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Future electricity generation systems may include the widespread use of renewables along with fossil fuels. In recent work we developed novel computational procedures for modeling and optimizing the operations of an integrated fossil-renewable power generation system with CO2 capture, subject to a daily average CO2 emission constraint. System components were modeled using energy and mass balances, and a formal optimization procedure was applied to determine the optimal hourly dispatch of system components to maximize operating profit in response to time-varying electricity prices and wind generation. In this study we extend this work by assessing other policy schemes and system designs. First, in lieu of an emission performance standard, CO2 taxes of $10/Mg CO2 to $70/Mg CO2 are applied. Second, we consider emission performance standards ranging from 0.326 Mg CO2/MWh to 1.001 Mg CO2/MWh for systems with oversized and heuristically-sized components. Optimized operating profit shows a nonlinear response to varying emission constraint levels. Taken together, our findings illustrate the effect of different policy schemes on optimized operating economics and CO2 emission levels, and quantify the potential benefits of flexibility in an integrated energy system.
We present a fast technique for modeling convective displacements which aredominated by large scale reservoir heterogeneities. The direction of flow atany time during the displacement is mapped by streamtubes, which arerecalculated as the fluid mobility distribution changes. A one dimensionalsolution is then mapped along each streamtube as a Riemann solution, i.e. as anintegration from 0 to tD + tD rather than from tD to tD + tD, as inconventional time-stepping algorithms.
The Riemann approach allows for the rapid computation of flow using two tothree orders of magnitude fewer matrix inversions than traditional finitedifference simulators. The resulting two dimensional solutions are free fromnumerical diffusion and can include the effects of gravity, any type ofmultiphase, multicomponent compositional process and longitudinal physicaldiffusion, but cannot account for transverse physical diffusion or mixing dueto viscous or capillary cross-flow.
We test our techniques on immiscible and ideal miscible displacementsthrough a variety of two dimensional heterogeneous systems. We show that theRiemann technique is accurate and converges in less than 1% of the time takenby conventional finite difference simulators. Using multiple realizations ofpermeability fields with identical statistics we show that the nonlinearity ofthe displacement process and reservoir heterogeneity combine to define thepossible spread in recovery curves. For the ideal miscible case, we show thatthe stream-tube method is an example of how to nest physical phenomena thatdominate at different scales in order to capture the physical process ofinterest.