Biomass pre-treatment for bioenergy

An increased demand for biomass means that greater mobilisation of biomass resources will be required to meet demand. The availability of biomass has been addressed in many studies and may be limited by various environmental, economic, logistical, technical or policy factors. Particularly in cases where the availability of a certain biomass type is limited by technical, economic or logistical factors, pretreatment technologies may be required.

This report summarizes the conclusions of an IEA Bioenergy Inter-Task project on Fuel pretreatment of biomass residues in the supply chain for thermal conversion. The report shows how currently available pretreatment technologies and technologies under development can potentially help in improving and enabling the supply chains for available solid biomass resources for thermochemical conversion. Five carefully selected case studies describe key options for pretreatment of solid biomass resources for energy generation, including their costs, effectiveness and commercial status. Case studies included biomass torrefaction, pretreatment practices of forest residues, treatment of municipal solid waste (MSW) to Solid Recovered Fuel for gasification, steam explosion of biomass, and leaching of herbaceous biomass.

General conclusions:

• It is important to diversify the resource base for bioenergy to lower grades of biomass, reducing logistic costs and increasing the fuel flexibility of various conversion technologies. Biomass pretreatment technologies that enable the production of a fuel with better defined specifications and increased energy densities can be instrumental in boosting the bioeconomy as a whole.

• Biomass pre-treatment steps such as washing, drying, sieving, leaching or thermal pretreatment may significantly improve characteristics of lower grade biomass and therefore provide an attractive approach for enabling the use of such residues, which may broaden the resource base.

• Logistical challenges and high transportation costs involved when using bulky biomass can be reduced through biomass pretreatment producing a fuel or energy carrier with increased volumetric energy density.

• Several pretreatment technologies have the objective to convert a biomass into a fuel that has technical specifications closer to that of the original fossil fuel, hence reducing the need for new infrastructures and lowering the impact on plant performance. This becomes attractive if the cost savings in plant modification at the end user are higher than the additional costs of pretreatment.