Reverse Osmosis Purification with Recycled Permeate
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Solution Overview
Problem
Reverse osmosis technology for water purification faces challenges such as low recovery ratio and membrane scaling due to high pressure across membranes, leading to increased costs and power consumption, and higher salt concentration in the concentrate side.
Innovation Solution
A method involving a series of reverse osmosis units with low rejection membranes and passing brine from the concentrate side to the permeate side to reduce the pressure gradient, followed by a final phase using a high rejection membrane to produce pure desalinated water.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high pressure is applied across the reverse osmosis membrane to increase recovery ratio, then the recovery ratio is improved, but membrane scaling and power consumption increase
Solution Approach 1:
The reverse osmosis process is divided into multiple stages with progressively increasing pressure. Each stage operates at a lower pressure than the total required pressure would demand, allowing the system to achieve high recovery ratios while managing energy consumption and preventing membrane scaling through staged pressure application.
Solution Approach 2:
The system changes operating parameters (pressure, flow rate) across different stages of the reverse osmosis process. By adjusting these parameters progressively through multiple stages rather than applying high pressure uniformly, the system achieves high recovery ratios while controlling power consumption and preventing membrane scaling.
2Productivity
If high pressure is applied across the reverse osmosis membrane to increase recovery ratio, then the recovery ratio is improved, but membrane scaling occurs
Solution Approach 1:
The reverse osmosis process is segmented into multiple stages, each operating at progressively higher pressures. This segmentation prevents membrane scaling by avoiding the application of excessively high pressure in a single stage, thereby maintaining recovery ratio while protecting the membrane from scaling damage.
Solution Approach 2:
The multi-stage design provides a cushioning effect against membrane scaling by distributing the pressure load across multiple membranes in sequence. Each membrane experiences lower individual pressure stress, preventing the compaction and scaling that would occur with single-stage high-pressure operation.
3Productivity
If high pressure is applied across the reverse osmosis membrane, then recovery ratio is improved, but salt concentration in concentrate side increases
Solution Approach 1:
The concentrate stream is processed through multiple reverse osmosis stages, with each stage removing additional salts progressively. This segmented approach achieves high recovery ratios while managing salt concentration in the final concentrate by distributing the salt removal across multiple membranes rather than concentrating all salts in a single high-pressure stage.
4Productivity
If high pressure is applied across the reverse osmosis membrane, then recovery ratio is improved, but device cost increases
Solution Approach 1:
The system uses multiple reverse osmosis membrane assemblies arranged in series across different stages. While this increases the number of components, each membrane operates at lower individual pressure, allowing the use of less expensive membrane materials and support structures compared to a single high-pressure membrane assembly designed to achieve the same recovery ratio.
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
This approach reduces the pressure gradient across membranes, decreases power consumption, and increases the recovery ratio while maintaining effective salt removal, thereby improving the efficiency and cost-effectiveness of the desalination process.
Implementation Method 1
reverse osmosis (RO), where a solvent is forced through a permeable membrane from a region of high solute concentration to a region of low solute concentration by applying a pressure greater than osmotic pressure
Implementation Method 2
by applying a pressure greater than osmotic pressure
Implementation Method 3
This small differential in ion concentration reduces the pressure gradient across the membrane
Data Source
AI summary
The method for purifying liquids purifies a saline liquid, e.g., salt water, using a plurality of first phase reverse osmosis (RO) units and at least one final phase reverse osmosis unit. The plurality of first phase reverse osmosis units are arranged in series. At least some of the concentrate in a last reverse osmosis unit of the series is recycled back to the permeate or output side of that unit to provide a mixed permeate. The mixed permeate is then passed successively to the permeate side of each preceding reverse osmosis unit in the series. This increases the salt content of the liquid in the permeate side of each phase, thus reducing the concentration differential across reverse osmosis membranes of the first phase reverse osmosis units.