New Energy Conservation Technologies

Transcription

1 Queensland University of Technology & University of Queensland Jan 2004 New Energy Conservation Technologies By Julian Dinsdale Executive Chairman, Ceramic Fuel Cells Limited ABSTRACT During the next one to two decades, we expect to see a profound change in the generation and usage of energy, influenced by such factors as environment, capital and production costs as well as numerous geo-political factors. Older power stations will start to reach the end of their useful life and nuclear power stations, such as in Europe, will be phased out. New power stations, having large output capacity, will be difficult to permit in many existing political climates. With global warming now apparent, the environment and efficient fuel utilisation have become significant factors in the adoption of newer and emerging energy conversion technologies. This paper discusses some of the emerging energy conversion technologies and their applications. The paper focuses on Fuel Cell technology as applied to energy systems up to 200 kw with particular emphasis to the automobile, distributed generation and combined heat and power applications. 1 INTRODUCTION There is an overall recognition by governments around the world for the need to significantly improve the generation and utilisation of energy in all its forms. Many billions of dollars have been and are committed by numerous countries and large and small corporations around the world to the research and implementation of new energy conversion technologies. Some have, in part, been successful, such as wind, wave and solar power. Others have, or are taking, significantly longer to develop and implement than was envisaged a few years ago the Fuel Cell industry is one example. Energy conversion and usage technologies are primarily associated with electricity generation, heat and or refrigeration. Whereas the energy conversion environmental issues are associated with emissions from the generation processes including raw material extraction and conversion together with the gas emissions into the atmosphere from coal deposits and biomass degradation (methane) There are a multitude of issues that affect the emergence of some of the new technologies, many of which are highly interrelated. This paper canvasses some of these issues and considers, as an example, the application of the emerging Fuel Cell technology in Combined Heat and Power (CHP) systems

2 Queensland University of Technology & University of Queensland Jan 2004 Page: 2 2 ENERGY CONVERSION TECHNOLOGIES Numerous energy conversion technologies are now being deployed in the generation of energy worldwide, the most predominant of which are coal, gas and oil which accounts for over an estimated 95% of the world s energy usage. The reserves of the hydrocarbon fuels are finite and many have geo-political implications. The reliance of the USA and other countries on oil reserves from the Middle East is an example. Another is the significant GDP export earnings of Australia s coal exports. There are still many developments in the usage of fossil and manufactured hydrocarbon fuels; however, the ultimate conversion efficiency using current thermal technologies is limited by the Carnot cycle and combustion temperatures to around 35%. The emergence of Carbon Dioxide sequestration technologies, if proved successful, is likely to extend and enhance the life of these existing technologies. Considerable interest is currently being shown in the environmentally friendly generation of power from wind, wave and solar technologies. Many wind and wave power generators have been installed in various parts of the world and provide a useful input to the power grid infrastructure. Their location is sometimes difficult due to visual and noise pollution issues and their output can fluctuate depending on wind, wave or sun conditions at the time of generation. Grid connectivity can be very expensive and the cost benefits will emerge over time as experience is gained with their usage. Solar generation, both thermal and photo voltaic, has now been deployed extensively over a number of years around the world in stationary and mobile applications. The cost of these systems is still relatively high on a cost per kw basis and they are dependant upon the weather and grid connectivity to electricity networks. The costs for packaging, inverter and battery technologies have not matched the downward cost trends of the solar portions of the systems. There is still extensive interest around the world in solar generation and the next two decades should see significant enhancement and refinement to this technology. As disposable refuge and sewerage increases at an enormous rate in both the developed and emerging countries around the world, the low-pressure methane gas developed as a natural bi-product is receiving much attention. Coal deposits that may be uneconomic to mine can produce low pressure methane. Methane gas is a significant cause of global environmental pollution and its capture and usage in energy generation is essential for responsible global environmental management. New technologies for efficiently capturing low pressure methane are now beginning to emerge and deployed in both small and large-scale operations. Coal seam methane projects are current in Australia, USA and Europe. Although it is yet to be made cost effective, sewerage methane gas electricity generation is common in sewerage plants around the world for internal usage at the treatment plant. Fuel Cell technology is one of a series of emerging technologies that has the potential to use a wide range of liquid and gaseous fuels more efficiently and in an environmentally friendly way. There are many types of Fuel Cells all based on similar operating principles of a fuel conversion reaction.

