Invention My present invention relates to a method of producing silicon from quartz and, more particularly, to a two-stage method of producing silicon from the reaction of qusrtz with carbon.
Backæround of the Invention Reference may be had, with respect to the production of silicon, to my U.S. Patents 4,364,974, 4,366,137 and 4,389,493 and to the prior German applications and other patent documents referred to therein.
It is known from these publications and others that it is possible to carry out a reaction between the silicon containing raw material, i.e. quartz and briquets of a reducing agent consistin~ predominantly of carbon at &
suitable temperature to ultimately reduce the quartz to silicon.
German Patent l9 15 905 and German Patent 30 32 720 describe briquets which are produced for this purpose.
The process is carried out in an electrical low-shaft furnace to which the quartz is supplied in granular or particulate form together with br;quets of the silicon-dioxide containing carbonaceous material so that the overall reaction proceeds in accordance with the equation Si02 + 3C = SiC + 2CO.
This reaction produces silicon ca~bide as a result of an excess of carbon and is carried out at an upper portion of the furnace at a temperature below 1600 C.
At a lower part of the furnace at a temperature above 1600 C and preferably in the range of 1800 to 2000 C, liquid quartz is reduced with the silicon carbide thus formed in accordance with the reaction scheme:
Si02 + 2SiC = 3Si + 2CO. The carbon monoxide gases are discharged from the furnace and molten silicon can be tapped from the furnace.
The briquets of the reducing medium are generally produced by hot briquetting and the raw material quartz which is used can be any of the silicon dioxide materials which have commonly been used as a source of silicon especially quartzite and quartz sand. For the production of the reducing agent briquets, quartz sand is ~enerally employed.
rj~
-- 1 ~
3~
The term "hot briquetting" as used herein is intended to refer to binderless briquetting in which the starting materials are heated to a temperature of ~30 C and 540 C and are pressed to form the briquets as in German Patent 19 15 905. ~owever, when briquets of a reducing aeent are described in this applicstion, it will be understood that they can be fabricated in other ways as well.
In the system of German Patent 30 32 720, the reduction-a~ent briquets which are used have only a slight stoichiometric excess of carbon with respect to the reaction SiO2 + 3C = SiC t 2CO.
Indeed, one of the goals of this system is to ma~imize the completeness of the reaction without leavin~ si~nificant carbon excess so that the subsequent reduction of the quartz can be effected in the liquid state with only SiC a5 the reductant.
Any carbon excess which is present is provided to compensate for the loss of carbon by the reaction with o~ygen from sources other than the SiO2.
Such carbon is of course lost insofar as the reduction of SiO2 is concerned.
The reducing briquets, after the initial stage, thus consist practically entirely of silicon carbide snd do not have any significant content of free carbon.
~hile the method tescribed in this last-mentioned patent and in my above-mentioned U.S. patents have generally been satisfactory, they can still be improved with respect to the yield of silicon and the energy efficiency, i.e. the energy consumption per unit of silicon produced.
Ob.iects of the Invention It is, therefore, ths principal object of the present invention to provide an improved method of producing silicon in a low-shaft electrical furnace in accordance with the principles described whereby the energy consumption per unit of silicon produced is markedly increased.
Another object of my invention is to provide a process of the class described but with an increased yield of silicon.
Here described is a process for producing silicon in a low-shaft electrical furnace to which quartz and reducing-agent briquets are supplied and which effects an initial reduction at an upper portion of the furnace at a temperature below 1600 C to transform silicon dio~ide in these briquets to silicon carbide which forms a reducing agent for the quartz at a lower high 3~
temperature region of the furnace, operating at 1800 C to 2000 C and in which the molten quartz reacts ~ith the silicon carbide to form molten silicon.
The reducin~-a~ent briquets which nre uged have a si~nificant excess of carbon, i.e. an e~cess over stoichiometric requirements of more than 50% by weight above that required for the reaction SiO2 ~ 3C = SiC + 2CO.
Furthermore, in this upper portion of the electrical furnace operatin~ at a temperature below 1600 C, the briquets are transformed at least in part to an activated carbon by a cokin~ operation so that the e~cess carbon of the briquets assumes a cokelike structure which remains until the briquets enter the liquid quartz phase so that the quartz in the lower part of the furnace is reduced not only by the silicon carbide which is quantitatively produced in the briquets, but also by the coke-structured activated carbon of the briquets.
