Engineering Solutions for CO2 Conversion. Группа авторов

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Engineering Solutions for CO2 Conversion - Группа авторов


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operating at unconventional turbine inlet temperatures and pressure ratios, either using natural gas as a fuel or coal through integrated gasification fuel cell (IGFC) concepts. Because most fuel is oxidized in the fuel cell to allow a high CO2 capture efficiency, the fuel cell (FC) generates the majority of the cycle power output. The alternative option offered by MCFCs is shown at the bottom of Figure 1.9, where the fuel cell can operate “draining” CO2 from the cathode inlet stream, receiving the flue gases of a conventional power plant. In this configuration, the fuel cell operates with a post‐combustion approach, although also oxidizing a minor portion of additional fuel with the same “oxyfuel” features discussed above.

      Currently, the main challenges for stationary fuel cells are cost and cell durability. For the IGFC system, the gas cleaning process adds another energy barrier to its power generation.

       1.2.5.1.1 Solid Oxide Fuel Cells (SOFCs)

      In the pre‐anode CO2 capture process, syngas is generated at high pressure through high pressure coal gasification or by reforming the natural gas available from a natural gas pipeline at high pressure. Similar to the above cases, the syngas can be optionally shifted using the WGS reaction, creating a stream of steam, H2, and CO2. Up to about 90% of the CO2 can then be recovered from the syngas (or shifted syngas) using absorption or adsorption technologies.

      The post‐anode CO2 capture has been extensively studied in SOFC IGCC and natural gas cycles. A simple IGFC system is similar to an IGCC system, but the gas turbine (GT) power island is replaced by a FC island. Some system configurations still have a gas or steam turbine to utilize the extra heat. “Post‐anode” CO2 capture can be applied via CO2 separation from H2O via H2O condensation (or via cooling, knockout, and additional drying) and can effectively result in a 100% CO2 removal. A separation system that uses condensation followed by a cascade of flash drums can be used to produce CO2 at high enough purity for pipeline transport at the SOFC anode exhaust pressure.

       1.2.5.1.2 Molten Carbonate Fuel Cells (MCFCs)

Schematic illustration of the superstructure of SOFC – CO2 capture process configurations.

      Source: Adams et al. [40].

      One example of an MCFC and CO2 capture system was developed by Fuel Cell Energy (FCE), namely, the Combined Electric Power and Carbon‐dioxide Separation (CEPACS). In the process of capturing >90% CO2. In this configuration, the system can generate up to 351 MWe additional power (net AC), after compensating for the auxiliary power requirements of CO2 capture and compression.5

      1.3.1 Integration of the Capture Unit in the Thermal Power Plant

      Source: Adapted from Adams and Mac Dowell [43], Gonzalez‐Salazar


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