Introduction  The realization of "dual carbon" goals in the construction of a new power system necessitates the transformation of existing thermal power plants to accommodate peak load operations. The safety of thermal power units during flexible operation is a critical element for enhancing the overall stability of the power system. Air preheater is the key auxiliary equipment that affects the wide-load operation capacity of thermal power units. This paper addresses the challenges associated with flue gas temperature fluctuations and blockage and corrosion induced by excessive ammonia injection. It is very important to develop a real-time assessment and safety status monitoring model for dust and blockage of rotary air preheaters.

  Method  Based on the big data of wide-load operation monitoring of 600 MW and 350 MW units in central China, the paper developed a model for air preheater blockage assessment based on approximation of the resistance coefficients in the case of various time scales. Furthermore, the flue gas temperature at the outlet of the air preheater and the cold end working temperature were used as monitoring indicators to count the proportion of parameters exceeding the limit in multiple load sections of the unit.

  Result  The results show that, at a peak regulation load of 39%, there is approximately a 20% probability of temperature exceedance. In addition, the independent calculation of the blockage risk based on the two indicators may result in a certain degree of underestimation of its degradation rate compared to the calculation based on a joint distribution. Besides, with the verification of data from the two units, the method can quantify the short-term (within the soot-blowing cycle) and mid-and-long term evolution of the air preheater blockage.

  Conclusion  This assessment strategy applies to other equipment and systems in thermal power plants, such as SCR denitrification systems and coal mills, providing a quantitative assessment of safety risks during peak load operation. It guides thermal power units to efficiently and stably cooperate with the new power system in dispatching.