Nitrogen oxide reduction with wood heating
Researchers at the Fraunhofer Institute UMSICHT have developed a technology that can reduce nitrogen oxide emissions from wood combustion by up to 80 %. The principle of fuel staging improves air quality and enables more environmentally friendly utilisation of wood waste.
Heating with wood has lost acceptance in recent years, as it releases pollutants such as particulate matter and nitrogen oxides in addition to greenhouse gases. In particular, the combustion of wood waste with a high nitrogen content, such as chipboard residues, produces high levels of NOx. Researchers at the Fraunhofer Institute have developed a technology that reduces nitrogen oxides by up to 80 % and thus lowers the environmental impact of wood heating systems.
Fuel staging for clean combustion
The new method centres on the principle of fuel staging. The fuel is burnt in two zones.
- The main combustion of solid wood residues takes place in the primary zone.
- In the secondary zone, an additional fuel creates a reduction zone in which nitrogen oxides are broken down using chemical processes.
Natural gas is currently used as a reduction fuel, but researchers are working on biogenic alternatives such as wood dust to replace fossil fuels in the long term.
Significant NOx reduction in tests
The tests were carried out in a 250 kW combustion plant that burnt chipboard residues. Without measures, NOx emissions were 1,955 mg/m³, but thanks to fuel staging, they were reduced to 361 mg/m³ – well below the limit value of 370 mg in the 44th Federal Immission Control Ordinance (BImSchV). These values show the potential of the new technology, which can be used in medium-sized combustion plants between 100 kW and 2 MW.
Retrofitting and new standards
As well as being used in new plants, the technology also offers a flexible retrofit option for existing combustion plants. This opens up sustainable prospects for the wood processing industry in particular, which wants to utilise wood waste efficiently. The technology could also prepare smaller biomass plants for future limit values, as the 1st BImSchV does not yet specify any NOx limit values for small plants.
Market readiness and further development
The Fraunhofer team is working with industrial partners to further optimise the technology and make it ready for the market. The aim is to develop a system that works completely without fossil fuels and further increases the efficiency of emission reduction.
The new technology for nitrogen oxide reduction when burning wood is a significant step towards environmentally friendly heating solutions. With its flexibility for retrofitting and the prospect of biogenic fuels, it offers a forward-looking solution for the wood industry and biomass plants.