Journal: Energy Procedia

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Elsevier

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1876-6102

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2009 - 200942010 - 201989
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Publications 1 - 10 of 93
  • Integrated design of ORC process and working fluid using PC-SAFT and Modelica
    Item type: Conference Paper
    Tillmanns, Dominik; Gertig, Christoph; Schilling, Johannes; et al. (2017)
    Energy Procedia ~ 4th International Seminar on ORC Power Systems
    Organic Rankine Cycles (ORC) use low-temperature heat to generate electrical power. To use the full potential of a heat source, the ORC has to be tailored to the specific application. Tailoring a cycle means an integrated design of both process and working fluid. This integrated design leads to complex mixed-integer nonlinear program (MINLP) optimization problems. To avoid this complexity, working fluid candidates are commonly preselected using heuristic guidelines; subsequently, the process is optimized for the set of preselected working fluids. However, the preselection can fail, leading to suboptimal solutions. An approach for integrated design of ORC process and working fluid is the Continuous-Molecular Targeting–Computer-aided Molecular Design (CoMT-CAMD) approach. CoMT-CAMD employs the physically-based Perturbed-chain Statistical Associating Fluid Theory (PC-SAFT) equation of state as thermodynamic model of the working fluid. In PC-SAFT, each working fluid is described by a set of pure component parameters. In a first step, the so-called CoMT step, the discrete pure component parameters are relaxed resulting in a hypothetical optimal working fluid and the corresponding optimal process. In a second step, real working fluids with similar properties are identified using Computer-aided Molecular Design and a second-order Taylor approximation of the objective function around the hypothetical optimum. So far, the process models in CoMT-CAMD were implemented in a procedural programming language, which hinders the reusability, the use for more complex processes and dynamic simulations. In this work, we integrate CoMT-CAMD into the object-oriented modelling language Modelica. For this purpose, Modelica is directly linked to PC-SAFT. Thereby, already existing model libraries for Modelica can be used to model the ORC process. The resulting design approach is applied to the integrated design of an ORC process and working fluid for a geothermal power station.
  • The effect of second-order hydrodynamics on floating offshore wind turbines
    Item type: Conference Paper
    Roald, Line; Jonkman, Jason; Robertson, Amy; et al. (2013)
    Energy Procedia ~ DeepWind'2013 – Selected papers from 10th Deep Sea Offshore Wind R&D Conference
    Offshore winds are generally stronger and more consistent than winds on land, making the offshore environment attractive for wind energy development. A large part of the offshore wind resource is however located in deep water, where floating turbines are the only economical way of harvesting the energy. The design of offshore floating wind turbines relies on the use of modeling tools that can simulate the entire coupled system behaviour. At present, most of these tools include only first-order hydrodynamic theory. However, observations of supposed second-order hydrodynamic responses in wave-tank tests performed by the DeepCwind consortium suggest that second-order effects might be critical. In this paper, the methodology used by the oil and gas industry has been modified to apply to the analysis of floating wind turbines, and is used to assess the effect of second-order hydrodynamics on floating offshore wind turbines. The method relies on combined use of the frequency-domain tool WAMIT and the time- domain tool FAST. The proposed assessment method has been applied to two different floating wind concepts, a spar and a tension-leg-platform (TLP), both supporting the NREL 5-MW baseline wind turbine. Results showing the hydrodynamic forces and motion response for these systems are presented and analysed, and compared to aerodynamic effects.
  • Model-based Process Design of Adsorption Processes for CO2 Capture in the Presence of Moisture
    Item type: Conference Paper
    Hefti, Max; Marx, Dorian; Joss, Lisa; et al. (2014)
    Energy Procedia ~ 12th International Conference on Greenhouse Gas Control Technologies, GHGT-12
    Separation processes based on adsorption show potential in the field of carbon dioxide capture and utilization or storage. Model- based process design is a powerful tool to fully exploit this potential. In order to get an accurate description of the behavior of the processes in a fixed bed, a reliable description of the equilibrium adsorption is necessary. In this work the potential of two types of zeolites, 13X and ZSM-5, is investigated in regards to their use in a temperature swing adsorption process for a post- combustion capture application. To this end, the single component adsorption equilibrium of CO2, N2, and H2O vapor is presented along with appropriate isotherms describing the data. This allows for a comparison of the two sorbents with respect to their cyclic CO2 adsorption capacity and selectivity for CO2. Additionally, the competition for adsorption sites between CO2 and N2 is investigated by applying the ideal adsorbed solution theory (IAST) to predict the binary adsorption equilibrium on both sorbents. These predictions indicate a very high selectivity of 13X for CO2, making this a very promising sorbent for temperature swing adsorption in a post-combustion capture environment, with the caveat that it also strongly adsorbs water vapor. This strong affinity for water vapor may imply that a flue gas stream would have to be dried before it enters the adsorption unit.
