Shaping Future Opportunities for Biomass Gasification - The Role of Integration

A considerable number of studies indicate that biofuels produced from lignocellulosic biomass will most probably play a significant role in achieving the climate goals stated in the Paris agreement. Several candidate technologies could be implemented to produce these fuels, and one of the most promising is thermal gasification. Gasification is a robust technology that has been demonstrated successfully at industrial scale and shown to be able to achieve high conversion efficiencies and relatively low production costs. However, there are currently no large-scale plants in operation or under construction, since such plants are unable to compete with their fossil counterparts under current conditions. This thesis explores how different forms and levels of integration could facilitate deployment of large-scale biomass gasification for future production of biofuels. Three levels of integration are considered, a technological level, a process level and a value-chain level. Different integration concepts are then assessed with respect to these levels. From a technology perspective, the implications of switching feedstock are studied. At the process level, heat integration with existing sawmill plants as well as integration of an electrolyser unit with a gasification plant are investigated. From a value chain perspective, integration with the value chain for producing fuels for use the Swedish iron and steel industry is considered, as well as integration with the electricity system. The results presented in this thesis indicate that the different integration options investigated can contribute to making biofuel production through biomass gasification more cost-efficient. Switching gasifier feedstock can lower biofuel production costs by up to 42%. Efficient heat integration with sawmills is the most attractive option to decrease production costs from a plant-owner perspective. Integration of a flexible gasification unit equipped with CO2 capture capacity for either long-term storage or re-use as feedstock for biomethane production through the Sabatier reaction with hydrogen produced through electrolysis increases the economic competitiveness of the gasification unit, while stimulating increased construction of renewable electricity generation capacity. The thesis thus demonstrates that well-planned integration of biomass gasification plants can contribute significantly to making the technology more competitiv

Cost-Effective Pathways for Gasification-Based Production of Biofuels

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

Large-scale introduction of forest-based biorefineries: Actor perspectives and the impacts of a dynamic biomass market

Large-scale implementation of forest-based biofuel production will have an impact on biomass prices, something which in turn will affect biofuel production costs. The profitability of emerging biofuel production technologies is usually assessed using techno-economic or market approaches. While techno-economic approaches have a detailed description of technologies within plant-level or supply chain system boundaries, they build on exogenously given static biomass prices. Conversely, market approaches have a consistent description of the economic system including market interactions for prices within local or national boundaries, but they generally lack technological depth. This paper combines these two approaches using an iterative framework for a case study optimising the production cost of liquefied biomethane (LBG) using different configurations of sawmill-integrated biomass gasification. Cost estimates are developed using system boundaries surrounding a LBG production plant, and the Swedish national borders, reflecting the plant-owner and policymaker perspectives, respectively. The results show that different plant configurations are favoured depending on the choice between minimising the biofuel production cost for the plant-owner or for the policymaker. Market dynamics simulated by the iterative procedure show that a direct policy support of 36–56 EUR/MWh would be needed to sustain large-scale LBG production, which is 12–31% higher than the necessary policy support estimated based on static biomass prices

Investigation of the strengthening mechanism in 316L stainless steel produced with laser powder bed fusion

Of the many benefits of the additive manufacturing process, laser powder bed fusion (L-PBF) has specifically been shown to produce hierarchical microstructures that circumvent the common strength-ductility trade-off. Typically, high strength materials have limited ductility, and vice versa. The L-PBF microstructure, consisting of fine cells, is formed during the rapid solidification of the laser powder bed fusion process. The cell boundaries are often characterized by the segregation of alloying elements and a dislocation network. While there are a number of works describing the strengthening mechanisms in L-PBF-produced 316L, there are still some gaps in understanding the effect of stress-relief and annealing at various annealing temperatures (400, 800 and 1200 \ub0C) on the plastic strain accumulation during deformation. In this study, the authors evaluated strain partitioning using electron backscatter diffraction and kernel average misorientation maps. The results show strain partitioning to be dependent on both the annealing temperature and the pre-straining of samples. Further, the results indicated that the dislocation structure was stable until 400 \ub0C, whereas at 800 \ub0C strain was no longer detected at the cell boundaries. Similarly, after the heat treatment at 800 \ub0C, elemental segregation at the cell walls was no longer detectable. Upon straining, the boundaries of as-built and annealed samples at 400 and 800 \ub0C registered accumulation of additional strain as compared to the unstrained states. The results demonstrate that even a weak array of dislocations along the cell walls can successfully pin dislocations, albeit at a reduced capability relative to the co-existent dislocation and segregate structures found in microstructures of the as-built and annealed samples at 400 \ub0C

