Fuel Cell Products

Stewart & Stevenson has achieved market dominance in engine driven products by keeping an eye and an open mind. Especially toward new developments that hold the promise of providing a product that better serves the needs of our customers. Often, this requires undertaking a leadership role in developing and applying new technologies. Utilizing our experience in power generation and customer knowledge base, assures new products are properly introduced to the marketplace. The latest example of this "eye-to-the-future" philosophy is our involvement in the development and commercialization of power plants utilizing Molten Carbonate fuel Cells (MCFC).

The IMHEX® Team is a partnership consisting of M-C Power Corporation, the fuel cell manufacturer; The Institute of Gas Technology, the fuel cell technology developer; Bechtel Corporation, the process designer; and Stewart & Stevenson Service, Inc., the system's integrator. Stewart & Stevenson is the exclusive distributor of IMHEX® MCFC power plants. The team is currently working on a 250 kW demonstration unit for San Diego Gas and Electric

Company. Construction is underway at the site, located at the Miramar Naval Air Station in San Diego, California. We have also begun a Department of Energy-sponsored program to produce a commercially viable one MW class power plant by the end of this decade. This technology promises extremely high fuel efficiency and immeasurably low emissions.

Advantages of Fuel Cell Power Plants. While fuel cell power units will contain many of the features common in Stewart & Stevenson's engine-driven products, they also offer advantage that distinguish this technology. A typical fuel cell power system is modular by design, including three basic sub-systems: (1) a fuel processor, (2) a power module (the fuel cell), and (3) the inverter. Many of the fuel cell's advantages are derived from the inherent benefits of these sub-systems.

Fuel cells offer notable fuel flexibility. Typically, the first stage of the fuel cell system is a fuel processor. Therefore, adapting the fuel cell requires only selecting the appropriate fuel processor. Possible fuels include natural gas, landfill gas, digester gas, coal-derived gas, bio-gas, alcohols, methanol, and low methane gas.

The heart of the power unit the fuel cell also is the source of most significant advantages. The electrochemical operation of the fuel cell frees it of the limitations of the Carnot Cycle. The result is a very high efficiency: 45 to 70 percent (LHV, or low heating value) simple cycle efficiency and 70 to 90 percent (LHV) in «¡generation configurations. The fuel cell's efficiency is only marginally affected by temperature and part-load extremes.

Most significantly, the quiet and clean operation of the fuel cell simplify siting and permitting issues. Natural gas fuel cell power plants have a blanket exemption from regulations in California's South Coast Air Quality Management District, producing less than one audible decibels (dBA) at 30 feet. The result is flexibility in site selection with desirable features, such as:

• Indoor or outdoor installation, at or near load points.

• Fully dispatchable, remotely controlled, and unattended operation.

• Compatible with a phased-construction approach.

The final stage of the fuel cell power unit is the inverter. Since the fuel cell's output is direct current, an inverter is required to interface the power unit to an alternating current utility grid. However, the addition of solid-state system improves power quality by eliminating voltage fluctuations and reducing harmonic.

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