Energetic, Exergetic, and Economic Analysis of MED-TVC Water Desalination Plant with and without Preheating

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.

Dynamic Optimization of Multieffect Seawater Distillation to Gain Insights into Various Feeding Patterns: Productivity, Thermodynamic, Economic, and Environmental Perspectives

“…The preheating of feed to a higher temperature yields more freshwater. 51 Similarly, from Figure 5d, it can be inferred that a higher motive steam pressure favors a higher PR, which is consistent with the study reported by ref 52. The last effect of brine temperature (T B,N ) determines the temperature driving force of the process.…”

Demystifying integrated power and desalination processes evaluation based on standard primary energy approach

“…The theoretical lowest separation energy of seawater of concentration 35000 mg/L and temperature of 28°C is around 0.78 kWh/m 3 [17,18]. Unfortunately, all practical desalination technologies, such as multi effect desalination (MED) [19][20][21][22][23][24][25][26], multi stage flash (MSF) [27][28][29] and Seawater reverse osmosis (SWRO) [30,31] are operating at 8-10 times higher than theoretical minimum energy requirement or thermodynamic limit (TL). Almost 95% online desalination capacity is based on these three major but practical processes.…”

Energy Efficient Seawater Desalination: Strategies and Opportunities

“…With more technological advancement such as coupling with thermo vapor compression (TVC) for lower temperature operation has promoted the economic feasibility hence the sharp increase in MED application in desalination market. [ 18 ] In VC, the vapor is compressed to generate heat for evaporating the seawater. Two methods are used, i.e., mechanical vapor compression (MVC) and TVC in which the vapor generated in the evaporator is compressed mechanically and thermally, respectively.…”