12600KVA Metal Silicon Furnace Technical Proposal

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Equipment manufacture and installation

of

12600KVA industrial silicon furnace

Technical documentation


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Contents

F I. Brief introduction of industrial silicon

F .Ⅱ Technical description

F .Ⅲ Design basis

F .Ⅳ Installation specification

F .Ⅴ Deviations on Technical Terms

F .Ⅵ Advantages of project implementation

F .Ⅶ Standard for design and construction


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I. Brief introduction of industrial silicon

1. Brand and usage of industrial silicon

1.1Brand of industrial silicon

According to the current market demand, smelting products is the chemical grade silicon.

The chemical composition should meet to the GB2881-91 requirement, and the industrial

silicon quality should meet table 1-1.

Table 1-1 Industrial Silicon’s chemical composition requirements:

Chemical Composition

Impurity content (%) Brand Si (%)

Fe Al Ca P

1515级 >99.6% =0.15 — =0.015 =0.004%

2202级 >99.5% =0.2 =0.2 =0.02 =0.004%

2203级 >99.5% =0.2 =0.2 =0.03 =0.004%

2503级 >99.5% =0.2 — =0.03 =0.004%

3103级 >99.4% =0.3 =0.1 =0.03 =0.005%

3303级 >99.3% =0.3 =0.3 =0.03 =0.005%

411级 >99.2% =0.4 0.04— 0.08 =0.1 —

421级 >99.2 % =0.4 0.1— 0.15 =0.1 —

441级 >99.0 % =0.4 =0.4 =0.1 —

553级 >98.5 % =0.5 =0.5 =0.3 —

1.2 Usage of industrial silicon

Industrial silicon (also called crystal silicon) is one of important materials used in

modern industrial production. Industrial silicon is widely used in fields of electronics,

steelmaking, photics, mechanics, automobile manufacture, chemical industry, metallurgy,

medicine, national defense, etc. It is acclaimed as “Industrial monosodium”.

Approximately 50% of industrial silicon is applied to manufacture of aluminum alloy.

Aluminum-silicon alloy has advantages of good heat stability, high abrasive resistance, and

smaller thermal expansion coefficient. Aluminum-silicon alloy is applied to fields of


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automobile manufacture, aviation industry, electric industry, shipbuilding, etc. Industrial

silicon can not only be used as addition agent of nonferrous alloy, but also as alloying agent

of high standard silicon steel. It is necessary deoxidizer in steelmaking and smelting of

nonferrous alloy. In steelmaking industry, 5 kg of industrial silicon is consumed to produce

1 ton of steel. Chemical grade industrial silicon is raw material for polycrystalline silicon

and monocrystalline silicon which are modern high- level technology product needed for

integrated circuit development encouraged by the nation. Industrial silicon can be

processed into raw material for circuit and electrical components. Japan referred steel,

aluminum and semiconductor grade silicon as three main metal materials. Industrial silicon

is applied to production of organic compound such as silicone oil, silicon rubber,

construction preservative, white carbon black, coating for agricultural plastic film,

annexing agent of high quality furniture, annexing agent of decorative painting, annexing

agent of ordinary industrial coating, etc. Industrial silicon is also used as reducing agent of

certain kinds of metal to produce new type of ceramic metal.

Until now, the silicon metal is widely used and still to be studied in new zone, such as

manufacturing the solar cell and manufacturing silicon nitride fiber synthesis and so on.

Solar cell now is the most attentioned green energy industry. The United States, Europe and

Japan all set the policy to precede their development in solar cell. In China, the government

has passed the RENEW ENERGY LAW on March 2005.These measures has greatly

proceed the solar cell development in China. According to the statistics, the internationa l

solar cell market keep high-speed increase from 1998 to 2007,and the annual increase speed

reach 30%.It is estimated that the increased speed shall be kept 25% after 2010.The

crystalline silicon now is the most mature and widely used material for solar cell that

occupy 85% in photovoltaic industry. Monocrystalline silicon solar cell’s conversion

efficiency is of 15% and the polycrystalline silicon solar cell’s conversion efficiency is of

12%.

