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Improving power plant flexibility

Tailoring stress calculators to specific plant needs

Coal-fired and combined cycle gas turbine (CCGT) power plants need to operate more flexibly, but they were not designed for this. In order to deal with this flexibility requirement, among other things, stress calculators have to be able to meet the needs of each individual power plant. Laborelec analyzed different stress calculators and discovered that there is a lot of potential to adjust them. In this way, the flexibility of power plants can be increased without jeopardizing plant safety.

Monitor the thermal stress  in power plants

Stress calculators monitor the thermal stress in power plants to prevent it from damaging power plant assets, such as rotors, control valves, and emergency shutdown valves.

stress calculator for steam turbines

Power plants experience the highest thermal stress during start-up. This is especially the case for the high pressure stages of the high and medium-pressure steam turbine rotors, as shown by the red zones in the figure. Laborelec adjusts stress calculators to the power plant’s individual needs, improving power plant flexibility.

This is especially important during start-up, when the highest stress occurs. When the material-specific stress limit is about to be exceeded, the stress calculator takes over, and start-up times increase. These excessive safety margins hamper the power plant’s flexibility.

Increasing the transparency of stress calculators

As part of its research program on clean coal and CCGT, Laborelec has started researching stress calculators. They are generally manufactured by the OEM that has developed and defined certain stress limits for certain materials. In 2012, Laborelec investigated, for example, how thermal stress is calculated, which material limits are imposed, and which margin is used. Our experts discovered that stress calculators are overly conservative black box systems that are not tailored to the specific needs of each individual power plant. In 2013, our experts are continuing their research by correctly defining the material limits and thermal stress factors. All this is done without compromising the structural integrity of the power plant during start-up.

Fine-tuning the stress calculator to the power plant’s needs

As a result of benchmarking the stress calculators and refining the material limits and thermal stress factors, Laborelec’s experts will be able to adjust the stress calculator specifications according to the needs of individual power plants. This will enable power plants to shorten their start-up and shut-down times, while guaranteeing their structural integrity. Laborelec is currently conducting the first pilot of a transparent stress calculator.

Interested in getting more information about stress calculators?