New Trend in the Development of ME-TVC Desalination System

Several low temperature Multi-Effect Thermal Vapor Compression (ME-TVC) desalination units have been installed recently in most of the GCC countries. The total installed capacity has increased up to 500 million imperial gallons per day (MIGD) between 2000 and 2010 as shown in (Table 1). The majority of these units were commissioned in the UAE by SIDEM Company. The unit size capacities of these units were increased exponentially from 1 to 8.5 (MIGD) between 1991 and 2008 as shown in Fig.1. The new trend of combining ME-TVC with conventional multi-effect units led to this tremendous increase, more than eight times, during a very short period. Moreover, the unit size capacity of this technology is currently available with 10 MIGD, and it is expected to increase up to 15 MIGD in the near future. Hence, this system has become highly attractive and competitive against Multi Stage Flash (MSF) desalination system and it is predicted to get a considerable increase in the desalination market in future, particularly, in the GCC countries because it includes the following attractive features: Operates at lower top brine temperature around 60 to 70 oC compared to 90 to 120 oC in the MSF, and this reduces the scale formation, corrosion problems, anti-scalant chemicals and maintenance shutdown time (Darwish & Alsairafi, 2004). Requires less pumping energy than MSF (1.5~2 kW/m3 compared to 4~5 kW/m3), because there is no need to re-circulate large quantities of brine as in MSF system. Produces higher gain output ratios (GOR) up to 16 with less number of effects compared to 8 GOR and 21 stages in the MSF (Wade, 2001). Uses falling film horizontal tube evaporator (HTE), which gives high heat transfer coefficient and reduces the needed heat transfer area and consequently the capital cost of the desalination plant (Reddy & Ghaffour, 2007). Better response to steam supply variation, so, it has more flexibility of operation than MSF (Darwish & Alsairafi, 2004). Table1 shows that ME-TVC technology is gaining more market shares recently in Bahrain, Saudi Arabia and Qatar with a total installed capacity of 60 MIGD, 176 MIGD and 63 MIGD, respectively.