ToolFusion
📋 Case Study

The Geysers Unit 16 ORC Augmentation – California, USA

Two-phase inlet flow causing expander cavitation; variable flow rates due to upstream steam turbine cycling; NEMA 4X enclosure requirement for coastal fog environment

🏗️ Project Overview

Addition of 3.2 MW transcritical ORC using R245fa to utilize 115°C two-phase geothermal effluent from existing dry-steam turbine condensate stream

🎯 Challenge

Two-phase inlet flow causing expander cavitation; variable flow rates due to upstream steam turbine cycling; NEMA 4X enclosure requirement for coastal fog environment

🔧 Design Approach

Vapor-liquid separator + flash drum upstream of expander; variable-speed axial turbine with anti-cavitation blade profile; stainless-clad NEMA 4X enclosure with desiccant air purge

📐 Design Diagram

INLET 2-Phase Flow (x = 0.38) V/L Separator + Flash Drum TURB VS Axial Expander σ = 1.82 NEMA 4X Stainless-clad Desiccant Purge Challenge: Cavitation • Cycling Flow • Fog Design Solution: V/L Separation • Flash Control Anti-Cavitation: VS Speed • Blade Profile Environment: Coastal Fog • Corrosion 30 mm The Geysers Unit 16 ORC Augmentation

AI-generated project design illustration

📐 Key Calculations

Flash Vapor Fraction

x = (h_in − h_f) / (h_g − h_f)
Result: 0.38
Dictated separator sizing and vapor feed rate to expander

Cavitation Number

σ = (P_in − P_vap) / (0.5·ρ·V²)
Result: 1.82
Confirmed safe operation above critical threshold of 1.2

📊 Results

Achieved 13.1% net efficiency across 60–100% load range; zero cavitation events in 36-month operation; 98.7% availability factor

💡 Lessons Learned

  • •Two-phase separation is non-negotiable for reliable ORC augmentation
  • •Cavitation number must be recalculated at every load point—not just design point
  • •Desiccant purge extended electronics service life by 3× in high-humidity environments

✅ Key Takeaways

  • 1Two-phase separation is non-negotiable for reliable ORC augmentation
  • 2Cavitation number must be recalculated at every load point—not just design point
  • 3Desiccant purge extended electronics service life by 3× in high-humidity environments