267 results found
Rhazaoui K, Cai Q, Shearing P, et al., 2011, Solid Oxide Fuel Cell Electrode 3D Microstructure and Performance Modeling, 12th International Symposium on Solid Oxide Fuel Cells (SOFC), Publisher: ELECTROCHEMICAL SOC INC, Pages: 1097-1105, ISSN: 1938-5862
Kleniati PM, Adjiman CS, 2011, Branch-and-Sandwich. An Algorithm for Optimistic Bi-Level Programming Problems, Computer Aided Chemical Engineering, Vol: 29, Pages: 602-606, ISSN: 1570-7946
We consider optimistic bi-level programming problems that possess a nonconvex inner program. We propose a solution strategy based on the refinement of two sets of converging lower and upper bounds. Namely, valid lower and upper bounds are computed simultaneously for the outer and inner objective values. Furthermore, appropriate fathoming tests are introduced in order to permit branching on all the variables without violating the hierarchical decision making. Examples are presented. © 2011 Elsevier B.V.
Vasileiadis M, Kazantsev AV, Karamertzanis PG, et al., 2011, The polymorphs of ROY: Application of crystal structure prediction techniques, Pages: 856-857
Struebing H, Ganase Z, Karamertzanis PG, et al., 2011, Solvent design for optimal kinetics: From quantum mechanical predictions to experimental validation, Pages: 39-40
Papaioannou V, Adjiman CS, Jackson G, et al., 2011, Modeling the solid-liquid equilibrium of organic compounds with the SAFT-g, Pages: 231-232
Pereira F, Galindo A, Jackson G, et al., 2011, On the impact of using a pressure solver on the solution of P,T phase equilibrium with equations of state, Pages: 335-336
Pereira FE, Jackson G, Galindo A, et al., 2010, A duality-based optimisation approach for the reliable solution of (P, T) phase equilibrium in volume-composition space, FLUID PHASE EQUILIBRIA, Vol: 299, Pages: 1-23, ISSN: 0378-3812
Dowell NM, Llovell F, Blas FJ, et al., 2010, Modelling the phase behaviour of the CO2+H2O+amine mixtures using transferable parameters with SAFT-VR - Towards solvent design, 10AIChE - 2010 AIChE Annual Meeting, Conference Proceedings
The reduction in CO2 emissions from anthropogenic sources has become a topic of widespread interest in recent years. As the power generation sector is by far the largest stationary-point-source of CO2, being responsible for approximately 35% of total global CO2 emissions this issue has special relevance for the energy sector. The current method of choice for large-scale CO2 capture is amine-based chemisorption; typically in packed columns, with the solvent of choice being a primary alkanolamine: monoethanolamine (MEA). However, MEA-based processes suffer from a number of significant disadvantages associated with the regeneration of the MEA solvent. Recently, blends of 2-amino-2-methyl-1-propanol (AMP) and ammonia (NH2) have been shown to be particularly promising novel solvent blends for CO2 capture applications owing to a greater capacity to absorb CO2, lower energy of regeneration and a significantly improved resistance to degradation problems when compared to MEA solvents. However, in order to include this mixture in solvent and process design activities, it is necessary to develop accurate and reliable physical models with which to describe their thermophysical properties and fluid phase behaviour. To this end, we use the statistical associating fluid theory (SAFT). This is a molecular approach, specifically suited to hydrogen-bonding, chain-like fluids. In this contribution we use the SAFT approach for potentials of variable range (SAFT-VR) to calculate the fluid phase behaviour of amine + H2O + CO2 mixtures. The molecules are modelled as homonuclear chains of attractive segments with a variable dispersion range, and a number of short-ranged off-centre attractive square-well sites are used to mediate the strong anisotropic interactions in the fluids. Following previous work on MEA, we propose an asymmetric model of AMP. By asymmetric we mean that we explicitly discriminate between the primary amine functional group and the hydroxyl functional group on the AMP m
Cai Q, Luna-Ortiz E, Adjiman CS, et al., 2010, The Effects of Operating Conditions on the Performance of a Solid Oxide Steam Electrolyser: A Model-Based Study, Fuel Cells, Vol: 10, Pages: 1114-1128, ISSN: 1615-6854
To support the development of hydrogen production by high temperature electrolysis using solid oxide electrolysis cells (SOECs), the effects of operating conditions on the performance of the SOECs were investigated using a one-dimensional model of a cathode-supported planar SOEC stack. Among all the operating parameters, temperature is the most influential factor on the performance of an SOEC, in terms of both cell voltage and operation mode (i.e. endothermic, thermoneutral and exothermic). Current density is another influential factor, in terms of both cell voltage and operation mode. For the conditions used in this study it is recommended that the SOEC be operated at 1,073 K and with an average current density of 10,000 A m–2, as this results in the stack operating at almost constant temperature along the cell length. Both the steam molar fraction at the inlet and the steam utilisation factor have little influence on the cell voltage of the SOEC but their influence on the temperature distribution cannot be neglected. Changes in the operating parameters of the SOEC can result in a transition between endothermic and exothermic operation modes, calling for careful temperature control. The introduction of air into the anode stream appears to be a promising approach to ensure small temperature variations along the cell.
