• Energy Research

Abstract In this study ten mixtures of spruce (Picea abies), short-rotation-coppice (SRC) willow (Salix spec.; Clone Tordis) and kaolin were pelletised and burned in a residential biomass boiler (12 kW). Focus is on usability of SRC willow in exchange of forestal biomass (spruce), as well as on kaolin as fuel additive for particulate emission reduction in small-scale biomass combustion. Moreover, fuel blends were intended to match quality criteria for the European market according EN 14961-2. Initially, ten raw material mixtures were pelletized and the produced blend pellets were physically and chemically characterized. Combustion experiments with these fuel blends show differences in gaseous emissions, chemical composition of emitted particles and boiler ash. Kaolin addition reduced emitted particle mass even in lowest kaolin concentrations (0.2 wt.%) in every combination of spruce and SRC-willow. Chemical analysis shows decreased K-contents in the collected particles for fuels with kaolin addition, but an increased share of Zn.

Abstract This study investigates the general concept of reduced firebed temperatures in residential wood pellet boilers. Residential wood pellet boiler development is more and more concerned with inorganic aerosols characterized by a temperature-dependent release from the firebed. Hence, different concepts are applied aiming to reduce firebed temperatures. Unfortunately, these concepts influence not only firebed temperatures, but also other important parameters like air flow rates which may cause unwanted side effects with respect to combustion quality or efficiency. Thus, a new approach was developed solely affecting firebed temperature by implementing a water-based firebed cooling in a 12 kW underfeed pellet boiler. The effectiveness of the cooling was monitored by comprehensive temperature measurement in the firebed. The cooling capacity ranged from 0.4 kW to 0.5 kW resulted in a significant decrease of firebed temperatures. Gaseous emissions remain stable showing no significant changes in major components (O 2 , CO 2 , NO x ). Furthermore, CO emissions were even reduced significantly by the activated cooling, which was supposedly caused by a stabilized devolatilization due to the firebed cooling. Moreover, the temperature-dependent release of aerosol forming elements was influenced at activated firebed cooling, which is proved by a decrease of 17 wt% of dust (Total Suspended Particles; TSP). At the same time the gaseous emissions of HCl increase, supposedly by a reduced potassium release from the firebed to the gas phase and a subsequently different particle formation. The general concept of reduced firebed temperatures proved to be successful decreasing overall aerosol emissions without impacting combustion quality.

AbstractThe temperature-dependent release of inorganic elements is the first step of the main formation pathway of particle emissions in automatically fired biomass burners. To investigate this step, a residential pellet boiler with an underfeed-burner was equipped with a direct firebed cooling. This test setup enabled decreased firebed temperatures without affecting further parameters like air flow rates or oxygen content in the firebed. A reduction of particle emissions in PM1-fraction at activated firebed cooling was found by impactor measurement and by optical particle counter. The affected particles were found in the size range <0.3 μm and have been composed mainly of potassium chloride (KCl). The chemical analysis of PM1 and boiler ash showed no statistically significant differences due to the firebed cooling. Therefore, our results indicate that the direct firebed cooling influenced the release of potassium (K) without affecting other chemical reactions.