(143b) Natural Gas Power Generation with High Efficiency and near-Zero Emissions

Natural gas is prized as a high value fuel that can be used for a wide variety of energy applications. For power generation, natural gas combined cycle (NGCC) plants require roughly 60-75% less capital expense to construct than coal-based counterparts, achieve higher efficiencies (by over 10 percentage points), and emit about half as much CO₂. However, by adding absorption-based 90% CO₂ capture capability, the cost of power production doubles and the thermal efficiency drops significantly [1]. Alternative techniques such as chemical looping [2] and oxycombustion [3] can enable 100% CO₂ capture without absorption, but still suffer a significant loss of efficiency.

In this paper, we present a process which overcomes the significant energy penalty associated with CO₂ capture for electricity production from natural gas. By replacing the combustion step with solid oxide fuel cells, electricity can be generated while preventing the fuel stream from mixing with the oxygen supply. This enables the use of air in the cathode without diluting the fuel exhaust with nitrogen while avoiding the high cost of generating pure O₂. As a result, the fuel exhaust consists primarily of CO₂ and water, which are separated with little energy penalty, providing for a total thermal efficiency significantly higher than the NGCC base case with CO₂ capture.

In addition to 100% CO₂ capture, the process has zero atmospheric emissions. Any H₂S, SO_X, unreacted hydrocarbons, or any other pollutants are sequestered along with the CO₂. Waste water is recovered from the exhaust in sufficient quantities to provide for all of the upstream steam needs. If waterless cooling systems are employed (such as air-cooling), a surplus of high-purity water is generated by the process, rather than consumed. Thus, the fuel-cell enabled process has significant environmental and efficiency advantages over the current alternatives.

References

[1] Woods MC, Capicotto PJ, Haslbeck JL, Kuehn NJ, Matuszewski M, Pinkerton LL, Rutkowski MD, Schoff RL, Vaysman V. Cost and Performance Baseline for Fossil Energy Plants. Volume 1: Bituminous Coal and Natural Gas to Electricity Final Report. DOE/NETL‐2007/1281, Revision 1, August 2007.

[2] Brandvoll O, Bolland O. Inherent CO₂ capture using chemical looping combustion in a natural gas fired power cycle. J Eng Gas Turbines Power 126:316-321 (2004).

[3] Zhang N, Lior N. Comparative study of two low CO₂ emission power generation system options with natural gas reforming. J Eng Gas Turbines Power 130:051701.1-051701.11 (2008).