Reducing emissions from wood burning with ceramic filters and catalysts

In the domestic heating sector (fireplaces, heating fireplaces and tiled stoves), wood and wood fuels make an important contribution to achieving the desired energy transition. However, the combustion of wood produces particulate matter and air pollutant emissions. In residential areas where many fireplaces are in use, temperature inversion conditions can therefore lead to increased pollution from particulate matter.

In order to sustainably reduce pollutant emissions and improve air quality, the first Ordinance for the Federal Immission Control Act (1. BImSchV) stipulates that by the end of 2024, older, inefficient and environmentally harmful stoves must either be replaced by modern, low-emission models or retrofitted with suitable emission-reducing technology. In addition, the new Blue Angel environmental label for wood-burning stoves (DEUZ 212) requires the use of filters, catalytic converters and automatic combustion air control to achieve dust and other exhaust emissions well below the legally prescribed limits.

In the “CleanKFA” project, Fraunhofer IKTS and DBI Gas- und Umwelttechnik GmbH developed and tested an integrated exhaust gas aftertreatment system (EGA) to reduce pollutants when burning wood in stoves. Significant reductions in pollutants were achieved compared with conventional fireplaces by using suitable ceramic foam filters, ceramic foam catalysts and heat storage elements, as well as by optimizing the combustion conditions (temperature, air supply, power). According to the criteria for awarding the environmental label, the catalytic exhaust gas treatment yielded very low values in emission measurements: 

• Carbon monoxide < 350 mg/m³ 
• Total organic carbon < 50 mg/m³
• Nitrogen oxides < 125 mg/m³

This ensures compliance with the requirements of the Blue Angel environmental label. The upstream particulate filter protects the catalytic converter from excessive temperatures and an excessive load of soot and ash particles. This in turn reduces the thermal and chemical aging of the catalytic converter and increases its long-term stability. Initial evidence of this was provided in the project for an operating period of 100 hours. During this time, no significant catalyst aging occurred, so that the emission reduction for the gaseous pollutants remained constant. 

By combining a ceramic foam filter with a catalytic converter, particulate emissions could also be significantly reduced. An extended emissions test that includes the heating phase shows that the particulate mass values are significantly below the legal requirements. In addition, the number of particles has been almost halved compared with the initial state of the fireplace. Fraunhofer IKTS offers stove manufacturers the development of filters and catalysts for EGA systems that are tailored to their requirements.