CO Capture and Storage - Energy and Climate: How to Achieve a Successful Energy Transition - page 108

This equipment operates at rather unfavourable conditions using large
volumes of flue gases at a low pressure and low CO 2 concentrations.
The installations are bulky, costly and require fairly large amounts of
energy, which can lead in some cases to almost double the energy
consumption.
Therefore, in the case of new installations, other options have to be
considered: one such option retrieves CO 2 before combustion by trans-
forming the fuel which is used into a clean one through pre-combustion
capture; another option consists of using pure oxygen instead of air in
order to produce CO 2 concentrated flue gases (oxy-fuel combustion).
In the first case (pre-combustion capture), the fossil fuel is first con-
verted into a synthesis gas, consisting of a mixture of carbon monoxide
(CO) and hydrogen, either by steam-reforming of natural gas or by
partial oxidation in the presence of pure oxygen from coal or biomass.
The CO present in the mixture is then reacted with steam water during a
'shift-conversion' stage in order to produce a mixture of CO 2 and
hydrogen.
Carbon dioxide is then separated from hydrogen at good operating
conditions, i.e. at a comparatively high pressure and concentration, and
sent to a storage location. Hydrogen can then be used for producing
energy (electricity and/or heat) without any CO 2 emission.
This option has been considered for the FutureGen project launched in
the USA. This project, for which a budget of around 1 billion US $ had
been announced, was due to be demonstrated on the scale of a 275MW
power plant, planned to be operational by 2012. The project is now
cancelled and restructured, which illustrates the difficulty of financing
such demonstrations.
Oxy-fuel combustion is operated in the presence of pure oxygen.
Carbon dioxide, which is at a high concentration in the flue gases, is
easily separated from steamwater withwhich it is mixed. This technology
is already operational and industrial pilot plants are to be tested on a scale
of around 30 thermal MW in Germany by the electricity producer
Vattenfall and in France by Total.
In the case of the project led by Total, CO 2 captured in the Lacq setting
will be transported through a pipe and injected in the depleted reservoir
of Rousse, located 30 km from Lacq. Pure oxygen which is required for
oxy-fuel combustion is currently produced by low-temperature distilla-
tion. Newoptions are presently being investigated for transferring oxygen
directly to the combustion zone. One of these options is to circulate a solid
phase, which extracts oxygen from air and then releases it back to the
combustion zone ('chemical looping').