1. Thermodynamic Principles
- Electrochemical Process; Molten Carbonate Fuel Cell (MCFC)
- MCFCs use a molten carbonate salt electrolyte suspended in a porous ceramic matrix of beta-alumina solid.
- Non-precious metals can be used as catalyst due to high temperature of MCFC opperation (600 deg celcius and above).
- Can withstand considerable contamination in comparision with other fuel cell types.
- Blanced Chemical Equations:
- Internal Reformer:
- CH4 + H2O –> 3H2 + CO
- H2 + CO3 –> H2O + CO2 + 2e
- 1/2 O2 + CO2 + 2e –> CO3
- Cell Combined Equation:
- H2 + 1/2 O2 + CO2 –> H2O + CO2
- Internal Reformer:
- Due to the high opperating temperature, no additional energy is needed to convert fuels to hydrogen fuel. Fuel is converted to hydrogen fuel inside the cell (internal reforming).
- MCFC can be utilized for waste streams from other industrial processes.
- Coal power plant gas. MCFC requires the introduction of CO2 into the cathode, which can be used to reduce the emission of CO2 into the atmopshere.
- Biogas from the break down of garbage and animal waste can be converted to electrical energy by MCFCs.
- Natural gas.
- The gas exiting the cell is around 400 degrees celcius, which makes it an ideal candiate for heat loss reduction by steam powered turbine electricity generation.
- The efficiency of MCFCs can be close to 60%, and if the waste heat is used to generate steam power, the efficiency can be close to 85%!
3. Engineering Details
- MCFCs are a fuel cell that has very limited application. They are used solely for the purpose of large-scale energy production.
- Uses alternate fuels, even waste.
- Due to the high opperating temperature and corrosivity of the electrolyte, MCFCs degrade quickly and require costly maintentance.
- Costs are recouped by the ability to use inexpensive metal catalysts, internal reforming, and the potential to recover energy from waste streams.
4. Environmental Concerns
- Due to the use of fossil fuels, MCFCs produce carbon dioxide gas. A portion of the CO2 gas is reused by the cell, not all.
- The adoption of MCFCs, while increasing the efficiency of coal-burning power plants, could act as a crutch to slow the complete replacement of fossil fuels by clean, renewable energy sources.
- Degradation of cell life due to high operating temperature and electroyte corrosivity increases the production of hazardous wastes.
5. Personal Thoughts
- Due to the incredible efficency of MCFCs, I think that they are a fantasic new resource for the conversion of waste gas from landfills and anerobic digestors to energy.
- I share the concern, however, that MCFCs will be used to support the continued use of coal burning.
- The unavoidable production of carbon dioxide gas is a big issue, especially with the push to develope energy sources that do not have greenhouse gas emissions.
- In all, I think that there are better alternatives for the waste gases from landfills and agriculture. The only real beneficial use of MCFCs is in conjunction with coal burning.
6. MCFC Schematic
7. Nernst Equation:
- “Types of Fuel Cells – Fuel Cell Energy”. www.fuelcellenergy.com. Retrieved 11-15-15
- “NFCRC Tutorial: Molten Carbonate Fuel Cell (MCFC)”. www.nfcrc.uci.edu. Retrieved 11-15-15.
- “Types of Fuel Cells | Department of Energy”. energy.gov. Retrieved 11-15-15.
- “High Temperature Fuel Cells” (PDF). University of Babylon. Retrieved 11-15-15.