Biomass pellets quality assessment by analysing combustion efficiencies and emissions

In current times, climate change due to greenhouse gas (GHG) emissions and rising fossil fuel prices creates the need to focus more on renewable energy to become energy independent. For that, the combustion of solid biomass (e.g., pellets) is a reliable option for thermal energy production. This work focuses on the quality analysis of carbon-rich solid fuel produced by hydrothermal carbonization (HTC) of green waste (such as leaves, small branches, and grass) at Engie Laborelec. The combustion and emission analysis of the new HTC pellets are compared with conventional wood pellets. Notably, the physicochemical properties of HTC pellets have an 18% higher lower heating value (LHV) than wood pellets.
The combustion experiments were conducted at VUB-biomass laboratory with a fully functional fixed bed boiler of 40 kW (TARM MULTIHEAT 4.0), which is connected to a thermal network for heat dissipation. Dekati electrical low pressure impactor (ELPI+) with a two-stage dilution system was used to measure particulate matter (PM) emissions, and a HORIBA PG-250 dry gas analyser for NOx, SOx, CO, CO2, and O2. The exhaust gas temperatures, ambient conditions, and circulation water conditions (temperature and flow rate) were continuously monitored. The boiler was installed on a floor balance to assess the fuel rate consumption. The tests found an increase in combustion efficiency with HTC pellets of about 6% with nearly the same combustion process conditions (air-fuel ratio, load, and ambient temperature). However, more PM and CO are released with the HTC pellets due to the higher carbon content of the fuel.