3 Queensland University of Technology & University of Queensland Jan 2004 Page: 3 3 FUEL CELL ENERGY CONVERSION Fuel Cells are electrochemical devices that convert chemical energy into electrical energy and heat. A typical schematic of a Fuel Cell is shown in Figure 1. Basic Fuel Cell 200 ma/cm 2 AIR 0.7 V FUEL Cathode -porous structure, electronic conduction Electrolyte - impervious structure, ionic conduction Anode - porous structure, electronic conduction Figure 1: Schematic Basic Fuel Cell A fuel cell consists of an Anode and Cathode separated by an Electrolyte. Fuel is passed over the surface of the Anode and Oxygen from air is passed over the Cathode. The Anode and Cathode are catalysts and the Electrolyte can be solid or liquid depending on the conduction mechanism used for a particular type of Fuel Cell. Depending upon the type of Anode, Cathode, Electrolyte and temperature, a reaction occurs whereby ions are transmitted through the Electrolyte causing an electric current to flow when an external load is present. Fuel Cells do not involve a thermal combustion process, as the fuel conversion is an electrochemical oxidation reaction. A typical open circuit voltage of a Fuel Cell is between 1.0 to 1.2 volts, so many are stacked together to provide larger voltages. When a current is drawn through an external load the voltage drops and a typical voltage load curve is shown in Figure 2.

4 Queensland University of Technology & University of Queensland Jan 2004 Page: 4 Ideal Voltage Cell Voltage Region of Activation Polarization Region of Omic Losses (IR) Region of Concentration Polarisation Figure 2: V-I Characteristic of Fuel Cell Current Density A single cell typically delivers about 0.5 to 0.7 volts under load. Characteristics which affect the Fuel Cell operation are its current carrying potential, internal resistance, internally generated heat, thermal management, etc. If electrical losses within the cell are minimised then Fuel Cells have the potential for very high fuel to total energy conversion efficiencies. The fuel for a Fuel Cell is typically Hydrogen, however, in high temperature Fuel Cells the use of Carbon Monoxide and Methane is also possible. 4 SUPPORT SYSTEMS A typical fuel cell system needs a number of support systems to function and these are generally referred to as Balance of Plant (BoP). They consist of a fuel processing system, heat exchangers and a power conditioning system. Depending on the type of Fuel Cell, the Balance of Plant can become the major influencing factor on the operation and cost of a Fuel Cell. If a fuel other than pure Hydrogen is used, then typically a reforming process needs to occur prior to the gas being used by the Fuel Cell. This consists of a fuel control system, fuel cleaning (eg. desulfurising), fuel processing (reforming) and potentially fuel heat exchangers. The airside of the Fuel Cell may also need conditioning. A typical Fuel Cell diagram is shown in Figure 3.

