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FUEL CELLS
What is a fuel cell?
How does a fuel cell compare with other energy production technologies? What is the difference between a fuel cell and a battery? What are the possible uses of fuel cells? What fuels can be used in a fuel cell? How large or small can a fuel cell be? What are the emissions from a fuel cell system? |
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What is a fuel cell? A fuel cell is an electrochemical device that combines hydrogen fuel and oxygen from the air to produce electricity, heat and water. Almost always the fuel is hydrogen or a hydrogen rich gas mixture. The fuel cell reaction is:
Hydrogen + Oxygen (from the air) --> Electricity + Water + Heat
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How does a fuel cell compare with other energy production technologies? The standard method of generating electric power is through the steam cycle. A fuel is burned to produce heat, the heat is used to produce steam, the steam turns a turbine, and the turbine's power is used to turn a generator to produce electricity. A fuel cell circumvents this complex and inherently inefficient process by directly converting the fuel's chemical energy to electricity in a single step. Since the fuel is converted directly to electricity, a fuel cell can operate at much higher efficiencies than internal combustion engines, extracting more electricity from the same amount of fuel. |
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What is the difference between a fuel cell and a battery? The major difference between fuel cells and batteries is that batteries carry a limited “internal” supply of solid fuel and oxidant (lead acid batteries contain sulphuric acid and lead plates that are converted to lead sulphate as electricity is used). Although fuel cells have similar reactions, the reactants are only gases (hydrogen and oxygen from the air) that can be fed into the fuel cell and constantly replenished. As long as there is a supply of gaseous reactants, the fuel cell can continue to power up and will not run down like a battery. Rechargeable batteries discharge over time; the colder the ambient temperature the quicker they discharge. The charge capacity of a battery decreases with the number of charge and discharge cycles. A fuel cell will not discharge over time, maintaining its full charge capacity almost indefinitely. |
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What are the possible uses of fuel cells? In theory, a fuel cell can power anything that runs on electricity. Fuel cells can power cars, buses, boats, trains, planes, scooters, even bicycles. There are fuel cell-powered vending machines, vacuum cleaners and highway road signs. Miniature fuel cells for cellular phones, laptop computers and portable electronics. Large fuel cells can replace existing power plants to provide electricity for a large number of users, or in smaller, distributed power generation plants to supply the electrical needs of, hospitals, credit card centres, police stations, industries, banks, etc. Wastewater treatment plants and landfills are reforming methane for use in fuel cells to generate and export electrical energy into the grid. Thus the possibilities are endless. |
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What fuels can be used in a fuel cell? A variety of fuels may potentially be used with fuel cells. The oxygen may be taken directly from air, while the hydrogen may be delivered either in pure form, from liquid or gaseous storage tanks, or extracted from hydrocarbon fuels including heavy oil, naphtha, ammonia (NH 3), diesel, kerosene, coal, methanol (CH 3 OH), gasoline (a mix of various hydrocarbons), natural gas (CH 4 ), propane (C 3 H 8 ), and others through the use of a reformer. Landfill or biogas may potentially be used either directly or indirectly (after undergoing reformation) in fuel cells. |
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How large or small can a fuel cell be? Fuel cells can be fabricated in a wide range of sizes without sacrificing either efficiency or environmental performance. This flexibility allows fuel cells to generate power in a clean, efficient manner for automobiles, utilities and buildings. Presently, there are micro fuel cells that are the size of a pencil eraser and generate only a few milliwatts of power while there are others large enough to provide the electrical needs of hundreds of homes. Since an individual fuel cell may theoretically produce an open circuit voltage of approximately 1 V, their power output is fully scalable by varying the cross-sectional area of each cell to obtain the desired current and by stacking multiple cells in series to obtain the desired voltage. |
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What are the emissions from a fuel cell system? The fuel cell system using hydrogen as fuel emits non-pollutants such as water. The other fuel cells using gasoline, natural gas, coal gas or other fuels containing hydrocarbons could emit carbon dioxide and nitrogen and their oxides. |
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