Potluck
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We want clean energy. Most consider the solar cell the best way to achieve that goal. And it's made known we can extract the silicon needed to make solar cells from sand. That is true but there is much more not being said about actually getting the silicon. The process requires carbon in the form of coke made from coal and large quantities of electrical power.
The problem lies in the use of coal. It's that fact not many are aware of. Yet, there's a war on coal and it's usage has become a big no-no. The extraction process, a chemical reaction SiO2 + 2C -> Si + 2CO, usually requires coke, depending on the purity desired. Coal in it's natural form can be used. Coke is coal that had been heated to remove most of the impurities. The purer the ingredients (carbon) the purer the finished product.
* We need to give coal a second look without hearing only the environmentalist's points of view.
* We need coal in the process below not only as an ingredient (a source of carbon in the form of coke) but also a source of power for the large quantities of electricity needed.
* We need to understand that building coal-fired power plants should not be viewed as a target for bankruptcy.
* We need to get serious about silicon production if we're to compete with China for solar cells made in the USA.
SAND TO SILICON
The real story
Silicon smelter courtesy TRU Group Inc.
The Furnace
The type of furnace now used to make silicon, the electric arc furnace, was first invented in 1899 by French inventor Paul Louis Toussaint Heroult to make steel. The first electric arc furnace in the United States was installed in Syracuse, New York in 1905. In recent years, furnace technology, including the electrodes used for heating elements, has improved. Voltages range from 400 to 900 volts at up to 44,000 amperes. A small 150kW Si-smelting furnace can make about 5kg of silicon per hour.
Raw Materials
Silicon metal is made from the reaction of silica (silicon dioxide, SiO2) and carbon materials like coke, coal and wood chips. Silica is typically received in the form of metallurgical grade gravel. This gravel is 99.5% silica, and is 3 x 1 or 6 x 1 in (8 x 3 cm or 15 x 3 cm) in size. The coal is usually of low ash content (1-3% to minimize calcium, aluminum, and iron impurities), contains around 60% carbon, and is sized to match that of the gravel. Wood chips are usually hardwood of 1/2 x 1/8 inch size (1 x. 3 cm size). All materials are received as specified by the manufacturer.
Manufacturing
The basic process heats silica and coke in a submerged electric arc furnace to high temperatures. High temperatures are required to produce a reaction where the oxygen is removed, leaving behind silicon. This is known as a reduction process. In this process, metal carbides usually form first at the lower temperatures. As silicon is formed, it displaces the carbon. Refining processes are used to improve purity.
The Reduction Process
* The raw materials are weighed and then placed into the furnace through the top using the fume hood, buckets, or cars. A typical batch contains 1000 lb (453 kg) each of gravel and chips, and 550 lb (250 kg) of coal. The lid of the furnace, which contains electrodes, is placed into position. Electric current is passed through the electrodes to form an arc. The heat generated by this arc (a temperature of 4000° F or 2350 ° C) melts the material and results in the reaction of sand with carbon to form silicon and carbon monoxide. This process takes about six to eight hours. The furnace is continuously charged with the batches of raw materials.
* While the metal is in the molten state, it is treated with oxygen and air to reduce the amount of calcium and aluminum impurities. Depending on the grade, silicon metal contains 98.5-99.99% silicon with trace amounts of iron, calcium and aluminum.
The problem lies in the use of coal. It's that fact not many are aware of. Yet, there's a war on coal and it's usage has become a big no-no. The extraction process, a chemical reaction SiO2 + 2C -> Si + 2CO, usually requires coke, depending on the purity desired. Coal in it's natural form can be used. Coke is coal that had been heated to remove most of the impurities. The purer the ingredients (carbon) the purer the finished product.
* We need to give coal a second look without hearing only the environmentalist's points of view.
* We need coal in the process below not only as an ingredient (a source of carbon in the form of coke) but also a source of power for the large quantities of electricity needed.
* We need to understand that building coal-fired power plants should not be viewed as a target for bankruptcy.
* We need to get serious about silicon production if we're to compete with China for solar cells made in the USA.
SAND TO SILICON
The real story
Silicon smelter courtesy TRU Group Inc.
The Furnace
The type of furnace now used to make silicon, the electric arc furnace, was first invented in 1899 by French inventor Paul Louis Toussaint Heroult to make steel. The first electric arc furnace in the United States was installed in Syracuse, New York in 1905. In recent years, furnace technology, including the electrodes used for heating elements, has improved. Voltages range from 400 to 900 volts at up to 44,000 amperes. A small 150kW Si-smelting furnace can make about 5kg of silicon per hour.
Raw Materials
Silicon metal is made from the reaction of silica (silicon dioxide, SiO2) and carbon materials like coke, coal and wood chips. Silica is typically received in the form of metallurgical grade gravel. This gravel is 99.5% silica, and is 3 x 1 or 6 x 1 in (8 x 3 cm or 15 x 3 cm) in size. The coal is usually of low ash content (1-3% to minimize calcium, aluminum, and iron impurities), contains around 60% carbon, and is sized to match that of the gravel. Wood chips are usually hardwood of 1/2 x 1/8 inch size (1 x. 3 cm size). All materials are received as specified by the manufacturer.
Manufacturing
The basic process heats silica and coke in a submerged electric arc furnace to high temperatures. High temperatures are required to produce a reaction where the oxygen is removed, leaving behind silicon. This is known as a reduction process. In this process, metal carbides usually form first at the lower temperatures. As silicon is formed, it displaces the carbon. Refining processes are used to improve purity.
The Reduction Process
* The raw materials are weighed and then placed into the furnace through the top using the fume hood, buckets, or cars. A typical batch contains 1000 lb (453 kg) each of gravel and chips, and 550 lb (250 kg) of coal. The lid of the furnace, which contains electrodes, is placed into position. Electric current is passed through the electrodes to form an arc. The heat generated by this arc (a temperature of 4000° F or 2350 ° C) melts the material and results in the reaction of sand with carbon to form silicon and carbon monoxide. This process takes about six to eight hours. The furnace is continuously charged with the batches of raw materials.
* While the metal is in the molten state, it is treated with oxygen and air to reduce the amount of calcium and aluminum impurities. Depending on the grade, silicon metal contains 98.5-99.99% silicon with trace amounts of iron, calcium and aluminum.
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It's a great post. The topic or summary of the thread is (it gradually became a debabte): greenhouse stuff...I can't remember.Threads keep disappearing. If we could manufacture a lid I would personally save important files in a pot.;)Good post.Time for another debate, maybe
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