Large-scale-power-generation-using-fuel-cell.doc

Large Scale Power Generation Using Fuel Cell

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CONTENTS i. ACNOWLEDGMENT ii. ABSTRCT iii. WHAT IS A FUEL CELL iv. PEM FUEL CELL v. PEM FUEL CELL APPLICATION vi. OTHER TYPES OF FUEL CELL vii. ADVANTAGES OF FUEL CELL viii. APPLICATIONS OF FUEL CELL ix. DISADVANTAGES OF FUEL CELL x. FUTURE APPLICATIONS OF FUEL CELL xi. FUTURE POTENTIALS OF FUEL CELL xii. CONCLUSION xiii. REFERENCES

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ABSTRACT

Fuel cell uses hydrogen and oxygen to produce electricity through electrochemical reaction. They have a potential to create much more reliable power with lower levels of undesirable emissions and noise and higher overall efficiency than more traditional power generation system. Fuel cells have many advantages. They are clean and reliable, no moving parts, easy thermal management and they are efficient They have application ranging from space crafts to private automobiles, large stationary power generating systems to small electronic devices. Fuel cells are poised to play and increasingly critical role in meeting the world’s growing demands for clean reliable power.

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INTRODUCTION Technology is increasing our energy needs, but it is also showing in new ways to generate power more effetely with less impact on the environment. One of the most promising options for supplementing future power supplies is the fuel cells. They have the potential to create much more reliable power, with lower levels of undesirable emissions and noise and higher over all efficiency than more traditional power generation systems with existing and projected applications ranging from space craft to private automobiles, large stationary power generator systems to small electronic devices, fuel cells are poised to play an increasingly critical role in meeting the world’s plowing demand for clean, reliable power.

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What is a fuel cell Fuel cell is an electrochemical energy conversion device which converts chemicals hydrogen and oxygen to produce electricity by slipping electrons from hydrogen. The hydrogen med is exceeded from natural gun, propane and other common fuel and oxygen is from air.

A fuel cell system consists of 3 major components 1. A fuel cell stack 2. A processor to extract pare hydrogen from the fuel source 3. A storage and conditioners system to adapt the fuel cell’s continuous power only out to fluctuating demand. 4. A mechanism for recovering heat from electrochemical process. The remainder of the system consists of pumps compressors and controls. Fuel cell stack: in fuel cell stack, purified hydrogen and oxygen from air pass through linked platter similar to those in battery .the electrochemical reaction generator electricity and heat. An energy storage and power conditioners system adapts the fuel cell’s maximum power flour to fluctuating power loads. A battery storage system with dc-ac inventor stores power from low demand periods for use during peak demand . Heat recovery system directs heat from the jacket of water surrounding the fuel cell in to a preheat tank for the domes tie hot water system.

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Types of fuel cells. There are different types of fuel cells Research is underway to develop proton exchange membrane fuel cell. Proton exchange membrane fuel cell user one of the simplest reactions of any fuel cell.

PEM fuel cell history PEM technology was developed after 1960. It was developed for U.S. Navy and Army. The first unit was fueled by hydrogen generated by mixing water and lithium hydride. The next development in PEM Technology was for NASA’s project Gemini in the early days of the U.S. piloted space program .batteries had provided power for earlier missions, but future missions would be longer repairing a different power source. By mid -1970s PEM cells were developed for under water life support leading to the US nay oxygen generation plant.

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COMPONENTS& WORIKNG OF PEM FUEL CELL

PEM fuel cell has 4 basic components The anode: it is the negative post of the fuel cell has several jobs .it conducts electrons that are freed from the hydrogen molecular so that they can be used in an external circuit. It was channels etched into if that disperse the hydrogen gun equally over the surface of the catalyst The cathode: it is the positive post of the fuel cell has channels etched in to if that distribute the oxygen to the surface of the catalyst it also conducts the Electrons back from the external circuit to the catalyst, where they can recombine with the hydrogen cons and oxygen to form water.

