Means and merits of higher temperature operation in dual-purpose plants

For the last 3 years, the SWCC-RDC conducted extensive R&D work on nanofiltration (NF) pretreatment of feed to SWRO and make-up to MSF pilot plants in dihybrid arrangement of NF-SWRO or NF-MSF, also in trihybrid of NFSWROreject-MSF, where the SWROreject from the dihybrid NF-SWRO is used as make-up to the MSF unit. In both di-/trihybrid the MSF unit was operated successfully at 120°C without further acidification, antiscalant or antifoam. The paper summarizes the MSF performance, which was established at operating Top Brine Temperature (TBT) of 120°C, in the dihybrid NF-MSF and trihybrid NF-SWROreject-MSF systems. Because of the excellent MSF performance at this TBT of 120°C, the paper also addresses the planned operation of MSF at elevated TBT of 120 to 160°C and above. These gained advantages in improved performance of MSF when make-up is directly or indirectly from NF (in di- or trihybrid, respectively) triggered a review of dual power and water production cycle of boiler turbine generator: BTG and multistage flash: MSF cycle design. Such combination, i.e., dual purpose BTG-MSF process, could lead to simultaneous increases in water and power production. Simulation model results of such increases are shown in this paper. The described MSF performance also revived interests in gas turbine generator: GTG, heat recovery steam generator: HRSG and steam turbine generator: STG, (with MSF) thus power and water (dual purpose) combined cycle: PWCC.