212650 Development of Asymmetric Membrane Gas Permeation Simulation Modules for Generalized Plant-Wide Optimization of Power Plants with CCS: Effect of Detailed Porous Support Transport Sub-Model

Tuesday, March 15, 2011: 1:50 PM
Columbus CD (Hyatt Regency Chicago)
Juan E. Morinelly and David C. Miller, U.S. Department of Energy, National Energy Technology Laboratory (NETL), Morgantown, WV

Development of asymmetric membrane gas permeation simulation modules for generalized plant-wide optimization of power plants with CCS: Effect of detailed porous support transport sub-model

NETL is currently developing a modular framework for the analysis and optimization of power generation systems, particularly coal-fired power plants with carbon capture and sequestration (CCS) [1]. The framework consists of a collection of simulation modules for various parts of a power plant and a structure that allows their integration into a specified configuration. Unlike most assessment studies for CCS technologies in literature, the integration of CCS modules to the modular framework provides plant-wide performance indicators and a common basis for the evaluation of new and existing CCS technologies. The modular approach is particularly advantageous given that beyond capital investment and the obvious compromises in operating cost and plant efficiency, CCS processes usually involve parasitic demands and modifications to other parts of the power generation system. This approach also permits the easy integration of new processes and the capability to carry out constrained multi-objective optimization routines by varying key system parameters for a given modular plant design. Rigorous models for gas permeation modules were developed in order to evaluate membrane carbon capture systems under the modular framework.

Gas permeation is a well established technology for many industrial applications [2]. As a carbon capture technology, a membrane system is advantageous because it does not require large amounts of water or solvents, and its non-moving, modular components are easy to operate and maintain. Recent studies conclude that multi-staged gas permeation processes can compete with amine absorption as a viable carbon capture technology [3-6]. Developments in membrane properties and process design are required in order to achieve the desired separation while minimizing energy and membrane area demands. Merkel et al. recently proposed a promising two-stage system configuration that incorporates different strategies to maximize the separation driving force [5]. The most prominent feature of the design is a counter-current sweep module that uses a portion of the air feed to the boiler as a sweep. The recirculation of carbon dioxide through the boiler increases its partial pressure in the flue gas stream to be treated, while the sweep flow decreases its permeate side partial pressure. Both effects increase the trans-membrane carbon dioxide partial pressure difference, which in turn reduce the process energy and area demands. A rigorous numerical model that captures the complexity of these effects is necessary when evaluating this type of processes.

There are several numerical models in the literature that describe the behavior of gas permeation in asymmetric membranes. Kaldis et al. provide a good summary of these efforts [7]. The asymmetric membrane architecture was developed in order to address conflicting requirements. In order to achieve high gas permeances the membrane must be sufficiently thin yet mechanically stable in order to endure the imposed pressure gradient. By coating a thin (0.5-1 μm) selective layer on a porous support two to three orders of magnitude thicker both requirements are fulfilled. The transport across the thin selective layer is usually modeled according to the solution-diffusion model, while simplifying assumptions about the gas transport in the porous support are usually made. Experimental results [8, 9] suggest that the simplifying assumptions about the porous support are not capable of predicting observed behavior for gas permeation systems with sweep streams.

One-dimensional, multicomponent, hollow-fiber gas permeation models were developed according to the shell and fiber lumen flow equations of Pan et al. [10] and the detailed model for the porous support gas transport similar to Chan et al. [11]. Equivalent models, according to the limiting assumptions about the porous support were also developed. The models were used to simulate the performance of a module with and without sweep for the carbon capture from a flue gas stream. The predicted performance for no-sweep operation was almost identical regardless of the porous support gas transport sub-model. On the other hand, significant discrepancies were predicted for modules with sweep streams. Since sweep operated modules are a vital feature of novel processes, simulation models must be developed with enough detail to predict their performance accurately. The analysis of the different models under the modular framework will determine the sensitivity of the overall performance to the assumed transport mechanism for the porous support. This will in turn justify or reject the inclusion of the detailed sub-model, and potentially enable the optimization of porous support properties.

References

1.      Miller, DC, Eslick, JC, Lee, A, Morinelly, JE. A modular framework for the analysis and optimization of power generation systems with CCS. Energy Procedia, 2010; In Press

2.      Coker, DT, Freeman, BD, Fleming, GK. Modeling multicomponent gas separation using hollow-fiber membrane contactors. AIChE J., 1998; 44:1289-1302

3.      Favre, E. Carbon dioxide recovery from post-combustion processes: Can gas permeation membranes compete with absorption? J. Membr. Sci., 2007;294:50-59

4.      Hussain, A, Hägg, M-B. A feasibility study of CO2 capture from flue gas by a facilitated transport membrane. J. Membr. Sci., 2010;359:140-148

5.      Merkel, TC, Lin, H, Wei, X, Baker, R. Power plant post-combustion carbon dioxide capture: An opportunity for membranes. J. Membr. Sci., 2010;359:126-139

6.      Zhao, L, Riensche, E, Blum, L, Stolten, D. Multi-stage gas separation membrane processes used in post-combustion capture: Energetic and economic analyses. J. Membr. Sci., 2010;359:160-172

7.      Kaldis, SP, Kapantaidakis, GC, Sakellaropoulos, GP. Simulation of multicomponent gas separation in a hollow fiber membrane by orthogonal collocation – hydrogen recovery from refinery gases. J. Membr. Sci., 2000;173:61-71

8.      Sandru, M, Haukebø, SV, Hägg, M-B. Composite hollow fiber membranes for CO2 capture. J. Membr. Sci., 2010;346:172-186

9.      Dittmeyer, R, Höllein, V, Daub, K. Membrane Reactors for hydrogenation and dehydrogenation processes based on supported palladium. J. Mol. Catal. A: Chem., 2001;173:135-184

10.  Pan, CY. Gas separation by high-flux, asymmetric hollow-fiber membrane. AIChE J. 1986;32:2020-2027

11.  Chan, CH, Khor, KA, Xia, ZT. A complete polarization model of a solid oxide fuel cell and its sensitivity to the change of cell component thickness. J Power Sources, 2001;93:130-140


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