Design, construction, and operation of the first industrial salinity-gradient solar pond in Europe: An efficiency analysis perspective

A 500 m2 industrial salinity-gradient solar pond (SGSP) was constructed in a mineral processing plant (Solvay Minerales) in Granada (Spain). This renewable energy technology was designed to supply a low-temperature heat (up to 60 °C) to achieve the temperature requirements of the flotation mineral purification stage. The low-temperature source was integrated to partially replace the fuel oil boiler used to heat the water used in the flotation stage. Theoretical calculations based on solar radiation indicated that the use of the SGSP would reduce the annual fuel consumption by more than 50%, thus providing a significant improvement at both economic and environmental levels. Two months after the SGSP was established, in August 2014, the temperature in the storage zone of the SGSP reached approximately 90 °C. The overall performance was evaluated in two periods (2014 and 2015) in terms of the retrofitting of mining facility with a solar pond and a new method to assess the thermal efficiency of the solar pond in a long-term perspective has been proposed. The overall efficiencies obtained after the first and second operation periods were 10 and 12%, respectively, with maximum values of 28 and 24% obtained during the first operation months. Regarding the economic savings, the fuel oil cost of the flotation unit was reduced by a higher percentage than the fuel oil consumption, due to the decreasing tendency of fuel oil prices during 2014 and 2015. Reductions of 52 and 68% were obtained in the first and second periods of operation, respectively, when compared to 2013. In addition, not only does the SGSP have considerably reduced operating costs but also the environmental costs are clearly reduced when considering the reduction of CO2 emissions.Peer ReviewedPostprint (author's final draft

Stability analysis of an industrial salinity gradient solar pond

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.Peer ReviewedPostprint (published version

Enhancing the efficiency of solar pond heat extraction by using both lateral and bottom heat exchangers

In this study, heat extraction from both the gradient and heat storage zones of a salinity-gradient solar pond (SGSP) has been evaluated. For this purpose, an experimental solar pond pilot plant was constructed in 2009 in Barcelona (Spain). The structure of the pond is a cylindrical tank of 3-m height and 8 m diameter with a total area of 50 m(2). The main objective was to evaluate a heat-extraction system from the SGSP designed to enhance the system efficiency under different conditions. Thus, an in-pond heat exchanger covering all of the lateral wall area of the pond was installed, and its performance was compared with the traditional in-pond heat exchanger situated on the bottom of the pond. Heat extraction experiments were performed using both heat exchangers individually or both at the same time. The study covers the experiments performed at three different seasonal temperature conditions: winter (December), summer (July) and autumn (October and November). The variations of the temperature inside the pond during the heat extraction were measured and analyzed. The results demonstrated that the efficiency of the pond increases when the heat is removed from the lateral heat exchanger alone compared to either using the bottom heat exchanger or using both heat exchangers simultaneouslyPostprint (author's final draft

Numerical Modeling and Analytical Validation for Transient Temperature Distribution in a Heterogeneous Geothermal Reservoir due to Cold-Water Reinjection

ABSTRACT Reinjection of cooled geothermal fluid after extraction of heat is a common practice in order to maintain the geothermal reservoir pressure, which gradually declines due to continuous extraction of geothermal fluid. Reinjection of geothermal fluid into the geothermal reservoir ensures its safe disposal and enhances the heat recovery the efficiency of the geothermal reservoir for extracting heat energy. But since the injected geothermal fluid is cooler than the geothermal reservoir it generates a cold front near the injection well which propagates through the reservoir domain. Heterogeneity of the geothermal aquifer is also an important factor to consider since homogeneous medium is practically very rare in nature and the thermo-hydrogeological properties of the medium varies in an aquifer. The present study deals with the modeling of the transient temperature distribution in a heterogeneous geothermal reservoir in response to injection of cold geothermal water. The heterogeneous geothermal aquifer considered here is a confined aquifer with homogeneous layers of finite length and overlain and underlain by impermeable rock media. All the different layers in the aquifer and the overlying and underlying rocks are of different thermo-hydrogeological properties. The numerical modeling for the transient temperature distribution in the porous aquifer is modeled here using a software code DuMu x . The heat transport modes considered are the advection, conduction and the heat loss to the confining rock media. Results show that heterogeneity plays a very significant role in determining the transient temperature distribution and controlling the advancement of the thermal front in the reservoir. The numerical model developed here is validated in this study using an analytical model. Temperature distribution derived by both methods match with each other quite well. INTRODUCTION In a geothermal power plant the heat energy of the geothermal water is extracted for power production. The waste-water which is produced after heat extraction is then reinjected back into the geothermal reservoir. One purpose of the reinjection is safe disposal of the thermal wastewater which otherwise could have created thermal pollution if disposed on surface. Moreover reinjection helps in keeping the reservoir pressure intact which gradually declines due to continuous extraction of geothermal fluid. Also according t

