High Steam Turbine Operating Flexibility Coupled With Service Interval Optimization

Historically steam turbine operations were designed for a market that was typically either base load or intermediate duty load operation. The optimal steam turbine start-up profile was established using the maximum allowable component stress and therefore optimizing service time consumption. Over the last few years, the market requirements have changed significantly. The market requires plant start-up flexibility with the ability to accurately predict start-up time, and reliably meet the start-up time. Applying the historical steam turbine start-up philosophy either limits the operating flexibility of the plant or exceeds steam turbine allowable stresses increasing service time consumption. Innovative concepts are being presented on how steam turbines can achieve reduced start-up times while minimizing service time consumption thereby improving availability. These concepts allow the customer to be able to accurately predict start-up times and reliably meet the dispatch bid. Therefore, an economic calculation may be performed to determine the most effective start-up mode. This economic calculation will evaluate the impact to service life (inspection and test intervals) versus the benefits of power generation. The new concepts provide one solution for base load, intermediate duty load operation, and plants requiring fast start up capability. The new market needs for flexible operation including fast start-up times require plant operability enhancements [1]. Some of the operability enhancements that can be implemented include: • steam turbine stress controller and stress monitoring systems which allow a selection of the start-up mode determining the start-up time, thermal stress and service time consumption; • high level of plant automation; • plant systems designed to provide steam conditions necessary for selected start-up mode. The benefit of these solutions will be presented by means of examples from recently modified power plants. It is possible to achieve a significant improvement in the plant operation and start-up with low costs.