Spray cooling system design and optimization for cooling performance enhancement of natural draft dry cooling tower in concentrated solar power plants

In concentrated solar power (CSP) plants built in dry and arid areas, natural draft dry cooling tower (NDDCT) are commonly employed to dissipate waste heat into the atmosphere. The cooling performance of NDDCT mainly depends on the induced air flow caused by the buoyancy effect. However, the high ambient temperature in summers reduce the cooling efficiency of dry cooling towers and cause significant power loss for CSP plants. To address this problem, spray cooling system utilizing water evaporation was developed to pre-cool the inlet hot air. Different designs of spray cooling systems were proposed and tested on a 20 m high experimental tower. Experimental data were collected to evaluate the performance of the spray cooling system. To our knowledge, this is the world's first attempt to practice spray cooling on a full-scale natural draft dry cooling tower. This study confirms the feasibility and effectiveness of employing spray cooling for cooling performance enhancement of NDDCT. With the goal of maximal cooling effect with least water consumption, the optimal design was proposed, which consists of 3 upward injections at the low level (Height = 2 m), 2 counterflow injections at the middle level (H = 3 m) and 3 counterflow injections at the high level (H = 4 m). The cooling capacity of NDDCT increases from 789 kW to 841.73 kW, as the result of an intensified natural convection. Moreover, in the spray zone, the presence of a low-temperature area is featured by high relative humidity (70%-80%). The intensified natural convection caused by pre-cooled air and the presence of high vapour concentration are attributed to spray evaporation, which confirms the necessity to introduce the spray cooling system. (C) 2018 Elsevier Ltd. All rights reserved.