Preventing wildfires through smart management and valorisation of residual forest biomass into biochar: experiences from the BioValChar project

Abstract

Forest management operations adequately integrated in the forestry value-chain are the gold standard in wildfire prevention. However, these operations generate considerable amounts of residual forest biomass (RFB) that cannot be legally disposed in land and further require suitable management. Residual biomass also includes highly flammable plants existing in the Portuguese forest such as gorse, broom, giant reed and acacia. Quite often wildfires in Portugal are linked with spreading of this residual biomass that promotes fuel accumulation. Besides deleterious impacts on rural and forestry economy, wildfires are also a driver for desertification and soil degradation. Alternative uses for this residual biomass to promote its valorisation and enable proper models of management of forest areas are needed, thus providing economic and environmental benefits towards decreasing of the fuel load. Though this biomass has reasonable carbon content and heating value, they also present inorganic composition (e.g. Na, K, Cl) that promotes operating problems in thermochemical conversion processes as combustion and gasification for useful energy production because of ash related problems (e.g., sintering/fouling), thus restricting their use in such applications. As such, biochar production by pyrolysis is a potential alternative to generate added-value. During pyrolysis the volatile matter of biomass is released to the gaseous phase, resulting a solid product, biochar, which is carbon-rich and contains most of the inorganics (nutrients) of the raw biomass. Exposure of biomass inorganics as free ashes is prevented in this process, and hence pyrolysis mitigates their negative effects. Nonetheless, the efficient pyrolysis of these types of biomass requires development of novel solutions optimized for energy and environmental performance. Enhancing of the energetic sustainability of the process and minimizing of the environmental impacts associated to the emission of gaseous pollutants are aspects of major relevance. Additionally, the biochar quality depends on biomass type, technology and operating conditions used. The BioValChar project (https://biovalchar.web.ua.pt/en/) seeks to answer these challenges related to valorisation of low-quality residual biomass through production of biochar by pyrolysis, which can return back to forest and rural soils. This approach will provide both carbon/nutrient cycling and synergies within forestry management, wildfire prevention, improvement of soil quality and rural development, under the circular economy principle. The research focus valorisation of residual forest biomass in full-control pyrolytic batch and continuous (auger-type reactor) processes, and testing of the resulting biochar performance as soil amendment. Moreover, a prototype of an integrated mobile unit for auto-thermal and continuous biochar production by pyrolysis of biomass is also being developed, by using the pyrolysis gases to provide the energetic needs of the process. Here we present the project overview, as well as some preliminary results on pyrolytic valorisation of one selected biomass (acacia) into biochar through distinct operating modes and conditions.