Abstract
Desalination is the sole proven technique that can provide the necessary fresh water in arid and semi-arid countries in sufficient quantities and meet the modern needs of a growing world population. Multi effect desalination with thermal vapour compression (MED-TVC) is one of most common applications of thermal desalination technologies. The present paper presents a comprehensive thermodynamic model of a 24 million litres per day thermal desalination plant, using specialised software packages. The proposed model was validated against a real data set for a large-scale desalination plant, and showed good agreement. The performance of the MED-TVC unit was investigated using different loads, entrained vapour, seawater temperature, salinity and number of effects in two configurations. The first configuration was the MED-TVC unit without preheating system, and the second integrated the MED-TVC unit with a preheating system. The study confirmed that the thermo-compressor and its effects are the main sources of exergy destruction in these desalination plants, at about 40% and 35% respectively. The desalination plant performance with preheating mode performs well due to high feed water temperature leading to the production of more distillate water. The seawater salinity was proportional to the fuel exergy and minimum separation work. High seawater salinity results in high exergy efficiency, which is not the case with membrane technology. The plant performance of the proposed system was enhanced by using a large number of effects due to greater utilisation of energy input and higher generation level. From an economic perspective, both indicators show that using a preheating system is more economically attractive.
Highlights
Potable water is a scare natural resource, and its ongoing supply is one of most critical issues facing humanity today
Energetic and exergetic analyses are conducted on a large scale Multi effect desalination with thermal vapour compression (MED-thermal vapour compression (TVC)) desalination plant at Energetic and exergetic analyses conductedison large scale desalination at an appropriate reference state
Thermal in entrained seawater temperature, seawater salinity, number effects and load were in desalination plantvapour, at different working conditions and configurations
Summary
Potable water is a scare natural resource, and its ongoing supply is one of most critical issues facing humanity today. Saltwater represents about 97.5% of the water resources on the earth and that make desalination technologies the sole reliable source for securing fresh water. Combining a multi-effect desalination (MED) unit with thermal vapour compression (TVC) is an attractive choice for water production due to operating flexibility, fewer rotating parts, minimum corrosion risk and high effectiveness [2]. The MED-TVC system reuses a portion of the energy extracted from the last effect through a thermo-compressor (steam ejector) to reduce the loss in the condenser and act as an energy source for the first effect [3].
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