Abstract
The utilization of geothermal energy remains underdeveloped, mainly due to the technical problem of silica scaling. The scaling can eventually disrupt the electricity production process due to frequent pipe maintenance. Although inevitable, scaling can be controlled by accelerating the precipitation process through the addition of silica seeds. Silica gel has an affinity to bind with dissolved silica in geothermal brine that therefore reduces the likelihood of silica to form scale on the pipeline surfaces. In the present work, brine was taken from geothermal well Unit 3A–3B at the Dieng geothermal power plant with an initial silica monomer concentration of approximately 420 ppm. Silica gel seeds were added to the brine at a precise pH and temperature and dissolved silica concentration was analyzed by detecting silica monomers with UV–visible spectrophotometry using the vanadate/molybdate (yellow) method. Experimental results showed that the silica concentration in the liquid phase could be reduced by the addition of these seeds. Silica precipitation was determined by mass transfer of silica monomers from the fluid phase onto solid surfaces, and it was found that precipitation decreased as pH and temperature increased. Calculations also showed that the mass transfer coefficient was enhanced by fluid agitation. The silica precipitation process was optimal at a pH of 7, a temperature of 40 °C and agitation speed of 800 rpm; the result was a mass transfer coefficient of 0.5924 cm/s. In a dimensionless correlation, the mass transfer coefficient can be expressed in the equation (kc·dp/DAB) = 1.4242·Re0.529·Sc0.3333.
Highlights
Depletion of fossil fuels has driven efforts to find other sources of renewable energy
The solubility of silica depends on the type of silica formed, which is largely influenced by the acidity of the solution
Our results demonstrated that the precipitated mass was less than that estimated by Sugita et al (2000)
Summary
Depletion of fossil fuels has driven efforts to find other sources of renewable energy. The Indonesian government plans to improve the utilization of geothermal power plants; as demonstrated, it can be seen that electricity generation from geothermal power plants in Indonesia has far increased only incrementally. The utilization of energy generation is dependent upon the quality of the geothermal fluid; such fluid is not always suitable for existing. In case of acidic geothermal fluid, the fluid may contain high concentration of dissolved minerals leading to the formation of scales as seen in Fig. 2 as occurred in Dieng’s geothermal power plant which frequently causes disruption of electric generation. In case of wet geothermal fluid, the brine from separator might contain high concentration of silica in an oversaturated condition (Haklidir and Balaban 2019). Without any intervention of scaling prevention, the silica in the brine tends to form scales on the surfaces of downstream equipment (Haklidir and Haklidir 2017)
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