Sustainable Energy Technology - Assignment Example

 Table of Contents Introduction 2 History of Fuel Cell Technology 3 Polymer Electrolyte Membrane Fuel Cell 6 Mechanism 6 Use of Hydrogen as a Fuel 7 Applications 8 Environmental Impact 9 Advantages and Disadvantages 11 Conclusion 11 Bibliography 12 Introduction Sustainable methods of production, conservation and storage of energy must be adopted in order to achieve significant level of sustainable existence in today’s energy dependent society. The sustainable conversion of energy can be achieved through the use of fuel cells in mobile as well as stationary power applications (Basu, 2007). Use of these cells offers consistency, energy and cost saving, planning litheness, unique operating attributes and potential for development in future. The amalgamation of fuel cell application along with storage and production methods of renewable source of energy can lead towards the realization of the sustainable energy requirements (Bradley, 2008). Fuel cells are defined as the potential energy systems with prospects of environment friendly conversion of energy, suitable for use in dynamic as well as stationary applications. Examples of stationary applications include power plants, small residential application and medium sized cogeneration applications while the mobile applications entails the use of low temperature fuel cells in large and heavy vehicles such as trains, passenger buses, boats and in the auxiliary power units of airplanes. Moreover, some low power systems with portability can also be used for different purposes (Srinvasan, 2006). Fuel cells are highly energy efficient devices and are believed to reduce the use of fossil fuels as well as emission of GHG (Green House Gases). The chemical reaction taking place in fuel cells is electrochemical in nature, the reforming steps require comparatively low temperature, the impurities such as sulphur have to be removed from the fuel before using it with fuel cells; all these features lead towards very ultra low emission of pollutants. It makes the fuel cells ideal for use in highly populated areas (Vasquez, 2007). Other advantages associated with fuel cell systems include eradication of gear shifts, compatibility with existing electronic devices, high latent steadfastness and novel options for the safety designs of passenger vehicles. The augmentation in the environmental operation standards associated with the new systems of energy conservation, different process involved in input and output including supply of fuel, energy production etc have become more relevant than ever before. The vehicle production only donates ten percent of the total GHG emission in conventional energy systems, this share may increase to 30% with the modern vehicles with high fuel conservation and efficiency. It is claimed that technologies which show high attributes during their use phase may cause definitive environmental impacts during their production due to the involvement of sophisticated components and materials. Therefore, the production of energy for the fuel cells and their environmental impacts are of great importance (Stolten, 2010). This essay aims to briefly examine the history of fuel cells and briefly describe the types that are available, before examining in detail polymer electrolyte membrane fuel cells, the advantages and disadvantages of this form of fuel cell as well as their applications. History of Fuel Cell Technology The origin of the fuel cell technology lies in the gas battery that was developed by Sir William Grove; he developed the first fuel cell of the human history in 1839. The basic principle of fuel cell was accidently discovered when he was conducting an electrolysis experiment. On disconnecting the battery from electrolyser and connecting the electrodes, it was observed that current was flowing in opposite direction and it was being produced due to the consumption of oxygen and hydrogen gas. This device was named as “Gas Battery” (Basu, 2007). It could only produce voltage up to one volt and utilized platinum electrodes with dilute sulfuric acid as electrolyte. Grove connected several gas batteries in series to structure a gas chain. Due to the use of unstable materials and corrosion problems, this fuel cell could not be used for practical purposes (Sorenson, 2005). The work on fuel cells lay neglected until 1930’s when Francis Bacon, a Cambridge graduate, devised first ever practical fuel cell. This cell used molten KOH (Potassium Hydroxide, an alkaline electrolyte) with nickel electrodes. Nickel was used in powder form to increase the surface area