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40                                             New Trends in Coal Conversion

         selectivity of 100% over N 2 and generates electricity. CEPACS will be demonstrated
         at 3 MW e scale on real coal flue gas at James M. Barry Electric Generating Station in
         Alabama in 2018. The pilot plant is designed to capture 90% of the inlet CO 2 produc-
         ing 67 t/d of CO 2 and 1,178 kW. A technoeconomic analysis carried out for a 550 MW
         supercritical coal-fired power plant points out that 4.3 Mt CO 2 /y could be captured at a
         90% capture rate with a plant efficiency of 40.7%, which is higher than that without
         capture (Ghezel-Ayagh, 2017).


         2.3   Oxy-combustion capture in coal power plants


         OXYCC refers to the combustion of fuel carried out with pure O 2 instead of air, result-
         ing in a flue gas that consists mainly of CO 2 and H 2 O(IPCC, 2005). Part of the flue
         gas, recycled flue gas (RFG), is fed to the boiler to lower its temperature. The concen-
         trated CO 2 stream needs to be dehydrated, compressed, and purified to meet storage
         specifications in a compression and purification unit (CPU). The main energy
         consuming elements of OXYCC are the air separation unit (ASU) required for O 2 pro-
         duction and the CPU.

         2.3.1  Oxy-combustion in pulverized coal boilers
         Oxy-combustion in pulverized coal boilers (OPC) is the OXYCC technology that has
         reached the highest technology readiness level (TRL) up to date: 7. The main design
         parameter in OPC is how the oxygen and the RFG are introduced into the boiler. The
         level of sulfur oxides needs to be limited to minimize corrosion issues, and the oxygen
         excess in flue gas needs to be minimum to ensure good combustion efficiency and sta-
         ble flame. RFG is generally split into primary RFG (30%e35%) that is used for fuel
         transport, and secondary RFG that is recycled to the boiler (see Fig. 2.2). Primary RFG


                                            Power generation
                 Nitrogen

                 Air separation unit         control           Condenser  Purification unit  Stack

          Air                               Particulate  Flue gas  desulfurization

                   Oxygen Mixer
                     Pulverized coal  Oxy-boiler  Gas gas heater  Fly ash  Sulfur  Water
                 Coal                                                  CO 2
             Coal
                  mill       Secondary RFG
                              Primary RFG
         Figure 2.2 Scheme of oxy-combustion technology in a pulverized coal boiler equipped with an
         air separation unit and a CO 2 purification unit. RFG, recycled flue gas.
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