Question: How much does an industrial wastewater evaporator cost? Capital cost for an industrial wastewater evaporator typically runs from around EUR 250,000 for a small forced-circulation unit handling a few cubic metres per day, to EUR 3 million or more for a mechanical vapour recompression system treating several hundred cubic metres per day. Operating cost is dominated by energy and generally falls between EUR 4 and EUR 25 per cubic metre evaporated, depending overwhelmingly on whether the unit uses mechanical vapour recompression or direct steam.
The purchase price is the smaller half of the decision. An evaporator is an energy machine, and over a fifteen-year life the energy bill will normally exceed the capital cost several times over. Choosing on quoted price rather than on specific energy consumption is the most expensive mistake available in this category.
Falling Film or Forced Circulation: Which and Why?
Question: What is the difference between a falling film and a forced circulation evaporator? A falling film evaporator distributes liquid as a thin film down the inside of heated tubes, achieving high heat transfer at low temperature difference, and suits clean, low-fouling, low-viscosity streams. A forced circulation evaporator pumps liquid through the heat exchanger at high velocity and suppresses boiling inside the tubes, which tolerates scaling, high solids and high viscosity at the cost of significantly higher pumping energy.
The selection is a fouling decision before it is an economic one. Falling film is the more efficient machine and the cheaper one to run, but it fails badly on streams that scale, because a dry patch on the tube wall becomes a deposit and the deposit becomes a cleaning outage. Forced circulation is chosen precisely for the streams that would destroy a falling film unit.
- Falling film suits streams low in scaling potential and suspended solids, operating well below saturation for the sparingly soluble salts, at moderate viscosity. Typical applications include first-stage concentration of a relatively clean effluent.
- Forced circulation suits streams at or near saturation, high in calcium sulphate or silica, carrying suspended solids, or being concentrated toward crystallisation. It is the standard choice for the final concentration stage and for crystalliser service.
- Hybrid arrangements use falling film for bulk water removal and forced circulation for the final concentration, capturing most of the efficiency while protecting the sensitive stage. On larger duties this is frequently the lowest lifetime cost configuration.
A common and costly error is selecting falling film on the basis of a design water analysis, then discovering that the real effluent carries periodic solids from an upstream upset. The evaporator is not the place to discover your feed variability.
Indicative planning ranges for early-stage budgeting in a Northwest European context. Actual cost is set by contaminant load, discharge standard and site conditions; a site-specific study is required before committing capital.
| Factor | Falling film | Forced circulation |
|---|---|---|
| Heat transfer | High, at low temperature difference | Lower; boiling suppressed in tubes |
| Energy use | Lower | Higher (large circulation pumps) |
| Fouling tolerance | Poor – dry patches cause scaling | High – designed for scaling duty |
| Suspended solids | Not tolerated | Tolerated |
| Viscosity limit | Low | High |
| Typical duty | First-stage bulk concentration | Final concentration, crystalliser service |
| Relative CAPEX | Lower per m³ evaporated | Higher |
Why Energy Configuration Matters More Than Evaporator Type
Question: What is the cheapest way to run an evaporator? Mechanical vapour recompression is normally the lowest operating cost configuration, because it recompresses the vapour produced and reuses its latent heat rather than condensing it away. Multiple-effect arrangements reuse heat across successive stages, and single-effect steam evaporation is the simplest and by far the most expensive to run.
The spread is large enough to dominate the entire economic comparison. A single-effect unit consumes broadly a tonne of steam per tonne of water evaporated. A mechanical vapour recompression unit replaces that steam demand with electrical compressor power that is a small fraction of the equivalent thermal energy. Whether that translates into lower cost depends on your local ratio of electricity price to steam price, which is why the same machine can be the right answer in one country and the wrong one in another.
For Northwest European sites without surplus low-grade steam, mechanical vapour recompression is usually the default. For sites with genuinely waste heat available, a multiple-effect arrangement driven by that heat can beat it. The analysis is site-specific and should be done with real energy prices rather than a vendor’s generic comparison.
What Drives Capital Cost?
Question: Why do evaporator quotations vary so much for the same duty? The dominant variables are materials of construction, heat transfer area, and whether the quotation covers a bare package or an installed system. Corrosion resistance alone can double the price of an otherwise identical unit.
- Materials. Concentrated chloride at elevated temperature is aggressive. Moving from stainless steel to a duplex grade, and from duplex to titanium or a nickel alloy, steps the price up sharply. Material selection is set by chloride concentration at the most concentrated point, not by the feed.
