Project Description:
This report presents a comprehensive process design that combines both thermochemical and separation processes to produce high-purity polycrystalline silicon for use in solar cells. The proposed plant uses quartz and charcoal as feedstock and starts with carbothermic reduction in a high-temperature Gibbs reactor furnace at 1550 °C and 0.1 atm to yield metallurgical-grade silicon (Mg-Si). A multistage purification process, including flash separation and fractional distillation, is then used to achieve a 99.99% purity of trichlorosilane (SiHCl₃). This is produced by chlorinating the Mg-Si with hydrogen chloride (HCl) in a fluidized bed reactor. Chemical vapor deposition (CVD) at 700°C is used for final reduction to polycrystalline silicon, and solid separation is used to obtain the final product. Optimal feed rates give 0.0254 mol/s of poly-Si, which is roughly equal to ~2 to 2.55 million solar cells annually. A capital investment of $42.3 million is estimated via economic analysis, with the most significant investments being the furnace and the fluidized bed reactors. Process optimization and heat exchanger integration lower the utility cost to $8,074 annually, with a payback period of 1.56 years and a return on investment of 63.64%. To reduce raw material input and corrosive waste, environmental and safety considerations include recycling HCl back into the process, catalytically oxidizing residual CO to CO₂, and converting byproduct CO and H₂ into synthetic methanol with a 93.3% conversion rate. These considerations improve environmental compliance and operator safety. The design includes strong instrumentation and control systems for efficient and safe operation, complies with regulatory requirements, and provides low-toxic emissions. With its economic viability, technical feasibility, and environmental sustainability, the project is poised for launch in Arizona, coinciding with the growing demand for local high-efficiency solar production.
