“HYDROGEN FUEL CELL” A TECHNOLOGY FOR FUTURE ENERGY GENERATION Prakash Aryal 061/BME/624
Abstract In today’s world energy crisis is the major problem with depleting source of conventional organic fossil fuels. A high-tech energy source like nuclear energy is not on everyone’s reach; and is not suitable for small scale and mobile purposes. Thus search for alternative renewable, non-polluting and easily available source of energy is today’s world utmost concern. Hydrogen fuel is one of them having highest possibility of being used as future fuel as it has the highest heating value, non-polluting with only water as byproduct. As Hydrogen is abundant element on earth it has high energy security. Hydrogen can be produced from a variety of sources: Traditional: natural gas, gasoline, diesel, propane Renewable/alternative fuels: landfill gas, bio-gas, methane methanol, ethanol,
cell. It will produce energy in the form of electricity and heat as long as fuel is supplied. In principle, a fuel cell operates like a battery. Unlike a battery, a fuel cell does not run down or require recharging. Many combinations of fuel and oxidant are possible. A hydrogen cell uses hydrogen as fuel and oxygen as oxidant. Other fuels include hydrocarbons and alcohols. Other oxidants include air, chlorine and chlorine dioxide. A fuel cell consists of two electrodes sandwiched around an electrolyte. Oxygen passes over one electrode and hydrogen over the other, generating electricity, water and heat.
Water: using electrolysis, solar or wind power. Hydrogen requires large storage facilities, low temperatures condition (-2520C) and special transportation system. Explosion hazards are major safety problems in public use of this fuel. Extensive research is being done for easy and safe storage of this fuel. What Is A Fuel Cell? A fuel cell is an electrochemical energy conversion device. It produces electricity from various external quantities of fuel (on the anode side) and oxidant (on the cathode side). These react in the presence of an electrolyte. Generally, the reactants flow in and products flow out while the electrolyte remains in the
Fig: Schematic Diagram of Hydrogen Fuel Cell Hydrogen fuel is fed into the "anode" of the fuel cell. Oxygen (or air) enters the fuel cell through the cathode. Encouraged by a catalyst, the hydrogen atom splits into a proton and an electron, which take different paths to the cathode. The proton passes through the electrolyte. The electrons create a separate current that can be utilized before they return to the cathode, to be reunited with the hydrogen and oxygen in a molecule of water.
E-VISION 2009
A fuel cell system which includes a "fuel reformer" can utilize the hydrogen from any hydrocarbon fuel from natural gas to methanol, and even gasoline. Since the fuel cell relies on chemistry and not combustion, emissions from this type of a system would still be much smaller than emissions from the cleanest fuel combustion processes. Fuel cell design In essence, a fuel cell works by catalysis, separating the component electrons and protons of the reactant fuel, and forcing the electrons to travel through a circuit, hence converting them to electrical power. The catalyst is typically comprised of a platinum group metal or alloy. Another catalytic process takes the electrons back in, combining them with the protons and the oxidant to form waste products (typically simple compounds like water and carbon dioxide). In the hydrogen–oxygen proton exchange membrane fuel cell (PEMFC) design, a proton-conducting polymer membrane, (the electrolyte), separates the anode and cathode sides. On the anode side, hydrogen diffuses to the anode catalyst where it later dissociates into protons and electrons. The protons are conducted through the membrane to the cathode, but the electrons are forced to travel in an external circuit (supplying power) because the membrane is electrically insulating. On
Engine Type H2O g/mile Gasoline Passenge r Car1 Gasoline Light Truck1 176.90 CO2 g/mile 415.49 20.9 1.39 CO g/mile NOx g/mile HC g/mile 2.80
the cathode catalyst, oxygen molecules react with the electrons (which have traveled through the external circuit) and protons to form water — in this example, the only waste product, either liquid or vapor. In addition to this pure hydrogen type, there are hydrocarbon fuels for fuel cells, including diesel, methanol (see: direct-methanol fuel cells) and chemical hydrides. The waste products with these types of fuel are carbon dioxide and water. To deliver the desired amount of energy, the fuel cells can be combined in series and parallel circuits, where series yield higher voltage, and parallel allows a stronger current to be drawn. Such a design is called a fuel cell stack. Further, the cell surface area can be increased, to allow stronger
Fig: Design of Hydrogen Fuel Cell current from each cell. Benefits of Hydrogen Fuel Cell No other energy generating technology carries the combination of benefits that fuel cells offer. These benefits include:
Low to Zero Emissions A fuel cell running on pure hydrogen is a zero-emission power source. Some stationary fuel cells use natural gas or hydrocarbons as a hydrogen feedstock, but even those produce far less emissions than conventional power plants. Fuel cells are also very quiet, which reduces noise pollution. Transportation Fuel cell vehicles are the least polluting of all vehicles that consume fuel directly.
