Dynamic Operation of Batch Reverse Osmosis and Batch Pressure Retarded Osmosis

Abstract

Optimal control theory is applied to dynamic operation of batch reverse osmosis (RO) for seawater desalination and batch pressure retarded osmosis (PRO) for power generation. It is proved that the water flux should be constant during the entire operation in order to minimize specific energy consumption (SEC) in RO or to maximize specific energy production (SEP) in PRO. A dimensionless parameter γ = A m L p π 0 t f /V 0 , similar to that used in continuous osmotic membrane processes, is proposed to characterize the energy performance. While the SEC in RO is a monotonic function of recovery and γ, the SEP in PRO is solely a monotonic function of γ. It is shown that batch RO/ PRO excels continuous RO/PRO because it mitigates the spatial variation of flux in a long pressure vessel observed in the latter. The batch operation provides an elegant way to implement continuous multistage RO with interstage pumps and an energy recovery device as well as continuous multistage PRO with interstage turbines. Some trade-off between the energy efficiency and flux is deemed necessary. A preliminary cyclic diagram to operate the batch PRO is proposed.

Investigation of the Mixing Rate and Channel Volume Efficiency of a Self-Driven Rotary Energy Recovery Device in the Reverse Osmosis System

“…15.5 5.3 2 (6) where φ denotes the mixing rate (%). The correlation coefficient (R 2 ) and adjusted R 2 were calculated to be 0.99, implying that the results are reliable.…”

“…The seawater-related industrial reverse osmosis (RO), which possesses lower energy requirements than conventional distillation-based desalination, is being developed rapidly to address water scarcity. − However, the power consumption of RO systems is considerably high owing to the seawater pressurization requirement . Therefore, the energy recovery device (ERD) that recovers energy from high-pressure brine rejected by the RO membrane and uses the energy to pressurize seawater plays an important role in the RO system. , There are two kinds of ERDs: isobaric and turbine. The isobaric ERD works on the positive displacement principle, which states that the pressure energy of brine gets directly transmitted to seawater without intermediate energy conversion.…”

“…4 Therefore, the energy recovery device (ERD) that recovers energy from high-pressure brine rejected by the RO membrane and uses the energy to pressurize seawater plays an important role in the RO system. 5,6 There are two kinds of ERDs: isobaric and turbine. The isobaric ERD works on the positive displacement principle, which states that the pressure energy of brine gets directly transmitted to seawater without intermediate energy conversion.…”

Comparison of Energy Efficiency between Atmospheric Batch Pressure-Retarded Osmosis and Single-Stage Pressure-Retarded Osmosis

“…The applied hydraulic pressure in BPRO varies with the osmotic pressure difference. The ideal performance of BPRO was evaluated by Li Mingheng [ 26 ], and the results demonstrated that BPRO outperforms single-stage and two- or three-stage PRO in terms of both energy production and power density, showing its potential for high-efficiency osmotic energy harvesting without additional stages and expenditures. However, in practical scenarios, scaling up the pressurized variable-volume tank remains challenging, restricting the application of BPRO [ 27 ].…”

Simultaneous Optimization of Size and Operation for Seawater Reverse Osmosis Network with Permeate Split and Interstage Permeate Split Designs

“…Many research studies of the optimal design of the RO system have been reported, including the superstructure-based optimization, − global optimization, , multiobjective optimization, , genetic algorithm-based meta-model, stochastic cost estimation approach, trace substance removal, ,, etc. New design concepts, such as low-salt-rejection reverse osmosis, permeate split (PS) design, ,,, internally staged design (ISD), , energy-efficient reverse osmosis, and batch RO, , could further decrease the water cost or provide large water flux and high energy efficiency.…”