An increase in population has increased the demand for energy. The major source of energy is oil, gas and coal. World Coal Institute estimates that there are over 984 billion tons of proven coal reserves globally, could last approximately 200 years at current consumption levels. Currently 33 percent of the US electricity is generated by coal. To produce energy, the conventional coal gasification process used releases Sulfur oxides, nitrogen oxides and particulates which pollute the environment. The energy efficiency is around 36 – 40 percent. So, the process calls for having carbon capture and sequestration, which increases the cost and decreases the efficiency. Thus, there is a need for technology improvements.
A Promising Route through Alternative Energy:
An alternative energy approach is to use solid oxide fuel cells (SOFC) in the coal gasification process. SOFC produces electricity directly by oxidizing the fuel. Syngas produced in the initial steps of coal gasification is sent to SOFC unit. Due to the high temperature of SOFC, H2 is derived from steam reforming and water gas shift reaction in SOFC at anode. Air entered at the cathode side of the fuel cell is heated. Oxide ions produced at cathode side diffuses through the electrolyte layer. The H2 derived at anode reacts with the oxide ions forming water and free electrons which produce electricity.
Benefits with SOFC:
With this alternative energy, there are a lot of benefits. There is no formation of sulfur oxide, nitrogen oxide particulates since there is no combustion taking place. Efficiency is higher around 60 percent. Water is the by-product. So the need for carbon capture and sequestration is eliminated. Moreover the heat produced in this process can be recycled to produce electricity.
Challenges with SOFC:
Despite having the potential to replace the conventional process with lesser emissions, higher efficiency, and recycling heat, SOFC faces some challenges. In SOFC, Zirconia-based electrolytes, such as yttria-stabilised-ZrO2 (YSZ), are the most common materials employed. They require high temperature (1000C) for ionization. The high temperature degrades the material of the cell overtime, thereby reducing the life of the cell. The practical applications of SOFCs on a large scale are limited by economic reasons, particularly due to the high costs of production of SOFC and issues in long term stability of the electrolyte in SOFC.
Since the high temperature causes a problem, let’s look at lowering the temperature. Lowering the temperature would lower the ionization properties of the electrolyte. The electrolyte materials selection results to be a crucial step for the development of suitable devices. Ongoing efforts aim to consider materials which could have high ionic conductivity at intermediate temperature range (600-800). This would ensure lower temperature of the SOFC.
Effort for Large Scale Application of SOFC:
Many literature works have suggested the improvement of ionic conductivity for the different ceramic based oxide electrolyte materials, like: zirconia, ceria, lanthanum gallate and bismuth based oxides such as La0.8Sr0.2Ga0.8Mg0.2O3−δ. (LSGM). The ceria-based electrolytes such as gadolinia-doped ceria (GDC) or lanthanum gallate-based electrolytes has proven to show high electric conductivity at intermediate temperatures.
Today, recognized institutes are undergoing small-scale demonstration projects illustrating the potential of SOFC technology to transfer to industry applications within the next 5 to 10 years.
Image courtesy of pixabay.com
Learn more about PreScouter at www.prescouter.com.
