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General Information Welcome Overview History Fuel Cell Bus Projects Generation I Generation II Generation III Further Information Partners Links Executives Contact |
Fuel Cell System
Fuel cells produce electricity by electrochemically combining hydrogen and oxygen to form water (see diagram below). The hydrogen is broken down into its components (protons and electrons) at the anode. The protons pass through the electrolyte of the fuel cell. The electrons are forced to pass through an external circuit (the light bulb in the diagram), thereby supplying electrical power to external loads. On the Georgetown Fuel Cell Buses, the external loads are the propulsion and auxiliary systems. Fuel Cell Diagram The Ballard Fuel Cell Bus uses a proton exchange membrane fuel cell, rated for 100 kW (133 hp) net. The oxygen needed for the cathode of the fuel cell is simply taken from air which has been pressurized and humidified. The hydrogen required for the anode is extracted from liquid methanol in a process called reformation. The methanol is first vaporized (along with water) in the two vaporizers. The two vaporized methanol/water mixtures are then fed into parallel fuel processing systems, each consisting of a low-temperature steam reformer and a selective oxidation (Selox) unit. The reformers break down the methanol into a hydrogen-rich gas. However, the resulting gas contains some carbon monoxide (CO), which can harm the catalyst present in the fuel cell stack. So the gas is fed directly into the Selox units, where the CO is oxidized into CO2. The resultant gas is called reformate, and is then fed into the anode of the fuel cell stack. Because not all of the hydrogen is consumed in the fuel cell, the anode exhaust is fed back into the reformers to maintain the temperature required for the reforming process. Also, water is recovered from the cathode exhaust to maintain the necessary water supply to the reformer. Ballard X1 Bus 100 kW PEMFC System Diagram Efficiency diagram of the PEM fuel cell in the X1 bus. Electric Propulsion System The fuel cell on the Ballard X1 bus can supply a maximum gross power of about 115 kW (153 hp), which is not enough for the operation of a typical urban transit bus. The fuel cell is supplemented by a traction battery pack, which provides surge power for acceleration and hill-climbing. The battery pack also provides a means to recapture energy through regenerative braking. Regenerative braking occurs when the traction motor is operated as a generator; this converts some of the kinetic energy of the bus into electrical energy which is fed into the batteries. X1 Bus Hybrid Propulsion System Layout For general information on the Ballard Fuel Cell Bus, please visit the General Information page. Or visit the photo gallery of the Ballard Bus. Downloadable 2-page brochure for the X1 Bus: X1 Bus Brochure (1.6 MB) Adobe Acrobat Reader is required to view this file. |
