To stay ahead of the curve in helping vessels become more environmentally friendly, Valmet started a project to reduce particle emissions from medium-speed ship engines by combining its proven closed-loop marine scrubber with its wet electrostatic precipitator (WESP). Valmet’s ambitious goal was to achieve an emission level lower than the Euro 6 standard, which is the benchmark for motorized vehicles.

Piloting the combination for viability

The theory was that by combining a WESP with a closed loop scrubber, particulate matter and black carbon emissions from a ship’s exhaust gas could be almost completely removed.

The WESP can efficiently reduce different emissions such as particulate matter and black carbon, heavy metals, acid mist, oil mist and visible plume. A very strong electrical field is created between discharge electrodes and collecting tubes by a transformer rectifier. Particulates that travel through the WESP are eletrically charged and they will be captured on collecting surfaces.

The closed loop scrubber circulates washwater and uses alkaline chemicals to capture sulfur dioxide. The exhaust after composition after a wet scrubber is suitable for WESP.

Since the idea of combining a marine scrubber and WESP was completely new, Valmet turned to the VTT Technical Research Centre of Finland Ltd to research and pilot test the system connected to a diesel engine. VTT had already studied emissions from ships that have a marine scrubber installed and could therefore easily compare earlier results to results from the new tests.

Valmet provided the marine scrubber and WESP pilot unit that had been studied and developed together with AWS Corporation S.r.L. VTT had a suitable marine engine and research equipment to validate the emission levels of particulate matter, black carbon, sulfur dioxide and carbon dioxide.

“The installation was challenging and required fast improvisation on a tight schedule. VTT really added value to the equipment configuration and fuel,” says Juha Jokiluoma, Product Manager at Valmet.

Valmet experts studying the results.
Valmet experts studying the results.

Amazing results

In the end, the research results were astounding:

  • Particle emissions decreased by more than 98.5%, both in number and in size
  • Black carbon emissions decreased by 99%
  • The engine setup functioned perfectly in the inclination test

The success of the unique combination of its wet scrubber and WESP means Valmet is now preparing a global go-to-market strategy for spreading the good news about successfully reducing emissions.

Since regulations will continue to tighten in the coming years, Valmet is now ready to install this innovative solution on both newbuilds and currently operating vessels that still use conventional fuels. This allows shipping companies to significantly reduce particle emissions while continuing operations as normal.

Some of the other clear benefits of this combined solution include:

  • Sustainable cruising – passengers are increasingly interested in environmental consciousness. Reducing visible plumes with Valmet’s WESP also helps improve a cruise company’s image.
  • Routing – low-emission ships can continue to access vulnerable ports and areas
  • Efficiency – the scrubber-WESP combination allows vessels to use cheaper fuels and run on auxiliary engines to generate electricity when docked
  • Versatility – the solution can be used with all ship engines and fuels
  • Compliance – vessels are more compliant with emerging regulations

“Together with Valmet’s proven marine exhaust gas scrubbers, this innovation has great potential to better protect our planet and allow shipping companies to stay ahead of tightening regulations,” Jokiluoma says.

– The text is based on the publication of VTT Technical Research Centre of Finland Ltd. –

For more information:

Timo Lamminen
timo.lamminen (at)