| Title | Significance of Pressure Let Down Station in Mitigating Effects of Silica Precipitation in Steam Pipelines: a Case Study of Olkaria 280MW Project |
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| Authors | J. Chumari and D. Odongo |
| Year | 2020 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | PLDS, De-superheating, Silica |
| Abstract | In 2012, KenGen began construction of two geothermal power plants: 140MWe Olkaria IV and 2 additional units, units 4 & 5 (Olkaria IAU) adding140MWe to Olkaria I and thereby increasing power generation in Kenya by 280MWe. The two power plants have turbine inlet pressures of 6.0 bara and 5.0 bara for Olkaria IV and Olkaria IAU respectively. This meant the steam gathering systems would also operate at that pressure. While the project was in progress, a new optimization study reported that the deeper wells in Domes, East and North East fields which serve the power plants with steam tap fluids from reservoirs that are rich in silica. The issue was compounded by high enthalpies of the wells averaging 1790kj/kg to 2300kj/kg thereby increasing silica solubility and chances of precipitation in steam pipelines. The concern raised resulted in KenGen incorporating Pressure Let down Stations (PLDS) in the two power plants that would maintain the steamfield pressure at the maximum but within the constraints of the already selected equipment, and then expand the steam adiabatically to drop its pressure to required values. This paper will use the case study of these power plants to highlight the significance of the Pressure Let down Stations in controlling the effects of silica deposition in steam gathering systems. |