Which heat exchanger for fouling, particle-laden or viscous fluids?
A fouling-resistant heat exchanger is one whose flow geometry prevents deposits from settling either through a self-cleaning single channel, or through channels with no cross-section reduction.
Nexson Group builds three such technologies, and one figure usually decides between them. GREENSPIRAL™ spiral plate heat exchangers handle particles up to 14 mm. GREENTUBE™ RT rectangular tube heat exchangers handle particles up to 30 mm on both sides, in wastewater treatment. GREENTUBE™ TT tube-in-tube heat exchangers handle viscosities up to 1,000 cP.
For sludge and biosolids, the spiral range has a dedicated configuration: the GREENSPIRAL™ Type 1 BB/BW, with free-flow channels, rated 150 °C and 8 bar up to 100 m².
Choosing the right one
None of these is a better exchanger than the others. Each has its limitations and meets all your needs.
| Criterion | Spiral plate — processGREENSPIRAL™ Type 1 / HP / 2 / 3 | Spiral plate — biosolidsGREENSPIRAL™ Type 1 BB / BW | Rectangular tubeGREENTUBE™ RT | Tube-in-tubeGREENTUBE™ TT |
|---|---|---|---|---|
| Maximum particle size | 14 mm | 14 mm, free-flow channels | 30 mm, both sides | solids without cross-section reduction, sized per duty |
| Viscosity | viscous media, sized per duty | raw and digested sludge | high-viscosity sludges | up to 1,000 cP |
| Temperature | −100 °C to 500 °C depending on model | up to 150 °C | up to 150 °C | −20 °C to 200 °C |
| Pressure | full vacuum to 100 bar depending on model | up to 8 bar | up to 8 bar | above 50 bar depending on configuration |
| Surface | 1 m² to 700 m² per unit | 1 m² to 100 m² | up to 60 m² per module, in series or parallel | modules up to 6 m, modular |
| Fouling mechanism | self-cleaning single channel | self-cleaning single channel, free flow on one or both sides | constant cross-section, smooth surfaces | anti-clogging concentric geometry |
| Cleaning access | openable end covers, full surface | BB: two independently openable channels. BW: one channel opens without dismantling the pipework | fully openable version, standard hydro-jetting | inner tubes cleaned without full disassembly |
| Typical field | process industries, oil & gas, refining, pulp and paper, chemicals, power | biogas and water treatment, digester sludge heating, raw sludge heating, effluent heat recovery, pasteurisation, methanisation | wastewater treatment only, sludge-to-sludge heat recovery, biosolids | sludge treatment, pasteurisation, bitumen, oil & gas |
This information is provided for guidance only; we are able to design fully tailor-made products and adapt to your production process.
In short. the GREENTUBE™ RT below 60 m² per module and up to 30 mm of particles, the GREENSPIRAL™ Type 1 BB/BW up to 100 m² with free-flow channels and up to 14 mm of particles, and the GREENTUBE™ TT when viscosity rather than particle size is the constraint.
Why each one resists fouling
Three distinct technologies. They are not interchangeable, and knowing which one applies tells you what happens when the duty drifts.
Self-cleaning single channel
GREENSPIRAL™ each circuit is one continuous channel. The whole flow passes through it, so a starting deposit narrows the section, raises local velocity and gets flushed away. No dead zones anywhere in the unit.
Constant cross-section
GREENTUBE™ RT smooth surfaces, no cross-section reduction, channel width sized to let debris through rather than trap it. Rounded turnaround areas limit both pressure loss and deposits.
Anti-clogging concentric geometry
GREENTUBE™ TT one fluid in the inner tube, the second in the annular space, with no cross-sectional reduction anywhere along the path. Suited to solids carried at low velocities.
Each technology in detail
Designed primarily for sludge-to-sludge heat recovery and biosolids treatment. Fully welded, no gaskets between tubes. Modular units connect in series or parallel and can be installed along a wall.
An openable version exists for fluids liable to clog or coagulate: struvite, fats from industrial waste, large particles. Hinges allow the channel to be opened without lifting equipment, and standard hydro-jetting applies.
Above 60 m², or in biogas rather than wastewater treatment, the BB/BW configuration takes over: up to 100 m², 150 °C, 8 bar. Two concentric channels rolled together, with spacing and width set by guideways chosen against the customer’s solids content.
