Mitigating the climate impact from aviation remains one of the tougher challenges in adapting society to fulfill stated climate targets. Long-range aviation cannot be electrified for the foreseeable future and the effects of combusting fuel at high altitude increase the climate impact compared to emissions of green-house gasses only, which further limits the range of sustainable fuel alternatives. We investigate seven different pathways for producing aviation biofuels coupled with either bio-energy carbon capture and storage (BECCS), or bio-energy carbon capture and utilization (BECCU). Both options allow for increased efficiency regarding utilization of feedstock carbon. Our analysis uses process-level carbon- and energy balances, with carbon efficiency, climate impact and levelized cost of production (LCOP) as primary performance indicators. The results show that CCS can achieve a negative carbon footprint for four out of the seven pathways, at a lower cost of GHG reduction than the base process option. Conversely, as a consequence of the electricity-intensive CO2 upgrading process, the CCU option shows less encouraging results with higher production costs, carbon footprints and costs of GHG reduction. Overall, pathways with large amounts of vented CO2, e.g., gasification of black liquor or bark, as well as fermentation of forest residues, reach a low GHG reduction cost for the CCS option. These are also pathways with a larger feedstock and corresponding production potential. Our results enable a differentiated comparison of the suitability of various alternatives for BECCS or BECCU in combination with aviation biofuel production. By quantifying the relative strengths and weaknesses of BECCS and BECCU and by highlighting cost, climate and carbon-efficient pathways, these results can be a source of support for both policymakers and the industry. © 2023 The Author(s)

This paper describes the development of a multiscale equivalent reactor network model for pressurized entrained flow biomass gasification to quantify the effect of operational parameters on the gasification process, including carbon conversion, cold gas efficiency, and syngas methane content. The model, implemented in the commercial software Aspen Plus, includes chemical kinetics as well as heat and mass transfer. Characteristic aspects of the model are the multiscale effect caused by the combination of transport phenomena at particle scale during heating, pyrolysis, and char burnout, as well as the effect of macroscopic gas flow, including gas recirculation. A validation using experimental data from a pilot-scale process shows that the model can provide accurate estimations of carbon conversion, concentrations of main syngas components, and cold gas efficiency over a wide range of oxygen-to-biomass ratios and reactor loads. The syngas methane content was most difficult to estimate accurately owing to the unavailability of accurate kinetic parameters for steam methane reforming.

Kraft lignin, a by-product from the production of pulp, is currently incinerated in the recovery boiler during the chemical recovery cycle, generating valuable bioenergy and recycling inorganic chemicals to the pulping process operation. Removing lignin from the black liquor or its gasification lowers the recovery boiler load enabling increased pulp production. During the past ten years, lignin separation technologies have emerged and the interest of the research community to valorize this underutilized resource has been invigorated. The aim of this review is to give (1) a dedicated overview of the kraft process with a focus on the lignin, (2) an overview of applications that are being developed, and (3) a techno-economic and life cycle asseeements of value chains from black liquor to different products. Overall, it is anticipated that this effort will inspire further work for developing and using kraft lignin as a commodity raw material for new applications undeniably promoting pivotal global sustainability concerns.

Entrained flow gasification of biomass has the potential to generate synthesis gas as a source of renewable chemicals, electricity, and heat. Nonetheless, formation of tar and soot is a major challenge for continuous operation due to the problems they cause at downstream of the gasifier. Our previous studies showed the addition of alkali in the fuel can bring significant suppression of such undesirable products.

The present work investigated, in a drop tube furnace, the effect of potassium on tar and soot formation (as well as on its intermediates) for three different types of fuels: an ash lean stemwood, a calcium rich bark and a silicon rich straw. The study focused on an optimal method for impregnating the biomass with potassium. Experiments were conducted for different impregnation methods; wet impregnation, spray impregnation, and solid mixing to investigate different levels of contact between the fuel and the potassium.

Potassium was shown to catalyze both homogenous and heterogeneous reactions. Wet and spray impregnation had similar effects on heterogeneous reactions (in char conversion) indicating that there was an efficient molecular contact between the potassium and the organic matrix even if potassium was in the form of precipitated salts at a micrometer scale. On the other hand, potassium in the gas phase led to much lower yields of C2 hydrocarbons, heavy tars and soot. These results revealed that potassium shifted the pathways related to tar and soot formation, reducing the likelihood of carbon to end up as soot and heavy tars by favouring the formation of lighter compounds such as benzene. A moderate interaction between the added potassium and the inherent ash forming elements were also observed: Potassium had a smaller effect when the fuel was naturally rich in silicon.

The combined results open the door to a gasification process that incorporates recirculation of naturally occurring potassium to improve entrained flow gasification of biomass.

The work investigates in a drop tube furnace the effect of potassium on carbon conversion for three different types of fuels: an ash lean stemwood, a calcium-rich bark and a silicon-rich straw. The study focuses on an optimal method for impregnating the biomass with potassium. The experiments are conducted for 3 different impregnation methods; wet impregnation, spray impregnation, and dry mixing to investigate different levels of contact between the fuel and the potassium. Potassium is found to catalyse both homogenous and heterogeneous reactions. All the impregnation methods showed a significant effect of potassium on heterogeneous reactions (char conversion). The fact that dry mixing of potassium in the biomass shows an effect reveals the existence of a gas-induced mechanism that supply and distributes potassium on the char particles. Concerning the effect of potassium on homogenous reactions, it is found that potassium in the gas phase leads to much lower yields of C2 hydrocarbons, heavy tars and soot. The results indicate that potassium reduces the likelihood of light aromatic to progress toward heavier polyaromatic hydrocarbons clusters, thereby inhibiting the formation of soot-like material. A moderate interaction between the added potassium and the inherent ash forming elements is also observed: Potassium has a smaller effect when the fuel is naturally rich in silicon. The combined results are of interest for the design of a gasification process that incorporates recirculation of naturally occurring potassium to improve entrained flow gasification of biomass. 

In this work, predictions from a reacting Computational Fluid Dynamics (CFD) model of a gasification reactor are compared to experimentally obtained data from an industrial pressurized black liquor gasification plant. The data consists of gas samples taken from the hot part of the gasification reactor using a water cooled sampling probe. During the considered experimental campaign, the oxygen-to-black liquor equivalence ratio (λ was varied in three increments, which resulted in a change in reactor temperature and gas composition. The presented numerical study consists of CFD and thermodynamic equilibrium calculations in the considered λ-range using boundary conditions obtained from the experimental campaign. Specifically, the influence of methane concentration on the gas composition is evaluated using both CFD and thermodynamic equilibrium. The results show that the main gas components (H 2, CO, CO2) can be predicted within a relative error of 5% using CFD if the modeled release of H2S and CH4 are specified a priori. In addition, the calculations also show that the methane concentration has large influence on the reactor outlet temperature and final carbon conversion.

This study evaluated the techno-economic performance and potential benefits of methanol production through catalytic gasification of forest residues and lignin. The results showed that while catalytic gasification enables increased cold gas efficiencies and methanol yields compared to non-catalytic gasification, the additional pre-treatment energy and loss of electricity production result in small or no system efficiency improvements. The resulting required methanol selling prices (90–130 €/MWh) are comparable with production costs for other biofuels. It is concluded that catalytic gasification of forest residues can be an attractive option as it provides operational advantages at production costs comparable to non-catalytic gasification. The addition of lignin would require lignin costs below 25 €/MWh to be economically beneficial.

Previous research has shown that alkali addition has operational advantages in entrained flow biomass gasification and allows for capture of up to 90% of the biomass sulfur in the slag phase. The resultant low-sulfur content syngas can create new possibilities for syngas cleaning processes. The aim was to assess the techno-economic performance of biofuel production via gasification of alkali impregnated biomass using a novel gas cleaning system comprised of (i) entrained flow catalytic gasification with in situ sulfur removal, (ii) further sulfur removal using a zinc bed, (iii) tar removal using a carbon filter, and (iv) CO2 reduction with zeolite membranes, in comparison to the expensive acid gas removal system (Rectisol technology). The results show that alkali impregnation increases methanol production allowing for selling prices similar to biofuel production from non-impregnated biomass. It was concluded that the methanol production using the novel cleaning system is comparable to the Rectisol technology in terms of energy efficiency, while showing an economic advantage derived from a methanol selling price reduction of 2–6 €/MWh. The results showed a high level of robustness to changes related to prices and operation. Methanol selling prices could be further reduced by choosing low sulfur content feedstocks.

