The importance of monitoring PCDD/F in the stack-gas emissions from the combustion of certain types of solid biofuels

The increasing use of indigenous renewable energy sources (RES) for energy aims to meet the targets set up by the European Union (EU) regarding energy and climate change policies. Thus, biomass combustion has become more and more attractive. In 2012, biomass already represented 55% of the entire renewable share in the primary energy production in Portugal. Although the emissions from biomass origin fuels combustion are considered CO2-neutral, fine particle emission is a major drawback for these fuels. This concern is refl ected in the Clean Air for Europe (CAFE) Directive, where particular importance to the reduction of pollutants emissions at source is given in order to achieve the protection of human health and the environment. In this Directive, Particulate Matter is regulated both for coarse particles (PM10) and fine particles (PM2.5).

The experimental work herein presented led to the identifi cation of pollutants emission minimisation during the co-combustion of coal with biomass origin material. In the tested mixtures, coal was replaced by 5%, 15% and 25% of RES material and the tests were done in two FB pilots of different nominal capacities (70kWth and 100kWth). Emissions of particulate matter (PM), CO, SO2, NOX, heavy metals (HM), HCl, and dioxins and furans (PCDD/F) were measured.

The investigation concluded that PCDD/F emissions from the biomass origin materials tested were above the Emission Limit Value (ELV) of 0.1 ng I-TEQ/Nm3. In some cases, cocombustion with coal was enough to reduce those emissions below the ELV. Although the emission monitoring is regulated by national and European regulations, PCDD/F monitoring is not an obligation for solid biomass combustion. The results presented should lead to a reflection on the importance of monitoring PCDD/F in the stack-gas emissions from the combustion of certain sort of solid biofuels.