Preferably, the briquets are provided so that the e~cess of carbon is less than 90% by wei~ht and generally is about 80% by wei~ht.
I have found that optimal results can be obtained when the total e~cess carbon of the briquets is sufficient by itself to reduce at least 50~ by weight of the quartz in the aforementioned lower portion of the low-shaft electrical furnace. This may be accomplished by properly proportioning the various components of the burden or char~e of the ~urnace.
Obviously I need not utilize exclusively the high~carbon e~cess briquets described and these briquets can be partly combined with briquets containing lesser amounts of carbon provided there is a substantial proportion of the sctivated carbon. In addition, I can make up part of the carbon requirements by the use of a classical charge or burden which can contain, for e~ample, 3 metric tons of quartz, 0.4 metric ton of charcoal, 0.4 metric ton of peat coke, 0.3 metric ton of petroleum coke and 0.5 metric ton of ash-free coal as long as sufficient activated carbon is provided by the reducin~ briquets described.
As has already been indicated, the manner and means for producing the red~cing briquets is optional and any conventional method of equipment csn be used for this purpose as long as the briquets are stable and can be introduced in the described manner as part of the burden or charge of the low-shaft electrical furnace, together with the quartz raw material.
In a preferred or best mode embodiment of the invention, however, hot briquetting is used and the briquets are of eg~ or pillow shape having a 7(1~
volume of 15 to 60 cm3. The carbon content of the reducing briquets which are to be fabricated by hot briquecting should preferably be predominantly caking coal and can include comparatively inert carbon carriers such as petroleum coke, anthracite, graphite, lignite co~e and pit coal or bituminous coke.
When it is desired to convert the silicon which is for~ed to other end products such as ferrosilicon and silicon-metal alloys of other compositions, suitable metal-containing substances such as iron chips or ~ranulated iron may be added.
The process is based upon my discovery that the activated carbon described above can promote a si~nificantly higher degree of reduction of the silicon dioxide in the lower portion of the furnace beyond that which would be expected merely from the addition of an equivalent amount of carbon as part of the burden and with a substantially reduced energy input.
More particularly in accordance with the invention there is provided, a method for producing silicon in an electrical-shaft furnace comprising the steps of:
(a) introducing into said furnsce reductant briquets containing silicon dioxide and a carbonaceous reducin~ agent together with quartz, said carbonaceous reducing agent being present within said briquets in more than 507~ and less than 90~ by weight excess of that stoichiomet~ically required for the reaction SiO2 + 3C = SiC + 2C0 in said briquets;
(b) reacting at a temperature below about 1600C said briquets at an upper portion of said furnace to transform the sllicon aioxide therein to silicon carbide and produce an activated carbon with a coke structure within said briquet, said briquets having an internal surface of between 20 and 230 m /g:
tc) reacting the silicon carbide thus produced with molten quartz at a lower portion of said furnace at a temperature above 1600C to reduce the quartz to siiicon; and (d) reducing with said activated carbon a further amount of molten quartz in said lower portion of said furnace.
Brief Description of the Drawin~
The above and other objects, features and advantages of the present invention will become more readily apparent from the following description and , ., ~ 4 -< .. , ~
~'7~32 examples, reference being made to the accompanyin~ drawing, the sole FIGURE of which is a diagra~matic vertical section through a low-shaft electrical furnace for carrying out the process embodying the present invention.
Specific ~escri~tion In the drawin~ I have shown a low-shaft electrical furnace 10 which has an upper portion 11 and a lower portion 12 located above the hearth 13 from which the molten silicon can be tspped through a tapping hole 14.
The burden or charge is introduced at 15 and can consist of silicon dioxide containing reductant briquets 16 which are formed by hot brlquetting as previously dsscribed with a minimum of 50% excess oP carbon above the stoichiometric quantity required for the conversion of all of the SiO2 of these briquets into silicon carbide.
The temperature at the upper portion 11 of the furnace is above the coking temperature of the carbon excess and is also above the temperature required for activation of the reduction of the silicon d~oxide of the briquets to silicon carbide in accordance with the equations presented earlier. The coking ~ases and the carbon monoxide which are formed are discharged at 17.
