Ceramic Valve Solutions for Polysilicon Reduction
Reliable flow control for trichlorosilane, hydrogen and abrasive silicon-bearing media in polysilicon reduction and tail gas systems
Ceramic valve solutions for abrasive silicon particles, corrosive chlorosilanes and high-purity service in polysilicon reduction and reduction tail gas systems
Trichlorosilane and high-purity hydrogen undergo a chemical vapor deposition reaction on the surface of heated silicon rods to produce high-purity polysilicon
Industry: Polysilicon
Operating Conditions
The process operates below 250°C and handles silicon powder, hydrogen, trichlorosilane, other chlorosilanes and amorphous silicon. Mixtures of hydrogen and chlorosilanes may be explosive if leaked. Precise control of the pressure and flow rate of the material entering the reduction furnace is essential to protect the silicon rods and directly affects the quality of the finished polysilicon
| Parameter | Value | Classification | Rating / Characteristic |
|---|---|---|---|
| Process medium | Silicon powder, hydrogen, chlorosilanes, hydrogen chloride and amorphous silicon | Gas-solid two-phase | Abrasive |
| Operating pressure | 5-6 bar | Nominal pressure | PN16/PN25 |
| Differential pressure | ≤1 MPa | Nominal size | DN50-300 |
| Temperature | <250°C | Thermal behavior | No thermal shock |
Medium Characteristics
| Property | Specification |
|---|---|
| Chemical composition | Chlorosilanes, hydrogen and hydrogen chloride |
| Corrosive constituents | Chlorosilanes and hydrogen chloride |
| pH | Not applicable |
| Solids content | Relatively high |
| Particle size | 150-600 μm |
| Particle hardness | Mohs 6-7, highly abrasive |
Special Characteristics of the Operating Conditions
Abrasion and Corrosion
- The medium contains highly diffusive hydrogen and relatively hard silicon powder, with abrasive wear being the primary concern
- Ultrafine amorphous silicon is both abrasive and prone to adhesion, scaling and deposit buildup. The valve flow path therefore requires an anti-accumulation design
- At elevated temperatures, hydrogen, hydrogen chloride and chlorosilanes act together, causing hydrogen embrittlement and intergranular corrosion
- Extremely tight sealing is required. External process leakage and inward leakage of air must both be prevented
Keywords: High hardness · Powder handling
Process Challenges and Key Opportunities
Materials and Designs of Existing Valves
Most existing valves are metal hard-seated valves, primarily ball valves and shut-off valves
Common Problems with Existing Valves
- High-hardness particles cause severe abrasive wear. Valve sticking can score the sealing surfaces, resulting in internal leakage
- Temperature fluctuations cause thermal expansion and contraction. Sealing components experience thermal-cycle fatigue, leading to leakage and failure of bellows seals
- Hydrogen chloride becomes highly corrosive in the presence of moisture
- Hydrogen atoms diffuse into and accumulate within metallic materials, reducing their ductility and mechanical strength and potentially causing hydrogen-induced brittle cracking
Replacement Intervals and Service Life
Typical service life ranges from approximately 3 to 6 months, depending on the valve position and operating conditions
Losses Caused by Shutdowns and Maintenance
- Interruptions to continuous production reduce overall production efficiency
- External leakage of flammable and explosive gases may result in serious process-safety incidents
Additional Considerations
Hydrogen is highly diffusive and can escape easily, causing atmospheric pollution and affecting downstream reaction quality. Frequent furnace changeovers expose valves to repeated hot-and-cold thermal cycling. The sealing surfaces must simultaneously resist corrosion, particle erosion and thermal fatigue
Keywords: High cost · Short service life · Frequent maintenance · Production incidents · Hydrogen embrittlement · Consistent product quality
Why Choose Ceramic Valves?