and contact between gases and electrolyte and it was less expensive as compared to platinum (Viswanathan and Scibioh, 2007). The next phase was the development of fuel cells for space application, the advantage of using fuel cell systems (FCS) in space over the conventional batteries was that these cells could produce greater amount of energy with the comparable unit of weight than the conventional batteries (Larminie and Dicks, 2003). The first FCS for the space was designed by International Fuel Cells (Windsor Connecticut) in 1960s for Apollo spaceship. Along with electricity at the rate of 1.5 KWs, the FCS also provided drinking water to the astronauts. Another milestone was achieved by the development of more powerful FCS for the NASA’s Orbiter Spaceship; three FCSs accomplished the entire energy requirements of the Orbiter during flight. The FSC was fueled by hydrogen and oxygen, this system produced power that was ten times higher than the power produced by the FSC of Apollo. The fuel cells demonstrated exceptional reliability (more than 99% accessibility). According to NASA, FCS have completed 106 missions and provided energy for more than 82,000 operational hours to date (Viswanathan and Scibioh, 2007). During this development, FCSs were also devised for terrestrial operations and energy production, Alkaline FCSs showed higher output with respect to power to weight ratio. Chemically, this was due to the high rate of oxygen reduction in the presence of alkaline electrolyte. For terrestrial application of fuel cells, the problem of CO2 poisoning of alkaline electrolyte was faced (Gou et al., 2008). Along with air, the presence of CO2 in the reformate gas, gas produced by reformation of fuel, further reinforced the problem. This problem led towards the development of FCS based on non-alkaline electrolyte from terrestrial application. Another milestone in fuel cell development was the invention of Polymer Electrolyte Membrane (PEM) fuel cell in 1960’s by General Electric USA (Barbir, 2005). The structure of PEM fuel cell is illustrated in the following figure. Figure 1: Polymer Electrolyte Membrane Fuel Cell The fuel cells viable for use terrestrially are classified into four categories based on the electrolyte used. These include SO (Solid Oxide), PA (Phosphoric Acid), MC (Molten Carbonate), and PEM (Polymer Electrolyte Membrane) fuel cells (Basu, 2007). Fuel cells are generally classified on the basis of electrolyte, but there are several other differences such as material used for their construction, manufacturing technology and system requirements. These differences can also be utilized as basis for the classification of fuel cells. Polymer Electrolyte Membrane Fuel Cell Mechanism One of the most interesting types of fuel cell is the PEM fuel cell. This kind of fuel cell is also known as a protein exchange membrane fuel cell. They work by utilizing the biological phenomena of proton transfer across a membrane that occurs within our bodies as well as many other sources. The reaction occurs slowly in the natural state, so as a consequence a catalyst needs to be used, generally platinum. No corrosive fluids are needed for either the construction or the utilization of the fuel cell and uses hydrogen and oxygen from the air as well as water to operate. In a PEM, as with other forms of fuel cell, a stream of constant hydrogen (either as a gas or as a liquid) is fed through channels in the cell, remaining in contact with the anode. At the same time an oxidant, most often the oxygen in the air, is fed through different channels, making constant contact with the cathode. Protons flow from the hydrogen fuel to the water, in the process generating current (Costa et al., 2006). The electrolyte for the PEM fuel cell is the membrane, and it must remain hydrated in order for it to function in transporting protons. The membrane is fixed between the cathode and the anode, and the rigidity of these as well as supporting plates, helps to provide structure for the entire cell. The membrane is semi-permeable, allowing the transfer of protons but blocking that of electrons. This maintains a gradient in charge between the two sides, which drives the transfer of protons across the membrane. Hydrogen gas is the fuel for the cell as the gas comes in contact with the platinum in the catalyst it splits from H2 into two H+ molecules and two electrons. The H+ ions will travel across the membrane, while the electrons are conducted by the anode and are used by the external circuit. The electrons constitute the current that the fuel cell generates. Any hydrogen that is not used