用碳化稻壳电热冶金法制备超冶金级硅的研究
发布时间：2018-09-01 19:16
【摘要】：全球煤、石油等传统能源的日益枯竭,能源危机已迫在眉睫,太阳能作为安全、分布广泛、清洁的可再生新能源得到了快速的发展,已成为21世纪最重要的新能源。硅是太阳能电池最重要的基础材料,降低硅材料的成本已成为发展光伏能源的关键,但是制备多晶硅的主要技术改良西门子法主要垄断在美、日、德等国手中。我国因没有掌握该法的核心技术,多晶硅主要依赖于进口。冶金法制备太阳能级多晶硅具有低成本、低能耗、无污染、生产安全的特点。研究拥有自主知识产权的冶金法制备多晶硅技术对发展我国光伏产业有着重要的战略意义。所谓超冶金级硅(UMG-Si)就是指Si纯度高于冶金级硅,Fe、Al、Ca、P、B等杂质的含量要低于国家A级工业硅的标准,是电热冶金法制备太阳能级多晶硅的中间产品。本文研究了用碳化稻壳电热冶金法制备超冶金级硅技术和机理,为电热冶金法制备太阳能级多晶硅奠定基础。由于碳化稻壳(CRH)含碳量较高(50%),而且还含有一定量的Si02(约25%)是冶炼Si时优良的碳质还原剂。主要内容有：(1)碳化稻壳粉的除杂研究；(2)配料及球团物理性能的研究；(3)粉体原料电热冶金法制备硅过程中热力学分析与验证；(4)碳化稻壳粉体原料熔炼硅的研究；(5)碳化稻壳粉和石油焦粉混合粉体原料熔炼超冶金级硅的研究；(6)冶金级硅吹气精炼除磷的研究。得到的主要结论有：(1)碳化稻壳最佳酸浸工艺为：CRH粉在75μm以下,盐酸浓度为5wt%,反应时间3h,水浴温度为60℃,浸出液固比14：1,搅拌速度60r/min,金属元素的总去除率达96.41%,非金属元素的总去除率为66.68%；超声酸浸后CRH粉中的杂质元素去除率要比机械搅拌酸浸后杂质去除率高,其中金属元素的总去除率达99.07%、非金属元素的总去除率为71.77%。超声酸浸过程中随着时间的延长除杂效果不明显。真空高温焙烧除杂的最佳工艺条件：CRH粒度在75μm以下、保温时间120min、保温温度1100℃、压力70kPa。此时,磷的去除率达91.85%、硫的去除率达88.96%。在真空条件下,除去碳化稻壳粉中的磷酸盐杂质是可行的,真空度越高,反应温度降低越显著。在体系压力为70kPa时,除磷反应的温度为1100℃(1373K)。(2)碳化稻壳与空气发生氧化反应的活化能E和指前因子A,分别为78.89 kJ·mol-1和2083.03min-1。计算表明,以碳化稻壳粉为碳质还原剂时球团的物料配比为：石英砂粉：碳化稻壳粉：粘结剂=100：85.14：0.56,其最佳工艺条件为：物料粒度75μm,压制压力15MPa,粘结剂加入量3%,配水量7wt%,此时,球团的抗压强度为3.0MPa,气孔率为38.6%。以混合碳质还原剂时球团的物料配比为：石英砂粉：碳化稻壳粉：石油焦粉：粘结剂=100：54.61：22.34：0.53,其最佳工艺条件为：物料粒度75μm,压制压力20MPa,粘结剂加入量3%,配水量6wt%。此时,球团的抗压强度为5.8MPa,气孔率为25.2%。(3)计算了Si-C-0体系中各反应的吉布斯自由能和温度的关系,确定了各反应发生的最低温度,同时通过HSC热力学计算软件验证了计算所得结果。在C还原Si02的‘过程中,存在着SiO和SiC生成和分解反应,当温度升高到1900℃,产物中才出现了Si相,同时存在SiC、SiO2相和少量的SiO相。(4)研究结果表明,利用碳化稻壳粉体原料作为碳质还原剂来熔炼硅是可行的,且得到了纯度为99.32wt%国家二级工业硅,其主要的铁、铝和钙等金属杂质含量均低于现有国家A级工业硅(化学用硅)标准,最重要的是产物硅中磷和硼分别只有26ppmw和15ppmw,均低于现有工业硅中磷(120～200ppmw)和硼(20～60ppmw)的含量,这说明可以通过控制原料中杂质含量来控制熔炼产物中杂质含量。(5)利用碳化稻壳粉和石油焦粉混合粉体为碳质还原剂时,研究结果表明,矿热炉冶炼过程中,当输出电流稳定在500A时,合适的输出电压为25-30V；额外碳配入量为30%时,Si的收率为最大值30.7%,此时炉底渣中的SiC的含量也较少；产物中硅的含量为99.68wt%,已经超过了国家A级工业硅(化学用硅)的标准(Si%≥99.60%),其主要的铁、铝和钙等金属杂质含量均低于现有国家A级工业硅标准,磷、硼含量分别为24ppmw和14ppmw,也都低于现有工业硅中磷和硼的含量。制备出了超过冶金级硅最高标准的超冶金级高品质硅。(6)冶金级硅吹气精炼除磷的研究,结果表明,在使用侧壁和底部多孔型喷嘴,精炼时间为3小时,精炼温度为1793K,精炼气温度为373K,精炼气流速为2L/min,作为最佳吹气精炼条件时,硅熔体中的磷元素由94ppmw降低到11 ppmw。从热力学和动力学分析可以得出,精炼气中的水蒸气和熔硅反应生成硅的氧化物和H2,部分H2溶解于熔硅中。然后熔硅中的[H]再和熔硅中的[P]反应生成PH3, PH3随后被氩气泡带离开熔硅。进而得出,吹气(Ar-H2O)精炼的方法能有效的去除冶金级硅熔液中的杂质磷。本研究实现了用碳化稻壳粉体原料电热冶金法制备超冶金级硅的工艺,这为用高纯粉体原料电热冶金法制备太阳能级多晶硅奠定了基础。
[Abstract]:As a safe, widely distributed and clean renewable energy, solar energy has developed rapidly and has become the most important new energy in the 21st century. Silicon is the most important basic material for solar cells. Reducing the cost of silicon materials has become the development of photovoltaic energy. The key point is that the main technological improvement of the Siemens method is mainly monopolized in the United States, Japan, Germany and other countries. China has not mastered the core technology of the method, and polycrystalline silicon mainly depends on imports. The technology of metallurgical preparation of polycrystalline silicon by weight is of strategic importance to the development of photovoltaic industry in China. The so-called super-metallurgical grade silicon (UMG-Si) means that the purity of silicon is higher than that of metallurgical grade silicon, such as Fe, Al, Ca, P and B, and the content of impurities is lower than the national A-grade industrial silicon standard. The technology and mechanism of preparing super-metallurgical grade silicon from carbonized rice husk by electrothermal metallurgy were studied, which laid a foundation for the preparation of solar grade polysilicon by electrothermal metallurgy. The carbonized rice husk (CRH) contains high carbon content (50%) and a certain amount of Si02 (about 25%) is an excellent carbon reducing agent for smelting Si. (2) Study on the proportioning and physical properties of pellets; (3) Thermodynamic analysis and verification in the preparation of silicon from powdered materials by electrothermal metallurgy; (4) Study