Vacuum-Assisted Draw Solution Recovery in Forward Osmosis Desalination
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Solution Overview
Problem
Existing desalination methods, particularly reverse osmosis and distillation, face high energy costs and expenses due to the need for high hydraulic pressure or heat to overcome saltwater's osmotic pressures, while forward osmosis systems struggle with costly draw solution recovery.
Innovation Solution
A water desalination system utilizing forward osmosis with ammonium bicarbonate as a draw solution, maintained under vacuum, efficiently recovers freshwater by using a heat pump to heat the diluted solution through a hydrophobic membrane, allowing multiple reuses of the regenerated draw solution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If reverse osmosis is used for desalination, then freshwater can be produced from saltwater, but high hydraulic pressure is required which increases energy costs
Solution Approach 1:
The patent inverts the conventional reverse osmosis approach by using forward osmosis with a draw solution (ammonium bicarbonate) that naturally pulls water through the membrane via osmotic pressure gradient, eliminating the need for high hydraulic pressure to force water through the membrane
Solution Approach 2:
The patent changes the driving parameter from hydraulic pressure (reverse osmosis) to osmotic pressure gradient (forward osmosis). By using ammonium bicarbonate as a draw solution with higher osmotic pressure than saltwater, the system creates a natural pressure gradient that drives water transport without mechanical compression
2Productivity
If distillation methods are used for desalination, then saltwater can be converted to freshwater, but high heat cost is required to overcome latent heat requirements
Solution Approach 1:
The patent replaces thermal energy (heat) with chemical energy (osmotic pressure). Instead of using heat to evaporate and condense water as in distillation, the system uses the osmotic pressure difference created by ammonium bicarbonate to directly transport water through the membrane, substituting a thermal process with a chemical/physical process
3Use of energy by moving object
If forward osmosis is used for desalination, then energy costs are reduced, but draw solution recovery becomes costly
Solution Approach 1:
The patent utilizes phase transition (evaporation and condensation) to separate and recover the draw solution. By heating the permeate stream, water evaporates and condenses on a separate condenser, leaving the ammonium bicarbonate draw solution behind for recovery and reuse, thus separating the draw solution from fresh water product
Solution Approach 2:
The patent extracts and separates the draw solution from the permeate stream through evaporation and condensation processes. The ammonium bicarbonate is extracted from the water stream and recovered in a separate stream, enabling its reuse and reducing overall system cost
4Productivity
If forward osmosis with ammonium bicarbonate is used, then high freshwater recovery rates are achieved, but vacuum maintenance is required which adds system complexity
Solution Approach 1:
The patent employs self-service mechanisms where the vacuum system is integrated into the existing process flow. The vacuum is maintained in specific chambers to facilitate evaporation and condensation, and the system uses its own operational parameters (temperature, pressure gradients) to maintain the vacuum state without requiring external complex vacuum generation equipment
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 high freshwater recovery rates (60-70%) with significantly reduced energy costs by leveraging ammonium bicarbonate's osmotic pressure and vacuum-assisted ion dissociation, making it more viable for high salinity water sources.
Implementation Method 1
Forward osmosis is another method of water desalination and involves the use of natural osmotic pressure (very little hydraulic pressure usually) to induce the flow of water through the membrane
Implementation Method 2
the system utilizes a heat pump to heat diluted ammonium bicarbonate solution that includes a high percentage of desalinated water (freshwater) to a desired temperature
Implementation Method 3
The system is maintained under a vacuum which advantageously allows the removal of the ammonium bicarbonate solution, which is the draw solution, from the freshwater in a more efficient manner and with lower temperatures required
Implementation Method 4
the method and system utilizes heat captured from a heat source to heat the diluted ammonium bicarbonate solution before passing the heated solution through a feed side of a hydrophobic membrane housing
Data Source
AI summary
A system and method for water desalination using forward osmosis to address problems associated with scarcity of freshwater around the world. The system uses ammonium bicarbonate as the draw solution to draw out freshwater through a forward osmosis (FO) membrane from an amount of saltwater or other contaminated water initially directed through one side of the FO membrane. The ammonium bicarbonate draws the desalinated water through the membrane of the FO membrane. Brine or other solutes are directed away. The combination of desalinated water and ammonium bicarbonate is directed through a series of valves and pumps, including a heat pump, and through a hydrophobic membrane that allows freshwater (product water) to be obtained from the desalination process in a more cost-effective and efficient manner. The ammonium bicarbonate is recycled and reused to generate additional draw solution for additional batches of saltwater or contaminated water for desalination.