In these years, as the demand of silicon metal is greatly increased in international

market, it also Stimulate China’s silicon metal industry’s development and proceed the

equipment suppliers and manufacturers to improve the process technology and devices

manufacturing. As the high technology zone and important base industry’s material for

structure and function, the silicon metal consumption has greatly increased. According to

the British authorities estimate, the demand for silicon metal shall be increased 8~12%


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around the world in these years, of which the chemical silicon has annually increased

12%.The high purity silicon metal can be processed to the monocrystalline silicon after

technology process(the silicon purity percent can reach 99.9999% above).The metal

material product with high technology, like the semi-conductor especially the electronic

components chip, is the technology achievement that promoted by the government.

II.Technical requirement of main raw material

2.1Main raw material

Silica and carbon reductant are the main raw material to smelt the industrial silicon.

(1) Silica (SiO2 over 99%)

Silica particle size requires 8 ~ 80mm, which is less than 20mm and not more than

20%.Qualified particle size requires over 90%.

To deal with the silica raw material, most mechanical crushing work shall be finished

at mine site. Because there will be some loss after crushing work. Some particle after

screening shall be used to manufacture the Quartz sand. The silica size meet the

requirement shall be transported to the plant. Some big size shall be manual crushed and

1~2 person is enough to finish the work.

Using the hexagonal screen or the rotary screen to wash the silica and to pour water from

the entrance. Besides the hexagonal screen or the rotary screen, it also needs infeed and

outfeed belt convey. The simple method is to put the silica into the weighing cart and then

wash it.

Chemical composition of Quartz: SiO2=99%, Fe2O3=0.057%, Al2O3=0.14%,

CaO=0.03%. Other impurities are less than 0.2%.

(2) The reductant for the industrial silicon smelting has the following: anthracite with low

ash, petroleum coke and wood.

Transport the mixed material to the front of furnace, and then use the hand cart and hoist to

transport the material to the second platform.

The productive practice shows that using the automatic charging is difficult to uniform

distribution of the silica and reducing agent, and it cannot meet the smelting process

requirement. Suggest using the manual charging method.

2.2 auxiliary materials

The auxiliary material for the industrial silicon such as the graphite electrode and


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oxygen shall be purchased from the market. The annual consumption of main raw material

and auxiliary material are as the table 2-1 shows.

Annual consumption of main raw material and auxiliary material for 1 set of 12600KVA

industrial silicon furnace (22ton/day, 12 months per year):

Table 2-1

No. Item Unit

consumption（t/t）

Day consumption （t/day）

Month consumption（t/month）

Year consumption（t/year）

1 quartz 2.65 58.3 1749 20988

2 petroleum coke 1.2 26.4 792 9504

3 Oxygen

(atmospheric) 35m3/t 770m3/d 23100m3/m 277200m3/a

4 compressed air 140m3/t 3080m3/d 92400m3/m 1108800m3/a

5 Water adding 10 220 6600 79200

6 electrode 0.065 1.43 42.9 514.8

2.3 Raw materials chemical composition and physical performance requirements

(1) Chemical composition of silica

SiO2 Fe2O3 Al2O3 CaO

>99.00% <0.057% <0.14% <0.03%

Silica particle size requires 8 ~ 80mm, which is less than 20mm and no more than

20%.Size pass rate requires over 90%.

（2）Chemical composition of coal

fixed carbon ash volatile component water content

>80% =1% <8.5% <8.5%

Physical state of coal, grain size 6 ~ 10mm, Quantity of coal's grain size smaller than

1mm into the furnace should be less than total quantity’s 20%. Large resistivity in high

temperature, good chemical reactivity, high porosity, qualified particle size is over 90%.

Use the washed coal of proper size.

（3）Chemical composition of petroleum coke


>87% <0.26% <12% <0.74%


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Physical state of petroleum coke, grain size 0 ~ 30mm.Quantity of petroleum coke's size

smaller than 3mm should no more than the total quantity's 20%.Crush it if the it is over than

30mm.

（4）Chemical composition of Wood:


>75% <2% <20% <10%

The physical state of charcoal size: 5 to 100mm.

