Biocarbon Emissions and Risks Assessment in Pyrolysis and Combustion.

Area of Science:

• Environmental Science and Engineering
• Chemical Engineering
• Combustion Science

Background:

• Industrial decarbonization necessitates reducing toxic gas emissions like polycyclic aromatic hydrocarbons (PAH).
• Biocarbon (Biochar) is a promising renewable alternative to fossil fuels due to its properties and biogenic emissions.
• Understanding the fate and toxicity of gaseous emissions from biocarbon during pyrolysis and combustion is crucial for its industrial application.

Purpose of the Study:

• To determine the gaseous emissions (CO, CO2, H2, CH4, PAH) from biocarbon during pyrolysis and combustion.
• To correlate emission factors (EF) with biocarbon's physicochemical characteristics, such as volatile matter (VM) content.
• To compare the toxicity of biocarbon emissions with those of fossil fuels using the toxicity equivalent factor (TEQ).

Main Methods:

• Pyrolysis and combustion experiments were conducted on biocarbon from solid refuse fuels (BC1) and two wood-based biocarbons (WBC1, WBC2) with varying VM content.
• Emission factors (EF) for permanent gases and PAH were calculated based on fuel characteristics.
• The toxicity equivalent factor (TEQ) was determined by assessing the carcinogenic potential and yield of released PAH.

Main Results:

• Biocarbon emission factors were directly linked to VM content and inorganic composition.
• High VM biocarbon (WBC1) exhibited higher CO2 emission factors but met standards for CH4+H2.
• While high VM biocarbon released less toxic PAH, its overall PAH emission factor and TEQ were higher than fossil fuels; however, optimized combustion drastically reduced emissions and PAH formation.

Conclusions:

• Biocarbon's physicochemical properties significantly influence its gaseous emissions during thermochemical conversion.
• Optimized combustion of biocarbon can substantially reduce condensable species, permanent gas emissions, and eliminate PAH, leading to lower toxicity.
• Biocarbon presents a viable renewable alternative to fossil fuels, provided that emission control strategies are effectively implemented.