5 Queensland University of Technology & University of Queensland Jan 2004 Page: 5 Typical SOFC Fuel Cell System Control System SOFC Stack Operating temp 850 C DC Power Electronics & Inverter AC Electricity Air Inlet Gas Inlet Fuel Handling & Desulfuriser 800 C 850 C Exhaust Treatment & Heat Recovery 200~500 C Water Heater / Boiler Hot Water <55 C Exhaust <100 C Water Inlet Figure 3: Typical SOFC Fuel Cell System 5 TYPES OF FUEL CELLS Numerous different types of Fuel Cells have been developed by different organisations around the world. Table 1 lists the most common types. FUEL CELL FUEL T(op) o C Alkaline Fuel Cell (AFC) Pure H Efficiency% KOH/matrix Electrolyte Proton exchange membrane FC (PEMFC) Pure H Sulfon-F-polymer Direct Methanol FC (DMFC) Methanol (>100) Sulfon-F-polymer (Novel polymer) Phosphoric acid FC (PAFC) H H 3 PO 4 /SiN matrix Molten carbonate FC (MCFC) H 2, CO, NG,HCs, alc (65) 2 Li-K-carbonate/ LiALO 4 matrix Solid Oxide FC (SOFC) as MCFC (70) 2 Yttria-zirconia 1 related to natural gas 2 combined cycle system

6 Queensland University of Technology & University of Queensland Jan 2004 Page: 6 FUEL CELL Anode Reaction Cathode Reaction PEM and PAFC H 2 2H + + 2e ½ O 2 + 2H + + 2e H 2 O AFC H 2 + 2OH - 2H 2 O + 2e ½ O 2 + H 2 O + 2e 2OH - DMFC CH 3 OH + H 2 O CO 2 + 6H e 3/2 O 2 + 6H + + 6e 3 H 2 O MCFC H 2 + CO 3 2- H 2 O + 2e + CO 2 CO + CO 3 2-2CO 2 + 2e ½ O 2 + CO 2 + 2e CO 3 2- SOFC H 2 + O 2- H 2 O + 2e CO + O 2- CO 2 + 2e CH 4 + 4O 2- CO 2 + H 2 O + 8e ½ O 2 + 2e O 2- Table 2: Electrochemical reactions in various types of fuel cells Alkaline Fuel Cells (AFC) have primarily been used by NASA on space missions and have attracted renewed interest for mobile applications. They can potentially achieve higher electric efficiencies than other low temperature fuel cells, don t use noble metal catalysts and are poisoned readily by CO2. The electrochemical species is a hydroxide ion. Proton Exchange Membrane Fuel Cells (PEMFC) operate at temperatures below 90 C and the electrochemical species is a proton ion. They exhibit high power density, fast start-up and fast load response. They require pure hydrogen as fuel. Carbon monoxide is a strong poison for PEM and therefore extensive gas cleaning for hydrogen produced from hydrocarbon reforming is necessary. They are primarily considered for mobile applications, but micro-chp (<10kW) for domestic applications and CHP systems (up to 300 kw) are under development. Due to the high manufacturing volumes required for mobile applications, low capital costs are expected. If the fuel hydrogen is produced from hydrocarbon fuels such as natural gas, the efficiency of PEMFCs is, at best, only about 35%. Direct Methanol Fuel Cells (DMFC) use a polymer membrane as the electrolyte similar to PEMFC. The anode in DMFC converts the methanol fuel directly and thus eliminates the need for a fuel reformer. Efficiencies of about 40% are expected for the low temperature version, and efficiencies of about 50% for operating temperatures above 100 C. A significant amount of investment has gone into micro-dmfc s for portable applications and commercial products are expected during Phosphoric Acid Fuel Cells (PAFC) are one of the most commercially developed type of fuel cells, and like PEMFC and DMFC also proton ion fuel cells. Several hundred co-generation systems (50kW 5MW) have been tested, some up to 40,000 hours. With an operating temperature of 200 C, the fuel cell still operates only with clean hydrogen as fuel and is more carbon monoxide tolerant than PEMFC. Their efficiency related to Natural Gas as fuel is about 40%. Molten Carbonate Fuel Cells (MCFC) and Solid Oxide Fuel Cells (SOFC) are high temperature fuel cells and promise the highest fuel-to-electricity efficiencies in particular for carbon based fuels. The operating temperatures for MCFC and SOFC