Thermal performance of 500m2 salinity gradient solar pond in Granada, Spain under strong weather conditions

In this study, an experimental investigation of temperature performance and efficiency of an industrial solar pond during strong winter conditions is presented. Several temperature sensors connected to a data logger were used to measure the temperature gradient in a 500¿m2 solar pond. During the winter 2015 there was a snowfall in the solar pond of Granada (Spain), reaching a minimum air ambient temperature of -2.4¿°C. The temperature of the storage zone in Granada solar pond remained constant (around 40¿°C) indicating the system responds positively to weather variations and confirming the fundamental role of the salinity gradient as a thermal insulation layer. The stored energy during January 2015 was 13.3¿GJ, the weekly efficiency reached 10% and finally, the solar pond was able to provide 247.1¿MJ to the flotation unit during the week of the snowfall.Peer ReviewedPostprint (author's final draft

Optimization of culture media for extracellular expression of streptokinase in Escherichia coli using response surface methodology in combination with Plackett-Burman Design

Purpose: To investigate the enhancement of streptokinase extracellular expression in Escherichia coli by adjusting culture media.Methods: Screening of 10 chemical factors (EDTA, peptone, glycine, triton X-100, glycerol, K2HPO4, KH2PO4, Ca2+ (calcium chloride), yeast and NaCl) in order to increase the secretion of extracellular protein was carried out by response surface methodology (RSM). The method was also employed to optimize the concentrations of critical factors that had been determined in the screening step.Results: The results indicate that glycine, triton X-100 and Ca2+ were the most effective chemical factors in terms of increase in extracellular expression of streptokinase with optimum levels of 0.878, 0.479 and 0.222 %, respectively. Expression of streptokinase under optimum concentrations of critical permeabilizing factors led to a 7-fold increase in the quantity of secreted recombinant protein (5824 U/mL) compared to the initial level (802 U/mL).Conclusion: The results show that medium optimization using RSM is effective in improving extracellular streptokinase expression. The optimization medium is considered fundamental and useful for efficient production of streptokinase on a large scale.Keywords: Streptokinase, Response surface methodology, Membrane permeabilization, Extracellular secretio

Increasing the storage capacity of a solar pond by using solar thermal collectors: heat extraction and heat supply processes using in-pond heat exchangers

In this study, an experimental investigation of the performance of a salinity gradient solar pond (SGSP) integrating solar collectors is presented. The SGSP is located in Barcelona (Spain) and has a cylindrical tank 3¿m in height and 8¿m in diameter with a total area of 50¿m2. For this purpose, four solar thermal collectors (10¿m2) are integrated, as an external source of heat, with the solar pond pilot plant in order to increase the storage capacity and its overall efficiency. The aim of this study is to evaluate heat extraction and heat supply processes from and to the SGSP under different seasonal conditions. Two in-pond heat exchangers are used, a conventional one situated on the bottom of the pond and a second one covering the lateral wall area of the pond. Heat extraction and supply experiments are performed using both heat exchangers individually or both at the same time. The experiments are conducted under two different seasonal temperature conditions: winter (February and March) and summer (July). The variations of the temperature inside the pond during the heat extraction/supply tests are monitored and analyzed. The results have indicated that the use of solar collectors as an extra source of heat for the solar pond led to a 50% increase in the daily efficiency during the cold season tests, while heat extraction only appeared as the best option during the warm season tests. Higher daily efficiency and heat supply results can only be obtained if large amounts of heat are extracted, otherwise, the daily efficiency of the solar pond could decrease. Finally, the solar collectors can be considered a good alternative for avoiding a significant decrease in solar pond temperatures (especially during the cold season), which would not only result in a significant energy storage efficiency improvement but also increase the capacity of the solar pond to supply heat to an external application.Peer ReviewedPostprint (author's final draft

