A FUEL CELL AS A PETROL SUBSTITUTE; A FEASABILITY STUDY

Transcription

1 A FUEL CELL AS A PETROL SUBSTITUTE; A FEASABILITY STUDY SALAH I. AL-MOUSLY, member, IEEE, and ZIAD K. ALHAMDANI, member, ASA Faculty of Electronic Engineering, P.O. Box 38645, Libya ABSTRACT In the end of the twentieth century many emerging energy options were evolved like solar cells for domestic use and vehicles. Their high cost, low efficiency and low power density ensures that, at least for the time being, petrol will maintain its dominance as the most appropriate energy source in electric power generation systems, combustion engines, and so on. In the last decade a new technology of another emerging energy was developed by the research institutes and industries, this is the fuel cells technology. This paper studies the fuel cells systems characteristics, applications, and cost. Moreover, this work encounters the target price of this product and to which extend they help meet energy needs, whilst contributing to environmental goals. Can such emerging energy compete with the cheap and widely abundant petrol, at present and in the future? I. INTRODUCION The fuel cell concept first saw light in 1839, when sir William Grove, a physicist in England, produced electricity from the electrochemical reaction of hydrogen and oxygen. In 1959 Francis Thomas Bacon, a British engineer from Cambridge University, demonstrated the first fully operational fuel cell. Through the 1960s and 1970s, fuel cells powered Gemini and Apollo Spacecraft, and nowadays they are used abroad the space shuttles. The fuel cell systems sent into space were special, built to the highest precision and for a high price. Their complexity, expense, and relatively low power density kept them from being widely regarded as a potentially practical power source. But over the last decade or so, concerns about fuel efficiency and the environment have inspired serious development and commercialization efforts [1]. The potential for fuel cells technology is recognized by major industrial organization worldwide. For example, British Gas, Johnson Matthey, Rolls Roys, BNFL, and VSEL in United Kingdom, Daimler-Benz AG, DaimlerChrysler, and Siemens in Germany, International Fuel cell and Westinghouse in the USA, and Mitsubishi, Fuji, Toshiba and Hitachi in Japan are very active in developing and demonstrating fuel cell systems for distributed power and transport applications [1]-[4]. A heightened worldwide awareness of the environment is accelerating fuel cell development for both vehicles and buildings (homes and hospitals). The fuel cells supreme virtue is that they generate clean dc power directly and efficiently, by oxidizing hydrogen and leaving only nonpolluting byproducts-water, heat and if the hydrogen was derived from a fossil fuel, carbon dioxide [2]. 1

2 Fuel cells have a number of potential advantages over a conventional electricity generating technologies. Primarily they are more efficient, as the lack of a combustion stage means that their efficiencies are not limited to those achieved by heat engines. This higher efficiency, whereby more power can be generated for less fuel, means that fuel cells could help offset the greenhouse effect. They also produce lower emissions of oxides of nitrogen than conventional systems, such as the internal combustion engine, thereby offering the possibility of improving air quality in the urban environment. In addition, fuel cell systems are likely to have significantly lower noise levels that conventional alternative [3]. II. FUEL CELL PRINCIPLES Fuel cells convert the chemical energy of the reaction between a fuel and an oxidant directly into low voltage direct current (DC) electricity. In principle, any fuel and suitable oxidant can be used; in practice, the former is generally hydrogen (H2) (or hydrogen-rich gas) and the latter is usually oxygen (O2) in air. The hydrogen can be supplied from an assortment of sources, either directly from storage, from a mixture of gases, as a product of a chemical process in an external fuel process, or by extracting it from gaseous hydrocarbons (reforming) within the fuel cell. Low temperature fuel cells, such as the proton exchange membrane (solid polymer), are therefore likely to require some form of fuel processor to generate hydrogen from these sources. This processor is known as the reformer. The high temperature fuel cell, such as solid oxide fuel cell, has the potential to reform the natural gas directly at its anode. The voltage from an individual cell is small, usually around V, so fuel cells are assembled in modules known as stacks to provide a large voltage and current [2], [3]. A fuel cell is composed of sets of porous positive and negative electrodes, which absorb fuel and oxidant gas, separated by an electrolyte, Fig. 1. Cell types are named after their electrolytes, the medium for transferring ions between electrodes. In all the types, H2 is fed to the anode [2]. In phosphoric acid and proton exchange membrane types, two electrons are stripped from each H2 molecule with the help of an electrocatalyst, usually platinum. They travel through an external circuit, performing useful work on a load. The H ions migrate through the electrolyte to the cathode where O ions have formed from the reaction of O2 and the electrons returning from the external circuit. The H ions react with the O ions to form water [2]. In solid oxide cells, oxygen reacts with returning electrons at the cathode, and the resulting ions traverse the electrolyte to the anode, where their electrons split off [2]. In molten carbonate fuel cells, electrons are removed at the anode from the carbonate ions formed at the cathode by the CO2 reaction with returning electrons, and are transmitted to the anode. Water is formed at the anode in solid oxide and molten carbonate cells [2]. 2

