Environmental Engineering Reference
In-Depth Information
is in development (as of August 2009) in the United States (DOE 2009; FutureGen Alliance 2009),
and a similar project is in development in China (GreenGen 2009; WRI 2009a). Although car-
bon sequestration can reduce power plant stack emissions, it does not reduce upstream life-cycle
impacts. For example, consider the upstream energy requirements of coal mining and transport
identified by Mann and Spath (2001) in Figure 11.23.
Another study by Spath and Mann (2004) compared coal (baseline), natural gas combined-
cycle, co-fired biomass, direct-fired biomass, and biomass gasification combined-cycle electricity
generation with and without carbon capture and sequestration (CO
2
-seq). The biomass co-fired
and biomass gasification combined-cycle systems are the same as those described in Sections
11.3.3.2 and 11.3.3.3 of this chapter, respectively, and the direct-fired system is modeled as using
the same biomass source as the co-fire system. Each of the systems were required to produce
600 MW of electricity in this study; for the biomass systems, achieving this output rate required
more than one facility (to reduce the biomass transportation distance, smaller dispersed plants
were assumed—refer to Figure 11.25, case S13). Chemical absorption using monoethanolamine
was selected as the carbon capture technology and was assumed to capture 90% of the power
pl a nt 's C O
2
emissions. Using CO
2
-seq technology, which includes capturing and compressing the
CO
2
gas, with a coal power plant required additional energy. The plant's electricity production
capacity was reduced from 600 to 457 MW. To compensate for this reduction, supplemental power
from a natural gas combined-cycle power plant was assumed to fill the gap. A small amount of
additional energy—less than 4% of what was required for carbon capture and compression—was
taken from the grid to transport the compressed CO
2
(up to 1800 km) by pipeline to an under-
ground sequestration site.
Figure 11.26 shows the life-cycle fossil energy requirements, per kilowatt-hour of electricity
produced, for the five power plant technologies, with and without CO
2
-seq. CO
2
-seq increased the
fossil energy requirements of every system in Spath and Mann (2004). Although capturing CO
2
in
the biomass systems led to a relatively large increase in energy consumption, net fossil fuel con-
sumption was more than 80% lower than that of coal, even without CO
2
-seq.
16
Additional fossil
energy required
for CO
2
capture
and sequestration
14
12
10
8
6
4
2
0
Coal
NGCC
Coal/biomass
co-fire
Biomass
direct-fire
Biomass IGCC
FIGure 11.26
Life-cycle fossil energy requirements of electricity generation with and without carbon cap-
ture and sequestration. (From Spath, P.L. and Mann, M.K.,
Biomass Power and Conventional Fossil Systems
with and without CO
2
Sequestration—Comparing the Energy Balance, Greenhouse Gas Emissions and
Economics
. NREL/TP-510-32575, National Renewable Energy Laboratory, Golden, CO, 2004.)
