Resumen de Reduction of emissions in biomass combustion systems
In the context of an increasing interest by both public and private stakeholders on the field of renewable energy and given the instabilities caused by changes in geopolitical relations between the EU and some of the leading producers of fossil fuels, the search for alternative fuels is seen as a promising alternative. The concept of sourcing energy from locally available materials and residues is old, but the challenge of selecting the best candidates and improving the combustion systems to ensure a minimal impact on the environment has experienced great advances in the last decades. The risk posed by particulate matter (PM) emissions on human health has been thoroughly studied, but other emissions such as volatile organic compounds (VOCs) havent been thoroughly considered in the field of biomass combustion, due to the elusive nature of these components and their diverse structure and composition.
Particulate matter abatement systems can be divided into two categories: primary and secondary systems. While primary systems focus on limiting the emission of pollutants during the combustion reaction by operating on the operational variables such as temperatures, air flow rates or fuel consumption, secondary systems comprise a diverse range of devices intended to limit the emission of said pollutants to the environment. These secondary systems include cyclones, electrostatic precipitators, baghouse filters or catalysers. The development of new particle abatement systems is of great interest to increase the adoption of biomass systems in detriment of fossil fuels, as it would ensure the compliance of the systems to present and future regulations.
This PhD dissertation is presented as a compilation of three scientific articles that represent advances in the knowledge about solid biofuels derived from non-woody sources and solutions to reduce their associated contaminants, either solid or gaseous. Besides, a novel PM abatement system is introduced and tested, and a system for the capture of volatile organics is proposed.
The inception of this work is the experimental work in the form of combustion tests in lab-scale facilities that were carried out with a variety of commercial and non-commercial fuels. The starting experiments studied the behaviour of the fuels under different combustion conditions and led to the proposal of variations of the fuels including additives. These additives improved the results of further tests in terms of slagging behaviour, although it was noted that an increase in the emission of particulate matter was also possible. Further analysis on these fuels confirmed the positive effects of additives, as activation energies for modified fuels improved.
To address the particulate matter emission issue, a ceramic non-reactive foam resistant to heat was proposed. This ceramic foam was introduced in the facilities and the results of the experiments showed promising reductions of contaminants. To expand on the knowledge of the origin of these substances, a system to adsorb volatile compounds was developed and tested, and thermogravimetric analysis confirmed the effectiveness of the system in the capture of mainly the lightest fractions of the volatiles.
Overall, the results indicate that the utilization of these locally sourced biofuels is viable from a technical point of view, as the feedstocks can be modified to improve their properties and abatement systems can be introduced to reduce pollutant emissions.
