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Case Study #1 239
A full range of operation from full speed no load to full speed full
load will be possible on all fuels and transfers, to or from syngas, can
take place down to thirty percent of base load. This maintains a minimum
pressure ratio across the fuel nozzle preventing transmission of
combustor dynamics or cross-talk between combustors. Co-firing is
also an option with the same thirty percent minimum limit apply to
each fuel. A low transfer load also minimizes the amount of syngas
flaring required.
The gasifier has a fixed maximum rate of syngas production. At
low ambient temperatures, fuel spiking is required to follow gas turbine
output. The MS6001FA gas turbine can accept a limited amount
of natural gas mixed with the syngas, to boost the Btu content. In this
application the maximum expected is about 8% and an orifice in the
natural gas mixing line will limit supply to 15% in the event of a valve
malfunction. This protects the gas turbine from excessive surges of
energy release in the combustor. On hot days power augmentation can
be achieved with steam injection or evaporative coolers.
The natural gas/doped propane fuel system, uses a modulating
stop ratio valve to provide a constant pressure to a “critical flow”
control valve. The position of the valve is then modulated, by the
Mk. V Speedtronic ® control to supply the desired fuel flow to the
combustors. When not in use, the natural gas/doped propane system
is purged with compressor discharge air.
Syngas is supplied from the gasifier at a temperature and pressure
of approximately 1000°F [538°C] and 240 psia [16.5Bars] respectively
(Table 14-3, Typical Syngas Composition).
Table 14-3. Typical Syngas Composition
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CONSTITUENT
PERCENTAGE BY VOLUME
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Hydrogen 14.58
Nitrogen 48.68
Carbon Monoxide 23.91
Carbon Dioxide 5.45
Methane 1.35
Water 5 45
Ammonia 0.02
Argon 0.56
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