2.4 Process calculation (by the following formula):

Q=24TPK1K2K3COSf/W

Which：Q— — output of silicon metal furnace（t/y）；

24— — operation time per day(24h)；

T— — operation time per year(340 day)；

P— — Furnace transformer rated capacity，kVA，12600；

COSf — — Electric natural power factor，0.90（after low-voltage compensation）；

K1— — Supply voltage fluctuation coefficient，0.98；

K2— — Furnace transformer power utilization factor，1；

K3— — Furnace operation time utilization factor，0.98；

W— — Product smelting power consumption，12000kWh/t。

Q=24×340×12600×0.98×1×0.98×0.90/12000= 7405.84t/y

Normal daily output is of up to 22t / d or more. Maximum daily output is of up to 28.6 / d.

Maximum annual output of one set furnace can reach 9724t / a.

3. Brief description of the process

3.1 process flowsheet as 5-1.

Industrial silicon production use the continuous smelting operation within a submerged

arc furnace, and the main process is using charcoal/all petroleum coke. Until now, three

methods of the smelting process in China: 1.using charcoal as the reductant ; 2.using

charcoal and petroleum coke as the reductant; 3.using coal and woodchip as the reductant.

The following process is the second method introduction.

3.2 process flowsheet (See the attached flowsheet).

3.3 Brief description of the process

Brief description of the process

Industrial Silicon is smelted through electrothermic method and the raw material is

silica and reducing agent such as charcoal and petroleum coke. Wash silica to remove the


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soil and other impurities. To crush the coal and petroleum coke to a certain size. Quartz,

charcoal, petroleum coke and others shall be proportioning and weighing as certain ration.

Suitable proportioning is the precondition to ensure the stabile operation situation of

furnace. The correct weighing must be ensured. The weighing error is not more than

1kg.After suitable proportioning; the material shall be well mixed and then charged into

the furnace. 7 feeding pipes for 1 set furnace to distributing material. The operator starts or stops

the button to feed according to the material situation inside furnace.

Considering the proportioning and charging system takes much area, to save cost,

two set furnace share one proportioning and charging system is the best choice.

Material consumption around furnace core and electrode are quicker than other areas,

so it needs to feed material timely. Material at furnace core should remain full state like

bread.

The industrial silicon is produced in the se-mi closed electric furnace and it is the

continuous working type. The current from the transformer shall go into the hearth

through the graphite electrode. During the smelting process, the current through the

electrode and resistance produce the heat and the electrode arc heat to make the material

up to 2000? .In this temperature, the silicon dioxide is reduced to the liquid silicon and

CO.CO shall be out through batch layer and also heat the material inside furnace. The

smelting process is of continuous type, the electrode has required depth inside furnace and

continues the arcing operation. Using three stocking machine to stock the furnace bottom

and add material timely to keep the material maintain a certain high level as the bread

shape. During the smelting process, if the material surface become incrusting or the material

feeding asymmetrical, it should use the wheel-distributing stoking machine to stoke the

furnace.

Use the stringer to open the taphole to let the liquid silicon pour into the ladle. When

the liquid silicon’s quantity up to the half level of ladle, the oxygen and air mixture shall

go inside to remove the calcium and aluminum and other impurities. When the liquid


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silicon is nearly finishing, use the mud ball made of electrode paste and coke powder to

close the taphole. Transport the ladle to the casting workshop by electrical cart and cast

the liquid silicon on the ingot mould. It shall become the silicon ingot after quick cooling.

The taphole shall open every 2 to 3 hours. The taphole shall open 3 to 4 times each

working shift (8 hours). Every day it shall produce about 22t metal silicon.

After the silicon ingots get cold, hanging them out by the crane and putting them in

the casting workshop according to the number. Transport them to the finished products

storage by cart. Crush them by manual, grading, weighing, packaging, warehousing, and

storage. Pack them according to the GB/T-5956-1995 technical requirement. Net weight

per bag is 1000 ± 5kg.

Smoke shall go to the gas duct through hood. A group of bag dust collector shall be

installed outside the plant. The flue gas emission concentration after treatment shall meet

the national discharge standards.

Furnace cooling water and transformer cooling water shall be supplied by the water

pump. The backwater return to the circulating water pool by difference of water level, and

get cooling by crossflow cooling tower. The cooling water can be used again for the

furnace and transformer. All the cooling water is soft water recycling and it just needs

adds new water to meet the consumption.

