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Rapport - Refereegranskat, 2020

Dry matter losses during biomass storage : measures to minimize feedstock degradation

Anerud, Erik; Krigstin, Sally; Routa, Johanna; Brännström, Hanna; Arshadi, Mehrdad; Helmeste, Christopher; Bergström, Dan; Egnell, Gustaf

Sammanfattning

The degradation of biomass during storage leads to several unfavourable outcomes including Greenhouse gas (GHG) emissions, feedstock/energy losses, and economic losses. Optimization of biomass storage along the supply chain for the reduction of these negative effects is essential in order to improve bioenergy as a renewable and profitable energy source. The overall effect of the biological, chemical and physical reactions, which occur in biomass piles, leads to a succession of microorganisms as pile temperatures increase, which in turn releases GHG emissions, such as CO2, CH4 and CO, into the atmosphere. Furthermore, valuable extractive compounds from tree biomass begin to diminish directly after harvesting occurs. Management that facilitates drying can reduce dry matter losses caused by microbial activity. Pre-storage in small heaps during favourable storage conditions can increase the drying rate at the harvesting site. However, forest residues stored at the harvest site will retain moisture more rapidly than windrows at landing during precipitation. Favourable exposure to sun and wind during storage is essential for the result. Coverage of forest residues stored in windrows can protect the biomass from rewetting leading to lower moisture content and higher net calorific value. The effect of coverage may be large on some landings and negligible in others and therefore location and season must be considered. Comminution to chips increase the surface area exposed to potential microbial degradation, increase pile compaction decrease the permeability leading to increased activity and temperature within the pile. It is highly recommended to strive to comminute to the largest possible particle size accepted from the end-user. Minimize compaction during storage both by avoid using heavy machinery on the piles and limit the height of piles below 7 m. Coverage with a semipermeable material can protect wood chips from rewetting leading to lower moisture content, which will reduce dry matter losses and energy losses. If possible, limit storage time to 3-4 months if possible and expect a major temperature increase during the first weeks of storage. Methods for monitoring degradation include calculating dry matter losses using sampling net bags in storage piles. However, other methods are used and there is no general standard. Predictive models of temperature development, fuel quality parameters and dry matter losses allow for the simulation of pile dynamics based on input parameters. As these models develop, they will allow useful information to be obtained for improved storage management without the need for excessive sampling. Thereby, adverse effects on storage can be reduced.

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Utgivare: IEA Bioenergy