Mafi-Trench's Response

Mafi-Trench describes how turbo-expander-based generating systems lower natural gas pressure from transmission levels to pressure suitable for use by large industrial facilities. As the turbo-expander steps down the pressure, the temperature of natural gas decreases. In an example provided by Mafi-Trench, the stepped-down natural gas is used to fuel steam generators. Waste heat from the flue gas stream of the boilers could be used to heat the natural gas to the required temperature, which would obviate the need for additional fuel.

Installed Costs

Mafi-Trench indicates that installed costs for a turbo-expander are dependent on the size of the project. Costs range from a low of $2.50 per watt for a one megawatt (MW) project to $8.00 per watt for a 100 per kilowatt (kW) system. Mafi-Trench estimates an installed system cost of $4/watt for an oil field project near Bakersfield. The project is expected to produce 500 kW on a continuous basis, for an annual savings of 4,000 MW per year. It is unclear whether eligible generator costs are included in these estimates.

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We note that in 2002, the average cost of a Level 3-N microturbine is $2.69/watt.⁸ We estimate the average cost for a Level 3-N internal combustion engine is approximately $2.16.

Market Potential

According to Mafi-Trench, potential customers for turbo-expander-based power recovery systems are pipeline operators and industrial facilities which use natural gas to produce steam or other forms of process heat, such as manufacturers of steel, glass, aluminum, gypsum, and petrochemicals. Mafi-Trench estimates there are between 100 and 300 candidate sites which could produce an average of 200kW per site, for a potential of 400 MW of generation.

Peak Load Reduction

The turbo expander will operate only when the industrial facility is operating and consuming natural gas. Mafi-Trench indicates turbo-expanders will generally reduce the facility's peak demand.

Efficiency

Mafi-Trench states it is not necessary to consider the total energy input into the natural gas system to estimate the efficiency of turbo-expanders versus traditional pressure regulating stations. Compression energy input to the transmission and distribution systems is necessary to operate these delivery

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systems, and is independent of whether the pressure "energy" is recovered at the point of use. Normal consideration of efficiency is not necessary, as turbo-

expanders do not use additional fuel for combustion, just waste heat that would normally be discarded.

Waste Heat Recovery and Reliability Requirements

Mafi-Trench contends that its proposed system exceeds the waste heat recovery requirements of Level 3 because it consumes waste heat and does not require fuel combustion. In contrast, microturbines combust fuel and produce waste heat.

Mafi-Trench indicates that its proposed system has a demonstrated availability of approximately 99% +/-0.5%, which equals or betters most combustion turbines.

Compliance Monitoring

Mafi-Trench believes turbo-expanders could be monitored in the same manner as other eligible technologies, to ensure the units are being used for their stated purpose: electrical production.