Entrained flow gasification of black liquor combined with downstream-gas-derived synthesis of biofuels in Kraft pulp mills has shown advantages regarding energy efficiency and economic performance when compared to combustion in a recovery boiler. To further increase the operation flexibility and the profitability of the biofuel plant while at the same time increase biofuel production, black liquor can be co-gasified with a secondary feedstock (blend-in feedstock). This work has evaluated the prospects of producing biofuels via co-gasification of black liquor and different blend-in feedstocks (crude glycerol, fermentation residues, pyrolysis liquids) at different blend ratios. Process modelling tools were used, in combination with techno-economic assessment methods. Two methanol grades, crude and grade AA methanol, were investigated. The results showed that the co-gasification concepts resulted in significant increases in methanol production volumes, as well as in improved conversion efficiencies, when compared with black liquor gasification; 5–11 and 4–10 percentage point in terms of cold gas efficiency and methanol conversion efficiency, respectively. The economic analysis showed that required methanol selling prices ranging from 55 to 101 €/MWh for crude methanol and 58–104 €/MWh for grade AA methanol were obtained for an IRR of 15%. Blend-in led to positive economies-of-scale effects and subsequently decreased required methanol selling prices, in particular for low cost blend-in feedstocks (prices below approximately 20 €/MWh). The co-gasification concepts showed economic competitiveness to other biofuel production routes. When compared with fossil fuels, the resulting crude methanol selling prices were above maritime gas oil prices. Nonetheless, for fossil derived methanol prices higher than 80 €/MWh, crude methanol from co-gasification could be an economically competitive option. Grade AA methanol could also compete with taxed gasoline. Crude glycerol turned out as the most attractive blend-in feedstock, from an economic perspective. When mixed with black liquor in a ratio of 50/50, grade AA methanol could even be cost competitive with untaxed gasoline.

Previous research shows that alkali addition in entrained flow biomass gasification can increase char conversion and decrease tar and soot formation through catalysis. This paper investigates two other potential benefits of alkali addition: increased slag flowability and in situ sulfur capture. Thermodynamic equilibrium calculations show that addition of 2–8% alkali catalyst to biomass completely changes the chemical domain of the gasifier slag phase to an alkali carbonate melt with low viscosity. This can increase feedstock flexibility and improve the operability of an entrained flow biomass gasification process. The alkali carbonate melt also leads to up to 90% sulfur capture through the formation of alkali sulfides. The resulting reduced syngas sulfur content can potentially simplify gas cleaning required for catalytic biofuel production. Alkali catalyst recovery and recycling is a precondition for the economic feasibility of the proposed process and is effected through a wet quench. It is shown that the addition of Zn for sulfur precipitation in the alkali recovery loop enables the separation of S, Ca and Mg from the recycle. For high Si and Cl biomass feedstocks, an alternative separation technology for these elements may be required to avoid build-up.

Co-gasification of fast pyrolysis oil and black liquor can be used to increase the size and improve profitability of pulp mill integrated biorefineries. The acids present in pyrolysis oil limit the amount that can be mixed into black liquor without causing precipitation of the black liquor dissolved lignin. This work shows that a simple model based on pyrolysis oil total acid number, including weak phenolic acids, can be used to predict the maximum pyrolysis oil fraction in blends. The maximum oil fraction is 20-25% for typical pyrolysis oil but can be increased up to at least 50% mass, corresponding to 70% energy, by addition of base. Thermodynamic equilibrium calculations are used to understand the effects of blend composition, including any added base, on the performance of a commercial scale gasification process. A substantial increase in overall gasification efficiency is observed with increasing pyrolysis oil fraction.