on melting silicon from carbonized rice husk powder; (5) Study on melting super-metallurgical grade silicon from the mixture of carbonized rice husk powder and petroleum coke powder; (6) Study on refining phosphorus removal from metallurgical grade silicon by gas blowing. The main conclusions are as follows: (1) The optimum acid leaching process for carbonized rice husk is as follows: CRH powder is below 75 micron, hydrochloric acid concentration is 5wt%, reaction time is 3h, water bath temperature is 60, leaching liquid-solid ratio is 14:1, stirring speed is 60r/min, the total removal rate of metal elements is 96.41%, the total removal rate of non-metal elements is 66.68%; the impurities in CRH powder after ultrasonic acid leaching are 66.68%. The total removal rate of metal elements and non-metal elements was 99.07% and 71.77% respectively. The removal effect was not obvious with the extension of ultrasonic acid leaching time. The phosphorus removal rate was 91.85% and the sulfur removal rate was 88.96%. It was feasible to remove the phosphate impurities in carbonized rice husk powder under vacuum condition. The higher the vacuum degree, the lower the reaction temperature was. When the system pressure was 70 kPa, the temperature of phosphorus removal reaction was 1100 ((1373K). (2) Carbonized rice husk and air. The activation energy E and pre-exponential factor A of the oxidation reaction were 78.89 kJ.mol-1 and 2083.03 min-1, respectively. The results showed that the material ratio of the pellets with carbonized rice husk powder as carbon reducing agent was quartz sand powder: carbonized rice husk powder: binder = 100:85.14:0.56, and the optimum technological conditions were as follows: the particle size of the pellets was 75 micron, the pressing pressure was 15 MPa, and the binder was 100:85.14:0.56. The compressive strength and porosity of the pellets were 3.0 MPa and 38.6% respectively when the dosage of the additive was 3% and the dosage of water was 7 wt%. When the mixture of carbon reducing agent was used, the pellets were composed of quartz sand powder, carbonized rice hull powder, petroleum coke powder, binder = 100:54.61:22.34:0.53. The compressive strength of the pellets was 5.8 MPa and the porosity was 25.2%. (3) The relationship between Gibbs free energy and temperature of the reactions in the Si-C-0 system was calculated, and the lowest temperature of the reactions was determined. The calculated results were verified by HSC thermodynamic calculation software. The formation and decomposition reactions of iO and SiC occur only when the temperature is raised to 1900 C, and there are SiC, SiO2 and a small amount of SiO phases in the product. (4) The results show that it is feasible to melt silicon by using carbonized rice husk powder as carbon reducing agent, and the secondary industrial silicon with purity of 99.32wt% is obtained. The content of impurities in the product silicon is only 26 ppmw and 15 ppmw respectively, which are lower than that of phosphorus (120-200 ppmw) and boron (20-60 ppmw) in the existing industrial silicon. (5) When the mixed powders of carbonized rice husk powder and petroleum coke powder are used as carbon reductants, the results show that the suitable output voltage is 25-30V when the output current is stable at 500A, and the maximum yield of silicon is 30.7% when the additional carbon content is 30%, and the content of silicon in the bottom slag is also less. The content is 99.68 wt%, which has exceeded the national A-grade industrial silicon (chemical silicon) standard (Si%>99.60%). The main iron, aluminum and calcium impurities are lower than the existing national A-grade industrial silicon standard. The contents of phosphorus and boron are 24 ppmw and 14 ppmw respectively, which are also lower than the existing industrial silicon