Energy 2.0

Fuel Cell

Posted on: July 26, 2008

 A fuel cell is an electrochemical energy conversion device which converts the chemicals hydrogen and oxygen into water, and in the process it produces electricity. The fuel cell essentially requires hydrogen and oxygen: while the oxygen is drawn from air, the hydrogen is either supplied directly or is reformed from hydrocarbon gases such as methane or other fuels like ethanol and methanol. Hydrogen and oxygen combine in the fuel cell to produce electricity, heat and water.  There are several different types of fuel cell but they are all based around a central design.

India needs an additional 1,00,000 MW at an estimated investment of nearly US$100bn to meet its power requirements in the next 15 years. Combined with the rising interest in non-conventional energy sources, this translates into great potential for entry of fuel cell power plants as power generators. Given the strong agrarian economy, ethanol (from sugarcane molasses) and methane (from biogas) are readily available as primary choices as fuels for fuel cell plants.

While setting up of the fuel cell stack and fuel processor are significant investments, the operation costs are much lower than conventional power generation facilities. A typical fuel cell plant using methane as a fuel could have raw electricity generation costs at Rs. 4-5 per kWh, which will drop down to a competitive Rs. 2-3 per kWh after factoring reductions in price due to environmental credits, savings on maintenance, increased reliability and use of the heat generated in the fuel cell process.

 The Most Promising Fuel Cell – Molten Carbonate Fuel Cell Technology (MCFC)

Molten carbonate fuel cells are designed to operate at higher temperatures than phosphoric acid or proton exchange membrane fuel cells and thus achieve higher fuel-to-electricity and overall energy use efficiencies (50%) than these low temperature cells (37-42%). When the waste heat is captured and used, overall thermal efficiencies can be as high as 85%. Conventional modes come no where near these figures. 

Type

Operating Template

Electrolyte

Typical Unit Size

Application

Alkaline Fuel Cell (AFC)

70-90

KOH

1-100

Space and Military

Proton Exchange Membrane Fuel Cell (PEMFC)

50-80

Polymeric Membrane

0.1-500

Residential, Portable  and Transportation

Phosphoric Acid Fuel Cell (PAFC)

160-210

Ortho- Phosphoric

5-200

Dispersed Power, Acid Combined Heat  & Power (CHP)

Molten Carbonate Fuel Cell (MCFC)

650

Molten Carbonate

100-2,000

Central Utilities

Solid Oxide Fuel Cell (SOFC)

800-1000

Zirconia

25-1,00,000

Central Utilities

In a molten carbonate fuel cell, the electrolyte is made up of lithium-potassium carbonate salts heated to about 1,200 degrees Fahrenheit (650 degrees Celsius). At these temperatures, the salts melt into a molten state that can conduct charged particles, called ions, between two porous electrodes.

Moreover, MCFCs eliminate the external fuel processors that other lower temperature fuel cells need to extract hydrogen from the fuel. When natural gas is the fuel, methane (the main ingredient of natural gas) and steam are converted into a hydrogen-rich gas inside the fuel cell stack (a process called “internal reforming”). At the anode, hydrogen reacts with the carbonate ions to produce water, carbon dioxide, and electrons. The electrons travel through an external circuit creating electricity and return to the cathode. There, oxygen from the air and carbon dioxide recycled from the anode react with the electrons to form carbonate ions that replenish the electrolyte and provide ionic conduction through the electrolyte, completing the circuit. The electrolyte in this fuel cell is a salt melting of combined alkali carbonates (Li2CO3 / K2CO3).   

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1 Response to "Fuel Cell"

[…] A fuel cell is an electrochemical energy conversion device which converts the chemicals hydrogen and oxygen into water, and in the process it produces electricity. The fuel cell essentially requires hydrogen and oxygen: while the oxygen … Read More […]

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