- 4a -z ~ phir of electrodes 18 extend into the furnace to pro~ide the heat required for meltin~ the quartz which is introduced together with the briquets as part of the burden so that at the lower portion 1~ or high tempernture bosh of the furnace, the silicon carbide from the fully reacted briquets and the e~cess activated carbon thereof can pass into the molten quartz and effect a further reduction. The molten silicon collects at 13 as previously noted and can be tapped from the furnace.
Specific Examples E~ample l For the production of about 600 metric tons of silicon, 1200 metric tons of briquets were produced which were introduced into the electrical low-shaft furnace together with an almost similar amount of lump quartz.
In the first step of the process, the briquets were produced from a mixture consisting of:
30% caking coal, 32% petroleum coke, and 38~ quartz and (99.8% SiO2) by the hot-briquetting process, i.e. the ~oal was used at temperatures of about 500 C as 8 binder. The finished cooled briquets were egamined. They contained 42(~ 0.4~% SiO2 and 52(~ 0.7~ Cfi .
A strength test showed that point pressure crushing strengths of 150 to 200 kg had been obtained, which are accounted for by the imbedding of the inert substances such as petroleum coke and sand in the fused and resolidified coal. Measurement of the internal surface of the briquets showed 0.5 to l.0 m ~g, indicating that no significant reaction surface is present on which heterogeneous reections between gases such as SiO and carbon can take place at high conversion efficiency.
In 8 second step of the process, the briquets were introduced into an electrical low-shaft furnace. Before introduction to the furnace the material arising from abrasion and fracture during transport was separated by screening. These fines amounted to less than 4~. This is a very good result. Indeed, charcoal, peat, and coals are destroyed to a much higher u 7~
degree. Values of more than 10~ are known.
A mi~ture of continuously fed lump quartz and briquets, statistically well distributed by shakin~, was heated in the electrical low-shaft furnace and brou~ht to reaction.
Considering the General reaction of the production of silicon SiO2 ~ 2C = Si + 2C0, one can see from the analysis o~ the briquets that carbon is present in substantial e~cess and that only the further renction with the lump quartz assures complete conversion. Since, however, before the formation of silicon, silicon carbide arises accordinG to the e~uation SiO2 + 3C = SiC + 2C0, there remains the question, whether sufficient carbon is present in the briquets for this reaction. Calculation shows that just less than twice as much carbon (about 80% e~cess) is present as is required for the reaction.
That is a molar ratio of 1 : ~ to 1 : 6. This has been aimed for, to maintain the coke-structures resulting from the hot-briquettin~, even if losses occur by the reaction to silicon carbide.
This theory was tested by use of thermocouples to determine the temperature zone at which the carbide reaction occurs. Samples were taken from the hot material havin~ a temperature of between 1500 and 1600 C, and showed clearly that the briquets still had their oriGinal shape, althou&h the conversion between carbon and silicon already had started or was even complete.
Most of the briquets showed a white surPace, indicatin~ that reaction had here occurred. Of more significance, however, was the measurement of the internal surface of the cooled briquets, which showed a considerably increased internal surface of between 20 and 230 m /g. The briquets were found to consist essentially of SiC and activated carbon with the coke structure.
This leads to a considerable decrease of the SiO2 precipitate in the ~as-cleaning. Closely connected therewith are the enerGy consumption Pnd the silicon yield. The consumption of electrical power in the furnace decreased by about 14%, whereas the silicon yield increased by more than 20%. An unexpected, but important economical advantaGe was the halving of the consumption of the electrodes, which dropped from 128 kg/T. Si to 59 k~/T. Si. The movements of the electrodes were minimized.
~'7~l3q~
Examole 2 In the production of ferrosilicon the situation is more favourable. Here the lo~ses by the formation of SiO are less.
If one proceeds as described in the foregoing e~ample such that the input of lump qusrtz and briquets rcmains in the ratio of 50 to 50, and scrap iron is added so that a 75% silicon alloy results, the advanta~es of the briquets are still clearly apparant, i.e. the consumption of electrisal power decreases by 8~ and the yield of silicon increases by 12~.