Shearing PR, Cai Q, Golbert JI, et al., 2010, Microstructural analysis of a solid oxide fuel cell anode using focused ion beam techniques coupled with electrochemical simulation, JOURNAL OF POWER SOURCES, Vol: 195, Pages: 4804-4810, ISSN: 0378-7753
Porous composite electrodes play a critical role in determining the performance and durability of solid oxide fuel cells, which are now emerging as a high efficiency, low emission energy conversion technology for a wide range of applications.In this paper we present work to combine experimental electrochemical and microstructural characterisation with electrochemical simulation to characterise a porous solid oxide fuel cell anode. Using a standard, electrolyte supported, screen printed Ni-YSZ anode, electrochemical impedance spectroscopy has been conducted in a symmetrical cell configuration. The electrode microstructure has been characterised using FIB tomography and the resulting microstructure has been used as the basis for electrochemical simulation. The outputs from this simulation have in turn been compared to the results of the electrochemical experiments.A sample of an SOFC anode of 6.68 mu m x 5.04 mu m x 1.50 mu m in size was imaged in three dimensions using FIB tomography and the total triple phase boundary density was found to be 13 mu m(-2). The extracted length-specific exchange current for hydrogen oxidation (97% H-2, 3% H2O) at a Ni-YSZ anode was found to be 0.94 x 10(-10), 2.14 x 10(-10), and 12.2 x 10(-10) A mu m(-1) at 800, 900 and 1000 degrees C, respectively, consistent with equivalent literature data for length-specific exchange currents for hydrogen at geometrically defined nickel electrodes on YSZ electrolytes. (C) 2010 Elsevier B.V. All rights reserved.
Cai Q, Brandon NP, Adjiman CS, 2010, Modelling the dynamic response of a solid oxide steam electrolyser to transient inputs during renewable hydrogen production, Frontiers of Energy and Power Engineering in China, Vol: 4, Pages: 211-222, ISSN: 1673-7504
Hydrogen is regarded as a leading candidate for alternative future fuels. Solid oxide electrolyser cells (SOEC) may provide a cost-effective and green route to hydrogen production especially when coupled to a source of renewable electrical energy. Developing an understanding of the response of the SOEC stack to transient events that may occur during its operation with intermittent electricity input is essential before the realisation of this technology. In this paper, a one-dimensional (1D) dynamic model of a planar SOEC stack has been employed to study the dynamic behaviour of such an SOEC and the prospect for stack temperature control through variation of the air flow rate. Step changes in the average current density from 1.0 to 0.75, 0.5 and 0.2 A/cm2 have been imposed on the stacks, replicating the situation in which changes in the supply of input electrical energy are experienced, or the sudden switch-off of the stack. Such simulations have been performed both for open-loop and closed-loop cases. The stack temperature and cell voltage are decreased by step changes in the average current density. Without temperature control via variation of the air flow rate, a sudden fall of the temperature and the cell potential occurs during all the step changes in average current density. The temperature excursions between the initial and final steady states are observed to be reduced by the manipulation of the air flow rate. Provided that the change in the average current density does not result in a transition from exothermic to endothermic operation of the SOEC, the use of the air flow rate to maintain a constant steady-state temperature is found to be successful.