The electrolyte: electrolyte is proton exchange membrane. The membrane is made from “nafion”, a sulfate polymer made by Dupont

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The catalyst: the catalyst is a special material that facilitates the reaction of oxygen and hydrogen. The usually used catalyst is platinum powder very thirty coaled on to carbon paper or cloth. The carbon is electrically neutral but conductive and also porous allowing the flow of gun and cons through it platinum coated side of the catalyst faces the PEM

WORKING OF PEM FUEL CELL

The pressurized hydrogen gas is entering the fuel on the anode side. This gun is forced through the catalyst by pressure. When Hz molecule comes in contact with the platinum on the catalyst, it splits on to two H+ cons and two electrons. The proton then travels through th membrane to the side of the fuel cell. But the electron can not permanently through the membrane. Instead it travels through an electric wire to get to the other side, and delivers its

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energy to a load along the way, such as a bulb .mean while on the cathode side of the fuel cell, oxygen gas (O2) is being forced through the catalyst where it forms oxygen atoms. Each of these atoms has a strong –ve change. The –ve charge attracts two H0 cons through the membrane where they recombine to oxygen atom and two water molecules are formed.

The reaction taking place is

Anode side: 2H2> 4H+ + 4e-

Cathode side: O2 + 4H+ + 4e- >2H2O

Net reaction:

2H2 + O2 > 2H2O + energy (electricity)

This reaction in a single fuel cell produces only about +ve but the voltage provided by each fuel cell that is large enough for practical application. Many fuel cells can be combined to form a fuel cell stack. The figure below shows a fuel cell stack

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PEM FUELL CELL CHARACTERISTICS

PEMIC operate at family low temperature (about 1760 F or 800 C), which means they watch up quickly and don’t require expensive containment structures. It has high power density and can vary their output quickly to meet shifts on power demand. PEM fuel cells are relatively smaller size, low material cost, high performance and high volume manufacturability make them ideal for transportation, stationary and portable applications.

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PEM FUEL CELL APPLICATIONS PEM started in space but they have applications that are more down to earth. PEM fuel cells can provide both stationary and portable power for many applications including lighting, communication, navigation, computation and entertainment.

Vehicle PEM application Vehicular applications include busses, long distance aircraft and cars. Fuel cell cars will be at least 50% more economical in operation than internal combustion cars. Car manufacturers are spending billions annually on development of PEMFC stacks for hybrid and electric cars.

Portable power PEM applications PEM fuel cells can be used in cellular phones, laptop computers and other portable electronic devices. The fuel cell stack made up of eight of these modules could power a cell phone. The goal is to power a cell phone for up to 40 days and 20 hours talk time. Also several PEM have been developed for notebook pc’s.

Renewable energy PEM applications Energy in 2000, PEM technology was selected to provide nighttime power for the solar powered Helios a long duration aircraft. The goal was to make unpiloted aircraft fly continuously for up to six months. Photovoltaic panels during the day ran electric motors and electrolyzed water. At night the fuel cell ran the motors by converting the hydrogen and oxygen back in to water.

Other applications are •

Military and space applications

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Residential power and heat

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Off grid

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Commercial building power and heat

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Assured power

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Distributed stationary power

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Central station power

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Hydrogen generation

Other types of fuel cells are 1. Solid oxide fuel cells. 2. Direct methanol fuel cell 3. Phosphoric acid fuel cell 4. Alkaline fuel cell 5. Molten carbonate fuel cell . At the heart of any fuel cell is the electrolyte which separates the two electrodes. There are several different types of electrolytes with very different properties, and hence very different fuel cell types have been built around them, mostly named after the electrolyte. They are:

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SOLID OXID EFUEL CELL (SOFC)

