Global optimality of RO seawater desalination networks with permeate reprocessing and recycle

ABSTRACT

In conjunction with the optimality of single-stage reverse osmosis (SRO) system, this work addresses the economic competence of prominent seawater desalination reverse osmosis systems with permeate reprocessing and recycle using differential evolution as global optimization tool. The optimization approach refers to nonlinear programming formulation consisting of mass balances and design specifications as equality constraints and other design specifications as inequality constraints. Further, MATLAB optimization toolbox-based analysis was conducted to compare the obtained solutions with deterministic optimization methods. Among all considered alternatives such as two stages reverse osmosis (TRO) series arrangement with retentate reprocessing and permeate recycle (TRO-TSRR-PR), SRO, TRO series arrangement with permeate bypass and permeate reprocessing and TRO with permeate reprocessing series arrangement processes, TRO-TSRR-RP process configuration has been evaluated to competitive with the SRO process with an optimal cost of 0.9527$/m³ obtained with DE-SQP. While the SRO remains the simplest cost-effective system in terms of topological complexity, the TRO-TSRR-PR process has been evaluated to be 5.75% better than the optimal freshwater production cost of SRO process reported in the literature with an optimal decision variable set values [68.51 bar, 7688, 5881.7 m³/h, 259.8 ppm, 2422, 322.9 m³/h and 1764.9 ppm] for [P₁^F, NM₁, W_RO^RF, C₁^RP, NM₂, W₂^RP, C₂^RP].

KEYWORDS:

• Desalination
• differential evolution
• optimization
• permeate reprocessing
• reverse osmosis
• seawater