Comparison on cooling performance of pre-cooled natural draft dry cooling towers using nozzles spray and wet medium

摘要

Evaporative pre-cooling technology improves the cooling performance of natural draft dry cooling towers (NDDCTs) by introducing a certain amount of water into the air entrance. This paper compares the effects of different evaporative pre-cooling systems (i.e., normal wet-medium arrangement, A-frame wet-medium arrangement and nozzle spray) on the cooling performance of a 167 m high NDDCT. Based on the meteorological data of Naomao lake in Xinjiang in 2015, two MATLAB programs were developed for case studies. This study finds all the evaporative pre-cooling systems can improve the NDDCT’s cooling performance in high temperature period. In non-high temperature period, the NDDCT’s performance improvement is unremarkable, and the NDDCT’s cooling performance even deteriorates in the case of evaporative pre-cooling using wet medium. In the hottest month of July, the water outlet temperatures of the NDDCT pre-cooled with normal wet-medium arrangement, A-frame wet-medium arrangement and nozzle spray drop 3.2 K, 3.5 K and 3.3 K, respectively when compared with no pre-cooling counterpart. The annual average water consumption values are 39.0 kg/s, 56.4 kg/s and 124.1 kg/s, respectively. Considering all the year around performance improvement, it is suggested to use nozzle spray pre-cooling system while intermittent operation or certain-time period operation should be considered to save water.