Page 69 - New Trends In Coal Conversion

Current status of CO 2 capture from coal facilities 35

require a fundamental redesign and integration of the power plant. Moreover,
POSTCC is the first capture technology that has reached commercial scale in the power
sector.
There are a series of separation processes that a priori can be applied to capture the
CO 2 present in flue gas: absorption, adsorption, separation with membranes, enzyme-
based operations, etc. However, these technologies are at different stages of develop-
ment. The technology currently used in the CCUS demonstration projects operating at
commercial scale in coal power plants is amine scrubbing. The goal of the Department
of Energy of the United States (DOE) for the second-generation technologies is to cap-
ture 90% of CO 2 at less than $40 per metric ton by 2020e25 to enable cost-effective
CO 2 capture and to ensure safe, reliable, and affordable energy from fossil fuels.

2.2.1 Amine-based POSTCC systems

Amine-based POSTCC systems involve the countercurrent contact of the flue gas with
aqueous amine solutions in the absorber, where the CO 2 reacts with the amine produc-
ing decarbonized flue gas. The spent solvent is sent to the stripper, where it releases the
captured CO 2 by means of low-pressure steam. The hot lean solvent is fed to a cross
heat exchanger to preheat the spent solvent and then sent back to the absorber to close
the loop (see Fig. 2.1). This technology implies a reduction of 20%e30% of the power
output from coal-fired power plants. Solvent development and process optimization
has led to a substantial reduction in the energy requirements of amine-based POSTCC
systems. However, there are some remaining issues, such as high water consumption,
solvent degradation, and emissions.

2.2.1.1 Commercial-scale demonstration of POSTCC at coal-fired
power plants
The first commercial-scale POSTCC system installed at a coal-fired power plant
started to operate in 2014 at Saskatchewan, Canada. The capture process makes use

Power generation

Stack

Particulate CO 2
control Flue gas desulfuirization
Air Absorber HX Stripper
Boiler
Coal Direct
contact
cooler
(DCC)
Reboiler
Figure 2.1 Scheme of an absorption-based post-combustion CO 2 capture process.