Photomicrogrph Atlas of Wood Pellet Components

Concerns about climate change, energy security, and the diversification of energy supplies have made renewable resources increasingly more attractive and important sources of energy. As interest grows, bioenergy (energy from bio-based sources) is becoming more environmentally friendly and economically viable and has started to play a more prominent role in the global energy mix. In this changing market, wood pellets have emerged as a sustainable source of power with the potential to become a mainstream fuel in the future energy market. Pellets are currently the most economical way of converting biomass into fuel, and they are a fast-growing component of the energy sector. Pellets can be made from various types of biomass including industrial waste and co-products, food waste, agricultural residues, and virgin lumber, which are compressed under high pressure. Among these, wood pellets are the most common, and they generally are made from raw trees, wood shavings, compacted sawdust, industrial wastes from the milling of lumber, manufacture of wood products and furniture, and construction. The wood pellets available on the market are sold as fuel (heating and grilling) or as absorbents for animal bedding. But while the wood pellets are a fast-growing component of the energy sector and important tool in fight with global warming, it is important to understand influence of wood pellet quality on combustion emissions, and how their usage impacts human health and environment. Thanks to wood pellet industry efforts, especially in the North America and European Union, many of the wood pellets follow rigorous production procedures, and certification. However, there are still some manufacturers that do not use the same production scrutiny, which can result in poorer quality of their pellets. Our research show that in some extreme cases these uncertified wood pellets contain more than 20 percent of impurities. While some of those contaminants are so big that can be visible even without microscope the majority of the contaminants are of micrometer size and can be detected and identify only under a microscope. While the current standards test the quality of pellets based on a variety of physical and chemical properties, some impurities in pellets (glass, plastic, metal, ceramics, coal, and coke) are not easily identified this way. Our research shows that reflected light microscopy can be successfully used to identify and quantify those contaminants. Although  reflected light microscopy technique is a well-known and widely used method allowing examination of various materials, this is a novel application for pellet fuels.