Remote sensing investigations combined with Geographical investigation systems (GIS) provide a rapid and cost-effective method for prospecting hydrothermal and geothermal systems. Most geothermal systems in Kenya are ...Remote sensing investigations combined with Geographical investigation systems (GIS) provide a rapid and cost-effective method for prospecting hydrothermal and geothermal systems. Most geothermal systems in Kenya are found in remote areas where accessibility is difficult. This study was carried out on Paka volcano which is located in the Kenyan rift valley. The aim of the study was to use remote sensing and GIS to investigate hydrothermal minerals and structures associated with geothermal activities. The study involves use of Landsat TM image classification using ENVI 5.1 and ArcGIS. Lineament extraction was done using PCI geomatics 2015 while Rose diagrams were generated using Rockworks 16. The research has shown that lithological, hydrothermal mineralization and structural maps can be generated form Landsat TM images using remote sensing and GIS. It has been shown that faults trend in the Northeast, North and Northwest direction. Hydrothermal minerals that are rich in iron and clays occur on Paka volcano mountain and its neighbouring areas.展开更多
At Olkaria （Kenya） geothermal energy has been used since 1981, to generate electricity and now there are currently 3 plants with a nominal capacity of 205 MW. Preliminary measurement and evaluation of possible mercu...At Olkaria （Kenya） geothermal energy has been used since 1981, to generate electricity and now there are currently 3 plants with a nominal capacity of 205 MW. Preliminary measurement and evaluation of possible mercury （Hg） emission from two plants has been investigated. Potential atmospheric Hg emission has been determined based on an existing model for estimating the transport of mercury along geothermal fluid flow streams as pertains to energy recovery and conversion from liquid dominated geothermal reservoirs. Hg concentrations, addition, retention and release rates were calculated at a number of locations in the geothermal power plants based on the plant operating parameters and steam flow process （turbine, condenser, non-condensable gas ejector, and cooling tower）. Potential Hg emission rates through plume range from 0.455 g/h to 2.17 g/h, or 10-30 mg/h per MWe. The emission per hour per MWe is 130-300 times lower compared to Hg levels reported for 88 MWe five operating geothermal power plants around Mt. Amiata area in Italy. These emissions are coupled with a release of 1.07 kg/h per MW of hydrogen sulphide （HzS）. The potential Hg release rates to the environment will depend greatly on the concentration of HzS in the system. Any higher HzS contents may reduce solubility of rig in the brine hence making it to be available in the steam. The volatile Hg may travel with the non-condensable gases as Hg vapour.展开更多
The Kenyan Olkaria geothermal field has incredibly high geothermal potential in the East African Rift, the Kenyan Rift Valley. While the Olkaria geothermal area has been primarily attributed to electricity generation ...The Kenyan Olkaria geothermal field has incredibly high geothermal potential in the East African Rift, the Kenyan Rift Valley. While the Olkaria geothermal area has been primarily attributed to electricity generation and direct uses, this research investigates the potential of epithermal deposits in the geothermal systems with particular interests in base metals (Zn, Pb, and Fe) and alkali metals (Li, Na, K) in geothermal rocks and fluids. The study employed geochemical, geological, and well-logging analyses to characterise and assess the conditions in the geothermal system suitable for forming and depositing epithermal minerals. Rock cuttings and fluid samples were collected from geothermal wells, fumaroles, and hot springs. Findings indicate that the mineralisation in the Olkaria wells occurs in microveins and disseminations in the rock matrix, majorly sulfides, and oxides in hydrothermal alteration zones. The reported Zn, Pb, and Fe mineralisation mainly relates to low sulphidation type from the characterised sulphur metal complexes and oxides. Fluid samples recorded the metals as follows: Fe (0.12 - 3.9 ppm), Zn (4.21 - 5.23 ppm), Pb (1.55 - 2.04 ppm), and lithium concentrations at ≤ 3 ppm, which is lower than extractible values in geothermal brines in the Salton Sea and geothermal fields of Europe. The economic characterisation of rocks and fluid samples in our area indicates that the concentration of base and alkali metals has not yielded economically viable values compared to other geothermal systems with economic grades. Detailed studies are recommended to quantify mineralisation in Olkaria geothermal fields and their extractability for sustainable management of the geothermal resource.展开更多