9061-~
Claims (8)
PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method for producing silicon in an electrical-shaft furnace comprising the steps of:
(a) introducing into said furnace reductant briquets containing silicon dioxide and a carbonaceous reducing agent together with quartz, said carbonaceous reducing agent being present within said briquets in more than 50% and less than 90% by weight excess of that stoichiometrically required for the reaction SiO2 + 3C = SiC + 2CO in said briquets;
(b) reacting at a temperature below ab out 1600°C said briquets at an upper portion of said furnace to transform the silicon dioxide therein to silicon carbide and produce an activated carbon with a coke structure within said briquet, said briquets having an internal surface of between 20 and 230 m2/g;
(c) reacting the silicon carbide thus produced with molten quartz at a lower portion of said furnace at a temperature above 1600°C to reduce thequartz to silicon; and (d) reducing with said activated carbon a further amount of molten quartz in said lower portion of said furnace.
(a) introducing into said furnace reductant briquets containing silicon dioxide and a carbonaceous reducing agent together with quartz, said carbonaceous reducing agent being present within said briquets in more than 50% and less than 90% by weight excess of that stoichiometrically required for the reaction SiO2 + 3C = SiC + 2CO in said briquets;
(b) reacting at a temperature below ab out 1600°C said briquets at an upper portion of said furnace to transform the silicon dioxide therein to silicon carbide and produce an activated carbon with a coke structure within said briquet, said briquets having an internal surface of between 20 and 230 m2/g;
(c) reacting the silicon carbide thus produced with molten quartz at a lower portion of said furnace at a temperature above 1600°C to reduce thequartz to silicon; and (d) reducing with said activated carbon a further amount of molten quartz in said lower portion of said furnace.
2. The method defined in claim 1 wherein step (d), the quantity of carbonaceous material incorporated into said briquets is about 80% by weight in excess of that stoichiometrically required for said reaction.
3. The method defined in claim 1 wherein said briquets are introduced into said furnace in such relationship to the quartz therein that said activated carbon reduces at least 50% of said quartz to silicon.
4. The method defined in claim 1 wherein said briquets are by hot briquetting.
5. The method defined in claim 4 wherein said briquets are formed in an egg shape.
6. The method defined in claim 4 wherein said briquets are formed in a pillow shape.
7. The method defined in claim 4 wherein said briquets are formed from a carbonaceous component consisting predominantly of caking coal and containing inorganic carbon in the form of petroleum coke, anthracite, graphite, lignite coke or pit-coal coke.
8. The method defined in claim 1, further comprising the step of transforming the silicon as it is produced into a metal-silicon-alloy by adding to said furnace a metal adapted to be incorporated into said alloy.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE3342890 | 1983-11-26 | ||
| DEP3342890.5 | 1983-11-26 | ||
| DEP3411731.8 | 1984-03-30 | ||
| DE19843411731 DE3411731A1 (en) | 1983-11-26 | 1984-03-30 | METHOD FOR PRODUCING SILICON FROM RAW MATERIAL QUARTZ IN AN ELECTRONIC LOWER FURNACE AND METHOD FOR REDUCING OXIDIC RAW MATERIALS |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1217032A true CA1217032A (en) | 1987-01-27 |
Family
ID=25815937
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000468603A Expired CA1217032A (en) | 1983-11-26 | 1984-11-26 | Method of producing silicon |
