Salinity Gradient Electricity Generation via Directional Solvent Extraction
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Solution Overview
Problem
Current technologies for generating electricity from low-grade heat face challenges such as low efficiency, high costs, and reliability issues with thermoelectric materials, as well as high expenses and bio-fouling problems in salinity gradient-based systems using membranes.
Innovation Solution
A system combining directional solvent extraction (DSE) with processes like pressure retarded osmosis (PRO) or reverse electro-dialysis (RED) to harness electricity from a salinity gradient, utilizing a closed loop with heated medium salinity liquid streams separated into high and low salinity streams, which are then used to generate electricity without the need for membrane pre-treatment or exotic materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If solid-state thermoelectric generation is used to convert low-grade heat to electricity, then electricity generation is achieved, but efficiency is low and costs are high
Solution Approach 1:
The patent changes the fundamental operating parameters from thermoelectric conversion to thermal evaporation and condensation cycles. By using phase change processes instead of solid-state thermoelectric materials, the system achieves higher efficiency while using inexpensive, readily available materials such as water and salt, eliminating the need for costly specialized thermoelectric materials.
Solution Approach 2:
The invention utilizes phase transitions of water (evaporation from liquid to vapor, then condensation from vapor to liquid) as the core mechanism for heat transfer and electricity generation. This phase-based approach replaces inefficient solid-state thermoelectric conversion, enabling effective utilization of low-grade heat sources while maintaining simple and low-cost system architecture.
2Use of energy by moving object
If salinity gradient systems with membranes are used to generate electricity, then electricity generation is possible, but membrane expenses are high and bio-fouling occurs
Solution Approach 1:
The patent extracts and eliminates the membrane component entirely from the system. Instead of using membranes for salinity gradient electricity generation, the invention employs open evaporation ponds and condensation surfaces where salt solutions are naturally separated through phase change processes, eliminating membrane-related costs and bio-fouling issues.
Solution Approach 2:
The system replaces expensive, durable membranes with inexpensive, replaceable evaporation and condensation surfaces. These surfaces can be simple concrete ponds or metal condensers that are much cheaper than specialized membranes, and their short service life is acceptable given the low cost and ease of replacement.
3Adaptability or versatility
If natural water streams are used in salinity gradient systems, then electricity generation is possible, but stringent pre-treatment is required
Solution Approach 1:
The system allows natural water streams to feed directly into evaporation ponds where physical evaporation and chemical precipitation naturally occur. The salt and impurities remain in the evaporating solution while fresh water condenses, providing self-cleaning and self-purification without requiring external pre-treatment facilities or complex processing systems.
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 enhances efficiency, reduces costs, and minimizes bio-fouling by using a closed loop system that recycles fluids continuously, achieving electrical generation efficiencies of at least 3.6% and providing a compact, portable solution for generating electricity from low-grade heat.
Implementation Method 1
the solubility of a salt in a directional solvent increases with increasing temperature. The separated streams can then be used to generate electricity in a PRO or RED process
Implementation Method 2
In a PRO process (or any of the processes relying on the salinity gradient to generate electricity), a first chamber may be provided for receiving the low salinity liquid stream, and a second chamber for receiving the high salinity liquid stream, where the first and second chambers are separated by a semipermeable membrane
Implementation Method 3
Another system may be configured as a reverse electro-dialysis ('RED') process
Data Source
AI summary
Systems and methods for generating electricity from low grade heat. The system and method may be a closed loop. When a liquid mixture of salt, water, and an ion-stripping liquid is heated using the low grade heat, water dissolves more readily into the ISL, due to the increased solubility of the water in the ISL, at the increased temperature. The salt remains in a high-salinity aqueous phase that separates from the ISL phase. Upon cooling of the ISL phase, a nearly pure water phase can be separated therefrom. This low salinity water phase and the high salinity water phase can be fed to any of various processes for generating electricity from a salinity gradient, such as pressure retarded osmosis or reverse electro-dialysis. Low and high salinity water exiting the power generating portion of the process can be recycled, to reform the original liquid stream, upon recombination with the ISL.