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As political will gathers behind the ideal of rapid decarbonization, the future looks increasingly dim for oil & gas exporters. CCS offers a pathway for continued operation in the longer-term as the world decarbonizes, but this is not a straightforward solution. Many oil & gas importers are opposed to CCS and are instead looking to replace oil & gas imports with greener alternatives. The alternative solution of converting cheap locally produced hydrocarbons to hydrogen and electricity with CCS substantially increases the cost and complexity of energy exports. This study explores an alternative solution: local utilization of clean hydrogen from natural gas to produce energy intensive industrial products like steel. Such products are much easier to export than hydrogen or electricity. The system-scale modelling assessment presented in this study shows that the energy costs of clean steel using blue hydrogen in Norway is 174 €/ton cheaper than when it is produced using green hydrogen in Germany. This difference amounts to about a third of total steel production costs, giving oil & gas exporters like Norway a large competitive advantage.

Is there a place for today’s fossil fuel exporters in a low-carbon future? This study explores trade channels between energy exporters and importers using a novel electricity-hydrogen-steel energy systems model calibrated to Norway, a major natural gas producer, and Germany, a major energy consumer. Under tight emission constraints, Norway can supply Germany with electricity, (blue) hydrogen, or natural gas with re-import of captured CO2. Alternatively, it can use hydrogen to produce steel through direct reduction and supply it to the world market, an export route not available to other energy carriers due to high transport costs. Although results show that natural gas imports with CO2 capture in Germany is the least-cost solution, avoiding local CO2 handling via imports of blue hydrogen (direct or embodied in steel) involves only moderately higher costs. A robust hydrogen demand would allow Norway to profitably export all its natural gas production as blue hydrogen. However, diversification into local steel production, as one example of easy-to-export industrial base products, offers an effective hedge against the possibility of lower European blue hydrogen demand. Thus, it is recommended that hydrocarbon exporters like Norway consider a strategic energy export transition to a diversified mix of blue hydrogen and climate-neutral industrial base products.

Chemical looping combustion (CLC) is a promising technology for hydrocarbon fuel combustion with integrated CO2 capture. The CLC process imposes almost no direct energy penalty for separating CO2, but a large indirect energy penalty is encountered when CLC reactors are integrated into a combined cycle power plant due to the maximum reactor operating temperature that is far below the inlet temperature of modern gas turbines. Previous works have shown that additional fuel combustion after the CLC reactors can almost eliminate this energy penalty, although more expensive hydrogen fuel must be used to avoid CO2 emissions. This study conducts CFD simulations of an added combustor fired with hydrogen, focusing mainly on mechanisms to reduce NOx formation. Three mechanisms are explored: 1) a greater number of fuel injectors, 2) increased turbulence, 3) and lower O2 content of the air stream due to flue gas recirculation. Option 2 proved the most effective at reducing NOx, followed by Option 3. When combined, these mechanisms could result in NOx emissions below 50 ppm using a very compact combustor. In conclusion, low-NOx operation of the added combustor appears to be feasible and it is recommended for inclusion in future studies of CLC combined cycle power plants.

Hydrogen is identified as one of the clean energy carriers in the future energy scenario. This work presents a process to produce low cost hydrogen with CO2 capture using gas switching reforming (GSR). The process steps include GSR, water-gas shift, pure hydrogen recovery in pressure-swing adsorption process and CO2 and hydrogen compression trains. The overall process, denoted as GSR-H2, produces 99.999% pure hydrogen with >96% CO2 capture. In this study, GSR-H2 is compared economically with the conventional steam-methane reforming (SMR) plant that produces hydrogen without CO2 capture. GSR-H2 produces 10% more hydrogen when compared to the SMR plant, but consumes significant imported electricity. The cost of hydrogen produced from the GSR-H2 and SMR plant is similar (1.67 €/kg-H2) with a CO2 tax of only 20 €/ton, even with GSR-H2 being a near zero emission plant. In a future energy scenario where the CO2 emission tax is high and the electricity price is low, GSR-H2 will significantly outperform the conventional SMR plant.

