Second law and sensitivity analysis of large ME-TVC desalination units

Large number of low temperature multi-effect thermal vapor compression (ME-TVC) desalination units have been installed recently in most of the GCC countries. The new trend of combining ME-TVC with conventional multi-effect led to tremendous increase in the unit size more than eight times during a very short period. The unit size capacity of this technology is currently available with 10 million imperial gallons per day (MIGD), and research studies are expected to increase this unit capacity up to 15 MIGD in the near future. Hence, this technology becomes highly attractive and competitive against multi stage flash desalination system. A mathematical model of ME-TVC desalination system is developed in this paper, using Engineering Equation Solver Software. This model is used to evaluate and improve the system performance of some new commercial ME-TVC units with capacities of 2.4, 3.8, and 6.5 MIGD using energy and exergy analysis. A sensitivity analysis is also presented in this paper to investigate the system performance of Al-Jubail ME-TVC unit in KSA, which is considered as the largest ME-TVC desalination plant in the world. Results showed that the first effect was found to be responsible for about 31% of the total effects exergy destruction in Al-Jubail, compared to 46% in ALBA and 36% in Umm Al-Nar. Results also showed that the specific exergy destruction is reduced significantly by increasing the number of effects as well as working at lower top brine temperatures.