Geothermal power plants are receiving increasing attention as regards the mobilization of mercury （Hg） to the environment. Hg is a trace element that may be present in the geothermal fluid, but due to its volatility...Geothermal power plants are receiving increasing attention as regards the mobilization of mercury （Hg） to the environment. Hg is a trace element that may be present in the geothermal fluid, but due to its volatility, it is transferred mainly into the vapor phase. Hence, it may be mostly discharged to the atmosphere with the non-condensable gases. Olkaria geothermal field hosts 3 geothermal power plants. In this area Hg deposition fluxes have not been studied. Concentrations and wet deposition fluxes of total mercury （T-Hg） were determined from April 2009 to May 2010 at 2 sites in this field. Event-based precipitation samples were collected using fabricated bulk precipitation samplers. Samples were treated according to trace metal protocol and analyzed by cold vapor atomic fluorescence spectrometry （CVAFS）. This paper thus reports the first ever determination of T-Hg concentrations and fluxes in precipitation. The T-Hg concentration in samples ranged from 0.002-0.0602 μg/L at the two sites, however, the volume-weighted mean concentration and wet deposition flux were 0.01974 and 0.02884μg.L^-1 and 0.0167-1.45 μg.m2 during the study period. The annual volume-weighted mean wet deposition fluxes of T-Hg for 2 sites were 13.74 and 19.83 μg.m-2.yr-1 with an average flux of 16.785μg.m-2.yr-1. Hg concentrations and the Hg fluxes in precipitation showed seasonal trends being lowest in the short-rains and highest in the long rains. The concentrations of T-Hg for the 2 sites is negatively correlated with the precipitation depth （r2 = 0.26 ＆ r2 = 0.0065）, suggesting that scavenging of particle-bound mercury from the atmosphere is an important mechanism contributing to mercury in rainwater. Mean Hg concentrations in precipitation at the study sites were comparable to the ranges reported for Canada and the USA by the Mercury Deposition Network （MDN）.展开更多
文摘Remote sensing investigations combined with Geographical investigation systems (GIS) provide a rapid and cost-effective method for prospecting hydrothermal and geothermal systems. Most geothermal systems in Kenya are found in remote areas where accessibility is difficult. This study was carried out on Paka volcano which is located in the Kenyan rift valley. The aim of the study was to use remote sensing and GIS to investigate hydrothermal minerals and structures associated with geothermal activities. The study involves use of Landsat TM image classification using ENVI 5.1 and ArcGIS. Lineament extraction was done using PCI geomatics 2015 while Rose diagrams were generated using Rockworks 16. The research has shown that lithological, hydrothermal mineralization and structural maps can be generated form Landsat TM images using remote sensing and GIS. It has been shown that faults trend in the Northeast, North and Northwest direction. Hydrothermal minerals that are rich in iron and clays occur on Paka volcano mountain and its neighbouring areas.
文摘At Olkaria （Kenya） geothermal energy has been used since 1981, to generate electricity and now there are currently 3 plants with a nominal capacity of 205 MW. Preliminary measurement and evaluation of possible mercury （Hg） emission from two plants has been investigated. Potential atmospheric Hg emission has been determined based on an existing model for estimating the transport of mercury along geothermal fluid flow streams as pertains to energy recovery and conversion from liquid dominated geothermal reservoirs. Hg concentrations, addition, retention and release rates were calculated at a number of locations in the geothermal power plants based on the plant operating parameters and steam flow process （turbine, condenser, non-condensable gas ejector, and cooling tower）. Potential Hg emission rates through plume range from 0.455 g/h to 2.17 g/h, or 10-30 mg/h per MWe. The emission per hour per MWe is 130-300 times lower compared to Hg levels reported for 88 MWe five operating geothermal power plants around Mt. Amiata area in Italy. These emissions are coupled with a release of 1.07 kg/h per MW of hydrogen sulphide （HzS）. The potential Hg release rates to the environment will depend greatly on the concentration of HzS in the system. Any higher HzS contents may reduce solubility of rig in the brine hence making it to be available in the steam. The volatile Hg may travel with the non-condensable gases as Hg vapour.
