Why Argon Gas Circulation and Purification

Argon gas circulation and purification systems usually run throughout the entire monocrystalline silicon production process. During the Czochralski (CZ) method of growing monocrystalline silicon, the furnace needs to continuously maintain a high-purity inert gas (argon) atmosphere to protect the silicon melt and the growing crystal from oxidation or contamination. As the crystal grows, the gas inside the furnace may become contaminated with trace impurities (such as silicon volatile compounds, small amounts of carbon oxides from the graphite hot zone, etc.).

Therefore, argon gas circulation and purification is needed to:

• Maintain Furnace Atmosphere Purity: Continuously remove impurities to ensure crystal quality.
• Lower Production Costs: Argon is a relatively expensive gas, and recycling it can significantly reduce its consumption.
• Protect the Environment: Reduce gas emissions.

The argon gas circulation and purification system constantly draws used inert gas from the furnace. This gas is then cooled, dedusted, and purified (removing impurities like oxygen, water vapor, and hydrocarbons) before being returned to the furnace for reuse. This is a continuous process that ensures the stability and purity of the monocrystalline silicon growth environment.

Argon Gas Circulation and Purification Process

In this setup, the argon gas circulation and purification system aims to recover and reuse argon gas containing trace amounts of dust and gaseous impurities, ensuring it meets the ultra-high purity requirements of monocrystalline silicon furnaces. Here is a breakdown of the gas circulation process and the role of the dust collector:

1. Exhaust Gas Discharge and Preliminary Cooling
   • Process: During the monocrystalline silicon pulling process, argon gas is continuously drawn out of the furnace by a vacuum pump. This extracted argon gas, in addition to trace silicon volatile compounds or carbides from the graphite hot zone, may contain very small amounts of active gases (such as oxygen, water vapor, despite efforts to control them).
   • Temperature: The gas is hot when discharged from the furnace, but its temperature will significantly decrease as it passes through piping and preliminary cooling devices, making it suitable for subsequent processing.
2. Pre-Filtration
   • Process: The gas enters the vacuum pump, where it is compressed and discharged. Before the vacuum pump, there is usually one or more pre-filters/cold traps.
   • Dust Removal: These pre-filters primarily capture larger particles and most condensable vapors to protect the vacuum pump from damage. They are typically oil mist filters, particulate filters, or cold traps that condense impurities by lowering the temperature.
3. Shaker Dust Removal
   • Process: After being discharged by the vacuum pump, a very small amount of extremely fine solid particles that were not completely captured by the pre-filters may still be discharged with the argon gas. This gas directly enters the shaker dust collector. A more efficient pulse jet dust collector is not used here to ensure the purity of the argon gas.
   • Role of the Dust Collector: The shaker dust collector acts as the final barrier for particulate matter removal. Its filter bags (which may be made of membrane filter material) can efficiently capture these sub-micron fine particles. Periodic shaking removes dust from the filter bags.
   • Gas State: At this stage, the argon gas entering the dust collector has been cooled, and its pressure is close to atmospheric pressure.
4. Gas Recovery and Preliminary Pressurization: After passing through the dust collector, the argon gas is free of solid particles but still contains gaseous impurities (such as trace amounts of O2, H2O, CO, etc.). This gas is collected and then undergoes preliminary pressurization by a recovery compressor, preparing it for entry into a high-pressure deep purification system.
5. Deep Purification System
   • Process: This is the core stage for argon gas recovery and reuse. The pressurized argon gas is fed into one or more series-connected gas purification units, each designed to remove different gaseous impurities:
     • Adsorption Unit: Contains adsorbents like molecular sieves and activated carbon, used to remove water vapor, carbon dioxide, and other polar molecules, as well as some organic compounds.
     • Catalytic Reduction Unit: Utilizes catalysts (e.g., palladium catalyst) that induce trace oxygen and hydrogen to react and form water under heated conditions, or convert carbon monoxide into carbon dioxide.
     • Cryogenic Separation Unit (Optional): For situations requiring extremely high purity or containing complex gaseous impurities, cryogenic technology may also be used to separate different gas components at extremely low temperatures.
   • Purity: After deep purification, the purity of the argon gas can be restored to 99.999% or even higher, often meeting or exceeding the purity of fresh argon gas.
6. Storage and Re-injection
   • Process: The now highly purified argon gas is transferred to storage tanks or high-pressure gas cylinders.
   • Re-injection: When needed, this high-purity argon gas is precisely re-injected into the monocrystalline silicon furnace, controlled by pressure regulators and flow meters, thereby completing the closed-loop circulation.

In this process, the shaker dust collector plays the role of a “secondary microparticle capture” or “safety emission guarantor,” rather than the primary equipment for purifying gaseous impurities. It ensures that the argon gas, after being extracted from the furnace and processed by the vacuum pump, meets environmental standards for solid particulate content before either being recirculated or ultimately released into the atmosphere, and prevents contamination of subsequent high-precision purification equipment.

For More Information

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