The furnace lining material are self-baking carbon brick, clay refractory brick, high

alumina refractory bricks, etc., and use new masonry technology .Furnace mouth use the

new type carbon brick work building. 4. Technology solutions for 12600KVA industrial silicon furnace:

Transformer capacity：4200KVA ×3 Primary Voltage：35KV Secondary Voltage: 127~ 151~ 175( V)

Secondary side voltage series: 17, differential: 3V

Common Voltage: 151( V)

Secondary current: 48178( A)

Electrode diameter：（F 960mm graphite石墨）

：Electrode current density 6.7/cm2


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Power ：～ factor 0.9（）after low voltage compensation

Electrode pitch circle Diameter： F 2450mm±100mm

Furnace inner diameter： F6100 (mm)

Furnace shell diameter： F 7858mm

Furnace inner height： 2400mm

Furnace shell height： 4500mm

Low-Hood Height： 2400mm

：Unit area power of Pitch circle 2 ㎡405.4 KW/

：㎡Unit area power of hearth 388 KW/

：Unit volume power of hearth 161.7W/m3

Electrode stroke： 1600mm Electrode Lifting Speed： 0.5m/min Cold Water Consumption： 340t/h The above specification is for reference.

.Ⅲ design basis

To meet the annual output of 50000 tons metal silicon, it shall need to build 7 set

furnaces of 12600KVA capacity. (1 set furnace can produce 22 tons metal silicon every day.

Annual production is calculated based on 330 days).The furnace needs low-voltage

compensation and the power factor can not less than 0.9.

1. Furnace Shell (Rotary furnace):

Furnace Shell Diameter: f7858mm

Furnace Shell Height: 4500mm

Number of Taphole: 5. (360°average arrangement)

Thickness of Furnace shell plate: 16mm

Bottom thickness: 20mm

Belt and vertical bars: 160mm channel steel

Thickness of bottom-beam: 280mm

Furnace shell is of open-sided split mouth before welding, using E43 of continuous

welding, full welded.

The working level use self-baking carbon brick, size is of 400mm × 400mm ×

400mm,bottom thickness is of 2100mm, furnace wall thickness is of 879mm; carbon brick


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cracks = 1 mm, filled material is of cold ramming paste (no gap between self-baking carbon

brick ) ; furnace wall edge gap = 2mm, filling materials is of cold ramming paste , no

leakage.

Insulating layer use new insulating refractory clay brick and high alumina bricks, furnace

wall is located above the carbon layer. High alumina bricks (Al2O3=65%) are as the

insulating material, size is of 55mm × 113mm × 230mm, the other parts use clay brick and

the size is 55mm×113mm×230mm.The refractory mortar shall be filled between all the

refractory brick, no leakage.

Pound flat layer use mixture of fine silica and slag, the particle size 3 ~

8mm .Requirement: tamping, ramming flat.

Aluminum silicate fiber felt as insulation material, thickness 30 ~ 40mm.

Graphite carbide-Silicon as furnace mouth materials and must be seamless.

Discharging is of circular shape, carbon brick of diversion trench longer 100mm than

steel plate. Furnace shell near furnace mouth use clay brick, a layer brick thick, height is

furnace mouth.

2. Water- ：cooled Hood

The hood edges is hexagon and the Hood height is 2400mm. 6 furnace gates for

feeding and ramming. The three large side door’s effective operation space height is

1600mm, furnace gate of Operation hole is hydraulic lifting, side wall with refractory

brick.

As the hood size large span, high structural strength is required. At the same time, the

current through the hood is strong, if it is not dealt properly, large eddy current losses. So

the Cover central area is of 1Gr18Ni9 stainless steel material, steel beam is 20 # channel

steel, and steel plate thickness is of 8mm. The water-cooled cover at the top of hood is of

active structure, easily to be maintained. During Industrial silicon furnace smelting process,

the pitch circle specification is important. During the electrode up-down movement,

seal-oriented devices is made in water-cooled large set in order to prevent electrode is

broken during swing and also prevent the pitch circle specification is changed. Also prevent

the gas escaped from the upper. During the silicon smelting process, because of reducing agent (charcoal) is of light

weight and low burning point, the smoke gas shall reverse and form the steamer effect if the


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smoke gas is difficult to get out. Thus the reductant shall partial oxidize and reduction effect

shall down. The result is the unit consumption shall increase and the quality shall down.

