Application of supersonic ejector principle to enhance flow in low-pressure geothermal production wells
Author: Daniel Wanga Odongo
Year: 2024
Supervisors: María Sigríður Guðjónsdóttir, Guðrún A. Sævarsdóttir, Ximena Guardia Muguruza
Abstract:
Geothermal wells are one of the key components and most capital-intensive parts of any geothermal power generation facility. However, they often experience pressure decline over their lifetime, leading in some cases to the well pressure falling below the power plant operating conditions, which make wells unusable for power generation. This can make the overall project more costly since additional wells must be drilled to compensate for the unavailable steam to maintain the desired power plant output. This study explores the possibility of using ejectors to solve that problem. Ejectors have been used in various applications in the oil and gas and refrigeration industries. In geothermal power generation, ejectors are widely used to extract non-condensable gases from the condenser. Ejectors are static devices that use kinetic energy from a high-pressure stream to induce flow from a lower-pressure stream. Supersonic ejectors work by using a convergent-divergent nozzle to accelerate a primary fluid to supersonic conditions. This creates an under-pressure that allows a secondary flow to enter, and the mixture exits at an intermediate pressure. The experiments described in this work were carried out in the Reykjavik University energy laboratory to fabricate and test a supersonic ejector on a laboratory-scale. It was set up to connect two streams of saturated steam at different pressures and compare the results with an analytical model developed in earlier studies. The experiment was focused on the effect of ejector dimensions on performance, specifically the constant area mixing section (CAMS). The experiment was successful in proving that the ejector works by showing gained pressure and entrainment of the secondary flow despite not having a good match with the analytical model. From the experiment, the 5 mm CAMS ejector provided the best results using entrainment ratio, gained pressure and outlet pressure to measure its performance. The analytical model was also used to design a potential supersonic ejector to connect two production wells in the Olkaria geothermal field in Kenya. The design showed that an additional 2.2 MW of electrical power could be generated using this ejector.