Reverse Osmosis Cascade with Low Salt Rejection Membranes
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Solution Overview
Problem
Current desalination methods using reverse osmosis are energy-intensive and face challenges with osmotic pressures exceeding conventional membrane capabilities, and electrodialysis methods suffer from back diffusion and scaling issues with high concentrate concentrations.
Innovation Solution
A reverse osmosis system incorporating a cascade of low salt-rejection reverse osmosis stages with pressure exchangers and monovalent selective electrodialysis to manage osmotic pressures and scaling, using recirculation and antiscalants to enhance efficiency and reduce energy consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional high salt rejection RO membranes are used for very high recovery reverse osmosis of brines, then salt rejection is improved, but the osmotic pressure exceeds 100 bar requiring expensive specialized membranes and pumps
Solution Approach 1:
The system divides the single high-pressure RO process into multiple sequential RO stages, each operating at progressively lower pressures. The first stage operates at lower pressure to produce permeate, while subsequent stages process concentrate at reduced pressures, avoiding the need for expensive high-pressure membranes and pumps while achieving high overall salt rejection
Solution Approach 2:
The system transitions from a single-dimensional high-pressure approach to a multi-dimensional staged approach, where multiple RO units operate in series at different pressure levels, effectively distributing the osmotic pressure challenge across multiple lower-pressure operations rather than concentrating it in one high-pressure system
2Productivity
If electrodialysis is used to treat RO concentrates, then recovery rates improve, but back diffusion occurs and electrical efficiency drops at high concentrate concentrations
Solution Approach 1:
The system performs preliminary RO treatment to concentrate the brine before applying electrodialysis, and then performs a second RO treatment on the electrodialysis permeate. This preliminary concentration step allows ED to operate more efficiently at lower concentrations, avoiding back diffusion and maintaining electrical efficiency while achieving higher overall recovery rates
3Productivity
If electrodialysis is used to treat RO concentrates, then recovery rates improve, but divalent scaling species cause scaling that can only be partially treated
Solution Approach 1:
The system uses a second RO stage as an intermediary treatment between electrodialysis and final product recovery. This intermediate RO stage removes divalent scaling species from the ED permeate that would otherwise cause scaling in subsequent operations, providing more complete scaling prevention than ED alone
4Manufacturing precision
If thermal methods are used to treat saline brines, then purification is achieved, but energy consumption is highly intensive
Solution Approach 1:
The system replaces thermal energy-intensive evaporation processes with mechanical membrane-based RO and electrodialysis processes. These membrane processes achieve equivalent or superior purification at significantly lower energy consumption by using pressure-driven filtration rather than thermal evaporation to separate salts from brine
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 effectively manages high osmotic pressures and scaling issues, achieving high recovery rates with reduced energy consumption and minimizing membrane fouling, enabling efficient desalination of saline brines.
Implementation Method 1
reverse osmosis (RO) cascade fluidly connected to the high pressure feed pump; wherein the RO cascade comprises: at least one low salt rejection reverse osmosis (LSRRO) stage including a LSRRO membrane
Implementation Method 2
the brines that would be generated from such operation would have osmotic pressures that exceed greater than 100 bar (1,450 psi)
Implementation Method 3
a pressure exchanger configured to recirculate at least a portion of a permeate output by the LSRRO stage to the input of said LSRRO stage or to the SWRO stage
Implementation Method 4
a monovalent selective electrodialysis (MSED) stage fluidly connected between the feed source and the RO cascade
Implementation Method 5
The MSED stage comprises an electrodialysis stack of alternating monovalent selective cation exchange membranes (CEM) and monovalent selective anion exchange membranes (AEM)
Data Source
AI summary
Described herein is a reverse osmosis system, comprising: a feed source input, a high pressure feed pump fluidly connected to the feed source input, a reverse osmosis (RO) cascade fluidly connected to the high pressure feed pump; wherein the RO cascade comprises at least one low salt rejection reverse osmosis (LSRRO) stage including a LSRRO membrane and a seawater reverse osmosis (SWRO) stage including a SWRO membrane fluidly connected to the at least one LSRRO stage.Also described herein is a reverse osmosis method, comprising: providing the reverse osmosis system of claim 1, inputting a high salinity fluid into the feed source input, increasing the pressure of the high salinity fluid via the high pressure feed pump, performing reverse osmosis via the RO cascade, and collecting at least one of a concentrate and a permeate.