| Abstract |
The removal of carbon dioxide and hydrogen sulphide at each successive stage of steam separation from a geothermal discharge leads to values in the residual waters which for New Zealand systems fall in the range 7.5 - In this range the dissociation of silicic acid to form silicate ions becomes significant and the solubility of amorphous silica increases. Recognition of this effect allows that, without the development of significant scaling potential, steam may be separated at pressures substantially lower than has normally been recommended in the past on the basis of the solubility silica in pure water. A computer program is described for the routine calculation of water and steam chemistry resulting from primary and secondary steam separation from well discharges. These data may be used in the design of flash plant and the management of geothermal fields to achieve maximum steam recovery while minimising problems due to silica deposition in pipeline systems. Data from Wairakei and the proposed Ohaki (Broadlands) field are given as examples. |