An investigation of the effects of flue gas injection on natural draft cooling tower performance

Flue gas injection into natural draft cooling towers offers a cost effective alternative to reheating scrubbed flue gas, prior to disposal into the atmosphere. A search of the publicly available literature indicates a need to investigate the effects of flue gas injection on natural draft cooling tower performance. This work addresses such an investigation through numerically simulating the transport phenomena in a natural draft cooling tower equipped with flue gas injection. The control volume finite difference method was used for discretizing the governing equations on an orthogonal boundary-fitted grid. Governing equations were expressed in axisymmetric form. The mechanism by which flue gas injection affects cooling tower performance is by either enhancing or restricting air flow through the tower. The five independent variables addressed in this study are flue gas flow rate, flue gas temperature, radial injection location, injection orientation, and liquid entrainment in the flue gas. Of these five, the flue gas temperature was found to have the most significant effect on tower performance (average cold water temperature). The study also indicates that except for very heavy rates of liquid entrainment and with drop diameters larger than 0.1 mm, the vertical injection orientation results in better performance as opposed to the laterally downward orientation.