Cooling tower packing efficiency

This paper points out important criteria for an efficient mass transfer packing. Also described is a new PVC packing for use in water/air or water/gas applications such as cooling towers. 4 refs, cited. 

A nuclear power plant produces 1000 MW of electricity with a power cycle thermodynamic efficiency of 30%. The heat rejected is removed by cooling water that enters the condenser at 293 K and is heated to 313 K. The hot water flows to two identical natural-draft cooling towers, where it is recooled to 293 K, and makeup water is added as necessary. The available air is at 298 K with a wet-bulb temperature of 285 K, and it will flow at a rate 1.2 times the minimum. Specialized packing will be used for which Kya is expected to be 1.0 kg/m3-s if the liquid mass velocity is at least 3.4 kg/m2-s and the gas mass velocity is at least 2.75 kg/m2-s. Compute the dimensions of the packed sections of the cooling towers and the makeup water requirement due to evaporation. 

In addition, these depths apply to packed beds with uniform liquid and gas distribution similar to that used in distillation columns. In many designs of commercial cooling towers, distribution is of a substantially lower quality. Thus, the packed depth specified must make allowance for these less efficient distributor designs. For large size dumped tower packings, the value of Hqg inay be 25% to 40% greater than that from Table 6-1 when commercial liquid distributors are used. 

Mass transfer of the ozone gas stream to the cooling-tower water is usually accomphshed through a venturi in a recirculation line connected to the sump of the cooling tower, where the temperature of the water is the lowest. Since the solubility of ozone is very temperature-dependent, the point of lowest temperature allows the maximum amount of ozone to be introduced in solution to the tower. Mass-transfer equipment can take other forms column-bubble diffiisers, positive-pressure injection (U-tube), turbine mixer tank, and packed tower. The coimtercurrent column-bubble contactor is the most efficient and cost-effective but is not always useful in a cooling-tower setting because of space constraints. ... 

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