Technical
Operator Tips: How to benefit from ‘peak shaving’ mode
The energy market faces major challenges in the face of energy transition and greater decentralization. In the past, it was primarily the required load that was unplannable and unpredictable. Today, the entire system needs more flexibility to be able to efficiently guarantee the security of supply.
The energy market faces major challenges in the face of energy transition and greater decentralization. In the past, it was primarily the required load that was unplannable and unpredictable. Today, the entire system needs more flexibility to be able to efficiently guarantee the security of supply.
The network frequency in the European power grid is 50 Hertz. Fluctuations between feeding in and withdrawing electricity from the network are allowed in the range between 49.8 and 50.2 Hertz. If levels overshoot or undercut this range, the system must compensate for the frequency fluctuation – this is where the so-called balancing energy or operating reserve comes into play.
Peaking plants address this imbalance and reduce stress on the electricity grid by providing power stability and flexibility to potentially avoid blackouts and maintain security of electrical supply. This creates new requirements from a power plant – for example, to allow the shortest possible defined ‘On’ and ‘Off’ times and steep load ramps. Gas engines in the upper power range are classically designed for stationary operation, and due to their inertia, suitable only to a limited extent for dynamic use. Due to our continuous developments and adjustments, the flexible mode of operation is constantly being expanded, so that the units meet the changed requirements.
Increased requirements
Field experience has shown that the operating profile can vary greatly among plants. A peaking plant may operate many hours a day, or it may operate for only a few hours per year, depending on the condition of the region’s electrical grid. Another key figure is the type of power output, which mainly differ in terms of speed of activation and adjustment.
In the German electricity market, there are three quality categories available for balancing energy – primary, secondary and minute reserve (also referred to as tertiary reserve). These three types of output differ in terms of their speed of activation and adjustment. For instance, the primary operating reserve must be made available within 30 seconds, and the secondary operating reserve within five minutes. The minute reserve requires activation within 15 minutes.
Maintenance to Operations
In an ideal scenario, the system is designed for an operating reserve mode from the beginning, and properly configured during commissioning routines. Where existing plants, designed for base load operation, are being switched to peak shaving application, the layout needs to be reviewed for suitability for this mode of operation.
A decisive role is played by various parameters which, in extreme cases, can drastically reduce the replacement interval of parts. When utilizing the ‘peak shaving’ mode with frequent engine start/stop cycles, the turbocharger components on the exhaust gas side are subjected to high thermal loads. This load can cause thermal fatigue when the operating time and number of engine start cycles increase, thereby resulting in wear and cracking of the components.
Frequent cold starts result in higher wear and shorter maintenance intervals. which means project-specific adjustments are necessary. In this mode of operation, an adjustment of the maintenance intervals should always be reviewed, and increased wear should also be taken into account.
In order to ensure an adequate service life for the equipment, ABB recommend that the service work includes visual controls, monitoring, measuring and inspection as well as functional checks. Service work enables the detection and rectification of changes to the turbocharger and ensures full operability of the turbocharger. If the turbocharger is used for the peak shaving mode with frequent engine start/stop cycles, the number of successful engine start/stop cycles must be taken into account in addition to the inspection interval for the bearing parts specified on the rating plate.
To prevent machine damage caused by ageing and downtime, ABB recommends having the rotor and bearing parts checked and maintained by an ABB Turbocharging Service Station after 5000 successful engine start cycles and/or 5 years after the last service, whatever comes first. This should also include the casing parts on the turbine end, including the nozzle ring.
For rotating components, the recommended replacement intervals of the compressor and turbine wheels are specified with the aid of the safety concept for rotating parts and dependent on the operating conditions. These intervals are shown on the rating plate of the turbocharger. When employing the peak shaving mode, ABB Turbo Systems generally recommends replacing the compressor and turbine wheel after TC type specific number of successful engine start/stop cycles (e.g 20000 start and/ stop for A100-H TC type) or after reaching the number of operating hours specified on the rating plate.
For non-rotating components, depending on the system-specific operating conditions, a differentiation must be made between the intervals to be expected for:
- replacing the bearing parts.
- replacing the non-rotating components exposed to hot gas.
ABB Turbo Systems therefore recommends having the components periodically inspected and replaced, if necessary, by an ABB Turbocharging Service Station. The individual components will generally be examined for wear and replaced, if necessary, during the prescribed periodic service work.
