Assessment of a Closed-Loop Geothermal System for Seasonal Freeze-Back Stabilization of Permafrost

ABSTRACT: Wastewater treatment lagoons are practical and cost-effective system for smaller towns across Canada to prevent wastewater seepage into the environment. Essentially all structures over permafrost that disrupt the natural winter temperatures contacting the ground surface initiates permafrost thawing over the long-term and this includes lagoons. KGS Group has been developing the concept of using conventional closed-loop geothermal systems within the sediments below the base of lagoon to allow a refrigerated solution to be circulated to freeze the soil below the lagoon. This paper assesses the effectiveness of the geothermal freeze-back concept using a heat transfer model developed in COMSOL Multiphysics. The model evaluates variable flow velocities of 0.5 m/s and 0.25 m/s with the circulation of the antifreeze solution to temperatures as low as -20°C. The results of this assessment will provide valuable understanding of the design and costs of a conventional geothermal freeze-back system for large developments over permafrost.