Planar design for a solid oxide fuel cell (exploded view) A SOFC uses yttria-stabilised zirconia as its electrolyte, sandwiched between the anode and the cathode. It runs at a temperature of around 1,000°C. The heat produced can be used in cogeneration applications or in a steam turbine to provide more electricity than that generated from the chemical reaction within the fuel cell (a bottoming cycle). A number of different 12

fuels can be used, from pure hydrogen to methane to carbon monoxide, and the nature of the emissions from the fuel cell will vary correspondingly with the fuel mix. There are three fundamental designs of SOFC - the tubular, planar and monolithic types. The first of these was designed by the Westinghouse Electric Corporation and operates with the fuel on the outside surfaces of a bundle of tubes, and the oxidant on the inside, the tube itself being composed of the electrolyte and electrode 'sandwich'. Planar SOFCs are under development by a number of companies, with Siemens and Fuji Electric two of the leaders. In this case the cells are flat plates bonded together and placed one on top of the other to form a stack. The advantages of this system over the tubular system are its relative ease of manufacture and a lower ohmic resistance of the electrolyte, resulting in reduced energy losses. Monolithic SOFCs are in a very early stage of design, with the process one of sintering and corrugation of the electrodes and electrolyte to form a honeycomb structure. Basic laboratory tests have been conducted, with results indicating that this form of fuel cell may be one of the most efficient.

Molten Carbonate Fuel Cells (MCFC) MCFCs are so named because the electrolyte they use is a molten alkali carbonate mixture, retained in a matrix. They operate at a temperature of about 650°C, meaning that once again useful heat is produced. In this case the cathode must be supplied with carbon dioxide, which reacts with the oxygen and electrons to form carbonate ions, which carry the ionic current through the electrolyte. At the anode these ions are consumed in the oxidation of hydrogen,

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which also forms water vapour and carbon dioxide to be transferred back to the cathode. There are two ways of doing this: either by burning the anode exhaust with excess air and removing the water vapour before mixing it with the cathode inlet gas; or by separating the CO2 from the exhaust gas using a 'product exchange device'. The fuel consumed in an MCFC is usually natural gas, though this must be reformed in some way to create a hydrogen-rich gas to feed to the stack. An MCFC produces heat and water vapour at the anode, which can be used for the steam reformation of methane. This means that it is inherently more efficient than a cell requiring external fuel processing. Again, the MCFC can use carbon monoxide at the anode as a fuel. The MCFC is seen by many as an ideal source for large scale power generation. One reason for this is the necessity for large amounts of ancillary equipment, which would render a small operation uneconomic. There is also no requirement for expensive catalysts as in low temperature fuel cells, and a third reason is the fact that the heat generated can be used for internal reformation of methane, a bottoming cycle and for fuel processing and cogeneration. This increases the efficiency of the fuel cell system.

Phosphoric Acid Fuel Cells (PAFC) The PAFC is one of the oldest and therefore most established fuel cell technologies, and is the only one in use in a small number of power generation projects. It uses phosphoric acid as its electrolyte, and is able to reform methane to a hydrogen-rich gas for use as a fuel with the waste heat from the fuel cell stack. This heat may also be utilised for space heating or hot water. It operates at temperatures around 200°C, so the waste heat is not of a high enough

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quality to be used in cogeneration applications. It is also possible to use alcohols such as methanol and ethanol as fuels, though care must be taken in all cases to avoid poisoning the anode by carbon monoxide and hydrogen sulphide which may be present in the reformed fuels. This results in a gradual reduction in performance and the eventual failure of the cell. Direct Methanol Fuel Cells (DMFC) This type of fuel cell is based on solid polymer technology but uses methanol directly as a fuel. If it can be made to work, that would be a big step forward in the automotive area where the storage or generation of hydrogen is one of the big obstacles for the introduction of fuel cells. Prototypes exist, but the development is at an early stage. There are principal problems, including the lower electrochemical activity of the methanol as compared to hydrogen, giving rise to lower cell voltages and, hence, efficiencies. Also, methanol is miscible in water, so some of it is liable to cross the water-saturated membrane and cause corrosion and exhaust gas problems on the cathode side. Nevertheless, the direct methanol fuel cell is an interesting proposition and a number of places are working on it, including Siemens in Germany, the University of Newcastle and Argonne National Laboratory.

