Fuell Cell Shafi

Recent trends in Non Conventional Energy sources: FUEL CELL TECHNOLOGY

FUEL CELL TECHNOLOGY ---------- A SOLUTION FOR EFFICIENT ENERGY CONSERVATION AND POLLUTION REDUCTION M. ABDUL SHAFI, 3rd B.TECH, MECHANICAL, A.I.T.S, RAJAMPET, KADAPA (DIST.), A.P. Email I.D: [email protected] Phone: 09247767812

ABSTRACT Fuel cells are considered for electric power generation with efficiency, neglecting pollution and negligible pollution and negligible noise, among many other advantages for stationary, mobile and portable power applications. Since the beginning of the space age , tremendous progress has been made in the development of many types of fuel cells depending upon the specific applications.

Fuel cells are regularly used in space vehicles and shuttle applications with 125-250 kW modules. The easier way to understand fuel cells is to think of them as a cousin to the ordinary battery both produce electricity through electrochemical reactions. The difference lies in a fuel cells ability to constantly produce electricity. The byproducts of the electrochemical reaction that occurs in a fuel cell are electricity, water vapour and heat. Theoretically the water vapour can be recycled to produce hydrogen. The waste heat can be utilized for heating water space heating and cooling.

The direct conversion of fuel into electricity allows fuels to achieve substantially higher efficiency than combustion which is limited by Carnot’s law of Thermodynamics. Fuel cells achieve efficiency of 35% to 90% depending on whether the waste heat is employed.

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Recent trends in Non Conventional Energy sources: FUEL CELL TECHNOLOGY

INTRODUCTION

A cell (or combination of cells) capable of generating an electric current by converting the chemical energy of a fuel directly into electrical energy is known as Fuel cell. The fuel cell is similar to other electric cells in the respect that it consists of positive and negative electrodes with an electrolyte between them. Fuel in a suitable form is supplied to the negative electrode and oxygen, often from air, to the positive electrode. When the cell operates, the fuel is oxidized and the chemical reaction provides the energy that is converted in to the electricity. Fuel cell differ from conventional electric cells in the respect that the active material (i.e. fuel and oxygen) are not contained with in the cell but are supplied from outside. But for its costs, pure hydrogen gas would be preferred fuel or fuel cells. Main uses of fuel cells are in power production, automobile vehicles and in special military use. The fuel cell was invented in 1839 by Sir William Grove of Swensa, Wales, and the fuel cell technology has been in development for over a century. The first applications were in National Aeronautic and Space Administration (NASA) of U.S.A, space missions because of fuel cell’s dual production of electric power and water, but these devices were too expensive for a wide range of commercial and consumer uses. With decreasing fossil fuel resources and increasing global pollution, the need has increased significantly for better power sources that produce high quality electric energy with higher energy conversion efficiency and negligible emissions with fossil, renewable and other energy resources. The fuel cell is an answer to many of these needs. Hence, the fuel cell is considered as one of the best alternatives to generate electricity for stationary, mobile and portable device applications.

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Recent trends in Non Conventional Energy sources: FUEL CELL TECHNOLOGY

Fuel cells can compete quite easily with combustion engines from high efficiency, low maintenance, negligible pollution, and low noise points of view. However, high cost is the major issue with the fuel cell power today. A single cell proton exchange membrane fuel cell (PEMFC) is shown Fig. below.

Types of Fuel Cells Fuel cells are classified primarily by the kind of electrolyte they employ. This determines the kind of chemical reactions that take place in the cell, the kind of catalysts required, the temperature range in which the cell operates, the fuel required, and other factors. These characteristics, in turn, affect the applications for which these cells are most suitable. There are several types of fuel cells currently under development, each with its own advantages, limitations, and potential applications.     

Polymer Electrolyte Membrane (PEM) Fuel Cells Direct Methanol Fuel Cells (DMFC) Alkaline Fuel Cells Phosphoric Acid Fuel Cells (PAFC) Molten Carbonate Fuel Cells (MCFC) 3

Recent trends in Non Conventional Energy sources: FUEL CELL TECHNOLOGY  Solid Oxide Fuel Cells (SOFC)  Regenerative Fuel Cells  Comparison of Fuel Cell Technologies The advantages of the low temperature portion exchange membrane fuel cells (PEMFC) for mobile (automotive) and residential electric power applications are: short startup and shutdown time and the use of many ordinary materials (such as polymers, metals and graphite) for components if hydrogen is used as the fuel. Since the CO tolerance level of the PEMFC is less than 10 ppm. The high temperature fuel cells (Molten Carbonate-MCFC and Solid Oxide-SOFC) can use diverse fuel source than low temperature fuel cells. It is ideal for mid-size (MW) distributed stationary power generation. They can have internal fuel reforming with natural gas, various fossil fuels, biogases and other fuels. Due to their high operating temperatures, cogeneration and hybrid systems are possible to achieve higher overall system efficiency.