phosphorus and boron content. High-quality super-metallurgical grade silicon. (6) Study on phosphorus removal from metallurgical grade silicon by gas blowing refining. The results show that phosphorus in silicon melt decreases from 94 ppmw when using side wall and bottom porous nozzles, refining time is 3 hours, refining temperature is 1793 K, refining temperature is 373 K and refining gas velocity is 2 L/min. From thermodynamic and kinetic analysis, it can be concluded that water vapor in refining gas reacts with molten silicon to form silicon oxide and H2, and part of H2 dissolves in molten silicon. Then [H] in molten silicon reacts with [P] in molten silicon to form PH3, which is then taken away from molten silicon by argon bubbles. In this study, the preparation of super-metallurgical silicon from carbonized rice husk powder by electrothermal metallurgy was realized, which laid a foundation for the preparation of solar-grade polysilicon by electrothermal metallurgy with high-purity powder.
【学位授予单位】：东北大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TN304.12
[Abstract]:As a safe, widely distributed and clean renewable energy, solar energy has developed rapidly and has become the most important new energy in the 21st century. Silicon is the most important basic material for solar cells. Reducing the cost of silicon materials has become the development of photovoltaic energy. The key point is that the main technological improvement of the Siemens method is mainly monopolized in the United States, Japan, Germany and other countries. China has not mastered the core technology of the method, and polycrystalline silicon mainly depends on imports. The technology of metallurgical preparation of polycrystalline silicon by weight is of strategic importance to the development of photovoltaic industry in China. The so-called super-metallurgical grade silicon (UMG-Si) means that the purity of silicon is higher than that of metallurgical grade silicon, such as Fe, Al, Ca, P and B, and the content of impurities is lower than the national A-grade industrial silicon standard. The technology and mechanism of preparing super-metallurgical grade silicon from carbonized rice husk by electrothermal metallurgy were studied, which laid a foundation for the preparation of solar grade polysilicon by electrothermal metallurgy. The carbonized rice husk (CRH) contains high carbon content (50%) and a certain amount of Si02 (about 25%) is an excellent carbon reducing agent for smelting Si. (2) Study on the proportioning and physical properties of pellets; (3) Thermodynamic analysis and verification in the preparation of silicon from powdered materials by electrothermal metallurgy; (4) Study on melting silicon from carbonized rice husk powder; (5) Study on melting super-metallurgical grade silicon from the mixture of carbonized rice husk powder and petroleum coke powder; (6) Study on refining phosphorus removal from metallurgical grade silicon by gas blowing. The main conclusions are as follows: (1) The optimum acid leaching process for carbonized rice husk is as follows: CRH powder is below 75 micron, hydrochloric acid concentration is 5wt%, reaction time is 3h, water bath temperature is 60, leaching liquid-solid ratio is 14:1, stirring speed is 60r/min, the total removal rate of metal elements is 96.41%, the total removal rate of non-metal elements is 66.68%; the impurities in CRH powder after ultrasonic acid leaching are 66.68%. The total removal rate of metal elements and non-metal elements was 99.07% and 71.77% respectively. The removal effect was not obvious with the extension of ultrasonic acid leaching time. The phosphorus removal rate was 91.85% and the sulfur removal rate was 88.96%. It was feasible to remove the phosphate impurities in carbonized rice husk powder under vacuum condition. The