00441 Numerical study of cluster and particle rebound effects in a circulating fluidised bed

16 Fuel science and technology (fundamental science, analysis, instrumentation) 06•00439 Monitoring of fluid-rock interaction and C O 2 storage through produced fluid sampling at the Weyburn C02-injection enhanced oil recovery site, Saskatchewan, Canada Emberley, S. et at. Applied GeochemisttT, 2005, 20, (6), 1131 1157. The Weyburn Oil Field is a carbonate reservoir in south central Saskatchewan, Canada and is the site of a large CO2 injection project for purposes of enhanced oil recovery. The Weyburn Field, in the Mississippian Midale Formation, was discovered in 1954 and was under primary production until secondary recovery by water flood began in 1964. The reservoir comprises two units, the Vnggy and the Marly, and primary and secondary recovery are thought to only have significantly depleted the Vuggy zone, leaving the Marly with higher oil saturations. In 2000, PanCanadian Resources (now EnCana), the operator of the field, began tertiary recovery by injection of CO2 and water, primarily into the Marly. The advent of this project was an opportunity to study the potential for geological storage of CO2. Using 43 Baseline samples collected in August 2000, before CO2 injection at Weyburn, and 44 monitoring samples collected in March 2001, changes in the fluid chemistry and isotope composition have been tracked. The initial fluid distribution showed water from discovery through water flood in the Midale Formation with C1 ranging from 25,000 to 60,000 rag/L, from the NW to the SE across the Phase IA area. By the time of Baseline sampling the produced water had been diluted to C1 of 25,000-50,000 mg/L as a result of the addition of make up water from the low TDS Blairmore Formation, but the pattern of distribution was still present. The CI distribution is mimicked by the distribution of other dissolved ions and variables, with Ca (1250-1500 rag/L) and NH3(aq) increasing from NW to SE, and alkalinity (700-300 mg/L), resistivity, and H2S (300-100 mg/L) decreasing. Based on chemical and isotopic data, the H2S is interpreted to result from bacterial SO4 reduction. After 6 months of injection of CO2, the general patterns are changed very little, except that the pH has decreased by 0.5 units and alkalinity has increased, with values over 1400 mg/L in the NW, decreasing to 500 mg/L in the SE. Calcium has increased to range from 1250 to 1750 rag/ L, but the pattern of N W - S E distribution is altered. Chemical and isotopic data suggest this change in distribution is caused by the dissolution of calcite due to water-rock reactions driven by CO2. The Baseline samples varied from 22 to 12%o 613C (V-PDB) for CO2 gas. The injected CO2 has an isotope ratio of 20%0. The Monitor-1 samples of produced CO2 ranged from - 1 8 to -13%,,, requiring a heavy source of C, most easily attributed to dissolution of carbonate minerals. Field measured pH had increased and alkalinity had decreased by the second monitoring trip (July 2001) to near Baseline values, suggesting continued reaction with reservoir minerals. Addition of CO2 to waterrock mixtures comprising carbonate minerals causes dissolution of carbonates and production of alkalinity. Geochemical modelling suggests dissolution is taking place, however more detail on wateroil-gas ratios needs to be gathered to obtain more accurate estimates of pH at the formation level. Geological storage of CO2 relies on the potential that, over the longer term, silicate minerals will buffer the pH, causing any added CO2 to be precipitated as calcite. Some initial modelling of water-rock reactions suggests that silica sources are available to the water resident in the Midale Formation, and that clay minerals may well be capable of acting as pH buffers, allowing injected CO2 to be stored as carbonate minerals. Further work is underway to document the mineralogy of the Midale Formation and associated units so as to define more accurately the potential for geological storage.

06•00440 Nanoscale surface observation of feldspar dissolved under supercritical C02-water-mineral system Sorai, M. et al. Energy, 2005, 30, (11 12), 2334~2343. As part of an assessment programme on underground carbon dioxide storage, the dissolution of feldspar was studied in aqueous solutions of supercritical carbon dioxide at 25, 50, 65, and 80°C with a constant carbon dioxide pressure of 10 MPa. Atomic force microscopy (AFM) was then used to observe nanoscale dissolution features on the feldspar surface. The average dissolution rates of anorthite during the initial week of dissolution were estimated from surface retreat based on vertical cross-section profiles.