Mac Dowell N, Llovell F, Adjiman CS, et al., 2010, Modeling the Fluid Phase Behavior of Carbon Dioxide in Aqueous Solutions of Monoethanolamine Using Transferable Parameters with the SAFT-VR Approach, INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH, Vol: 49, Pages: 1883-1899, ISSN: 0888-5885
Kazantsev AV, Karamertzanis PG, Pantelides CC, et al., 2010, Ab Initio Crystal Structure Prediction for Flexible Molecules, 20th European Symposium on Computer Aided Process Engineering (ESCAPE), Publisher: ELSEVIER SCIENCE BV, Pages: 817-822, ISSN: 1570-7946
Brandon NP, Matian M, Marquis AJ, et al., 2010, THERMAL MANAGEMENT ISSUES IN FUEL CELL TECHNOLOGY, 14th International Heat Transfer Conference, Publisher: AMER SOC MECHANICAL ENGINEERS, Pages: 591-599
Mac Dowell N, Galindo A, Jackson G, et al., 2010, Integrated solvent and process design for the reactive separation of CO₂ from flue gas, 20TH EUROPEAN SYMPOSIUM ON COMPUTER AIDED PROCESS ENGINEERING, Vol: 28, Pages: 1231-1236, ISSN: 1570-7946
Struebing H, Karamertzanis PG, Pistikopoulos EN, et al., 2010, Solvent design for a Menschutkin reaction by using CAMD and DFT calculations, 20th European Symposium on Computer Aided Process Engineering (ESCAPE), Publisher: ELSEVIER SCIENCE BV, Pages: 1291-1296, ISSN: 1570-7946
Pereira FE, Jackson G, Galindo A, et al., 2010, Robust algorithms for the calculation of phase equilibrium, 20TH EUROPEAN SYMPOSIUM ON COMPUTER AIDED PROCESS ENGINEERING, Vol: 28, Pages: 79-84, ISSN: 1570-7946
Mac Dowell N, Galindo A, Adjiman CS, et al., 2009, Modelling the phase behaviour of the CO2+H2O+ Amine Mixtures Using Transferable Parameters with SAFT-VR, Conference Proceedings - 2009 AIChE Annual Meeting, 09AIChE
The reduction in CO2 emissions from anthropogenic sources has become a topic of widespread interest in recent years. As the power generation sector is by far the largest stationary-point-source of CO2, being responsible for approximately 35% of total global CO2 emissions this issue has particular relevance for the energy sector. The current method of choice for large-scale CO2 capture is amine-based chemisorption; typically in packed columns, with the solvent of choice being a primary alkanolamine: monoethanolamine (MEA). Despite the widespread use if this technique, there is an ongoing debate as to how best to model these systems, owing to the complex reactions and phase equilibrium they exhibit. To capture the interactions that occur in these systems, we use the statistical associating fluid theory (SAFT). This is a molecular approach, specifically suited to hydrogen-bonding, chain-like fluids. In this contribution we use the SAFT approach for potentials of variable range (SAFT-VR) to calculate the fluid phase behaviour of amine + H2O + CO2 mixtures. The molecules are modelled as homonuclear chains of bonded square-well segments of variable range, and a number of short-ranged off-centre attractive square-well sites are used to mediate the anisotropic effects due to association in the fluids. We model MEA as a pair of tangentially bonded homonuclear spherical segments. Six distinct association sites are required to mediate the hydrogen bonding interactions exhibited by this molecule. In discriminating between potential models of MEA, we consider both symmetric models - where no distinction is made between the functional groups on MEA - and asymmetric models of MEA - where we explicitly consider the multifunctional nature of MEA. We find that despite giving an adequate description of the MEA + H2O phase behaviour a purely symmetric model of MEA is not suitable for describing either the phase behaviour MEA + CO2 binary mixture or that of the MEA + CO2 + H2O mixture.
