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The greatest barrier to capturing carbon dioxide is the high proportion of nitrogen present in the combustion air. Nitrogen does not contribute to the combustion process, yet must be swept through the entire plant. The solution: use of the Integrated Gasification Combined Cycle (IGCC). IGCC uses pure oxygen to turn pulverised coal into a synthesis gas comprised primarily of carbon monoxide and hydrogen. The subsequent CO shift reaction converts most of the carbon monoxide into carbon dioxide and additional hydrogen using steam.
The CO2 is then easy to separate with a scrubbing agent. It is subsequently desulphurised and compressed or liquefied, making it much easier to transport.
IGCC plants are referred to as combined cycle plants as they synergise gas and steam turbines for extremely efficient electricity generation. Hydrogen resulting from the IGCC process is burnt in the gas turbine, which in turn drives an electricity generator. The resulting emissions consist primarily of atmospheric nitrogen and pure water vapour and are used to generate steam, which powers a steam turbine and thus a second electricity generator.
The benefits of this procedure include higher plant efficiency levels and flexibility. As the IGCC process chain produces an interim synthesis gas, not only electricity can be generated, but even various chemical products or even fuel. The hydrogen produced during the IGCC process chain with CO2 capture can, for example, be recovered directly. It can thus be used as fuel for fuel-cell vehicles running on hydrogen. Biomass or waste materials can also replace some of the coal in IGCC plants.
How pre-combustion capture works
Linde was involved in setting up the ENCAP (Enhanced Capture of CO2) project as early as the start of 2003. The programme was officially launched in 2004 under the EU's Sixth Framework Programme. The goal of ENCAP was to develop suitable technologies for CO2 separation in power plant processes. Altogether, 33 industry partners and several universities and research bodies supported the project, which ran until early 2009.
Further information is available online at www.encapco2.org.
Linde was involved in the collaborative projects OXYCOAL-AC, ADECOS and COORIVA, which were organised within the framework of the COORETEC (CO2 REduction TEChnologies in fossil-fuel power plants) programme run by the German Ministry of Economics and Technology.
OXYCOAL-AC focussed on developing a CO2-free coal-burning process for generating power. ADECOS researched solutions for the oxyfuel process. COORIVA was a collaboration between the TU Bergakademie Freiberg, The Linde Group and further industry partners that carried out feasibility studies for a lignite and pit coal-fired IGCC reference power plant to be built from 2015 on and equipped with CO2 separation technology.
Further information is available online at www.cooretec.de.