N/A
521.63
27.70
1.81
3.51
68.04 Methano : Emissions from Table 113.40 l FCV2 Hydroge n FCV2 113.40 0.00
Ve0.016 s hicle
0.00
0.0025
0.0034 0.00
0.00
Source: 1 2000 U.S. EPA Average Annual Emission for Passenger Cars and Light Trucks 2 Calculations from Desert Research Institute
2
E-VISION 2009
Fuel cell vehicles operating on hydrogen stored on-board the vehicles produce zero pollution in the conventional sense. Neither conventional pollutants nor green house gases are emitted. The only byproducts are water and heat. The simple reaction that takes place inside the fuel cell is highly efficient. Even if the hydrogen is produced from fossil fuels, fuel cell vehicles can reduce emissions of carbon dioxide, a global warming concern, by more than half. High Efficiency In large-scale building systems, these fuel cell cogeneration systems can reduce facility energy service costs by 20% to 40% compared to conventional energy service. Systems fueled by hydrogen can consistently provide more than 50 percent efficiency. Even more efficient systems are under development. In combination with a turbine, electrical efficiencies can exceed 60 percent. Fuel cell passenger vehicles are expected to be up to three times more efficient than internal combustion engines, which now operate at 10 to 16 percent efficiency. High Reliability/High Quality Power A fuel cell system running on hydrogen can be compact, lightweight, has no major moving parts and do not involve combustion, in ideal conditions they can achieve up to 99.9999% reliability. Fuel cells offer clean, high quality power, crucial to an economy that depends on increasingly sensitive computers, medical equipment and machines. Fuel cells can be configured to provide backup power to a gridconnected customer, should the grid fail. They can be configured to provide completely gridindependent power or can use the grid as the backup system. Fuel Flexibility Most fuel cells run on hydrogen and will continue to generate power as long as fuel is supplied. The fuel cell doesn't care where the hydrogen comes from, so a fuel cell system that includes a "fuel reformer" can generate hydrogen from diverse, domestic resources including fossil fuels, such as natural gas and coal; alcohol fuels, such as methanol or ethanol; from hydrogen compounds containing no carbon, such as ammonia; or from biomass, methane, landfill gas or anaerobic digester gas from wastewater treatment plants. Hydrogen can also be produced from electricity from conventional, nuclear or renewable sources such as solar or wind. Security Hydrogen can be produced from domestic sources, eliminating the need to import foreign oil. Because they don't have to be attached to the electric grid, fuel cells allow the country to move away from reliance on high voltage central station power generation which are the most likely terrorist targets in any attempt to cripple the energy infrastructure. Modularity/Scalability/Flexible Siting The beauty of fuel cells is their versatility - since they are scalable, fuel cells can be stacked until the desired power output is reached. Larger fuel cells can be linked together to achieve megawatt outputs. Fuel cells are quiet, which allows for siting close to business or residences. They are also durable and rugged, so they can withstand any terrain or weather conditions. Lightweight, Long-lasting Battery Alternative Fuel cells are being developed for portable electronic devices such as laptops, cellular phones, etc. Fuel cells are providing a much longer operating life than a battery would, in a package of lighter or equal weight per unit of power output. Fuel cells also have an environmental advantage over batteries, since certain kinds of batteries require special disposal treatment. Fuel cells provide a much higher
3
E-VISION 2009
power density, packing more power in a smaller space. Application of Fuel Cell Remote Location Fuel cells are very useful as power sources in remote locations, such as spacecraft, remote weather stations, large parks, rural locations, and in certain military applications. Heat and power supply for domestic purpose A new application is micro combined heat and power, which is cogeneration for family homes, office buildings and factories. This type of system generates constant electric power (selling excess power back to the grid when it is not consumed), and at the same time produces hot air and water from the waste heat Stationary In hospitals, nursing homes, hotels, office buildings, schools, utility power plants - either connected to the electric grid to provide supplemental power and backup assurance for critical areas, or installed as a grid-independent generator for on-site service in areas that are inaccessible by power lines. Telecommunications With the use of computers, internet, and communication networks steadily increasing, there comes a need for more reliable power than is available on the current electrical grid, and fuel cells have proven to be up to 99.999% (five nines) reliable. Landfills/Wastewater Treatment Plants Fuel cells currently operate at landfills and wastewater treatment plants, proving themselves as a valid technology for reducing emissions and generating power from the methane gas they produce.
Transportation Different vehicles like two wheelers, cars, buses etc, using petrol or diesel as fuel can be operated using fuel cell after slight modification in the design. Trains - Fuel cells are being developed for mining locomotives since they produce no emissions. An international consortium is developing the world’s largest fuel cell vehicle, a 109 metric-ton, 1 MW locomotive for military and commercial railway applications. Planes - Fuel cells are an attractive option for aviation since they produce zero or low emissions and make barely any noise. Companies like Boeing are heavily involved in developing a fuel cell plane.
Portable Power Fuel cells can provide power where no electric grid is available and they are quiet which reduces noise pollution.
Micro Power Consumer Electronics- Fuel cells will change the telecommuting world, powering cellular phones, laptops and palm pilots hours longer than batteries. Base load power plants The hydrogen fuel cell power plants for base load can be established for fulfilling continuous demand of the electricity.
Conclusion From the above described benefits and possible application areas of hydrogen fuel cell, we can say that hydrogen is sure to replace conventional fuel as major fuel in coming days. Special precautions should be taken in handling and storage of hydrogen fuels. Hydrogen fuel cell is very versatile in nature having wide fields of applications so research and development of this fuel cell must be promoted worldwide.
References www.fuelcells.org www.en.wikipedia.org/wiki/Fuel_cell www.howstuffworks.com/fuel-cell.htm
4