06/00441 Numerical study of cluster and particle rebound effects in a circulating fluidised bed Helland, E. ef al. Chemical Engineering Science, 2005, 60, (1), 27 40. Gas-particle flows in a vertical two-dimensional configuration appropriate for circulating fluidized bed applications were investigated numerically. In the computational study presented herein the motion of particles was calculated based on a Lagrangian approach and particles were assumed to interact through binary, instantaneous, nonfrontal, inelastic collisions including friction. The model for the interstitial gas phase is based on the Navier-Stokes equations for two-phase flows. The numerical study of cluster structures has been validated with experimental results from literature in a previous investigation. Numerical experiments were performed in order to study the effects of different cluster and particle rebound character-

60

Fuel and Energy Abstracts

January 2006

istics on the gas-particle flow behaviour. Firstly, the authors investigated the hard sphere collision model and its effect on gasparticle flow behaviour. The coefficient of restitution in an impact depends not only on the material properties of the colliding objects, but also on their relative impact velocity. The authors compared the effect of a variable restitution coefficient, dependent on the relative impact velocity, with the classical approach, which supposes the coefficient of restitution to be constant and independent of the relative impact velocity. Secondly, the authors studied the effects of different cluster properties on the gas-particle flow behaviour. Opposing clustering effects have been observed for different particle concentrations: within a range of low concentrations, groups of particles fall faster than individual particles due to cluster formation, and within a well-defined higher concentration range, return flow predominates and hindered settling characterizes the suspension. A drag law is proposed, which takes into account both opposing effects and have compared the resulting flow behavionr with that predicted by a classical drag law, which takes into account only the hindered settling effect.

06•00442 On the determination of transit times during flow oscillations Manera, A. et al. Annals o/'Nuclear Energy, 2005, 32, (7), 693 711. The determination of transit times of single-phase flow during flow oscillations is treated. Starting from theoretical considerations derived on the basis of noise analysis techniques, numerical simulations have been carried out to understand the physical meaning of the cross correlation function and of the phase shift between the noise signals of two axially separated sensors during constant-amplitude flow oscillations. The analysis of experiments performed on a natural circulation cooled water/steam loop is also reported.

06/00443 On turbulence models for rod bundle flow computations Hfizi, G. Annals o f Nut~ear Energ;y, 2005, 32, (7), 755 761. In commercial computational fluid dynamics codes there is more than one turbulence model built in. It is the user responsibility to choose one of those models, suitable for the problem studied. In the last decade, several computations were presented using computational fluid dynamics for the simulation of various problems of the nuclear industry. A common feature in a number of those simulations is that they were performed using the standard k e turbulence model without justifying the choice of the model. The simulation results were rarely satisfactory. This paper considers the flow in a fuel rod bundle as a case study and discuss why the application of the standard k e model fails to give reasonable results in this situation. It also shows that a turbulence model based on the Reynolds stress transport equations can provide qualitatively correct results. Generally, the aim is pedagogical, to call the readers attention to the fact that turbulence models have to be selected based on theoretical considerations and/or adequate information obtained from measurements.

06•00444 Optical simulation of the role of reflecting interlayers in tandem micromorph silicon solar cells Krc, J. el al. Solar Energy Materials and Solar Cells, 2005, 86, (4), 537 550. The role of a reflecting interlayer in micromorph silicon thin-film solar cells is investigated from the optical point of view. Detailed optical modelling and simulation are used to study the effects of different interlayers on quantum efficiency and short-circuit current of the top, amorphous silicon, and bottom, microcrystalline silicon, solar cell. The role of refractive index of interlayers on quantum efficiency of the top and bottom cell is analysed. Critical issues, such as enhanced total reflection from the solar cell and decreased quantum efficiency of the bottom cell due to interlayer are studied. Besides the single interlayer concept, double and triple interlayer stacks are investigated and improvements in comparison to the single ZnO interlayer are demonstrated. Potential thickness reductions of the top amorphous silicon cell related to different interlayers are presented.

06•00445 Optimisation of interdigitated back contacts solar cells by two-dimensional numerical simulation Nichiporuk, O. et al. Solar Energy Maferia/s and So/ar Cells, 2005, 86, (4), 517 526. This paper presents the results of the simulation of interdigitated back contacts solar cell on thin-film (~50 pm) silicon layer. The influence of several parameters (surface recombination rate, substrate thickness and type, diffusion length, device geometry, doping levels) on device characteristics are simulated using the accurate two-dimensional numerical simulator DESSIS that allows to optimize the cell design.

06•00446 Optimization of the incision size and cold-end temperature of a thermoelectric device Kubo, M. et al. Energy, 2005, 30, (11 12), 2156 2170.