Filtered Two Fluid Models (fTFMs) aim to enable accurate industrial-scale simulations of fluidized beds by means of closures accounting for the effects of bubbles and clusters. The present study aims to improve anisotropic closures for the drift velocity, which is the primary sub-grid effect altering the filtered drag force, by deriving increasingly complex closures by considering additional independent variables (markers). Three different anisotropic closures, as well as an isotropic closure, are evaluated. A priori tests revealed a significant increase in the predictive capability of the closures as the complexity, in terms of the number of markers considered, increases. However, this improvement is relatively small when compared to the effect of considering anisotropy. Next, a posteriori tests were completed by comparing coarse-grid simulations of bubbling, turbulent and core-annular fluidization against benchmark resolved TFM simulations. This analysis shows good performance of all anisotropic closures, with negligible to minor effects of increasing the drag closure’s complexity by considering additional markers. On the other hand, the isotropic closure lacks generality and shows poor grid independence behaviour. It is therefore concluded that it is essential to include important physical effects, such as anisotropy, in fTFM closures, while complexity in terms of the number of markers considered is of lesser importance.

This paper focuses on the techno-economic comparison of gas-fired combined cycle power plants with CO2 capture and tworeforming methods, chemical looping reforming (CLR) and gas-switching reforming (GSR). The overall processes are denoted asCLR-CC and GSR-CC respectively. The net electrical efficiency of the CLR-CC and GSR-CC is 42.1% and 46.2% respectively.Anyhow, with improvements in the gas turbine configuration, the net electrical efficiency improves by 2.5%. GSR-CC has ahigher CO2 avoidance (>95%). The levelised cost of electricity (LCOE) for CLR-CC is lower than that of GSR-CC for basedload operation of the power plant. Anyhow, GSR-CC provides flexibility in terms of output, electricity or pure H2. The capitalrequirement in the GSR-CC is higher due to the requirement of multiple standalone reactors to maintain a steady flow of thesyngas produced from the GSR. The LCOE of both the processes is sensitive to the fuel cost. Further improvements in the GSRCCprocess can make the process competitive to post-combustion capture. QC 20191127

Filtered modelling of dynamic gas-particle flows has been actively studied by various groups around the world for more than a decade. Even so, the great complexity of this field of study means that several important knowledge gaps still exist. This thesis represents a significant step forward by closing several of the most important knowledge gaps through the development and rigorous assessment of new closures via detailed a priori and a posteriori analyses. The resulting set of filtered closures clearly outperforms the current state of the art, resulting in several valuable conclusions and recommendations. The primary conclusion from the present work is related to the critical importance of accounting for anisotropy in the filtered closures for drag and solids mesoscale stresses. For the filtered drag force, it was found that conventional isotropic closures strongly underpredict the drag correction in the directions perpendicular to gravity. A new formulation based on the drift velocity concept was found to account for this anisotropic effect in an efficient and natural manner. For the solids mesoscale stresses, the present work confirmed that the conventional approach based on the Boussinesq approximation results in large errors. In fact, studies showed that coarse grid simulations completely neglecting the solids mesoscale stresses perform better than those relying on the Boussinesq-based approach. Based on this knowledge, a new closure formulation was devised, conveniently allowing the prediction of the anisotropic solids mesoscale stresses via a single expression. Findings from the present study also challenged other conventions in the field. Firstly, the use of the filtered slip velocity as a second marker in the filtered drag force closure was found to lead to poor model performance. Secondly, a filter size to grid size ratio of unity appears to be the fundamentally correct ratio instead of the commonly employed ratio of 2. And thirdly, the 2D models derived in this work outperformed a 3D model from the literature in a validation study, suggesting that domain size independence of resolved simulations is more important than performing simulations in 3D. For reactive flows, the present work showed that a relatively simple closure can accurately predict the filtered reaction rate. In addition, the closure for the mesoscale species dispersion rate used in the filtered species transport equation was shown to have only a minor effect on reactor performance predictions. However, coarse grid reactive simulations were sensitive to the accuracy of the hydrodynamic filtered closures employed. Good hydrodynamic modelling is therefore the most important prerequisite for accurate large scale reactor performance predictions. Despite the progress made in this thesis, some important knowledge gaps persist. Firstly, this study did not attempt to quantify the generality of the proposed closures to flow situations with different particle and fluid properties. Such studies are required before the newly proposed closures can be recommended for use in reactors with particle and fluid properties that are very different from the FCC-type system considered in the present work. Secondly, an important effect related to the ratio of the domain width to the length of macro-clusters resolved in coarse grid simulations was identified. This effect required the use of a larger filter size to grid size ratio in narrow domains and further studies are required to find a general solution to this challenge. However, informed application of the anisotropic closures proposed in this thesis to real fluidized bed reactor problems can already be recommended. Experience from such studies can further accelerate the development of closures for filtered models towards the goal of their ubiquitous deployment for design, optimization and scale-up of fluidized bed reactors in industry.

