PERFORMANCE STUDY OF FORWARD FEED MULTI-EFFECT DESALINATION PLANT DRIVEN BY SOLAR ENERGY DURING STEADY AND UNSTEADY CONDITIONS

Abstract

Abstract The world is increasingly interested in desalination techniques as a quick and effective solution to confront the risks posed by water scarcity and climate change, but these technologies are still a little spread in poor countries, especially with the increasing prices of traditional energy sources so that the interest in multi-effect desalination MED plants that operate by thermal energy has especially increased due to the possibility of integration with traditional electric power generation plants or with one of the technologies for collecting and storing solar energy. This thesis aims to investigate the economic and thermal performance of a forward feed multi-effect distillation unit with a thermal vapor compressor (FF-MED-TVC) which is integrated with a unit of concentrating and storing the solar power (CSP), in order to provide a clear view of the dynamic response in each unit of the plant when it is exposed to the most sudden disturbances that occur in the real work environment. These disturbances would negatively affect the performance of the plant, and may lead to damage in some of its parts over time, in addition to cause a sudden shutdown for the entire plant in sometimes, especially when the plant is integrated with a solar thermal source, as in the studied case, due to the instability of solar energy. Accordingly, two mathematical models for both the steady and unsteady states were developed and solved using the EES and Matlab programs, and then the validation of these two models was conducted against the published experimental and theoretical data. For the same percentage of studied disturbances (10%), the results indicate that the change in the seawater mass flow rate has the greatest impact on the stability of the plant, while the change in the mass flow rate of HTF in parabolic trough collector has the least impact, also the change in the seawater mass flow rate has the greatest impact on the productivity and performance ratio of the MED plant, while in MSF plant, the effect of the change in the seawater temperature is more serious than the same percentage of disturbance in the seawater mass flow rate. For the studied disturbance (a decrease by 100 % on instantaneous values of the intensity of the solar radiation), the results indicate that the MED is the least stable unit in the plant, where it takes about 3600 seconds to return to the steady state after the disturbance is removed, while both the parabolic trough and the storage return to the steady state after 1722 seconds of disturbance removal. On the other hand, the steam generator is the most stable unit, where the needed time to return to the steady state is the shortest. The cost per cubic meter of distilled water is about 3.93 $⁄m^3 for proposed desalination plant which is driven by solar energy in addition to conventional system as auxiliary source where the initial capital cost was estimated by 52500 $. The cost per cubic meter increases to 4.22$⁄m^3 in the same plant which is driven by only conventional energy source (natural gas) where the initial capital cost was estimated by 17200 $. As a result, the most important economic parameters and a clear view of the dynamic response in the whole plant were obtained when the plant is exposed to the most common disturbances, which would improve the control strategies and increase the stability of the plant's work.