Exceptional Abrasion Resistance
- Engineered ceramics have a hardness of up to HRA 90, substantially higher than silicon powder, which is approximately HRA 70, providing excellent resistance to abrasive wear
- Their inorganic, non-metallic, chemically inert properties and stable covalently bonded crystal structure prevent hydrogen-related micro-erosion, surface fatigue and hydrogen embrittlement of the sealing components
Exceptional Corrosion Resistance
- Engineered ceramics possess inherent corrosion resistance and effectively withstand complex corrosive media containing chlorosilanes and hydrogen chloride, as well as the associated corrosion-erosion effects
- Their non-metallic construction eliminates metal-related hydrogen embrittlement
Fully Ceramic-Lined Ball-Valve Design
- The fully ceramic-lined construction provides a continuous ceramic flow path, preventing the process medium from contacting the metal valve body
- Its self-cleaning action helps prevent material buildup and valve sticking
- The ceramic flow path retains its erosion resistance throughout extended service
Service-Life Commitment
Minimum service life: control valves ≥3 years; on/off valves ≥5 years
Ceramic valves reduce replacement frequency, plant shutdowns and production losses, delivering lower lifecycle costs together with safer and more reliable operation
Conclusion
Specialized ceramic materials successfully resolve the severe valve wear and high-velocity erosion encountered in polysilicon production. These valves have been successfully applied at critical positions in synthesis and cold-hydrogenation systems operated by several of the world’s top ten polysilicon and organosilicon producers, providing proven solutions to longstanding operational challenges
Case Study
End Users
- Xinte Energy Co., Ltd., China, in service since 2016
- Inner Mongolia Shenzhou Silicon Industry Co., Ltd., China, in service since 2018
- Xinjiang Xinte Crystal Silicon High-Tech Co., Ltd., China, in service since 2018
- Yunnan Tongwei High-Purity Crystalline Silicon Co., Ltd., China, in service since 2021
- Inner Mongolia Xinte Silicon Materials Co., Ltd., China, in service since 2022
Application Background and Results
The reduction off-gas unit is part of the process in which polysilicon rods are ultimately formed. Initially, the unit was equipped with valves from foreign brands. These valves were expensive and developed abrasive wear, internal leakage and sticking after entering service
The silicon-powder concentration in this section is lower than in the synthesis and cold-hydrogenation units, so wear progresses more slowly. However, conventional metal valves still cannot fundamentally prevent sealing-surface damage caused by silicon powder and chlorosilanes
After a Chinese polysilicon producer trialed KOWOV ceramic valves, the valves operated continuously for six years. Annual inspections confirmed that the sealing surfaces remained in excellent condition. This delivered substantial savings in replacement and maintenance costs while reducing the need for manual intervention
Conclusion
Proven service life
- Control valves: 6 years
- On/off valves: ≥6 years
Polysilicon Reduction: site photographs
Commonly Used Products
FCCV1
Standard Ceramic Ball Valve
The FCCV1 series is the standard model in the ceramic ball-valve range. It is designed for highly corrosive and severely abrasive service at temperatures up to 180°C and differential pressures up to 2.0 MPa
- Wide sealing surfaces and scraper-type valve seats provide reliable shutoff and extended service life
- The ball and valve-seat sealing surfaces are match-lapped to ensure tight sealing
- The stuffing box incorporates live loading that maintains a constant packing load even after substantial wear, extending packing service life
- The symmetrical valve design provides bidirectional sealing with no flow-direction restrictions
- Wide ceramic flange-sealing surfaces protect the metal flanges from erosion and corrosion by the process medium
ELCV
Economical Ceramic Ball Valve
The ELCV uses essentially the same basic structural design as the FCCV1 but does not include a top mounting platform. Materials can be selected flexibly according to the operating conditions, providing a more economical ceramic-valve solution, although overall reliability is slightly lower than that of the FCCV1
| Parameter | Specification |
|---|---|
| Valve design | Floating-ball construction |
| Flange standards | ASME B16.5 / HG / DIN / JIS |
| Pressure rating | PN10-PN50 / ASME Class 150-300 |
| Operating temperature | −40°C to 180°C |
FCRV
Ceramic C-Ball Valve
The valve features a special C-shaped design. Its ball consists of a C-shaped metal support and a one-piece ceramic ball segment mechanically connected and securely embedded together. The ceramic segment protects the metal support from direct erosion by the process medium
The concentric design keeps the ceramic ball segment in continuous contact with the seat during operation, allowing it to scrape away deposits adhering to the sealing surfaces and maintain reliable shut-off performance. It is particularly suitable for media prone to crystallization, scaling, agglomeration, high solids loading and valve jamming. Its cavity-free design minimizes material accumulation inside the valve
Size range: DN50-400
View FCRVContact Us
Talk to our team about your polysilicon reduction application
Discuss your application
