Ejector Membrane Distillation for Low-Energy Water Desalination
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Solution Overview
Problem
Existing membrane distillation technologies face challenges with high energy consumption, maintenance requirements, and scalability issues due to the use of mechanical vacuum pumps, particularly in humid air streams, which affect efficiency and lifespan.
Innovation Solution
A system utilizing an ejector module to create vacuum conditions without a vacuum pump, employing kinetic energy from a high-velocity fluid stream to draw water vapor through a hydrophobic microporous membrane, combined with a dehumidifier to condense vapor into freshwater.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If vacuum pumps are used to create vacuum in the permeate channel, then vapor mass transfer resistance is reduced and productivity is improved, but energy consumption increases and maintenance requirements increase
Solution Approach 1:
The patent extracts the vacuum pump from the system by using a sweeping gas flow to create negative pressure in the permeate channel. The sweeping gas (inert gas like nitrogen or argon) flows through the permeate channel, carrying water vapor away from the membrane surface, which creates a pressure gradient that drives vapor transport without requiring mechanical vacuum pumps.
Solution Approach 2:
The patent uses pneumatic principles by employing a sweeping gas flow to create the driving force for vapor transport. The inert gas flow through the permeate channel creates pressure differential and carries vapor molecules away, replacing the mechanical vacuum pump with a pneumatic sweeping mechanism.
2Productivity
If vacuum pumps are used to maintain vacuum levels, then process efficiency is improved, but system complexity and maintenance needs increase
Solution Approach 1:
The patent removes the vacuum pump component entirely from the system. Instead of using mechanical vacuum generation, the system uses a sweeping gas flow to create the necessary pressure differential, thereby eliminating the complex mechanical subsystem and its associated maintenance requirements.
Solution Approach 2:
The patent replaces the mechanical vacuum pump system with a pneumatic sweeping gas flow system. This substitution eliminates moving parts, mechanical seals, and complex control mechanisms while maintaining the essential function of creating vacuum conditions for efficient vapor transport.
3Productivity
If vacuum pumps operate with humid air streams, then vapor removal is enhanced, but pump performance decreases and lifespan reduces due to vapor condensation
Solution Approach 1:
The patent uses inexpensive inert gas (such as nitrogen or argon) as a disposable sweeping medium that flows through the permeate channel. This gas absorbs water vapor and is then vented or recycled, avoiding the problem of vapor condensation in mechanical pumps. The sweeping gas acts as a single-use carrier that prevents reliability issues.
Solution Approach 2:
The inert sweeping gas acts as an intermediary between the water vapor and the external environment. It carries vapor molecules away from the membrane surface without requiring direct contact with condensation-prone mechanical components, thus protecting the system from vapor-related degradation.
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
Reduces energy consumption, maintenance needs, and operational costs while enhancing scalability and efficiency by eliminating the need for vacuum pumps, improving freshwater production.
Implementation Method 1
employing kinetic energy from a high-velocity fluid stream to draw water vapor through a hydrophobic microporous membrane
Implementation Method 2
The temperature difference between the two sides of the membrane creates a vapor pressure difference, allowing water vapor to pass through the membrane pores from the hot feed side to the permeate side
Implementation Method 3
combined with a dehumidifier to condense vapor into freshwater
Data Source
AI summary
A system for desalinating water using membrane distillation (MD) integrated with an ejector includes an ejector module and a membrane module. The ejector module includes a water ejector, a first water circulation pump, and a freshwater tank. Freshwater is continuously pumped from the freshwater tank, through the water ejector, and back to the freshwater tank. The membrane module includes a feed tank, a second water circulation pump, a water heater, and a membrane distillation unit. Salt water from the feed tank is pumped through the water heater to form vapor, which is then directed to the membrane distillation unit. The membrane distillation unit comprises a feed chamber, a membrane, and a vapor chamber. Vapor passes through the membrane to the vapor chamber, which has an air inlet for pressure differential and is connected to the water ejector. Desalinated water is collected in the freshwater tank.