For a long time, the selection of fuels for biomass combustion, in terms of avoiding problems such as slagging and fouling of the reactors, often was carried out based on trial and error. About a decade into the 21st century, a group of Sweden-based researchers with long-standing experience in high-temperature conversion of woody feedstock to heat and power started to mull over a more systematic approach to assessing the reactions in thermal conversion of the chief trouble-making content of the biomass: the inorganic compounds forming the ash.
In 2012, the scientist, brought together under the umbrella of Bio4Energy, published an article on Ash Transformation Chemistry during Combustion of Biomass in the interdisciplinary scientific journal Energy & Fuels by the American Chemical Society (ASC). The article describes a conceptual model by which any type of biomass—whether originating from wood, woody or agricultural residue or other types of combustible waste—may be characterised, and thus understood, in terms of the basic chemical reactions that take place during thermal conversion of biomass into heat, power, fuels and chemicals.
After having been amply cited by other researchers around the world, this spring, the article by Bio4Energy scientists received the 2017 Energy & Fuels Joint Award for Excellence in Publication.
“This is a milestone paper on the fundamental ash chemistry related to ash transformation reactions… The paper provides a useful and concise conceptual model for guiding the understanding [of] the behaviour of ash matter during thermochemical processing and utilisation of any biomass fuel”, said Mike Klein, Energy & Fuels’ editor-in-chief.
Is the conceptual model proposed equally relevant for current or future biorefinery operators trying to choose which feedstock to use?
“When it comes to thermal conversion of biomass, that is the conversion of a bio-based feedstock at high temperatures, the purpose is to transform the organic content of the biomass—carbon, hydrogen, oxygen—to gases [such as] carbon dioxide, water [vapour] and nitrogen”, said Boström, who is a professor at Umeå University and programme manager of Bio4Energy.
“However, after the conversion what remains is almost always a residue, the ash. Whenever you have such inorganic residue, I would recommend referring to the basic principles of chemistry that we have outlined in the conceptual model we have proposed.
“[The model] is an attempt to organise, or rather to guide, the thought process when trying to understand the reactions in ash transformation mechanisms, and thus ash-related problems in the thermal conversion process. With minor modifications, the model can be applied [not only to biomass combustion, but also] to pyrolysis and gasification”.
Nils Skoglund, Alejandro Grimm, Christoffer Boman, Marcus Öhman, Markus Broström and Rainer Backman are co-authors of the article and representing three of seven Bio4Energy research and development platforms: Thermochemical Conversion Technologies, Environment and Nutrient Recycling and Wood Pre-processing.
In August, Boström and some of his colleagues will be travelling to Washington D.C., U.S.A., to present their work to the 2017 Fall National Meeting of the ASC.