Selecting the Right Industrial Wastewater Evaporator or Crystallizer

Comparing evaporator and crystallizer technologies used for zero and minimal liquid discharge

Apr 6th 2018

Four fundamental types of industrial evaporators and crystallizers are used for wastewater treatment, brine management, or improving water reuse. Lower your risks and improve costs by understanding the trade-offs between the different evaporator types and choosing the right fit for achieving zero and minimal liquid discharge.

Key Takeaways

  • Before investing in an evaporator or crystallizer, reduce costs by maximizing the freshwater recovery achieved by upstream membrane systems.
  • Understand the application and fit for different industrial evaporator/crystallizer types before deciding on the suitable technology for your project.
  • Protect your investment by engaging experts to help you prevent scale and corrosion, which diminishes evaporator performance.
  • Avoid extensive chemical pre-treatment, which drives up operating costs.
  • Traditionally, evaporators were used to concentrate saltwater, and crystallizers were used to produce solids. However, modern evaporator-crystallizer hybrids can do both.

Get the Most out of Membrane Treatment Systems Before Considering Evaporators

A photo of a Saltworks XtremeRO reverse osmosis plant
Saltworks' XtremeRO advanced membrane treatment system

Reverse osmosis (RO) systems are usually the most cost-effective water treatment solution. If the concentration of total dissolved solids (TDS) is less than 70,000 mg/L, even if you have reached scaling limits, you still have options to further utilize RO and concentrate brines up to 130,000 mg/L. This will reduce your total costs by lowering the size of the downstream evaporator and the energy it consumes. To optimize your project economics, ensure that you maximize the performance of your RO system before considering evaporators or other thermal treatment systems.

The Four Major Types of Industrial Evaporators

Evaporators treat wastewater by heating it, evaporating volatile solvents—including water—from the solution, and then cooling and condensing the vapour to produce a liquid that is mostly freshwater. This leaves behind non-volatile solutes such as inorganic salts and organic compounds in a much more concentrated wastewater stream, with a much smaller volume.


There are four common industrial wastewater evaporators, as listed below.

Photo of a conventional technology industrial evaporator
Traditional industrial evaporator technology and infrastructure

1. Mechanical Vapour-Recompresssion (MVR) Evaporators

MVR evaporators use a blower, compressor or jet ejector to compress, and thus, increase the pressure of the vapour produced. This increase in pressure results in an increase in the condensation temperature of the vapour. This vapour is then condensed in a heat exchanger, returning heat to the evaporating water in the next stage. This forms a cyclical process that recycles thermal energy, but requires electrical energy to run the large vapour compressor.


Tips for choosing an MVR evaporator:

  • Ensure that the vapour compressor you select can handle high rotation speeds and stands up to severe vibrations.
  • Consider redundancy, since compressor failures can occur.

2. Multiple Effect Evaporators

Photo of a multiple effect evaporator - Photo © Evelyn Simak (cc-by-sa/2.0)
Multiple-effect evaporator. Photo © Evelyn Simak (cc-by-sa/2.0)

A multiple effect evaporator combines two or more vessels, each maintained at a lower pressure than the last. Heat energy is supplied to the first vessel where evaporation occurs at a relatively higher temperature. Vapours from the first vessel move to the second vessel due to the pressure difference, where the vapour is condensed. This releases heat that is used to evaporate wastewater in a subsequent vessel. Temperature is lowered in each effect as the heat energy is recycled, and eventually rejected close to atmospheric temperature.


Tips for choosing a multiple effect evaporator:

  • Specify non-scaling and non-corroding materials of construction to improve long-term performance.
  • Ask about tube scaling on your specific water, and how it can be prevented.
  • Plan for maintenance access to any of the vessels, including access to the tubes for cleaning, as well as confined-space entry points and safety equipment.

3. Atmospheric Evaporators

Atmospheric evaporators release their evaporated freshwater directly to atmosphere. Energy consumption is much higher, since the water vapour formed during the evaporation process is not condensed, eliminating the opportunity to reuse the energy.


Tips for choosing an atmospheric evaporator:

  • Ensure that you have an abundant source of waste heat, to make the atmospheric evaporator more economic.
  • Verify the concentrations of ammonia and volatile organic compounds, such as benzene, toluene, methanol and others. They will create air pollution and odors if evaporated.
  • Plan for corrosion-proof specifications and confined space entry during maintenance.

4. Humidification-Dehumidification Evaporators

Photo of a humidification-dehumidification evaporator
Saltworks' humidification-dehumidification evaporators

Humidification-dehumidification (HDH) evaporators operate similarly to multiple-effect evaporators, although they recycle heat across the effects at lower temperatures.