- Heat transfer area. Driven by the temperature difference available and the fouling allowance assumed. A generous fouling factor buys uptime and costs metal, and vendors differ substantially in how much they assume.
- Boiling point elevation. High-salinity streams boil above the pure-water temperature, eroding the driving force and forcing more area or more compressor duty. This is frequently underweighted in early estimates.
- Scope. Feed tanks, pretreatment, condensate handling, concentrate transfer, cleaning systems, civils and installation are often excluded. As with any treatment package, installed cost commonly reaches two to three times the equipment price.
The Pretreatment Question
Question: Do I need pretreatment before an evaporator? Almost always. Hardness, silica and suspended solids cause scaling that reduces heat transfer, forces cleaning outages and shortens tube life. Softening, pH adjustment or antiscalant dosing upstream is inexpensive relative to the operating penalty of running a fouled evaporator.
There is a broader design principle here. Thermal evaporation is the most energy-intensive step in the chain, so every cubic metre that reaches it should have been reduced as far as cheaper methods allow. Membrane concentration ahead of the evaporator removes bulk water at a fraction of the energy cost, and the evaporator is then sized for a much smaller stream. Pushing recovery as far as membranes will take it before the thermal stage begins is the single largest cost lever in the whole system, as set out in our guide to the brine treatment process.
Where the site falls within the scope of the Industrial Emissions Directive, the treatment standard the evaporator must help achieve is set by reference to BAT conclusions rather than by the operator. (Source: Directive 2010/75/EU on industrial emissions) For chemical sector installations the relevant reference document is the BAT reference document for common waste water and waste gas treatment, whose conclusions were adopted as Commission Implementing Decision (EU) 2016/902. (Source: European Commission JRC, CWW BREF)
What Happens to the Concentrate?
Question: Does an evaporator solve the disposal problem? No. It reduces volume. The concentrate leaving the evaporator still requires a disposal or crystallisation route, and its handling cost per cubic metre is far higher than the feed’s. An evaporator business case without a costed concentrate route is incomplete.
The options are a crystalliser to produce a handleable solid, disposal of the liquid concentrate as hazardous or non-hazardous waste, or, where chemistry permits, recovery of the salt as a saleable product. Recovery is attractive and often oversold: it requires a stream clean enough and consistent enough to produce a salt someone will buy, which excludes many industrial effluents. Assess it honestly rather than assuming it.
Against the cost sits the recovered condensate, which is usually high quality and can displace demineralised water purchase or boiler makeup. On sites with expensive process water this can carry a meaningful share of the operating cost.
Frequently Asked Questions
Is an evaporator cheaper than tankering effluent off site?
Frequently yes, above a certain volume. Disposal of liquid waste by road is priced per tonne, so the saving scales directly with the volume reduction achieved. Payback of two to four years is common where disposal costs are high, but the calculation must include the concentrate that still leaves site.
How much water does an evaporator recover?
Volume reduction of 80 to 95 percent is typical for a brine concentrator, with the condensate recovered as high-quality water. Pushing beyond that generally requires a crystallisation stage.
What maintenance does an evaporator need?
Periodic cleaning to remove scale, compressor maintenance on mechanical vapour recompression units, and eventual tube replacement. Cleaning frequency is set by feed chemistry and pretreatment quality, and is the main determinant of availability.
Is an evaporator the same as zero liquid discharge?
No. An evaporator is a stage within a ZLD system, which normally also requires crystallisation to reach a solid residue. Many sites find that minimum liquid discharge, stopping short of full ZLD, achieves most of the benefit at materially lower cost. See minimum liquid discharge versus ZLD.
Specifying an Evaporator That Pays Back
Specify on specific energy consumption and availability, not on quoted price. Establish chloride concentration at the most concentrated point before discussing materials. Reduce the stream with membranes as far as it will go before the thermal stage. Cost the concentrate route in the same model. Get those four right and the machine will pay back; get them wrong and no amount of procurement pressure will fix it.
Brine Consulting advises industrial operators independently. We do not manufacture or represent evaporator suppliers, so our selection between falling film, forced circulation and hybrid arrangements reflects your effluent rather than a product range. Related reading: industrial wastewater treatment plant cost and zero liquid discharge technology.
Written by the Brine Consulting advisory team. Brine Consulting’s thermal and crystallization expertise includes George Iacovou, a salicultural technologist with more than 23 years in crystallization, MVR systems and salt processing, and Prof. Basel Abusharkh, a specialist in brine valorization, ZLD and high-recovery desalination. Meet our experts.