Country Status (27)
| Country | Link |
|---|---|
| AT (1) | AT396460B (en) |
| AU (1) | AU568166B2 (en) |
| BE (1) | BE901114A (en) |
| BR (1) | BR8405974A (en) |
| CA (1) | CA1217032A (en) |
| CH (1) | CH663610A5 (en) |
| DD (1) | DD229102A5 (en) |
| DE (1) | DE3411731A1 (en) |
| DK (1) | DK168003B1 (en) |
| ES (1) | ES537973A0 (en) |
| FI (1) | FI76056C (en) |
| FR (1) | FR2555565B1 (en) |
| GB (1) | GB2150128B (en) |
| IE (1) | IE57642B1 (en) |
| IN (1) | IN162374B (en) |
| IT (1) | IT1177279B (en) |
| LU (1) | LU85649A1 (en) |
| MX (1) | MX162694A (en) |
| MY (1) | MY100749A (en) |
| NL (1) | NL8403572A (en) |
| NO (1) | NO163004B (en) |
| PH (1) | PH22408A (en) |
| PL (1) | PL148125B1 (en) |
| PT (1) | PT79544B (en) |
| SE (1) | SE461647B (en) |
| YU (1) | YU43676B (en) |
| ZW (1) | ZW19184A1 (en) |
Families Citing this family (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3356169A (en) * | 1966-04-01 | 1967-12-05 | Emery Co A H | Batch weigher with respective dials for successive loads and total weight |
| DE3541125A1 (en) * | 1985-05-21 | 1986-11-27 | International Minerals & Chemical Corp., Northbrook, Ill. | METHOD FOR THE PRODUCTION OF SILICON OR FERROSILICIUM IN AN ELECTRONIC SHELL OVEN AND FOR THE METHOD SUITABLE RAW MATERIALS |
| US4981668A (en) * | 1986-04-29 | 1991-01-01 | Dow Corning Corporation | Silicon carbide as a raw material for silicon production |
| DE3724541A1 (en) * | 1987-07-24 | 1989-02-02 | Applied Ind Materials | METHOD AND SYSTEM FOR THE PRODUCTION OF RAW MATERIAL BRIQUETTES FOR THE PRODUCTION OF SILICON OR SILICON CARBIDE OR FERROSILICIUM |
| SE461037B (en) * | 1987-10-09 | 1989-12-18 | Skf Plasma Tech | COATED BY COAL AND SILICON Dioxide CONTINUOUSLY MAKING LIQUID SILICONE IN A REACTOR |
| US4997474A (en) * | 1988-08-31 | 1991-03-05 | Dow Corning Corporation | Silicon smelting process |
| US4897852A (en) * | 1988-08-31 | 1990-01-30 | Dow Corning Corporation | Silicon smelting process |
| US4898712A (en) * | 1989-03-20 | 1990-02-06 | Dow Corning Corporation | Two-stage ferrosilicon smelting process |
| DE3923446C1 (en) * | 1989-07-15 | 1990-07-26 | Applied Industrial Materials Corp. Aimcor, Deerfield, Ill., Us | |
| EP2331462A2 (en) * | 2008-09-30 | 2011-06-15 | Evonik Degussa GmbH | Production of solar-grade silicon from silicon dioxide |
| WO2012163534A1 (en) * | 2011-06-03 | 2012-12-06 | Evonik Solar Norge As | Starting materials for production of solar grade silicon feedstock |
| EP2530050A1 (en) * | 2011-06-03 | 2012-12-05 | Evonik Solar Norge AS | Starting materials for production of solar grade silicon feedstock |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR1530655A (en) * | 1967-05-19 | 1968-06-28 | Pechiney Prod Chimiques Sa | Manufacture of silicon and its alloys by carbothermal energy |
| DE1915905C3 (en) * | 1969-03-28 | 1974-07-11 | Eschweiler Bergwerks-Verein, 5122 Kohlscheid | Process for the production of hot briquettes |
| BE759122A (en) * | 1969-11-19 | 1971-05-18 | Union Carbide Corp | PROCESS AND CHARGE FOR THE PRODUCTION OF SILICON IN AN ELECTRIC ARC OVEN BY CARBOTHERMAL REDUCTION OF SILICA |
| GB2008559A (en) * | 1977-09-09 | 1979-06-06 | Goldblatt N Z | Production of silicon |
| DE3009808C2 (en) * | 1980-03-14 | 1982-02-18 | Coc-Luxembourg S.A., Luxembourg | Process for the production of raw material blanks containing silicon and carbon and the use of the raw material blanks |
| DE3032720C2 (en) * | 1980-08-30 | 1982-12-16 | International Minerals & Chemical Luxembourg S.A., 2010 Luxembourg | Process for the production of silicon from quartz and carbon in an electric furnace |
-
1984
