Forest residues to reuse

Limbs, sawdust and treetops are some of the components so called forest residues. Unwanted by products from wood processing industries and forest harvesting have in my opinion a large potential in the field of bioenergy.

The largest biomass potential on the earth calculated per unit area are from forests, which covers approximately one third of the earth´s surface (Biomassa, 2020). Woody biomass in general is today the most common used biomass, and using the forest as material and energy source is not something new. But the increasing problem with deforestation is critical and contribute to loss of biodiversity and decreased carbon uptake capacity (FAO & UNEP, 2020).

I think that we must become better at taking care of the unwanted by products that arise along the process chain in a more sustainable way. Felling in the form of thinning is something that is needed to maintain the forests and ensure that all other vegetation thrives and can be used as biomass in conversion to energy (FAO & UNEP, 2020). There is a potential to increase harvest of biomass without increasing the harvest area by using forest residues. In Figure 1 below the energy use from residues 2015 and an estimation of potential energy use from residues are shown. In the high case the estimation is based on a sustainable enhanced residue collection, without compromising ecosystems (IRENA, 2019).  

 
Figure 1. Actual and enhanced residue collection in Sweden 2015.

Forest residues is categorized as a second generation biomass as well as an second generation biofuel (Cheng, 2017). The residues can either be processed towards an end-product as biofuel in forms of biodiesel or electricity/heat generation as pellets or biogas. The advantages of using forest residues in energy conversion are the use and optimization of residues along process chains that operate regardless and the potential in supply is large. Slash, stumps and treetops are used instead of rotten in the forest. However, forest residues have a few disadvantages that is important to keep in mind (Cambero, Sowlati, Marinescu & Röser, 2015). The residues have a low energy density and heating values, there is high costs in the supply chain mostly regarding transport. Mixed characteristics in the forest residues is also a disadvantage when it comes to the technical conversion process in energy recovery (Belyakov, 2020).

Sources
Biomassa.(2020, September 17). In Nationalencyklopedin. Retrieved September 17, 2020, from  http://www.ne.se/uppslagsverk/encyklopedi/lång/biomassa 

Belyakov, N. (2020). Sustainable Power Generation – Current Status, Future Challenges, and Perspectives. (1. ed.) Elsevier Inc. DOI:10.1016/c2018-0-01215-3.

Cheng, Jay (2017). North Carolina State University: Biomass to renewable energy processes (2. ed) Taylor & Francis Inc.

Cambero, C., Sowlati, T., Marinescu, M., & Röser, D. (2015).
Strategic optimization of forest residues to bioenergy and biofuel supply chain. INTERNATIONAL JOURNAL OF ENERGY RESEARCH Int. J. Energy Res. Wiley Online Library, 39, 439–452. DOI: 10.1002/er.3233

FAO and UNEP. (2020). The State of the World’s Forests 2020. Forests, biodiversity and people. Rome. https://doi.org/10.4060/ca8642en

IRENA (2019), Bioenergy from boreal forests: Swedish approach to sustainable wood use, International Renewable Energy Agency, Abu Dhabi.