Non Condensable Gas Reinjection Trial at Ngatamariki Geothermal Power Plant

Abstract

As a baseload low emissions source of renewable energy, geothermal development will play a key role in the transition to a low carbon future. On average, the emissions intensity from currently producing geothermal power stations in New Zealand is 73gCO2e/kWh (McLean, Richardson, Quinao, Clark, & Owens, 2020). While this is significantly lower than many other sources of power generation, there is still an opportunity for the industry to reduce greenhouse gas emissions in the coming years.
This paper describes the feasibility studies and initial results for large scale testing of reinjection of ‘Non-Condensable Gases’ (NCGs) into the Ngatamariki geothermal reservoir. The testing aimed to trial reinjection of a quarter of the power station’s produced NCGs into the brine stream as an opportunity to reduce emissions and evaluate NCG injection as a means of addressing mineral scaling in the formation. Key design considerations from a reservoir, chemistry, and process engineering viewpoint are discussed.