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Corrosion Risk Assessment for Reinjection of Aerated Condensate

Nga Awa Purua geothermal power station (NAP) operates a conventional direct contact condenser with recirculating cooling water and forced air cooling towers. The power station is located at the Rotokawa Geothermal field, near Taupō in the North Island of New Zealand. The field supports two power stations: NAP, which was commissioned in 2010 with an installed capacity of 140 MW; and Rotokawa I, a binary power plant which has been in operation since 1997.

Product Number: 51323-19023-SG
Author: Sigit Prabowo, Kelly Melia, Alice Young, Aimee Calibugan, Keith Lichti, Farrell Siega
Publication Date: 2023
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Geothermal power stations that use direct contact condensers and forced air cooling towers typically use shallow reinjection for disposal of cooling tower blowdown. The reinjected fluid can be taken from the hot well pump return line to the cooling tower to give a minimum oxygen concentration, however, a low level of oxygen will invariably be present. This paper provides a theoretical analysis of the effect of reinjecting an oxygen containing cooling tower blowdown into a corrosive intermediate aquifer where the reinjected water may reach nearby wells cased in carbon steel. The procedures used for this assessment and the resultant effect on the corrosion risk for nearby wells are described. The results obtained show that the risk of additional corrosion may be slightly enhanced for nearby wells but of little impact for wells at some distance from the reinjection site.

Geothermal power stations that use direct contact condensers and forced air cooling towers typically use shallow reinjection for disposal of cooling tower blowdown. The reinjected fluid can be taken from the hot well pump return line to the cooling tower to give a minimum oxygen concentration, however, a low level of oxygen will invariably be present. This paper provides a theoretical analysis of the effect of reinjecting an oxygen containing cooling tower blowdown into a corrosive intermediate aquifer where the reinjected water may reach nearby wells cased in carbon steel. The procedures used for this assessment and the resultant effect on the corrosion risk for nearby wells are described. The results obtained show that the risk of additional corrosion may be slightly enhanced for nearby wells but of little impact for wells at some distance from the reinjection site.

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