- 1984-03-30 DE DE19843411731 patent/DE3411731A1/en active Granted
- 1984-11-13 IN IN781/CAL/84A patent/IN162374B/en unknown
- 1984-11-15 GB GB08428898A patent/GB2150128B/en not_active Expired
- 1984-11-15 CH CH5468/84A patent/CH663610A5/en not_active IP Right Cessation
- 1984-11-21 DD DD84269725A patent/DD229102A5/en not_active IP Right Cessation
- 1984-11-21 IT IT23680/84A patent/IT1177279B/en active
- 1984-11-22 PH PH31474A patent/PH22408A/en unknown
- 1984-11-23 NL NL8403572A patent/NL8403572A/en active Search and Examination
- 1984-11-23 SE SE8405904A patent/SE461647B/en not_active Application Discontinuation
- 1984-11-23 LU LU85649A patent/LU85649A1/en unknown
- 1984-11-23 FI FI844617A patent/FI76056C/en not_active IP Right Cessation
- 1984-11-23 IE IE3012/84A patent/IE57642B1/en not_active IP Right Cessation
- 1984-11-23 BR BR8405974A patent/BR8405974A/en not_active IP Right Cessation
- 1984-11-23 DK DK557384A patent/DK168003B1/en not_active IP Right Cessation
- 1984-11-23 FR FR8417923A patent/FR2555565B1/en not_active Expired
- 1984-11-23 NO NO844668A patent/NO163004B/en unknown
- 1984-11-23 YU YU1987/84A patent/YU43676B/en unknown
- 1984-11-23 BE BE2/60552A patent/BE901114A/en not_active IP Right Cessation
- 1984-11-23 PT PT79544A patent/PT79544B/en not_active IP Right Cessation
- 1984-11-26 ES ES537973A patent/ES537973A0/en active Granted
- 1984-11-26 PL PL1984250592A patent/PL148125B1/en unknown
- 1984-11-26 AU AU35869/84A patent/AU568166B2/en not_active Ceased
- 1984-11-26 MX MX203487A patent/MX162694A/en unknown
- 1984-11-26 AT AT0373684A patent/AT396460B/en not_active IP Right Cessation
- 1984-11-26 CA CA000468603A patent/CA1217032A/en not_active Expired
- 1984-11-26 ZW ZW191/84A patent/ZW19184A1/en unknown
-
1986
- 1986-12-17 MY MYPI86000216A patent/MY100749A/en unknown
Also Published As
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| CA1217032A (en) | Method of producing silicon | |
| Tangstad | Ferrosilicon and silicon technology | |
| US4366137A (en) | Process for producing silicon | |
| CA1288214C (en) | Addition of calcium compounds to the carbothermic reduction of silica | |
| FI70259C (en) | SAETT ATT FRAMSTAELLA FERROKISEL | |
| Tangstad | Handbook of Ferroalloys: Chapter 6. Ferrosilicon and Silicon Technology | |
| JPH026815B2 (en) | ||
| US4728358A (en) | Iron bearing briquet and method of making | |
| JPS60145352A (en) | Manufacture of ferroboron | |
| US3661562A (en) | Reactor and method of making aluminum-silicon alloys | |
| JPS6179744A (en) | Continuous production of silicon base composite alloyed iron | |
| KR100206500B1 (en) | Method for manufacturing hardened coal for direct steel melting furnace | |
| JPS6144804B2 (en) | ||
| CA1174854A (en) | Production of abrasion-resistant pressed articles mainly consisting of metal | |
| WO2001025496A1 (en) | Carbon-containing agglomerates | |
| US5401464A (en) | Solid state reaction of silicon or manganese oxides to carbides and their alloying with ferrous melts | |
| JPS61117110A (en) | Process and apparatus for preparing metallic silicon | |
| Kyaw et al. | Use of Agglomerates in Silicon Production | |
| Vorob’ev | Carborundum-bearing reducing agents in high-silicon alloy production | |
| Paull, JM & See | The interaction of silicon monoxide gas with carbonaceous reducing agents | |
| CA2075466C (en) | Method of producing silicon and an electric-arc low-shaft furnace and briquette for carrying out the process | |
| Fairchild | Electric furnace manufacture of silicon metal | |
| EP0719348B1 (en) | METHOD FOR PRODUCTION OF FeSi | |
| GB1032747A (en) | Manufacture of ferro-silicon | |
| WO2020096462A1 (en) | Carbon based raw material |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |