Diffusers for Heated Water Disposal from Power Plants

Power plant cooling is a major consumer of water. The two major methods of cooling that use water are once-through or closed-loop with cooling towers. Once-through extracts huge amounts of water but returns almost all of it with little consumed; cooling tower systems extract much less water but consume more. Both systems discharge heated water that can have environmental impacts. To meet receiving water temperature requirements, discharge is often through a diffuser. The major types of thermal diffusers for the main water body types are briefly reviewed and examples are given of the design of two diffusers. The first is a once- through discharge into a shallow, tidal, estuary. It consists of an alternating diffuser with jets inclined upwards. Dilution is mainly a result of the momentum of the discharging jets. The second is for a power plant with a cooling tower discharging into a river. It is a unidirectional diffuser with multiple horizontal buoyant jets. Dilution is mainly due to the momentum and buoyancy of the discharge. Simulations with the mathematical model UM3 of Visual Plumes showed that the surface temperature regulations would be met. A diffuser system is an effective means of disposing of heated water from power plants. They mix and dilute the heated water so that temperature rises are rapidly reduced with little environmental impacts. To optimize water use and consumption, it may be possible to design plants to operate with once-through cooling and cooling towers at different times of the year.