Bimodal RO/PRO Framework for Price-Responsive Water and Power
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Solution Overview
Problem
Reverse osmosis (RO) desalination faces economic challenges in renewable-dependent grids due to fluctuating electricity prices, while pressure retarded osmosis (PRO) struggles to produce enough power to justify capital expense at an industrial scale, necessitating high-selectivity, high-permeability membranes that combine the benefits of both.
Innovation Solution
A bimodal system integrating RO and PRO processes using the same components, with a variable energy recovery device and optimized membranes, allowing dynamic switching between modes based on electricity and water prices to maximize profit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If reverse osmosis is used for desalination, then water production is achieved, but economic viability deteriorates due to fluctuating electricity prices
Solution Approach 1:
The patent combines reverse osmosis (RO) and pressure retarded osmosis (PRO) into a single hybrid system that shares common components including membranes, pressure vessels, and energy recovery devices. This merging allows the system to perform both desalination and power generation functions, enabling economic viability by producing both water and electricity to offset operating costs
Solution Approach 2:
The hybrid system is designed with multi-functionality where the same core components serve dual purposes: the semi-permeable membranes enable both water separation in RO mode and power generation in PRO mode, while the energy recovery device functions as both a pressure exchanger and a turbine generator. This universality reduces capital expense while maximizing operational flexibility
2Power
If pressure retarded osmosis is used for power generation, then energy production is achieved, but capital expense justification deteriorates due to insufficient power output
Solution Approach 1:
The patent merges PRO power generation with RO desalination in a hybrid system where the same membranes and pressure vessels serve both functions. This combination justifies capital expense by ensuring the membranes are utilized for both water production and power generation, maximizing return on investment through dual revenue streams
Solution Approach 2:
The system dynamically switches between RO and PRO operational modes based on real-time electricity and water prices. The control system adjusts operating parameters to maximize profit, transitioning from power generation when electricity prices are low to desalination when water prices are high, thereby optimizing economic returns on capital investment
3Productivity
If high-selectivity membranes are used for RO, then water production efficiency is improved, but power density in PRO deteriorates due to membrane permeability constraints
Solution Approach 1:
The patent employs membranes with specifically engineered parameters that balance selectivity and permeability. By optimizing the membrane structural parameter (S) and water permeability coefficient (A), the system achieves sufficient salt rejection for RO while maintaining adequate water flux for PRO power generation, resolving the trade-off between water production efficiency and power density
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system achieves cost-effective and power-effective operation by optimizing profit through dynamic mode switching, leveraging RO for water production and PRO for energy generation, enhancing efficiency and economic viability in renewable energy environments.
Implementation Method 1
when the hydraulic pressure, P, exceeds the osmotic pressure, π, of the saline water, water is forced through a semi-permeable membrane
Implementation Method 2
PRO is a closely related clean energy technology that, with current materials, struggles to produce enough power to justify capital expense at an industrial scale
Data Source
AI summary
A method of operating a dual reverse osmosis/pressure retarded osmosis plant, including when electricity costs less than a first predetermined price, moderate salinity water is pumped into the first portion of a pressure vessel having first and second portions separated by a water permeable/salt impermeable osmotic membrane to yield desalinated permeate in the second portion and brine in the first portion. Further, when electricity costs greater than the first predetermined price, low salinity water is pumped into the second portion and brine is pumped into the first portion to yield pressurized moderate salinity water in the second portion which is run through an energy recovery device to generate electricity. The salinity of the low salinity water is lower than the salinity of the moderate salinity water, and the salinity of the moderate salinity water is lower than the salinity of the brine.