Choose BB (biosolids/biosolids) when both sides are loaded free flow on both sides, raw and digested sludge, two independently openable and inspectable channels. Choose BW (biosolids/water) when only one side carries solids free flow on the biosolids side, from low to high concentration, and one channel opens without dismantling the pipework.
Typical duties: digester sludge heating, raw sludge heating, heat recovery from effluents, pasteurisation, methanisation.
The choice when viscosity dominates rather than particle size. Concentric geometry: one fluid in the inner tube, the second in the annular space.
Typical duties: maintaining anaerobic digester temperature, preheating raw sludge before digestion, heat recovery between digested and incoming sludge, pasteurisation and sanitisation, hydrothermal carbonisation, cooling sludge from thermophilic processes.
Type 1 is the reference for fouling, loaded or viscous liquids across oil & gas, refining, pulp and paper, chemicals, heavy industry, power, food and clean energy. −100 °C to 450 °C, full vacuum to 25 bar, 1 to 700 m², approach down to 3 °C. Up to 3 times more thermally efficient than a traditional shell-and-tube; in some liquid-to-liquid duties one unit replaces three shell-and-tube units.
Type 1 HP extends the same design to high pressure: full vacuum to 100 bar (1,450 psi), −100 °C to 500 °C, same 700 m² ceiling.
Type 3 heats a fouling or viscous medium with steam: −100 °C to 450 °C, full vacuum to 25 bar, 1 to 700 m². Steam flows crossways through a fully open channel across the full width of the unit; the tough medium runs in a closed spiral channel where the self-cleaning effect limits fouling.
Type 2 covers evaporation and reboiling of fouling media: the medium circulates in an adjusted, fully open channel gap, and the whole heat transfer surface stays accessible for inspection and mechanical cleaning.
“The particle size limit is not a marketing figure, it comes from the channel gap. Above 14 mm we stop recommending a spiral and move to a rectangular tube design, because the channel geometry decides, not the technology’s reputation.”
Nexson Group design office
Frequently asked questions
What makes a heat exchanger resistant to fouling?
Its flow geometry. A spiral plate exchanger uses a single continuous channel: the entire flow must pass through it, so any deposit narrows the section, raises local velocity and gets flushed away. A rectangular tube or tube-in-tube exchanger uses channels with no cross-section reduction, sized so that solids pass through rather than accumulate.
What particle size can a spiral heat exchanger handle?
Nexson GREENSPIRAL™ spiral plate heat exchangers handle particles up to 14 mm. The channel gap is sized per project against the particle size and the required pressure drop.
What if particles are larger than 14 mm?
Use a rectangular tube heat exchanger. The Nexson GREENTUBE™ RT handles particles up to 30 mm on both sides of the exchanger, at up to 150 °C and 8 bar.
How viscous can the fluid be?
Nexson GREENTUBE™ TT tube-in-tube heat exchangers manage viscosities up to 1,000 cP, with a pressure drop below 1 bar depending on configuration.
Which exchanger for digester sludge heating?
For sludge-to-sludge heat recovery and biosolids treatment, the GREENTUBE™ RT is designed for that duty, up to 60 m² per module and connectable in series or parallel. Above that capacity, the GREENSPIRAL™ Type 1 BB handles raw and digested sludge on both sides, up to 100 m².
How are these exchangers cleaned?
Openable end covers give access to the whole heat transfer surface for mechanical cleaning. The GREENTUBE™ RT has a fully openable version, with hinges that avoid lifting equipment, and accepts standard hydro-jetting. Tube-in-tube inner tubes are cleaned without full disassembly.
What pressure and temperature can a spiral heat exchanger reach?
It depends on the model. GREENSPIRAL™ Type 1, Type 2 and Type 3 are designed for full vacuum to 25 bar and −100 °C to 450 °C. The Type 1 HP reaches full vacuum to 100 bar and 500 °C. The Type 1 BB/BW, dedicated to biosolids, is rated 8 bar and 150 °C.
Which materials are available?
For spiral plate and rectangular tube exchangers: 304L, 316L, duplex and superduplex stainless steel; 254 SMO, C276, 904L and Alloy 59 nickel-based alloys; titanium Gr1 and Gr2; SA516 Gr60 and Gr70 carbon steel. Tube-in-tube exchangers are built in carbon steel, stainless steel, duplex and super duplex, titanium, and other alloys on request.
A thermal constraint or a challenging fluid?
Please provide us with your flow rates, temperatures, and solids content. Our sales representatives and engineering team will design the exact solution for your process.
