New On-Site Test-Procedure for Field Investigations on Groundwater in Aquifer Thermal Energy Storage Systems with Mobile Test Equipment

Abstract

Operational experience with High-Temperature Aquifer Thermal Energy Storage (HT-ATES) systems sometimes revealed technical problems due to calcite precipitation in heat exchangers. However, no satisfying prediction of scaling behavior in heat exchangers is possible. In order to gain reliable information on the behavior of groundwater in heat exchangers during heating at scheduled HT-ATES sites a mobile test rig has been constructed for preliminary investigations on groundwater for use in HT-ATES plants. Furthermore, a new on-site test procedure - scaling test - has been worked out by which an uncritical temperature level in respect to calcite formation in heat exchangers can be evaluated. Up to now, results of experiments with diverse groundwater types have shown both a distinct influence of groundwater chemistry and of temperature level on calcite precipitation in the test rig. It is estimated that carbonate containing groundwater might be heated up to about 60?C (140?F), whereas saline groundwater can be heated up to more than 70?C (158?F) without causing calcite precipitation. However, it is not yet recommended to transfer these results on scheduled HT-ATES plants with similar groundwater, but to carry out special investigations.