Advanced fluidised bed gasification for carbon capture and fuel cell applications

Abstract

The rapid global economic and population growth requires consistent supply of energy. Gasification is a promising technology for processing solid fuels. One of the technology options is the integration of coal gasification with combined cycle (IGCC). As concerns over enhanced global warming have increased, more advanced technology such as integration of IGCC system with carbon capture and storage (CCS) has been proposed, such as oxyfuel IGCC. Another technology for power generation that can be used instead of IGCC is integrated gasification fuel cell (IGFC). IGFC can also be combined with oxyfuel concept to mitigate global warming. The main objectives of this work are to obtain a greater understanding of oxyfuel gasification of coal and to assess the impact of gases produced on typical materials used in fuel cells. A laboratory scale continuous pressurised fluidised bed reactor has been modified to study CO2 and steam (concentration up to 40%mol.) gasification of coal at 850 °C and pressures up to 10 bara. A second stage fixed bed reactor has been specially designed and constructed to study degradation of different solid oxide fuel cell (SOFC) anode materials (nickel/yttrium stabilised zirconium oxide (Ni/YSZ) and nickel/gadolinium-doped ceria (Ni/CGO)) after exposure to real fuel gas at 765 °C. The main findings include: (1) C conversion decreased significantly at high pressure. This drop was mainly caused by the char deactivation through repolymerisation of the volatiles. (2) Input steam increased C conversion, as steam was more reactive than CO2. However, moisture from feedstock behaved differently compared to steam addition in the gasification gas. (3) Ni/CGO showed a better performance than Ni/YSZ in terms of carbon and sulphur deposition. Fuel gas from CO2/H2O gasification tended to form less carbon and sulphur on tested anode materials than that from CO2 gasification.