My research includes novel hybrid systems, energy autonomy scenarios for remote regions, and the development of new optimization tools. Address: Marchstr. 18 10587 Berlin
European Biomass Conference and Exhibition Proceedings, 2013
Liquid biofuels, such as biodiesel and bioethanol, are expected to play a leading role in achievi... more Liquid biofuels, such as biodiesel and bioethanol, are expected to play a leading role in achieving a more secure, reliable and sustainable energy sector. Microalgae are seen as a possible feedstock for future bioenergy systems, due to their high productivity and potentially high oil or carbohydrate content. In the present study, the life-cycle environmental performance of a hypothetical "microalgae-to-ethanol" system was evaluated. The system includes cultivation of the carbohydrate-rich microalgal strain Chlorella vulgaris in open raceway ponds, flocculation, centrifugation, dilute acid hydrolysis, fermentation with Zymomonas mobilis bacteria, and distillation. The main processes contributing to the potential environmental impacts were identified. Improvement actions should focus on minimizing the nutrient and energy needs of the cultivation stage, as well as on optimizing the energy demand of the hydrolysis process and its consumption of chemicals. When compared to conventional first-generation bioethanol, microalgal ethanol showed a worse life-cycle performance. However, in comparison with microalgal biodiesel under a well-to-wheels perspective, microalgal ethanol could be a more appropriate biofuel. Further research is needed in order to provide a sustainable microalgal ethanol system.
A very important component to achieve sustainable development in the energy sector is the improve... more A very important component to achieve sustainable development in the energy sector is the improvement of energy efficiency of widely applied thermodynamic processes. Evaluation and optimization methods of energy processes play a crucial role in fulfilling this goal. A suitable method for the evaluation and optimization of energy conversion systems has been proven to be the exergetic analysis. In this work, three parabolic trough solar thermal power plants are simulated using commercial software, and they are further analyzed and compared using exergetic analysis. The goal is to detect thermodynamic inefficiencies of the three different configurations and propose measures to minimize them. The first simulated solar thermal plant uses a thermal fluid to produce the steam required in a steam generator, the second plant produces the steam directly in the solar field, while the third power plant is used to find trade-offs between the first two alternatives by generating part of the necessary steam using a thermal fluid and part of it in the solar field. The analysis involves the evaluation of the individual components of the power plants, as well as the performance evaluation of the overall structures. When examining the first two simulated plants, we find similar main sources of exergy destruction: the solar field (parabolic trough solar collectors), followed by the steam generator. This shows the importance of an optimal design of these particular components, which could reduce inefficiencies present in the system. Performing a sensitivity analysis using the configuration of the third available power plant we find the best possible combination that minimizes the thermodynamic inefficiencies of the first two alternatives for the generation of steam. The differences in the exergy destruction and exergetic efficiencies of individual components of the three plants are analyzed based on comparable operational conditions. The analysis shows the convenience of using a hybrid configuration where steam is directly generated in the solar field, white it is reheated using a heat transfer fluid.
Rising water scarcity and abundant brine water resources, especially in desert locations, call fo... more Rising water scarcity and abundant brine water resources, especially in desert locations, call for the wider adaptation of desalination techniques. Furthermore, the interdependency of water and energy has gained more attention in recent years and it is expected to play an important role in the near future. The present study deals with both topics in that it presents the coupling of a power plant with desalination units for the simultaneous generation of energy and water in Iran. The power plant used in the analysis is the Qom combined-cycle power plant. The plant is integrated, first, with a multi-stage flash (MSF) unit and, then, with a multi-effect desalination (MED) unit, and it is evaluated using energy and exergy analyses. We find that the generated power of the integrated systems is decreased by 9.7% and 8.5% with the MED and the MSF units, respectively. Lastly, the freshwater production in the plant using MED is significantly higher than in the plant with MSF (1,000 versus 1,...
Water dependency of power plants undermines energy security by making power generation susceptibl... more Water dependency of power plants undermines energy security by making power generation susceptible to water scarcity. This study evaluates the economic performance of a novel dry-cooling system for a water-independent solar power plant. The proposed cooling system is based on the concept of earth–air heat exchangers, approaching zero environmental impact. The viability of the proposed design is discussed based on both costs and benefits, and it is compared to both conventional dry- and wet-cooling systems. The installation costs of the plant are found to be EUR 13,728/kW, resulting in the substantial levelized cost of electricity of EUR 505.97/MWh. The net present value of the studied design assuming a water-cost saving of EUR 1/m3 is found to be MEUR –139.59. Significantly higher water prices in the future might eventually make the proposed system economically attractive when compared to water-cooling systems. However, the new system would require drastic modifications to become mo...
