Here’s a detailed explanation of Pressure Vessels & Safety Valves in the context of Supercritical Fluid Extraction (SFE):
1. Pressure Vessels in SFE
Pressure vessels are high-pressure containers designed to hold supercritical CO₂ and feedstock under pressures above the critical point (typically 100–600 bar).
Functions:
- Contain the supercritical fluid during extraction
- Maintain controlled pressure and temperature
- Provide a safe environment for high-pressure operations
Design Considerations:
- Material: Stainless steel (SS 316L/304), Hastelloy, or other high-strength alloys
- Wall thickness: Calculated based on maximum operating pressure (MOP) and safety factor (usually 1.5–2×)
- Shape: Cylindrical with hemispherical or torispherical ends for even stress distribution
- Volume: Lab-scale (50–500 mL), pilot-scale (1–20 L), industrial-scale (50–500+ L)
- Corrosion resistance: Essential if co-solvents (e.g., ethanol) or reactive compounds are used
- Instrumentation: Ports for pressure sensors, thermocouples, CO₂ inlet/outlet, sampling
2. Safety Valves
Safety valves protect pressure vessels from overpressure, preventing catastrophic failure.
Types of Safety Valves in SFE Systems:
- Spring-loaded Safety Relief Valves
- Opens when pressure exceeds set point
- Automatically closes once pressure drops
- Common in lab, pilot, and industrial systems
- Burst Discs (Rupture Discs)
- One-time, sacrificial device
- Bursts at a preset pressure
- Often used in redundant safety systems
- Pressure Relief Lines
- Directs CO₂ safely to vent or recovery system
- Prevents exposure to personnel
3. Operational Considerations
- Set point selection: Slightly above normal operating pressure, below vessel design limit
- Redundancy: Use of valve + burst disc for double protection
- Regular testing: Annual or semi-annual inspection per ASME / local regulations
- Venting: Safe venting of CO₂ to avoid asphyxiation hazards
4. Regulatory & Standards
- ASME Boiler & Pressure Vessel Code: governs design, fabrication, and testing
- PED (Pressure Equipment Directive): for EU compliance
- Material certification: ensures vessel can handle expected pressure and corrosion
5. Summary Table
| Component | Purpose / Function |
|---|---|
| Pressure Vessel | Contain supercritical CO₂ & feedstock safely |
| Material | Stainless steel, corrosion-resistant alloys |
| Shape | Cylindrical, hemispherical ends for stress distribution |
| Safety Valve | Automatically releases pressure above set point |
| Burst Disc | One-time overpressure protection |
| Pressure Relief Line | Safely vents CO₂ to atmosphere or recovery |
| Instrumentation | Pressure sensors, thermocouples, sampling ports |
✅ Bottom Line:
Pressure vessels and safety valves are critical to SFE operation, ensuring process control, operator safety, and regulatory compliance. Proper design, rating, and maintenance directly affect system reliability and extraction consistency.
I can also create a schematic showing a pressure vessel with CO₂ inlet, outlet, safety valve, and burst disc for training or presentations.
Do you want me to make that schematic?