This study compares several forest biomass-based biofuels and some electrofuels, for use in cars and trucks, in terms of economic and climate performance and resource efficiency from a Swedish perspective. Both dropin fuels possible to blend in conventional fuels and single molecule fuels requiring new vehicles and infrastructure are included. Mature costs for feedstock, production, distribution, and vehicles are included. There is no clear winner between drop-in and single-molecular fuels when considering both costs, GHG emissions and resource efficiency, neither for cars nor trucks. For trucks, both single-molecular fuels in the form of methanol and DME (dimethyl ether) and drop-in fuels in the form of diesel based on lignin and from hydropyrolysis perform best (given a process designed to reach high GHG performance). For cars drop-in fuels such as petrol produced from lignin or hydropyrolysis perform well, closely followed by the single molecular fuels methanol, DME and methane and some of the other drop-in fuels. For cars, where electrification is progressing fast, it is reasonable to apply the drop-in fuel strategy. For trucks, either continue with the drop-in fuel strategy or, due to uncertainties linked to new fuel production processes, invest in single molecule fuels such as methanol and DME.

The potential future role of different biofuels, hydrogen, and so-called electrofuels/power-to-X (produced by electricity, water, and carbon dioxide, CO2) in different transportation sectors remains uncertain. The CO2 abatement cost, i.e., the cost for reducing a certain amount of greenhouse gas (GHG) emissions, is central from a societal and business perspective, the latter specifically in the case of an emission reduction obligation system (like in Germany and Sweden). The abatement cost of a specific fuel value chain depends on the production cost and the GHG reduction provided by the fuel. This paper analyses the CO2 abatement costs for different types of biofuels, biomass-based jet fuels and electrofuels for road transport and aviation, relevant for the Swedish and EU context. Since most assessed alternative fuel pathways achieve substantial GHG emission reduction compared to fossil fuels, the fuel production cost is, in general, more important to achieve a low CO2 abatement cost. The estimated CO2 abatement cost ranges from -0.37 to 4.03 SEK/kgCO2 equivalent. Fuels based on waste feedstock, have a relatively low CO2 abatement cost. Fuel pathways based on electricity or electricity and biomass have relatively high CO2 abatement cost. The CO2 abatement cost for lignocellulosic based pathways generally ends up in between. 

The introduction of alkali catalyst during hydrothermal liquefaction (HTL) improves conversion and allows the aqueous liquid product to be used as gasification feedstock. This study investigates the effect of reaction temperature (240–300°C), sawdust mass fraction (9.1–25%) and reaction time (0–60 min) during K2CO3-catalytic HTL of pine sawdust. The highest biomass conversion (75.2% carbon conversion and 83.0% mass conversion) was achieved at a reaction temperature of 270°C, 9.1% sawdust mass fraction and 30 min reaction time; meanwhile, the maximum aqueous product (AP) yield (69.0% carbon yield and 73.5% mass yield) was found at a reaction temperature of 300°C, 9.1% sawdust mass fraction and 60 min reaction time. Based on the main experimental results, models for carbon and mass yields of the products were developed according to face-centered central composite design using response surface methodology. Biomass conversion and product yields had a positive correlation with reaction temperature and reaction time, while they had an inverse correlation with sawdust mass fraction. Further investigation of the effects of biomass/water and biomass/K2CO3 ratios revealed that both high water loading and high K2CO3 loading enhanced conversion and AP yield.

Promoting the deployment of forest-based drop-in and high blend biofuels is considered strategically important in Sweden but many aspects of the overall performance of the foremost production technologies are as yet unexamined. This paper evaluates the technology maturity, profitability, investment requirements, GHG performance and Swedish biofuel production potential of six commercially interesting forest-based biofuel production pathways.

