Plasma Furnace Silicon Refining With Methane and Getter Purification
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing silicon refining processes are costly and inefficient, particularly for producing solar-grade silicon, due to the use of high-cost raw materials and hazardous chemicals like silicon tetrachloride and explosive silane, and they struggle with impurity removal, especially boron and phosphorus.
Innovation Solution
A plasma furnace process using low-cost silica powder, methane, and a rotating donut-shaped plasma to produce solar-grade silicon, eliminating the need for silicon tetrachloride and silane, and incorporating a getter to volatilize impurities, followed by unidirectional solidification to achieve high purity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional Siemens process is used to produce solar-grade silicon, then high purity (9N) silicon can be achieved, but production cost increases to $16-20 per kilogram and hazardous chemicals like silicon tetrachloride and explosive silane are required
Solution Approach 1:
The patent replaces expensive, hazardous chemicals (silicon tetrachloride, explosive silane) with inexpensive, safe alternatives (silica powder, methane gas). The plasma furnace uses low-cost silica powder as feedstock and methane as a safe reducing agent, eliminating the need for costly and dangerous chemicals while maintaining high production efficiency and purity
Solution Approach 2:
The patent replaces the complex multi-step chemical process (SiO2 → SiCl4 → SiH4 → Si) with a direct plasma-based reduction process (SiO2 + CH4 → Si + CO + H2O). The plasma furnace creates a controlled environment where silica powder is reduced by methane through plasma chemistry, eliminating multiple distillation and decomposition steps required in traditional processes
2Quantity of substance
If traditional coke reduction process is used in submerged arc furnace, then metallurgical-grade silicon can be produced, but impurity removal becomes difficult and multiple secondary refining steps are required
Solution Approach 1:
The patent changes the fundamental reaction parameters by using plasma instead of thermal reduction. The plasma furnace operates at lower temperatures with different chemical pathways, using methane as a reducing agent that produces fewer impurities compared to coke. This parameter change enables direct production of solar-grade silicon with boron and phosphorus impurities already reduced to acceptable levels
Solution Approach 2:
The patent introduces methane as an intermediary reducing agent that mediates the reduction of silica to silicon. Methane decomposes in the plasma to provide carbon and hydrogen for the reduction reaction, while its combustion products (CO and H2O) are easily removed. This intermediary approach avoids the introduction of coke-derived impurities and simplifies the refining process
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The process significantly reduces production costs to approximately $6 per kilogram of polysilicon, achieves high purity, and eliminates hazardous chemicals, while effectively removing impurities, resulting in a more efficient and cost-effective method for producing solar-grade silicon.
Implementation Method 1
a plasma furnace process using low-cost silica powder, methane, and a rotating donut-shaped plasma
Implementation Method 2
incorporating a getter to volatilize impurities
Implementation Method 3
a rotating donut-shaped plasma
Data Source
AI summary
A process for producing solar grade silicon from silica sand employs a plurality of plasma furnaces to perform a sequence of chemical reactions together with other process steps to produce solar grade silicon. The plasma furnace generates a stable dirty-air, donut-shaped plasma into which particulate matter can be introduced. The plasma in the first two stages is formed by gases from the chemical reactions and in the third from inert gasses. Cyclone separators are used to extract particulates from the plasma in an inert gas that prevents reverse reactions as the particulate cools.