Abstract
We study the design and optimization of a multicomponent seawater desalination process with zero liquid discharge (ZLD). The designed process is highly integrated with multiple sub processing units that include humidification-dehumidification, Lithium Bromide absorption chiller, multi-effect evaporators, mechanical vapor compression, and crystallization. Aspen Plus software with E-NRTL and SOLIDS thermodynamic packages are used for modeling and simulation of desalination and crystallization units, respectively. In addition to this, we use data-driven optimization to find the best operating condition (i.e., the temperature of the last effect evaporator) that minimizes the overall energy consumption of the designed plant with an output constraint imposed on the mass fraction of salts going to the ZLD system should be greater than 20 wt.% to achieve the ZLD goal. We use a local sample-based data-driven optimizer, Nonlinear Optimization with the Mesh Adaptive Direct Search (NOMAD) algorithm, to perform constrained simulation-based optimization. The results show that at the optimized temperature (71.58 °C), our design produces 1777 kg/hr drinking water with an energy consumption of 536 kW in comparison to 580 kW of energy consumption for the same plant output in the base case design (not optimized). Thus, data-driven optimization of the evaporator temperature improves the overall energy consumption by 7.5% and achieves higher desalination efficiency. Further, the integration of the crystallizer unit into the overall desalination process allows us to produce about 43 kg/h of NaCl and achieve ZLD.