Modern Pumping Today November 2024 - 19

One core start-up improvement concept, for example,
involves the parallel ramping of both gas and steam
turbines. Consider the scenario of an overnight shutdown
of a CCPP. The next day, parallel ramping may help
reduce start-up times to approximately thirty minutes in
some cases.
A Low Load Turn Down concept can help reduce the
minimum part-load capability of the gas turbine. This can
assist CCPP operators who seek to enhance the operating
flexibility of their gas turbines even further, potentially
improving response times to grid demands and enabling
combined cycle applications where part-load efficiency is
desired. For example, when applied to an SGT6-5000F gas
turbine, this concept may optimize and extend the partload
operation range by as much as 40 percent.
PLANT OPTIMIZATION FOR HOT STARTS HELPS
CUT START-UP TIMES IN HALF
Plant start optimization for hot starts can help reduce
CCPP hot and warm start times. Although most CCPPs
were originally built as base load facilities, they now must
often operate as peak load plants or cycling plants with
frequent start-ups due to changing market conditions and
fuel prices. This challenges their operators to achieve
fast and predictable start-up times while maintaining
high dispatch capability and in- market availability. By
implementing this flexibility optimization concept CCPP
operators can potentially reduce the cost of each hot start
and further reduce carbon emissions. Additionally, with an
improved start-up time producers can potentially generate
additional revenue in times of high electricity prices.
The limitations affecting load output include pressure
and temperature transients in the steam turbine, waiting
times for establishing required steam chemistry
conditions, and warm-up times for the steam turbine,
balance of plant, and main piping systems.
One key modification is a start-up on the fly process for
the CCPP's steam turbine. During this process, the turbine
is rolled off with the very first " cold " steam produced
in the heat recovery steam generator (HRSG), using full
pressure and temperature transients. As a result, a start-up
time of less than 50 percent may be possible for a CCPP
after an overnight shutdown
Figure 8 illustrates the potential improvement a parallel
gas and steam turbine start-up process can provide
compared to starting them sequentially. This procedure
is a highly integrated orchestration of the gas and steam
turbine and HRSG operations.
Figure 9: The load ramping speed of using the warm-start concept can
be substantial.
Figure 8: The hot-start concept using parallel gas and steam turbine start-ups
can accelerate load ramping times by as much as 50 percent.
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PLANT OPTIMIZATION FOR WARM STARTS:
FASTER START-UPS, LOWER FUEL COSTS
Plant start optimization for warm starts uses many hotstart
techniques to help reduce CCPP start-up times
by up to 50 percent when the plant block is still warm.
For instance, if the start-up time of a warm start at a
SGT6-5000F GT can be reduced by 50 minutes, a CCPP
operator can use the warm-start concept to potentially
cut start-up fuel consumption by more than 800 MMBtus,
saving fuel costs and potentially avoiding associated
emissions of up to 44 tons of carbon per warm start. The
savings depend on the size and temperature of the gas
turbine and can potentially increase responsiveness to
transmission demand signals from ISOs /RTOs.
Figure 9 illustrates how the plant-start optimization
concept can substantially improve CCPP start-up
efficiency. This can significantly reduce combined cycle
warm start-up times, in some cases to less than sixty
minutes. The potential for time reductions and efficiency
improvements during start-ups can be fully tapped by
implementing a fast start-up load gradient of up to 30MW
per minute, although this load gradient can vary across
different gas turbine frames.
MPT
NOVEMBER 2024 | 19
http://WWW.MPTMAG.COM
Modern Pumping Today November 2024

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