4.1 FUEL BAG LABELING
Transparent and accurate biomass pellet bag labeling provides essential information regarding fuel origin, composition, quality, and certifications. This information promotes consumers’ awareness and trust in making informed choices and confidence in the product’s quality. Transparent labeling also holds manufacturers accountable for the accuracy of their product information which, in turn, encourages responsible production practices and discourages deceptive marketing.
Nowadays, the market offers a wide variety of biomass fuel labeling designs, often with insufficient information or even absent details regarding the biomass source and fuel characteristics. This situation can lead to confusion among consumers, who find it challenging to make informed product comparisons due to the lack of relevant information. Although ENplus, a leading certification scheme for wood pellets, has provided some guidelines for bag design (ENplus 2018), addressing this challenge requires a broader initiative and widespread standardization for consistent bag labeling and informative shopping experience.
The biomass pellet market in Upper Silesia offers a diverse variety of bag designs. They range from minimalistic plastic bags or cardboard boxes with no product information to bags with elaborate designs containing fuel properties and eco-friendly graphics. While some bags featured details about biomass origin (typically very general), material properties, and quality certification logos, others provided very limited or no data (Fig. 2). Specifically, out of 30 pellets:
- 9 bags had no producer name (Fig. 3)
- 12 bags had no producer contact information
- 10 bags contained no fuel properties information
- 15 bags contained no fuel storage information
- 19 samples had no information about the type of biomass used to produce the fuel
Producers provided also, sometimes in multiple languages, information regarding the fuel origin and certifications received:
- 14 bags displayed a DINplus or ENplus certification logo
- 6 bags contained an FSC (Forest Stewardship Council) logo - responsible sourcing certificate
- 2 bags displayed logos of the Polish Pellet Council
- 1 bag contained information of being BIOCONTROL overseen pellet
- 1 bag displayed a logo of SGS (Société Générale de Surveillance SA.) certification
- 4 purchased bags contained pellets produced in Ukraine
Furthermore, some of the bags contained additional information such as:
- material source (for instance, from flooring production)
- statements that the product contains no glues or chemical additions
- the possibility of using ash as fertilizer
- the fuel being 100 % economical and natural
- information that pellet production followed norm A1
- information about CO2 emissions:
a) 0 % emissions of CO2 (sample 16)
b) CO2 emissions when the product is burned are equal to the amount of CO2 absorbed by the plant
during growth, which means that no additional CO2 is emitted into the atmosphere (sample 19).
Some of the pellet bags were additionally marked with symbols and statements showcasing their high quality, high calorific value, good price, producer participation in a tree planting program (sample 9), the fuel being a biofuel of the future (sample 17), a source of positive energy (sample 22), or energy of the nature (sample 25). Many of the bags contained information about the possibility of recycling the bag.
4.2 PHYSICAL PROPERTIES OF PELLETS
Purchased biomass pellets came in small cylindrical shapes and a variety of colors depending on the origin of the source materials and technology of production. Several of the samples exhibited an easily noticeable lack of material homogeneity, and some contained an assortment of impurities visible even to the naked eye (Fig. 4). The most typical undesired addition detected megascopically was bark, followed by pieces of plastic, inorganic matter, and clusters of flour binder.
Physical analyses of the samples (diameter and length, fines content, mechanical durability, and bulk density) revealed that the properties of some of the pellets are not within the DINplus and ENplus certification limits (even if the pellet was certified) and, in some cases, those properties do not correspond with parameter values provided by the pellet producer (Figs. 5-6).
While all purchased pellets met the diameter and length limits, values of mechanical durability and the content of fines were not within the certification thresholds for 10 out of the 30 samples. Additionally, three out of four non-woody pellets and one of the wood pellet samples (number 29) showed too low values of bulk density (Figs. 5-6). This shows that a significant number of purchased fuels are not strong enough to withstand mechanical stress during their production, handling, and transportation, which makes them prone to breaking apart and creating dust. This, in turn, affects the fuel transport and efficiency of combustion and may lead to boiler clogging, increased emissions of pollutants, and increased risk of fire or dust explosion (Williams et al. 2018; Gilvari et al. 2019, 2021; Kuranc et al. 2020).
