International Energy Agency (IEA) Bioenergy Task 42 has developed the following definition for biorefinery (IEA Bioenergy, 2010):

Biorefining is the sustainable processing of biomass into a spectrum of bio-based

products (food, feed, chemicals and/or materials) and bioenergy (biofuels, power

and/or heat).

This means that biorefinery can be a concept, a facility, a process, a plant or even a cluster of facilities.

A main driver for the establishment of biorefineries is the sustainability aspect. All biorefineries should be assessed for the entire value chain on their environmental, economic and social sustainability. This assessment should also take into account the possible consequences due to the competition for food and biomass resources, the impact on water use and quality, changes in land-use, soil carbon stock balance and fertility, net balance of greenhouse gases, impact on biodiversity, potential toxicological risks and energy efficiency. Impacts on international and regional dynamics, end-users and consumer needs, and investment feasibility are also important aspects to take into consideration.

A biorefinery is the integral upstream, midstream and downstream processing of biomass into a range of products. A biorefinery can use all kinds of biomass, including wood and agricultural crops, organic residues (both plant and animal derived), forest residues and aquatic biomass (algae and sea weeds). A biorefinery should produce a spectrum of marketable products and energy. The products can be both intermediates and final products, and include food, feed, materials and chemicals; whereas energy includes fuels, power and/or heat.

The main focus of biorefinery systems which will come into operation within the next years is on the production of transportation biofuels. The selection of the most interesting biofuels is based on the possibility that they can be mixed with gasoline, diesel and natural gas, reflecting the main advantage of using the already existing infrastructure in the transportation sector. IEA Bioenergy Task 42 has defined that both multiple energetic and non-energetic outlets need to be produced to become a true biorefinery. The volume and prices of present and forecasted products should be market competitive.

Generally, both Energy-driven and Product-driven Biorefineries can be distinguished. In Energy-driven Biorefineries, the biomass is primarily used for the production of secondary energy carriers (biofuels, power and/or heat); process residues are sold as feed (current situation), or even better are upgraded to added — value bio-based products to optimise economics and environmental benefits of the full biomass supply chain. In Product-driven Biorefineries, the biomass is fractionised into a portfolio of bio-based products with maximal added-value and overall environmental benefits after which the process residues are used for power and/or heat production for both internal use and selling of the surplus to national grids.

A biorefinery is not a completely new concept. Many of the traditional biomass converting technologies such as the sugar, starch and pulp and paper industry used aspects connected with a biorefinery approach. However, several economic and environmental drivers such as global warming, energy conservation, security of supply and agricultural policies have also directed those industries to further improve their operations in a biorefinery manner. This should result in improved integration and optimisation aspects of all the biorefinery subsystems.