Revised control strategy for coal-fired power plants during transient processes considering heat transfer deterioration of cooling wall: Flexibility enhancement and security operation

The increasing integration of intermittent renewable energy sources has heightened the need for enhanced deep peaking and operational flexibility within thermal power plants. This trend poses an enormous threat to the safe operation of boilers, especially cooling wall, underscoring the critical importance of scrutinizing the thermo-hydraulic performance of cooling walls during transient operations. In this study, a 1100 MW ultra-supercritical thermal power plant is used as the research object. A comprehensive one-dimensional dynamic model of the cooling wall is devised, grounded in fundamental principles encompassing mass conservation, momentum conservation, energy conservation, state, metal heat storage, and heat transfer Equations. The analysis yields temperature distributions of the working fluid, inner wall, and outer wall along the height direction of the cooling wall, unveiling instances of dry-out phenomenon during load cycling processes. The investigation reveals that heat transfer deterioration stands out as a primary factor behind intermittent fluctuations in metal wall temperatures. At load cycling rates of 2.5% Pe/min and 3.0% Pe/min, the maximum temperatures of the metal tube wall during the loading up process surge to 527.9°C and 557.3°C, respectively. Furthermore, a revised control strategy is proposed based on the identified heat transfer deterioration characteristics of the cooling wall. Notably, during the loading up process, the peak wall temperature is substantially curtailed from 557.3°C to 502.2°C at a rate of 3.0% Pe/min. This strategic adjustment results in an augmented maximum power ramp rate, escalating from 2.5% Pe/min to 3.0% Pe/min, upon the adoption of the revised control strategy.