| Abstract |
ABSTRACT Binary power plants are widely used all over the world because of its ability to generate electricity at low temperatures. There is a lot of potential in the utilization of brine from Olkaria geothermal field but the main challenges are cooling of reservoir and silica scaling in the reinjection pipeline. There has been evolution on the way silica scaling is being managed to harness as much heat as possible from the geothermal fluid. Interest in silica scaling moved from actual concentration, to concentration ration, to incubation period and to polymerization. Silica scaling kinetics is affected by silica degree of super saturation, aeration, salinity, purity of geothermal fluid, pH and temperature. This study took into consideration cooling of reservoir and silica scaling kinetics in the determination of the binary power plant brine discharge temperature. Olkaria IV power plant was commissioned in September, 2014 and has two single flash units each with an installed capacity of 74,924 kW. Olkaria IV steam field has a two phase fluid with separation temperatures of about 187 ˚C – 189˚C and the brine is directly re-injected after separation. There exists an opportunity to utilize high temperatures of brine while avoiding and managing scaling impact. Binary power plant design is based on: separators pressures and temperatures, steam chemistry and flow rates, dry cell cooling tower and the ambient temperatures of Olkaria IV. Four options of utilizing Olkaria IV field brine for power generation are analyzed based on individual separators and combined flow rates. Silica scaling in heat exchangers, piping and reinjection wells are considered in plant design for sustainable operations and maintenance. The proposed binary power plant unlike conventional plants will be relatively cheap to implement because it uses an exciting steam gathering system, reinjection wells and developed site. The binary power plant will increase overall steam utilization factor and can take a shorter period to commission. |