Cost-Effective Pathways for Gasification-Based Production of Biofuels
Licentiate thesis, 2018
A considerable number of studies indicate that biomethane produced through gasification of lignocellulosic biomass could contribute significantly to greenhouse gas emissions reduction in the transport sector. However, the production costs are high compared to fossil-based alternatives, which has limited deployment of the technology. This thesis evaluates three possible options for decreasing the cost of gasification-based biomethane production: (i) utilization of shredded bark as feedstock, (ii) integration of power-to-gas concepts, (iii) process integration of the biomethane plant with a sawmill to increase the well-to-tank efficiency of the value chain. Utilization of low-value bark biomass as feedstock could potentially reduce the costs of biomethane production as well as releasing high quality biomass to be used for more specialized purposes. The use of electricity to increase the product output from gasification-based biofuel production constitutes an additional possibility for increased cost efficiency. Hydrogen produced from electrolysis of water can be reacted with effluent CO2 streams in the biomethane plant to produce additional biomethane, thereby increasing the biomethane output per unit of biomass fed to the plant. By integrating the biomethane plant with a sawmill, biomass residues from the sawmill can be used as feedstock and the excess heat from the gasifier can be recovered to satisfy the heating requirements of the biomethane plant.
The results show how all evaluated pathways could contribute to decreasing costs for gasification-based production of biomethane. Analysis of demonstration tests performed at industrial scale show that bark gasification is technically feasible for production of advanced biofuels. The feedstock related cost for production of biomethane from bark (dried to about 8%) is in the range of 24.2-32.7 EUR/MWh; a reduction of about 35-45% compared to wood pellets. The evaluation of four different process configurations for utilization of hydrogen produced from electrolysis of water (power-to-gas) in the biomethane plant show that the operating revenue increases with increased addition of hydrogen. The results for the sawmill-integrated gasification-based liquefied biomethane production plant show that the size of the production plant has the largest impact on fuel production cost, followed by feedstock transportation costs for larger plants. It can be concluded that there are clear gains to be obtained by integrating gasification-based liquefied biomethane production at sawmill sites, and that the gains increase with the size of the sawmill.