This paper presents the design and analysis of an energy/water system that combines a 20 MW hybri... more This paper presents the design and analysis of an energy/water system that combines a 20 MW hybrid concentrated solar/biomass power plant with an advanced wastewater treatment facility. Designed to be installed in one of the most demanding areas of the Iberian Peninsula, the Spanish region of Andalusia, this plant seeks to provide the area with potable water and electricity. The solar block works with a mixture of molten salts, while the biomass backup system of the power plant uses olive pomace. The implementation of a direct potable reuse facility further enhances the sustainability of the project. Urban sewage from the region is collected and passed through a series of purification procedures in order to generate potable water ready to be directly blended into the water distribution system. A sensitivity analysis is conducted to determine the feasibility of the co-generation of electricity and water in the area. With a capacity factor of 85% and an annual operation of 7,446 hours...
European Biomass Conference and Exhibition Proceedings, 2013
Liquid biofuels, such as biodiesel and bioethanol, are expected to play a leading role in achievi... more Liquid biofuels, such as biodiesel and bioethanol, are expected to play a leading role in achieving a more secure, reliable and sustainable energy sector. Microalgae are seen as a possible feedstock for future bioenergy systems, due to their high productivity and potentially high oil or carbohydrate content. In the present study, the life-cycle environmental performance of a hypothetical "microalgae-to-ethanol" system was evaluated. The system includes cultivation of the carbohydrate-rich microalgal strain Chlorella vulgaris in open raceway ponds, flocculation, centrifugation, dilute acid hydrolysis, fermentation with Zymomonas mobilis bacteria, and distillation. The main processes contributing to the potential environmental impacts were identified. Improvement actions should focus on minimizing the nutrient and energy needs of the cultivation stage, as well as on optimizing the energy demand of the hydrolysis process and its consumption of chemicals. When compared to conventional first-generation bioethanol, microalgal ethanol showed a worse life-cycle performance. However, in comparison with microalgal biodiesel under a well-to-wheels perspective, microalgal ethanol could be a more appropriate biofuel. Further research is needed in order to provide a sustainable microalgal ethanol system.
A very important component to achieve sustainable development in the energy sector is the improve... more A very important component to achieve sustainable development in the energy sector is the improvement of energy efficiency of widely applied thermodynamic processes. Evaluation and optimization methods of energy processes play a crucial role in fulfilling this goal. A suitable method for the evaluation and optimization of energy conversion systems has been proven to be the exergetic analysis. In this work, three parabolic trough solar thermal power plants are simulated using commercial software, and they are further analyzed and compared using exergetic analysis. The goal is to detect thermodynamic inefficiencies of the three different configurations and propose measures to minimize them. The first simulated solar thermal plant uses a thermal fluid to produce the steam required in a steam generator, the second plant produces the steam directly in the solar field, while the third power plant is used to find trade-offs between the first two alternatives by generating part of the necessary steam using a thermal fluid and part of it in the solar field. The analysis involves the evaluation of the individual components of the power plants, as well as the performance evaluation of the overall structures. When examining the first two simulated plants, we find similar main sources of exergy destruction: the solar field (parabolic trough solar collectors), followed by the steam generator. This shows the importance of an optimal design of these particular components, which could reduce inefficiencies present in the system. Performing a sensitivity analysis using the configuration of the third available power plant we find the best possible combination that minimizes the thermodynamic inefficiencies of the first two alternatives for the generation of steam. The differences in the exergy destruction and exergetic efficiencies of individual components of the three plants are analyzed based on comparable operational conditions. The analysis shows the convenience of using a hybrid configuration where steam is directly generated in the solar field, white it is reheated using a heat transfer fluid.
