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Polysilicon

Twenty-five (25) CA-1AS 2-inch to 8-inch valves were chosen for this manufacturer of polycrystalline silicon materials and high-purity silicon products. Primary media was trichlorosilanes. All valves were oxygen cleaned.

Polycrystalline silicon, or polysilicon, is a high purity, polycrystalline form of silicon, used as a raw material by the electronics industry and on solar cells to directly convert sunlight into electricity.

Production of polysilicon is a severe service for valves, and material selection is crucial. Extreme corrosion occurs from the beginning of the process at the fluidized bed reactor and extends throughout the plant.

Around the Chemical Vapor Deposition (CVD) reactor, temperatures are elevated up to 1650 F. There are numerous lower temperature and lower pressure processes that are difficult for other valve manufacturers to handle. This is due to the corrosive nature of chemicals produced during the manufacture of pure silicone, such as Trichlorosilane

Trichlorosilane is a colorless liquid with a sharp, choking odor. This chemical readily burns readily and rapidly vaporizes at atmospheric pressure and normal ambient temperature. Inhalation causes severe irritation of respiratory system, and as a liquid, severely burns the eyes and skin.

Other hazardous, corrosive chemicals in the manufacturer of polysilicon include:

  • Silicon Tetrachloride
  • Dichlorosilane
  • Boron Trichloride
  • Phosphate Pentachloride
  • Hydrochloric Acid

Valves must absolutely isolate—and not just during the initial pressure test—but for years into polysilicon production. 

Materials and Coatings
The application-specific materials and coatings of MOGAS valves provide enhanced corrosion resistance, reduce refurbishment costs, and extend valve life and run times—which means reliable endurance of critical path valves.

Stem Designs
Linear rising stem valve designs have an extremely difficult time maintaining a leak-free stem seal due to high friction, shaft wear, erosion and backlash.

The MOGAS valve stem design has proven a reliable choice. It has independent stem seals which include:
• pressure-energized and mate-lapped stem seal bearing
• stem packing that uses two anti-extrusion rings and three application-specific packing rings
• optional lantern rings, piped to a detector
• live loading system

Precision Cleaning
MOGAS' in-house cleanroom keeps impurities from corrupting the integrity of the chemical composition of the media. As part of our stringent cleaning procedures, verifiable absence is determined through the use of qualitative and quantitative inspections. Each job is fully documented to define, control and monitor processes such as material flow, cleaning details, inspection results, packaging and labeling.
 

Typical Operating Conditions:
  • Temperature: -50 – 1650° F (-4 – 900° C)
  • Pressure: 50 – 100 psig (3.4 – 6.9 bar g)

Polysilicon Process Flow Diagram
  1. Metallurgical-grade Silicon Feed
  2. Hydrochloric Acid Feed
  3. Fresh Hydrogen Feed
  4. Fluidized Bed Reactor
  5. Hydrogen Recycle
  6. Hydrogen Separator
  7. Boron TriChloride Waste
  8. TriChloroSilane Distillation Tower 1
  9. TriChloroSilane Distillation Tower 2
  10. Phosphate PentaChloride Waste
  11. TriChloroSilane Distillation Tower 3
  12. TetraChloroSilane (TET) Waste
  13. Chemical Vapor Deposition (CVD) Reactor Inlet
  14. Chemical Vapor Deposition (CVD) Reactor Outlet
  15. Silicon Product
  16. Silicon Separator
  17. Unreacted TriChloroSilane Distillation Tower
  18. TetraChloroSilane (TET) Waste
  19. Hydrochloric Acid Distillation Tower
  20. TriChloroSilane Recycle
  21. Hydrolysis Reactor
  22. SiliconDioxyde Cyclone Gas
  23. SiliconDioxyde Product
 
  • Heat Exchanger (not shown)
  • General Ball Valves (not shown)