7 Queensland University of Technology & University of Queensland Jan 2004 Page: 7 are 650 C and >750 C respectively. This allows a better integration of fuel processors and fuel cell. Efficiencies on carbon based fuels are predicted to be around 50-60% for a single cycle and above 65% for a combined cycle (Fuel Cell plus gas turbine, steam turbine or Stirling engine). As indicated by their name the electrochemical transfer species in MCFC is a carbonate ion and in SOFC an oxide ion. 6 APPLICATIONS The automobile or mobile application for Fuel Cells is achieving considerable publicity around the world. Many billions of dollars have been spent by numerous governments and companies on the research and development of PEMFC for integration into automobiles. The PEMFC is used for its low temperature operation and fast start characteristics. A large number of demonstration projects are underway in the transport arena and encompass cars, buses, forklift trucks, and similar applications. However PEMFC exhibiting a low cost and long-term reliability still remain elusive. The PEMFC industry relies on the availability of a large and diversified supply of pure hydrogen and hence the need for a Hydrogen Infrastructure to be developed. There are many arguments for and against the development of a Hydrogen Economy. Currently the main source of Hydrogen is reformed natural gas or gasified coal. If environmental pollution is an issue then by using this technology the emissions are typically moved from a vehicle to a hydrogen manufacturing plant. Extracting Hydrogen from natural gas also lowers the overall efficiency of gas to energy conversion in the motor vehicle and some have suggested this may be as low as under 30%. Many governments and large organisations are undertaking research and development project to extract Hydrogen from water typically using steam reforming or electrolysis using green energy. The use of Fuel Cells in Distributed Generation is probably as large a market, if not larger, than the automobile market. It covers the diverse market of electricity generation that is generated closer to the energy user than the large power stations and transmission networks. This could be a 100 to 200kW generator on a commercial site through to a 1 kw combined heat and power (CHP) unit in residential premises. Both the 100 to 200 kw distributed generators and the CHP units are attracting attention from many developers and users throughout the world. These systems can deploy various types of fuel cells with the Balance of Plant customised to meet a particular fuel and energy efficiency. The main objective for Distributed Generation is to increase overall efficiency by utilising the heat energy for either further generation or direct heat energy as distinct from releasing the waste heat into the atmosphere. In the 100 to 200 kw generators this could take the form of steam turbines whilst in the CHP units the waste heat is used for hydronic or hot water heating in the home.

8 Queensland University of Technology & University of Queensland Jan 2004 Page: 8 Other markets for Fuel Cell applications are in the Back-up power and Auxiliary power markets. The Back-up power market applies where power is lost from a grid outage and the Auxiliary power markets replaces say a temporary diesel generator on a building site or entertainment function. 7 FACTORS AFFECTING CHOICE AND DEPLOYMENT There are numerous drivers that affect the choice and deployment of new conversion technologies in the energy industry that particularly apply to the Fuel Cell industry. The two of the most profound are costs and legislation. Cost drivers are paramount unless legislation dictates otherwise. A consumer in general will not pay very much more for green energy. A utility typically will not pay more for a new energy conversion technology unless that cost can be passed on to the consumer or legislated to do otherwise. Costs can be considered as both initial capital costs and ongoing costs. Both affect the choice of a new technology. Domestic Combined Heat & Power micro-chp Hot water system Hot Water <55 C Hydronic heating Air Inlet Water Storage/ Aux Boiler Exhaust <100 C Gas Inlet Water Inlet CHP Unit Power Electronics & Inverter AC Electricity to home Mains Electricity Figure 4: Typical CHP Schematic - Residential It is interesting to consider the factors affecting the deployment of CHP units in residential properties in various parts of the world.

