**3. Availability of different types of challenging biomass feedstock**

Low-grade biomass feedstocks from primary production like agricultural residues, clearing and thinning residues, and energy crops are largely available in many parts of the world [2]. The utilization of these feedstocks for energy and chemicals involves large-scale industrial processes. Despite their availability in large quantities and at low prices, their low energy densities and high moisture contents decrease their availability in practice. This is because of the high transportation costs and long distances involved with the centralized processing of these feedstocks.

The biomass feedstocks from industrial sidestreams are food or material industry by-products. The forest industry produces sawdust and bark or more processed feedstocks like black liquor or tall oil. These types of feedstocks are already inside the fence of a production site, and they pose severe waste-related problems if not utilized. However, there are still some challenges. Heat, steam, or electricity production is not always in the interest of the industry where the feedstocks are generated, or there might be a lack of competence or experience to utilize them for energy and chemicals production.

**Table 1** shows the 2019 world production of the top 10 crops and estimates of the crop residues they generated in the field during harvesting and after they were processed on industrial sites. The estimates for the crop residues were made based on the data obtained from The Food and Agriculture Organization of the United Nations (FAO) [2]. As seen from the table, close to 15,000 million metric tons of agricultural residues were generated, indicating the high availability of these feedstocks for energy and chemicals production.

#### **3.1 Availability and energy density**

In the Nordic countries, residues from primary production like wheat straw and logging residues find their way to the local heat and power plants for conversion by combustion to district heating and electricity. Only a certain distance from the heat and power plant is suitable for collecting these biomasses; too long distances make the transportation costs too high [14].


**Table 1.** *World production of the top 10 crops and their residues generated in the field and on industrial processing sites [2, 13].*
