Dynamic study on improving the load ramp rate of a 630 MW subcritical coal-fired boiler by introducing a small pulverized coal silo

To accommodate large-scale renewable energy integration, enhancing the flexible load ramp capability of Coal-Fired Power Plants (CFPPs) is crucial. However, the inherent physical delay of traditional direct-fired pulverizing systems severely restricts further improvements in the boiler load ramp rate. This paper proposes a flexible fuel-feeding method based on a small pulverized coal silo (SPCS) system and develops a dynamic simulation model of a 630 MW subcritical coal-fired boiler coupled with the SPCS. Based on this model, the effects of various SPCS coal feeding strategies, including feeding rate, ramp-up duration, and holding time, on dynamic characteristics of the boiler during load transitions are systematically investigated. The results indicate that the average boiler load ramp rate increases substantially from the 1.27%Pe/min baseline to 3.82%Pe/min with an SPCS feeding rate of 12 kg/s. Simultaneously, the dynamic impacts of the rapid SPCS coal supply on the flue gas and metal wall temperatures are deeply analyzed. The transient temperature increments of the flue gas attenuate sequentially along the flow path, and the platen superheater exhibits the highest thermal response sensitivity. Even under rapid SPCS coal supply conditions, the peak wall temperatures across all heating surfaces strictly remain within their respective safe operating thresholds. Furthermore, to mitigate the main steam temperature variations caused by the SPCS coal supply, a dynamic feedwater compensation strategy based on an optimal WFR SPCS of 7 is introduced. This strategy successfully reduces the transient peak deviation of the main steam temperature from +10.5 °C to +4.5 °C, reliably ensuring the smooth evolution of key steam parameters. This research provides solid theoretical support for the flexible and safe operation of CFPPs equipped with the SPCS system.