Significant heterogeneity in technology maturity was observed. Lack of technical demonstration in industrially representative scales renders the liquefaction-hydrotreatment route for drop-in biofuels less mature than its gasification-catalytic upgrading counterpart. It is a paradox that short-term priority being accorded to pathways with the lowest technology maturity. Nth-of-a-kind investments in (a) gasification-based methanol, (b) hydropyrolysis-based petrol/diesel, and (c) lignin depolymerization-based petrol/diesel were profitable for a range of plant sizes. The profitability of pulp mill-integrated small gasification units (<100 MW) goes against the common perception of gasification being economically feasible only in large scales. New low-cost options for debottlenecking production at recovery boiler-limited kraft mills appear worth investigating. GHG emission reductions ranged from 66 to 95%; a penalty was incurred for high consumption of natural gas-based hydrogen. Swedish biofuel production potentials ranged from 4 to 27 TWh/y but a more feasible upper limit is 12–15 TWh/y.

As fossil-reliant industries turn to sustainable biomass for energy and material supply, the competition for biogenic carbon is expected to intensify. Using process level carbon and energy balance models, this paper shows how the capture of residual CO2 in conjunction with either permanent storage (CCS) or biofuel production (CCU) benefits fourteen largely residue-based biofuel production pathways. With a few noteworthy exceptions, most pathways have low carbon utilization efficiencies (30–40%) without CCS/U. CCS can double these numbers and deliver negative emission biofuels with GHG footprints below −50 g CO2 eq./MJ for several pathways. Compared to CCS with no revenue from CO2 sequestration, CCU can offer the same efficiency gains at roughly two-third the biofuel production cost (e.g., 99 EUR/MWh vs. 162 EUR/MWh) but the GHG reduction relative to fossil fuels is significantly smaller (18 g CO2 eq./MJ vs. −99 g CO2 eq./MJ). From a combined carbon, cost and climate perspective, although commercial pathways deliver the cheapest biofuels, it is the emerging pathways that provide large-scale carbon-efficient GHG reductions. There is thus some tension between alternatives that are societally best and those that are economically most interesting for investors. Biofuel pathways vent CO2 in both concentrated and dilute streams Capturing both provides the best environomic outcomes. Existing pathways that can deliver low-cost GHG reductions but generate relatively small quantities of CO2 are unlikely to be able to finance the transport infrastructure required for transformative bio-CCS deployment. CCS and CCU are accordingly important tools for simultaneously reducing biogenic carbon wastage and GHG emissions, but to unlock their full benefits in a cost-effective manner, emerging biofuel technology based on the gasification and hydrotreatment of forest residues need to be commercially deployed imminently. Copyright © 2022 Jafri, Ahlström, Furusjö, Harvey, Pettersson, Svensson and Wetterlund.

Forest-based biofuels are strategically important in forest-rich countries like Sweden but the technical performance of several promising production pathways is poorly documented. This study examines product yields and energy efficiencies in six commercially relevant forest-based “drop-in” and “high blend” biofuel production pathways by developing detailed spreadsheet energy balance models. The models are in turn based on pilot-scale performance data from the literature, supplemented with input from technology developers and experts. In most pathways, biofuel production is integrated with a market pulp mill and/or a crude oil refinery. Initial conversion is by pyrolysis, gasification or lignin depolymerization and intermediate products are upgraded by hydrotreatment or catalytic synthesis. While lignin oil (LO) hydrodeoxygenation had the highest expanded system efficiency, considerable uncertainty surrounds product yields owing to absence of suitable experimental data on LO upgrading. Co-feeding vacuum gas oil and fast pyrolysis oil in a fluidized catalytic cracker has a complex and uncertain effect on fossil yields, which requires further investigation. Co-locating bio-oil hydrotreatment at the refinery improves heat utilization, leading to higher system efficiencies. Explicit consideration of mill type and energy requirements is required to avoid performance misestimation as an assumption of energy surplus can confer a definite advantage.

