Heating network regulation optimization for multi-source cascade heating systems with the anti-freezing correction of direct air-cooling island

Driven by the demand for energy conservation and high-efficiency utilization in combined heat and power (CHP) units, optimizing the primary heating network regulation of multi-source cascade heating systems—integrating high back-pressure exhaust steam, steam ejectors, and extraction steam—is essential for the minimum power generation energy consumption. This study examines a 2 × 660 MW direct air-cooling CHP system as a case, investigating the characteristics of three primary heating network regulation strategies—quality regulation, staged-flow quality regulation, and combined quality–quantity regulation—and evaluating the heating load distribution, energy consumption, and corresponding unit operating parameters required to meet the demand heating load in a multi-source cascade heating system. Additionally, parameter corrections are made for heating operations that do not meet the minimum anti-freezing flow constraint of the direct air-cooling island, taking into account the winter anti-freezing requirements. The optimization strategy aims to minimize power generation energy consumption in the multi-source cascade heating system. Results show that under the quality regulation method, the standard coal consumption rate for power generation is the lowest across all outdoor temperatures and load conditions, making it an effective energy-saving regulation strategy for the heating network. Under the 50% THA operating condition, the unit achieves the highest energy efficiency, with the standard coal consumption rate for power generation reduced by 26.29 g·(kWh) −1 and 11.72 g·(kWh) −1 compared to the 100% THA and 75% THA conditions, respectively. Energy utilization efficiency increases by 9.94% and 4.84%, respectively. To ensure safe operation of the equipment and address the winter anti-freezing concerns of the direct air-cooling island, the minimum anti-freezing flow is used to correct heating operations that fail to meet anti-freezing requirements. For outdoor temperatures of −14°C and −13°C under the 75% THA condition, the high back-pressure exhaust steam volume is adjusted, resulting in 43.56 t·h⁻¹ and 39.68 t·h⁻¹ of steam entering the direct air-cooling island, thereby satisfying the anti-freezing requirements. Under the 50% THA condition, for outdoor temperatures of −8°C and −7°C, the steam entering the direct air-cooling island is adjusted to 25.00 t·h⁻¹ and 22.00 t·h⁻¹, respectively, to meet the anti-freezing requirements.