Gaseous and particulate matter emissions from the combustion of biomass-based insulation materials at end-of-life in a small-scale biomass heating boiler

Abstract

To alleviate the unbearable pressure on forests in Europe, the use of lower quality woody materials or wastes and agricultural fuels is emerging for the production of heat. The two major challenges of using these types of fuels are associated with the chemical composition variability and some fuel characteristics that could trigger potential issues throughout the burning process. This study aimed to investigate the environmental and technical performance of a small-scale multi-fuel biomass heating boiler (20 kW) fired with DINplus certified wood pellets and two granulated biomass-based insulation materials, namely hemp fibers and wood fibers under standard laboratory conditions. The boiler efficiency, particulate matter, and gaseous emissions were evaluated and compared to the legally permissible values specified in EN 303–5:2021. Hemp fiber pellets fulfilled the requirements for residential pellets, while wood fiber pellets showed lower durability and higher nitrogen and sulfur contents than the European standard limits. To respect the emissions regulation, blending wood fibers with certified wood is therefore necessary. Pellets type was noticed to significantly affect the gaseous and dust emissions but marginally the boiler efficiency. This latter was near 80 % for all fuels owing to high sensible and latent heat losses. Hemp fiber pellets showed high CO and dust emissions attributed to their high bulk density and high ash content, respectively, while the wood fiber pellets showed high NOx and SOx emissions accredited to their elemental composition. Gaseous and dust emissions were reduced through the blending of hemp and wood fibers with certified wood pellets. The particulate mass concentrations of the tested pellets fluctuated between 38 and 360 mg.Nm−3. Particulates were mainly composed of potassium, chlorine, sulfur, silicate, calcium, and zinc. From a number perspective, particles with diameters below 1 µm were dominant and their concentration varied between 104 and 106 particles.cm−3. Pelletized biomass-based insulation materials mixed with certified wood could be considered an attractive alternative fuel for residential biomass boilers.