Influence of sulphur addition on emissions of polycyclic aromatic hydrocarbons during biomass combustion

Emissions of polycyclic aromatic hydrocarbons (PAH) in the flue gas of a bark fuelled combustion facility were monitored in real time by time-of-flight mass spectrometry combined with resonance-enhanced multiphoton ionization. Sampling and on-line analysis could be maintained up to more than six hours consecutively, providing an insight in the aromatic profile of gaseous emissions as a function of varying combustion conditions. Naphthalene concentrations were quantified by determining a response factor of the ionization signal relative to toluene, which served as an external standard. Limits of detection of 1 ppb could be achieved with a time resolution of ten seconds. The emission of PAH occurred in peaks displaying exceeding levels of concentration. Between such emission peaks PAH concentration could drop to ground level near the limit of detection. Addition of sulphur to the combustion chamber - either as ammonium sulphate solution or elemental sulphur pellets - caused a significant decrease in the number of emission peaks, yielding an overall diminishment of average PAH concentration up to 88%. This was accompanied by a simultaneous decrease in concentration of carbon monoxide and volatile organic compounds, indicating an improvement in combustion quality after sulphur injection.