  • Integration of process and solvent design towards a novel generation of CO2 absorption capture systems
    Item type: Conference Paper
    Oyarzún, Bernardo; Bardow, André; Groß, Joachim (2011)
    Energy Procedia ~ 10th International Conference on Greenhouse Gas Control Technologies
    A method for the integrated process and solvent design of absorption separation systems is proposed in this work. The method is employed here to improve the energetic performance of a pre-combustion CO2 absorption capture process by simultaneous optimization of process and solvent variables. In the proposed design method, the discrete nature of solvent molecules is relaxed avoiding the introduction of integer variables in the solution of the optimization problem. For this purpose, a molecular-based thermodynamic model, the perturbed-chain polar (PCPSAFT) equation of state, is used to establish a direct relationship between the process performance and the molecular characteristics of a hypothetical target solvent. Real solvent candidates are selected in a subsequent stage of molecular mapping by assessing substances from a data-base, using a Taylor approximation of the objective function. The simultaneous design method is shown to yield major improvements of the performance of CO2 absorption processes.
  • On the Potential of Phase-change Adsorbents for CO2 Capture by Temperature Swing Adsorption
    Item type: Conference Paper
    Joss, Lisa; Hefti, Max; Bjelobrk, Zoran; et al. (2017)
    Energy Procedia ~ 13th International Conference on Greenhouse Gas Control Technologies, GHGT-13
    The objective of this work is to assess the potential of a novel class of metal organic framework (MOF) materials recently introduced [McDonald et al., Nature, 2015, 519, 303] for post-combustion CO2 capture by temperature swing adsorption (TSA). In particular, we present figures for the process performance obtained from optimizing operating conditions of a four-step TSA cycle. Our results show that high purity and high recovery can be attained. Subsequently, we benchmark the performance in terms of energy consumption and productivity to a state-of-the-art TSA process using zeolite 13X [Joss. et al. Chem. Eng. Sci. under review]. While the energy consumption is similar, a higher productivity can be obtained using these MOF materials. Finally, we make a comparison to amine-scrubbing processes and show that, after applying heat integration, similar performance can be expected.
  • Thermoheliodome design, optimization and fabrication
    Item type: Conference Paper
    Read, Jake R.; Meggers, Forrest; Houchois, Nicholas; et al. (2015)
    Energy Procedia ~ 6th International Building Physics Conference, IBPC 2015
    The Thermoheliodome, a digitally fabricated radiant cooling pavilion, addresses the energy challenge of buildings through a novel form and concept. We control the effective radiant temperature of a large area by expanding the surface area through reflection, which minimizes convective losses. Our novel geometric analysis for capture and concentration of diffuse heat emission from bodies resulted in a cone-shaped ‘lamp’ form. The optimization resulted in a hexagonal array of 55 cones across a 6 meter dome, which expands radiant emission surface area by a factor of 6, shifting outdoor comfort perception with minimal losses to the outside air.
  • Geomechanical modeling of fault responses and the potential for notable seismic events during underground CO2 injection
    Item type: Conference Paper
    Rutqvist, Jonny; Cappa, Frederic; Mazzoldi, Alberto; et al. (2013)
    Energy Procedia ~ GHGT-11 Proceedings of the 11th International Conference on Greenhouse Gas Control Technologies
    We summarize a number of recent modeling studies related to the potential for fault reactivations and induced seismicity during underground CO2 injection. The model simulations were conducted using coupled multiphase fluid flow and geomechanics, including fault-frictional weakening enabling analysis of sudden (seismic) fault rupture, with some of the numerical analyses extended to dynamic modeling of seismic source, wave propagation, and ground motion. These model simulations show that the critical factors in determining the likelihood and magnitude of such an event are the local in situ stress field, fault orientation and size, fault strength, and injection pressure. We analyzed the case of activation of a 1 km long minor fault that might have gone undetected during the site investigation and show that the maximum seismic magnitudes would likely be less than about 3.6, even if the entire 1 km fault would to be activated. We then include seismic wave propagation generated by the rupture and show how the acceleration and deceleration of the rupture generate waves and result in a peak ground acceleration of about 0.1 g, except for a localized –0.6 g of horizontal peak acceleration at the faults intersection with the ground surface. The modeling shows that these are high frequency events that would not cause any substantial damage but could certainly be felt by the local population. We may also considered that fault reactivation, even associated with relatively small seismic or aseismic events, could potentially increase CO2 seepage out of the intended storage complex and therefore reduce the effectiveness of a CO2 storage operation. Under these circumstances, we recommend a staged, learn-as-you-go approach, involving a gradual increase of injection rates combined with continuous monitoring of geomechanical changes, as well as siting beneath a multiple layered overburden for multiple flow barrier protection, should an unexpected deep fault activation occur.
