Measuring and Predicting the Slagging of Woody and Herbaceous Mediterranean Biomass Fuels on a Domestic Pellet Boiler

Abstract

One of the main barriers for the successful utilization of new biomass feedstocks in commercial pellet boilers is the lack of knowledge about the combustion behavior of such fuels, particularly in terms of ash slagging, which can potentially damage the boiler and limit combustion efficiency. The VI Framework European project Domoheat studied the combustion of 15 Mediterranean woody and herbaceous biomass fuels in commercial 60 kW domestic pellet boilers. The performance of several methods for the prediction of measured boiler slagging was tested, including ash composition-based slagging indices, standard ash initial deformation temperature (IDT), and a new slagging laboratory method, the BioSlag test, based on the sieving of the ash and slag obtained in the combustion of 250 g of fuel in a furnace at controlled temperature conditions. IDT values allowed us to identify slagging in fuels with high silica (e.g., rye straw pellet) or alkali contents (e.g., almond shell) but failed to discriminate medium slagging of fuels such as contaminated poplar chip. Slagging indices based on silica and alkali content of the ashes showed success for predicting boiler-observed slagging. The BioSlag test predicted observed slagging percentage in the boiler with R 2 = 0.87. This test could discriminate both high slagging of fuels with high Si content (e.g., rye straw pellet, pinecone seed shell) and the medium slagging tendency caused by alkali elements (e.g., almond shell, olive stone) and by moderate Si contents (e.g., contaminated poplar chip).

Analysis of Selected Physical Properties of Conifer Cones with Relevance to Energy Production Efficiency

“…The amount of ash remaining after fuel combustion is an important factor that largely determines the applicability of a given type of fuel. Ashes from the combustion of plant material may prove difficult to utilize especially those ashes that tend to slag [54,55]. Ash content in the studied cones is presented in Table 4.…”

Effects of Shoot Size and Genotype on Energy Properties of Poplar Biomass in Short Rotation Crops

“…A relevant energy property that has not been addressed in this study is the slagging risk. The potential slagging risk can be determined by analyzing ash composition-based slagging indices against ash fusion temperatures or combustion experiments [61,62]. This deficiency must be addressed and the differences in the slagging risk explored in relation to genotype and diameter in future studies.…”

Assessing the suitability of recovering shrub biowaste involved in wildland fires in the South of Europe through torrefaction mobile units

“…In some cases, the suitability of these biomasses was directly tested in combustion boilers (Mediavilla et al, 2017;Viana et al, 2012). In other cases, the production of pellets for energy purposes was also considered as an alternative (Vega-Nieva et al, 2016). The results of these studies have pointed out that this shrub biowaste appears as a promising resource for energetic valorization, due to its acceptable and stable high heating value as raw material (HHV,∼20 MJ kg −1 ) and its high availability (G onzález-G onzález et al, 2017;Núñez-Regueira et al, 2004).…”