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MD | Membrane Distillation

Membrane Distillation Overview

Membrane distillation (MD) is a thermally driven separation process that uses a hydrophobic microporous membrane.
Water evaporates on the hot feed side, passes through the membrane pores as vapor, and condenses on the colder side. Non-volatile substances, including salts and minerals, remain in the feed.
Because only water vapor passes through the membrane, MD can produce very high-purity water regardless of feed salinity.

Innoflow AGMD Concept

AGMD System Concept — External Condensation and Heat Recovery
AGMD System Concept — External Condensation and Heat Recovery

Innoflow Technologies is developing an AGMD system that combines waste heat utilization, vacuum-assisted vapor transfer and external condensation with an established AGMD configuration.

The condensation function is moved outside the conventional AGMD module. Water vapor passing through the membrane and air in the air gap are drawn into an external condenser under reduced pressure.

The external condenser condenses the vapor to recover product water. The dried and cooled air can then be recirculated to the air gap.

This separates the membrane stack and condensation system functionally, simplifying the stack and enabling external heat recovery and thermal optimization.

Operating Principle

  1. Feed Heating

    Industrial waste heat or a low-temperature heat source heats the feed.

  2. Vapor Generation

    The vapor pressure difference between the heated feed and the permeate side causes water to evaporate at the membrane surface.

  3. Selective Vapor Transport

    The vapor passes through the hydrophobic membrane pores, while salts and most non-volatile substances remain in the feed.

  4. Vacuum-Assisted Transfer

    Controlled vacuum in the air gap reduces mass-transfer resistance from non-condensable gases and transfers vapor to the external condenser.

  5. External Condensation

    The vapor is cooled and condensed outside the stack, recovering high-purity product water.

  6. Heat & Air Recovery

    Condensation heat can be recovered for feed preheating. Depending on system configuration, cooled air can be recirculated to the air gap.

AGMD Advantages

Low-Temperature Waste Heat Utilization

Operates with relatively low-temperature heat sources and can integrate industrial waste heat, low-pressure steam, hot water and other low-grade heat.

Concentration of High-Salinity Feedwater

The vapor pressure difference drives the process without the direct osmotic-pressure limitations of pressure-driven membrane processes, enabling treatment of high-salinity brines and industrial wastewater.

High Rejection of Non-Volatile Substances

Under normal operating conditions without membrane wetting, the process can achieve very high rejection of salts and most non-volatile substances.

Vacuum-Assisted Mass Transfer

Controlling non-condensable gases in the air gap reduces air-gap mass-transfer resistance, a major resistance in conventional AGMD.

External Condensation

External condensation allows condenser capacity, cooling conditions and operating conditions to be optimized independently.

Heat Recovery Integration

Latent heat recovered during external condensation can be reused for feed heating, facilitating integration with heat pumps and heat recovery systems.

Modular & Scalable Design

A modular membrane stack and external condenser configuration can be expanded to match treatment capacity.

Key Operating Characteristics

Driving Force
Water vapor partial-pressure difference across the membrane
Heat Source
Industrial waste heat, low-temperature steam, hot water and other low-grade heat
Feed Temperature
Typically applicable at approximately 40–80°C, optimized for the feedwater and system conditions
Feed Pressure
Low hydraulic pressure process without high-pressure operation
Permeate Side
Controlled vacuum applied to the air gap
Separation Target
Water Vapor / Non-volatile Solute Separation
System Configuration
AGMD Stack + Vacuum System + External Condenser + Heat Recovery System

Applications

Concentration of high-salinity wastewater

  • High-salinity wastewater from battery manufacturing
  • Saline wastewater from chemical and materials industries
  • Concentration of RO concentrate and brine
  • Highly concentrated inorganic salt wastewater

ZLD / MLD Process

  • Concentration before evaporation and crystallization
  • Reduced crystallizer load
  • High-concentration brine volume reduction
  • Pretreatment and concentration for ZLD and MLD systems

Industrial Waste Heat Recovery

  • Utilization of process hot wastewater
  • Water treatment using low-temperature waste heat
  • Waste heat utilization in cogeneration and power generation
  • Factory utility heat recovery

Resource Recovery

  • Integration of salt concentration and crystallization
  • Concentration of valuable components in industrial wastewater
  • Process water recovery and reuse

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Contact: +82-31-8002-2500
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