higher the vacuum degree, the lower the reaction temperature was. When the system pressure was 70 kPa, the temperature of phosphorus removal reaction was 1100 ((1373K). (2) Carbonized rice husk and air. The activation energy E and pre-exponential factor A of the oxidation reaction were 78.89 kJ.mol-1 and 2083.03 min-1, respectively. The results showed that the material ratio of the pellets with carbonized rice husk powder as carbon reducing agent was quartz sand powder: carbonized rice husk powder: binder = 100:85.14:0.56, and the optimum technological conditions were as follows: the particle size of the pellets was 75 micron, the pressing pressure was 15 MPa, and the binder was 100:85.14:0.56. The compressive strength and porosity of the pellets were 3.0 MPa and 38.6% respectively when the dosage of the additive was 3% and the dosage of water was 7 wt%. When the mixture of carbon reducing agent was used, the pellets were composed of quartz sand powder, carbonized rice hull powder, petroleum coke powder, binder = 100:54.61:22.34:0.53. The compressive strength of the pellets was 5.8 MPa and the porosity was 25.2%. (3) The relationship between Gibbs free energy and temperature of the reactions in the Si-C-0 system was calculated, and the lowest temperature of the reactions was determined. The calculated results were verified by HSC thermodynamic calculation software. The formation and decomposition reactions of iO and SiC occur only when the temperature is raised to 1900 C, and there are SiC, SiO2 and a small amount of SiO phases in the product. (4) The results show that it is feasible to melt silicon by using carbonized rice husk powder as carbon reducing agent, and the secondary industrial silicon with purity of 99.32wt% is obtained. The content of impurities in the product silicon is only 26 ppmw and 15 ppmw respectively, which are lower than that of phosphorus (120-200 ppmw) and boron (20-60 ppmw) in the existing industrial silicon. (5) When the mixed powders of carbonized rice husk powder and petroleum coke powder are used as carbon reductants, the results show that the suitable output voltage is 25-30V when the output current is stable at 500A, and the maximum yield of silicon is 30.7% when the additional carbon content is 30%, and the content of silicon in the bottom slag is also less. The content is 99.68 wt%, which has exceeded the national A-grade industrial silicon (chemical silicon) standard (Si%>99.60%). The main iron, aluminum and calcium impurities are lower than the existing national A-grade industrial silicon standard. The contents of phosphorus and boron are 24 ppmw and 14 ppmw respectively, which are also lower than the existing industrial silicon phosphorus and boron content. High-quality super-metallurgical grade silicon. (6) Study on phosphorus removal from metallurgical grade silicon by gas blowing refining. The results show that phosphorus in silicon melt decreases from 94 ppmw when using side wall and bottom porous nozzles, refining time is 3 hours, refining temperature is 1793 K, refining temperature is 373 K and refining gas velocity is 2 L/min. From thermodynamic and kinetic analysis, it can be concluded that water vapor in refining gas reacts with molten silicon to form silicon oxide and H2, and part of H2 dissolves in molten silicon. Then [H] in molten silicon reacts with [P] in molten silicon to form PH3, which is then taken away from molten silicon by argon bubbles. In this study, the preparation of super-metallurgical silicon from carbonized rice husk powder by electrothermal metallurgy was realized, which laid a foundation for the preparation of solar-grade polysilicon by electrothermal metallurgy with high-purity powder.
【学位授予单位】：东北大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TN304.12
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