Effects of Temperature on the Evolution of Yield Surface and Stress Asymmetry in A356–T7 Cast Aluminium Alloy

As the electrification of vehicle powertrains takes prominence to meet stringent emission norms, parts of internal combustion engines like cylinder heads are subjected to an increased number of thermal load cycles. The cost-effective design of such structures subjected to cyclic thermo-mechanical loads relies on the development of accurate material models capable of describing the continuum deformation behaviour of the material. This study investigates the effect of temperature on the evolution of flow stress under cyclic loading in A356-T7 + 0.5% Cu cast aluminium alloy commonly used in modern internal combustion engine cylinder heads. The material exhibits peak stress and flow stress asymmetry with the stress response and flow stress of the material under compressive loading higher than under tension. This peak and flow stress asymmetry decrease with an increase in temperature. To compare this stress asymmetry against conventional steel, cyclic strain-controlled fatigue tests are run on fully pearlitic R260 railway steel material. To study the effect of mean strain on the cyclic mean stress evolution and fatigue behaviour of the alloy, tests with tensile and compressive mean strains of +0.2% and −0.2% are compared against fully reversed (Rε\ua0= −1) strain-controlled tests. The material exhibits greater stress asymmetry between the peak tensile and peak compressive stresses for the strain-controlled tests with a compressive mean strain than the tests with an identical magnitude tensile mean strain. The material exhibits mean stress relaxation at all temperatures. Reduced durability of the material is observed for the tests with tensile mean strains at lower test temperatures of up to 150 \ub0C. The tensile mean strains at elevated temperatures do not exhibit such a detrimental effect on the endurance limit of the material

Deformation and fatigue behaviour of A356-T7 cast aluminium alloys used in high specific power IC engines

The continuous drive towards higher specific power and lower displacement engines in recent years place increasingly higher loads on the internal combustion engine materials. This necessitates a more robust collection of reliable material data for computational fatigue life prediction to develop reliable engines and reduce developmental costs. Monotonic tensile testing and cyclic stress and strain-controlled testing of A356-T7 + 0.5 wt.% Cu cast aluminium alloys have been performed. The uniaxial tests were performed on polished test bars extracted from highly loaded areas of cast cylinder heads. The monotonic deformation tests indicate that the material has an elastic-plastic monotonic response with plastic hardening. The strain controlled uniaxial low cycle fatigue tests were run at multiple load levels to capture the cyclic deformation behaviour and the corresponding fatigue lives. The equivalent stress-controlled fatigue tests were performed to study the influence of the loading mode on the cyclic deformation and fatigue lives. The two types of tests exhibit similar fatigue lives and stress-strain responses indicating minimal influence of the mode of loading in fatigue testing of A356 + T7 alloys. The material exhibits a non-linear deformation behaviour with a mixed isotropic and kinematic hardening behaviour that saturates after the initial few cycles. There exists significant scatter in the tested replicas for both monotonic and cyclic loading

Effect of Temperature on Deformation and Fatigue Behaviour of A356–T7 Cast Aluminium Alloys Used in High Specific Power IC Engine Cylinder Heads

