Exergy and Economic Analysis of Catalytic Coal Gasifiers Coupled With Solid Oxide Fuel Cells

Abstract

Listen

Translate article

The National Energy Technology Laboratory (NETL) as well as Li et al. [1] have shown that integrating a catalytic coal gasifier with a solid oxide fuel cell (SOFC) can achieve high system efficiencies (∼60%) while capturing and sequestering >90% of the carbon dioxide. Integration of a catalytic gasifier with a SOFC is aided by the minimal exergy destruction inside a catalytic, steam-coal gasifier producing a high-methane content syngas, and the decreased exergy destruction in the SOFC due to the ability to operate at lower air stoichiometric flow ratios compared with a SOFC operating only on hydrogen. For a given temperature difference across the inlet and outlet of the fuel cell and for a given current density, a SOFC can be operated at a lower air stoichiometric ratio if there is a significant amount of methane in syngas and if the pressure of the fuel cell is above atmospheric pressure. Here, we present both an exergy analysis of one possible way of integrating a SOFC with a catalytic gasifier. The gasifier is a fluidized bed gasifier that uses ∼20%wt potassium carbonate along with the coal. Before entering the SOFC, carbon dioxide in the syngas is captured using lime, and then the anode tail gas from the SOFC is recycled back to the gasifier, similar to the configuration modeled by Li et al. [2]. We will present the exergy efficiency as a function of the pressure of the SOFC, and compare the exergy efficiency to other coal-based powerplants on the scale of 100–500 MWe. In addition, we use capital and other cost estimates from NETL [3] and others [4] to estimate the internal rate of return on investment (IRR) of various coal based fuel cell power plants, and compare the IRR of these plants with other fossil fuel based base load power plants. We also present the IRR of the catalytic gasification-SOFC power plant as a function of the pressure of the SOFC. Assuming recent fuel & electricity prices, a natural gas combined cycle (NGCC) power plant yields the highest value of rate of return on investment. However, our results suggest that, in the case of a CO2 tax near $30/t CO2, then three different configurations are equally viable economically: NGCC, advanced IGCC-CCS-EOR, and advanced IGFC-CCS-EOR that integrates a catalytic coal gasifier with a pressurized SOFC.