The main problem with CO2 capture from air-blown units is the low CO2 concentration in the flue gas due to nitrogen dilution. This can be solved by substituting oxygen for air. For PC combustion, this is Oxy-Fuel PC combustion. Another approach is to gasify the coal with oxygen and steam, and remove the CO2 at high pressure prior to combustion of the syngas in a gas turbine. This approach is Integrated Gasification Combined Cycle (IGCC) power generation.
Oxy-fuel combustion, shown schematically in Fig. 2.7, addresses the high CO2 capture and recovery costs, but it does so at the expense of an air-separation unit and its associated energy costs [18, 19]. The advantage is gained through being able to cool the flue gas, condensing out water, and leaving almost pure CO2 which can then be compressed, with further drying, to produce supercritical CO2 for geologic storage. A parasitic energy diagram for oxy-fuel is shown in Fig. 2.8.
Efficiency Loss: Supercritical Oxy-Fuel
Boiler efficiency is improved somewhat, but this gain is more than offset by the power requirements of the oxygen separation unit.
The technology is in active pilot plant development, and the early stages of commercial demonstration. A 30 MWth oxy-fuel pilot plant was commissioned in Schwarze Pumpe, Germany in mid-2008, with plans for a 300 MW demonstration plant followed by a 1,000 MW commercial plant [20, 21]. Because of the early state of commercial development, the performance and cost estimates are not as firm as those for PC or IGCC. Oxy-fuel PC has the potential for lower cost of electricity (COE) and lower CO2 avoided cost than with PC capture. The development of this technology should be monitored.
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