Some combined cycle power plants which were originally built as base load plants are now operating as peak load plants or as cycling plants with frequent start-ups. Hot starts after an overnight shutdown may need to be performed fast, using predictable and reliable measures to provide a high dispatch ability and in-market availability.

Hot Start on the Fly is an innovative upgrade for combined cycle power plants designed to significantly reduce the plant’s hot start times down to a plant specific value of - in many cases - approx. 30 minutes.

Depending on the operational limitations and requirements of your power plant, the benefits of the improved Hot Start on the Fly may include: 

• Increased start-up efficiency
• Significantly reduced combined cycle start-up time
• Higher plant load transients due to combination of GT & ST load output, resulting in reduced specific start-up costs
• Minimized fuel consumption for hot start-up
• Reduced CO₂-emissions during start-up

^{** Example for illustration. Actual results may vary depending on plant conditions and other factors.}

A start-up from warm conditions may take considerable time for a power plant originally built for less volatile operating profiles.

In competitive markets, the ability to start up your plant faster can help reduce time spent in transient conditions with non-optimal efficiency and make a difference in dispatch.

Warm Start on the Fly has been designed to support

• Increased start-up efficiency
• Significantly reduced combined cycle warm start-up time, in some cases to less than 45 min*
• Reduced start-up fuel consumption and reduced associated emissions from reduced start-up time
• Increased responsiveness to the transmission system operator (TSO)

*50Hz F-class 1x1 reference case - example only -actual results may vary

Applicable for many combined cycle power plants with Siemens Energy Design steam turbines and control system

• Engineering of enhanced control philosophy and component evaluation as needed
• Automation and logic modifications within unit master control and major component subsystems
• Implementation of logic changes into the plant control system; typically no hardware required

A plant shutdown may consume considerable time and fuel for the unloading processes.

In competitive markets, the ability to shutdown your plant faster can help reduce time spent in transient conditions with non-optimal efficiencies and enhance responsiveness.

Fast Plant Shutdown has been designed to support

• Significantly reduced combined cycle shutdown time, in some cases down to below 15 min*
• Reduced shutdown fuel consumption and reduced associated emissions, from reduced shutdown time

_{*50Hz F-class 1x1 reference case - example only -actual results may vary}

Applicable for combined cycle power plants with Siemens Energy Design turbines and control system

• Engineering of enhanced shutdown control concept and component evaluation as needed
• Automation and logic modifications within unit master control and major component subsystems
• Implementation of logic changes into the plant control system; typically no hardware required

A start-up from a condition where the water-steam cycle has already cooled down significantly may require long holding and waiting times where the gas turbine is running in lower part load for the water-steam cycle to warm up and achieve start release.

The Steam Turbine FlexStart upgrades comprise a range of features focused on the steam turbine designed to shorten the start-up time and enhance start-up flexibibility. Many of the features mainly address enhancements of start-ups from more cooled down conditions, while some of them can also help enhance warm or hot start-ups for combined cycles.

Potential benefits can include:

• Reduced waiting and warm-up times as well as optimized speed and load gradients
  
• Increased responsiveness to the transmission system operator (TSO)
• More efficient start-up process
• Potential for reduced fuel consumption and emissions during start-up

Scope

• Unit-specific engineering evaluation of boundaries and applicable features
• Engineering of necessary adaptations & logic changes
• Implementation of control logic upgrades
• Typically no or only minor hardware required

In combined cycle mode, start-up times are greatly influenced by the configuration and requirements of the water-steam cycle. However, an increase of the gas turbine gradient capabilities may also help with start-up times and start-up efficiency. For the SGT5-4000F, Siemens Energy has developed a start gradient optimization which is designed to

• Increase gas turbine start-load gradient to a maximum value of up to 30 MW/min*
• Reduce gas consumption per start resulting from reduced start-up time
  
• Help further reduce combined cycle start times when combined with relevant start optimization products for water-steam cycle (e. g. Hot Start on the Fly, Warm Start on the Fly, Fast Plant Shutdown, Advanced Fast Loading)

* achievable values may vary by site

The Modified ST Valve Staggering upgrade is designed to support lower load operation and to reduce loss of efficiency in this operating condition.

Amongst other criteria, minimum load is typically restricted by logic to avoid high HP exhaust temperatures, and may lead to opening of bypass stations or even shutdown for protection.

The Modified ST Valve Staggering introduces an upgraded logic which has been designed to facilitate modified operations to support lower minimum part load with same or improved margins.

The Modified Valve Staggering upgrade modifies the valve staggering logic for part load operation to help:

• Avoid losses from opening of the IP bypass station
• More efficient operation in part load
• Lower potential for tripping on high HP exhaust temperature
• Lessen throttling of reheat control valve

Scope

• Assessment of current part load operation
• Engineering and implementation of the recommended process logic changes
• Typically no hardware changes required

Many Gas Turbines have been designed to operate most efficiently at maximum load conditions. With today´s changing market, the need to efficiently operate at part load is becoming more important as well. Siemens Energy has developed a range of solutions to enhance part load capabilities, which can help to:

• increase operational flexibility
• reduce part load fuel consumption
• reduce minimum emission compliant part load
• enhance part load efficiency

With natural cooling, it may take multiple days for a steam turbine to be sufficiently cooled down to access for inspection or outage work.

Through extensive analysis, Siemens Energy is able to offer Fast Cooling of Steam Turbines which has been designed to significantly accelerate cool-down time and thus help get access to components sooner after shutdown.

Fast Cooling is designed to save up to 3.5 days of cool down time (site specific; actual values may vary) compared to natural cooling,

which may support

• reduced overall total outage duration
• increased availability

• Engineering & Process optimization - Detailed analyses of the cool down process taking into account material strength limits, plant specific operating variables and usage factors. Site specific check of the existing cool down procedure and engineering of optimized process
• Hardware modifications - improvements for accessibility, ease of activation can be proposed and implemented
• Automation - degree of automation of the cool down process can be increased and optimized.

For turbines already equipped with the forced cooling system, Fast Cooling may offer incremental optimization, e. g. improved handling and automation, improved process, etc.

Steam Turbine standstills can lead to increased exposure to air moisture which can result in parts corrosion. Preservation measures are recommended to remove and control residual moisture to below recommended thresholds.

Siemens Energy has developed an enhanced preservation system for steam turbines and its auxiliaries to support more flexible shutdowns and longer standstills.

This enhanced dry air system has been designed to help

• Reduce the potential for corrosion and resulting damage during shutdowns, contributing to improved reliability
• Reduce time and effort for installing and disconnecting the preservation system after shutdown and during start preparations
• Support better responsiveness and availability through reduced time for connecting / disconnecting to the dry air supply
• Enhance installation ease through redesigned and relocated access points.
• Better control of preservation operation through automation and measuring points (optional) 

After a shutdown, the steam turbine and other plant components increasingly cool down the longer the shutdown lasts. Consequently, startup times can correspondingly increase with the duration of the preceding shutdown. Siemens Energy has developed a trace heating system which can keep the relevant steam turbine sections warm or heat them up, and enable a startup from a warmer condition.

Steam Turbine Hot Standby can help

• Increased responsiveness and operational flexibility based on enabling usage of a shorter warm startup process
• Reduced startup life consumption for steam turbine by avoiding cold condition starts
• More efficient startup operation & reduced startup fuel consumption by enabling a shorter warm startup process even after longer shutdown periods