New Opportunities and Applications for Closed-Loop Geothermal Energy Systems

摘要

Geothermal energy, the world's most abundant continuous heat supply, is available worldwide. Renewable geothermal energy systems generate clean, reliable, secure, and resilient electric power. Despite burgeoning demand for power, geothermal energy growth has been paradoxically low due to the limitations of legacy hydrothermal technology. However, attempts to use enhanced geothermal systems (EGS) to remedy legacy limitations have yet to succeed, due to the complexity of finding, fracturing, and maintaining the subsurface resources to allow the adequate flow of heated geo-fluids. In contrast, Closed-Loop Geothermal (CLG) energy systems overcome permeability and flow issues by circulating fluid through sealed wells and pipes. CLG systems are defined as commercial-scale installations that provide geothermal heat for power generation, energy storage, or industrial applications by using an enclosed down-hole heat exchanger (DHX) or sealed pipes recycling a working fluid. CLG technologies transfer subsurface heat into a thermal transport fluid continuously circulating within the sealed wellbore. The versatility of carbon-free CLG applications is evidenced by the wide variety of different well and pipe configurations that can be evaluated to optimize site-specific costs and performance and by the use of different working fluids, such as water and supercritical CO_2 (sCO_2). This paper first focuses on how CLG expands the range of clean geothermal power generation to include significant, but previously inaccessible, geothermal resources and how CLG enables retrofits of unproductive geothermal and oil and gas wells. It then discusses the unique ability of CLG to provide both continuous renewable electric power and precise flows of heat at high pressure to increase the efficiency and reduce the costs of high-value industrial applications, such as hydrogen production and lithium extraction from brines, all while reducing emissions of global greenhouse gases (GHG).