Scaling Rate Reduction at Wairakei Binary Through Application of Scale Inhibitor

Abstract

Silica scaling at the Wairakei binary plant heat exchangers increases resistance to flow and thus causes reduced flow of separated geothermal water through the facility, wastage of geothermal energy and reduced power generation.
Historically this has been managed by mechanical or chemical cleaning of the heat exchangers on a performance basis, with associated cost and loss of generation during the cleaning outage.
Following a system review and improvements to the asset surveillance program, periods of unusually high scaling rate were identified and, through integrated review, linked to downhole chemical injection (Nalco GEO907) deployed to inhibit calcite scaling in a production well.
Through plant trials, a link between the injection of this chemical and reduced silica scaling rate of the binary was demonstrated. This enabled an opportunity to reduce the scaling rate by over 90% through sustained injection of the chemical to the binary plant, independent of the production well flowing to the plant.