The status of particulate matter (PM) emission reduction methodologies applicable to non-industrial pellet boilers (<500 kW) are summarized and the potentiality of PM emission reduction from these appliances as well as the related challenges are reported. The primary and secondary control methods are presented by indicating the particulate matter removal mechanisms involved and the abatement performances observed.
Primary control measures based on boiler design, air-staging, optimized process control and fuel-quality-enhancement are found to be successfully applied for PM reduction from pellet boilers but may not be sufficient to comply with more and more stringent emission regulations without combination with secondary measures. It emerges that promising results have been obtained for some secondary methods (e.g., metal mesh filters, electrostatic precipitation, wet scrubbers, open-cell ceramic filters) in terms of abatement performance but many operational issues (e.g., deterioration of performances with ageing, high maintenance need, unsustainable pressure drops, eventual waste streams etc.) are still to be minimized for these systems to constitute a feasible solution to PM control especially in smaller appliances for residential heating.