These evaporators have the following advantages:

  • Operate at atmospheric pressure, avoiding both pressure vessels and vacuums, resulting in simpler permitting and maintenance.
  • Constructed with non-metallic materials that leverage reinforced fiberglass to avoid corrosion and reduce scaling potential. This provides reduced surface energy, which acts like Teflon in a frying pan, to decrease the sticking potential of salt.
  • The volumetric chambers used in HDH evaporators cost less than steam-based chambers and are less prone to corrosion, although they are roughly three times larger.

Combining the Advantages of Each Evaporator

Photo of a SaltMaker MultiEffect evaporator crystallizer installed at a site in British Columbia
SaltMaker MultiEffect Evaporator Crystallizer Installed at BC Site

The SaltMaker MultiEffect evaporator crystallizer combines three of the above industrial evaporator designs. First, it leverages the HDH cycle so it can be constructed from lower cost, fiber-reinforced plastics, which enable easy maintenance and reduce the risk of scaling and corrosion. The SaltMaker also comes in two optional configurations:

  • The multiple-effect configuration enables greater energy efficiency and recycles the 80–95°C heat through four or five effects.
  • The open-to-atmosphere configuration can use low-grade waste heat of 60°C or more and offers a higher treatment capacity per unit of plant size.

The SaltMaker is also designed for dual operation:

  1. As an evaporator to concentrate brines.
  2. As a crystallizer to produce and extract solids.

Read more in the table below about the advantages that the SaltMaker design offers, compared to conventional evaporator and crystallizer designs.


Contact Saltworks for help with selecting the suitable industrial evaporator for your project.

Evaporators Fit & Tips Installation/Operability Economic Sweet Spot
Mechanical Vapor Recompression (MVR) Widely used where appropriate, namely on non-scaling flows as a concentrator of up to 20% salt mass (80% water).

Ensure metallurgy and maintenance access/chemical cleans are planned for during design phase.
Custom designed and built to each need.

Must consider chemical pre-treatment for scale.

Pressure vessels and high-speed compressor operating on “wet” vapour represent a severe and common single point of failure risk.
No low-grade waste heat and thermal energy is expensive, while electric power is available.

Low scaling potential brines, or chemical pre-treatment included.
Multiple Effect Evaporators More common where heat recycling is desired and non-scaling flows need to be concentrated up to 20% salt mass.

Ensure metallurgy and maintenance access.

Ensure chemical cleans are planned for during design phase.
Custom designed and built to each need.

Must consider chemical pre-treatment for scaling.

Considered very reliable due to reliance on thermal energy and cooling source, rather than compressor.
Low-pressure steam is available at low cost.

Brine has low scaling potential or requires extensive chemical pre-treatment.
Atmospheric Evaporators Carefully check for volatile potential in discharge to prevent a stranded investment.

Commonly only able to concentrate to 15–18% salt mass.

Consider if low grade waste heat is abundant.

Scaling can be more troublesome due to air injection.
Low cost and easy to install; however, a plume will be present, and this could include odors and release of damaging volatiles.

Some of these plants have been shut down after less than one year of use due to stakeholder concerns of air pollution and health hazards.
Non-volatile, low scaling potential water source with abundant waste heat and ability to form a vapour plume to air.
Humidification Dehumidification (HDH) More suitable on scaling flows, and pre-treatment costs can be avoided in intelligently designed plants with self-cleaning, such as the SaltMaker.

Requires more footprint than conventional steam-based evaporators (2x ground footprint).

Concentrates to 30% salt mass with ease, or produces solids due to non-corroding, non-stick materials.
Plan for space requirements, and modular installation in the case of SaltMaker.

No steam ticketed operators required; however, basic handy person, process understanding, and computer skills required.
Desire to concentrate higher than conventional evaporators, or produce solids and achieve zero liquid discharge.

Ability to stage investment and expand production capacity in the future by adding modules.

Thermal energy is reasonably priced (SaltMaker) or waste heat abundant (AirBreather).

About Saltworks

Saltworks Technologies is a leader in the development and delivery of solutions for industrial wastewater treatment and lithium refining. By working with customers to understand their unique challenges and focusing on continuous innovation, Saltworks’ solutions provide best-in-class performance and reliability. From its headquarters in Richmond, BC, Canada, Saltworks’ team designs, builds, and operates full-scale plants, and offers comprehensive onsite and offsite testing services with its fleet of mobile pilots.

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Our innovative brine management solutions maximize freshwater recovery and minimize waste products, reducing disposal costs. We optimize costs with the correct blend of membrane and evaporator crystallizer solutions.