3 Fig. 1. Dominant fuel cell types showing chemical reactions. 3

4 III. FUEL CELL SYSTEM CHARACTERISICS Fuel cells resemble batteries in that both use an electrochemical process to produce a direct current (DC). In both, two electrodes, an anode and a cathode, are separated by an electrolyte. Like batteries, too, fuel cells are grouped in series in what are called stacks, in order to obtain a usable voltage and power output. On the other hand, unlike batteries, fuel cells do not release energy stored in the cell or run down when the energy is used. Instead, they electrochemically convert the energy in a hydrogen-rich fuel directly into electricity and operate as long as the fuel stream lasts. Possible hydrocarbon feedstock includes not only natural gas but also coal-derived gas, landfill gas, and such alcohol as methanol [2]. A fuel cell must be integrated with several subsystems in order to function. In this regard, it is like the engine block in a vehicle. Subsystems are required to store and control fuel, compress and control the oxidant air, and provide thermal management, control, and power conditioning. A system might also include a reformer - a small chemical reactor - to extract a hydrogen-rich gas steam from readily available fuels such as natural gas, methanol, and gasoline [1]. A fuel cell may be categorized by the type of electrolyte it uses. Some electrolytes such as phosphoric and molten carbonate are not easily managed. Each type of cell operates in a specific temperature regime that ranges from as low as 80 o C to as high as 1000 o C. Table (1) list the characteristics of each fuel cell technology according to its electrolyte type [1]. Phosphoric Acid Table (1) Fuel cell system characteristics Alkaline Proton Exchange Membrane Molton Carbonate Solid Oxide Electrolyte H3PO4 KOH/H2O Polymer Molton salt Ceramic Operating 190 o C o C 80 0 C 650 o C 1000 o C temperature Fuels Hydrogen, reformate Hydrogen Hydrogen, reformate Hydrogen, reformate Hydrogen, carbon monoxide, reformate Reforming External N/A External External, internal External, internal Oxidant Oxygen, air Oxygen Oxygen, air Carbon Oxygen, air dioxide, oxygen, air Efficiency % > 60 > 60 Scale 200 kw to 100 W to W to > 100 MW > 100 MW 10 MW kw 10 MW Applications Small utility Aerospace Motive, small unit Utility Utility 4

5 IV. FEUL CELLS APPLICATIONTIONS In the interim, several companies are making their mark, among them ONSI, Energy Research, MC-Power, Siemense Westinghouse, and Ballard Power System. Table (2) list the products and applications of each fuel cell technology in present and future [2], [4]. Table (2) Fuel cell products and applications in present and future FUEL CELL MAJOR APPLICATIONS STATUS TECHNOLOGY Alkaline Space Commercial Phosphoric acid 200 kw distributed power Commercial-over 170 delivered Proton exchange (or polymer electrolyte) 220 kw bus drives 250 kw distributed power Six buses in service Six test units in field in membrane (PEM) 150 W personal power Six units being tested by U.S. Army Solid oxide, tubular (SOFC) Molten carbonate (MCFC) (unpressurized, internal reforming of fuel; external manifolding of air and fuel supply) 3-10 kw residential power 7 kw residential power W battery recharger Vehicle power Personal power 250 kw distributed power 250 kw 3 MW SOFC/gas turbine (GT) distributed power 300 kw distributed power MW grid-support power Prototype in operation; several dozen others ordered by utilities for testing Prototype in operation 65 units sold to New Jersey Department of Transportation for repowering sign batteries Automotive and bus power systems W H2-O2 PEM systems 100 kw test unit operational in the Netherlands, plus smaller units elsewhere; 250 kw plant sales projected for 2001 Prototype test planned in 1999 Available for field test in 1999; from MTU, Germany 1.8 MW field test demo 1996/97; 1 MW prototype test due 2000; 2.4 MW commercial delivery in

