Methods
A process model was created in Aspen Plus. Examples of the overall
flowsheet are shown in Figure 2, and Figures S1 and S2. The Volume
Translated Peng-Robinson equation of state (VTPR) property set was used
throughout the CO2 capture process, while the
International Association for the Properties of Water and Steam 1995
(IAPWS-95) property set was used to model the generation of BFW
preheater steam using available heat from the pulverized coal power
cycle. DOE Case 11a from Cost and Performance Baseline for Fossil
Energy Plants Volume 1 34 for post-combustion
CO2 capture from a supercritical pulverized coal power
plant was used as a model baseline for the CO2 product
feed. For this analysis, the flue gas composition was simplified to only
include CO2, N2, and
H2O. The ~1% other contaminants
(O2 and Ar) were not considered in the analysis and were
grouped in with N2. The expected inlet composition and
conditions of the flue gas acting as the inlet to the process are in
Table S1 stream 1. The final conditioned CO2 is
delivered at pipeline conditions (35 °C and 120 bar).
Within the process model several assumptions were made, which are
outlined in more detail in the Supporting Information. Pressure drops
through heat exchangers in this preliminary analysis were taken as 0.1
bar, while the pressure drops through the pressure driven separation
unit (membrane or adsorbent) was taken as 0.2 bar. The adsorbent drier
bed, pressure-driven separation unit, and the downstream vacuum pump
were assumed to operate isothermally. The vacuum pump was modeled as a
compressor followed by a heater to simulate the operation of an actual
isothermal vacuum pump, as Aspen Plus does not have a built-in vacuum
pump model. System compressors and expanders acting on the feed and
N2 rich product were assumed axial compressors operating
at a 90% polytropic efficiency sharing a common driveshaft. The
volumetric flow rates of flue gas entering the system are on the scale
where axial compressors would be viable, and polytropic efficiencies
ranging from 88-92% are typical for these systems.35The vacuum pump, liquefaction compressor, and recycle pressure changer
(compressor or turbine depending on the required pressure change) were
not in the required size range for axial compressors, so centrifugal
compressors were considered instead.
Capital costs for all major equipment were estimated using common cost
estimation tools, discussed in further detail in the Supporting
Information S2.1. A five year equipment lifetime was taken as basis, and
an escalation factor of two was employed to adjust for installation
cost. The coal plant was expected to be operational 350 days a year,
with an 85% capacity factor. A levelized cost of electricity of
$0.04/kWh was used to estimate the energy cost for calculating the
total cost per tonne of captured CO2. Cost estimation of
composite fiber sorbent module construction is outlined in the
Supporting Information S2.2 for MOF and zeolite fiber sorbents
containing microencapsulated phase change materials for local heat
management.