Benefits of Integrated Upgrading of Biofuels in Biorefineries - Systems Analysis

Doctoral thesis, 2007

As a result of increasing concerns about climate change, there is considerable current interest in increasing use of CO2-neutral biofuel in the energy system. Increased use of biomass fuel requires that it be upgraded in order to facilitate transportation and distribution to end-users. Advanced level upgrading is necessary if biomass is to be used as a transportation fuel. Biomass upgrading requires energy, and the conversion efficiency can be maximized if achieved in energy-efficient biorefinery processes. The main objective of this thesis is to analyze biorefinery concepts with respect to energy efficiency, profitability and CO2 emissions. Special attention is paid to integrated biorefinery concepts in which a biofuel upgrading production process is integrated with another process enabling exchange of useful energy or material streams. The thesis aims at quantifying the extent to which such integrated concepts are more profitable, energy efficient and CO2-lean than stand-alone production units. The biorefinery processes evaluated are pellet production and hydrogen production from gasified black liquor integrated with a pulp mill, and hydrogen production from gasified biomass integrated with a natural gas combined cycle heat and power plant. These processes are evaluated using different possible future energy market scenarios. Pellet production integrated with a pulp mill is shown to be beneficial from a CO2 perspective. The economic benefits depend on the biomass dryer technology used for integrated pellet production, which tend to be more costly compared to the Stand-alone pellet production. However, integrated pellet production benefits from surplus material, common personnel and infrastructure available at the site. If gasified, black liquor can be used for increased electricity production or for synthesis of e.g. methanol and hydrogen. Hydrogen production from gasified black liquor has the greatest potential for net CO2 reduction in four of five future energy market scenarios used for the evaluation. This indicates that for many possible future scenarios, hydrogen production from gasified black liquor will be an efficient way to use biofuel. Hydrogen production enables pre-combustion carbon capture and storage and this contributes to profitability and CO2 emissions reduction. A final conclusion is that it is important to adopt a systems perspective when performing studies to identify the most effective ways to use limited biomass for resources when developing sustainable energy system solutions for the future.