Our company has basically solved this problem after many times communicating with our

customers and obtain good results.

3. Smoke Exhaust System：

(1) Main gas duct: According to the flue gas produced and the amount of semi-closed

furnace nokaze during smelting process, the two gas duct diameter are F2000mm.Because

of the gas high temperature, at the bottom is about 3.5 m high double- layer water to

improve the working conditions. The material is of Q235 and the thickness is of 8mm, and

using two insulating flange connection. Insulation is of HP-5. The remaining is of

single- layer, and the material is Q235 and the thickness is of 6mm.At the top of the gas pipe,

there is a dust collection connector, the connector end is a bell valve and the bell valve is of

hydraulic automatic control.

(2)Accessory chimney flue: including tapping holegas cover and gas duct, and Manual flap

valve. Accessory chimney is connected with Main chimney flue in the third platform.

Tapping hole gas cover brings the gas when discharging. Accessory chimney flue is

insulated with the furnace shell and reliable.

4. Electrode system

（）1 Electrode lifting

Graphite electrode with F960mm diameter, including top carrying cylinder ,bottom

carrying cylinder holder, water cooling large set, Cylinder pressure ring, Conductive

Copper Tube holding device and hanging device. Top carrying cylinder diameter is

F1080mm; material is Q235 and 10mm thickness. Both Water-cooled large set and bottom

carrying cylinder use stainless steel (1Cr18Ni9Ti) to reduce current losses during smelting

process. Bottom carrying cylinder diameter is F1080mm and 10mm thickness.

Water-cooled large set is of 4, easily to install and remove. Electrode lifting is hydraulic

mechanism, working smoothly. Cylinder in the third tier platform is hanging structure.

Each electrode uses two lift cylinder of F220. Lift height is 1.6 meters and the speed is

0.5m/min. Copper tile Hold mechanism adopts cylinder pressure ring clamps copper tiles.

As each cylinder works independently, thus making each tile can be closely contact with the

electrode to prevent fire between copper tile and electrode which will affect copper tile life,

keeping the current delivered stably, contact resistance is small, and low power loss.


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Pressure ring and water-cooled protection cover are water cooled. No water flow dead

area when design.

（）2 electrode slip

Electrode slip is carried out by three pressure-releases Cylinder of double hydraulic

brake. Diameter of the pressure-release cylinder is F100mm; stroke is 100mm. Hydraulic

brake with disc spring to hold hydraulic to relax, vulcanized rubber brake, 10mm thick of

insulating rubber. Disc spring hold is mechanical hold, which can effectively prevent

electrode decline because of hydraulic and electrical failures, at the same time mechanical

strength can be adjusted. Brake loose, tight and electrode slip is of automatic

control .Electrode slip volume is made as needed.

Method of electrode slipping

1) To pour the hydraulic oil into the upper hydraulic brake, and to overcome the upper

hydraulic brake's spring pressure through oil pressure.

2) Lift the three pressure tanks to the required height, and the upper hydraulic brake shall be

raised to the required height at the same time.

3) The upper hydraulic brake release the oil pressure and the disc spring hold the electrode

again.

4) To pour the hydraulic oil into the lower hydraulic brake, and to overcome the upper

hydraulic brake's disc spring pressure through oil pressure.

5) To low down the three pressure tanks to the required height, and to low down the upper

hydraulic brake to the required height at the same time.

6) The lower hydraulic brake release the oil pressure and the disc spring hold the electrode

again.

