Abstract
Extending the operational lifespan and expanding generation capacity in brownfield geothermal assets without drilling additional production wells represents a high-value pathway for sustainable energy transitions. This study presents the design optimization, thermodynamic exergy analysis, mechanical sizing, and techno-economic validation of a modernized hybrid Gas Extraction System (GES) for the rehabilitation of the 40-year-old Olkaria I Geothermal Power Plant (Units 1, 2, and 3) in Kenya. The legacy two-stage steam-jet ejector configuration exhibited severe exergy destruction (a rational exergy efficiency of only 17.0%, unrecoverably destroying 1.56 MW out of 1.89 MW input exergy), heavy parasitic motive steam consumption (8,880 kg/h), condenser gas-blanketing under non-condensable gas (NCG) surges, and ambient hydrogen sulfide (H2S) corrosion. To support a net station capacity uprate from 45.0 MW to 63.3 MW (+18.3 MW, a +40.7% capacity expansion) at an unchanged primary steam flow of 150.0 t/h per unit, an optimized hybrid GES (Case-C) was developed. The architecture integrates first-stage split steam-jet ejectors with a 70% / 50% / 30% capacity split (150% total suction capacity) for dynamic step-control under fluctuating reservoir NCG fractions (0.50 wt% guarantee to 1.00 wt% peak load), second-stage electric motor-driven Liquid Ring Vacuum Pumps (2 x 50% LRVPs) backed by a 100% standby steam ejector, and exhaust gas rerouting into cooling tower fan stacks for atmospheric updraft dilution. Thermodynamic modeling demonstrates that the preferred design lowers inter-condenser thermal load to 3,251,051.1 kJ/h under guarantee load while maintaining a stable main condenser vacuum of 0.100 bar(a). Replacing second-stage steam ejectors with motor-driven LRVPs conserves 4,635.0 kg/h of high-pressure motive steam across the plant, generating +652.8 kW of equivalent electrical power and yielding a net auxiliary electrical surplus of +322.8 kW after powering LRVP motors (330.0 kW). Rational exergy efficiency surges to 54.8% (a 3.2x gain), while exergy destruction drops by 82.1% to 0.28 MW. Financial analysis confirms an avoided drilling capital expenditure of USD $20.25 Million, a simple payback period of 1 year on a USD $14.50 Million investment, an NPV of USD $103.77 Million (8% WACC over 30 years), and an IRR of 72.4%.