was found that MSF–RO plants had higher water recovery rates than MSF due to
scale formation 57. Hassan et al. 58–60 proposed a
NF–RO–MSF desalination process as shown in Figure (22), in which NF membranes
were used to remove scale forming ions from seawater, allowing higher TBT
operation of the MSF processes. Not only was the water productivity improved
but also the service life of cascade staging of MSF distillers was extended.
However, the feed water had to be heated process in winter 61–64.
Hamed et al. 65
showed that the NF process could reject 82.8% of the hardness ions and 26.5% of
the TDS at the recovery rate of 64–69%. The TBT and water conversion ratio of
MSF unit could reach the high temperature of 130–160 °C. The combination of
NF–MSF and NF–RO–MSF with power plant could achieve less capital costs, high
plant availability and better water production, when the local low cost
electricity from the power plant applied to the NF and RO membrane processes,
and the waste heat could be used by the MSF process.
Mabrouk et al. 66–67
evaluated the desalination performance of concentrated solar
power–NF–MSF–deaeration and brine mix (CSP–NF–MSF–DBM) process. When about 90%
of sulfate and calcium ions were rejected by NF, the TBT of the NF–MSF–DBM
plant could be raised to 100–130 °C to achieve a gain output ratio (GOR) of
15–16, doubled from the existing multistage flash-brine recirculation (MSF-BR)
plant. Fresh water production was increased by 19% at 14% less cost. When the
discharged concentrated brine was further used as feed for the crystallization,
NF–MSF–Crystallization (NF–MSF–Cr) or NF–RO–MSF– Crystallization (NF–RO–MSF–Cr)
systems produced not only fresh water but also high quality salt crystals 68.
Their water production costs were about 0.71 $/m3 and 0.43 $/m3.
Subtracting the salt price of 30 $/ton 69, the cost of fresh water production
could be further lowered to 0.37 $/m3 70.