文摘The Kenyan Olkaria geothermal field has incredibly high geothermal potential in the East African Rift, the Kenyan Rift Valley. While the Olkaria geothermal area has been primarily attributed to electricity generation and direct uses, this research investigates the potential of epithermal deposits in the geothermal systems with particular interests in base metals (Zn, Pb, and Fe) and alkali metals (Li, Na, K) in geothermal rocks and fluids. The study employed geochemical, geological, and well-logging analyses to characterise and assess the conditions in the geothermal system suitable for forming and depositing epithermal minerals. Rock cuttings and fluid samples were collected from geothermal wells, fumaroles, and hot springs. Findings indicate that the mineralisation in the Olkaria wells occurs in microveins and disseminations in the rock matrix, majorly sulfides, and oxides in hydrothermal alteration zones. The reported Zn, Pb, and Fe mineralisation mainly relates to low sulphidation type from the characterised sulphur metal complexes and oxides. Fluid samples recorded the metals as follows: Fe (0.12 - 3.9 ppm), Zn (4.21 - 5.23 ppm), Pb (1.55 - 2.04 ppm), and lithium concentrations at ≤ 3 ppm, which is lower than extractible values in geothermal brines in the Salton Sea and geothermal fields of Europe. The economic characterisation of rocks and fluid samples in our area indicates that the concentration of base and alkali metals has not yielded economically viable values compared to other geothermal systems with economic grades. Detailed studies are recommended to quantify mineralisation in Olkaria geothermal fields and their extractability for sustainable management of the geothermal resource.
文摘Geothermal power plants are receiving increasing attention as regards the mobilization of mercury （Hg） to the environment. Hg is a trace element that may be present in the geothermal fluid, but due to its volatility, it is transferred mainly into the vapor phase. Hence, it may be mostly discharged to the atmosphere with the non-condensable gases. Olkaria geothermal field hosts 3 geothermal power plants. In this area Hg deposition fluxes have not been studied. Concentrations and wet deposition fluxes of total mercury （T-Hg） were determined from April 2009 to May 2010 at 2 sites in this field. Event-based precipitation samples were collected using fabricated bulk precipitation samplers. Samples were treated according to trace metal protocol and analyzed by cold vapor atomic fluorescence spectrometry （CVAFS）. This paper thus reports the first ever determination of T-Hg concentrations and fluxes in precipitation. The T-Hg concentration in samples ranged from 0.002-0.0602 μg/L at the two sites, however, the volume-weighted mean concentration and wet deposition flux were 0.01974 and 0.02884μg.L^-1 and 0.0167-1.45 μg.m2 during the study period. The annual volume-weighted mean wet deposition fluxes of T-Hg for 2 sites were 13.74 and 19.83 μg.m-2.yr-1 with an average flux of 16.785μg.m-2.yr-1. Hg concentrations and the Hg fluxes in precipitation showed seasonal trends being lowest in the short-rains and highest in the long rains. The concentrations of T-Hg for the 2 sites is negatively correlated with the precipitation depth （r2 = 0.26 ＆ r2 = 0.0065）, suggesting that scavenging of particle-bound mercury from the atmosphere is an important mechanism contributing to mercury in rainwater. Mean Hg concentrations in precipitation at the study sites were comparable to the ranges reported for Canada and the USA by the Mercury Deposition Network （MDN）.
