|Design Capacity:||27 Tons Per Day||Control:||Siemens PLC|
industrial smelting furnace,
continuous heat treatment furnace
Industrial Silicon Saf (Submerged Arc Furnace) Making Machine/Production Line
Industrial silicon SAF (submerged arc furnace)
1 The brand and use of Industrial Silicon
1.1The brand of Industrial Silicon
According to the current market demand, smelting products are chemical grade industrial silicon. The chemical composition and performance should be implemented by GB2881-91. The quality of industrial silicon should meet the requirements of the following table.
|Silicon content(%)||Impurity content(%)|
|Level 421||>99.2 %||≤0.4||0.1—0.15||≤0.1||—|
|Level 441||>99.0 %||≤0.4||≤0.4||≤0.1||—|
|Level 553||>98.5 %||≤0.5||≤0.5||≤0.3||—|
1.2 The use of Industrial Silicon
Industrial silicon (also called crystalline silicon, silicon metal) is one of the important materials in modern industrial production, the use of industrial silicon is very wide, can be used in electronics, steel-making, optics, machinery, automobile manufacturing, chemical industry, metallurgy, medicine, national defense and other fields, known as the "industrial monosodium glutamate". The amount of using industrial silicon in the production of aluminum alloy accounts for more than 50% of the total. Aluminum-silicon alloys are widely used in automobile manufacturing, aviation industry, electrical industry and ship manufacturing because of the good heat resistance, good wear resistance and low thermal expansion coefficient. Industrial silicon can be used as an additive for non-ferrous alloys, and also as an alloy agent for strict silicon steel. It is an essential deoxidizer for steelmaking and non-ferrous alloy smelting. In the steel industry, every one ton production consumes about 5 kg of industrial silicon. Chemical grade industrial silicon is the raw material of polycrystalline silicon and monocrystalline silicon, which are required by the state to encourage the development of integrated circuits. Industrial silicon is processed into a necessary raw material for circuit and electronic components. In Japan, the three major metal materials are made of steel, aluminum and semiconductor silicon. Industrial silicon is used in chemical industry to produce organic compounds such as silicone oil, silicone rubber, building preservatives, silica, agricultural film coatings, high-grade furniture coatings additives, decorative paint additives, general industrial coatings additives and so on. Industrial silicon is also used as a reducing agent for some metals, which is used to make new ceramic alloys.
At present, the application of industrial silicon is still developing new fields, such as manufacturing solar cells, making silicon nitride synthetic fibers and so on. Solar energy has now become the most concerned green energy industry. The United States, Europe and Japan have formulated policies to vigorously promote the development of their own solar energy, and our country also passed the <Renewable Energy Law> in March 2005. These measures have greatly promoted the development of the solar cell industry. According to statistics, from 1998~2007 years, the market of international solar photovoltaic cells has maintained a rapid growth, even with a blowout trend. The annual average growth rate is up to 30%. It is expected that after 2010, it will remain at least 25% growth rate. Currently, crystalline silicon is the most mature and widely used solar cell material, accounting for more than 85% of photovoltaic industry. The photoelectric conversion efficiency of monocrystalline silicon solar cells is 15%, and the photoelectric conversion efficiency of polycrystalline silicon solar cells is 12%.
In recent years, with the increasing demand of industrial silicon in the international market, the development of China's industrial silicon production industry has been stimulated, and the industrial silicon production technology and equipment have been improved. As a kind of functional and structural materials being widely used in high-tech fields and important basic industries, industrial silicon consumption has increased rapidly, according to the British authorities CRU forecast, industrial silicon demand in the next few years in the world with an average annual growth rate of 8 to 12%, of all, the chemical industrial silicon will have an annual increase of 12%.With multi process processing, high purity industrial silicon can become the production of monocrystalline silicon (The purity of the product contains more than 99.9999% silicon), the high-technology metal material product is key material for semiconductors, especially electronic component chips, which belongs to the national scientific and technological achievement promotion project"95".
2 Technical requirements for main raw materials
According to the past orders, the owners require reductant based on auxiliary part of wood chips. This plan is compiled according to this requirement.
2.1 Main raw materials
Silicon carbide and carbonaceous reducing agent are the main raw materials for smelting silicon.
(1)Silica, containing more than 99% SiO2
To handle the silica raw materials, a large number of mechanical crushing should be placed in the mine because of the mechanical crushing which has a big loss (8 ~ 28%) problem. These fines sifted can be unified to produce the quartz sand. The silica entering the factory should basically meet the requirements of the block requirements. Some large pieces should be picked out for manual crushing, only 1~2 people are required.
