| Title | The Role of Ammonia in the Coso Geothermal Field |
|---|---|
| Authors | Cliff BUCK |
| Year | 2025 |
| Conference | Stanford Geothermal Workshop |
| Keywords | ammonia, cooling towers, magmatic signature, partitioning |
| Abstract | Vapor phase ammonia results have been produced from the Coso Geothermal Field for over 20 years with no large increase or decrease in concentrations. After the steam turbine all of the ammonia partitions into the liquid condensate that goes to the Cooling Towers which concentrates it through evaporation from 3 ppm in produced steam to 10 ppm in winter and to 45 ppm in summer. All the other gases CO2, H2S, H2, and CH4 partition into the vapor phase. Very little of the H2S partitions into the condensate at Coso compared to other geothermal power plants. The cooling tower blow down is injected back into the resource where small differences in ammonia concentration can be monitored in the steam produced. These are plotted to show the returns of injection. In the Navy I area of Coso the wells are mostly dry steam wells where these plots have been most useful. Other areas of Coso have wells with both brine and steam phases and the condensate is mixed with the brine before injection and the ammonia changes are not as pronounced. The vapor phase ammonia is in equilibrium with the ammonia in the brine. Ammonia is not measured in the brine but is calculated from equations by Fournier and Giggenbach. The highest concentrations of ammonia in steam are 20 ppm from three wells that are a hot spot with a magmatic signature. This is a NH4Cl species similar to the Northwest Geysers but at a lower level. Upon completion of drilling Prati State 10 had the highest dry gas ammonia concentration at 10%. Coso wells are much lower at less than 0.5 percent. After years of injecting all of the ammonia back into the resource that has been produced there has not been a large increase in ammonia concentrations in steam. |