Membrane Separation Process for Salt Crystallization
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Solution Overview
Problem
Current membrane separation technologies for aqueous salt solutions face issues such as low recovery efficiency, crystallization at the membrane surface leading to clogging, and the need to discharge concentrated brine waste, which are not economically or environmentally viable.
Innovation Solution
A membrane separation process is implemented where a controlled temperature difference between the retentate and distillate creates a positive driving force for water vapor permeation, preventing crystallization at the membrane surface by maintaining a higher temperature at the retentate outlet and using a stripping agent to reduce water vapor pressure at the distillate side, thereby avoiding scaling and clogging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If reverse osmosis is used for seawater desalination, then mechanical energy overcomes osmotic pressure to produce purified water, but recovery efficiency is limited to 40-50% for seawater due to scaling and very high mechanical pressures required
Solution Approach 1:
The invention changes the driving force parameter from mechanical pressure to temperature difference. By heating the feed solution to increase vapor pressure and maintaining the permeate side at lower temperature, the system achieves high recovery efficiency without requiring very high mechanical pressures that cause scaling
Solution Approach 2:
The invention utilizes phase transition of water from liquid to vapor on the feed side, through the membrane, and condensation back to liquid on the permeate side. This phase change mechanism enables high recovery efficiency while avoiding the scaling problems associated with high-pressure reverse osmosis
2Productivity
If membrane distillation is used to achieve higher water quality and yield, then thermal energy drives vapor through hydrophobic membrane, but crystallisation occurs at membrane surface causing reduction of flux or blockage
Solution Approach 1:
The invention optimizes temperature parameters by controlling the temperature difference across the membrane and maintaining feed solution temperature below the crystallization point. This parameter control prevents salt crystallization at the membrane surface while sustaining high water vapor flux through the hydrophobic membrane
Solution Approach 2:
The invention applies preliminary action by pre-heating the feed solution to a controlled temperature before it contacts the membrane, and pre-cooling the permeate side. This preliminary temperature control prevents crystallization from occurring at the membrane surface during the distillation process
3Quantity of substance
If forward osmosis is used with high osmotic pressure solution to draw water through membrane, then osmotic pressure drives separation, but energy costs are high due to thermal evaporation and pH adjustment required for agent regeneration
Solution Approach 1:
The invention replaces the chemical/osmotic driving force of forward osmosis with a thermal driving force. By using temperature difference to create vapor pressure gradient, the system achieves water transfer through the membrane without requiring high-cost chemical agents and their subsequent thermal evaporation or pH adjustment for regeneration
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 process enhances the separation efficiency by reducing membrane clogging and increasing water recovery, allowing for the effective separation of pure water and salt, while also enabling the recycling of the stripping agent, thus improving the overall process economics and environmental sustainability.
Implementation Method 1
a positive driving force for water vapour permeation through the membrane is created by controlling the water vapour pressure difference between the retentate and the distillate
Implementation Method 2
a controlled temperature difference between the retentate and distillate creates a positive driving force for water vapor permeation
Implementation Method 3
using a stripping agent to reduce water vapor pressure at the distillate side
Implementation Method 4
water vapor permeation through the membrane
Implementation Method 5
water vapor permeation through the membrane
Data Source
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AI summary
The invention is directed to a membrane separation process of an aqueous feed solution. In one aspect the membrane separation process of the invention comprises passing an aqueous feed comprising one or more dissolved compounds having an increasing water solubility with increasing temperature through a membrane module comprising a feed inlet and a liquid retentate outlet, wherein the temperature in the outlet is higher than the temperature in the inlet, and wherein a positive driving force for water vapour permeation is created by maintaining the water vapour pressure at the distillate side lower than at the retentate side by other means than by a temperature difference, such that one or more of said dissolved compounds at least partially crystallise in said retentate, and wherein the relative temperatures of the feed inlet and the liquid retentate outlet are set. In another aspect, the membrane separation process of the invention comprises: - subjecting an aqueous feed comprising one or more dissolved compounds to a membrane distillation process, and - thereafter, preferably directly thereafter, passing the retentate from the membrane distillation process through a membrane module comprising a feed inlet and a liquid retentate outlet, wherein the temperature in the outlet is equal to or higher than the temperature in the inlet, and wherein a positive driving force for water vapour permeation is created by maintaining the water vapour pressure at the distillate side lower than at the retentate side by other means than by a temperature difference, such that one or more of said dissolved compounds at least partially crystallise in said retentate, and wherein the relative temperatures of the feed inlet and the liquid retentate outlet are set.