Looking forward to energy efficiency
Fuel cells are being widely touted as a clean power generation technology that looks particularly appropriate for medium-scale applications where both the electric power and by-product heat can be used. Steve Barrett reports.
Fuel cells are attracting a great deal of interest at the moment, in a wide variety of applications across a huge range of system sizes. Their clean and quiet operation essentially combines hydrogen and oxygen to produce electricity and heat without combustion, with pure water as the ‘waste’ product (and perhaps a small amount of CO2 depending on the technology and the fuel gas).
The increase in research and development activity is being accompanied by a tremendous surge in interest from manufacturers of subsystems, materials and components that can be used in fuel cell systems. Many companies are investigating the opportunities to enter a potentially enormous new market for their products, either off-the-shelf or with additional development.
Most of the commercialisation activity – and almost all of the widespread publicity – is for low-temperature fuel cells, such as PEM, direct methanol and alkaline. However, these technologies are generally better suited to small- and micro-scale applications, from vehicles to residential power systems, mobile generators and portable electronics such as laptop computers and mobile phones.
While the fuel cell types that operate at lower temperatures tend to grab the headlines, it is the higher-temperature fuel cells that are more appropriate for combined heat and power (CHP) applications. This is because high-temperature fuel cells – phosphoric acid (160-220°C), molten carbonate (650°C) and solid oxide (800-1000°C) – produce a significant amount of useful thermal energy in addition to electric power. This combination of useful energy production considerably boosts their efficiency, to as high as 90 per cent including heat recovery, making their economics more attractive to utility companies and medium-scale energy users. They are also able to operate on natural gas and even other gases such as waste gas from sewage treatment, as long as it contains hydrogen.
The most established technology is phosphoric acid fuel cells, which have been in more or less commercial application for more than a decade. The main manufacturer is UTC Fuel Cells in Connecticut, USA, which has supplied more than 250 systems around the world, for a wide variety of installations. The company’s PC25 fuel cells – which produce 200kW of electric power at 37 per cent electrical efficiency, or 90 per cent efficiency with heat recovery – have been installed at 30 US Department of Defense (DoD) sites since 1994, successfully demonstrating long-term fuel cell capabilities in real-world situations.
The DoD Fuel Cell Demonstration Program sites (www.dodfuelcells.com) represent a broad spectrum of facilities from Alaska to Florida. Several of the units are configured to provide back-up electrical power in case the local grid experiences a power outage. The thermal output (more than 900,000 BTU per hour) is used for heating boiler make-up water, domestic hot water, space heating, condensate return, process hot water etc.
In the UK, Woking Borough Council has bought and installed one of these units for its ‘Pool in the Park’ leisure complex. Working in tandem with other CHP and photovoltaic systems, it provides heating, cooling and electricity to three municipal swimming pools and a leisure complex, with the surplus power supplying over 1100 households on local community heating systems.
The fuel cell system runs on natural gas, from which the necessary hydrogen is extracted, with the required oxygen obtained from the air. The system offers much greater efficiency for power generation with much lower CO2 and other harmful emissions, meeting the government’s sustainability criteria for exemption from the Climate Change Levy.
Other high-temperature fuel cell technologies are starting to enter field trials. Molten carbonate fuel cells are also being targeted for medium- and large-scale power generation, with Connecticut-based FuelCell Energy Inc and its European partner, MTU CFC Solutions GmbH in Germany, the most advanced in their developments. Both have installed several systems in the past year or so, with MTU commissioning systems at locations ranging from the Rhön Klinikum hospital in Bad Neustadt to the utility RWE’s energy park in Essen, Germany. FuelCell Energy has commissioned plants at a Mercedes-Benz manufacturing plant in Alabama and the first of two systems for the Los Angeles Department of Water & Power.
A number of companies are developing solid oxide fuel cells (SOFCs), with Siemens Westinghouse Power Corporation in Pennsylvania the biggest and longest established. The company completed a two-year demonstration of an SOFC unit producing 100kW of electric power in the Netherlands, and is currently developing pre-commercial 300kW hybrid fuel cell/micro gas turbine systems. Demonstration units are scheduled for the University of Toronto in Canada this autumn, as well as for RWE in Germany, Edison SpA in Italy and Shell in Norway.
In the UK, Rolls Royce is developing a 1MW SOFC/gas turbine hybrid system, although a prototype is not expected until 2004-2005.
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