Co-Start System
™
Achieve full plant output in much
less time than a traditional plant
White Paper | June 2016
Being able to start quickly and efficiently has become essential for competitive
operation. The first step for combined cycles was the unrestricted fast gas turbine
start in Siemens Flex-PlantTM combined cycles, but a big part of combined cycle
output comes from the steam turbine. That is where Siemens Co-Start capability
comes in. Co-Start adds the fast start of the steam turbine to the cycle, resulting in
full plant output in much less time.
A Flex-Plant with Siemens Co-Start technology enables the fast gas turbine start
followed by a fast steam turbine ramp up. The main resulting effect is that the
system supports renewable integration and also adds value for traditional dispatch
modes. A fast start combined cycle achieves high-efficiency operation much sooner
than traditional technology. This translates to reduced plant start-up costs, enabling
faster megawatts on the grid as well as the ability to generate profit from your plant
in a more timely fashion. This can result in more revenue, even for short dispatch
events. Higher efficiency operation also means the Co-Start system will lower startup emissions and, thus, produce less greenhouse gas per kW. Partnered with the
fast start gas turbine, which reduces start-up emissions by approximately 90%, a
Siemens Flex-Plant with Co-Start is an environmentally friendly solution for today’s
generating needs.
Introduction
Siemens Co-Start technology enables the Flex-Plant to go one step further when it
comes nt start-ups.
Gas turbines typically can start fast. The challenge in starting combined cycle power
plants quickly is in the design of the rest of the power plant systems and equipment.
The Siemens Flex-Plant with Co-Start enables fast start of the entire power plant and
a full operational life, even with frequent fast starts.
Subject to change without prior notice.
© Siemens Energy, Inc. 2016. All rights reserved.
siemens.com/powerplants
White paper | Co-Start System | June 2016
Co-Start technology includes integrated process controls,
enabling gas turbines to start quickly and simultaneously,
and includes a water-steam cycle designed for flexible
operation which allows an earlier start of the steam turbine.
This fast start cycle operation is made possible by Unit
Coordination Control, which includes intelligent logic for
reliable plant fast start operation over the life of the plant.
These features enable a Flex-Plant with Co-Start to deliver full
plant power in 30 minutes (or less) from turning gear for a hot
start, and in under an hour for a warm start. Like prior FlexPlants, plants with Co-Start have the capability to ramp the gas
turbine to base load without hold points. This allows the HRSG
to be produced quicker, which then warms up steam turbine
components in a more timely fashion.
Discussion
In a conventional combined cycle, the gas turbines start slowly
and sit at low load hold points to gently warm the equipment
used in the steam cycle. Fast gas turbine starts were realized
with the early Flex-Plants, eliminating low load hold points
and facilitating quicker output and much lower start-up
emissions. Co-Start takes the next step – enabling fast steam
turbine start for full plant power in much less time than
conventional plants.
In a Flex-Plant with Co-Start, the steam turbine also ramps up
fast – about 30 minutes earlier than a conventional plant –
resulting in an overall savings of around 8500 pounds of fuel
per full start from an overnight shutdown per GT. Co-Start
offers the fastest total plant power output.
PLANT LOAD
50 min
Co-Start
30 min
Improvement
Conv. Start
PLANT LOAD
The Flex-Plant with Co-Start demonstrates the following
characteristics:
•Gas turbine start-up without load holds
•Hot start early steam turbine roll off with first steam
production
•Continuous steam turbine ramp up and loading up to
synchronization speed, synchronization and loading during
a continuous pressure increase
•Early closing of steam bypass valves thus reducing overall
plant start-up times, fuel consumption, and water usage
•Starting both gas turbines at the same time for multishaft
configurations
•Lower start-up costs
•Faster megawatts on the grid
•Reduced greenhouse gas generation during start-up
Plant Start-up On Short Notice
Co-Start
Conv. Start
START-UP TIME
Analysis
One of the first hurdles to fast starting is the HRSG design.
Conventional HRSGs have thick-walled structures which are
subject to low cycle fatigue failure when exposed to rapid,
high temperature thermal cycling. Siemens Flex-Plant
combined cycles use NEM™ DrumPlus™ technology, or Siemens
Benson technology. Both of these design options avoid
features that lead to low high cycle fatigue life. As part of the
equipment design, either technology option offers full life
capability when exposed to high thermal cycling.
Thick to thin wall interfaces were avoided and more robust
structures for thermal cycling were included. These new
design features greatly enhance low cycle fatigue life. For
Co-Start, this design philosophy was extended to the rest of
the plant design, greatly increasing life under cycling
conditions. These mechanical design changes are partnered
START-UP TIME
Subject to change without prior notice.
© Siemens Energy, Inc. 2016. All rights reserved.
2
White paper | Co-Start System | June 2016
with integrated plant controls to manage and control
temperature gradients, further enhancing system robustness
and enabling reliable operation over the full plant life, even
with frequent, fast cycling.
This faster start and more frequent cycling ability translates
directly into additional revenue for the plant operator.
Elimination of low load holds, as well as allowing the GTs to
ramp quickly to baseload, result in significant fuel savings.
Conclusion
Siemens is focused on providing innovative and competitive
solutions that help power plants meet the needs of the future.
Flex-Plants with Co-Start technology have been proven to
provide the flexibility and reliability needed when it comes to
repeated stopping and starting of plants to handle peak and
intermediate loads.
Co-Start adds the ability for a high efficiency combined cycle
to provide power quickly and efficiently with lower start-up
costs. Depending on fuel cost assumptions, the savings
compared to a traditional combined cycle can be greater than
$20 million net present value over a 20 year operating life.
This technology also offers the potential for additional
revenue available from increased dispatch, ancillary services,
or premium power rates for grid support.
The utilization of the combined cycle with Co-Start technology
is the next step in our evolution of creating
eco-friendly and integrated power generation.
Siemens Energy, Inc.
4400 Alafaya Trail
Orlando, FL 32826-2399
USA
Tel: 888-593-7876
The information in this document contains general descriptions
of the technical options available, which may not apply in all
cases. The required technical options should therefore be
specified in the contract.
Subject to change without prior notice.
© Siemens Energy, Inc. 2016. All rights reserved.
3