Ant stings in military forces on three Persian islands of Abu-Musa, Greater Tunb and Lesser Tunb

Aims: Ants with the ability of biting and injecting venom to human body are called sting ants. This study was conducted to identify and determine the ant species and the prevalence of ant sting and related epidemiological factors in three Greater Tunb, Lesser Tunb and Abu-Musa islands, Iran. Methods: This descriptive cross-sectional study was performed during Jan-July 2010 in Greater Tunb, Lesser Tunb and Abu-Musa islands on 318 military individuals who were selected by random sampling method. The ant collection was done by active hand-catch method. The ant sting prevalence and related epidemiological factors were determined by questionnaire. Data were analyzed by descriptive statistical methods including Chi-square test, Mann-Whitney test and Spearman and Gamma correlation. Results: Sting ants in these islands were identified as Pachycondyla sennaarensis (Mayr, 1862) (Hymenoptera: Formicidae). The mean prevalence of ant stings was 70.1%. The seasonal incidence of sting in three islands had the same pattern and was more common in spring and summer. 84.4% of ant stings had occurred in limbs. The main symptoms caused by the ant stings include pain, severe itching and local inflammation and blisters in some cases. Conclusion: Although ant stings in these islands is not much dangerous and does not lead to anaphylactic shock and death, ant stings prevalence is very high and the pain, itching and burning would cause discomfort for soldiers and reduce their efficiency. Therefore, preventive measures and control of these ants should be considered

Solar Energy Sciences and Engineering Applications

As the world’s conventional energy supply nears its peak, and with the demand for that energy increasing year on year, it is expected that balancing supply and demand will become increasingly challenging. Consequently it is expected that non-conventional energy sources and renewable energy resources are likely to play a greater role in addressing the imbalance between supply and demand. Many experts advocate increased harnessing of renewable energy as an important alternative energy source. Utilization of renewable energy resources is sometimes expensive and difficult to apply fully in particular sectors of society because of the location, intensity and nature of the applications. Therefore specific matching of the renewable energy source to the application is a very important aspect of maximizing the utilization of renewable energy. Solar energy is available in differing intensities in different parts of the planet. Maximization of its potential as a primary alternative renewable energy source depends however on the specific usage made of it. Hence, this book was conceived to serve the purpose of identifying primary and secondary applications of solar energy in order to maximize their potential. As solar energy applications can span almost the entire spectrum of human activity, including for example biological processes, chemical processes, mechanical processes and other aspects of our daily lives, preparation of a book that considers all these facets is very important in determining how existing sciences and technologies can further refine and expand solar energy utilization and applications.

On increasing the thermal mass of a salinity gradient solar pond with external heat addition: A transient study

In salinity gradient solar ponds (SGSPs) solar thermal energy is mainly stored in the lower-convective zone (LCZ) the volume of which defines the thermal mass of storage. The present study explores the provision of increasing the heat storage in a SGSP by increasing the thermal mass of it. It also addresses the method of enhancing the thermal performance of a SGSP by increasing the thermal mass, while adding heat from external sources. Earlier studies have proved that adding external heat to the SGSP for storage enhances the thermal performance of it significantly. This study aims to prove that increasing the thermal mass of storage further increases the energy efficiency of a SGSP when external heat is added to it. A hybrid system of a SGSP coupled with evacuated tube solar collectors (ETSCs) is used in this study. Several parameters like storage temperature in LCZ, heat addition flux and heat addition efficiency of ETSC, instantaneous efficiency of SGSP, heat extraction from SGSP are studied in this paper for different cases of with and without heat addition and with normal and enhanced thermal mass. It is found that increasing thermal mass can significantly enhance the thermal performance and efficiency of a SGSP