Managing landfill leachate effectively is one of the more persistent operational challenges facing waste facilities. While there are several established technologies for leachate evaporation — including forced-feed reboilers and deep vacuum shell and tube heat exchangers — there’s a simpler, cost-effective alternative for sites where high-temperature gaseous heat is already available: the humidifier evaporator.
This technology takes hot gases, typically from a landfill gas engine, and passes them directly over the leachate. The result is a straightforward, one-step conversion of leachate into moisture carried away within the gas stream — no intermediate service fluids, no complex heat transfer loops, just direct energy utilisation.
What Is a Humidifier Evaporator?
A humidifier evaporator is a unit process that brings hot exhaust gases into direct contact with leachate, causing the liquid to evaporate into the gas phase. Unlike indirect heat exchange systems that require a transfer fluid to move energy between processes, humidifier evaporators apply the available heat straight to the evaporative duty.
The great advantage of humidifier evaporators is that no service fluids are required to transfer energy from one unit process to another — the available energy is passed directly to the evaporative process.
For sites operating a closed loop, an air-cooled condenser can be added downstream to recover condensate from the exit gases, further improving the environmental footprint of the system.
How the Technology Works
Engine exhaust gases typically leave the engine at approximately 450°C to 500°C, saturated to a dew point of around 50°C. When these gases are brought into contact with leachate in a suitably designed unit, the exhaust gas temperature drops while its dew point rises as it picks up moisture. In theory, moisture take-up can reach 100%.
There are two main approaches to achieving this gas-liquid contact:
- Packed columns using stainless steel packing rated for the thermal duty of the application.
- Organics Sy-Clone™ units, which atomise the leachate and use cyclonic action to maximise contact between the liquid and gas phases.
Benefits of the Sy-Clone™ Packing-Free System
The Sy-Clone™ option (detailed further in Datasheet ODSP10) offers several practical advantages over traditional packed columns:
- No plates or packing that can foul during operation
- High-impact contact between liquor and gas for better efficiency
- Reduced plant sizes compared to packed alternatives
- Maximised performance for a given duty
This technology has been deployed successfully across a number of sites where waste heat is available, using leachate itself as the wetting medium — simultaneously supporting process objectives while reducing leachate volumes requiring disposal. Because the system relies only on vessels, pumps, and fans, it remains mechanically simple and highly reliable.
Performance Expectations
Moisture take-up in cooling towers and humidifiers of this type is extremely rapid. Careful design of gas and liquid flow rates allows engineers to tune the system to specific performance objectives.
A humidification evaporator will typically lift the exit dew point to around 65°C, with exit gas temperatures in the region of 100°C.
Where ambient air cooling is applied, discharge temperatures can be reduced to within 10°C of ambient, achieving moisture removal in the order of 85%. For applications demanding greater removal rates, refrigeration techniques can be incorporated into the design.
Technical Specifications
| Parameter | Detail |
|---|---|
| Flow rates available | 10 to 2,000 m³ per day |
| Materials | High-temperature stainless steel (gas transfer), high-quality alloys (hot leachate duty) |
| Heat sources | Engine exhaust gases, flare exhaust gases |
| Energy requirement | ~2,000 MJ per m³ of leachate evaporated (equivalent to 120 m³ of landfill gas at 50% methane) |
| Engine correlation | A 1 MW electrical engine’s exhaust waste heat can evaporate 20–25 m³/day of leachate |
| Chemicals required | Anti-foaming agents (dependent on process selected) |
| Pre-treatment | Coarse filtration for solids over 2 mm diameter |
| Land requirement | ~25 m² for a 20 m³/day evaporator |
| Exit dew point | Approximately 65°C |
| Exit gas temperature | Approximately 100°C |
| Closed loop cooling | Air-cooled condensers or refrigerated systems |
| Moisture removal (air cooling) | ~85% |
Applications and Suitability
Humidifier evaporators are particularly well suited to landfill sites already operating gas engines for electricity generation, since the exhaust heat that would otherwise be wasted can be redirected into leachate management. This dual-purpose use of waste heat makes the technology attractive both economically and environmentally, reducing the volume of leachate requiring off-site tankering or further treatment.
Typical pre-treatment is minimal — just coarse filtration to remove solids larger than 2 mm — and depending on the specific process configuration, anti-foaming agents may be dosed into the leachate stream to maintain stable operation.
Key Takeaways
- Humidifier evaporators use hot exhaust gases (typically 450–500°C from landfill gas engines) to evaporate leachate directly, with no intermediate service fluid required.
- The Organics Sy-Clone™ system offers a packing-free alternative to traditional packed columns, reducing fouling risk and plant footprint.
- Roughly 2,000 MJ of energy is needed per cubic metre of leachate evaporated — a 1 MW engine can support 20–25 m³/day of evaporation from its exhaust alone.
- Systems are compact, mechanically simple (vessels, pumps, and fans), and can achieve around 85% moisture removal with air cooling, or higher with refrigeration.
- Suitable flow rates range from 10 to 2,000 m³ per day, making the technology scalable from small to large sites.
Get in Touch
If your site generates waste heat from landfill gas engines or flares and you’re looking for a reliable, low-complexity way to reduce leachate volumes, a humidifier evaporator system could be an excellent fit. Contact our team today to discuss your site’s specific requirements and find out how this technology can be tailored to your leachate management strategy.