Contributions to the reduction of particulate matter emissions in biomass combustion processes

Resumo

Given the need to adapt domestic biomass combustion plants to increasingly stringent environmental standards, the present doctoral thesis is proposed. The main aim of this research work is to study the capacity for mitigation and control of emissions presented by three primary strategies to improve combustion processes, which were applied to low power systems. Specifically, the techniques investigated were: air stratification, flue gas recirculation (FGR), and fuel bed cooling. Their effects on the most relevant combustion parameters, such as temperatures, flue gas composition and particulate emission, were analyzed. With regard to this last variable, special emphasis was placed on the description of the type of particulate matter released, both in terms of size and shape (morphology) and chemical composition. Experimental data was obtained by conducting tests in a pilot plant, which was designed ad-hoc to meet the needs of the project. Furthermore, the research work was complemented with the application of a wide variety of sampling techniques (isokinetic sampling, low pressure impactor – LPI, thermophoretic sampling – TPS), as well as analytical techniques (SEM-EDX, TEM, ICP-OES, TG-DSC, etc.). In general, the results confirmed the great potential for emission mitigation presented by the proposed strategies. The use of adequate air distribution, in combination with other primary measures based on bed temperature control, has effectively reduced CO formation and PM release. This has opened up new spaces for the potential optimization of the aforementioned systems and their future implementation in commercial domestic appliances, supporting the continuity of biomass use in the residential sector in the short run.