World Energy Outlook 2007

compression of the gas and its transportation (usually via pipelines) to a storage
site, such as a deep saline formation, depleted oil/gas field or unmineable coal
seam (Figure 5.16). The CO 2
may also be used for enhanced oil or gas recovery.
CCS processes can currently capture more than 85% of the CO 2
that would
otherwise be emitted by a power plant, but they reduce the plant’s thermal
efficiency by about 8 to 12 percentage points and, thus, increase fossil-fuel
inputs, because of the additional energy consumed in capturing the gas.
Initially, CCS is expected to be deployed primarily in coal-fired power stations,
because the CO 2
emissions to be captured are proportionately larger than in
oil- or natural-gas-fired plants, reducing the per-tonne cost.
5
Figure 5.16: CO 2
Capture, Transport and Storage Infrastructure
CO2
compression
plant
CO2
separation
plant
Power plant/
factory
Coal
CO2
injection
Enhanced
oil recovery
CO storage
2
Fossil fuels
CO 2
Hydrogen
Electricity
The process of capturing CO 2
generally represents the largest component of
CCS costs. There are three main processes currently available:
Pre-combustion capture: This process can be used in plants using coal or natural
gas. The fuel is reacted with air or oxygen, generating carbon monoxide and
hydrogen, which is further processed in a shift reactor to produce a mixture of
hydrogen and CO 2
. The gases are separated, with the hydrogen used to
generate electricity and heat in a combined-cycle gas turbine.
Post-combustion capture: This involves removing the CO 2
from flue gas from
power stations or industrial plants. The gas contains between 3% and 4% of
CO 2
by volume in a gas-fired plant and around 15% in a coal-fired plant.
Chapter 5 - Global Environmental Repercussions 217