5. Hydraulic System

Hydraulic system, including the hydraulic station, accumulator, two oil pumps and two

motors, is the power source of electrode slip, electrode lifting, copper tile clamping, Bell

valve cylinder, furnace gate lifting cylinder and charging control valve cylinder. System

pressure is up to 12MPa, hydraulic stations adds cooling device. The electrode slip device is

of hydraulic brake, and between the two brakes is of nine cylinders with f100mm and

100mm stroke. Hydraulic system piping is designed with insulation. 、6 Short bus bar


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Three single-phase transformers, brass side outlet, outlet terminal is near the

transformer center, each transformer is of 16 outlet terminals, each group in two rows, total

48. Three transformers are installed on the transformer platform, angle of 120 °. Short bus

bar system consists of three single-phase transformers, 48 water-cooled compensator , 48

water-cooled cable , 48 level conductive copper pipe , 48 vertical conductive copper pipe ,

24 forged copper tile . Three single-phase transformers to eliminate the weak-phase of

Short bus bar, making Short bus bar shorter and short bus bar power loss lower. Forging

copper tile height 860mm, thickness 80mm, material T2. Forging copper tile copper is of

high density, good conductivity. Water compensator is of pipe to pipe connections, copper

wire cross section 1600mm2, 800mm length. Water-cooled cable is of dual nut pipe to pipe

connections, copper strands cross section 1600mm2, 1000mm length. Double nut structure

with double cone sets, increasing conductive area, easily installed. At the same time,

2300mm length not only meets the electrodes stroke requirements but also make the

water-cooled cable’s inductive reactance smaller during normal smelting, less power loss.

Conductive copper F70 × 10, material is of T2. After Copper manufacture, two times

insulating paint, wrapped two glass fiber cloths around, and then one time insulating paint.

Short bus bar hanging clamp insulation device, plywood material is 3240, external is

stainless steel plates to reduce eddy current losses. Bar bolt of upper vases for second

insulation.

、7 Water cooling system

Cooling water system is the cooling device to cool the component (including the bus

bar, pressure ring, large sleeve, furnace shell, gas hood, chimney) that working under high

temperature. The water cooling system consists of water segregator, water collecting tank,

pressure meter, valve doors, pipes and hoses, fittings and other components.

Thermocouples and flow meters are installed on the return water pipe.

Pressure ring of the bus bar (including copper pipe inside furnace, water-cooled cables,

copper tiles) has the water drainage device to discharge water during the emergency repair

time.

The cooling water's inlet temperature shall not exceed 30 , return water temperature ℃

shall not exceed 50 , ℃ and inlet water pressure should be not less than 0.25MPa.

The water cooling system's forth and back water pipe is 1.5 inch gas pipe. The bus bar

is 24 in and 24 out, the transformer is 6 in and 6 out, the gas pipe is 2 in and 2 out, the low


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gas hood is 16 in and 16 out, the water cooled sleeve is 6 in and 6 out, the pressure ring is 6

in and 6 out, spare is 2 in and 2 out, total 62 waterways.

8、Tapping system:

Including stringer, ladle, cart, cart rail, ingot mold, hanging device and so on.

、9 Electrical Equipment

Electrical equipment for 12600KVA industrial silicon furnace includes high-voltage

power supply system, transformers, low voltage power supply, and control system.

9.1 high voltage supply system

Power supply system for submerged arc furnace includes the switching station,

furnace transformers, bus, other power protection equipment and measuring instruments,

and other distribution facilities.

Submerged arc furnace is allowed to have a power cut in operation shortly, so using a

separate power supply can meet the requirements. Transmission process is that energy from

the high voltage power grid via high voltage bus high-voltage isolating switches and circuit

breaker to the furnace transformer, and then after a short network(bus) to reach the

electrode.

9.1.1 High voltage distribution equipment

Furnace uses 33KV voltage level, its high voltage distribution equipment usually

brings high voltage power into the plant firstly by high pressure power, and then using

underground cables into the plant control room’s the line high-voltage switch cabinet.

Master control room usually has three switch cabinets: One, the line of high voltage is

called switchgear cabinet, with switch, less oil circuit breakers, current transformer, and its

capacity to be sufficient to meet the entire electrical load driven. Two, high voltage

switchgear also known as PT cabinet, with switch, current transformer, voltage transformer,

for connection of the measuring instruments, while the active form, a three-phase ammeter

and voltmeter, and the introduction of the secondary phase voltage. This table has lead to

the front console cabinet in order to manipulate the electrode movements and the amount of

load control. There, high-voltage vacuum switch cabinet also know as outlet, with switch,

vacuum circuit breaker or oil circuit breakers, and the current transformer with compatible


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Documents

12600KVA Metal Silicon Furnace Technical Proposal