A POWER plant with solid oxide fuel cells powered by natural gas has been proposed by scientists from the Massachusetts Institute of Technology (MIT).
Thomas Adams, a postdoctoral assistant, and Paul Barton, Lammot du Pont professor of chemical engineering, say their system would not produce carbon dioxide emissions and makes use only of technologies either already available and tested or in advanced stages of development. The components in the proposed system are placed in a different configuration to standard systems.
The proposed system has an electrical efficiency of 74% HHV (higher heating value) and zero atmospheric emissions. The system is essentially based on a standard natural gas combined cycle plant, replacing the turbines with the solid oxide fuel cells, which produce electricity electrochemically.
The exhaust from the fuel cell contains mainly water and CO2, which can be separated easily by condensation of the water, avoiding an energy-intensive CO2 absorption step.
Natural gas at temperatures of 550°C with steam at a 2:1 ratio is fed into a pre-reformer to allow near-complete conversion of ethane, propane and butane. The resulting gas is then heated to 950°C and enters the reformer to produce syngas. Carrying out this step upstream of the fuel cell power generation step avoids the problem of carbon deposition at the anode. A water-gas-shift reaction removes most of the CO.
The fuel cells operate at temperatures of around 950°C and at pressures of 10.1 bar. Heat from the system can be recovered and used to heat the steam required for pre-reforming, reforming and water-gas-shift stages, using a heat exchanger network.
Exhaust gases are cooled to 21°C and CO2 is then recovered using a three-stage flash cascade process. It is then condensed to a liquid for transportation and sequestration. Any NOX gases produced are condensed and sequestered with the CO2.
Adams and Barton compared the costs of producing energy with their system and others already in use and say that if carbon credits were introduced in the US, the price would be comparable to, or even less than if coal were used, incentivising carbon capture technology. A patent has been applied for.