Drop-in biofuels from forest by-products such as black liquor can help deliver deep reductions in transport greenhouse gas emissions by replacing fossil fuels in our vehicle fleet. Black liquor is produced at pulp mills that can increase their pulping capacity by upgrading some of it to drop-in biofuels but this is not well-studied. We evaluate the techno-economic and greenhouse gas performance of five drop-in biofuel pathways based on BL lignin separation with hydrotreatment or black liquor gasification with catalytic synthesis. We also assess how integrated biofuel production impacts different types of pulp mills and a petroleum refinery by using energy and material balances assembled from experimental data supplemented by expert input. Our results indicate that drop-in biofuels from black liquor part-streams can be produced for ~80 EUR2017/MWh, which puts black liquor on the same footing (or better) as comparable forest residue-based alternatives. The best pathways in both production routes have comparable costs and their principal biofuel products (petrol for black liquor gasification and diesel for lignin hydrotreatment) complement each other. All pathways surpass European Union's sustainability criteria for greenhouse gas savings from new plants. Supplementing black liquor with pyrolysis oil or electrolysis hydrogen can improve biofuel production potentials and feedstock diversity, but better economic performance does not accompany these benefits. Fossil hydrogen represents the cheaper option for lignin hydrotreatment by some margin, but greenhouse gas savings from renewable hydrogen are nearly twice as great. Research on lignin upgrading in industrial conditions is recommended for reducing the presently significant performance uncertainties. © 2020 The Authors

Dimethyl ether (DME), is an excellent diesel fuel that can be produced through gasification from multiple feedstocks. One particularly interesting renewable feedstock is the energy rich by-product from the pulping process called black liquor (BL). The concept of utilizing BL as gasifier feed, converting it via syngas to DME and then compensating the withdrawal of BL energy from the pulp mill by supplying biomass to a conventional combined heat and power plant, is estimated to be one of the most efficient conversion concepts of biomass to a renewable fuel on a well-to-wheel basis. This concept has been demonstrated by the four-year BioDME project, including field tests of DME-fueled heavy-duty trucks that are operated commercially. Up till the summer of 2013 more than 500 tons of BioDME has been produced and distributed to 10 HD trucks, which in total has run more than 1 million km in commercial service. © 2014 American Institute of Chemical Engineers Environ Prog, 33: 744–750, 2014

Demand for biofuels will likely increase, driven by intensifying obligations to decarbonize aviation and maritime sectors. Sustainable biomass is a finite resource, and the forest harvesting level is a topic of ongoing discussions, in relation to biodiversity preservation and the short-term role of forests as carbon sinks. State-of-the-art technologies for converting lignocellulosic feedstock into transportation biofuels achieves a carbon utilization rate ranging from 25% to 50%. Mature technologies like second-generation ethanol and gasification-based processes tend to fall toward the lower end of this spectrum. This study explores how electrification can enhance the carbon efficiency of biorefinery concepts and investigates its impact on energy, economics and greenhouse gas emissions. Results show that electrification increases carbon efficiency from 28% to 123% for gasification processes, from 28% to 45% for second-generation ethanol, and from 50% to 65% for direct liquefaction processes. Biofuels are produced to a cost range 60–140 EUR/MWh-biofuel, depending on the chosen technology pathway, feedstock and electricity prices. Notably, production in electrified biorefineries proves cost-competitive when compared to pure electrofuel (E-fuels) tracks. Depending on the selected technology pathway and the extent of electrification, a reduction in GHG emissions ranging from 75% to 98% is achievable, particularly when powered by a low-carbon electricity mix. 

The aim of this work was to develop a model of an integrated biomass-to-liquid process consisting of hydrothermal liquefaction, evaporation, gasification and Fischer-Tropsch synthesis process using lignocellulosic forest residues as feedstock to produce hydrocarbons suitable for upgrading into drop-in biofuels. The energy, mass and carbon efficiencies achieved were 35%, 20% and 32%, respectively. The Fischer-Tropsch crude carbon chain length distribution peaked at carbon chain length 10 with a heavy right tail, a profile favorable for upgrading to jet fuel. The life cycle assessment showed high greenhouse gas performance in the Norrbotten coastal area and in Kalmar, both in Sweden. The reduction of life cycle greenhouse gas emissions, compared to the fossil fuel comparator and according to the European Union Renewable Energy Directive II, amounted to 85-95% for the Fischer-Tropsch crude produced in Norrbotten, and to 92-97% in Kalmar, depending on transportation distances and feedstock used.