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 NF–SWROreject–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 120ºC without further acidification, antiscalant or antifoam. The paper summarizes the MSF performance, which was established at operating Top Brine Temperature (TBT) of 120ºC, in the dihybrid NF–MSF and trihybrid NF–SWROreject–MSF systems. Because of the excellent MSF performance at this TBT of 120ºC, the paper also addresses the planned operation of MSF at elevated TBT of 120 to 160ºC 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.

SWCC–RDC have come up with a true break-through in operating MSF with low to no scale control chemical treatment other than nanofiltration of make-up. Moreover, MSF operation utilizing SWRO reject again with very limited scale control chemical treatment became feasible, i.e. hybrid concept. These achievements were possible at TBT 120°C in either case. It is envisioned that higher TBT will be attainable which will lead to better designed dual-purpose plant of higher overall efficiency at increased production of water and power. The expected goal is to get more for less, i.e. increased production at reduced costs.