Using a mechanical equipment to clean the silica, which can be watered from the entrance with six angle sieves or cylindrical sieves. Besides six angle sieves or cylindrical sieves, the ore belt conveyor and the material belt conveyor are also needed. The simplest way is to load the ore into a weighing hopper to flush.
(2) There are a lot of reducing agents needed for industrial silicon smelting, but with charcoal smelting as the basic way, according to the user’s requirements,the following kinds of reducing agents are selected: petroleum coke, fine coal and wood chips.
2.2 Auxiliary materials
The graphite electrode, oxygen and other auxiliary materials needed for the production of industrial silicon are all purchased by the market. The table of the main raw materials and auxiliary materials can be seen at the table:
2.3 Chemical composition and physical properties requirements of raw materials
(1) Chemical composition of silica
The grain size of silica is 8 ~ 80mm,of which those less than 20mm shouldn’t be more than 20%, and the granularity qualification rate should be more than 90%.
(2) Technical requirements for petroleum coke are as follows
|Fixed carbon||Ash content||Volatile matter||Water content||Ash content|
Grain size requirement: the grain size of petroleum coke is 5~15 mm.
(3) Chemical composition of coal
|Fixed carbon||Ash content||Volatile matter||Water content|
The physical state of coal is 6 to 10mm in size, and the content less than 1mm should be less than 20% of the total amount put into the furnace. The large high temperature specific resistance , the good chemical reaction , the high porosity , and the particle size pass rate should be more than 90%.Select the small uniform size coal which after water separation .
(4) Wood: 10 ~ 100mm,of which content is less than 30mm should be less than 20%
The production of industrial silicon is to be smelted by continuous operation method in the ore heat furnace, and the main production process is made of full-charcoal smelting.
The silica is washed by water to remove dirt and other impurities. Coal and petroleum coke, wood chips are broken to a certain size. The qualified raw materials are loaded into the corresponding batching silo through the loader. There are 6 ingredients in the material silo, of which silica and coal both are 2, and 1 of the petroleum coke and the wood of each. The bottom of each bin is equipped with vibrating feeder, weighing device and other equipments. Through PLC automatic control, all kinds of raw materials are weighed according to the ratio of the process, then fall on the mixing belt in the lower part and transport them to the temporary storage bin.
Charging car from the temporary storage bin receives the raw material and puts them into the furnace according to the charge level of the mouth. When the furnace core material is going to wear out, should supplement the materials in time .The furnace core should be full like a steamed bread. The raw materials will be distributed according to the requirement of process by the dialing skip.
Industrial silicon is produced continuously in a semi closed rotary electric furnace. A current introduced by a transformer via the electrode enter into the furnace of which the hearth is full.. In the process of smelting, the heat generated by the electric current through the electrode and the furnace material resistance and the arc heat at the end of the electrode heat the furnace to more than 2000℃.Under the temperature, silicon dioxide is reduced to industrial silicon liquid and carbon monoxide (CO) gas by carbon reduction. The CO gas escapes through the material layer and preheat the furnace material.
The smelting process is a continuous work. The electrode has the proper working depth in the furnace, stably inserted into the furnace to do the submerged-arc operation. With the charge level collapsing, feeding immediately after three pounding furnace ramming it. When the charge level maintains a certain high level steamed buns shape, start smoldering.
At regular time, using an arc burner to open the mouth to burn out the industrial silicon. Liquid flows from the mouth into the silicon water bag. When the water flow to the half of the bag, access the oxygen and air mixed gas by the bottom of the bag in order to remove calcium, aluminum and other impurities. In the almost end of the silicon water, timely use the mud ball made by the electrode paste and coke powder to plug the mouth. With electric chartered car transporting the bags to the casting room and cast into the ingot mold .After the rapid cooling, it become a silicon ingot .This design is produced every 2~3 hours a furnace, 3~4 furnaces of each class, and the normal production of industrial silicon is about 27t per day.
When the silicon ingot is cooled, it is hoisted by a crane and is stacked in the casting room according to the number of the furnace. It is transported by a small car to a finished warehouse and is artificially broken, graded, weighed, packaged, stored and stored. Packing is in accordance with the technical requirements specified of GB/T-5956-1995.The net content of each bag is 1000±5kg standard.
The flue gas produced during the smelting passes through the two chimneys on the hood to enter the dusting flue and each chimney is connected with a dedusting flue respectively. It goes through the cooler, the separator, the fan into the dust collector,then after treating ,the flue gas emission concentration reaches the relevant emission standards. The microparticles collected by the dust collector (microsilicon powder) are discharged at regular intervals after the density of the encrypted equipment is increased.