Assessing Impurity Impacts on Phase Stability in CO2-Based Closed-Loop Heat Exchangers for Super-Hot Geothermal Systems

Document Type

Conference Proceeding

Publication Date

1-1-2025

Abstract

The use of CO2 as a geofluid in closed-loop geothermal heat exchangers offers high heat transfer performance and reduced pumping power, but impurities from supply sources and potential ingress complicate phase behavior. This study investigates the effects of nitrogen (N2) and water (H2O) on phase stability and thermal output in super-hot conditions (>374 °C, >22 MPa) using numerical simulations of a Deep Borehole Heat Exchanger (DBHE). N2 represents pre-existing/residual noncondensables (baseline ≤5 mol%, stress-test 10-15 mol%), while H2O represents naturally occurring moisture (baseline 600 ppm) and ingress at 5-15 mol %. Pure CO2 cases show strong buoyancy-driven circulation, low factional losses, and high outlet temperatures. Increasing N2 content progressively lowers heat extraction and outlet Cp, whereas H2O raises both but reduces buoyancy. The results highlight that mixture-aware property models and composition control are critical for maintaining single-phase stability and high-quality thermal output in super-hot closed-loop systems.

Publication Source (Journal or Book title)

Transactions Geothermal Resources Council

First Page

317

Last Page

337

This document is currently not available here.

Share

COinS