How Vapor Compression Distillation Works

Aquaback’s thin film vapor compression distillation technology utilizes over 50 years of combined water purification and heat transfer technology knowledge to deliver the next generation of water purification solutions. Unlike other purification processes that require multiple steps (chemical treatment, filtration, reverse osmosis, forward osmosis, MBR, ultraviolet) each used to target and remove known contaminants.

Distillation is the process of heating water to the point of evaporation (leaving contaminants behind), then condensing that steam into pure water. It is a simple one-step, physical process - the same process that nature uses - that generates reliable high quality water every time. Our products remove contaminants, use no chemicals or other disposables, operate close to maintenance free, and require no custom engineering to accommodate different contaminants in the water.

Below is a summary of the different components within Aquaback's revolutionary product that will deliver the most energy efficient purified water on the market.

Vapor Compression Distillation

Vapor Compressor Flow Diagram

(numbers reference the points in the diagrams above and below)

1. Incoming water (influent) enters the system and runs through two heat exchangers which transfer heat to the influent from the outgoing pure water (distillate) and grey water (concentrate). Aquaback has optimized this preheating process to bring the water close to its boiling point of 212 degrees Fahrenheit (100 degrees C).

2. The influent is applied to the hot evaporator surface causing the water to turn to steam in the evaporator chamber. Contaminants left behind on the evaporator surface are collected as concentrate and then exit the system though a heat exchanger.

3. The steam is drawn through the compressor increasing the pressure and temperature of the steam.

4. The higher pressure, superheated steam is sent to the condenser chamber.

5. Pure hot steam condenses on the condenser surface to produce pure water (distillate). The condenser and evaporator surfaces are opposite sides of sheets of conductive metal which form the evaporator/condenser.

6. Hot distillate leaves the system through a heat exchanger to cool it down to around 5 degrees Fahrenheit (2.8 degrees C) above the influent temperature, while heating the incoming water.

Tracing the distillation cycle above along the saturation curve for steam with respect to temperature (T) and entropy (s) we get the following diagram. Entropy is the thermodynamic property which measures the energy available to do useful work.

T-s Diagram

The temperature in the evaporator is maintained at 212 degrees Fahrenheit (100 degrees C) at ambient pressure (P_evap) for proper evaporation, which also ensures that all source influent is sterilized. The patent pending self-cleaning design collects any dead pathogens and bacteria along with any other elements (calcium carbonate, arsenic, magnesium, sodium, etc.) and ejects them from the system through the concentrate stream, which is sterile. The self-cleaning system also ensures a long working product life, with minimal maintenance requirements.

The compressor moves the steam from state 3 to 4. It increases the pressure of the steam which, through the laws of thermodynamics, increases the temperature at which steam condenses. This temperature difference is represented above by the delta (triangle) T between the two lines of constant pressure, P_cond and P_evap. As the temperature difference is decreased, the amount of pressure needed to maintain the temperature difference is reduced. This creates a virtuous relationship from an energy use perspective: a lower temperature difference equates to a lower pressure difference which means less energy is required by the compressor. Since the compressor is the primary power consumer, it is the major factor in the low energy consumption of the distiller.

T-P Diagram

Counterflow Heat Exchanger

A counterflow heat exchanger is used because it is the most efficient method of recovering heat in a balanced flow system such as the distiller. The heat exchanger works by having a hot fluid flowing in the opposite direction from a colder fluid, separated by a barrier with a low thermal resistance. In the graphic, below, the colder fluid is heated to a temperature slightly below the inlet temperature of the hot stream (T_h,i), while the hot fluid is cooled to a temperature slightly above the inlet temperature of the cold stream (T_c,i). The temperature profiles below and total amount of heat transfer that takes place in the heat exchanger is dependent on the length of the fluid ducts. Logically, the longer the flows are in contact with each other, the smaller the delta T.

counterflow explanation

Aquaback has utilized years of experience in heat transfer and heat exchangers (Bill Zebuhr, Co-CEO / CTO, invented the highly efficient Z-duct) to design and build the ultimate high efficiency counterflow heat exchanger for maximum heat recovery, eliminating the need for any supplemental heat.

Aquaback approached the design of the evaporator/condenser (E/C) from a clean slate in order to make a vapor compression distiller (VCD) more efficient than any existing VCDs. Influent is applied to the evaporator side of the E/C and is turned into steam by the heat being released from the steam condensing on the condenser surface of the E/C. Aquaback's evaporator uses a patent pending application system to apply liquid over the surface of the E/C. Controlling the volume of liquid minimizes the motor power requirement to turn that liquid to steam.

Evaporator / Condenser

evaporator condenser explanation


The compressor increases the temperature and pressure of the steam. Aquaback Technologies has designed its own high efficiency, centrifugal flow compressor to power the system and keep fluid flow rates and energy transfer in balance. Unlike most other compressors on the market today, the Aquaback compressor utilizes its proprietary water bearing design to ensure the system has a long life with minimal maintenance.

Ammonia Removal

Removal of ammonia by distillation is inherently difficult. The ammonia vaporizes with the influent water and "joins" itself to the water vapor molecules in the steam before it can be evacuated from the system. In order to be the ultimate water treatment solution and meet EPA requirements for wastewater recycling, Aquaback has designed a patent pending system to remove ammonia from the distiller, along with any other contaminating gases.

Concentrate Evaporator

When zero liquid discharge (ZLD) is desired, Aquaback’s DRM includes a multistage thermal evaporator to recover all remaining water from the concentrate as high quality distillate. Dissolved solids exit the DRM as a sterile dry powder, while any heat released during the drying process is recovered and reused. Utilizing the energy content of the solutes allows us to maintain the same great system efficiency, while providing a significant increase in capability.