Impact of Steam Chemistry on Power Development at Ohaaki, Mokai, Rotokawa and Tauhara Geothermal Fields

Abstract

Power station chemistry in a direct contact condenser and binary plant heat exchanger was modelled using gas compositions typical of steam from Ohaaki, Mokai, Rotokawa and Tauhara geothermal fields at an arbitrary flow rate of 100 partitioning of gases and the condensate chemistry was directly related to the gas partial pressures and the concentration of ammonia in the steam. Oxidation of 30%of the dissolved sulphide to sulphuric acid in the direct contact condenser circuit required dosing with 20 NaOH for Rotokawa, 11 for Mokai and 7 for Tauhara and type steam to maintain acceptable values (about 6) around the circuit. Mokai and Tauhara steam condensed in the heat exchanger to form acidic solutions at 4 and 4.5 respectively. Ohaaki and Rotokawa steam contains higher concentrations of ammonia so this type of steam condensed to form a less acidic fluid at 5.