Alkaline Fuel Cells (AFC) Alkaline fuel cells use a solution of potassium hydroxide in water as their electrolyte, making them sensitive not to CO as the SPFC is, but to CO 2, meaning that oxygen has traditionally been used as the oxidant in the system. This has led to few uses outside aerospace, although some of the first experimental vehicles were powered by AFCs. They use comparatively

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cheap materials in their electrodes but are not as power dense as SPFCs, making them bulky in some situations. The alkaline fuel cell has been used with great success in the past in space missions, dating back to the Apollo and Gemini missions in the 1960s. It is still in use in the Space Shuttle today and provides not only the power but also the drinking water for the astronauts.

ADVANTAGES OF FUEL CELL 1. fuel cells are clean and reliable Fuel cell uses hydrogen and oxygen for producing electricity and the only byproducts are water, heat and small amount of CO2. So there is a lower level of undesirable emissions. 2. No moving parts.

Fuel cells have no moving parts, so they make much noise, break down or quickly wear out.

3. Efficient

This is a major long term advantage. Fuels cells are not limited by the thermodynamic constraints that heat based combustion type process are subject to. Efficiency is higher than more traditional power generation system.

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Fuel cell’s efficiency, multy fuel capability and modular structure make it uniquely suited for use in a wide variety of stationary, vehicular and portable energy or power application. Fuel cell cars using H2 as a fuel only emit water vapor CO2 and they do not emit pollutants.

4. Easy thermal management.

No need to add a separate liquid or air heating or cooling system.H2 is a very efficient fuel. Each kg of it packs 42kwh of energy that is 3 times as much as the same weight of gasoline and 1000 times as much as a lead acid battery.

The benefits are national energy security, cleaner air and economic opportunity. APPLICATION OF FUEL CELL Fuel cells can be used from space craft to private automobiles, large stationary power generation system to small electronic devices. 1. It can be used in small electronic devices. 2. It can be used in military space applications 3. It can be used in lap top computers and vacuum cleaners. 4. To power facilities such as hospitals that needs a source of non interruptible power.

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DISADVANTAGES OF FUEL CELL 1. Fuel cell uses hydrogen and oxygen to produce electricity. The o2 required for a fuel cell comes from the air. But H2 is not readily available.H2 is difficult to store and distribute. This problem is addressed by a device called reformer turns hydrocarbon or alcohol fuel into H2 ,but the problem is that it also produces some other gases also. 2.

Platinum catalysts are expensive.

FUTURE APPLICATIONS OF FUEL CELL The ultimate goal of fuel cell research is to produce a totally non polluting mobile, stationary or portable power generator. In China a company eVonyx is developing metal based fuel cells. This fuel cells use Aluminum and Zinc etc as their fuels. If successful, these could go a long way toward cleaning up the air where scooters and cars powered by highly polluting two stroke engines. In the near term metal based fuel cells could replace back generators driven by internal combustion engines. Metal based fuel cells starts a lot of energy in a small space both conveniently and safely.

FUTURE POTENTIALS OF FUEL CELL 1. Fuel cell in vehicles combine very high energy efficiency with zero exhaust emissions and potentially low noise without diminishing its performance and range

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In the medium to long term , fuel cells have a strong energy saving potential for decentralized co-generation in household and building and for power production.

3. In the long term they could replace a large part of the current combustion systems in all energy end use sectors.

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CONCLUSION The ultimate goal of fuel cell research is to produce a totally non polluting mobile, stationary or portable power generator. And we can expect to have fuel cells in cars, buildings and industries!

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REFERENCE

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http://science.howstuffworks.com/fuel-cell.htm http://www.seminarsonly.com

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http://www.nmsea.org/curriculum/7_12/fuel_cells/fuel_cells.htm

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http://www.bpa.gov/energy/N/Tech/fuel cell/pem_fuel_cells.cfm

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http://www.e-sources.com/fuelcell/fcexpln.html

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