Aristides M. Bonanos

Experimental evaluation of a multiple-effect distillation unit in low seawater flow conditions

AbstractIn this work, we evaluate experimentally the performance of a multiple-effect distillation (MED) unit in low seawater flow conditions and the potential of its integration with a concentrated solar power system. The innovation of this MED unit is the introduction of a flow distributor within the parallel plates of the falling film heat exchanger, designed to improve the system performance and efficiency under low seawater flow conditions. The main parameters examined were the thermal input power and the flow rate of the inlet seawater to each effect and the inlet seawater temperature of the single unit. Furthermore, the experimental results were compared with a control volume energy conservation model. The results showed that lower heat input load results to a higher value of the performance ratio (PR) of the unit and also under constant heat load, a higher temperature of the seawater lead to higher distillate product for the single effect unit. As the number of effects is increased the PR of the u...

CSP cogeneration of electricity and desalinated water at the Pentakomo field facility

The Cyprus Institute’s Pentakomo Field Facility (PFF) is a major infrastructure for research, development and testing of technologies relating to concentrated solar power (CSP) and solar seawater desalination. It is located at the south coast of Cyprus near the sea and its environmental conditions are fully monitored. It provides a test facility specializing in the development of CSP systems suitable for island and coastal environments with particular emphasis on small units (<25 MWth) endowed with substantial storage, suitable for use in isolation or distributed in small power grids. The first major experiment to take place at the PFF concerns the development of a pilot/experimental facility for the co-generation of electricity and desalinated seawater from CSP. Specifically, the experimental plant consists of a heliostat-central receiver system for solar harvesting, thermal energy storage in molten salts followed by a Rankine cycle for electricity production and a multiple-effect distillation (MED) unit...

Evaluation of a solar powered distillation unit as a mitigation to water scarcity and climate change in Cyprus

AbstractCyprus, an island facing water scarcity periods throughout its history, has to cope with even more intense periods due to climate change as it is predicted by several climate models. The aim of the present study is to evaluate the performance of a single-effect distillation unit and the potential of its integration with a concentrated solar power system as a mitigation technique to the water scarcity. Specifically, a single-effect distillation unit for seawater desalination was developed and its performance in terms of performance ratio (PR) (ratio of distillate product and steam fed to the unit) was experimentally investigated. The main parameters examined were the thermal input power, and the temperature and flow rate of the inlet seawater. For several seawater flow rates, three different initial heat loads were used (Tst,1, Tst,2, Tst,3). Experiments were repeated for two seawater inlet temperatures, Tsw1, Tsw2. A one-dimensional model based on conservation of mass and energy was developed to p...

Evaluation of a Multiple-Effect Distillation Unit under Partial Load Operating Conditions

The design of a multiple-effect distillation (MED) system is presented, and the results for partial load operation of a single-effect distillation unit are presented. The MED is designed to be driven by solar energy, and thus the dynamic performance and partial load operation production are of interest. Two operating modes are considered in the analysis, with and without the use of a flow distributor. Various tests were performed varying the heating steam flow rate and the intake seawater flow rate. Results are presented as a function of the performance ratio, representing the amount of distillate produced per unit mass of steam input. Results indicate that a higher performance is obtained with the use of the flow distributor.

Caustics as an Alternate of Ray Tracing to Evaluate Heliostat Mirrors

Solar thermal power generation is based on the concept of concentrating solar radiation to provide high temperature heat for electricity generation via conventional power cycles. The high relative cost of optical subsystems necessitates a careful study of their components. The capital cost of the heliostat field in central receiver power plants is significant, reaching up to 50% of the capital investment. Therefore, it is essential to maximize the energy yield from a heliostat with a given mirror area. Solar collector fields are typically modeled by ray-tracing or convolution methods; however, no general method is available for engineering analysis. We propose the use of caustics to predict the image of the sun reflected by an arbitrary mirror of focal length and aperture on a target. The method of caustics was validated against SolTRACE, a ray-tracing code developed by the US National Renewable Energy Laboratory (NREL).

Error analysis for concentrated solar collectors

Error sources introduced into mirror tracking systems, arising from component limitations, construction and placement of the reflectors, and the discrete motion of the tracking system itself, are examined. The main mechanisms contributing to these sources are identified and modeled. The effect of these optical and geometrical errors is numerically simulated using a ray-tracing code and their relative significance is assessed.

Optical evaluation of heliostat mirrors using caustics

Solar thermal power generation is based on the concept of concentrating solar radiation to provide high temperature heat for electricity generation via conventional power cycles. The high relative cost of optical subsystems necessitates a careful study of their components. Solar collector fields are typically modeled by ray-tracing or convolution methods; however, no general method is available for engineering analysis. We propose the use of caustics to predict the image of the sun reflected by an arbitrary mirror of focal length F and aperture a on a target. The mirror surface is described parametrically by a quadric and placed at a distance L from the target on a heliostat. The method of caustics was validated against SolTRACE, a ray-tracing code developed by U.S. National Renewable Energy Laboratories . We show that there is a value of aF which depends on aL, for which the incident average energy flux to the target reaches a maximum. The method of caustics allows the efficient computation of the image ...

CSP+D: The case study at the PROTEAS facility

The PROTEAS facility, located on the southern coastline of Cyprus, hosts an experiment aiming to investigate the co-generation of electricity and desalinated seawater from concentrated solar power, providing a unique opportunity to test on a pilot-scale the CSP+D co-generation scheme. In the present paper, heat sources that would otherwise be rejected to the environment are explored along with their potential thermal contribution, and the performance of a thermal distillation unit utilizing these sources is investigated. Several low-temperature heat sources are available to be used for seawater preheating, whereas the novelty of the design of the receiver allows for its thermal losses to be harnessed and used to drive the desalination cycle.The PROTEAS facility, located on the southern coastline of Cyprus, hosts an experiment aiming to investigate the co-generation of electricity and desalinated seawater from concentrated solar power, providing a unique opportunity to test on a pilot-scale the CSP+D co-generation scheme. In the present paper, heat sources that would otherwise be rejected to the environment are explored along with their potential thermal contribution, and the performance of a thermal distillation unit utilizing these sources is investigated. Several low-temperature heat sources are available to be used for seawater preheating, whereas the novelty of the design of the receiver allows for its thermal losses to be harnessed and used to drive the desalination cycle.