OPERATION OF FUEL CELL (H2 –O2 or Hydrox cell):The operation of the fuel cell can best be described with reference of specific device. Fuel cell can be adopted to a variety of fuels by changing the catalyst. Here Hydrogen, Oxygen (Hydrox) cell is described below. The electro chemical reactions occurring at the electrodes of a hydrogenoxygen cell may very with the nature of the electrolyte, but basically they are as follows. At the negative electrode, hydrogen gas (H2) is converted into hydrogen ions (H+) i.e. hydrogen with a positive electric charge, plus an equivalent number of electrons (i.e. e); thus H2

2 H+ + 2 e

At this electrode, hydrogen is diffused through the permeable nickel in which is embedded a catalyst. The catalyst enables the hydrogen molecules, H 2 to be absorbed, on the electrode surface as hydrogen atoms, which reacts with the hydroxyl ions (OH-) in the electrolyte to form water. When the cell is operating and producing current, the electrons flow through the external load to the positive electrode ; here they interact with oxygen (O2) and water (H2O) from the electrolyte to form negatively charged hydroxyl (OH-) ions ; thus 2OH-

1/2 O2 + H2O + 2 e

The hydrogen and hydroxyl ions then combine in the electrolyte to produce water H+ + OH-

H2O

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Recent trends in Non Conventional Energy sources: FUEL CELL TECHNOLOGY

The electrolyte is typically 40%KOH solution because of its high electrical conductivity and it is less corrosive than acids.

The above equation shows that hydroxyl ions produced at one electrode are involved in the reaction at the other. Also electrons are absorbed from the oxygen electrode and released to the hydrogen electrode. Addition of the three forgoing reactions show that when the cell is operating, the overall process is the chemical combination of hydrogen and oxygen (gases) to form water that is H2 + 1/2 O2

H2O

The oxygen and hydrogen are converted to water, which is the waste product of the cell. The reactants are stored outside the cell (note difference from storage battery), and the electrodes and electrolyte are not consumed in the overall process. These properties lead to the design of convenient small size and long life power units.

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Recent trends in Non Conventional Energy sources: FUEL CELL TECHNOLOGY

Applications: Domestic use: Fuel cell generates direct current which can be used for electric lamps and some small applications such as heat pumps, motors etc., and conversion into alternating current by means of an inverter might be necessary.  Automotive Power Generation: Low temperature fuel cell like proton exchange fuel cells (PEMFC) operate at a temperature below 1300C and are most widely investigated for automobile applications due to their fast startup and transient operation.

 Space-Shuttle Power Generation: Alkaline fuel cells pure hydrogen and oxygen (stored at cryogenics temperatures in liquid state) are used for electric power generation in space shuttles.

 Portable Power Generation: Many devices use portable power using batteries. Some examples are : digital cameras, personal digital assistance (PDAs), portable audio, mobile phones, camcorders power range for these devices is 11-50 W and Laptops in the power range less than 10 W, military applications etc.,

 Fuel Cell Power For Submarines: The development of fuel cell power for submarine by German Navy started with alkaline fuel cells, followed by solid polymer fuel cells and now PEMFCs are considered for the submarine applications due the following superiority reasons: high power density, favorable temperature cycling and load changing behavior, no need for regeneration after shutdown, absence of corrosive, liquid electrolyte, favorable efficiency and noiseless operation.

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Recent trends in Non Conventional Energy sources: FUEL CELL TECHNOLOGY

COMPARISION BETWEEN FUELCELL AND TRADITIONAL BATTERY: Fuel cell

Traditional battery

Fuel cell ability to constantly produce

Battery’s

Electricity depends on the availability

working depends on its recharging

It since a fuel cell doesn’t store energy internally, it will not rundown like a battery

Battery stores energy which tends them to run down

Fuel cell directly converts the fuel in to Electricity

Battery has to replenish its electricity from an external source

They are compact and less in weight for some amount of energy

They are some what bulky due to their basic construction than fuel cell

To increase the power in a fuel cell more fuel is introduce into the system

To increase the power of a battery more batteries have to be added which increases the weight and complexity of system

The vehicles powered by fuels offer the range power, responsiveness and rapid fueling

Vehicles which use batteries cant offer more power range and responsiveness when compared with a fuel cell

Fuel cells operates quietly and are zero to low emissions

Batteries results in uncomfortable noises due to vibrations

They will not cause pollution

They causes severe Air pollution

Due to their compactness they does not limit the vehicles range and capacity

Due to their heavy weight they become a hindrance to the vehicle range and capacity

They does not contain and toxin elements

The batteries are composed of toxic 7

ability

for

continuous

Recent trends in Non Conventional Energy sources: FUEL CELL TECHNOLOGY and have a longer lifetime

material and have a limited lifetime leading to disposal problems.

Conclusion: Tremendous progress has been made in the development of fuel cell systems for stationary, portable and mobile power generation during the last 10 years. Currently the status of various applications is as follows. For stationary power, PAFCs are commercially available. MCFCs and SOFCs have been installed at many places around the world as prototype units, and the experience is being build up for the durability and reliability. Most of the fuel cell systems are available in 125 kW and higher power modules. For automotive power, most major automotive manufactures have prototype cars, trucks and busses operating on the road to gain the experience debug the system and make them cost effective For portable power, the technology has developed to the stage that fuel cell powered cell phones, laptops, and PDAs will be marked in the early 2004 this will use methanol as the fuel for fuel cells. For other portable devices, both DMFCs and PEMFCs are being developed and many prototype units are being used by the US military today. It is anticipated that with in one generation, their will be considerable use of fuel cell for electric power generation impacting the energy conversion efficiency, reducing the pollution and making the society less dependent on the fossil fuels.

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