Natural Draft Cooling Towers By: Nicholas Berkholz ENG 3060 Section 003 What is a Natural Draft Cooling Tower • • • • • What is a Natural Draft Cooling Tower? A Few Important Terms Components How it Works Remarks • • • • • A natural draft cooling tower is a means to remove waste heat from a system and release it into the atmosphere. Typically used at oil refineries, chemical plants and power plants to remove heat absorbed from circulating cool water systems. A common shape is the hyperboloid (See Fig. 1) Cooling towers have been around for over 100 years. However, in their early for were only about 20 meters high. Today, some can reach over 200 meters. “As recently as 20 years ago, cooling towers were more the exception than the rule in the industry because of their severely high operating cost and the large amount of capital required for construction. But with today's need for water conservation and minimal environmental impact. industry is turning more and more to recycling water.”(GC3) Fig. 1 Important Terms • • • • •• • • Wht isisaa What Natural Natural Draft Draft Cooling Cooling Tower? Tower? A Few A Few Important Important Terms Terms Components Components How it Works How it Works Remarks • • • • Wet Bulb Air Temperature - the temperature a volume of air would have if cooled adiabatically to saturation at constant pressure by evaporation of water into it, all latent heat being supplied by the volume of air(Wiki 1). Also known as the dew point of ambient air. Adiabatically - in meteorology, referred to also as adiabatic cooling: when air cools or heats as it expands or contracts with pressure change without losing or gaining heat energy by radiation or to its surroundings. (Wiki 2) Dry Bulb Air Temperature – The temperature at which a thermometer reads freely in air but is shielded from radiation and moisture. Natural Draft or Stack Effect – When there is a large pressure differential between the outside air and air within a structure. Warm, moist air is less dense than dry air of the same pressure thus causing the warm, moist air to rise. Components •• • •• • • • • • What Whatisisa a Natural Draft Natural Draft Cooling Tower? Cooling A Few Important Terms Tower? Components A Few How it Works Important Remarks Terms Components How it Works Remarks • • • Supply Basin Tower Pumps Cooling Towers – – – – • • Hot Water Inlet Fill – – • • • Vertical Ribs Reinforced Concrete Shell Internal Void Diagonal Columns Splash Film Hot Water Distribution System Cold Water Collection Drift Eliminators - Drift is water lost from cooling towers as liquid droplets are entrained in the exhaust air. The drift loss is independent of the water lost by evaporation. The drift loss may be expressed in units of lb/hr or percentage of circulating water flow. Drift eliminators are used to control this drift loss from the tower. (Mist) Components • • • • • What is a Natural Draft Cooling Tower? A Few Important Terms Components How it Works Remarks How it Works • • • • • What is a Natural Draft Cooling Tower? A Few Important Terms Components How it Works Remarks • Step 1 - As hot water enters the natural draft cooling towers, through a series of pumps, to the warm water inlet How it Works • • • • • What is a Natural Draft Cooling Tower? A Few Important Terms Components How it Works Remarks • Step 2 - The warm water is then distributed into through a packing or fill material inside the tower keeps the water evenly distributed. This is plays a major role and contributes heavily to the efficiency of the tower. – (i.e. better the distribution allows for more contact time, and greater surface area, which allows for more heat removal) How it Works • • • • • What is a Natural Draft Cooling Tower? A Few Important Terms Components How it Works Remarks • Step 3 - As the water is being distributed, the exposed lower portion of the tower allows for air to pass over the cold water basin. It’s this passing of the ambient air over the cold water basin which actually creates the differential, thus cause the natural draft or “Stack Effect.” How it Works • • • • • What is a Natural Draft Cooling Tower? A Few Important Terms Components How it Works Remarks • Step 4 - As this differential is being produced the shape of the tower itself, the hyperbolic shape, induces current upwards. Remarks • • • • • What is a Natural Draft Cooling Tower? A Few Important Terms Components How it Works Remarks • • • This system is over all extremely efficient and typically requires no fans or mechanical means to cool the water. Very common practice now due to the structures strength and minimum required materials to construct. Efficiency of the tower depends on the ambient temperature.