*Challenging Biomass Feedstocks for Energy and Chemicals DOI: http://dx.doi.org/10.5772/intechopen.103936*

It is mainly the demand for heat in the winter that makes this feasible. The Nordic countries have systems for district heating in all cities and even in smaller municipalities. In most countries globally, there is no market or infrastructure for district heating. Instead, converting the biomass into high-grade chemicals for materials and fuels for transportation is a sustainable alternative to replace fossil-based raw materials for these commodities.

Low energy density is the result of low bulk densities (100 kg/m3 ), high moisture contents (typically 40%), and low heating values (about 20 MJ/kg dry solids) of the feedstocks. This results in low energy densities, around 1000 MJ/m3 . Compared to crude oil, 35,000 MJ/m3 , and bituminous coal, 25,000 MJ/m3 , biomass feedstocks should not be transported long distances without first upgrading.

The oxygen content of the biomass feedstocks is high; a typical empirical formula for biomass is CH2O. The maximum available thermal energy per kilogram from these feedstocks is 20 MJ, which is obtained when they are fully oxidized to CO2 and H2O [15]. This is relatively low compared to other primary energy sources, like natural gas, crude oil, and bituminous coal, which are 55, 45, and 30 MJ/kg, respectively.

High porosity is due to the vascular structure of biomass. It leads to the overall low density: maximum 900 kg/m3 for dry solid hardwood, but typically much lower bulk densities: 30–170 kg dry solids per cubic meter, kgD.S./m3 [13]. Higher bulk densities usually include moisture, which is of no value for its utilization for energy and chemicals.

Biomass feedstocks are naturally hygroscopic and contain some 20% moisture in equilibrium with air humidity. It dries further by applying heat and may obtain close to zero moisture content before utilization. Fresh biomass from newly harvested feedstock contains over 50% of moisture. Each percent of moisture content lowers the effective heating value by 1.125%; i.e., moisture content of 40% reduces the effective heating value of the biomass by 45%, expressed as energy released per kilogram biomass combusted.

#### **3.2 Availability of typical industrial by-products**

Biomass feedstocks from industrial by-products such as rapeseed oil cake, molasses, vinasse, and black liquor are much easier to access since these biomass feedstocks are already inside the industry gate. The challenge is if the industries where these feedstocks are generated do not find use(s) for them and if there are no proven techniques to have them processed.

The pulp and paper industry have a long tradition of utilizing all the sidestreams it generates. The largest sidestream is the spent liquor from wood pulping: black liquor. Its utilization has a long history in Scandinavian countries, but the primary purpose of processing it further within the pulp mill is to recover the inorganic cooking chemicals, which are contained in the black liquor. For every ton of pulp, seven tons of black liquor are produced. After concentrating the black liquor to a dry solid content of about 75%, it is burned in a chemical recovery boiler to produce heat and electricity for the pulp mill, which is often self-sufficient in energy. Roughly 195 million metric tons of black liquor are produced annually as a by-product from all the Kraft pulping processes in the world [16].

The integrated sugar-ethanol industry produces molasses and vinasse as byproducts. The amount of molasses produced annually is about 70 million metric tons with a thermal energy value of approximately 225 TWh [17]. For every liter of ethanol produced, 10–15 liters of vinasse form as a by-product. In Brazil alone, 370 million cubic meters of vinasse is generated annually [18]. There is not yet a sustainable use for these by-product streams. They are both potential biomass feedstock for the production of energy and chemicals.
