Abstract
The energy mix in most European countries is now characterized by a growing share of renewable energy sources (RES). The random nature of RES entails the need to balance the differences between the current amount of power generated in the system and the actual power demand. For this reason, power units incorporating steam boilers are most often operated under sub-peak rather than base load regimes. This creates many challenges to boiler operators due to the advanced age of the power units in service. In Poland, for instance, 77% of power units are more than 20 years old and 45% have been working for more than 30 years, which means that most of them are approaching their design life time. Further operation of these units requires a detailed analysis of the degree of wear of critical pressure components, including a thermal and mechanical stress-state analysis. The paper aims to present a methodology of wear degree calculations incorporated in the power unit control system. The performed calculations are based on real measurement data obtained from 8 months of operation of a boiler unit with the steam output of 650·103 kg/h. Wear degree calculations and a thermal and mechanical FEM-based analysis are performed to assess the possibility of shortening start-ups to address the dynamic requirements that power units operating in the Polish power generation system will have to meet.
Highlights
If much electricity is to be generated from renewable sources, wind power in the first place, due to the random character of renewable energy sources (RES)-based production, the power system has to be provided with stable energy sources [1, 2, 3]
The effect of the obligation to adopt electricity generation from renewable sources is that a conventional power plant reserve capacity is held as a hot or a cold reserve, which means that boilers are kept in a standby mode, ready for a quick start-up, or they are shut down completely
It should be noted that damage to pressure elements is caused by creep and low-cycle loads
Summary
If much electricity is to be generated from renewable sources, wind power in the first place, due to the random character of RES-based production, the power system has to be provided with stable energy sources [1, 2, 3]. There are more and more plants which, due to their large capacity, have been operating in base-load regimes and are used for balancing the demand for electricity in the national power system This is the effect of new highly efficient largecapacity supercritical power plants operating under the base load all year round. As their older power units operate with lower efficiency, the plants find it profitable to use them to satisfy the peak and sub-peak demand because it is possible to sell generated energy at higher intervention prices on the power market [4]. The consumption of expensive mazout is reduced and start-up boiler’s losses are minimized [5] Another important issue is limiting the emissions of pollutants arising when heavy fuel oil is fired. Issues related to the wear degree assessment are essential in terms of the safety of the boiler current operation and the possibility of extending the boiler safe operation beyond the design life
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