leaves the cell to be reused again later. The cell will continue to operate as long as it has a constant supply of both hydrogen and water, but will stop if either one of these run out. Use of Hydrogen as a Fuel The production of hydrogen gas through steam reforming of natural gas is estimated to be approximately 48% of the worldwide production of hydrogen, 30% hydrogen is obtained from crude oil, 18% from coal and three percent hydrogen is obtained as a byproduct of chlor-alkali processes (Stolten, 2010). There are several other technological and more innovative processes for hydrogen production, examples include the Kvaerner’s carbon black and hydrogen process, carbon black is obtained as a byproduct during this reaction, electrolysis by using different sources of electricity and biomass gasification (Sorenson, 2005). For lowering GHG emissions due to the hydrogen supply, sequestration of CO2 and its commercial use have been recommended. The supply of hydrogen greatly differs in its mode of distribution. The onsite reforming and pipeline transportation of natural gas, transport of hydrogen in gaseous (GH2) and liquid (LH2) form through road transport along with the HVDC (High voltage direct current) supply with conversion of hydrogen to the end user are examples of hydrogen supply (Stolten, 2010). The most common method for hydrogen production is the steam reforming of natural gas. Efficiency of this process can be enhanced by utilizing the steam produced during this process as a byproduct (Vasquez, 2007). The efficiency of this process was measured to be 80% by Barbir (2005) and 70% by Larminie and Dicks (2003). Helen and Jeremy (2000) assessed an efficiency of 81% if the byproduct (steam) is required for further processes. According to Bradley (2008), the gasification of biomass as well as water electrolysis through electricity (renewable) is striking processes for hydrogen production. However, it is evident from the above discussion that hydrogen cannot be graded as zero emission fuel. Applications One of the key applications of a PEM fuel cell, like most fuel cells, is in transportation. The good power-to-weight ratio of the PEM fuel cell, the fact that it is relatively insensitive to its orientation and the fast startup time make PEM fuel cells an excellent candidate for alternative methods of fueling vehicles. One current hindrance to this is the storage of hydrogen. Hydrogen needs to be stored as a high pressure compressed gas for this application, however the low density of hydrogen gas compared to gasoline means that storing a significant quantity is difficult. As a consequence, vehicles based on this technology would need to stop more frequently for refueling than gasoline powered vehicles. The idea of using fuel cells in vehicles is popular for several reasons. Firstly, there is concern about global warming. The waste that is produced by traditional vehicles can have significantly negative effects on earth’s atmosphere. Powering cars using fuel cells instead of gasoline can reduce this. In the case of PEM fuel cells, pollutant production isn’t completely prevented, but it is substantially reduced compared to conventional vehicles. A second concern is the use of fossil fuels. Gasoline is produced from oil, of which there is a limited supply. As a resource, oil is technically renewable, however the long time frame that is involved in the development of oil within the earth means that in practice, oil is a limited resource and we risk running out of it. The use of oil is continuing to rise, and it is important that we develop alternatives before we have none left. Finally, there is the potential for fuel cells to increase the efficiency of the vehicle. While this is not currently the case, it may be with future research. Environmental Impact Fuel cells have been assessed for their environmental and other impacts by number of researchers (e.g.Danial, 2001, Larminie and Dicks, 2003). Larminie and Dicks (2003) reported that environmental impacts of fuel cell utilization mainly depend on the type of fuel used and percentage of hydrogen in the fuel source. If pure hydrogen is used as a fuel in fuel cells, the emissions are zero except the water. However, pure hydrogen is rarely used due to problems with its transportation and storage but it is highly predicted that solar hydrogen economy is going to emerge in the near future. Green house gas emissions are mostly associated with the process of fuel production in the fuel cell power plants. The use of methanol from biomass in fuel production does not add any net CO2 in the atmosphere since the