April 2023

Fuel combustion creates emissions of nitrogen oxides (NOx) and sulfur dioxides (SOx) which are associated with adverse effects on human health and environmental concerns. These emissions are considered a global concern and stricter legislations have been proposed for pulp and paper mills in Europe as well as globally. This has created a demand from the pulp and paper industry for cost-effective NOx and SOx reduction techniques.

Anette Heijnesson Hultén, technical project manager and specialist within Research and Development at Nouryon, has been working with a chlorine dioxide (ClO2)-based NOx reduction (De-NOx) technology for the past few years. Since 2022, Nouryon has been working together with Valmet, a leading global technology provider, to offer the new De-NOx technology to customers in the pulp and paper industry.

During a two-day conference in Uppsala, Sweden, the technical development in the heat and power sector was highlighted and discussed. At the event, Anette, together with Jonas Ståhls from Valmet, talked about NOx reduction in flue gases with a new De-NOx technology and shared their respective experiences regarding the development work, from lab/pilot scale to full-scale De-NOx installations.

Anette and Jonas presented the technical possibilities to reduce the amount of NOx in flue gases from recovery boilers, but also for boilers that are not suitable for selective catalytic reduction (SCR) or selective non-catalytic reduction (SNCR).

Results from a continuous De-NOx pilot test on a waste boiler where ClO2 was dosed as gas were reviewed. These results show that ClO2 has a very high selectivity towards nitric oxide (NO) and converts it to nitrogen dioxide (NO2) efficiently, even under tough processing conditions. The total NOx reduction during the trials was between 80% and 97%, while sulfur dioxide (SO2) and hydrochloric acid (HCl) were completely reduced. Valmet, for its part, talked about its full-scale De-NOx installations in Asia where ClO2 is dosed as a liquid. The first De-NOx scrubber was installed at Sun Paper in Shandong Province in China and has been run continuously for six years with a high reduction of both NOx and SOx.

During the development work, Nouryon has had a close and rewarding collaboration with a research group led by Professor Fredrik Normann at Chalmers University of Technology in Gothenburg, Sweden. The research project has been carried out with financial support from the Swedish Energy Agency and resulted in seven scientific articles, one licentiate and one doctoral degree.

Anette Heijnesson Hultén, technical project manager and specialist within Research and Development at Nouryon
Anette Heijnesson Hultén, technical project manager and specialist within Research and Development at Nouryon

The ClO2-based De-NOx technology is suitable for use in industries with large NOx emissions and where the process conditions are such that the SCR or SNCR technology does not work, for example for soda recovery boilers and lime kilns. Valmet has successfully installed eight De-NOx plants with ClO2 dosed as liquid on soda recovery boilers and lime kilns in Asia and six more are under construction. Furthermore, the technology is suitable for industrial boilers with a need for multi-pollutant purification technology.

Advantages of the technology are the high degree of NOx reduction, and for other pollutants such as SOx, HCl, dust, etc. in the flue gas. Additionally, the technology is flexible and an "end-of-pipe" technology, which means that it does not affect the operation of the boiler.


Read more about the technology and conference

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