  • Pumped heat electricity storage: potential analysis and orc requirements
    Item type: Conference Paper
    Roskosch, Dennis; Atakan, Burak (2017)
    Energy Procedia ~ 4th International Seminar on ORC Power Systems
    The rising share of renewable energy sources in power generation leads to the need of energy storage capacities. In this context, also some interest in thermal energy storages, especially in a concept called pumped heat electricity storage (PHES), arises. One possible design of such a PHES system consists of a compression heat pump, a thermal storage and an organic Rankine cycle (ORC). The present work analyses the general thermodynamic potential and limits of such a system and deals with the unusual requirements for the ORC. The potential analysis starts with the optimal case of combining two Carnot cycles with irreversible heat transfer. It is found that the efficiency of the entire process increases with increasing storage temperature and in general roundtrip efficiencies up to 70 % are predicted. Afterwards the cycles are transferred to cycles that are more realistic by considering technical aspects and a hypothetical working fluid which is optimized by an inverse engineering approach. This leads to lowered roundtrip efficiencies, which now, decrease with increasing storage temperatures. In a second step the specific ORC requirements as part of a PHES are considered, emphasizing the working fluid parameters. Especially, the use of a latent thermal energy storage leads to an ORC design differing from common (e.g. geothermal) applications. It is shown that the efficiency of the ORC and of the entire process strongly depends on the superheating at the expander inlet; here, the superheating must be held as small as possible, contrary to ORCs using common heat sources.
  • Comparison of commercial and new adsorbent materials for pre-combustion CO2 capture by pressure swing adsorption
    Item type: Conference Paper
    Schell, Johanna; Casas, Nathalie; Marx, Dorian; et al. (2013)
    Energy Procedia ~ GHGT-11 Proceedings of the 11th International Conference on Greenhouse Gas Control Technologies
    The IGCC technology (Integrated Gasification Combined Cycle) with pre-combustion CO2 capture is a promising approach for near-zero CO2 emission power plants to be realized in the near future. A key challenge within this technology is the separation of the CO2/H2 gas mixture resulting from the water gas shift reaction that follows the gasification of coal. For the CO2 stream a purity of about 95% is required; additionally a CO2 capture rate of 90% is desired, which implies that both streams, H2 and CO2, are required at rather high purity (∼95%). In contrast to post- combustion capture from power plants, where a large gas stream at low pressure and low CO2 content has to be treated, in pre-combustion capture a gas mixture at up to 40 bar has to be separated; therefore an adsorption based process, such as pressure swing adsorption (PSA), constitutes a promising method for CO2 removal from H2. In this work, new materials, namely USO-2-Ni MOF, UiO-67/MCM-41 Hybrid and MCM-41, are characterized in terms of equilibrium adsorption isotherms. Excess adsorption isotherms of CO2 and H2 on these materials are measured at different temperatures (25 °C 140 °C) and in a wide pressure range (up to 150 bar). The experimental data are then described with a suitable isotherm model, in our case Langmuir, Sips and Quadratic. In addition, the cyclic working capacity of CO2 on each material is computed as a further assessment of the suitability of these materials for pre-combustion capture.
  • Modelling the Energy Future of Switzerland after the Phase Out of Nuclear Power Plants
    Item type: Conference Paper
    Díaz Redondo, Paula; van Vliet, Oscar (2015)
    Energy Procedia ~ European Geosciences Union General Assembly 2015 - Division Energy, Resources and Environment, EGU 2015
    This paper evaluates the feasibility of future electricity scenarios drawn in the Swiss Energy Strategy 2050. These scenarios are characterized by a nuclear phase-out and high shares of renewables. We use Calliope, a linear programming model, special to model transition to renewables. Results show that it will be impossible to cover future demand only with domestic production, even if Switzerland reduces the consumption as envisaged. The daily profile of solar and limited capacity of wind lead to scenarios with maximum generation during peak hours. Moreover, we find a need to rearrange generation by flexible technologies to cover future demand.
Publications 1 - 10 of 93