Aggressive downsizing of the internal combustion engines used as part of electrified powertrains in recent years have resulted in increasing thermal loads on the cylinder heads and consequently, the susceptibility to premature thermo-mechanical fatigue failures. To enable a reliable computer aided engineering (CAE) prediction of the component lives, we need more reliable material deformation and fatigue performance data. Material for testing was extracted from the highly loaded valve bridge area of specially cast cylinder heads to study the monotonic and cyclic deformation behaviour of the A356–T7 + 0.5% Cu alloy at various temperatures. Monotonic tensile tests performed at different temperatures indicate decreasing strength from 211 MPa at room temperature to 73 MPa at 300 \ub0C and a corresponding increase in ductility. Completely reversed, strain controlled, uniaxial fatigue tests were carried out at 150, 200 and 250 \ub0C. A dilatometric study carried out to study the thermal expansion behaviour of the alloy in the temperature range 25–360 \ub0C shows a thermal expansion coefficient of (25–30) 7 10−6\ua0\ub0C−1. Under cyclic loading, increasing plastic strains are observed with increasing temperatures for similar load levels. The experimental data of the cyclic deformation behaviour are calibrated against a nonlinear combined kinematic–isotropic hardening model with both a linear and non-linear backstress

Thermomechanical testing and modelling of railway wheel steel

Studies of thermal effects of tread braking on railway wheels show that the wheel temperatures may reach above 600 \ub0C, at which the mechanical properties of the wheel steel are significantly impaired. Computational models that simulate the thermomechanical behaviour of the wheels are commonly based on results from laboratory tests which do not reflect actual in-service scenarios. Anisothermal testing and modelling are omitted due to the difficulties in designing relevant experiments and implementation of the results. In this paper, a preexisting numerical material model is extended in order to implement fully anisothermal behaviour. This is done by performing several thermomechanical experiments mimicking real-world service and worst-case scenarios ranging from room temperature up to 650 \ub0C. The results from the laboratory testing are then used in combination with data from traditional isothermal tests to optimise the numerical material model by calibrating its material parameters. As part of this process it was found necessary to include a time- and temperature-dependent, non-recoverable (irreversible) mechanism for material softening and microstructural changes which occur above 400 \ub0C. Finite element simulations with the material model using the new parameters and the softening law show markedly improved adherence to anisothermal and strain-controlled experimental results compared to the preexisting model(s). The results demonstrate that anisothermal testing is a requirement for models that are intended to simulate material behaviour for thermomechanical loads and thermally induced microstructural changes

Homogenization based macroscopic model of phase transformations and cyclic plasticity in pearlitic steel

In this contribution macroscopic modeling of phase transformations and mechanical behavior of low alloy steels are developed and investigated. Such modeling is of importance in simulations of transient thermo-mechanical processes which can cause phase transformations, examples from the railway industry include train braking induced frictional heating as well as rail grinding and welding operations. We adopt a modeling approach which includes phase transformation kinetics and individual constitutive models for the phases in combination with different homogenization methods. Algorithmic implementations of the isostrain, isostress and self-consistent homogenization methods are presented and demonstrated in finite element simulations of a laser heating experiment. Stress field results from the different homogenization methods are compared against each other and also against experimental data. The importance of including transformation induced plasticity in the modeling is highlighted, as well as the multi-phase stages of the heating and cooling

The role of biomass gasification in the future flexible power system – BECCS or CCU?

In this work we study if biomass gasification for production of advanced biofuels can also play a role in managing variability in the electricity system. The idea is a CCU/power-to-gas concept to enhance methane production from biomass gasification. The suggested process is flexible in that CO2 not used for methane production can be stored through a BECCS concept that implies negative GHG emissions. For this purpose, rigorous models of three different gasification process configurations were simplified through surrogate modeling and integrated into a dynamic optimization model of regional electricity systems. The results show the diverse advantages of flexible operation between CCU and BECCS and that it is economically beneficial for the system to invest in gasification at the investigated levels of CO2 charge. The gasification option also provides value for low-priced electricity and thus stimulate increased investments in renewable electricity generation, which indicates the importance of considering geographical diversities in the assessment and highlights the importance of studying this type of concept with a time-resolved model. It is clear that the BECCS option is the most used, however, the limited quantities of CO2 used for the CCU option has a large impact on the investments made in the electricity system