Enhancing biomass utilization by combined pulp and fuel production

Abstract

A shift from fossil fuels to renewable energy sources is essential to reduce global greenhouse gas emissions and climate change effects. Biofuels represent a promising low-carbon alternative for sectors that are hard to electrify, such as freight transport or aviation. This work investigates possible pathways for increasing the value of biomass at a Kraft pulp mill, focusing on black liquor and bark streams. Mathematical programming is coupled with superstructure optimization and systematic solution exploration to identify meaningful process configurations. The analysis of solutions under market variations allows for the identification of robust and competitive configurations for the co-production of pulp and fossil fuel alternatives. The results show that the integration of biorefineries in pulp mills results in better resource use and higher energy efficiency - diversifying the product portfolio and providing bio-based fuel products to the market while being economically viable. By incorporating fuel production in the conventional Kraft process, the carbon conversion efficiency of the mill can be increased from 48% to up to 67%. Extending the analysis, up to 2% of the European road freight transportation fuel could be provided with combined pulp and fuel production, and 5% of the worldwide fuel demand for passenger aviation.

Closing the balance – on the role of integrating biorefineries in the future energy system

“…The superstructure deployed to generate solutions is adapted and enhanced from Granacher et al , 23 where the addition of fuel synthesis process units to a Kraft pulp mill is explored.…”

“…In the Kraft mill superstructure developed in ref. 23, bark can be gasified and resulting producer gas can be upgraded to various biofuels, whereas for black liquor, hydrothermal gasification is considered. For all enabled biofuel production routes in the superstructure, upgrading and selling of crude fuel is included.…”

Biodiesel from Bark and Black Liquor—A Techno-Economic, Social, and Environmental Assessment

“…The models of the BtL processes, considering relevant mass flows, flow compositions, heat and electricity demands, were integrated with a pulp mill model, yielding a superstructure for pulp production and potential fuel synthesis [31,32]. Economic optimization was applied to determine the process design for different scenarios [31,32]. The superstructure of process models and the solution generation approach were based on the work of Granacher et al [31,32].…”

“…Economic optimization was applied to determine the process design for different scenarios [31,32]. The superstructure of process models and the solution generation approach were based on the work of Granacher et al [31,32]. A summary of the process models for BtL (adapted from Granacher et al [31]) relevant to this research follows.…”

“…The superstructure of process models and the solution generation approach were based on the work of Granacher et al [31,32]. A summary of the process models for BtL (adapted from Granacher et al [31]) relevant to this research follows. Further details can be found in [31,32] and in the Supplementary Materials.…”