Rising water scarcity and abundant brine water resources, especially in desert locations, call fo... more Rising water scarcity and abundant brine water resources, especially in desert locations, call for the wider adaptation of desalination techniques. Furthermore, the interdependency of water and energy has gained more attention in recent years and it is expected to play an important role in the near future. The present study deals with both topics in that it presents the coupling of a power plant with desalination units for the simultaneous generation of energy and water in Iran. The power plant used in the analysis is the Qom combined-cycle power plant. The plant is integrated, first, with a multi-stage flash (MSF) unit and, then, with a multi-effect desalination (MED) unit, and it is evaluated using energy and exergy analyses. We find that the generated power of the integrated systems is decreased by 9.7% and 8.5% with the MED and the MSF units, respectively. Lastly, the freshwater production in the plant using MED is significantly higher than in the plant with MSF (1,000 versus 1,...
Water dependency of power plants undermines energy security by making power generation susceptibl... more Water dependency of power plants undermines energy security by making power generation susceptible to water scarcity. This study evaluates the economic performance of a novel dry-cooling system for a water-independent solar power plant. The proposed cooling system is based on the concept of earth–air heat exchangers, approaching zero environmental impact. The viability of the proposed design is discussed based on both costs and benefits, and it is compared to both conventional dry- and wet-cooling systems. The installation costs of the plant are found to be EUR 13,728/kW, resulting in the substantial levelized cost of electricity of EUR 505.97/MWh. The net present value of the studied design assuming a water-cost saving of EUR 1/m3 is found to be MEUR –139.59. Significantly higher water prices in the future might eventually make the proposed system economically attractive when compared to water-cooling systems. However, the new system would require drastic modifications to become mo...
This paper presents the design and analysis of an energy/water system that combines a 20 MW hybri... more This paper presents the design and analysis of an energy/water system that combines a 20 MW hybrid concentrated solar/biomass power plant with an advanced wastewater treatment facility. Designed to be installed in one of the most demanding areas of the Iberian Peninsula, the Spanish region of Andalusia, this plant seeks to provide the area with potable water and electricity. The solar block works with a mixture of molten salts, while the biomass backup system of the power plant uses olive pomace. The implementation of a direct potable reuse facility further enhances the sustainability of the project. Urban sewage from the region is collected and passed through a series of purification procedures in order to generate potable water ready to be directly blended into the water distribution system. A sensitivity analysis is conducted to determine the feasibility of the co-generation of electricity and water in the area. With a capacity factor of 85% and an annual operation of 7,446 hours...
\textcopyright} 2017 Author(s). Since the operation of a concentrating solar power plant depends ... more \textcopyright} 2017 Author(s). Since the operation of a concentrating solar power plant depends on the intermittent character of solar energy, the steam generator is subject to daily start-ups, stops and load variations. Faster start-up and load changes increase the plant flexibility and the daily energy production. However, it involves high thermal stresses on thick-walled components. Continuous operational conditions may eventually lead to a material failure. For these reasons, it is important to evaluate the transient behavior of the proposed designs in order to assure the reliability. The aim of this work is to analyze different steam generator designs for solar power tower plants using molten salt as heat transfer fluid. A conceptual steam generator design is proposed and associated heat transfer areas and steam drum size are calculated. Then, dynamic models for the main parts of the steam generator are developed to represent its transient performance. A temperature change rate that ensures safe hot start-up conditions is studied for the molten salt. The thermal stress evolution on the steam drum is calculated as key component of the steam generator.
Although conventional exergy-based analyses uncover a path towards plant improvement, they suffer... more Although conventional exergy-based analyses uncover a path towards plant improvement, they suffer from some limitations, which are addressed by advanced exergy-based analyses. Advanced exergy-based methods identify interdependencies among plant components, and reveal the potential of improvement both at the component and plant level. Thus, data obtained from these methods pinpoint strengths and weaknesses of energy conversion systems and are of great importance when complex plants with a large number of interconnected components are considered. In this paper an advanced exergoeconomic analysis is applied to an advanced zero emission plant (AZEP). The most important components, in terms of the total avoidable costs, are the components constituting the main gas turbine system, while of particular importance are also the components of the mixed conducting membrane reactor incorporated in the plant. It has been found that for the most influential components of the plant, the largest part of investment cost rates and costs of exergy destruction are unavoidable. Additionally, for both the investment cost and the cost of exergy destruction, the interactions among the components are in most cases of lower importance, since for the majority of the components, the endogenous parts of the costs (related to the operation of the components themselves) are significantly larger than the corresponding exogenous parts (related to the operation of the remaining components). Nevertheless, strong interactions have been found among the components of the mixed conducting membrane reactor. Copyright {\textcopyright} 2011 by ASME.
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