Membrane Filtration Flow Reversal for Precipitation Fouling
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current membrane filtration processes for desalination face challenges with precipitation fouling, which limits recovery rates and requires high chemical costs and antiscalant usage, especially in low-pressure reverse osmosis and nanofiltration systems.
Innovation Solution
The process involves periodically reversing the flow direction in the membrane filtration system to prevent precipitation of sparingly soluble salts and minerals, using flow reversal to maintain the solution below the induction time for precipitation, thereby avoiding fouling and allowing higher recovery rates without the need for excessive antiscalants.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If recovery rate is increased in pressure-driven membrane processes, then more water is recovered from the feed stream, but precipitation fouling occurs due to supersaturation of sparingly soluble salts in the concentrate stream
Solution Approach 1:
The patent applies periodic flow reversal to the concentrate stream, switching the flow direction at intervals less than the induction time for precipitation. This periodic action prevents supersaturated salts from precipitating on the membrane surface by continuously disrupting the concentration boundary layer, allowing high recovery rates without fouling.
Solution Approach 2:
The system performs preliminary action by reversing the flow direction before precipitation can occur. By operating at a flow reversal frequency higher than the induction time for salt precipitation, the system proactively prevents fouling before it starts, rather than reacting to fouling after it occurs.
2Reliability
If conventional continuous flow is used to prevent precipitation fouling, then flow rates must be maintained above minimum thresholds, but this increases energy consumption and limits recovery rates
Solution Approach 1:
Instead of maintaining continuous high flow rates to prevent fouling, the system uses periodic flow reversal at controlled intervals. This allows the system to operate at lower average flow rates while still preventing precipitation fouling, thereby reducing energy consumption without sacrificing reliability.
Solution Approach 2:
The system changes the operational parameter from continuous flow rate to periodic flow reversal frequency. By controlling the reversal frequency to be higher than the induction time for precipitation, the system achieves fouling prevention through parameter optimization rather than maintaining high energy-consuming flow rates.
3Object-affected harmful factors
If antiscalants are added to prevent precipitation fouling, then fouling is reduced, but chemical costs and complexity increase
Solution Approach 1:
The system uses the concentrate stream's own flow to prevent fouling by periodically reversing it. This self-service approach eliminates the need for external chemical agents (antiscalants) to prevent precipitation, reducing both chemical costs and system complexity while maintaining effective fouling prevention.
Solution Approach 2:
The patent extracts the need for chemical antiscalants from the system by using physical flow reversal instead. This removes the chemical treatment component entirely, simplifying the system and eliminating chemical costs while achieving the same fouling prevention objective.
4Reliability
If flow reversal frequency is increased to prevent precipitation, then fouling is better controlled, but the system complexity and control requirements increase
Solution Approach 1:
The system optimizes the flow reversal frequency parameter to be just above the induction time threshold for precipitation. This parameter optimization achieves effective fouling control without excessive frequency, thereby minimizing control system complexity while maintaining reliability.
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 effectively prevents precipitation fouling, allows for higher recovery rates, reduces chemical consumption, and relaxes design constraints related to flow rates and concentration polarization, enabling more efficient desalination processes.
Implementation Method 1
pressure-driven membrane processes... in reverse osmosis and nanofiltration pressure-driven filtration processes
Implementation Method 2
a pressure difference across the membranes causes the solvent (usually water) to pass from the feed space to the permeate space
Implementation Method 3
preventing precipitation fouling... due to precipitation of sparingly soluble salts and minerals
Implementation Method 4
exposed to supersaturation conditions evolving in said water stream for a period of time which is less then the time required for said supersaturated water stream to precipitate
Data Source
AI summary
The invention provides a process for purifying water containing soluble species capable of forming one or more sparingly soluble salts or minerals, said process comprising feeding a pressurized water stream into a treatment zone having one or more membranes disposed therein, passing said stream along said membrane(s) to recover a permeate and to withdraw a concentrate therefrom while periodically reversing the direction of the flow of said stream in said treatment zone, wherein the periodicity of the flow reversal is such that said one or more membranes are exposed to supersaturation conditions evolving in said water stream for a period of time which is less then the time required for said supersaturated water stream to precipitate one or more of said sparingly soluble salts and/or minerals therefrom.