Numerical Simulation and Application of Natural Draft Direct Air-Cooling Tower for Large Coal-Fired Power Units
To investigate the flow and heat transfer characteristics of natural draft direct air-cooling towers (NDC) for large coal-fired power generating units, a three-dimensional CFD numerical model covering major plant buildings, air-cooled radiators, and ambient wind fields was established based on the NDC systems of a 2×660 MW unit of a power plant. The influences of meteorological factors, including ambient wind speed, ambient temperature, and ambient wind direction, as well as regulation measures such as rolling shutters, louvers, and bypass windows on the heat dissipation performance of NDC towers were systematically analyzed. The results demonstrate that ambient wind speed acts as the dominant factor governing the performance of the NDC system. As wind speed rose, the uneven distribution of air intake volume and heat dissipation among each cooling delta increased remarkably, which elevated the unit back pressure, and the upstream tower suffered more severe impacts than the downstream one. Ambient temperature exerted a slight effect on circumferential flow distribution, yet substantially changed the overall back pressure of the system. In terms of regulation strategies, closing rolling shutters in the windward zone and reducing the opening of partial louvers can improve air flow redistribution to a certain extent, but will reduce the total air flow rate and total heat dissipation of the entire tower. By contrast, bottom bypass windows can effectively optimize the air intake on the leeward side and boost heat dissipation under high-wind operating conditions, whereas top bypass windows deliver only limited improvement effects. This research can provide fundamental data and technical references for the optimal design, operational regulation, and energy-saving retrofitting of large NDC units.