Karamertzanis PG, Kazantsev AV, Issa N, et al., 2009, Can the Formation of Pharmaceutical Cocrystals Be Computationally Predicted? 2. Crystal Structure Prediction, JOURNAL OF CHEMICAL THEORY AND COMPUTATION, Vol: 5, Pages: 1432-1448, ISSN: 1549-9618
Pollock M, Adjiman CS, Galindo A, et al., 2009, Integrated Modeling of Mixture Fluid Phase Equilibrium Experiments Using SAFT-VR Applied to Xenon plus Diborane, Xenon plus Cyclopropane, Xenon plus Boron Trifluoride, INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH, Vol: 48, Pages: 2188-2198, ISSN: 0888-5885
Giovanoglou A, Adjiman CS, Jackson G, et al., 2009, Fluid phase stability and equilibrium calculations in binary mixtures Part II: Application to single-point calculations and the construction of phase diagrams, FLUID PHASE EQUILIBRIA, Vol: 275, Pages: 95-104, ISSN: 0378-3812
Giovanoglou A, Galindo A, Jackson G, et al., 2009, Fluid phase stability and equilibrium calculations in binary mixtures Part I: Theoretical development for non-azeotropic mixtures, FLUID PHASE EQUILIBRIA, Vol: 275, Pages: 79-94, ISSN: 0378-3812
Adjiman C, Atkinson A, Azad A, et al., 2009, A Review of Progress in the UK Supergen Fuel Cell Programme, 11th International Symposium on Solid Oxide Fuel Cells (SOFC), Publisher: ELECTROCHEMICAL SOC INC, Pages: 35-42, ISSN: 1938-5862
Lymperiadis A, Adjiman CS, Jackson G, et al., 2008, A generalisation of the SAFT-gamma group contribution method for groups comprising multiple spherical segments, FLUID PHASE EQUILIBRIA, Vol: 274, Pages: 85-104, ISSN: 0378-3812
A new group contribution (GC) approach based on the statistical associating fluid theory (SAFT-gamma) has recently been proposed [A. Lymperiadis, C. S. Adjiman, A. Galindo, G. Jackson, J. Chem. Phys. 127 (2007) 234903]. In this continuum equation of state CC approach, the molecules are formed from fused heteronuclear spherical segments each of which represents a distinct chemical functional group. The different segments are characterised by size and attractive energy (well-depth and range) parameters, and a shape-factor parameter which describes the contribution that each segment makes to the overall molecular properties. In addition a number of bonding sites are included on a given segment to deal with association interactions where appropriate; the association between sites introduces two additional energy and range parameters. Our heteronuclear molecular models are thus fundamentally different from the homonuclear models employed with other GC versions of SAFT in which the GC concept is introduced to obtain average molecular parameters. In the Current work, we generalise the SAFY-gamma equation of state to treat chemical groups which are represented by more than a single spherical segment. This allows for a good description of the properties of large functional groups such as carboxyl and carbonyl groups. The original parameter table for the CH(3), CH(2), CH(3)CH, ACH (where AC denotes an aromatic carbon), ACCH(2), CH(2)=, CH= and OH groups is now extended to include the C=O, COCH, and NH(2) groups by examining the vapour-liquid equilibria (VLE) of pure 2-ketones, carboxylic acids, and primary amines. It is demonstrated that the proposed theory provides an excellent description of the vapour-liquid equilibria for all of the chemical families considered, and that the new group parameters can be used in a predictive fashion to model the phase behaviour of larger compounds not included in the estimation database. One of the principal advantages of the SAFT-gamma for
Luna-Ortiz E, Lawrence P, Pantelides CC, et al., 2008, Optimal flow assurance policies for hydrate prevention in deep-water gas production systems, AIChE Annual Meeting, Conference Proceedings
Giner B, Sheldon T, Pollock M, et al., 2008, An approach for developing intermolecular models for use within Saft-Vr from quantum mechanical calculations and experimental data, AIChE Annual Meeting, Conference Proceedings
Dowell NM, Adjiman CS, Galindo A, et al., 2008, Modeling CO2 capture in amine solvents with an advanced association model: Process optimisation and a platform for solvent design, AIChE Annual Meeting, Conference Proceedings
Kazantsev AV, Karamertzanis PG, Adjiman CS, et al., 2008, Computational prediction of effects of pressure on organic crystal structure, AIChE Annual Meeting, Conference Proceedings
Kazantsev AV, Karamertzanis PG, Adjiman CS, et al., 2008, A computationally efficient algorithm for accurate local energy minimization of crystal structures containing flexible molecules, AIChE Annual Meeting, Conference Proceedings
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