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.
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.
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.
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:
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:
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:
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:
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 SaltMaker is also designed for dual operation:
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). |
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.
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.
Zero liquid discharge (ZLD) is an engineering approach to water treatment where all water is recovered and contaminants are reduced to solid waste.
Saltworks Technologies has been chosen to deliver two full-scale saline water treatment systems for a precious metals mine in the Canadian North. The zero liquid discharge (ZLD) plants will desalinate mine shaft water, and enable the site to achieve their treatment goals.
Convention teaches that ZLD requires energy-intensive boiling to produce solids. Our engineers recently broke that convention and helped a mining client achieve solid salt production in a novel membrane-chiller hybrid plant using UHP-RO.