9 Queensland University of Technology & University of Queensland Jan 2004 Page: 9 A major factor associated with CHP units is their quiet operation and the ability to convert gas into heat and electricity with efficiencies approaching 85%. System transmission and distribution losses are also significantly reduced or reduced to zero. Demographic factors also tend to dominate the positioning of CHP units. In colder climates, residential property needs more heating for a longer period than in warmer climates. We have therefore seen most interest for CHP units emerging from USA, Canada, Europe, UK, Scandinavia and Japan. Currently in these countries there are electricity transmission and distribution networks which service residential customers. There are also gas distribution networks direct to the household or delivery systems to gas holding tanks on the premises. The fuel supply for a CHP unit is typically from a natural gas distribution network although this could be propane via local underground tanks. As the CHP unit generates both heat and electricity, it is necessary to use both to increase the overall unit efficiency. Some of the electricity from the CHP unit is used to directly power the pumps associated with the hydronic heating with the remainder being used via the standard residential electrical connection. Any load greater than that which can be supplied from the CHP unit is taken from the grid. Fuel Cells do not have fast load following characteristics (as do batteries) and thus transient load fluctuations need also to be supplied from the grid or some form of energy backup. Any surplus power generated from the CHP unit needs to be supplied into the grid. A major issue for a CHP unit is its turn down ability. During the summer months there is a need to reduce the requirement for heating whilst at the same time maintaining electricity output. Typical residential base loads in Europe are around 1 kw and 5kW in the USA with peaks of up to 7 to 10 kw to be expected. In general, electricity to the residence is supplied to the consumer via a distribution utilities which may or may not be the gas supply utility. Gas suppliers who are not electricity suppliers would probably like to supply electricity. CHP units now pose a problem as they: connect to the gas supply; connect to the electricity supply; want to supply surplus electricity back into the grid; want to draw electricity from the supply network on demand; and do not want to supply the local grid in the event of a grid failure. Legislation is usually required to give effect to the installation of a CHP unit. There are differing aspirations of consumer and the various utilities. The consumer wants to draw power on demand from the grid however he wants to obtain a full credit for any power put back into the grid. The electrical distributor has a capital and running cost for grid infrastructure which is not being used by the gas distributor. Charges for energy services now need to change. As the cost of electricity or gas is primarily determined by governments, legislation is usually required to give effect to CHP units. In Europe we are seeing the distribution utilities wanting to own the CHP units

10 Queensland University of Technology & University of Queensland Jan 2004 Page: 10 and thus potentially charging the consumer for the combined heat and electricity consumed. In the USA a Federal law was enacted in 2003 that allows net metering from a residence up to 10kW Other issues which arise with the introduction of the CHP units are the electricity grid management. Typically, if the grid fails, then the individual CHP units should disconnect from the grid and return when the grid is restored. If each household in an area is connected to a local grid then the operation of that grid must be carefully considered. Issues such as safety, protection and operation of the local and extended grid become paramount. Another major issue is one of cost and volume production. The SECA program in the USA has a target system manufactured cost of under $400 US for a SOFC system. This requires significant government and industry support and the ultimate ability to manufacture Fuel Cells and there associated Balance of Plant in sufficient volume to bring prices to this level. This support is now evident in both the USA and Europe. 8 CONCLUSION The Fuel Cell is a significant example of a new and emerging energy conversion technology. The technology is sufficiently different from existing technologies that special considerations must be given to its use. Fuel Cell technology is able to use hydrocarbon fuels in an oxidation reaction and derive electricity and heat without combustion. The case for its usage will be based substantially on cost and legislative actions. Governments will play a vital role in drafting energy policies in the areas of energy industry Deregulation, Environmental criteria, and energy pricing. The CHP technology is an example of the application of Fuel Cell usage which need to be given time to prove itself to be robust, reliable and useable in existing electricity grid networks.

11 Queensland University of Technology & University of Queensland Jan 2004 Page: 11 REFERENCES The following websites contain extensive information on fuel cells. World Fuel Cell Council: Fuel Cells 2000: US Fuel Cell Council: American H2 Assoc.: Ceramic Fuel Cells Ltd: Solid State Energy Conversion Alliance Stationary Fuel Cell Markets European Commission re Hydrogen Energy and Fuel Cells