Impact of Fluid Chemistry on Power Development at Rotokawa, New Zealand

Abstract

Power station chemistry in a HP turbine with two types of direct contact condenser systems and in a HP turbine with a binary plant heat exchanger were modelled using gas compositions from well RK5 in the Rotokawa geothermal field. For all three options a steam flow rate of 90 was input to the model. The partitioning of gases and the condensate chemistry in each option was directly related to the partial pressure of the carbon dioxide, hydrogen sulphide, and other sparingly soluble gases, and to the concentration of ammonia in the steam. For the direct contact options oxidation of 30% of the total dissolved produced sulphuric acid that required biocide dosing or 12 and 5 of NaOH to maintain an acceptable value (about 6) around the circuit. Dosing can be minimised by using the second design in which water flow from the ancillary gas coolers was directed to the condenser and by optimising the operating conditions. In a binary plant the acidity is mainly due to and 0.5 of NaOH (45 is needed to a value of 6. A silica saturation index of 1.02 is calculated for a separation temperature of 210?C at a pressure of 19 Mixing the separated water at 210?C with 45?C condensate from the outlet of the binary plant is a viable option as the silica saturation index is not changed.