Stability analysis of an industrial salinity gradient solar pond

Abstract

In this study, an assessment of salinity gradient stability of an industrial solar pond during two operation seasons (2014 and 2105) is presented. An industrial solar pond was constructed to supply a low-temperature heat (up to 60 °C) to achieve the temperature requirements of the flotation stage in a mineral processing plant (Solvay Minerales in Granada (Spain)). Along the first season, the salinity gradient was considered technically destroyed in April 2015 as the height to the upper convective zone increases from 0.3 m in July 2014 to 0.8 m. Two different methodologies based on the stratification principle were adapted and used in order to evaluate the salinity gradient stability. The boundaries of the salinity gradient appeared as the main source of instability. In the upper zone it is associated with the environmental parameters (e.g., rain and wind) that affect the upper convective zone and the upper layers of the non-convective zone that subsequently transmit the instability to the lower layers. In the bottom zone it is caused by operation parameters, such as the heat extraction or the addition of salt. Both methodologies provided similar predictive capability of stability results. However, the results provided by the stability analysis using the thermal and salinity expansion coefficients are a more useful tool in the control of the salinity gradient for solar pond technology.