6 As a real life example of fuel cells application in the welfare of man kind, a fuel cell power plant for distributed generation are being marketed commercially by ONSI Corp. of south Windsor, USA. More than 170 units of its 200-kW PC25 units have been delivered to customers. Present models, Fig. 2, are sold as self-contained boxes, 3 meters wide by 5.5 meters long by 3 meters high. Natural gas or other fuel is piped into the box and the electricity produced is connected to an external circuit. Recent price have fluctuated in the $3000-$4500 range [2]. Clean exhaust Steam Natural gas Fuel processor Hydg.- rich gas Powerproducing section Dc power Powerconditioner Ac power Air Usable heat and clean water Fig. 2. Fuel cell plant for homes and hospitals. V. HYBRID POWER GENERATION SYSTEM A combination of fuel cell with gas turbine can be used for power generation. Such combination can decreases the installation cost per-kilowatt and in the same time increases the system efficiency. Development of hybrid systems of this kind is picking up steam. The fuel cell serves as the combustor for the gas turbine, that is, the fuel cell system provides the hot-gas flow needed to drive the turbine generating additional electricity. With this combination, the efficiency of the total process (conversion of fuel into electricity) rises above 60 percent, even at sizes of less than 1 MW. Such efficiency is a good deal higher than in the case with any other generation system. With larger systems, in the MW range, efficiency can be above 6

7 75 percent overall. While gas turbines in that range are commercially available, the scaleup of fuel cell production capacity to supply large of this size is likely to require one to two more decades. Thus, small, or micro, turbine and fuel cell combined cycles are likely to loom larger above research horizon [2]. Fig. 3. A typical solid-oxide fuel cell and gas turbine power plant arrangement. V. CONCLUSION 1. Petrol will not last forever, therefor, one should always search for alternative resources. 2. During the course of research different fuel alternatives were developed, e.g. Solar cells. But they were rather expensive and produce such low power that makes them impractical for real life applications (i.e. cars, power, etc.). 3. The alternative energy source should possess the following characteristics; low cost, high efficiency, high power capability, and applicability. 4. These characteristics are almost entirely manifested in the newly developed energy source (fuel cells), the only drawback is price, which is relatively high as compared with hydrocarbon fuel. 5. When combined with gas turbine, the fuel cells can decrease the installation cost per kilowatts and in the same time increases the system efficiency of the power generation plant. 6. In contrast to hydrocarbon the fuel cells can be considered as the most environment friendly energy source ever been discovered. Since the world population increasing dramatically and exponentially, the need for clean and healthy environment should be our first priority. The authors believe that fuel cells research should claim even more interest by the world research institutes. 7

8 REFERENCES [1] Tom Gilchrist, Fuel cells to the fore, IEEE spectrum, The Institute of Electrical and Electronics Engineers, Inc., November 1998, pp [2] Ronald H. Wolk, Fuel cells for homes and hospitals, IEEE spectrum, The Institute of Electrical and Electronics Engineers, Inc., May 1999, pp [3] Philip Michael, Fuel cells-an Emerging Energy Option, Science & Technology Now, The Quarterly Journal of the Arab-British Chamber of Commerece, Issue No. 9/10, Autumn/Winter 1995/6, pp [4] Michael J. Riezenman, Fuel cell bus hits the mannheim streets, IEEE spectrum, The Institute of Electrical and Electronics Engineers, Inc., March 1998, pp