PSI - Issue 77

Michal Holubčík et al. / Procedia Structural Integrity 77 (2026) 413– 423 “Mi chal Holubčík” / Structural Integrity Procedia 00 (2026) 000 – 000

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improve fuel utilization. These developments support the transition towards sustainable, cleaner energy solutions while addressing environmental and regulatory requirements. 1.1. Emissions from Small-Scale Biomass Combustion Small-scale biomass boilers are an important source of residential heating in Europe, yet they significantly contribute to air pollution through carbon monoxide (CO), particulate matter (PM), nitrogen oxides (NOₓ), volatile organic compounds (VOCs), and ca rbon dioxide (CO₂). These emissions harm human health and degrade air quality, particularly in urban and rural areas with high solid fuel use. Backa et al. (2025) showed that emissions and temperature fields inside pellet boilers are highly uneven, underlining the need for precise monitoring and control to ensure stable and efficient combustion [1]. The European Green Deal aims to cut greenhouse gas emissions by 55% by 2030 and achieve climate neutrality by 2050, requiring not only reductions in CO₂ but also in harmful air pollutants. Understanding the nature and impacts of emissions from small-scale boilers is therefore critical for designing intelligent combustion control and meeting long-term climate and health objectives. Table 1 : Overview of health and environmental impacts of emissions from small-scale combustion

Substance

Health Impact

Environmental Impact

Carbon monoxide (CO) Carbon dioxide (CO₂) Nitrogen oxides (NO ₓ : NO, NO ₂ ) Particulate matter (PM₁₀, PM₂.₅) Volatile organic compounds (VOCs)

Reduces oxygen transport in blood; causes headaches, dizziness, can be lethal in high concentrations Not toxic at typical ambient levels, but high concentrations can cause drowsiness and acidosis Irritation of lungs and airways; exacerbates asthma and respiratory diseases Penetrates deep into lungs, increases risk of cardiovascular and respiratory diseases, carcinogenic effects Some are toxic and carcinogenic (e.g., benzene, formaldehyde); cause eye and respiratory irritation Strong oxidant, damages lung tissue and reduces lung function

Contributes indirectly to ozone formation (as a precursor) Main greenhouse gas driving climate change Precursor to smog and acid rain; contributes to ground-level ozone Reduces air quality and visibility; deposits affect ecosystems and soils Ozone and secondary organic aerosol precursors

Ozone (O₃) Contributes to photochemical smog; harmful to crops and vegetation Sulfur oxides (SO ₓ ) Irritates eyes and respiratory tract; worsens asthma Acid rain, soil and water acidification 1.2. Parameters of combustion quality Combustion quality in small-scale biomass boilers determines both energy efficiency and environmental performance. High-quality combustion is characterized by complete fuel oxidation, stable thermal output, and low concentrations of harmful emissions. In contrast, poor combustion leads to heat losses, increased particulate matter, and elevated carbon monoxide levels, which are particularly problematic in residential areas. Key indicators of combustion quality include: 1. Air– fuel ratio (λ factor): Ideally maintained between 1.5–2.0 for biomass to ensure complete combustion. 2. Emission levels: Concentrations of CO, NOₓ, and PM are direct markers of combustion efficiency. 3. Combustion temperature and stability: Adequate flame temperature supports oxidation of volatile compounds and reduces unburned residues. 4. Thermal efficiency of the boiler (calculated by equation 1)

The thermal efficiency of the boiler is determined by the mass flow rate of the heating water, the difference in temperature, the heat capacity of the wooden pellets, and the mass flow rate of the pellets.