(317h) Post-Combustion Gas Permeation Carbon Capture System Models

Post-Combustion Gas Permeation Carbon Capture System Models

Juan E. Morinelly,
David C. Miller

National Energy Technology
Laboratory (NETL)

Gas
permeation membranes have been proposed as an alternative to amine absorption
for post-combustion carbon capture [1,2].
Industrial-scale membrane systems have been successfully applied in natural gas
sweetening, and their use in other separations is expected to grow in the near
future [3]. Under the constraints imposed by the performance limits of
state-of-the-art gas permeation membranes multi-stage processes are required to
obtain a high purity CO₂ stream suitable for sequestration. An
effective design for such a process entails balancing of numerous factors,
including the pressure ratio across the membrane stages, which affects the
parasitic power load, and the size of the membrane modules, which affects the
capital cost. Merkel et al. (2010) introduced a multi-stage process that
incorporates permeate recirculation, the use of the boiler's air feed as sweep,
compression of the feed, and pulling vacuum on the permeate side. The main
challenge from a modeling perspective is that, unlike conventional CO₂
capture processes, this is not a purely ?end of pipe' process. The proposed
process is integrated with other parts of the power plant. A modeling strategy
that captures undesired effects such as higher flows due to the recirculation
of gases is required in order to accurately evaluate its performance.

Two steady-state
process models were built in Aspen Custom Modeler® (ACM) based on the work by
Merkel et al. (2010) and Toy et al. (2011). These models include modules for
the boiler, air pre-heater, and FGD units that can be tuned to a given
pulverized coal (PC) power plant system. A one-dimensional, multi-component,
distributed model was developed for the membrane stages within the process
models. This device-scale gas permeation model incorporates pressure drop
effects and can be adjusted to varying dimensions for the module as well as
membrane properties. The process models are linked to a simulation interface
that allows the optimization of key process parameters with respect to
system-level functions such as the cost of electricity (COE). In addition to a
description of the process models and their features, this presentation will
describe the results of varying levels of membrane properties. The base power
plant in this analysis is a supercritical PC with a net output of 650 MWe
before the capture and compression systems are integrated. Constraints on the
capture level (>90%), the purity of the sequestration stream (>95%), and
the increase in flow of the flue gas stream out of the boiler (<15%) were
included in the optimization routine.

References

1.      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

2.      Favre, E. Carbon Dioxide Recovery from Post-Combustion
Processes: Can Gas Permeation Membranes Compete with Absorption? J. Membr. Sci.,
2007;294:50-59

3.      Bernardo, P, Drioli, E, Golemme, G. Membrane Gas Separation: A Review/State of the
Art. Ind. Eng. Chem. Res.,
2009;48:4638-4663

4.      Toy, L. CO2 Capture Membrane Process for Power Plant
Flue Gas. Presented at the 2011 NETL Capture Technology Meeting. Pittsburgh,
PA, August 22, 2011.