Colloquia

Summary

Geothermal energy is a promising renewable heat source that extracts thermal energy from hot brine originating in deep underground aquifers. A key component in these systems is the gas–liquid separator: a large vessel that removes natural gas bubbles that form as the brine is pumped to the surface. Although separators are well established in the oil and gas industry, their performance under geothermal conditions is still poorly understood. As a result, current designs may be oversized, expensive, and vulnerable to severe corrosion due to the highly saline and corrosive nature of geothermal brine. 

In this thesis, the multiphase flow of geothermal brine was studied to gain insight into the degassing process occurring within the separator. To achieve this, a custom sight-glass instrument was developed to provide visual access to the flow just before it enters the separator. Using a high-speed camera equipped with a microscopic lens, sharp images and videos were taken from which the bubble size distribution was determined. It was found that the bubble sizes range from 10 to 100 µm, with a Sauter mean diameter of 47 µm.

These experimental data were combined with rise-velocity models adapted to geothermal conditions, allowing for an analysis of the degassing dynamics within the separator. The results show that the current configuration does not achieve complete separation, with the smallest bubbles requiring tens of minutes to reach the water surface. Explanations for this inefficient separation are discussed, along with practical implications for future separator design.