CFD simulations of fluidized bed reactors are generally limited to the laboratory scale because of the fine grid sizes that are required to resolve complex particle clustering phenomena. The filtered Two Fluid Model (fTFM) approach has recently emerged as a promising method for allowing reasonable predictions of largescale fluidized beds. This paper presents a verification study of new two-marker fTFM closures. In general, the fTFMs matched well to the resolved simulations. It was shown that the two-marker models significantly increased the predicted degree of phase segregation (resolved in coarse grid simulations), and hence have superior capabilities compared to simpler one-marker models. Also, the two-marker model predicted a more dynamic transient flow behaviour. However, further work is recommended to extend the present study over a wider range of flow conditions The authors would like to express their gratitude for the financial support from the European Commission under the NanoSim grant (project number: 604656), as well as for the computational resources provided at NTNU by UNINETT Sigma2 AS, https://www.sigma2.no.

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Fluidized bed simulations carried out within the Kinetic Theory of Granular Flows framework utilize a number of model coefficients which are strongly case dependent and difficult to determine accurately. The most important of these are the specularity coefficient (the degree of friction at the wall) and the particle-particle restitution coefficient (inelasticity of inter-particle collisions). This paper demonstrated that modification of these coefficients can trigger a regime change in very narrow and fast risers, thereby introducing a great amount of uncertainty. For situations sufficiently far from the dilute transport regime, however, sudden regime changes were not observed and the influence of these unknown parameters is more systematic. It was shown that in the case of wide bubbling beds, the effect of these unknown model coefficients can become negligible, making these reactors attractive for simulation studies. Faster and narrower geometries, on the other hand, exhibited greater sensitivity to changes in the specularity coefficient and particle-particle restitution coefficient, thereby introducing ever-increasing quantities of uncertainty stemming from these unknown model coefficients. ACKNOWLEDGEMENTS. The authors gratefully acknowledge the research funding received from the Research Council of Norway as well as the Notur supercomputing facilities used to carry out the expensive riser simulations in this paper.

Hydrogen is identified as one of the clean energy carriers in the future energy scenario. This work presents a process to produce low cost hydrogen with CO2 capture using gas switching reforming (GSR). The process steps include GSR, water-gas shift, pure hydrogen recovery in pressure-swing adsorption process and CO2 and hydrogen compression trains. The overall process, denoted as GSR-H2, produces 99.999% pure hydrogen with >96% CO2 capture. In this study, GSR-H2 is compared economically with the conventional steam-methane reforming (SMR) plant that produces hydrogen without CO2 capture. GSR-H2 produces 10% more hydrogen when compared to the SMR plant, but consumes significant imported electricity. The cost of hydrogen produced from the GSR-H2 and SMR plant is similar (1.67 €/kg-H2) with a CO2 tax of only 20 €/ton, even with GSR-H2 being a near zero emission plant. In a future energy scenario where the CO2 emission tax is high and the electricity price is low, GSR-H2 will significantly outperform the conventional SMR plant.