4.3 CHEMICAL PROPERTIES OF PELLETS
Chemical analysis of the purchased samples (moisture, ash, sulfur, and nitrogen content, ash melting temperatures, and net calorific value) showed that almost all of the samples had moisture content within the recommended range of up to 10 wt %. However, the majority (over 50 %) of the fuels had ash content higher than the certifications threshold (Figs. 7-8), with two of the samples (11 and 29) more than double the ash limit for DINplus certification. However, sample 27 (Fig. 8) yielded the highest amount of ash of all the samples, reaching 14.3 wt %, equivalent to 139 % over the recommended limit, significantly impacting the fuel calorific value.
Another observed discrepancy between values provided by the pellet producers and data acquired in this study turned out to be ash melting temperature, which is closely related to boiler performance, combustion efficiency, and creation of sinter and slag deposits, which, in some cases can lead to boiler damage (Holubcik et al. 2015; Radačovská et al. 2017; Čajová Kantová et al. 2023). Almost half of the tested samples did not meet the certification guidelines of ENplus and DINplus which recommend an ash melting temperature above 1200 oC. These fuels (Figs. 9-10) showed a temperature lower than the certification thresholds by 10 to 150oC. While norms do not exist for non-woody biomass regarding this parameter, sample 24 showed ash shrinking temperature below 1200 oC.
Three samples (5, 15, and 27) showed also significantly higher nitrogen content than DINplus and ENplus limits (Figs. 9-10). While the source of nitrogen in the pellets is unknown, nitrogen content might have implications for combustion efficiency, increased corrosion, fouling of a boiler, or formation of NOx and ammonia, and therefore can lead to negative environmental impacts (Glarborg et al. 2003; Klason and Bai 2007; Petrocelli and Lezzi 2014; Schmid et al. 2020).
4.4 PETROGRAPHIC COMPOSITION OF PELLETS
Although numerous countries around the world have adopted quality standards to govern the quality of biomass pellets, several studies have identified challenges and issues with the current standardized testing and have advocated for reevaluation of the standards (Chandrasekaran et al. 2012; Duca et al. 2014; Rahman and Hopke 2017; Thiffault et al. 2019; Jelonek et al. 2020a, b, 2021; Drobniak et al. 2021a, b, 2022, 2023a; Mencarelli et al. 2023). One proposed enhancement to the current testing methods is the adoption of petrographic analysis in reflected light (Drobniak et al. 2022, 2023b). While this method is firmly established and routinely employed in the examination of coal, source rocks, metals, ceramics, and polymers, utilizing it for evaluating solid biomass fuels has been very limited. A recent development is the introduction of a groundbreaking PL-US BIO certification program in Poland that combines traditional physicochemical testing with reflected light microscopy analysis (PL-US BIO 2023).
For the pellets studied, results obtained from petrographic analysis showed that 70 % of the examined pellets would not meet the criteria set for PL-US BIO certification (PL-US BIO 2023) due to the presence of elevated levels of impurities. While nine of the 30 evaluated samples had impurities lower than the recommended 3 vol. %, for 21 samples, the level of undesired additions ranged volumetrically between 3.1 % and 18 % (Figs. 11). Among these undesirable inclusions, bark, present in quantities from 0.5 % to 17.8 vol. %, emerged as the most frequent unwanted impurity (Figs. 12). While bark is a type of biomass, it has been considered as an unwanted addition in pellet fuels due to its association with harmful particulate matter and smog emissions (Drobniak et al. 2022). The presence of bark can also introduce an increased concentration of inorganic elements, including soil or sand residues that might originate from transportation. As a direct consequence, the ash content in pellets tends to be higher when bark is a significant component. Furthermore, when bark content surpasses a threshold of approximately 2.5 % to 3 %, it has been observed to correlate with the formation of sinter and slag during combustion (Holubcik et al. 2015; Radačovská et al. 2017; Drobniak et al. 2022; Čajová Kantová et al. 2023).
Other impurities found in the pellets included inorganic matter (0.1 to 1.3 vol. %); traces of petroleum products, most commonly glues and plastic (0.1 to 0.8 vol. %); and fossil fuels (up to 0.8 vol. %). The content of binders (typically flour) and additives was estimated from 0 to 2.2%, with one sample (number 10) containing a binder content level above the certification threshold.