photosynthetic plants consume the CO2 emitted. But high temperature combustion e.g. spark while igniting the engine fuelled by methanol, results in the production of nitrous oxides (NOx), these oxides react with water vapors in the atmosphere and cause acid rains. This problem is only with the fuel cells that operate at high temperature while the fuel cells with lower temperature chemical reactions have successfully eliminated the NOx emissions (Stolten, 2010). The emissions of CO2 and SO2 are associated with the fuel cells that utilize processed fossil fuels as source of energy but the rate of emission of these gases is lower than conventional power plants or spark engines. The fuel cells have better efficiency and less fuel is consumed in energy production or travelling and it also ensures low emission of CO2 and SO2. It is claimed that hydrogen production is the process where fuel cells contribute towards GHG emission. The following graph shows the emission of different gases during the production of hydrogen. Figure 2: Air emissions from hydrogen production (Source:Spath and Mann, 2001). It clearly shows that natural gas emission is the maximum with the hydrogen as the fuel while Nitric, Sulfur and carbon oxides emissions are quite low. Although the GHG emissions are also associated with fuel cells yet they are safer for the environment as compared to the conventional fuels. Advantages and Disadvantages Compared to other types of fuel cells, PEM cells are lighter and have less volume. Because they have no corrosive fluids, they are safer in the circumstance of a crash or other unforeseen event. They have a low start up temperature, requiring only 176°F (80°C) for the reaction to begin. Because of this they require less time to warm up, and are able start faster. It also has fewer problems with corrosion and crossover of gases than other types of fuel cell have (Pehnt, 2003). However, this type of fuel cell requires the use of a platinum catalyst. This catalyst is sensitive to poisoning from the CO in the cell, so has a consequence a reactor needs to be added to the cell to reduce the presence of CO in the cell. This adds to the cost, although alternatives to a pure platinum catalyst are being examined (Barbir, 2005). Conclusion Fuel cells offer an alternative method of developing energy that does not rely on fossil fuels and releases fewer pollutants into the air than conventional energy sources. One particularly promising type of fuel cell is polymer electrolyte membrane fuel cells, applications for these in vehicles as well as other applications have been discussed extensively in the literature. Although they are not currently as efficient as conventional forms of energy, the technology is continuing to develop. Bibliography Barbir, F. 2005. Pem Fuel Cell: Theory and Practice, California, Elsevier Academic Press,  Basu, S. 2007. Recent Trends in Fuel Cell Science and Technology. , New York, Springer, Bradley, T. H. 2008. Modeling, Design and Energy Management of Fuel Cell Systems for Aircraft. Doctor of Philosophy, Georgia Institute of Technology. Costa, R., Camacho, J., Guimarães Jr, S. & Salerno, C. 2006. The Polymer Electrolyte Membrane Fuel Cell as Electric Energy Source, Steady State and Dynamic Behavior. Online, Danial, E. D. 2001. Fuel Processors for Automotive Fuel Cell Systems: A Parametric Analysis. Journal of Power Sources, 102, 1-5. Gou, B., Ki Na, W. & Diong, B. 2008. Fuel Cells Ii, New York, Springer, Helen, L. M. & M., J. P. 2000. Miniature Fuel Cells for Portable Power: Design Considerations and Challenges. Journal of Vacuum Science & Technology, B, 1287-1297. Larminie, J. & Dicks, A. 2003. Fuel Cell Systems Explained, New York, John Wiley and Sons, Pehnt, M. 2003. Life-Cycle Analysis of Fuel Cell System Components. . In: Vielstich, W., Lamm, A. & Gasteiger, H. A. (eds.) Handbook of Fuel Cells – Fundamentals, Technology and Applications. Chichester: John Wiley and Sons, Ltd., Sorenson, B. 2005. Hydrogen and Fuel Cells: Emerging Technologies and Applications, California, Elsevier Academic Press, Spath, P. L. & Mann, M. K. 2001. Life Cycle Assessment of Hydrogen Production Via Natural Gas Steam Reforming. National Renewable Energy Laboratory, Srinvasan, S. 2006. Fuel Cells: From Fundamentals to Application., New York, Springer Stolten, D. 2010. Hydrogen and Fuel Cells: Fundamentals, Technologies and Applications. , Germany, Willey VCH, Vasquez, L. O. 2007. Fuel Cell Research Trends, New York, Nova Science Publishers, Inc., Viswanathan, B. & Scibioh, M. A. 2007. Fuel Cells: Principles and Applications. , Taylor and Francis Press., Read More