Integrating phase-change thermal storage into the indirect dry-cooling system of a thermal power unit and optimal operation strategy

Abstract

Extreme conditions (high ambient temperature and crosswind speed) reduce the cooling efficiency of dry cooling towers, consequently impairing the thermal performance of thermal power units (TPUs). Phase-change material thermal storage equipment (PCMTSE) is integrated into an indirect dry-cooling system of the TPU to realize a partial cooling load of the cooling tower, thereby stabilizing and improving the thermal performance of the TPU. A model of the TPU and numerical model of the hybrid indirect dry-cooling system are established and coupled, with the inlet cooling water temperature of the condenser serving as the iterative criterion. Two integration schemes are proposed, one with the PCMTSE downstream (Scheme A) and the other with it upstream (Scheme B) of the dry cooling tower. The results show that Scheme A is recommended owing to its superior efficiency in terms of coal savings. The effects of the unit power load on the coal-savings efficiency of the PCMTSE during its charging and discharging processes have been revealed. Operating the PCMTSE at higher power loads aids in improving the thermal efficiency of the TPU during the PCMTSE charging and discharging processes. The charging process should be started at the “three high” working conditions: a high ambient temperature, crosswind speed, and unit power load. The working conditions that allow only one cooling water pump to operate should first be considered for the discharging process, and the “three high” working conditions should then be selected. The TPU equipped with the PCMTSE can save 11.42 tons and 12.74 tons of coal in two typical extreme daily conditions with the implementation of the proposed operating strategy.